RISC DISC 1/RISC_DISC_1.iso/pd_share/code/gcc/!GCC/docs/UsingGCC

GNU Info File | 1994-10-03 | 460.1 KB | 11,164 lines

This is Info file @.Distr.UsingGCC, produced by Makeinfo-1.55 from the
input file gcc.texi.

   This file documents the use of the GNU compiler.

   Published by the Free Software Foundation 675 Massachusetts Avenue
Cambridge, MA 02139 USA

   Copyright (C) 1988, 1989, 1992, 1993 Free Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the sections entitled "GNU General Public License" and "Protect
Your Freedom--Fight `Look And Feel'" are included exactly as in the
original, and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to this
one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the sections entitled "GNU General Public
License" and "Protect Your Freedom--Fight `Look And Feel'", and this
permission notice, may be included in translations approved by the Free
Software Foundation instead of in the original English.


File: @.Distr.UsingGCC,  Node: Top,  Next: Copying,  Up: (DIR)

Introduction
************

   This manual documents how to run and install the GNU compiler, as
well as its new features and incompatibilities, and how to report bugs.
It corresponds to GNU CC version 2.4.

* Menu:

* Copying::         GNU General Public License says
                     how you can copy and share GNU CC.
* Contributors::    People who have contributed to GNU CC.
* Boycott::        Protect your freedom--fight "look and feel".

* G++ and GCC::     You can compile C or C++ programs.
* Invoking GCC::    Command options supported by `gcc'.
* Installation::    How to configure, compile and install GNU CC.
* C Extensions::    GNU extensions to the C language family.
* C++ Extensions::  GNU extensions to the C++ language.
* Trouble::         If you have trouble installing GNU CC.
* Bugs::            How, why and where to report bugs.
* Service::         How to find suppliers of support for GNU CC.
* VMS::             Using GNU CC on VMS.

* Index::        Index of concepts and symbol names.


File: @.Distr.UsingGCC,  Node: Copying,  Next: Contributors,  Prev: Top,  Up: Top

GNU GENERAL PUBLIC LICENSE
**************************

                         Version 2, June 1991

     Copyright (C) 1989, 1991 Free Software Foundation, Inc.
     675 Mass Ave, Cambridge, MA 02139, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

Preamble
========

   The licenses for most software are designed to take away your
freedom to share and change it.  By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  You can apply it to
your programs, too.

   When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it in
new free programs; and that you know you can do these things.

   To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

   For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

   We protect your rights with two steps: (1) copyright the software,
and (2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

   Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

   Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

   The precise terms and conditions for copying, distribution and
modification follow.

    TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. This License applies to any program or other work which contains a
     notice placed by the copyright holder saying it may be distributed
     under the terms of this General Public License.  The "Program",
     below, refers to any such program or work, and a "work based on
     the Program" means either the Program or any derivative work under
     copyright law: that is to say, a work containing the Program or a
     portion of it, either verbatim or with modifications and/or
     translated into another language.  (Hereinafter, translation is
     included without limitation in the term "modification".)  Each
     licensee is addressed as "you".

     Activities other than copying, distribution and modification are
     not covered by this License; they are outside its scope.  The act
     of running the Program is not restricted, and the output from the
     Program is covered only if its contents constitute a work based on
     the Program (independent of having been made by running the
     Program).  Whether that is true depends on what the Program does.

  1. You may copy and distribute verbatim copies of the Program's
     source code as you receive it, in any medium, provided that you
     conspicuously and appropriately publish on each copy an appropriate
     copyright notice and disclaimer of warranty; keep intact all the
     notices that refer to this License and to the absence of any
     warranty; and give any other recipients of the Program a copy of
     this License along with the Program.

     You may charge a fee for the physical act of transferring a copy,
     and you may at your option offer warranty protection in exchange
     for a fee.

  2. You may modify your copy or copies of the Program or any portion
     of it, thus forming a work based on the Program, and copy and
     distribute such modifications or work under the terms of Section 1
     above, provided that you also meet all of these conditions:

       a. You must cause the modified files to carry prominent notices
          stating that you changed the files and the date of any change.

       b. You must cause any work that you distribute or publish, that
          in whole or in part contains or is derived from the Program
          or any part thereof, to be licensed as a whole at no charge
          to all third parties under the terms of this License.

       c. If the modified program normally reads commands interactively
          when run, you must cause it, when started running for such
          interactive use in the most ordinary way, to print or display
          an announcement including an appropriate copyright notice and
          a notice that there is no warranty (or else, saying that you
          provide a warranty) and that users may redistribute the
          program under these conditions, and telling the user how to
          view a copy of this License.  (Exception: if the Program
          itself is interactive but does not normally print such an
          announcement, your work based on the Program is not required
          to print an announcement.)

     These requirements apply to the modified work as a whole.  If
     identifiable sections of that work are not derived from the
     Program, and can be reasonably considered independent and separate
     works in themselves, then this License, and its terms, do not
     apply to those sections when you distribute them as separate
     works.  But when you distribute the same sections as part of a
     whole which is a work based on the Program, the distribution of
     the whole must be on the terms of this License, whose permissions
     for other licensees extend to the entire whole, and thus to each
     and every part regardless of who wrote it.

     Thus, it is not the intent of this section to claim rights or
     contest your rights to work written entirely by you; rather, the
     intent is to exercise the right to control the distribution of
     derivative or collective works based on the Program.

     In addition, mere aggregation of another work not based on the
     Program with the Program (or with a work based on the Program) on
     a volume of a storage or distribution medium does not bring the
     other work under the scope of this License.

  3. You may copy and distribute the Program (or a work based on it,
     under Section 2) in object code or executable form under the terms
     of Sections 1 and 2 above provided that you also do one of the
     following:

       a. Accompany it with the complete corresponding machine-readable
          source code, which must be distributed under the terms of
          Sections 1 and 2 above on a medium customarily used for
          software interchange; or,

       b. Accompany it with a written offer, valid for at least three
          years, to give any third party, for a charge no more than your
          cost of physically performing source distribution, a complete
          machine-readable copy of the corresponding source code, to be
          distributed under the terms of Sections 1 and 2 above on a
          medium customarily used for software interchange; or,

       c. Accompany it with the information you received as to the offer
          to distribute corresponding source code.  (This alternative is
          allowed only for noncommercial distribution and only if you
          received the program in object code or executable form with
          such an offer, in accord with Subsection b above.)

     The source code for a work means the preferred form of the work for
     making modifications to it.  For an executable work, complete
     source code means all the source code for all modules it contains,
     plus any associated interface definition files, plus the scripts
     used to control compilation and installation of the executable.
     However, as a special exception, the source code distributed need
     not include anything that is normally distributed (in either
     source or binary form) with the major components (compiler,
     kernel, and so on) of the operating system on which the executable
     runs, unless that component itself accompanies the executable.

     If distribution of executable or object code is made by offering
     access to copy from a designated place, then offering equivalent
     access to copy the source code from the same place counts as
     distribution of the source code, even though third parties are not
     compelled to copy the source along with the object code.

  4. You may not copy, modify, sublicense, or distribute the Program
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense or distribute the Program is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

  5. You are not required to accept this License, since you have not
     signed it.  However, nothing else grants you permission to modify
     or distribute the Program or its derivative works.  These actions
     are prohibited by law if you do not accept this License.
     Therefore, by modifying or distributing the Program (or any work
     based on the Program), you indicate your acceptance of this
     License to do so, and all its terms and conditions for copying,
     distributing or modifying the Program or works based on it.

  6. Each time you redistribute the Program (or any work based on the
     Program), the recipient automatically receives a license from the
     original licensor to copy, distribute or modify the Program
     subject to these terms and conditions.  You may not impose any
     further restrictions on the recipients' exercise of the rights
     granted herein.  You are not responsible for enforcing compliance
     by third parties to this License.

  7. If, as a consequence of a court judgment or allegation of patent
     infringement or for any other reason (not limited to patent
     issues), conditions are imposed on you (whether by court order,
     agreement or otherwise) that contradict the conditions of this
     License, they do not excuse you from the conditions of this
     License.  If you cannot distribute so as to satisfy simultaneously
     your obligations under this License and any other pertinent
     obligations, then as a consequence you may not distribute the
     Program at all.  For example, if a patent license would not permit
     royalty-free redistribution of the Program by all those who
     receive copies directly or indirectly through you, then the only
     way you could satisfy both it and this License would be to refrain
     entirely from distribution of the Program.

     If any portion of this section is held invalid or unenforceable
     under any particular circumstance, the balance of the section is
     intended to apply and the section as a whole is intended to apply
     in other circumstances.

     It is not the purpose of this section to induce you to infringe any
     patents or other property right claims or to contest validity of
     any such claims; this section has the sole purpose of protecting
     the integrity of the free software distribution system, which is
     implemented by public license practices.  Many people have made
     generous contributions to the wide range of software distributed
     through that system in reliance on consistent application of that
     system; it is up to the author/donor to decide if he or she is
     willing to distribute software through any other system and a
     licensee cannot impose that choice.

     This section is intended to make thoroughly clear what is believed
     to be a consequence of the rest of this License.

  8. If the distribution and/or use of the Program is restricted in
     certain countries either by patents or by copyrighted interfaces,
     the original copyright holder who places the Program under this
     License may add an explicit geographical distribution limitation
     excluding those countries, so that distribution is permitted only
     in or among countries not thus excluded.  In such case, this
     License incorporates the limitation as if written in the body of
     this License.

  9. The Free Software Foundation may publish revised and/or new
     versions of the General Public License from time to time.  Such
     new versions will be similar in spirit to the present version, but
     may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies a version number of this License which applies
     to it and "any later version", you have the option of following
     the terms and conditions either of that version or of any later
     version published by the Free Software Foundation.  If the Program
     does not specify a version number of this License, you may choose
     any version ever published by the Free Software Foundation.

 10. If you wish to incorporate parts of the Program into other free
     programs whose distribution conditions are different, write to the
     author to ask for permission.  For software which is copyrighted
     by the Free Software Foundation, write to the Free Software
     Foundation; we sometimes make exceptions for this.  Our decision
     will be guided by the two goals of preserving the free status of
     all derivatives of our free software and of promoting the sharing
     and reuse of software generally.

                                NO WARRANTY

 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
     WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
     LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
     HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
     WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
     NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
     FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS TO THE
     QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
     PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY
     SERVICING, REPAIR OR CORRECTION.

 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
     MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
     LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
     INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
     INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
     DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU
     OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY
     OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
     ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

                      END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Programs
=============================================

   If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

   To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) 19YY  NAME OF AUTHOR

     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
     (at your option) any later version.

     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software
     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

   Also add information on how to contact you by electronic and paper
mail.

   If the program is interactive, make it output a short notice like
this when it starts in an interactive mode:

     Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR
     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
     type `show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type `show c' for details.

   The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.

   You should also get your employer (if you work as a programmer) or
your school, if any, to sign a "copyright disclaimer" for the program,
if necessary.  Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright interest in the program
     `Gnomovision' (which makes passes at compilers) written by James Hacker.

     SIGNATURE OF TY COON, 1 April 1989
     Ty Coon, President of Vice

   This General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Library General Public License instead of this License.


File: @.Distr.UsingGCC,  Node: Contributors,  Next: Boycott,  Prev: Copying,  Up: Top

Contributors to GNU CC
**********************

   In addition to Richard Stallman, several people have written parts
of GNU CC.

   * The idea of using RTL and some of the optimization ideas came from
     the program PO written at the University of Arizona by Jack
     Davidson and Christopher Fraser.  See "Register Allocation and
     Exhaustive Peephole Optimization", Software Practice and
     Experience 14 (9), Sept. 1984, 857-866.

   * Paul Rubin wrote most of the preprocessor.

   * Leonard Tower wrote parts of the parser, RTL generator, and RTL
     definitions, and of the Vax machine description.

   * Ted Lemon wrote parts of the RTL reader and printer.

   * Jim Wilson implemented loop strength reduction and some other loop
     optimizations.

   * Nobuyuki Hikichi of Software Research Associates, Tokyo,
     contributed the support for the Sony NEWS machine.

   * Charles LaBrec contributed the support for the Integrated Solutions
     68020 system.

   * Michael Tiemann of Cygnus Support wrote the front end for C++, as
     well as the support for inline functions and instruction
     scheduling.  Also the descriptions of the National Semiconductor
     32000 series cpu, the SPARC cpu and part of the Motorola 88000 cpu.

   * Jan Stein of the Chalmers Computer Society provided support for
     Genix, as well as part of the 32000 machine description.

   * Randy Smith finished the Sun FPA support.

   * Robert Brown implemented the support for Encore 32000 systems.

   * David Kashtan of SRI adapted GNU CC to the Vomit-Making System
     (VMS).

   * Alex Crain provided changes for the 3b1.

   * Greg Satz and Chris Hanson assisted in making GNU CC work on HP-UX
     for the 9000 series 300.

   * William Schelter did most of the work on the Intel 80386 support.

   * Christopher Smith did the port for Convex machines.

   * Paul Petersen wrote the machine description for the Alliant FX/8.

   * Alain Lichnewsky ported GNU CC to the Mips cpu.

   * Devon Bowen, Dale Wiles and Kevin Zachmann ported GNU CC to the
     Tahoe.

   * Jonathan Stone wrote the machine description for the Pyramid
     computer.

   * Gary Miller ported GNU CC to Charles River Data Systems machines.

   * Richard Kenner of the New York University Ultracomputer Research
     Laboratory wrote the machine descriptions for the AMD 29000, the
     DEC Alpha, the IBM RT PC, and the IBM RS/6000 as well as the
     support for instruction attributes.  He also made changes to
     better support RISC processors including changes to common
     subexpression elimination, strength reduction, function calling
     sequence handling, and condition code support, in addition to
     generalizing the code for frame pointer elimination.

   * Richard Kenner and Michael Tiemann jointly developed reorg.c, the
     delay slot scheduler.

   * Mike Meissner and Tom Wood of Data General finished the port to the
     Motorola 88000.

   * Masanobu Yuhara of Fujitsu Laboratories implemented the machine
     description for the Tron architecture (specifically, the Gmicro).

   * NeXT, Inc. donated the front end that supports the Objective C
     language.

   * James van Artsdalen wrote the code that makes efficient use of the
     Intel 80387 register stack.

   * Mike Meissner at the Open Software Foundation finished the port to
     the MIPS cpu, including adding ECOFF debug support.

   * Ron Guilmette implemented the `protoize' and `unprotoize' tools,
     the support for Dwarf symbolic debugging information, and much of
     the support for System V Release 4.  He has also worked heavily on
     the Intel 386 and 860 support.

   * Torbjorn Granlund of the Swedish Institute of Computer Science
     implemented multiply-by-constant optimization and better long long
     support, and improved leaf function register allocation.

   * Mike Stump implemented the support for Elxsi 64 bit CPU.

   * John Wehle added the machine description for the Western Electric
     32000 processor used in several 3b series machines (no relation to
     the National Semiconductor 32000 processor).

   * Holger Teutsch provided the support for the Clipper cpu.

   * Kresten Krab Thorup wrote the run time support for the Objective C
     language.

   * Stephen Moshier contributed the floating point emulator that
     assists in cross-compilation and permits support for floating
     point numbers wider than 64 bits.

   * Steve Chamberlain wrote the support for the Hitachi SH processor.


File: @.Distr.UsingGCC,  Node: Boycott,  Next: G++ and GCC,  Prev: Contributors,  Up: Top

Protect Your Freedom--Fight "Look And Feel"
*******************************************

     This section is a political message from the League for Programming
     Freedom to the users of GNU CC.  It is included here as an
     expression of support for the League on the part of the Free
     Software Foundation.

   Apple and Lotus are trying to create a new form of legal monopoly: a
copyright on a class of user interfaces.  These monopolies would cause
serious problems for users and developers of computer software and
systems.  Xerox, too, has tried to make a monopoly for itself on window
systems; their suit against Apple was thrown out on a technicality, but
Xerox has not said anything to indicate it wouldn't try again.

   Until a few years ago, the law seemed clear: no one could restrict
others from using a user interface; programmers were free to implement
any interface they chose.  Imitating interfaces, sometimes with changes,
was standard practice in the computer field.  The interfaces we know
evolved gradually in this way; for example, the Macintosh user interface
drew ideas from the Xerox interface, which in turn drew on work done at
Stanford and SRI.  1-2-3 imitated VisiCalc, and dBase imitated a
database program from JPL.

   Most computer companies, and nearly all computer users, were happy
with this state of affairs.  The companies that are suing say it does
not offer "enough incentive" to develop their products, but they must
have considered it "enough" when they made their decision to do so.  It
seems they are not satisfied with the opportunity to continue to compete
in the marketplace--not even with a head start.

   If companies like Xerox, Lotus, and Apple are permitted to make law
through the courts, the precedent will hobble the software industry:

   * Gratuitous incompatibilities will burden users.  Imagine if each
     car manufacturer had to arrange the pedals in a different order.

   * Software will become and remain more expensive.  Users will be
     "locked in" to proprietary interfaces, for which there is no real
     competition.

   * Large companies have an unfair advantage wherever lawsuits become
     commonplace.  Since they can easily afford to sue, they can
     intimidate small companies with threats even when they don't
     really have a case.

   * User interface improvements will come slower, since incremental
     evolution through creative imitation will no longer be permitted.

   * Even Apple, etc., will find it harder to make improvements if they
     can no longer adapt the good ideas that others introduce, for fear
     of weakening their own legal positions.  Some users suggest that
     this stagnation may already have started.

   * If you use GNU software, you might find it of some concern that
     user interface copyright will make it hard for the Free Software
     Foundation to develop programs compatible with the interfaces that
     you already know.

   To protect our freedom from lawsuits like these, a group of
programmers and users have formed a new grass-roots political
organization, the League for Programming Freedom.

   The purpose of the League is to oppose new monopolistic practices
such as user-interface copyright and software patents; it calls for a
return to the legal policies of the recent past, in which these
practices were not allowed.  The League is not concerned with free
software as an issue, and not affiliated with the Free Software
Foundation.

   The League's membership rolls include John McCarthy, inventor of
Lisp, Marvin Minsky, founder of the Artificial Intelligence lab, Guy L.
Steele, Jr., author of well-known books on Lisp and C, as well as
Richard Stallman, the developer of GNU CC.  Please join and add your
name to the list.  Membership dues in the League are $42 per year for
programmers, managers and professionals; $10.50 for students; $21 for
others.

   The League needs both activist members and members who only pay their
dues.

   To join, or for more information, phone [phone] or write to:

     League for Programming Freedom
     1 Kendall Square #143
     P.O. Box 9171
     Cambridge, MA 02139

   You can also send electronic mail to `[e-mail]'.

   Here are some suggestions from the League for things you can do to
protect your freedom to write programs:

   * Don't buy from Xerox, Lotus or Apple.  Buy from their competitors
     or from the defendants they are suing.

   * Don't develop software to work with the systems made by these
     companies.

   * Port your existing software to competing systems, so that you
     encourage users to switch.

   * Write letters to company presidents to let them know their conduct
     is unacceptable.

   * Tell your friends and colleagues about this issue and how it
     threatens to ruin the computer industry.

   * Above all, don't work for the look-and-feel plaintiffs, and don't
     accept contracts from them.

   * Write to Congress to explain the importance of this issue.

          House Subcommittee on Intellectual Property
          2137 Rayburn Bldg
          Washington, DC 20515

          Senate Subcommittee on Patents, Trademarks and Copyrights
          United States Senate
          Washington, DC 20510

     (These committees have received lots of mail already; let's give
     them even more.)

   Express your opinion!  You can make a difference.


File: @.Distr.UsingGCC,  Node: G++ and GCC,  Next: Invoking GCC,  Prev: Boycott,  Up: Top

Compile C, C++, or Objective C
******************************

   The C, C++, and Objective C versions of the compiler are integrated;
the GNU C compiler can compile programs written in C, C++, or Objective
C.

   "GCC" is a common shorthand term for the GNU C compiler.  This is
both the most general name for the compiler, and the name used when the
emphasis is on compiling C programs.

   When referring to C++ compilation, it is usual to call the compiler
"G++".  Since there is only one compiler, it is also accurate to call
it "GCC" no matter what the language context; however, the term "G++"
is more useful when the emphasis is on compiling C++ programs.

   G++ is a *compiler*, not merely a preprocessor.  G++ builds object
code directly from your C++ program source.  There is no intermediate C
version of the program.  (By contrast, for example, some other
implementations use a program that generates a C program from your C++
source.)  Avoiding an intermediate C representation of the program means
that you get better object code, and better debugging information.  The
GNU debugger, GDB, works with this information in the object code to
give you comprehensive C++ source-level editing capabilities (*note C
and C++: (gdb.info)C.).


File: @.Distr.UsingGCC,  Node: Invoking GCC,  Next: Installation,  Prev: G++ and GCC,  Up: Top

GNU CC Command Options
**********************

   When you invoke GNU CC, it normally does preprocessing, compilation,
assembly and linking.  The "overall options" allow you to stop this
process at an intermediate stage.  For example, the `-c' option says
not to run the linker.  Then the output consists of object files output
by the assembler.

   Other options are passed on to one stage of processing.  Some options
control the preprocessor and others the compiler itself.  Yet other
options control the assembler and linker; most of these are not
documented here, since you rarely need to use any of them.

   Most of the command line options that you can use with GNU CC are
useful for C programs; when an option is only useful with another
language (usually C++), the explanation says so explicitly.  If the
description for a particular option does not mention a source language,
you can use that option with all supported languages.

   *Note Compiling C++ Programs: Invoking G++, for a summary of special
options for compiling C++ programs.

   The `gcc' program accepts options and file names as operands.  Many
options have multiletter names; therefore multiple single-letter options
may *not* be grouped: `-dr' is very different from `-d -r'.

   You can mix options and other arguments.  For the most part, the
order you use doesn't matter.  Order does matter when you use several
options of the same kind; for example, if you specify `-L' more than
once, the directories are searched in the order specified.

   Many options have long names starting with `-f' or with `-W'--for
example, `-fforce-mem', `-fstrength-reduce', `-Wformat' and so on.
Most of these have both positive and negative forms; the negative form
of `-ffoo' would be `-fno-foo'.  This manual documents only one of
these two forms, whichever one is not the default.

* Menu:

* Option Summary::    Brief list of all options, without explanations.
* Overall Options::     Controlling the kind of output:
                        an executable, object files, assembler files,
                        or preprocessed source.
* Invoking G++::    Compiling C++ programs.
* C Dialect Options::   Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Warning Options::     How picky should the compiler be?
* Debugging Options::   Symbol tables, measurements, and debugging dumps.
* Optimize Options::    How much optimization?
* Preprocessor Options:: Controlling header files and macro definitions.
                         Also, getting dependency information for Make.
* Assembler Options::   Passing options to the assembler.
* Link Options::        Specifying libraries and so on.
* Directory Options::   Where to find header files and libraries.
                        Where to find the compiler executable files.
* Target Options::      Running a cross-compiler, or an old version of GNU CC.
* Submodel Options::    Specifying minor hardware or convention variations,
                        such as 68010 vs 68020.
* Code Gen Options::    Specifying conventions for function calls, data layout
                        and register usage.
* Environment Variables:: Env vars that affect GNU CC.
* Running Protoize::    Automatically adding or removing function prototypes.


File: @.Distr.UsingGCC,  Node: Option Summary,  Next: Overall Options,  Up: Invoking GCC

Option Summary
==============

   Here is a summary of all the options, grouped by type.  Explanations
are in the following sections.

*Overall Options*
     *Note Options Controlling the Kind of Output: Overall Options.
          -c  -S  -E  -o FILE  -pipe  -v  -x LANGUAGE

*C Language Options*
     *Note Options Controlling C Dialect: C Dialect Options.
          -ansi  -fcond-mismatch  -fno-asm  -fno-builtin
          -fsigned-bitfields  -fsigned-char
          -funsigned-bitfields  -funsigned-char  -fwritable-strings
          -traditional  -traditional-cpp  -trigraphs

*C++ Language Options*
     *Note Options Controlling C++ Dialect: C++ Dialect Options.
          -fall-virtual  -fdollars-in-identifiers
          -felide-constructors  -fenum-int-equiv  -fmemoize-lookups
          -fno-strict-prototype  -fnonnull-objects
          -fthis-is-variable  -nostdinc++

*Warning Options*
     *Note Options to Request or Suppress Warnings: Warning Options.
          -fsyntax-only  -pedantic  -pedantic-errors
          -w  -W  -Wall  -Waggregate-return  -Wcast-align
          -Wcast-qual  -Wchar-subscript  -Wcomment  -Wconversion
          -Wenum-clash  -Werror  -Wformat  -Wid-clash-LEN
          -Wimplicit  -Wimport  -Winline  -Wmissing-prototypes
          -Wnested-externs  -Woverloaded-virtual  -Wparentheses
          -Wpointer-arith  -Wredundant-decls  -Wreturn-type
          -Wshadow  -Wstrict-prototypes  -Wswitch
          -Wtemplate-debugging  -Wtraditional  -Wtrigraphs
          -Wuninitialized  -Wunused  -Wwrite-strings

*Debugging Options*
     *Note Options for Debugging Your Program or GCC: Debugging Options.
          -a  -dLETTERS  -fpretend-float
          -g  -gLEVEL -ggdb  -gdwarf -gdwarf+
          -gstabs  -gstabs+  -gcoff -gxcoff  -gxcoff+
          -p  -pg  -save-temps  -print-libgcc-file-name

*Optimization Options*
     *Note Options that Control Optimization: Optimize Options.
          -fcaller-saves  -fcse-follow-jumps  -fcse-skip-blocks
          -fdelayed-branch   -fexpensive-optimizations
          -ffast-math  -ffloat-store  -fforce-addr  -fforce-mem
          -finline-functions  -fkeep-inline-functions
          -fno-default-inline  -fno-defer-pop  -fno-function-cse
          -fno-inline  -fno-peephole  -fomit-frame-pointer
          -frerun-cse-after-loop  -fschedule-insns
          -fschedule-insns2  -fstrength-reduce  -fthread-jumps
          -funroll-all-loops  -funroll-loops
          -O  -O2

*Preprocessor Options*
     *Note Options Controlling the Preprocessor: Preprocessor Options.
          -AASSERTION  -C  -dD  -dM  -dN
          -DMACRO[=DEFN]  -E  -H
          -idirafter DIR
          -include FILE  -imacros FILE
          -iprefix FILE  -iwithprefix DIR
          -M  -MD  -MM  -MMD  -nostdinc  -P  -trigraphs  -UMACRO

*Assembler Option*
     *Note Passing Options to the Assembler: Assembler Options.
          -Wa,OPTION

*Linker Options*
     *Note Options for Linking: Link Options.
          OBJECT-FILE-NAME
          -lLIBRARY  -nostartfiles  -nostdlib
          -static  -shared  -symbolic
          -Wl,OPTION  -Xlinker OPTION
          -u SYMBOL

*Directory Options*
     *Note Options for Directory Search: Directory Options.
          -BPREFIX  -IDIR  -I-  -LDIR

*Target Options*
     *Note Target Options::.
          -b MACHINE  -V VERSION

*Machine Dependent Options*
     *Note Hardware Models and Configurations: Submodel Options.
          *M680x0 Options*
          -m68000  -m68020  -m68020-40  -m68030  -m68040  -m68881
          -mbitfield  -mc68000  -mc68020  -mfpa  -mnobitfield
          -mrtd  -mshort  -msoft-float

          *VAX Options*
          -mg  -mgnu  -munix

          *SPARC Options*
          -mepilogue  -mfpu  -mhard-float
          -mno-fpu  -mno-epilogue  -msoft-float
          -msparclite  -mv8

          *Convex Options*
          -mc1  -mc2  -mc32  -mc34  -mc38
          -margcount  -mnoargcount
          -mlong32  -mlong64
          -mbolatile-cache  -mvolatile-nocache

          *AMD29K Options*
          -m29000  -m29050  -mbw  -mdw  -mkernel-registers
          -mlarge  -mnbw  -mnodw  -msmall  -mstack-check
          -muser-registers

          *M88K Options*
          -m88000  -m88100  -m88110  -mbig-pic
          -mcheck-zero-division  -mhandle-large-shift
          -midentify-revision  -mno-check-zero-division
          -mno-ocs-debug-info  -mno-ocs-frame-position
          -mno-optimize-arg-area  -mno-serialize-volatile
          -mno-underscores  -mocs-debug-info
          -mocs-frame-position  -moptimize-arg-area
          -mserialize-volatile  -mshort-data-NUM  -msvr3
          -msvr4  -mtrap-large-shift  -muse-div-instruction
          -mversion-03.00  -mwarn-passed-structs

          *RS/6000 Options*
          -mfp-in-toc  -mno-fop-in-toc

          *RT Options*
          -mcall-lib-mul  -mfp-arg-in-fpregs  -mfp-arg-in-gregs
          -mfull-fp-blocks  -mhc-struct-return  -min-line-mul
          -mminimum-fp-blocks  -mnohc-struct-return

          *MIPS Options*
          -mcpu=CPU  TYPE  -mips2  -mips3  -mint64
          -mlong64  -mlonglong128  -mmips-as  -mgas  -mrnames
          -mno-rnames  -mgpopt  -mno-gpopt  -mstats  -mno-stats
          -mmemcpy  -mno-memcpy  -mno-mips-tfile  -mmips-tfile
          -msoft-float  -mhard-float  -mabicalls  -mno-abicalls
          -mhalf-pic  -mno-half-pic -mlong-calls -mno-long-calls
          -G  NUM  -nocpp

          *i386 Options*
          -m486  -mno-486  -msoft-float  -msvr3-shlib  -mieee-fp
          -mno-fp-ret-in-387

          *HPPA Options*
          -mpa-risc-1-0
          -mpa-risc-1-1
          -mkernel
          -mshared-libs
          -mno-shared-libs
          -mlong-calls
          -mdisable-fpregs
          -mdisable-indexing
          -mtrailing-colon

          *Intel 960 Options*
          -mCPU TYPE
          -mnumerics  -msoft-float
          -mcode-align  -mno-code-align
          -mleaf-procedures  -mno-leaf-procedures
          -mtail-call  -mno-tail-call
          -mcomplex-addr  -mno-complex-addr
          -mclean-linkage  -mno-clean-linkage
          -mic-compat  -mic2.0-compat  -mic3.0-compat
          -masm-compat  -mintel-asm
          -mstrict-align  -mno-strict-align
          -mold-align  -mno-old-align

          *DEC Alpha Options*
          -mfp-regs  -mno-fp-regs  -mno-soft-float
          -msoft-float

          *System V Options*
          -G  -Qy  -Qn  -YP,PATHS  -Ym,DIR

*Code Generation Options*
     *Note Options for Code Generation Conventions: Code Gen Options.
          -fcall-saved-REG  -fcall-used-REG
          -ffixed-REG  -finhibit-size-directive
          -fno-common  -fno-ident
          -fno-gnu-linker  -fpcc-struct-return  -fpic  -fPIC
          -freg-struct-return  -fshared-data  -fshort-enums
          -fshort-double  -fvolatile  -fvolatile-global
          -fverbose-asm

* Menu:

* Overall Options::     Controlling the kind of output:
                        an executable, object files, assembler files,
                        or preprocessed source.
* C Dialect Options::   Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Warning Options::     How picky should the compiler be?
* Debugging Options::   Symbol tables, measurements, and debugging dumps.
* Optimize Options::    How much optimization?
* Preprocessor Options:: Controlling header files and macro definitions.
                         Also, getting dependency information for Make.
* Assembler Options::   Passing options to the assembler.
* Link Options::        Specifying libraries and so on.
* Directory Options::   Where to find header files and libraries.
                        Where to find the compiler executable files.
* Target Options::      Running a cross-compiler, or an old version of GNU CC.


File: @.Distr.UsingGCC,  Node: Overall Options,  Next: Invoking G++,  Prev: Option Summary,  Up: Invoking GCC

Options Controlling the Kind of Output
======================================

   Compilation can involve up to four stages: preprocessing, compilation
proper, assembly and linking, always in that order.  The first three
stages apply to an individual source file, and end by producing an
object file; linking combines all the object files (those newly
compiled, and those specified as input) into an executable file.

   For any given input file, the file name suffix determines what kind
of compilation is done:

`FILE.c'
     C source code which must be preprocessed.

`FILE.i'
     C source code which should not be preprocessed.

`FILE.ii'
     C++ source code which should not be preprocessed.

`FILE.m'
     Objective-C source code.  Note that you must link with the library
     `libobjc.a' to make an Objective-C program work.

`FILE.h'
     C header file (not to be compiled or linked).

`FILE.cc'
`FILE.cxx'
`FILE.C'
     C++ source code which must be preprocessed.  Note that in `.cxx',
     the last two letters must both be literally `x'.  Likewise, `.C'
     refers to a literal capital C.

`FILE.s'
     Assembler code.

`FILE.S'
     Assembler code which must be preprocessed.

`OTHER'
     An object file to be fed straight into linking.  Any file name
     with no recognized suffix is treated this way.

   You can specify the input language explicitly with the `-x' option:

`-x LANGUAGE'
     Specify explicitly the LANGUAGE for the following input files
     (rather than letting the compiler choose a default based on the
     file name suffix).  This option applies to all following input
     files until the next `-x' option.  Possible values for LANGUAGE
     are:
          c  objective-c  c++
          c-header  cpp-output  c++-cpp-output
          assembler  assembler-with-cpp

`-x none'
     Turn off any specification of a language, so that subsequent files
     are handled according to their file name suffixes (as they are if
     `-x' has not been used at all).

   If you only want some of the stages of compilation, you can use `-x'
(or filename suffixes) to tell `gcc' where to start, and one of the
options `-c', `-S', or `-E' to say where `gcc' is to stop.  Note that
some combinations (for example, `-x cpp-output -E' instruct `gcc' to do
nothing at all.

`-c'
     Compile or assemble the source files, but do not link.  The linking
     stage simply is not done.  The ultimate output is in the form of an
     object file for each source file.

     By default, the object file name for a source file is made by
     replacing the suffix `.c', `.i', `.s', etc., with `.o'.

     Unrecognized input files, not requiring compilation or assembly,
     are ignored.

`-S'
     Stop after the stage of compilation proper; do not assemble.  The
     output is in the form of an assembler code file for each
     non-assembler input file specified.

     By default, the assembler file name for a source file is made by
     replacing the suffix `.c', `.i', etc., with `.s'.

     Input files that don't require compilation are ignored.

`-E'
     Stop after the preprocessing stage; do not run the compiler
     proper.  The output is in the form of preprocessed source code,
     which is sent to the standard output.

     Input files which don't require preprocessing are ignored.

`-o FILE'
     Place output in file FILE.  This applies regardless to whatever
     sort of output is being produced, whether it be an executable file,
     an object file, an assembler file or preprocessed C code.

     Since only one output file can be specified, it does not make
     sense to use `-o' when compiling more than one input file, unless
     you are producing an executable file as output.

     If `-o' is not specified, the default is to put an executable file
     in `a.out', the object file for `SOURCE.SUFFIX' in `SOURCE.o', its
     assembler file in `SOURCE.s', and all preprocessed C source on
     standard output.

`-v'
     Print (on standard error output) the commands executed to run the
     stages of compilation.  Also print the version number of the
     compiler driver program and of the preprocessor and the compiler
     proper.

`-pipe'
     Use pipes rather than temporary files for communication between the
     various stages of compilation.  This fails to work on some systems
     where the assembler is unable to read from a pipe; but the GNU
     assembler has no trouble.


File: @.Distr.UsingGCC,  Node: Invoking G++,  Next: C Dialect Options,  Prev: Overall Options,  Up: Invoking GCC

Compiling C++ Programs
======================

   C++ source files conventionally use one of the suffixes `.C', `.cc',
or `.cxx'; preprocessed C++ files use the suffix `.ii'.  GNU CC
recognizes files with these names and compiles them as C++ programs
even if you call the compiler the same way as for compiling C programs
(usually with the name `gcc').

   However, C++ programs often require class libraries as well as a
compiler that understands the C++ language--and under some
circumstances, you might want to compile programs from standard input,
or otherwise without a suffix that flags them as C++ programs.  `g++'
is a shell script that calls GNU CC with the default language set to
C++, and automatically specifies linking against the GNU class library
libg++.  (1) On many systems, the script `g++' is also installed with
the name `c++'.

   When you compile C++ programs, you may specify many of the same
command-line options that you use for compiling programs in any
language; or command-line options meaningful for C and related
languages; or options that are meaningful only for C++ programs.  *Note
Options Controlling C Dialect: C Dialect Options, for explanations of
options for languages related to C.  *Note Options Controlling C++
Dialect: C++ Dialect Options, for explanations of options that are
meaningful only for C++ programs.

   ---------- Footnotes ----------

   (1)  Prior to release 2 of the compiler, there was a separate `g++'
compiler.  That version was based on GNU CC, but not integrated with
it.  Versions of `g++' with a `1.XX' version number--for example, `g++'
version 1.37 or 1.42--are much less reliable than the versions
integrated with GCC 2.  Moreover, combining G++ `1.XX' with a version 2
GCC will simply not work.


File: @.Distr.UsingGCC,  Node: C Dialect Options,  Next: C++ Dialect Options,  Prev: Invoking G++,  Up: Invoking GCC

Options Controlling C Dialect
=============================

   The following options control the dialect of C (or languages derived
from C, such as C++ and Objective C) that the compiler accepts:

`-ansi'
     Support all ANSI standard C programs.

     This turns off certain features of GNU C that are incompatible
     with ANSI C, such as the `asm', `inline' and `typeof' keywords, and
     predefined macros such as `unix' and `vax' that identify the type
     of system you are using.  It also enables the undesirable and
     rarely used ANSI trigraph feature, and disallows `$' as part of
     identifiers.

     The alternate keywords `__asm__', `__extension__', `__inline__'
     and `__typeof__' continue to work despite `-ansi'.  You would not
     want to use them in an ANSI C program, of course, but it useful to
     put them in header files that might be included in compilations
     done with `-ansi'.  Alternate predefined macros such as `__unix__'
     and `__vax__' are also available, with or without `-ansi'.

     The `-ansi' option does not cause non-ANSI programs to be rejected
     gratuitously.  For that, `-pedantic' is required in addition to
     `-ansi'.  *Note Warning Options::.

     The macro `__STRICT_ANSI__' is predefined when the `-ansi' option
     is used.  Some header files may notice this macro and refrain from
     declaring certain functions or defining certain macros that the
     ANSI standard doesn't call for; this is to avoid interfering with
     any programs that might use these names for other things.

     The functions `alloca', `abort', `exit', and `_exit' are not
     builtin functions when `-ansi' is used.

`-fno-asm'
     Do not recognize `asm', `inline' or `typeof' as a keyword.  These
     words may then be used as identifiers.  You can use the keywords
     `__asm__', `__inline__' and `__typeof__' instead.  `-ansi' implies
     `-fno-asm'.

`-fno-builtin'
     Don't recognize built-in functions that do not begin with two
     leading underscores.  Currently, the functions affected include
     `abort', `abs', `alloca', `cos', `exit', `fabs', `ffs', `labs',
     `memcmp', `memcpy', `sin', `sqrt', `strcmp', `strcpy', and
     `strlen'.

     The `-ansi' option prevents `alloca' and `ffs' from being builtin
     functions, since these functions do not have an ANSI standard
     meaning.

`-trigraphs'
     Support ANSI C trigraphs.  You don't want to know about this
     brain-damage.  The `-ansi' option implies `-trigraphs'.

`-traditional'
     Attempt to support some aspects of traditional C compilers.
     Specifically:

        * All `extern' declarations take effect globally even if they
          are written inside of a function definition.  This includes
          implicit declarations of functions.

        * The newer keywords `typeof', `inline', `signed', `const' and
          `volatile' are not recognized.  (You can still use the
          alternative keywords such as `__typeof__', `__inline__', and
          so on.)

        * Comparisons between pointers and integers are always allowed.

        * Integer types `unsigned short' and `unsigned char' promote to
          `unsigned int'.

        * Out-of-range floating point literals are not an error.

        * Certain constructs which ANSI regards as a single invalid
          preprocessing number, such as `0xe-0xd', are treated as
          expressions instead.

        * String "constants" are not necessarily constant; they are
          stored in writable space, and identical looking constants are
          allocated separately.  (This is the same as the effect of
          `-fwritable-strings'.)

        * All automatic variables not declared `register' are preserved
          by `longjmp'.  Ordinarily, GNU C follows ANSI C: automatic
          variables not declared `volatile' may be clobbered.

        * In the preprocessor, comments convert to nothing at all,
          rather than to a space.  This allows traditional token
          concatenation.

        * In the preprocessor, macro arguments are recognized within
          string constants in a macro definition (and their values are
          stringified, though without additional quote marks, when they
          appear in such a context).  The preprocessor always considers
          a string constant to end at a newline.

        * The predefined macro `__STDC__' is not defined when you use
          `-traditional', but `__GNUC__' is (since the GNU extensions
          which `__GNUC__' indicates are not affected by
          `-traditional').  If you need to write header files that work
          differently depending on whether `-traditional' is in use, by
          testing both of these predefined macros you can distinguish
          four situations: GNU C, traditional GNU C, other ANSI C
          compilers, and other old C compilers.  *Note Standard
          Predefined Macros: (cpp.info)Standard Predefined, for more
          discussion of these and other predefined macros.

        * The preprocessor considers a string constant to end at a
          newline (unless the newline is escaped with `\').  (Without
          `-traditional', string constants can contain the newline
          character as typed.)

        * The character escape sequences `\x' and `\a' evaluate as the
          literal characters `x' and `a' respectively.  Without
          `-traditional', `\x' is a prefix for the hexadecimal
          representation of a character, and `\a' produces a bell.

        * In C++ programs, assignment to `this' is permitted with
          `-traditional'.  (The option `-fthis-is-variable' also has
          this effect.)

     You may wish to use `-fno-builtin' as well as `-traditional' if
     your program uses names that are normally GNU C builtin functions
     for other purposes of its own.

`-traditional-cpp'
     Attempt to support some aspects of traditional C preprocessors.
     This includes the last three items in the table immediately above,
     but none of the other effects of `-traditional'.

`-fcond-mismatch'
     Allow conditional expressions with mismatched types in the second
     and third arguments.  The value of such an expression is void.

`-funsigned-char'
     Let the type `char' be unsigned, like `unsigned char'.

     Each kind of machine has a default for what `char' should be.  It
     is either like `unsigned char' by default or like `signed char' by
     default.

     Ideally, a portable program should always use `signed char' or
     `unsigned char' when it depends on the signedness of an object.
     But many programs have been written to use plain `char' and expect
     it to be signed, or expect it to be unsigned, depending on the
     machines they were written for.  This option, and its inverse, let
     you make such a program work with the opposite default.

     The type `char' is always a distinct type from each of `signed
     char' or `unsigned char', even though its behavior is always just
     like one of those two.

`-fsigned-char'
     Let the type `char' be signed, like `signed char'.

     Note that this is equivalent to `-fno-unsigned-char', which is the
     negative form of `-funsigned-char'.  Likewise, the option
     `-fno-signed-char' is equivalent to `-funsigned-char'.

`-fsigned-bitfields'
`-funsigned-bitfields'
`-fno-signed-bitfields'
`-fno-unsigned-bitfields'
     These options control whether a bitfield is signed or unsigned,
     when the declaration does not use either `signed' or `unsigned'.
     By default, such a bitfield is signed, because this is consistent:
     the basic integer types such as `int' are signed types.

     However, when `-traditional' is used, bitfields are all unsigned
     no matter what.

`-fwritable-strings'
     Store string constants in the writable data segment and don't
     uniquize them.  This is for compatibility with old programs which
     assume they can write into string constants.  The option
     `-traditional' also has this effect.

     Writing into string constants is a very bad idea; "constants"
     should be constant.


File: @.Distr.UsingGCC,  Node: C++ Dialect Options,  Next: Warning Options,  Prev: C Dialect Options,  Up: Invoking GCC

Options Controlling C++ Dialect
===============================

   This section describes the command-line options that are only
meaningful for C++ programs; but you can also use most of the GNU
compiler options regardless of what language your program is in.  For
example, you might compile a file `firstClass.C' like this:

     g++ -g -felide-constructors -O -c firstClass.C

In this example, only `-felide-constructors' is an option meant only
for C++ programs; you can use the other options with any language
supported by GNU CC.

   Here is a list of options that are *only* for compiling C++ programs:

`-fall-virtual'
     Treat all possible member functions as virtual, implicitly.  All
     member functions (except for constructor functions and `new' or
     `delete' member operators) are treated as virtual functions of the
     class where they appear.

     This does not mean that all calls to these member functions will
     be made through the internal table of virtual functions.  Under
     some circumstances, the compiler can determine that a call to a
     given virtual function can be made directly; in these cases the
     calls are direct in any case.

`-fdollars-in-identifiers'
     Accept `$' in identifiers.  You can also explicitly prohibit use of
     `$' with the option `-fno-dollars-in-identifiers'.  (GNU C++
     allows `$' by default on some target systems but not others.)
     Traditional C allowed the character `$' to form part of
     identifiers.  However, ANSI C and C++ forbid `$' in identifiers.

`-felide-constructors'
     Elide constructors when this seems plausible.  With this option,
     GNU C++ initializes `y' directly from the call to `foo' without
     going through a temporary in the following code:

          A foo ();
          A y = foo ();

     Without this option, GNU C++ (1) initializes `y' by calling the
     appropriate constructor for type `A'; (2) assigns the result of
     `foo' to a temporary; and, finally, (3) replaces the initial value
     of `y' with the temporary.

     The default behavior (`-fno-elide-constructors') is specified by
     the draft ANSI C++ standard.  If your program's constructors have
     side effects, `-felide-constructors' can change your program's
     behavior, since some constructor calls may be omitted.

`-fenum-int-equiv'
     Permit implicit conversion of `int' to enumeration types.  Normally
     GNU C++ allows conversion of `enum' to `int', but not the other
     way around.

`-fmemoize-lookups'
`-fsave-memoized'
     Use heuristics to compile faster.  These heuristics are not
     enabled by default, since they are only effective for certain
     input files.  Other input files compile more slowly.

     The first time the compiler must build a call to a member function
     (or reference to a data member), it must (1) determine whether the
     class implements member functions of that name; (2) resolve which
     member function to call (which involves figuring out what sorts of
     type conversions need to be made); and (3) check the visibility of
     the member function to the caller.  All of this adds up to slower
     compilation.  Normally, the second time a call is made to that
     member function (or reference to that data member), it must go
     through the same lengthy process again.  This means that code like
     this:

          cout << "This " << p << " has " << n << " legs.\n";

     makes six passes through all three steps.  By using a software
     cache, a "hit" significantly reduces this cost.  Unfortunately,
     using the cache introduces another layer of mechanisms which must
     be implemented, and so incurs its own overhead.
     `-fmemoize-lookups' enables the software cache.

     Because access privileges (visibility) to members and member
     functions may differ from one function context to the next, G++
     may need to flush the cache.  With the `-fmemoize-lookups' flag,
     the cache is flushed after every function that is compiled.  The
     `-fsave-memoized' flag enables the same software cache, but when
     the compiler determines that the context of the last function
     compiled would yield the same access privileges of the next
     function to compile, it preserves the cache.  This is most helpful
     when defining many member functions for the same class: with the
     exception of member functions which are friends of other classes,
     each member function has exactly the same access privileges as
     every other, and the cache need not be flushed.

`-fno-strict-prototype'
     Treat a function declaration with no arguments, such as `int foo
     ();', as C would treat it--as saying nothing about the number of
     arguments or their types.  Normally, such a declaration in C++
     means that the function `foo' takes no arguments.

`-fnonnull-objects'
     Assume that objects reached through references are not null.

     Normally, GNU C++ makes conservative assumptions about objects
     reached through references.  For example, the compiler must check
     that `a' is not null in code like the following:

          obj &a = g ();
          a.f (2);

     Checking that references of this sort have non-null values requires
     extra code, however, and it is unnecessary for many programs.  You
     can use `-fnonnull-objects' to omit the checks for null, if your
     program doesn't require checking.

`-fthis-is-variable'
     Permit assignment to `this'.  The incorporation of user-defined
     free store management into C++ has made assignment to `this' an
     anachronism.  Therefore, by default it is invalid to assign to
     `this' within a class member function; that is, GNU C++ treats the
     type of `this' in a member function of class `X' to be `X *const'.
     However, for backwards compatibility, you can make it valid with
     `-fthis-is-variable'.

`-nostdinc++'
     Do not search for header files in the standard directories
     specific to C++, but do still search the other standard
     directories.  (This option is used when building libg++.)

`-traditional'
     For C++ programs (in addition to the effects that apply to both C
     and C++), this has the same effect as `-fthis-is-variable'.  *Note
     Options Controlling C Dialect: C Dialect Options.

   In addition, these optimization, warning, and code generation options
have meanings only for C++ programs:

`-fno-default-inline'
     Do not assume `inline' for functions defined inside a class scope.
     *Note Options That Control Optimization: Optimize Options.

`-Wenum-clash'
`-Woverloaded-virtual'
`-Wtemplate-debugging'
     Warnings that apply only to C++ programs.  *Note Options to
     Request or Suppress Warnings: Warning Options.

`+eN'
     Control how virtual function definitions are used, in a fashion
     compatible with `cfront' 1.x.  *Note Options for Code Generation
     Conventions: Code Gen Options.


File: @.Distr.UsingGCC,  Node: Warning Options,  Next: Debugging Options,  Prev: C++ Dialect Options,  Up: Invoking GCC

Options to Request or Suppress Warnings
=======================================

   Warnings are diagnostic messages that report constructions which are
not inherently erroneous but which are risky or suggest there may have
been an error.

   You can request many specific warnings with options beginning `-W',
for example `-Wimplicit' to request warnings on implicit declarations.
Each of these specific warning options also has a negative form
beginning `-Wno-' to turn off warnings; for example, `-Wno-implicit'.
This manual lists only one of the two forms, whichever is not the
default.

   These options control the amount and kinds of warnings produced by
GNU CC:

`-fsyntax-only'
     Check the code for syntax errors, but don't do anything beyond
     that.

`-w'
     Inhibit all warning messages.

`-Wno-import'
     Inhibit warning messages about the use of `#import'.

`-pedantic'
     Issue all the warnings demanded by strict ANSI standard C; reject
     all programs that use forbidden extensions.

     Valid ANSI standard C programs should compile properly with or
     without this option (though a rare few will require `-ansi').
     However, without this option, certain GNU extensions and
     traditional C features are supported as well.  With this option,
     they are rejected.

     `-pedantic' does not cause warning messages for use of the
     alternate keywords whose names begin and end with `__'.  Pedantic
     warnings are also disabled in the expression that follows
     `__extension__'.  However, only system header files should use
     these escape routes; application programs should avoid them.
     *Note Alternate Keywords::.

     This option is not intended to be useful; it exists only to satisfy
     pedants who would otherwise claim that GNU CC fails to support the
     ANSI standard.

     Some users try to use `-pedantic' to check programs for strict ANSI
     C conformance.  They soon find that it does not do quite what they
     want: it finds some non-ANSI practices, but not all--only those
     for which ANSI C *requires* a diagnostic.

     A feature to report any failure to conform to ANSI C might be
     useful in some instances, but would require considerable
     additional work and would be quite different from `-pedantic'.  We
     recommend, rather, that users take advantage of the extensions of
     GNU C and disregard the limitations of other compilers.  Aside
     from certain supercomputers and obsolete small machines, there is
     less and less reason ever to use any other C compiler other than
     for bootstrapping GNU CC.

`-pedantic-errors'
     Like `-pedantic', except that errors are produced rather than
     warnings.

`-W'
     Print extra warning messages for these events:

        * A nonvolatile automatic variable might be changed by a call to
          `longjmp'.  These warnings as well are possible only in
          optimizing compilation.

          The compiler sees only the calls to `setjmp'.  It cannot know
          where `longjmp' will be called; in fact, a signal handler
          could call it at any point in the code.  As a result, you may
          get a warning even when there is in fact no problem because
          `longjmp' cannot in fact be called at the place which would
          cause a problem.

        * A function can return either with or without a value.
          (Falling off the end of the function body is considered
          returning without a value.)  For example, this function would
          evoke such a warning:

               foo (a)
               {
                 if (a > 0)
                   return a;
               }

        * An expression-statement contains no side effects.

        * An unsigned value is compared against zero with `>' or `<='.

        * A comparison like `x<=y<=z' appears; this is equivalent to
          `(x<=y ? 1 : 0) <= z', which is a different interpretation
          from that of ordinary mathematical notation.

        * Storage-class specifiers like `static' are not the first
          things in a declaration.  According to the C Standard, this
          usage is obsolescent.

        * An aggregate has a partly bracketed initializer.  For
          example, the following code would evoke such a warning,
          because braces are missing around the initializer for `x.h':

               struct s { int f, g; };
               struct t { struct s h; int i; };
               struct t x = { 1, 2, 3 };

`-Wimplicit'
     Warn whenever a function or parameter is implicitly declared.

`-Wreturn-type'
     Warn whenever a function is defined with a return-type that
     defaults to `int'.  Also warn about any `return' statement with no
     return-value in a function whose return-type is not `void'.

`-Wunused'
     Warn whenever a local variable is unused aside from its
     declaration, whenever a function is declared static but never
     defined, and whenever a statement computes a result that is
     explicitly not used.

     If you want to prevent a warning for a particular variable, you
     can use this macro:

          #define USE(var) \
            static void * use_##var = (&use_##var, (void *) &var)

          USE (string);

`-Wswitch'
     Warn whenever a `switch' statement has an index of enumeral type
     and lacks a `case' for one or more of the named codes of that
     enumeration.  (The presence of a `default' label prevents this
     warning.)  `case' labels outside the enumeration range also
     provoke warnings when this option is used.

`-Wcomment'
     Warn whenever a comment-start sequence `/*' appears in a comment.

`-Wtrigraphs'
     Warn if any trigraphs are encountered (assuming they are enabled).

`-Wformat'
     Check calls to `printf' and `scanf', etc., to make sure that the
     arguments supplied have types appropriate to the format string
     specified.

`-Wchar-subscripts'
     Warn if an array subscript has type `char'.  This is a common cause
     of error, as programmers often forget that this type is signed on
     some machines.

`-Wuninitialized'
     An automatic variable is used without first being initialized.

     These warnings are possible only in optimizing compilation,
     because they require data flow information that is computed only
     when optimizing.  If you don't specify `-O', you simply won't get
     these warnings.

     These warnings occur only for variables that are candidates for
     register allocation.  Therefore, they do not occur for a variable
     that is declared `volatile', or whose address is taken, or whose
     size is other than 1, 2, 4 or 8 bytes.  Also, they do not occur for
     structures, unions or arrays, even when they are in registers.

     Note that there may be no warning about a variable that is used
     only to compute a value that itself is never used, because such
     computations may be deleted by data flow analysis before the
     warnings are printed.

     These warnings are made optional because GNU CC is not smart
     enough to see all the reasons why the code might be correct
     despite appearing to have an error.  Here is one example of how
     this can happen:

          {
            int x;
            switch (y)
              {
              case 1: x = 1;
                break;
              case 2: x = 4;
                break;
              case 3: x = 5;
              }
            foo (x);
          }

     If the value of `y' is always 1, 2 or 3, then `x' is always
     initialized, but GNU CC doesn't know this.  Here is another common
     case:

          {
            int save_y;
            if (change_y) save_y = y, y = new_y;
            ...
            if (change_y) y = save_y;
          }

     This has no bug because `save_y' is used only if it is set.

     Some spurious warnings can be avoided if you declare all the
     functions you use that never return as `volatile'.  *Note Function
     Attributes::.

`-Wparentheses'
     Warn if parentheses are omitted in certain contexts, such as when
     there is an assignment in a context where a truth value is
     expected, or when operators are nested whose precedence people
     often get confused about.

`-Wenum-clash'
     Warn about conversion between different enumeration types.  (C++
     only).

`-Wtemplate-debugging'
     When using templates in a C++ program, warn if debugging is not yet
     fully available (C++ only).

`-Wall'
     All of the above `-W' options combined.  These are all the options
     which pertain to usage that we recommend avoiding and that we
     believe is easy to avoid, even in conjunction with macros.

   The remaining `-W...' options are not implied by `-Wall' because
they warn about constructions that we consider reasonable to use, on
occasion, in clean programs.

`-Wtraditional'
     Warn about certain constructs that behave differently in
     traditional and ANSI C.

        * Macro arguments occurring within string constants in the
          macro body.  These would substitute the argument in
          traditional C, but are part of the constant in ANSI C.

        * A function declared external in one block and then used after
          the end of the block.

        * A `switch' statement has an operand of type `long'.

`-Wshadow'
     Warn whenever a local variable shadows another local variable.

`-Wid-clash-LEN'
     Warn whenever two distinct identifiers match in the first LEN
     characters.  This may help you prepare a program that will compile
     with certain obsolete, brain-damaged compilers.

`-Wpointer-arith'
     Warn about anything that depends on the "size of" a function type
     or of `void'.  GNU C assigns these types a size of 1, for
     convenience in calculations with `void *' pointers and pointers to
     functions.

`-Wcast-qual'
     Warn whenever a pointer is cast so as to remove a type qualifier
     from the target type.  For example, warn if a `const char *' is
     cast to an ordinary `char *'.

`-Wcast-align'
     Warn whenever a pointer is cast such that the required alignment
     of the target is increased.  For example, warn if a `char *' is
     cast to an `int *' on machines where integers can only be accessed
     at two- or four-byte boundaries.

`-Wwrite-strings'
     Give string constants the type `const char[LENGTH]' so that
     copying the address of one into a non-`const' `char *' pointer
     will get a warning.  These warnings will help you find at compile
     time code that can try to write into a string constant, but only
     if you have been very careful about using `const' in declarations
     and prototypes.  Otherwise, it will just be a nuisance; this is
     why we did not make `-Wall' request these warnings.

`-Wconversion'
     Warn if a prototype causes a type conversion that is different
     from what would happen to the same argument in the absence of a
     prototype.  This includes conversions of fixed point to floating
     and vice versa, and conversions changing the width or signedness
     of a fixed point argument except when the same as the default
     promotion.

     Also, warn if a negative integer constant expression is implicitly
     converted to an unsigned type.  For example, warn about the
     assignment `x = -1' if `x' is unsigned.  But do not warn about
     explicit casts like `(unsigned) -1'.

`-Waggregate-return'
     Warn if any functions that return structures or unions are defined
     or called.  (In languages where you can return an array, this also
     elicits a warning.)

`-Wstrict-prototypes'
     Warn if a function is declared or defined without specifying the
     argument types.  (An old-style function definition is permitted
     without a warning if preceded by a declaration which specifies the
     argument types.)

`-Wmissing-prototypes'
     Warn if a global function is defined without a previous prototype
     declaration.  This warning is issued even if the definition itself
     provides a prototype.  The aim is to detect global functions that
     fail to be declared in header files.

`-Wredundant-decls'
     Warn if anything is declared more than once in the same scope,
     even in cases where multiple declaration is valid and changes
     nothing.

`-Wnested-externs'
     Warn if an `extern' declaration is encountered within an function.

`-Winline'
     Warn if a function can not be inlined, and either it was declared
     as inline, or else the `-finline-functions' option was given.

`-Woverloaded-virtual'
     Warn when a derived class function declaration may be an error in
     defining a virtual function (C++ only).  In a derived class, the
     definitions of virtual functions must match the type signature of a
     virtual function declared in the base class.  With this option, the
     compiler warns when you define a function with the same name as a
     virtual function, but with a type signature that does not match any
     declarations from the base class.

`-Werror'
     Make all warnings into errors.


File: @.Distr.UsingGCC,  Node: Debugging Options,  Next: Optimize Options,  Prev: Warning Options,  Up: Invoking GCC

Options for Debugging Your Program or GNU CC
============================================

   GNU CC has various special options that are used for debugging
either your program or GCC:

`-g'
     Produce debugging information in the operating system's native
     format (stabs, COFF, XCOFF, or DWARF).  GDB can work with this
     debugging information.

     On most systems that use stabs format, `-g' enables use of extra
     debugging information that only GDB can use; this extra information
     makes debugging work better in GDB but will probably make other
     debuggers crash or refuse to read the program.  If you want to
     control for certain whether to generate the extra information, use
     `-gstabs+', `-gstabs', `-gxcoff+', `-gxcoff', `-gdwarf+', or
     `-gdwarf' (see below).

     Unlike most other C compilers, GNU CC allows you to use `-g' with
     `-O'.  The shortcuts taken by optimized code may occasionally
     produce surprising results: some variables you declared may not
     exist at all; flow of control may briefly move where you did not
     expect it; some statements may not be executed because they
     compute constant results or their values were already at hand;
     some statements may execute in different places because they were
     moved out of loops.

     Nevertheless it proves possible to debug optimized output.  This
     makes it reasonable to use the optimizer for programs that might
     have bugs.

     The following options are useful when GNU CC is generated with the
     capability for more than one debugging format.

`-ggdb'
     Produce debugging information in the native format (if that is
     supported), including GDB extensions if at all possible.

`-gstabs'
     Produce debugging information in stabs format (if that is
     supported), without GDB extensions.  This is the format used by
     DBX on most BSD systems.

`-gstabs+'
     Produce debugging information in stabs format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program.

`-gcoff'
     Produce debugging information in COFF format (if that is
     supported).  This is the format used by SDB on most System V
     systems prior to System V Release 4.

`-gxcoff'
     Produce debugging information in XCOFF format (if that is
     supported).  This is the format used by the DBX debugger on IBM
     RS/6000 systems.

`-gxcoff+'
     Produce debugging information in XCOFF format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program.

`-gdwarf'
     Produce debugging information in DWARF format (if that is
     supported).  This is the format used by SDB on most System V
     Release 4 systems.

`-gdwarf+'
     Produce debugging information in DWARF format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program.

`-gLEVEL'
`-ggdbLEVEL'
`-gstabsLEVEL'
`-gcoffLEVEL'
`-gxcoffLEVEL'
`-gdwarfLEVEL'
     Request debugging information and also use LEVEL to specify how
     much information.  The default level is 2.

     Level 1 produces minimal information, enough for making backtraces
     in parts of the program that you don't plan to debug.  This
     includes descriptions of functions and external variables, but no
     information about local variables and no line numbers.

     Level 3 includes extra information, such as all the macro
     definitions present in the program.  Some debuggers support macro
     expansion when you use `-g3'.

`-p'
     Generate extra code to write profile information suitable for the
     analysis program `prof'.  You must use this option when compiling
     the source files you want data about, and you must also use it when
     linking.

`-pg'
     Generate extra code to write profile information suitable for the
     analysis program `gprof'.  You must use this option when compiling
     the source files you want data about, and you must also use it when
     linking.

`-a'
     Generate extra code to write profile information for basic blocks,
     which will record the number of times each basic block is executed.
     This data could be analyzed by a program like `tcov'.  Note,
     however, that the format of the data is not what `tcov' expects.
     Eventually GNU `gprof' should be extended to process this data.

`-dLETTERS'
     Says to make debugging dumps during compilation at times specified
     by LETTERS.  This is used for debugging the compiler.  The file
     names for most of the dumps are made by appending a word to the
     source file name (e.g.  `foo.c.rtl' or `foo.c.jump').  Here are the
     possible letters for use in LETTERS, and their meanings:

    `M'
          Dump all macro definitions, at the end of preprocessing, and
          write no output.

    `N'
          Dump all macro names, at the end of preprocessing.

    `D'
          Dump all macro definitions, at the end of preprocessing, in
          addition to normal output.

    `y'
          Dump debugging information during parsing, to standard error.

    `r'
          Dump after RTL generation, to `FILE.rtl'.

    `x'
          Just generate RTL for a function instead of compiling it.
          Usually used with `r'.

    `j'
          Dump after first jump optimization, to `FILE.jump'.

    `s'
          Dump after CSE (including the jump optimization that sometimes
          follows CSE), to `FILE.cse'.

    `L'
          Dump after loop optimization, to `FILE.loop'.

    `t'
          Dump after the second CSE pass (including the jump
          optimization that sometimes follows CSE), to `FILE.cse2'.

    `f'
          Dump after flow analysis, to `FILE.flow'.

    `c'
          Dump after instruction combination, to the file
          `FILE.combine'.

    `S'
          Dump after the first instruction scheduling pass, to
          `FILE.sched'.

    `l'
          Dump after local register allocation, to `FILE.lreg'.

    `g'
          Dump after global register allocation, to `FILE.greg'.

    `R'
          Dump after the second instruction scheduling pass, to
          `FILE.sched2'.

    `J'
          Dump after last jump optimization, to `FILE.jump2'.

    `d'
          Dump after delayed branch scheduling, to `FILE.dbr'.

    `k'
          Dump after conversion from registers to stack, to
          `FILE.stack'.

    `a'
          Produce all the dumps listed above.

    `m'
          Print statistics on memory usage, at the end of the run, to
          standard error.

    `p'
          Annotate the assembler output with a comment indicating which
          pattern and alternative was used.

`-fpretend-float'
     When running a cross-compiler, pretend that the target machine
     uses the same floating point format as the host machine.  This
     causes incorrect output of the actual floating constants, but the
     actual instruction sequence will probably be the same as GNU CC
     would make when running on the target machine.

`-save-temps'
     Store the usual "temporary" intermediate files permanently; place
     them in the current directory and name them based on the source
     file.  Thus, compiling `foo.c' with `-c -save-temps' would produce
     files `foo.i' and `foo.s', as well as `foo.o'.

`-print-libgcc-file-name'
     Print the full absolute name of the library file `libgcc.a' that
     would be used when linking--and don't do anything else.  With this
     option, GNU CC does not compile or link anything; it just prints
     the file name.

     This is useful when you use `-nostdlib' but you do want to link
     with `libgcc.a'.  You can do

          gcc -nostdlib FILES... `gcc -print-libgcc-file-name`


File: @.Distr.UsingGCC,  Node: Optimize Options,  Next: Preprocessor Options,  Prev: Debugging Options,  Up: Invoking GCC

Options That Control Optimization
=================================

   These options control various sorts of optimizations:

`-O'
`-O1'
     Optimize.  Optimizing compilation takes somewhat more time, and a
     lot more memory for a large function.

     Without `-O', the compiler's goal is to reduce the cost of
     compilation and to make debugging produce the expected results.
     Statements are independent: if you stop the program with a
     breakpoint between statements, you can then assign a new value to
     any variable or change the program counter to any other statement
     in the function and get exactly the results you would expect from
     the source code.

     Without `-O', only variables declared `register' are allocated in
     registers.  The resulting compiled code is a little worse than
     produced by PCC without `-O'.

     With `-O', the compiler tries to reduce code size and execution
     time.

     When `-O' is specified, the two options `-fthread-jumps' and
     `-fdelayed-branch' are turned on.  On some machines other flags may
     also be turned on.

`-O2'
     Optimize even more.  Nearly all supported optimizations that do not
     involve a space-speed tradeoff are performed.  As compared to `-O',
     this option increases both compilation time and the performance of
     the generated code.

     `-O2' turns on all optional optimizations except for loop unrolling
     and frame pointer elimination.

`-O0'
     Do not optimize.

     If you use multiple `-O' options, with or without level numbers,
     the last such option is the one that is effective.

   Options of the form `-fFLAG' specify machine-independent flags.
Most flags have both positive and negative forms; the negative form of
`-ffoo' would be `-fno-foo'.  In the table below, only one of the forms
is listed--the one which is not the default.  You can figure out the
other form by either removing `no-' or adding it.

`-ffloat-store'
     Do not store floating point variables in registers, and inhibit
     other options that might change whether a floating point value is
     taken from a register or memory.

     This option prevents undesirable excess precision on machines such
     as the 68000 where the floating registers (of the 68881) keep more
     precision than a `double' is supposed to have.  For most programs,
     the excess precision does only good, but a few programs rely on the
     precise definition of IEEE floating point.  Use `-ffloat-store' for
     such programs.

`-fno-default-inline'
     Do not make member functions inline by default merely because they
     are defined inside the class scope (C++ only).  Otherwise, when
     you specify `-O', member functions defined inside class scope are
     compiled inline by default; i.e., you don't need to add `inline'
     in front of the member function name.

`-fno-defer-pop'
     Always pop the arguments to each function call as soon as that
     function returns.  For machines which must pop arguments after a
     function call, the compiler normally lets arguments accumulate on
     the stack for several function calls and pops them all at once.

`-fforce-mem'
     Force memory operands to be copied into registers before doing
     arithmetic on them.  This may produce better code by making all
     memory references potential common subexpressions.  When they are
     not common subexpressions, instruction combination should
     eliminate the separate register-load.  I am interested in hearing
     about the difference this makes.

`-fforce-addr'
     Force memory address constants to be copied into registers before
     doing arithmetic on them.  This may produce better code just as
     `-fforce-mem' may.  I am interested in hearing about the
     difference this makes.

`-fomit-frame-pointer'
     Don't keep the frame pointer in a register for functions that
     don't need one.  This avoids the instructions to save, set up and
     restore frame pointers; it also makes an extra register available
     in many functions.  *It also makes debugging impossible on some
     machines.*

     On some machines, such as the Vax, this flag has no effect, because
     the standard calling sequence automatically handles the frame
     pointer and nothing is saved by pretending it doesn't exist.  The
     machine-description macro `FRAME_POINTER_REQUIRED' controls
     whether a target machine supports this flag.  *Note Register
     Usage: (gcc.info)Registers.

`-fno-inline'
     Don't pay attention to the `inline' keyword.  Normally this option
     is used to keep the compiler from expanding any functions inline.
     Note that if you are not optimizing, no functions can be expanded
     inline.

`-finline-functions'
     Integrate all simple functions into their callers.  The compiler
     heuristically decides which functions are simple enough to be worth
     integrating in this way.

     If all calls to a given function are integrated, and the function
     is declared `static', then the function is normally not output as
     assembler code in its own right.

`-fkeep-inline-functions'
     Even if all calls to a given function are integrated, and the
     function is declared `static', nevertheless output a separate
     run-time callable version of the function.

`-fno-function-cse'
     Do not put function addresses in registers; make each instruction
     that calls a constant function contain the function's address
     explicitly.

     This option results in less efficient code, but some strange hacks
     that alter the assembler output may be confused by the
     optimizations performed when this option is not used.

`-ffast-math'
     This option allows GCC to violate some ANSI or IEEE rules and/or
     specifications in the interest of optimizing code for speed.  For
     example, it allows the compiler to assume arguments to the `sqrt'
     function are non-negative numbers.

     This option should never be turned on by any `-O' option since it
     can result in incorrect output for programs which depend on an
     exact implementation of IEEE or ANSI rules/specifications for math
     functions.

   The following options control specific optimizations.  The `-O2'
option turns on all of these optimizations except `-funroll-loops' and
`-funroll-all-loops'.  On most machines, the `-O' option turns on the
`-fthread-jumps' and `-fdelayed-branch' options, but specific machines
may handle it differently.

   You can use the following flags in the rare cases when "fine-tuning"
of optimizations to be performed is desired.

`-fstrength-reduce'
     Perform the optimizations of loop strength reduction and
     elimination of iteration variables.

`-fthread-jumps'
     Perform optimizations where we check to see if a jump branches to a
     location where another comparison subsumed by the first is found.
     If so, the first branch is redirected to either the destination of
     the second branch or a point immediately following it, depending
     on whether the condition is known to be true or false.

`-fcse-follow-jumps'
     In common subexpression elimination, scan through jump instructions
     when the target of the jump is not reached by any other path.  For
     example, when CSE encounters an `if' statement with an `else'
     clause, CSE will follow the jump when the condition tested is
     false.

`-fcse-skip-blocks'
     This is similar to `-fcse-follow-jumps', but causes CSE to follow
     jumps which conditionally skip over blocks.  When CSE encounters a
     simple `if' statement with no else clause, `-fcse-skip-blocks'
     causes CSE to follow the jump around the body of the `if'.

`-frerun-cse-after-loop'
     Re-run common subexpression elimination after loop optimizations
     has been performed.

`-fexpensive-optimizations'
     Perform a number of minor optimizations that are relatively
     expensive.

`-fdelayed-branch'
     If supported for the target machine, attempt to reorder
     instructions to exploit instruction slots available after delayed
     branch instructions.

`-fschedule-insns'
     If supported for the target machine, attempt to reorder
     instructions to eliminate execution stalls due to required data
     being unavailable.  This helps machines that have slow floating
     point or memory load instructions by allowing other instructions
     to be issued until the result of the load or floating point
     instruction is required.

`-fschedule-insns2'
     Similar to `-fschedule-insns', but requests an additional pass of
     instruction scheduling after register allocation has been done.
     This is especially useful on machines with a relatively small
     number of registers and where memory load instructions take more
     than one cycle.

`-fcaller-saves'
     Enable values to be allocated in registers that will be clobbered
     by function calls, by emitting extra instructions to save and
     restore the registers around such calls.  Such allocation is done
     only when it seems to result in better code than would otherwise
     be produced.

     This option is enabled by default on certain machines, usually
     those which have no call-preserved registers to use instead.

`-funroll-loops'
     Perform the optimization of loop unrolling.  This is only done for
     loops whose number of iterations can be determined at compile time
     or run time.  `-funroll-loop' implies both `-fstrength-reduce' and
     `-frerun-cse-after-loop'.

`-funroll-all-loops'
     Perform the optimization of loop unrolling.  This is done for all
     loops and usually makes programs run more slowly.
     `-funroll-all-loops' implies `-fstrength-reduce' as well as
     `-frerun-cse-after-loop'.

`-fno-peephole'
     Disable any machine-specific peephole optimizations.


File: @.Distr.UsingGCC,  Node: Preprocessor Options,  Next: Assembler Options,  Prev: Optimize Options,  Up: Invoking GCC

Options Controlling the Preprocessor
====================================

   These options control the C preprocessor, which is run on each C
source file before actual compilation.

   If you use the `-E' option, nothing is done except preprocessing.
Some of these options make sense only together with `-E' because they
cause the preprocessor output to be unsuitable for actual compilation.

`-include FILE'
     Process FILE as input before processing the regular input file.
     In effect, the contents of FILE are compiled first.  Any `-D' and
     `-U' options on the command line are always processed before
     `-include FILE', regardless of the order in which they are
     written.  All the `-include' and `-imacros' options are processed
     in the order in which they are written.

`-imacros FILE'
     Process FILE as input, discarding the resulting output, before
     processing the regular input file.  Because the output generated
     from FILE is discarded, the only effect of `-imacros FILE' is to
     make the macros defined in FILE available for use in the main
     input.

     Any `-D' and `-U' options on the command line are always processed
     before `-imacros FILE', regardless of the order in which they are
     written.  All the `-include' and `-imacros' options are processed
     in the order in which they are written.

`-idirafter DIR'
     Add the directory DIR to the second include path.  The directories
     on the second include path are searched when a header file is not
     found in any of the directories in the main include path (the one
     that `-I' adds to).

`-iprefix PREFIX'
     Specify PREFIX as the prefix for subsequent `-iwithprefix' options.

`-iwithprefix DIR'
     Add a directory to the second include path.  The directory's name
     is made by concatenating PREFIX and DIR, where PREFIX was
     specified previously with `-iprefix'.

`-nostdinc'
     Do not search the standard system directories for header files.
     Only the directories you have specified with `-I' options (and the
     current directory, if appropriate) are searched.  *Note Directory
     Options::, for information on `-I'.

     By using both `-nostdinc' and `-I-', you can limit the include-file
     search path to only those directories you specify explicitly.

`-undef'
     Do not predefine any nonstandard macros.  (Including architecture
     flags).

`-E'
     Run only the C preprocessor.  Preprocess all the C source files
     specified and output the results to standard output or to the
     specified output file.

`-C'
     Tell the preprocessor not to discard comments.  Used with the `-E'
     option.

`-P'
     Tell the preprocessor not to generate `#line' commands.  Used with
     the `-E' option.

`-M'
     Tell the preprocessor to output a rule suitable for `make'
     describing the dependencies of each object file.  For each source
     file, the preprocessor outputs one `make'-rule whose target is the
     object file name for that source file and whose dependencies are
     all the `#include' header files it uses.  This rule may be a
     single line or may be continued with `\'-newline if it is long.
     The list of rules is printed on standard output instead of the
     preprocessed C program.

     `-M' implies `-E'.

     Another way to specify output of a `make' rule is by setting the
     environment variable `DEPENDENCIES_OUTPUT' (*note Environment
     Variables::.).

`-MM'
     Like `-M' but the output mentions only the user header files
     included with `#include "FILE"'.  System header files included
     with `#include <FILE>' are omitted.

`-MD'
     Like `-M' but the dependency information is written to files with
     names made by replacing `.o' with `.d' at the end of the output
     file names.  This is in addition to compiling the input files as
     specified--`-MD' does not inhibit ordinary compilation the way
     `-M' does.

     The Mach utility `md' can be used to merge the `.d' files into a
     single dependency file suitable for using with the `make' command.

`-MMD'
     Like `-MD' except mention only user header files, not system
     header files.

`-H'
     Print the name of each header file used, in addition to other
     normal activities.

`-AQUESTION(ANSWER)'
     Assert the answer ANSWER for QUESTION, in case it is tested with a
     preprocessor conditional such as `#if #QUESTION(ANSWER)'.  `-A-'
     disables the standard assertions that normally describe the target
     machine.

`-DMACRO'
     Define macro MACRO with the string `1' as its definition.

`-DMACRO=DEFN'
     Define macro MACRO as DEFN.  All instances of `-D' on the command
     line are processed before any `-U' options.

`-UMACRO'
     Undefine macro MACRO.  `-U' options are evaluated after all `-D'
     options, but before any `-include' and `-imacros' options.

`-dM'
     Tell the preprocessor to output only a list of the macro
     definitions that are in effect at the end of preprocessing.  Used
     with the `-E' option.

`-dD'
     Tell the preprocessing to pass all macro definitions into the
     output, in their proper sequence in the rest of the output.

`-dN'
     Like `-dD' except that the macro arguments and contents are
     omitted.  Only `#define NAME' is included in the output.

`-trigraphs'
     Support ANSI C trigraphs.  You don't want to know about this
     brain-damage.  The `-ansi' option also has this effect.


File: @.Distr.UsingGCC,  Node: Assembler Options,  Next: Link Options,  Prev: Preprocessor Options,  Up: Invoking GCC

Passing Options to the Assembler
================================

`-Wa,OPTION'
     Pass OPTION as an option to the assembler.  If OPTION contains
     commas, it is split into multiple options at the commas.


File: @.Distr.UsingGCC,  Node: Link Options,  Next: Directory Options,  Prev: Assembler Options,  Up: Invoking GCC

Options for Linking
===================

   These options come into play when the compiler links object files
into an executable output file.  They are meaningless if the compiler is
not doing a link step.

`OBJECT-FILE-NAME'
     A file name that does not end in a special recognized suffix is
     considered to name an object file or library.  (Object files are
     distinguished from libraries by the linker according to the file
     contents.)  If linking is done, these object files are used as
     input to the linker.

`-c'
`-S'
`-E'
     If any of these options is used, then the linker is not run, and
     object file names should not be used as arguments.  *Note Overall
     Options::.

`-lLIBRARY'
     Search the library named LIBRARY when linking.

     It makes a difference where in the command you write this option;
     the linker searches processes libraries and object files in the
     order they are specified.  Thus, `foo.o -lz bar.o' searches
     library `z' after file `foo.o' but before `bar.o'.  If `bar.o'
     refers to functions in `z', those functions may not be loaded.

     The linker searches a standard list of directories for the library,
     which is actually a file named `libLIBRARY.a'.  The linker then
     uses this file as if it had been specified precisely by name.

     The directories searched include several standard system
     directories plus any that you specify with `-L'.

     Normally the files found this way are library files--archive files
     whose members are object files.  The linker handles an archive
     file by scanning through it for members which define symbols that
     have so far been referenced but not defined.  But if the file that
     is found is an ordinary object file, it is linked in the usual
     fashion.  The only difference between using an `-l' option and
     specifying a file name is that `-l' surrounds LIBRARY with `lib'
     and `.a' and searches several directories.

`-lobjc'
     You need this special case of the `-l' option in order to link an
     Objective C program.

`-nostartfiles'
     Do not use the standard system startup files when linking.  The
     standard libraries are used normally.

`-nostdlib'
     Don't use the standard system libraries and startup files when
     linking.  Only the files you specify will be passed to the linker.

`-static'
     On systems that support dynamic linking, this prevents linking
     with the shared libraries.  On other systems, this option has no
     effect.

`-shared'
     Produce a shared object which can then be linked with other
     objects to form an executable.  Only a few systems support this
     option.

`-symbolic'
     Bind references to global symbols when building a shared object.
     Warn about any unresolved references (unless overridden by the
     link editor option `-Xlinker -z -Xlinker defs').  Only a few
     systems support this option.

`-Xlinker OPTION'
     Pass OPTION as an option to the linker.  You can use this to
     supply system-specific linker options which GNU CC does not know
     how to recognize.

     If you want to pass an option that takes an argument, you must use
     `-Xlinker' twice, once for the option and once for the argument.
     For example, to pass `-assert definitions', you must write
     `-Xlinker -assert -Xlinker definitions'.  It does not work to write
     `-Xlinker "-assert definitions"', because this passes the entire
     string as a single argument, which is not what the linker expects.

`-Wl,OPTION'
     Pass OPTION as an option to the linker.  If OPTION contains
     commas, it is split into multiple options at the commas.

`-u SYMBOL'
     Pretend the symbol SYMBOL is undefined, to force linking of
     library modules to define it.  You can use `-u' multiple times with
     different symbols to force loading of additional library modules.


File: @.Distr.UsingGCC,  Node: Directory Options,  Next: Target Options,  Prev: Link Options,  Up: Invoking GCC

Options for Directory Search
============================

   These options specify directories to search for header files, for
libraries and for parts of the compiler:

`-IDIR'
     Append directory DIR to the list of directories searched for
     include files.

`-I-'
     Any directories you specify with `-I' options before the `-I-'
     option are searched only for the case of `#include "FILE"'; they
     are not searched for `#include <FILE>'.

     If additional directories are specified with `-I' options after
     the `-I-', these directories are searched for all `#include'
     directives.  (Ordinarily *all* `-I' directories are used this way.)

     In addition, the `-I-' option inhibits the use of the current
     directory (where the current input file came from) as the first
     search directory for `#include "FILE"'.  There is no way to
     override this effect of `-I-'.  With `-I.' you can specify
     searching the directory which was current when the compiler was
     invoked.  That is not exactly the same as what the preprocessor
     does by default, but it is often satisfactory.

     `-I-' does not inhibit the use of the standard system directories
     for header files.  Thus, `-I-' and `-nostdinc' are independent.

`-LDIR'
     Add directory DIR to the list of directories to be searched for
     `-l'.

`-BPREFIX'
     This option specifies where to find the executables, libraries and
     data files of the compiler itself.

     The compiler driver program runs one or more of the subprograms
     `cpp', `cc1', `as' and `ld'.  It tries PREFIX as a prefix for each
     program it tries to run, both with and without `MACHINE/VERSION/'
     (*note Target Options::.).

     For each subprogram to be run, the compiler driver first tries the
     `-B' prefix, if any.  If that name is not found, or if `-B' was
     not specified, the driver tries two standard prefixes, which are
     `/usr/lib/gcc/' and `/usr/local/lib/gcc-lib/'.  If neither of
     those results in a file name that is found, the unmodified program
     name is searched for using the directories specified in your
     `PATH' environment variable.

     `-B' prefixes that effectively specify directory names also apply
     to libraries in the linker, because the compiler translates these
     options into `-L' options for the linker.

     The run-time support file `libgcc.a' can also be searched for using
     the `-B' prefix, if needed.  If it is not found there, the two
     standard prefixes above are tried, and that is all.  The file is
     left out of the link if it is not found by those means.

     Another way to specify a prefix much like the `-B' prefix is to use
     the environment variable `GCC_EXEC_PREFIX'.  *Note Environment
     Variables::.


File: @.Distr.UsingGCC,  Node: Target Options,  Next: Submodel Options,  Prev: Directory Options,  Up: Invoking GCC

Specifying Target Machine and Compiler Version
==============================================

   By default, GNU CC compiles code for the same type of machine that
you are using.  However, it can also be installed as a cross-compiler,
to compile for some other type of machine.  In fact, several different
configurations of GNU CC, for different target machines, can be
installed side by side.  Then you specify which one to use with the
`-b' option.

   In addition, older and newer versions of GNU CC can be installed side
by side.  One of them (probably the newest) will be the default, but
you may sometimes wish to use another.

`-b MACHINE'
     The argument MACHINE specifies the target machine for compilation.
     This is useful when you have installed GNU CC as a cross-compiler.

     The value to use for MACHINE is the same as was specified as the
     machine type when configuring GNU CC as a cross-compiler.  For
     example, if a cross-compiler was configured with `configure
     i386v', meaning to compile for an 80386 running System V, then you
     would specify `-b i386v' to run that cross compiler.

     When you do not specify `-b', it normally means to compile for the
     same type of machine that you are using.

`-V VERSION'
     The argument VERSION specifies which version of GNU CC to run.
     This is useful when multiple versions are installed.  For example,
     VERSION might be `2.0', meaning to run GNU CC version 2.0.

     The default version, when you do not specify `-V', is controlled
     by the way GNU CC is installed.  Normally, it will be a version
     that is recommended for general use.

   The `-b' and `-V' options actually work by controlling part of the
file name used for the executable files and libraries used for
compilation.  A given version of GNU CC, for a given target machine, is
normally kept in the directory `/usr/local/lib/gcc-lib/MACHINE/VERSION'.

   Thus, sites can customize the effect of `-b' or `-V' either by
changing the names of these directories or adding alternate names (or
symbolic links).  If in directory `/usr/local/lib/gcc-lib/' the file
`80386' is a link to the file `i386v', then `-b 80386' becomes an alias
for `-b i386v'.

   In one respect, the `-b' or `-V' do not completely change to a
different compiler: the top-level driver program `gcc' that you
originally invoked continues to run and invoke the other executables
(preprocessor, compiler per se, assembler and linker) that do the real
work.  However, since no real work is done in the driver program, it
usually does not matter that the driver program in use is not the one
for the specified target and version.

   The only way that the driver program depends on the target machine is
in the parsing and handling of special machine-specific options.
However, this is controlled by a file which is found, along with the
other executables, in the directory for the specified version and
target machine.  As a result, a single installed driver program adapts
to any specified target machine and compiler version.

   The driver program executable does control one significant thing,
however: the default version and target machine.  Therefore, you can
install different instances of the driver program, compiled for
different targets or versions, under different names.

   For example, if the driver for version 2.0 is installed as `ogcc'
and that for version 2.1 is installed as `gcc', then the command `gcc'
will use version 2.1 by default, while `ogcc' will use 2.0 by default.
However, you can choose either version with either command with the
`-V' option.


File: @.Distr.UsingGCC,  Node: Submodel Options,  Next: Code Gen Options,  Prev: Target Options,  Up: Invoking GCC

Hardware Models and Configurations
==================================

   Earlier we discussed the standard option `-b' which chooses among
different installed compilers for completely different target machines,
such as Vax vs. 68000 vs. 80386.

   In addition, each of these target machine types can have its own
special options, starting with `-m', to choose among various hardware
models or configurations--for example, 68010 vs 68020, floating
coprocessor or none.  A single installed version of the compiler can
compile for any model or configuration, according to the options
specified.

   Some configurations of the compiler also support additional special
options, usually for compatibility with other compilers on the same
platform.

* Menu:

* M680x0 Options::
* VAX Options::
* SPARC Options::
* Convex Options::
* AMD29K Options::
* M88K Options::
* RS/6000 Options::
* RT Options::
* MIPS Options::
* i386 Options::
* HPPA Options::
* Intel 960 Options::
* DEC Alpha Options::
* System V Options::


File: @.Distr.UsingGCC,  Node: M680x0 Options,  Next: VAX Options,  Up: Submodel Options

M680x0 Options
--------------

   These are the `-m' options defined for the 68000 series.  The default
values for these options depends on which style of 68000 was selected
when the compiler was configured; the defaults for the most common
choices are given below.

`-m68000'
`-mc68000'
     Generate output for a 68000.  This is the default when the
     compiler is configured for 68000-based systems.

`-m68020'
`-mc68020'
     Generate output for a 68020.  This is the default when the
     compiler is configured for 68020-based systems.

`-m68881'
     Generate output containing 68881 instructions for floating point.
     This is the default for most 68020 systems unless `-nfp' was
     specified when the compiler was configured.

`-m68030'
     Generate output for a 68030.  This is the default when the
     compiler is configured for 68030-based systems.

`-m68040'
     Generate output for a 68040.  This is the default when the
     compiler is configured for 68040-based systems.

`-m68020-40'
     Generate output for a 68040, without using any of the new
     instructions.  This results in code which can run relatively
     efficiently on either a 68020/68881 or a 68030 or a 68040.

`-mfpa'
     Generate output containing Sun FPA instructions for floating point.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not part of GNU CC.
     Normally the facilities of the machine's usual C compiler are
     used, but this can't be done directly in cross-compilation.  You
     must make your own arrangements to provide suitable library
     functions for cross-compilation.

`-mshort'
     Consider type `int' to be 16 bits wide, like `short int'.

`-mnobitfield'
     Do not use the bit-field instructions.  The `-m68000' option
     implies `-mnobitfield'.

`-mbitfield'
     Do use the bit-field instructions.  The `-m68020' option implies
     `-mbitfield'.  This is the default if you use a configuration
     designed for a 68020.

`-mrtd'
     Use a different function-calling convention, in which functions
     that take a fixed number of arguments return with the `rtd'
     instruction, which pops their arguments while returning.  This
     saves one instruction in the caller since there is no need to pop
     the arguments there.

     This calling convention is incompatible with the one normally used
     on Unix, so you cannot use it if you need to call libraries
     compiled with the Unix compiler.

     Also, you must provide function prototypes for all functions that
     take variable numbers of arguments (including `printf'); otherwise
     incorrect code will be generated for calls to those functions.

     In addition, seriously incorrect code will result if you call a
     function with too many arguments.  (Normally, extra arguments are
     harmlessly ignored.)

     The `rtd' instruction is supported by the 68010 and 68020
     processors, but not by the 68000.


File: @.Distr.UsingGCC,  Node: VAX Options,  Next: SPARC Options,  Prev: M680x0 Options,  Up: Submodel Options

VAX Options
-----------

   These `-m' options are defined for the Vax:

`-munix'
     Do not output certain jump instructions (`aobleq' and so on) that
     the Unix assembler for the Vax cannot handle across long ranges.

`-mgnu'
     Do output those jump instructions, on the assumption that you will
     assemble with the GNU assembler.

`-mg'
     Output code for g-format floating point numbers instead of
     d-format.


File: @.Distr.UsingGCC,  Node: SPARC Options,  Next: Convex Options,  Prev: VAX Options,  Up: Submodel Options

SPARC Options
-------------

   These `-m' switches are supported on the SPARC:

`-mfpu'
`-mhard-float'
     Generate output containing floating point instructions.  This is
     the default.

`-mno-fpu'
`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* there is no GNU floating-point library for SPARC.
     Normally the facilities of the machine's usual C compiler are
     used, but this cannot be done directly in cross-compilation.  You
     must make your own arrangements to provide suitable library
     functions for cross-compilation.

     `-msoft-float' changes the calling convention in the output file;
     therefore, it is only useful if you compile *all* of a program with
     this option.  In particular, you need to compile `libgcc.a', the
     library that comes with GNU CC, with `-msoft-float' in order for
     this to work.

`-mno-epilogue'
`-mepilogue'
     With `-mepilogue' (the default), the compiler always emits code for
     function exit at the end of each function.  Any function exit in
     the middle of the function (such as a return statement in C) will
     generate a jump to the exit code at the end of the function.

     With `-mno-epilogue', the compiler tries to emit exit code inline
     at every function exit.

`-mv8'
`-msparclite'
     These two options select variations on the SPARC architecture.

     By default (unless specifically configured for the Fujitsu
     SPARClite), GCC generates code for the v7 variant of the SPARC
     architecture.

     `-mv8' will give you SPARC v8 code.  The only difference from v7
     code is that the compiler emits the integer multiply and integer
     divide instructions which exist in SPARC v8 but not in SPARC v7.

     `-msparclite' will give you SPARClite code.  This adds the integer
     multiply, integer divide step and scan (`ffs') instructions which
     exist in SPARClite but not in SPARC v7.


File: @.Distr.UsingGCC,  Node: Convex Options,  Next: AMD29K Options,  Prev: SPARC Options,  Up: Submodel Options

Convex Options
--------------

   These `-m' options are defined for Convex:

`-mc1'
     Generate output for C1.  The code will run on any Convex machine.
     The preprocessor symbol `__convex__c1__' is defined.

`-mc2'
     Generate output for C2.  Uses instructions not available on C1.
     Scheduling and other optimizations are chosen for max performance
     on C2.  The preprocessor symbol `__convex_c2__' is defined.

`-mc32'
     Generate output for C32xx.  Uses instructions not available on C1.
     Scheduling and other optimizations are chosen for max performance
     on C32.  The preprocessor symbol `__convex_c32__' is defined.

`-mc34'
     Generate output for C34xx.  Uses instructions not available on C1.
     Scheduling and other optimizations are chosen for max performance
     on C34.  The preprocessor symbol `__convex_c34__' is defined.

`-mc38'
     Generate output for C38xx.  Uses instructions not available on C1.
     Scheduling and other optimizations are chosen for max performance
     on C38.  The preprocessor symbol `__convex_c38__' is defined.

`-margcount'
     Generate code which puts an argument count in the word preceding
     each argument list.  This is compatible with regular CC, and a few
     programs may need the argument count word.  GDB and other
     source-level debuggers do not need it; this info is in the symbol
     table.

`-mnoargcount'
     Omit the argument count word.  This is the default.

`-mvolatile-cache'
     Allow volatile references to be cached.  This is the default.

`-mvolatile-nocache'
     Volatile references bypass the data cache, going all the way to
     memory.  This is only needed for multi-processor code that does
     not use standard synchronization instructions.  Making
     non-volatile references to volatile locations will not necessarily
     work.

`-mlong32'
     Type long is 32 bits, the same as type int.  This is the default.

`-mlong64'
     Type long is 64 bits, the same as type long long.  This option is
     useless, because no library support exists for it.


File: @.Distr.UsingGCC,  Node: AMD29K Options,  Next: M88K Options,  Prev: Convex Options,  Up: Submodel Options

AMD29K Options
--------------

   These `-m' options are defined for the AMD Am29000:

`-mdw'
     Generate code that assumes the `DW' bit is set, i.e., that byte and
     halfword operations are directly supported by the hardware.  This
     is the default.

`-mnodw'
     Generate code that assumes the `DW' bit is not set.

`-mbw'
     Generate code that assumes the system supports byte and halfword
     write operations.  This is the default.

`-mnbw'
     Generate code that assumes the systems does not support byte and
     halfword write operations.  `-mnbw' implies `-mnodw'.

`-msmall'
     Use a small memory model that assumes that all function addresses
     are either within a single 256 KB segment or at an absolute
     address of less than 256k.  This allows the `call' instruction to
     be used instead of a `const', `consth', `calli' sequence.

`-mlarge'
     Do not assume that the `call' instruction can be used; this is the
     default.

`-m29050'
     Generate code for the Am29050.

`-m29000'
     Generate code for the Am29000.  This is the default.

`-mkernel-registers'
     Generate references to registers `gr64-gr95' instead of to
     registers `gr96-gr127'.  This option can be used when compiling
     kernel code that wants a set of global registers disjoint from
     that used by user-mode code.

     Note that when this option is used, register names in `-f' flags
     must use the normal, user-mode, names.

`-muser-registers'
     Use the normal set of global registers, `gr96-gr127'.  This is the
     default.

`-mstack-check'
     Insert a call to `__msp_check' after each stack adjustment.  This
     is often used for kernel code.


File: @.Distr.UsingGCC,  Node: M88K Options,  Next: RS/6000 Options,  Prev: AMD29K Options,  Up: Submodel Options

M88K Options
------------

   These `-m' options are defined for Motorola 88k architectures:

`-m88000'
     Generate code that works well on both the m88100 and the m88110.

`-m88100'
     Generate code that works best for the m88100, but that also runs
     on the m88110.

`-m88110'
     Generate code that works best for the m88110, and may not run on
     the m88100.

`-mbig-pic'
     Obsolete option to be removed from the next revision.  Use `-fPIC'.

`-midentify-revision'
     Include an `ident' directive in the assembler output recording the
     source file name, compiler name and version, timestamp, and
     compilation flags used.

`-mno-underscores'
     In assembler output, emit symbol names without adding an underscore
     character at the beginning of each name.  The default is to use an
     underscore as prefix on each name.

`-mocs-debug-info'
`-mno-ocs-debug-info'
     Include (or omit) additional debugging information (about
     registers used in each stack frame) as specified in the 88open
     Object Compatibility Standard, "OCS".  This extra information
     allows debugging of code that has had the frame pointer
     eliminated.  The default for DG/UX, SVr4, and Delta 88 SVr3.2 is
     to include this information; other 88k configurations omit this
     information by default.

`-mocs-frame-position'
     When emitting COFF debugging information for automatic variables
     and parameters stored on the stack, use the offset from the
     canonical frame address, which is the stack pointer (register 31)
     on entry to the function.  The DG/UX, SVr4, Delta88 SVr3.2, and
     BCS configurations use `-mocs-frame-position'; other 88k
     configurations have the default `-mno-ocs-frame-position'.

`-mno-ocs-frame-position'
     When emitting COFF debugging information for automatic variables
     and parameters stored on the stack, use the offset from the frame
     pointer register (register 30).  When this option is in effect,
     the frame pointer is not eliminated when debugging information is
     selected by the -g switch.

`-moptimize-arg-area'
`-mno-optimize-arg-area'
     Control how function arguments are stored in stack frames.
     `-moptimize-arg-area' saves space by optimizing them, but this
     conflicts with the 88open specifications.  The opposite
     alternative, `-mno-optimize-arg-area', agrees with 88open
     standards.  By default GNU CC does not optimize the argument area.

`-mshort-data-NUM'
     Generate smaller data references by making them relative to `r0',
     which allows loading a value using a single instruction (rather
     than the usual two).  You control which data references are
     affected by specifying NUM with this option.  For example, if you
     specify `-mshort-data-512', then the data references affected are
     those involving displacements of less than 512 bytes.
     `-mshort-data-NUM' is not effective for NUM greater than 64k.

`-mserialize-volatile'
`-mno-serialize-volatile'
     Do, or do not, generate code to guarantee sequential consistency of
     volatile memory references.

     GNU CC always guarantees consistency by default, for the preferred
     processor submodel.  How this is done depends on the submodel.

     The m88100 processor does not reorder memory references and so
     always provides sequential consistency.  If you use `-m88100', GNU
     CC does not generate any special instructions for sequential
     consistency.

     The order of memory references made by the m88110 processor does
     not always match the order of the instructions requesting those
     references.  In particular, a load instruction may execute before
     a preceding store instruction.  Such reordering violates
     sequential consistency of volatile memory references, when there
     are multiple processors.  When you use `-m88000' or `-m88110', GNU
     CC generates special instructions when appropriate, to force
     execution in the proper order.

     The extra code generated to guarantee consistency may affect the
     performance of your application.  If you know that you can safely
     forgo this guarantee, you may use the option
     `-mno-serialize-volatile'.

     If you use the `-m88100' option but require sequential consistency
     when running on the m88110 processor, you should use
     `-mserialize-volatile'.

`-msvr4'
`-msvr3'
     Turn on (`-msvr4') or off (`-msvr3') compiler extensions related
     to System V release 4 (SVr4).  This controls the following:

       1. Which variant of the assembler syntax to emit (which you can
          select independently using `-mversion-03.00').

       2. `-msvr4' makes the C preprocessor recognize `#pragma weak'
          that is used on System V release 4.

       3. `-msvr4' makes GNU CC issue additional declaration directives
          used in SVr4.

     `-msvr3' is the default for all m88k configurations except the
     SVr4 configuration.

`-mversion-03.00'
     In the DG/UX configuration, there are two flavors of SVr4.  This
     option modifies `-msvr4' to select whether the hybrid-COFF or
     real-ELF flavor is used.  All other configurations ignore this
     option.

`-mno-check-zero-division'
`-mcheck-zero-division'
     Early models of the 88k architecture had problems with division by
     zero; in particular, many of them didn't trap.  Use these options
     to avoid including (or to include explicitly) additional code to
     detect division by zero and signal an exception.  All GNU CC
     configurations for the 88k use `-mcheck-zero-division' by default.

`-muse-div-instruction'
     Do not emit code to check both the divisor and dividend when doing
     signed integer division to see if either is negative, and adjust
     the signs so the divide is done using non-negative numbers.
     Instead, rely on the operating system to calculate the correct
     value when the `div' instruction traps.  This results in different
     behavior when the most negative number is divided by -1, but is
     useful when most or all signed integer divisions are done with
     positive numbers.

`-mtrap-large-shift'
`-mhandle-large-shift'
     Include code to detect bit-shifts of more than 31 bits;
     respectively, trap such shifts or emit code to handle them
     properly.  By default GNU CC makes no special provision for large
     bit shifts.

`-mwarn-passed-structs'
     Warn when a function passes a struct as an argument or result.
     Structure-passing conventions have changed during the evolution of
     the C language, and are often the source of portability problems.
     By default, GNU CC issues no such warning.


File: @.Distr.UsingGCC,  Node: RS/6000 Options,  Next: RT Options,  Prev: M88K Options,  Up: Submodel Options

IBM RS/6000 Options
-------------------

   Only one pair of `-m' options is defined for the IBM RS/6000:

`-mfp-in-toc'
`-mno-fp-in-toc'
     Control whether or not floating-point constants go in the Table of
     Contents (TOC), a table of all global variable and function
     addresses.  By default GNU CC puts floating-point constants there;
     if the TOC overflows, `-mno-fp-in-toc' will reduce the size of the
     TOC, which may avoid the overflow.


File: @.Distr.UsingGCC,  Node: RT Options,  Next: MIPS Options,  Prev: RS/6000 Options,  Up: Submodel Options

IBM RT Options
--------------

   These `-m' options are defined for the IBM RT PC:

`-min-line-mul'
     Use an in-line code sequence for integer multiplies.  This is the
     default.

`-mcall-lib-mul'
     Call `lmul$$' for integer multiples.

`-mfull-fp-blocks'
     Generate full-size floating point data blocks, including the
     minimum amount of scratch space recommended by IBM.  This is the
     default.

`-mminimum-fp-blocks'
     Do not include extra scratch space in floating point data blocks.
     This results in smaller code, but slower execution, since scratch
     space must be allocated dynamically.

`-mfp-arg-in-fpregs'
     Use a calling sequence incompatible with the IBM calling
     convention in which floating point arguments are passed in
     floating point registers.  Note that `varargs.h' and `stdargs.h'
     will not work with floating point operands if this option is
     specified.

`-mfp-arg-in-gregs'
     Use the normal calling convention for floating point arguments.
     This is the default.

`-mhc-struct-return'
     Return structures of more than one word in memory, rather than in a
     register.  This provides compatibility with the MetaWare HighC (hc)
     compiler.  Use the option `-fpcc-struct-return' for compatibility
     with the Portable C Compiler (pcc).

`-mnohc-struct-return'
     Return some structures of more than one word in registers, when
     convenient.  This is the default.  For compatibility with the
     IBM-supplied compilers, use the option `-fpcc-struct-return' or the
     option `-mhc-struct-return'.


File: @.Distr.UsingGCC,  Node: MIPS Options,  Next: i386 Options,  Prev: RT Options,  Up: Submodel Options

MIPS Options
------------

   These `-m' options are defined for the MIPS family of computers:

`-mcpu=CPU TYPE'
     Assume the defaults for the machine type CPU TYPE when scheduling
     instructions.  The default CPU TYPE is `default', which picks the
     longest cycles times for any of the machines, in order that the
     code run at reasonable rates on all MIPS cpu's.  Other choices for
     CPU TYPE are `r2000', `r3000', `r4000', and `r6000'.  While
     picking a specific CPU TYPE will schedule things appropriately for
     that particular chip, the compiler will not generate any code that
     does not meet level 1 of the MIPS ISA (instruction set
     architecture) without the `-mips2' or `-mips3' switches being used.

`-mips2'
     Issue instructions from level 2 of the MIPS ISA (branch likely,
     square root instructions).  The `-mcpu=r4000' or `-mcpu=r6000'
     switch must be used in conjunction with `-mips2'.

`-mips3'
     Issue instructions from level 3 of the MIPS ISA (64 bit
     instructions).  You must use the `-mcpu=r4000' switch along with
     `-mips3'.

`-mint64'
`-mlong64'
`-mlonglong128'
     These options don't work at present.

`-mmips-as'
     Generate code for the MIPS assembler, and invoke `mips-tfile' to
     add normal debug information.  This is the default for all
     platforms except for the OSF/1 reference platform, using the
     OSF/rose object format.  If the either of the `-gstabs' or
     `-gstabs+' switches are used, the `mips-tfile' program will
     encapsulate the stabs within MIPS ECOFF.

`-mgas'
     Generate code for the GNU assembler.  This is the default on the
     OSF/1 reference platform, using the OSF/rose object format.

`-mrnames'
`-mno-rnames'
     The `-mrnames' switch says to output code using the MIPS software
     names for the registers, instead of the hardware names (ie, A0
     instead of $4).  The GNU assembler does not support the `-mrnames'
     switch, and the MIPS assembler will be instructed to run the MIPS
     C preprocessor over the source file.  The `-mno-rnames' switch is
     default.

`-mgpopt'
`-mno-gpopt'
     The `-mgpopt' switch says to write all of the data declarations
     before the instructions in the text section, this allows the MIPS
     assembler to generate one word memory references instead of using
     two words for short global or static data items.  This is on by
     default if optimization is selected.

`-mstats'
`-mno-stats'
     For each non-inline function processed, the `-mstats' switch
     causes the compiler to emit one line to the standard error file to
     print statistics about the program (number of registers saved,
     stack size, etc.).

`-mmemcpy'
`-mno-memcpy'
     The `-mmemcpy' switch makes all block moves call the appropriate
     string function (`memcpy' or `bcopy') instead of possibly
     generating inline code.

`-mmips-tfile'
`-mno-mips-tfile'
     The `-mno-mips-tfile' switch causes the compiler not postprocess
     the object file with the `mips-tfile' program, after the MIPS
     assembler has generated it to add debug support.  If `mips-tfile'
     is not run, then no local variables will be available to the
     debugger.  In addition, `stage2' and `stage3' objects will have
     the temporary file names passed to the assembler embedded in the
     object file, which means the objects will not compare the same.
     The `-mno-mips-tfile' switch should only be used when there are
     bugs in the `mips-tfile' program that prevents compilation.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not part of GNU CC.
     Normally the facilities of the machine's usual C compiler are
     used, but this can't be done directly in cross-compilation.  You
     must make your own arrangements to provide suitable library
     functions for cross-compilation.

`-mhard-float'
     Generate output containing floating point instructions.  This is
     the default if you use the unmodified sources.

`-mfp64'
     Assume that the FR bit in the status word is on, and that there
     are 32 64-bit floating point registers, instead of 32 32-bit
     floating point registers.  You must also specify the `-mcpu=r4000'
     and `-mips3' switches.

`-mfp32'
     Assume that there are 32 32-bit floating point registers.  This is
     the default.

`-mabicalls'
`-mno-abicalls'
     Emit (or do not emit) the pseudo operations `.abicalls',
     `.cpload', and `.cprestore' that some System V.4 ports use for
     position independent code.

`-mlong-calls'
`-mlong-calls'
     Do all calls with the `JALR' instruction, which requires loading
     up a function's address into a register before the call.  You need
     to use this switch, if you call outside of the current 512
     megabyte segment to functions that are not through pointers.

`-mhalf-pic'
`-mno-half-pic'
     Put pointers to extern references into the data section and load
     them up, rather than put the references in the text section.

`-G NUM'
     Put global and static items less than or equal to NUM bytes into
     the small data or bss sections instead of the normal data or bss
     section.  This allows the assembler to emit one word memory
     reference instructions based on the global pointer (GP or $28),
     instead of the normal two words used.  By default, NUM is 8 when
     the MIPS assembler is used, and 0 when the GNU assembler is used.
     The `-G NUM' switch is also passed to the assembler and linker.
     All modules should be compiled with the same `-G NUM' value.

`-nocpp'
     Tell the MIPS assembler to not run it's preprocessor over user
     assembler files (with a `.s' suffix) when assembling them.


File: @.Distr.UsingGCC,  Node: i386 Options,  Next: HPPA Options,  Prev: MIPS Options,  Up: Submodel Options

Intel 386 Options
-----------------

   These `-m' options are defined for the i386 family of computers:

`-m486'
`-mno-486'
     Control whether or not code is optimized for a 486 instead of an
     386.  Code generated for an 486 will run on a 386 and vice versa.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not part of GNU CC.
     Normally the facilities of the machine's usual C compiler are
     used, but this can't be done directly in cross-compilation.  You
     must make your own arrangements to provide suitable library
     functions for cross-compilation.

     On machines where a function returns floating point results in the
     80387 register stack, some floating point opcodes may be emitted
     even if `-msoft-float' is used.

`-mno-fp-ret-in-387'
     Do not use the FPU registers for return values of functions.

     The usual calling convention has functions return values of types
     `float' and `double' in an FPU register, even if there is no FPU.
     The idea is that the operating system should emulate an FPU.

     The option `-mno-fp-ret-in-387' causes such values to be returned
     in ordinary CPU registers instead.


File: @.Distr.UsingGCC,  Node: HPPA Options,  Next: Intel 960 Options,  Prev: i386 Options,  Up: Submodel Options

HPPA Options
------------

   These `-m' options are defined for the HPPA family of computers:

`-mpa-risc-1-0'
     Generate code for a PA 1.0 processor.

`-mpa-risc-1-1'
     Generate code for a PA 1.1 processor.

`-mkernel'
     Generate code which is suitable for use in kernels.  Specifically,
     avoid `add' instructions in which one of the arguments is the DP
     register; generate `addil' instructions instead.  This avoids a
     rather serious bug in the HP-UX linker.

`-mshared-libs'
     Generate code that can be linked against HP-UX shared libraries.
     This option is not fully function yet, and is not on by default
     for any PA target.  Using this option can cause incorrect code to
     be generated by the compiler.

`-mno-shared-libs'
     Don't generate code that will be linked against shared libraries.
     This is the default for all PA targets.

`-mlong-calls'
     Generate code which allows calls to functions greater than 256k
     away from the caller when the caller and callee are in the same
     source file.  Do not turn this option on unless code refuses to
     link with "branch out of range errors" from the linker.

`-mdisable-fpregs'
     Prevent floating point registers from being used in any manner.
     This is necessary for compiling kernels which perform lazy context
     switching of floating point registers.  If you use this option and
     attempt to perform floating point operations, the compiler will
     abort.

`-mdisable-indexing'
     Prevent the compiler from using indexing address modes.  This
     avoids some rather obscure problems when compiling MIG generated
     code under MACH.

`-mtrailing-colon'
     Add a colon to the end of label definitions (for ELF assemblers).


File: @.Distr.UsingGCC,  Node: Intel 960 Options,  Next: DEC Alpha Options,  Prev: HPPA Options,  Up: Submodel Options

Intel 960 Options
-----------------

   These `-m' options are defined for the Intel 960 implementations:

`-mCPU TYPE'
     Assume the defaults for the machine type CPU TYPE for some of the
     other options, including instruction scheduling, floating point
     support, and addressing modes.  The choices for CPU TYPE are `ka',
     `kb', `mc', `ca', `cf', `sa', and `sb'.  The default is `kb'.

`-mnumerics'
`-msoft-float'
     The `-mnumerics' option indicates that the processor does support
     floating-point instructions.  The `-msoft-float' option indicates
     that floating-point support should not be assumed.

`-mleaf-procedures'
`-mno-leaf-procedures'
     Do (or do not) attempt to alter leaf procedures to be callable
     with the `bal' instruction as well as `call'.  This will result in
     more efficient code for explicit calls when the `bal' instruction
     can be substituted by the assembler or linker, but less efficient
     code in other cases, such as calls via function pointers, or using
     a linker that doesn't support this optimization.

`-mtail-call'
`-mno-tail-call'
     Do (or do not) make additional attempts (beyond those of the
     machine-independent portions of the compiler) to optimize
     tail-recursive calls into branches.  You may not want to do this
     because the detection of cases where this is not valid is not
     totally complete.  The default is `-mno-tail-call'.

`-mcomplex-addr'
`-mno-complex-addr'
     Assume (or do not assume) that the use of a complex addressing
     mode is a win on this implementation of the i960.  Complex
     addressing modes may not be worthwhile on the K-series, but they
     definitely are on the C-series.  The default is currently
     `-mcomplex-addr' for all processors except the CB and CC.

`-mcode-align'
`-mno-code-align'
     Align code to 8-byte boundaries for faster fetching (or don't
     bother).  Currently turned on by default for C-series
     implementations only.

`-mic-compat'
`-mic2.0-compat'
`-mic3.0-compat'
     Enable compatibility with iC960 v2.0 or v3.0.

`-masm-compat'
`-mintel-asm'
     Enable compatibility with the iC960 assembler.

`-mstrict-align'
`-mno-strict-align'
     Do not permit (do permit) unaligned accesses.

`-mold-align'
     Enable structure-alignment compatibility with Intel's gcc release
     version 1.3 (based on gcc 1.37).  Currently this is buggy in that
     `#pragma align 1' is always assumed as well, and cannot be turned
     off.


File: @.Distr.UsingGCC,  Node: DEC Alpha Options,  Next: System V Options,  Prev: Intel 960 Options,  Up: Submodel Options

DEC Alpha Options
-----------------

   These `-m' options are defined for the DEC Alpha implementations:

`-mno-soft-float'
`-msoft-float'
     Use (do not use) the hardware floating-point instructions for
     floating-point operations.  When `-msoft-float' is specified,
     functions in `libgcc1.c' will be used to perform floating-point
     operations.  Unless they are replaced by routines that emulate the
     floating-point operations, or compiled in such a way as to call
     such emulations routines, these routines will issue floating-point
     operations.   If you are compiling for an Alpha without
     floating-point operations, you must ensure that the library is
     built so as not to call them.

     Note that Alpha implementations without floating-point operations
     are required to have floating-point registers.

`-mfp-reg'
`-mno-fp-regs'
     Generate code that uses (does not use) the floating-point register
     set.  `-mno-fp-regs' implies `-msoft-float'.  If the floating-point
     register set is not used, floating point operands are passed in
     integer registers as if they were integers and floating-point
     results are passed in $0 instead of $f0.  This is a non-standard
     calling sequence, so any function with a floating-point argument
     or return value called by code compiled with `-mno-fp-regs' must
     also be compiled with that option.

     A typical use of this option is building a kernel that does not
     use, and hence need not save and restore, any floating-point
     registers.


File: @.Distr.UsingGCC,  Node: System V Options,  Prev: DEC Alpha Options,  Up: Submodel Options

Options for System V
--------------------

   These additional options are available on System V Release 4 for
compatibility with other compilers on those systems:

`-Qy'
     Identify the versions of each tool used by the compiler, in a
     `.ident' assembler directive in the output.

`-Qn'
     Refrain from adding `.ident' directives to the output file (this is
     the default).

`-YP,DIRS'
     Search the directories DIRS, and no others, for libraries
     specified with `-l'.

`-Ym,DIR'
     Look in the directory DIR to find the M4 preprocessor.  The
     assembler uses this option.


File: @.Distr.UsingGCC,  Node: Code Gen Options,  Next: Environment Variables,  Prev: Submodel Options,  Up: Invoking GCC

Options for Code Generation Conventions
=======================================

   These machine-independent options control the interface conventions
used in code generation.

   Most of them have both positive and negative forms; the negative form
of `-ffoo' would be `-fno-foo'.  In the table below, only one of the
forms is listed--the one which is not the default.  You can figure out
the other form by either removing `no-' or adding it.

`-fpcc-struct-return'
     Return "short" `struct' and `union' values in memory like longer
     ones, rather than in registers.  This convention is less
     efficient, but it has the advantage of allowing intercallability
     between GNU CC-compiled files and files compiled with other
     compilers.

     The precise convention for returning structures in memory depends
     on the target configuration macros.

     Short structures and unions are those whose size and alignment
     match that of some integer type.

`-freg-struct-return'
     Use the convention that `struct' and `union' values are returned
     in registers when possible.  This is more efficient for small
     structures than `-fpcc-struct-return'.

     If you specify neither `-fpcc-struct-return' nor its contrary
     `-freg-struct-return', GNU CC defaults to whichever convention is
     standard for the target.  If there is no standard convention, GNU
     CC defaults to `-fpcc-struct-return', except on targets where GNU
     CC is the principal compiler.  In those cases, we can choose the
     standard, and we chose the more efficient register return
     alternative.

`-fshort-enums'
     Allocate to an `enum' type only as many bytes as it needs for the
     declared range of possible values.  Specifically, the `enum' type
     will be equivalent to the smallest integer type which has enough
     room.

`-fshort-double'
     Use the same size for `double' as for `float'.

`-fshared-data'
     Requests that the data and non-`const' variables of this
     compilation be shared data rather than private data.  The
     distinction makes sense only on certain operating systems, where
     shared data is shared between processes running the same program,
     while private data exists in one copy per process.

`-fno-common'
     Allocate even uninitialized global variables in the bss section of
     the object file, rather than generating them as common blocks.
     This has the effect that if the same variable is declared (without
     `extern') in two different compilations, you will get an error
     when you link them.  The only reason this might be useful is if
     you wish to verify that the program will work on other systems
     which always work this way.

`-fno-ident'
     Ignore the `#ident' directive.

`-fno-gnu-linker'
     Do not output global initializations (such as C++ constructors and
     destructors) in the form used by the GNU linker (on systems where
     the GNU linker is the standard method of handling them).  Use this
     option when you want to use a non-GNU linker, which also requires
     using the `collect2' program to make sure the system linker
     includes constructors and destructors.  (`collect2' is included in
     the GNU CC distribution.)  For systems which *must* use
     `collect2', the compiler driver `gcc' is configured to do this
     automatically.

`-finhibit-size-directive'
     Don't output a `.size' assembler directive, or anything else that
     would cause trouble if the function is split in the middle, and the
     two halves are placed at locations far apart in memory.  This
     option is used when compiling `crtstuff.c'; you should not need to
     use it for anything else.

`-fverbose-asm'
     Put extra commentary information in the generated assembly code to
     make it more readable.  This option is generally only of use to
     those who actually need to read the generated assembly code
     (perhaps while debugging the compiler itself).

`-fvolatile'
     Consider all memory references through pointers to be volatile.

`-fvolatile-global'
     Consider all memory references to extern and global data items to
     be volatile.

`-fpic'
     Generate position-independent code (PIC) suitable for use in a
     shared library, if supported for the target machine.  Such code
     accesses all constant addresses through a global offset table
     (GOT).  If the GOT size for the linked executable exceeds a
     machine-specific maximum size, you get an error message from the
     linker indicating that `-fpic' does not work; in that case,
     recompile with `-fPIC' instead.  (These maximums are 16k on the
     m88k, 8k on the Sparc, and 32k on the m68k and RS/6000.  The 386
     has no such limit.)

     Position-independent code requires special support, and therefore
     works only on certain machines.  For the 386, GNU CC supports PIC
     for System V but not for the Sun 386i.  Code generated for the IBM
     RS/6000 is always position-independent.

     The GNU assembler does not fully support PIC.  Currently, you must
     use some other assembler in order for PIC to work.  We would
     welcome volunteers to upgrade GAS to handle this; the first part
     of the job is to figure out what the assembler must do differently.

`-fPIC'
     If supported for the target machine, emit position-independent
     code, suitable for dynamic linking and avoiding any limit on the
     size of the global offset table.  This option makes a difference
     on the m68k, m88k and the Sparc.

     Position-independent code requires special support, and therefore
     works only on certain machines.

`-ffixed-REG'
     Treat the register named REG as a fixed register; generated code
     should never refer to it (except perhaps as a stack pointer, frame
     pointer or in some other fixed role).

     REG must be the name of a register.  The register names accepted
     are machine-specific and are defined in the `REGISTER_NAMES' macro
     in the machine description macro file.

     This flag does not have a negative form, because it specifies a
     three-way choice.

`-fcall-used-REG'
     Treat the register named REG as an allocatable register that is
     clobbered by function calls.  It may be allocated for temporaries
     or variables that do not live across a call.  Functions compiled
     this way will not save and restore the register REG.

     Use of this flag for a register that has a fixed pervasive role in
     the machine's execution model, such as the stack pointer or frame
     pointer, will produce disastrous results.

     This flag does not have a negative form, because it specifies a
     three-way choice.

`-fcall-saved-REG'
     Treat the register named REG as an allocatable register saved by
     functions.  It may be allocated even for temporaries or variables
     that live across a call.  Functions compiled this way will save
     and restore the register REG if they use it.

     Use of this flag for a register that has a fixed pervasive role in
     the machine's execution model, such as the stack pointer or frame
     pointer, will produce disastrous results.

     A different sort of disaster will result from the use of this flag
     for a register in which function values may be returned.

     This flag does not have a negative form, because it specifies a
     three-way choice.

`+e0'
`+e1'
     Control whether virtual function definitions in classes are used to
     generate code, or only to define interfaces for their callers.
     (C++ only).

     These options are provided for compatibility with `cfront' 1.x
     usage; the recommended alternative GNU C++ usage is in flux.
     *Note Declarations and Definitions in One Header: C++ Interface.

     With `+e0', virtual function definitions in classes are declared
     `extern'; the declaration is used only as an interface
     specification, not to generate code for the virtual functions (in
     this compilation).

     With `+e1', G++ actually generates the code implementing virtual
     functions defined in the code, and makes them publicly visible.


File: @.Distr.UsingGCC,  Node: Environment Variables,  Next: Running Protoize,  Prev: Code Gen Options,  Up: Invoking GCC

Environment Variables Affecting GNU CC
======================================

   This section describes several environment variables that affect how
GNU CC operates.  They work by specifying directories or prefixes to use
when searching for various kinds of files.

   Note that you can also specify places to search using options such as
`-B', `-I' and `-L' (*note Directory Options::.).  These take
precedence over places specified using environment variables, which in
turn take precedence over those specified by the configuration of GNU
CC.

`TMPDIR'
     If `TMPDIR' is set, it specifies the directory to use for temporary
     files.  GNU CC uses temporary files to hold the output of one
     stage of compilation which is to be used as input to the next
     stage: for example, the output of the preprocessor, which is the
     input to the compiler proper.

`GCC_EXEC_PREFIX'
     If `GCC_EXEC_PREFIX' is set, it specifies a prefix to use in the
     names of the subprograms executed by the compiler.  No slash is
     added when this prefix is combined with the name of a subprogram,
     but you can specify a prefix that ends with a slash if you wish.

     If GNU CC cannot find the subprogram using the specified prefix, it
     tries looking in the usual places for the subprogram.

     Other prefixes specified with `-B' take precedence over this
     prefix.

     This prefix is also used for finding files such as `crt0.o' that
     are used for linking.

     In addition, the prefix is used in an unusual way in finding the
     directories to search for header files.  For each of the standard
     directories whose name normally begins with
     `/usr/local/lib/gcc-lib' (more precisely, with the value of
     `GCC_INCLUDE_DIR'), GNU CC tries replacing that beginning with the
     specified prefix to produce an alternate directory name.  Thus,
     with `-Bfoo/', GNU CC will search `foo/bar' where it would
     normally search `/usr/local/lib/bar'.  These alternate directories
     are searched first; the standard directories come next.

`COMPILER_PATH'
     The value of `COMPILER_PATH' is a colon-separated list of
     directories, much like `PATH'.  GNU CC tries the directories thus
     specified when searching for subprograms, if it can't find the
     subprograms using `GCC_EXEC_PREFIX'.

`LIBRARY_PATH'
     The value of `LIBRARY_PATH' is a colon-separated list of
     directories, much like `PATH'.  GNU CC tries the directories thus
     specified when searching for special linker files, if it can't
     find them using `GCC_EXEC_PREFIX'.  Linking using GNU CC also uses
     these directories when searching for ordinary libraries for the
     `-l' option (but directories specified with `-L' come first).

`C_INCLUDE_PATH'
`CPLUS_INCLUDE_PATH'
`OBJC_INCLUDE_PATH'
     These environment variables pertain to particular languages.  Each
     variable's value is a colon-separated list of directories, much
     like `PATH'.  When GNU CC searches for header files, it tries the
     directories listed in the variable for the language you are using,
     after the directories specified with `-I' but before the standard
     header file directories.

`DEPENDENCIES_OUTPUT'
     If this variable is set, its value specifies how to output
     dependencies for Make based on the header files processed by the
     compiler.  This output looks much like the output from the `-M'
     option (*note Preprocessor Options::.), but it goes to a separate
     file, and is in addition to the usual results of compilation.

     The value of `DEPENDENCIES_OUTPUT' can be just a file name, in
     which case the Make rules are written to that file, guessing the
     target name from the source file name.  Or the value can have the
     form `FILE TARGET', in which case the rules are written to file
     FILE using TARGET as the target name.


File: @.Distr.UsingGCC,  Node: Running Protoize,  Prev: Environment Variables,  Up: Invoking GCC

Running Protoize
================

   The program `protoize' is an optional part of GNU C.  You can use it
to add prototypes to a program, thus converting the program to ANSI C
in one respect.  The companion program `unprotoize' does the reverse:
it removes argument types from any prototypes that are found.

   When you run these programs, you must specify a set of source files
as command line arguments.  The conversion programs start out by
compiling these files to see what functions they define.  The
information gathered about a file FOO is saved in a file named `FOO.X'.

   After scanning comes actual conversion.  The specified files are all
eligible to be converted; any files they include (whether sources or
just headers) are eligible as well.

   But not all the eligible files are converted.  By default,
`protoize' and `unprotoize' convert only source and header files in the
current directory.  You can specify additional directories whose files
should be converted with the `-d DIRECTORY' option.  You can also
specify particular files to exclude with the `-x FILE' option.  A file
is converted if it is eligible, its directory name matches one of the
specified directory names, and its name within the directory has not
been excluded.

   Basic conversion with `protoize' consists of rewriting most function
definitions and function declarations to specify the types of the
arguments.  The only ones not rewritten are those for varargs functions.

   `protoize' optionally inserts prototype declarations at the
beginning of the source file, to make them available for any calls that
precede the function's definition.  Or it can insert prototype
declarations with block scope in the blocks where undeclared functions
are called.

   Basic conversion with `unprotoize' consists of rewriting most
function declarations to remove any argument types, and rewriting
function definitions to the old-style pre-ANSI form.

   Both conversion programs print a warning for any function
declaration or definition that they can't convert.  You can suppress
these warnings with `-q'.

   The output from `protoize' or `unprotoize' replaces the original
source file.  The original file is renamed to a name ending with
`.save'.  If the `.save' file already exists, then the source file is
simply discarded.

   `protoize' and `unprotoize' both depend on GNU CC itself to scan the
program and collect information about the functions it uses.  So
neither of these programs will work until GNU CC is installed.

   Here is a table of the options you can use with `protoize' and
`unprotoize'.  Each option works with both programs unless otherwise
stated.

`-B DIRECTORY'
     Look for the file `SYSCALLS.c.X' in DIRECTORY, instead of the
     usual directory (normally `/usr/local/lib').  This file contains
     prototype information about standard system functions.  This option
     applies only to `protoize'.

`-c COMPILATION-OPTIONS'
     Use  COMPILATION-OPTIONS as the options when running `gcc' to
     produce the `.X' files.  The special option `-aux-info' is always
     passed in addition, to tell `gcc' to write a `.X' file.

     Note that the compilation options must be given as a single
     argument to `protoize' or `unprotoize'.  If you want to specify
     several `gcc' options, you must quote the entire set of
     compilation options to make them a single word in the shell.

     There are certain `gcc' arguments that you cannot use, because they
     would produce the wrong kind of output.  These include `-g', `-O',
     `-c', `-S', and `-o' If you include these in the
     COMPILATION-OPTIONS, they are ignored.

`-C'
     Rename files to end in `.C' instead of `.c'.  This is convenient
     if you are converting a C program to C++.  This option applies
     only to `protoize'.

`-g'
     Add explicit global declarations.  This means inserting explicit
     declarations at the beginning of each source file for each function
     that is called in the file and was not declared.  These
     declarations precede the first function definition that contains a
     call to an undeclared function.  This option applies only to
     `protoize'.

`-i STRING'
     Indent old-style parameter declarations with the string STRING.
     This option applies only to `protoize'.

     `unprotoize' converts prototyped function definitions to old-style
     function definitions, where the arguments are declared between the
     argument list and the initial `{'.  By default, `unprotoize' uses
     five spaces as the indentation.  If you want to indent with just
     one space instead, use `-i " "'.

`-k'
     Keep the `.X' files.  Normally, they are deleted after conversion
     is finished.

`-l'
     Add explicit local declarations.  `protoize' with `-l' inserts a
     prototype declaration for each function in each block which calls
     the function without any declaration.  This option applies only to
     `protoize'.

`-n'
     Make no real changes.  This mode just prints information about the
     conversions that would have been done without `-n'.

`-N'
     Make no `.save' files.  The original files are simply deleted.
     Use this option with caution.

`-p PROGRAM'
     Use the program PROGRAM as the compiler.  Normally, the name `gcc'
     is used.

`-q'
     Work quietly.  Most warnings are suppressed.

`-v'
     Print the version number, just like `-v' for `gcc'.

   If you need special compiler options to compile one of your program's
source files, then you should generate that file's `.X' file specially,
by running `gcc' on that source file with the appropriate options and
the option `-aux-info'.  Then run `protoize' on the entire set of
files.  `protoize' will use the existing `.X' file because it is newer
than the source file.  For example:

     gcc -Dfoo=bar file1.c -aux-info
     protoize *.c

You need to include the special files along with the rest in the
`protoize' command, even though their `.X' files already exist, because
otherwise they won't get converted.

   *Note Protoize Caveats::, for more information on how to use
`protoize' successfully.


File: @.Distr.UsingGCC,  Node: Installation,  Next: C Extensions,  Prev: Invoking GCC,  Up: Top

Installing GNU CC
*****************

   Here is the procedure for installing GNU CC on a Unix system.

* Menu:

* Other Dir::     Compiling in a separate directory (not where the source is).
* Cross-Compiler::   Building and installing a cross-compiler.
* PA Install::    See below for installation on the HP Precision Architecture.
* Sun Install::   See below for installation on the Sun.
* 3b1 Install::   See below for installation on the 3b1.
* Unos Install::  See below for installation on Unos (from CRDS).
* VMS Install::   See below for installation on VMS.
* WE32K Install:: See below for installation on the 3b* aside from the 3b1.
* MIPS Install::  See below for installation on the MIPS Architecture.
* Collect2::      How `collect2' works; how it finds `ld'.
* Header Dirs::   Understanding the standard header file directories.

   You cannot install GNU C by itself on MSDOS; it will not compile
under any MSDOS compiler except itself.  You need to get the complete
compilation package DJGPP, which includes binaries as well as sources,
and includes all the necessary compilation tools and libraries.

  1. If you have built GNU CC previously in the same directory for a
     different target machine, do `make distclean' to delete all files
     that might be invalid.  One of the files this deletes is
     `Makefile'; if `make distclean' complains that `Makefile' does not
     exist, it probably means that the directory is already suitably
     clean.

  2. On a System V release 4 system, make sure `/usr/bin' precedes
     `/usr/ucb' in `PATH'.  The `cc' command in `/usr/ucb' uses
     libraries which have bugs.

  3. Specify the host and target machine configurations.  You do this by
     running the file `configure' with appropriate arguments.

     If you are building a compiler to produce code for the machine it
     runs on, specify just one machine type, with the `--target'
     option; the host type will default to be the same as the target.
     (For information on building a cross-compiler, see *Note
     Cross-Compiler::.)  Here is an example:

          configure --target=sparc-sun-sunos4.1

     If you run `configure' without specifying configuration arguments,
     `configure' tries to guess the type of host you are on, and uses
     that configuration type for both host and target.  So you don't
     need to specify a configuration, for building a native compiler,
     unless `configure' cannot figure out what your configuration is.

     A configuration name may be canonical or it may be more or less
     abbreviated.

     A canonical configuration name has three parts, separated by
     dashes.  It looks like this: `CPU-COMPANY-SYSTEM'.  (The three
     parts may themselves contain dashes; `configure' can figure out
     which dashes serve which purpose.)  For example,
     `m68k-sun-sunos4.1' specifies a Sun 3.

     You can also replace parts of the configuration by nicknames or
     aliases.  For example, `sun3' stands for `m68k-sun', so
     `sun3-sunos4.1' is another way to specify a Sun 3.  You can also
     use simply `sun3-sunos', since the version of SunOS is assumed by
     default to be version 4.  `sun3-bsd' also works, since `configure'
     knows that the only BSD variant on a Sun 3 is SunOS.

     You can specify a version number after any of the system types,
     and some of the CPU types.  In most cases, the version is
     irrelevant, and will be ignored.  So you might as well specify the
     version if you know it.

     Here are the possible CPU types:

          a29k, alpha, arm, cN, clipper, elxsi, h8300, hppa1.0, hppa1.1,
          i370, i386, i486, i860, i960, m68000, m68k, m88k, mips,
          ns32k, pyramid, romp, rs6000, sh, sparc, sparclite, vax,
          we32k.

     Here are the recognized company names.  As you can see, customary
     abbreviations are used rather than the longer official names.

          alliant, altos, apollo, att, bull, cbm, convergent, convex,
          crds, dec, dg, dolphin, elxsi, encore, harris, hitachi, hp,
          ibm, intergraph, isi, mips, motorola, ncr, next, ns, omron,
          plexus, sequent, sgi, sony, sun, tti, unicom.

     The company name is meaningful only to disambiguate when the rest
     of the information supplied is insufficient.  You can omit it,
     writing just `CPU-SYSTEM', if it is not needed.  For example,
     `vax-ultrix4.2' is equivalent to `vax-dec-ultrix4.2'.

     Here is a list of system types:

          aix, acis, aos, bsd, clix, ctix, dgux, dynix, genix, hpux,
          isc, linux, luna, lynxos, mach, minix, newsos, osf, osfrose,
          riscos, sco, solaris, sunos, sysv, ultrix, unos, vms.

     You can omit the system type; then `configure' guesses the
     operating system from the CPU and company.

     You can add a version number to the system type; this may or may
     not make a difference.  For example, you can write `bsd4.3' or
     `bsd4.4' to distinguish versions of BSD.  In practice, the version
     number is most needed for `sysv3' and `sysv4', which are often
     treated differently.

     If you specify an impossible combination such as `i860-dg-vms',
     then you may get an error message from `configure', or it may
     ignore part of the information and do the best it can with the
     rest.  `configure' always prints the canonical name for the
     alternative that it used.

     Often a particular model of machine has a name.  Many machine
     names are recognized as aliases for CPU/company combinations.
     Thus, the machine name `sun3', mentioned above, is an alias for
     `m68k-sun'.  Sometimes we accept a company name as a machine name,
     when the name is popularly used for a particular machine.  Here is
     a table of the known machine names:

          3300, 3b1, 3bN, 7300, altos3068, altos, apollo68, att-7300,
          balance, convex-cN, crds, decstation-3100, decstation, delta,
          encore, fx2800, gmicro, hp7NN, hp8NN, hp9k2NN, hp9k3NN,
          hp9k7NN, hp9k8NN, iris4d, iris, isi68, m3230, magnum, merlin,
          miniframe, mmax, news-3600, news800, news, next, pbd, pc532,
          pmax, ps2, risc-news, rtpc, sun2, sun386i, sun386, sun3,
          sun4, symmetry, tower-32, tower.

     Remember that a machine name specifies both the cpu type and the
     company name.

     There are four additional options you can specify independently to
     describe variant hardware and software configurations.  These are
     `--with-gnu-as', `--with-gnu-ld', `--with-stabs' and `--nfp'.

    `--with-gnu-as'
          If you will use GNU CC with the GNU assembler (GAS), you
          should declare this by using the `--with-gnu-as' option when
          you run `configure'.

          Using this option does not install GAS.  It only modifies the
          output of GNU CC to work with GAS.  Building and installing
          GAS is up to you.

          Conversely, if you *do not* wish to use GAS and do not specify
          `--with-gnu-as' when building GNU CC, it is up to you to make
          sure that GAS is not installed.  GNU CC searches for a
          program named `as' in various directories; if the program it
          finds is GAS, then it runs GAS.  If you are not sure where
          GNU CC finds the assembler it is using, try specifying `-v'
          when you run it.

          The systems where it makes a difference whether you use GAS
          are
          `hppa1.0-ANY-ANY', `hppa1.1-ANY-ANY', `i386-ANY-sysv',
          `i386-ANY-isc',
          `i860-ANY-bsd', `m68k-bull-sysv', `m68k-hp-hpux',
          `m68k-sony-bsd',
          `m68k-altos-sysv', `m68000-hp-hpux', `m68000-att-sysv', and
          `mips-ANY').  On any other system, `--with-gnu-as' has no
          effect.

          On the systems listed above (except for the HP-PA and for ISC
          on the 386), if you use GAS, you should also use the GNU
          linker (and specify `--with-gnu-ld').

    `--with-gnu-ld'
          Specify the option `--with-gnu-ld' if you plan to use the GNU
          linker with GNU CC.

          This option does not cause the GNU linker to be installed; it
          just modifies the behavior of GNU CC to work with the GNU
          linker.  Specifically, it inhibits the installation of
          `collect2', a program which otherwise serves as a front-end
          for the system's linker on most configurations.

    `--with-stabs'
          On MIPS based systems and on Alphas, you must specify whether
          you want GNU CC to create the normal ECOFF debugging format,
          or to use BSD-style stabs passed through the ECOFF symbol
          table.  The normal ECOFF debug format cannot fully handle
          languages other than C.  BSD stabs format can handle other
          languages, but it only works with the GNU debugger GDB.

          Normally, GNU CC uses the ECOFF debugging format by default;
          if you prefer BSD stabs, specify `--with-stabs' when you
          configure GNU CC.

          No matter which default you choose when you configure GNU CC,
          the user can use the `-gcoff' and `-gstabs+' options to
          specify explicitly the debug format for a particular
          compilation.

          `--with-stabs' is meaningful on the ISC system on the 386,
          also, if `--with-gas' is used.  It selects use of stabs
          debugging information embedded in COFF output.  This kind of
          debugging information supports C++ well; ordinary COFF
          debugging information does not.

    `--nfp'
          On certain systems, you must specify whether the machine has
          a floating point unit.  These systems include
          `m68k-sun-sunosN' and `m68k-isi-bsd'.  On any other system,
          `--nfp' currently has no effect, though perhaps there are
          other systems where it could usefully make a difference.

     If you want to install your own homemade configuration files, you
     can use `local' as the company name to access them.  If you use
     configuration `CPU-local', the configuration name without the cpu
     prefix is used to form the configuration file names.

     Thus, if you specify `m68k-local', configuration uses files
     `local.md', `local.h', `local.c', `xm-local.h', `t-local', and
     `x-local', all in the directory `config/m68k'.

     Here is a list of configurations that have special treatment or
     special things you must know:

    `alpha-*-osf1'
          Systems using processors that implement the DEC Alpha
          architecture and are running the OSF/1 operating system, for
          example the DEC Alpha AXP systems.  (VMS on the Alpha is not
          currently supported by GNU CC.)

          Objective C and C++ do not yet work on the Alpha.  We hope to
          support C++ in version 2.6.

          GNU CC writes a `.verstamp' directive to the assembler output
          file unless it is built as a cross-compiler.  It gets the
          version to use from the system header file
          `/usr/include/stamp.h'.  If you install a new version of
          OSF/1, you should rebuild GCC to pick up the new version
          stamp.

          Note that since the Alpha is a 64-bit architecture,
          cross-compilers from 32-bit machines will not generate as
          efficient code as that generated when the compiler is running
          on a 64-bit machine because many optimizations that depend on
          being able to represent a word on the target in an integral
          value on the host cannot be performed.  Building
          cross-compilers on the Alpha for 32-bit machines has only
          been tested in a few cases and may not work properly.

          `make compare' may fail on some versions of OSF/1 unless you
          add `-save-temps' to `CFLAGS'.  The same problem occurs on
          Irix version 5.1.1.  On these systems, the name of the
          assembler input file is stored in the object file, and that
          makes comparison fail if it differs between the `stage1' and
          `stage2' compilations.  The option `-save-temps' forces a
          fixed name to be used for the assembler input file, instead
          of a randomly chosen name in `/tmp'.

          GNU CC now supports both the native (ECOFF) debugging format
          used by DBX and GDB and an encapsulated STABS format for use
          only with GDB.  See the discussion of the `--with-stabs'
          option of `configure' above for more information on these
          formats and how to select them.

          There is a bug in DEC's assembler that produces incorrect
          line numbers for ECOFF format when the `.align' directive is
          used.  To work around this problem, GNU CC will not emit such
          alignment directives even if optimization is being performed
          if it is writing ECOFF format debugging information.
          Unfortunately, this has the very undesirable side-effect that
          code addresses when `-O' is specified are different depending
          on whether or not `-g' is also specified.

          To avoid this behavior, specify `-gstabs+' and use GDB
          instead of DBX.  DEC is now aware of this problem with the
          assembler and hopes to provide a fix shortly.

    `a29k'
          AMD Am29k-family processors.  These are normally used in
          embedded applications.  There are no standard Unix
          configurations.  This configuration corresponds to AMD's
          standard calling sequence and binary interface and is
          compatible with other 29k tools.

          You may need to make a variant of the file `a29k.h' for your
          particular configuration.

    `a29k-*-bsd'
          AMD Am29050 used in a system running a variant of BSD Unix.

    `elxsi-elxsi-bsd'
          The Elxsi's C compiler has known limitations that prevent it
          from compiling GNU C.  Please contact `[e-mail]' for
          more details.

    `hppa*-*-*'
          Using GAS is highly recommended for all HP-PA configurations.
          See *Note PA Install:: for the special procedures needed to
          compile GNU CC for the HP-PA.

    `i386-*-sco'
          Compilation with RCC is recommended.  Also, it may be a good
          idea to link with GNU malloc instead of the malloc that comes
          with the system.

    `i386-*-sco3.2.4'
          Use this configuration for SCO release 3.2 version 4.

    `i386-*-isc'
          It may be good idea to link with GNU malloc instead of the
          malloc that comes with the system.

    `i386-*-esix'
          It may be good idea to link with GNU malloc instead of the
          malloc that comes with the system.

    `i386-ibm-aix'
          You need to use GAS version 2.1 or later, and and LD from GNU
          binutils version 2.2 or later.

    `i386-sequent'
          Go to the Berkeley universe before compiling.  In addition,
          you probably need to create a file named `string.h'
          containing just one line: `#include <strings.h>'.

    `i386-sun-sunos4'
          You may find that you need another version of GNU CC to begin
          bootstrapping with, since the current version when built with
          the system's own compiler seems to get an infinite loop
          compiling part of `libgcc2.c'.  GNU CC version 2 compiled
          with GNU CC (any version) seems not to have this problem.

    `i860-intel-osf1'
          This is the Paragon.  If you have version 1.0 of the
          operating system, see *Note Installation Problems::, for
          special things you need to do to compensate for peculiarities
          in the system.

    `m68000-att'
          AT&T 3b1, a.k.a. 7300 PC.  Special procedures are needed to
          compile GNU CC with this machine's standard C compiler, due
          to bugs in that compiler.  *Note 3b1 Install::.  You can
          bootstrap it more easily with previous versions of GNU CC if
          you have them.

    `m68000-hp-bsd'
          HP 9000 series 200 running BSD.  Note that the C compiler
          that comes with this system cannot compile GNU CC; contact
          `[e-mail]' to get binaries of GNU CC for bootstrapping.

    `m68k-altos'
          Altos 3068.  You must use the GNU assembler, linker and
          debugger.  Also, you must fix a kernel bug.  Details in the
          file `README.ALTOS'.

    `m68k-bull-sysv'
          Bull DPX/2 series 200 and 300 with BOS-2.00.45 up to
          BOS-2.01. GNU CC works either with native assembler or GNU
          assembler. You can use GNU assembler with native coff
          generation by providing `--gas' to the configure script or
          use GNU assembler with dbx-in-coff encapsulation by providing
          `--gas --stabs'. For any problem with native assembler or for
          availability of the DPX/2 port of GAS, contact
          `[e-mail]'.

    `m68k-hp-hpux'
          HP 9000 series 300 or 400 running HP-UX.  HP-UX version 8.0
          has a bug in the assembler that prevents compilation of GNU
          CC.  To fix it, get patch PHCO_0800 from HP.

          In addition, `--gas' does not currently work with this
          configuration.  Changes in HP-UX have broken the library
          conversion tool and the linker.

    `m68k-sun'
          Sun 3.  We do not provide a configuration file to use the Sun
          FPA by default, because programs that establish signal
          handlers for floating point traps inherently cannot work with
          the FPA.

    `m88k-*-svr3'
          Motorola m88k running the AT&T/Unisoft/Motorola V.3 reference
          port.  These systems tend to use the Green Hills C, revision
          1.8.5, as the standard C compiler.  There are apparently bugs
          in this compiler that result in object files differences
          between stage 2 and stage 3.  If this happens, make the stage
          4 compiler and compare it to the stage 3 compiler.  If the
          stage 3 and stage 4 object files are identical, this suggests
          you encountered a problem with the standard C compiler; the
          stage 3 and 4 compilers may be usable.

          It is best, however, to use an older version of GNU CC for
          bootstrapping if you have one.

    `m88k-*-dgux'
          Motorola m88k running DG/UX.  To build native or cross
          compilers on DG/UX, you must first change to the 88open BCS
          software development environment.  This is done by issuing
          this command:

               eval `sde-target m88kbcs`

    `m88k-tektronix-sysv3'
          Tektronix XD88 running UTekV 3.2e.  Do not turn on
          optimization while building stage1 if you bootstrap with the
          buggy Green Hills compiler.  Also, The bundled LAI System V
          NFS is buggy so if you build in an NFS mounted directory,
          start from a fresh reboot, or avoid NFS all together.
          Otherwise you may have trouble getting clean comparisons
          between stages.

    `mips-mips-bsd'
          MIPS machines running the MIPS operating system in BSD mode.
          It's possible that some old versions of the system lack the
          functions `memcpy', `memcmp', and `memset'.  If your system
          lacks these, you must remove or undo the definition of
          `TARGET_MEM_FUNCTIONS' in `mips-bsd.h'.

    `mips-sgi-*'
          Silicon Graphics MIPS machines running IRIX.  In order to
          compile GCC on an SGI the "c.hdr.lib" option must be
          installed from the CD-ROM supplied from Silicon Graphics.
          This is found on the 2nd CD in release 4.0.1.

    `mips-sony-sysv'
          Sony MIPS NEWS.  This works in NEWSOS 5.0.1, but not in 5.0.2
          (which uses ELF instead of COFF).  Support for 5.0.2 will
          probably be provided soon by volunteers.  In particular, the
          linker does not like the code generated by GCC when shared
          libraries are linked in.

    `ns32k-encore'
          Encore ns32000 system.  Encore systems are supported only
          under BSD.

    `ns32k-*-genix'
          National Semiconductor ns32000 system.  Genix has bugs in
          `alloca' and `malloc'; you must get the compiled versions of
          these from GNU Emacs.

    `ns32k-sequent'
          Go to the Berkeley universe before compiling.  In addition,
          you probably need to create a file named `string.h'
          containing just one line: `#include <strings.h>'.

    `ns32k-utek'
          UTEK ns32000 system ("merlin").  The C compiler that comes
          with this system cannot compile GNU CC; contact
          `tektronix!reed!mason' to get binaries of GNU CC for
          bootstrapping.

    `romp-*-aos'
    `romp-*-mach'
          The only operating systems supported for the IBM RT PC are
          AOS and MACH.  GNU CC does not support AIX running on the RT.
          We recommend you compile GNU CC with an earlier version of
          itself; if you compile GNU CC with `hc', the Metaware
          compiler, it will work, but you will get mismatches between
          the stage 2 and stage 3 compilers in various files.  These
          errors are minor differences in some floating-point constants
          and can be safely ignored; the stage 3 compiler is correct.

    `rs6000-*-aix'
          *Read the file `README.RS6000' for information on how to get
          a fix for problems in the IBM assembler that interfere with
          GNU CC.* You must either obtain the new assembler or avoid
          using the `-g' switch.  Note that `Makefile.in' uses `-g' by
          default when compiling `libgcc2.c'.

          The PowerPC and POWER2 architectures are now supported, but
          have not been extensively tested due to lack of appropriate
          systems.  Only AIX is supported on the PowerPC.

          Objective C does not work on this architecture.

          XLC version 1.3.0.0 will miscompile `jump.c'.  XLC version
          1.3.0.1 or later fixes this problem.  We do not yet have a
          PTF number for this fix.

    `vax-dec-ultrix'
          Don't try compiling with Vax C (`vcc').  It produces
          incorrect code in some cases (for example, when `alloca' is
          used).

          Meanwhile, compiling `cp-parse.c' with pcc does not work
          because of an internal table size limitation in that
          compiler.  To avoid this problem, compile just the GNU C
          compiler first, and use it to recompile building all the
          languages that you want to run.

     Here we spell out what files will be set up by `configure'.
     Normally you need not be concerned with these files.

        * A symbolic link named `config.h' is made to the top-level
          config file for the machine you plan to run the compiler on
          (*note The Configuration File: (gcc.info)Config.).  This file
          is responsible for defining information about the host
          machine.  It includes `tm.h'.

          The top-level config file is located in the subdirectory
          `config'.  Its name is always `xm-SOMETHING.h'; usually
          `xm-MACHINE.h', but there are some exceptions.

          If your system does not support symbolic links, you might
          want to set up `config.h' to contain a `#include' command
          which refers to the appropriate file.

        * A symbolic link named `tconfig.h' is made to the top-level
          config file for your target machine.  This is used for
          compiling certain programs to run on that machine.

        * A symbolic link named `tm.h' is made to the
          machine-description macro file for your target machine.  It
          should be in the subdirectory `config' and its name is often
          `MACHINE.h'.

        * A symbolic link named `md' will be made to the machine
          description pattern file.  It should be in the `config'
          subdirectory and its name should be `MACHINE.md'; but MACHINE
          is often not the same as the name used in the `tm.h' file
          because the `md' files are more general.

        * A symbolic link named `aux-output.c' will be made to the
          output subroutine file for your machine.  It should be in the
          `config' subdirectory and its name should be `MACHINE.c'.

        * The command file `configure' also constructs the file
          `Makefile' by adding some text to the template file
          `Makefile.in'.  The additional text comes from files in the
          `config' directory, named `t-TARGET' and `x-HOST'.  If these
          files do not exist, it means nothing needs to be added for a
          given target or host.

  4. The standard directory for installing GNU CC is `/usr/local/lib'.
     If you want to install its files somewhere else, specify
     `--prefix=DIR' when you run `configure'.  Here DIR is a directory
     name to use instead of `/usr/local' for all purposes with one
     exception: the directory `/usr/local/include' is searched for
     header files no matter where you install the compiler.

  5. Specify `--local-prefix=DIR' if you want the compiler to search
     directory `DIR/include' for header files *instead* of
     `/usr/local/include'.  (This is for systems that have different
     conventions for where to put site-specific things.)

     Unless you have a convention other than `/usr/local' for
     site-specific files, it is a bad idea to specify `--local-prefix'.

  6. Make sure the Bison parser generator is installed.  (This is
     unnecessary if the Bison output files `c-parse.c' and `cexp.c' are
     more recent than `c-parse.y' and `cexp.y' and you do not plan to
     change the `.y' files.)

     Bison versions older than Sept 8, 1988 will produce incorrect
     output for `c-parse.c'.

  7. If you have chosen a configuration for GNU CC which requires other
     GNU tools (such as GAS or the GNU linker) instead of the standard
     system tools, install the required tools in the build directory
     under the names `as', `ld' or whatever is appropriate.  This will
     enable the compiler to find the proper tools for compilation of
     the program `enquire'.

     Alternatively, you can do subsequent compilation using a value of
     the `PATH' environment variable such that the necessary GNU tools
     come before the standard system tools.

  8. Build the compiler.  Just type `make LANGUAGES=c' in the compiler
     directory.

     `LANGUAGES=c' specifies that only the C compiler should be
     compiled.  The makefile normally builds compilers for all the
     supported languages; currently, C, C++ and Objective C.  However,
     C is the only language that is sure to work when you build with
     other non-GNU C compilers.  In addition, building anything but C
     at this stage is a waste of time.

     In general, you can specify the languages to build by typing the
     argument `LANGUAGES="LIST"', where LIST is one or more words from
     the list `c', `c++', and `objective-c'.

     Ignore any warnings you may see about "statement not reached" in
     `insn-emit.c'; they are normal.  Also, warnings about "unknown
     escape sequence" are normal in `genopinit.c' and perhaps some
     other files.  Any other compilation errors may represent bugs in
     the port to your machine or operating system, and should be
     investigated and reported (*note Bugs::.).

     Some commercial compilers fail to compile GNU CC because they have
     bugs or limitations.  For example, the Microsoft compiler is said
     to run out of macro space.  Some Ultrix compilers run out of
     expression space; then you need to break up the statement where
     the problem happens.

     If you are building with a previous GNU C compiler, do not use
     `CC=gcc' on the make command or by editing the Makefile.  Instead,
     use a full pathname to specify the compiler, such as
     `CC=/usr/local/bin/gcc'.  This is because make might execute the
     `gcc' in the current directory before all of the compiler
     components have been built.

  9. If you are building a cross-compiler, stop here.  *Note
     Cross-Compiler::.

 10. Move the first-stage object files and executables into a
     subdirectory with this command:

          make stage1

     The files are moved into a subdirectory named `stage1'.  Once
     installation is complete, you may wish to delete these files with
     `rm -r stage1'.

 11. If you have chosen a configuration for GNU CC which requires other
     GNU tools (such as GAS or the GNU linker) instead of the standard
     system tools, install the required tools in the `stage1'
     subdirectory under the names `as', `ld' or whatever is
     appropriate.  This will enable the stage 1 compiler to find the
     proper tools in the following stage.

     Alternatively, you can do subsequent compilation using a value of
     the `PATH' environment variable such that the necessary GNU tools
     come before the standard system tools.

 12. Recompile the compiler with itself, with this command:

          make CC="stage1/xgcc -Bstage1/" CFLAGS="-g -O"

     This is called making the stage 2 compiler.

     The command shown above builds compilers for all the supported
     languages.  If you don't want them all, you can specify the
     languages to build by typing the argument `LANGUAGES="LIST"'.  LIST
     should contain one or more words from the list `c', `c++',
     `objective-c', and `proto'.  Separate the words with spaces.
     `proto' stands for the programs `protoize' and `unprotoize'; they
     are not a separate language, but you use `LANGUAGES' to enable or
     disable their installation.

     If you are going to build the stage 3 compiler, then you might
     want to build only the C language in stage 2.

     Once you have built the stage 2 compiler, if you are short of disk
     space, you can delete the subdirectory `stage1'.

     On a 68000 or 68020 system lacking floating point hardware, unless
     you have selected a `tm.h' file that expects by default that there
     is no such hardware, do this instead:

          make CC="stage1/xgcc -Bstage1/" CFLAGS="-g -O -msoft-float"

 13. If you wish to test the compiler by compiling it with itself one
     more time, install any other necessary GNU tools (such as GAS or
     the GNU linker) in the `stage2' subdirectory as you did in the
     `stage1' subdirectory, then do this:

          make stage2
          make CC="stage2/xgcc -Bstage2/" CFLAGS="-g -O"

     This is called making the stage 3 compiler.  Aside from the `-B'
     option, the compiler options should be the same as when you made
     the stage 2 compiler.  But the `LANGUAGES' option need not be the
     same.  The command shown above builds compilers for all the
     supported languages; if you don't want them all, you can specify
     the languages to build by typing the argument `LANGUAGES="LIST"',
     as described above.

     Then compare the latest object files with the stage 2 object
     files--they ought to be identical, aside from time stamps (if any).

     On some systems, meaningful comparison of object files is
     impossible; they always appear "different."  This is currently
     true on Solaris and probably on all systems that use ELF object
     file format.  Some other systems where this is so are listed below.

     Use this command to compare the files:

          make compare

     This will mention any object files that differ between stage 2 and
     stage 3.  Any difference, no matter how innocuous, indicates that
     the stage 2 compiler has compiled GNU CC incorrectly, and is
     therefore a potentially serious bug which you should investigate
     and report (*note Bugs::.).

     If your system does not put time stamps in the object files, then
     this is a faster way to compare them (using the Bourne shell):

          for file in *.o; do
          cmp $file stage2/$file
          done

     If you have built the compiler with the `-mno-mips-tfile' option on
     MIPS machines, you will not be able to compare the files.

     The Alpha stores file names of internal temporary files in the
     object files and `make compare' does not know how to ignore them,
     so normally you cannot compare on the Alpha.  However, if you use
     the `-save-temps' option when compiling *both* stage 2 and stage
     3, this causes the same file names to be used in both stages; then
     you can do the comparison.

 14. Build the Objective C library (if you have built the Objective C
     compiler).  Here is the command to do this:

          make objc-runtime CC="stage2/xgcc -Bstage2/" CFLAGS="-g -O"

 15. Install the compiler driver, the compiler's passes and run-time
     support with `make install'.  Use the same value for `CC',
     `CFLAGS' and `LANGUAGES' that you used when compiling the files
     that are being installed.  One reason this is necessary is that
     some versions of Make have bugs and recompile files gratuitously
     when you do this step.  If you use the same variable values, those
     files will be recompiled properly.

     For example, if you have built the stage 2 compiler, you can use
     the following command:

          make install CC="stage2/xgcc -Bstage2/" CFLAGS="-g -O" LANGUAGES="LIST"

     This copies the files `cc1', `cpp' and `libgcc.a' to files `cc1',
     `cpp' and `libgcc.a' in the directory
     `/usr/local/lib/gcc-lib/TARGET/VERSION', which is where the
     compiler driver program looks for them.  Here TARGET is the target
     machine type specified when you ran `configure', and VERSION is
     the version number of GNU CC.  This naming scheme permits various
     versions and/or cross-compilers to coexist.

     This also copies the driver program `xgcc' into
     `/usr/local/bin/gcc', so that it appears in typical execution
     search paths.

     On some systems, this command causes recompilation of some files.
     This is usually due to bugs in `make'.  You should either ignore
     this problem, or use GNU Make.

     *Warning: there is a bug in `alloca' in the Sun library.  To avoid
     this bug, be sure to install the executables of GNU CC that were
     compiled by GNU CC.  (That is, the executables from stage 2 or 3,
     not stage 1.)  They use `alloca' as a built-in function and never
     the one in the library.*

     (It is usually better to install GNU CC executables from stage 2
     or 3, since they usually run faster than the ones compiled with
     some other compiler.)

 16. Install the Objective C library (if you are installing the
     Objective C compiler).  Here is the command to do this:

          make install-libobjc CC="stage2/xgcc -Bstage2/" CFLAGS="-g -O"

 17. If you're going to use C++, it's likely that you need to also
     install the libg++ distribution.  It should be available from the
     same place where you got the GNU C distribution.  Just as GNU C
     does not distribute a C runtime library, it also does not include
     a C++ run-time library.  All I/O functionality, special class
     libraries, etc., are available in the libg++ distribution.


File: @.Distr.UsingGCC,  Node: Other Dir,  Next: Cross-Compiler,  Up: Installation

Compilation in a Separate Directory
===================================

   If you wish to build the object files and executables in a directory
other than the one containing the source files, here is what you must
do differently:

  1. Make sure you have a version of Make that supports the `VPATH'
     feature.  (GNU Make supports it, as do Make versions on most BSD
     systems.)

  2. If you have ever run `configure' in the source directory, you must
     undo the configuration.  Do this by running:

          make distclean

  3. Go to the directory in which you want to build the compiler before
     running `configure':

          mkdir gcc-sun3
          cd gcc-sun3

     On systems that do not support symbolic links, this directory must
     be on the same file system as the source code directory.

  4. Specify where to find `configure' when you run it:

          ../gcc/configure ...

     This also tells `configure' where to find the compiler sources;
     `configure' takes the directory from the file name that was used to
     invoke it.  But if you want to be sure, you can specify the source
     directory with the `--srcdir' option, like this:

          ../gcc/configure --srcdir=../gcc sun3

     The directory you specify with `--srcdir' need not be the same as
     the one that `configure' is found in.

   Now, you can run `make' in that directory.  You need not repeat the
configuration steps shown above, when ordinary source files change.  You
must, however, run `configure' again when the configuration files
change, if your system does not support symbolic links.


File: @.Distr.UsingGCC,  Node: Cross-Compiler,  Next: PA Install,  Prev: Other Dir,  Up: Installation

Building and Installing a Cross-Compiler
========================================

   GNU CC can function as a cross-compiler for many machines, but not
all.

   * Cross-compilers for the Mips as target using the Mips assembler
     currently do not work, because the auxiliary programs
     `mips-tdump.c' and `mips-tfile.c' can't be compiled on anything
     but a Mips.  It does work to cross compile for a Mips if you use
     the GNU assembler and linker.

   * Cross-compilers between machines with different floating point
     formats have not all been made to work.  GNU CC now has a floating
     point emulator with which these can work, but each target machine
     description needs to be updated to take advantage of it.

   * Cross-compilation between machines of different word sizes has not
     really been addressed yet.

   Since GNU CC generates assembler code, you probably need a
cross-assembler that GNU CC can run, in order to produce object files.
If you want to link on other than the target machine, you need a
cross-linker as well.  You also need header files and libraries suitable
for the target machine that you can install on the host machine.

* Menu:

* Steps of Cross::      Using a cross-compiler involves several steps
                          that may be carried out on different machines.
* Configure Cross::     Configuring a cross-compiler.
* Tools and Libraries:: Where to put the linker and assembler, and the C library.
* Cross Headers::       Finding and installing header files
                          for a cross-compiler.
* Cross Runtime::       Supplying arithmetic runtime routines (`libgcc1.a').
* Build Cross::         Actually compiling the cross-compiler.


File: @.Distr.UsingGCC,  Node: Steps of Cross,  Next: Configure Cross,  Up: Cross-Compiler

Steps of Cross-Compilation
--------------------------

   To compile and run a program using a cross-compiler involves several
steps:

   * Run the cross-compiler on the host machine to produce assembler
     files for the target machine.  This requires header files for the
     target machine.

   * Assemble the files produced by the cross-compiler.  You can do this
     either with an assembler on the target machine, or with a
     cross-assembler on the host machine.

   * Link those files to make an executable.  You can do this either
     with a linker on the target machine, or with a cross-linker on the
     host machine.  Whichever machine you use, you need libraries and
     certain startup files (typically `crt....o') for the target
     machine.

   It is most convenient to do all of these steps on the same host
machine, since then you can do it all with a single invocation of GNU
CC.  This requires a suitable cross-assembler and cross-linker.  For
some targets, the GNU assembler and linker are available.


File: @.Distr.UsingGCC,  Node: Configure Cross,  Next: Tools and Libraries,  Prev: Steps of Cross,  Up: Cross-Compiler

Configuring a Cross-Compiler
----------------------------

   To build GNU CC as a cross-compiler, you start out by running
`configure'.  You must specify two different configurations, the host
and the target.  Use the `--host=HOST' option for the host and
`--target=TARGET' to specify the target type.  For example, here is how
to configure for a cross-compiler that runs on a hypothetical Intel 386
system and produces code for an HP 68030 system running BSD:

     configure --target=m68k-hp-bsd4.3 --host=i386-bozotheclone-bsd4.3


File: @.Distr.UsingGCC,  Node: Tools and Libraries,  Next: Cross Headers,  Prev: Configure Cross,  Up: Cross-Compiler

Tools and Libraries for a Cross-Compiler
----------------------------------------

   If you have a cross-assembler and cross-linker available, you should
install them now.  Put them in the directory `/usr/local/TARGET/bin'.
Here is a table of the tools you should put in this directory:

`as'
     This should be the cross-assembler.

`ld'
     This should be the cross-linker.

`ar'
     This should be the cross-archiver: a program which can manipulate
     archive files (linker libraries) in the target machine's format.

`ranlib'
     This should be a program to construct a symbol table in an archive
     file.

   The installation of GNU CC will find these programs in that
directory, and copy or link them to the proper place to for the
cross-compiler to find them when run later.

   The easiest way to provide these files is to build the Binutils
package and GAS.  Configure them with the same `--host' and `--target'
options that you use for configuring GNU CC, then build and install
them.  They install their executables automatically into the proper
directory.  Alas, they do not support all the targets that GNU CC
supports.

   If you want to install libraries to use with the cross-compiler,
such as a standard C library, put them in the directory
`/usr/local/TARGET/lib'; installation of GNU CC copies all all the
files in that subdirectory into the proper place for GNU CC to find
them and link with them.  Here's an example of copying some libraries
from a target machine:

     ftp TARGET-MACHINE
     lcd /usr/local/TARGET/lib
     cd /lib
     get libc.a
     cd /usr/lib
     get libg.a
     get libm.a
     quit

The precise set of libraries you'll need, and their locations on the
target machine, vary depending on its operating system.

   Many targets require "start files" such as `crt0.o' and `crtn.o'
which are linked into each executable; these too should be placed in
`/usr/local/TARGET/lib'.  There may be several alternatives for
`crt0.o', for use with profiling or other compilation options.  Check
your target's definition of `STARTFILE_SPEC' to find out what start
files it uses.  Here's an example of copying these files from a target
machine:

     ftp TARGET-MACHINE
     lcd /usr/local/TARGET/lib
     prompt
     cd /lib
     mget *crt*.o
     cd /usr/lib
     mget *crt*.o
     quit


File: @.Distr.UsingGCC,  Node: Cross Runtime,  Next: Build Cross,  Prev: Cross Headers,  Up: Cross-Compiler

`libgcc.a' and Cross-Compilers
------------------------------

   Code compiled by GNU CC uses certain runtime support functions
implicitly.  Some of these functions can be compiled successfully with
GNU CC itself, but a few cannot be.  These problem functions are in the
source file `libgcc1.c'; the library made from them is called
`libgcc1.a'.

   When you build a native compiler, these functions are compiled with
some other compiler-the one that you use for bootstrapping GNU CC.
Presumably it knows how to open code these operations, or else knows how
to call the run-time emulation facilities that the machine comes with.
But this approach doesn't work for building a cross-compiler.  The
compiler that you use for building knows about the host system, not the
target system.

   So, when you build a cross-compiler you have to supply a suitable
library `libgcc1.a' that does the job it is expected to do.

   To compile `libgcc1.c' with the cross-compiler itself does not work.
The functions in this file are supposed to implement arithmetic
operations that GNU CC does not know how to open code, for your target
machine.  If these functions are compiled with GNU CC itself, they will
compile into infinite recursion.

   On any given target, most of these functions are not needed.  If GNU
CC can open code an arithmetic operation, it will not call these
functions to perform the operation.  It is possible that on your target
machine, none of these functions is needed.  If so, you can supply an
empty library as `libgcc1.a'.

   Many targets need library support only for multiplication and
division.  If you are linking with a library that contains functions for
multiplication and division, you can tell GNU CC to call them directly
by defining the macros `MULSI3_LIBCALL', and the like.  These macros
need to be defined in the target description macro file.  For some
targets, they are defined already.  This may be sufficient to avoid the
need for libgcc1.a; if so, you can supply an empty library.

   Some targets do not have floating point instructions; they need other
functions in `libgcc1.a', which do floating arithmetic.  Recent
versions of GNU CC have a file which emulates floating point.  With a
certain amount of work, you should be able to construct a floating
point emulator that can be used as `libgcc1.a'.  Perhaps future
versions will contain code to do this automatically and conveniently.
That depends on whether someone wants to implement it.

   If your target system has another C compiler, you can configure GNU
CC as a native compiler on that machine, build just `libgcc1.a' with
`make libgcc1.a' on that machine, and use the resulting file with the
cross-compiler.  To do this, execute the following on the target
machine:

     cd TARGET-BUILD-DIR
     configure --host=sparc --target=sun3
     make libgcc1.a

And then this on the host machine:

     ftp TARGET-MACHINE
     binary
     cd TARGET-BUILD-DIR
     get libgcc1.a
     quit

   Another way to provide the functions you need in `libgcc1.a' is to
define the appropriate `perform_...' macros for those functions.  If
these definitions do not use the C arithmetic operators that they are
meant to implement, you should be able to compile them with the
cross-compiler you are building.  (If these definitions already exist
for your target file, then you are all set.)

   To build `libgcc1.a' using the perform macros, use
`LIBGCC1=libgcc1.a OLDCC=./xgcc' when building the compiler.
Otherwise, you should place your replacement library under the name
`libgcc1.a' in the directory in which you will build the
cross-compiler, before you run `make'.


File: @.Distr.UsingGCC,  Node: Cross Headers,  Next: Cross Runtime,  Prev: Tools and Libraries,  Up: Cross-Compiler

Cross-Compilers and Header Files
--------------------------------

   If you are cross-compiling a standalone program or a program for an
embedded system, then you may not need any header files except the few
that are part of GNU CC (and those of your program).  However, if you
intend to link your program with a standard C library such as `libc.a',
then you probably need to compile with the header files that go with
the library you use.

   The GNU C compiler does not come with these files, because (1) they
are system-specific, and (2) they belong in a C library, not in a
compiler.

   If the GNU C library supports your target machine, then you can get
the header files from there (assuming you actually use the GNU library
when you link your program).

   If your target machine comes with a C compiler, it probably comes
with suitable header files also.  If you make these files accessible
from the host machine, the cross-compiler can use them also.

   Otherwise, you're on your own in finding header files to use when
cross-compiling.

   When you have found suitable header files, put them in
`/usr/local/TARGET/include', before building the cross compiler.  Then
installation will run fixincludes properly and install the corrected
versions of the header files where the compiler will use them.

   Provide the header files before you build the cross-compiler, because
the build stage actually runs the cross-compiler to produce parts of
`libgcc.a'.  (These are the parts that *can* be compiled with GNU CC.)
Some of them need suitable header files.

   Here's an example showing how to copy the header files from a target
machine.  On the target machine, do this:

     (cd /usr/include; tar cf - .) > tarfile

   Then, on the host machine, do this:

     ftp TARGET-MACHINE
     lcd /usr/local/TARGET/include
     get tarfile
     quit
     tar xf tarfile


File: @.Distr.UsingGCC,  Node: Build Cross,  Prev: Cross Runtime,  Up: Cross-Compiler

Actually Building the Cross-Compiler
------------------------------------

   Now you can proceed just as for compiling a single-machine compiler
through the step of building stage 1.  If you have not provided some
sort of `libgcc1.a', then compilation will give up at the point where
it needs that file, printing a suitable error message.  If you do
provide `libgcc1.a', then building the compiler will automatically
compile and link a test program called `cross-test'; if you get errors
in the linking, it means that not all of the necessary routines in
`libgcc1.a' are available.

   If you are making a cross-compiler for an embedded system, and there
is no `stdio.h' header for it, then the compilation of `enquire' will
probably fail.  The job of `enquire' is to run on the target machine
and figure out by experiment the nature of its floating point
representation.  `enquire' records its findings in the header file
`float.h'.  If you can't produce this file by running `enquire' on the
target machine, then you will need to come up with a suitable `float.h'
in some other way (or else, avoid using it in your programs).

   Do not try to build stage 2 for a cross-compiler.  It doesn't work to
rebuild GNU CC as a cross-compiler using the cross-compiler, because
that would produce a program that runs on the target machine, not on the
host.  For example, if you compile a 386-to-68030 cross-compiler with
itself, the result will not be right either for the 386 (because it was
compiled into 68030 code) or for the 68030 (because it was configured
for a 386 as the host).  If you want to compile GNU CC into 68030 code,
whether you compile it on a 68030 or with a cross-compiler on a 386, you
must specify a 68030 as the host when you configure it.

   To install the cross-compiler, use `make install', as usual.


File: @.Distr.UsingGCC,  Node: PA Install,  Next: Sun Install,  Prev: Cross-Compiler,  Up: Installation

Installing on the HP Precision Architecture
===========================================

   There are two variants of this CPU, called 1.0 and 1.1, which have
different machine descriptions.  You must use the right one for your
machine.  All 7NN machines and 8N7 machines use 1.1, while all other
8NN machines use 1.0.

   The easiest way to handle this problem is to use `configure hpNNN'
or `configure hpNNN-hpux', where NNN is the model number of the
machine.  Then `configure' will figure out if the machine is a 1.0 or
1.1.  Use `uname -a' to find out the model number of your machine.

   `-g' does not work on HP-UX, since that system uses a peculiar
debugging format which GNU CC does not know about.  There are
preliminary versions of GAS and GDB for the HP-PA which do work with
GNU CC for debugging.  You can get them by anonymous ftp from
`jaguar.cs.utah.edu' `dist' subdirectory.  You would need to install
GAS in the file

     /usr/local/lib/gcc-lib/CONFIGURATION/GCCVERSION/as

where CONFIGURATION is the configuration name (perhaps `hpNNN-hpux')
and GCCVERSION is the GNU CC version number.  Do this *before* starting
the build process, otherwise you will get errors from the HPUX
assembler while building `libgcc2.a'.  The command

     make install-dir

will create the necessary directory hierarchy so you can install GAS
before building GCC.

   If you obtained GAS before October 6, 1992 it is highly recommended
you get a new one to avoid several bugs which have been discovered
recently.

   To enable debugging, configure GNU CC with the `--gas' option before
building.

   It has been reported that GNU CC produces invalid assembly code for
1.1 machines running HP-UX 8.02 when using the HP assembler.  Typically
the errors look like this:
     as: bug.s @line#15 [err#1060]
       Argument 0 or 2 in FARG upper
              - lookahead = ARGW1=FR,RTNVAL=GR
     as: foo.s @line#28 [err#1060]
       Argument 0 or 2 in FARG upper
              - lookahead = ARGW1=FR

   You can check the version of HP-UX you are running by executing the
command `uname -r'.   If you are indeed running HP-UX 8.02 on a PA and
using the HP assembler then configure GCC with "hpNNN-hpux8.02".


File: @.Distr.UsingGCC,  Node: Sun Install,  Next: 3b1 Install,  Prev: PA Install,  Up: Installation

Installing GNU CC on the Sun
============================

   On Solaris (version 2.1), do not use the linker or other tools in
`/usr/ucb' to build GNU CC.  Use `/usr/ccs/bin'.

   Make sure the environment variable `FLOAT_OPTION' is not set when
you compile `libgcc.a'.  If this option were set to `f68881' when
`libgcc.a' is compiled, the resulting code would demand to be linked
with a special startup file and would not link properly without special
pains.

   The GNU compiler does not really support the Super SPARC processor
that is used in SPARC Station 10 and similar class machines.  You can
get code that runs by specifying `sparc' as the cpu type; however, its
performance is not very good, and may vary widely according to the
compiler version and optimization options used.  This is because the
instruction scheduling parameters designed for the Sparc are not correct
for the Super SPARC.  Implementing scheduling parameters for the Super
SPARC might be a good project for someone who is willing to learn a
great deal about instruction scheduling in GNU CC.

   There is a bug in `alloca' in certain versions of the Sun library.
To avoid this bug, install the binaries of GNU CC that were compiled by
GNU CC.  They use `alloca' as a built-in function and never the one in
the library.

   Some versions of the Sun compiler crash when compiling GNU CC.  The
problem is a segmentation fault in cpp.  This problem seems to be due to
the bulk of data in the environment variables.  You may be able to avoid
it by using the following command to compile GNU CC with Sun CC:

     make CC="TERMCAP=x OBJS=x LIBFUNCS=x STAGESTUFF=x cc"


File: @.Distr.UsingGCC,  Node: 3b1 Install,  Next: Unos Install,  Prev: Sun Install,  Up: Installation

Installing GNU CC on the 3b1
============================

   Installing GNU CC on the 3b1 is difficult if you do not already have
GNU CC running, due to bugs in the installed C compiler.  However, the
following procedure might work.  We are unable to test it.

  1. Comment out the `#include "config.h"' line on line 37 of `cccp.c'
     and do `make cpp'.  This makes a preliminary version of GNU cpp.

  2. Save the old `/lib/cpp' and copy the preliminary GNU cpp to that
     file name.

  3. Undo your change in `cccp.c', or reinstall the original version,
     and do `make cpp' again.

  4. Copy this final version of GNU cpp into `/lib/cpp'.

  5. Replace every occurrence of `obstack_free' in the file `tree.c'
     with `_obstack_free'.

  6. Run `make' to get the first-stage GNU CC.

  7. Reinstall the original version of `/lib/cpp'.

  8. Now you can compile GNU CC with itself and install it in the normal
     fashion.


File: @.Distr.UsingGCC,  Node: Unos Install,  Next: VMS Install,  Prev: 3b1 Install,  Up: Installation

Installing GNU CC on Unos
=========================

   Use `configure unos' for building on Unos.

   The Unos assembler is named `casm' instead of `as'.  For some
strange reason linking `/bin/as' to `/bin/casm' changes the behavior,
and does not work.  So, when installing GNU CC, you should install the
following script as `as' in the subdirectory where the passes of GCC
are installed:

     #!/bin/sh
     casm $*

   The default Unos library is named `libunos.a' instead of `libc.a'.
To allow GNU CC to function, either change all references to `-lc' in
`gcc.c' to `-lunos' or link `/lib/libc.a' to `/lib/libunos.a'.

   When compiling GNU CC with the standard compiler, to overcome bugs in
the support of `alloca', do not use `-O' when making stage 2.  Then use
the stage 2 compiler with `-O' to make the stage 3 compiler.  This
compiler will have the same characteristics as the usual stage 2
compiler on other systems.  Use it to make a stage 4 compiler and
compare that with stage 3 to verify proper compilation.

   (Perhaps simply defining `ALLOCA' in `x-crds' as described in the
comments there will make the above paragraph superfluous.  Please
inform us of whether this works.)

   Unos uses memory segmentation instead of demand paging, so you will
need a lot of memory.  5 Mb is barely enough if no other tasks are
running.  If linking `cc1' fails, try putting the object files into a
library and linking from that library.


File: @.Distr.UsingGCC,  Node: VMS Install,  Next: WE32K Install,  Prev: Unos Install,  Up: Installation

Installing GNU CC on VMS
========================

   The VMS version of GNU CC is distributed in a backup saveset
containing both source code and precompiled binaries.

   To install the `gcc' command so you can use the compiler easily, in
the same manner as you use the VMS C compiler, you must install the VMS
CLD file for GNU CC as follows:

  1. Define the VMS logical names `GNU_CC' and `GNU_CC_INCLUDE' to
     point to the directories where the GNU CC executables
     (`gcc-cpp.exe', `gcc-cc1.exe', etc.) and the C include files are
     kept respectively.  This should be done with the commands:

          $ assign /system /translation=concealed -
            disk:[gcc.] gnu_cc
          $ assign /system /translation=concealed -
            disk:[gcc.include.] gnu_cc_include

     with the appropriate disk and directory names.  These commands can
     be placed in your system startup file so they will be executed
     whenever the machine is rebooted.  You may, if you choose, do this
     via the `GCC_INSTALL.COM' script in the `[GCC]' directory.

  2. Install the `GCC' command with the command line:

          $ set command /table=sys$common:[syslib]dcltables -
            /output=sys$common:[syslib]dcltables gnu_cc:[000000]gcc
          $ install replace sys$common:[syslib]dcltables

  3. To install the help file, do the following:

          $ library/help sys$library:helplib.hlb gcc.hlp

     Now you can invoke the compiler with a command like `gcc /verbose
     file.c', which is equivalent to the command `gcc -v -c file.c' in
     Unix.

   If you wish to use GNU C++ you must first install GNU CC, and then
perform the following steps:

  1. Define the VMS logical name `GNU_GXX_INCLUDE' to point to the
     directory where the preprocessor will search for the C++ header
     files.  This can be done with the command:

          $ assign /system /translation=concealed -
            disk:[gcc.gxx_include.] gnu_gxx_include

     with the appropriate disk and directory name.  If you are going to
     be using libg++, this is where the libg++ install procedure will
     install the libg++ header files.

  2. Obtain the file `gcc-cc1plus.exe', and place this in the same
     directory that `gcc-cc1.exe' is kept.

     The GNU C++ compiler can be invoked with a command like `gcc /plus
     /verbose file.cc', which is equivalent to the command `g++ -v -c
     file.cc' in Unix.

   We try to put corresponding binaries and sources on the VMS
distribution tape.  But sometimes the binaries will be from an older
version than the sources, because we don't always have time to update
them.  (Use the `/version' option to determine the version number of
the binaries and compare it with the source file `version.c' to tell
whether this is so.)  In this case, you should use the binaries you get
to recompile the sources.  If you must recompile, here is how:

  1. Execute the command procedure `vmsconfig.com' to set up the files
     `tm.h', `config.h', `aux-output.c', and `md.', and to create files
     `tconfig.h' and `hconfig.h'.  This procedure also creates several
     linker option files used by `make-cc1.com' and a data file used by
     `make-l2.com'.

          $ @vmsconfig.com

  2. Setup the logical names and command tables as defined above.  In
     addition, define the VMS logical name `GNU_BISON' to point at the
     to the directories where the Bison executable is kept.  This
     should be done with the command:

          $ assign /system /translation=concealed -
            disk:[bison.] gnu_bison

     You may, if you choose, use the `INSTALL_BISON.COM' script in the
     `[BISON]' directory.

  3. Install the `BISON' command with the command line:

          $ set command /table=sys$common:[syslib]dcltables -
            /output=sys$common:[syslib]dcltables -
            gnu_bison:[000000]bison
          $ install replace sys$common:[syslib]dcltables

  4. Type `@make-gcc' to recompile everything (alternatively, submit
     the file `make-gcc.com' to a batch queue).  If you wish to build
     the GNU C++ compiler as well as the GNU CC compiler, you must
     first edit `make-gcc.com' and follow the instructions that appear
     in the comments.

  5. In order to use GCC, you need a library of functions which GCC
     compiled code will call to perform certain tasks, and these
     functions are defined in the file `libgcc2.c'.  To compile this
     you should use the command procedure `make-l2.com', which will
     generate the library `libgcc2.olb'.  `libgcc2.olb' should be built
     using the compiler built from the same distribution that
     `libgcc2.c' came from, and `make-gcc.com' will automatically do
     all of this for you.

     To install the library, use the following commands:

          $ library gnu_cc:[000000]gcclib/delete=(new,eprintf)
          $ library gnu_cc:[000000]gcclib/delete=L_*
          $ library libgcc2/extract=*/output=libgcc2.obj
          $ library gnu_cc:[000000]gcclib libgcc2.obj

     The first command simply removes old modules that will be replaced
     with modules from `libgcc2' under different module names.  The
     modules `new' and `eprintf' may not actually be present in your
     `gcclib.olb'--if the VMS librarian complains about those modules
     not being present, simply ignore the message and continue on with
     the next command.  The second command removes the modules that
     came from the previous version of the library `libgcc2.c'.

     Whenever you update the compiler on your system, you should also
     update the library with the above procedure.

  6. You may wish to build GCC in such a way that no files are written
     to the directory where the source files reside.  An example would
     be the when the source files are on a read-only disk.  In these
     cases, execute the following DCL commands (substituting your
     actual path names):

          $ assign dua0:[gcc.build_dir.]/translation=concealed, -
                   dua1:[gcc.source_dir.]/translation=concealed  gcc_build
          $ set default gcc_build:[000000]

     where the directory `dua1:[gcc.source_dir]' contains the source
     code, and the directory `dua0:[gcc.build_dir]' is meant to contain
     all of the generated object files and executables.  Once you have
     done this, you can proceed building GCC as described above.  (Keep
     in mind that `gcc_build' is a rooted logical name, and thus the
     device names in each element of the search list must be an actual
     physical device name rather than another rooted logical name).

  7. *If you are building GNU CC with a previous version of GNU CC, you
     also should check to see that you have the newest version of the
     assembler*.  In particular, GNU CC version 2 treats global constant
     variables slightly differently from GNU CC version 1, and GAS
     version 1.38.1 does not have the patches required to work with GCC
     version 2.  If you use GAS 1.38.1, then `extern const' variables
     will not have the read-only bit set, and the linker will generate
     warning messages about mismatched psect attributes for these
     variables.  These warning messages are merely a nuisance, and can
     safely be ignored.

     If you are compiling with a version of GNU CC older than 1.33,
     specify `/DEFINE=("inline=")' as an option in all the
     compilations.  This requires editing all the `gcc' commands in
     `make-cc1.com'.  (The older versions had problems supporting
     `inline'.)  Once you have a working 1.33 or newer GNU CC, you can
     change this file back.

  8. If you want to build GNU CC with the VAX C compiler, you will need
     to make minor changes in `make-cccp.com' and `make-cc1.com' to
     choose alternate definitions of `CC', `CFLAGS', and `LIBS'.  See
     comments in those files.  However, you must also have a working
     version of the GNU assembler (GNU as, aka GAS) as it is used as
     the back-end for GNU CC to produce binary object modules and is
     not included in the GNU CC sources.  GAS is also needed to compile
     `libgcc2' in order to build `gcclib' (see above); `make-l2.com'
     expects to be able to find it operational in
     `gnu_cc:[000000]gnu-as.exe'.

     To use GNU CC on VMS, you need the VMS driver programs `gcc.exe',
     `gcc.com', and `gcc.cld'.  They are distributed with the VMS
     binaries (`gcc-vms') rather than the GNU CC sources.  GAS is also
     included in `gcc-vms', as is Bison.

     Once you have successfully built GNU CC with VAX C, you should use
     the resulting compiler to rebuild itself.  Before doing this, be
     sure to restore the `CC', `CFLAGS', and `LIBS' definitions in
     `make-cccp.com' and `make-cc1.com'.  The second generation
     compiler will be able to take advantage of many optimizations that
     must be suppressed when building with other compilers.

   Under previous versions of GNU CC, the generated code would
occasionally give strange results when linked with the sharable
`VAXCRTL' library.  Now this should work.

   Even with this version, however, GNU CC itself should not be linked
with the sharable `VAXCRTL'.  The version of `qsort' in `VAXCRTL' has a
bug (known to be present in VMS versions V4.6 through V5.5) which
causes the compiler to fail.

   The executables are generated by `make-cc1.com' and `make-cccp.com'
use the object library version of `VAXCRTL' in order to make use of the
`qsort' routine in `gcclib.olb'.  If you wish to link the compiler
executables with the shareable image version of `VAXCRTL', you should
edit the file `tm.h' (created by `vmsconfig.com') to define the macro
`QSORT_WORKAROUND'.

   `QSORT_WORKAROUND' is always defined when GNU CC is compiled with
VAX C, to avoid a problem in case `gcclib.olb' is not yet available.


File: @.Distr.UsingGCC,  Node: WE32K Install,  Next: MIPS Install,  Prev: VMS Install,  Up: Installation

Installing GNU CC on the WE32K
==============================

   These computers are also known as the 3b2, 3b5, 3b20 and other
similar names.  (However, the 3b1 is actually a 68000; see *Note 3b1
Install::.)

   Don't use `-g' when compiling with the system's compiler.  The
system's linker seems to be unable to handle such a large program with
debugging information.

   The system's compiler runs out of capacity when compiling `stmt.c'
in GNU CC.  You can work around this by building `cpp' in GNU CC first,
then use that instead of the system's preprocessor with the system's C
compiler to compile `stmt.c'.  Here is how:

     mv /lib/cpp /lib/cpp.att
     cp cpp /lib/cpp.gnu
     echo '/lib/cpp.gnu -traditional ${1+"$@"}' > /lib/cpp
     chmod +x /lib/cpp

   The system's compiler produces bad code for some of the GNU CC
optimization files.  So you must build the stage 2 compiler without
optimization.  Then build a stage 3 compiler with optimization.  That
executable should work.  Here are the necessary commands:

     make LANGUAGES=c CC=stage1/xgcc CFLAGS="-Bstage1/ -g"
     make stage2
     make CC=stage2/xgcc CFLAGS="-Bstage2/ -g -O"

   You may need to raise the ULIMIT setting to build a C++ compiler, as
the file `cc1plus' is larger than one megabyte.


File: @.Distr.UsingGCC,  Node: MIPS Install,  Next: Collect2,  Prev: WE32K Install,  Up: Installation

Installing GNU CC on the MIPS
=============================

   See *Note Installation:: about whether to use either of the options
`--with-stabs' or `--with-gnu-as'.

   The MIPS C compiler needs to be told to increase its table size for
switch statements with the `-Wf,-XNg1500' option in order to compile
`cp-parse.c'.  If you use the `-O2' optimization option, you also need
to use `-Olimit 3000'.  Both of these options are automatically
generated in the `Makefile' that the shell script `configure' builds.
If you override the `CC' make variable and use the MIPS compilers, you
may need to add `-Wf,-XNg1500 -Olimit 3000'.

   MIPS computers running RISC-OS can support four different
personalities: default, BSD 4.3, System V.3, and System V.4 (older
versions of RISC-OS don't support V.4).  To configure GCC for these
platforms use the following configurations:

`mips-mips-riscos`rev''
     Default configuration for RISC-OS, revision `rev'.

`mips-mips-riscos`rev'bsd'
     BSD 4.3 configuration for RISC-OS, revision `rev'.

`mips-mips-riscos`rev'sysv4'
     System V.4 configuration for RISC-OS, revision `rev'.

`mips-mips-riscos`rev'sysv'
     System V.3 configuration for RISC-OS, revision `rev'.

   The revision `rev' mentioned above is the revision of RISC-OS to
use.  You must reconfigure GCC when going from a RISC-OS revision 4 to
RISC-OS revision 5.  This has the effect of avoiding a linker bug (see
*Note Installation Problems:: for more details).

   DECstations can support three different personalities: Ultrix, DEC
OSF/1, and OSF/rose.  To configure GCC for these platforms use the
following configurations:

`decstation-ultrix'
     Ultrix configuration.

`decstation-osf1'
     Dec's version of OSF/1.

`decstation-osfrose'
     Open Software Foundation reference port of OSF/1 which uses the
     OSF/rose object file format instead of ECOFF.  Normally, you would
     not select this configuration.

   On Irix version 4.0.5F, and perhaps on some other versions as well,
there is an assembler bug that reorders instructions incorrectly.  To
work around it, specify the target configuration `mips-sgi-irix4loser'.
This configuration inhibits assembler optimization.

   You can turn off assembler optimization in a compiler configured with
target `mips-sgi-irix4' using the `-noasmopt' option.  This compiler
option passes the option `-O0' to the assembler, to inhibit reordering.

   The `-noasmopt' option can be useful for testing whether a problem
is due to erroneous assembler reordering.  Even if a problem does not go
away with `-noasmopt', it may still be due to assembler
reordering--perhaps GNU CC itself was miscompiled as a result.

   We know this is inconvenient, but it's the best that can be done at
the last minute.


File: @.Distr.UsingGCC,  Node: Collect2,  Next: Header Dirs,  Prev: MIPS Install,  Up: Installation

`collect2'
==========

   Many target systems do not have support in the assembler and linker
for "constructors"--initialization functions to be called before the
official "start" of `main'.  On such systems, GNU CC uses a utility
called `collect2' to arrange to call these functions at start time.

   The program `collect2' works by linking the program once and looking
through the linker output file for symbols with particular names
indicating they are constructor functions.  If it finds any, it creates
a new temporary `.c' file containing a table of them, compiles it, and
links the program a second time including that file.

   The actual calls to the constructors are carried out by a subroutine
called `__main', which is called (automatically) at the beginning of
the body of `main' (provided `main' was compiled with GNU CC).

   The program `collect2' is installed as `ld' in the directory where
the passes of the compiler are installed.  When `collect2' needs to
find the *real* `ld', it tries the following file names:

   * `gld' in the directories listed in the compiler's search
     directories.

   * `gld' in the directories listed in the environment variable `PATH'.

   * `real-ld' in the compiler's search directories.

   * `real-ld' in `PATH'.

   * `ld' in `PATH'.

   "The compiler's search directories" means all the directories where
`gcc' searches for passes of the compiler.  This includes directories
that you specify with `-B'.

   Cross-compilers search a little differently:

   * `gld' in the compiler's search directories.

   * `TARGET-gld' in `PATH'.

   * `real-ld' in the compiler's search directories.

   * `TARGET-real-ld' in `PATH'.

   * `TARGET-ld' in `PATH'.

   `collect2' does not search for `ld' using the compiler's search
directories, because if it did, it would find itself--not the real
`ld'--and this could lead to infinite recursion.  However, the
directory where `collect2' is installed might happen to be in `PATH'.
That could lead `collect2' to invoke itself anyway.  when looking for
`ld'.

   To prevent this, `collect2' explicitly avoids running `ld' using the
file name under which `collect2' itself was invoked.  In fact, it
remembers up to two such names--in case one copy of `collect2' finds
another copy (or version) of `collect2' installed as `ld' in a second
place in the search path.

   If two file names to avoid are not sufficient, you may still
encounter an infinite recursion of `collect2' processes.  When this
happens.  check all the files installed as `ld' in any of the
directories searched, and straighten out the situation.

   (In a future version, we will probably change `collect2' to avoid
any reinvocation of a file from which any parent `collect2' was run.)


File: @.Distr.UsingGCC,  Node: Header Dirs,  Prev: Collect2,  Up: Installation

Standard Header File Directories
================================

   `GCC_INCLUDE_DIR' means the same thing for native and cross.  It is
where GNU CC stores its private include files, and also where GNU CC
stores the fixed include files.  A cross compiled GNU CC runs
`fixincludes' on the header files in `$(tooldir)/include'.  (If the
cross compilation header files need to be fixed, they must be installed
before GNU CC is built.  If the cross compilation header files are
already suitable for ANSI C and GNU CC, nothing special need be done).

   `GPLUS_INCLUDE_DIR' means the same thing for native and cross.  It
is where `g++' looks first for header files.  `libg++' installs only
target independent header files in that directory.

   `LOCAL_INCLUDE_DIR' is used only for a native compiler.  It is
normally `/usr/local/include'.  GNU CC searches this directory so that
users can install header files in `/usr/local/include'.

   `CROSS_INCLUDE_DIR' is used only for a cross compiler.  GNU CC
doesn't install anything there.

   `TOOL_INCLUDE_DIR' is used for both native and cross compilers.  It
is the place for other packages to install header files that GNU CC will
use.  For a cross-compiler, this is the equivalent of `/usr/include'.
When you build a cross-compiler, `fixincludes' processes any header
files in this directory.


File: @.Distr.UsingGCC,  Node: C Extensions,  Next: C++ Extensions,  Prev: Installation,  Up: Top

Extensions to the C Language Family
***********************************

   GNU C provides several language features not found in ANSI standard
C.  (The `-pedantic' option directs GNU CC to print a warning message if
any of these features is used.)  To test for the availability of these
features in conditional compilation, check for a predefined macro
`__GNUC__', which is always defined under GNU CC.

   These extensions are available in C and in the languages derived from
it, C++ and Objective C.  *Note Extensions to the C++ Language: C++
Extensions, for extensions that apply *only* to C++.

* Menu:

* Statement Exprs::     Putting statements and declarations inside expressions.
* Local Labels::        Labels local to a statement-expression.
* Labels as Values::    Getting pointers to labels, and computed gotos.
* Nested Functions::    As in Algol and Pascal, lexical scoping of functions.
* Constructing Calls::    Dispatching a call to another function.
* Naming Types::        Giving a name to the type of some expression.
* Typeof::              `typeof': referring to the type of an expression.
* Lvalues::             Using `?:', `,' and casts in lvalues.
* Conditionals::        Omitting the middle operand of a `?:' expression.
* Long Long::        Double-word integers--`long long int'.
* Zero Length::         Zero-length arrays.
* Variable Length::     Arrays whose length is computed at run time.
* Macro Varargs::    Macros with variable number of arguments.
* Subscripting::        Any array can be subscripted, even if not an lvalue.
* Pointer Arith::       Arithmetic on `void'-pointers and function pointers.
* Initializers::        Non-constant initializers.
* Constructors::        Constructor expressions give structures, unions
                         or arrays as values.
* Labeled Elements::    Labeling elements of initializers.
* Cast to Union::       Casting to union type from any member of the union.
* Case Ranges::        `case 1 ... 9' and such.
* Function Attributes:: Declaring that functions have no side effects,
                         or that they can never return.
* Function Prototypes:: Prototype declarations and old-style definitions.
* Dollar Signs::        Dollar sign is allowed in identifiers.
* Character Escapes::   `\e' stands for the character ESC.
* Variable Attributes::    Specifying attributes of variables.
* Alignment::           Inquiring about the alignment of a type or variable.
* Inline::              Defining inline functions (as fast as macros).
* Extended Asm::        Assembler instructions with C expressions as operands.
                         (With them you can define "built-in" functions.)
* Constraints::         Constraints for asm operands
* Asm Labels::          Specifying the assembler name to use for a C symbol.
* Explicit Reg Vars::   Defining variables residing in specified registers.
* Alternate Keywords::  `__const__', `__asm__', etc., for header files.
* Incomplete Enums::    `enum foo;', with details to follow.
* Function Names::    Printable strings which are the name of the current
             function.


File: @.Distr.UsingGCC,  Node: Statement Exprs,  Next: Local Labels,  Up: C Extensions

Statements and Declarations in Expressions
==========================================

   A compound statement enclosed in parentheses may appear as an
expression in GNU C.  This allows you to use loops, switches, and local
variables within an expression.

   Recall that a compound statement is a sequence of statements
surrounded by braces; in this construct, parentheses go around the
braces.  For example:

     ({ int y = foo (); int z;
        if (y > 0) z = y;
        else z = - y;
        z; })

is a valid (though slightly more complex than necessary) expression for
the absolute value of `foo ()'.

   The last thing in the compound statement should be an expression
followed by a semicolon; the value of this subexpression serves as the
value of the entire construct.  (If you use some other kind of statement
last within the braces, the construct has type `void', and thus
effectively no value.)

   This feature is especially useful in making macro definitions "safe"
(so that they evaluate each operand exactly once).  For example, the
"maximum" function is commonly defined as a macro in standard C as
follows:

     #define max(a,b) ((a) > (b) ? (a) : (b))

But this definition computes either A or B twice, with bad results if
the operand has side effects.  In GNU C, if you know the type of the
operands (here let's assume `int'), you can define the macro safely as
follows:

     #define maxint(a,b) \
       ({int _a = (a), _b = (b); _a > _b ? _a : _b; })

   Embedded statements are not allowed in constant expressions, such as
the value of an enumeration constant, the width of a bit field, or the
initial value of a static variable.

   If you don't know the type of the operand, you can still do this,
but you must use `typeof' (*note Typeof::.) or type naming (*note
Naming Types::.).


File: @.Distr.UsingGCC,  Node: Local Labels,  Next: Labels as Values,  Prev: Statement Exprs,  Up: C Extensions

Locally Declared Labels
=======================

   Each statement expression is a scope in which "local labels" can be
declared.  A local label is simply an identifier; you can jump to it
with an ordinary `goto' statement, but only from within the statement
expression it belongs to.

   A local label declaration looks like this:

     __label__ LABEL;

or

     __label__ LABEL1, LABEL2, ...;

   Local label declarations must come at the beginning of the statement
expression, right after the `({', before any ordinary declarations.

   The label declaration defines the label *name*, but does not define
the label itself.  You must do this in the usual way, with `LABEL:',
within the statements of the statement expression.

   The local label feature is useful because statement expressions are
often used in macros.  If the macro contains nested loops, a `goto' can
be useful for breaking out of them.  However, an ordinary label whose
scope is the whole function cannot be used: if the macro can be
expanded several times in one function, the label will be multiply
defined in that function.  A local label avoids this problem.  For
example:

     #define SEARCH(array, target)                     \
     ({                                               \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { value = i; goto found; }              \
       value = -1;                                     \
      found:                                           \
       value;                                          \
     })


File: @.Distr.UsingGCC,  Node: Labels as Values,  Next: Nested Functions,  Prev: Local Labels,  Up: C Extensions

Labels as Values
================

   You can get the address of a label defined in the current function
(or a containing function) with the unary operator `&&'.  The value has
type `void *'.  This value is a constant and can be used wherever a
constant of that type is valid.  For example:

     void *ptr;
     ...
     ptr = &&foo;

   To use these values, you need to be able to jump to one.  This is
done with the computed goto statement(1), `goto *EXP;'.  For example,

     goto *ptr;

Any expression of type `void *' is allowed.

   One way of using these constants is in initializing a static array
that will serve as a jump table:

     static void *array[] = { &&foo, &&bar, &&hack };

   Then you can select a label with indexing, like this:

     goto *array[i];

Note that this does not check whether the subscript is in bounds--array
indexing in C never does that.

   Such an array of label values serves a purpose much like that of the
`switch' statement.  The `switch' statement is cleaner, so use that
rather than an array unless the problem does not fit a `switch'
statement very well.

   Another use of label values is in an interpreter for threaded code.
The labels within the interpreter function can be stored in the
threaded code for super-fast dispatching.

   You can use this mechanism to jump to code in a different function.
If you do that, totally unpredictable things will happen.  The best way
to avoid this is to store the label address only in automatic variables
and never pass it as an argument.

   ---------- Footnotes ----------

   (1)  The analogous feature in Fortran is called an assigned goto,
but that name seems inappropriate in C, where one can do more than
simply store label addresses in label variables.


File: @.Distr.UsingGCC,  Node: Nested Functions,  Next: Constructing Calls,  Prev: Labels as Values,  Up: C Extensions

Nested Functions
================

   A "nested function" is a function defined inside another function.
(Nested functions are not supported for GNU C++.)  The nested function's
name is local to the block where it is defined.  For example, here we
define a nested function named `square', and call it twice:

     foo (double a, double b)
     {
       double square (double z) { return z * z; }

       return square (a) + square (b);
     }

   The nested function can access all the variables of the containing
function that are visible at the point of its definition.  This is
called "lexical scoping".  For example, here we show a nested function
which uses an inherited variable named `offset':

     bar (int *array, int offset, int size)
     {
       int access (int *array, int index)
         { return array[index + offset]; }
       int i;
       ...
       for (i = 0; i < size; i++)
         ... access (array, i) ...
     }

   Nested function definitions are permitted within functions in the
places where variable definitions are allowed; that is, in any block,
before the first statement in the block.

   It is possible to call the nested function from outside the scope of
its name by storing its address or passing the address to another
function:

     hack (int *array, int size)
     {
       void store (int index, int value)
         { array[index] = value; }

       intermediate (store, size);
     }

   Here, the function `intermediate' receives the address of `store' as
an argument.  If `intermediate' calls `store', the arguments given to
`store' are used to store into `array'.  But this technique works only
so long as the containing function (`hack', in this example) does not
exit.  If you try to call the nested function through its address after
the containing function has exited, all hell will break loose.

   GNU CC implements taking the address of a nested function using a
technique called "trampolines".  A paper describing them is available
from `maya.idiap.ch' in directory `pub/tmb', file `usenix88-lexic.ps.Z'.

   A nested function can jump to a label inherited from a containing
function, provided the label was explicitly declared in the containing
function (*note Local Labels::.).  Such a jump returns instantly to the
containing function, exiting the nested function which did the `goto'
and any intermediate functions as well.  Here is an example:

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       int i;
       ...
       for (i = 0; i < size; i++)
         ... access (array, i) ...
       ...
       return 0;

      /* Control comes here from `access'
         if it detects an error.  */
      failure:
       return -1;
     }

   A nested function always has internal linkage.  Declaring one with
`extern' is erroneous.  If you need to declare the nested function
before its definition, use `auto' (which is otherwise meaningless for
function declarations).

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       auto int access (int *, int);
       ...
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       ...
     }


File: @.Distr.UsingGCC,  Node: Constructing Calls,  Next: Naming Types,  Prev: Nested Functions,  Up: C Extensions

Constructing Function Calls
===========================

   Using the built-in functions described below, you can record the
arguments a function received, and call another function with the same
arguments, without knowing the number or types of the arguments.

   You can also record the return value of that function call, and
later return that value, without knowing what data type the function
tried to return (as long as your caller expects that data type).

`__builtin_apply_args ()'
     This built-in function returns a pointer of type `void *' to data
     describing how to perform a call with the same arguments as were
     passed to the current function.

     The function saves the arg pointer register, structure value
     address, and all registers that might be used to pass arguments to
     a function into a block of memory allocated on the stack.  Then it
     returns the address of that block.

`__builtin_apply (FUNCTION, ARGUMENTS, SIZE)'
     This built-in function invokes FUNCTION (type `void (*)()') with a
     copy of the parameters described by ARGUMENTS (type `void *') and
     SIZE (type `int').

     The value of ARGUMENTS should be the value returned by
     `__builtin_apply_args'.  The argument SIZE specifies the size of
     the stack argument data, in bytes.

     This function returns a pointer of type `void *' to data describing
     how to return whatever value was returned by FUNCTION.  The data
     is saved in a block of memory allocated on the stack.

     It is not always simple to compute the proper value for SIZE.  The
     value is used by `__builtin_apply' to compute the amount of data
     that should be pushed on the stack and copied from the incoming
     argument area.

`__builtin_return (RESULT)'
     This built-in function returns the value described by RESULT from
     the containing function.  You should specify, for RESULT, a value
     returned by `__builtin_apply'.


File: @.Distr.UsingGCC,  Node: Naming Types,  Next: Typeof,  Prev: Constructing Calls,  Up: C Extensions

Naming an Expression's Type
===========================

   You can give a name to the type of an expression using a `typedef'
declaration with an initializer.  Here is how to define NAME as a type
name for the type of EXP:

     typedef NAME = EXP;

   This is useful in conjunction with the statements-within-expressions
feature.  Here is how the two together can be used to define a safe
"maximum" macro that operates on any arithmetic type:

     #define max(a,b) \
       ({typedef _ta = (a), _tb = (b);  \
         _ta _a = (a); _tb _b = (b);     \
         _a > _b ? _a : _b; })

   The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within
the expressions that are substituted for `a' and `b'.  Eventually we
hope to design a new form of declaration syntax that allows you to
declare variables whose scopes start only after their initializers;
this will be a more reliable way to prevent such conflicts.


File: @.Distr.UsingGCC,  Node: Typeof,  Next: Lvalues,  Prev: Naming Types,  Up: C Extensions

Referring to a Type with `typeof'
=================================

   Another way to refer to the type of an expression is with `typeof'.
The syntax of using of this keyword looks like `sizeof', but the
construct acts semantically like a type name defined with `typedef'.

   There are two ways of writing the argument to `typeof': with an
expression or with a type.  Here is an example with an expression:

     typeof (x[0](1))

This assumes that `x' is an array of functions; the type described is
that of the values of the functions.

   Here is an example with a typename as the argument:

     typeof (int *)

Here the type described is that of pointers to `int'.

   If you are writing a header file that must work when included in
ANSI C programs, write `__typeof__' instead of `typeof'.  *Note
Alternate Keywords::.

   A `typeof'-construct can be used anywhere a typedef name could be
used.  For example, you can use it in a declaration, in a cast, or
inside of `sizeof' or `typeof'.

   * This declares `y' with the type of what `x' points to.

          typeof (*x) y;

   * This declares `y' as an array of such values.

          typeof (*x) y[4];

   * This declares `y' as an array of pointers to characters:

          typeof (typeof (char *)[4]) y;

     It is equivalent to the following traditional C declaration:

          char *y[4];

     To see the meaning of the declaration using `typeof', and why it
     might be a useful way to write, let's rewrite it with these macros:

          #define pointer(T)  typeof(T *)
          #define array(T, N) typeof(T [N])

     Now the declaration can be rewritten this way:

          array (pointer (char), 4) y;

     Thus, `array (pointer (char), 4)' is the type of arrays of 4
     pointers to `char'.


File: @.Distr.UsingGCC,  Node: Lvalues,  Next: Conditionals,  Prev: Typeof,  Up: C Extensions

Generalized Lvalues
===================

   Compound expressions, conditional expressions and casts are allowed
as lvalues provided their operands are lvalues.  This means that you
can take their addresses or store values into them.

   For example, a compound expression can be assigned, provided the last
expression in the sequence is an lvalue.  These two expressions are
equivalent:

     (a, b) += 5
     a, (b += 5)

   Similarly, the address of the compound expression can be taken.
These two expressions are equivalent:

     &(a, b)
     a, &b

   A conditional expression is a valid lvalue if its type is not void
and the true and false branches are both valid lvalues.  For example,
these two expressions are equivalent:

     (a ? b : c) = 5
     (a ? b = 5 : (c = 5))

   A cast is a valid lvalue if its operand is an lvalue.  A simple
assignment whose left-hand side is a cast works by converting the
right-hand side first to the specified type, then to the type of the
inner left-hand side expression.  After this is stored, the value is
converted back to the specified type to become the value of the
assignment.  Thus, if `a' has type `char *', the following two
expressions are equivalent:

     (int)a = 5
     (int)(a = (char *)(int)5)

   An assignment-with-arithmetic operation such as `+=' applied to a
cast performs the arithmetic using the type resulting from the cast,
and then continues as in the previous case.  Therefore, these two
expressions are equivalent:

     (int)a += 5
     (int)(a = (char *)(int) ((int)a + 5))

   You cannot take the address of an lvalue cast, because the use of its
address would not work out coherently.  Suppose that `&(int)f' were
permitted, where `f' has type `float'.  Then the following statement
would try to store an integer bit-pattern where a floating point number
belongs:

     *&(int)f = 1;

   This is quite different from what `(int)f = 1' would do--that would
convert 1 to floating point and store it.  Rather than cause this
inconsistency, we think it is better to prohibit use of `&' on a cast.

   If you really do want an `int *' pointer with the address of `f',
you can simply write `(int *)&f'.


File: @.Distr.UsingGCC,  Node: Conditionals,  Next: Long Long,  Prev: Lvalues,  Up: C Extensions

Conditionals with Omitted Operands
==================================

   The middle operand in a conditional expression may be omitted.  Then
if the first operand is nonzero, its value is the value of the
conditional expression.

   Therefore, the expression

     x ? : y

has the value of `x' if that is nonzero; otherwise, the value of `y'.

   This example is perfectly equivalent to

     x ? x : y

In this simple case, the ability to omit the middle operand is not
especially useful.  When it becomes useful is when the first operand
does, or may (if it is a macro argument), contain a side effect.  Then
repeating the operand in the middle would perform the side effect
twice.  Omitting the middle operand uses the value already computed
without the undesirable effects of recomputing it.


File: @.Distr.UsingGCC,  Node: Long Long,  Next: Zero Length,  Prev: Conditionals,  Up: C Extensions

Double-Word Integers
====================

   GNU C supports data types for integers that are twice as long as
`long int'.  Simply write `long long int' for a signed integer, or
`unsigned long long int' for an unsigned integer.  To make an integer
constant of type `long long int', add the suffix `LL' to the integer.
To make an integer constant of type `unsigned long long int', add the
suffix `ULL' to the integer.

   You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types
are open-coded on all types of machines.  Multiplication is open-coded
if the machine supports fullword-to-doubleword a widening multiply
instruction.  Division and shifts are open-coded only on machines that
provide special support.  The operations that are not open-coded use
special library routines that come with GNU CC.

   There may be pitfalls when you use `long long' types for function
arguments, unless you declare function prototypes.  If a function
expects type `int' for its argument, and you pass a value of type `long
long int', confusion will result because the caller and the subroutine
will disagree about the number of bytes for the argument.  Likewise, if
the function expects `long long int' and you pass `int'.  The best way
to avoid such problems is to use prototypes.


File: @.Distr.UsingGCC,  Node: Complex

Complex Numbers
===============

   GNU C supports complex data types.  You can declare both complex
integer types and complex floating types, using the keyword
`__complex__'.

   For example, `__complex__ double x;' declares `x' as a variable
whose real part and imaginary part are both of type `double'.
`__complex__ short int y;' declares `y' to have real and imaginary
parts of type `short int'; this is not likely to be useful, but it
shows that the set of complex types is complete.

   To write a constant with a complex data type, use the suffix `i' or
`j' (either one; they are equivalent).  For example, `2.5fi' has type
`__complex__ float' and `3i' has type `__complex__ int'.  Such a
constant always has a pure imaginary value, but you can form any
complex value you like by adding one to a real constant.

   To extract the real part of a complex-valued expression EXP, write
`__real__ EXP'.  Likewise, use `__imag__' to extract the imaginary part.

   The operator `~' performs complex conjugation when used on a value
with a complex type.

   GNU CC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice-versa).  None of the
supported debugging info formats has a way to represent noncontiguous
allocation like this, so GNU CC describes a noncontiguous complex
variable as if it were two separate variables of noncomplex type.  If
the variable's actual name is `foo', the two fictitious variables are
named `foo$real' and `foo$imag'.  You can examine and set these two
fictitious variables with your debugger.

   A future version of GDB will know how to recognize such pairs and
treat them as a single variable with a complex type.


File: @.Distr.UsingGCC,  Node: Zero Length,  Next: Variable Length,  Prev: Long Long,  Up: C Extensions

Arrays of Length Zero
=====================

   Zero-length arrays are allowed in GNU C.  They are very useful as
the last element of a structure which is really a header for a
variable-length object:

     struct line {
       int length;
       char contents[0];
     };

     {
       struct line *thisline = (struct line *)
         malloc (sizeof (struct line) + this_length);
       thisline->length = this_length;
     }

   In standard C, you would have to give `contents' a length of 1, which
means either you waste space or complicate the argument to `malloc'.


File: @.Distr.UsingGCC,  Node: Variable Length,  Next: Macro Varargs,  Prev: Zero Length,  Up: C Extensions

Arrays of Variable Length
=========================

   Variable-length automatic arrays are allowed in GNU C.  These arrays
are declared like any other automatic arrays, but with a length that is
not a constant expression.  The storage is allocated at the point of
declaration and deallocated when the brace-level is exited.  For
example:

     FILE *
     concat_fopen (char *s1, char *s2, char *mode)
     {
       char str[strlen (s1) + strlen (s2) + 1];
       strcpy (str, s1);
       strcat (str, s2);
       return fopen (str, mode);
     }

   Jumping or breaking out of the scope of the array name deallocates
the storage.  Jumping into the scope is not allowed; you get an error
message for it.

   You can use the function `alloca' to get an effect much like
variable-length arrays.  The function `alloca' is available in many
other C implementations (but not in all).  On the other hand,
variable-length arrays are more elegant.

   There are other differences between these two methods.  Space
allocated with `alloca' exists until the containing *function* returns.
The space for a variable-length array is deallocated as soon as the
array name's scope ends.  (If you use both variable-length arrays and
`alloca' in the same function, deallocation of a variable-length array
will also deallocate anything more recently allocated with `alloca'.)

   You can also use variable-length arrays as arguments to functions:

     struct entry
     tester (int len, char data[len][len])
     {
       ...
     }

   The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
`sizeof'.

   If you want to pass the array first and the length afterward, you can
use a forward declaration in the parameter list--another GNU extension.

     struct entry
     tester (int len; char data[len][len], int len)
     {
       ...
     }

   The `int len' before the semicolon is a "parameter forward
declaration", and it serves the purpose of making the name `len' known
when the declaration of `data' is parsed.

   You can write any number of such parameter forward declarations in
the parameter list.  They can be separated by commas or semicolons, but
the last one must end with a semicolon, which is followed by the "real"
parameter declarations.  Each forward declaration must match a "real"
declaration in parameter name and data type.


File: @.Distr.UsingGCC,  Node: Macro Varargs,  Next: Subscripting,  Prev: Variable Length,  Up: C Extensions

Macros with Variable Numbers of Arguments
=========================================

   In GNU C, a macro can accept a variable number of arguments, much as
a function can.  The syntax for defining the macro looks much like that
used for a function.  Here is an example:

     #define eprintf(format, args...)  \
      fprintf (stderr, format , ## args)

   Here `args' is a "rest argument": it takes in zero or more
arguments, as many as the call contains.  All of them plus the commas
between them form the value of `args', which is substituted into the
macro body where `args' is used.  Thus, we have this expansion:

     eprintf ("%s:%d: ", input_file_name, line_number)
     ==>
     fprintf (stderr, "%s:%d: " , input_file_name, line_number)

Note that the comma after the string constant comes from the definition
of `eprintf', whereas the last comma comes from the value of `args'.

   The reason for using `##' is to handle the case when `args' matches
no arguments at all.  In this case, `args' has an empty value.  In this
case, the second comma in the definition becomes an embarrassment: if
it got through to the expansion of the macro, we would get something
like this:

     fprintf (stderr, "success!\n" , )

which is invalid C syntax.  `##' gets rid of the comma, so we get the
following instead:

     fprintf (stderr, "success!\n")

   This is a special feature of the GNU C preprocessor: `##' before a
rest argument that is empty discards the preceding sequence of
non-whitespace characters from the macro definition.  (If another macro
argument precedes, none of it is discarded.)

   It might be better to discard the last preprocessor token instead of
the last preceding sequence of non-whitespace characters; in fact, we
may someday change this feature to do so.  We advise you to write the
macro definition so that the preceding sequence of non-whitespace
characters is just a single token, so that the meaning will not change
if we change the definition of this feature.


File: @.Distr.UsingGCC,  Node: Subscripting,  Next: Pointer Arith,  Prev: Macro Varargs,  Up: C Extensions

Non-Lvalue Arrays May Have Subscripts
=====================================

   Subscripting is allowed on arrays that are not lvalues, even though
the unary `&' operator is not.  For example, this is valid in GNU C
though not valid in other C dialects:

     struct foo {int a[4];};

     struct foo f();

     bar (int index)
     {
       return f().a[index];
     }


File: @.Distr.UsingGCC,  Node: Pointer Arith,  Next: Initializers,  Prev: Subscripting,  Up: C Extensions

Arithmetic on `void'- and Function-Pointers
===========================================

   In GNU C, addition and subtraction operations are supported on
pointers to `void' and on pointers to functions.  This is done by
treating the size of a `void' or of a function as 1.

   A consequence of this is that `sizeof' is also allowed on `void' and
on function types, and returns 1.

   The option `-Wpointer-arith' requests a warning if these extensions
are used.


File: @.Distr.UsingGCC,  Node: Initializers,  Next: Constructors,  Prev: Pointer Arith,  Up: C Extensions

Non-Constant Initializers
=========================

   The elements of an aggregate initializer for an automatic variable
are not required to be constant expressions in GNU C.  Here is an
example of an initializer with run-time varying elements:

     foo (float f, float g)
     {
       float beat_freqs[2] = { f-g, f+g };
       ...
     }


File: @.Distr.UsingGCC,  Node: Constructors,  Next: Labeled Elements,  Prev: Initializers,  Up: C Extensions

Constructor Expressions
=======================

   GNU C supports constructor expressions.  A constructor looks like a
cast containing an initializer.  Its value is an object of the type
specified in the cast, containing the elements specified in the
initializer.

   Usually, the specified type is a structure.  Assume that `struct
foo' and `structure' are declared as shown:

     struct foo {int a; char b[2];} structure;

Here is an example of constructing a `struct foo' with a constructor:

     structure = ((struct foo) {x + y, 'a', 0});

This is equivalent to writing the following:

     {
       struct foo temp = {x + y, 'a', 0};
       structure = temp;
     }

   You can also construct an array.  If all the elements of the
constructor are (made up of) simple constant expressions, suitable for
use in initializers, then the constructor is an lvalue and can be
coerced to a pointer to its first element, as shown here:

     char **foo = (char *[]) { "x", "y", "z" };

   Array constructors whose elements are not simple constants are not
very useful, because the constructor is not an lvalue.  There are only
two valid ways to use it: to subscript it, or initialize an array
variable with it.  The former is probably slower than a `switch'
statement, while the latter does the same thing an ordinary C
initializer would do.  Here is an example of subscripting an array
constructor:

     output = ((int[]) { 2, x, 28 }) [input];

   Constructor expressions for scalar types and union types are is also
allowed, but then the constructor expression is equivalent to a cast.


File: @.Distr.UsingGCC,  Node: Labeled Elements,  Next: Cast to Union,  Prev: Constructors,  Up: C Extensions

Labeled Elements in Initializers
================================

   Standard C requires the elements of an initializer to appear in a
fixed order, the same as the order of the elements in the array or
structure being initialized.

   In GNU C you can give the elements in any order, specifying the array
indices or structure field names they apply to.

   To specify an array index, write `[INDEX]' before the element value.
For example,

     int a[6] = { [4] 29, [2] 15 };

is equivalent to

     int a[6] = { 0, 0, 15, 0, 29, 0 };

The index values must be constant expressions, even if the array being
initialized is automatic.

   In a structure initializer, specify the name of a field to initialize
with `FIELDNAME:' before the element value.  For example, given the
following structure,

     struct point { int x, y; };

the following initialization

     struct point p = { y: yvalue, x: xvalue };

is equivalent to

     struct point p = { xvalue, yvalue };

   You can also use an element label when initializing a union, to
specify which element of the union should be used.  For example,

     union foo { int i; double d; };

     union foo f = { d: 4 };

will convert 4 to a `double' to store it in the union using the second
element.  By contrast, casting 4 to type `union foo' would store it
into the union as the integer `i', since it is an integer.  (*Note Cast
to Union::.)

   You can combine this technique of naming elements with ordinary C
initialization of successive elements.  Each initializer element that
does not have a label applies to the next consecutive element of the
array or structure.  For example,

     int a[6] = { [1] v1, v2, [4] v4 };

is equivalent to

     int a[6] = { 0, v1, v2, 0, v4, 0 };

   Labeling the elements of an array initializer is especially useful
when the indices are characters or belong to an `enum' type.  For
example:

     int whitespace[256]
       = { [' '] 1, ['\t'] 1, ['\h'] 1,
           ['\f'] 1, ['\n'] 1, ['\r'] 1 };


File: @.Distr.UsingGCC,  Node: Case Ranges,  Next: Function Attributes,  Prev: Cast to Union,  Up: C Extensions

Case Ranges
===========

   You can specify a range of consecutive values in a single `case'
label, like this:

     case LOW ... HIGH:

This has the same effect as the proper number of individual `case'
labels, one for each integer value from LOW to HIGH, inclusive.

   This feature is especially useful for ranges of ASCII character
codes:

     case 'A' ... 'Z':

   *Be careful:* Write spaces around the `...', for otherwise it may be
parsed wrong when you use it with integer values.  For example, write
this:

     case 1 ... 5:

rather than this:

     case 1...5:

     *Warning to C++ users:* When compiling C++, you must write two dots
     `..' rather than three to specify a range in case statements, thus:

          case 'A' .. 'Z':

     This is an anachronism in the GNU C++ front end, and will be
     rectified in a future release.


File: @.Distr.UsingGCC,  Node: Cast to Union,  Next: Case Ranges,  Prev: Labeled Elements,  Up: C Extensions

Cast to a Union Type
====================

   A cast to union type is similar to other casts, except that the type
specified is a union type.  You can specify the type either with `union
TAG' or with a typedef name.  A cast to union is actually a constructor
though, not a cast, and hence does not yield an lvalue like normal
casts.  (*Note Constructors::.)

   The types that may be cast to the union type are those of the members
of the union.  Thus, given the following union and variables:

     union foo { int i; double d; };
     int x;
     double y;

both `x' and `y' can be cast to type `union' foo.

   Using the cast as the right-hand side of an assignment to a variable
of union type is equivalent to storing in a member of the union:

     union foo u;
     ...
     u = (union foo) x  ==  u.i = x
     u = (union foo) y  ==  u.d = y

   You can also use the union cast as a function argument:

     void hack (union foo);
     ...
     hack ((union foo) x);


File: @.Distr.UsingGCC,  Node: Function Attributes,  Next: Function Prototypes,  Prev: Case Ranges,  Up: C Extensions

Declaring Attributes of Functions
=================================

   In GNU C, you declare certain things about functions called in your
program which help the compiler optimize function calls.

   A few standard library functions, such as `abort' and `exit', cannot
return.  GNU CC knows this automatically.  Some programs define their
own functions that never return.  You can declare them `volatile' to
tell the compiler this fact.  For example,

     typedef void voidfn ();

     volatile voidfn fatal;

     void
     fatal (...)
     {
       ... /* Print error message. */ ...
       exit (1);
     }

   The `volatile' keyword tells the compiler to assume that `fatal'
cannot return.  It can then optimize without regard to what would
happen if `fatal' ever did return.  This makes slightly better code.
More importantly, it helps avoid spurious warnings of uninitialized
variables.

   Do not assume that registers saved by the calling function are
restored before calling the `volatile' function.

   It does not make sense for a `volatile' function to have a return
type other than `void'.

   Many functions do not examine any values except their arguments, and
have no effects except the return value.  Such a function can be subject
to common subexpression elimination and loop optimization just as an
arithmetic operator would be.  These functions should be declared
`const'.  For example,

     typedef int intfn ();

     extern const intfn square;

says that the hypothetical function `square' is safe to call fewer
times than the program says.

   Note that a function that has pointer arguments and examines the data
pointed to must *not* be declared `const'.  Likewise, a function that
calls a non-`const' function usually must not be `const'.  It does not
make sense for a `const' function to return `void'.

   The examples above use `typedef' because that is the only way to
declare a function `const' or `volatile'.  A declaration like this:

     extern const int square ();

does not have this effect; it says that the return type of `square' is
`const', not `square' itself.

   Some people object to this feature, suggesting that ANSI C's
`#pragma' should be used instead.  There are two reasons for not doing
this.

  1. It is impossible to generate `#pragma' commands from a macro.

  2. There is no telling what the same `#pragma' might mean in another
     compiler.

   These two reasons apply to almost any application that might be
proposed for `#pragma'.  It is basically a mistake to use `#pragma' for
*anything*.

   The keyword `__attribute__' allows you to specify special attributes
when making a declaration.  This keyword is followed by an attribute
specification inside double parentheses.  One attribute, `format', is
currently defined for functions.  Others are implemented for variables
and structure fields (*note Variable Attributes::.).

`format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)'
     The `format' attribute specifies that a function takes `printf' or
     `scanf' style arguments which should be type-checked against a
     format string.  For example, the declaration:

          extern int
          my_printf (void *my_object, const char *my_format, ...)
                __attribute__ ((format (printf, 2, 3)));

     causes the compiler to check the arguments in calls to `my_printf'
     for consistency with the `printf' style format string argument
     `my_format'.

     The parameter ARCHETYPE determines how the format string is
     interpreted, and should be either `printf' or `scanf'.  The
     parameter STRING-INDEX specifies which argument is the format
     string argument (starting from 1), while FIRST-TO-CHECK is the
     number of the first argument to check against the format string.
     For functions where the arguments are not available to be checked
     (such as `vprintf'), specify the third parameter as zero.  In this
     case the compiler only checks the format string for consistency.

     In the example above, the format string (`my_format') is the second
     argument of the function `my_print', and the arguments to check
     start with the third argument, so the correct parameters for the
     format attribute are 2 and 3.

     The `format' attribute allows you to identify your own functions
     which take format strings as arguments, so that GNU CC can check
     the calls to these functions for errors.  The compiler always
     checks formats for the ANSI library functions `printf', `fprintf',
     `sprintf', `scanf', `fscanf', `sscanf', `vprintf', `vfprintf' and
     `vsprintf' whenever such warnings are requested (using
     `-Wformat'), so there is no need to modify the header file
     `stdio.h'.


File: @.Distr.UsingGCC,  Node: Function Prototypes,  Next: Dollar Signs,  Prev: Function Attributes,  Up: C Extensions

Prototypes and Old-Style Function Definitions
=============================================

   GNU C extends ANSI C to allow a function prototype to override a
later old-style non-prototype definition.  Consider the following
example:

     /* Use prototypes unless the compiler is old-fashioned.  */
     #if __STDC__
     #define P(x) x
     #else
     #define P(x) ()
     #endif

     /* Prototype function declaration.  */
     int isroot P((uid_t));

     /* Old-style function definition.  */
     int
     isroot (x)   /* ??? lossage here ??? */
          uid_t x;
     {
       return x == 0;
     }

   Suppose the type `uid_t' happens to be `short'.  ANSI C does not
allow this example, because subword arguments in old-style
non-prototype definitions are promoted.  Therefore in this example the
function definition's argument is really an `int', which does not match
the prototype argument type of `short'.

   This restriction of ANSI C makes it hard to write code that is
portable to traditional C compilers, because the programmer does not
know whether the `uid_t' type is `short', `int', or `long'.  Therefore,
in cases like these GNU C allows a prototype to override a later
old-style definition.  More precisely, in GNU C, a function prototype
argument type overrides the argument type specified by a later
old-style definition if the former type is the same as the latter type
before promotion.  Thus in GNU C the above example is equivalent to the
following:

     int isroot (uid_t);

     int
     isroot (uid_t x)
     {
       return x == 0;
     }


File: @.Distr.UsingGCC,  Node: Dollar Signs,  Next: Character Escapes,  Prev: Function Prototypes,  Up: C Extensions

Dollar Signs in Identifier Names
================================

   In GNU C, you may use dollar signs in identifier names.  This is
because many traditional C implementations allow such identifiers.

   On some machines, dollar signs are allowed in identifiers if you
specify `-traditional'.  On a few systems they are allowed by default,
even if you do not use `-traditional'.  But they are never allowed if
you specify `-ansi'.

   There are certain ANSI C programs (obscure, to be sure) that would
compile incorrectly if dollar signs were permitted in identifiers.  For
example:

     #define foo(a) #a
     #define lose(b) foo (b)
     #define test$
     lose (test)


File: @.Distr.UsingGCC,  Node: Character Escapes,  Next: Variable Attributes,  Prev: Dollar Signs,  Up: C Extensions

The Character ESC in Constants
==============================

   You can use the sequence `\e' in a string or character constant to
stand for the ASCII character ESC.


File: @.Distr.UsingGCC,  Node: Alignment,  Next: Inline,  Prev: Variable Attributes,  Up: C Extensions

Inquiring on Alignment of Types or Variables
============================================

   The keyword `__alignof__' allows you to inquire about how an object
is aligned, or the minimum alignment usually required by a type.  Its
syntax is just like `sizeof'.

   For example, if the target machine requires a `double' value to be
aligned on an 8-byte boundary, then `__alignof__ (double)' is 8.  This
is true on many RISC machines.  On more traditional machine designs,
`__alignof__ (double)' is 4 or even 2.

   Some machines never actually require alignment; they allow reference
to any data type even at an odd addresses.  For these machines,
`__alignof__' reports the *recommended* alignment of a type.

   When the operand of `__alignof__' is an lvalue rather than a type,
the value is the largest alignment that the lvalue is known to have.
It may have this alignment as a result of its data type, or because it
is part of a structure and inherits alignment from that structure.  For
example, after this declaration:

     struct foo { int x; char y; } foo1;

the value of `__alignof__ (foo1.y)' is probably 2 or 4, the same as
`__alignof__ (int)', even though the data type of `foo1.y' does not
itself demand any alignment.

   A related feature which lets you specify the alignment of an object
is `__attribute__ ((aligned (ALIGNMENT)))'; see the following section.


File: @.Distr.UsingGCC,  Node: Variable Attributes,  Next: Alignment,  Prev: Character Escapes,  Up: C Extensions

Specifying Attributes of Variables
==================================

   The keyword `__attribute__' allows you to specify special attributes
of variables or structure fields.  This keyword is followed by an
attribute specification inside double parentheses.  Four attributes are
currently defined: `aligned', `format', `mode' and `packed'.  `format'
is used for functions, and thus not documented here; see *Note Function
Attributes::.

`aligned (ALIGNMENT)'
     This attribute specifies a minimum alignment for the variable or
     structure field, measured in bytes.  For example, the declaration:

          int x __attribute__ ((aligned (16))) = 0;

     causes the compiler to allocate the global variable `x' on a
     16-byte boundary.  On a 68040, this could be used in conjunction
     with an `asm' expression to access the `move16' instruction which
     requires 16-byte aligned operands.

     You can also specify the alignment of structure fields.  For
     example, to create a double-word aligned `int' pair, you could
     write:

          struct foo { int x[2] __attribute__ ((aligned (8))); };

     This is an alternative to creating a union with a `double' member
     that forces the union to be double-word aligned.

     It is not possible to specify the alignment of functions; the
     alignment of functions is determined by the machine's requirements
     and cannot be changed.  You cannot specify alignment for a typedef
     name because such a name is just an alias, not a distinct type.

     The `aligned' attribute can only increase the alignment; but you
     can decrease it by specifying `packed' as well.  See below.

     The linker of your operating system imposes a maximum alignment.
     If the linker aligns each object file on a four byte boundary,
     then it is beyond the compiler's power to cause anything to be
     aligned to a larger boundary than that.  For example, if  the
     linker happens to put this object file at address 136 (eight more
     than a multiple of 64), then the compiler cannot guarantee an
     alignment of more than 8 just by aligning variables in the object
     file.

`mode (MODE)'
     This attribute specifies the data type for the
     declaration--whichever type corresponds to the mode MODE.  This in
     effect lets you request an integer or floating point type
     according to its width.

`packed'
     The `packed' attribute specifies that a variable or structure field
     should have the smallest possible alignment--one byte for a
     variable, and one bit for a field, unless you specify a larger
     value with the `aligned' attribute.

   To specify multiple attributes, separate them by commas within the
double parentheses: for example, `__attribute__ ((aligned (16),
packed))'.


File: @.Distr.UsingGCC,  Node: Inline,  Next: Extended Asm,  Prev: Alignment,  Up: C Extensions

An Inline Function is As Fast As a Macro
========================================

   By declaring a function `inline', you can direct GNU CC to integrate
that function's code into the code for its callers.  This makes
execution faster by eliminating the function-call overhead; in
addition, if any of the actual argument values are constant, their known
values may permit simplifications at compile time so that not all of the
inline function's code needs to be included.  The effect on code size is
less predictable; object code may be larger or smaller with function
inlining, depending on the particular case.  Inlining of functions is an
optimization and it really "works" only in optimizing compilation.  If
you don't use `-O', no function is really inline.

   To declare a function inline, use the `inline' keyword in its
declaration, like this:

     inline int
     inc (int *a)
     {
       (*a)++;
     }

   (If you are writing a header file to be included in ANSI C programs,
write `__inline__' instead of `inline'.  *Note Alternate Keywords::.)

   You can also make all "simple enough" functions inline with the
option `-finline-functions'.  Note that certain usages in a function
definition can make it unsuitable for inline substitution.

   For C++ programs, GNU CC automatically inlines member functions even
if they are not explicitly declared `inline'.  (You can override this
with `-fno-default-inline'; *note Options Controlling C++ Dialect: C++
Dialect Options..)

   When a function is both inline and `static', if all calls to the
function are integrated into the caller, and the function's address is
never used, then the function's own assembler code is never referenced.
In this case, GNU CC does not actually output assembler code for the
function, unless you specify the option `-fkeep-inline-functions'.
Some calls cannot be integrated for various reasons (in particular,
calls that precede the function's definition cannot be integrated, and
neither can recursive calls within the definition).  If there is a
nonintegrated call, then the function is compiled to assembler code as
usual.  The function must also be compiled as usual if the program
refers to its address, because that can't be inlined.

   When an inline function is not `static', then the compiler must
assume that there may be calls from other source files; since a global
symbol can be defined only once in any program, the function must not
be defined in the other source files, so the calls therein cannot be
integrated.  Therefore, a non-`static' inline function is always
compiled on its own in the usual fashion.

   If you specify both `inline' and `extern' in the function
definition, then the definition is used only for inlining.  In no case
is the function compiled on its own, not even if you refer to its
address explicitly.  Such an address becomes an external reference, as
if you had only declared the function, and had not defined it.

   This combination of `inline' and `extern' has almost the effect of a
macro.  The way to use it is to put a function definition in a header
file with these keywords, and put another copy of the definition
(lacking `inline' and `extern') in a library file.  The definition in
the header file will cause most calls to the function to be inlined.
If any uses of the function remain, they will refer to the single copy
in the library.

   GNU C does not inline any functions when not optimizing.  It is not
clear whether it is better to inline or not, in this case, but we found
that a correct implementation when not optimizing was difficult.  So we
did the easy thing, and turned it off.


File: @.Distr.UsingGCC,  Node: Extended Asm,  Next: Constraints,  Prev: Inline,  Up: C Extensions

Assembler Instructions with C Expression Operands
=================================================

   In an assembler instruction using `asm', you can now specify the
operands of the instruction using C expressions.  This means no more
guessing which registers or memory locations will contain the data you
want to use.

   You must specify an assembler instruction template much like what
appears in a machine description, plus an operand constraint string for
each operand.

   For example, here is how to use the 68881's `fsinx' instruction:

     asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));

Here `angle' is the C expression for the input operand while `result'
is that of the output operand.  Each has `"f"' as its operand
constraint, saying that a floating point register is required.  The `='
in `=f' indicates that the operand is an output; all output operands'
constraints must use `='.  The constraints use the same language used
in the machine description (*note Constraints::.).

   Each operand is described by an operand-constraint string followed
by the C expression in parentheses.  A colon separates the assembler
template from the first output operand, and another separates the last
output operand from the first input, if any.  Commas separate output
operands and separate inputs.  The total number of operands is limited
to ten or to the maximum number of operands in any instruction pattern
in the machine description, whichever is greater.

   If there are no output operands, and there are input operands, then
there must be two consecutive colons surrounding the place where the
output operands would go.

   Output operand expressions must be lvalues; the compiler can check
this.  The input operands need not be lvalues.  The compiler cannot
check whether the operands have data types that are reasonable for the
instruction being executed.  It does not parse the assembler
instruction template and does not know what it means, or whether it is
valid assembler input.  The extended `asm' feature is most often used
for machine instructions that the compiler itself does not know exist.

   The output operands must be write-only; GNU CC will assume that the
values in these operands before the instruction are dead and need not be
generated.  Extended asm does not support input-output or read-write
operands.  For this reason, the constraint character `+', which
indicates such an operand, may not be used.

   When the assembler instruction has a read-write operand, or an
operand in which only some of the bits are to be changed, you must
logically split its function into two separate operands, one input
operand and one write-only output operand.  The connection between them
is expressed by constraints which say they need to be in the same
location when the instruction executes.  You can use the same C
expression for both operands, or different expressions.  For example,
here we write the (fictitious) `combine' instruction with `bar' as its
read-only source operand and `foo' as its read-write destination:

     asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));

The constraint `"0"' for operand 1 says that it must occupy the same
location as operand 0.  A digit in constraint is allowed only in an
input operand, and it must refer to an output operand.

   Only a digit in the constraint can guarantee that one operand will
be in the same place as another.  The mere fact that `foo' is the value
of both operands is not enough to guarantee that they will be in the
same place in the generated assembler code.  The following would not
work:

     asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));

   Various optimizations or reloading could cause operands 0 and 1 to
be in different registers; GNU CC knows no reason not to do so.  For
example, the compiler might find a copy of the value of `foo' in one
register and use it for operand 1, but generate the output operand 0 in
a different register (copying it afterward to `foo''s own address).  Of
course, since the register for operand 1 is not even mentioned in the
assembler code, the result will not work, but GNU CC can't tell that.

   Some instructions clobber specific hard registers.  To describe
this, write a third colon after the input operands, followed by the
names of the clobbered hard registers (given as strings).  Here is a
realistic example for the Vax:

     asm volatile ("movc3 %0,%1,%2"
                   : /* no outputs */
                   : "g" (from), "g" (to), "g" (count)
                   : "r0", "r1", "r2", "r3", "r4", "r5");

   If you refer to a particular hardware register from the assembler
code, then you will probably have to list the register after the third
colon to tell the compiler that the register's value is modified.  In
many assemblers, the register names begin with `%'; to produce one `%'
in the assembler code, you must write `%%' in the input.

   If your assembler instruction can alter the condition code register,
add `cc' to the list of clobbered registers.  GNU CC on some machines
represents the condition codes as a specific hardware register; `cc'
serves to name this register.  On other machines, the condition code is
handled differently, and specifying `cc' has no effect.  But it is
valid no matter what the machine.

   If your assembler instruction modifies memory in an unpredictable
fashion, add `memory' to the list of clobbered registers.  This will
cause GNU CC to not keep memory values cached in registers across the
assembler instruction.

   You can put multiple assembler instructions together in a single
`asm' template, separated either with newlines (written as `\n') or with
semicolons if the assembler allows such semicolons.  The GNU assembler
allows semicolons and all Unix assemblers seem to do so.  The input
operands are guaranteed not to use any of the clobbered registers, and
neither will the output operands' addresses, so you can read and write
the clobbered registers as many times as you like.  Here is an example
of multiple instructions in a template; it assumes that the subroutine
`_foo' accepts arguments in registers 9 and 10:

     asm ("movl %0,r9;movl %1,r10;call _foo"
          : /* no outputs */
          : "g" (from), "g" (to)
          : "r9", "r10");

   Unless an output operand has the `&' constraint modifier, GNU CC may
allocate it in the same register as an unrelated input operand, on the
assumption that the inputs are consumed before the outputs are produced.
This assumption may be false if the assembler code actually consists of
more than one instruction.  In such a case, use `&' for each output
operand that may not overlap an input.  *Note Modifiers::.

   If you want to test the condition code produced by an assembler
instruction, you must include a branch and a label in the `asm'
construct, as follows:

     asm ("clr %0;frob %1;beq 0f;mov #1,%0;0:"
          : "g" (result)
          : "g" (input));

This assumes your assembler supports local labels, as the GNU assembler
and most Unix assemblers do.

   Speaking of labels, jumps from one `asm' to another are not
supported.  The compiler's optimizers do not know about these jumps,
and therefore they cannot take account of them when deciding how to
optimize.

   Usually the most convenient way to use these `asm' instructions is to
encapsulate them in macros that look like functions.  For example,

     #define sin(x)       \
     ({ double __value, __arg = (x);   \
        asm ("fsinx %1,%0": "=f" (__value): "f" (__arg));  \
        __value; })

Here the variable `__arg' is used to make sure that the instruction
operates on a proper `double' value, and to accept only those arguments
`x' which can convert automatically to a `double'.

   Another way to make sure the instruction operates on the correct
data type is to use a cast in the `asm'.  This is different from using a
variable `__arg' in that it converts more different types.  For
example, if the desired type were `int', casting the argument to `int'
would accept a pointer with no complaint, while assigning the argument
to an `int' variable named `__arg' would warn about using a pointer
unless the caller explicitly casts it.

   If an `asm' has output operands, GNU CC assumes for optimization
purposes that the instruction has no side effects except to change the
output operands.  This does not mean that instructions with a side
effect cannot be used, but you must be careful, because the compiler
may eliminate them if the output operands aren't used, or move them out
of loops, or replace two with one if they constitute a common
subexpression.  Also, if your instruction does have a side effect on a
variable that otherwise appears not to change, the old value of the
variable may be reused later if it happens to be found in a register.

   You can prevent an `asm' instruction from being deleted, moved
significantly, or combined, by writing the keyword `volatile' after the
`asm'.  For example:

     #define set_priority(x)  \
     asm volatile ("set_priority %0": /* no outputs */ : "g" (x))

An instruction without output operands will not be deleted or moved
significantly, regardless, unless it is unreachable.

   Note that even a volatile `asm' instruction can be moved in ways
that appear insignificant to the compiler, such as across jump
instructions.  You can't expect a sequence of volatile `asm'
instructions to remain perfectly consecutive.  If you want consecutive
output, use a single `asm'.

   It is a natural idea to look for a way to give access to the
condition code left by the assembler instruction.  However, when we
attempted to implement this, we found no way to make it work reliably.
The problem is that output operands might need reloading, which would
result in additional following "store" instructions.  On most machines,
these instructions would alter the condition code before there was time
to test it.  This problem doesn't arise for ordinary "test" and
"compare" instructions because they don't have any output operands.

   If you are writing a header file that should be includable in ANSI C
programs, write `__asm__' instead of `asm'.  *Note Alternate Keywords::.


File: @.Distr.UsingGCC,  Node: Constraints,  Next: Asm Labels,  Prev: Extended Asm,  Up: C Extensions

Constraints for `asm' Operands
==============================

   Here are specific details on what constraint letters you can use with
`asm' operands.  Constraints can say whether an operand may be in a
register, and which kinds of register; whether the operand can be a
memory reference, and which kinds of address; whether the operand may
be an immediate constant, and which possible values it may have.
Constraints can also require two operands to match.

* Menu:

* Simple Constraints::  Basic use of constraints.
* Multi-Alternative::   When an insn has two alternative constraint-patterns.
* Modifiers::           More precise control over effects of constraints.
* Machine Constraints:: Special constraints for some particular machines.


File: @.Distr.UsingGCC,  Node: Simple Constraints,  Next: Multi-Alternative,  Up: Constraints

Simple Constraints
------------------

   The simplest kind of constraint is a string full of letters, each of
which describes one kind of operand that is permitted.  Here are the
letters that are allowed:

`m'
     A memory operand is allowed, with any kind of address that the
     machine supports in general.

`o'
     A memory operand is allowed, but only if the address is
     "offsettable".  This means that adding a small integer (actually,
     the width in bytes of the operand, as determined by its machine
     mode) may be added to the address and the result is also a valid
     memory address.

     For example, an address which is constant is offsettable; so is an
     address that is the sum of a register and a constant (as long as a
     slightly larger constant is also within the range of
     address-offsets supported by the machine); but an autoincrement or
     autodecrement address is not offsettable.  More complicated
     indirect/indexed addresses may or may not be offsettable depending
     on the other addressing modes that the machine supports.

     Note that in an output operand which can be matched by another
     operand, the constraint letter `o' is valid only when accompanied
     by both `<' (if the target machine has predecrement addressing)
     and `>' (if the target machine has preincrement addressing).

`V'
     A memory operand that is not offsettable.  In other words,
     anything that would fit the `m' constraint but not the `o'
     constraint.

`<'
     A memory operand with autodecrement addressing (either
     predecrement or postdecrement) is allowed.

`>'
     A memory operand with autoincrement addressing (either
     preincrement or postincrement) is allowed.

`r'
     A register operand is allowed provided that it is in a general
     register.

`d', `a', `f', ...
     Other letters can be defined in machine-dependent fashion to stand
     for particular classes of registers.  `d', `a' and `f' are defined
     on the 68000/68020 to stand for data, address and floating point
     registers.

`i'
     An immediate integer operand (one with constant value) is allowed.
     This includes symbolic constants whose values will be known only at
     assembly time.

`n'
     An immediate integer operand with a known numeric value is allowed.
     Many systems cannot support assembly-time constants for operands
     less than a word wide.  Constraints for these operands should use
     `n' rather than `i'.

`I', `J', `K', ... `P'
     Other letters in the range `I' through `P' may be defined in a
     machine-dependent fashion to permit immediate integer operands with
     explicit integer values in specified ranges.  For example, on the
     68000, `I' is defined to stand for the range of values 1 to 8.
     This is the range permitted as a shift count in the shift
     instructions.

`E'
     An immediate floating operand (expression code `const_double') is
     allowed, but only if the target floating point format is the same
     as that of the host machine (on which the compiler is running).

`F'
     An immediate floating operand (expression code `const_double') is
     allowed.

`G', `H'
     `G' and `H' may be defined in a machine-dependent fashion to
     permit immediate floating operands in particular ranges of values.

`s'
     An immediate integer operand whose value is not an explicit
     integer is allowed.

     This might appear strange; if an insn allows a constant operand
     with a value not known at compile time, it certainly must allow
     any known value.  So why use `s' instead of `i'?  Sometimes it
     allows better code to be generated.

     For example, on the 68000 in a fullword instruction it is possible
     to use an immediate operand; but if the immediate value is between
     -128 and 127, better code results from loading the value into a
     register and using the register.  This is because the load into
     the register can be done with a `moveq' instruction.  We arrange
     for this to happen by defining the letter `K' to mean "any integer
     outside the range -128 to 127", and then specifying `Ks' in the
     operand constraints.

`g'
     Any register, memory or immediate integer operand is allowed,
     except for registers that are not general registers.

`X'
     Any operand whatsoever is allowed.

`0', `1', `2', ... `9'
     An operand that matches the specified operand number is allowed.
     If a digit is used together with letters within the same
     alternative, the digit should come last.

     This is called a "matching constraint" and what it really means is
     that the assembler has only a single operand that fills two roles
     which `asm' distinguishes.  For example, an add instruction uses
     two input operands and an output operand, but on most CISC
     machines an add instruction really has only two operands, one of
     them an input-output operand:

          addl #35,r12

     Matching constraints are used in these circumstances.  More
     precisely, the two operands that match must include one input-only
     operand and one output-only operand.  Moreover, the digit must be a
     smaller number than the number of the operand that uses it in the
     constraint.

`p'
     An operand that is a valid memory address is allowed.  This is for
     "load address" and "push address" instructions.

     `p' in the constraint must be accompanied by `address_operand' as
     the predicate in the `match_operand'.  This predicate interprets
     the mode specified in the `match_operand' as the mode of the memory
     reference for which the address would be valid.

`Q', `R', `S', ... `U'
     Letters in the range `Q' through `U' may be defined in a
     machine-dependent fashion to stand for arbitrary operand types.


File: @.Distr.UsingGCC,  Node: Multi-Alternative,  Next: Modifiers,  Prev: Simple Constraints,  Up: Constraints

Multiple Alternative Constraints
--------------------------------

   Sometimes a single instruction has multiple alternative sets of
possible operands.  For example, on the 68000, a logical-or instruction
can combine register or an immediate value into memory, or it can
combine any kind of operand into a register; but it cannot combine one
memory location into another.

   These constraints are represented as multiple alternatives.  An
alternative can be described by a series of letters for each operand.
The overall constraint for an operand is made from the letters for this
operand from the first alternative, a comma, the letters for this
operand from the second alternative, a comma, and so on until the last
alternative.

   If all the operands fit any one alternative, the instruction is
valid.  Otherwise, for each alternative, the compiler counts how many
instructions must be added to copy the operands so that that
alternative applies.  The alternative requiring the least copying is
chosen.  If two alternatives need the same amount of copying, the one
that comes first is chosen.  These choices can be altered with the `?'
and `!' characters:

`?'
     Disparage slightly the alternative that the `?' appears in, as a
     choice when no alternative applies exactly.  The compiler regards
     this alternative as one unit more costly for each `?' that appears
     in it.

`!'
     Disparage severely the alternative that the `!' appears in.  This
     alternative can still be used if it fits without reloading, but if
     reloading is needed, some other alternative will be used.


File: @.Distr.UsingGCC,  Node: Modifiers,  Next: Machine Constraints,  Prev: Multi-Alternative,  Up: Constraints

Constraint Modifier Characters
------------------------------

`='
     Means that this operand is write-only for this instruction: the
     previous value is discarded and replaced by output data.

`+'
     Means that this operand is both read and written by the
     instruction.

     When the compiler fixes up the operands to satisfy the constraints,
     it needs to know which operands are inputs to the instruction and
     which are outputs from it.  `=' identifies an output; `+'
     identifies an operand that is both input and output; all other
     operands are assumed to be input only.

`&'
     Means (in a particular alternative) that this operand is written
     before the instruction is finished using the input operands.
     Therefore, this operand may not lie in a register that is used as
     an input operand or as part of any memory address.

     `&' applies only to the alternative in which it is written.  In
     constraints with multiple alternatives, sometimes one alternative
     requires `&' while others do not.  See, for example, the `movdf'
     insn of the 68000.

     `&' does not obviate the need to write `='.

`%'
     Declares the instruction to be commutative for this operand and the
     following operand.  This means that the compiler may interchange
     the two operands if that is the cheapest way to make all operands
     fit the constraints.

`#'
     Says that all following characters, up to the next comma, are to be
     ignored as a constraint.  They are significant only for choosing
     register preferences.


File: @.Distr.UsingGCC,  Node: Machine Constraints,  Prev: Modifiers,  Up: Constraints

Constraints for Particular Machines
-----------------------------------

   Whenever possible, you should use the general-purpose constraint
letters in `asm' arguments, since they will convey meaning more readily
to people reading your code.  Failing that, use the constraint letters
that usually have very similar meanings across architectures.  The most
commonly used constraints are `m' and `r' (for memory and
general-purpose registers respectively; *note Simple Constraints::.),
and `I', usually the letter indicating the most common
immediate-constant format.

   For each machine architecture, the `config/MACHINE.h' file defines
additional constraints.  These constraints are used by the compiler
itself for instruction generation, as well as for `asm' statements;
therefore, some of the constraints are not particularly interesting for
`asm'.  The constraints are defined through these macros:

`REG_CLASS_FROM_LETTER'
     Register class constraints (usually lower case).

`CONST_OK_FOR_LETTER_P'
     Immediate constant constraints, for non-floating point constants of
     word size or smaller precision (usually upper case).

`CONST_DOUBLE_OK_FOR_LETTER_P'
     Immediate constant constraints, for all floating point constants
     and for constants of greater than word size precision (usually
     upper case).

`EXTRA_CONSTRAINT'
     Special cases of registers or memory.  This macro is not required,
     and is only defined for some machines.

   Inspecting these macro definitions in the compiler source for your
machine is the best way to be certain you have the right constraints.
However, here is a summary of the machine-dependent constraints
available on some particular machines.

*AMD 29000 family--`a29k.h'*
    `l'
          Local register 0

    `b'
          Byte Pointer (`BP') register

    `q'
          `Q' register

    `h'
          Special purpose register

    `A'
          First accumulator register

    `a'
          Other accumulator register

    `f'
          Floating point register

    `I'
          Constant greater than 0, less than 0x100

    `J'
          Constant greater than 0, less than 0x10000

    `K'
          Constant whose high 24 bits are on (1)

    `L'
          16 bit constant whose high 8 bits are on (1)

    `M'
          32 bit constant whose high 16 bits are on (1)

    `N'
          32 bit negative constant that fits in 8 bits

    `O'
          The constant 0x80000000 or, on the 29050, any 32 bit constant
          whose low 16 bits are 0.

    `P'
          16 bit negative constant that fits in 8 bits

    `G'
    `H'
          A floating point constant (in `asm' statements, use the
          machine independent `E' or `F' instead)

*IBM RS6000--`rs6000.h'*
    `b'
          Address base register

    `f'
          Floating point register

    `h'
          `MQ', `CTR', or `LINK' register

    `q'
          `MQ' register

    `c'
          `CTR' register

    `l'
          `LINK' register

    `x'
          `CR' register (condition register) number 0

    `y'
          `CR' register (condition register)

    `I'
          Signed 16 bit constant

    `J'
          Constant whose low 16 bits are 0

    `K'
          Constant whose high 16 bits are 0

    `L'
          Constant suitable as a mask operand

    `M'
          Constant larger than 31

    `N'
          Exact power of 2

    `O'
          Zero

    `P'
          Constant whose negation is a signed 16 bit constant

    `G'
          Floating point constant that can be loaded into a register
          with one instruction per word

    `Q'
          Memory operand that is an offset from a register (`m' is
          preferable for `asm' statements)

*Intel 386--`i386.h'*
    `q'
          `a', `b', `c', or `d' register

    `f'
          Floating point register

    `t'
          First (top of stack) floating point register

    `u'
          Second floating point register

    `a'
          `a' register

    `b'
          `b' register

    `c'
          `c' register

    `d'
          `d' register

    `D'
          `di' register

    `S'
          `si' register

    `I'
          Constant in range 0 to 31 (for 32 bit shifts)

    `J'
          Constant in range 0 to 63 (for 64 bit shifts)

    `K'
          `0xff'

    `L'
          `0xffff'

    `M'
          0, 1, 2, or 3 (shifts for `lea' instruction)

    `G'
          Standard 80387 floating point constant

*Intel 960--`i960.h'*
    `f'
          Floating point register (`fp0' to `fp3')

    `l'
          Local register (`r0' to `r15')

    `b'
          Global register (`g0' to `g15')

    `d'
          Any local or global register

    `I'
          Integers from 0 to 31

    `J'
          0

    `K'
          Integers from -31 to 0

    `G'
          Floating point 0

    `H'
          Floating point 1

*MIPS--`mips.h'*
    `d'
          General-purpose integer register

    `f'
          Floating-point register (if available)

    `h'
          `Hi' register

    `l'
          `Lo' register

    `x'
          `Hi' or `Lo' register

    `y'
          General-purpose integer register

    `z'
          Floating-point status register

    `I'
          Signed 16 bit constant (for arithmetic instructions)

    `J'
          Zero

    `K'
          Zero-extended 16-bit constant (for logic instructions)

    `L'
          Constant with low 16 bits zero (can be loaded with `lui')

    `M'
          32 bit constant which requires two instructions to load (a
          constant which is not `I', `K', or `L')

    `N'
          Negative 16 bit constant

    `O'
          Exact power of two

    `P'
          Positive 16 bit constant

    `G'
          Floating point zero

    `Q'
          Memory reference that can be loaded with more than one
          instruction (`m' is preferable for `asm' statements)

    `R'
          Memory reference that can be loaded with one instruction (`m'
          is preferable for `asm' statements)

    `S'
          Memory reference in external OSF/rose PIC format (`m' is
          preferable for `asm' statements)

*Motorola 680x0--`m68k.h'*
    `a'
          Address register

    `d'
          Data register

    `f'
          68881 floating-point register, if available

    `x'
          Sun FPA (floating-point) register, if available

    `y'
          First 16 Sun FPA registers, if available

    `I'
          Integer in the range 1 to 8

    `J'
          16 bit signed number

    `K'
          Signed number whose magnitude is greater than 0x80

    `L'
          Integer in the range -8 to -1

    `G'
          Floating point constant that is not a 68881 constant

    `H'
          Floating point constant that can be used by Sun FPA

*SPARC--`sparc.h'*
    `f'
          Floating-point register

    `I'
          Signed 13 bit constant

    `J'
          Zero

    `K'
          32 bit constant with the low 12 bits clear (a constant that
          can be loaded with the `sethi' instruction)

    `G'
          Floating-point zero

    `H'
          Signed 13 bit constant, sign-extended to 32 or 64 bits

    `Q'
          Memory reference that can be loaded with one instruction
          (`m' is more appropriate for `asm' statements)

    `S'
          Constant, or memory address

    `T'
          Memory address aligned to an 8-byte boundary

    `U'
          Even register


File: @.Distr.UsingGCC,  Node: Asm Labels,  Next: Explicit Reg Vars,  Prev: Constraints,  Up: C Extensions

Controlling Names Used in Assembler Code
========================================

   You can specify the name to be used in the assembler code for a C
function or variable by writing the `asm' (or `__asm__') keyword after
the declarator as follows:

     int foo asm ("myfoo") = 2;

This specifies that the name to be used for the variable `foo' in the
assembler code should be `myfoo' rather than the usual `_foo'.

   On systems where an underscore is normally prepended to the name of
a C function or variable, this feature allows you to define names for
the linker that do not start with an underscore.

   You cannot use `asm' in this way in a function *definition*; but you
can get the same effect by writing a declaration for the function
before its definition and putting `asm' there, like this:

     extern func () asm ("FUNC");

     func (x, y)
          int x, y;
     ...

   It is up to you to make sure that the assembler names you choose do
not conflict with any other assembler symbols.  Also, you must not use a
register name; that would produce completely invalid assembler code.
GNU CC does not as yet have the ability to store static variables in
registers.  Perhaps that will be added.


File: @.Distr.UsingGCC,  Node: Explicit Reg Vars,  Next: Alternate Keywords,  Prev: Asm Labels,  Up: C Extensions

Variables in Specified Registers
================================

   GNU C allows you to put a few global variables into specified
hardware registers.  You can also specify the register in which an
ordinary register variable should be allocated.

   * Global register variables reserve registers throughout the program.
     This may be useful in programs such as programming language
     interpreters which have a couple of global variables that are
     accessed very often.

   * Local register variables in specific registers do not reserve the
     registers.  The compiler's data flow analysis is capable of
     determining where the specified registers contain live values, and
     where they are available for other uses.

     These local variables are sometimes convenient for use with the
     extended `asm' feature (*note Extended Asm::.), if you want to
     write one output of the assembler instruction directly into a
     particular register.  (This will work provided the register you
     specify fits the constraints specified for that operand in the
     `asm'.)

* Menu:

* Global Reg Vars::
* Local Reg Vars::


File: @.Distr.UsingGCC,  Node: Global Reg Vars,  Next: Local Reg Vars,  Up: Explicit Reg Vars

Defining Global Register Variables
----------------------------------

   You can define a global register variable in GNU C like this:

     register int *foo asm ("a5");

Here `a5' is the name of the register which should be used.  Choose a
register which is normally saved and restored by function calls on your
machine, so that library routines will not clobber it.

   Naturally the register name is cpu-dependent, so you would need to
conditionalize your program according to cpu type.  The register `a5'
would be a good choice on a 68000 for a variable of pointer type.  On
machines with register windows, be sure to choose a "global" register
that is not affected magically by the function call mechanism.

   In addition, operating systems on one type of cpu may differ in how
they name the registers; then you would need additional conditionals.
For example, some 68000 operating systems call this register `%a5'.

   Eventually there may be a way of asking the compiler to choose a
register automatically, but first we need to figure out how it should
choose and how to enable you to guide the choice.  No solution is
evident.

   Defining a global register variable in a certain register reserves
that register entirely for this use, at least within the current
compilation.  The register will not be allocated for any other purpose
in the functions in the current compilation.  The register will not be
saved and restored by these functions.  Stores into this register are
never deleted even if they would appear to be dead, but references may
be deleted or moved or simplified.

   It is not safe to access the global register variables from signal
handlers, or from more than one thread of control, because the system
library routines may temporarily use the register for other things
(unless you recompile them specially for the task at hand).

   It is not safe for one function that uses a global register variable
to call another such function `foo' by way of a third function `lose'
that was compiled without knowledge of this variable (i.e. in a
different source file in which the variable wasn't declared).  This is
because `lose' might save the register and put some other value there.
For example, you can't expect a global register variable to be
available in the comparison-function that you pass to `qsort', since
`qsort' might have put something else in that register.  (If you are
prepared to recompile `qsort' with the same global register variable,
you can solve this problem.)

   If you want to recompile `qsort' or other source files which do not
actually use your global register variable, so that they will not use
that register for any other purpose, then it suffices to specify the
compiler option `-ffixed-REG'.  You need not actually add a global
register declaration to their source code.

   A function which can alter the value of a global register variable
cannot safely be called from a function compiled without this variable,
because it could clobber the value the caller expects to find there on
return.  Therefore, the function which is the entry point into the part
of the program that uses the global register variable must explicitly
save and restore the value which belongs to its caller.

   On most machines, `longjmp' will restore to each global register
variable the value it had at the time of the `setjmp'.  On some
machines, however, `longjmp' will not change the value of global
register variables.  To be portable, the function that called `setjmp'
should make other arrangements to save the values of the global register
variables, and to restore them in a `longjmp'.  This way, the same
thing will happen regardless of what `longjmp' does.

   All global register variable declarations must precede all function
definitions.  If such a declaration could appear after function
definitions, the declaration would be too late to prevent the register
from being used for other purposes in the preceding functions.

   Global register variables may not have initial values, because an
executable file has no means to supply initial contents for a register.

   On the Sparc, there are reports that g3 ... g7 are suitable
registers, but certain library functions, such as `getwd', as well as
the subroutines for division and remainder, modify g3 and g4.  g1 and
g2 are local temporaries.

   On the 68000, a2 ... a5 should be suitable, as should d2 ... d7.  Of
course, it will not do to use more than a few of those.


File: @.Distr.UsingGCC,  Node: Local Reg Vars,  Prev: Global Reg Vars,  Up: Explicit Reg Vars

Specifying Registers for Local Variables
----------------------------------------

   You can define a local register variable with a specified register
like this:

     register int *foo asm ("a5");

Here `a5' is the name of the register which should be used.  Note that
this is the same syntax used for defining global register variables,
but for a local variable it would appear within a function.

   Naturally the register name is cpu-dependent, but this is not a
problem, since specific registers are most often useful with explicit
assembler instructions (*note Extended Asm::.).  Both of these things
generally require that you conditionalize your program according to cpu
type.

   In addition, operating systems on one type of cpu may differ in how
they name the registers; then you would need additional conditionals.
For example, some 68000 operating systems call this register `%a5'.

   Eventually there may be a way of asking the compiler to choose a
register automatically, but first we need to figure out how it should
choose and how to enable you to guide the choice.  No solution is
evident.

   Defining such a register variable does not reserve the register; it
remains available for other uses in places where flow control determines
the variable's value is not live.  However, these registers are made
unavailable for use in the reload pass.  I would not be surprised if
excessive use of this feature leaves the compiler too few available
registers to compile certain functions.


File: @.Distr.UsingGCC,  Node: Alternate Keywords,  Next: Incomplete Enums,  Prev: Explicit Reg Vars,  Up: C Extensions

Alternate Keywords
==================

   The option `-traditional' disables certain keywords; `-ansi'
disables certain others.  This causes trouble when you want to use GNU C
extensions, or ANSI C features, in a general-purpose header file that
should be usable by all programs, including ANSI C programs and
traditional ones.  The keywords `asm', `typeof' and `inline' cannot be
used since they won't work in a program compiled with `-ansi', while
the keywords `const', `volatile', `signed', `typeof' and `inline' won't
work in a program compiled with `-traditional'.

   The way to solve these problems is to put `__' at the beginning and
end of each problematical keyword.  For example, use `__asm__' instead
of `asm', `__const__' instead of `const', and `__inline__' instead of
`inline'.

   Other C compilers won't accept these alternative keywords; if you
want to compile with another compiler, you can define the alternate
keywords as macros to replace them with the customary keywords.  It
looks like this:

     #ifndef __GNUC__
     #define __asm__ asm
     #endif

   `-pedantic' causes warnings for many GNU C extensions.  You can
prevent such warnings within one expression by writing `__extension__'
before the expression.  `__extension__' has no effect aside from this.


File: @.Distr.UsingGCC,  Node: Incomplete Enums,  Next: Function Names,  Prev: Alternate Keywords,  Up: C Extensions

Incomplete `enum' Types
=======================

   You can define an `enum' tag without specifying its possible values.
This results in an incomplete type, much like what you get if you write
`struct foo' without describing the elements.  A later declaration
which does specify the possible values completes the type.

   You can't allocate variables or storage using the type while it is
incomplete.  However, you can work with pointers to that type.

   This extension may not be very useful, but it makes the handling of
`enum' more consistent with the way `struct' and `union' are handled.


File: @.Distr.UsingGCC,  Node: Function Names,  Prev: Incomplete Enums,  Up: C Extensions

Function Names as Strings
=========================

   GNU CC predefines two string variables to be the name of the current
function.  The variable `__FUNCTION__' is the name of the function as
it appears in the source.  The variable `__PRETTY_FUNCTION__' is the
name of the function pretty printed in a language specific fashion.

   These names are always the same in a C function, but in a C++
function they may be different.  For example, this program:

     extern "C" {
     extern int printf (char *, ...);
     }

     class a {
      public:
       sub (int i)
         {
           printf ("__FUNCTION__ = %s\n", __FUNCTION__);
           printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
         }
     };

     int
     main (void)
     {
       a ax;
       ax.sub (0);
       return 0;
     }

gives this output:

     __FUNCTION__ = sub
     __PRETTY_FUNCTION__ = int  a::sub (int)


File: @.Distr.UsingGCC,  Node: C++ Extensions,  Next: Trouble,  Prev: C Extensions,  Up: Top

Extensions to the C++ Language
******************************

   The GNU compiler provides these extensions to the C++ language (and
you can also use most of the C language extensions in your C++
programs).  If you want to write code that checks whether these
features are available, you can test for the GNU compiler the same way
as for C programs: check for a predefined macro `__GNUC__'.  You can
also use `__GNUG__' to test specifically for GNU C++ (*note Standard
Predefined Macros: (cpp.info)Standard Predefined.).

* Menu:

* Naming Results::      Giving a name to C++ function return values.
* Min and Max::        C++ Minimum and maximum operators.
* Destructors and Goto:: Goto is safe to use in C++ even when destructors
                           are needed.
* C++ Interface::       You can use a single C++ header file for both
                         declarations and definitions.


File: @.Distr.UsingGCC,  Node: Naming Results,  Next: Min and Max,  Up: C++ Extensions

Named Return Values in C++
==========================

   GNU C++ extends the function-definition syntax to allow you to
specify a name for the result of a function outside the body of the
definition, in C++ programs:

     TYPE
     FUNCTIONNAME (ARGS) return RESULTNAME;
     {
       ...
       BODY
       ...
     }

   You can use this feature to avoid an extra constructor call when a
function result has a class type.  For example, consider a function
`m', declared as `X v = m ();', whose result is of class `X':

     X
     m ()
     {
       X b;
       b.a = 23;
       return b;
     }

   Although `m' appears to have no arguments, in fact it has one
implicit argument: the address of the return value.  At invocation, the
address of enough space to hold `v' is sent in as the implicit argument.
Then `b' is constructed and its `a' field is set to the value 23.
Finally, a copy constructor (a constructor of the form `X(X&)') is
applied to `b', with the (implicit) return value location as the
target, so that `v' is now bound to the return value.

   But this is wasteful.  The local `b' is declared just to hold
something that will be copied right out.  While a compiler that
combined an "elision" algorithm with interprocedural data flow analysis
could conceivably eliminate all of this, it is much more practical to
allow you to assist the compiler in generating efficient code by
manipulating the return value explicitly, thus avoiding the local
variable and copy constructor altogether.

   Using the extended GNU C++ function-definition syntax, you can avoid
the temporary allocation and copying by naming `r' as your return value
as the outset, and assigning to its `a' field directly:

     X
     m () return r;
     {
       r.a = 23;
     }

The declaration of `r' is a standard, proper declaration, whose effects
are executed *before* any of the body of `m'.

   Functions of this type impose no additional restrictions; in
particular, you can execute `return' statements, or return implicitly by
reaching the end of the function body ("falling off the edge").  Cases
like

     X
     m () return r (23);
     {
       return;
     }

(or even `X m () return r (23); { }') are unambiguous, since the return
value `r' has been initialized in either case.  The following code may
be hard to read, but also works predictably:

     X
     m () return r;
     {
       X b;
       return b;
     }

   The return value slot denoted by `r' is initialized at the outset,
but the statement `return b;' overrides this value.  The compiler deals
with this by destroying `r' (calling the destructor if there is one, or
doing nothing if there is not), and then reinitializing `r' with `b'.

   This extension is provided primarily to help people who use
overloaded operators, where there is a great need to control not just
the arguments, but the return values of functions.  For classes where
the copy constructor incurs a heavy performance penalty (especially in
the common case where there is a quick default constructor), this is a
major savings.  The disadvantage of this extension is that you do not
control when the default constructor for the return value is called: it
is always called at the beginning.


File: @.Distr.UsingGCC,  Node: Min and Max,  Next: Destructors and Goto,  Prev: Naming Results,  Up: C++ Extensions

Minimum and Maximum Operators in C++
====================================

   It is very convenient to have operators which return the "minimum"
or the "maximum" of two arguments.  In GNU C++ (but not in GNU C),

`A <? B'
     is the "minimum", returning the smaller of the numeric values A
     and B;

`A >? B'
     is the "maximum", returning the larger of the numeric values A and
     B.

   These operations are not primitive in ordinary C++, since you can
use a macro to return the minimum of two things in C++, as in the
following example.

     #define MIN(X,Y) ((X) < (Y) ? : (X) : (Y))

You might then use `int min = MIN (i, j);' to set MIN to the minimum
value of variables I and J.

   However, side effects in `X' or `Y' may cause unintended behavior.
For example, `MIN (i++, j++)' will fail, incrementing the smaller
counter twice.  A GNU C extension allows you to write safe macros that
avoid this kind of problem (*note Naming an Expression's Type: Naming
Types.).  However, writing `MIN' and `MAX' as macros also forces you to
use function-call notation notation for a fundamental arithmetic
operation.  Using GNU C++ extensions, you can write `int min = i <? j;'
instead.

   Since `<?' and `>?' are built into the compiler, they properly
handle expressions with side-effects;  `int min = i++ <? j++;' works
correctly.


File: @.Distr.UsingGCC,  Node: Destructors and Goto,  Next: C++ Interface,  Prev: Min and Max,  Up: C++ Extensions

`goto' and Destructors in GNU C++
=================================

   In C++ programs, you can safely use the `goto' statement.  When you
use it to exit a block which contains aggregates requiring destructors,
the destructors will run before the `goto' transfers control.  (In ANSI
C++, `goto' is restricted to targets within the current block.)

   The compiler still forbids using `goto' to *enter* a scope that
requires constructors.


File: @.Distr.UsingGCC,  Node: C++ Interface,  Prev: Destructors and Goto,  Up: C++ Extensions

Declarations and Definitions in One Header
==========================================

   C++ object definitions can be quite complex.  In principle, your
source code will need two kinds of things for each object that you use
across more than one source file.  First, you need an "interface"
specification, describing its structure with type declarations and
function prototypes.  Second, you need the "implementation" itself.  It
can be tedious to maintain a separate interface description in a header
file, in parallel to the actual implementation.  It is also dangerous,
since separate interface and implementation definitions may not remain
parallel.

   With GNU C++, you can use a single header file for both purposes.

     *Warning:* The mechanism to specify this is in transition.  For the
     nonce, you must use one of two `#pragma' commands; in a future
     release of GNU C++, an alternative mechanism will make these
     `#pragma' commands unnecessary.

   The header file contains the full definitions, but is marked with
`#pragma interface' in the source code.  This allows the compiler to
use the header file only as an interface specification when ordinary
source files incorporate it with `#include'.  In the single source file
where the full implementation belongs, you can use either a naming
convention or `#pragma implementation' to indicate this alternate use
of the header file.

`#pragma interface'
     Use this directive in *header files* that define object classes,
     to save space in most of the object files that use those classes.
     Normally, local copies of certain information (backup copies of
     inline member functions, debugging information, and the internal
     tables that implement virtual functions) must be kept in each
     object file that includes class definitions.  You can use this
     pragma to avoid such duplication.  When a header file containing
     `#pragma interface' is included in a compilation, this auxiliary
     information will not be generated (unless the main input source
     file itself uses `#pragma implementation').  Instead, the object
     files will contain references to be resolved at link time.

`#pragma implementation'
`#pragma implementation "OBJECTS.h"'
     Use this pragma in a *main input file*, when you want full output
     from included header files to be generated (and made globally
     visible).  The included header file, in turn, should use `#pragma
     interface'.  Backup copies of inline member functions, debugging
     information, and the internal tables used to implement virtual
     functions are all generated in implementation files.

     `#pragma implementation' is *implied* whenever the basename(1) of
     your source file matches the basename of a header file it
     includes.  There is no way to turn this off (other than using a
     different name for one of the two files).  In the same vein, if
     you use `#pragma implementation' with no argument, it applies to an
     include file with the same basename as your source file.  For
     example, in `allclass.cc', `#pragma implementation' by itself is
     equivalent to `#pragma implementation "allclass.h"'; but even if
     you do not say `#pragma implementation' at all, `allclass.h' is
     treated as an implementation file whenever you include it from
     `allclass.cc'.

     If you use an explicit `#pragma implementation', it must appear in
     your source file *before* you include the affected header files.

     Use the string argument if you want a single implementation file to
     include code from multiple header files.  (You must also use
     `#include' to include the header file; `#pragma implementation'
     only specifies how to use the file--it doesn't actually include
     it.)

     There is no way to split up the contents of a single header file
     into multiple implementation files.

   `#pragma implementation' and `#pragma interface' also have an effect
on function inlining.

   If you define a class in a header file marked with `#pragma
interface', the effect on a function defined in that class is similar to
an explicit `extern' declaration--the compiler emits no code at all to
define an independent version of the function.  Its definition is used
only for inlining with its callers.

   Conversely, when you include the same header file in a main source
file that declares it as `#pragma implementation', the compiler emits
code for the function itself; this defines a version of the function
that can be found via pointers (or by callers compiled without
inlining).

   ---------- Footnotes ----------

   (1)  A file's "basename" is the name stripped of all leading path
information and of trailing suffixes, such as `.h' or `.C' or `.cc'.


File: @.Distr.UsingGCC,  Node: Trouble,  Next: Bugs,  Prev: C++ Extensions,  Up: Top

Known Causes of Trouble with GNU CC
***********************************

   This section describes known problems that affect users of GNU CC.
Most of these are not GNU CC bugs per se--if they were, we would fix
them.  But the result for a user may be like the result of a bug.

   Some of these problems are due to bugs in other software, some are
missing features that are too much work to add, and some are places
where people's opinions differ as to what is best.

* Menu:

* Actual Bugs::              Bugs we will fix later.
* Installation Problems::     Problems that manifest when you install GNU CC.
* Cross-Compiler Problems::   Common problems of cross compiling with GNU CC.
* Interoperation::      Problems using GNU CC with other compilers,
               and with certain linkers, assemblers and debuggers.
* External Bugs::    Problems compiling certain programs.
* Incompatibilities::   GNU CC is incompatible with traditional C.
* Disappointments::     Regrettable things we can't change, but not quite bugs.
* C++ Misunderstandings::     Common misunderstandings with GNU C++.
* Protoize Caveats::    Things to watch out for when using `protoize'.
* Non-bugs::        Things we think are right, but some others disagree.
* Warnings and Errors:: Which problems in your code get warnings,
                         and which get errors.


File: @.Distr.UsingGCC,  Node: Actual Bugs,  Next: Installation Problems,  Up: Trouble

Actual Bugs We Haven't Fixed Yet
================================

   * The `fixincludes' script interacts badly with automounters; if the
     directory of system header files is automounted, it tends to be
     unmounted while `fixincludes' is running.  This would seem to be a
     bug in the automounter.  We don't know any good way to work around
     it.

   * Loop unrolling doesn't work properly for certain C++ programs.
     This is because of difficulty in updating the debugging
     information within the loop being unrolled.  We plan to revamp the
     representation of debugging information so that this will work
     properly, but we have not done this in version 2.4 because we
     don't want to delay it any further.


File: @.Distr.UsingGCC,  Node: Installation Problems,  Next: Cross-Compiler Problems,  Prev: Actual Bugs,  Up: Trouble

Installation Problems
=====================

   This is a list of problems (and some apparent problems which don't
really mean anything is wrong) that show up during installation of GNU
CC.

   * On certain systems, defining certain environment variables such as
     `CC' can interfere with the functioning of `make'.

   * If you encounter seemingly strange errors when trying to build the
     compiler in a directory other than the source directory, it could
     be because you have previously configured the compiler in the
     source directory.  Make sure you have done all the necessary
     preparations.  *Note Other Dir::.

   * In previous versions of GNU CC, the `gcc' driver program looked for
     `as' and `ld' in various places; for example, in files beginning
     with `/usr/local/lib/gcc-'.  GNU CC version 2 looks for them in
     the directory `/usr/local/lib/gcc-lib/TARGET/VERSION'.

     Thus, to use a version of `as' or `ld' that is not the system
     default, for example `gas' or GNU `ld', you must put them in that
     directory (or make links to them from that directory).

   * Some commands executed when making the compiler may fail (return a
     non-zero status) and be ignored by `make'.  These failures, which
     are often due to files that were not found, are expected, and can
     safely be ignored.

   * It is normal to have warnings in compiling certain files about
     unreachable code and about enumeration type clashes.  These files'
     names begin with `insn-'.  Also, `real.c' may get some warnings
     that you can ignore.

   * Sometimes `make' recompiles parts of the compiler when installing
     the compiler.  In one case, this was traced down to a bug in
     `make'.  Either ignore the problem or switch to GNU Make.

   * If you have installed a program known as purify, you may find that
     it causes errors while linking `enquire', which is part of building
     GNU CC.  The fix is to get rid of the file `real-ld' which purify
     installs--so that GNU CC won't try to use it.

   * On Linux SLS 1.01, there is a problem with `libc.a': it does not
     contain the obstack functions.  However, GNU CC assumes that the
     obstack functions are in `libc.a' when it is the GNU C library.
     To work around this problem, change the `__GNU_LIBRARY__'
     conditional around line 31 to `#if 1'.

   * On some 386 systems, building the compiler never finishes because
     `enquire' hangs due to a hardware problem in the motherboard--it
     reports floating point exceptions to the kernel incorrectly.  You
     can install GNU CC except for `float.h' by patching out the
     command to run `enquire'.  You may also be able to fix the problem
     for real by getting a replacement motherboard.  This problem was
     observed in Revision E of the Micronics motherboard, and is fixed
     in Revision F.

   * On some 386 systems, GNU CC crashes trying to compile `enquire.c'.
     This happens on machines that don't have a 387 FPU chip.  On 386
     machines, the system kernel is supposed to emulate the 387 when you
     don't have one.  The crash is due to a bug in the emulator.

     One of these systems is the Unix from Interactive Systems: 386/ix.
     On this system, an alternate emulator is provided, and it does
     work.  To use it, execute this command as super-user:

          ln /etc/emulator.rel1 /etc/emulator

     and then reboot the system.  (The default emulator file remains
     present under the name `emulator.dflt'.)

     Try using `/etc/emulator.att', if you have such a problem on the
     SCO system.

     Another system which has this problem is Esix.  We don't know
     whether it has an alternate emulator that works.

     On NetBSD 0.8, a similar problem manifests itself as these error
     messages:

          enquire.c: In function `fprop':
          enquire.c:2328: floating overflow

   * Sometimes on a Sun 4 you may observe a crash in the program
     `genflags' or `genoutput' while building GNU CC.  This is said to
     be due to a bug in `sh'.  You can probably get around it by running
     `genflags' or `genoutput' manually and then retrying the `make'.

   * On Solaris 2, executables of GNU CC version 2.0.2 are commonly
     available, but they have a bug that shows up when compiling current
     versions of GNU CC: undefined symbol errors occur during assembly
     if you use `-g'.

     The solution is to compile the current version of GNU CC without
     `-g'.  That makes a working compiler which you can use to recompile
     with `-g'.

   * Solaris 2 comes with a number of optional OS packages.  Six of
     these packages are needed to use GNU CC fully.  If you did not
     install all optional packages when installing Solaris, you will
     need to verify that these six packages are installed.

     The six packages that GNU CC needs are: `SUNWarc', `SUNWbtool',
     `SUNWesu', `SUNWhea', `SUNWlibm', and `SUNWtoo'.  To check whether
     an optional package is installed, use the `pkginfo' command.  To
     add an optional package, use the `pkgadd' command.  For further
     details, see the Solaris documentation.

   * On Solaris 2, trying to use the linker and other tools in
     `/usr/ucb' to install GNU CC has been observed to cause trouble.
     For example, the linker may hang indefinitely.  The fix is to
     remove `/usr/ucb' from your `PATH'.

   * If you use the 1.31 version of the MIPS assembler (such as was
     shipped with Ultrix 3.1), you will need to use the
     -fno-delayed-branch switch when optimizing floating point code.
     Otherwise, the assembler will complain when the GCC compiler fills
     a branch delay slot with a floating point instruction, such as
     add.d.

   * If on a MIPS system you get an error message saying "does not have
     gp sections for all it's [sic] sectons [sic]", don't worry about
     it.  This happens whenever you use GAS with the MIPS linker, but
     there is not really anything wrong, and it is okay to use the
     output file.  You can stop such warnings by installing the GNU
     linker.

     It would be nice to extend GAS to produce the gp tables, but they
     are optional, and there should not be a warning about their
     absence.

   * Users have reported some problems with version 2.0 of the MIPS
     compiler tools that were shipped with Ultrix 4.1.  Version 2.10
     which came with Ultrix 4.2 seems to work fine.

   * Some versions of the MIPS linker will issue an assertion failure
     when linking code that uses `alloca' against shared libraries on
     RISC-OS 5.0, and DEC's OSF/1 systems.  This is a bug in the
     linker, that is supposed to be fixed in future revisions.  To
     protect against this, GCC passes `-non_shared' to the linker
     unless you pass an explicit `-shared' or `-call_shared' switch.

   * On System V release 3, you may get this error message while
     linking:

          ld fatal: failed to write symbol name SOMETHING
           in strings table for file WHATEVER

     This probably indicates that the disk is full or your ULIMIT won't
     allow the file to be as large as it needs to be.

     This problem can also result because the kernel parameter `MAXUMEM'
     is too small.  If so, you must regenerate the kernel and make the
     value much larger.  The default value is reported to be 1024; a
     value of 32768 is said to work.  Smaller values may also work.

   * On System V, if you get an error like this,

          /usr/local/lib/bison.simple: In function `yyparse':
          /usr/local/lib/bison.simple:625: virtual memory exhausted

     that too indicates a problem with disk space, ULIMIT, or `MAXUMEM'.

   * Current GNU CC versions probably do not work on version 2 of the
     NeXT operating system.

   * On the Tower models 4N0 and 6N0, by default a process is not
     allowed to have more than one megabyte of memory.  GNU CC cannot
     compile itself (or many other programs) with `-O' in that much
     memory.

     To solve this problem, reconfigure the kernel adding the following
     line to the configuration file:

          MAXUMEM = 4096

   * On HP 9000 series 300 or 400 running HP-UX release 8.0, there is a
     bug in the assembler that must be fixed before GNU CC can be
     built.  This bug manifests itself during the first stage of
     compilation, while building `libgcc2.a':

          _floatdisf
          cc1: warning: `-g' option not supported on this version of GCC
          cc1: warning: `-g1' option not supported on this version of GCC
          ./xgcc: Internal compiler error: program as got fatal signal 11

     A patched version of the assembler is available by anonymous ftp
     from `altdorf.ai.mit.edu' as the file
     `archive/cph/hpux-8.0-assembler'.  If you have HP software support,
     the patch can also be obtained directly from HP, as described in
     the following note:

          This is the patched assembler, to patch SR#1653-010439, where
          the assembler aborts on floating point constants.

          The bug is not really in the assembler, but in the shared
          library version of the function "cvtnum(3c)".  The bug on
          "cvtnum(3c)" is SR#4701-078451.  Anyway, the attached
          assembler uses the archive library version of "cvtnum(3c)"
          and thus does not exhibit the bug.

     This patch is also known as PHCO_0800.

   * To build GCC for HP PA model 1.1 machines running HP-UX versions
     earlier than 8.07, you have to configure for HP PA model 1.0.
     This is because a bug in the PA configuration that probably will
     be fixed in the next release of the compiler.

   * On HP-UX version 9.01 on the HP PA, the HP compiler `cc' does not
     compile GNU CC correctly.  We do not yet know why.  However, GNU CC
     compiled on earlier HP-UX versions works properly on HP-UX 9.01
     and can compile itself properly on 9.01.

   * Another assembler problem on the HP PA results in an error message
     like this while compiling part of `libgcc2.a':

          as: /usr/tmp/cca08196.s @line#30 [err#1060]
            Argument 1 or 3 in FARG upper
                   - lookahead = RTNVAL=GR

     This happens because HP changed the assembler syntax after system
     release 8.02.  GNU CC assumes the newer syntax; if your assembler
     wants the older syntax, comment out this line in the file
     `pa1-hpux.h':

          #define HP_FP_ARG_DESCRIPTOR_REVERSED

   * Some versions of the Pyramid C compiler are reported to be unable
     to compile GNU CC.  You must use an older version of GNU CC for
     bootstrapping.  One indication of this problem is if you get a
     crash when GNU CC compiles the function `muldi3' in file
     `libgcc2.c'.

     You may be able to succeed by getting GNU CC version 1, installing
     it, and using it to compile GNU CC version 2.  The bug in the
     Pyramid C compiler does not seem to affect GNU CC version 1.

   * There may be similar problems on System V Release 3.1 on 386
     systems.

   * On the Altos 3068, programs compiled with GNU CC won't work unless
     you fix a kernel bug.  This happens using system versions V.2.2
     1.0gT1 and V.2.2 1.0e and perhaps later versions as well.  See the
     file `README.ALTOS'.

   * You will get several sorts of compilation and linking errors on the
     we32k if you don't follow the special instructions.  *Note WE32K
     Install::.


File: @.Distr.UsingGCC,  Node: Cross-Compiler Problems,  Next: Interoperation,  Prev: Installation Problems,  Up: Trouble

Cross-Compiler Problems
=======================

   You may run into problems with cross compilation on certain machines,
for several reasons.

   * Cross compilation can run into trouble for certain machines because
     some target machines' assemblers require floating point numbers to
     be written as *integer* constants in certain contexts.

     The compiler writes these integer constants by examining the
     floating point value as an integer and printing that integer,
     because this is simple to write and independent of the details of
     the floating point representation.  But this does not work if the
     compiler is running on a different machine with an incompatible
     floating point format, or even a different byte-ordering.

     In addition, correct constant folding of floating point values
     requires representing them in the target machine's format.  (The C
     standard does not quite require this, but in practice it is the
     only way to win.)

     It is now possible to overcome these problems by defining macros
     such as `REAL_VALUE_TYPE'.  But doing so is a substantial amount of
     work for each target machine.  *Note Cross Compilation and
     Floating Point Format: (gcc.info)Cross-compilation.

   * At present, the program `mips-tfile' which adds debug support to
     object files on MIPS systems does not work in a cross compile
     environment.


File: @.Distr.UsingGCC,  Node: Interoperation,  Next: External Bugs,  Prev: Cross-Compiler Problems,  Up: Trouble

Interoperation
==============

   This section lists various difficulties encountered in using GNU C or
GNU C++ together with other compilers or with the assemblers, linkers,
libraries and debuggers on certain systems.

   * If you are using version 2.3 of libg++, you need to rebuild it with
     `make CC=gcc' to avoid mismatches in the definition of `size_t'.

   * Objective C does not work on the RS/6000, the Alpha, or the HP PA.

   * C++ does not work on the Alpha.

   * GNU C++ does not do name mangling in the same way as other C++
     compilers.  This means that object files compiled with one compiler
     cannot be used with another.

     This effect is intentional, to protect you from more subtle
     problems.  Compilers differ as to many internal details of C++
     implementation, including: how class instances are laid out, how
     multiple inheritance is implemented, and how virtual function
     calls are handled.  If the name encoding were made the same, your
     programs would link against libraries provided from other
     compilers--but the programs would then crash when run.
     Incompatible libraries are then detected at link time, rather than
     at run time.

   * Older GDB versions sometimes fail to read the output of GNU CC
     version 2.  If you have trouble, get GDB version 4.4 or later.

   * DBX rejects some files produced by GNU CC, though it accepts
     similar constructs in output from PCC.  Until someone can supply a
     coherent description of what is valid DBX input and what is not,
     there is nothing I can do about these problems.  You are on your
     own.

   * The GNU assembler (GAS) does not support PIC.  To generate PIC
     code, you must use some other assembler, such as `/bin/as'.

   * On some BSD systems including some versions of Ultrix, use of
     profiling causes static variable destructors (currently used only
     in C++) not to be run.

   * Use of `-I/usr/include' may cause trouble.

     Many systems come with header files that won't work with GNU CC
     unless corrected by `fixincludes'.  The corrected header files go
     in a new directory; GNU CC searches this directory before
     `/usr/include'.  If you use `-I/usr/include', this tells GNU CC to
     search `/usr/include' earlier on, before the corrected headers.
     The result is that you get the uncorrected header files.

     Instead, you should use these options (when compiling C programs):

          -I/usr/local/lib/gcc-lib/TARGET/VERSION/include -I/usr/include

     For C++ programs, GNU CC also uses a special directory that
     defines C++ interfaces to standard C subroutines.  This directory
     is meant to be searched *before* other standard include
     directories, so that it takes precedence.  If you are compiling
     C++ programs and specifying include directories explicitly, use
     this option first, then the two options above:

          -I/usr/local/lib/g++-include

   * On a Sparc, GNU CC aligns all values of type `double' on an 8-byte
     boundary, and it expects every `double' to be so aligned.  The Sun
     compiler usually gives `double' values 8-byte alignment, with one
     exception: function arguments of type `double' may not be aligned.

     As a result, if a function compiled with Sun CC takes the address
     of an argument of type `double' and passes this pointer of type
     `double *' to a function compiled with GNU CC, dereferencing the
     pointer may cause a fatal signal.

     One way to solve this problem is to compile your entire program
     with GNU CC.  Another solution is to modify the function that is
     compiled with Sun CC to copy the argument into a local variable;
     local variables are always properly aligned.  A third solution is
     to modify the function that uses the pointer to dereference it via
     the following function `access_double' instead of directly with
     `*':

          inline double
          access_double (double *unaligned_ptr)
          {
            union d2i { double d; int i[2]; };

            union d2i *p = (union d2i *) unaligned_ptr;
            union d2i u;

            u.i[0] = p->i[0];
            u.i[1] = p->i[1];

            return u.d;
          }

     Storing into the pointer can be done likewise with the same union.

   * On Solaris, the `malloc' function in the `libmalloc.a' library may
     allocate memory that is only 4 byte aligned.  Since GNU CC on the
     Sparc assumes that doubles are 8 byte aligned, this may result in a
     fatal signal if doubles are stored in memory allocated by the
     `libmalloc.a' library.

     The solution is to not use the `libmalloc.a' library.  Use instead
     `malloc' and related functions from `libc.a'; they do not have
     this problem.

   * On a Sun, linking using GNU CC fails to find a shared library and
     reports that the library doesn't exist at all.

     This happens if you are using the GNU linker, because it does only
     static linking and looks only for unshared libraries.  If you have
     a shared library with no unshared counterpart, the GNU linker
     won't find anything.

     We hope to make a linker which supports Sun shared libraries, but
     please don't ask when it will be finished--we don't know.

   * Sun forgot to include a static version of `libdl.a' with some
     versions of SunOS (mainly 4.1).  This results in undefined symbols
     when linking static binaries (that is, if you use `-static').  If
     you see undefined symbols `_dlclose', `_dlsym' or `_dlopen' when
     linking, compile and link against the file `mit/util/misc/dlsym.c'
     from the MIT version of X windows.

   * On the HP PA machine, ADB sometimes fails to work on functions
     compiled with GNU CC.  Specifically, it fails to work on functions
     that use `alloca' or variable-size arrays.  This is because GNU CC
     doesn't generate HP-UX unwind descriptors for such functions.  It
     may even be impossible to generate them.

   * Debugging (`-g') is not supported on the HP PA machine, unless you
     use the preliminary GNU tools (*note Installation::.).

   * The HP-UX linker has a bug which can cause programs which make use
     of `const' variables to fail in unusual ways.  If your program
     makes use of global `const' variables, we suggest you compile with
     the following additional options:

          -Dconst="" -D__const="" -D__const__="" -fwritable-strings

     This will force the `const' variables into the DATA subspace which
     will avoid the linker bug.

     Another option you can use to work around this problem is
     `-mkernel'.  This changes how the address of variables is computed
     to a sequence less likely to tickle the HP-UX linker bug.

     We hope to work around this problem in a later version, if HP does
     not fix it.

   * Taking the address of a label may generate errors from the HP-UX
     PA assembler.  GAS for the PA does not have this problem.

   * GNU CC produced code will not yet link against HP-UX 8.0 shared
     libraries.  We expect to fix this problem in GNU CC 2.4.

   * GNU CC compiled code sometimes emits warnings from the HP-UX
     assembler of the form:

          (warning) Use of GR3 when
            frame >= 8192 may cause conflict.

     These warnings are harmless and can be safely ignored.

   * The current version of the assembler (`/bin/as') for the RS/6000
     has certain problems that prevent the `-g' option in GCC from
     working.  Note that `Makefile.in' uses `-g' by default when
     compiling `libgcc2.c'.

     IBM has produced a fixed version of the assembler.  The upgraded
     assembler unfortunately was not included in any of the AIX 3.2
     update PTF releases (3.2.2, 3.2.3, or 3.2.3e).  Users of AIX 3.1
     should request PTF U403044 from IBM and users of AIX 3.2 should
     request PTF U416277.  See the file `README.RS6000' for more
     details on these updates.

     You can test for the presense of a fixed assembler by using the
     command

          as -u < /dev/null

     If the command exits normally, the assembler fix already is
     installed.  If the assembler complains that "-u" is an unknown
     flag, you need to order the fix.

   * On the IBM RS/6000, compiling code of the form

          extern int foo;

          ... foo ...

          static int foo;

     will cause the linker to report an undefined symbol `foo'.
     Although this behavior differs from most other systems, it is not a
     bug because redefining an `extern' variable as `static' is
     undefined in ANSI C.

   * AIX on the RS/6000 provides support (NLS) for environments outside
     of the United States.  Compilers and assemblers use NLS to support
     locale-specific representations of various objects including
     floating-point numbers ("." vs "," for separating decimal
     fractions).  There have been problems reported where the library
     linked with GCC does not produce the same floating-point formats
     that the assembler accepts.  If you have this problem, set the
     LANG environment variable to "C" or "En_US".

   * There is an assembler bug in versions of DG/UX prior to 5.4.2.01
     that occurs when the `fldcr' instruction is used.  GNU CC uses
     `fldcr' on the 88100 to serialize volatile memory references.  Use
     the option `-fno-serialize-volatile' if your version of the
     assembler has this bug.

   * On VMS, GAS versions 1.38.1 and earlier may cause spurious warning
     messages from the linker.  These warning messages complain of
     mismatched psect attributes.  You can ignore them.  *Note VMS
     Install::.

   * On NewsOS version 3, if you include both of the files `stddef.h'
     and `sys/types.h', you get an error because there are two typedefs
     of `size_t'.  You should change `sys/types.h' by adding these
     lines around the definition of `size_t':

          #ifndef _SIZE_T
          #define _SIZE_T
          ACTUAL TYPEDEF HERE
          #endif

   * On the Alliant, the system's own convention for returning
     structures and unions is unusual, and is not compatible with GNU
     CC no matter what options are used.

   * On the IBM RT PC, the MetaWare HighC compiler (hc) uses a different
     convention for structure and union returning.  Use the option
     `-mhc-struct-return' to tell GNU CC to use a convention compatible
     with it.

   * On Ultrix, the Fortran compiler expects registers 2 through 5 to
     be saved by function calls.  However, the C compiler uses
     conventions compatible with BSD Unix: registers 2 through 5 may be
     clobbered by function calls.

     GNU CC uses the same convention as the Ultrix C compiler.  You can
     use these options to produce code compatible with the Fortran
     compiler:

          -fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5

   * On the WE32k, you may find that programs compiled with GNU CC do
     not work with the standard shared C ilbrary.  You may need to link
     with the ordinary C compiler.  If you do so, you must specify the
     following options:

          -L/usr/local/lib/gcc-lib/we32k-att-sysv/2.4 -lgcc -lc_s

     The first specifies where to find the library `libgcc.a' specified
     with the `-lgcc' option.

     GNU CC does linking by invoking `ld', just as `cc' does, and there
     is no reason why it *should* matter which compilation program you
     use to invoke `ld'.  If someone tracks this problem down, it can
     probably be fixed easily.

   * On the Alpha, you may get assembler errors about invalid syntax as
     a result of floating point constants.  This is due to a bug in the
     C library functions `ecvt', `fcvt' and `gcvt'.  Given valid
     floating point numbers, they sometimes print `NaN'.

   * On Irix 4.0.5F (and perhaps in some other versions), an assembler
     bug sometimes reorders instructions incorrectly when optimization
     is turned on.  If you think this may be happening to you, try
     using the GNU assembler; GAS version 2.1 supports ECOFF on Irix.

     Or use the `-noasmopt' option when you compile GNU CC with itself,
     and then again when you compile your program.  (This is a temporary
     kludge to turn off assembler optimization on Irix.)  If this
     proves to be what you need, edit the assembler spec in the file
     `specs' so that it unconditionally passes `-O0' to the assembler,
     and never passes `-O2' or `-O3'.


File: @.Distr.UsingGCC,  Node: External Bugs,  Next: Incompatibilities,  Prev: Interoperation,  Up: Trouble

Problems Compiling Certain Programs
===================================

   * Parse errors may occur compiling X11 on a Decstation running
     Ultrix 4.2 because of problems in DEC's versions of the X11 header
     files `X11/Xlib.h' and `X11/Xutil.h'.  People recommend adding
     `-I/usr/include/mit' to use the MIT versions of the header files,
     using the `-traditional' switch to turn off ANSI C, or fixing the
     header files by adding this:

          #ifdef __STDC__
          #define NeedFunctionPrototypes 0
          #endif

   * On various 386 Unix systems derived from System V, including SCO,
     ISC, and ESIX, you may get error messages about running out of
     virtual memory while compiling certain programs.

     You can prevent this problem by linking GNU CC with the GNU malloc
     (which thus replaces the malloc that comes with the system).  GNU
     malloc is available as a separate package, and also in the file
     `src/gmalloc.c' in the GNU Emacs 19 distribution.

     If you have installed GNU malloc as a separate library package,
     use this option when you relink GNU CC:

          MALLOC=/usr/local/lib/libgmalloc.a

     Alternatively, if you have compiled `gmalloc.c' from Emacs 19, copy
     the object file to `gmalloc.o' and use this option when you relink
     GNU CC:

          MALLOC=gmalloc.o


File: @.Distr.UsingGCC,  Node: Incompatibilities,  Next: Disappointments,  Prev: External Bugs,  Up: Trouble

Incompatibilities of GNU CC
===========================

   There are several noteworthy incompatibilities between GNU C and most
existing (non-ANSI) versions of C.  The `-traditional' option
eliminates many of these incompatibilities, *but not all*, by telling
GNU C to behave like the other C compilers.

   * GNU CC normally makes string constants read-only.  If several
     identical-looking string constants are used, GNU CC stores only one
     copy of the string.

     One consequence is that you cannot call `mktemp' with a string
     constant argument.  The function `mktemp' always alters the string
     its argument points to.

     Another consequence is that `sscanf' does not work on some systems
     when passed a string constant as its format control string or
     input.  This is because `sscanf' incorrectly tries to write into
     the string constant.  Likewise `fscanf' and `scanf'.

     The best solution to these problems is to change the program to use
     `char'-array variables with initialization strings for these
     purposes instead of string constants.  But if this is not possible,
     you can use the `-fwritable-strings' flag, which directs GNU CC to
     handle string constants the same way most C compilers do.
     `-traditional' also has this effect, among others.

   * `-2147483648' is positive.

     This is because 2147483648 cannot fit in the type `int', so
     (following the ANSI C rules) its data type is `unsigned long int'.
     Negating this value yields 2147483648 again.

   * GNU CC does not substitute macro arguments when they appear inside
     of string constants.  For example, the following macro in GNU CC

          #define foo(a) "a"

     will produce output `"a"' regardless of what the argument A is.

     The `-traditional' option directs GNU CC to handle such cases
     (among others) in the old-fashioned (non-ANSI) fashion.

   * When you use `setjmp' and `longjmp', the only automatic variables
     guaranteed to remain valid are those declared `volatile'.  This is
     a consequence of automatic register allocation.  Consider this
     function:

          jmp_buf j;

          foo ()
          {
            int a, b;

            a = fun1 ();
            if (setjmp (j))
              return a;

            a = fun2 ();
            /* `longjmp (j)' may occur in `fun3'. */
            return a + fun3 ();
          }

     Here `a' may or may not be restored to its first value when the
     `longjmp' occurs.  If `a' is allocated in a register, then its
     first value is restored; otherwise, it keeps the last value stored
     in it.

     If you use the `-W' option with the `-O' option, you will get a
     warning when GNU CC thinks such a problem might be possible.

     The `-traditional' option directs GNU C to put variables in the
     stack by default, rather than in registers, in functions that call
     `setjmp'.  This results in the behavior found in traditional C
     compilers.

   * Programs that use preprocessor directives in the middle of macro
     arguments do not work with GNU CC.  For example, a program like
     this will not work:

          foobar (
          #define luser
                  hack)

     ANSI C does not permit such a construct.  It would make sense to
     support it when `-traditional' is used, but it is too much work to
     implement.

   * Declarations of external variables and functions within a block
     apply only to the block containing the declaration.  In other
     words, they have the same scope as any other declaration in the
     same place.

     In some other C compilers, a `extern' declaration affects all the
     rest of the file even if it happens within a block.

     The `-traditional' option directs GNU C to treat all `extern'
     declarations as global, like traditional compilers.

   * In traditional C, you can combine `long', etc., with a typedef
     name, as shown here:

          typedef int foo;
          typedef long foo bar;

     In ANSI C, this is not allowed: `long' and other type modifiers
     require an explicit `int'.  Because this criterion is expressed by
     Bison grammar rules rather than C code, the `-traditional' flag
     cannot alter it.

   * PCC allows typedef names to be used as function parameters.  The
     difficulty described immediately above applies here too.

   * PCC allows whitespace in the middle of compound assignment
     operators such as `+='.  GNU CC, following the ANSI standard, does
     not allow this.  The difficulty described immediately above
     applies here too.

   * GNU CC complains about unterminated character constants inside of
     preprocessor conditionals that fail.  Some programs have English
     comments enclosed in conditionals that are guaranteed to fail; if
     these comments contain apostrophes, GNU CC will probably report an
     error.  For example, this code would produce an error:

          #if 0
          You can't expect this to work.
          #endif

     The best solution to such a problem is to put the text into an
     actual C comment delimited by `/*...*/'.  However, `-traditional'
     suppresses these error messages.

   * Many user programs contain the declaration `long time ();'.  In the
     past, the system header files on many systems did not actually
     declare `time', so it did not matter what type your program
     declared it to return.  But in systems with ANSI C headers, `time'
     is declared to return `time_t', and if that is not the same as
     `long', then `long time ();' is erroneous.

     The solution is to change your program to use `time_t' as the
     return type of `time'.

   * When compiling functions that return `float', PCC converts it to a
     double.  GNU CC actually returns a `float'.  If you are concerned
     with PCC compatibility, you should declare your functions to return
     `double'; you might as well say what you mean.

   * When compiling functions that return structures or unions, GNU CC
     output code normally uses a method different from that used on most
     versions of Unix.  As a result, code compiled with GNU CC cannot
     call a structure-returning function compiled with PCC, and vice
     versa.

     The method used by GNU CC is as follows: a structure or union
     which is 1, 2, 4 or 8 bytes long is returned like a scalar.  A
     structure or union with any other size is stored into an address
     supplied by the caller (usually in a special, fixed register, but
     on some machines it is passed on the stack).  The
     machine-description macros `STRUCT_VALUE' and
     `STRUCT_INCOMING_VALUE' tell GNU CC where to pass this address.

     By contrast, PCC on most target machines returns structures and
     unions of any size by copying the data into an area of static
     storage, and then returning the address of that storage as if it
     were a pointer value.  The caller must copy the data from that
     memory area to the place where the value is wanted.  GNU CC does
     not use this method because it is slower and nonreentrant.

     On some newer machines, PCC uses a reentrant convention for all
     structure and union returning.  GNU CC on most of these machines
     uses a compatible convention when returning structures and unions
     in memory, but still returns small structures and unions in
     registers.

     You can tell GNU CC to use a compatible convention for all
     structure and union returning with the option
     `-fpcc-struct-return'.


File: @.Distr.UsingGCC,  Node: Disappointments,  Next: C++ Misunderstandings,  Prev: Incompatibilities,  Up: Trouble

Disappointments and Misunderstandings
=====================================

   These problems are perhaps regrettable, but we don't know any
practical way around them.

   * Certain local variables aren't recognized by debuggers when you
     compile with optimization.

     This occurs because sometimes GNU CC optimizes the variable out of
     existence.  There is no way to tell the debugger how to compute the
     value such a variable "would have had", and it is not clear that
     would be desirable anyway.  So GNU CC simply does not mention the
     eliminated variable when it writes debugging information.

     You have to expect a certain amount of disagreement between the
     executable and your source code, when you use optimization.

   * Users often think it is a bug when GNU CC reports an error for code
     like this:

          int foo (struct mumble *);

          struct mumble { ... };

          int foo (struct mumble *x)
          { ... }

     This code really is erroneous, because the scope of `struct
     mumble' in the prototype is limited to the argument list
     containing it.  It does not refer to the `struct mumble' defined
     with file scope immediately below--they are two unrelated types
     with similar names in different scopes.

     But in the definition of `foo', the file-scope type is used
     because that is available to be inherited.  Thus, the definition
     and the prototype do not match, and you get an error.

     This behavior may seem silly, but it's what the ANSI standard
     specifies.  It is easy enough for you to make your code work by
     moving the definition of `struct mumble' above the prototype.
     It's not worth being incompatible with ANSI C just to avoid an
     error for the example shown above.

   * Accesses to bitfields even in volatile objects works by accessing
     larger objects, such as a byte or a word.  You cannot rely on what
     size of object is accessed in order to read or write the bitfield;
     it may even vary for a given bitfield according to the precise
     usage.

     If you care about controlling the amount of memory that is
     accessed, use volatile but do not use bitfields.

   * GNU CC comes with shell scripts to fix certain known problems in
     system header files.  They install corrected copies of various
     header files in a special directory where only GNU CC will
     normally look for them.  The scripts adapt to various systems by
     searching all the system header files for the problem cases that
     we know about.

     If new system header files are installed, nothing automatically
     arranges to update the corrected header files.  You will have to
     reinstall GNU CC to fix the new header files.  More specifically,
     go to the build directory and delete the files `stmp-fixinc' and
     `stmp-headers', and the subdirectory `include'; then do `make
     install' again.

   * On 68000 systems, you can get paradoxical results if you test the
     precise values of floating point numbers.  For example, you can
     find that a floating point value which is not a NaN is not equal
     to itself.  This results from the fact that the the floating point
     registers hold a few more bits of precision than fit in a `double'
     in memory.  Compiled code moves values between memory and floating
     point registers at its convenience, and moving them into memory
     truncates them.

     You can partially avoid this problem by using the `-ffloat-store'
     option (*note Optimize Options::.).

   * On the MIPS, variable argument functions using `varargs.h' cannot
     have a floating point value for the first argument.  The reason
     for this is that in the absence of a prototype in scope, if the
     first argument is a floating point, it is passed in a floating
     point register, rather than an integer register.

     If the code is rewritten to use the ANSI standard `stdarg.h'
     method of variable arguments, and the prototype is in scope at the
     time of the call, everything will work fine.


File: @.Distr.UsingGCC,  Node: C++ Misunderstandings,  Next: Protoize Caveats,  Prev: Disappointments,  Up: Trouble

Common Misunderstandings with GNU C++
=====================================

   C++ is a complex language and an evolving one, and its standard
definition (the ANSI C++ draft standard) is also evolving.  As a result,
your C++ compiler may occasionally surprise you, even when its behavior
is correct.  This section discusses some areas that frequently give
rise to questions of this sort.

* Menu:

* Static Definitions::  Static member declarations are not definitions
* Temporaries::         Temporaries may vanish before you expect


File: @.Distr.UsingGCC,  Node: Static Definitions,  Next: Temporaries,  Up: C++ Misunderstandings

Declare *and* Define Static Members
-----------------------------------

   When a class has static data members, it is not enough to *declare*
the static member; you must also *define* it.  For example:

     class Foo
     {
       ...
       void method();
       static int bar;
     };

   This declaration only establishes that the class `Foo' has an `int'
named `Foo::bar', and a member function named `Foo::method'.  But you
still need to define *both* `method' and `bar' elsewhere.  According to
the draft ANSI standard, you must supply an initializer in one (and
only one) source file, such as:

     int Foo::bar = 0;

   Other C++ compilers may not correctly implement the standard
behavior.  As a result, when you switch to `g++' from one of these
compilers, you may discover that a program that appeared to work
correctly in fact does not conform to the standard: `g++' reports as
undefined symbols any static data members that lack definitions.


File: @.Distr.UsingGCC,  Node: Temporaries,  Prev: Static Definitions,  Up: C++ Misunderstandings

Temporaries May Vanish Before You Expect
----------------------------------------

   It is dangerous to use pointers or references to *portions* of a
temporary object.  The compiler may very well delete the object before
you expect it to, leaving a pointer to garbage.  The most common place
where this problem crops up is in classes like the libg++ `String'
class, that define a conversion function to type `char *' or `const
char *'.  However, any class that returns a pointer to some internal
structure is potentially subject to this problem.

   For example, a program may use a function `strfunc' that returns
`String' objects, and another function `charfunc' that operates on
pointers to `char':

     String strfunc ();
     void charfunc (const char *);

In this situation, it may seem natural to write
`charfunc (strfunc ());' based on the knowledge that class `String' has
an explicit conversion to `char' pointers.  However, what really
happens is akin to `charfunc (strfunc ().convert ());', where the
`convert' method is a function to do the same data conversion normally
performed by a cast.  Since the last use of the temporary `String'
object is the call to the conversion function, the compiler may delete
that object before actually calling `charfunc'.  The compiler has no
way of knowing that deleting the `String' object will invalidate the
pointer.  The pointer then points to garbage, so that by the time
`charfunc' is called, it gets an invalid argument.

   Code like this may run successfully under some other compilers,
especially those that delete temporaries relatively late.  However, the
GNU C++ behavior is also standard-conformant, so if your program depends
on late destruction of temporaries it is not portable.

   If you think this is surprising, you should be aware that the ANSI
C++ committee continues to debate the lifetime-of-temporaries problem.

   For now, at least, the safe way to write such code is to give the
temporary a name, which forces it to remain until the end of the scope
of the name.  For example:

     String& tmp = strfunc ();
     charfunc (tmp);


File: @.Distr.UsingGCC,  Node: Protoize Caveats,  Next: Non-bugs,  Prev: C++ Misunderstandings,  Up: Trouble

Caveats of using `protoize'
===========================

   The conversion programs `protoize' and `unprotoize' can sometimes
change a source file in a way that won't work unless you rearrange it.

   * `protoize' can insert references to a type name or type tag before
     the definition, or in a file where they are not defined.

     If this happens, compiler error messages should show you where the
     new references are, so fixing the file by hand is straightforward.

   * There are some C constructs which `protoize' cannot figure out.
     For example, it can't determine argument types for declaring a
     pointer-to-function variable; this you must do by hand.  `protoize'
     inserts a comment containing `???' each time it finds such a
     variable; so you can find all such variables by searching for this
     string.  ANSI C does not require declaring the argument types of
     pointer-to-function types.

   * Using `unprotoize' can easily introduce bugs.  If the program
     relied on prototypes to bring about conversion of arguments, these
     conversions will not take place in the program without prototypes.
     One case in which you can be sure `unprotoize' is safe is when you
     are removing prototypes that were made with `protoize'; if the
     program worked before without any prototypes, it will work again
     without them.

     You can find all the places where this problem might occur by
     compiling the program with the `-Wconversion' option.  It prints a
     warning whenever an argument is converted.

   * Both conversion programs can be confused if there are macro calls
     in and around the text to be converted.  In other words, the
     standard syntax for a declaration or definition must not result
     from expanding a macro.  This problem is inherent in the design of
     C and cannot be fixed.  If only a few functions have confusing
     macro calls, you can easily convert them manually.

   * `protoize' cannot get the argument types for a function whose
     definition was not actually compiled due to preprocessor
     conditionals.  When this happens, `protoize' changes nothing in
     regard to such a function.  `protoize' tries to detect such
     instances and warn about them.

     You can generally work around this problem by using `protoize' step
     by step, each time specifying a different set of `-D' options for
     compilation, until all of the functions have been converted.
     There is no automatic way to verify that you have got them all,
     however.

   * Confusion may result if there is an occasion to convert a function
     declaration or definition in a region of source code where there
     is more than one formal parameter list present.  Thus, attempts to
     convert code containing multiple (conditionally compiled) versions
     of a single function header (in the same vicinity) may not produce
     the desired (or expected) results.

     If you plan on converting source files which contain such code, it
     is recommended that you first make sure that each conditionally
     compiled region of source code which contains an alternative
     function header also contains at least one additional follower
     token (past the final right parenthesis of the function header).
     This should circumvent the problem.

   * `unprotoize' can become confused when trying to convert a function
     definition or declaration which contains a declaration for a
     pointer-to-function formal argument which has the same name as the
     function being defined or declared.  We recommand you avoid such
     choices of formal parameter names.

   * You might also want to correct some of the indentation by hand and
     break long lines.  (The conversion programs don't write lines
     longer than eighty characters in any case.)


File: @.Distr.UsingGCC,  Node: Non-bugs,  Next: Warnings and Errors,  Prev: Protoize Caveats,  Up: Trouble

Certain Changes We Don't Want to Make
=====================================

   This section lists changes that people frequently request, but which
we do not make because we think GNU CC is better without them.

   * Checking the number and type of arguments to a function which has
     an old-fashioned definition and no prototype.

     Such a feature would work only occasionally--only for calls that
     appear in the same file as the called function, following the
     definition.  The only way to check all calls reliably is to add a
     prototype for the function.  But adding a prototype eliminates the
     motivation for this feature.  So the feature is not worthwhile.

   * Warning about using an expression whose type is signed as a shift
     count.

     Shift count operands are probably signed more often than unsigned.
     Warning about this would cause far more annoyance than good.

   * Warning about assigning a signed value to an unsigned variable.

     Such assignments must be very common; warning about them would
     cause more annoyance than good.

   * Warning about unreachable code.

     It's very common to have unreachable code in machine-generated
     programs.  For example, this happens normally in some files of GNU
     C itself.

   * Warning when a non-void function value is ignored.

     Coming as I do from a Lisp background, I balk at the idea that
     there is something dangerous about discarding a value.  There are
     functions that return values which some callers may find useful;
     it makes no sense to clutter the program with a cast to `void'
     whenever the value isn't useful.

   * Assuming (for optimization) that the address of an external symbol
     is never zero.

     This assumption is false on certain systems when `#pragma weak' is
     used.

   * Making `-fshort-enums' the default.

     This would cause storage layout to be incompatible with most other
     C compilers.  And it doesn't seem very important, given that you
     can get the same result in other ways.  The case where it matters
     most is when the enumeration-valued object is inside a structure,
     and in that case you can specify a field width explicitly.

   * Making bitfields unsigned by default on particular machines where
     "the ABI standard" says to do so.

     The ANSI C standard leaves it up to the implementation whether a
     bitfield declared plain `int' is signed or not.  This in effect
     creates two alternative dialects of C.

     The GNU C compiler supports both dialects; you can specify the
     signed dialect with `-fsigned-bitfields' and the unsigned dialect
     with `-funsigned-bitfields'.  However, this leaves open the
     question of which dialect to use by default.

     Currently, the preferred dialect makes plain bitfields signed,
     because this is simplest.  Since `int' is the same as `signed int'
     in every other context, it is cleanest for them to be the same in
     bitfields as well.

     Some computer manufacturers have published Application Binary
     Interface standards which specify that plain bitfields should be
     unsigned.  It is a mistake, however, to say anything about this
     issue in an ABI.  This is because the handling of plain bitfields
     distinguishes two dialects of C.  Both dialects are meaningful on
     every type of machine.  Whether a particular object file was
     compiled using signed bitfields or unsigned is of no concern to
     other object files, even if they access the same bitfields in the
     same data structures.

     A given program is written in one or the other of these two
     dialects.  The program stands a chance to work on most any machine
     if it is compiled with the proper dialect.  It is unlikely to work
     at all if compiled with the wrong dialect.

     Many users appreciate the GNU C compiler because it provides an
     environment that is uniform across machines.  These users would be
     inconvenienced if the compiler treated plain bitfields differently
     on certain machines.

     Occasionally users write programs intended only for a particular
     machine type.  On these occasions, the users would benefit if the
     GNU C compiler were to support by default the same dialect as the
     other compilers on that machine.  But such applications are rare.
     And users writing a program to run on more than one type of
     machine cannot possibly benefit from this kind of compatibility.

     This is why GNU CC does and will treat plain bitfields in the same
     fashion on all types of machines (by default).

     There are some arguments for making bitfields unsigned by default
     on all machines.  If, for example, this becomes a universal de
     facto standard, it would make sense for GNU CC to go along with
     it.  This is something to be considered in the future.

     (Of course, users strongly concerned about portability should
     indicate explicitly in each bitfield whether it is signed or not.
     In this way, they write programs which have the same meaning in
     both C dialects.)

   * Undefining `__STDC__' when `-ansi' is not used.

     Currently, GNU CC defines `__STDC__' as long as you don't use
     `-traditional'.  This provides good results in practice.

     Programmers normally use conditionals on `__STDC__' to ask whether
     it is safe to use certain features of ANSI C, such as function
     prototypes or ANSI token concatenation.  Since plain `gcc' supports
     all the features of ANSI C, the correct answer to these questions
     is "yes".

     Some users try to use `__STDC__' to check for the availability of
     certain library facilities.  This is actually incorrect usage in
     an ANSI C program, because the ANSI C standard says that a
     conforming freestanding implementation should define `__STDC__'
     even though it does not have the library facilities.  `gcc -ansi
     -pedantic' is a conforming freestanding implementation, and it is
     therefore required to define `__STDC__', even though it does not
     come with an ANSI C library.

     Sometimes people say that defining `__STDC__' in a compiler that
     does not completely conform to the ANSI C standard somehow
     violates the standard.  This is illogical.  The standard is a
     standard for compilers that claim to support ANSI C, such as `gcc
     -ansi'--not for other compilers such as plain `gcc'.  Whatever the
     ANSI C standard says is relevant to the design of plain `gcc'
     without `-ansi' only for pragmatic reasons, not as a requirement.

   * Undefining `__STDC__' in C++.

     Programs written to compile with C++-to-C translators get the
     value of `__STDC__' that goes with the C compiler that is
     subsequently used.  These programs must test `__STDC__' to
     determine what kind of C preprocessor that compiler uses: whether
     they should concatenate tokens in the ANSI C fashion or in the
     traditional fashion.

     These programs work properly with GNU C++ if `__STDC__' is defined.
     They would not work otherwise.

     In addition, many header files are written to provide prototypes
     in ANSI C but not in traditional C.  Many of these header files
     can work without change in C++ provided `__STDC__' is defined.  If
     `__STDC__' is not defined, they will all fail, and will all need
     to be changed to test explicitly for C++ as well.

   * Deleting "empty" loops.

     GNU CC does not delete "empty" loops because the most likely reason
     you would put one in a program is to have a delay.  Deleting them
     will not make real programs run any faster, so it would be
     pointless.

     It would be different if optimization of a nonempty loop could
     produce an empty one.  But this generally can't happen.

   * Making side effects happen in the same order as in some other
     compiler.

     It is never safe to depend on the order of evaluation of side
     effects.  For example, a function call like this may very well
     behave differently from one compiler to another:

          void func (int, int);

          int i = 2;
          func (i++, i++);

     There is no guarantee (in either the C or the C++ standard language
     definitions) that the increments will be evaluated in any
     particular order.  Either increment might happen first.  `func'
     might get the arguments `3, 4', or it might get `4, 3', or even
     `3, 3'.

   * Using the "canonical" form of the target configuration name as the
     directory for installation.

     This would be an improvement in some respects, but it would also
     cause problems.  For one thing, users might expect to use in the
     `-b' option the same name specified at installation; if
     installation used the canonical form, that would not work.  What's
     more, the canonical name might be too long for certain file
     systems.

     We suggest you make a link to the installation directory under the
     canonical name, if you want to use that name in the `-b' option.


File: @.Distr.UsingGCC,  Node: Warnings and Errors,  Prev: Non-bugs,  Up: Trouble

Warning Messages and Error Messages
===================================

   The GNU compiler can produce two kinds of diagnostics: errors and
warnings.  Each kind has a different purpose:

     *Errors* report problems that make it impossible to compile your
     program.  GNU CC reports errors with the source file name and line
     number where the problem is apparent.

     *Warnings* report other unusual conditions in your code that *may*
     indicate a problem, although compilation can (and does) proceed.
     Warning messages also report the source file name and line number,
     but include the text `warning:' to distinguish them from error
     messages.

   Warnings may indicate danger points where you should check to make
sure that your program really does what you intend; or the use of
obsolete features; or the use of nonstandard features of GNU C or C++.
Many warnings are issued only if you ask for them, with one of the `-W'
options (for instance, `-Wall' requests a variety of useful warnings).

   GNU CC always tries to compile your program if possible; it never
gratuituously rejects a program whose meaning is clear merely because
(for instance) it fails to conform to a standard.  In some cases,
however, the C and C++ standards specify that certain extensions are
forbidden, and a diagnostic *must* be issued by a conforming compiler.
The `-pedantic' option tells GNU CC to issue warnings in such cases;
`-pedantic-errors' says to make them errors instead.  This does not
mean that *all* non-ANSI constructs get warnings or errors.

   *Note Options to Request or Suppress Warnings: Warning Options, for
more detail on these and related command-line options.


File: @.Distr.UsingGCC,  Node: Bugs,  Next: Service,  Prev: Trouble,  Up: Top

Reporting Bugs
**************

   Your bug reports play an essential role in making GNU CC reliable.

   When you encounter a problem, the first thing to do is to see if it
is already known.  *Note Trouble::.  If it isn't known, then you should
report the problem.

   Reporting a bug may help you by bringing a solution to your problem,
or it may not.  (If it does not, look in the service directory; see
*Note Service::.)  In any case, the principal function of a bug report
is to help the entire community by making the next version of GNU CC
work better.  Bug reports are your contribution to the maintenance of
GNU CC.

   In order for a bug report to serve its purpose, you must include the
information that makes for fixing the bug.

* Menu:

* Criteria:  Bug Criteria.   Have you really found a bug?
* Where: Bug Lists.         Where to send your bug report.
* Reporting: Bug Reporting.  How to report a bug effectively.
* Patches: Sending Patches.  How to send a patch for GNU CC.
* Known: Trouble.            Known problems.
* Help: Service.             Where to ask for help.


File: @.Distr.UsingGCC,  Node: Bug Criteria,  Next: Bug Lists,  Up: Bugs

Have You Found a Bug?
=====================

   If you are not sure whether you have found a bug, here are some
guidelines:

   * If the compiler gets a fatal signal, for any input whatever, that
     is a compiler bug.  Reliable compilers never crash.

   * If the compiler produces invalid assembly code, for any input
     whatever (except an `asm' statement), that is a compiler bug,
     unless the compiler reports errors (not just warnings) which would
     ordinarily prevent the assembler from being run.

   * If the compiler produces valid assembly code that does not
     correctly execute the input source code, that is a compiler bug.

     However, you must double-check to make sure, because you may have
     run into an incompatibility between GNU C and traditional C (*note
     Incompatibilities::.).  These incompatibilities might be considered
     bugs, but they are inescapable consequences of valuable features.

     Or you may have a program whose behavior is undefined, which
     happened by chance to give the desired results with another C or
     C++ compiler.

     For example, in many nonoptimizing compilers, you can write `x;'
     at the end of a function instead of `return x;', with the same
     results.  But the value of the function is undefined if `return'
     is omitted; it is not a bug when GNU CC produces different results.

     Problems often result from expressions with two increment
     operators, as in `f (*p++, *p++)'.  Your previous compiler might
     have interpreted that expression the way you intended; GNU CC might
     interpret it another way.  Neither compiler is wrong.  The bug is
     in your code.

     After you have localized the error to a single source line, it
     should be easy to check for these things.  If your program is
     correct and well defined, you have found a compiler bug.

   * If the compiler produces an error message for valid input, that is
     a compiler bug.

   * If the compiler does not produce an error message for invalid
     input, that is a compiler bug.  However, you should note that your
     idea of "invalid input" might be my idea of "an extension" or
     "support for traditional practice".

   * If you are an experienced user of C or C++ compilers, your
     suggestions for improvement of GNU CC or GNU C++ are welcome in
     any case.


File: @.Distr.UsingGCC,  Node: Bug Lists,  Next: Bug Reporting,  Prev: Bug Criteria,  Up: Bugs

Where to Report Bugs
====================

   Send bug reports for GNU C to one of these addresses:

     [e-mail]
     {ucbvax|mit-eddie|uunet}!prep.ai.mit.edu!bug-gcc

   Send bug reports for GNU C++ to one of these addresses:

     [e-mail]
     {ucbvax|mit-eddie|uunet}!prep.ai.mit.edu!bug-g++

   If your bug involves the C++ class library libg++, send mail to
`[e-mail]'.  If you're not sure, you can send the
bug report to both lists.

   *Do not send bug reports to the mailing list `help-gcc', or to the
newsgroup `gnu.gcc.help'.* Most users of GNU CC do not want to receive
bug reports.  Those that do, have asked to be on `bug-gcc' and/or
`bug-g++'.

   The mailing lists `bug-gcc' and `bug-g++' both have newsgroups which
serve as repeaters: `gnu.gcc.bug' and `gnu.g++.bug'.  Each mailing list
and its newsgroup carry exactly the same messages.

   Often people think of posting bug reports to the newsgroup instead of
mailing them.  This appears to work, but it has one problem which can be
crucial: a newsgroup posting does not contain a mail path back to the
sender.  Thus, if maintainers need more information, they may be unable
to reach you.  For this reason, you should always send bug reports by
mail to the proper mailing list.

   As a last resort, send bug reports on paper to:

     GNU Compiler Bugs
     Free Software Foundation
     675 Mass Ave
     Cambridge, MA 02139


File: @.Distr.UsingGCC,  Node: Bug Reporting,  Next: Sending Patches,  Prev: Bug Lists,  Up: Bugs

How to Report Bugs
==================

   The fundamental principle of reporting bugs usefully is this:
*report all the facts*.  If you are not sure whether to state a fact or
leave it out, state it!

   Often people omit facts because they think they know what causes the
problem and they conclude that some details don't matter.  Thus, you
might assume that the name of the variable you use in an example does
not matter.  Well, probably it doesn't, but one cannot be sure.
Perhaps the bug is a stray memory reference which happens to fetch from
the location where that name is stored in memory; perhaps, if the name
were different, the contents of that location would fool the compiler
into doing the right thing despite the bug.  Play it safe and give a
specific, complete example.  That is the easiest thing for you to do,
and the most helpful.

   Keep in mind that the purpose of a bug report is to enable someone to
fix the bug if it is not known.  It isn't very important what happens if
the bug is already known.  Therefore, always write your bug reports on
the assumption that the bug is not known.

   Sometimes people give a few sketchy facts and ask, "Does this ring a
bell?"  This cannot help us fix a bug, so it is basically useless.  We
respond by asking for enough details to enable us to investigate.  You
might as well expedite matters by sending them to begin with.

   Try to make your bug report self-contained.  If we have to ask you
for more information, it is best if you include all the previous
information in your response, as well as the information that was
missing.

   To enable someone to investigate the bug, you should include all
these things:

   * The version of GNU CC.  You can get this by running it with the
     `-v' option.

     Without this, we won't know whether there is any point in looking
     for the bug in the current version of GNU CC.

   * A complete input file that will reproduce the bug.  If the bug is
     in the C preprocessor, send a source file and any header files
     that it requires.  If the bug is in the compiler proper (`cc1'),
     run your source file through the C preprocessor by doing `gcc -E
     SOURCEFILE > OUTFILE', then include the contents of OUTFILE in the
     bug report.  (When you do this, use the same `-I', `-D' or `-U'
     options that you used in actual compilation.)

     A single statement is not enough of an example.  In order to
     compile it, it must be embedded in a complete file of compiler
     input; and the bug might depend on the details of how this is done.

     Without a real example one can compile, all anyone can do about
     your bug report is wish you luck.  It would be futile to try to
     guess how to provoke the bug.  For example, bugs in register
     allocation and reloading frequently depend on every little detail
     of the function they happen in.

     Even if the input file that fails comes from a GNU program, you
     should still send the complete test case.  Don't ask the GNU CC
     maintainers to do the extra work of obtaining the program in
     question--they are all overworked as it is.  Also, the problem may
     depend on what is in the header files on your system; it is
     unreliable for the GNU CC maintainers to try the problem with the
     header files available to them.  By sending CPP output, you can
     eliminate this source of uncertainty and save us a certain
     percentage of wild goose chases.

   * The command arguments you gave GNU CC or GNU C++ to compile that
     example and observe the bug.  For example, did you use `-O'?  To
     guarantee you won't omit something important, list all the options.

     If we were to try to guess the arguments, we would probably guess
     wrong and then we would not encounter the bug.

   * The type of machine you are using, and the operating system name
     and version number.

   * The operands you gave to the `configure' command when you installed
     the compiler.

   * A complete list of any modifications you have made to the compiler
     source.  (We don't promise to investigate the bug unless it
     happens in an unmodified compiler.  But if you've made
     modifications and don't tell us, then you are sending us on a wild
     goose chase.)

     Be precise about these changes.  A description in English is not
     enough--send a context diff for them.

     Adding files of your own (such as a machine description for a
     machine we don't support) is a modification of the compiler source.

   * Details of any other deviations from the standard procedure for
     installing GNU CC.

   * A description of what behavior you observe that you believe is
     incorrect.  For example, "The compiler gets a fatal signal," or,
     "The assembler instruction at line 208 in the output is incorrect."

     Of course, if the bug is that the compiler gets a fatal signal,
     then one can't miss it.  But if the bug is incorrect output, the
     maintainer might not notice unless it is glaringly wrong.  None of
     us has time to study all the assembler code from a 50-line C
     program just on the chance that one instruction might be wrong.
     We need *you* to do this part!

     Even if the problem you experience is a fatal signal, you should
     still say so explicitly.  Suppose something strange is going on,
     such as, your copy of the compiler is out of synch, or you have
     encountered a bug in the C library on your system.  (This has
     happened!)  Your copy might crash and the copy here would not.  If
     you said to expect a crash, then when the compiler here fails to
     crash, we would know that the bug was not happening.  If you don't
     say to expect a crash, then we would not know whether the bug was
     happening.  We would not be able to draw any conclusion from our
     observations.

     If the problem is a diagnostic when compiling GNU CC with some
     other compiler, say whether it is a warning or an error.

     Often the observed symptom is incorrect output when your program
     is run.  Sad to say, this is not enough information unless the
     program is short and simple.  None of us has time to study a large
     program to figure out how it would work if compiled correctly,
     much less which line of it was compiled wrong.  So you will have
     to do that.  Tell us which source line it is, and what incorrect
     result happens when that line is executed.  A person who
     understands the program can find this as easily as finding a bug
     in the program itself.

   * If you send examples of assembler code output from GNU CC or GNU
     C++, please use `-g' when you make them.  The debugging information
     includes source line numbers which are essential for correlating
     the output with the input.

   * If you wish to mention something in the GNU CC source, refer to it
     by context, not by line number.

     The line numbers in the development sources don't match those in
     your sources.  Your line numbers would convey no useful
     information to the maintainers.

   * Additional information from a debugger might enable someone to
     find a problem on a machine which he does not have available.
     However, you need to think when you collect this information if
     you want it to have any chance of being useful.

     For example, many people send just a backtrace, but that is never
     useful by itself.  A simple backtrace with arguments conveys little
     about GNU CC because the compiler is largely data-driven; the same
     functions are called over and over for different RTL insns, doing
     different things depending on the details of the insn.

     Most of the arguments listed in the backtrace are useless because
     they are pointers to RTL list structure.  The numeric values of the
     pointers, which the debugger prints in the backtrace, have no
     significance whatever; all that matters is the contents of the
     objects they point to (and most of the contents are other such
     pointers).

     In addition, most compiler passes consist of one or more loops that
     scan the RTL insn sequence.  The most vital piece of information
     about such a loop--which insn it has reached--is usually in a
     local variable, not in an argument.

     What you need to provide in addition to a backtrace are the values
     of the local variables for several stack frames up.  When a local
     variable or an argument is an RTX, first print its value and then
     use the GDB command `pr' to print the RTL expression that it points
     to.  (If GDB doesn't run on your machine, use your debugger to call
     the function `debug_rtx' with the RTX as an argument.)  In
     general, whenever a variable is a pointer, its value is no use
     without the data it points to.

   Here are some things that are not necessary:

   * A description of the envelope of the bug.

     Often people who encounter a bug spend a lot of time investigating
     which changes to the input file will make the bug go away and which
     changes will not affect it.

     This is often time consuming and not very useful, because the way
     we will find the bug is by running a single example under the
     debugger with breakpoints, not by pure deduction from a series of
     examples.  You might as well save your time for something else.

     Of course, if you can find a simpler example to report *instead* of
     the original one, that is a convenience.  Errors in the output
     will be easier to spot, running under the debugger will take less
     time, etc.  Most GNU CC bugs involve just one function, so the
     most straightforward way to simplify an example is to delete all
     the function definitions except the one where the bug occurs.
     Those earlier in the file may be replaced by external declarations
     if the crucial function depends on them.  (Exception: inline
     functions may affect compilation of functions defined later in the
     file.)

     However, simplification is not vital; if you don't want to do this,
     report the bug anyway and send the entire test case you used.

   * In particular, some people insert conditionals `#ifdef BUG' around
     a statement which, if removed, makes the bug not happen.  These
     are just clutter; we won't pay any attention to them anyway.
     Besides, you should send us cpp output, and that can't have
     conditionals.

   * A patch for the bug.

     A patch for the bug is useful if it is a good one.  But don't omit
     the necessary information, such as the test case, on the
     assumption that a patch is all we need.  We might see problems
     with your patch and decide to fix the problem another way, or we
     might not understand it at all.

     Sometimes with a program as complicated as GNU CC it is very hard
     to construct an example that will make the program follow a
     certain path through the code.  If you don't send the example, we
     won't be able to construct one, so we won't be able to verify that
     the bug is fixed.

     And if we can't understand what bug you are trying to fix, or why
     your patch should be an improvement, we won't install it.  A test
     case will help us to understand.

     *Note Sending Patches::, for guidelines on how to make it easy for
     us to understand and install your patches.

   * A guess about what the bug is or what it depends on.

     Such guesses are usually wrong.  Even I can't guess right about
     such things without first using the debugger to find the facts.

   * A core dump file.

     We have no way of examining a core dump for your type of machine
     unless we have an identical system--and if we do have one, we
     should be able to reproduce the crash ourselves.


File: @.Distr.UsingGCC,  Node: Sending Patches,  Prev: Bug Reporting,  Up: Bugs

Sending Patches for GNU CC
==========================

   If you would like to write bug fixes or improvements for the GNU C
compiler, that is very helpful.  When you send your changes, please
follow these guidelines to avoid causing extra work for us in studying
the patches.

   If you don't follow these guidelines, your information might still be
useful, but using it will take extra work.  Maintaining GNU C is a lot
of work in the best of circumstances, and we can't keep up unless you do
your best to help.

   * Send an explanation with your changes of what problem they fix or
     what improvement they bring about.  For a bug fix, just include a
     copy of the bug report, and explain why the change fixes the bug.

     (Referring to a bug report is not as good as including it, because
     then we will have to look it up, and we have probably already
     deleted it if we've already fixed the bug.)

   * Always include a proper bug report for the problem you think you
     have fixed.  We need to convince ourselves that the change is
     right before installing it.  Even if it is right, we might have
     trouble judging it if we don't have a way to reproduce the problem.

   * Include all the comments that are appropriate to help people
     reading the source in the future understand why this change was
     needed.

   * Don't mix together changes made for different reasons.  Send them
     *individually*.

     If you make two changes for separate reasons, then we might not
     want to install them both.  We might want to install just one.  If
     you send them all jumbled together in a single set of diffs, we
     have to do extra work to disentangle them--to figure out which
     parts of the change serve which purpose.  If we don't have time
     for this, we might have to ignore your changes entirely.

     If you send each change as soon as you have written it, with its
     own explanation, then the two changes never get tangled up, and we
     can consider each one properly without any extra work to
     disentangle them.

     Ideally, each change you send should be impossible to subdivide
     into parts that we might want to consider separately, because each
     of its parts gets its motivation from the other parts.

   * Send each change as soon as that change is finished.  Sometimes
     people think they are helping us by accumulating many changes to
     send them all together.  As explained above, this is absolutely
     the worst thing you could do.

     Since you should send each change separately, you might as well
     send it right away.  That gives us the option of installing it
     immediately if it is important.

   * Use `diff -c' to make your diffs.  Diffs without context are hard
     for us to install reliably.  More than that, they make it hard for
     us to study the diffs to decide whether we want to install them.
     Unidiff format is better than contextless diffs, but not as easy
     to read as `-c' format.

     If you have GNU diff, use `diff -cp', which shows the name of the
     function that each change occurs in.

   * Write the change log entries for your changes.  We get lots of
     changes, and we don't have time to do all the change log writing
     ourselves.

     Read the `ChangeLog' file to see what sorts of information to put
     in, and to learn the style that we use.  The purpose of the change
     log is to show people where to find what was changed.  So you need
     to be specific about what functions you changed; in large
     functions, it's often helpful to indicate where within the
     function the change was.

     On the other hand, once you have shown people where to find the
     change, you need not explain its purpose.  Thus, if you add a new
     function, all you need to say about it is that it is new.  If you
     feel that the purpose needs explaining, it probably does--but the
     explanation will be much more useful if you put it in comments in
     the code.

     If you would like your name to appear in the header line for who
     made the change, send us the header line.

   * When you write the fix, keep in mind that we can't install a
     change that would break other systems.

     People often suggest fixing a problem by changing
     machine-independent files such as `toplev.c' to do something
     special that a particular system needs.  Sometimes it is totally
     obvious that such changes would break GNU CC for almost all users.
     We can't possibly make a change like that.  At best it might tell
     us how to write another patch that would solve the problem
     acceptably.

     Sometimes people send fixes that *might* be an improvement in
     general--but it is hard to be sure of this.  It's hard to install
     such changes because we have to study them very carefully.  Of
     course, a good explanation of the reasoning by which you concluded
     the change was correct can help convince us.

     The safest changes are changes to the configuration files for a
     particular machine.  These are safe because they can't create new
     bugs on other machines.

     Please help us keep up with the workload by designing the patch in
     a form that is good to install.


File: @.Distr.UsingGCC,  Node: Service,  Next: VMS,  Prev: Bugs,  Up: Top

How To Get Help with GNU CC
***************************

   If you need help installing, using or changing GNU CC, there are two
ways to find it:

   * Send a message to a suitable network mailing list.  First try
     `[e-mail]', and if that brings no response, try
     `[e-mail]'.

   * Look in the service directory for someone who might help you for a
     fee.  The service directory is found in the file named `SERVICE'
     in the GNU CC distribution.


File: @.Distr.UsingGCC,  Node: VMS,  Next: Index,  Prev: Service,  Up: Top

Using GNU CC on VMS
*******************

* Menu:

* Include Files and VMS::  Where the preprocessor looks for the include files.
* Global Declarations::    How to do globaldef, globalref and globalvalue with
                           GNU CC.
* VMS Misc::           Misc information.


File: @.Distr.UsingGCC,  Node: Include Files and VMS,  Next: Global Declarations,  Up: VMS

Include Files and VMS
=====================

   Due to the differences between the filesystems of Unix and VMS, GNU
CC attempts to translate file names in `#include' into names that VMS
will understand.  The basic strategy is to prepend a prefix to the
specification of the include file, convert the whole filename to a VMS
filename, and then try to open the file.  GNU CC tries various prefixes
one by one until one of them succeeds:

  1. The first prefix is the `GNU_CC_INCLUDE:' logical name: this is
     where GNU C header files are traditionally stored.  If you wish to
     store header files in non-standard locations, then you can assign
     the logical `GNU_CC_INCLUDE' to be a search list, where each
     element of the list is suitable for use with a rooted logical.

  2. The next prefix tried is `SYS$SYSROOT:[SYSLIB.]'.  This is where
     VAX-C header files are traditionally stored.

  3. If the include file specification by itself is a valid VMS
     filename, the preprocessor then uses this name with no prefix in
     an attempt to open the include file.

  4. If the file specification is not a valid VMS filename (i.e. does
     not contain a device or a directory specifier, and contains a `/'
     character), the preprocessor tries to convert it from Unix syntax
     to VMS syntax.

     Conversion works like this: the first directory name becomes a
     device, and the rest of the directories are converted into
     VMS-format directory names.  For example, the name `X11/foobar.h'
     is translated to `X11:[000000]foobar.h' or `X11:foobar.h',
     whichever one can be opened.  This strategy allows you to assign a
     logical name to point to the actual location of the header files.

  5. If none of these strategies succeeds, the `#include' fails.

   Include directives of the form:

     #include foobar

are a common source of incompatibility between VAX-C and GNU CC.  VAX-C
treats this much like a standard `#include <foobar.h>' directive.  That
is incompatible with the ANSI C behavior implemented by GNU CC: to
expand the name `foobar' as a macro.  Macro expansion should eventually
yield one of the two standard formats for `#include':

     #include "FILE"
     #include <FILE>

   If you have this problem, the best solution is to modify the source
to convert the `#include' directives to one of the two standard forms.
That will work with either compiler.  If you want a quick and dirty fix,
define the file names as macros with the proper expansion, like this:

     #define stdio <stdio.h>

This will work, as long as the name doesn't conflict with anything else
in the program.

   Another source of incompatibility is that VAX-C assumes that:

     #include "foobar"

is actually asking for the file `foobar.h'.  GNU CC does not make this
assumption, and instead takes what you ask for literally; it tries to
read the file `foobar'.  The best way to avoid this problem is to
always specify the desired file extension in your include directives.

   GNU CC for VMS is distributed with a set of include files that is
sufficient to compile most general purpose programs.  Even though the
GNU CC distribution does not contain header files to define constants
and structures for some VMS system-specific functions, there is no
reason why you cannot use GNU CC with any of these functions.  You first
may have to generate or create header files, either by using the public
domain utility `UNSDL' (which can be found on a DECUS tape), or by
extracting the relevant modules from one of the system macro libraries,
and using an editor to construct a C header file.

   A `#include' file name cannot contain a DECNET node name.  The
preprocessor reports an I/O error if you attempt to use a node name,
whether explicitly, or implicitly via a logical name.


File: @.Distr.UsingGCC,  Node: Global Declarations,  Next: VMS Misc,  Prev: Include Files and VMS,  Up: VMS

Global Declarations and VMS
===========================

   GNU CC does not provide the `globalref', `globaldef' and
`globalvalue' keywords of VAX-C.  You can get the same effect with an
obscure feature of GAS, the GNU assembler.  (This requires GAS version
1.39 or later.)  The following macros allow you to use this feature in
a fairly natural way:

     #ifdef __GNUC__
     #define GLOBALREF(TYPE,NAME)                      \
       TYPE NAME                                       \
       asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME)
     #define GLOBALDEF(TYPE,NAME,VALUE)                \
       TYPE NAME                                       \
       asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) \
         = VALUE
     #define GLOBALVALUEREF(TYPE,NAME)                 \
       const TYPE NAME[1]                              \
       asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME)
     #define GLOBALVALUEDEF(TYPE,NAME,VALUE)           \
       const TYPE NAME[1]                              \
       asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME)  \
         = {VALUE}
     #else
     #define GLOBALREF(TYPE,NAME) \
       globalref TYPE NAME
     #define GLOBALDEF(TYPE,NAME,VALUE) \
       globaldef TYPE NAME = VALUE
     #define GLOBALVALUEDEF(TYPE,NAME,VALUE) \
       globalvalue TYPE NAME = VALUE
     #define GLOBALVALUEREF(TYPE,NAME) \
       globalvalue TYPE NAME
     #endif

(The `_$$PsectAttributes_GLOBALSYMBOL' prefix at the start of the name
is removed by the assembler, after it has modified the attributes of
the symbol).  These macros are provided in the VMS binaries
distribution in a header file `GNU_HACKS.H'.  An example of the usage
is:

     GLOBALREF (int, ijk);
     GLOBALDEF (int, jkl, 0);

   The macros `GLOBALREF' and `GLOBALDEF' cannot be used
straightforwardly for arrays, since there is no way to insert the array
dimension into the declaration at the right place.  However, you can
declare an array with these macros if you first define a typedef for the
array type, like this:

     typedef int intvector[10];
     GLOBALREF (intvector, foo);

   Array and structure initializers will also break the macros; you can
define the initializer to be a macro of its own, or you can expand the
`GLOBALDEF' macro by hand.  You may find a case where you wish to use
the `GLOBALDEF' macro with a large array, but you are not interested in
explicitly initializing each element of the array.  In such cases you
can use an initializer like: `{0,}', which will initialize the entire
array to `0'.

   A shortcoming of this implementation is that a variable declared with
`GLOBALVALUEREF' or `GLOBALVALUEDEF' is always an array.  For example,
the declaration:

     GLOBALVALUEREF(int, ijk);

declares the variable `ijk' as an array of type `int [1]'.  This is
done because a globalvalue is actually a constant; its "value" is what
the linker would normally consider an address.  That is not how an
integer value works in C, but it is how an array works.  So treating
the symbol as an array name gives consistent results--with the
exception that the value seems to have the wrong type.  *Don't try to
access an element of the array.*  It doesn't have any elements.  The
array "address" may not be the address of actual storage.

   The fact that the symbol is an array may lead to warnings where the
variable is used.  Insert type casts to avoid the warnings.  Here is an
example; it takes advantage of the ANSI C feature allowing macros that
expand to use the same name as the macro itself.

     GLOBALVALUEREF (int, ss$_normal);
     GLOBALVALUEDEF (int, xyzzy,123);
     #ifdef __GNUC__
     #define ss$_normal ((int) ss$_normal)
     #define xyzzy ((int) xyzzy)
     #endif

   Don't use `globaldef' or `globalref' with a variable whose type is
an enumeration type; this is not implemented.  Instead, make the
variable an integer, and use a `globalvaluedef' for each of the
enumeration values.  An example of this would be:

     #ifdef __GNUC__
     GLOBALDEF (int, color, 0);
     GLOBALVALUEDEF (int, RED, 0);
     GLOBALVALUEDEF (int, BLUE, 1);
     GLOBALVALUEDEF (int, GREEN, 3);
     #else
     enum globaldef color {RED, BLUE, GREEN = 3};
     #endif


File: @.Distr.UsingGCC,  Node: VMS Misc,  Prev: Global Declarations,  Up: VMS

Other VMS Issues
================

   GNU CC automatically arranges for `main' to return 1 by default if
you fail to specify an explicit return value.  This will be interpreted
by VMS as a status code indicating a normal successful completion.
Version 1 of GNU CC did not provide this default.

   GNU CC on VMS works only with the GNU assembler, GAS.  You need
version 1.37 or later of GAS in order to produce value debugging
information for the VMS debugger.  Use the ordinary VMS linker with the
object files produced by GAS.

   Under previous versions of GNU CC, the generated code would
occasionally give strange results when linked to the sharable `VAXCRTL'
library.  Now this should work.

   A caveat for use of `const' global variables: the `const' modifier
must be specified in every external declaration of the variable in all
of the source files that use that variable.  Otherwise the linker will
issue warnings about conflicting attributes for the variable.  Your
program will still work despite the warnings, but the variable will be
placed in writable storage.

   Although the VMS linker does distinguish between upper and lower case
letters in global symbols, most VMS compilers convert all such symbols
into upper case and most run-time library routines also have upper case
names.  To be able to reliably call such routines, GNU CC (by means of
the assembler GAS) converts global symbols into upper case like other
VMS compilers.  However, since the usual practice in C is to distinguish
case, GNU CC (via GAS) tries to preserve usual C behavior by augmenting
each name that is not all lower case.  This means truncating the name
to at most 23 characters and then adding more characters at the end
which encode the case pattern of those 23.   Names which contain at
least one dollar sign are an exception; they are converted directly into
upper case without augmentation.

   Name augmentation yields bad results for programs that use
precompiled libraries (such as Xlib) which were generated by another
compiler.  You can use the compiler option `/NOCASE_HACK' to inhibit
augmentation; it makes external C functions and variables
case-independent as is usual on VMS.  Alternatively, you could write
all references to the functions and variables in such libraries using
lower case; this will work on VMS, but is not portable to other
systems.  The compiler option `/NAMES' also provides control over
global name handling.

   Function and variable names are handled somewhat differently with GNU
C++.  The GNU C++ compiler performs "name mangling" on function names,
which means that it adds information to the function name to describe
the data types of the arguments that the function takes.  One result of
this is that the name of a function can become very long.  Since the
VMS linker only recognizes the first 31 characters in a name, special
action is taken to ensure that each function and variable has a unique
name that can be represented in 31 characters.

   If the name (plus a name augmentation, if required) is less than 32
characters in length, then no special action is performed.  If the name
is longer than 31 characters, the assembler (GAS) will generate a hash
string based upon the function name, truncate the function name to 23
characters, and append the hash string to the truncated name.  If the
`/VERBOSE' compiler option is used, the assembler will print both the
full and truncated names of each symbol that is truncated.

   The `/NOCASE_HACK' compiler option should not be used when you are
compiling programs that use libg++.  libg++ has several instances of
objects (i.e.  `Filebuf' and `filebuf') which become indistinguishable
in a case-insensitive environment.  This leads to cases where you need
to inhibit augmentation selectively (if you were using libg++ and Xlib
in the same program, for example).  There is no special feature for
doing this, but you can get the result by defining a macro for each
mixed case symbol for which you wish to inhibit augmentation.  The
macro should expand into the lower case equivalent of itself.  For
example:

     #define StuDlyCapS studlycaps

   These macro definitions can be placed in a header file to minimize
the number of changes to your source code.


File: @.Distr.UsingGCC,  Node: Index,  Prev: VMS,  Up: Top

Index
*****

* Menu:

* $:                                    Dollar Signs.
* ':                                    Incompatibilities.
* 3b1 installation:                     3b1 Install.
* <?:                                   Min and Max.
* >?:                                   Min and Max.
* ?: side effect:                       Conditionals.
* #pragma implementation, implied:      C++ Interface.
* #pragma, reason for not using:        Function Attributes.
* ?: extensions:                        Lvalues.
* ?: extensions:                        Conditionals.
* aligned attribute:                    Variable Attributes.
* alloca and SunOs:                     Installation.
* alloca vs variable-length arrays:     Variable Length.
* alloca, for SunOs:                    Sun Install.
* alloca, for Unos:                     Unos Install.
* asm constraints:                      Constraints.
* asm expressions:                      Extended Asm.
* const applied to function:            Function Attributes.
* float as function value type:         Incompatibilities.
* format attribute:                     Function Attributes.
* fscanf, and constant strings:         Incompatibilities.
* g++ 1.XX:                             Invoking G++.
* g++ older version:                    Invoking G++.
* g++, separate compiler:               Invoking G++.
* genflags, crash on Sun 4:             Installation Problems.
* goto in C++:                          Destructors and Goto.
* gprof:                                Debugging Options.
* inline automatic for C++ member fns:  Inline.
* long long data types:                 Long Long.
* longjmp and automatic variables:      C Dialect Options.
* longjmp incompatibilities:            Incompatibilities.
* longjmp warnings:                     Warning Options.
* main and the exit status:             VMS Misc.
* mktemp, and constant strings:         Incompatibilities.
* mode attribute:                       Variable Attributes.
* packed attribute:                     Variable Attributes.
* prof:                                 Debugging Options.
* qsort, and global register variables: Global Reg Vars.
* return, in C++ function header:       Naming Results.
* scanf, and constant strings:          Incompatibilities.
* setjmp incompatibilities:             Incompatibilities.
* sscanf, and constant strings:         Incompatibilities.
* tcov:                                 Debugging Options.
* volatile applied to function:         Function Attributes.
* stdarg.h and RT PC:                   RT Options.
* varargs.h and RT PC:                  RT Options.
* VAXCRTL:                              VMS Misc.
* ! in constraint:                      Multi-Alternative.
* # in constraint:                      Modifiers.
* % in constraint:                      Modifiers.
* & in constraint:                      Modifiers.
* + in constraint:                      Modifiers.
* 0 in constraint:                      Simple Constraints.
* < in constraint:                      Simple Constraints.
* = in constraint:                      Modifiers.
* > in constraint:                      Simple Constraints.
* ? in constraint:                      Multi-Alternative.
* d in constraint:                      Simple Constraints.
* E in constraint:                      Simple Constraints.
* F in constraint:                      Simple Constraints.
* g in constraint:                      Simple Constraints.
* G in constraint:                      Simple Constraints.
* H in constraint:                      Simple Constraints.
* I in constraint:                      Simple Constraints.
* i in constraint:                      Simple Constraints.
* m in constraint:                      Simple Constraints.
* n in constraint:                      Simple Constraints.
* o in constraint:                      Simple Constraints.
* p in constraint:                      Simple Constraints.
* Q, in constraint:                     Simple Constraints.
* r in constraint:                      Simple Constraints.
* s in constraint:                      Simple Constraints.
* V in constraint:                      Simple Constraints.
* X in constraint:                      Simple Constraints.
* _ in variables in macros:             Naming Types.
* address constraints:                  Simple Constraints.
* address of a label:                   Labels as Values.
* address_operand:                      Simple Constraints.
* alignment:                            Alignment.
* Alliant:                              Interoperation.
* alternate keywords:                   Alternate Keywords.
* AMD29K options:                       AMD29K Options.
* ANSI support:                         C Dialect Options.
* apostrophes:                          Incompatibilities.
* arguments in frame (88k):             M88K Options.
* arrays of length zero:                Zero Length.
* arrays of variable length:            Variable Length.
* arrays, non-lvalue:                   Subscripting.
* assembler instructions:               Extended Asm.
* assembler names for identifiers:      Asm Labels.
* assembler syntax, 88k:                M88K Options.
* assembly code, invalid:               Bug Criteria.
* attribute of variables:               Variable Attributes.
* autoincrement/decrement addressing:   Simple Constraints.
* automatic inline for C++ member fns:  Inline.
* backtrace for bug reports:            Bug Reporting.
* Bison parser generator:               Installation.
* bit shift overflow (88k):             M88K Options.
* bug criteria:                         Bug Criteria.
* bug report mailing lists:             Bug Lists.
* bugs:                                 Bugs.
* bugs, known:                          Trouble.
* C compilation options:                Invoking GCC.
* C intermediate output, nonexistent:   G++ and GCC.
* C language extensions:                C Extensions.
* C language, traditional:              C Dialect Options.
* C++:                                  G++ and GCC.
* c++:                                  Invoking G++.
* C++ compilation options:              Invoking GCC.
* C++ interface and implementation headers: C++ Interface.
* C++ language extensions:              C++ Extensions.
* C++ member fns, automatically inline: Inline.
* C++ misunderstandings:                C++ Misunderstandings.
* C++ named return value:               Naming Results.
* C++ options, command line:            C++ Dialect Options.
* C++ pragmas, effect on inlining:      C++ Interface.
* C++ source file suffixes:             Invoking G++.
* C++ static data, declaring and defining: Static Definitions.
* case labels in initializers:          Labeled Elements.
* case ranges:                          Case Ranges.
* case sensitivity and VMS:             VMS Misc.
* cast to a union:                      Cast to Union.
* casts as lvalues:                     Lvalues.
* code generation conventions:          Code Gen Options.
* command options:                      Invoking GCC.
* compilation in a separate directory:  Other Dir.
* compiler bugs, reporting:             Bug Reporting.
* compiler compared to C++ preprocessor: G++ and GCC.
* compiler options, C++:                C++ Dialect Options.
* compiler version, specifying:         Target Options.
* COMPILER_PATH:                        Environment Variables.
* complex numbers:                      Complex.
* compound expressions as lvalues:      Lvalues.
* computed gotos:                       Labels as Values.
* conditional expressions as lvalues:   Lvalues.
* conditional expressions, extensions:  Conditionals.
* conflicting types:                    Disappointments.
* constants in constraints:             Simple Constraints.
* constraint modifier characters:       Modifiers.
* constraint, matching:                 Simple Constraints.
* constraints, asm:                     Constraints.
* constraints, machine specific:        Machine Constraints.
* constructing calls:                   Constructing Calls.
* constructor expressions:              Constructors.
* constructors vs goto:                 Destructors and Goto.
* contributors:                         Contributors.
* Convex options:                       Convex Options.
* core dump:                            Bug Criteria.
* CPLUS_INCLUDE_PATH:                   Environment Variables.
* cross compiling:                      Target Options.
* cross-compiler, installation:         Cross-Compiler.
* C_INCLUDE_PATH:                       Environment Variables.
* DBX:                                  Interoperation.
* deallocating variable length arrays:  Variable Length.
* debugging information options:        Debugging Options.
* debugging, 88k OCS:                   M88K Options.
* debug_rtx:                            Bug Reporting.
* declaration scope:                    Incompatibilities.
* declarations inside expressions:      Statement Exprs.
* declaring attributes of functions:    Function Attributes.
* declaring static data in C++:         Static Definitions.
* defining static data in C++:          Static Definitions.
* dependencies for make as output:      Environment Variables.
* dependencies, make:                   Preprocessor Options.
* DEPENDENCIES_OUTPUT:                  Environment Variables.
* destructors vs goto:                  Destructors and Goto.
* detecting -traditional:               C Dialect Options.
* dialect options:                      C Dialect Options.
* digits in constraint:                 Simple Constraints.
* directory options:                    Directory Options.
* divide instruction, 88k:              M88K Options.
* dollar signs in identifier names:     Dollar Signs.
* double-word arithmetic:               Long Long.
* downward funargs:                     Nested Functions.
* enumeration clash warnings:           Warning Options.
* environment variables:                Environment Variables.
* error messages:                       Warnings and Errors.
* escape sequences, traditional:        C Dialect Options.
* exclamation point:                    Multi-Alternative.
* exit status and VMS:                  VMS Misc.
* explicit register variables:          Explicit Reg Vars.
* expressions containing statements:    Statement Exprs.
* expressions, compound, as lvalues:    Lvalues.
* expressions, conditional, as lvalues: Lvalues.
* expressions, constructor:             Constructors.
* extended asm:                         Extended Asm.
* extensible constraints:               Simple Constraints.
* extensions, ?::                       Lvalues.
* extensions, ?::                       Conditionals.
* extensions, C language:               C Extensions.
* extensions, C++ language:             C++ Extensions.
* external declaration scope:           Incompatibilities.
* fatal signal:                         Bug Criteria.
* file name suffix:                     Overall Options.
* file names:                           Link Options.
* forwarding calls:                     Constructing Calls.
* function attributes:                  Function Attributes.
* function pointers, arithmetic:        Pointer Arith.
* function prototype declarations:      Function Prototypes.
* function, size of pointer to:         Pointer Arith.
* functions that have no side effects:  Function Attributes.
* functions that never return:          Function Attributes.
* G++:                                  G++ and GCC.
* g++:                                  Invoking G++.
* GCC:                                  G++ and GCC.
* GCC_EXEC_PREFIX:                      Environment Variables.
* generalized lvalues:                  Lvalues.
* global offset table:                  Code Gen Options.
* global register after longjmp:        Global Reg Vars.
* global register variables:            Global Reg Vars.
* GLOBALDEF:                            Global Declarations.
* GLOBALREF:                            Global Declarations.
* GLOBALVALUEDEF:                       Global Declarations.
* GLOBALVALUEREF:                       Global Declarations.
* GNU CC command options:               Invoking GCC.
* goto with computed label:             Labels as Values.
* gp-relative references (MIPS):        MIPS Options.
* grouping options:                     Invoking GCC.
* hardware models and configurations, specifying: Submodel Options.
* header files and VMS:                 Include Files and VMS.
* HPPA Options:                         HPPA Options.
* i386 Options:                         i386 Options.
* IBM RS/6000 Options:                  RS/6000 Options.
* IBM RT options:                       RT Options.
* IBM RT PC:                            Interoperation.
* identifier names, dollar signs in:    Dollar Signs.
* identifiers, names in assembler code: Asm Labels.
* identifying source, compiler (88k):   M88K Options.
* implicit argument: return value:      Naming Results.
* implied #pragma implementation:       C++ Interface.
* include files and VMS:                Include Files and VMS.
* incompatibilities of GNU CC:          Incompatibilities.
* increment operators:                  Bug Criteria.
* initializations in expressions:       Constructors.
* initializers with labeled elements:   Labeled Elements.
* initializers, non-constant:           Initializers.
* inline functions:                     Inline.
* inline functions, omission of:        Inline.
* inlining and C++ pragmas:             C++ Interface.
* installation trouble:                 Trouble.
* installing GNU CC:                    Installation.
* installing GNU CC on the 3b1:         3b1 Install.
* installing GNU CC on the Sun:         Sun Install.
* installing GNU CC on Unos:            Unos Install.
* installing GNU CC on VMS:             VMS Install.
* integrating function code:            Inline.
* Intel 386 Options:                    i386 Options.
* interface and implementation headers, C++: C++ Interface.
* intermediate C version, nonexistent:  G++ and GCC.
* introduction:                         Top.
* invalid assembly code:                Bug Criteria.
* invalid input:                        Bug Criteria.
* invoking g++:                         Invoking G++.
* keywords, alternate:                  Alternate Keywords.
* known causes of trouble:              Trouble.
* labeled elements in initializers:     Labeled Elements.
* labels as values:                     Labels as Values.
* language dialect options:             C Dialect Options.
* large bit shifts (88k):               M88K Options.
* length-zero arrays:                   Zero Length.
* Libraries:                            Link Options.
* LIBRARY_PATH:                         Environment Variables.
* link options:                         Link Options.
* load address instruction:             Simple Constraints.
* local labels:                         Local Labels.
* local variables in macros:            Naming Types.
* local variables, specifying registers: Local Reg Vars.
* longjmp:                              Global Reg Vars.
* lvalues, generalized:                 Lvalues.
* M680x0 options:                       M680x0 Options.
* M88k options:                         M88K Options.
* machine dependent options:            Submodel Options.
* machine specific constraints:         Machine Constraints.
* macro with variable arguments:        Macro Varargs.
* macros containing asm:                Extended Asm.
* macros, inline alternative:           Inline.
* macros, local labels:                 Local Labels.
* macros, local variables in:           Naming Types.
* macros, statements in expressions:    Statement Exprs.
* macros, types of arguments:           Typeof.
* make:                                 Preprocessor Options.
* matching constraint:                  Simple Constraints.
* maximum operator:                     Min and Max.
* member fns, automatically inline:     Inline.
* memory references in constraints:     Simple Constraints.
* messages, warning:                    Warning Options.
* messages, warning and error:          Warnings and Errors.
* middle-operands, omitted:             Conditionals.
* minimum operator:                     Min and Max.
* MIPS options:                         MIPS Options.
* misunderstandings in C++:             C++ Misunderstandings.
* modifiers in constraints:             Modifiers.
* multiple alternative constraints:     Multi-Alternative.
* multiprecision arithmetic:            Long Long.
* name augmentation:                    VMS Misc.
* named return value in C++:            Naming Results.
* names used in assembler code:         Asm Labels.
* naming convention, implementation headers: C++ Interface.
* naming types:                         Naming Types.
* nested functions:                     Nested Functions.
* newline vs string constants:          C Dialect Options.
* non-constant initializers:            Initializers.
* non-static inline function:           Inline.
* OBJC_INCLUDE_PATH:                    Environment Variables.
* Objective C:                          G++ and GCC.
* obstack_free:                         3b1 Install.
* OCS (88k):                            M88K Options.
* offsettable address:                  Simple Constraints.
* old-style function definitions:       Function Prototypes.
* omitted middle-operands:              Conditionals.
* open coding:                          Inline.
* operand constraints, asm:             Constraints.
* optimize options:                     Optimize Options.
* options to control warnings:          Warning Options.
* options, C++:                         C++ Dialect Options.
* options, code generation:             Code Gen Options.
* options, debugging:                   Debugging Options.
* options, dialect:                     C Dialect Options.
* options, directory search:            Directory Options.
* options, GNU CC command:              Invoking GCC.
* options, grouping:                    Invoking GCC.
* options, linking:                     Link Options.
* options, optimization:                Optimize Options.
* options, order:                       Invoking GCC.
* options, preprocessor:                Preprocessor Options.
* order of evaluation, side effects:    Non-bugs.
* order of options:                     Invoking GCC.
* other directory, compilation in:      Other Dir.
* output file option:                   Overall Options.
* overloaded virtual fn, warning:       Warning Options.
* parameter forward declaration:        Variable Length.
* parser generator, Bison:              Installation.
* PIC:                                  Code Gen Options.
* pointer arguments:                    Function Attributes.
* portions of temporary objects, pointers to: Temporaries.
* pragma, reason for not using:         Function Attributes.
* pragmas in C++, effect on inlining:   C++ Interface.
* pragmas, interface and implementation: C++ Interface.
* preprocessor options:                 Preprocessor Options.
* promotion of formal parameters:       Function Prototypes.
* push address instruction:             Simple Constraints.
* question mark:                        Multi-Alternative.
* r0-relative references (88k):         M88K Options.
* ranges in case statements:            Case Ranges.
* read-only strings:                    Incompatibilities.
* register positions in frame (88k):    M88K Options.
* register positions in frame (88k):    M88K Options.
* register variable after longjmp:      Global Reg Vars.
* registers:                            Extended Asm.
* registers for local variables:        Local Reg Vars.
* registers in constraints:             Simple Constraints.
* registers, global allocation:         Explicit Reg Vars.
* registers, global variables in:       Global Reg Vars.
* reporting bugs:                       Bugs.
* rest argument (in macro):             Macro Varargs.
* return value of main:                 VMS Misc.
* return value, named, in C++:          Naming Results.
* RS/6000 Options:                      RS/6000 Options.
* RT options:                           RT Options.
* RT PC:                                Interoperation.
* run-time options:                     Code Gen Options.
* scope of a variable length array:     Variable Length.
* scope of declaration:                 Disappointments.
* scope of external declarations:       Incompatibilities.
* search path:                          Directory Options.
* second include path:                  Preprocessor Options.
* separate directory, compilation in:   Other Dir.
* sequential consistency on 88k:        M88K Options.
* setjmp:                               Global Reg Vars.
* shared strings:                       Incompatibilities.
* shared VMS run time system:           VMS Misc.
* side effect in ?::                    Conditionals.
* side effects, macro argument:         Statement Exprs.
* side effects, order of evaluation:    Non-bugs.
* simple constraints:                   Simple Constraints.
* sizeof:                               Typeof.
* smaller data references (88k):        M88K Options.
* smaller data references (MIPS):       MIPS Options.
* SPARC options:                        SPARC Options.
* specified registers:                  Explicit Reg Vars.
* specifying compiler version and target machine: Target Options.
* specifying hardware config:           Submodel Options.
* specifying machine version:           Target Options.
* specifying registers for local variables: Local Reg Vars.
* stage1:                               Installation.
* start files:                          Tools and Libraries.
* statements inside expressions:        Statement Exprs.
* static data in C++, declaring and defining: Static Definitions.
* string constants:                     Incompatibilities.
* string constants vs newline:          C Dialect Options.
* structure passing (88k):              M88K Options.
* structures:                           Incompatibilities.
* structures, constructor expression:   Constructors.
* submodel options:                     Submodel Options.
* subscripting:                         Subscripting.
* subscripting and function values:     Subscripting.
* suffixes for C++ source:              Invoking G++.
* Sun installation:                     Sun Install.
* suppressing warnings:                 Warning Options.
* surprises in C++:                     C++ Misunderstandings.
* SVr4:                                 M88K Options.
* syntax checking:                      Warning Options.
* target machine, specifying:           Target Options.
* target options:                       Target Options.
* template debugging:                   Warning Options.
* temporaries, lifetime of:             Temporaries.
* thunks:                               Nested Functions.
* TMPDIR:                               Environment Variables.
* traditional C language:               C Dialect Options.
* type alignment:                       Alignment.
* typedef names as function parameters: Incompatibilities.
* typeof:                               Typeof.
* Ultrix calling convention:            Interoperation.
* undefined behavior:                   Bug Criteria.
* undefined function value:             Bug Criteria.
* underscores in variables in macros:   Naming Types.
* underscores, avoiding (88k):          M88K Options.
* union, casting to a:                  Cast to Union.
* unions:                               Incompatibilities.
* Unos installation:                    Unos Install.
* value after longjmp:                  Global Reg Vars.
* variable alignment:                   Alignment.
* variable attributes:                  Variable Attributes.
* variable number of arguments:         Macro Varargs.
* variable-length array scope:          Variable Length.
* variable-length arrays:               Variable Length.
* variables in specified registers:     Explicit Reg Vars.
* variables, local, in macros:          Naming Types.
* Vax calling convention:               Interoperation.
* VAX options:                          VAX Options.
* VMS and case sensitivity:             VMS Misc.
* VMS and include files:                Include Files and VMS.
* VMS installation:                     VMS Install.
* void pointers, arithmetic:            Pointer Arith.
* void, size of pointer to:             Pointer Arith.
* warning for enumeration conversions:  Warning Options.
* warning for overloaded virtual fn:    Warning Options.
* warning messages:                     Warning Options.
* warnings vs errors:                   Warnings and Errors.
* whitespace:                           Incompatibilities.
* zero division on 88k:                 M88K Options.
* zero-length arrays:                   Zero Length.
* __builtin_apply:                      Constructing Calls.
* __builtin_apply_args:                 Constructing Calls.
* __builtin_return:                     Constructing Calls.



Tag Table:
Node: Top1295
Node: Copying2372
Node: Contributors21528
Node: Boycott26137
Node: G++ and GCC31663
Node: Invoking GCC33006
Node: Option Summary36393
Node: Overall Options44450
Node: Invoking G++49010
Node: C Dialect Options50890
Node: C++ Dialect Options59160
Node: Warning Options66239
Node: Debugging Options79484
Node: Optimize Options87649
Node: Preprocessor Options97642
Node: Assembler Options103236
Node: Link Options103568
Node: Directory Options107584
Node: Target Options110492
Node: Submodel Options114227
Node: M680x0 Options115358
Node: VAX Options118452
Node: SPARC Options118995
Node: Convex Options121059
Node: AMD29K Options123248
Node: M88K Options125048
Node: RS/6000 Options131849
Node: RT Options132422
Node: MIPS Options134122
Node: i386 Options140004
Node: HPPA Options141358
Node: Intel 960 Options143227
Node: DEC Alpha Options145845
Node: System V Options147526
Node: Code Gen Options148223
Node: Environment Variables156496
Node: Running Protoize160512
Node: Installation166749
Node: Other Dir202161
Node: Cross-Compiler203853
Node: Steps of Cross205673
Node: Configure Cross206799
Node: Tools and Libraries207456
Node: Cross Runtime209907
Node: Cross Headers213667
Node: Build Cross215660
Node: PA Install217573
Node: Sun Install219883
Node: 3b1 Install221630
Node: Unos Install222671
Node: VMS Install224219
Node: WE32K Install234162
Node: MIPS Install235549
Node: Collect2238419
Node: Header Dirs241270
Node: C Extensions242692
Node: Statement Exprs245872
Node: Local Labels247774
Node: Labels as Values249844
Node: Nested Functions251717
Node: Constructing Calls255278
Node: Naming Types257343
Node: Typeof258445
Node: Lvalues260318
Node: Conditionals262591
Node: Long Long263490
Node: Complex264946
Node: Zero Length266759
Node: Variable Length267443
Node: Macro Varargs269976
Node: Subscripting272087
Node: Pointer Arith272578
Node: Initializers273151
Node: Constructors273605
Node: Labeled Elements275307
Node: Case Ranges277422
Node: Cast to Union278389
Node: Function Attributes279475
Node: Function Prototypes284339
Node: Dollar Signs286052
Node: Character Escapes286847
Node: Alignment287136
Node: Variable Attributes288620
Node: Inline291527
Node: Extended Asm295270
Node: Constraints305566
Node: Simple Constraints306417
Node: Multi-Alternative312342
Node: Modifiers314061
Node: Machine Constraints315753
Node: Asm Labels323233
Node: Explicit Reg Vars324559
Node: Global Reg Vars325815
Node: Local Reg Vars330388
Node: Alternate Keywords331988
Node: Incomplete Enums333398
Node: Function Names334114
Node: C++ Extensions335127
Node: Naming Results336115
Node: Min and Max339437
Node: Destructors and Goto340895
Node: C++ Interface341453
Node: Trouble346328
Node: Actual Bugs347746
Node: Installation Problems348576
Node: Cross-Compiler Problems360173
Node: Interoperation361710
Node: External Bugs374366
Node: Incompatibilities375830
Node: Disappointments383532
Node: C++ Misunderstandings387764
Node: Static Definitions388419
Node: Temporaries389481
Node: Protoize Caveats391693
Node: Non-bugs395656
Node: Warnings and Errors404866
Node: Bugs406645
Node: Bug Criteria407811
Node: Bug Lists410249
Node: Bug Reporting411795
Node: Sending Patches423747
Node: Service429107
Node: VMS429676
Node: Include Files and VMS430033
Node: Global Declarations433931
Node: VMS Misc438248
Node: Index442582

End Tag Table