GCC(1) GNU Tools GCC(1)
NAME
gcc, g++ - GNU project C and C++ Compiler (egcs-1.1.1)
SYNOPSIS
gcc [ option | filename ]... g++ [ option | filename ]...
WARNING
The information in this man page is an extract from the full documentation of the GNU C compiler, and is limited to the meaning of the options. This man page is not kept up to date except when volun- teers want to maintain it. If you find a discrepancy between the man page and the software, please check the Info file, which is the authoritative documentation. If we find that the things in this man page that are out of date cause significant confusion or complaints, we will stop distributing the man page. The alternative, updating the man page when we update the Info file, is impossible because the rest of the work of maintaining GNU CC leaves us no time for that. The GNU project regards man pages as obsolete and should not let them take time away from other things. For complete and current documentation, refer to the Info file `gcc' or the manual Using and Porting GNU CC (for version 2.0). Both are made from the Texinfo source file gcc.texinfo.
DESCRIPTION
The C and C++ compilers are integrated. Both process input files through one or more of four stages: prepro- cessing, compilation, assembly, and linking. Source file- name suffixes identify the source language, but which name you use for the compiler governs default assumptions: gcc assumes preprocessed (.i) files are C and assumes C style linking. g++ assumes preprocessed (.i) files are C++ and assumes C++ style linking. Suffixes of source file names indicate the language and kind of processing to be done: .c C source; preprocess, compile, assemble .C C++ source; preprocess, compile, assemble .cc C++ source; preprocess, compile, assemble .cxx C++ source; preprocess, compile, assemble .m Objective-C source; preprocess, compile, assemble .i preprocessed C; compile, assemble .ii preprocessed C++; compile, assemble GNU Tools 1 GCC(1) GNU Tools GCC(1) .s Assembler source; assemble .S Assembler source; preprocess, assemble .h Preprocessor file; not usually named on command line Files with other suffixes are passed to the linker. Com- mon cases include: .o Object file .a Archive file Linking is always the last stage unless you use one of the -c, -S, or -E options to avoid it (or unless compilation errors stop the whole process). For the link stage, all .o files corresponding to source files, -l libraries, unrecognized filenames (including named .o object files and .a archives) are passed to the linker in command-line order.
OPTIONS
Options must be separate: `-dr' is quite different from `-d -r '. Most `-f' and `-W' options have two contrary forms: -fname and -fno-name (or -Wname and -Wno-name). Only the non- default forms are shown here. Here is a summary of all the options, grouped by type. Explanations are in the following sections. Overall Options -c -S -E -o file -pipe -v -x language Language Options -ansi -fall-virtual -fcond-mismatch -fdollars-in-identifiers -fenum-int-equiv -fexternal-templates -fno-asm -fno-builtin -fhosted -fno-hosted -ffreestanding -fno-freestanding -fno-strict-prototype -fsigned-bitfields -fsigned-char -fthis-is-variable -funsigned-bitfields -funsigned-char -fwritable-strings -traditional -traditional-cpp -trigraphs Warning Options -fsyntax-only -pedantic -pedantic-errors -w -W -Wall -Waggregate-return -Wcast-align -Wcast-qual -Wchar-subscript -Wcomment -Wconversion -Wenum-clash -Werror -Wformat -Wid-clash-len -Wimplicit -Wimplicit-int -Wimplicit-function-declaration -Winline -Wlong-long -Wmain -Wmissing-prototypes -Wmissing-declarations -Wnested-externs -Wno-import -Wparentheses -Wpointer-arith -Wredundant-decls -Wreturn-type -Wshadow -Wstrict-prototypes -Wswitch GNU Tools 2 GCC(1) GNU Tools GCC(1) -Wtemplate-debugging -Wtraditional -Wtrigraphs -Wuninitialized -Wunused -Wwrite-strings Debugging Options -a -dletters -fpretend-float -g -glevel -gcoff -gxcoff -gxcoff+ -gdwarf -gdwarf+ -gstabs -gstabs+ -ggdb -p -pg -save-temps -print-file-name=library -print-libgcc-file-name -print-prog-name=program Optimization Options -fcaller-saves -fcse-follow-jumps -fcse-skip-blocks -fdelayed-branch -felide-constructors -fexpensive-optimizations -ffast-math -ffloat-store -fforce-addr -fforce-mem -finline-functions -fkeep-inline-functions -fmemoize-lookups -fno-default-inline -fno-defer-pop -fno-function-cse -fno-inline -fno-peephole -fomit-frame-pointer -frerun-cse-after-loop -fschedule-insns -fschedule-insns2 -fstrength-reduce -fthread-jumps -funroll-all-loops -funroll-loops -O -O2 -O3 Preprocessor Options -Aassertion -C -dD -dM -dN -Dmacro[=defn] -E -H -idirafter dir -include file -imacros file -iprefix file -iwithprefix dir -M -MD -MM -MMD -nostdinc -P -Umacro -undef Assembler Option -Wa,option Linker Options -llibrary -nostartfiles -nostdlib -static -shared -symbolic -Xlinker option -Wl,option -u symbol Directory Options -Bprefix -Idir -I- -Ldir Target Options -b machine -V version Configuration Dependent Options M680x0 Options -m68000 -m68020 -m68020-40 -m68030 -m68040 -m68881 -mbitfield -mc68000 -mc68020 -mfpa -mnobitfield -mrtd -mshort -msoft-float VAX Options -mg -mgnu -munix SPARC Options -mepilogue -mfpu -mhard-float -mno-fpu -mno-epilogue -msoft-float -msparclite -mv8 -msupersparc -mcypress GNU Tools 3 GCC(1) GNU Tools GCC(1) Convex Options -margcount -mc1 -mc2 -mnoargcount AMD29K Options -m29000 -m29050 -mbw -mdw -mkernel-registers -mlarge -mnbw -mnodw -msmall -mstack-check -muser-registers M88K Options -m88000 -m88100 -m88110 -mbig-pic -mcheck-zero-division -mhandle-large-shift -midentify-revision -mno-check-zero-division -mno-ocs-debug-info -mno-ocs-frame-position -mno-optimize-arg-area -mno-serialize-volatile -mno-underscores -mocs-debug-info -mocs-frame-position -moptimize-arg-area -mserialize-volatile -mshort-data-num -msvr3 -msvr4 -mtrap-large-shift -muse-div-instruction -mversion-03.00 -mwarn-passed-structs RS6000 Options -mfp-in-toc -mno-fop-in-toc RT Options -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs -mfull-fp-blocks -mhc-struct-return -min-line-mul -mminimum-fp-blocks -mnohc-struct-return MIPS Options -mcpu=cpu type -mips2 -mips3 -mint64 -mlong64 -mlonglong128 -mmips-as -mgas -mrnames -mno-rnames -mgpopt -mno-gpopt -mstats -mno-stats -mmemcpy -mno-memcpy -mno-mips-tfile -mmips-tfile -msoft-float -mhard-float -mabicalls -mno-abicalls -mhalf-pic -mno-half-pic -G num -nocpp i386 Options -m486 -mno-486 -msoft-float -mno-fp-ret-in-387 HPPA Options -mpa-risc-1-0 -mpa-risc-1-1 -mkernel -mshared-libs -mno-shared-libs -mlong-calls -mdisable-fpregs -mdisable-indexing -mtrailing-colon i960 Options -mcpu-type -mnumerics -msoft-float -mleaf-procedures -mno-leaf-procedures -mtail-call -mno-tail-call -mcomplex-addr -mno-complex-addr -mcode-align -mno-code-align -mic-compat -mic2.0-compat -mic3.0-compat -masm-compat -mintel-asm -mstrict-align -mno-strict-align -mold-align -mno-old-align DEC Alpha Options GNU Tools 4 GCC(1) GNU Tools GCC(1) -mfp-regs -mno-fp-regs -mno-soft-float -msoft-float System V Options -G -Qy -Qn -YP,paths -Ym,dir Code Generation Options -fcall-saved-reg -fcall-used-reg -ffixed-reg -finhibit-size-directive -fnonnull-objects -fno-common -fno-ident -fno-gnu-linker -fpcc-struct-return -fpic -fPIC -freg-struct-return -fshared-data -fshort-enums -fshort-double -fvolatile -fvolatile-global -fverbose-asm
OVERALL OPTIONS
-x language Specify explicitly the language for the following input files (rather than choosing a default based on the file name suffix) . This option applies to all following input files until the next `-x' op- tion. Possible values of language are `c', `objective-c', `c-header', `c++', `cpp-output', `assembler', and `assembler-with-cpp'. -x none Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if `-x' has not been used at all). If you want only some of the four stages (preprocess, com- pile, assemble, link), you can use `-x' (or filename suf- fixes) to tell gcc where to start, and one of the options `-c', `-S', or `-E' to say where gcc is to stop. Note that some combinations (for example, `-x cpp-output -E') instruct gcc to do nothing at all. -c Compile or assemble the source files, but do not link. The compiler output is an object file corre- sponding to each source file. By default, GCC makes the object file name for a source file by replacing the suffix `.c', `.i', `.s', etc., with `.o'. Use -o to select another name. GCC ignores any unrecognized input files (those that do not require compilation or assembly) with the -c option. -S Stop after the stage of compilation proper; do not assemble. The output is an assembler code file for each non-assembler input file specified. By default, GCC makes the assembler file name for a GNU Tools 5 GCC(1) GNU Tools GCC(1) source file by replacing the suffix `.c', `.i', etc., with `.s'. Use -o to select another name. GCC ignores any input files that don't require com- pilation. -E Stop after the preprocessing stage; do not run the compiler proper. The output is preprocessed source code, which is sent to the standard output. GCC ignores input files which don't require prepro- cessing. -o file Place output in file file. This applies regardless to whatever sort of output GCC is producing, whether it be an executable file, an object file, an assembler file or preprocessed C code. Since only one output file can be specified, it does not make sense to use `-o' when compiling more than one input file, unless you are producing an executable file as output. If you do not specify `-o', the default is to put an executable file in `a.out', the object file for `source.suffix' in `source.o', its assembler file in `source.s', and all preprocessed C source on standard output. -v Print (on standard error output) the commands exe- cuted to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the compiler proper. -pipe Use pipes rather than temporary files for communi- cation between the various stages of compilation. This fails to work on some systems where the assem- bler cannot read from a pipe; but the GNU assembler has no trouble.
LANGUAGE OPTIONS
The following options control the dialect of C that the compiler accepts: -ansi Support all ANSI standard C programs. This turns off certain features of GNU C that are incompatible with ANSI C, such as the asm, inline and typeof keywords, and predefined macros such as unix and vax that identify the type of system you are using. It also enables the undesirable and rarely used ANSI trigraph feature, and disallows GNU Tools 6 GCC(1) GNU Tools GCC(1) `$' as part of identifiers. The alternative keywords __asm__, __extension__, __inline__ and __typeof__ continue to work despite `-ansi'. You would not want to use them in an ANSI C program, of course, but it is useful to put them in header files that might be included in compila- tions done with `-ansi'. Alternative predefined macros such as __unix__ and __vax__ are also avail- able, with or without `-ansi'. The `-ansi' option does not cause non-ANSI programs to be rejected gratuitously. For that, `-pedantic' is required in addition to `-ansi'. The preprocessor predefines a macro __STRICT_ANSI__ when you use the `-ansi' option. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the ANSI standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. -fno-asm Do not recognize asm, inline or typeof as a key- word. These words may then be used as identifiers. You can use __asm__, __inline__ and __typeof__ in- stead. `-ansi' implies `-fno-asm'. -fno-builtin Don't recognize built-in functions that do not be- gin with two leading underscores. Currently, the functions affected include _exit, abort, abs, allo- ca, cos, exit, fabs, labs, memcmp, memcpy, sin, sqrt, strcmp, strcpy, and strlen. The `-ansi' option prevents alloca and _exit from being builtin functions. -fhosted Compile for a hosted environment; this implies the `-fbuiltin' option, and implies that suspicious declarations of main should be warned about. -ffreestanding Compile for a freestanding environment; this im- plies the `-fno-builtin' option, and implies that main has no special requirements. -fno-strict-prototype Treat a function declaration with no arguments, such as `int foo ();', as C would treat it--as say- ing nothing about the number of arguments or their types (C++ only). Normally, such a declaration in GNU Tools 7 GCC(1) GNU Tools GCC(1) C++ means that the function foo takes no arguments. -trigraphs Support ANSI C trigraphs. The `-ansi' option im- plies `-trigraphs'. -traditional Attempt to support some aspects of traditional C compilers. For details, see the GNU C Manual; the duplicate list here has been deleted so that we won't get complaints when it is out of date. But one note about C++ programs only (not C). `-traditional' has one additional effect for C++: assignment to this is permitted. This is the same as the effect of `-fthis-is-variable'. -traditional-cpp Attempt to support some aspects of traditional C preprocessors. This includes the items that specifically mention the preprocessor above, but none of the other effects of `-traditional'. -fdollars-in-identifiers Permit the use of `$' in identifiers (C++ only). You can also use `-fno-dollars-in-identifiers' to explicitly prohibit use of `$'. (GNU C++ allows `$' by default on some target systems but not oth- ers.) -fenum-int-equiv Permit implicit conversion of int to enumeration types (C++ only). Normally GNU C++ allows conver- sion of enum to int, but not the other way around. -fexternal-templates Produce smaller code for template declarations, by generating only a single copy of each template function where it is defined (C++ only). To use this option successfully, you must also mark all files that use templates with either `#pragma implementation' (the definition) or `#pragma interface' (declarations). When your code is compiled with `-fexternal-templates', all template instantiations are external. You must arrange for all necessary instantiations to appear in the implementation file; you can do this with a typedef that refer- ences each instantiation needed. Conversely, when you compile using the default option `-fno-external-templates', all template instantia- tions are explicitly internal. GNU Tools 8 GCC(1) GNU Tools GCC(1) -fall-virtual Treat all possible member functions as virtual, im- plicitly. All member functions (except for con- structor functions and new or delete member opera- tors) are treated as virtual functions of the class where they appear. This does not mean that all calls to these member functions will be made through the internal table of virtual functions. Under some circumstances, the compiler can determine that a call to a given virtual function can be made directly; in these cases the calls are direct in any case. -fcond-mismatch Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. -fthis-is-variable Permit assignment to this (C++ only). The incorpo- ration of user-defined free store management into C++ has made assignment to `this' an anachronism. Therefore, by default it is invalid to assign to this within a class member function. However, for backwards compatibility, you can make it valid with `-fthis-is-variable'. -funsigned-char Let the type char be unsigned, like unsigned char. Each kind of machine has a default for what char should be. It is either like unsigned char by de- fault or like signed char by default. Ideally, a portable program should always use signed char or unsigned char when it depends on the signedness of an object. But many programs have been written to use plain char and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default. The type char is always a distinct type from each of signed char and unsigned char, even though its behavior is always just like one of those two. -fsigned-char Let the type char be signed, like signed char. Note that this is equivalent to `-fno-unsigned-char', which is the negative form of `-funsigned-char'. Likewise, `-fno-signed-char' is GNU Tools 9 GCC(1) GNU Tools GCC(1) equivalent to `-funsigned-char'. -fsigned-bitfields -funsigned-bitfields -fno-signed-bitfields -fno-unsigned-bitfields These options control whether a bitfield is signed or unsigned, when declared with no explicit `signed' or `unsigned' qualifier. By default, such a bitfield is signed, because this is consistent: the basic integer types such as int are signed types. However, when you specify `-traditional', bitfields are all unsigned no matter what. -fwritable-strings Store string constants in the writable data segment and don't uniquize them. This is for compatibility with old programs which assume they can write into string constants. `-traditional' also has this ef- fect. Writing into string constants is a very bad idea; "constants" should be constant.
PREPROCESSOR OPTIONS
These options control the C preprocessor, which is run on each C source file before actual compilation. If you use the `-E' option, GCC does nothing except pre- processing. Some of these options make sense only togeth- er with `-E' because they cause the preprocessor output to be unsuitable for actual compilation. -include file Process file as input before processing the regular input file. In effect, the contents of file are compiled first. Any `-D' and `-U' options on the command line are always processed before `-include file', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are writ- ten. -imacros file Process file as input, discarding the resulting output, before processing the regular input file. Because the output generated from file is discard- ed, the only effect of `-imacros file' is to make the macros defined in file available for use in the GNU Tools 10 GCC(1) GNU Tools GCC(1) main input. The preprocessor evaluates any `-D' and `-U' options on the command line before pro- cessing `-imacrosfile', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are written. -idirafter dir Add the directory dir to the second include path. The directories on the second include path are searched when a header file is not found in any of the directories in the main include path (the one that `-I' adds to). -iprefix prefix Specify prefix as the prefix for subsequent `-iwithprefix' options. -iwithprefix dir Add a directory to the second include path. The directory's name is made by concatenating prefix and dir, where prefix was specified previously with `-iprefix'. -nostdinc Do not search the standard system directories for header files. Only the directories you have speci- fied with `-I' options (and the current directory, if appropriate) are searched. By using both `-nostdinc' and `-I-', you can limit the include-file search file to only those directo- ries you specify explicitly. -nostdinc++ Do not search for header files in the C++-specific standard directories, but do still search the other standard directories. (This option is used when building `libg++'.) -undef Do not predefine any nonstandard macros. (Includ- ing architecture flags). -E Run only the C preprocessor. Preprocess all the C source files specified and output the results to standard output or to the specified output file. -C Tell the preprocessor not to discard comments. Used with the `-E' option. -P Tell the preprocessor not to generate `#line' com- mands. Used with the `-E' option. GNU Tools 11 GCC(1) GNU Tools GCC(1) -M [ -MG ] Tell the preprocessor to output a rule suitable for make describing the dependencies of each object file. For each source file, the preprocessor out- puts one make-rule whose target is the object file name for that source file and whose dependencies are all the files `#include'd in it. This rule may be a single line or may be continued with `\'-new- line if it is long. The list of rules is printed on standard output instead of the preprocessed C program. `-M' implies `-E'. `-MG' says to treat missing header files as gener- ated files and assume they live in the same direc- tory as the source file. It must be specified in addition to `-M'. -MM [ -MG ] Like `-M' but the output mentions only the user header files included with `#include file"'. Sys- tem header files included with `#include <file>' are omitted. -MD Like `-M' but the dependency information is written to files with names made by replacing `.o' with `.d' at the end of the output file names. This is in addition to compiling the file as specified--`-MD' does not inhibit ordinary compila- tion the way `-M' does. The Mach utility `md' can be used to merge the `.d' files into a single dependency file suitable for using with the `make' command. -MMD Like `-MD' except mention only user header files, not system header files. -H Print the name of each header file used, in addi- tion to other normal activities. -Aquestion(answer) Assert the answer answer for question, in case it is tested with a preprocessor conditional such as `#if #question(answer)'. `-A-' disables the stan- dard assertions that normally describe the target machine. -Aquestion (answer) Assert the answer answer for question, in case it is tested with a preprocessor conditional such as `#if #question(answer)'. `-A-' disables the standard assertions that normally describe the GNU Tools 12 GCC(1) GNU Tools GCC(1) target machine. -Dmacro Define macro macro with the string `1' as its defi- nition. -Dmacro=defn Define macro macro as defn. All instances of `-D' on the command line are processed before any `-U' options. -Umacro Undefine macro macro. `-U' options are evaluated after all `-D' options, but before any `-include' and `-imacros' options. -dM Tell the preprocessor to output only a list of the macro definitions that are in effect at the end of preprocessing. Used with the `-E' option. -dD Tell the preprocessor to pass all macro definitions into the output, in their proper sequence in the rest of the output. -dN Like `-dD' except that the macro arguments and con- tents are omitted. Only `#define name' is included in the output.
ASSEMBLER OPTION
-Wa,option Pass option as an option to the assembler. If op- tion contains commas, it is split into multiple op- tions at the commas.
LINKER OPTIONS
These options come into play when the compiler links ob- ject files into an executable output file. They are mean- ingless if the compiler is not doing a link step. object-file-name A file name that does not end in a special recog- nized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file con- tents.) If GCC 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. GNU Tools 13 GCC(1) GNU Tools GCC(1) 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 scan- ning 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. -lobjc You need this special case of the -l option in or- der to link an Objective C program. -nostartfiles Do not use the standard system startup files when linking. The standard libraries are used normally. -nostdlib Don't use the standard system libraries and startup files when linking. Only the files you specify will be passed to the linker. This option is also passed to the linker, which may change the library search path. -static On systems that support dynamic linking, this pre- vents linking with the shared libraries. On other systems, this option has no effect. -shared Produce a shared object which can then be linked with other objects to form an executable. Only a few systems support this option. -symbolic Bind references to global symbols when building a shared object. Warn about any unresolved refer- ences (unless overridden by the link editor option `-Xlinker -z -Xlinker defs'). Only a few systems support this option. -Xlinker option Pass option as an option to the linker. You can use this to supply system-specific linker options which GNU CC does not know how to recognize. If you want to pass an option that takes an argu- ment, you must use `-Xlinker' twice, once for the GNU Tools 14 GCC(1) GNU Tools GCC(1) option and once for the argument. For example, to pass `-assert definitions', you must write `-Xlink- er -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
These options specify directories to search for header files, for libraries and for parts of the compiler: -Idir Append directory dir to the list of directories searched for include files. -I- Any directories you specify with `-I' options be- fore 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. (Ordinari- ly 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 `#in- clude "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 sys- tem 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 executa- GNU Tools 15 GCC(1) GNU Tools GCC(1) bles, libraries and data files of the compiler it- self. The compiler driver program runs one or more of the subprograms `cpp', `cc1' (or, for C++, `cc1plus'), `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 two standard prefixes, which are `/usr/lib/gcc/' and `/usr/local/lib/gcc-lib/'. If neither of those results in a file name that is found, the compiler driver searches for the unmodi- fied program name, using the directories specified in your `PATH' environment variable. The run-time support file `libgcc.a' is also searched for using the `-B' prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means. Most of the time, on most machines, `libgcc.a' is not actually necessary. 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
Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there may have been an error. These options control the amount and kinds of warnings produced by GNU 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 GNU Tools 16 GCC(1) GNU Tools GCC(1) extensions. Valid ANSI standard C programs should compile prop- erly with or without this option (though a rare few will require `-ansi'). However, without this op- tion, certain GNU extensions and traditional C fea- tures 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 alternative keywords whose names begin and end with `__'. Pedantic warnings are also disabled in the expression that follows __extension__. How- ever, only system header files should use these es- cape 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: o 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. o A function can return either with or without a val- ue. (Falling off the end of the function body is considered returning without a value.) For exam- ple, this function would evoke such a warning: foo (a) { if (a > 0) return a; } Spurious warnings can occur because GNU CC does not realize that certain functions (including abort and longjmp) will never return. o An expression-statement or the left-hand side of a comma expression contains no side effects. To sup- press the warning, cast the unused expression to GNU Tools 17 GCC(1) GNU Tools GCC(1) void. For example, an expression such as `x[i,j]' will cause a warning, but `x[(void)i,j]' will not. o An unsigned value is compared against zero with `>' or `<='. -Wimplicit-int Warn whenever a declaration does not specify a type. -Wimplicit-function-declaration Warn whenever a function is used before being de- clared. -Wimplicit Same as -Wimplicit-int and -Wimplicit-function-dec- laration. -Wmain Warn if the main function is declared or defined with a suspicious type. Typically, it is a func- tion with external linkage, returning int, and tak- ing zero or two arguments. -Wreturn-type Warn whenever a function is defined with a return- type that defaults to int. Also warn about any re- turn 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). GNU Tools 18 GCC(1) GNU Tools GCC(1) -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 for- get 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 com- pilation, because they require data flow informa- tion 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 delet- ed by data flow analysis before the warnings are printed. These warnings are made optional because GNU CC is not smart enough to see all the reasons why the code might be correct despite appearing to have an error. Here is one example of how this can happen: { int x; switch (y) { case 1: x = 1; break; case 2: x = 4; break; case 3: x = 5; } foo (x); } If the value of y is always 1, 2 or 3, then x is always initialized, but GNU CC doesn't know this. GNU Tools 19 GCC(1) GNU Tools GCC(1) 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 de- clare as volatile all the functions you use that never return. -Wparentheses Warn if parentheses are omitted in certain con- texts. -Wtemplate-debugging When using templates in a C++ program, warn if de- bugging 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 rec- ommend 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 differ- ently in traditional and ANSI C. o Macro arguments occurring within string constants in the macro body. These would substitute the ar- gument in traditional C, but are part of the con- stant in ANSI C. o A function declared external in one block and then used after the end of the block. o A switch statement has an operand of type long. -Wshadow Warn whenever a local variable shadows another lo- cal variable. -Wid-clash-len Warn whenever two distinct identifiers match in the GNU Tools 20 GCC(1) GNU Tools GCC(1) first len characters. This may help you prepare a program that will compile with certain obsolete, brain-damaged compilers. -Wpointer-arith Warn about anything that depends on the "size of" a function type or of void. GNU C assigns these types a size of 1, for convenience in calculations with void * pointers and pointers to functions. -Wcast-qual Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a const char * is cast to an ordinary char *. -Wcast-align Warn whenever a pointer is cast such that the re- quired 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 ar- gument in the absence of a prototype. This in- cludes 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 warn- ing.) -Wstrict-prototypes Warn if a function is declared or defined without specifying the argument types. (An old-style func- tion definition is permitted without a warning if preceded by a declaration which specifies the argu- GNU Tools 21 GCC(1) GNU Tools GCC(1) ment types.) -Wmissing-prototypes Warn if a global function is defined without a pre- vious prototype declaration. This warning is is- sued even if the definition itself provides a pro- totype. The aim is to detect global functions that fail to be declared in header files. -Wmissing-declarations Warn if a global function is defined without a pre- vious declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files. -Wredundant-decls Warn if anything is declared more than once in the same scope, even in cases where multiple declara- tion 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). -Wlong-long Warn if long long type is used. This is default. To inhibit the warning messages, use flag `-Wno-long-long'. Flags `-W-long-long' and `-Wno-long-long' are taken into account only when flag `-pedantic' is used. -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 signa- ture 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 -fin- line-functions option was given. GNU Tools 22 GCC(1) GNU Tools GCC(1) -Werror Treat warnings as errors; abort compilation after any warning.
DEBUGGING OPTIONS
GNU CC has various special options that are used for de- bugging either your program or GCC: -g Produce debugging information in the operating sys- tem's native format (stabs, COFF, XCOFF, or DWARF). GDB can work with this debugging information. On most systems that use stabs format, `-g' enables use of extra debugging information that only GDB can use; this extra information makes debugging work better in GDB but will probably make other de- buggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use `-gstabs+', `-gstabs', `-gxcoff+', `-gxcoff', `-gdwarf+', or `-gdwarf' (see below). Unlike most other C compilers, GNU CC allows you to use `-g' with `-O'. The shortcuts taken by opti- mized code may occasionally produce surprising re- sults: 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 val- ues were already at hand; some statements may exe- cute 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 opti- mizer for programs that might have bugs. The following options are useful when GNU CC is generated with the capability for more than one debugging format. -ggdb Produce debugging information in the native format (if that is supported), including GDB extensions if at all possible. -gstabs Produce debugging information in stabs format (if that is supported), without GDB extensions. This is the format used by DBX on most BSD systems. -gstabs+ Produce debugging information in stabs format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB). The use of these extensions is likely to make other debuggers crash GNU Tools 23 GCC(1) GNU Tools GCC(1) or refuse to read the program. -gcoff Produce debugging information in COFF format (if that is supported). This is the format used by SDB on most System V systems prior to System V Release 4. -gxcoff Produce debugging information in XCOFF format (if that is supported). This is the format used by the DBX debugger on IBM RS/6000 systems. -gxcoff+ Produce debugging information in XCOFF format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB). The use of these extensions is likely to make other debuggers crash or refuse to read the program. -gdwarf Produce debugging information in DWARF format (if that is supported). This is the format used by SDB on most System V Release 4 systems. -gdwarf+ Produce debugging information in DWARF format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB). The use of these extensions is likely to make other debuggers crash or refuse to read the program. -glevel -ggdblevel -gstabslevel -gcofflevel -gxcofflevel -gdwarflevel Request debugging information and also use level to specify how much information. The default level is 2. Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, but no informa- tion about local variables and no line numbers. Level 3 includes extra information, such as all the macro definitions present in the program. Some de- buggers support macro expansion when you use `-g3'. -p Generate extra code to write profile information suitable for the analysis program prof. GNU Tools 24 GCC(1) GNU Tools GCC(1) -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 ex- tended to process this data. -ax Generate extra code to read basic block profiling parameters from file `bb.in' and write profiling results to file `bb.out'. `bb.in' contains a list of functions. Whenever a function on the list is entered, profiling is turned on. When the outmost function is left, profiling is turned off. If a function name is prefixed with `-' the function is excluded from profiling. If a function name is not unique it can be disambiguated by writing `/path/filename.d:functionname'. `bb.out' will list some available filenames. Four function names have a special meaning: `__bb_jumps__' will cause jump frequencies to be written to `bb.out'. `__bb_trace__' will cause the sequence of basic blocks to be piped into `gzip' and written to file `bbtrace.gz'. `__bb_hidecall__' will cause call instructions to be excluded from the trace. `__bb_showret__' will cause return instructions to be included in the trace. -dletters Says to make debugging dumps during compilation at times specified by letters. This is used for de- bugging 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 prepro- cessing, and write no output. -dN Dump all macro names, at the end of preprocessing. -dD Dump all macro definitions, at the end of prepro- cessing, in addition to normal output. -dy Dump debugging information during parsing, to stan- dard error. -dr Dump after RTL generation, to `file.rtl'. -dx Just generate RTL for a function instead of compil- ing it. Usually used with `r'. GNU Tools 25 GCC(1) GNU Tools GCC(1) -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 indi- cating which pattern and alternative was used. -fpretend-float When running a cross-compiler, pretend that the target machine uses the same floating point format as the host machine. This causes incorrect output of the actual floating constants, but the actual instruction sequence will probably be the same as GNU CC would make when running on the target ma- chine. GNU Tools 26 GCC(1) GNU Tools GCC(1) -save-temps Store the usual "temporary" intermediate files per- manently; place them in the current directory and name them based on the source file. Thus, compil- ing `foo.c' with `-c -save-temps' would produce files `foo.cpp' and `foo.s', as well as `foo.o'. -print-file-name=library Print the full absolute name of the library file library that would be used when linking--and do not do anything else. With this option, GNU CC does not compile or link anything; it just prints the file name. -print-libgcc-file-name Same as `-print-file-name=libgcc.a'. -print-prog-name=program Like `-print-file-name', but searches for a program such as `cpp'.
OPTIMIZATION OPTIONS
These options control various sorts of optimizations: -O -O1 Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large func- tion. 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 re- sults 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', the two options `-fthread-jumps' and `-fdefer-pop' are turned on. On machines that have delay slots, the `-fdelayed-branch' option is turned on. For those machines that can support debugging even without a frame pointer, the `-fomit-frame-pointer' option is turned on. On some machines other flags may also GNU Tools 27 GCC(1) GNU Tools GCC(1) be turned on. -O2 Optimize even more. Nearly all supported optimiza- tions that do not involve a space-speed tradeoff are performed. Loop unrolling and function inlin- ing are not done, for example. As compared to -O, this option increases both compilation time and the performance of the generated code. -O3 Optimize yet more. This turns on everything -O2 does, along with also turning on -finline-func- tions. -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 ma- chines such as the 68000 where the floating regis- ters (of the 68881) keep more precision than a dou- ble is supposed to have. For most programs, the excess precision does only good, but a few programs rely on the precise defi- nition 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 GNU Tools 28 GCC(1) GNU Tools GCC(1) 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 intro- duces another layer of mechanisms which must be im- plemented, and so incurs its own overhead. `-fmemoize-lookups' enables the software cache. Because access privileges (visibility) to members and member functions may differ from one function context to the next, g++ may need to flush the cache. With the `-fmemoize-lookups' flag, the cache is flushed after every function that is com- piled. 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 privi- leges as every other, and the cache need not be flushed. -fno-default-inline Don't make member functions inline by default mere- ly 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 com- piler 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 poten- tial common subexpressions. When they are not com- mon subexpressions, instruction combination should eliminate the separate register-load. I am inter- ested in hearing about the difference this makes. GNU Tools 29 GCC(1) GNU Tools GCC(1) -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 in- structions to save, set up and restore frame point- ers; 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 auto- matically 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 GCC nor- mally 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 regis- ters 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 ma- chines, usually those which have no call-preserved registers to use instead. -fkeep-inline-functions Even if all calls to a given function are integrat- ed, and the function is declared static, neverthe- less 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 GNU Tools 30 GCC(1) GNU Tools GCC(1) 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 optimiza- tions. -ffast-math This option allows GCC to violate some ANSI or IEEE rules/specifications in the interest of optimizing code for speed. For example, it allows the compil- er 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 func- tions. 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 reduc- tion and elimination of iteration variables. -fthread-jumps Perform optimizations where we check to see if a jump branches to a location where another compari- son subsumed by the first is found. If so, the first branch is redirected to either the destina- tion 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. GNU Tools 31 GCC(1) GNU Tools GCC(1) -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, GNU C++ initializes y di- rectly from the call to foo without going through a temporary in the following code: A foo (); A y = foo (); Without this option, GNU C++ 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 value of `y' with the temporary. The default behavior (`-fno-elide-constructors') is specified by the draft ANSI C++ standard. If your program's constructors have side effects, 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 re- order instructions to exploit instruction slots available after delayed branch instructions. GNU Tools 32 GCC(1) GNU Tools GCC(1) -fschedule-insns If supported for the target machine, attempt to re- order 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 ad- ditional pass of instruction scheduling after reg- ister 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.
TARGET OPTIONS
By default, GNU CC compiles code for the same type of ma- chine that you are using. However, it can also be in- stalled as a cross-compiler, to compile for some other type of machine. In fact, several different configura- tions of GNU CC, for different target machines, can be in- stalled side by side. Then you specify which one to use with the `-b' option. In addition, older and newer versions of GNU CC can be in- stalled side by side. One of them (probably the newest) will be the default, but you may sometimes wish to use an- other. -b machine The argument machine specifies the target machine for compilation. This is useful when you have in- stalled GNU CC as a cross-compiler. The value to use for machine is the same as was specified as the machine type when configuring GNU CC as a cross-compiler. For example, if a cross- compiler was configured with `configure i386v', meaning to compile for an 80386 running System V, then you would specify `-b i386v' to run that cross compiler. When you do not specify `-b', it normally means to compile for the same type of machine that you are using. -V version The argument version specifies which version of GNU CC to run. This is useful when multiple versions are installed. For example, version might be `2.0', meaning to run GNU CC version 2.0. GNU Tools 33 GCC(1) GNU Tools GCC(1) The default version, when you do not specify `-V', is controlled by the way GNU CC is installed. Nor- mally, it will be a version that is recommended for general use.
MACHINE DEPENDENT OPTIONS
Each of the target machine types can have its own special options, starting with `-m', to choose among various hard- ware models or configurations--for example, 68010 vs 68020, floating coprocessor or none. A single installed version of the compiler can compile for any model or con- figuration, according to the options specified. Some configurations of the compiler also support addition- al 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. GNU Tools 34 GCC(1) GNU Tools GCC(1) -mfpa Generate output containing Sun FPA instructions for floating point. -msoft-float Generate output containing library calls for float- ing point. WARNING: the requisite libraries are not part of GNU CC. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable li- brary 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' im- plies `-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 argu- ments 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 Vax: -munix Do not output certain jump instructions (aobleq and so on) that the Unix assembler for the Vax cannot handle across long ranges. GNU Tools 35 GCC(1) GNU Tools GCC(1) -mgnu Do output those jump instructions, on the assump- tion that you will assemble with the GNU assembler. -mg Output code for g-format floating point numbers in- stead of d-format. These `-m' switches are supported on the SPARC: -mfpu -mhard-float Generate output containing floating point instruc- tions. This is the default. -mno-fpu -msoft-float Generate output containing library calls for float- ing point. Warning: there is no GNU floating-point library for SPARC. Normally the facilities of the machine's usual C compiler are used, but this can- not be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. -msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. -mno-epilogue -mepilogue With -mepilogue (the default), the compiler always emits code for function exit at the end of each function. Any function exit in the middle of the function (such as a return statement in C) will generate a jump to the exit code at the end of the function. With -mno-epilogue, the compiler tries to emit exit code inline at every function exit. -mno-v8 -mv8 -msparclite These three options select variations on the SPARC architecture. By default (unless specifically configured for the Fujitsu SPARClite), GCC generates code for the v7 variant of the SPARC architecture. GNU Tools 36 GCC(1) GNU Tools GCC(1) -mv8 will give you SPARC v8 code. The only differ- ence from v7 code is that the compiler emits the integer multiply and integer divide instructions which exist in SPARC v8 but not in SPARC v7. -msparclite will give you SPARClite code. This adds the integer multiply, integer divide step and scan (ffs) instructions which exist in SPARClite but not in SPARC v7. -mcypress -msupersparc These two options select the processor for which the code is optimised. With -mcypress (the default), the compiler optimis- es code for the Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series. This is also appropriate for the older SparcStation 1, 2, IPX etc. With -msupersparc the compiler optimises code for the SuperSparc cpu, as used in the SparcStation 10, 1000 and 2000 series. This flag also enables use of the full SPARC v8 instruction set. These `-m' options are defined for the Convex: -mc1 Generate output for a C1. This is the default when the compiler is configured for a C1. -mc2 Generate output for a C2. This is the default when the compiler is configured for a C2. -margcount Generate code which puts an argument count in the word preceding each argument list. Some non- portable Convex and Vax programs need this word. (Debuggers don't, except for functions with vari- able-length argument lists; this info is in the symbol table.) -mnoargcount Omit the argument count word. This is the default if you use the unmodified sources. These `-m' options are defined for the AMD Am29000: -mdw Generate code that assumes the DW bit is set, i.e., that byte and halfword operations are directly sup- ported by the hardware. This is the default. -mnodw Generate code that assumes the DW bit is not set. GNU Tools 37 GCC(1) GNU Tools GCC(1) -mbw Generate code that assumes the system supports byte and halfword write operations. This is the de- fault. -mnbw Generate code that assumes the systems does not support byte and halfword write operations. This implies `-mnodw'. -msmall Use a small memory model that assumes that all function addresses are either within a single 256 KB segment or at an absolute address of less than 256K. This allows the call instruction to be used instead of a const, consth, calli sequence. -mlarge Do not assume that the call instruction can be used; this is the default. -m29050 Generate code for the Am29050. -m29000 Generate code for the Am29000. This is the de- fault. -mkernel-registers Generate references to registers gr64-gr95 instead of gr96-gr127. This option can be used when com- piling kernel code that wants a set of global reg- isters disjoint from that used by user-mode code. Note that when this option is used, register names in `-f' flags must use the normal, user-mode, names. -muser-registers Use the normal set of global registers, gr96-gr127. This is the default. -mstack-check Insert a call to __msp_check after each stack ad- justment. This is often used for kernel code. These `-m' options are defined for Motorola 88K architec- tures: -m88000 Generate code that works well on both the m88100 and the m88110. -m88100 Generate code that works best for the m88100, but that also runs on the m88110. GNU Tools 38 GCC(1) GNU Tools GCC(1) -m88110 Generate code that works best for the m88110, and may not run on the m88100. -midentify-revision Include an ident directive in the assembler output recording the source file name, compiler name and version, timestamp, and compilation flags used. -mno-underscores In assembler output, emit symbol names without adding an underscore character at the beginning of each name. The default is to use an underscore as prefix on each name. -mno-check-zero-division -mcheck-zero-division Early models of the 88K architecture had problems with division by zero; in particular, many of them didn't trap. Use these options to avoid including (or to include explicitly) additional code to de- tect division by zero and signal an exception. All GCC configurations for the 88K use `-mcheck-zero-division' by default. -mocs-debug-info -mno-ocs-debug-info Include (or omit) additional debugging information (about registers used in each stack frame) as spec- ified in the 88Open Object Compatibility Standard, "OCS". This extra information is not needed by GDB. The default for DG/UX, SVr4, and Delta 88 SVr3.2 is to include this information; other 88k configurations omit this information by default. -mocs-frame-position -mno-ocs-frame-position Force (or do not require) register values to be stored in a particular place in stack frames, as specified in OCS. The DG/UX, Delta88 SVr3.2, and BCS configurations use `-mocs-frame-position'; oth- er 88k configurations have the default `-mno-ocs-frame-position'. -moptimize-arg-area -mno-optimize-arg-area Control how to store function arguments in stack frames. `-moptimize-arg-area' saves space, but may break some debuggers (not GDB). `-mno-optimize-arg-area' conforms better to stan- GNU Tools 39 GCC(1) GNU Tools GCC(1) dards. By default GCC does not optimize the argu- ment area. -mshort-data-num num Generate smaller data references by making them relative to r0, which allows loading a value using a single instruction (rather than the usual two). You control which data references are affected by specifying num with this option. For example, if you specify `-mshort-data-512', then the data ref- erences affected are those involving displacements of less than 512 bytes. `-mshort-data-num' is not effective for num greater than 64K. -mserialize-volatile -mno-serialize-volatile Do, or do not, generate code to guarantee sequen- tial consistency of volatile memory references. GNU CC always guarantees consistency by default, for the preferred processor submodel. How this is done depends on the submodel. The m88100 processor does not reorder memory refer- ences and so always provides sequential consisten- cy. If you use `-m88100', GNU CC does not generate any special instructions for sequential consisten- cy. The order of memory references made by the m88110 processor does not always match the order of the instructions requesting those references. In par- ticular, a load instruction may execute before a preceding store instruction. Such reordering vio- lates sequential consistency of volatile memory references, when there are multiple processors. When you use `-m88000' or `-m88110', GNU CC gener- ates special instructions when appropriate, to force execution in the proper order. The extra code generated to guarantee consistency may affect the performance of your application. If you know that you can safely forgo this guarantee, you may use the option `-mno-serialize-volatile'. If you use the `-m88100' option but require sequen- tial consistency when running on the m88110 proces- sor, you should use `-mserialize-volatile'. -msvr4 -msvr3 Turn on (`-msvr4') or off (`-msvr3') compiler ex- tensions related to System V release 4 (SVr4). GNU Tools 40 GCC(1) GNU Tools GCC(1) This controls the following: o Which variant of the assembler syntax to emit (which you can select independently using `-mversion-03.00'). o `-msvr4' makes the C preprocessor recognize `#prag- ma weak' o `-msvr4' makes GCC issue additional declaration di- rectives used in SVr4. `-msvr3' is the default for all m88K configurations except the SVr4 configuration. -mtrap-large-shift -mhandle-large-shift Include code to detect bit-shifts of more than 31 bits; respectively, trap such shifts or emit code to handle them properly. By default GCC makes no special provision for large bit shifts. -muse-div-instruction Very early models of the 88K architecture didn't have a divide instruction, so GCC avoids that in- struction by default. Use this option to specify that it's safe to use the divide instruction. -mversion-03.00 In the DG/UX configuration, there are two flavors of SVr4. This option modifies -msvr4 to select whether the hybrid-COFF or real-ELF flavor is used. All other configurations ignore this option. -mwarn-passed-structs Warn when a function passes a struct as an argument or result. Structure-passing conventions have changed during the evolution of the C language, and are often the source of portability problems. By default, GCC issues no such warning. These options are defined for the IBM RS6000: -mfp-in-toc -mno-fp-in-toc Control whether or not floating-point constants go in the Table of Contents (TOC), a table of all global variable and function addresses. By default GCC puts floating-point constants there; if the TOC overflows, `-mno-fp-in-toc' will reduce the size of the TOC, which may avoid the overflow. GNU Tools 41 GCC(1) GNU Tools GCC(1) These `-m' options are defined for the IBM RT PC: -min-line-mul Use an in-line code sequence for integer multi- plies. This is the default. -mcall-lib-mul Call lmul$$ for integer multiples. -mfull-fp-blocks Generate full-size floating point data blocks, in- cluding the minimum amount of scratch space recom- mended by IBM. This is the default. -mminimum-fp-blocks Do not include extra scratch space in floating point data blocks. This results in smaller code, but slower execution, since scratch space must be allocated dynamically. -mfp-arg-in-fpregs Use a calling sequence incompatible with the IBM calling convention in which floating point argu- ments are passed in floating point registers. Note that varargs.h and stdargs.h will not work with floating point operands if this option is speci- fied. -mfp-arg-in-gregs Use the normal calling convention for floating point arguments. This is the default. -mhc-struct-return Return structures of more than one word in memory, rather than in a register. This provides compati- bility with the MetaWare HighC (hc) compiler. Use `-fpcc-struct-return' for compatibility with the Portable C Compiler (pcc). -mnohc-struct-return Return some structures of more than one word in registers, when convenient. This is the default. For compatibility with the IBM-supplied compilers, use either `-fpcc-struct-return' or `-mhc-struct-return'. These `-m' options are defined for the MIPS family of com- puters: -mcpu=cpu-type Assume the defaults for the machine type cpu-type when scheduling instructions. The default cpu-type is default, which picks the longest cycles times for any of the machines, in order that the code run GNU Tools 42 GCC(1) GNU Tools GCC(1) at reasonable rates on all MIPS cpu's. Other choices for cpu-type are r2000, r3000, r4000, and r6000. While picking a specific cpu-type will schedule things appropriately for that particular chip, the compiler will not generate any code that does not meet level 1 of the MIPS ISA (instruction set architecture) without the -mips2 or -mips3 switches being used. -mips2 Issue instructions from level 2 of the MIPS ISA (branch likely, square root instructions). The -mcpu=r4000 or -mcpu=r6000 switch must be used in conjunction with -mips2. -mips3 Issue instructions from level 3 of the MIPS ISA (64 bit instructions). The -mcpu=r4000 switch must be used in conjunction with -mips2. -mint64 -mlong64 -mlonglong128 These options don't work at present. -mmips-as Generate code for the MIPS assembler, and invoke mips-tfile to add normal debug information. This is the default for all platforms except for the OSF/1 reference platform, using the OSF/rose object format. If any of the -ggdb, -gstabs, or -gstabs+ switches are used, the mips-tfile program will en- capsulate the stabs within MIPS ECOFF. -mgas Generate code for the GNU assembler. This is the default on the OSF/1 reference platform, using the OSF/rose object format. -mrnames -mno-rnames The -mrnames switch says to output code using the MIPS software names for the registers, instead of the hardware names (ie, a0 instead of $4). The GNU assembler does not support the -mrnames switch, and the MIPS assembler will be instructed to run the MIPS C preprocessor over the source file. The -mno-rnames switch is default. -mgpopt -mno-gpopt The -mgpopt switch says to write all of the data declarations before the instructions in the text GNU Tools 43 GCC(1) GNU Tools GCC(1) section, to all the MIPS assembler to generate one word memory references instead of using two words for short global or static data items. This is on by default if optimization is selected. -mstats -mno-stats For each non-inline function processed, the -mstats switch causes the compiler to emit one line to the standard error file to print statistics about the program (number of registers saved, stack size, etc.). -mmemcpy -mno-memcpy The -mmemcpy switch makes all block moves call the appropriate string function (memcpy or bcopy) in- stead of possibly generating inline code. -mmips-tfile -mno-mips-tfile The -mno-mips-tfile switch causes the compiler not postprocess the object file with the mips-tfile program, after the MIPS assembler has generated it to add debug support. If mips-tfile is not run, then no local variables will be available to the debugger. In addition, stage2 and stage3 objects will have the temporary file names passed to the assembler embedded in the object file, which means the objects will not compare the same. -msoft-float Generate output containing library calls for float- ing point. WARNING: the requisite libraries are not part of GNU CC. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable li- brary functions for cross-compilation. -mhard-float Generate output containing floating point instruc- tions. This is the default if you use the unmodi- fied sources. -mfp64 Assume that the FR bit in the status word is on, and that there are 32 64-bit floating point regis- ters, instead of 32 32-bit floating point regis- ters. You must also specify the -mcpu=r4000 and -mips3 switches. GNU Tools 44 GCC(1) GNU Tools GCC(1) -mfp32 Assume that there are 32 32-bit floating point reg- isters. This is the default. -mabicalls -mno-abicalls Emit (or do not emit) the .abicalls, .cpload, and .cprestore pseudo operations that some System V.4 ports use for position independent code. -mhalf-pic -mno-half-pic The -mhalf-pic switch says to put pointers to ex- tern references into the data section and load them up, rather than put the references in the text sec- tion. This option does not work at present. -Gnum Put global and static items less than or equal to num bytes into the small data or bss sections in- stead of the normal data or bss section. This al- lows the assembler to emit one word memory refer- ence instructions based on the global pointer (gp or $28), instead of the normal two words used. By default, num is 8 when the MIPS assembler is used, and 0 when the GNU assembler is used. The -Gnum switch is also passed to the assembler and linker. All modules should be compiled with the same -Gnum value. -nocpp Tell the MIPS assembler to not run its preprocessor over user assembler files (with a `.s' suffix) when assembling them. 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 float- ing point. Warning: the requisite libraries are not part of GNU CC. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable li- brary 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. GNU Tools 45 GCC(1) GNU Tools GCC(1) -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 regis- ter, 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 com- puters: -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 func- tion yet, and is not on by default for any PA tar- get. 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 ker- nels which perform lazy context switching of float- ing point registers. If you use this option and attempt to perform floating point operations, the compiler will abort. GNU Tools 46 GCC(1) GNU Tools GCC(1) -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). These `-m' options are defined for the Intel 80960 family of computers: -mcpu-type Assume the defaults for the machine type cpu-type for instruction and addressing-mode availability and alignment. The default cpu-type is kb; other choices are ka, mc, ca, cf, sa, and sb. -mnumerics -msoft-float The -mnumerics option indicates that the processor does support floating-point instructions. The -msoft-float option indicates that floating-point support should not be assumed. -mleaf-procedures -mno-leaf-procedures Do (or do not) attempt to alter leaf procedures to be callable with the bal instruction as well as call. This will result in more efficient code for explicit calls when the bal instruction can be sub- stituted by the assembler or linker, but less effi- cient code in other cases, such as calls via func- tion pointers, or using a linker that doesn't sup- port this optimization. -mtail-call -mno-tail-call Do (or do not) make additional attempts (beyond those of the machine-independent portions of the compiler) to optimize tail-recursive calls into branches. You may not want to do this because the detection of cases where this is not valid is not totally complete. The default is -mno-tail-call. -mcomplex-addr -mno-complex-addr Assume (or do not assume) that the use of a complex addressing mode is a win on this implementation of the i960. Complex addressing modes may not be GNU Tools 47 GCC(1) GNU Tools GCC(1) worthwhile on the K-series, but they definitely are on the C-series. The default is currently -mcom- plex-addr for all processors except the CB and CC. -mcode-align -mno-code-align Align code to 8-byte boundaries for faster fetching (or don't bother). Currently turned on by default for C-series implementations only. -mic-compat -mic2.0-compat -mic3.0-compat Enable compatibility with iC960 v2.0 or v3.0. -masm-compat -mintel-asm Enable compatibility with the iC960 assembler. -mstrict-align -mno-strict-align Do not permit (do permit) unaligned accesses. -mold-align Enable structure-alignment compatibility with In- tel's gcc release version 1.3 (based on gcc 1.37). Currently this is buggy in that #pragma align 1 is always assumed as well, and cannot be turned off. These `-m' options are defined for the DEC Alpha implemen- tations: -mno-soft-float -msoft-float Use (do not use) the hardware floating-point in- structions for floating-point operations. When -msoft-float is specified, functions in `libgcc1.c' will be used to perform floating-point operations. Unless they are replaced by routines that emulate the floating-point operations, or compiled in such a way as to call such emulations routines, these routines will issue floating-point operations. If you are compiling for an Alpha without floating- point operations, you must ensure that the library is built so as not to call them. Note that Alpha implementations without floating- point operations are required to have floating- GNU Tools 48 GCC(1) GNU Tools GCC(1) point registers. -mfp-reg -mno-fp-regs Generate code that uses (does not use) the float- ing-point register set. -mno-fp-regs implies -msoft-float. If the floating-point register set is not used, floating point operands are passed in integer registers as if they were integers and floating-point results are passed in $0 instead of $f0. This is a non-standard calling sequence, so any function with a floating-point argument or re- turn value called by code compiled with -mno-fp- regs must also be compiled with that option. A typical use of this option is building a kernel that does not use, and hence need not save and re- store, any floating-point registers. These additional options are available on System V Release 4 for compatibility with other compilers on those systems: -G On SVr4 systems, gcc accepts the option `-G' (and passes it to the system linker), for compatibility with other compilers. However, we suggest you use `-symbolic' or `-shared' as appropriate, instead of supplying linker options on the gcc command line. -Qy Identify the versions of each tool used by the com- piler, in a .ident assembler directive in the out- put. -Qn Refrain from adding .ident directives to the output file (this is the default). -YP,dirs Search the directories dirs, and no others, for li- braries specified with `-l'. You can separate di- rectory entries in dirs from one another with colons. -Ym,dir Look in the directory dir to find the M4 preproces- sor. The assembler uses this option.
CODE GENERATION OPTIONS
These machine-independent options control the interface conventions used in code generation. 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 GNU Tools 49 GCC(1) GNU Tools GCC(1) 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, GNU C++ makes conservative assumptions about objects reached through references. For ex- ample, 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 un- necessary 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 allow- ing 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, GNU CC defaults to whichever convention is standard for the target. If there is no standard convention, GNU 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 GNU Tools 50 GCC(1) GNU Tools GCC(1) operating systems, where shared data is shared be- tween 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 gener- ating them as common blocks. This has the effect that if the same variable is declared (without ex- tern) in two different compilations, you will get an error when you link them. The only reason this might be useful is if you wish to verify that the program will work on other systems which always work this way. -fno-ident Ignore the `#ident' directive. -fno-gnu-linker Do not output global initializations (such as C++ constructors and destructors) in the form used by the GNU linker (on systems where the GNU linker is the standard method of handling them). Use this option when you want to use a non-GNU linker, which also requires using the collect2 program to make sure the system linker includes constructors and destructors. (collect2 is included in the GNU CC distribution.) For systems which must use col- lect2, the compiler driver gcc is configured to do this automatically. -finhibit-size-directive Don't output a .size assembler directive, or any- thing 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 op- tion 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 op- tion is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself). -fvolatile Consider all memory references through pointers to be volatile. -fvolatile-global Consider all memory references to extern and global data items to be volatile. GNU Tools 51 GCC(1) GNU Tools GCC(1) -fpic If supported for the target machines, generate po- sition-independent code, suitable for use in a shared library. -fPIC If supported for the target machine, emit position- independent code, suitable for dynamic linking, even if branches need large displacements. -ffixed-reg Treat the register named reg as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role). reg must be the name of a register. The register names accepted are machine-specific and are defined in the REGISTER_NAMES macro in the machine descrip- tion macro file. This flag does not have a negative form, because it specifies a three-way choice. -fcall-used-reg Treat the register named reg as an allocable regis- ter that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions compiled this way will not save and restore the register reg. Use of this flag for a register that has a fixed pervasive role in the machine's execution model, such as the stack pointer or frame pointer, will produce disastrous results. This flag does not have a negative form, because it specifies a three-way choice. -fcall-saved-reg Treat the register named reg as an allocable regis- ter saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way will save and restore the register reg if they use it. Use of this flag for a register that has a fixed pervasive role in the machine's execution model, such as the stack pointer or frame pointer, will produce disastrous results. A different sort of disaster will result from the use of this flag for a register in which function values may be returned. This flag does not have a negative form, because it GNU Tools 52 GCC(1) GNU Tools GCC(1) specifies a three-way choice.
PRAGMAS
Two `#pragma' directives are supported for GNU C++, to permit using the same header file for two purposes: as a definition of interfaces to a given object class, and as the full definition of the contents of that object class. #pragma interface (C++ only.) Use this directive in header files that define object classes, to save space in most of the object files that use those classes. Nor- mally, local copies of certain information (backup copies of inline member functions, debugging infor- mation, and the internal tables that implement vir- tual functions) must be kept in each object file that includes class definitions. You can use this pragma to avoid such duplication. When a header file containing `#pragma interface' is included in a compilation, this auxiliary information will not be generated (unless the main input source file it- self uses `#pragma implementation'). Instead, the object files will contain references to be resolved at link time. #pragma implementation #pragma implementation "objects.h" (C++ only.) Use this pragma in a main input file, when you want full output from included header files to be generated (and made globally visible). The included header file, in turn, should use `#pragma interface'. Backup copies of inline mem- ber functions, debugging information, and the in- ternal tables used to implement virtual functions are all generated in implementation files. If you use `#pragma implementation' with no argu- ment, it applies to an include file with the same basename as your source file; for example, in `allclass.cc', `#pragma implementation' by itself is equivalent to `#pragma implementation "allclass.h"'. Use the string argument if you want a single implementation file to include code from multiple header files. There is no way to split up the contents of a sin- gle header file into multiple implementation files.
FILES
file.c C source file file.h C header (preprocessor) file file.i preprocessed C source file file.C C++ source file GNU Tools 53 GCC(1) GNU Tools GCC(1) file.cc C++ source file file.cxx C++ source file file.m Objective-C source file file.s assembly language file file.o object file a.out link edited output TMPDIR/cc* temporary files LIBDIR/cpp preprocessor LIBDIR/cc1 compiler for C LIBDIR/cc1plus compiler for C++ LIBDIR/collect linker front end needed on some machines LIBDIR/libgcc.a GCC subroutine library /lib/crt[01n].o start-up routine LIBDIR/ccrt0 additional start-up routine for C++ /lib/libc.a standard C library, see intro(3) /usr/include standard directory for #include files LIBDIR/include standard gcc directory for #include files LIBDIR/g++-include additional g++ directory for #include LIBDIR is usually /usr/local/lib/machine/version. TMPDIR comes from the environment variable TMPDIR (default /var/tmp if available, else /tmp).
SEE ALSO
cpp(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1). `gcc', `cpp', `as', `ld', and `gdb' entries in info. Using and Porting GNU CC (for version 2.0), Richard M. Stallman; The C Preprocessor, Richard M. Stallman; Debug- ging with GDB: the GNU Source-Level Debugger, Richard M. Stallman and Roland H. Pesch; Using as: the GNU Assembler, Dean Elsner, Jay Fenlason & friends; ld: the GNU linker, Steve Chamberlain and Roland Pesch.
BUGS
For instructions on reporting bugs, see the GCC manual.
COPYING
Copyright 1991, 1992, 1993 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified ver- sions of this manual under the conditions for verbatim copying, 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 con- ditions for modified versions, except that this permission notice may be included in translations approved by the GNU Tools 54 GCC(1) GNU Tools GCC(1) Free Software Foundation instead of in the original En- glish.
AUTHORS
See the GNU CC Manual for the contributors to GNU CC. GNU Tools 55
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