This is Info file gcc.info, produced by Makeinfo version 1.68 from the input file ../../../src/gcc-2.95.3/gcc/gcc.texi. INFO-DIR-SECTION Programming START-INFO-DIR-ENTRY * gcc: (gcc). The GNU Compiler Collection. END-INFO-DIR-ENTRY 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, 1996, 1997, 1998, 1999, 2000 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. 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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 those 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_SHORTEN_MODE (MIN_OFFSET, MAX_OFFSET, BODY)' Optional: return the preferred mode for an `addr_diff_vec' when the minimum and maximum offset are known. If you define this, it enables extra code in branch shortening to deal with `addr_diff_vec'. To make this work, you also have to define INSN_ALIGN and make the alignment for `addr_diff_vec' explicit. The BODY argument is provided so that the offset_unsigned and scale flags can be updated. `CASE_VECTOR_PC_RELATIVE' Define this macro to be a C expression to indicate when jump-tables should contain relative addresses. If jump-tables never contain relative addresses, then you need not define this macro. `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'. `SHORT_IMMEDIATES_SIGN_EXTEND' Define this macro if loading short immediate values into registers sign extends. `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 between memory and registers or between two memory locations. `MAX_MOVE_MAX' The maximum number of bytes that a single instruction can move quickly between memory and registers or between two memory locations. 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 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 (GETC, UNGETC, NAME)' Define this macro if you want to implement any pragmas. If defined, it is a C expression whose value is 1 if the pragma was handled by the macro, zero otherwise. The argument GETC is a function of type `int (*)(void)' which will return the next character in the input stream, or EOF if no characters are left. The argument UNGETC is a function of type `void (*)(int)' which will push a character back into the input stream. The argument NAME is the word following #pragma in the input stream. The input stream pointer will be pointing just beyond the end of this word. The input stream should be left undistrubed if the expression returns zero, otherwise it should be pointing at the next character after the end of the pragma. Any characters remaining on the line will be ignored. 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. If the pragma can be implemented by atttributes then the macro `INSERT_ATTRIBUTES' might be a useful one to define as well. Note: older versions of this macro only had two arguments: STREAM and TOKEN. The macro was changed in order to allow it to work when gcc is built both with and without a cpp library. `HANDLE_SYSV_PRAGMA' Define this macro (to a value of 1) if you want the System V style pragmas `#pragma pack()' and `#pragma weak [=]' to be supported by gcc. The pack pragma specifies the maximum alignment (in bytes) of fields within a structure, in much the same way as the `__aligned__' and `__packed__' `__attribute__'s do. A pack value of zero resets the behaviour to the default. The weak pragma only works if `SUPPORTS_WEAK' and `ASM_WEAKEN_LABEL' are defined. If enabled it allows the creation of specifically named weak labels, optionally with a value. `HANDLE_PRAGMA_PACK_PUSH_POP' Define this macro (to a value of 1) if you want to support the Win32 style pragmas `#pragma pack(push,)' and `#pragma pack(pop)'. The pack(push,) pragma specifies the maximum alignment (in bytes) of fields within a structure, in much the same way as the `__aligned__' and `__packed__' `__attribute__'s do. A pack value of zero resets the behaviour to the default. Successive invocations of this pragma cause the previous values to be stacked, so that invocations of `#pragma pack(pop)' will return to the previous value. `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. `MERGE_MACHINE_TYPE_ATTRIBUTES (TYPE1, TYPE2)' Define this macro if the merging of type attributes needs special handling. If defined, the result is a list of the combined TYPE_ATTRIBUTES of TYPE1 and TYPE2. It is assumed that comptypes has already been called and returned 1. `MERGE_MACHINE_DECL_ATTRIBUTES (OLDDECL, NEWDECL)' Define this macro if the merging of decl attributes needs special handling. If defined, the result is a list of the combined DECL_MACHINE_ATTRIBUTES of OLDDECL and NEWDECL. NEWDECL is a duplicate declaration of OLDDECL. Examples of when this is needed are when one attribute overrides another, or when an attribute is nullified by a subsequent definition. `INSERT_ATTRIBUTES (NODE, ATTR_PTR, PREFIX_PTR)' Define this macro if you want to be able to add attributes to a decl when it is being created. This is normally useful for backends which wish to implement a pragma by using the attributes which correspond to the pragma's effect. The NODE argument is the decl which is being created. The ATTR_PTR argument is a pointer to the attribute list for this decl. The PREFIX_PTR is a pointer to the list of attributes that have appeared after the specifiers and modifiers of the declaration, but before the declaration proper. `SET_DEFAULT_DECL_ATTRIBUTES (DECL, ATTRIBUTES)' If defined, a C statement that assigns default attributes to newly defined DECL. `DOLLARS_IN_IDENTIFIERS' Define this macro to control use of the character `$' in identifier names. 0 means `$' is not allowed by default; 1 means it is allowed. 1 is the default; there is no need to define this macro in that case. This macro controls the compiler proper; it does not affect the preprocessor. `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 neither `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. `MULTIPLE_SYMBOL_SPACES' Define this macro if in some cases global symbols from one translation unit may not be bound to undefined symbols in another translation unit without user intervention. For instance, under Microsoft Windows symbols must be explicitly imported from shared libraries (DLLs). `ISSUE_RATE' A C expression that returns how many instructions can be issued at the same time if the machine is a superscalar machine. This is only used by the `Haifa' scheduler, and not the traditional scheduler. `MD_SCHED_INIT (FILE, VERBOSE)' A C statement which is executed by the `Haifa' scheduler at the beginning of each block of instructions that are to be scheduled. FILE is either a null pointer, or a stdio stream to write any debug output to. VERBOSE is the verbose level provided by `-fsched-verbose-'N. `MD_SCHED_REORDER (FILE, VERBOSE, READY, N_READY)' A C statement which is executed by the `Haifa' scheduler after it has scheduled the ready list to allow the machine description to reorder it (for example to combine two small instructions together on `VLIW' machines). FILE is either a null pointer, or a stdio stream to write any debug output to. VERBOSE is the verbose level provided by `-fsched-verbose-'N. READY is a pointer to the ready list of instructions that are ready to be scheduled. N_READY is the number of elements in the ready list. The scheduler reads the ready list in reverse order, starting with READY[N_READY-1] and going to READY[0]. `MD_SCHED_VARIABLE_ISSUE (FILE, VERBOSE, INSN, MORE)' A C statement which is executed by the `Haifa' scheduler after it has scheduled an insn from the ready list. FILE is either a null pointer, or a stdio stream to write any debug output to. VERBOSE is the verbose level provided by `-fsched-verbose-'N. INSN is the instruction that was scheduled. MORE is the number of instructions that can be issued in the current cycle. The `MD_SCHED_VARIABLE_ISSUE' macro is responsible for updating the value of MORE (typically by MORE-). `MAX_INTEGER_COMPUTATION_MODE' Define this to the largest integer machine mode which can be used for operations other than load, store and copy operations. You need only define this macro if the target holds values larger than `word_mode' in general purpose registers. Most targets should not define this macro. `MATH_LIBRARY' Define this macro as a C string constant for the linker argument to link in the system math library, or `""' if the target does not have a separate math library. You need only define this macro if the default of `"-lm"' is wrong.  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 GCC 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. (GCC 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 GCC 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. `MULTIBYTE_CHARS' Define this macro to enable support for multibyte characters in the input to GCC. This requires that the host system support the ANSI C library functions for converting multibyte characters to wide characters. `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'. 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. Autoconf normally defines `SYS_SIGLIST_DECLARED' when it finds a declaration of `sys_siglist' in the system header files. However, when you define `sys_siglist' to a different name autoconf will not automatically define `SYS_SIGLIST_DECLARED'. Therefore, if you define `sys_siglist', you should also define `SYS_SIGLIST_DECLARED'. `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 GCC. 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 GCC. 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. `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 GCC displays file names, the character you specify will be used. GCC 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, GCC 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, GCC 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 GCC, in order to take advantage of the benefit of GCC's built-in `alloca'.  File: gcc.info, Node: Fragments, Next: Funding, Prev: Config, Up: Top Makefile Fragments ****************** When you configure GCC 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::. `CRTSTUFF_T_CFLAGS_S' Special flags used when compiling `crtstuff.c' for shared linking. Used if you use `crtbeginS.o' and `crtendS.o' in `EXTRA-PARTS'. *Note Initialization::. `MULTILIB_OPTIONS' For some targets, invoking GCC in different ways produces objects that can not be linked together. For example, for some targets GCC 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 GCC 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 following sets of 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 set to `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', GCC 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'. `MULTILIB_EXCEPTIONS' Sometimes when there are multiple sets of `MULTILIB_OPTIONS' being specified, there are combinations that should not be built. In that case, set `MULTILIB_EXCEPTIONS' to be all of the switch exceptions in shell case syntax that should not be built. For example, in the PowerPC embedded ABI support, it was not desirable to build libraries that compiled with the `-mcall-aixdesc' option and either of the `-mcall-aixdesc' or `-mlittle' options at the same time, and therefore `MULTILIB_EXCEPTIONS' is set to `*mrelocatable/*mcall-aixdesc* *mlittle/*mcall-aixdesc*'. `MULTILIB_EXTRA_OPTS' Sometimes it is desirable that when building multiple versions of `libgcc.a' certain options should always be passed on to the compiler. In that case, set `MULTILIB_EXTRA_OPTS' to be the list of options to be used for all builds.  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.  File: gcc.info, Node: Funding, Next: GNU/Linux, Prev: Fragments, Up: Top Funding Free Software ********************* If you want to have more free software a few years from now, it makes sense for you to help encourage people to contribute funds for its development. The most effective approach known is to encourage commercial redistributors to donate. Users of free software systems can boost the pace of development by encouraging for-a-fee distributors to donate part of their selling price to free software developers--the Free Software Foundation, and others. The way to convince distributors to do this is to demand it and expect it from them. So when you compare distributors, judge them partly by how much they give to free software development. Show distributors they must compete to be the one who gives the most. To make this approach work, you must insist on numbers that you can compare, such as, "We will donate ten dollars to the Frobnitz project for each disk sold." Don't be satisfied with a vague promise, such as "A portion of the profits are donated," since it doesn't give a basis for comparison. Even a precise fraction "of the profits from this disk" is not very meaningful, since creative accounting and unrelated business decisions can greatly alter what fraction of the sales price counts as profit. If the price you pay is $50, ten percent of the profit is probably less than a dollar; it might be a few cents, or nothing at all. Some redistributors do development work themselves. This is useful too; but to keep everyone honest, you need to inquire how much they do, and what kind. Some kinds of development make much more long-term difference than others. For example, maintaining a separate version of a program contributes very little; maintaining the standard version of a program for the whole community contributes much. Easy new ports contribute little, since someone else would surely do them; difficult ports such as adding a new CPU to the GNU Compiler Collection contribute more; major new features or packages contribute the most. By establishing the idea that supporting further development is "the proper thing to do" when distributing free software for a fee, we can assure a steady flow of resources into making more free software. Copyright (C) 1994 Free Software Foundation, Inc. Verbatim copying and redistribution of this section is permitted without royalty; alteration is not permitted.  File: gcc.info, Node: GNU/Linux, Next: Copying, Prev: Funding, Up: Top Linux and the GNU Project ************************* Many computer users run a modified version of the GNU system every day, without realizing it. Through a peculiar turn of events, the version of GNU which is widely used today is more often known as "Linux", and many users are not aware of the extent of its connection with the GNU Project. There really is a Linux; it is a kernel, and these people are using it. But you can't use a kernel by itself; a kernel is useful only as part of a whole system. The system in which Linux is typically used is a modified variant of the GNU system--in other words, a Linux-based GNU system. Many users are not fully aware of the distinction between the kernel, which is Linux, and the whole system, which they also call "Linux". The ambiguous use of the name doesn't promote understanding. Programmers generally know that Linux is a kernel. But since they have generally heard the whole system called "Linux" as well, they often envisage a history which fits that name. For example, many believe that once Linus Torvalds finished writing the kernel, his friends looked around for other free software, and for no particular reason most everything necessary to make a Unix-like system was already available. What they found was no accident--it was the GNU system. The available free software added up to a complete system because the GNU Project had been working since 1984 to make one. The GNU Manifesto had set forth the goal of developing a free Unix-like system, called GNU. By the time Linux was written, the system was almost finished. Most free software projects have the goal of developing a particular program for a particular job. For example, Linus Torvalds set out to write a Unix-like kernel (Linux); Donald Knuth set out to write a text formatter (TeX); Bob Scheifler set out to develop a window system (X Windows). It's natural to measure the contribution of this kind of project by specific programs that came from the project. If we tried to measure the GNU Project's contribution in this way, what would we conclude? One CD-ROM vendor found that in their "Linux distribution", GNU software was the largest single contingent, around 28% of the total source code, and this included some of the essential major components without which there could be no system. Linux itself was about 3%. So if you were going to pick a name for the system based on who wrote the programs in the system, the most appropriate single choice would be "GNU". But we don't think that is the right way to consider the question. The GNU Project was not, is not, a project to develop specific software packages. It was not a project to develop a C compiler, although we did. It was not a project to develop a text editor, although we developed one. The GNU Project's aim was to develop *a complete free Unix-like system*. Many people have made major contributions to the free software in the system, and they all deserve credit. But the reason it is *a system*--and not just a collection of useful programs--is because the GNU Project set out to make it one. We wrote the programs that were needed to make a *complete* free system. We wrote essential but unexciting major components, such as the assembler and linker, because you can't have a system without them. A complete system needs more than just programming tools, so we wrote other components as well, such as the Bourne Again SHell, the PostScript interpreter Ghostscript, and the GNU C library. By the early 90s we had put together the whole system aside from the kernel (and we were also working on a kernel, the GNU Hurd, which runs on top of Mach). Developing this kernel has been a lot harder than we expected, and we are still working on finishing it. Fortunately, you don't have to wait for it, because Linux is working now. When Linus Torvalds wrote Linux, he filled the last major gap. People could then put Linux together with the GNU system to make a complete free system: a Linux-based GNU system (or GNU/Linux system, for short). Putting them together sounds simple, but it was not a trivial job. The GNU C library (called glibc for short) needed substantial changes. Integrating a complete system as a distribution that would work "out of the box" was a big job, too. It required addressing the issue of how to install and boot the system--a problem we had not tackled, because we hadn't yet reached that point. The people who developed the various system distributions made a substantial contribution. The GNU Project supports GNU/Linux systems as well as *the* GNU system--even with funds. We funded the rewriting of the Linux-related extensions to the GNU C library, so that now they are well integrated, and the newest GNU/Linux systems use the current library release with no changes. We also funded an early stage of the development of Debian GNU/Linux. We use Linux-based GNU systems today for most of our work, and we hope you use them too. But please don't confuse the public by using the name "Linux" ambiguously. Linux is the kernel, one of the essential major components of the system. The system as a whole is more or less the GNU system.