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GNU Info File | 1995-11-26 | 35.8 KB | 853 lines

This is Info file gcc.info, produced by Makeinfo-1.55 from the input file gcc.texi. This file documents the use and the internals of the GNU compiler. Published by the Free Software Foundation 59 Temple Place - Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995 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," "Funding for Free Software," 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," "Funding for Free Software," 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: gcc.info, Node: Cross-compilation, Next: Misc, Prev: Debugging Info, Up: Target Macros Cross Compilation and Floating Point ==================================== While all modern machines use 2's complement representation for integers, there are a variety of representations for floating point numbers. This means that in a cross-compiler the representation of floating point numbers in the compiled program may be different from that used in the machine doing the compilation. Because different representation systems may offer different amounts of range and precision, the cross compiler cannot safely use the host machine's floating point arithmetic. Therefore, floating point constants must be represented in the target machine's format. This means that the cross compiler cannot use `atof' to parse a floating point constant; it must have its own special routine to use instead. Also, constant folding must emulate the target machine's arithmetic (or must not be done at all). The macros in the following table should be defined only if you are cross compiling between different floating point formats. Otherwise, don't define them. Then default definitions will be set up which use `double' as the data type, `==' to test for equality, etc. You don't need to worry about how many times you use an operand of any of these macros. The compiler never uses operands which have side effects. `REAL_VALUE_TYPE' A macro for the C data type to be used to hold a floating point value in the target machine's format. Typically this would be a `struct' containing an array of `int'. `REAL_VALUES_EQUAL (X, Y)' A macro for a C expression which compares for equality the two values, X and Y, both of type `REAL_VALUE_TYPE'. `REAL_VALUES_LESS (X, Y)' A macro for a C expression which tests whether X is less than Y, both values being of type `REAL_VALUE_TYPE' and interpreted as floating point numbers in the target machine's representation. `REAL_VALUE_LDEXP (X, SCALE)' A macro for a C expression which performs the standard library function `ldexp', but using the target machine's floating point representation. Both X and the value of the expression have type `REAL_VALUE_TYPE'. The second argument, SCALE, is an integer. `REAL_VALUE_FIX (X)' A macro whose definition is a C expression to convert the target-machine floating point value X to a signed integer. X has type `REAL_VALUE_TYPE'. `REAL_VALUE_UNSIGNED_FIX (X)' A macro whose definition is a C expression to convert the target-machine floating point value X to an unsigned integer. X has type `REAL_VALUE_TYPE'. `REAL_VALUE_RNDZINT (X)' A macro whose definition is a C expression to round the target-machine floating point value X towards zero to an integer value (but still as a floating point number). X has type `REAL_VALUE_TYPE', and so does the value. `REAL_VALUE_UNSIGNED_RNDZINT (X)' A macro whose definition is a C expression to round the target-machine floating point value X towards zero to an unsigned integer value (but still represented as a floating point number). x has type `REAL_VALUE_TYPE', and so does the value. `REAL_VALUE_ATOF (STRING, MODE)' A macro for a C expression which converts STRING, an expression of type `char *', into a floating point number in the target machine's representation for mode MODE. The value has type `REAL_VALUE_TYPE'. `REAL_INFINITY' Define this macro if infinity is a possible floating point value, and therefore division by 0 is legitimate. `REAL_VALUE_ISINF (X)' A macro for a C expression which determines whether X, a floating point value, is infinity. The value has type `int'. By default, this is defined to call `isinf'. `REAL_VALUE_ISNAN (X)' A macro for a C expression which determines whether X, a floating point value, is a "nan" (not-a-number). The value has type `int'. By default, this is defined to call `isnan'. Define the following additional macros if you want to make floating point constant folding work while cross compiling. If you don't define them, cross compilation is still possible, but constant folding will not happen for floating point values. `REAL_ARITHMETIC (OUTPUT, CODE, X, Y)' A macro for a C statement which calculates an arithmetic operation of the two floating point values X and Y, both of type `REAL_VALUE_TYPE' in the target machine's representation, to produce a result of the same type and representation which is stored in OUTPUT (which will be a variable). The operation to be performed is specified by CODE, a tree code which will always be one of the following: `PLUS_EXPR', `MINUS_EXPR', `MULT_EXPR', `RDIV_EXPR', `MAX_EXPR', `MIN_EXPR'. The expansion of this macro is responsible for checking for overflow. If overflow happens, the macro expansion should execute the statement `return 0;', which indicates the inability to perform the arithmetic operation requested. `REAL_VALUE_NEGATE (X)' A macro for a C expression which returns the negative of the floating point value X. Both X and the value of the expression have type `REAL_VALUE_TYPE' and are in the target machine's floating point representation. There is no way for this macro to report overflow, since overflow can't happen in the negation operation. `REAL_VALUE_TRUNCATE (MODE, X)' A macro for a C expression which converts the floating point value X to mode MODE. Both X and the value of the expression are in the target machine's floating point representation and have type `REAL_VALUE_TYPE'. However, the value should have an appropriate bit pattern to be output properly as a floating constant whose precision accords with mode MODE. There is no way for this macro to report overflow. `REAL_VALUE_TO_INT (LOW, HIGH, X)' A macro for a C expression which converts a floating point value X into a double-precision integer which is then stored into LOW and HIGH, two variables of type INT. `REAL_VALUE_FROM_INT (X, LOW, HIGH)' A macro for a C expression which converts a double-precision integer found in LOW and HIGH, two variables of type INT, into a floating point value which is then stored into X. File: gcc.info, Node: Misc, Prev: Cross-compilation, Up: Target Macros Miscellaneous Parameters ======================== Here are several miscellaneous parameters. `PREDICATE_CODES' Define this if you have defined special-purpose predicates in the file `MACHINE.c'. This macro is called within an initializer of an array of structures. The first field in the structure is the name of a predicate and the second field is an array of rtl codes. For each predicate, list all rtl codes that can be in expressions matched by the predicate. The list should have a trailing comma. Here is an example of two entries in the list for a typical RISC machine: #define PREDICATE_CODES \ {"gen_reg_rtx_operand", {SUBREG, REG}}, \ {"reg_or_short_cint_operand", {SUBREG, REG, CONST_INT}}, Defining this macro does not affect the generated code (however, incorrect definitions that omit an rtl code that may be matched by the predicate can cause the compiler to malfunction). Instead, it allows the table built by `genrecog' to be more compact and efficient, thus speeding up the compiler. The most important predicates to include in the list specified by this macro are thoses used in the most insn patterns. `CASE_VECTOR_MODE' An alias for a machine mode name. This is the machine mode that elements of a jump-table should have. `CASE_VECTOR_PC_RELATIVE' Define this macro if jump-tables should contain relative addresses. `CASE_DROPS_THROUGH' Define this if control falls through a `case' insn when the index value is out of range. This means the specified default-label is actually ignored by the `case' insn proper. `CASE_VALUES_THRESHOLD' Define this to be the smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches. The default is four for machines with a `casesi' instruction and five otherwise. This is best for most machines. `WORD_REGISTER_OPERATIONS' Define this macro if operations between registers with integral mode smaller than a word are always performed on the entire register. Most RISC machines have this property and most CISC machines do not. `LOAD_EXTEND_OP (MODE)' Define this macro to be a C expression indicating when insns that read memory in MODE, an integral mode narrower than a word, set the bits outside of MODE to be either the sign-extension or the zero-extension of the data read. Return `SIGN_EXTEND' for values of MODE for which the insn sign-extends, `ZERO_EXTEND' for which it zero-extends, and `NIL' for other modes. This macro is not called with MODE non-integral or with a width greater than or equal to `BITS_PER_WORD', so you may return any value in this case. Do not define this macro if it would always return `NIL'. On machines where this macro is defined, you will normally define it as the constant `SIGN_EXTEND' or `ZERO_EXTEND'. `IMPLICIT_FIX_EXPR' An alias for a tree code that should be used by default for conversion of floating point values to fixed point. Normally, `FIX_ROUND_EXPR' is used. `FIXUNS_TRUNC_LIKE_FIX_TRUNC' Define this macro if the same instructions that convert a floating point number to a signed fixed point number also convert validly to an unsigned one. `EASY_DIV_EXPR' An alias for a tree code that is the easiest kind of division to compile code for in the general case. It may be `TRUNC_DIV_EXPR', `FLOOR_DIV_EXPR', `CEIL_DIV_EXPR' or `ROUND_DIV_EXPR'. These four division operators differ in how they round the result to an integer. `EASY_DIV_EXPR' is used when it is permissible to use any of those kinds of division and the choice should be made on the basis of efficiency. `MOVE_MAX' The maximum number of bytes that a single instruction can move quickly from memory to memory. `MAX_MOVE_MAX' The maximum number of bytes that a single instruction can move quickly from memory to memory. If this is undefined, the default is `MOVE_MAX'. Otherwise, it is the constant value that is the largest value that `MOVE_MAX' can have at run-time. `SHIFT_COUNT_TRUNCATED' A C expression that is nonzero if on this machine the number of bits actually used for the count of a shift operation is equal to the number of bits needed to represent the size of the object being shifted. When this macro is non-zero, the compiler will assume that it is safe to omit a sign-extend, zero-extend, and certain bitwise `and' instructions that truncates the count of a shift operation. On machines that have instructions that act on bitfields at variable positions, which may include `bit test' instructions, a nonzero `SHIFT_COUNT_TRUNCATED' also enables deletion of truncations of the values that serve as arguments to bitfield instructions. If both types of instructions truncate the count (for shifts) and position (for bitfield operations), or if no variable-position bitfield instructions exist, you should define this macro. However, on some machines, such as the 80386 and the 680x0, truncation only applies to shift operations and not the (real or pretended) bitfield operations. Define `SHIFT_COUNT_TRUNCATED' to be zero on such machines. Instead, add patterns to the `md' file that include the implied truncation of the shift instructions. You need not define this macro if it would always have the value of zero. `TRULY_NOOP_TRUNCATION (OUTPREC, INPREC)' A C expression which is nonzero if on this machine it is safe to "convert" an integer of INPREC bits to one of OUTPREC bits (where OUTPREC is smaller than INPREC) by merely operating on it as if it had only OUTPREC bits. On many machines, this expression can be 1. When `TRULY_NOOP_TRUNCATION' returns 1 for a pair of sizes for modes for which `MODES_TIEABLE_P' is 0, suboptimal code can result. If this is the case, making `TRULY_NOOP_TRUNCATION' return 0 in such cases may improve things. `STORE_FLAG_VALUE' A C expression describing the value returned by a comparison operator with an integral mode and stored by a store-flag instruction (`sCOND') when the condition is true. This description must apply to *all* the `sCOND' patterns and all the comparison operators whose results have a `MODE_INT' mode. A value of 1 or -1 means that the instruction implementing the comparison operator returns exactly 1 or -1 when the comparison is true and 0 when the comparison is false. Otherwise, the value indicates which bits of the result are guaranteed to be 1 when the comparison is true. This value is interpreted in the mode of the comparison operation, which is given by the mode of the first operand in the `sCOND' pattern. Either the low bit or the sign bit of `STORE_FLAG_VALUE' be on. Presently, only those bits are used by the compiler. If `STORE_FLAG_VALUE' is neither 1 or -1, the compiler will generate code that depends only on the specified bits. It can also replace comparison operators with equivalent operations if they cause the required bits to be set, even if the remaining bits are undefined. For example, on a machine whose comparison operators return an `SImode' value and where `STORE_FLAG_VALUE' is defined as `0x80000000', saying that just the sign bit is relevant, the expression (ne:SI (and:SI X (const_int POWER-OF-2)) (const_int 0)) can be converted to (ashift:SI X (const_int N)) where N is the appropriate shift count to move the bit being tested into the sign bit. There is no way to describe a machine that always sets the low-order bit for a true value, but does not guarantee the value of any other bits, but we do not know of any machine that has such an instruction. If you are trying to port GNU CC to such a machine, include an instruction to perform a logical-and of the result with 1 in the pattern for the comparison operators and let us know (*note How to Report Bugs: Bug Reporting.). Often, a machine will have multiple instructions that obtain a value from a comparison (or the condition codes). Here are rules to guide the choice of value for `STORE_FLAG_VALUE', and hence the instructions to be used: * Use the shortest sequence that yields a valid definition for `STORE_FLAG_VALUE'. It is more efficient for the compiler to "normalize" the value (convert it to, e.g., 1 or 0) than for the comparison operators to do so because there may be opportunities to combine the normalization with other operations. * For equal-length sequences, use a value of 1 or -1, with -1 being slightly preferred on machines with expensive jumps and 1 preferred on other machines. * As a second choice, choose a value of `0x80000001' if instructions exist that set both the sign and low-order bits but do not define the others. * Otherwise, use a value of `0x80000000'. Many machines can produce both the value chosen for `STORE_FLAG_VALUE' and its negation in the same number of instructions. On those machines, you should also define a pattern for those cases, e.g., one matching (set A (neg:M (ne:M B C))) Some machines can also perform `and' or `plus' operations on condition code values with less instructions than the corresponding `sCOND' insn followed by `and' or `plus'. On those machines, define the appropriate patterns. Use the names `incscc' and `decscc', respectively, for the the patterns which perform `plus' or `minus' operations on condition code values. See `rs6000.md' for some examples. The GNU Superoptizer can be used to find such instruction sequences on other machines. You need not define `STORE_FLAG_VALUE' if the machine has no store-flag instructions. `FLOAT_STORE_FLAG_VALUE' A C expression that gives a non-zero floating point value that is returned when comparison operators with floating-point results are true. Define this macro on machine that have comparison operations that return floating-point values. If there are no such operations, do not define this macro. `Pmode' An alias for the machine mode for pointers. On most machines, define this to be the integer mode corresponding to the width of a hardware pointer; `SImode' on 32-bit machine or `DImode' on 64-bit machines. On some machines you must define this to be one of the partial integer modes, such as `PSImode'. The width of `Pmode' must be at least as large as the value of `POINTER_SIZE'. If it is not equal, you must define the macro `POINTERS_EXTEND_UNSIGNED' to specify how pointers are extended to `Pmode'. `FUNCTION_MODE' An alias for the machine mode used for memory references to functions being called, in `call' RTL expressions. On most machines this should be `QImode'. `INTEGRATE_THRESHOLD (DECL)' A C expression for the maximum number of instructions above which the function DECL should not be inlined. DECL is a `FUNCTION_DECL' node. The default definition of this macro is 64 plus 8 times the number of arguments that the function accepts. Some people think a larger threshold should be used on RISC machines. `SCCS_DIRECTIVE' Define this if the preprocessor should ignore `#sccs' directives and print no error message. `NO_IMPLICIT_EXTERN_C' Define this macro if the system header files support C++ as well as C. This macro inhibits the usual method of using system header files in C++, which is to pretend that the file's contents are enclosed in `extern "C" {...}'. `HANDLE_PRAGMA (STREAM)' Define this macro if you want to implement any pragmas. If defined, it should be a C statement to be executed when `#pragma' is seen. The argument STREAM is the stdio input stream from which the source text can be read. It is generally a bad idea to implement new uses of `#pragma'. The only reason to define this macro is for compatibility with other compilers that do support `#pragma' for the sake of any user programs which already use it. `VALID_MACHINE_DECL_ATTRIBUTE (DECL, ATTRIBUTES, IDENTIFIER, ARGS)' If defined, a C expression whose value is nonzero if IDENTIFIER with arguments ARGS is a valid machine specific attribute for DECL. The attributes in ATTRIBUTES have previously been assigned to DECL. `VALID_MACHINE_TYPE_ATTRIBUTE (TYPE, ATTRIBUTES, IDENTIFIER, ARGS)' If defined, a C expression whose value is nonzero if IDENTIFIER with arguments ARGS is a valid machine specific attribute for TYPE. The attributes in ATTRIBUTES have previously been assigned to TYPE. `COMP_TYPE_ATTRIBUTES (TYPE1, TYPE2)' If defined, a C expression whose value is zero if the attributes on TYPE1 and TYPE2 are incompatible, one if they are compatible, and two if they are nearly compatible (which causes a warning to be generated). `SET_DEFAULT_TYPE_ATTRIBUTES (TYPE)' If defined, a C statement that assigns default attributes to newly defined TYPE. `DOLLARS_IN_IDENTIFIERS' Define this macro to control use of the character `$' in identifier names. The value should be 0, 1, or 2. 0 means `$' is not allowed by default; 1 means it is allowed by default if `-traditional' is used; 2 means it is allowed by default provided `-ansi' is not used. 1 is the default; there is no need to define this macro in that case. `NO_DOLLAR_IN_LABEL' Define this macro if the assembler does not accept the character `$' in label names. By default constructors and destructors in G++ have `$' in the identifiers. If this macro is defined, `.' is used instead. `NO_DOT_IN_LABEL' Define this macro if the assembler does not accept the character `.' in label names. By default constructors and destructors in G++ have names that use `.'. If this macro is defined, these names are rewritten to avoid `.'. `DEFAULT_MAIN_RETURN' Define this macro if the target system expects every program's `main' function to return a standard "success" value by default (if no other value is explicitly returned). The definition should be a C statement (sans semicolon) to generate the appropriate rtl instructions. It is used only when compiling the end of `main'. `HAVE_ATEXIT' Define this if the target system supports the function `atexit' from the ANSI C standard. If this is not defined, and `INIT_SECTION_ASM_OP' is not defined, a default `exit' function will be provided to support C++. `EXIT_BODY' Define this if your `exit' function needs to do something besides calling an external function `_cleanup' before terminating with `_exit'. The `EXIT_BODY' macro is only needed if netiher `HAVE_ATEXIT' nor `INIT_SECTION_ASM_OP' are defined. `INSN_SETS_ARE_DELAYED (INSN)' Define this macro as a C expression that is nonzero if it is safe for the delay slot scheduler to place instructions in the delay slot of INSN, even if they appear to use a resource set or clobbered in INSN. INSN is always a `jump_insn' or an `insn'; GNU CC knows that every `call_insn' has this behavior. On machines where some `insn' or `jump_insn' is really a function call and hence has this behavior, you should define this macro. You need not define this macro if it would always return zero. `INSN_REFERENCES_ARE_DELAYED (INSN)' Define this macro as a C expression that is nonzero if it is safe for the delay slot scheduler to place instructions in the delay slot of INSN, even if they appear to set or clobber a resource referenced in INSN. INSN is always a `jump_insn' or an `insn'. On machines where some `insn' or `jump_insn' is really a function call and its operands are registers whose use is actually in the subroutine it calls, you should define this macro. Doing so allows the delay slot scheduler to move instructions which copy arguments into the argument registers into the delay slot of INSN. You need not define this macro if it would always return zero. `MACHINE_DEPENDENT_REORG (INSN)' In rare cases, correct code generation requires extra machine dependent processing between the second jump optimization pass and delayed branch scheduling. On those machines, define this macro as a C statement to act on the code starting at INSN. File: gcc.info, Node: Config, Next: Fragments, Prev: Target Macros, Up: Top The Configuration File ********************** The configuration file `xm-MACHINE.h' contains macro definitions that describe the machine and system on which the compiler is running, unlike the definitions in `MACHINE.h', which describe the machine for which the compiler is producing output. Most of the values in `xm-MACHINE.h' are actually the same on all machines that GNU CC runs on, so large parts of all configuration files are identical. But there are some macros that vary: `USG' Define this macro if the host system is System V. `VMS' Define this macro if the host system is VMS. `FATAL_EXIT_CODE' A C expression for the status code to be returned when the compiler exits after serious errors. `SUCCESS_EXIT_CODE' A C expression for the status code to be returned when the compiler exits without serious errors. `HOST_WORDS_BIG_ENDIAN' Defined if the host machine stores words of multi-word values in big-endian order. (GNU CC does not depend on the host byte ordering within a word.) `HOST_FLOAT_WORDS_BIG_ENDIAN' Define this macro to be 1 if the host machine stores `DFmode', `XFmode' or `TFmode' floating point numbers in memory with the word containing the sign bit at the lowest address; otherwise, define it to be zero. This macro need not be defined if the ordering is the same as for multi-word integers. `HOST_FLOAT_FORMAT' A numeric code distinguishing the floating point format for the host machine. See `TARGET_FLOAT_FORMAT' in *Note Storage Layout:: for the alternatives and default. `HOST_BITS_PER_CHAR' A C expression for the number of bits in `char' on the host machine. `HOST_BITS_PER_SHORT' A C expression for the number of bits in `short' on the host machine. `HOST_BITS_PER_INT' A C expression for the number of bits in `int' on the host machine. `HOST_BITS_PER_LONG' A C expression for the number of bits in `long' on the host machine. `ONLY_INT_FIELDS' Define this macro to indicate that the host compiler only supports `int' bit fields, rather than other integral types, including `enum', as do most C compilers. `OBSTACK_CHUNK_SIZE' A C expression for the size of ordinary obstack chunks. If you don't define this, a usually-reasonable default is used. `OBSTACK_CHUNK_ALLOC' The function used to allocate obstack chunks. If you don't define this, `xmalloc' is used. `OBSTACK_CHUNK_FREE' The function used to free obstack chunks. If you don't define this, `free' is used. `USE_C_ALLOCA' Define this macro to indicate that the compiler is running with the `alloca' implemented in C. This version of `alloca' can be found in the file `alloca.c'; to use it, you must also alter the `Makefile' variable `ALLOCA'. (This is done automatically for the systems on which we know it is needed.) If you do define this macro, you should probably do it as follows: #ifndef __GNUC__ #define USE_C_ALLOCA #else #define alloca __builtin_alloca #endif so that when the compiler is compiled with GNU CC it uses the more efficient built-in `alloca' function. `FUNCTION_CONVERSION_BUG' Define this macro to indicate that the host compiler does not properly handle converting a function value to a pointer-to-function when it is used in an expression. `HAVE_VPRINTF' Define this if the library function `vprintf' is available on your system. `MULTIBYTE_CHARS' Define this macro to enable support for multibyte characters in the input to GNU CC. This requires that the host system support the ANSI C library functions for converting multibyte characters to wide characters. `HAVE_PUTENV' Define this if the library function `putenv' is available on your system. `POSIX' Define this if your system is POSIX.1 compliant. `NO_SYS_SIGLIST' Define this if your system *does not* provide the variable `sys_siglist'. `DONT_DECLARE_SYS_SIGLIST' Define this if your system has the variable `sys_siglist', and there is already a declaration of it in the system header files. `USE_PROTOTYPES' Define this to be 1 if you know that the host compiler supports prototypes, even if it doesn't define __STDC__, or define it to be 0 if you do not want any prototypes used in compiling GNU CC. If `USE_PROTOTYPES' is not defined, it will be determined automatically whether your compiler supports prototypes by checking if `__STDC__' is defined. `NO_MD_PROTOTYPES' Define this if you wish suppression of prototypes generated from the machine description file, but to use other prototypes within GNU CC. If `USE_PROTOTYPES' is defined to be 0, or the host compiler does not support prototypes, this macro has no effect. `MD_CALL_PROTOTYPES' Define this if you wish to generate prototypes for the `gen_call' or `gen_call_value' functions generated from the machine description file. If `USE_PROTOTYPES' is defined to be 0, or the host compiler does not support prototypes, or `NO_MD_PROTOTYPES' is defined, this macro has no effect. As soon as all of the machine descriptions are modified to have the appropriate number of arguments, this macro will be removed. Some systems do provide this variable, but with a different name such as `_sys_siglist'. On these systems, you can define `sys_siglist' as a macro which expands into the name actually provided. `NO_STAB_H' Define this if your system does not have the include file `stab.h'. If `USG' is defined, `NO_STAB_H' is assumed. `PATH_SEPARATOR' Define this macro to be a C character constant representing the character used to separate components in paths. The default value is. the colon character `DIR_SEPARATOR' If your system uses some character other than slash to separate directory names within a file specification, define this macro to be a C character constant specifying that character. When GNU CC displays file names, the character you specify will be used. GNU CC will test for both slash and the character you specify when parsing filenames. `OBJECT_SUFFIX' Define this macro to be a C string representing the suffix for object files on your machine. If you do not define this macro, GNU CC will use `.o' as the suffix for object files. `EXECUTABLE_SUFFIX' Define this macro to be a C string representing the suffix for executable files on your machine. If you do not define this macro, GNU CC will use the null string as the suffix for object files. `COLLECT_EXPORT_LIST' If defined, `collect2' will scan the individual object files specified on its command line and create an export list for the linker. Define this macro for systems like AIX, where the linker discards object files that are not referenced from `main' and uses export lists. In addition, configuration files for system V define `bcopy', `bzero' and `bcmp' as aliases. Some files define `alloca' as a macro when compiled with GNU CC, in order to take advantage of the benefit of GNU CC's built-in `alloca'. File: gcc.info, Node: Fragments, Next: Index, Prev: Config, Up: Top Makefile Fragments ****************** When you configure GNU CC using the `configure' script (*note Installation::.), it will construct the file `Makefile' from the template file `Makefile.in'. When it does this, it will incorporate makefile fragment files from 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. * Menu: * Target Fragment:: Writing the `t-TARGET' file. * Host Fragment:: Writing the `x-HOST' file. File: gcc.info, Node: Target Fragment, Next: Host Fragment, Up: Fragments The Target Makefile Fragment ============================ The target makefile fragment, `t-TARGET', defines special target dependent variables and targets used in the `Makefile': `LIBGCC1' The rule to use to build `libgcc1.a'. If your target does not need to use the functions in `libgcc1.a', set this to empty. *Note Interface::. `CROSS_LIBGCC1' The rule to use to build `libgcc1.a' when building a cross compiler. If your target does not need to use the functions in `libgcc1.a', set this to empty. *Note Cross Runtime::. `LIBGCC2_CFLAGS' Compiler flags to use when compiling `libgcc2.c'. `LIB2FUNCS_EXTRA' A list of source file names to be compiled or assembled and inserted into `libgcc.a'. `CRTSTUFF_T_CFLAGS' Special flags used when compiling `crtstuff.c'. *Note Initialization::. `MULTILIB_OPTIONS' For some targets, invoking GNU CC in different ways produces objects that can not be linked together. For example, for some targets GNU CC produces both big and little endian code. For these targets, you must arrange for multiple versions of `libgcc.a' to be compiled, one for each set of incompatible options. When GNU CC invokes the linker, it arranges to link in the right version of `libgcc.a', based on the command line options used. The `MULTILIB_OPTIONS' macro lists the set of options for which special versions of `libgcc.a' must be built. Write options that are mutually incompatible side by side, separated by a slash. Write options that may be used together separated by a space. The build procedure will build all combinations of compatible options. For example, if you set `MULTILIB_OPTIONS' to `m68000/m68020 msoft-float', `Makefile' will build special versions of `libgcc.a' using the options `-m68000', `-m68020', `-msoft-float', `-m68000 -msoft-float', and `-m68020 -msoft-float'. `MULTILIB_DIRNAMES' If `MULTILIB_OPTIONS' is used, this variable specifies the directory names that should be used to hold the various libraries. Write one element in `MULTILIB_DIRNAMES' for each element in `MULTILIB_OPTIONS'. If `MULTILIB_DIRNAMES' is not used, the default value will be `MULTILIB_OPTIONS', with all slashes treated as spaces. For example, if `MULTILIB_OPTIONS' is `m68000/m68020 msoft-float', then the default value of `MULTILIB_DIRNAMES' is `m68000 m68020 msoft-float'. You may specify a different value if you desire a different set of directory names. `MULTILIB_MATCHES' Sometimes the same option may be written in two different ways. If an option is listed in `MULTILIB_OPTIONS', GNU CC needs to know about any synonyms. In that case, set `MULTILIB_MATCHES' to a list of items of the form `option=option' to describe all relevant synonyms. For example, `m68000=mc68000 m68020=mc68020'. File: gcc.info, Node: Host Fragment, Prev: Target Fragment, Up: Fragments The Host Makefile Fragment ========================== The host makefile fragment, `x-HOST', defines special host dependent variables and targets used in the `Makefile': `CC' The compiler to use when building the first stage. `CLIB' Additional host libraries to link with. `OLDCC' The compiler to use when building `libgcc1.a' for a native compilation. `OLDAR' The version of `ar' to use when building `libgcc1.a' for a native compilation. `INSTALL' The install program to use.