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When you invoke GNU CC, it normally does preprocessing, compilation,
assembly and linking. The "overall options" allow you to stop this
process at an intermediate stage. For example, the `-c' option
says not to run the linker. Then the output consists of object files
output by the assembler.
Other options are passed on to one stage of processing. Some options
control the preprocessor and others the compiler itself. Yet other
options control the assembler and linker; most of these are not
documented here, since you rarely need to use any of them.
Most of the command line options that you can use with GNU CC are useful
for C programs; when an option is only useful with another language
(usually C++), the explanation says so explicitly. If the description
for a particular option does not mention a source language, you can use
that option with all supported languages.
See section Compiling C++ Programs, for a summary of special
options for compiling C++ programs.
The gcc
program accepts options and file names as operands. Many
options have multiletter names; therefore multiple single-letter options
may not be grouped: `-dr' is very different from `-d
-r'.
You can mix options and other arguments. For the most part, the order
you use doesn't matter. Order does matter when you use several options
of the same kind; for example, if you specify `-L' more than once,
the directories are searched in the order specified.
Many options have long names starting with `-f' or with
`-W'---for example, `-fforce-mem',
`-fstrength-reduce', `-Wformat' and so on. Most of
these have both positive and negative forms; the negative form of
`-ffoo' would be `-fno-foo'. This manual documents
only one of these two forms, whichever one is not the default.
- Option Summary: Brief list of all options, without explanations.
- Overall Options: Controlling the kind of output:
an executable, object files, assembler files,
or preprocessed source.
- Invoking G++: Compiling C++ programs.
- C Dialect Options: Controlling the variant of C language compiled.
- C++ Dialect Options: Variations on C++.
- Warning Options: How picky should the compiler be?
- Debugging Options: Symbol tables, measurements, and debugging dumps.
- Optimize Options: How much optimization?
- Preprocessor Options: Controlling header files and macro definitions.
Also, getting dependency information for Make.
- Assembler Options: Passing options to the assembler.
- Link Options: Specifying libraries and so on.
- Directory Options: Where to find header files and libraries.
Where to find the compiler executable files.
- Target Options: Running a cross-compiler, or an old version of GNU CC.
- Submodel Options: Specifying minor hardware or convention variations,
such as 68010 vs 68020.
- Code Gen Options: Specifying conventions for function calls, data layout
and register usage.
- Environment Variables: Env vars that affect GNU CC.
- Running Protoize: Automatically adding or removing function prototypes.
Here is a summary of all the options, grouped by type. Explanations are
in the following sections.
- Overall Options
-
See section Options Controlling the Kind of Output.
-c -S -E -o file -pipe -v -x language
- C Language Options
-
See section Options Controlling C Dialect.
-ansi -fallow-single-precision -fcond-mismatch -fno-asm
-fno-builtin -fsigned-bitfields -fsigned-char
-funsigned-bitfields -funsigned-char -fwritable-strings
-traditional -traditional-cpp -trigraphs
- C++ Language Options
-
See section Options Controlling C++ Dialect.
-fall-virtual -fdollars-in-identifiers -felide-constructors
-fenum-int-equiv -fexternal-templates -ffor-scope -fno-for-scope
-fhandle-signatures -fmemoize-lookups -fno-default-inline -fno-gnu-keywords
-fnonnull-objects -foperator-names -fstrict-prototype
-fthis-is-variable -nostdinc++ -traditional +en
- Warning Options
-
See section Options to Request or Suppress Warnings.
-fsyntax-only -pedantic -pedantic-errors
-w -W -Wall -Waggregate-return -Wbad-function-cast
-Wcast-align -Wcast-qual -Wchar-subscript -Wcomment
-Wconversion -Wenum-clash -Werror -Wformat
-Wid-clash-len -Wimplicit -Wimport -Winline
-Wlarger-than-len -Wmissing-declarations
-Wmissing-prototypes -Wnested-externs
-Wno-import -Woverloaded-virtual -Wparentheses
-Wpointer-arith -Wredundant-decls -Wreorder -Wreturn-type -Wshadow
-Wstrict-prototypes -Wswitch -Wsynth -Wtemplate-debugging
-Wtraditional -Wtrigraphs -Wuninitialized -Wunused
-Wwrite-strings
- Debugging Options
-
See section Options for Debugging Your Program or GNU CC.
-a -dletters -fpretend-float
-g -glevel -gcoff -gdwarf -gdwarf+
-ggdb -gstabs -gstabs+ -gxcoff -gxcoff+
-p -pg -print-file-name=library -print-libgcc-file-name
-print-prog-name=program -print-search-dirs -save-temps
- Optimization Options
-
See section Options That Control Optimization.
-fcaller-saves -fcse-follow-jumps -fcse-skip-blocks
-fdelayed-branch -fexpensive-optimizations
-ffast-math -ffloat-store -fforce-addr -fforce-mem
-finline-functions -fkeep-inline-functions
-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 -O0 -O1 -O2 -O3
- Preprocessor Options
-
See section Options Controlling the Preprocessor.
-Aquestion(answer) -C -dD -dM -dN
-Dmacro[=defn] -E -H
-idirafter dir
-include file -imacros file
-iprefix file -iwithprefix dir
-iwithprefixbefore dir -isystem dir
-M -MD -MM -MMD -MG -nostdinc -P -trigraphs
-undef -Umacro -Wp,option
- Assembler Option
-
See section Passing Options to the Assembler.
-Wa,option
- Linker Options
-
See section Options for Linking.
object-file-name -llibrary
-nostartfiles -nodefaultlibs -nostdlib
-s -static -shared -symbolic
-Wl,option -Xlinker option
-u symbol
- Directory Options
-
See section Options for Directory Search.
-Bprefix -Idir -I- -Ldir
- Target Options
-
See section Specifying Target Machine and Compiler Version.
-b machine -V version
- Machine Dependent Options
-
See section Hardware Models and Configurations.
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
-mapp-regs -mcypress -mepilogue -mflat -mfpu -mhard-float
-mhard-quad-float -mno-app-regs -mno-flat -mno-fpu
-mno-epilogue -mno-unaligned-doubles
-msoft-float -msoft-quad-float
-msparclite -msupersparc -munaligned-doubles -mv8
SPARC V9 compilers support the following options
in addition to the above:
-mmedlow -mmedany
-mint32 -mint64 -mlong32 -mlong64
-mno-stack-bias -mstack-bias
Convex Options
-mc1 -mc2 -mc32 -mc34 -mc38
-margcount -mnoargcount
-mlong32 -mlong64
-mvolatile-cache -mvolatile-nocache
AMD29K Options
-m29000 -m29050 -mbw -mnbw -mdw -mndw
-mlarge -mnormal -msmall
-mkernel-registers -mno-reuse-arg-regs
-mno-stack-check -mno-storem-bug
-mreuse-arg-regs -msoft-float -mstack-check
-mstorem-bug -muser-registers
ARM Options
-mapcs -m2 -m3 -m6 -mbsd -mxopen -mno-symrename
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
RS/6000 and PowerPC Options
-mcpu=cpu type
-mpower -mno-power -mpower2 -mno-power2
-mpowerpc -mno-powerpc
-mpowerpc-gpopt -mno-powerpc-gpopt
-mpowerpc-gfxopt -mno-powerpc-gfxopt
-mnew-mnemonics -mno-new-mnemonics
-mfull-toc -mminimal-toc -mno-fop-in-toc -mno-sum-in-toc
-msoft-float -mhard-float -mmultiple -mno-multiple
-mstring -mno-string -mbit-align -mno-bit-align
-mstrict-align -mno-strict-align -mrelocatable -mno-relocatable
-mtoc -mno-toc -mtraceback -mno-traceback
-mlittle -mlittle-endian -mbig -mbig-endian
-mcall-aix -mcall-sysv -mprototype
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
-mabicalls -mcpu=cpu type -membedded-data
-membedded-pic -mfp32 -mfp64 -mgas -mgp32 -mgp64
-mgpopt -mhalf-pic -mhard-float -mint64 -mips1
-mips2 -mips3 -mlong64 -mlong-calls -mmemcpy
-mmips-as -mmips-tfile -mno-abicalls
-mno-embedded-data -mno-embedded-pic
-mno-gpopt -mno-long-calls
-mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats
-mrnames -msoft-float
-m4650 -msingle-float -mmad
-mstats -EL -EB -G num -nocpp
i386 Options
-m486 -m386 -mieee-fp -mno-fancy-math-387
-mno-fp-ret-in-387 -msoft-float -msvr3-shlib
-mno-wide-multiply -mrtd -malign-double
-mreg-alloc=list -mregparm=num
-malign-jumps=num -malign-loops=num
-malign-functions=num
HPPA Options
-mdisable-fpregs -mdisable-indexing -mfast-indirect-calls
-mgas -mjump-in-delay -mlong-millicode-calls -mno-disable-fpregs
-mno-disable-indexing -mno-fast-indirect-calls -mno-gas
-mno-jump-in-delay -mno-millicode-long-calls
-mno-portable-runtime -mno-soft-float -msoft-float
-mpa-risc-1-0 -mpa-risc-1-1 -mportable-runtime -mschedule=list
Intel 960 Options
-mcpu type -masm-compat -mclean-linkage
-mcode-align -mcomplex-addr -mleaf-procedures
-mic-compat -mic2.0-compat -mic3.0-compat
-mintel-asm -mno-clean-linkage -mno-code-align
-mno-complex-addr -mno-leaf-procedures
-mno-old-align -mno-strict-align -mno-tail-call
-mnumerics -mold-align -msoft-float -mstrict-align
-mtail-call
DEC Alpha Options
-mfp-regs -mno-fp-regs -mno-soft-float
-msoft-float
Clipper Options
-mc300 -mc400
H8/300 Options
-mrelax -mh
System V Options
-Qy -Qn -YP,paths -Ym,dir
- Code Generation Options
-
See section Options for Code Generation Conventions.
-fcall-saved-reg -fcall-used-reg
-ffixed-reg -finhibit-size-directive
-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 -fpack-struct +e0 +e1
Compilation can involve up to four stages: preprocessing, compilation
proper, assembly and linking, always in that order. The first three
stages apply to an individual source file, and end by producing an
object file; linking combines all the object files (those newly
compiled, and those specified as input) into an executable file.
For any given input file, the file name suffix determines what kind of
compilation is done:
file.c
-
C source code which must be preprocessed.
file.i
-
C source code which should not be preprocessed.
file.ii
-
C++ source code which should not be preprocessed.
file.m
-
Objective-C source code. Note that you must link with the library
`libobjc.a' to make an Objective-C program work.
file.h
-
C header file (not to be compiled or linked).
file.cc
-
file.cxx
-
file.cpp
-
file.C
-
C++ source code which must be preprocessed. Note that in `.cxx',
the last two letters must both be literally `x'. Likewise,
`.C' refers to a literal capital C.
file.s
-
Assembler code.
file.S
-
Assembler code which must be preprocessed.
other
-
An object file to be fed straight into linking.
Any file name with no recognized suffix is treated this way.
You can specify the input language explicitly with the `-x' option:
-x language
-
Specify explicitly the language for the following input files
(rather than letting the compiler choose a default based on the file
name suffix). This option applies to all following input files until
the next `-x' option. Possible values for language are:
c objective-c c++
c-header cpp-output c++-cpp-output
assembler assembler-with-cpp
-x none
-
Turn off any specification of a language, so that subsequent files are
handled according to their file name suffixes (as they are if `-x'
has not been used at all).
If you only want some of the stages of compilation, you can use
`-x' (or filename suffixes) 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 linking
stage simply is not done. The ultimate output is in the form of an
object file for each source file.
By default, the object file name for a source file is made by replacing
the suffix `.c', `.i', `.s', etc., with `.o'.
Unrecognized input files, not requiring compilation or assembly, are
ignored.
-S
-
Stop after the stage of compilation proper; do not assemble. The output
is in the form of an assembler code file for each non-assembler input
file specified.
By default, the assembler file name for a source file is made by
replacing the suffix `.c', `.i', etc., with `.s'.
Input files that don't require compilation are ignored.
-E
-
Stop after the preprocessing stage; do not run the compiler proper. The
output is in the form of preprocessed source code, which is sent to the
standard output.
Input files which don't require preprocessing are ignored.
-o file
-
Place output in file file. This applies regardless to whatever
sort of output is being produced, 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 `-o' is not specified, 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 version 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 is unable to read from a pipe; but the GNU assembler has
no trouble.
C++ source files conventionally use one of the suffixes `.C',
`.cc', `cpp', or `.cxx'; preprocessed C++ files use the
suffix `.ii'. GNU CC recognizes files with these names and
compiles them as C++ programs even if you call the compiler the same way
as for compiling C programs (usually with the name gcc
).
However, C++ programs often require class libraries as well as a
compiler that understands the C++ language--and under some
circumstances, you might want to compile programs from standard input,
or otherwise without a suffix that flags them as C++ programs.
g++
is a program that calls GNU CC with the default language
set to C++, and automatically specifies linking against the GNU class
library libg++.
(1) On many systems, the script g++
is also
installed with the name c++
.
When you compile C++ programs, you may specify many of the same
command-line options that you use for compiling programs in any
language; or command-line options meaningful for C and related
languages; or options that are meaningful only for C++ programs.
See section Options Controlling C Dialect, for
explanations of options for languages related to C.
See section Options Controlling C++ Dialect, for
explanations of options that are meaningful only for C++ programs.
The following options control the dialect of C (or languages derived
from C, such as C++ and Objective C) that the compiler accepts:
-ansi
-
Support all ANSI standard C programs.
This turns off certain features of GNU C that are incompatible with ANSI
C, such as the
asm
, inline
and typeof
keywords, and
predefined macros such as unix
and vax
that identify the
type of system you are using. It also enables the undesirable and
rarely used ANSI trigraph feature, disallows `$' as part of
identifiers, and disables recognition of C++ style `//' comments.
The alternate keywords __asm__
, __extension__
,
__inline__
and __typeof__
continue to work despite
`-ansi'. You would not want to use them in an ANSI C program, of
course, but it is useful to put them in header files that might be included
in 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 required in
addition to `-ansi'. See section Options to Request or Suppress Warnings.
The macro __STRICT_ANSI__
is predefined when the `-ansi'
option is used. 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.
The functions alloca
, abort
, exit
, and
_exit
are not builtin functions when `-ansi' is used.
-fno-asm
-
Do not recognize
asm
, inline
or typeof
as a
keyword, so that code can use these words as identifiers. You can use
the keywords __asm__
, __inline__
and __typeof__
instead. `-ansi' implies `-fno-asm'.
In C++, this switch only affects the typeof
keyword, since
asm
and inline
are standard keywords. You may want to
use the `-fno-gnu-keywords' flag instead, as it also disables the
other, C++-specific, extension keywords such as headof
.
-fno-builtin
-
Don't recognize builtin functions that do not begin with two leading
underscores. Currently, the functions affected include
abort
,
abs
, alloca
, cos
, exit
, fabs
,
ffs
, labs
, memcmp
, memcpy
, sin
,
sqrt
, strcmp
, strcpy
, and strlen
.
GCC normally generates special code to handle certain builtin functions
more efficiently; for instance, calls to alloca
may become single
instructions that adjust the stack directly, and calls to memcpy
may become inline copy loops. The resulting code is often both smaller
and faster, but since the function calls no longer appear as such, you
cannot set a breakpoint on those calls, nor can you change the behavior
of the functions by linking with a different library.
The `-ansi' option prevents alloca
and ffs
from being
builtin functions, since these functions do not have an ANSI standard
meaning.
-trigraphs
-
Support ANSI C trigraphs. You don't want to know about this
brain-damage. The `-ansi' option implies `-trigraphs'.
-traditional
-
Attempt to support some aspects of traditional C compilers.
Specifically:
-
All
extern
declarations take effect globally even if they
are written inside of a function definition. This includes implicit
declarations of functions.
-
The newer keywords
typeof
, inline
, signed
, const
and volatile
are not recognized. (You can still use the
alternative keywords such as __typeof__
, __inline__
, and
so on.)
-
Comparisons between pointers and integers are always allowed.
-
Integer types
unsigned short
and unsigned char
promote
to unsigned int
.
-
Out-of-range floating point literals are not an error.
-
Certain constructs which ANSI regards as a single invalid preprocessing
number, such as `0xe-0xd', are treated as expressions instead.
-
String "constants" are not necessarily constant; they are stored in
writable space, and identical looking constants are allocated
separately. (This is the same as the effect of
`-fwritable-strings'.)
-
All automatic variables not declared
register
are preserved by
longjmp
. Ordinarily, GNU C follows ANSI C: automatic variables
not declared volatile
may be clobbered.
-
The character escape sequences `\x' and `\a' evaluate as the
literal characters `x' and `a' respectively. Without
`-traditional', `\x' is a prefix for the hexadecimal
representation of a character, and `\a' produces a bell.
-
In C++ programs, assignment to
this
is permitted with
`-traditional'. (The option `-fthis-is-variable' also has
this effect.)
You may wish to use `-fno-builtin' as well as `-traditional'
if your program uses names that are normally GNU C builtin functions for
other purposes of its own.
You cannot use `-traditional' if you include any header files that
rely on ANSI C features. Some vendors are starting to ship systems with
ANSI C header files and you cannot use `-traditional' on such
systems to compile files that include any system headers.
-
In the preprocessor, comments convert to nothing at all, rather than
to a space. This allows traditional token concatenation.
-
In preprocessing directive, the `#' symbol must appear as the first
character of a line.
-
In the preprocessor, macro arguments are recognized within string
constants in a macro definition (and their values are stringified,
though without additional quote marks, when they appear in such a
context). The preprocessor always considers a string constant to end
at a newline.
-
The predefined macro
__STDC__
is not defined when you use
`-traditional', but __GNUC__
is (since the GNU extensions
which __GNUC__
indicates are not affected by
`-traditional'). If you need to write header files that work
differently depending on whether `-traditional' is in use, by
testing both of these predefined macros you can distinguish four
situations: GNU C, traditional GNU C, other ANSI C compilers, and other
old C compilers. The predefined macro __STDC_VERSION__
is also
not defined when you use `-traditional'. See section `Standard Predefined Macros' in The C Preprocessor,
for more discussion of these and other predefined macros.
-
The preprocessor considers a string constant to end at a newline (unless
the newline is escaped with `\'). (Without `-traditional',
string constants can contain the newline character as typed.)
-traditional-cpp
-
Attempt to support some aspects of traditional C preprocessors.
This includes the last five items in the table immediately above,
but none of the other effects of `-traditional'.
-fcond-mismatch
-
Allow conditional expressions with mismatched types in the second and
third arguments. The value of such an expression is void.
-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
or unsigned char
, even though its behavior
is always just like one of those two.
-fsigned-char
-
Let the type
char
be signed, like signed char
.
Note that this is equivalent to `-fno-unsigned-char', which is
the negative form of `-funsigned-char'. Likewise, the option
`-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 the
declaration does not use either
signed
or unsigned
. By
default, such a bitfield is signed, because this is consistent: the
basic integer types such as int
are signed types.
However, when `-traditional' is used, 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. The option `-traditional' also has
this effect.
Writing into string constants is a very bad idea; "constants" should
be constant.
-fallow-single-precision
-
Do not promote single precision math operations to double precision,
even when compiling with `-traditional'.
Traditional K&R C promotes all floating point operations to double
precision, regardless of the sizes of the operands. On the
architecture for which you are compiling, single precision may be faster
than double precision. If you must use `-traditional', but want
to use single precision operations when the operands are single
precision, use this option. This option has no effect when compiling
with ANSI or GNU C conventions (the default).
This section describes the command-line options that are only meaningful
for C++ programs; but you can also use most of the GNU compiler options
regardless of what language your program is in. For example, you
might compile a file firstClass.C
like this:
g++ -g -felide-constructors -O -c firstClass.C
In this example, only `-felide-constructors' is an option meant
only for C++ programs; you can use the other options with any
language supported by GNU CC.
Here is a list of options that are only for compiling C++ programs:
-fno-access-control
-
Turn off all access checking. This switch is mainly useful for working
around bugs in the access control code.
-fall-virtual
-
Treat all possible member functions as virtual, implicitly.
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 functions will be made
through the internal table of virtual functions. Under some
circumstances, the compiler can determine that a call to a given virtual
function can be made directly; in these cases the calls are direct in
any case.
-fcheck-new
-
Check that the pointer returned by
operator new
is non-null
before attempting to modify the storage allocated. The current Working
Paper requires that operator new
never return a null pointer, so
this check is normally unnecessary.
-fconserve-space
-
Put uninitialized or runtime-initialized global variables into the
common segment, as C does. This saves space in the executable at the
cost of not diagnosing duplicate definitions. If you compile with this
flag and your program mysteriously crashes after
main()
has
completed, you may have an object that is being destroyed twice because
two definitions were merged.
-fdollars-in-identifiers
-
Accept `$' in identifiers. You can also explicitly prohibit use of
`$' with the option `-fno-dollars-in-identifiers'. (GNU C++
allows `$' by default on some target systems but not others.)
Traditional C allowed the character `$' to form part of
identifiers. However, ANSI C and C++ forbid `$' in identifiers.
-fenum-int-equiv
-
Anachronistically permit implicit conversion of
int
to
enumeration types. Current C++ allows conversion of enum
to
int
, but not the other way around.
-fexternal-templates
-
Cause template instantiations to obey `#pragma interface' and
`implementation'; template instances are emitted or not according
to the location of the template definition. See section Where's the Template?, for more information.
-falt-external-templates
-
Similar to -fexternal-templates, but template instances are emitted or
not according to the place where they are first instantiated.
See section Where's the Template?, for more information.
-ffor-scope
-
-fno-for-scope
-
If -ffor-scope is specified, the scope of variables declared in
a for-init-statement is limited to the `for' loop itself,
as specified by the draft C++ standard.
If -fno-for-scope is specified, the scope of variables declared in
a for-init-statement extends to the end of the enclosing scope,
as was the case in old versions of gcc, and other (traditional)
implementations of C++.
The default if neither flag is given to follow the standard,
but to allow and give a warning for old-style code that would
otherwise be invalid, or have different behavior.
-fno-gnu-keywords
-
Do not recognize
classof
, headof
, signature
,
sigof
or typeof
as a keyword, so that code can use these
words as identifiers. You can use the keywords __classof__
,
__headof__
, __signature__
, __sigof__
, and
__typeof__
instead. `-ansi' implies
`-fno-gnu-keywords'.
-fno-implicit-templates
-
Never emit code for templates which are instantiated implicitly (i.e. by
use); only emit code for explicit instantiations. See section Where's the Template?, for more information.
-fhandle-signatures
-
Recognize the
signature
and sigof
keywords for specifying
abstract types. The default (`-fno-handle-signatures') is not to
recognize them. See section Type Abstraction using Signatures.
-fhuge-objects
-
Support virtual function calls for objects that exceed the size
representable by a `short int'. Users should not use this flag by
default; if you need to use it, the compiler will tell you so. If you
compile any of your code with this flag, you must compile all of
your code with this flag (including libg++, if you use it).
This flag is not useful when compiling with -fvtable-thunks.
-fno-implement-inlines
-
To save space, do not emit out-of-line copies of inline functions
controlled by `#pragma implementation'. This will cause linker
errors if these functions are not inlined everywhere they are called.
-fmemoize-lookups
-
-fsave-memoized
-
Use heuristics to compile faster. These heuristics are not enabled by
default, since they are only effective for certain input files. Other
input files compile more slowly.
The first time the compiler must build a call to a member function (or
reference to a data member), it must (1) determine whether the class
implements member functions of that name; (2) resolve which member
function to call (which involves figuring out what sorts of type
conversions need to be made); and (3) check the visibility of the member
function to the caller. All of this adds up to slower compilation.
Normally, the second time a call is made to that member function (or
reference to that data member), it must go through the same lengthy
process again. This means that code like this:
cout << "This " << p << " has " << n << " legs.\n";
makes six passes through all three steps. By using a software cache, a
"hit" significantly reduces this cost. Unfortunately, using the cache
introduces another layer of mechanisms which must be implemented, and so
incurs its own overhead. `-fmemoize-lookups' enables the software
cache.
Because access privileges (visibility) to members and member functions
may differ from one function context to the next, 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 compiler determines that
the context of the last function compiled would yield the same access
privileges of the next function to compile, it preserves the cache.
This is most helpful when defining many member functions for the same
class: with the exception of member functions which are friends of other
classes, each member function has exactly the same access privileges as
every other, and the cache need not be flushed.
The code that implements these flags has rotted; you should probably
avoid using them.
-fstrict-prototype
-
Within an `extern "C"' linkage specification, treat a function
declaration with no arguments, such as `int foo ();', as declaring
the function to take no arguments. Normally, such a declaration means
that the function
foo
can take any combination of arguments, as
in C. `-pedantic' implies `-fstrict-prototype' unless
overridden with `-fno-strict-prototype'.
This flag no longer affects declarations with C++ linkage.
-fno-nonnull-objects
-
Don't assume that a reference is initialized to refer to a valid object.
Although the current C++ Working Paper prohibits null references, some
old code may rely on them, and you can use `-fno-nonnull-objects'
to turn on checking.
At the moment, the compiler only does this checking for conversions to
virtual base classes.
-foperator-names
-
Recognize the operator name keywords
and
, bitand
,
bitor
, compl
, not
, or
and xor
as
synonyms for the symbols they refer to. `-ansi' implies
`-foperator-names'.
-fthis-is-variable
-
Permit assignment to
this
. The incorporation 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; that is, GNU C++ treats
`this' in a member function of class X
as a non-lvalue of
type `X *'. However, for backwards compatibility, you can make it
valid with `-fthis-is-variable'.
-fvtable-thunks
-
Use `thunks' to implement the virtual function dispatch table
(`vtable'). The traditional (cfront-style) approach to
implementing vtables was to store a pointer to the function and two
offsets for adjusting the `this' pointer at the call site. Newer
implementations store a single pointer to a `thunk' function which
does any necessary adjustment and then calls the target function.
This option also enables a heuristic for controlling emission of
vtables; if a class has any non-inline virtual functions, the vtable
will be emitted in the translation unit containing the first one of
those.
-nostdinc++
-
Do not search for header files in the standard directories specific to
C++, but do still search the other standard directories. (This option
is used when building libg++.)
-traditional
-
For C++ programs (in addition to the effects that apply to both C and
C++), this has the same effect as `-fthis-is-variable'.
See section Options Controlling C Dialect.
In addition, these optimization, warning, and code generation options
have meanings only for C++ programs:
-fno-default-inline
-
Do not assume `inline' for functions defined inside a class scope.
See section Options That Control Optimization.
-Wenum-clash
-
-Woverloaded-virtual
-
-Wtemplate-debugging
-
Warnings that apply only to C++ programs. See section Options to Request or Suppress Warnings.
+en
-
Control how virtual function definitions are used, in a fashion
compatible with
cfront
1.x. See section Options for Code Generation Conventions.
Warnings are diagnostic messages that report constructions which
are not inherently erroneous but which are risky or suggest there
may have been an error.
You can request many specific warnings with options beginning `-W',
for example `-Wimplicit' to request warnings on implicit
declarations. Each of these specific warning options also has a
negative form beginning `-Wno-' to turn off warnings;
for example, `-Wno-implicit'. This manual lists only one of the
two forms, whichever is not the default.
These options control the amount and kinds of warnings produced by GNU
CC:
-fsyntax-only
-
Check the code for syntax errors, but don't do anything beyond that.
-pedantic
-
Issue all the warnings demanded by strict ANSI standard C; reject
all programs that use forbidden extensions.
Valid ANSI standard C programs should compile properly with or without
this option (though a rare few will require `-ansi'). However,
without this option, certain GNU extensions and traditional C features
are supported as well. With this option, they are rejected.
`-pedantic' does not cause warning messages for use of the
alternate keywords whose names begin and end with `__'. Pedantic
warnings are also disabled in the expression that follows
__extension__
. However, only system header files should use
these escape routes; application programs should avoid them.
See section Alternate Keywords.
This option is not intended to be useful; it exists only to satisfy
pedants who would otherwise claim that GNU CC fails to support the ANSI
standard.
Some users try to use `-pedantic' to check programs for strict ANSI
C conformance. They soon find that it does not do quite what they want:
it finds some non-ANSI practices, but not all--only those for which
ANSI C requires a diagnostic.
A feature to report any failure to conform to ANSI C might be useful in
some instances, but would require considerable additional work and would
be quite different from `-pedantic'. We recommend, rather, that
users take advantage of the extensions of GNU C and disregard the
limitations of other compilers. Aside from certain supercomputers and
obsolete small machines, there is less and less reason ever to use any
other C compiler other than for bootstrapping GNU CC.
-pedantic-errors
-
Like `-pedantic', except that errors are produced rather than
warnings.
-w
-
Inhibit all warning messages.
-Wno-import
-
Inhibit warning messages about the use of `#import'.
-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.
-Wcomment
-
Warn whenever a comment-start sequence `/*' appears in a comment.
-Wformat
-
Check calls to
printf
and scanf
, etc., to make sure that
the arguments supplied have types appropriate to the format string
specified.
-Wimplicit
-
Warn whenever a function or parameter is implicitly declared.
-Wparentheses
-
Warn if parentheses are omitted in certain contexts, such
as when there is an assignment in a context where a truth value
is expected, or when operators are nested whose precedence people
often get confused about.
-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
.
-Wswitch
-
Warn whenever a
switch
statement has an index of enumeral type
and lacks a case
for one or more of the named codes of that
enumeration. (The presence of a default
label prevents this
warning.) case
labels outside the enumeration range also
provoke warnings when this option is used.
-Wtrigraphs
-
Warn if any trigraphs are encountered (assuming they are enabled).
-Wunused
-
Warn whenever a variable is unused aside from its declaration,
whenever a function is declared static but never defined, whenever a
label is declared but not used, and whenever a statement computes a
result that is explicitly not used.
To suppress this warning for an expression, simply cast it to void. For
unused variables and parameters, use the `unused' attribute
(see section Specifying Attributes of Variables).
-Wuninitialized
-
An automatic variable is used without first being initialized.
These warnings are possible only in optimizing compilation,
because they require data flow information that is computed only
when optimizing. If you don't specify `-O', you simply won't
get these warnings.
These warnings occur only for variables that are candidates for
register allocation. Therefore, they do not occur for a variable that
is declared
volatile
, or whose address is taken, or whose size
is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
structures, unions or arrays, even when they are in registers.
Note that there may be no warning about a variable that is used only
to compute a value that itself is never used, because such
computations may be deleted by data flow analysis before the warnings
are printed.
These warnings are made optional because 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 all the functions
you use that never return as noreturn
. See section Declaring Attributes of Functions.
-Wenum-clash
-
Warn about conversion between different enumeration types.
(C++ only).
-Wreorder (C++ only)
-
Warn when the order of member initializers given in the code does not
match the order in which they must be executed. For instance:
struct A {
int i;
int j;
A(): j (0), i (1) { }
};
Here the compiler will warn that the member initializers for `i'
and `j' will be rearranged to match the declaration order of the
members.
-Wtemplate-debugging
-
When using templates in a C++ program, warn if debugging is not yet
fully available (C++ only).
-Wall
-
All of the above `-W' options combined. These are all the
options which pertain to usage that we recommend avoiding and that we
believe is easy to avoid, even in conjunction with macros.
The remaining `-W...' options are not implied by `-Wall'
because they warn about constructions that we consider reasonable to
use, on occasion, in clean programs.
-W
-
Print extra warning messages for these events:
-
A nonvolatile automatic variable might be changed by a call to
longjmp
. These warnings as well are possible only in
optimizing compilation.
The compiler sees only the calls to setjmp
. It cannot know
where longjmp
will be called; in fact, a signal handler could
call it at any point in the code. As a result, you may get a warning
even when there is in fact no problem because longjmp
cannot
in fact be called at the place which would cause a problem.
-
A function can return either with or without a value. (Falling
off the end of the function body is considered returning without
a value.) For example, this function would evoke such a
warning:
foo (a)
{
if (a > 0)
return a;
}
-
An expression-statement or the left-hand side of a comma expression
contains no side effects.
To suppress the warning, cast the unused expression to void.
For example, an expression such as `x[i,j]' will cause a warning,
but `x[(void)i,j]' will not.
-
An unsigned value is compared against zero with `<' or `<='.
-
A comparison like `x<=y<=z' appears; this is equivalent to
`(x<=y ? 1 : 0) <= z', which is a different interpretation from
that of ordinary mathematical notation.
-
Storage-class specifiers like
static
are not the first things in
a declaration. According to the C Standard, this usage is obsolescent.
-
If `-Wall' or `-Wunused' is also specified, warn about unused
arguments.
-
An aggregate has a partly bracketed initializer.
For example, the following code would evoke such a warning,
because braces are missing around the initializer for
x.h
:
struct s { int f, g; };
struct t { struct s h; int i; };
struct t x = { 1, 2, 3 };
-Wtraditional
-
Warn about certain constructs that behave differently in traditional and
ANSI C.
-
Macro arguments occurring within string constants in the macro body.
These would substitute the argument in traditional C, but are part of
the constant in ANSI C.
-
A function declared external in one block and then used after the end of
the block.
-
A
switch
statement has an operand of type long
.
-Wshadow
-
Warn whenever a local variable shadows another local variable.
-Wid-clash-len
-
Warn whenever two distinct identifiers match in the first len
characters. This may help you prepare a program that will compile
with certain obsolete, brain-damaged compilers.
-Wlarger-than-len
-
Warn whenever an object of larger than len bytes is defined.
-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.
-Wbad-function-cast
-
Warn whenever a function call is cast to a non-matching type.
For example, warn if
int malloc()
is cast to anything *
.
-Wcast-qual
-
Warn whenever a pointer is cast so as to remove a type qualifier from
the target type. For example, warn if a
const char *
is cast
to an ordinary char *
.
-Wcast-align
-
Warn whenever a pointer is cast such that the required alignment of the
target is increased. For example, warn if a
char *
is cast to
an int *
on machines where integers can only be accessed at
two- or four-byte boundaries.
-Wwrite-strings
-
Give string constants the type
const char[length]
so that
copying the address of one into a non-const
char *
pointer will get a warning. These warnings will help you find at
compile time code that can try to write into a string constant, but
only if you have been very careful about using const
in
declarations and prototypes. Otherwise, it will just be a nuisance;
this is why we did not make `-Wall' request these warnings.
-Wconversion
-
Warn if a prototype causes a type conversion that is different from what
would happen to the same argument in the absence of a prototype. This
includes conversions of fixed point to floating and vice versa, and
conversions changing the width or signedness of a fixed point argument
except when the same as the default promotion.
Also, warn if a negative integer constant expression is implicitly
converted to an unsigned type. For example, warn about the assignment
x = -1
if x
is unsigned. But do not warn about explicit
casts like (unsigned) -1
.
-Waggregate-return
-
Warn if any functions that return structures or unions are defined or
called. (In languages where you can return an array, this also elicits
a warning.)
-Wstrict-prototypes
-
Warn if a function is declared or defined without specifying the
argument types. (An old-style function definition is permitted without
a warning if preceded by a declaration which specifies the argument
types.)
-Wmissing-prototypes
-
Warn if a global function is defined without a previous prototype
declaration. This warning is issued even if the definition itself
provides a prototype. The aim is to detect global functions that fail
to be declared in header files.
-Wmissing-declarations
-
Warn if a global function is defined without a previous declaration.
Do so even if the definition itself provides a prototype.
Use this option to detect global functions that are not declared in
header files.
-Wredundant-decls
-
Warn if anything is declared more than once in the same scope, even in
cases where multiple declaration is valid and changes nothing.
-Wnested-externs
-
Warn if an
extern
declaration is encountered within an function.
-Winline
-
Warn if a function can not be inlined, and either it was declared as inline,
or else the `-finline-functions' option was given.
-Woverloaded-virtual
-
Warn when a derived class function declaration may be an error in
defining a virtual function (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. With this option, the
compiler warns when you define a function with the same name as a
virtual function, but with a type signature that does not match any
declarations from the base class.
-Wsynth (C++ only)
-
Warn when g++'s synthesis behavior does not match that of cfront. For
instance:
struct A {
operator int ();
A& operator = (int);
};
main ()
{
A a,b;
a = b;
}
In this example, g++ will synthesize a default `A& operator =
(const A&);', while cfront will use the user-defined `operator ='.
-Werror
-
Make all warnings into errors.
GNU CC has various special options that are used for debugging
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
refuse to read the program. If you want to control for certain whether
to generate the extra information, use `-gstabs+', `-gstabs',
`-gxcoff+', `-gxcoff', `-gdwarf+', or `-gdwarf'
(see below).
Unlike most other C compilers, GNU CC allows you to use `-g' with
`-O'. The shortcuts taken by optimized code may occasionally
produce surprising results: some variables you declared may not exist
at all; flow of control may briefly move where you did not expect it;
some statements may not be executed because they compute constant
results or their values were already at hand; some statements may
execute in different places because they were moved out of loops.
Nevertheless it proves possible to debug optimized output. This makes
it reasonable to use the optimizer for programs that might have bugs.
The following options are useful when 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. On MIPS, Alpha and System V Release 4 systems this option
produces stabs debugging output which is not understood by DBX or SDB.
On System V Release 4 systems this option requires the GNU assembler.
-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 debugger on IBM RS/6000 systems.
-gxcoff+
-
Produce debugging information in XCOFF format (if that is supported),
using GNU extensions understood only by the GNU debugger (GDB). The
use of these extensions is likely to make other debuggers crash or
refuse to read the program, and may cause assemblers other than the GNU
assembler (GAS) to fail with an error.
-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 debuggers support macro expansion when
you use `-g3'.
-p
-
Generate extra code to write profile information suitable for the
analysis program
prof
. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
-pg
-
Generate extra code to write profile information suitable for the
analysis program
gprof
. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
-a
-
Generate extra code to write profile information for basic blocks, which will
record the number of times each basic block is executed, the basic block start
address, and the function name containing the basic block. If `-g' is
used, the line number and filename of the start of the basic block will also be
recorded. If not overridden by the machine description, the default action is
to append to the text file `bb.out'.
This data could be analyzed by a program like
tcov
. Note,
however, that the format of the data is not what tcov
expects.
Eventually GNU gprof
should be extended to process this data.
-dletters
-
Says to make debugging dumps during compilation at times specified by
letters. This is used for debugging the compiler. The file names
for most of the dumps are made by appending a word to the source file
name (e.g. `foo.c.rtl' or `foo.c.jump'). Here are the
possible letters for use in letters, and their meanings:
- `M'
-
Dump all macro definitions, at the end of preprocessing, and write no
output.
- `N'
-
Dump all macro names, at the end of preprocessing.
- `D'
-
Dump all macro definitions, at the end of preprocessing, in addition to
normal output.
- `y'
-
Dump debugging information during parsing, to standard error.
- `r'
-
Dump after RTL generation, to `file.rtl'.
- `x'
-
Just generate RTL for a function instead of compiling it. Usually used
with `r'.
- `j'
-
Dump after first jump optimization, to `file.jump'.
- `s'
-
Dump after CSE (including the jump optimization that sometimes
follows CSE), to `file.cse'.
- `L'
-
Dump after loop optimization, to `file.loop'.
- `t'
-
Dump after the second CSE pass (including the jump optimization that
sometimes follows CSE), to `file.cse2'.
- `f'
-
Dump after flow analysis, to `file.flow'.
- `c'
-
Dump after instruction combination, to the file
`file.combine'.
- `S'
-
Dump after the first instruction scheduling pass, to
`file.sched'.
- `l'
-
Dump after local register allocation, to
`file.lreg'.
- `g'
-
Dump after global register allocation, to
`file.greg'.
- `R'
-
Dump after the second instruction scheduling pass, to
`file.sched2'.
- `J'
-
Dump after last jump optimization, to `file.jump2'.
- `d'
-
Dump after delayed branch scheduling, to `file.dbr'.
- `k'
-
Dump after conversion from registers to stack, to `file.stack'.
- `a'
-
Produce all the dumps listed above.
- `m'
-
Print statistics on memory usage, at the end of the run, to
standard error.
- `p'
-
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 permanently; place them
in the current directory and name them based on the source file. Thus,
compiling `foo.c' with `-c -save-temps' would produce files
`foo.i' 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 don't do anything else. With this
option, GNU CC does not compile or link anything; it just prints the
file name.
-print-prog-name=program
-
Like `-print-file-name', but searches for a program such as `cpp'.
-print-libgcc-file-name
-
Same as `-print-file-name=libgcc.a'.
This is useful when you use `-nostdlib' or `-nodefaultlibs'
but you do want to link with `libgcc.a'. You can do
gcc -nostdlib files... `gcc -print-libgcc-file-name`
-print-search-dirs
-
Print the name of the configured installation directory and a list of
program and library directories gcc will search--and don't do anything else.
This is useful when gcc prints the error message
`installation problem, cannot exec cpp: No such file or directory'.
To resolve this you either need to put `cpp' and the other compiler
components where gcc expects to find them, or you can set the environment
variable
GCC_EXEC_PREFIX
to the directory where you installed them.
Don't forget the trailing '/'.
See section Environment Variables Affecting GNU CC.
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 expected results.
Statements are independent: if you stop the program with a breakpoint
between statements, you can then assign a new value to any variable or
change the program counter to any other statement in the function and
get exactly the results you would expect from the source code.
Without `-O', the compiler only allocates variables declared
register
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 compiler turns on `-fthread-jumps'
and `-fdefer-pop' on all machines. The compiler turns on
`-fdelayed-branch' on machines that have delay slots, and
`-fomit-frame-pointer' on machines that can support debugging even
without a frame pointer. On some machines the compiler also turns
on other flags.
-O2
-
Optimize even more. GNU CC performs nearly all supported optimizations
that do not involve a space-speed tradeoff. The compiler does not
perform loop unrolling or function inlining when you specify `-O2'.
As compared to `-O', this option increases both compilation time
and the performance of the generated code.
`-O2' turns on all optional optimizations except for loop unrolling
and function inlining. It also turns on the `-fforce-mem' option
on all machines and frame pointer elimination on machines where doing so
does not interfere with debugging.
-O3
-
Optimize yet more. `-O3' turns on all optimizations specified by
`-O2' and also turns on the `inline-functions' option.
-O0
-
Do not optimize.
If you use multiple `-O' options, with or without level numbers,
the last such option is the one that is effective.
Options of the form `-fflag' specify machine-independent
flags. Most flags have both positive and negative forms; the negative
form of `-ffoo' would be `-fno-foo'. 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.
-ffloat-store
-
Do not store floating point variables in registers, and inhibit other
options that might change whether a floating point value is taken from a
register or memory.
This option prevents undesirable excess precision on machines such as
the 68000 where the floating registers (of the 68881) keep more
precision than a
double
is supposed to have. For most programs,
the excess precision does only good, but a few programs rely on the
precise definition of IEEE floating point. Use `-ffloat-store' for
such programs.
-fno-default-inline
-
Do not make member functions inline by default merely because they are
defined inside the class scope (C++ only). Otherwise, when you specify
`-O', member functions defined inside class scope are compiled
inline by default; i.e., you don't need to add `inline' in front of
the member function name.
-fno-defer-pop
-
Always pop the arguments to each function call as soon as that function
returns. For machines which must pop arguments after a function call,
the compiler normally lets arguments accumulate on the stack for several
function calls and pops them all at once.
-fforce-mem
-
Force memory operands to be copied into registers before doing
arithmetic on them. This produces better code by making all memory
references potential common subexpressions. When they are not common
subexpressions, instruction combination should eliminate the separate
register-load. The `-O2' option turns on this option.
-fforce-addr
-
Force memory address constants to be copied into registers before
doing arithmetic on them. This may produce better code just as
`-fforce-mem' may.
-fomit-frame-pointer
-
Don't keep the frame pointer in a register for functions that
don't need one. This avoids the instructions to save, set up and
restore frame pointers; it also makes an extra register available
in many functions. It also makes debugging impossible on
some machines.
On some machines, such as the Vax, this flag has no effect, because
the standard calling sequence automatically handles the frame pointer
and nothing is saved by pretending it doesn't exist. The
machine-description macro
FRAME_POINTER_REQUIRED
controls
whether a target machine supports this flag. See section Register Usage.
-fno-inline
-
Don't pay attention to the
inline
keyword. Normally this option
is used to keep the compiler from expanding any functions inline.
Note that if you are not optimizing, no functions can be expanded inline.
-finline-functions
-
Integrate all simple functions into their callers. The compiler
heuristically decides which functions are simple enough to be worth
integrating in this way.
If all calls to a given function are integrated, and the function is
declared
static
, then the function is normally not output as
assembler code in its own right.
-fkeep-inline-functions
-
Even if all calls to a given function are integrated, and the function
is declared
static
, nevertheless output a separate run-time
callable version of the function.
-fno-function-cse
-
Do not put function addresses in registers; make each instruction that
calls a constant function contain the function's address explicitly.
This option results in less efficient code, but some strange hacks
that alter the assembler output may be confused by the optimizations
performed when this option is not used.
-ffast-math
-
This option allows GCC to violate some ANSI or IEEE rules and/or
specifications in the interest of optimizing code for speed. For
example, it allows the compiler to assume arguments to the
sqrt
function are non-negative numbers and that no floating-point values
are NaNs.
This option should never be turned on by any `-O' option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ANSI rules/specifications for
math functions.
The following options control specific optimizations. The `-O2'
option turns on all of these optimizations except `-funroll-loops'
and `-funroll-all-loops'. On most machines, the `-O' option
turns on the `-fthread-jumps' and `-fdelayed-branch' options,
but specific machines may handle it differently.
You can use the following flags in the rare cases when "fine-tuning"
of optimizations to be performed is desired.
-fstrength-reduce
-
Perform the optimizations of loop strength reduction and
elimination of iteration variables.
-fthread-jumps
-
Perform optimizations where we check to see if a jump branches to a
location where another comparison subsumed by the first is found. If
so, the first branch is redirected to either the destination of the
second branch or a point immediately following it, depending on whether
the condition is known to be true or false.
-fcse-follow-jumps
-
In common subexpression elimination, scan through jump instructions
when the target of the jump is not reached by any other path. For
example, when CSE encounters an
if
statement with an
else
clause, CSE will follow the jump when the condition
tested is false.
-fcse-skip-blocks
-
This is similar to `-fcse-follow-jumps', but causes CSE to
follow jumps which conditionally skip over blocks. When CSE
encounters a simple
if
statement with no else clause,
`-fcse-skip-blocks' causes CSE to follow the jump around the
body of the if
.
-frerun-cse-after-loop
-
Re-run common subexpression elimination after loop optimizations has been
performed.
-fexpensive-optimizations
-
Perform a number of minor optimizations that are relatively expensive.
-fdelayed-branch
-
If supported for the target machine, attempt to reorder instructions
to exploit instruction slots available after delayed branch
instructions.
-fschedule-insns
-
If supported for the target machine, attempt to reorder instructions to
eliminate execution stalls due to required data being unavailable. This
helps machines that have slow floating point or memory load instructions
by allowing other instructions to be issued until the result of the load
or floating point instruction is required.
-fschedule-insns2
-
Similar to `-fschedule-insns', but requests an additional pass of
instruction scheduling after register allocation has been done. This is
especially useful on machines with a relatively small number of
registers and where memory load instructions take more than one cycle.
-fcaller-saves
-
Enable values to be allocated in registers that will be clobbered by
function calls, by emitting extra instructions to save and restore the
registers around such calls. Such allocation is done only when it
seems to result in better code than would otherwise be produced.
This option is enabled by default on certain machines, usually those
which have no call-preserved registers to use instead.
-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-loop' implies both `-fstrength-reduce' and
`-frerun-cse-after-loop'.
-funroll-all-loops
-
Perform the optimization of loop unrolling. This is done for all loops
and usually makes programs run more slowly. `-funroll-all-loops'
implies `-fstrength-reduce' as well as `-frerun-cse-after-loop'.
-fno-peephole
-
Disable any machine-specific peephole optimizations.
These options control the C preprocessor, which is run on each C source
file before actual compilation.
If you use the `-E' option, nothing is done except preprocessing.
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 input file.
In effect, the contents of file are compiled first. Any `-D'
and `-U' options on the command line are always processed before
`-include file', regardless of the order in which they are
written. All the `-include' and `-imacros' options are
processed in the order in which they are 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 effect of `-imacros file'
is to make the macros defined in file available for use in the
main input.
Any `-D' and `-U' options on the command line are always
processed before `-imacros file', regardless of the order in
which they are written. All the `-include' and `-imacros'
options are processed in the order in which they are written.
-idirafter dir
-
Add the directory dir to the second include path. The directories
on the second include path are searched when a header file is not found
in any of the directories in the main include path (the one that
`-I' adds to).
-iprefix prefix
-
Specify prefix as the prefix for subsequent `-iwithprefix'
options.
-iwithprefix dir
-
Add a directory to the second include path. The directory's name is
made by concatenating prefix and dir, where prefix was
specified previously with `-iprefix'. If you have not specified a
prefix yet, the directory containing the installed passes of the
compiler is used as the default.
-iwithprefixbefore dir
-
Add a directory to the main include path. The directory's name is made
by concatenating prefix and dir, as in the case of
`-iwithprefix'.
-isystem dir
-
Add a directory to the beginning of the second include path, marking it
as a system directory, so that it gets the same special treatment as
is applied to the standard system directories.
-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 appropriate) are searched. See section Options for Directory Search, for information on `-I'.
By using both `-nostdinc' and `-I-', you can limit the include-file
search path to only those directories you specify explicitly.
-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 standard output or to the
specified output file.
-C
-
Tell the preprocessor not to discard comments. Used with the
`-E' option.
-P
-
Tell the preprocessor not to generate `#line' directives.
Used with the `-E' option.
-M
-
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
#include
header files it uses. 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'.
Another way to specify output of a make
rule is by setting
the environment variable DEPENDENCIES_OUTPUT
(see section Environment Variables Affecting GNU CC).
-MM
-
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 a file made by
replacing ".c" with ".d" at the end of the input file names.
This is in addition to compiling the file as specified---`-MD' does
not inhibit ordinary compilation the way `-M' does.
In Mach, you can use the utility
md
to merge multiple dependency
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.
-MG
-
Treat missing header files as generated files and assume they live in the
same directory as the source file. If you specify `-MG', you
must also specify either `-M' or `-MM'. `-MG' is not
supported with `-MD' or `-MMD'.
-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 preprocessing 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 definition.
-Dmacro=defn
-
Define macro macro as defn. All instances of `-D' on
the command line are processed before any `-U' options.
-Umacro
-
Undefine macro macro. `-U' options are evaluated after all
`-D' options, but before any `-include' and `-imacros'
options.
-dM
-
Tell the preprocessor to output only a list of the macro definitions
that are in effect at the end of preprocessing. Used with the `-E'
option.
-dD
-
Tell the preprocessing 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.
-trigraphs
-
Support ANSI C trigraphs. The `-ansi' option also has this effect.
-Wp,option
-
Pass option as an option to the preprocessor. If option
contains commas, it is split into multiple options at the commas.
You can pass options to the assembler.
-Wa,option
-
Pass option as an option to the assembler. If option
contains commas, it is split into multiple options at the commas.
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 linking is done, these object files are used as input
to the linker.
-c
-
-S
-
-E
-
If any of these options is used, then the linker is not run, and
object file names should not be used as arguments. See section Options Controlling the Kind of Output.
-llibrary
-
Search the library named library when linking.
It makes a difference where in the command you write this option; the
linker searches processes libraries and object files in the order they
are specified. Thus, `foo.o -lz bar.o' searches library `z'
after file `foo.o' but before `bar.o'. If `bar.o' refers
to functions in `z', those functions may not be loaded.
The linker searches a standard list of directories for the library,
which is actually a file named `liblibrary.a'. The linker
then uses this file as if it had been specified precisely by name.
The directories searched include several standard system directories
plus any that you specify with `-L'.
Normally the files found this way are library files--archive files
whose members are object files. The linker handles an archive file by
scanning through it for members which define symbols that have so far
been referenced but not defined. But if the file that is found is an
ordinary object file, it is linked in the usual fashion. The only
difference between using an `-l' option and specifying a file name
is that `-l' surrounds library with `lib' and `.a'
and searches several directories.
-lobjc
-
You need this special case of the `-l' option in order to
link an Objective C program.
-nostartfiles
-
Do not use the standard system startup files when linking.
The standard system libraries are used normally, unless
-nostdlib
or -nodefaultlibs
is used.
-nodefaultlibs
-
Do not use the standard system libraries when linking.
Only the libraries you specify will be passed to the linker.
The standard startup files are used normally, unless
-nostartfiles
is used.
-nostdlib
-
Do not use the standard system startup files or libraries when linking.
No startup files and only the libraries you specify will be passed to
the linker.
One of the standard libraries bypassed by `-nostdlib' and
`-nodefaultlibs' is `libgcc.a', a library of internal subroutines
that GNU CC uses to overcome shortcomings of particular machines, or special
needs for some languages.
(See section Interfacing to GNU CC Output, for more discussion of
`libgcc.a'.)
In most cases, you need `libgcc.a' even when you want to avoid
other standard libraries. In other words, when you specify `-nostdlib'
or `-nodefaultlibs' you should usually specify `-lgcc' as well.
This ensures that you have no unresolved references to internal GNU CC
library subroutines. (For example, `__main', used to ensure C++
constructors will be called; see section
collect2
.)
-s
-
Remove all symbol table and relocation information from the executable.
-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 systems support this option.
-symbolic
-
Bind references to global symbols when building a shared object. Warn
about any unresolved references (unless overridden by the link editor
option `-Xlinker -z -Xlinker defs'). Only a few systems support
this option.
-Xlinker option
-
Pass option as an option to the linker. You can use this to
supply system-specific linker options which 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 contains
commas, it is split into multiple options at the commas.
-u symbol
-
Pretend the symbol symbol is undefined, to force linking of
library modules to define it. You can use `-u' multiple times with
different symbols to force loading of additional library modules.
These options specify directories to search for header files, for
libraries and for parts of the compiler:
-Idir
-
Add the directory directory to the head of the list of directories
to be searched for header files. This can be used to override a system
header file, substituting your own version, since these directories are
searched before the system header file directories. If you use more
than one `-I' option, the directories are scanned in left-to-right
order; the standard system directories come after.
-I-
-
Any directories you specify with `-I' options before the `-I-'
option are searched only for the case of `#include "file"';
they are not searched for `#include <file>'.
If additional directories are specified with `-I' options after
the `-I-', these directories are searched for all `#include'
directives. (Ordinarily all `-I' directories are used
this way.)
In addition, the `-I-' option inhibits the use of the current
directory (where the current input file came from) as the first search
directory for `#include "file"'. There is no way to
override this effect of `-I-'. With `-I.' you can specify
searching the directory which was current when the compiler was
invoked. That is not exactly the same as what the preprocessor does
by default, but it is often satisfactory.
`-I-' does not inhibit the use of the standard system directories
for header files. Thus, `-I-' and `-nostdinc' are
independent.
-Ldir
-
Add directory dir to the list of directories to be searched
for `-l'.
-Bprefix
-
This option specifies where to find the executables, libraries,
include files, and data files of the compiler itself.
The compiler driver program runs one or more of the subprograms
`cpp', `cc1', `as' and `ld'. It tries
prefix as a prefix for each program it tries to run, both with and
without `machine/version/' (see section Specifying Target Machine and Compiler 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 unmodified program
name is searched for using the directories specified in your
`PATH' environment variable.
`-B' prefixes that effectively specify directory names also apply
to libraries in the linker, because the compiler translates these
options into `-L' options for the linker. They also apply to
includes files in the preprocessor, because the compiler translates these
options into `-isystem' options for the preprocessor. In this case,
the compiler appends `include' to the prefix.
The run-time support file `libgcc.a' can also be 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.
Another way to specify a prefix much like the `-B' prefix is to use
the environment variable
GCC_EXEC_PREFIX
. See section Environment Variables Affecting GNU CC.
By default, GNU CC compiles code for the same type of machine that you
are using. However, it can also be installed 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 installed 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 specified as the
machine type when configuring GNU CC as a cross-compiler. For
example, if a cross-compiler was configured with `configure
i386v', meaning to compile for an 80386 running System V, then you
would specify `-b i386v' to run that cross compiler.
When you do not specify `-b', it normally means to compile for
the same type of machine that you are using.
-V version
-
The argument version specifies which version of GNU CC to run.
This is useful when multiple versions are installed. For example,
version might be `2.0', meaning to run GNU CC version 2.0.
The default version, when you do not specify `-V', is the last
version of GNU CC that you installed.
The `-b' and `-V' options actually work by controlling part of
the file name used for the executable files and libraries used for
compilation. A given version of GNU CC, for a given target machine, is
normally kept in the directory `/usr/local/lib/gcc-lib/machine/version'.
Thus, sites can customize the effect of `-b' or `-V' either by
changing the names of these directories or adding alternate names (or
symbolic links). If in directory `/usr/local/lib/gcc-lib/' the
file `80386' is a link to the file `i386v', then `-b
80386' becomes an alias for `-b i386v'.
In one respect, the `-b' or `-V' do not completely change
to a different compiler: the top-level driver program gcc
that you originally invoked continues to run and invoke the other
executables (preprocessor, compiler per se, assembler and linker)
that do the real work. However, since no real work is done in the
driver program, it usually does not matter that the driver program
in use is not the one for the specified target and version.
The only way that the driver program depends on the target machine is
in the parsing and handling of special machine-specific options.
However, this is controlled by a file which is found, along with the
other executables, in the directory for the specified version and
target machine. As a result, a single installed driver program adapts
to any specified target machine and compiler version.
The driver program executable does control one significant thing,
however: the default version and target machine. Therefore, you can
install different instances of the driver program, compiled for
different targets or versions, under different names.
For example, if the driver for version 2.0 is installed as ogcc
and that for version 2.1 is installed as gcc
, then the command
gcc
will use version 2.1 by default, while ogcc
will use
2.0 by default. However, you can choose either version with either
command with the `-V' option.
Earlier we discussed the standard option `-b' which chooses among
different installed compilers for completely different target
machines, such as Vax vs. 68000 vs. 80386.
In addition, each of these 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 configuration, according to the
options specified.
Some configurations of the compiler also support additional special
options, usually for compatibility with other compilers on the same
platform.
These options are defined by the macro TARGET_SWITCHES
in the
machine description. The default for the options is also defined by
that macro, which enables you to change the defaults.
These are the `-m' options defined for the 68000 series. The default
values for these options depends on which style of 68000 was selected when
the compiler was configured; the defaults for the most common choices are
given below.
-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. 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 systems unless `-nfp' was
specified when the compiler was configured.
-m68030
-
Generate output for a 68030. This is the default when the compiler is
configured for 68030-based systems.
-m68040
-
Generate output for a 68040. This is the default when the compiler is
configured for 68040-based systems.
This option inhibits the use of 68881/68882 instructions that have to be
emulated by software on the 68040. If your 68040 does not have code to
emulate those instructions, use `-m68040'.
-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. The generated code does use the
68881 instructions that are emulated on the 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 available for all m68k
targets. 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. The embedded targets `m68k-*-aout' and
`m68k-*-coff' do provide software floating point support.
-mshort
-
Consider type
int
to be 16 bits wide, like short int
.
-mnobitfield
-
Do not use the bit-field instructions. The `-m68000' option
implies `-mnobitfield'.
-mbitfield
-
Do use the bit-field instructions. The `-m68020' option implies
`-mbitfield'. This is the default if you use a configuration
designed for a 68020.
-mrtd
-
Use a different function-calling convention, in which functions
that take a fixed number of arguments return with the
rtd
instruction, which pops their arguments while returning. This
saves one instruction in the caller since there is no need to pop
the arguments there.
This calling convention is incompatible with the one normally
used on Unix, so you cannot use it if you need to call libraries
compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including printf
);
otherwise incorrect code will be generated for calls to those
functions.
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
The rtd
instruction is supported by the 68010 and 68020
processors, but not by the 68000.
These `-m' options are defined for the 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:
-mno-app-regs
-
-mapp-regs
-
Specify `-mapp-regs' to generate output using the global registers
2 through 4, which the SPARC SVR4 ABI reserves for applications. This
is the default.
To be fully SVR4 ABI compliant at the cost of some performance loss,
specify `-mno-app-regs'. You should compile libraries and system
software with this option.
-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: the requisite libraries are not available for all SPARC
targets. 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. The embedded targets `sparc-*-aout' and
`sparclite-*-*' do provide software floating point support.
`-msoft-float' changes the calling convention in the output file;
therefore, it is only useful if you compile all of a program with
this option. In particular, you need to compile `libgcc.a', the
library that comes with GNU CC, with `-msoft-float' in order for
this to work.
-mhard-quad-float
-
Generate output containing quad-word (long double) floating point
instructions.
-msoft-quad-float
-
Generate output containing library calls for quad-word (long double)
floating point instructions. The functions called are those specified
in the SPARC ABI. This is the default.
As of this writing, there are no sparc implementations that have hardware
support for the quad-word floating point instructions. They all invoke
a trap handler for one of these instructions, and then the trap handler
emulates the effect of the instruction. Because of the trap handler overhead,
this is much slower than calling the ABI library routines. Thus the
`-msoft-quad-float' option is the default.
-mno-epilogue
-
-mepilogue
-
With `-mepilogue' (the default), the compiler always emits code for
function exit at the end of each function. Any function exit in
the middle of the function (such as a return statement in C) will
generate a jump to the exit code at the end of the function.
With `-mno-epilogue', the compiler tries to emit exit code inline
at every function exit.
-mno-flat
-
-mflat
-
With `-mflat', the compiler does not generate save/restore instructions
and will use a "flat" or single register window calling convention.
This model uses %i7 as the frame pointer and is compatible with the normal
register window model. Code from either may be intermixed although
debugger support is still incomplete. The local registers and the input
registers (0-5) are still treated as "call saved" registers and will be
saved on the stack as necessary.
With `-mno-flat' (the default), the compiler emits save/restore
instructions (except for leaf functions) and is the normal mode of operation.
-mno-unaligned-doubles
-
-munaligned-doubles
-
Assume that doubles have 8 byte alignment. This is the default.
With `-munaligned-doubles', GNU CC assumes that doubles have 8 byte
alignment only if they are contained in another type, or if they have an
absolute address. Otherwise, it assumes they have 4 byte alignment.
Specifying this option avoids some rare compatibility problems with code
generated by other compilers. It is not the default because it results
in a performance loss, especially for floating point code.
-mv8
-
-msparclite
-
These two options select variations on the SPARC architecture.
By default (unless specifically configured for the Fujitsu SPARClite),
GCC generates code for the v7 variant of the SPARC architecture.
`-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 optimizes code for the
Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series.
This is also appropriate for the older SparcStation 1, 2, IPX etc.
With `-msupersparc' the compiler optimizes 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.
In a future version of GCC, these options will very likely be
renamed to `-mcpu=cypress' and `-mcpu=supersparc'.
These `-m' switches are supported in addition to the above
on SPARC V9 processors:
-mmedlow
-
Generate code for the Medium/Low code model: assume a 32 bit address space.
Programs are statically linked, PIC is not supported. Pointers are still
64 bits.
It is very likely that a future version of GCC will rename this option.
-mmedany
-
Generate code for the Medium/Anywhere code model: assume a 32 bit text
segment starting at offset 0, and a 32 bit data segment starting anywhere
(determined at link time). Programs are statically linked, PIC is not
supported. Pointers are still 64 bits.
It is very likely that a future version of GCC will rename this option.
-mint64
-
Types long and int are 64 bits.
-mlong32
-
Types long and int are 32 bits.
-mlong64
-
-mint32
-
Type long is 64 bits, and type int is 32 bits.
-mstack-bias
-
-mno-stack-bias
-
With `-mstack-bias', GNU CC assumes that the stack pointer, and
frame pointer if present, are offset by -2047 which must be added back
when making stack frame references.
Otherwise, assume no such offset is present.
These `-m' options are defined for Convex:
-mc1
-
Generate output for C1. The code will run on any Convex machine.
The preprocessor symbol
__convex__c1__
is defined.
-mc2
-
Generate output for C2. Uses instructions not available on C1.
Scheduling and other optimizations are chosen for max performance on C2.
The preprocessor symbol
__convex_c2__
is defined.
-mc32
-
Generate output for C32xx. Uses instructions not available on C1.
Scheduling and other optimizations are chosen for max performance on C32.
The preprocessor symbol
__convex_c32__
is defined.
-mc34
-
Generate output for C34xx. Uses instructions not available on C1.
Scheduling and other optimizations are chosen for max performance on C34.
The preprocessor symbol
__convex_c34__
is defined.
-mc38
-
Generate output for C38xx. Uses instructions not available on C1.
Scheduling and other optimizations are chosen for max performance on C38.
The preprocessor symbol
__convex_c38__
is defined.
-margcount
-
Generate code which puts an argument count in the word preceding each
argument list. This is compatible with regular CC, and a few programs
may need the argument count word. GDB and other source-level debuggers
do not need it; this info is in the symbol table.
-mnoargcount
-
Omit the argument count word. This is the default.
-mvolatile-cache
-
Allow volatile references to be cached. This is the default.
-mvolatile-nocache
-
Volatile references bypass the data cache, going all the way to memory.
This is only needed for multi-processor code that does not use standard
synchronization instructions. Making non-volatile references to volatile
locations will not necessarily work.
-mlong32
-
Type long is 32 bits, the same as type int. This is the default.
-mlong64
-
Type long is 64 bits, the same as type long long. This option is useless,
because no library support exists for it.
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 supported by the hardware. This is the
default.
-mndw
-
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. `-mnbw' implies `-mndw'.
-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.
-mnormal
-
Use the normal memory model: Generate
call
instructions only when
calling functions in the same file and calli
instructions
otherwise. This works if each file occupies less than 256 KB but allows
the entire executable to be larger than 256 KB. This is the default.
-mlarge
-
Always use
calli
instructions. Specify this option if you expect
a single file to compile into more than 256 KB of code.
-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 to
registers gr96-gr127
. This option can be used when compiling
kernel code that wants a set of global registers disjoint from that used
by user-mode code.
Note that when this option is used, register names in `-f' flags
must use the normal, user-mode, names.
-muser-registers
-
Use the normal set of global registers,
gr96-gr127
. This is the
default.
-mstack-check
-
-mno-stack-check
-
Insert (or do not insert) a call to
__msp_check
after each stack
adjustment. This is often used for kernel code.
-mstorem-bug
-
-mno-storem-bug
-
`-mstorem-bug' handles 29k processors which cannot handle the
separation of a mtsrim insn and a storem instruction (most 29000 chips
to date, but not the 29050).
-mno-reuse-arg-regs
-
-mreuse-arg-regs
-
`-mno-reuse-arg-regs' tells the compiler to only use incoming argument
registers for copying out arguments. This helps detect calling a function
with fewer arguments than it was declared with.
-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.
These `-m' options are defined for Advanced RISC Machines (ARM)
architectures:
-m2
-
-m3
-
These options are identical. Generate code for the ARM2 and ARM3
processors. This option is the default. You should also use this
option to generate code for ARM6 processors that are running with a
26-bit program counter.
-m6
-
Generate code for the ARM6 processor when running with a 32-bit program
counter.
-mapcs
-
Generate a stack frame that is compliant with the ARM Procedure Call
Standard for all functions, even if this is not strictly necessary for
correct execution of the code.
-mbsd
-
This option only applies to RISC iX. Emulate the native BSD-mode
compiler. This is the default if `-ansi' is not specified.
-mxopen
-
This option only applies to RISC iX. Emulate the native X/Open-mode
compiler.
-mno-symrename
-
This option only applies to RISC iX. Do not run the assembler
post-processor, `symrename', after code has been assembled.
Normally it is necessary to modify some of the standard symbols in
preparation for linking with the RISC iX C library; this option
suppresses this pass. The post-processor is never run when the
compiler is built for cross-compilation.
These `-m' options are defined for Motorola 88k architectures:
-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.
-mbig-pic
-
Obsolete option to be removed from the next revision.
Use `-fPIC'.
-midentify-revision
-
Include an
ident
directive in the assembler output recording the
source file name, compiler name and version, timestamp, and compilation
flags used.
-mno-underscores
-
In assembler output, emit symbol names without adding an underscore
character at the beginning of each name. The default is to use an
underscore as prefix on each name.
-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 allows debugging of code that
has had the frame pointer eliminated. The default for DG/UX, SVr4, and
Delta 88 SVr3.2 is to include this information; other 88k configurations
omit this information by default.
-mocs-frame-position
-
When emitting COFF debugging information for automatic variables and
parameters stored on the stack, use the offset from the canonical frame
address, which is the stack pointer (register 31) on entry to the
function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use
`-mocs-frame-position'; other 88k configurations have the default
`-mno-ocs-frame-position'.
-mno-ocs-frame-position
-
When emitting COFF debugging information for automatic variables and
parameters stored on the stack, use the offset from the frame pointer
register (register 30). When this option is in effect, the frame
pointer is not eliminated when debugging information is selected by the
-g switch.
-moptimize-arg-area
-
-mno-optimize-arg-area
-
Control how function arguments are stored in stack frames.
`-moptimize-arg-area' saves space by optimizing them, but this
conflicts with the 88open specifications. The opposite alternative,
`-mno-optimize-arg-area', agrees with 88open standards. By default
GNU CC does not optimize the argument area.
-mshort-data-num
-
Generate smaller data references by making them relative to
r0
,
which allows loading a value using a single instruction (rather than the
usual two). You control which data references are affected by
specifying num with this option. For example, if you specify
`-mshort-data-512', then the data 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 don't, generate code to guarantee sequential consistency
of volatile memory references. By default, consistency is
guaranteed.
The order of memory references made by the MC88110 processor does
not always match the order of the instructions requesting those
references. In particular, a load instruction may execute before
a preceding store instruction. Such reordering violates
sequential consistency of volatile memory references, when there
are multiple processors. When consistency must be guaranteed,
GNU C generates special instructions, as needed, to force
execution in the proper order.
The MC88100 processor does not reorder memory references and so
always provides sequential consistency. However, by default, GNU
C generates the special instructions to guarantee consistency
even when you use `-m88100', so that the code may be run on an
MC88110 processor. If you intend to run your code only on the
MC88100 processor, you may use `-mno-serialize-volatile'.
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 `-mno-serialize-volatile'.
-msvr4
-
-msvr3
-
Turn on (`-msvr4') or off (`-msvr3') compiler extensions
related to System V release 4 (SVr4). This controls the following:
-
Which variant of the assembler syntax to emit.
-
`-msvr4' makes the C preprocessor recognize `#pragma weak'
that is used on System V release 4.
-
`-msvr4' makes GNU CC issue additional declaration directives used in
SVr4.
`-msvr4' is the default for the m88k-motorola-sysv4 and
m88k-dg-dgux m88k configurations. `-msvr3' is the default for all
other m88k configurations.
-mversion-03.00
-
This option is obsolete, and is ignored.
-mno-check-zero-division
-
-mcheck-zero-division
-
Do, or don't, generate code to guarantee that integer division by
zero will be detected. By default, detection is guaranteed.
Some models of the MC88100 processor fail to trap upon integer
division by zero under certain conditions. By default, when
compiling code that might be run on such a processor, GNU C
generates code that explicitly checks for zero-valued divisors
and traps with exception number 503 when one is detected. Use of
mno-check-zero-division suppresses such checking for code
generated to run on an MC88100 processor.
GNU C assumes that the MC88110 processor correctly detects all
instances of integer division by zero. When `-m88110' is
specified, both `-mcheck-zero-division' and
`-mno-check-zero-division' are ignored, and no explicit checks for
zero-valued divisors are generated.
-muse-div-instruction
-
Use the div instruction for signed integer division on the
MC88100 processor. By default, the div instruction is not used.
On the MC88100 processor the signed integer division instruction
div) traps to the operating system on a negative operand. The
operating system transparently completes the operation, but at a
large cost in execution time. By default, when compiling code
that might be run on an MC88100 processor, GNU C emulates signed
integer division using the unsigned integer division instruction
divu), thereby avoiding the large penalty of a trap to the
operating system. Such emulation has its own, smaller, execution
cost in both time and space. To the extent that your code's
important signed integer division operations are performed on two
nonnegative operands, it may be desirable to use the div
instruction directly.
On the MC88110 processor the div instruction (also known as the
divs instruction) processes negative operands without trapping to
the operating system. When `-m88110' is specified,
`-muse-div-instruction' is ignored, and the div instruction is used
for signed integer division.
Note that the result of dividing INT_MIN by -1 is undefined. In
particular, the behavior of such a division with and without
`-muse-div-instruction' may differ.
-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 GNU CC
makes no special provision for large bit shifts.
-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,
GNU CC issues no such warning.
These `-m' options are defined for the IBM RS/6000 and PowerPC:
-mpower
-
-mno-power
-
-mpower2
-
-mno-power2
-
-mpowerpc
-
-mno-powerpc
-
-mpowerpc-gpopt
-
-mno-powerpc-gpopt
-
-mpowerpc-gfxopt
-
-mno-powerpc-gfxopt
-
GNU CC supports two related instruction set architectures for the
RS/6000 and PowerPC. The POWER instruction set are those
instructions supported by the `rios' chip set used in the original
RS/6000 systems and the PowerPC instruction set is the
architecture of the Motorola MPC6xx microprocessors. The PowerPC
architecture defines 64-bit instructions, but they are not supported by
any current processors.
Neither architecture is a subset of the other. However there is a
large common subset of instructions supported by both. An MQ
register is included in processors supporting the POWER architecture.
You use these options to specify which instructions are available on the
processor you are using. The default value of these options is
determined when configuring GNU CC. Specifying the
`-mcpu=cpu_type' overrides the specification of these
options. We recommend you use that option rather than these.
The `-mpower' option allows GNU CC to generate instructions that
are found only in the POWER architecture and to use the MQ register.
Specifying `-mpower2' implies `-power' and also allows GNU CC
to generate instructions that are present in the POWER2 architecture but
not the original POWER architecture.
The `-mpowerpc' option allows GNU CC to generate instructions that
are found only in the 32-bit subset of the PowerPC architecture.
Specifying `-mpowerpc-gpopt' implies `-mpowerpc' and also allows
GNU CC to use the optional PowerPC architecture instructions in the
General Purpose group, including floating-point square root. Specifying
`-mpowerpc-gfxopt' implies `-mpowerpc' and also allows GNU CC to
use the optional PowerPC architecture instructions in the Graphics
group, including floating-point select.
If you specify both `-mno-power' and `-mno-powerpc', GNU CC
will use only the instructions in the common subset of both
architectures plus some special AIX common-mode calls, and will not use
the MQ register. Specifying both `-mpower' and `-mpowerpc'
permits GNU CC to use any instruction from either architecture and to
allow use of the MQ register; specify this for the Motorola MPC601.
-mnew-mnemonics
-
-mold-mnemonics
-
Select which mnemonics to use in the generated assembler code.
`-mnew-mnemonics' requests output that uses the assembler mnemonics
defined for the PowerPC architecture, while `-mold-mnemonics'
requests the assembler mnemonics defined for the POWER architecture.
Instructions defined in only one architecture have only one mnemonic;
GNU CC uses that mnemonic irrespective of which of these options is
specified.
PowerPC assemblers support both the old and new mnemonics, as will later
POWER assemblers. Current POWER assemblers only support the old
mnemonics. Specify `-mnew-mnemonics' if you have an assembler that
supports them, otherwise specify `-mold-mnemonics'.
The default value of these options depends on how GNU CC was configured.
Specifying `-mcpu=cpu_type' sometimes overrides the value of
these option. Unless you are building a cross-compiler, you should
normally not specify either `-mnew-mnemonics' or
`-mold-mnemonics', but should instead accept the default.
-mcpu=cpu_type
-
Set architecture type, register usage, choice of mnemonics, and instruction
scheduling parameters for machine type cpu_type. By default,
cpu_type is the target system defined when GNU CC was configured.
Supported values for cpu_type are `rios1', `rios2', `rsc',
`601', `603', `604', `power', `powerpc', `403',
and `common'. `-mcpu=power' and `-mcpu=powerpc' specify generic
POWER and pure PowerPC (i.e., not MPC601) architecture machine types, with an
appropriate, generic processor model assumed for scheduling purposes.
Specifying `-mcpu=rios1', `-mcpu=rios2', `-mcpu=rsc', or
`-mcpu=power' enables the `-mpower' option and disables the
`-mpowerpc' option; `-mcpu=601' enables both the `-mpower' and
`-mpowerpc' options; `-mcpu=603', `-mcpu=604', `-mcpu=403',
and `-mcpu=powerpc' enable the `-mpowerpc' option and disable the
`-mpower' option; `-mcpu=common' disables both the `-mpower' and
`-mpowerpc' options.
To generate code that will operate on all members of the RS/6000 and
PowerPC families, specify `-mcpu=common'. In that case, GNU CC
will use only the instructions in the common subset of both
architectures plus some special AIX common-mode calls, and will not use
the MQ register. GNU CC assumes a generic processor model for scheduling
purposes.
Specifying `-mcpu=rios1', `-mcpu=rios2', `-mcpu=rsc', or
`-mcpu=power' also disables the `new-mnemonics' option.
Specifying `-mcpu=601', `-mcpu=603', `-mcpu=604',
`403', or `-mcpu=powerpc' also enables the `new-mnemonics'
option.
-mfull-toc
-
-mno-fp-in-toc
-
-mno-sum-in-toc
-
-mminimal-toc
-
Modify generation of the TOC (Table Of Contents), which is created for
every executable file. The `-mfull-toc' option is selected by
default. In that case, GNU CC will allocate at least one TOC entry for
each unique non-automatic variable reference in your program. GNU CC
will also place floating-point constants in the TOC. However, only
16,384 entries are available in the TOC.
If you receive a linker error message that saying you have overflowed
the available TOC space, you can reduce the amount of TOC space used
with the `-mno-fp-in-toc' and `-mno-sum-in-toc' options.
`-mno-fp-in-toc' prevents GNU CC from putting floating-point
constants in the TOC and `-mno-sum-in-toc' forces GNU CC to
generate code to calculate the sum of an address and a constant at
run-time instead of putting that sum into the TOC. You may specify one
or both of these options. Each causes GNU CC to produce very slightly
slower and larger code at the expense of conserving TOC space.
If you still run out of space in the TOC even when you specify both of
these options, specify `-mminimal-toc' instead. This option causes
GNU CC to make only one TOC entry for every file. When you specify this
option, GNU CC will produce code that is slower and larger but which
uses extremely little TOC space. You may wish to use this option
only on files that contain less frequently executed code.
-msoft-float
-
-mhard-float
-
Generate code that does not use (uses) the floating-point register set.
Software floating point emulation is provided if you use the
`-msoft-float' option, and pass the option to GNU CC when linking.
-mmultiple
-
-mno-multiple
-
Generate code that uses (does not use) the load multiple word
instructions and the store multiple word instructions. These
instructions are generated by default on POWER systems, and not
generated on PowerPC systems. Do not use `-mmultiple' on little
endian PowerPC systems, since those instructions do not work when the
processor is in little endian mode.
-mstring
-
-mno-string
-
Generate code that uses (does not use) the load string instructions and the
store string word instructions to save multiple registers and do small block
moves. These instructions are generated by default on POWER systems, anod not
generated on PowerPC systems. Do not use `-mstring' on little endian
PowerPC systems, since those instructions do not work when the processor is in
little endian mode.
-mno-bit-align
-
-mbit-align
-
On System V.4 and embedded PowerPC systems do not (do) force structures
and unions that contain bit fields to be aligned to the base type of the
bit field.
For example, by default a structure containing nothing but 8
unsigned
bitfields of length 1 would be aligned to a 4 byte
boundary and have a size of 4 bytes. By using `-mno-bit-align',
the structure would be aligned to a 1 byte boundary and be one byte in
size.
-mno-strict-align
-
-mstrict-align
-
On System V.4 and embedded PowerPC systems do not (do) assume that
unaligned memory references will be handled by the system.
-mrelocatable
-
-mno-relocatable
-
On embedded PowerPC systems generate code that allows (does not allow)
the program to be relocated to a different address at runtime.
-mno-toc
-
-mtoc
-
On System V.4 and embedded PowerPC systems do not (do) assume that
register 2 contains a pointer to a global area pointing to the addresses
used in the program.
-mno-traceback
-
-mtraceback
-
On embedded PowerPC systems do not (do) generate a traceback tag before
the start of the function. This tag can be used by the debugger to
identify where the start of a function is.
-mlittle
-
-mlittle-endian
-
On System V.4 and embedded PowerPC systems compile code for the
processor in little endian mode. The `-mlittle-endian' option is
the same as `-mlittle'.
-mbig
-
-mbig-endian
-
On System V.4 and embedded PowerPC systems compile code for the
processor in big endian mode. The `-mbig-endian' option is
the same as `-mbig'.
-mcall-sysv
-
On System V.4 and embedded PowerPC systems compile code using calling
conventions that adheres to the March 1995 draft of the System V
Application Binary Interface, PowerPC processor supplement. This is the
default unless you configured GCC using `powerpc-*-eabiaix'.
-mcall-aix
-
On System V.4 and embedded PowerPC systems compile code using calling
conventions that are similar to those used on AIX. This is the
default if you configured GCC using `powerpc-*-eabiaix'.
-mprototype
-
-mno-prototype
-
On System V.4 and embedded PowerPC systems assume that all calls to
variable argument functions are properly prototyped. Otherwise, the
compiler must insert an instruction before every non prototyped call to
set or clear bit 6 of the condition code register (CR) to
indicate whether floating point values were passed in the floating point
registers in case the function takes a variable arguments. With
`-mprototype', only calls to prototyped variable argument functions
will set or clear the bit.
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, including 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 dynamically.
-mfp-arg-in-fpregs
-
Use a calling sequence incompatible with the IBM calling 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 the option `-fpcc-struct-return' for compatibility
with the Portable C Compiler (pcc).
-mnohc-struct-return
-
Return some structures of more than one word in registers, when
convenient. This is the default. For compatibility with the
IBM-supplied compilers, use the option `-fpcc-struct-return' or the
option `-mhc-struct-return'.
These `-m' options are defined for the MIPS family of computers:
-mcpu=cpu type
-
Assume the defaults for the machine type cpu type when scheduling
instructions. The choices for cpu type are `r2000', `r3000',
`r4000', `r4400', `r4600', and `r6000'. While picking a
specific cpu type will schedule things appropriately for that
particular chip, the compiler will not generate any code that does not
meet level 1 of the MIPS ISA (instruction set architecture) without
the `-mips2' or `-mips3' switches being used.
-mips1
-
Issue instructions from level 1 of the MIPS ISA. This is the default.
`r3000' is the default cpu type at this ISA level.
-mips2
-
Issue instructions from level 2 of the MIPS ISA (branch likely, square
root instructions). `r6000' is the default cpu type at this
ISA level.
-mips3
-
Issue instructions from level 3 of the MIPS ISA (64 bit instructions).
`r4000' is the default cpu type at this ISA level.
This option does not change the sizes of any of the C data types.
-mfp32
-
Assume that 32 32-bit floating point registers are available. This is
the default.
-mfp64
-
Assume that 32 64-bit floating point registers are available. This is
the default when the `-mips3' option is used.
-mgp32
-
Assume that 32 32-bit general purpose registers are available. This is
the default.
-mgp64
-
Assume that 32 64-bit general purpose registers are available. This is
the default when the `-mips3' option is used.
-mint64
-
Types long, int, and pointer are 64 bits. This works only if `-mips3'
is also specified.
-mlong64
-
Types long and pointer are 64 bits, and type int is 32 bits.
This works only if `-mips3' is also specified.
-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 the either of the `-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 default on the OSF/1
reference platform, using the OSF/rose object format.
-mrnames
-
-mno-rnames
-
The `-mrnames' switch says to output code using the MIPS software
names for the registers, instead of the hardware names (ie, a0
instead of $4). The only known assembler that supports this option
is the Algorithmics assembler.
-mgpopt
-
-mno-gpopt
-
The `-mgpopt' switch says to write all of the data declarations
before the instructions in the text section, this allows the MIPS
assembler to generate one word memory references instead of using two
words for short global or static data items. This is on by default if
optimization is selected.
-mstats
-
-mno-stats
-
For each non-inline function processed, the `-mstats' switch
causes the compiler to emit one line to the standard error file to
print statistics about the program (number of registers saved, stack
size, etc.).
-mmemcpy
-
-mno-memcpy
-
The `-mmemcpy' switch makes all block moves call the appropriate
string function (`memcpy' or `bcopy') 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' program,
after the MIPS assembler has generated it to add debug support. If
`mips-tfile' is not run, then no local variables will be
available to the debugger. In addition, `stage2' and
`stage3' objects will have the temporary file names passed to the
assembler embedded in the object file, which means the objects will
not compare the same. The `-mno-mips-tfile' switch should only
be used when there are bugs in the `mips-tfile' program that
prevents compilation.
-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.
-mabicalls
-
-mno-abicalls
-
Emit (or do not emit) the pseudo operations `.abicalls',
`.cpload', and `.cprestore' that some System V.4 ports use for
position independent code.
-mlong-calls
-
-mno-long-calls
-
Do all calls with the `JALR' instruction, which requires
loading up a function's address into a register before the call.
You need to use this switch, if you call outside of the current
512 megabyte segment to functions that are not through pointers.
-mhalf-pic
-
-mno-half-pic
-
Put pointers to extern references into the data section and load them
up, rather than put the references in the text section.
-membedded-pic
-
-mno-embedded-pic
-
Generate PIC code suitable for some embedded systems. All calls are made
using PC relative address, and all data is addressed using the $gp register.
This requires GNU as and GNU ld which do most of the work.
-membedded-data
-
-mno-embedded-data
-
Allocate variables to the read-only data section first if possible, then
next in the small data section if possible, otherwise in data. This gives
slightly slower code than the default, but reduces the amount of RAM required
when executing, and thus may be preferred for some embedded systems.
-msingle-float
-
-mdouble-float
-
The `-msingle-float' switch tells gcc to assume that the floating
point coprocessor only supports single precision operations, as on the
`r4650' chip. The `-mdouble-float' switch permits gcc to use
double precision operations. This is the default.
-mmad
-
-mno-mad
-
Permit use of the `mad', `madu' and `mul' instructions,
as on the `r4650' chip.
-m4650
-
Turns on `-msingle-float', `-mmad', and, at least for now,
`-mcpu=r4650'.
-EL
-
Compile code for the processor in little endian mode.
The requisite libraries are assumed to exist.
-EB
-
Compile code for the processor in big endian mode.
The requisite libraries are assumed to exist.
-G num
-
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 assembler is used, and 0 when the GNU assembler is used. The
`-G num' switch is also passed to the assembler and linker.
All modules should be compiled with the same `-G num'
value.
-nocpp
-
Tell the MIPS assembler to not run it's preprocessor over user
assembler files (with a `.s' suffix) when assembling them.
These options are defined by the macro
TARGET_SWITCHES
in the machine description. The default for the
options is also defined by that macro, which enables you to change the
defaults.
These `-m' options are defined for the i386 family of computers:
-m486
-
-m386
-
Control whether or not code is optimized for a 486 instead of an
386. Code generated for an 486 will run on a 386 and vice versa.
-mieee-fp
-
-mno-ieee-fp
-
Control whether or not the compiler uses IEEE floating point
comparisons. These handle correctly the case where the result of a
comparison is unordered.
-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 functions.
The usual calling convention has functions return values of types
float
and double
in an FPU register, even if there
is no FPU. The idea is that the operating system should emulate
an FPU.
The option `-mno-fp-ret-in-387' causes such values to be returned
in ordinary CPU registers instead.
-mno-fancy-math-387
-
Some 387 emulators do not support the
sin
, cos
and
sqrt
instructions for the 387. Specify this option to avoid
generating those instructions. This option is the default on FreeBSD.
As of revision 2.6.1, these instructions are not generated unless you
also use the `-ffast-math' switch.
-malign-double
-
-mno-align-double
-
Control whether GNU CC aligns
double
, long double
, and
long long
variables on a two word boundary or a one word
boundary. Aligning double
variables on a two word boundary will
produce code that runs somewhat faster on a `Pentium' at the
expense of more memory.
Warning: if you use the `-malign-double' switch,
structures containing the above types will be aligned differently than
the published application binary interface specifications for the 386.
-msvr3-shlib
-
-mno-svr3-shlib
-
Control whether GNU CC places uninitialized locals into
bss
or
data
. `-msvr3-shlib' places these locals into bss
.
These options are meaningful only on System V Release 3.
-mno-wide-multiply
-
-mwide-multiply
-
Control whether GNU CC uses the
mul
and imul
that produce
64 bit results in eax:edx
from 32 bit operands to do long
long
multiplies and 32-bit division by constants.
-mrtd
-
Use a different function-calling convention, in which functions that
take a fixed number of arguments return with the
ret
num
instruction, which pops their arguments while returning. This saves one
instruction in the caller since there is no need to pop the arguments
there.
You can specify that an individual function is called with this calling
sequence with the function attribute `stdcall'. You can also
override the `-mrtd' option by using the function attribute
`cdecl'. See section Declaring Attributes of Functions
Warning: this calling convention is incompatible with the one
normally used on Unix, so you cannot use it if you need to call
libraries compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including printf
);
otherwise incorrect code will be generated for calls to those
functions.
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
-mreg-alloc=regs
-
Control the default allocation order of integer registers. The
string regs is a series of letters specifying a register. The
supported letters are:
a
allocate EAX; b
allocate EBX;
c
allocate ECX; d
allocate EDX; S
allocate ESI;
D
allocate EDI; B
allocate EBP.
-mregparm=num
-
Control how many registers are used to pass integer arguments. By
default, no registers are used to pass arguments, and at most 3
registers can be used. You can control this behavior for a specific
function by using the function attribute `regparm'. See section Declaring Attributes of Functions
Warning: if you use this switch, and
num is nonzero, then you must build all modules with the same
value, including any libraries. This includes the system libraries and
startup modules.
-malign-loops=num
-
Align loops to a 2 raised to a num byte boundary. If
`-malign-loops' is not specified, the default is 2.
-malign-jumps=num
-
Align instructions that are only jumped to to a 2 raised to a num
byte boundary. If `-malign-jumps' is not specified, the default is
2 if optimizing for a 386, and 4 if optimizing for a 486.
-malign-functions=num
-
Align the start of functions to a 2 raised to num byte boundary.
If `-malign-jumps' is not specified, the default is 2 if optimizing
for a 386, and 4 if optimizing for a 486.
These `-m' options are defined for the HPPA family of computers:
-mpa-risc-1-0
-
Generate code for a PA 1.0 processor.
-mpa-risc-1-1
-
Generate code for a PA 1.1 processor.
-mjump-in-delay
-
Fill delay slots of function calls with unconditional jump instructions
by modifying the return pointer for the function call to be the target
of the conditional jump.
-mmillicode-long-calls
-
Generate code which assumes millicode routines can not be reached
by the standard millicode call sequence, linker-generated long-calls,
or linker-modified millicode calls. In practice this should only be
needed for dynamicly linked executables with extremely large SHLIB_INFO
sections.
-mdisable-fpregs
-
Prevent floating point registers from being used in any manner. This is
necessary for compiling kernels which perform lazy context switching of
floating point registers. If you use this option and attempt to perform
floating point operations, the compiler will abort.
-mdisable-indexing
-
Prevent the compiler from using indexing address modes. This avoids some
rather obscure problems when compiling MIG generated code under MACH.
-mfast-indirect-calls
-
Generate code which performs faster indirect calls. Such code is suitable
for kernels and for static linking. The fast indirect call code will fail
miserably if it's part of a dynamically linked executable and in the presense
of nested functions.
-mportable-runtime
-
Use the portable calling conventions proposed by HP for ELF systems.
-mgas
-
Enable the use of assembler directives only GAS understands.
-mschedule=cpu type
-
Schedule code according to the constraints for the machine type
cpu type. The choices for cpu type are `700' for
7n0 machines, `7100' for 7n5 machines, and `7100'
for 7n2 machines. `700' is the default for cpu type.
Note the `7100LC' scheduling information is incomplete and using
`7100LC' often leads to bad schedules. For now it's probably best
to use `7100' instead of `7100LC' for the 7n2 machines.
-msoft-float
-
Generate output containing library calls for floating point.
Warning: the requisite libraries are not available for all HPPA
targets. 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. The embedded target `hppa1.1-*-pro'
does provide software floating point support.
`-msoft-float' changes the calling convention in the output file;
therefore, it is only useful if you compile all of a program with
this option. In particular, you need to compile `libgcc.a', the
library that comes with GNU CC, with `-msoft-float' in order for
this to work.
These `-m' options are defined for the Intel 960 implementations:
-mcpu type
-
Assume the defaults for the machine type cpu type for some of
the other options, including instruction scheduling, floating point
support, and addressing modes. The choices for cpu type are
`ka', `kb', `mc', `ca', `cf',
`sa', and `sb'.
The default is
`kb'.
-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 addressing 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 implementations:
-mno-soft-float
-
-msoft-float
-
Use (do not use) the hardware floating-point instructions for
floating-point operations. When
-msoft-float
is specified,
functions in `libgcc1.c' will be used to perform floating-point
operations. Unless they are replaced by routines that emulate the
floating-point operations, or compiled in such a way as to call such
emulations routines, these routines will issue floating-point
operations. If you are compiling for an Alpha without floating-point
operations, you must ensure that the library is built so as not to call
them.
Note that Alpha implementations without floating-point operations are
required to have floating-point registers.
-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, floating point operands are passed in integer
registers as if they were integers and floating-point results are passed
in $0 instead of $f0. This is a non-standard calling sequence, so any
function with a floating-point argument or 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 `-m' options are defined for the Clipper implementations:
-mc300
-
Produce code for a C300 Clipper processor. This is the default.
-mc400
-
Produce code for a C400 Clipper processor i.e. use floating point
registers f8..f15.
These `-m' options are defined for the H8/300 implementations:
-mrelax
-
Shorten some address references at link time, when possible; uses the
linker option `-relax'. See section `
ld
and the H8/300' in Using ld, for a fuller description.
-mh
-
Generate code for the H8/300H.
These additional options are available on System V Release 4 for
compatibility with other compilers on those systems:
-Qy
-
Identify the versions of each tool used by the compiler, 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 libraries
specified with `-l'.
-Ym,dir
-
Look in the directory dir to find the M4 preprocessor.
The assembler uses this option.
These machine-independent options control the interface conventions
used in code generation.
Most of them have both positive and negative forms; the negative form
of `-ffoo' would be `-fno-foo'. In the table below, only
one of the forms is listed--the one which is not the default. You
can figure out the other form by either removing `no-' or adding
it.
-fpcc-struct-return
-
Return "short"
struct
and union
values in memory like
longer ones, rather than in registers. This convention is less
efficient, but it has the advantage of allowing intercallability between
GNU CC-compiled files and files compiled with other compilers.
The precise convention for returning structures in memory depends
on the target configuration macros.
Short structures and unions are those whose size and alignment match
that of some integer type.
-freg-struct-return
-
Use the convention that
struct
and union
values are
returned in registers when possible. This is more efficient for small
structures than `-fpcc-struct-return'.
If you specify neither `-fpcc-struct-return' nor its contrary
`-freg-struct-return', GNU CC defaults to whichever convention is
standard for the target. If there is no standard convention, GNU CC
defaults to `-fpcc-struct-return', except on targets where GNU CC
is the principal compiler. In those cases, we can choose the standard,
and we chose the more efficient register return alternative.
-fshort-enums
-
Allocate to an
enum
type only as many bytes as it needs for the
declared range of possible values. Specifically, the enum
type
will be equivalent to the smallest integer type which has enough room.
-fshort-double
-
Use the same size for
double
as for float
.
-fshared-data
-
Requests that the data and non-
const
variables of this
compilation be shared data rather than private data. The distinction
makes sense only on certain operating systems, where shared data is
shared between processes running the same program, while private data
exists in one copy per process.
-fno-common
-
Allocate even uninitialized global variables in the bss section of the
object file, rather than generating them as common blocks. This has the
effect that if the same variable is declared (without
extern
) in
two different compilations, you will get an error when you link them.
The only reason this might be useful is if you wish to verify that the
program will work on other systems which always work this way.
-fno-ident
-
Ignore the `#ident' directive.
-fno-gnu-linker
-
Do not output global initializations (such as C++ constructors and
destructors) in the form used by the GNU linker (on systems where the GNU
linker is the standard method of handling them). Use this option when
you want to use a non-GNU linker, which also requires using the
collect2
program to make sure the system linker includes
constructors and destructors. (collect2
is included in the GNU CC
distribution.) For systems which must use collect2
, the
compiler driver gcc
is configured to do this automatically.
-finhibit-size-directive
-
Don't output a
.size
assembler directive, or anything else that
would cause trouble if the function is split in the middle, and the
two halves are placed at locations far apart in memory. This option is
used when compiling `crtstuff.c'; you should not need to use it
for anything else.
-fverbose-asm
-
Put extra commentary information in the generated assembly code to
make it more readable. This option is generally only of use to those
who actually need to read the generated assembly code (perhaps while
debugging the compiler itself).
-fvolatile
-
Consider all memory references through pointers to be volatile.
-fvolatile-global
-
Consider all memory references to extern and global data items to
be volatile.
-fpic
-
Generate position-independent code (PIC) suitable for use in a shared
library, if supported for the target machine. Such code accesses all
constant addresses through a global offset table (GOT). If the GOT size
for the linked executable exceeds a machine-specific maximum size, you
get an error message from the linker indicating that `-fpic' does
not work; in that case, recompile with `-fPIC' instead. (These
maximums are 16k on the m88k, 8k on the Sparc, and 32k on the m68k and
RS/6000. The 386 has no such limit.)
Position-independent code requires special support, and therefore works
only on certain machines. For the 386, GNU CC supports PIC for System V
but not for the Sun 386i. Code generated for the IBM RS/6000 is always
position-independent.
The GNU assembler does not fully support PIC. Currently, you must use
some other assembler in order for PIC to work. We would welcome
volunteers to upgrade GAS to handle this; the first part of the job is
to figure out what the assembler must do differently.
-fPIC
-
If supported for the target machine, emit position-independent code,
suitable for dynamic linking and avoiding any limit on the size of the
global offset table. This option makes a difference on the m68k, m88k
and the Sparc.
Position-independent code requires special support, and therefore works
only on certain machines.
-ffixed-reg
-
Treat the register named reg as a fixed register; generated code
should never refer to it (except perhaps as a stack pointer, frame
pointer or in some other fixed role).
reg must be the name of a register. The register names accepted
are machine-specific and are defined in the
REGISTER_NAMES
macro in the machine 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 allocatable register that is
clobbered by function calls. It may be allocated for temporaries or
variables that do not live across a call. Functions compiled this way
will not save and restore the register reg.
Use of this flag for a register that has a fixed pervasive role in the
machine's execution model, such as the stack pointer or frame pointer,
will produce disastrous results.
This flag does not have a negative form, because it specifies a
three-way choice.
-fcall-saved-reg
-
Treat the register named reg as an allocatable register saved by
functions. It may be allocated even for temporaries or variables that
live across a call. Functions compiled this way will save and restore
the register reg if they use it.
Use of this flag for a register that has a fixed pervasive role in the
machine's execution model, such as the stack pointer or frame pointer,
will produce disastrous results.
A different sort of disaster will result from the use of this flag for
a register in which function values may be returned.
This flag does not have a negative form, because it specifies a
three-way choice.
-fpack-struct
-
Pack all structure members together without holes. Usually you would
not want to use this option, since it makes the code suboptimal, and
the offsets of structure members won't agree with system libraries.
+e0
-
+e1
-
Control whether virtual function definitions in classes are used to
generate code, or only to define interfaces for their callers. (C++
only).
These options are provided for compatibility with
cfront
1.x
usage; the recommended alternative GNU C++ usage is in flux. See section Declarations and Definitions in One Header.
With `+e0', virtual function definitions in classes are declared
extern
; the declaration is used only as an interface
specification, not to generate code for the virtual functions (in this
compilation).
With `+e1', G++ actually generates the code implementing virtual
functions defined in the code, and makes them publicly visible.
This section describes several environment variables that affect how GNU
CC operates. They work by specifying directories or prefixes to use
when searching for various kinds of files.
Note that you can also specify places to search using options such as
`-B', `-I' and `-L' (see section Options for Directory Search). These
take precedence over places specified using environment variables, which
in turn take precedence over those specified by the configuration of GNU
CC. See section Controlling the Compilation Driver, `gcc'.
TMPDIR
-
If
TMPDIR
is set, it specifies the directory to use for temporary
files. GNU CC uses temporary files to hold the output of one stage of
compilation which is to be used as input to the next stage: for example,
the output of the preprocessor, which is the input to the compiler
proper.
GCC_EXEC_PREFIX
-
If
GCC_EXEC_PREFIX
is set, it specifies a prefix to use in the
names of the subprograms executed by the compiler. No slash is added
when this prefix is combined with the name of a subprogram, but you can
specify a prefix that ends with a slash if you wish.
If GNU CC cannot find the subprogram using the specified prefix, it
tries looking in the usual places for the subprogram.
The default value of GCC_EXEC_PREFIX
is
`prefix/lib/gcc-lib/' where prefix is the value
of prefix
when you ran the `configure' script.
Other prefixes specified with `-B' take precedence over this prefix.
This prefix is also used for finding files such as `crt0.o' that are
used for linking.
In addition, the prefix is used in an unusual way in finding the
directories to search for header files. For each of the standard
directories whose name normally begins with `/usr/local/lib/gcc-lib'
(more precisely, with the value of GCC_INCLUDE_DIR
), GNU CC tries
replacing that beginning with the specified prefix to produce an
alternate directory name. Thus, with `-Bfoo/', GNU CC will search
`foo/bar' where it would normally search `/usr/local/lib/bar'.
These alternate directories are searched first; the standard directories
come next.
COMPILER_PATH
-
The value of
COMPILER_PATH
is a colon-separated list of
directories, much like PATH
. GNU CC tries the directories thus
specified when searching for subprograms, if it can't find the
subprograms using GCC_EXEC_PREFIX
.
LIBRARY_PATH
-
The value of
LIBRARY_PATH
is a colon-separated list of
directories, much like PATH
. When configured as a native compiler,
GNU CC tries the directories thus specified when searching for special
linker files, if it can't find them using GCC_EXEC_PREFIX
. Linking
using GNU CC also uses these directories when searching for ordinary
libraries for the `-l' option (but directories specified with
`-L' come first).
C_INCLUDE_PATH
-
CPLUS_INCLUDE_PATH
-
OBJC_INCLUDE_PATH
-
These environment variables pertain to particular languages. Each
variable's value is a colon-separated list of directories, much like
PATH
. When GNU CC searches for header files, it tries the
directories listed in the variable for the language you are using, after
the directories specified with `-I' but before the standard header
file directories.
DEPENDENCIES_OUTPUT
-
If this variable is set, its value specifies how to output dependencies
for Make based on the header files processed by the compiler. This
output looks much like the output from the `-M' option
(see section Options Controlling the Preprocessor), but it goes to a separate file, and is
in addition to the usual results of compilation.
The value of
DEPENDENCIES_OUTPUT
can be just a file name, in
which case the Make rules are written to that file, guessing the target
name from the source file name. Or the value can have the form
`file target', in which case the rules are written to
file file using target as the target name.
The program protoize
is an optional part of GNU C. You can use
it to add prototypes to a program, thus converting the program to ANSI
C in one respect. The companion program unprotoize
does the
reverse: it removes argument types from any prototypes that are found.
When you run these programs, you must specify a set of source files as
command line arguments. The conversion programs start out by compiling
these files to see what functions they define. The information gathered
about a file foo is saved in a file named `foo.X'.
After scanning comes actual conversion. The specified files are all
eligible to be converted; any files they include (whether sources or
just headers) are eligible as well.
But not all the eligible files are converted. By default,
protoize
and unprotoize
convert only source and header
files in the current directory. You can specify additional directories
whose files should be converted with the `-d directory'
option. You can also specify particular files to exclude with the
`-x file' option. A file is converted if it is eligible, its
directory name matches one of the specified directory names, and its
name within the directory has not been excluded.
Basic conversion with protoize
consists of rewriting most
function definitions and function declarations to specify the types of
the arguments. The only ones not rewritten are those for varargs
functions.
protoize
optionally inserts prototype declarations at the
beginning of the source file, to make them available for any calls that
precede the function's definition. Or it can insert prototype
declarations with block scope in the blocks where undeclared functions
are called.
Basic conversion with unprotoize
consists of rewriting most
function declarations to remove any argument types, and rewriting
function definitions to the old-style pre-ANSI form.
Both conversion programs print a warning for any function declaration or
definition that they can't convert. You can suppress these warnings
with `-q'.
The output from protoize
or unprotoize
replaces the
original source file. The original file is renamed to a name ending
with `.save'. If the `.save' file already exists, then
the source file is simply discarded.
protoize
and unprotoize
both depend on GNU CC itself to
scan the program and collect information about the functions it uses.
So neither of these programs will work until GNU CC is installed.
Here is a table of the options you can use with protoize
and
unprotoize
. Each option works with both programs unless
otherwise stated.
-B directory
-
Look for the file `SYSCALLS.c.X' in directory, instead of the
usual directory (normally `/usr/local/lib'). This file contains
prototype information about standard system functions. This option
applies only to
protoize
.
-c compilation-options
-
Use compilation-options as the options when running
gcc
to
produce the `.X' files. The special option `-aux-info' is
always passed in addition, to tell gcc
to write a `.X' file.
Note that the compilation options must be given as a single argument to
protoize
or unprotoize
. If you want to specify several
gcc
options, you must quote the entire set of compilation options
to make them a single word in the shell.
There are certain gcc
arguments that you cannot use, because they
would produce the wrong kind of output. These include `-g',
`-O', `-c', `-S', and `-o' If you include these in
the compilation-options, they are ignored.
-C
-
Rename files to end in `.C' instead of `.c'.
This is convenient if you are converting a C program to C++.
This option applies only to
protoize
.
-g
-
Add explicit global declarations. This means inserting explicit
declarations at the beginning of each source file for each function
that is called in the file and was not declared. These declarations
precede the first function definition that contains a call to an
undeclared function. This option applies only to
protoize
.
-i string
-
Indent old-style parameter declarations with the string string.
This option applies only to
protoize
.
unprotoize
converts prototyped function definitions to old-style
function definitions, where the arguments are declared between the
argument list and the initial `{'. By default, unprotoize
uses five spaces as the indentation. If you want to indent with just
one space instead, use `-i " "'.
-k
-
Keep the `.X' files. Normally, they are deleted after conversion
is finished.
-l
-
Add explicit local declarations.
protoize
with `-l' inserts
a prototype declaration for each function in each block which calls the
function without any declaration. This option applies only to
protoize
.
-n
-
Make no real changes. This mode just prints information about the conversions
that would have been done without `-n'.
-N
-
Make no `.save' files. The original files are simply deleted.
Use this option with caution.
-p program
-
Use the program program as the compiler. Normally, the name
`gcc' is used.
-q
-
Work quietly. Most warnings are suppressed.
-v
-
Print the version number, just like `-v' for
gcc
.
If you need special compiler options to compile one of your program's
source files, then you should generate that file's `.X' file
specially, by running gcc
on that source file with the
appropriate options and the option `-aux-info'. Then run
protoize
on the entire set of files. protoize
will use
the existing `.X' file because it is newer than the source file.
For example:
gcc -Dfoo=bar file1.c -aux-info
protoize *.c
You need to include the special files along with the rest in the
protoize
command, even though their `.X' files already
exist, because otherwise they won't get converted.
See section Caveats of using protoize
, for more information on how to use
protoize
successfully.
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