CC

-Wa,option

Pass option as an option to the assembler. If option contains commas, it is split into multiple options at the commas.

LINKER OPTIONS

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 cc does a link step, these object files are used as input to the linker.

-llibrary

Use the library named library when linking.

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. However, if the linker finds an ordinary object file rather than a library, the object file 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.

-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.

-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 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.

DIRECTORY OPTIONS

-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', `cc1obj' (or, for C++, `cc1objplus'), `as' and `ld'. It tries prefix as a prefix for each program it tries to run, both with and without `machine/version/'.

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 the directory `/lib/arch/'. Otherwise, the compiler driver searches for the unmodified program name, using the directories specified in your `PATH' environment variable.

You can get a similar result from the environment variable GCC_EXEC_PREFIX; if it is defined, its value is used as a prefix in the same way. If both the `-B' option and the GCC_EXEC_PREFIX variable are present, the `-B' option is used first and the environment variable value second.

WARNING OPTIONS

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

-fsyntax-only

Check the code for syntax errors, but don't emit any output.

-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. There is no reason to use this option; it exists only to satisfy pedants.

`-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.

-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 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;
}

Spurious warnings can occur because cc does not realize that certain functions (including abort and longjmp) will never return.

   *

An expression-statement contains no side effects.

   *

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

-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.

-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 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 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 as volatile all the functions you use that never return.

-Wparentheses

Warn if parentheses are omitted in certain contexts.

-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. cc 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.

-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.

-Wenum-clash

Warn about conversion between different enumeration types (C++ only).

-Woverloaded-virtual

(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. Use this option to request warnings when a derived class declares a function that may be an erroneous attempt to define a virtual function: that is, warn when a function with the same name as a virtual function in the base class, but with a type signature that doesn't match any virtual functions from the base class.

-Winline

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

-Wprecomp

Warn if a precompiled header cannot be used.

-Wno-precomp

Suppress warnings when a precompiled header cannot be used.

-Werror

Treat warnings as errors; abort compilation after any warning.

DEBUGGING OPTIONS

-g

Produce debugging information in the operating system's native format. 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.

Unlike most other C compilers, 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 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.

-p

Generate extra code to write profile information suitable for the analysis program prof.

-pg

Generate extra code to write profile information suitable for the analysis program gprof.

-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').

-dM

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

-dN

Dump all macro names, at the end of preprocessing.

-dD

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

-dy

Dump debugging information during parsing, to standard error.

-dr

Dump after RTL generation, to `file.rtl'.

-dx

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

-dj

Dump after first jump optimization, to `file.jump'.

-ds

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

-dL

Dump after loop optimization, to `file.loop'.

-dt

Dump after the second CSE pass (including the jump optimization that sometimes follows CSE), to `file.cse2'.

-df

Dump after flow analysis, to `file.flow'.

-dc

Dump after instruction combination, to `file.combine'.

-dS

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

-dl

Dump after local register allocation, to `file.lreg'.

-dg

Dump after global register allocation, to `file.greg'.

-dR

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

-dJ

Dump after last jump optimization, to `file.jump2'.

-dd

Dump after delayed branch scheduling, to `file.dbr'.

-dk

Dump after conversion from registers to stack, to `file.stack'.

-da

Produce all the dumps listed above.

-dm

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

-dp

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 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.cpp' 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 do not do anything else. With this option, cc does not compile or link anything; it just prints the file name.

OPTIMIZATION OPTIONS

-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 you specify `-O', `-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 -fflag options that enable more optimization, except for -funroll-loops, -funroll-all-loops and -fomit-frame-pointer.

-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'. The following list shows only one form---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. This 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.

-fmemoize-lookups

-fsave-memoized

Use heuristics to compile faster (C++ only). 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, cc 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-default-inline

Don't make member functions inline by default merely because they are defined inside the class scope (C++ only).

-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 most 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.

-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 cc normally does not output the function as assembler code in its own right.

-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.

-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.

-fno-peephole

Disable any machine-specific peephole optimizations.

-ffast-math

This option allows cc to violate some ANSI or IEEE rules/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'.

The `-O' option usually turns on the `-fthread-jumps' and `-fdelayed-branch' options, but specific machines may change the default optimizations.

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.

-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-all-loops

Perform the optimization of loop unrolling. This is done for all loops. This usually makes programs run more slowly.

-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.

-felide-constructors

Elide constructors when this seems plausible (C++ only). With this flag, cc 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, cc first initializes y by calling the appropriate constructor for type A; then assigns the result of foo to a temporary; and, finally, replaces the initial valyue 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, using `-felide-constructors' can make your program act differently, since some constructor calls may be omitted.

-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.

MACHINE DEPENDENT OPTIONS

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

These are the `-m' options defined for the 68000 series:

-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 (rather than a 68000). 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-based 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 the GNU C compiler. 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. `-m68000' implies `-mnobitfield'.

-mbitfield

Do use the bit-field instructions. `-m68020' implies `-mbitfield'. This is the default if you use the unmodified sources.

-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.

These `-m' options are defined for the Intel 80386 family of computers:

-m486

-mno-486

Control whether or not code is optimized for a 486 instead of an 386. Code generated for a 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 the GNU C compiler. 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.

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).

CODE GENERATION OPTIONS

Most of them begin with `-f'. These options 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.

-fnonnull-objects

Assume that objects reached through references are not null (C++ only).

Normally, cc 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.

-fpcc-struct-return

Use the same convention for returning struct and union values that is used by the usual C compiler on your system. This convention is less efficient for small structures, and on many machines it fails to be reentrant; but it has the advantage of allowing intercallability between GCC-compiled code and PCC-compiled code.

-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 -freg-struct-return, cc defaults to whichever convention is standard for the target. If there is no standard convention, cc defaults to -fpcc-struct-return.

-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-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 C 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 volati