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NAME
gcc, g++ - GNU project C and C++ Compiler (gcc-2.95)
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 volunteers
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If we find that the things in this man page that are out of
date cause significant confusion or complaints, we will stop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 ver-
sion 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: preprocessing,
compilation, assembly, and linking. Source filename suf-
fixes 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
.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. Common
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, unrecog-
nized 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
-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
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
-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' option. 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 sub-
sequent 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 corresponding 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 op-
tion.
-S Stop after the stage of compilation proper; do not as-
semble. The output is an assembler code file for each
non-assembler input file specified.
By default, GCC makes the assembler file name for a
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 compila-
tion.
-E Stop after the preprocessing stage; do not run the com-
piler proper. The output is preprocessed source code,
which is sent to the standard output.
GCC ignores input files which don't require preprocess-
ing.
-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 executed
to run the stages of compilation. Also print the ver-
sion number of the compiler driver program and of the
preprocessor and the compiler proper.
-pipe
Use pipes rather than temporary files for communication
between the various stages of compilation. This fails
to work on some systems where the assembler cannot read
from a pipe; but the GNU assembler has no trouble.
LANGUAGE OPTIONS
The following options control the dialect of C that the com-
piler accepts:
-ansi
Support all ANSI standard C programs.
This turns off certain features of GNU C that are in-
compatible 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 tri-
graph feature, and disallows `$' as part of identif-
iers.
The alternate keywords __asm__, __extension__, __in-
line__ 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 compilations done with
`-ansi'. Alternate predefined macros such as __unix__
and __vax__ are also available, with or without
`-ansi'.
The `-ansi' option does not cause non-ANSI programs to
be rejected gratuitously. For that, `-pedantic' is re-
quired 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 keyword.
These words may then be used as identifiers. You can
use __asm__, __inline__ and __typeof__ instead.
`-ansi' implies `-fno-asm'.
-fno-builtin
Don't recognize built-in functions that do not begin
with two leading underscores. Currently, the functions
affected include _exit, abort, abs, alloca, 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 de-
clarations of main should be warned about.
-ffreestanding
Compile for a freestanding environment; this implies
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 saying nothing
about the number of arguments or their types (C++
only). Normally, such a declaration in C++ means that
the function foo takes no arguments.
-trigraphs
Support ANSI C trigraphs. The `-ansi' option implies
`-trigraphs'.
-traditional
Attempt to support some aspects of traditional C com-
pilers. For details, see the GNU C Manual; the dupli-
cate 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). `-tradi-
tional' 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 specifi-
cally 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 explicit-
ly prohibit use of `$'. (GNU C++ allows `$' by default
on some target systems but not others.)
-fenum-int-equiv
Permit implicit conversion of int to enumeration types
(C++ only). Normally GNU C++ allows conversion of enum
to int, but not the other way around.
-fexternal-templates
Produce smaller code for template declarations, by gen-
erating 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 de-
finition) or `#pragma interface' (declarations).
When your code is compiled with `-fexternal-templates',
all template instantiations are external. You must ar-
range for all necessary instantiations to appear in the
implementation file; you can do this with a typedef
that references each instantiation needed. Conversely,
when you compile using the default option
`-fno-external-templates', all template instantiations
are explicitly internal.
-fall-virtual
Treat all possible member functions as virtual, impli-
citly. All member functions (except for constructor
functions and new or delete member operators) are
treated as virtual functions of the class where they
appear.
This does not mean that all calls to these member func-
tions will be made through the internal table of virtu-
al 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 incorpora-
tion 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 compati-
bility, 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 default or like
signed char by default.
Ideally, a portable program should always use signed
char or unsigned char when it depends on the signedness
of an object. But many programs have been written to
use plain char and expect it to be signed, or expect it
to be unsigned, depending on the machines they were
written for. This option, and its inverse, let you
make such a program work with the opposite default.
The type char is always a distinct type from each of
signed char 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'. Like-
wise, `-fno-signed-char' is equivalent to
`-funsigned-char'.
-fsigned-bitfields
-funsigned-bitfields
-fno-signed-bitfields
-fno-unsigned-bitfields
These options control whether a bitfield is signed or
unsigned, when 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 effect.
Writing into string constants is a very bad idea; "con-
stants" 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 prepro-
cessing. Some of these options make sense only together
with `-E' because they cause the preprocessor output to be
unsuitable for actual compilation.
-include file
Process file as input before processing the regular in-
put 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 `-in-
clude' and `-imacros' options are processed in the ord-
er in which they are written.
-imacros file
Process file as input, discarding the resulting output,
before processing the regular input file. Because the
output generated from file is discarded, the only ef-
fect of `-imacros file' is to make the macros defined
in file available for use in the main input. The
preprocessor evaluates any `-D' and `-U' options on the
command line before processing `-imacrosfile', regard-
less 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 direc-
tories in the main include path (the one that `-I' adds
to).
-iprefix prefix
Specify prefix as the prefix for subsequent `-iwithpre-
fix' 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 `-ipre-
fix'.
-nostdinc
Do not search the standard system directories for
header files. Only the directories you have specified
with `-I' options (and the current directory, if ap-
propriate) are searched.
By using both `-nostdinc' and `-I-', you can limit the
include-file search file to only those directories 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 build-
ing `libg++'.)
-undef
Do not predefine any nonstandard macros. (Including
architecture flags).
-E Run only the C preprocessor. Preprocess all the C
source files specified and output the results to stan-
dard output or to the specified output file.
-C Tell the preprocessor not to discard comments. Used
with the `-E' option.
-P Tell the preprocessor not to generate `#line' commands.
Used with the `-E' option.
-M [ -MG ]
Tell the preprocessor to output a rule suitable for
make describing the dependencies of each object file.
For each source file, the preprocessor outputs one
make-rule whose target is the object file name for that
source file and whose dependencies are all the files
`#include'd in it. This rule may be a single line or
may be continued with `\'-newline if it is long. The
list of rules is printed on standard output instead of
the preprocessed C program.
`-M' implies `-E'.
`-MG' says to treat missing header files as generated
files and assume they live in the same directory 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"'. System header
files included with `#include <file>' are omitted.
-MD Like `-M' but the dependency information is written to
files with names made by replacing `.o' with `.d' at
the end of the output file names. This is in addition
to compiling the file as specified-`-MD' does not inhi-
bit ordinary compilation the way `-M' does.
The Mach utility `md' can be used to merge the `.d'
files into a single dependency file suitable for using
with the `make' command.
-MMD Like `-MD' except mention only user header files, not
system header files.
-H Print the name of each header file used, in addition to
other normal activities.
-Aquestion(answer)
Assert the answer answer for question, in case it is
tested with a preprocessor conditional such as `#if
#question(answer)'. `-A-' disables the standard asser-
tions 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 target machine.
-Dmacro
Define macro macro with the string `1' as its defini-
tion.
-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 `-imac-
ros' options.
-dM Tell the preprocessor to output only a list of the mac-
ro definitions that are in effect at the end of prepro-
cessing. 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 contents
are omitted. Only `#define name' is included in the
output.
ASSEMBLER OPTION
-Wa,option
Pass option as an option to the assembler. If option
contains commas, it is split into multiple options at
the commas.
LINKER OPTIONS
These options come into play when the compiler links object
files into an executable output file. They are meaningless
if the compiler is not doing a link step.
object-file-name
A file name that does not end in a special recognized
suffix is considered to name an object file or library.
(Object files are distinguished from libraries by the
linker according to the file contents.) If 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.
The directories searched include several standard sys-
tem directories plus any that you specify with `-L'.
Normally the files found this way are library files-
archive files whose members are object files. The
linker handles an archive file by scanning through it
for members which define symbols that have so far been
referenced but not defined. However, if the linker
finds an ordinary object file rather than a library,
the object file is linked in the usual fashion. The
only difference between using an `-l' option and speci-
fying a file name is that `-l' surrounds library with
`lib' and `.a' and searches several directories.
-lobjc
You need this special case of the -l option in order to
link an Objective C program.
-nostartfiles
Do not use the standard system startup files when link-
ing. The standard libraries are used normally.
-nostdlib
Don't use the standard system libraries and startup
files when linking. Only the files you specify will be
passed to the linker.
-static
On systems that support dynamic linking, this prevents
linking with the shared libraries. On other systems,
this option has no effect.
-shared
Produce a shared object which can then be linked with
other objects to form an executable. Only a few sys-
tems support this option.
-symbolic
Bind references to global symbols when building a
shared object. Warn about any unresolved references
(unless overridden by the link editor option `-Xlinker
-z -Xlinker defs'). Only a few systems support this
option.
-Xlinker option
Pass option as an option to the linker. You can use
this to supply system-specific linker options which GNU
CC does not know how to recognize.
If you want to pass an option that takes an argument,
you must use `-Xlinker' twice, once for the option and
once for the argument. For example, to pass `-assert
definitions', you must write `-Xlinker -assert -Xlinker
definitions'. It does not work to write `-Xlinker
"-assert definitions"', because this passes the entire
string as a single argument, which is not what the
linker expects.
-Wl,option
Pass option as an option to the linker. If option con-
tains commas, it is split into multiple options at the
commas.
-u symbol
Pretend the symbol symbol is undefined, to force link-
ing 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 before
the `-I-' option are searched only for the case of
`#include "file"'; they are not searched for `#include
<file>'.
If additional directories are specified with `-I' op-
tions after the `-I-', these directories are searched
for all `#include' directives. (Ordinarily all `-I'
directories are used this way.)
In addition, the `-I-' option inhibits the use of the
current directory (where the current input file came
from) as the first search directory for `#include
"file"'. There is no way to override this effect of
`-I-'. With `-I.' you can specify searching the direc-
tory which was current when the compiler was invoked.
That is not exactly the same as what the preprocessor
does by default, but it is often satisfactory.
`-I-' does not inhibit the use of the standard system
directories for header files. Thus, `-I-' and `-nost-
dinc' are independent.
-Ldir
Add directory dir to the list of directories to be
searched for `-l'.
-Bprefix
This option specifies where to find the executables,
libraries and data files of the compiler itself.
The compiler driver program runs one or more of the
subprograms `cpp', `cc1' (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 unmodified 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 vari-
able GCC_EXEC_PREFIX; if it is defined, its value is
used as a prefix in the same way. If both the `-B' op-
tion 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 pro-
duced 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 extensions.
Valid ANSI standard C programs should compile properly
with or without this option (though a rare few will re-
quire `-ansi'). However, without this option, certain
GNU extensions and traditional C features are supported
as well. With this option, they are rejected. There
is no reason to use this option; it exists only to
satisfy pedants.
`-pedantic' does not cause warning messages for use of
the alternate keywords whose names begin and end with
`__'. Pedantic warnings are also disabled in the ex-
pression that follows __extension__. However, only
system header files should use these escape routes; ap-
plication programs should avoid them.
-pedantic-errors
Like `-pedantic', except that errors are produced rath-
er 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 value.
(Falling off the end of the function body is considered
returning without a value.) For example, this function
would evoke such a warning:
foo (a)
{
if (a > 0)
return a;
}
Spurious warnings can occur because 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 com-
ma expression contains no side effects. To suppress the
warning, cast the unused expression to void. For exam-
ple, an expression such as `x[i,j]' will cause a warn-
ing, 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 declared.
-Wimplicit
Same as -Wimplicit-int and -Wimplicit-function-
declaration.
-Wmain
Warn if the main function is declared or defined with a
suspicious type. Typically, it is a function with
external linkage, returning int, and taking zero or two
arguments.
-Wreturn-type
Warn whenever a function is defined with a return-type
that defaults to int. Also warn about any return
statement with no return-value in a function whose
return-type is not void.
-Wunused
Warn whenever a local variable is unused aside from its
declaration, whenever a function is declared static but
never defined, and whenever a statement computes a
result that is explicitly not used.
-Wswitch
Warn whenever a switch statement has an index of
enumeral type and lacks a case for one or more of the
named codes of that enumeration. (The presence of a
default label prevents this warning.) case labels out-
side the enumeration range also provoke warnings when
this option is used.
-Wcomment
Warn whenever a comment-start sequence `/*' appears in
a comment.
-Wtrigraphs
Warn if any trigraphs are encountered (assuming they
are enabled).
-Wformat
Check calls to printf and scanf, etc., to make sure
that the arguments supplied have types appropriate to
the format string specified.
-Wchar-subscripts
Warn if an array subscript has type char. This is a
common cause of error, as programmers often forget that
this type is signed on some machines.
-Wuninitialized
An automatic variable is used without first being ini-
tialized.
These warnings are possible only in optimizing compila-
tion, because they require data flow information that
is computed only when optimizing. If you don't specify
`-O', you simply won't get these warnings.
These warnings occur only for variables that are candi-
dates 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 struc-
tures, unions or arrays, even when they are in regis-
ters.
Note that there may be no warning about a variable that
is used only to compute a value that itself is never
used, because such computations may be deleted by data
flow analysis before the warnings are printed.
These warnings are made optional because GNU CC is not
smart enough to see all the reasons why the code might
be correct despite appearing to have an error. Here is
one example of how this can happen:
{
int x;
switch (y)
{
case 1: x = 1;
break;
case 2: x = 4;
break;
case 3: x = 5;
}
foo (x);
}
If the value of y is always 1, 2 or 3, then x is always
initialized, but GNU CC doesn't know this. Here is
another common case:
{
int save_y;
if (change_y) save_y = y, y = new_y;
...
if (change_y) y = save_y;
}
This has no bug because save_y is used only if it is
set.
Some spurious warnings can be avoided if you declare as
volatile all the functions you use that never return.
-Wparentheses
Warn if parentheses are omitted in certain contexts.
-Wtemplate-debugging
When using templates in a C++ program, warn if debug-
ging is not yet fully available (C++ only).
-Wall
All of the above `-W' options combined. These are all
the options which pertain to usage that we recommend
avoiding and that we believe is easy to avoid, even in
conjunction with macros.
The remaining `-W...' options are not implied by `-Wall' be-
cause they warn about constructions that we consider reason-
able to use, on occasion, in clean programs.
-Wtraditional
Warn about certain constructs that behave differently
in traditional and ANSI C.
o Macro arguments occurring within string constants in
the macro body. These would substitute the argument in
traditional C, but are part of the constant in ANSI C.
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 local
variable.
-Wid-clash-len
Warn whenever two distinct identifiers match in the
first len characters. This may help you prepare a pro-
gram that will compile with certain obsolete, brain-
damaged compilers.
-Wpointer-arith
Warn about anything that depends on the "size of" a
function type or of void. GNU C assigns these types a
size of 1, for convenience in calculations with void *
pointers and pointers to functions.
-Wcast-qual
Warn whenever a pointer is cast so as to remove a type
qualifier from the target type. For example, warn if a
const char * is cast to an ordinary char *.
-Wcast-align
Warn whenever a pointer is cast such that the required
alignment of the target is increased. For example,
warn if a char * is cast to an int * on machines where
integers can only be accessed at two- or four-byte
boundaries.
-Wwrite-strings
Give string constants the type const char[length] so
that copying the address of one into a non-const char *
pointer will get a warning. These warnings will help
you find at compile time code that can try to write
into a string constant, but only if you have been very
careful about using const in declarations and proto-
types. Otherwise, it will just be a nuisance; this is
why we did not make `-Wall' request these warnings.
-Wconversion
Warn if a prototype causes a type conversion that is
different from what would happen to the same argument
in the absence of a prototype. This includes conver-
sions 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 pro-
motion.
-Waggregate-return
Warn if any functions that return structures or unions
are defined or called. (In languages where you can re-
turn an array, this also elicits a warning.)
-Wstrict-prototypes
Warn if a function is declared or defined without
specifying the argument types. (An old-style function
definition is permitted without a warning if preceded
by a declaration which specifies the argument types.)
-Wmissing-prototypes
Warn if a global function is defined without a previous
prototype declaration. This warning is issued even if
the definition itself provides a prototype. The aim is
to detect global functions that fail to be declared in
header files.
-Wmissing-declarations
Warn if a global function is defined without a previous
declaration. Do so even if the definition itself pro-
vides 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 declaration is
valid and changes nothing.
-Wnested-externs
Warn if an extern declaration is encountered within an
function.
-Wenum-clash
Warn about conversion between different enumeration
types (C++ only).
-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 de-
clares a function that may be an erroneous attempt to
define a virtual function: that is, warn when a func-
tion with the same name as a virtual function in the
base class, but with a type signature that doesn't
match any virtual functions from the base class.
-Winline
Warn if a function can not be inlined, and either it
was declared as inline, or else the -finline-functions
option was given.
-Werror
Treat warnings as errors; abort compilation after any
warning.
DEBUGGING OPTIONS
GNU CC has various special options that are used for debug-
ging either your program or GCC:
-g Produce debugging information in the operating system's
native format (stabs, COFF, XCOFF, or DWARF). GDB can
work with this debugging information.
On most systems that use stabs format, `-g' enables use
of extra debugging information that only GDB can use;
this extra information makes debugging work better in
GDB but will probably make other debuggers crash or re-
fuse to read the program. If you want to control for
certain whether to generate the extra information, use
`-gstabs+', `-gstabs', `-gxcoff+', `-gxcoff',
`-gdwarf+', or `-gdwarf' (see below).
Unlike most other C compilers, GNU CC allows you to use
`-g' with `-O'. The shortcuts taken by optimized code
may occasionally produce surprising results: some vari-
ables you declared may not exist at all; flow of con-
trol may briefly move where you did not expect it; some
statements may not be executed because they compute
constant results or their values were already at hand;
some statements may execute in different places because
they were moved out of loops.
Nevertheless it proves possible to debug optimized out-
put. This makes it reasonable to use the optimizer for
programs that might have bugs.
The following options are useful when GNU CC is generated
with the capability for more than one debugging format.
-ggdb
Produce debugging information in the native format (if
that is supported), including GDB extensions if at all
possible.
-gstabs
Produce debugging information in stabs format (if that
is supported), without GDB extensions. This is the
format used by DBX on most BSD systems.
-gstabs+
Produce debugging information in stabs format (if that
is supported), using GNU extensions understood only by
the GNU debugger (GDB). The use of these extensions is
likely to make other debuggers crash or refuse to read
the program.
-gcoff
Produce debugging information in COFF format (if that
is supported). This is the format used by SDB on most
System V systems prior to System V Release 4.
-gxcoff
Produce debugging information in XCOFF format (if that
is supported). This is the format used by the DBX de-
bugger on IBM RS/6000 systems.
-gxcoff+
Produce debugging information in XCOFF format (if that
is supported), using GNU extensions understood only by
the GNU debugger (GDB). The use of these extensions is
likely to make other debuggers crash or refuse to read
the program.
-gdwarf
Produce debugging information in DWARF format (if that
is supported). This is the format used by SDB on most
System V Release 4 systems.
-gdwarf+
Produce debugging information in DWARF format (if that
is supported), using GNU extensions understood only by
the GNU debugger (GDB). The use of these extensions is
likely to make other debuggers crash or refuse to read
the program.
-glevel
-ggdblevel
-gstabslevel
-gcofflevel -gxcofflevel
-gdwarflevel
Request debugging information and also use level to
specify how much information. The default level is 2.
Level 1 produces minimal information, enough for making
backtraces in parts of the program that you don't plan
to debug. This includes descriptions of functions and
external variables, but no information about local
variables and no line numbers.
Level 3 includes extra information, such as all the
macro definitions present in the program. Some de-
buggers support macro expansion when you use `-g3'.
-p Generate extra code to write profile information suit-
able for the analysis program prof.
-pg Generate extra code to write profile information suit-
able 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. Even-
tually GNU gprof should be extended 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 profil-
ing. If a function name is not unique it can be disam-
biguated 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 in-
structions 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 debugging
the compiler. The file names for most of the dumps are
made by appending a word to the source file name (e.g.
`foo.c.rtl' or `foo.c.jump').
-dM Dump all macro definitions, at the end of preprocess-
ing, and write no output.
-dN Dump all macro names, at the end of preprocessing.
-dD Dump all macro definitions, at the end of preprocess-
ing, in addition to normal output.
-dy Dump debugging information during parsing, to standard
error.
-dr Dump after RTL generation, to `file.rtl'.
-dx Just generate RTL for a function instead of compiling
it. Usually used with `r'.
-dj Dump after first jump optimization, to `file.jump'.
-ds Dump after CSE (including the jump optimization that
sometimes follows CSE), to `file.cse'.
-dL Dump after loop optimization, to `file.loop'.
-dt Dump after the second CSE pass (including the jump op-
timization that sometimes follows CSE), to `file.cse2'.
-df Dump after flow analysis, to `file.flow'.
-dc Dump after instruction combination, to `file.combine'.
-dS Dump after the first instruction scheduling pass, to
`file.sched'.
-dl Dump after local register allocation, to `file.lreg'.
-dg Dump after global register allocation, to `file.greg'.
-dR Dump after the second instruction scheduling pass, to
`file.sched2'.
-dJ Dump after last jump optimization, to `file.jump2'.
-dd Dump after delayed branch scheduling, to `file.dbr'.
-dk Dump after conversion from registers to stack, to
`file.stack'.
-da Produce all the dumps listed above.
-dm Print statistics on memory usage, at the end of the
run, to standard error.
-dp Annotate the assembler output with a comment indicating
which pattern and alternative was used.
-fpretend-float
When running a cross-compiler, pretend that the target
machine uses the same floating point format as the host
machine. This causes incorrect output of the actual
floating constants, but the actual instruction sequence
will probably be the same as GNU CC would make when
running on the target machine.
-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, compiling `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 com-
pile 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 function.
Without `-O', the compiler's goal is to reduce the cost
of compilation and to make debugging produce the ex-
pected results. Statements are independent: if you
stop the program with a breakpoint between statements,
you can then assign a new value to any variable or
change the program counter to any other statement in
the function and get exactly the results you would ex-
pect from the source code.
Without `-O', only variables declared register are al-
located 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' op-
tion is turned on. On some machines other flags may
also be turned on.
-O2 Optimize even more. Nearly all supported optimizations
that do not involve a space-speed tradeoff are per-
formed. Loop unrolling and function inlining are not
done, for example. As compared to -O, this option in-
creases 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-functions.
-O0 Do not optimize.
If you use multiple -O options, with or without level
numbers, the last such option is the one that is effec-
tive.
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 fol-
lowing list shows only one form-the one which is not the de-
fault. You can figure out the other form by either removing
`no-' or adding it.
-ffloat-store
Do not store floating point variables in registers.
This prevents undesirable excess precision on machines
such as the 68000 where the floating registers (of the
68881) keep more precision than a double is supposed to
have.
For most programs, the excess precision does only good,
but a few programs rely on the precise definition of
IEEE floating point. Use `-ffloat-store' for such pro-
grams.
-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 func-
tion to call (which involves figuring out what sorts of
type conversions need to be made); and (3) check the
visibility of the member function to the caller. All
of this adds up to slower compilation. Normally, the
second time a call is made to that member function (or
reference to that data member), it must go through the
same lengthy process again. This means that code like
this
cout << "This " << p << " has " << n << " legs.\n";
makes six passes through all three steps. By using a
software cache, a "hit" significantly reduces this
cost. Unfortunately, using the cache introduces anoth-
er layer of mechanisms which must be implemented, and
so incurs its own overhead. `-fmemoize-lookups' en-
ables the software cache.
Because access privileges (visibility) to members and
member functions may differ from one function context
to the next, g++ may need to flush the cache. With the
`-fmemoize-lookups' flag, the cache is flushed after
every function that is compiled. The `-fsave-memoized'
flag enables the same software cache, but when the com-
piler 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 func-
tion has exactly the same access privileges as every
other, and the cache need not be flushed.
-fno-default-inline
Don't make member functions inline by default merely
because they are defined inside the class scope (C++
only).
-fno-defer-pop
Always pop the arguments to each function call as soon
as that function returns. For machines which must pop
arguments after a function call, the compiler normally
lets arguments accumulate on the stack for several
function calls and pops them all at once.
-fforce-mem
Force memory operands to be copied into registers be-
fore doing arithmetic on them. This may produce better
code by making all memory references potential common
subexpressions. When they are not common subexpres-
sions, instruction combination should eliminate the
separate register-load. I am interested in hearing
about the difference this makes.
-fforce-addr
Force memory address constants to be copied into regis-
ters 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 func-
tions that don't need one. This avoids the instruc-
tions to save, set up and restore frame pointers; it
also makes an extra register available in many func-
tions. It also makes debugging impossible on .
On some machines, such as the Vax, this flag has no ef-
fect, because the standard calling sequence automati-
cally 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 sim-
ple 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 normally does
not output the function as assembler code in its own
right.
-fcaller-saves
Enable values to be allocated in registers that will be
clobbered by function calls, by emitting extra instruc-
tions to save and restore the registers around such
calls. Such allocation is done only when it seems to
result in better code than would otherwise be produced.
This option is enabled by default on certain machines,
usually those which have no call-preserved registers to
use instead.
-fkeep-inline-functions
Even if all calls to a given function are integrated,
and the function is declared static, nevertheless out-
put a separate run-time callable version of the func-
tion.
-fno-function-cse
Do not put function addresses in registers; make each
instruction that calls a constant function contain the
function's address explicitly.
This option results in less efficient code, but some
strange hacks that alter the assembler output may be
confused by the optimizations performed when this op-
tion is not used.
-fno-peephole
Disable any machine-specific peephole optimizations.
-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 compiler to as-
sume arguments to the sqrt function are non-negative
numbers.
This option should never be turned on by any `-O' op-
tion since it can result in incorrect output for pro-
grams which depend on an exact implementation of IEEE
or ANSI rules/specifications for math functions.
The following options control specific optimizations. The
`-O2' option turns on all of these optimizations except
`-funroll-loops' and `-funroll-all-loops'.
The `-O' option usually turns on the `-fthread-jumps' and
`-fdelayed-branch' options, but specific machines may change
the default optimizations.
You can use the following flags in the rare cases when
"fine-tuning" of optimizations to be performed is desired.
-fstrength-reduce
Perform the optimizations of loop strength reduction
and elimination of iteration variables.
-fthread-jumps
Perform optimizations where we check to see if a jump
branches to a location where another comparison sub-
sumed by the first is found. If so, the first branch
is redirected to either the destination of the second
branch or a point immediately following it, depending
on whether the condition is known to be true or false.
-funroll-loops
Perform the optimization of loop unrolling. This is
only done for loops whose number of iterations can be
determined at compile time or run time.
-funroll-all-loops
Perform the optimization of loop unrolling. This is
done for all loops. This usually makes programs run
more slowly.
-fcse-follow-jumps
In common subexpression elimination, scan through jump
instructions when the target of the jump is not reached
by any other path. For example, when CSE encounters an
if statement with an else clause, CSE will follow the
jump when the condition tested is false.
-fcse-skip-blocks
This is similar to `-fcse-follow-jumps', but causes CSE
to follow jumps which conditionally skip over blocks.
When CSE encounters a simple if statement with no else
clause, `-fcse-skip-blocks' causes CSE to follow the
jump around the body of the if.
-frerun-cse-after-loop
Re-run common subexpression elimination after loop op-
timizations has been performed.
-felide-constructors
Elide constructors when this seems plausible (C++
only). With this flag, GNU C++ initializes y directly
from the call to foo without going through a temporary
in the following code:
A foo (); A y = foo ();
Without this option, GNU C++ 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 dif-
ferently, since some constructor calls may be omitted.
-fexpensive-optimizations
Perform a number of minor optimizations that are rela-
tively expensive.
-fdelayed-branch
If supported for the target machine, attempt to reorder
instructions to exploit instruction slots available
after delayed branch instructions.
-fschedule-insns
If supported for the target machine, attempt to reorder
instructions to eliminate execution stalls due to re-
quired data being unavailable. This helps machines
that have slow floating point or memory load instruc-
tions 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 addi-
tional pass of instruction scheduling after register
allocation has been done. This is especially useful on
machines with a relatively small number of registers
and where memory load instructions take more than one
cycle.
TARGET OPTIONS
By default, GNU CC compiles code for the same type of
machine 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 configurations of
GNU CC, for different target machines, can be installed side
by side. Then you specify which one to use with the `-b'
option.
In addition, older and newer versions of GNU CC can be in-
stalled side by side. One of them (probably the newest)
will be the default, but you may sometimes wish to use
another.
-b machine
The argument machine specifies the target machine for
compilation. This is useful when you have installed
GNU CC as a cross-compiler.
The value to use for machine is the same as was speci-
fied 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 com-
pile 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 in-
stalled. For example, version might be `2.0', meaning
to run GNU CC version 2.0.
The default version, when you do not specify `-V', is
controlled by the way GNU CC is installed. Normally,
it will be a version that is recommended for general
use.
MACHINE DEPENDENT OPTIONS
Each of the target machine types can have its own special
options, starting with `-m', to choose among various
hardware models or configurations-for example, 68010 vs
68020, floating coprocessor or none. A single installed
version of the compiler can compile for any model or confi-
guration, according to the options specified.
Some configurations of the compiler also support additional
special options, usually for command-line compatibility with
other compilers on the same platform.
These are the `-m' options defined for the 68000 series:
-m68000
-mc68000
Generate output for a 68000. This is the default when
the compiler is configured for 68000-based systems.
-m68020
-mc68020
Generate output for a 68020 (rather than a 68000).
This is the default when the compiler is configured for
68020-based systems.
-m68881
Generate output containing 68881 instructions for
floating point. This is the default for most 68020-
based systems unless -nfp was specified when the com-
piler was configured.
-m68030
Generate output for a 68030. This is the default when
the compiler is configured for 68030-based systems.
-m68040
Generate output for a 68040. This is the default when
the compiler is configured for 68040-based systems.
-m68020-40
Generate output for a 68040, without using any of the
new instructions. This results in code which can run
relatively efficiently on either a 68020/68881 or a
68030 or a 68040.
-mfpa
Generate output containing Sun FPA instructions for
floating point.
-msoft-float
Generate output containing library calls for floating
point. WARNING: the requisite libraries are not part
of GNU CC. Normally the facilities of the machine's
usual C compiler are used, but this can't be done
directly in cross-compilation. You must make your own
arrangements to provide suitable library functions for
cross-compilation.
-mshort
Consider type int to be 16 bits wide, like short int.
-mnobitfield
Do not use the bit-field instructions. `-m68000' im-
plies `-mnobitfield'.
-mbitfield
Do use the bit-field instructions. `-m68020' implies
`-mbitfield'. This is the default if you use the unmo-
dified sources.
-mrtd
Use a different function-calling convention, in which
functions that take a fixed number of arguments return
with the rtd instruction, which pops their arguments
while returning. This saves one instruction in the
caller since there is no need to pop the arguments
there.
This calling convention is incompatible with the one
normally used on Unix, so you cannot use it if you need
to call libraries compiled with the Unix compiler.
Also, you must provide function prototypes for all
functions that take variable numbers of arguments (in-
cluding printf); otherwise incorrect code will be gen-
erated for calls to those functions.
In addition, seriously incorrect code will result if
you call a function with too many arguments. (Normal-
ly, 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.
-mgnu
Do output those jump instructions, on the assumption
that you will assemble with the GNU assembler.
-mg Output code for g-format floating point numbers instead
of d-format.
These `-m' switches are supported on the SPARC:
-mfpu
-mhard-float
Generate output containing floating point instructions.
This is the default.
-mno-fpu
-msoft-float
Generate output containing library calls for floating
point. Warning: there is no GNU floating-point library
for SPARC. Normally the facilities of the machine's
usual C compiler are used, but this cannot be done
directly in cross-compilation. You must make your own
arrangements to provide suitable library functions for
cross-compilation.
-msoft-float changes the calling convention in the out-
put 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 em-
its 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 ar-
chitecture.
By default (unless specifically configured for the
Fujitsu SPARClite), GCC generates code for the v7 vari-
ant of the SPARC architecture.
-mv8 will give you SPARC v8 code. The only difference
from v7 code is that the compiler emits the integer
multiply and integer divide instructions which exist in
SPARC v8 but not in SPARC v7.
-msparclite will give you SPARClite code. This adds
the integer multiply, integer divide step and scan
(ffs) instructions which exist in SPARClite but not in
SPARC v7.
-mcypress
-msupersparc
These two options select the processor for which the
code is optimised.
With -mcypress (the default), the compiler optimises
code for the Cypress CY7C602 chip, as used in the
SparcStation/SparcServer 3xx series. This is also ap-
propriate 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 nonportable Convex
and Vax programs need this word. (Debuggers don't, ex-
cept for functions with variable-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 support-
ed by the hardware. This is the default.
-mnodw
Generate code that assumes the DW bit is not set.
-mbw Generate code that assumes the system supports byte and
halfword write operations. This is the default.
-mnbw
Generate code that assumes the systems does not support
byte and halfword write operations. 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 default.
-mkernel-registers
Generate references to registers gr64-gr95 instead of
gr96-gr127. This option can be used when compiling
kernel code that wants a set of global registers dis-
joint 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 adjust-
ment. 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.
-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 ver-
sion, 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 in-
clude explicitly) additional code to detect 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 specified
in the 88Open Object Compatibility Standard, "OCS".
This extra information is not needed by GDB. The de-
fault for DG/UX, SVr4, and Delta 88 SVr3.2 is to in-
clude 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'; other 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 standards.
By default GCC does not optimize the argument area.
-mshort-data-num
num Generate smaller data references by making them re-
lative to r0, which allows loading a value using a sin-
gle instruction (rather than the usual two). You con-
trol which data references are affected by specifying
num with this option. For example, if you specify
`-mshort-data-512', then the data references affected
are those involving displacements of less than 512
bytes. `-mshort-data-num' is not effective for num
greater than 64K.
-mserialize-volatile
-mno-serialize-volatile
Do, or do not, generate code to guarantee sequential
consistency of volatile memory references.
GNU CC always guarantees consistency by default, for
the preferred processor submodel. How this is done
depends on the submodel.
The m88100 processor does not reorder memory references
and so always provides sequential consistency. If you
use `-m88100', GNU CC does not generate any special in-
structions for sequential consistency.
The order of memory references made by the m88110 pro-
cessor does not always match the order of the instruc-
tions requesting those references. In particular, a
load instruction may execute before a preceding store
instruction. Such reordering violates sequential con-
sistency of volatile memory references, when there are
multiple processors. When you use `-m88000' or
`-m88110', GNU CC generates special instructions when
appropriate, to force execution in the proper order.
The extra code generated to guarantee consistency may
affect the performance of your application. If you
know that you can safely forgo this guarantee, you may
use the option `-mno-serialize-volatile'.
If you use the `-m88100' option but require sequential
consistency when running on the m88110 processor, you
should use `-mserialize-volatile'.
-msvr4
-msvr3
Turn on (`-msvr4') or off (`-msvr3') compiler exten-
sions related to System V release 4 (SVr4). This con-
trols 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 `#pragma
weak'
o `-msvr4' makes GCC issue additional declaration direc-
tives 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 provi-
sion for large bit shifts.
-muse-div-instruction
Very early models of the 88K architecture didn't have a
divide instruction, so GCC avoids that instruction 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.
These `-m' options are defined for the IBM RT PC:
-min-line-mul
Use an in-line code sequence for integer multiplies.
This is the default.
-mcall-lib-mul
Call lmul$$ for integer multiples.
-mfull-fp-blocks
Generate full-size floating point data blocks, includ-
ing the minimum amount of scratch space recommended by
IBM. This is the default.
-mminimum-fp-blocks
Do not include extra scratch space in floating point
data blocks. This results in smaller code, but slower
execution, since scratch space must be allocated dynam-
ically.
-mfp-arg-in-fpregs
Use a calling sequence incompatible with the IBM cal-
ling convention in which floating point arguments are
passed in floating point registers. Note that
varargs.h and stdargs.h will not work with floating
point operands if this option is specified.
-mfp-arg-in-gregs
Use the normal calling convention for floating point
arguments. This is the default.
-mhc-struct-return
Return structures of more than one word in memory,
rather than in a register. This provides compatibility
with the MetaWare HighC (hc) compiler. Use
`-fpcc-struct-return' for compatibility with the Port-
able C Compiler (pcc).
-mnohc-struct-return
Return some structures of more than one word in regis-
ters, when convenient. This is the default. For com-
patibility 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 de-
fault, which picks the longest cycles times for any of
the machines, in order that the code run at reasonable
rates on all MIPS cpu's. Other choices for cpu-type
are r2000, r3000, r4000, and r6000. While picking a
specific cpu-type will schedule things appropriately
for that particular chip, the compiler will not gen-
erate 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 encapsulate the stabs
within MIPS ECOFF.
-mgas
Generate code for the GNU assembler. This is the de-
fault 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 assem-
bler does not support the -mrnames switch, and the MIPS
assembler will be instructed to run the MIPS C prepro-
cessor over the source file. The -mno-rnames switch is
default.
-mgpopt
-mno-gpopt
The -mgpopt switch says to write all of the data de-
clarations before the instructions in the text 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 optimi-
zation 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 pro-
gram (number of registers saved, stack size, etc.).
-mmemcpy
-mno-memcpy
The -mmemcpy switch makes all block moves call the ap-
propriate string function (memcpy or bcopy) instead of
possibly generating inline code.
-mmips-tfile
-mno-mips-tfile
The -mno-mips-tfile switch causes the compiler not
postprocess the object file with the mips-tfile pro-
gram, 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 addi-
tion, stage2 and stage3 objects will have the temporary
file names passed to the assembler embedded in the ob-
ject file, which means the objects will not compare the
same.
-msoft-float
Generate output containing library calls for floating
point. WARNING: the requisite libraries are not part
of GNU CC. Normally the facilities of the machine's
usual C compiler are used, but this can't be done
directly in cross-compilation. You must make your own
arrangements to provide suitable library functions for
cross-compilation.
-mhard-float
Generate output containing floating point instructions.
This is the default if you use the unmodified sources.
-mfp64
Assume that the FR bit in the status word is on, and
that there are 32 64-bit floating point registers, in-
stead of 32 32-bit floating point registers. You must
also specify the -mcpu=r4000 and -mips3 switches.
-mfp32
Assume that there are 32 32-bit floating point regis-
ters. 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 extern
references into the data section and load them up,
rather than put the references in the text section.
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 instead of the normal
data or bss section. This allows the assembler to emit
one word memory reference instructions based on the
global pointer (gp or $28), instead of the normal two
words used. By default, num is 8 when the MIPS assem-
bler 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 as-
sembling 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 in-
stead of an 386. Code generated for a 486 will run on
a 386 and vice versa.
-msoft-float
Generate output containing library calls for floating
point. Warning: the requisite libraries are not part
of GNU CC. Normally the facilities of the machine's
usual C compiler are used, but this can't be done
directly in cross-compilation. You must make your own
arrangements to provide suitable library functions for
cross-compilation.
On machines where a function returns floating point
results in the 80387 register stack, some floating
point opcodes may be emitted even if `-msoft-float' is
used.
-mno-fp-ret-in-387
Do not use the FPU registers for return values of func-
tions.
The usual calling convention has functions return
values of types float and double in an FPU register,
even if there is no FPU. The idea is that the operat-
ing 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 in-
structions instead. This avoids a rather serious bug
in the HP-UX linker.
-mshared-libs
Generate code that can be linked against HP-UX shared
libraries. This option is not fully function yet, and
is not on by default for any PA target. Using this op-
tion 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 cal-
lee are in the same source file. Do not turn this op-
tion on unless code refuses to link with "branch out of
range errors from the linker.
-mdisable-fpregs
Prevent floating point registers from being used in any
manner. This is necessary for compiling kernels which
perform lazy context switching of floating point regis-
ters. If you use this option and attempt to perform
floating point operations, the compiler will abort.
-mdisable-indexing
Prevent the compiler from using indexing address modes.
This avoids some rather obscure problems when compiling
MIG generated code under MACH.
-mtrailing-colon
Add a colon to the end of label definitions (for ELF
assemblers).
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 align-
ment. 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 substituted by
the assembler or linker, but less efficient code in
other cases, such as calls via function pointers, or
using a linker that doesn't support this optimization.
-mtail-call
-mno-tail-call
Do (or do not) make additional attempts (beyond those
of the machine-independent portions of the compiler) to
optimize tail-recursive calls into branches. You may
not want to do this because the detection of cases
where this is not valid is not totally complete. The
default is -mno-tail-call.
-mcomplex-addr
-mno-complex-addr
Assume (or do not assume) that the use of a complex ad-
dressing mode is a win on this implementation of the
i960. Complex addressing modes may not be worthwhile
on the K-series, but they definitely are on the C-
series. The default is currently -mcomplex-addr for
all processors except the CB and CC.
-mcode-align
-mno-code-align
Align code to 8-byte boundaries for faster fetching (or
don't bother). Currently turned on by default for C-
series implementations only.
-mic-compat
-mic2.0-compat
-mic3.0-compat
Enable compatibility with iC960 v2.0 or v3.0.
-masm-compat
-mintel-asm
Enable compatibility with the iC960 assembler.
-mstrict-align
-mno-strict-align
Do not permit (do permit) unaligned accesses.
-mold-align
Enable structure-alignment compatibility with Intel's
gcc release version 1.3 (based on gcc 1.37). Currently
this is buggy in that #pragma align 1 is always assumed
as well, and cannot be turned off.
These `-m' options are defined for the DEC Alpha implementa-
tions:
-mno-soft-float
-msoft-float
Use (do not use) the hardware floating-point instruc-
tions for floating-point operations. When -msoft-float
is specified, functions in `libgcc1.c' will be used to
perform floating-point operations. Unless they are re-
placed by routines that emulate the floating-point
operations, or compiled in such a way as to call such
emulations routines, these routines will issue
floating-point operations. If you are compiling for
an Alpha without floating-point operations, you must
ensure that the library is built so as not to call
them.
Note that Alpha implementations without floating-point
operations are required to have floating-point regis-
ters.
-mfp-reg
-mno-fp-regs
Generate code that uses (does not use) the floating-
point register set. -mno-fp-regs implies -msoft-float.
If the floating-point register set is not used, float-
ing point operands are passed in integer registers as
if they were integers and floating-point results are
passed in $0 instead of $f0. This is a non-standard
calling sequence, so any function with a floating-point
argument or return value called by code compiled with
-mno-fp-regs must also be compiled with that option.
A typical use of this option is building a kernel that
does not use, and hence need not save and restore, any
floating-point registers.
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 `-symbol-
ic' 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 output.
-Qn Refrain from adding .ident directives to the output
file (this is the default).
-YP,dirs
Search the directories dirs, and no others, for li-
braries specified with `-l'. You can separate directo-
ry entries in dirs from one another with colons.
-Ym,dir
Look in the directory dir to find the M4 preprocessor.
The assembler uses this option.
CODE GENERATION OPTIONS
These machine-independent options control the interface con-
ventions used in code generation.
Most of them begin with `-f'. These options have both posi-
tive and negative forms; the negative form of `-ffoo' would
be `-fno-foo'. In the table below, only one of the forms is
listed-the one which is not the default. You can figure out
the other form by either removing `no-' or adding it.
-fnonnull-objects
Assume that objects reached through references are not
null (C++ only).
Normally, GNU C++ makes conservative assumptions about
objects reached through references. For example, the
compiler must check that a is not null in code like the
following:
obj &a = g (); a.f (2);
Checking that references of this sort have non-null
values requires extra code, however, and it is unneces-
sary 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 reen-
trant; but it has the advantage of allowing intercalla-
bility between GCC-compiled code and PCC-compiled code.
-freg-struct-return
Use the convention that struct and union values are re-
turned in registers when possible. This is more effi-
cient for small structures than -fpcc-struct-return.
If you specify neither -fpcc-struct-return nor
-freg-struct-return, GNU CC defaults to whichever con-
vention 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. Specifical-
ly, the enum type will be equivalent to the smallest
integer type which has enough room.
-fshort-double
Use the same size for double as for float .
-fshared-data
Requests that the data and non-const variables of this
compilation be shared data rather than private data.
The distinction makes sense only on certain operating
systems, where shared data is shared between processes
running the same program, while private data exists in
one copy per process.
-fno-common
Allocate even uninitialized global variables in the bss
section of the object file, rather than generating them
as common blocks. This has the effect that if the same
variable is declared (without extern) in two different
compilations, you will get an error when you link them.
The only reason this might be useful is if you wish to
verify that the program will work on other systems
which always work this way.
-fno-ident
Ignore the `#ident' directive.
-fno-gnu-linker
Do not output global initializations (such as C++ con-
structors 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 in-
cludes constructors and destructors. (collect2 is in-
cluded in the GNU CC distribution.) For systems which
must use collect2, the compiler driver gcc is config-
ured to do this automatically.
-finhibit-size-directive
Don't output a .size assembler directive, or anything
else that would cause trouble if the function is split
in the middle, and the two halves are placed at loca-
tions far apart in memory. This option is used when
compiling `crtstuff.c'; you should not need to use it
for anything else.
-fverbose-asm
Put extra commentary information in the generated as-
sembly code to make it more readable. This option is
generally only of use to those who actually need to
read the generated assembly code (perhaps while debug-
ging the compiler itself).
-fvolatile
Consider all memory references through pointers to be
volatile.
-fvolatile-global
Consider all memory references to extern and global
data items to be volatile.
-fpic
If supported for the target machines, generate
position-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; gen-
erated code should never refer to it (except perhaps as
a stack pointer, frame pointer or in some other fixed
role).
reg must be the name of a register. The register names
accepted are machine-specific and are defined in the
REGISTER_NAMES macro in the machine description macro
file.
This flag does not have a negative form, because it
specifies a three-way choice.
-fcall-used-reg
Treat the register named reg as an allocable register
that is clobbered by function calls. It may be allo-
cated 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 per-
vasive role in the machine's execution model, such as
the stack pointer or frame pointer, will produce disas-
trous 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 register
saved by functions. It may be allocated even for tem-
poraries or variables that live across a call. Func-
tions compiled this way will save and restore the re-
gister reg if they use it.
Use of this flag for a register that has a fixed per-
vasive role in the machine's execution model, such as
the stack pointer or frame pointer, will produce disas-
trous results.
A different sort of disaster will result from the use
of this flag for a register in which function values
may be returned.
This flag does not have a negative form, because it
specifies a three-way choice.
PRAGMAS
Two `#pragma' directives are supported for GNU C++, to per-
mit using the same header file for two purposes: as a defin-
ition 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 ob-
ject files that use those classes. Normally, local
copies of certain information (backup copies of inline
member functions, debugging information, and the inter-
nal tables that implement virtual functions) must be
kept in each object file that includes class defini-
tions. You can use this pragma to avoid such duplica-
tion. When a header file containing `#pragma inter-
face' is included in a compilation, this auxiliary in-
formation will not be generated (unless the main input
source file itself uses `#pragma implementation'). In-
stead, 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 member functions, debugging in-
formation, and the internal tables used to implement
virtual functions are all generated in implementation
files.
If you use `#pragma implementation' with no argument,
it applies to an include file with the same basename as
your source file; for example, in `allclass.cc',
`#pragma implementation' by itself is equivalent to
`#pragma implementation "allclass.h"'. 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 single
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
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
/usr/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; Debugging
with GDB: the GNU Source-Level Debugger, Richard M. Stallman
and Roland H. Pesch; Using as: the GNU Assembler, Dean Els-
ner, Jay Fenlason & friends; ld: the GNU linker, Steve Cham-
berlain 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 per-
mission notice are preserved on all copies.
Permission is granted to copy and distribute modified ver-
sions of this manual under the conditions for verbatim copy-
ing, provided that the entire resulting derived work is dis-
tributed 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 condi-
tions for modified versions, except that this permission no-
tice may be included in translations approved by the Free
Software Foundation instead of in the original English.
AUTHORS
See the GNU CC Manual for the contributors to GNU CC.
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