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INFO-DIR-SECTION Programming
START-INFO-DIR-ENTRY
* gcc: (gcc).                  The GNU Compiler Collection.
END-INFO-DIR-ENTRY
   This file documents the use of the GNU compilers.

   Published by the Free Software Foundation
59 Temple Place - Suite 330
Boston, MA 02111-1307 USA

   Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
1999, 2000, 2001, 2002 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License" and "Funding Free
Software", the Front-Cover texts being (a) (see below), and with the
Back-Cover Texts being (b) (see below).  A copy of the license is
included in the section entitled "GNU Free Documentation License".

   (a) The FSF's Front-Cover Text is:

   A GNU Manual

   (b) The FSF's Back-Cover Text is:

   You have freedom to copy and modify this GNU Manual, like GNU
software.  Copies published by the Free Software Foundation raise
funds for GNU development.


File: gcc.info,  Node: Top,  Next: G++ and GCC,  Up: (DIR)

Introduction
************

This manual documents how to use the GNU compilers, as well as their
features and incompatibilities, and how to report bugs.  It corresponds
to GCC version 3.2.2.  The internals of the GNU compilers, including
how to port them to new targets and some information about how to write
front ends for new languages, are documented in a separate manual.
*Note Introduction: (gccint)Top.

* Menu:

* G++ and GCC::     You can compile C or C++ programs.
* Standards::       Language standards supported by GCC.
* Invoking GCC::    Command options supported by `gcc'.
* C Implementation:: How GCC implements the ISO C specification.
* C Extensions::    GNU extensions to the C language family.
* C++ Extensions::  GNU extensions to the C++ language.
* Objective-C::     GNU Objective-C runtime features.
* Compatibility::   Binary Compatibility
* Gcov::            `gcov'---a test coverage program.
* Trouble::         If you have trouble using GCC.
* Bugs::            How, why and where to report bugs.
* Service::         How to find suppliers of support for GCC.
* Contributing::    How to contribute to testing and developing GCC.
* VMS::             Using GCC on VMS.

* Funding::         How to help assure funding for free software.
* GNU Project::     The GNU Project and GNU/Linux.

* Copying::         GNU General Public License says
                     how you can copy and share GCC.
* GNU Free Documentation License:: How you can copy and share this manual.
* Contributors::    People who have contributed to GCC.

* Option Index::    Index to command line options.
* Index::	    Index of concepts and symbol names.


File: gcc.info,  Node: G++ and GCC,  Next: Standards,  Prev: Top,  Up: Top

1 Compile C, C++, Objective-C, Ada, Fortran, or Java
****************************************************

Several versions of the compiler (C, C++, Objective-C, Ada, Fortran,
and Java) are integrated; this is why we use the name "GNU Compiler
Collection".  GCC can compile programs written in any of these
languages.  The Ada, Fortran, and Java compilers are described in
separate manuals.

   "GCC" is a common shorthand term for the GNU Compiler Collection.
This is both the most general name for the compiler, and the name used
when the emphasis is on compiling C programs (as the abbreviation
formerly stood for "GNU C Compiler").

   When referring to C++ compilation, it is usual to call the compiler
"G++".  Since there is only one compiler, it is also accurate to call
it "GCC" no matter what the language context; however, the term "G++"
is more useful when the emphasis is on compiling C++ programs.

   Similarly, when we talk about Ada compilation, we usually call the
compiler "GNAT", for the same reasons.

   We use the name "GCC" to refer to the compilation system as a whole,
and more specifically to the language-independent part of the compiler.
For example, we refer to the optimization options as affecting the
behavior of "GCC" or sometimes just "the compiler".

   Front ends for other languages, such as Mercury and Pascal exist but
have not yet been integrated into GCC.  These front ends, like that for
C++, are built in subdirectories of GCC and link to it.  The result is
an integrated compiler that can compile programs written in C, C++,
Objective-C, or any of the languages for which you have installed front
ends.

   In this manual, we only discuss the options for the C, Objective-C,
and C++ compilers and those of the GCC core.  Consult the documentation
of the other front ends for the options to use when compiling programs
written in other languages.

   G++ is a _compiler_, not merely a preprocessor.  G++ builds object
code directly from your C++ program source.  There is no intermediate C
version of the program.  (By contrast, for example, some other
implementations use a program that generates a C program from your C++
source.)  Avoiding an intermediate C representation of the program means
that you get better object code, and better debugging information.  The
GNU debugger, GDB, works with this information in the object code to
give you comprehensive C++ source-level editing capabilities (*note C
and C++: (gdb.info)C.).


File: gcc.info,  Node: Standards,  Next: Invoking GCC,  Prev: G++ and GCC,  Up: Top

2 Language Standards Supported by GCC
*************************************

For each language compiled by GCC for which there is a standard, GCC
attempts to follow one or more versions of that standard, possibly with
some exceptions, and possibly with some extensions.

   GCC supports three versions of the C standard, although support for
the most recent version is not yet complete.

   The original ANSI C standard (X3.159-1989) was ratified in 1989 and
published in 1990.  This standard was ratified as an ISO standard
(ISO/IEC 9899:1990) later in 1990.  There were no technical differences
between these publications, although the sections of the ANSI standard
were renumbered and became clauses in the ISO standard.  This standard,
in both its forms, is commonly known as "C89", or occasionally as
"C90", from the dates of ratification.  The ANSI standard, but not the
ISO standard, also came with a Rationale document.  To select this
standard in GCC, use one of the options `-ansi', `-std=c89' or
`-std=iso9899:1990'; to obtain all the diagnostics required by the
standard, you should also specify `-pedantic' (or `-pedantic-errors' if
you want them to be errors rather than warnings).  *Note Options
Controlling C Dialect: C Dialect Options.

   Errors in the 1990 ISO C standard were corrected in two Technical
Corrigenda published in 1994 and 1996.  GCC does not support the
uncorrected version.

   An amendment to the 1990 standard was published in 1995.  This
amendment added digraphs and `__STDC_VERSION__' to the language, but
otherwise concerned the library.  This amendment is commonly known as
"AMD1"; the amended standard is sometimes known as "C94" or "C95".  To
select this standard in GCC, use the option `-std=iso9899:199409'
(with, as for other standard versions, `-pedantic' to receive all
required diagnostics).

   A new edition of the ISO C standard was published in 1999 as ISO/IEC
9899:1999, and is commonly known as "C99".  GCC has incomplete support
for this standard version; see
`http://gcc.gnu.org/gcc-3.1/c99status.html' for details.  To select this
standard, use `-std=c99' or `-std=iso9899:1999'.  (While in
development, drafts of this standard version were referred to as "C9X".)

   Errors in the 1999 ISO C standard were corrected in a Technical
Corrigendum published in 2001.  GCC does not support the uncorrected
version.

   GCC also has some limited support for traditional (pre-ISO) C with
the `-traditional' option.  This support may be of use for compiling
some very old programs that have not been updated to ISO C, but should
not be used for new programs.  It will not work with some modern C
libraries such as the GNU C library.

   By default, GCC provides some extensions to the C language that on
rare occasions conflict with the C standard.  *Note Extensions to the C
Language Family: C Extensions.  Use of the `-std' options listed above
will disable these extensions where they conflict with the C standard
version selected.  You may also select an extended version of the C
language explicitly with `-std=gnu89' (for C89 with GNU extensions) or
`-std=gnu99' (for C99 with GNU extensions).  The default, if no C
language dialect options are given, is `-std=gnu89'; this will change to
`-std=gnu99' in some future release when the C99 support is complete.
Some features that are part of the C99 standard are accepted as
extensions in C89 mode.

   The ISO C standard defines (in clause 4) two classes of conforming
implementation.  A "conforming hosted implementation" supports the
whole standard including all the library facilities; a "conforming
freestanding implementation" is only required to provide certain
library facilities: those in `<float.h>', `<limits.h>', `<stdarg.h>',
and `<stddef.h>'; since AMD1, also those in `<iso646.h>'; and in C99,
also those in `<stdbool.h>' and `<stdint.h>'.  In addition, complex
types, added in C99, are not required for freestanding implementations.
The standard also defines two environments for programs, a
"freestanding environment", required of all implementations and which
may not have library facilities beyond those required of freestanding
implementations, where the handling of program startup and termination
are implementation-defined, and a "hosted environment", which is not
required, in which all the library facilities are provided and startup
is through a function `int main (void)' or `int main (int, char *[])'.
An OS kernel would be a freestanding environment; a program using the
facilities of an operating system would normally be in a hosted
implementation.

   GCC aims towards being usable as a conforming freestanding
implementation, or as the compiler for a conforming hosted
implementation.  By default, it will act as the compiler for a hosted
implementation, defining `__STDC_HOSTED__' as `1' and presuming that
when the names of ISO C functions are used, they have the semantics
defined in the standard.  To make it act as a conforming freestanding
implementation for a freestanding environment, use the option
`-ffreestanding'; it will then define `__STDC_HOSTED__' to `0' and not
make assumptions about the meanings of function names from the standard
library, with exceptions noted below.  To build an OS kernel, you may
well still need to make your own arrangements for linking and startup.
*Note Options Controlling C Dialect: C Dialect Options.

   GCC does not provide the library facilities required only of hosted
implementations, nor yet all the facilities required by C99 of
freestanding implementations; to use the facilities of a hosted
environment, you will need to find them elsewhere (for example, in the
GNU C library).  *Note Standard Libraries: Standard Libraries.

   Most of the compiler support routines used by GCC are present in
`libgcc', but there are a few exceptions.  GCC requires the
freestanding environment provide `memcpy', `memmove', `memset' and
`memcmp'.  Some older ports of GCC are configured to use the BSD
`bcopy', `bzero' and `bcmp' functions instead, but this is deprecated
for new ports.  Finally, if `__builtin_trap' is used, and the target
does not implement the `trap' pattern, then GCC will emit a call to
`abort'.

   For references to Technical Corrigenda, Rationale documents and
information concerning the history of C that is available online, see
`http://gcc.gnu.org/readings.html'

   There is no formal written standard for Objective-C.  The most
authoritative manual is "Object-Oriented Programming and the
Objective-C Language", available at a number of web sites

   * `http://developer.apple.com/techpubs/macosx/Cocoa/ObjectiveC/' is
     a recent version

   * `http://www.toodarkpark.org/computers/objc/' is an older example

   * `http://www.gnustep.org' has additional useful information

   *Note GNAT Reference Manual: (gnat_rm)Top, for information on
standard conformance and compatibility of the Ada compiler.

   *Note The GNU Fortran Language: (g77)Language, for details of the
Fortran language supported by GCC.

   *Note Compatibility with the Java Platform: (gcj)Compatibility, for
details of compatibility between `gcj' and the Java Platform.


File: gcc.info,  Node: Invoking GCC,  Next: C Implementation,  Prev: Standards,  Up: Top

3 GCC Command Options
*********************

When you invoke GCC, 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 GCC 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.

   *Note Compiling C++ Programs: Invoking G++, for a summary of special
options for compiling C++ programs.

   The `gcc' program accepts options and file names as operands.  Many
options have multi-letter 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.

   *Note Option Index::, for an index to GCC's options.

* Menu:

* 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++.
* Objective-C Dialect Options:: Variations on Objective-C.
* Language Independent Options:: Controlling how diagnostics should be
                        formatted.
* 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.
* Spec Files::          How to pass switches to sub-processes.
* Target Options::      Running a cross-compiler, or an old version of GCC.
* 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 GCC.
* Running Protoize::    Automatically adding or removing function prototypes.


File: gcc.info,  Node: Option Summary,  Next: Overall Options,  Up: Invoking GCC

3.1 Option Summary
==================

Here is a summary of all the options, grouped by type.  Explanations are
in the following sections.

_Overall Options_
     *Note Options Controlling the Kind of Output: Overall Options.
          -c  -S  -E  -o FILE  -pipe  -pass-exit-codes  -x LANGUAGE
          -v  -###  --help  --target-help  --version

_C Language Options_
     *Note Options Controlling C Dialect: C Dialect Options.
          -ansi  -std=STANDARD  -aux-info FILENAME
          -fno-asm  -fno-builtin -fno-builtin-FUNCTION
          -fhosted  -ffreestanding
          -trigraphs  -no-integrated-cpp  -traditional  -traditional-cpp
          -fallow-single-precision  -fcond-mismatch
          -fsigned-bitfields  -fsigned-char
          -funsigned-bitfields  -funsigned-char
          -fwritable-strings

_C++ Language Options_
     *Note Options Controlling C++ Dialect: C++ Dialect Options.
          -fno-access-control  -fcheck-new  -fconserve-space
          -fno-const-strings  -fdollars-in-identifiers
          -fno-elide-constructors
          -fno-enforce-eh-specs  -fexternal-templates
          -falt-external-templates
          -ffor-scope  -fno-for-scope  -fno-gnu-keywords
          -fno-implicit-templates
          -fno-implicit-inline-templates
          -fno-implement-inlines  -fms-extensions
          -fno-nonansi-builtins  -fno-operator-names
          -fno-optional-diags  -fpermissive
          -frepo  -fno-rtti  -fstats  -ftemplate-depth-N
          -fuse-cxa-atexit  -fvtable-gc  -fno-weak  -nostdinc++
          -fno-default-inline -Wabi -Wctor-dtor-privacy
          -Wnon-virtual-dtor  -Wreorder
          -Weffc++  -Wno-deprecated
          -Wno-non-template-friend  -Wold-style-cast
          -Woverloaded-virtual  -Wno-pmf-conversions
          -Wsign-promo  -Wsynth

_Objective-C Language Options_
     *Note Options Controlling Objective-C Dialect: Objective-C Dialect
     Options.
          -fconstant-string-class=CLASS-NAME
          -fgnu-runtime  -fnext-runtime  -gen-decls
          -Wno-protocol  -Wselector

_Language Independent Options_
     *Note Options to Control Diagnostic Messages Formatting: Language
     Independent Options.
          -fmessage-length=N
          -fdiagnostics-show-location=[once|every-line]

_Warning Options_
     *Note Options to Request or Suppress Warnings: Warning Options.
          -fsyntax-only  -pedantic  -pedantic-errors
          -w  -W  -Wall -Waggregate-return
          -Wcast-align  -Wcast-qual  -Wchar-subscripts  -Wcomment
          -Wconversion  -Wno-deprecated-declarations
          -Wdisabled-optimization  -Wdiv-by-zero  -Werror
          -Wfloat-equal  -Wformat  -Wformat=2
          -Wformat-nonliteral  -Wformat-security
          -Wimplicit  -Wimplicit-int
          -Wimplicit-function-declaration
          -Werror-implicit-function-declaration
          -Wimport  -Winline
          -Wlarger-than-LEN  -Wlong-long
          -Wmain  -Wmissing-braces
          -Wmissing-format-attribute  -Wmissing-noreturn
          -Wmultichar  -Wno-format-extra-args  -Wno-format-y2k
          -Wno-import  -Wpacked  -Wpadded
          -Wparentheses  -Wpointer-arith  -Wredundant-decls
          -Wreturn-type  -Wsequence-point  -Wshadow
          -Wsign-compare  -Wswitch  -Wsystem-headers
          -Wtrigraphs  -Wundef  -Wuninitialized
          -Wunknown-pragmas  -Wunreachable-code
          -Wunused  -Wunused-function  -Wunused-label  -Wunused-parameter
          -Wunused-value  -Wunused-variable  -Wwrite-strings

_C-only Warning Options_
          -Wbad-function-cast  -Wmissing-declarations
          -Wmissing-prototypes  -Wnested-externs
          -Wstrict-prototypes  -Wtraditional

_Debugging Options_
     *Note Options for Debugging Your Program or GCC: Debugging Options.
          -dLETTERS  -dumpspecs  -dumpmachine  -dumpversion
          -fdump-unnumbered -fdump-translation-unit[-N]
          -fdump-class-hierarchy[-N]
          -fdump-tree-original[-N] -fdump-tree-optimized[-N]
          -fdump-tree-inlined[-N]
          -fmem-report  -fpretend-float
          -fprofile-arcs  -fsched-verbose=N
          -ftest-coverage  -ftime-report
          -g  -gLEVEL  -gcoff  -gdwarf  -gdwarf-1  -gdwarf-1+  -gdwarf-2
          -ggdb  -gstabs  -gstabs+  -gvms  -gxcoff  -gxcoff+
          -p  -pg  -print-file-name=LIBRARY  -print-libgcc-file-name
          -print-multi-directory  -print-multi-lib
          -print-prog-name=PROGRAM  -print-search-dirs  -Q
          -save-temps  -time

_Optimization Options_
     *Note Options that Control Optimization: Optimize Options.
          -falign-functions=N  -falign-jumps=N
          -falign-labels=N  -falign-loops=N
          -fbounds-check
          -fbranch-probabilities  -fcaller-saves -fcprop-registers
          -fcse-follow-jumps  -fcse-skip-blocks  -fdata-sections
          -fdelayed-branch  -fdelete-null-pointer-checks
          -fexpensive-optimizations  -ffast-math  -ffloat-store
          -fforce-addr  -fforce-mem  -ffunction-sections
          -fgcse  -fgcse-lm  -fgcse-sm
          -finline-functions  -finline-limit=N  -fkeep-inline-functions
          -fkeep-static-consts  -fmerge-constants  -fmerge-all-constants
          -fmove-all-movables  -fno-branch-count-reg
          -fno-default-inline  -fno-defer-pop
          -fno-function-cse  -fno-guess-branch-probability
          -fno-inline  -fno-math-errno  -fno-peephole  -fno-peephole2
          -funsafe-math-optimizations -fno-trapping-math
          -fomit-frame-pointer  -foptimize-register-move
          -foptimize-sibling-calls  -fprefetch-loop-arrays
          -freduce-all-givs -fregmove  -frename-registers
          -frerun-cse-after-loop  -frerun-loop-opt
          -fschedule-insns  -fschedule-insns2
          -fno-sched-interblock  -fno-sched-spec
          -fsched-spec-load  -fsched-spec-load-dangerous
          -fsingle-precision-constant  -fssa -fssa-ccp -fssa-dce
          -fstrength-reduce  -fstrict-aliasing  -fthread-jumps
          -ftrapv -funroll-all-loops  -funroll-loops
          --param NAME=VALUE
          -O  -O0  -O1  -O2  -O3  -Os

_Preprocessor Options_
     *Note Options Controlling the Preprocessor: Preprocessor Options.
          -$  -AQUESTION=ANSWER  -A-QUESTION[=ANSWER]
          -C  -dD  -dI  -dM  -dN
          -DMACRO[=DEFN]  -E  -H
          -idirafter DIR
          -include FILE  -imacros FILE
          -iprefix FILE  -iwithprefix DIR
          -iwithprefixbefore DIR  -isystem DIR
          -M  -MM  -MF  -MG  -MP  -MQ  -MT  -nostdinc  -P  -remap
          -trigraphs  -undef  -UMACRO  -Wp,OPTION

_Assembler Option_
     *Note Passing Options to the Assembler: Assembler Options.
          -Wa,OPTION

_Linker Options_
     *Note Options for Linking: Link Options.
          OBJECT-FILE-NAME  -lLIBRARY
          -nostartfiles  -nodefaultlibs  -nostdlib
          -s  -static  -static-libgcc  -shared  -shared-libgcc  -symbolic
          -Wl,OPTION  -Xlinker OPTION
          -u SYMBOL

_Directory Options_
     *Note Options for Directory Search: Directory Options.
          -BPREFIX  -IDIR  -I-  -LDIR  -specs=FILE

_Target Options_
     *Note Target Options::.
          -b MACHINE  -V VERSION

_Machine Dependent Options_
     *Note Hardware Models and Configurations: Submodel Options.

     _M680x0 Options_
          -m68000  -m68020  -m68020-40  -m68020-60  -m68030  -m68040
          -m68060  -mcpu32  -m5200  -m68881  -mbitfield  -mc68000  -mc68020
          -mfpa  -mnobitfield  -mrtd  -mshort  -msoft-float  -mpcrel
          -malign-int  -mstrict-align

     _M68hc1x Options_
          -m6811  -m6812  -m68hc11  -m68hc12
          -mauto-incdec  -mshort  -msoft-reg-count=COUNT

     _VAX Options_
          -mg  -mgnu  -munix

     _SPARC Options_
          -mcpu=CPU-TYPE
          -mtune=CPU-TYPE
          -mcmodel=CODE-MODEL
          -m32  -m64
          -mapp-regs  -mbroken-saverestore  -mcypress
          -mfaster-structs  -mflat
          -mfpu  -mhard-float  -mhard-quad-float
          -mimpure-text  -mlive-g0  -mno-app-regs
          -mno-faster-structs  -mno-flat  -mno-fpu
          -mno-impure-text  -mno-stack-bias  -mno-unaligned-doubles
          -msoft-float  -msoft-quad-float  -msparclite  -mstack-bias
          -msupersparc  -munaligned-doubles  -mv8

     _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-frame  -mno-apcs-frame
          -mapcs-26  -mapcs-32
          -mapcs-stack-check  -mno-apcs-stack-check
          -mapcs-float  -mno-apcs-float
          -mapcs-reentrant  -mno-apcs-reentrant
          -msched-prolog  -mno-sched-prolog
          -mlittle-endian  -mbig-endian  -mwords-little-endian
          -malignment-traps  -mno-alignment-traps
          -msoft-float  -mhard-float  -mfpe
          -mthumb-interwork  -mno-thumb-interwork
          -mcpu=NAME  -march=NAME  -mfpe=NAME
          -mstructure-size-boundary=N
          -mbsd -mxopen  -mno-symrename
          -mabort-on-noreturn
          -mlong-calls  -mno-long-calls
          -msingle-pic-base  -mno-single-pic-base
          -mpic-register=REG
          -mnop-fun-dllimport
          -mpoke-function-name
          -mthumb  -marm
          -mtpcs-frame  -mtpcs-leaf-frame
          -mcaller-super-interworking  -mcallee-super-interworking

     _MN10200 Options_
          -mrelax

     _MN10300 Options_
          -mmult-bug  -mno-mult-bug
          -mam33  -mno-am33
          -mno-crt0  -mrelax

     _M32R/D Options_
          -m32rx -m32r -mcode-model=MODEL-TYPE  -msdata=SDATA-TYPE
          -G NUM

     _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
          -mtune=CPU-TYPE
          -mpower  -mno-power  -mpower2  -mno-power2
          -mpowerpc  -mpowerpc64  -mno-powerpc
          -maltivec -mno-altivec
          -mpowerpc-gpopt  -mno-powerpc-gpopt
          -mpowerpc-gfxopt  -mno-powerpc-gfxopt
          -mnew-mnemonics  -mold-mnemonics
          -mfull-toc   -mminimal-toc  -mno-fp-in-toc  -mno-sum-in-toc
          -m64  -m32  -mxl-call  -mno-xl-call  -mpe
          -msoft-float  -mhard-float  -mmultiple  -mno-multiple
          -mstring  -mno-string  -mupdate  -mno-update
          -mfused-madd  -mno-fused-madd  -mbit-align  -mno-bit-align
          -mstrict-align  -mno-strict-align  -mrelocatable
          -mno-relocatable  -mrelocatable-lib  -mno-relocatable-lib
          -mtoc  -mno-toc -mlittle  -mlittle-endian  -mbig  -mbig-endian
          -mcall-aix -mcall-sysv -mcall-netbsd
          -maix-struct-return -msvr4-struct-return
          -mabi=altivec -mabi=no-altivec
          -mprototype  -mno-prototype
          -msim  -mmvme  -mads  -myellowknife  -memb -msdata
          -msdata=OPT  -mvxworks -G NUM -pthread

     _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 -march=CPU-TYPE -mtune=CPU=TYPE
          -mcpu=CPU-TYPE -membedded-data  -muninit-const-in-rodata
          -membedded-pic  -mfp32  -mfp64  -mfused-madd  -mno-fused-madd
          -mgas  -mgp32  -mgp64
          -mgpopt  -mhalf-pic  -mhard-float  -mint64  -mips1
          -mips2  -mips3  -mips4  -mlong64  -mlong32  -mlong-calls  -mmemcpy
          -mmips-as  -mmips-tfile  -mno-abicalls
          -mno-embedded-data  -mno-uninit-const-in-rodata
          -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
          -mabi=32  -mabi=n32  -mabi=64  -mabi=eabi
          -mfix7000  -mno-crt0 -mflush-func=FUNC -mno-flush-func

     _i386 and x86-64 Options_
          -mcpu=CPU-TYPE  -march=CPU-TYPE -mfpmath=UNIT
          -masm=DIALECT  -mno-fancy-math-387
          -mno-fp-ret-in-387  -msoft-float  -msvr3-shlib
          -mno-wide-multiply  -mrtd  -malign-double
          -mpreferred-stack-boundary=NUM
          -mmmx  -msse -msse2 -m3dnow
          -mthreads  -mno-align-stringops  -minline-all-stringops
          -mpush-args  -maccumulate-outgoing-args  -m128bit-long-double
          -m96bit-long-double  -mregparm=NUM  -momit-leaf-frame-pointer
          -mno-red-zone
          -mcmodel=CODE-MODEL
          -m32 -m64

     _HPPA Options_
          -march=ARCHITECTURE-TYPE
          -mbig-switch  -mdisable-fpregs  -mdisable-indexing
          -mfast-indirect-calls  -mgas  -mjump-in-delay
          -mlong-load-store  -mno-big-switch  -mno-disable-fpregs
          -mno-disable-indexing  -mno-fast-indirect-calls  -mno-gas
          -mno-jump-in-delay  -mno-long-load-store
          -mno-portable-runtime  -mno-soft-float
          -mno-space-regs  -msoft-float  -mpa-risc-1-0
          -mpa-risc-1-1  -mpa-risc-2-0  -mportable-runtime
          -mschedule=CPU-TYPE  -mspace-regs

     _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_
          -mno-fp-regs  -msoft-float  -malpha-as  -mgas
          -mieee  -mieee-with-inexact  -mieee-conformant
          -mfp-trap-mode=MODE  -mfp-rounding-mode=MODE
          -mtrap-precision=MODE  -mbuild-constants
          -mcpu=CPU-TYPE  -mtune=CPU-TYPE
          -mbwx  -mmax  -mfix  -mcix
          -mfloat-vax  -mfloat-ieee
          -mexplicit-relocs  -msmall-data  -mlarge-data
          -mmemory-latency=TIME

     _DEC Alpha/VMS Options_
          -mvms-return-codes

     _Clipper Options_
          -mc300  -mc400

     _H8/300 Options_
          -mrelax  -mh  -ms  -mint32  -malign-300

     _SH Options_
          -m1  -m2  -m3  -m3e
          -m4-nofpu  -m4-single-only  -m4-single  -m4
          -m5-64media -m5-64media-nofpu
          -m5-32media -m5-32media-nofpu
          -m5-compact -m5-compact-nofpu
          -mb  -ml  -mdalign  -mrelax
          -mbigtable  -mfmovd  -mhitachi  -mnomacsave
          -mieee  -misize  -mpadstruct  -mspace
          -mprefergot  -musermode

     _System V Options_
          -Qy  -Qn  -YP,PATHS  -Ym,DIR

     _ARC Options_
          -EB  -EL
          -mmangle-cpu  -mcpu=CPU  -mtext=TEXT-SECTION
          -mdata=DATA-SECTION  -mrodata=READONLY-DATA-SECTION

     _TMS320C3x/C4x Options_
          -mcpu=CPU  -mbig  -msmall  -mregparm  -mmemparm
          -mfast-fix  -mmpyi  -mbk  -mti  -mdp-isr-reload
          -mrpts=COUNT  -mrptb  -mdb  -mloop-unsigned
          -mparallel-insns  -mparallel-mpy  -mpreserve-float

     _V850 Options_
          -mlong-calls  -mno-long-calls  -mep  -mno-ep
          -mprolog-function  -mno-prolog-function  -mspace
          -mtda=N  -msda=N  -mzda=N
          -mv850  -mbig-switch

     _NS32K Options_
          -m32032  -m32332  -m32532  -m32081  -m32381
          -mmult-add  -mnomult-add  -msoft-float  -mrtd  -mnortd
          -mregparam  -mnoregparam  -msb  -mnosb
          -mbitfield  -mnobitfield  -mhimem  -mnohimem

     _AVR Options_
          -mmcu=MCU  -msize  -minit-stack=N  -mno-interrupts
          -mcall-prologues  -mno-tablejump  -mtiny-stack

     _MCore Options_
          -mhardlit  -mno-hardlit  -mdiv  -mno-div  -mrelax-immediates
          -mno-relax-immediates  -mwide-bitfields  -mno-wide-bitfields
          -m4byte-functions  -mno-4byte-functions  -mcallgraph-data
          -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes  -mno-lsim
          -mlittle-endian  -mbig-endian  -m210  -m340  -mstack-increment

     _MMIX Options_
          -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu
          -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols
          -melf -mbranch-predict -mno-branch-predict -mbase-addresses
          -mno-base-addresses

     _IA-64 Options_
          -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld  -mno-pic
          -mvolatile-asm-stop  -mb-step  -mregister-names  -mno-sdata
          -mconstant-gp  -mauto-pic  -minline-divide-min-latency
          -minline-divide-max-throughput  -mno-dwarf2-asm
          -mfixed-range=REGISTER-RANGE

     _D30V Options_
          -mextmem  -mextmemory  -monchip  -mno-asm-optimize
          -masm-optimize -mbranch-cost=N -mcond-exec=N

     _S/390 and zSeries Options_
          -mhard-float  -msoft-float  -mbackchain  -mno-backchain
          -msmall-exec  -mno-small-exec  -mmvcle -mno-mvcle
          -m64 -m31 -mdebug -mno-debug

     _CRIS Options_
          -mcpu=CPU -march=CPU -mtune=CPU
          -mmax-stack-frame=N -melinux-stacksize=N
          -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects
          -mstack-align -mdata-align -mconst-align
          -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt
          -melf -maout -melinux -mlinux -sim -sim2

     _PDP-11 Options_
          -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45  -m10
          -mbcopy  -mbcopy-builtin  -mint32  -mno-int16
          -mint16  -mno-int32  -mfloat32  -mno-float64
          -mfloat64  -mno-float32  -mabshi  -mno-abshi
          -mbranch-expensive  -mbranch-cheap
          -msplit  -mno-split  -munix-asm  -mdec-asm

     _Xstormy16 Options_
          -msim

     _Xtensa Options_
          -mbig-endian -mlittle-endian
          -mdensity -mno-density
          -mmac16 -mno-mac16
          -mmul16 -mno-mul16
          -mmul32 -mno-mul32
          -mnsa -mno-nsa
          -mminmax -mno-minmax
          -msext -mno-sext
          -mbooleans -mno-booleans
          -mhard-float -msoft-float
          -mfused-madd -mno-fused-madd
          -mserialize-volatile -mno-serialize-volatile
          -mtext-section-literals -mno-text-section-literals
          -mtarget-align -mno-target-align
          -mlongcalls -mno-longcalls

_Code Generation Options_
     *Note Options for Code Generation Conventions: Code Gen Options.
          -fcall-saved-REG  -fcall-used-REG
          -ffixed-REG -fexceptions
          -fnon-call-exceptions  -funwind-tables
          -fasynchronous-unwind-tables
          -finhibit-size-directive  -finstrument-functions
          -fno-common  -fno-ident  -fno-gnu-linker
          -fpcc-struct-return  -fpic  -fPIC
          -freg-struct-return  -fshared-data  -fshort-enums
          -fshort-double  -fshort-wchar -fvolatile
          -fvolatile-global  -fvolatile-static
          -fverbose-asm  -fpack-struct  -fstack-check
          -fstack-limit-register=REG  -fstack-limit-symbol=SYM
          -fargument-alias  -fargument-noalias
          -fargument-noalias-global  -fleading-underscore


* Menu:

* Overall Options::     Controlling the kind of output:
                        an executable, object files, assembler files,
                        or preprocessed source.
* C Dialect Options::   Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C Dialect Options:: Variations on Objective-C.
* Language Independent Options:: Controlling how diagnostics should be
                        formatted.
* 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.
* Spec Files::          How to pass switches to sub-processes.
* Target Options::      Running a cross-compiler, or an old version of GCC.


File: gcc.info,  Node: Overall Options,  Next: Invoking G++,  Prev: Option Summary,  Up: Invoking GCC

3.2 Options Controlling the Kind of Output
==========================================

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.mi'
     Objective-C source code which should not be preprocessed.

`FILE.h'
     C header file (not to be compiled or linked).

`FILE.cc'
`FILE.cp'
`FILE.cxx'
`FILE.cpp'
`FILE.c++'
`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.f'
`FILE.for'
`FILE.FOR'
     Fortran source code which should not be preprocessed.

`FILE.F'
`FILE.fpp'
`FILE.FPP'
     Fortran source code which must be preprocessed (with the
     traditional preprocessor).

`FILE.r'
     Fortran source code which must be preprocessed with a RATFOR
     preprocessor (not included with GCC).

     *Note Options Controlling the Kind of Output: (g77)Overall
     Options, for more details of the handling of Fortran input files.

`FILE.ads'
     Ada source code file which contains a library unit declaration (a
     declaration of a package, subprogram, or generic, or a generic
     instantiation), or a library unit renaming declaration (a package,
     generic, or subprogram renaming declaration).  Such files are also
     called "specs".

`FILE.adb'
     Ada source code file containing a library unit body (a subprogram
     or package body).  Such files are also called "bodies".

`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  c-header  cpp-output
          c++  c++-cpp-output
          objective-c  objc-cpp-output
          assembler  assembler-with-cpp
          ada
          f77  f77-cpp-input  ratfor
          java

`-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).

`-pass-exit-codes'
     Normally the `gcc' program will exit with the code of 1 if any
     phase of the compiler returns a non-success return code.  If you
     specify `-pass-exit-codes', the `gcc' program will instead return
     with numerically highest error produced by any phase that returned
     an error indication.

   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.

`-###'
     Like `-v' except the commands are not executed and all command
     arguments are quoted.  This is useful for shell scripts to capture
     the driver-generated command lines.

`-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.

`--help'
     Print (on the standard output) a description of the command line
     options understood by `gcc'.  If the `-v' option is also specified
     then `--help' will also be passed on to the various processes
     invoked by `gcc', so that they can display the command line options
     they accept.  If the `-W' option is also specified then command
     line options which have no documentation associated with them will
     also be displayed.

`--target-help'
     Print (on the standard output) a description of target specific
     command line options for each tool.

`--version'
     Display the version number and copyrights of the invoked GCC.


File: gcc.info,  Node: Invoking G++,  Next: C Dialect Options,  Prev: Overall Options,  Up: Invoking GCC

3.3 Compiling C++ Programs
==========================

C++ source files conventionally use one of the suffixes `.C', `.cc',
`.cpp', `.c++', `.cp', or `.cxx'; preprocessed C++ files use the suffix
`.ii'.  GCC 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 GCC with the default language set to C++, and
automatically specifies linking against the C++ library.  On many
systems, `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.  *Note
Options Controlling C Dialect: C Dialect Options, for explanations of
options for languages related to C.  *Note Options Controlling C++
Dialect: C++ Dialect Options, for explanations of options that are
meaningful only for C++ programs.


File: gcc.info,  Node: C Dialect Options,  Next: C++ Dialect Options,  Prev: Invoking G++,  Up: Invoking GCC

3.4 Options Controlling C Dialect
=================================

The following options control the dialect of C (or languages derived
from C, such as C++ and Objective-C) that the compiler accepts:

`-ansi'
     In C mode, support all ISO C89 programs.  In C++ mode, remove GNU
     extensions that conflict with ISO C++.

     This turns off certain features of GCC that are incompatible with
     ISO C89 (when compiling C code), or of standard C++ (when
     compiling C++ code), such as the `asm' 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 ISO trigraph feature.  For the C compiler, it disables
     recognition of C++ style `//' comments as well as the `inline'
     keyword.

     The alternate keywords `__asm__', `__extension__', `__inline__'
     and `__typeof__' continue to work despite `-ansi'.  You would not
     want to use them in an ISO 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-ISO programs to be rejected
     gratuitously.  For that, `-pedantic' is required in addition to
     `-ansi'.  *Note Warning Options::.

     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
     ISO standard doesn't call for; this is to avoid interfering with
     any programs that might use these names for other things.

     Functions which would normally be built in but do not have
     semantics defined by ISO C (such as `alloca' and `ffs') are not
     built-in functions with `-ansi' is used.  *Note Other built-in
     functions provided by GCC: Other Builtins, for details of the
     functions affected.

`-std='
     Determine the language standard.  This option is currently only
     supported when compiling C.  A value for this option must be
     provided; possible values are

    `c89'
    `iso9899:1990'
          ISO C89 (same as `-ansi').

    `iso9899:199409'
          ISO C89 as modified in amendment 1.

    `c99'
    `c9x'
    `iso9899:1999'
    `iso9899:199x'
          ISO C99.  Note that this standard is not yet fully supported;
          see `http://gcc.gnu.org/gcc-3.1/c99status.html' for more
          information.  The names `c9x' and `iso9899:199x' are
          deprecated.

    `gnu89'
          Default, ISO C89 plus GNU extensions (including some C99
          features).

    `gnu99'

    `gnu9x'
          ISO C99 plus GNU extensions.  When ISO C99 is fully
          implemented in GCC, this will become the default.  The name
          `gnu9x' is deprecated.


     Even when this option is not specified, you can still use some of
     the features of newer standards in so far as they do not conflict
     with previous C standards.  For example, you may use
     `__restrict__' even when `-std=c99' is not specified.

     The `-std' options specifying some version of ISO C have the same
     effects as `-ansi', except that features that were not in ISO C89
     but are in the specified version (for example, `//' comments and
     the `inline' keyword in ISO C99) are not disabled.

     *Note Language Standards Supported by GCC: Standards, for details
     of these standard versions.

`-aux-info FILENAME'
     Output to the given filename prototyped declarations for all
     functions declared and/or defined in a translation unit, including
     those in header files.  This option is silently ignored in any
     language other than C.

     Besides declarations, the file indicates, in comments, the origin
     of each declaration (source file and line), whether the
     declaration was implicit, prototyped or unprototyped (`I', `N' for
     new or `O' for old, respectively, in the first character after the
     line number and the colon), and whether it came from a declaration
     or a definition (`C' or `F', respectively, in the following
     character).  In the case of function definitions, a K&R-style list
     of arguments followed by their declarations is also provided,
     inside comments, after the declaration.

`-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, which has the same effect.  In
     C99 mode (`-std=c99' or `-std=gnu99'), this switch only affects
     the `asm' and `typeof' keywords, since `inline' is a standard
     keyword in ISO C99.

`-fno-builtin'
`-fno-builtin-FUNCTION (C and Objective-C only)'
     Don't recognize built-in functions that do not begin with
     `__builtin_' as prefix.  *Note Other built-in functions provided
     by GCC: Other Builtins, for details of the functions affected,
     including those which are not built-in functions when `-ansi' or
     `-std' options for strict ISO C conformance are used because they
     do not have an ISO standard meaning.

     GCC normally generates special code to handle certain built-in
     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.

     In C++, `-fno-builtin' is always in effect.  The `-fbuiltin'
     option has no effect.  Therefore, in C++, the only way to get the
     optimization benefits of built-in functions is to call the function
     using the `__builtin_' prefix.  The GNU C++ Standard Library uses
     built-in functions to implement many functions (like
     `std::strchr'), so that you automatically get efficient code.

     With the `-fno-builtin-FUNCTION' option, not available when
     compiling C++, only the built-in function FUNCTION is disabled.
     FUNCTION must not begin with `__builtin_'.  If a function is named
     this is not built-in in this version of GCC, this option is
     ignored.  There is no corresponding `-fbuiltin-FUNCTION' option;
     if you wish to enable built-in functions selectively when using
     `-fno-builtin' or `-ffreestanding', you may define macros such as:

          #define abs(n)          __builtin_abs ((n))
          #define strcpy(d, s)    __builtin_strcpy ((d), (s))

`-fhosted'
     Assert that compilation takes place in a hosted environment.  This
     implies `-fbuiltin'.  A hosted environment is one in which the
     entire standard library is available, and in which `main' has a
     return type of `int'.  Examples are nearly everything except a
     kernel.  This is equivalent to `-fno-freestanding'.

`-ffreestanding'
     Assert that compilation takes place in a freestanding environment.
     This implies `-fno-builtin'.  A freestanding environment is one
     in which the standard library may not exist, and program startup
     may not necessarily be at `main'.  The most obvious example is an
     OS kernel.  This is equivalent to `-fno-hosted'.

     *Note Language Standards Supported by GCC: Standards, for details
     of freestanding and hosted environments.

`-trigraphs'
     Support ISO C trigraphs.  The `-ansi' option (and `-std' options
     for strict ISO C conformance) implies `-trigraphs'.

`-no-integrated-cpp'
     Invoke the external cpp during compilation.  The default is to use
     the integrated cpp (internal cpp).  This option also allows a
     user-supplied cpp via the `-B' option.  This flag is applicable in
     both C and C++ modes.

     We do not guarantee to retain this option in future, and we may
     change its semantics.

`-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 ISO 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 ISO 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.

     This option is deprecated and may be removed.

     You may wish to use `-fno-builtin' as well as `-traditional' if
     your program uses names that are normally GNU C built-in functions
     for other purposes of its own.

     You cannot use `-traditional' if you include any header files that
     rely on ISO C features.  Some vendors are starting to ship systems
     with ISO C header files and you cannot use `-traditional' on such
     systems to compile files that include any system headers.

     The `-traditional' option also enables `-traditional-cpp'.

`-traditional-cpp'
     Attempt to support some aspects of traditional C preprocessors.
     See the GNU CPP manual for details.

`-fcond-mismatch'
     Allow conditional expressions with mismatched types in the second
     and third arguments.  The value of such an expression is void.
     This option is not supported for C++.

`-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 bit-field is signed or unsigned,
     when the declaration does not use either `signed' or `unsigned'.
     By default, such a bit-field is signed, because this is
     consistent: the basic integer types such as `int' are signed types.

     However, when `-traditional' is used, bit-fields 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 ISO or GNU C conventions (the default).


File: gcc.info,  Node: C++ Dialect Options,  Next: Objective-C Dialect Options,  Prev: C Dialect Options,  Up: Invoking GCC

3.5 Options Controlling C++ Dialect
===================================

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 -frepo -O -c firstClass.C

In this example, only `-frepo' is an option meant only for C++
programs; you can use the other options with any language supported by
GCC.

   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.

`-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.

     An alternative to using this option is to specify that your
     `operator new' does not throw any exceptions; if you declare it
     `throw()', G++ will check the return value.  See also `new
     (nothrow)'.

`-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.

     This option is no longer useful on most targets, now that support
     has been added for putting variables into BSS without making them
     common.

`-fno-const-strings'
     Give string constants type `char *' instead of type `const char
     *'.  By default, G++ uses type `const char *' as required by the
     standard.  Even if you use `-fno-const-strings', you cannot
     actually modify the value of a string constant, unless you also use
     `-fwritable-strings'.

     This option might be removed in a future release of G++.  For
     maximum portability, you should structure your code so that it
     works with string constants that have type `const char *'.

`-fdollars-in-identifiers'
     Accept `$' in identifiers.  You can also explicitly prohibit use of
     `$' with the option `-fno-dollars-in-identifiers'.  (GNU C allows
     `$' by default on most target systems, but there are a few
     exceptions.)  Traditional C allowed the character `$' to form part
     of identifiers.  However, ISO C and C++ forbid `$' in identifiers.

`-fno-elide-constructors'
     The C++ standard allows an implementation to omit creating a
     temporary which is only used to initialize another object of the
     same type.  Specifying this option disables that optimization, and
     forces G++ to call the copy constructor in all cases.

`-fno-enforce-eh-specs'
     Don't check for violation of exception specifications at runtime.
     This option violates the C++ standard, but may be useful for
     reducing code size in production builds, much like defining
     `NDEBUG'.  The compiler will still optimize based on the exception
     specifications.

`-fexternal-templates'
     Cause `#pragma interface' and `implementation' to apply to
     template instantiation; template instances are emitted or not
     according to the location of the template definition.  *Note
     Template Instantiation::, for more information.

     This option is deprecated.

`-falt-external-templates'
     Similar to `-fexternal-templates', but template instances are
     emitted or not according to the place where they are first
     instantiated.  *Note Template Instantiation::, for more
     information.

     This option is deprecated.

`-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 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
     G++, 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 `typeof' as a keyword, so that code can use this
     word as an identifier.  You can use the keyword `__typeof__'
     instead.  `-ansi' implies `-fno-gnu-keywords'.

`-fno-implicit-templates'
     Never emit code for non-inline templates which are instantiated
     implicitly (i.e. by use); only emit code for explicit
     instantiations.  *Note Template Instantiation::, for more
     information.

`-fno-implicit-inline-templates'
     Don't emit code for implicit instantiations of inline templates,
     either.  The default is to handle inlines differently so that
     compiles with and without optimization will need the same set of
     explicit instantiations.

`-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.

`-fms-extensions'
     Disable pedantic warnings about constructs used in MFC, such as
     implicit int and getting a pointer to member function via
     non-standard syntax.

`-fno-nonansi-builtins'
     Disable built-in declarations of functions that are not mandated by
     ANSI/ISO C.  These include `ffs', `alloca', `_exit', `index',
     `bzero', `conjf', and other related functions.

`-fno-operator-names'
     Do not treat the operator name keywords `and', `bitand', `bitor',
     `compl', `not', `or' and `xor' as synonyms as keywords.

`-fno-optional-diags'
     Disable diagnostics that the standard says a compiler does not
     need to issue.  Currently, the only such diagnostic issued by G++
     is the one for a name having multiple meanings within a class.

`-fpermissive'
     Downgrade messages about nonconformant code from errors to
     warnings.  By default, G++ effectively sets `-pedantic-errors'
     without `-pedantic'; this option reverses that.  This behavior and
     this option are superseded by `-pedantic', which works as it does
     for GNU C.

`-frepo'
     Enable automatic template instantiation at link time.  This option
     also implies `-fno-implicit-templates'.  *Note Template
     Instantiation::, for more information.

`-fno-rtti'
     Disable generation of information about every class with virtual
     functions for use by the C++ runtime type identification features
     (`dynamic_cast' and `typeid').  If you don't use those parts of
     the language, you can save some space by using this flag.  Note
     that exception handling uses the same information, but it will
     generate it as needed.

`-fstats'
     Emit statistics about front-end processing at the end of the
     compilation.  This information is generally only useful to the G++
     development team.

`-ftemplate-depth-N'
     Set the maximum instantiation depth for template classes to N.  A
     limit on the template instantiation depth is needed to detect
     endless recursions during template class instantiation.  ANSI/ISO
     C++ conforming programs must not rely on a maximum depth greater
     than 17.

`-fuse-cxa-atexit'
     Register destructors for objects with static storage duration with
     the `__cxa_atexit' function rather than the `atexit' function.
     This option is required for fully standards-compliant handling of
     static destructors, but will only work if your C library supports
     `__cxa_atexit'.

`-fvtable-gc'
     Emit special relocations for vtables and virtual function
     references so that the linker can identify unused virtual
     functions and zero out vtable slots that refer to them.  This is
     most useful with `-ffunction-sections' and `-Wl,--gc-sections', in
     order to also discard the functions themselves.

     This optimization requires GNU as and GNU ld.  Not all systems
     support this option.  `-Wl,--gc-sections' is ignored without
     `-static'.

`-fno-weak'
     Do not use weak symbol support, even if it is provided by the
     linker.  By default, G++ will use weak symbols if they are
     available.  This option exists only for testing, and should not be
     used by end-users; it will result in inferior code and has no
     benefits.  This option may be removed in a future release of G++.

`-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 the C++ library.)

   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.
     *Note Options That Control Optimization: Optimize Options.  Note
     that these functions will have linkage like inline functions; they
     just won't be inlined by default.

`-Wabi (C++ only)'
     Warn when G++ generates code that is probably not compatible with
     the vendor-neutral C++ ABI.  Although an effort has been made to
     warn about all such cases, there are probably some cases that are
     not warned about, even though G++ is generating incompatible code.
     There may also be cases where warnings are emitted even though
     the code that is generated will be compatible.

     You should rewrite your code to avoid these warnings if you are
     concerned about the fact that code generated by G++ may not be
     binary compatible with code generated by other compilers.

     The known incompatibilites at this point include:

        * Incorrect handling of tail-padding for bit-fields.  G++ may
          attempt to pack data into the same byte as a base class.  For
          example:

               struct A { virtual void f(); int f1 : 1; };
               struct B : public A { int f2 : 1; };

          In this case, G++ will place `B::f2' into the same byte
          as`A::f1'; other compilers will not.  You can avoid this
          problem by explicitly padding `A' so that its size is a
          multiple of the byte size on your platform; that will cause
          G++ and other compilers to layout `B' identically.

        * Incorrect handling of tail-padding for virtual bases.  G++
          does not use tail padding when laying out virtual bases.  For
          example:

               struct A { virtual void f(); char c1; };
               struct B { B(); char c2; };
               struct C : public A, public virtual B {};

          In this case, G++ will not place `B' into the tail-padding for
          `A'; other compilers will.  You can avoid this problem by
          explicitly padding `A' so that its size is a multiple of its
          alignment (ignoring virtual base classes); that will cause
          G++ and other compilers to layout `C' identically.


`-Wctor-dtor-privacy (C++ only)'
     Warn when a class seems unusable, because all the constructors or
     destructors in a class are private and the class has no friends or
     public static member functions.

`-Wnon-virtual-dtor (C++ only)'
     Warn when a class declares a non-virtual destructor that should
     probably be virtual, because it looks like the class will be used
     polymorphically.

`-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.

   The following `-W...' options are not affected by `-Wall'.

`-Weffc++ (C++ only)'
     Warn about violations of the following style guidelines from Scott
     Meyers' `Effective C++' book:

        * Item 11:  Define a copy constructor and an assignment
          operator for classes with dynamically allocated memory.

        * Item 12:  Prefer initialization to assignment in constructors.

        * Item 14:  Make destructors virtual in base classes.

        * Item 15:  Have `operator=' return a reference to `*this'.

        * Item 23:  Don't try to return a reference when you must
          return an object.


     and about violations of the following style guidelines from Scott
     Meyers' `More Effective C++' book:

        * Item 6:  Distinguish between prefix and postfix forms of
          increment and decrement operators.

        * Item 7:  Never overload `&&', `||', or `,'.


     If you use this option, you should be aware that the standard
     library headers do not obey all of these guidelines; you can use
     `grep -v' to filter out those warnings.

`-Wno-deprecated (C++ only)'
     Do not warn about usage of deprecated features.  *Note Deprecated
     Features::.

`-Wno-non-template-friend (C++ only)'
     Disable warnings when non-templatized friend functions are declared
     within a template.  With the advent of explicit template
     specification support in G++, if the name of the friend is an
     unqualified-id (i.e., `friend foo(int)'), the C++ language
     specification demands that the friend declare or define an
     ordinary, nontemplate function.  (Section 14.5.3).  Before G++
     implemented explicit specification, unqualified-ids could be
     interpreted as a particular specialization of a templatized
     function.  Because this non-conforming behavior is no longer the
     default behavior for G++, `-Wnon-template-friend' allows the
     compiler to check existing code for potential trouble spots, and
     is on by default.  This new compiler behavior can be turned off
     with `-Wno-non-template-friend' which keeps the conformant
     compiler code but disables the helpful warning.

`-Wold-style-cast (C++ only)'
     Warn if an old-style (C-style) cast to a non-void type is used
     within a C++ program.  The new-style casts (`static_cast',
     `reinterpret_cast', and `const_cast') are less vulnerable to
     unintended effects, and much easier to grep for.

`-Woverloaded-virtual (C++ only)'
     Warn when a function declaration hides virtual functions from a
     base class.  For example, in:

          struct A {
            virtual void f();
          };

          struct B: public A {
            void f(int);
          };

     the `A' class version of `f' is hidden in `B', and code like this:

          B* b;
          b->f();

     will fail to compile.

`-Wno-pmf-conversions (C++ only)'
     Disable the diagnostic for converting a bound pointer to member
     function to a plain pointer.

`-Wsign-promo (C++ only)'
     Warn when overload resolution chooses a promotion from unsigned or
     enumeral type to a signed type over a conversion to an unsigned
     type of the same size.  Previous versions of G++ would try to
     preserve unsignedness, but the standard mandates the current
     behavior.

`-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 ='.


File: gcc.info,  Node: Objective-C Dialect Options,  Next: Language Independent Options,  Prev: C++ Dialect Options,  Up: Invoking GCC

3.6 Options Controlling Objective-C Dialect
===========================================

This section describes the command-line options that are only meaningful
for Objective-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 `some_class.m' like this:

     gcc -g -fgnu-runtime -O -c some_class.m

In this example, only `-fgnu-runtime' is an option meant only for
Objective-C programs; you can use the other options with any language
supported by GCC.

   Here is a list of options that are _only_ for compiling Objective-C
programs:

`-fconstant-string-class=CLASS-NAME'
     Use CLASS-NAME as the name of the class to instantiate for each
     literal string specified with the syntax `@"..."'.  The default
     class name is `NXConstantString'.

`-fgnu-runtime'
     Generate object code compatible with the standard GNU Objective-C
     runtime.  This is the default for most types of systems.

`-fnext-runtime'
     Generate output compatible with the NeXT runtime.  This is the
     default for NeXT-based systems, including Darwin and Mac OS X.

`-gen-decls'
     Dump interface declarations for all classes seen in the source
     file to a file named `SOURCENAME.decl'.

`-Wno-protocol'
     Do not warn if methods required by a protocol are not implemented
     in the class adopting it.

`-Wselector'
     Warn if a selector has multiple methods of different types defined.



File: gcc.info,  Node: Language Independent Options,  Next: Warning Options,  Prev: Objective-C Dialect Options,  Up: Invoking GCC

3.7 Options to Control Diagnostic Messages Formatting
=====================================================

Traditionally, diagnostic messages have been formatted irrespective of
the output device's aspect (e.g. its width, ...).  The options described
below can be used to control the diagnostic messages formatting
algorithm, e.g. how many characters per line, how often source location
information should be reported.  Right now, only the C++ front end can
honor these options.  However it is expected, in the near future, that
the remaining front ends would be able to digest them correctly.

`-fmessage-length=N'
     Try to format error messages so that they fit on lines of about N
     characters.  The default is 72 characters for `g++' and 0 for the
     rest of the front ends supported by GCC.  If N is zero, then no
     line-wrapping will be done; each error message will appear on a
     single line.

`-fdiagnostics-show-location=once'
     Only meaningful in line-wrapping mode.  Instructs the diagnostic
     messages reporter to emit _once_ source location information; that
     is, in case the message is too long to fit on a single physical
     line and has to be wrapped, the source location won't be emitted
     (as prefix) again, over and over, in subsequent continuation
     lines.  This is the default behavior.

`-fdiagnostics-show-location=every-line'
     Only meaningful in line-wrapping mode.  Instructs the diagnostic
     messages reporter to emit the same source location information (as
     prefix) for physical lines that result from the process of breaking
     a message which is too long to fit on a single line.



File: gcc.info,  Node: Warning Options,  Next: Debugging Options,  Prev: Language Independent Options,  Up: Invoking GCC

3.8 Options to Request or Suppress Warnings
===========================================

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.

   The following options control the amount and kinds of warnings
produced by GCC; for further, language-specific options also refer to
*Note C++ Dialect Options:: and *Note Objective-C Dialect Options::.

`-fsyntax-only'
     Check the code for syntax errors, but don't do anything beyond
     that.

`-pedantic'
     Issue all the warnings demanded by strict ISO C and ISO C++;
     reject all programs that use forbidden extensions, and some other
     programs that do not follow ISO C and ISO C++.  For ISO C, follows
     the version of the ISO C standard specified by any `-std' option
     used.

     Valid ISO C and ISO C++ programs should compile properly with or
     without this option (though a rare few will require `-ansi' or a
     `-std' option specifying the required version of ISO C).  However,
     without this option, certain GNU extensions and traditional C and
     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.
     *Note Alternate Keywords::.

     Some users try to use `-pedantic' to check programs for strict ISO
     C conformance.  They soon find that it does not do quite what they
     want: it finds some non-ISO practices, but not all--only those for
     which ISO C _requires_ a diagnostic, and some others for which
     diagnostics have been added.

     A feature to report any failure to conform to ISO C might be
     useful in some instances, but would require considerable
     additional work and would be quite different from `-pedantic'.  We
     don't have plans to support such a feature in the near future.

     Where the standard specified with `-std' represents a GNU extended
     dialect of C, such as `gnu89' or `gnu99', there is a corresponding
     "base standard", the version of ISO C on which the GNU extended
     dialect is based.  Warnings from `-pedantic' are given where they
     are required by the base standard.  (It would not make sense for
     such warnings to be given only for features not in the specified
     GNU C dialect, since by definition the GNU dialects of C include
     all features the compiler supports with the given option, and
     there would be nothing to warn about.)

`-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, or whenever a Backslash-Newline 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, and that the conversions specified in the format string
     make sense.  This includes standard functions, and others
     specified by format attributes (*note Function Attributes::), in
     the `printf', `scanf', `strftime' and `strfmon' (an X/Open
     extension, not in the C standard) families.

     The formats are checked against the format features supported by
     GNU libc version 2.2.  These include all ISO C89 and C99 features,
     as well as features from the Single Unix Specification and some
     BSD and GNU extensions.  Other library implementations may not
     support all these features; GCC does not support warning about
     features that go beyond a particular library's limitations.
     However, if `-pedantic' is used with `-Wformat', warnings will be
     given about format features not in the selected standard version
     (but not for `strfmon' formats, since those are not in any version
     of the C standard).  *Note Options Controlling C Dialect: C
     Dialect Options.

     `-Wformat' is included in `-Wall'.  For more control over some
     aspects of format checking, the options `-Wno-format-y2k',
     `-Wno-format-extra-args', `-Wformat-nonliteral',
     `-Wformat-security' and `-Wformat=2' are available, but are not
     included in `-Wall'.

`-Wno-format-y2k'
     If `-Wformat' is specified, do not warn about `strftime' formats
     which may yield only a two-digit year.

`-Wno-format-extra-args'
     If `-Wformat' is specified, do not warn about excess arguments to a
     `printf' or `scanf' format function.  The C standard specifies
     that such arguments are ignored.

     Where the unused arguments lie between used arguments that are
     specified with `$' operand number specifications, normally
     warnings are still given, since the implementation could not know
     what type to pass to `va_arg' to skip the unused arguments.
     However, in the case of `scanf' formats, this option will suppress
     the warning if the unused arguments are all pointers, since the
     Single Unix Specification says that such unused arguments are
     allowed.

`-Wformat-nonliteral'
     If `-Wformat' is specified, also warn if the format string is not a
     string literal and so cannot be checked, unless the format function
     takes its format arguments as a `va_list'.

`-Wformat-security'
     If `-Wformat' is specified, also warn about uses of format
     functions that represent possible security problems.  At present,
     this warns about calls to `printf' and `scanf' functions where the
     format string is not a string literal and there are no format
     arguments, as in `printf (foo);'.  This may be a security hole if
     the format string came from untrusted input and contains `%n'.
     (This is currently a subset of what `-Wformat-nonliteral' warns
     about, but in future warnings may be added to `-Wformat-security'
     that are not included in `-Wformat-nonliteral'.)

`-Wformat=2'
     Enable `-Wformat' plus format checks not included in `-Wformat'.
     Currently equivalent to `-Wformat -Wformat-nonliteral
     -Wformat-security'.

`-Wimplicit-int'
     Warn when a declaration does not specify a type.

`-Wimplicit-function-declaration'
`-Werror-implicit-function-declaration'
     Give a warning (or error) whenever a function is used before being
     declared.

`-Wimplicit'
     Same as `-Wimplicit-int' and `-Wimplicit-function-declaration'.

`-Wmain'
     Warn if the type of `main' is suspicious.  `main' should be a
     function with external linkage, returning int, taking either zero
     arguments, two, or three arguments of appropriate types.

`-Wmissing-braces'
     Warn if an aggregate or union initializer is not fully bracketed.
     In the following example, the initializer for `a' is not fully
     bracketed, but that for `b' is fully bracketed.

          int a[2][2] = { 0, 1, 2, 3 };
          int b[2][2] = { { 0, 1 }, { 2, 3 } };

`-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.

     Also warn about constructions where there may be confusion to which
     `if' statement an `else' branch belongs.  Here is an example of
     such a case:

          {
            if (a)
              if (b)
                foo ();
            else
              bar ();
          }

     In C, every `else' branch belongs to the innermost possible `if'
     statement, which in this example is `if (b)'.  This is often not
     what the programmer expected, as illustrated in the above example
     by indentation the programmer chose.  When there is the potential
     for this confusion, GCC will issue a warning when this flag is
     specified.  To eliminate the warning, add explicit braces around
     the innermost `if' statement so there is no way the `else' could
     belong to the enclosing `if'.  The resulting code would look like
     this:

          {
            if (a)
              {
                if (b)
                  foo ();
                else
                  bar ();
              }
          }

`-Wsequence-point'
     Warn about code that may have undefined semantics because of
     violations of sequence point rules in the C standard.

     The C standard defines the order in which expressions in a C
     program are evaluated in terms of "sequence points", which
     represent a partial ordering between the execution of parts of the
     program: those executed before the sequence point, and those
     executed after it.  These occur after the evaluation of a full
     expression (one which is not part of a larger expression), after
     the evaluation of the first operand of a `&&', `||', `? :' or `,'
     (comma) operator, before a function is called (but after the
     evaluation of its arguments and the expression denoting the called
     function), and in certain other places.  Other than as expressed
     by the sequence point rules, the order of evaluation of
     subexpressions of an expression is not specified.  All these rules
     describe only a partial order rather than a total order, since,
     for example, if two functions are called within one expression
     with no sequence point between them, the order in which the
     functions are called is not specified.  However, the standards
     committee have ruled that function calls do not overlap.

     It is not specified when between sequence points modifications to
     the values of objects take effect.  Programs whose behavior
     depends on this have undefined behavior; the C standard specifies
     that "Between the previous and next sequence point an object shall
     have its stored value modified at most once by the evaluation of
     an expression.  Furthermore, the prior value shall be read only to
     determine the value to be stored.".  If a program breaks these
     rules, the results on any particular implementation are entirely
     unpredictable.

     Examples of code with undefined behavior are `a = a++;', `a[n] =
     b[n++]' and `a[i++] = i;'.  Some more complicated cases are not
     diagnosed by this option, and it may give an occasional false
     positive result, but in general it has been found fairly effective
     at detecting this sort of problem in programs.

     The present implementation of this option only works for C
     programs.  A future implementation may also work for C++ programs.

     The C standard is worded confusingly, therefore there is some
     debate over the precise meaning of the sequence point rules in
     subtle cases.  Links to discussions of the problem, including
     proposed formal definitions, may be found on our readings page, at
     `http://gcc.gnu.org/readings.html'.

`-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'.

     For C++, a function without return type always produces a
     diagnostic message, even when `-Wno-return-type' is specified.
     The only exceptions are `main' and functions defined in system
     headers.

`-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 that might change the
     meaning of the program (trigraphs within comments are not warned
     about).

`-Wunused-function'
     Warn whenever a static function is declared but not defined or a
     non\-inline static function is unused.

`-Wunused-label'
     Warn whenever a label is declared but not used.

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-parameter'
     Warn whenever a function parameter is unused aside from its
     declaration.

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-variable'
     Warn whenever a local variable or non-constant static variable is
     unused aside from its declaration

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-value'
     Warn whenever a statement computes a result that is explicitly not
     used.

     To suppress this warning cast the expression to `void'.

`-Wunused'
     All all the above `-Wunused' options combined.

     In order to get a warning about an unused function parameter, you
     must either specify `-W -Wunused' or separately specify
     `-Wunused-parameter'.

`-Wuninitialized'
     Warn if an automatic variable is used without first being
     initialized or if a variable may be clobbered by a `setjmp' call.

     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 GCC 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 GCC 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.

     This option also warns when a non-volatile 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.

     Some spurious warnings can be avoided if you declare all the
     functions you use that never return as `noreturn'.  *Note Function
     Attributes::.

`-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:

`-Wunknown-pragmas'
     Warn when a #pragma directive is encountered which is not
     understood by GCC.  If this command line option is used, warnings
     will even be issued for unknown pragmas in system header files.
     This is not the case if the warnings were only enabled by the
     `-Wall' command line option.

`-Wall'
     All of the above `-W' options combined.  This enables all the
     warnings about constructions that some users consider
     questionable, and that are easy to avoid (or modify to prevent the
     warning), even in conjunction with macros.

`-Wdiv-by-zero'
     Warn about compile-time integer division by zero.  This is
     default.  To inhibit the warning messages, use `-Wno-div-by-zero'.
     Floating point division by zero is not warned about, as it can be
     a legitimate way of obtaining infinities and NaNs.

`-Wmultichar'
     Warn if a multicharacter constant (`'FOOF'') is used.  This is
     default.  To inhibit the warning messages, use `-Wno-multichar'.
     Usually they indicate a typo in the user's code, as they have
     implementation-defined values, and should not be used in portable
     code.

`-Wsystem-headers'
     Print warning messages for constructs found in system header files.
     Warnings from system headers are normally suppressed, on the
     assumption that they usually do not indicate real problems and
     would only make the compiler output harder to read.  Using this
     command line option tells GCC to emit warnings from system headers
     as if they occurred in user code.  However, note that using
     `-Wall' in conjunction with this option will _not_ warn about
     unknown pragmas in system headers--for that, `-Wunknown-pragmas'
     must also be used.

   The following `-W...' options are not implied by `-Wall'.  Some of
them warn about constructions that users generally do not consider
questionable, but which occasionally you might wish to check for;
others warn about constructions that are necessary or hard to avoid in
some cases, and there is no simple way to modify the code to suppress
the warning.

`-W'
     Print extra warning messages for these events:

        * 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.

        * The return type of a function has a type qualifier such as
          `const'.  Such a type qualifier has no effect, since the
          value returned by a function is not an lvalue.  (But don't
          warn about the GNU extension of `volatile void' return types.
          That extension will be warned about if `-pedantic' is
          specified.)

        * If `-Wall' or `-Wunused' is also specified, warn about unused
          arguments.

        * A comparison between signed and unsigned values could produce
          an incorrect result when the signed value is converted to
          unsigned.  (But don't warn if `-Wno-sign-compare' is also
          specified.)

        * 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 };

        * An aggregate has an initializer which does not initialize all
          members.  For example, the following code would cause such a
          warning, because `x.h' would be implicitly initialized to
          zero:

               struct s { int f, g, h; };
               struct s x = { 3, 4 };

`-Wfloat-equal'
     Warn if floating point values are used in equality comparisons.

     The idea behind this is that sometimes it is convenient (for the
     programmer) to consider floating-point values as approximations to
     infinitely precise real numbers.  If you are doing this, then you
     need to compute (by analysing the code, or in some other way) the
     maximum or likely maximum error that the computation introduces,
     and allow for it when performing comparisons (and when producing
     output, but that's a different problem).  In particular, instead
     of testing for equality, you would check to see whether the two
     values have ranges that overlap; and this is done with the
     relational operators, so equality comparisons are probably
     mistaken.

`-Wtraditional (C only)'
     Warn about certain constructs that behave differently in
     traditional and ISO C.  Also warn about ISO C constructs that have
     no traditional C equivalent, and/or problematic constructs which
     should be avoided.

        * Macro parameters that appear within string literals in the
          macro body.  In traditional C macro replacement takes place
          within string literals, but does not in ISO C.

        * In traditional C, some preprocessor directives did not exist.
          Traditional preprocessors would only consider a line to be a
          directive if the `#' appeared in column 1 on the line.
          Therefore `-Wtraditional' warns about directives that
          traditional C understands but would ignore because the `#'
          does not appear as the first character on the line.  It also
          suggests you hide directives like `#pragma' not understood by
          traditional C by indenting them.  Some traditional
          implementations would not recognize `#elif', so it suggests
          avoiding it altogether.

        * A function-like macro that appears without arguments.

        * The unary plus operator.

        * The `U' integer constant suffix, or the `F' or `L' floating
          point constant suffixes.  (Traditional C does support the `L'
          suffix on integer constants.)  Note, these suffixes appear in
          macros defined in the system headers of most modern systems,
          e.g. the `_MIN'/`_MAX' macros in `<limits.h>'.  Use of these
          macros in user code might normally lead to spurious warnings,
          however gcc's integrated preprocessor has enough context to
          avoid warning in these cases.

        * 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'.

        * A non-`static' function declaration follows a `static' one.
          This construct is not accepted by some traditional C
          compilers.

        * The ISO type of an integer constant has a different width or
          signedness from its traditional type.  This warning is only
          issued if the base of the constant is ten.  I.e. hexadecimal
          or octal values, which typically represent bit patterns, are
          not warned about.

        * Usage of ISO string concatenation is detected.

        * Initialization of automatic aggregates.

        * Identifier conflicts with labels.  Traditional C lacks a
          separate namespace for labels.

        * Initialization of unions.  If the initializer is zero, the
          warning is omitted.  This is done under the assumption that
          the zero initializer in user code appears conditioned on e.g.
          `__STDC__' to avoid missing initializer warnings and relies
          on default initialization to zero in the traditional C case.

        * Conversions by prototypes between fixed/floating point values
          and vice versa.  The absence of these prototypes when
          compiling with traditional C would cause serious problems.
          This is a subset of the possible conversion warnings, for the
          full set use `-Wconversion'.

`-Wundef'
     Warn if an undefined identifier is evaluated in an `#if' directive.

`-Wshadow'
     Warn whenever a local variable shadows another local variable,
     parameter or global variable or whenever a built-in function is
     shadowed.

`-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 (C only)'
     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'
     When compiling C, 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; when compiling
     C++, warn about the deprecated conversion from string constants to
     `char *'.  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'.

`-Wsign-compare'
     Warn when a comparison between signed and unsigned values could
     produce an incorrect result when the signed value is converted to
     unsigned.  This warning is also enabled by `-W'; to get the other
     warnings of `-W' without this warning, use `-W -Wno-sign-compare'.

`-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 (C only)'
     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 (C only)'
     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.

`-Wmissing-noreturn'
     Warn about functions which might be candidates for attribute
     `noreturn'.  Note these are only possible candidates, not absolute
     ones.  Care should be taken to manually verify functions actually
     do not ever return before adding the `noreturn' attribute,
     otherwise subtle code generation bugs could be introduced.  You
     will not get a warning for `main' in hosted C environments.

`-Wmissing-format-attribute'
     If `-Wformat' is enabled, also warn about functions which might be
     candidates for `format' attributes.  Note these are only possible
     candidates, not absolute ones.  GCC will guess that `format'
     attributes might be appropriate for any function that calls a
     function like `vprintf' or `vscanf', but this might not always be
     the case, and some functions for which `format' attributes are
     appropriate may not be detected.  This option has no effect unless
     `-Wformat' is enabled (possibly by `-Wall').

`-Wno-deprecated-declarations'
     Do not warn about uses of functions, variables, and types marked as
     deprecated by using the `deprecated' attribute.  (*note Function
     Attributes::, *note Variable Attributes::, *note Type
     Attributes::.)

`-Wpacked'
     Warn if a structure is given the packed attribute, but the packed
     attribute has no effect on the layout or size of the structure.
     Such structures may be mis-aligned for little benefit.  For
     instance, in this code, the variable `f.x' in `struct bar' will be
     misaligned even though `struct bar' does not itself have the
     packed attribute:

          struct foo {
            int x;
            char a, b, c, d;
          } __attribute__((packed));
          struct bar {
            char z;
            struct foo f;
          };

`-Wpadded'
     Warn if padding is included in a structure, either to align an
     element of the structure or to align the whole structure.
     Sometimes when this happens it is possible to rearrange the fields
     of the structure to reduce the padding and so make the structure
     smaller.

`-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 (C only)'
     Warn if an `extern' declaration is encountered within a function.

`-Wunreachable-code'
     Warn if the compiler detects that code will never be executed.

     This option is intended to warn when the compiler detects that at
     least a whole line of source code will never be executed, because
     some condition is never satisfied or because it is after a
     procedure that never returns.

     It is possible for this option to produce a warning even though
     there are circumstances under which part of the affected line can
     be executed, so care should be taken when removing
     apparently-unreachable code.

     For instance, when a function is inlined, a warning may mean that
     the line is unreachable in only one inlined copy of the function.

     This option is not made part of `-Wall' because in a debugging
     version of a program there is often substantial code which checks
     correct functioning of the program and is, hopefully, unreachable
     because the program does work.  Another common use of unreachable
     code is to provide behavior which is selectable at compile-time.

`-Winline'
     Warn if a function can not be inlined and it was declared as
     inline.

`-Wlong-long'
     Warn if `long long' type is used.  This is default.  To inhibit
     the warning messages, use `-Wno-long-long'.  Flags `-Wlong-long'
     and `-Wno-long-long' are taken into account only when `-pedantic'
     flag is used.

`-Wdisabled-optimization'
     Warn if a requested optimization pass is disabled.  This warning
     does not generally indicate that there is anything wrong with your
     code; it merely indicates that GCC's optimizers were unable to
     handle the code effectively.  Often, the problem is that your code
     is too big or too complex; GCC will refuse to optimize programs
     when the optimization itself is likely to take inordinate amounts
     of time.

`-Werror'
     Make all warnings into errors.


File: gcc.info,  Node: Debugging Options,  Next: Optimize Options,  Prev: Warning Options,  Up: Invoking GCC

3.9 Options for Debugging Your Program or GCC
=============================================

GCC 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-1+',
     `-gdwarf-1', or `-gvms' (see below).

     Unlike most other C compilers, GCC 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 GCC is generated with the
     capability for more than one debugging format.

`-ggdb'
     Produce debugging information for use by GDB.  This means to use
     the most expressive format available (DWARF 2, stabs, or the
     native format if neither of those are 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 version 1 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 version 1 format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program.

`-gdwarf-2'
     Produce debugging information in DWARF version 2 format (if that is
     supported).  This is the format used by DBX on IRIX 6.

`-gvms'
     Produce debugging information in VMS debug format (if that is
     supported).  This is the format used by DEBUG on VMS systems.

`-gLEVEL'
`-ggdbLEVEL'
`-gstabsLEVEL'
`-gcoffLEVEL'
`-gxcoffLEVEL'
`-gvmsLEVEL'
     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'.

     Note that in order to avoid confusion between DWARF1 debug level 2,
     and DWARF2, neither `-gdwarf' nor `-gdwarf-2' accept a
     concatenated debug level.  Instead use an additional `-gLEVEL'
     option to change the debug level for DWARF1 or DWARF2.

`-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.

`-Q'
     Makes the compiler print out each function name as it is compiled,
     and print some statistics about each pass when it finishes.

`-ftime-report'
     Makes the compiler print some statistics about the time consumed
     by each pass when it finishes.

`-fmem-report'
     Makes the compiler print some statistics about permanent memory
     allocation when it finishes.

`-fprofile-arcs'
     Instrument "arcs" during compilation to generate coverage data or
     for profile-directed block ordering.  During execution the program
     records how many times each branch is executed and how many times
     it is taken.  When the compiled program exits it saves this data
     to a file called `SOURCENAME.da' for each source file.

     For profile-directed block ordering, compile the program with
     `-fprofile-arcs' plus optimization and code generation options,
     generate the arc profile information by running the program on a
     selected workload, and then compile the program again with the same
     optimization and code generation options plus
     `-fbranch-probabilities' (*note Options that Control Optimization:
     Optimize Options.).

     The other use of `-fprofile-arcs' is for use with `gcov', when it
     is used with the `-ftest-coverage' option.

     With `-fprofile-arcs', for each function of your program GCC
     creates a program flow graph, then finds a spanning tree for the
     graph.  Only arcs that are not on the spanning tree have to be
     instrumented: the compiler adds code to count the number of times
     that these arcs are executed.  When an arc is the only exit or
     only entrance to a block, the instrumentation code can be added to
     the block; otherwise, a new basic block must be created to hold
     the instrumentation code.

`-ftest-coverage'
     Create data files for the `gcov' code-coverage utility (*note
     `gcov'--a Test Coverage Program: Gcov.).  The data file names
     begin with the name of your source file:

    `SOURCENAME.bb'
          A mapping from basic blocks to line numbers, which `gcov'
          uses to associate basic block execution counts with line
          numbers.

    `SOURCENAME.bbg'
          A list of all arcs in the program flow graph.  This allows
          `gcov' to reconstruct the program flow graph, so that it can
          compute all basic block and arc execution counts from the
          information in the `SOURCENAME.da' file.

     Use `-ftest-coverage' with `-fprofile-arcs'; the latter option
     adds instrumentation to the program, which then writes execution
     counts to another data file:

    `SOURCENAME.da'
          Runtime arc execution counts, used in conjunction with the arc
          information in the file `SOURCENAME.bbg'.

     Coverage data will map better to the source files if
     `-ftest-coverage' is used without optimization.

`-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 pass number
     and a word to the source file name (e.g.  `foo.c.00.rtl' or
     `foo.c.01.sibling').  Here are the possible letters for use in
     LETTERS, and their meanings:

    `A'
          Annotate the assembler output with miscellaneous debugging
          information.

    `b'
          Dump after computing branch probabilities, to `FILE.14.bp'.

    `B'
          Dump after block reordering, to `FILE.29.bbro'.

    `c'
          Dump after instruction combination, to the file
          `FILE.16.combine'.

    `C'
          Dump after the first if conversion, to the file `FILE.17.ce'.

    `d'
          Dump after delayed branch scheduling, to `FILE.31.dbr'.

    `D'
          Dump all macro definitions, at the end of preprocessing, in
          addition to normal output.

    `e'
          Dump after SSA optimizations, to `FILE.04.ssa' and
          `FILE.07.ussa'.

    `E'
          Dump after the second if conversion, to `FILE.26.ce2'.

    `f'
          Dump after life analysis, to `FILE.15.life'.

    `F'
          Dump after purging `ADDRESSOF' codes, to `FILE.09.addressof'.

    `g'
          Dump after global register allocation, to `FILE.21.greg'.

    `h'
          Dump after finalization of EH handling code, to `FILE.02.eh'.

    `k'
          Dump after reg-to-stack conversion, to `FILE.28.stack'.

    `o'
          Dump after post-reload optimizations, to `FILE.22.postreload'.

    `G'
          Dump after GCSE, to `FILE.10.gcse'.

    `i'
          Dump after sibling call optimizations, to `FILE.01.sibling'.

    `j'
          Dump after the first jump optimization, to `FILE.03.jump'.

    `k'
          Dump after conversion from registers to stack, to
          `FILE.32.stack'.

    `l'
          Dump after local register allocation, to `FILE.20.lreg'.

    `L'
          Dump after loop optimization, to `FILE.11.loop'.

    `M'
          Dump after performing the machine dependent reorganisation
          pass, to `FILE.30.mach'.

    `n'
          Dump after register renumbering, to `FILE.25.rnreg'.

    `N'
          Dump after the register move pass, to `FILE.18.regmove'.

    `r'
          Dump after RTL generation, to `FILE.00.rtl'.

    `R'
          Dump after the second scheduling pass, to `FILE.27.sched2'.

    `s'
          Dump after CSE (including the jump optimization that
          sometimes follows CSE), to `FILE.08.cse'.

    `S'
          Dump after the first scheduling pass, to `FILE.19.sched'.

    `t'
          Dump after the second CSE pass (including the jump
          optimization that sometimes follows CSE), to `FILE.12.cse2'.

    `w'
          Dump after the second flow pass, to `FILE.23.flow2'.

    `X'
          Dump after SSA dead code elimination, to `FILE.06.ssadce'.

    `z'
          Dump after the peephole pass, to `FILE.24.peephole2'.

    `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.  The length of each
          instruction is also printed.

    `P'
          Dump the RTL in the assembler output as a comment before each
          instruction.  Also turns on `-dp' annotation.

    `v'
          For each of the other indicated dump files (except for
          `FILE.00.rtl'), dump a representation of the control flow
          graph suitable for viewing with VCG to `FILE.PASS.vcg'.

    `x'
          Just generate RTL for a function instead of compiling it.
          Usually used with `r'.

    `y'
          Dump debugging information during parsing, to standard error.

`-fdump-unnumbered'
     When doing debugging dumps (see `-d' option above), suppress
     instruction numbers and line number note output.  This makes it
     more feasible to use diff on debugging dumps for compiler
     invocations with different options, in particular with and without
     `-g'.

`-fdump-translation-unit (C and C++ only)'
`-fdump-translation-unit-OPTIONS (C and C++ only)'
     Dump a representation of the tree structure for the entire
     translation unit to a file.  The file name is made by appending
     `.tu' to the source file name.  If the `-OPTIONS' form is used,
     OPTIONS controls the details of the dump as described for the
     `-fdump-tree' options.

`-fdump-class-hierarchy (C++ only)'
`-fdump-class-hierarchy-OPTIONS (C++ only)'
     Dump a representation of each class's hierarchy and virtual
     function table layout to a file.  The file name is made by
     appending `.class' to the source file name.  If the `-OPTIONS'
     form is used, OPTIONS controls the details of the dump as
     described for the `-fdump-tree' options.

`-fdump-tree-SWITCH (C++ only)'
`-fdump-tree-SWITCH-OPTIONS (C++ only)'
     Control the dumping at various stages of processing the
     intermediate language tree to a file.  The file name is generated
     by appending a switch specific suffix to the source file name.  If
     the `-OPTIONS' form is used, OPTIONS is a list of `-' separated
     options that control the details of the dump. Not all options are
     applicable to all dumps, those which are not meaningful will be
     ignored. The following options are available

    `address'
          Print the address of each node.  Usually this is not
          meaningful as it changes according to the environment and
          source file. Its primary use is for tying up a dump file with
          a debug environment.

    `slim'
          Inhibit dumping of members of a scope or body of a function
          merely because that scope has been reached. Only dump such
          items when they are directly reachable by some other path.

    `all'
          Turn on all options.

     The following tree dumps are possible:
    `original'
          Dump before any tree based optimization, to `FILE.original'.

    `optimized'
          Dump after all tree based optimization, to `FILE.optimized'.

    `inlined'
          Dump after function inlining, to `FILE.inlined'.

`-fsched-verbose=N'
     On targets that use instruction scheduling, this option controls
     the amount of debugging output the scheduler prints.  This
     information is written to standard error, unless `-dS' or `-dR' is
     specified, in which case it is output to the usual dump listing
     file, `.sched' or `.sched2' respectively.  However for N greater
     than nine, the output is always printed to standard error.

     For N greater than zero, `-fsched-verbose' outputs the same
     information as `-dRS'.  For N greater than one, it also output
     basic block probabilities, detailed ready list information and
     unit/insn info.  For N greater than two, it includes RTL at abort
     point, control-flow and regions info.  And for N over four,
     `-fsched-verbose' also includes dependence info.

`-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 GCC 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'.  This creates a
     preprocessed `foo.i' output file even though the compiler now
     normally uses an integrated preprocessor.

`-time'
     Report the CPU time taken by each subprocess in the compilation
     sequence.  For C source files, this is the compiler proper and
     assembler (plus the linker if linking is done).  The output looks
     like this:

          # cc1 0.12 0.01
          # as 0.00 0.01

     The first number on each line is the "user time," that is time
     spent executing the program itself.  The second number is "system
     time," time spent executing operating system routines on behalf of
     the program.  Both numbers are in seconds.

`-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, GCC does not compile or link anything; it just prints the
     file name.

`-print-multi-directory'
     Print the directory name corresponding to the multilib selected by
     any other switches present in the command line.  This directory is
     supposed to exist in `GCC_EXEC_PREFIX'.

`-print-multi-lib'
     Print the mapping from multilib directory names to compiler
     switches that enable them.  The directory name is separated from
     the switches by `;', and each switch starts with an `@' instead of
     the `-', without spaces between multiple switches.  This is
     supposed to ease shell-processing.

`-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 cpp0: No such file or directory'.  To resolve
     this you either need to put `cpp0' 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 '/'.  *Note Environment
     Variables::.

`-dumpmachine'
     Print the compiler's target machine (for example,
     `i686-pc-linux-gnu')--and don't do anything else.

`-dumpversion'
     Print the compiler version (for example, `3.0')--and don't do
     anything else.

`-dumpspecs'
     Print the compiler's built-in specs--and don't do anything else.
     (This is used when GCC itself is being built.)  *Note Spec Files::.


File: gcc.info,  Node: Optimize Options,  Next: Preprocessor Options,  Prev: Debugging Options,  Up: Invoking GCC

3.10 Options That Control Optimization
======================================

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.

     With `-O', the compiler tries to reduce code size and execution
     time, without performing any optimizations that take a great deal
     of compilation time.

`-O2'
     Optimize even more.  GCC 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, function inlining, and register renaming.  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.

     Please note the warning under `-fgcse' about invoking `-O2' on
     programs that use computed gotos.

`-O3'
     Optimize yet more.  `-O3' turns on all optimizations specified by
     `-O2' and also turns on the `-finline-functions' and
     `-frename-registers' options.

`-O0'
     Do not optimize.

`-Os'
     Optimize for size.  `-Os' enables all `-O2' optimizations that do
     not typically increase code size.  It also performs further
     optimizations designed to reduce code size.

     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.  Similarly for the
     x86 architecture.  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, after
     modifying them to store all pertinent intermediate computations
     into variables.

`-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.  *Note Register
     Usage: (gccint)Registers.

`-foptimize-sibling-calls'
     Optimize sibling and tail recursive calls.

`-ftrapv'
     This option generates traps for signed overflow on addition,
     subtraction, multiplication operations.

`-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.

`-finline-limit=N'
     By default, gcc limits the size of functions that can be inlined.
     This flag allows the control of this limit for functions that are
     explicitly marked as inline (ie marked with the inline keyword or
     defined within the class definition in c++).  N is the size of
     functions that can be inlined in number of pseudo instructions
     (not counting parameter handling).  The default value of N is 600.
     Increasing this value can result in more inlined code at the cost
     of compilation time and memory consumption.  Decreasing usually
     makes the compilation faster and less code will be inlined (which
     presumably means slower programs).  This option is particularly
     useful for programs that use inlining heavily such as those based
     on recursive templates with C++.

     _Note:_ pseudo instruction represents, in this particular context,
     an abstract measurement of function's size.  In no way, it
     represents a count of assembly instructions and as such its exact
     meaning might change from one release to an another.

`-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.  This switch does not
     affect `extern inline' functions.

`-fkeep-static-consts'
     Emit variables declared `static const' when optimization isn't
     turned on, even if the variables aren't referenced.

     GCC enables this option by default.  If you want to force the
     compiler to check if the variable was referenced, regardless of
     whether or not optimization is turned on, use the
     `-fno-keep-static-consts' option.

`-fmerge-constants'
     Attempt to merge identical constants (string constants and
     floating point constants) accross compilation units.

     This option is default for optimized compilation if assembler and
     linker support it.  Use `-fno-merge-constants' to inhibit this
     behavior.

`-fmerge-all-constants'
     Attempt to merge identical constants and identical variables.

     This option implies `-fmerge-constants'.  In addition to
     `-fmerge-constants' this considers e.g. even constant initialized
     arrays or initialized constant variables with integral or floating
     point types.  Languages like C or C++ require each non-automatic
     variable to have distinct location, so using this option will
     result in non-conforming behavior.

`-fno-branch-count-reg'
     Do not use "decrement and branch" instructions on a count register,
     but instead generate a sequence of instructions that decrement a
     register, compare it against zero, then branch based upon the
     result.  This option is only meaningful on architectures that
     support such instructions, which include x86, PowerPC, IA-64 and
     S/390.

`-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'
     Sets `-fno-math-errno', `-funsafe-math-optimizations', and
     `-fno-trapping-math'.

     This option causes the preprocessor macro `__FAST_MATH__' to be
     defined.

     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 ISO rules/specifications for math
     functions.

`-fno-math-errno'
     Do not set ERRNO after calling math functions that are executed
     with a single instruction, e.g., sqrt.  A program that relies on
     IEEE exceptions for math error handling may want to use this flag
     for speed while maintaining IEEE arithmetic compatibility.

     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 ISO rules/specifications for math
     functions.

     The default is `-fmath-errno'.

`-funsafe-math-optimizations'
     Allow optimizations for floating-point arithmetic that (a) assume
     that arguments and results are valid and (b) may violate IEEE or
     ANSI standards.  When used at link-time, it may include libraries
     or startup files that change the default FPU control word or other
     similar optimizations.

     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 ISO rules/specifications for math
     functions.

     The default is `-fno-unsafe-math-optimizations'.

`-fno-trapping-math'
     Compile code assuming that floating-point operations cannot
     generate user-visible traps.  Setting this option may allow faster
     code if one relies on "non-stop" IEEE arithmetic, for example.

     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 ISO rules/specifications for math
     functions.

     The default is `-ftrapping-math'.

`-fbounds-check'
     For front-ends that support it, generate additional code to check
     that indices used to access arrays are within the declared range.
     This is currenly only supported by the Java and Fortran 77
     front-ends, where this option defaults to true and false
     respectively.


   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.

   Not all of the optimizations performed by GCC have `-f' options to
control them.

`-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.

`-frerun-loop-opt'
     Run the loop optimizer twice.

`-fgcse'
     Perform a global common subexpression elimination pass.  This pass
     also performs global constant and copy propagation.

     _Note:_ When compiling a program using computed gotos, a GCC
     extension, you may get better runtime performance if you disable
     the global common subexpression elmination pass by adding
     `-fno-gcse' to the command line.

`-fgcse-lm'
     When `-fgcse-lm' is enabled, global common subexpression
     elimination will attempt to move loads which are only killed by
     stores into themselves.  This allows a loop containing a
     load/store sequence to be changed to a load outside the loop, and
     a copy/store within the loop.

`-fgcse-sm'
     When `-fgcse-sm' is enabled, A store motion pass is run after
     global common subexpression elimination.  This pass will attempt
     to move stores out of loops.  When used in conjunction with
     `-fgcse-lm', loops containing a load/store sequence can be changed
     to a load before the loop and a store after the loop.

`-fdelete-null-pointer-checks'
     Use global dataflow analysis to identify and eliminate useless
     checks for null pointers.  The compiler assumes that dereferencing
     a null pointer would have halted the program.  If a pointer is
     checked after it has already been dereferenced, it cannot be null.

     In some environments, this assumption is not true, and programs can
     safely dereference null pointers.  Use
     `-fno-delete-null-pointer-checks' to disable this optimization for
     programs which depend on that behavior.

`-fexpensive-optimizations'
     Perform a number of minor optimizations that are relatively
     expensive.

`-foptimize-register-move'
`-fregmove'
     Attempt to reassign register numbers in move instructions and as
     operands of other simple instructions in order to maximize the
     amount of register tying.  This is especially helpful on machines
     with two-operand instructions.  GCC enables this optimization by
     default with `-O2' or higher.

     Note `-fregmove' and `-foptimize-register-move' are the same
     optimization.

`-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.

`-fno-sched-interblock'
     Don't schedule instructions across basic blocks.  This is normally
     enabled by default when scheduling before register allocation, i.e.
     with `-fschedule-insns' or at `-O2' or higher.

`-fno-sched-spec'
     Don't allow speculative motion of non-load instructions.  This is
     normally enabled by default when scheduling before register
     allocation, i.e.  with `-fschedule-insns' or at `-O2' or higher.

`-fsched-spec-load'
     Allow speculative motion of some load instructions.  This only
     makes sense when scheduling before register allocation, i.e. with
     `-fschedule-insns' or at `-O2' or higher.

`-fsched-spec-load-dangerous'
     Allow speculative motion of more load instructions.  This only
     makes sense when scheduling before register allocation, i.e. with
     `-fschedule-insns' or at `-O2' or higher.

`-ffunction-sections'
`-fdata-sections'
     Place each function or data item into its own section in the output
     file if the target supports arbitrary sections.  The name of the
     function or the name of the data item determines the section's name
     in the output file.

     Use these options on systems where the linker can perform
     optimizations to improve locality of reference in the instruction
     space.  HPPA processors running HP-UX and Sparc processors running
     Solaris 2 have linkers with such optimizations.  Other systems
     using the ELF object format as well as AIX may have these
     optimizations in the future.

     Only use these options when there are significant benefits from
     doing so.  When you specify these options, the assembler and
     linker will create larger object and executable files and will
     also be slower.  You will not be able to use `gprof' on all
     systems if you specify this option and you may have problems with
     debugging if you specify both this option and `-g'.

`-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 always enabled by default on certain machines,
     usually those which have no call-preserved registers to use
     instead.

     For all machines, optimization level 2 and higher enables this
     flag by default.

`-funroll-loops'
     Unroll loops whose number of iterations can be determined at
     compile time or upon entry to the loop.  `-funroll-loops' implies
     both `-fstrength-reduce' and `-frerun-cse-after-loop'.  This
     option makes code larger, and may or may not make it run faster.

`-funroll-all-loops'
     Unroll all loops, even if their number of iterations is uncertain
     when the loop is entered.  This usually makes programs run more
     slowly.  `-funroll-all-loops' implies the same options as
     `-funroll-loops',

`-fprefetch-loop-arrays'
     If supported by the target machine, generate instructions to
     prefetch memory to improve the performance of loops that access
     large arrays.

`-fmove-all-movables'
     Forces all invariant computations in loops to be moved outside the
     loop.

`-freduce-all-givs'
     Forces all general-induction variables in loops to be
     strength-reduced.

     _Note:_ When compiling programs written in Fortran,
     `-fmove-all-movables' and `-freduce-all-givs' are enabled by
     default when you use the optimizer.

     These options may generate better or worse code; results are highly
     dependent on the structure of loops within the source code.

     These two options are intended to be removed someday, once they
     have helped determine the efficacy of various approaches to
     improving loop optimizations.

     Please let us (<gcc@gcc.gnu.org> and <fortran@gnu.org>) know how
     use of these options affects the performance of your production
     code.  We're very interested in code that runs _slower_ when these
     options are _enabled_.

`-fno-peephole'
`-fno-peephole2'
     Disable any machine-specific peephole optimizations.  The
     difference between `-fno-peephole' and `-fno-peephole2' is in how
     they are implemented in the compiler; some targets use one, some
     use the other, a few use both.

`-fbranch-probabilities'
     After running a program compiled with `-fprofile-arcs' (*note
     Options for Debugging Your Program or `gcc': Debugging Options.),
     you can compile it a second time using `-fbranch-probabilities',
     to improve optimizations based on the number of times each branch
     was taken.  When the program compiled with `-fprofile-arcs' exits
     it saves arc execution counts to a file called `SOURCENAME.da' for
     each source file  The information in this data file is very
     dependent on the structure of the generated code, so you must use
     the same source code and the same optimization options for both
     compilations.

     With `-fbranch-probabilities', GCC puts a `REG_EXEC_COUNT' note on
     the first instruction of each basic block, and a `REG_BR_PROB'
     note on each `JUMP_INSN' and `CALL_INSN'.  These can be used to
     improve optimization.  Currently, they are only used in one place:
     in `reorg.c', instead of guessing which path a branch is mostly to
     take, the `REG_BR_PROB' values are used to exactly determine which
     path is taken more often.

`-fno-guess-branch-probability'
     Do not guess branch probabilities using a randomized model.

     Sometimes gcc will opt to use a randomized model to guess branch
     probabilities, when none are available from either profiling
     feedback (`-fprofile-arcs') or `__builtin_expect'.  This means that
     different runs of the compiler on the same program may produce
     different object code.

     In a hard real-time system, people don't want different runs of the
     compiler to produce code that has different behavior; minimizing
     non-determinism is of paramount import.  This switch allows users
     to reduce non-determinism, possibly at the expense of inferior
     optimization.

`-fstrict-aliasing'
     Allows the compiler to assume the strictest aliasing rules
     applicable to the language being compiled.  For C (and C++), this
     activates optimizations based on the type of expressions.  In
     particular, an object of one type is assumed never to reside at
     the same address as an object of a different type, unless the
     types are almost the same.  For example, an `unsigned int' can
     alias an `int', but not a `void*' or a `double'.  A character type
     may alias any other type.

     Pay special attention to code like this:
          union a_union {
            int i;
            double d;
          };

          int f() {
            a_union t;
            t.d = 3.0;
            return t.i;
          }
     The practice of reading from a different union member than the one
     most recently written to (called "type-punning") is common.  Even
     with `-fstrict-aliasing', type-punning is allowed, provided the
     memory is accessed through the union type.  So, the code above
     will work as expected.  However, this code might not:
          int f() {
            a_union t;
            int* ip;
            t.d = 3.0;
            ip = &t.i;
            return *ip;
          }

     Every language that wishes to perform language-specific alias
     analysis should define a function that computes, given an `tree'
     node, an alias set for the node.  Nodes in different alias sets
     are not allowed to alias.  For an example, see the C front-end
     function `c_get_alias_set'.

`-falign-functions'
`-falign-functions=N'
     Align the start of functions to the next power-of-two greater than
     N, skipping up to N bytes.  For instance, `-falign-functions=32'
     aligns functions to the next 32-byte boundary, but
     `-falign-functions=24' would align to the next 32-byte boundary
     only if this can be done by skipping 23 bytes or less.

     `-fno-align-functions' and `-falign-functions=1' are equivalent
     and mean that functions will not be aligned.

     Some assemblers only support this flag when N is a power of two;
     in that case, it is rounded up.

     If N is not specified, use a machine-dependent default.

`-falign-labels'
`-falign-labels=N'
     Align all branch targets to a power-of-two boundary, skipping up to
     N bytes like `-falign-functions'.  This option can easily make
     code slower, because it must insert dummy operations for when the
     branch target is reached in the usual flow of the code.

     If `-falign-loops' or `-falign-jumps' are applicable and are
     greater than this value, then their values are used instead.

     If N is not specified, use a machine-dependent default which is
     very likely to be `1', meaning no alignment.

`-falign-loops'
`-falign-loops=N'
     Align loops to a power-of-two boundary, skipping up to N bytes
     like `-falign-functions'.  The hope is that the loop will be
     executed many times, which will make up for any execution of the
     dummy operations.

     If N is not specified, use a machine-dependent default.

`-falign-jumps'
`-falign-jumps=N'
     Align branch targets to a power-of-two boundary, for branch targets
     where the targets can only be reached by jumping, skipping up to N
     bytes like `-falign-functions'.  In this case, no dummy operations
     need be executed.

     If N is not specified, use a machine-dependent default.

`-fssa'
     Perform optimizations in static single assignment form.  Each
     function's flow graph is translated into SSA form, optimizations
     are performed, and the flow graph is translated back from SSA
     form.  Users should not specify this option, since it is not yet
     ready for production use.

`-fssa-ccp'
     Perform Sparse Conditional Constant Propagation in SSA form.
     Requires `-fssa'.  Like `-fssa', this is an experimental feature.

`-fssa-dce'
     Perform aggressive dead-code elimination in SSA form.  Requires
     `-fssa'.  Like `-fssa', this is an experimental feature.

`-fsingle-precision-constant'
     Treat floating point constant as single precision constant instead
     of implicitly converting it to double precision constant.

`-frename-registers'
     Attempt to avoid false dependencies in scheduled code by making use
     of registers left over after register allocation.  This
     optimization will most benefit processors with lots of registers.
     It can, however, make debugging impossible, since variables will
     no longer stay in a "home register".

`-fno-cprop-registers'
     After register allocation and post-register allocation instruction
     splitting, we perform a copy-propagation pass to try to reduce
     scheduling dependencies and occasionally eliminate the copy.

`--param NAME=VALUE'
     In some places, GCC uses various constants to control the amount of
     optimization that is done.  For example, GCC will not inline
     functions that contain more that a certain number of instructions.
     You can control some of these constants on the command-line using
     the `--param' option.

     In each case, the VALUE is an integer.  The allowable choices for
     NAME are given in the following table:

    `max-delay-slot-insn-search'
          The maximum number of instructions to consider when looking
          for an instruction to fill a delay slot.  If more than this
          arbitrary number of instructions is searched, the time
          savings from filling the delay slot will be minimal so stop
          searching.  Increasing values mean more aggressive
          optimization, making the compile time increase with probably
          small improvement in executable run time.

    `max-delay-slot-live-search'
          When trying to fill delay slots, the maximum number of
          instructions to consider when searching for a block with
          valid live register information.  Increasing this arbitrarily
          chosen value means more aggressive optimization, increasing
          the compile time.  This parameter should be removed when the
          delay slot code is rewritten to maintain the control-flow
          graph.

    `max-gcse-memory'
          The approximate maximum amount of memory that will be
          allocated in order to perform the global common subexpression
          elimination optimization.  If more memory than specified is
          required, the optimization will not be done.

    `max-gcse-passes'
          The maximum number of passes of GCSE to run.

    `max-pending-list-length'
          The maximum number of pending dependencies scheduling will
          allow before flushing the current state and starting over.
          Large functions with few branches or calls can create
          excessively large lists which needlessly consume memory and
          resources.

    `max-inline-insns'
          If an function contains more than this many instructions, it
          will not be inlined.  This option is precisely equivalent to
          `-finline-limit'.



File: gcc.info,  Node: Preprocessor Options,  Next: Assembler Options,  Prev: Optimize Options,  Up: Invoking GCC

3.11 Options Controlling the Preprocessor
=========================================

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.

   You can use `-Wp,OPTION' to bypass the compiler driver and pass
OPTION directly through to the preprocessor.  If OPTION contains
commas, it is split into multiple options at the commas.  However, many
options are modified, translated or interpreted by the compiler driver
before being passed to the preprocessor, and `-Wp' forcibly bypasses
this phase.  The preprocessor's direct interface is undocumented and
subject to change, so whenever possible you should avoid using `-Wp'
and let the driver handle the options instead.

`-D NAME'
     Predefine NAME as a macro, with definition `1'.

`-D NAME=DEFINITION'
     Predefine NAME as a macro, with definition DEFINITION.  There are
     no restrictions on the contents of DEFINITION, but if you are
     invoking the preprocessor from a shell or shell-like program you
     may need to use the shell's quoting syntax to protect characters
     such as spaces that have a meaning in the shell syntax.

     If you wish to define a function-like macro on the command line,
     write its argument list with surrounding parentheses before the
     equals sign (if any).  Parentheses are meaningful to most shells,
     so you will need to quote the option.  With `sh' and `csh',
     `-D'NAME(ARGS...)=DEFINITION'' works.

     `-D' and `-U' options are processed in the order they are given on
     the command line.  All `-imacros FILE' and `-include FILE' options
     are processed after all `-D' and `-U' options.

`-U NAME'
     Cancel any previous definition of NAME, either built in or
     provided with a `-D' option.

`-undef'
     Do not predefine any system-specific macros.  The common predefined
     macros remain defined.

`-I DIR'
     Add the directory DIR to the list of directories to be searched
     for header files.  Directories named by `-I' are searched before
     the standard system include directories.

     It is dangerous to specify a standard system include directory in
     an `-I' option.  This defeats the special treatment of system
     headers .  It can also defeat the repairs to buggy system headers
     which GCC makes when it is installed.

`-o FILE'
     Write output to FILE.  This is the same as specifying FILE as the
     second non-option argument to `cpp'.  `gcc' has a different
     interpretation of a second non-option argument, so you must use
     `-o' to specify the output file.

`-Wall'
     Turns on all optional warnings which are desirable for normal
     code.  At present this is `-Wcomment' and `-Wtrigraphs'.  Note that
     many of the preprocessor's warnings are on by default and have no
     options to control them.

`-Wcomment'
`-Wcomments'
     Warn whenever a comment-start sequence `/*' appears in a `/*'
     comment, or whenever a backslash-newline appears in a `//' comment.
     (Both forms have the same effect.)

`-Wtrigraphs'
     Warn if any trigraphs are encountered.  This option used to take
     effect only if `-trigraphs' was also specified, but now works
     independently.  Warnings are not given for trigraphs within
     comments, as they do not affect the meaning of the program.

`-Wtraditional'
     Warn about certain constructs that behave differently in
     traditional and ISO C.  Also warn about ISO C constructs that have
     no traditional C equivalent, and problematic constructs which
     should be avoided.

`-Wimport'
     Warn the first time `#import' is used.

`-Wundef'
     Warn whenever an identifier which is not a macro is encountered in
     an `#if' directive, outside of `defined'.  Such identifiers are
     replaced with zero.

`-Werror'
     Make all warnings into hard errors.  Source code which triggers
     warnings will be rejected.

`-Wsystem-headers'
     Issue warnings for code in system headers.  These are normally
     unhelpful in finding bugs in your own code, therefore suppressed.
     If you are responsible for the system library, you may want to see
     them.

`-w'
     Suppress all warnings, including those which GNU CPP issues by
     default.

`-pedantic'
     Issue all the mandatory diagnostics listed in the C standard.
     Some of them are left out by default, since they trigger
     frequently on harmless code.

`-pedantic-errors'
     Issue all the mandatory diagnostics, and make all mandatory
     diagnostics into errors.  This includes mandatory diagnostics that
     GCC issues without `-pedantic' but treats as warnings.

`-M'
     Instead of outputting the result of preprocessing, output a rule
     suitable for `make' describing the dependencies of the main source
     file.  The preprocessor outputs one `make' rule containing the
     object file name for that source file, a colon, and the names of
     all the included files, including those coming from `-include' or
     `-imacros' command line options.

     Unless specified explicitly (with `-MT' or `-MQ'), the object file
     name consists of the basename of the source file with any suffix
     replaced with object file suffix.  If there are many included
     files then the rule is split into several lines using `\'-newline.
     The rule has no commands.

     This option does not suppress the preprocessor's debug output,
     such as `-dM'.  To avoid mixing such debug output with the
     dependency rules you should explicitly specify the dependency
     output file with `-MF', or use an environment variable like
     `DEPENDENCIES_OUTPUT' (*note DEPENDENCIES_OUTPUT::).  Debug output
     will still be sent to the regular output stream as normal.

     Passing `-M' to the driver implies `-E'.

`-MM'
     Like `-M' but do not mention header files that are found in system
     header directories, nor header files that are included, directly
     or indirectly, from such a header.

     This implies that the choice of angle brackets or double quotes in
     an `#include' directive does not in itself determine whether that
     header will appear in `-MM' dependency output.  This is a slight
     change in semantics from GCC versions 3.0 and earlier.

`-MF FILE'
     When used with `-M' or `-MM', specifies a file to write the
     dependencies to.  If no `-MF' switch is given the preprocessor
     sends the rules to the same place it would have sent preprocessed
     output.

     When used with the driver options `-MD' or `-MMD', `-MF' overrides
     the default dependency output file.

`-MG'
     When used with `-M' or `-MM', `-MG' says to treat missing header
     files as generated files and assume they live in the same
     directory as the source file.  It suppresses preprocessed output,
     as a missing header file is ordinarily an error.

     This feature is used in automatic updating of makefiles.

`-MP'
     This option instructs CPP to add a phony target for each dependency
     other than the main file, causing each to depend on nothing.  These
     dummy rules work around errors `make' gives if you remove header
     files without updating the `Makefile' to match.

     This is typical output:

          test.o: test.c test.h

          test.h:

`-MT TARGET'
     Change the target of the rule emitted by dependency generation.  By
     default CPP takes the name of the main input file, including any
     path, deletes any file suffix such as `.c', and appends the
     platform's usual object suffix.  The result is the target.

     An `-MT' option will set the target to be exactly the string you
     specify.  If you want multiple targets, you can specify them as a
     single argument to `-MT', or use multiple `-MT' options.

     For example, `-MT '$(objpfx)foo.o'' might give

          $(objpfx)foo.o: foo.c

`-MQ TARGET'
     Same as `-MT', but it quotes any characters which are special to
     Make.  `-MQ '$(objpfx)foo.o'' gives

          $$(objpfx)foo.o: foo.c

     The default target is automatically quoted, as if it were given
     with `-MQ'.

`-MD'
     `-MD' is equivalent to `-M -MF FILE', except that `-E' is not
     implied.  The driver determines FILE based on whether an `-o'
     option is given.  If it is, the driver uses its argument but with
     a suffix of `.d', otherwise it take the basename of the input file
     and applies a `.d' suffix.

     If `-MD' is used in conjunction with `-E', any `-o' switch is
     understood to specify the dependency output file (but *note
     -MF::), but if used without `-E', each `-o' is understood to
     specify a target object file.

     Since `-E' is not implied, `-MD' can be used to generate a
     dependency output file as a side-effect of the compilation process.

`-MMD'
     Like `-MD' except mention only user header files, not system
     -header files.

`-x c'
`-x c++'
`-x objective-c'
`-x assembler-with-cpp'
     Specify the source language: C, C++, Objective-C, or assembly.
     This has nothing to do with standards conformance or extensions;
     it merely selects which base syntax to expect.  If you give none
     of these options, cpp will deduce the language from the extension
     of the source file: `.c', `.cc', `.m', or `.S'.  Some other common
     extensions for C++ and assembly are also recognized.  If cpp does
     not recognize the extension, it will treat the file as C; this is
     the most generic mode.

     *Note_* Previous versions of cpp accepted a `-lang' option which
     selected both the language and the standards conformance level.
     This option has been removed, because it conflicts with the `-l'
     option.

`-std=STANDARD'
`-ansi'
     Specify the standard to which the code should conform.  Currently
     cpp only knows about the standards for C; other language standards
     will be added in the future.

     STANDARD may be one of:
    `iso9899:1990'
    `c89'
          The ISO C standard from 1990.  `c89' is the customary
          shorthand for this version of the standard.

          The `-ansi' option is equivalent to `-std=c89'.

    `iso9899:199409'
          The 1990 C standard, as amended in 1994.

    `iso9899:1999'
    `c99'
    `iso9899:199x'
    `c9x'
          The revised ISO C standard, published in December 1999.
          Before publication, this was known as C9X.

    `gnu89'
          The 1990 C standard plus GNU extensions.  This is the default.

    `gnu99'
    `gnu9x'
          The 1999 C standard plus GNU extensions.

`-I-'
     Split the include path.  Any directories specified with `-I'
     options before `-I-' are searched only for headers requested with
     `#include "FILE"'; they are not searched for `#include <FILE>'.
     If additional directories are specified with `-I' options after
     the `-I-', those directories are searched for all `#include'
     directives.

     In addition, `-I-' inhibits the use of the directory of the current
     file directory as the first search directory for `#include "FILE"'.

`-nostdinc'
     Do not search the standard system directories for header files.
     Only the directories you have specified with `-I' options (and the
     directory of the current file, if appropriate) are searched.

`-nostdinc++'
     Do not search for header files in the C++-specific standard
     directories, but do still search the other standard directories.
     (This option is used when building the C++ library.)

`-include FILE'
     Process FILE as if `#include "file"' appeared as the first line of
     the primary source file.  However, the first directory searched
     for FILE is the preprocessor's working directory _instead of_ the
     directory containing the main source file.  If not found there, it
     is searched for in the remainder of the `#include "..."' search
     chain as normal.

     If multiple `-include' options are given, the files are included
     in the order they appear on the command line.

`-imacros FILE'
     Exactly like `-include', except that any output produced by
     scanning FILE is thrown away.  Macros it defines remain defined.
     This allows you to acquire all the macros from a header without
     also processing its declarations.

     All files specified by `-imacros' are processed before all files
     specified by `-include'.

`-idirafter DIR'
     Search DIR for header files, but do it _after_ all directories
     specified with `-I' and the standard system directories have been
     exhausted.  DIR is treated as a system include directory.

`-iprefix PREFIX'
     Specify PREFIX as the prefix for subsequent `-iwithprefix'
     options.  If the prefix represents a directory, you should include
     the final `/'.

`-iwithprefix DIR'
`-iwithprefixbefore DIR'
     Append DIR to the prefix specified previously with `-iprefix', and
     add the resulting directory to the include search path.
     `-iwithprefixbefore' puts it in the same place `-I' would;
     `-iwithprefix' puts it where `-idirafter' would.

     Use of these options is discouraged.

`-isystem DIR'
     Search DIR for header files, after all directories specified by
     `-I' but before the standard system directories.  Mark it as a
     system directory, so that it gets the same special treatment as is
     applied to the standard system directories.

`-fpreprocessed'
     Indicate to the preprocessor that the input file has already been
     preprocessed.  This suppresses things like macro expansion,
     trigraph conversion, escaped newline splicing, and processing of
     most directives.  The preprocessor still recognizes and removes
     comments, so that you can pass a file preprocessed with `-C' to
     the compiler without problems.  In this mode the integrated
     preprocessor is little more than a tokenizer for the front ends.

     `-fpreprocessed' is implicit if the input file has one of the
     extensions `.i', `.ii' or `.mi'.  These are the extensions that
     GCC uses for preprocessed files created by `-save-temps'.

`-ftabstop=WIDTH'
     Set the distance between tab stops.  This helps the preprocessor
     report correct column numbers in warnings or errors, even if tabs
     appear on the line.  If the value is less than 1 or greater than
     100, the option is ignored.  The default is 8.

`-fno-show-column'
     Do not print column numbers in diagnostics.  This may be necessary
     if diagnostics are being scanned by a program that does not
     understand the column numbers, such as `dejagnu'.

`-A PREDICATE=ANSWER'
     Make an assertion with the predicate PREDICATE and answer ANSWER.
     This form is preferred to the older form `-A PREDICATE(ANSWER)',
     which is still supported, because it does not use shell special
     characters.

`-A -PREDICATE=ANSWER'
     Cancel an assertion with the predicate PREDICATE and answer ANSWER.

`-A-'
     Cancel all predefined assertions and all assertions preceding it on
     the command line.  Also, undefine all predefined macros and all
     macros preceding it on the command line.  (This is a historical
     wart and may change in the future.)

`-dCHARS'
     CHARS is a sequence of one or more of the following characters,
     and must not be preceded by a space.  Other characters are
     interpreted by the compiler proper, or reserved for future
     versions of GCC, and so are silently ignored.  If you specify
     characters whose behavior conflicts, the result is undefined.

    `M'
          Instead of the normal output, generate a list of `#define'
          directives for all the macros defined during the execution of
          the preprocessor, including predefined macros.  This gives
          you a way of finding out what is predefined in your version
          of the preprocessor.  Assuming you have no file `foo.h', the
          command

               touch foo.h; cpp -dM foo.h

          will show all the predefined macros.

    `D'
          Like `M' except in two respects: it does _not_ include the
          predefined macros, and it outputs _both_ the `#define'
          directives and the result of preprocessing.  Both kinds of
          output go to the standard output file.

    `N'
          Like `D', but emit only the macro names, not their expansions.

    `I'
          Output `#include' directives in addition to the result of
          preprocessing.

`-P'
     Inhibit generation of linemarkers in the output from the
     preprocessor.  This might be useful when running the preprocessor
     on something that is not C code, and will be sent to a program
     which might be confused by the linemarkers.

`-C'
     Do not discard comments.  All comments are passed through to the
     output file, except for comments in processed directives, which
     are deleted along with the directive.

     You should be prepared for side effects when using `-C'; it causes
     the preprocessor to treat comments as tokens in their own right.
     For example, comments appearing at the start of what would be a
     directive line have the effect of turning that line into an
     ordinary source line, since the first token on the line is no
     longer a `#'.

`-gcc'
     Define the macros __GNUC__, __GNUC_MINOR__ and
     __GNUC_PATCHLEVEL__.  These are defined automatically when you use
     `gcc -E'; you can turn them off in that case with `-no-gcc'.

`-traditional'
     Try to imitate the behavior of old-fashioned C, as opposed to ISO
     C.

`-trigraphs'
     Process trigraph sequences.  These are three-character sequences,
     all starting with `??', that are defined by ISO C to stand for
     single characters.  For example, `??/' stands for `\', so `'??/n''
     is a character constant for a newline.  By default, GCC ignores
     trigraphs, but in standard-conforming modes it converts them.  See
     the `-std' and `-ansi' options.

     The nine trigraphs and their replacements are

          Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
          Replacement:      [    ]    {    }    #    \    ^    |    ~

`-remap'
     Enable special code to work around file systems which only permit
     very short file names, such as MS-DOS.

`-$'
     Forbid the use of `$' in identifiers.  The C standard allows
     implementations to define extra characters that can appear in
     identifiers.  By default GNU CPP permits `$', a common extension.

`-h'
`--help'
`--target-help'
     Print text describing all the command line options instead of
     preprocessing anything.

`-v'
     Verbose mode.  Print out GNU CPP's version number at the beginning
     of execution, and report the final form of the include path.

`-H'
     Print the name of each header file used, in addition to other
     normal activities.  Each name is indented to show how deep in the
     `#include' stack it is.

`-version'
`--version'
     Print out GNU CPP's version number.  With one dash, proceed to
     preprocess as normal.  With two dashes, exit immediately.


File: gcc.info,  Node: Assembler Options,  Next: Link Options,  Prev: Preprocessor Options,  Up: Invoking GCC

3.12 Passing Options to the Assembler
=====================================

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.


File: gcc.info,  Node: Link Options,  Next: Directory Options,  Prev: Assembler Options,  Up: Invoking GCC

3.13 Options for Linking
========================

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.  *Note Overall
     Options::.

`-lLIBRARY'
`-l LIBRARY'
     Search the library named LIBRARY when linking.  (The second
     alternative with the library as a separate argument is only for
     POSIX compliance and is not recommended.)

     It makes a difference where in the command you write this option;
     the linker searches and 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.
     The compiler may generate calls to memcmp, memset, and memcpy for
     System V (and ISO C) environments or to bcopy and bzero for BSD
     environments.  These entries are usually resolved by entries in
     libc.  These entry points should be supplied through some other
     mechanism when this option is specified.

`-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.  The compiler may generate calls to
     memcmp, memset, and memcpy for System V (and ISO C) environments
     or to bcopy and bzero for BSD environments.  These entries are
     usually resolved by entries in libc.  These entry points should be
     supplied through some other mechanism when this option is
     specified.

     One of the standard libraries bypassed by `-nostdlib' and
     `-nodefaultlibs' is `libgcc.a', a library of internal subroutines
     that GCC uses to overcome shortcomings of particular machines, or
     special needs for some languages.  (*Note Interfacing to GCC
     Output: (gccint)Interface, 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 GCC
     library subroutines.  (For example, `__main', used to ensure C++
     constructors will be called; *note `collect2': (gccint)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.  Not all systems support this
     option.  For predictable results, you must also specify the same
     set of options that were used to generate code (`-fpic', `-fPIC',
     or model suboptions) when you specify this option.(1)

`-shared-libgcc'
`-static-libgcc'
     On systems that provide `libgcc' as a shared library, these options
     force the use of either the shared or static version respectively.
     If no shared version of `libgcc' was built when the compiler was
     configured, these options have no effect.

     There are several situations in which an application should use the
     shared `libgcc' instead of the static version.  The most common of
     these is when the application wishes to throw and catch exceptions
     across different shared libraries.  In that case, each of the
     libraries as well as the application itself should use the shared
     `libgcc'.

     Therefore, the G++ and GCJ drivers automatically add
     `-shared-libgcc' whenever you build a shared library or a main
     executable, because C++ and Java programs typically use
     exceptions, so this is the right thing to do.

     If, instead, you use the GCC driver to create shared libraries,
     you may find that they will not always be linked with the shared
     `libgcc'.  If GCC finds, at its configuration time, that you have
     a GNU linker that does not support option `--eh-frame-hdr', it
     will link the shared version of `libgcc' into shared libraries by
     default.  Otherwise, it will take advantage of the linker and
     optimize away the linking with the shared version of `libgcc',
     linking with the static version of libgcc by default.  This allows
     exceptions to propagate through such shared libraries, without
     incurring relocation costs at library load time.

     However, if a library or main executable is supposed to throw or
     catch exceptions, you must link it using the G++ or GCJ driver, as
     appropriate for the languages used in the program, or using the
     option `-shared-libgcc', such that it is linked with the shared
     `libgcc'.

`-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 GCC 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.

   ---------- Footnotes ----------

   (1) On some systems, `gcc -shared' needs to build supplementary stub
code for constructors to work.  On multi-libbed systems, `gcc -shared'
must select the correct support libraries to link against.  Failing to
supply the correct flags may lead to subtle defects.  Supplying them in
cases where they are not necessary is innocuous.


File: gcc.info,  Node: Directory Options,  Next: Spec Files,  Prev: Link Options,  Up: Invoking GCC

3.14 Options for Directory Search
=================================

These options specify directories to search for header files, for
libraries and for parts of the compiler:

`-IDIR'
     Add the directory DIR 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.  However, you should not use this option to add
     directories that contain vendor-supplied system header files (use
     `-isystem' for that).  If you use more than one `-I' option, the
     directories are scanned in left-to-right order; the standard
     system directories come after.

     If a standard system include directory, or a directory specified
     with `-isystem', is also specified with `-I', the `-I' option will
     be ignored.  The directory will still be searched but as a system
     directory at its normal position in the system include chain.
     This is to ensure that GCC's procedure to fix buggy system headers
     and the ordering for the include_next directive are not
     inadvertantly changed.  If you really need to change the search
     order for system directories, use the `-nostdinc' and/or
     `-isystem' options.

`-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/'
     (*note Target Options::).

     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.

     The compiler will check to see if the path provided by the `-B'
     refers to a directory, and if necessary it will add a directory
     separator character at the end of the path.

     `-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'.  *Note Environment
     Variables::.

     As a special kludge, if the path provided by `-B' is
     `[dir/]stageN/', where N is a number in the range 0 to 9, then it
     will be replaced by `[dir/]include'.  This is to help with
     boot-strapping the compiler.

`-specs=FILE'
     Process FILE after the compiler reads in the standard `specs'
     file, in order to override the defaults that the `gcc' driver
     program uses when determining what switches to pass to `cc1',
     `cc1plus', `as', `ld', etc.  More than one `-specs=FILE' can be
     specified on the command line, and they are processed in order,
     from left to right.


File: gcc.info,  Node: Spec Files,  Next: Target Options,  Prev: Directory Options,  Up: Invoking GCC

3.15 Specifying subprocesses and the switches to pass to them
=============================================================

`gcc' is a driver program.  It performs its job by invoking a sequence
of other programs to do the work of compiling, assembling and linking.
GCC interprets its command-line parameters and uses these to deduce
which programs it should invoke, and which command-line options it
ought to place on their command lines.  This behavior is controlled by
"spec strings".  In most cases there is one spec string for each
program that GCC can invoke, but a few programs have multiple spec
strings to control their behavior.  The spec strings built into GCC can
be overridden by using the `-specs=' command-line switch to specify a
spec file.

   "Spec files" are plaintext files that are used to construct spec
strings.  They consist of a sequence of directives separated by blank
lines.  The type of directive is determined by the first non-whitespace
character on the line and it can be one of the following:

`%COMMAND'
     Issues a COMMAND to the spec file processor.  The commands that can
     appear here are:

    `%include <FILE>'
          Search for FILE and insert its text at the current point in
          the specs file.

    `%include_noerr <FILE>'
          Just like `%include', but do not generate an error message if
          the include file cannot be found.

    `%rename OLD_NAME NEW_NAME'
          Rename the spec string OLD_NAME to NEW_NAME.


`*[SPEC_NAME]:'
     This tells the compiler to create, override or delete the named
     spec string.  All lines after this directive up to the next
     directive or blank line are considered to be the text for the spec
     string.  If this results in an empty string then the spec will be
     deleted.  (Or, if the spec did not exist, then nothing will
     happened.)  Otherwise, if the spec does not currently exist a new
     spec will be created.  If the spec does exist then its contents
     will be overridden by the text of this directive, unless the first
     character of that text is the `+' character, in which case the
     text will be appended to the spec.

`[SUFFIX]:'
     Creates a new `[SUFFIX] spec' pair.  All lines after this directive
     and up to the next directive or blank line are considered to make
     up the spec string for the indicated suffix.  When the compiler
     encounters an input file with the named suffix, it will processes
     the spec string in order to work out how to compile that file.
     For example:

          .ZZ:
          z-compile -input %i

     This says that any input file whose name ends in `.ZZ' should be
     passed to the program `z-compile', which should be invoked with the
     command-line switch `-input' and with the result of performing the
     `%i' substitution.  (See below.)

     As an alternative to providing a spec string, the text that
     follows a suffix directive can be one of the following:

    `@LANGUAGE'
          This says that the suffix is an alias for a known LANGUAGE.
          This is similar to using the `-x' command-line switch to GCC
          to specify a language explicitly.  For example:

               .ZZ:
               @c++

          Says that .ZZ files are, in fact, C++ source files.

    `#NAME'
          This causes an error messages saying:

               NAME compiler not installed on this system.

     GCC already has an extensive list of suffixes built into it.  This
     directive will add an entry to the end of the list of suffixes, but
     since the list is searched from the end backwards, it is
     effectively possible to override earlier entries using this
     technique.


   GCC has the following spec strings built into it.  Spec files can
override these strings or create their own.  Note that individual
targets can also add their own spec strings to this list.

     asm          Options to pass to the assembler
     asm_final    Options to pass to the assembler post-processor
     cpp          Options to pass to the C preprocessor
     cc1          Options to pass to the C compiler
     cc1plus      Options to pass to the C++ compiler
     endfile      Object files to include at the end of the link
     link         Options to pass to the linker
     lib          Libraries to include on the command line to the linker
     libgcc       Decides which GCC support library to pass to the linker
     linker       Sets the name of the linker
     predefines   Defines to be passed to the C preprocessor
     signed_char  Defines to pass to CPP to say whether `char' is signed
                  by default
     startfile    Object files to include at the start of the link

   Here is a small example of a spec file:

     %rename lib                 old_lib

     *lib:
     --start-group -lgcc -lc -leval1 --end-group %(old_lib)

   This example renames the spec called `lib' to `old_lib' and then
overrides the previous definition of `lib' with a new one.  The new
definition adds in some extra command-line options before including the
text of the old definition.

   "Spec strings" are a list of command-line options to be passed to
their corresponding program.  In addition, the spec strings can contain
`%'-prefixed sequences to substitute variable text or to conditionally
insert text into the command line.  Using these constructs it is
possible to generate quite complex command lines.

   Here is a table of all defined `%'-sequences for spec strings.  Note
that spaces are not generated automatically around the results of
expanding these sequences.  Therefore you can concatenate them together
or combine them with constant text in a single argument.

`%%'
     Substitute one `%' into the program name or argument.

`%i'
     Substitute the name of the input file being processed.

`%b'
     Substitute the basename of the input file being processed.  This
     is the substring up to (and not including) the last period and not
     including the directory.

`%B'
     This is the same as `%b', but include the file suffix (text after
     the last period).

`%d'
     Marks the argument containing or following the `%d' as a temporary
     file name, so that that file will be deleted if GCC exits
     successfully.  Unlike `%g', this contributes no text to the
     argument.

`%gSUFFIX'
     Substitute a file name that has suffix SUFFIX and is chosen once
     per compilation, and mark the argument in the same way as `%d'.
     To reduce exposure to denial-of-service attacks, the file name is
     now chosen in a way that is hard to predict even when previously
     chosen file names are known.  For example, `%g.s ... %g.o ... %g.s'
     might turn into `ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s'.  SUFFIX
     matches the regexp `[.A-Za-z]*' or the special string `%O', which
     is treated exactly as if `%O' had been preprocessed.  Previously,
     `%g' was simply substituted with a file name chosen once per
     compilation, without regard to any appended suffix (which was
     therefore treated just like ordinary text), making such attacks
     more likely to succeed.

`%uSUFFIX'
     Like `%g', but generates a new temporary file name even if
     `%uSUFFIX' was already seen.

`%USUFFIX'
     Substitutes the last file name generated with `%uSUFFIX',
     generating a new one if there is no such last file name.  In the
     absence of any `%uSUFFIX', this is just like `%gSUFFIX', except
     they don't share the same suffix _space_, so `%g.s ... %U.s ...
     %g.s ... %U.s' would involve the generation of two distinct file
     names, one for each `%g.s' and another for each `%U.s'.
     Previously, `%U' was simply substituted with a file name chosen
     for the previous `%u', without regard to any appended suffix.

`%jSUFFIX'
     Substitutes the name of the `HOST_BIT_BUCKET', if any, and if it is
     writable, and if save-temps is off; otherwise, substitute the name
     of a temporary file, just like `%u'.  This temporary file is not
     meant for communication between processes, but rather as a junk
     disposal mechanism.

`%.SUFFIX'
     Substitutes .SUFFIX for the suffixes of a matched switch's args
     when it is subsequently output with `%*'.  SUFFIX is terminated by
     the next space or %.

`%w'
     Marks the argument containing or following the `%w' as the
     designated output file of this compilation.  This puts the argument
     into the sequence of arguments that `%o' will substitute later.

`%o'
     Substitutes the names of all the output files, with spaces
     automatically placed around them.  You should write spaces around
     the `%o' as well or the results are undefined.  `%o' is for use in
     the specs for running the linker.  Input files whose names have no
     recognized suffix are not compiled at all, but they are included
     among the output files, so they will be linked.

`%O'
     Substitutes the suffix for object files.  Note that this is
     handled specially when it immediately follows `%g, %u, or %U',
     because of the need for those to form complete file names.  The
     handling is such that `%O' is treated exactly as if it had already
     been substituted, except that `%g, %u, and %U' do not currently
     support additional SUFFIX characters following `%O' as they would
     following, for example, `.o'.

`%p'
     Substitutes the standard macro predefinitions for the current
     target machine.  Use this when running `cpp'.

`%P'
     Like `%p', but puts `__' before and after the name of each
     predefined macro, except for macros that start with `__' or with
     `_L', where L is an uppercase letter.  This is for ISO C.

`%I'
     Substitute a `-iprefix' option made from `GCC_EXEC_PREFIX'.

`%s'
     Current argument is the name of a library or startup file of some
     sort.  Search for that file in a standard list of directories and
     substitute the full name found.

`%eSTR'
     Print STR as an error message.  STR is terminated by a newline.
     Use this when inconsistent options are detected.

`%|'
     Output `-' if the input for the current command is coming from a
     pipe.

`%(NAME)'
     Substitute the contents of spec string NAME at this point.

`%[NAME]'
     Like `%(...)' but put `__' around `-D' arguments.

`%x{OPTION}'
     Accumulate an option for `%X'.

`%X'
     Output the accumulated linker options specified by `-Wl' or a `%x'
     spec string.

`%Y'
     Output the accumulated assembler options specified by `-Wa'.

`%Z'
     Output the accumulated preprocessor options specified by `-Wp'.

`%v1'
     Substitute the major version number of GCC.  (For version 2.9.5,
     this is 2.)

`%v2'
     Substitute the minor version number of GCC.  (For version 2.9.5,
     this is 9.)

`%v3'
     Substitute the patch level number of GCC.  (For version 2.9.5,
     this is 5.)

`%a'
     Process the `asm' spec.  This is used to compute the switches to
     be passed to the assembler.

`%A'
     Process the `asm_final' spec.  This is a spec string for passing
     switches to an assembler post-processor, if such a program is
     needed.

`%l'
     Process the `link' spec.  This is the spec for computing the
     command line passed to the linker.  Typically it will make use of
     the `%L %G %S %D and %E' sequences.

`%D'
     Dump out a `-L' option for each directory that GCC believes might
     contain startup files.  If the target supports multilibs then the
     current multilib directory will be prepended to each of these
     paths.

`%M'
     Output the multilib directory with directory separators replaced
     with `_'.  If multilib directories are not set, or the multilib
     directory is `.' then this option emits nothing.

`%L'
     Process the `lib' spec.  This is a spec string for deciding which
     libraries should be included on the command line to the linker.

`%G'
     Process the `libgcc' spec.  This is a spec string for deciding
     which GCC support library should be included on the command line
     to the linker.

`%S'
     Process the `startfile' spec.  This is a spec for deciding which
     object files should be the first ones passed to the linker.
     Typically this might be a file named `crt0.o'.

`%E'
     Process the `endfile' spec.  This is a spec string that specifies
     the last object files that will be passed to the linker.

`%C'
     Process the `cpp' spec.  This is used to construct the arguments
     to be passed to the C preprocessor.

`%c'
     Process the `signed_char' spec.  This is intended to be used to
     tell cpp whether a char is signed.  It typically has the
     definition:
          %{funsigned-char:-D__CHAR_UNSIGNED__}

`%1'
     Process the `cc1' spec.  This is used to construct the options to
     be passed to the actual C compiler (`cc1').

`%2'
     Process the `cc1plus' spec.  This is used to construct the options
     to be passed to the actual C++ compiler (`cc1plus').

`%*'
     Substitute the variable part of a matched option.  See below.
     Note that each comma in the substituted string is replaced by a
     single space.

`%{`S'}'
     Substitutes the `-S' switch, if that switch was given to GCC.  If
     that switch was not specified, this substitutes nothing.  Note that
     the leading dash is omitted when specifying this option, and it is
     automatically inserted if the substitution is performed.  Thus the
     spec string `%{foo}' would match the command-line option `-foo'
     and would output the command line option `-foo'.

`%W{`S'}'
     Like %{`S'} but mark last argument supplied within as a file to be
     deleted on failure.

`%{`S'*}'
     Substitutes all the switches specified to GCC whose names start
     with `-S', but which also take an argument.  This is used for
     switches like `-o', `-D', `-I', etc.  GCC considers `-o foo' as
     being one switch whose names starts with `o'.  %{o*} would
     substitute this text, including the space.  Thus two arguments
     would be generated.

`%{^`S'*}'
     Like %{`S'*}, but don't put a blank between a switch and its
     argument.  Thus %{^o*} would only generate one argument, not two.

`%{`S'*&`T'*}'
     Like %{`S'*}, but preserve order of `S' and `T' options (the order
     of `S' and `T' in the spec is not significant).  There can be any
     number of ampersand-separated variables; for each the wild card is
     optional.  Useful for CPP as `%{D*&U*&A*}'.

`%{<`S'}'
     Remove all occurrences of `-S' from the command line.  Note--this
     command is position dependent.  `%' commands in the spec string
     before this option will see `-S', `%' commands in the spec string
     after this option will not.

`%{`S'*:`X'}'
     Substitutes `X' if one or more switches whose names start with
     `-S' are specified to GCC.  Note that the tail part of the `-S'
     option (i.e. the part matched by the `*') will be substituted for
     each occurrence of `%*' within `X'.

`%{`S':`X'}'
     Substitutes `X', but only if the `-S' switch was given to GCC.

`%{!`S':`X'}'
     Substitutes `X', but only if the `-S' switch was _not_ given to
     GCC.

`%{|`S':`X'}'
     Like %{`S':`X'}, but if no `S' switch, substitute `-'.

`%{|!`S':`X'}'
     Like %{!`S':`X'}, but if there is an `S' switch, substitute `-'.

`%{.`S':`X'}'
     Substitutes `X', but only if processing a file with suffix `S'.

`%{!.`S':`X'}'
     Substitutes `X', but only if _not_ processing a file with suffix
     `S'.

`%{`S'|`P':`X'}'
     Substitutes `X' if either `-S' or `-P' was given to GCC.  This may
     be combined with `!' and `.' sequences as well, although they have
     a stronger binding than the `|'.  For example a spec string like
     this:

          %{.c:-foo} %{!.c:-bar} %{.c|d:-baz} %{!.c|d:-boggle}

     will output the following command-line options from the following
     input command-line options:

          fred.c        -foo -baz
          jim.d         -bar -boggle
          -d fred.c     -foo -baz -boggle
          -d jim.d      -bar -baz -boggle


   The conditional text `X' in a %{`S':`X'} or %{!`S':`X'} construct
may contain other nested `%' constructs or spaces, or even newlines.
They are processed as usual, as described above.

   The `-O', `-f', `-m', and `-W' switches are handled specifically in
these constructs.  If another value of `-O' or the negated form of a
`-f', `-m', or `-W' switch is found later in the command line, the
earlier switch value is ignored, except with {`S'*} where `S' is just
one letter, which passes all matching options.

   The character `|' at the beginning of the predicate text is used to
indicate that a command should be piped to the following command, but
only if `-pipe' is specified.

   It is built into GCC which switches take arguments and which do not.
(You might think it would be useful to generalize this to allow each
compiler's spec to say which switches take arguments.  But this cannot
be done in a consistent fashion.  GCC cannot even decide which input
files have been specified without knowing which switches take arguments,
and it must know which input files to compile in order to tell which
compilers to run).

   GCC also knows implicitly that arguments starting in `-l' are to be
treated as compiler output files, and passed to the linker in their
proper position among the other output files.


File: gcc.info,  Node: Target Options,  Next: Submodel Options,  Prev: Spec Files,  Up: Invoking GCC

3.16 Specifying Target Machine and Compiler Version
===================================================

By default, GCC 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 GCC, 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 GCC 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 GCC as a cross-compiler.

     The value to use for MACHINE is the same as was specified as the
     machine type when configuring GCC 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 GCC to run.  This
     is useful when multiple versions are installed.  For example,
     VERSION might be `2.0', meaning to run GCC version 2.0.

     The default version, when you do not specify `-V', is the last
     version of GCC 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 GCC, 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.  It is common for the interface to the other
executables to change incompatibly between compiler versions, so unless
the version specified is very close to that of the driver (for example,
`-V 3.0' with a driver program from GCC version 3.0.1), use of `-V' may
not work; for example, using `-V 2.95.2' will not work with a driver
program from GCC 3.0.

   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 sufficiently similar compiler
versions.

   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.


File: gcc.info,  Node: Submodel Options,  Next: Code Gen Options,  Prev: Target Options,  Up: Invoking GCC

3.17 Hardware Models and Configurations
=======================================

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.

* Menu:

* M680x0 Options::
* M68hc1x Options::
* VAX Options::
* SPARC Options::
* Convex Options::
* AMD29K Options::
* ARM Options::
* MN10200 Options::
* MN10300 Options::
* M32R/D Options::
* M88K Options::
* RS/6000 and PowerPC Options::
* RT Options::
* MIPS Options::
* i386 and x86-64 Options::
* HPPA Options::
* Intel 960 Options::
* DEC Alpha Options::
* DEC Alpha/VMS Options::
* Clipper Options::
* H8/300 Options::
* SH Options::
* System V Options::
* TMS320C3x/C4x Options::
* V850 Options::
* ARC Options::
* NS32K Options::
* AVR Options::
* MCore Options::
* IA-64 Options::
* D30V Options::
* S/390 and zSeries Options::
* CRIS Options::
* MMIX Options::
* PDP-11 Options::
* Xstormy16 Options::
* Xtensa Options::


File: gcc.info,  Node: M680x0 Options,  Next: M68hc1x Options,  Up: Submodel Options

3.17.1 M680x0 Options
---------------------

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.

     Use this option for microcontrollers with a 68000 or EC000 core,
     including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.

`-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.  Use this option if your
     68040 does not have code to emulate those instructions.

`-m68060'
     Generate output for a 68060.  This is the default when the
     compiler is configured for 68060-based systems.

     This option inhibits the use of 68020 and 68881/68882 instructions
     that have to be emulated by software on the 68060.  Use this
     option if your 68060 does not have code to emulate those
     instructions.

`-mcpu32'
     Generate output for a CPU32.  This is the default when the
     compiler is configured for CPU32-based systems.

     Use this option for microcontrollers with a CPU32 or CPU32+ core,
     including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
     68341, 68349 and 68360.

`-m5200'
     Generate output for a 520X "coldfire" family cpu.  This is the
     default when the compiler is configured for 520X-based systems.

     Use this option for microcontroller with a 5200 core, including
     the MCF5202, MCF5203, MCF5204 and MCF5202.

`-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.

`-m68020-60'
     Generate output for a 68060, 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 68060.

`-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', `-mcpu32'
     and `-m5200' options imply `-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, 68020, 68030,
     68040, 68060 and CPU32 processors, but not by the 68000 or 5200.

`-malign-int'
`-mno-align-int'
     Control whether GCC aligns `int', `long', `long long', `float',
     `double', and `long double' variables on a 32-bit boundary
     (`-malign-int') or a 16-bit boundary (`-mno-align-int').  Aligning
     variables on 32-bit boundaries produces code that runs somewhat
     faster on processors with 32-bit busses at the expense of more
     memory.

     *Warning:* if you use the `-malign-int' switch, GCC will align
     structures containing the above types  differently than most
     published application binary interface specifications for the m68k.

`-mpcrel'
     Use the pc-relative addressing mode of the 68000 directly, instead
     of using a global offset table.  At present, this option implies
     `-fpic', allowing at most a 16-bit offset for pc-relative
     addressing.  `-fPIC' is not presently supported with `-mpcrel',
     though this could be supported for 68020 and higher processors.

`-mno-strict-align'
`-mstrict-align'
     Do not (do) assume that unaligned memory references will be
     handled by the system.



File: gcc.info,  Node: M68hc1x Options,  Next: VAX Options,  Prev: M680x0 Options,  Up: Submodel Options

3.17.2 M68hc1x Options
----------------------

These are the `-m' options defined for the 68hc11 and 68hc12
microcontrollers.  The default values for these options depends on
which style of microcontroller was selected when the compiler was
configured; the defaults for the most common choices are given below.

`-m6811'
`-m68hc11'
     Generate output for a 68HC11.  This is the default when the
     compiler is configured for 68HC11-based systems.

`-m6812'
`-m68hc12'
     Generate output for a 68HC12.  This is the default when the
     compiler is configured for 68HC12-based systems.

`-mauto-incdec'
     Enable the use of 68HC12 pre and post auto-increment and
     auto-decrement addressing modes.

`-mshort'
     Consider type `int' to be 16 bits wide, like `short int'.

`-msoft-reg-count=COUNT'
     Specify the number of pseudo-soft registers which are used for the
     code generation.  The maximum number is 32.  Using more pseudo-soft
     register may or may not result in better code depending on the
     program.  The default is 4 for 68HC11 and 2 for 68HC12.



File: gcc.info,  Node: VAX Options,  Next: SPARC Options,  Prev: M68hc1x Options,  Up: Submodel Options

3.17.3 VAX Options
------------------

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.


File: gcc.info,  Node: SPARC Options,  Next: Convex Options,  Prev: VAX Options,  Up: Submodel Options

3.17.4 SPARC Options
--------------------

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 GCC, 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-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.  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', GCC 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.

`-mno-faster-structs'
`-mfaster-structs'
     With `-mfaster-structs', the compiler assumes that structures
     should have 8 byte alignment.  This enables the use of pairs of
     `ldd' and `std' instructions for copies in structure assignment,
     in place of twice as many `ld' and `st' pairs.  However, the use
     of this changed alignment directly violates the Sparc ABI.  Thus,
     it's intended only for use on targets where the developer
     acknowledges that their resulting code will not be directly in
     line with the rules of the ABI.

`-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.

     These options are deprecated and will be deleted in a future GCC
     release.  They have been replaced with `-mcpu=xxx'.

`-mcypress'
`-msupersparc'
     These two options select the processor for which the code is
     optimized.

     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.

     These options are deprecated and will be deleted in a future GCC
     release.  They have been replaced with `-mcpu=xxx'.

`-mcpu=CPU_TYPE'
     Set the instruction set, register set, and instruction scheduling
     parameters for machine type CPU_TYPE.  Supported values for
     CPU_TYPE are `v7', `cypress', `v8', `supersparc', `sparclite',
     `hypersparc', `sparclite86x', `f930', `f934', `sparclet',
     `tsc701', `v9', and `ultrasparc'.

     Default instruction scheduling parameters are used for values that
     select an architecture and not an implementation.  These are `v7',
     `v8', `sparclite', `sparclet', `v9'.

     Here is a list of each supported architecture and their supported
     implementations.

              v7:             cypress
              v8:             supersparc, hypersparc
              sparclite:      f930, f934, sparclite86x
              sparclet:       tsc701
              v9:             ultrasparc

`-mtune=CPU_TYPE'
     Set the instruction scheduling parameters for machine type
     CPU_TYPE, but do not set the instruction set or register set that
     the option `-mcpu=CPU_TYPE' would.

     The same values for `-mcpu=CPU_TYPE' can be used for
     `-mtune=CPU_TYPE', but the only useful values are those that
     select a particular cpu implementation.  Those are `cypress',
     `supersparc', `hypersparc', `f930', `f934', `sparclite86x',
     `tsc701', and `ultrasparc'.


   These `-m' switches are supported in addition to the above on the
SPARCLET processor.

`-mlittle-endian'
     Generate code for a processor running in little-endian mode.

`-mlive-g0'
     Treat register `%g0' as a normal register.  GCC will continue to
     clobber it as necessary but will not assume it always reads as 0.

`-mbroken-saverestore'
     Generate code that does not use non-trivial forms of the `save' and
     `restore' instructions.  Early versions of the SPARCLET processor
     do not correctly handle `save' and `restore' instructions used with
     arguments.  They correctly handle them used without arguments.  A
     `save' instruction used without arguments increments the current
     window pointer but does not allocate a new stack frame.  It is
     assumed that the window overflow trap handler will properly handle
     this case as will interrupt handlers.

   These `-m' switches are supported in addition to the above on SPARC
V9 processors in 64-bit environments.

`-mlittle-endian'
     Generate code for a processor running in little-endian mode.

`-m32'
`-m64'
     Generate code for a 32-bit or 64-bit environment.  The 32-bit
     environment sets int, long and pointer to 32 bits.  The 64-bit
     environment sets int to 32 bits and long and pointer to 64 bits.

`-mcmodel=medlow'
     Generate code for the Medium/Low code model: the program must be
     linked in the low 32 bits of the address space.  Pointers are 64
     bits.  Programs can be statically or dynamically linked.

`-mcmodel=medmid'
     Generate code for the Medium/Middle code model: the program must
     be linked in the low 44 bits of the address space, the text
     segment must be less than 2G bytes, and data segment must be
     within 2G of the text segment.  Pointers are 64 bits.

`-mcmodel=medany'
     Generate code for the Medium/Anywhere code model: the program may
     be linked anywhere in the address space, the text segment must be
     less than 2G bytes, and data segment must be within 2G of the text
     segment.  Pointers are 64 bits.

`-mcmodel=embmedany'
     Generate code for the Medium/Anywhere code model for embedded
     systems: assume a 32-bit text and a 32-bit data segment, both
     starting anywhere (determined at link time).  Register %g4 points
     to the base of the data segment.  Pointers are still 64 bits.
     Programs are statically linked, PIC is not supported.

`-mstack-bias'
`-mno-stack-bias'
     With `-mstack-bias', GCC 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.


File: gcc.info,  Node: Convex Options,  Next: AMD29K Options,  Prev: SPARC Options,  Up: Submodel Options

3.17.5 Convex Options
---------------------

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.


File: gcc.info,  Node: AMD29K Options,  Next: ARM Options,  Prev: Convex Options,  Up: Submodel Options

3.17.6 AMD29K Options
---------------------

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.

`-mno-impure-text'
`-mimpure-text'
     `-mimpure-text', used in addition to `-shared', tells the compiler
     to not pass `-assert pure-text' to the linker when linking a
     shared object.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not part of GCC.  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.

`-mno-multm'
     Do not generate multm or multmu instructions.  This is useful for
     some embedded systems which do not have trap handlers for these
     instructions.


File: gcc.info,  Node: ARM Options,  Next: MN10200 Options,  Prev: AMD29K Options,  Up: Submodel Options

3.17.7 ARM Options
------------------

These `-m' options are defined for Advanced RISC Machines (ARM)
architectures:

`-mapcs-frame'
     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.  Specifying
     `-fomit-frame-pointer' with this option will cause the stack
     frames not to be generated for leaf functions.  The default is
     `-mno-apcs-frame'.

`-mapcs'
     This is a synonym for `-mapcs-frame'.

`-mapcs-26'
     Generate code for a processor running with a 26-bit program
     counter, and conforming to the function calling standards for the
     APCS 26-bit option.  This option replaces the `-m2' and `-m3'
     options of previous releases of the compiler.

`-mapcs-32'
     Generate code for a processor running with a 32-bit program
     counter, and conforming to the function calling standards for the
     APCS 32-bit option.  This option replaces the `-m6' option of
     previous releases of the compiler.

`-mthumb-interwork'
     Generate code which supports calling between the ARM and Thumb
     instruction sets.  Without this option the two instruction sets
     cannot be reliably used inside one program.  The default is
     `-mno-thumb-interwork', since slightly larger code is generated
     when `-mthumb-interwork' is specified.

`-mno-sched-prolog'
     Prevent the reordering of instructions in the function prolog, or
     the merging of those instruction with the instructions in the
     function's body.  This means that all functions will start with a
     recognizable set of instructions (or in fact one of a choice from
     a small set of different function prologues), and this information
     can be used to locate the start if functions inside an executable
     piece of code.  The default is `-msched-prolog'.

`-mhard-float'
     Generate output containing floating point instructions.  This is
     the default.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not available for all ARM
     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.

     `-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 GCC, with `-msoft-float' in order for this
     to work.

`-mlittle-endian'
     Generate code for a processor running in little-endian mode.  This
     is the default for all standard configurations.

`-mbig-endian'
     Generate code for a processor running in big-endian mode; the
     default is to compile code for a little-endian processor.

`-mwords-little-endian'
     This option only applies when generating code for big-endian
     processors.  Generate code for a little-endian word order but a
     big-endian byte order.  That is, a byte order of the form
     `32107654'.  Note: this option should only be used if you require
     compatibility with code for big-endian ARM processors generated by
     versions of the compiler prior to 2.8.

`-malignment-traps'
     Generate code that will not trap if the MMU has alignment traps
     enabled.  On ARM architectures prior to ARMv4, there were no
     instructions to access half-word objects stored in memory.
     However, when reading from memory a feature of the ARM
     architecture allows a word load to be used, even if the address is
     unaligned, and the processor core will rotate the data as it is
     being loaded.  This option tells the compiler that such misaligned
     accesses will cause a MMU trap and that it should instead
     synthesise the access as a series of byte accesses.  The compiler
     can still use word accesses to load half-word data if it knows
     that the address is aligned to a word boundary.

     This option is ignored when compiling for ARM architecture 4 or
     later, since these processors have instructions to directly access
     half-word objects in memory.

`-mno-alignment-traps'
     Generate code that assumes that the MMU will not trap unaligned
     accesses.  This produces better code when the target instruction
     set does not have half-word memory operations (i.e.
     implementations prior to ARMv4).

     Note that you cannot use this option to access unaligned word
     objects, since the processor will only fetch one 32-bit aligned
     object from memory.

     The default setting for most targets is `-mno-alignment-traps',
     since this produces better code when there are no half-word memory
     instructions available.

`-mshort-load-bytes'
`-mno-short-load-words'
     These are deprecated aliases for `-malignment-traps'.

`-mno-short-load-bytes'
`-mshort-load-words'
     This are deprecated aliases for `-mno-alignment-traps'.

`-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.

`-mcpu=NAME'
     This specifies the name of the target ARM processor.  GCC uses
     this name to determine what kind of instructions it can emit when
     generating assembly code.  Permissible names are: `arm2', `arm250',
     `arm3', `arm6', `arm60', `arm600', `arm610', `arm620', `arm7',
     `arm7m', `arm7d', `arm7dm', `arm7di', `arm7dmi', `arm70', `arm700',
     `arm700i', `arm710', `arm710c', `arm7100', `arm7500', `arm7500fe',
     `arm7tdmi', `arm8', `strongarm', `strongarm110', `strongarm1100',
     `arm8', `arm810', `arm9', `arm9e', `arm920', `arm920t', `arm940t',
     `arm9tdmi', `arm10tdmi', `arm1020t', `xscale'.

`-mtune=NAME'
     This option is very similar to the `-mcpu=' option, except that
     instead of specifying the actual target processor type, and hence
     restricting which instructions can be used, it specifies that GCC
     should tune the performance of the code as if the target were of
     the type specified in this option, but still choosing the
     instructions that it will generate based on the cpu specified by a
     `-mcpu=' option.  For some ARM implementations better performance
     can be obtained by using this option.

`-march=NAME'
     This specifies the name of the target ARM architecture.  GCC uses
     this name to determine what kind of instructions it can emit when
     generating assembly code.  This option can be used in conjunction
     with or instead of the `-mcpu=' option.  Permissible names are:
     `armv2', `armv2a', `armv3', `armv3m', `armv4', `armv4t', `armv5',
     `armv5t', `armv5te'.

`-mfpe=NUMBER'
`-mfp=NUMBER'
     This specifies the version of the floating point emulation
     available on the target.  Permissible values are 2 and 3.  `-mfp='
     is a synonym for `-mfpe=', for compatibility with older versions
     of GCC.

`-mstructure-size-boundary=N'
     The size of all structures and unions will be rounded up to a
     multiple of the number of bits set by this option.  Permissible
     values are 8 and 32.  The default value varies for different
     toolchains.  For the COFF targeted toolchain the default value is
     8.  Specifying the larger number can produce faster, more
     efficient code, but can also increase the size of the program.
     The two values are potentially incompatible.  Code compiled with
     one value cannot necessarily expect to work with code or libraries
     compiled with the other value, if they exchange information using
     structures or unions.

`-mabort-on-noreturn'
     Generate a call to the function `abort' at the end of a `noreturn'
     function.  It will be executed if the function tries to return.

`-mlong-calls'
`-mno-long-calls'
     Tells the compiler to perform function calls by first loading the
     address of the function into a register and then performing a
     subroutine call on this register.  This switch is needed if the
     target function will lie outside of the 64 megabyte addressing
     range of the offset based version of subroutine call instruction.

     Even if this switch is enabled, not all function calls will be
     turned into long calls.  The heuristic is that static functions,
     functions which have the `short-call' attribute, functions that
     are inside the scope of a `#pragma no_long_calls' directive and
     functions whose definitions have already been compiled within the
     current compilation unit, will not be turned into long calls.  The
     exception to this rule is that weak function definitions,
     functions with the `long-call' attribute or the `section'
     attribute, and functions that are within the scope of a `#pragma
     long_calls' directive, will always be turned into long calls.

     This feature is not enabled by default.  Specifying
     `-mno-long-calls' will restore the default behavior, as will
     placing the function calls within the scope of a `#pragma
     long_calls_off' directive.  Note these switches have no effect on
     how the compiler generates code to handle function calls via
     function pointers.

`-mnop-fun-dllimport'
     Disable support for the `dllimport' attribute.

`-msingle-pic-base'
     Treat the register used for PIC addressing as read-only, rather
     than loading it in the prologue for each function.  The run-time
     system is responsible for initializing this register with an
     appropriate value before execution begins.

`-mpic-register=REG'
     Specify the register to be used for PIC addressing.  The default
     is R10 unless stack-checking is enabled, when R9 is used.

`-mpoke-function-name'
     Write the name of each function into the text section, directly
     preceding the function prologue.  The generated code is similar to
     this:

               t0
                   .ascii "arm_poke_function_name", 0
                   .align
               t1
                   .word 0xff000000 + (t1 - t0)
               arm_poke_function_name
                   mov     ip, sp
                   stmfd   sp!, {fp, ip, lr, pc}
                   sub     fp, ip, #4

     When performing a stack backtrace, code can inspect the value of
     `pc' stored at `fp + 0'.  If the trace function then looks at
     location `pc - 12' and the top 8 bits are set, then we know that
     there is a function name embedded immediately preceding this
     location and has length `((pc[-3]) & 0xff000000)'.

`-mthumb'
     Generate code for the 16-bit Thumb instruction set.  The default
     is to use the 32-bit ARM instruction set.

`-mtpcs-frame'
     Generate a stack frame that is compliant with the Thumb Procedure
     Call Standard for all non-leaf functions.  (A leaf function is one
     that does not call any other functions.)  The default is
     `-mno-tpcs-frame'.

`-mtpcs-leaf-frame'
     Generate a stack frame that is compliant with the Thumb Procedure
     Call Standard for all leaf functions.  (A leaf function is one
     that does not call any other functions.)  The default is
     `-mno-apcs-leaf-frame'.

`-mcallee-super-interworking'
     Gives all externally visible functions in the file being compiled
     an ARM instruction set header which switches to Thumb mode before
     executing the rest of the function.  This allows these functions
     to be called from non-interworking code.

`-mcaller-super-interworking'
     Allows calls via function pointers (including virtual functions) to
     execute correctly regardless of whether the target code has been
     compiled for interworking or not.  There is a small overhead in
     the cost of executing a function pointer if this option is enabled.



File: gcc.info,  Node: MN10200 Options,  Next: MN10300 Options,  Prev: ARM Options,  Up: Submodel Options

3.17.8 MN10200 Options
----------------------

These `-m' options are defined for Matsushita MN10200 architectures:
`-mrelax'
     Indicate to the linker that it should perform a relaxation
     optimization pass to shorten branches, calls and absolute memory
     addresses.  This option only has an effect when used on the
     command line for the final link step.

     This option makes symbolic debugging impossible.


File: gcc.info,  Node: MN10300 Options,  Next: M32R/D Options,  Prev: MN10200 Options,  Up: Submodel Options

3.17.9 MN10300 Options
----------------------

These `-m' options are defined for Matsushita MN10300 architectures:

`-mmult-bug'
     Generate code to avoid bugs in the multiply instructions for the
     MN10300 processors.  This is the default.

`-mno-mult-bug'
     Do not generate code to avoid bugs in the multiply instructions
     for the MN10300 processors.

`-mam33'
     Generate code which uses features specific to the AM33 processor.

`-mno-am33'
     Do not generate code which uses features specific to the AM33
     processor.  This is the default.

`-mno-crt0'
     Do not link in the C run-time initialization object file.

`-mrelax'
     Indicate to the linker that it should perform a relaxation
     optimization pass to shorten branches, calls and absolute memory
     addresses.  This option only has an effect when used on the
     command line for the final link step.

     This option makes symbolic debugging impossible.


File: gcc.info,  Node: M32R/D Options,  Next: M88K Options,  Prev: MN10300 Options,  Up: Submodel Options

3.17.10 M32R/D Options
----------------------

These `-m' options are defined for Mitsubishi M32R/D architectures:

`-m32rx'
     Generate code for the M32R/X.

`-m32r'
     Generate code for the M32R.  This is the default.

`-mcode-model=small'
     Assume all objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the `ld24' instruction), and assume
     all subroutines are reachable with the `bl' instruction.  This is
     the default.

     The addressability of a particular object can be set with the
     `model' attribute.

`-mcode-model=medium'
     Assume objects may be anywhere in the 32-bit address space (the
     compiler will generate `seth/add3' instructions to load their
     addresses), and assume all subroutines are reachable with the `bl'
     instruction.

`-mcode-model=large'
     Assume objects may be anywhere in the 32-bit address space (the
     compiler will generate `seth/add3' instructions to load their
     addresses), and assume subroutines may not be reachable with the
     `bl' instruction (the compiler will generate the much slower
     `seth/add3/jl' instruction sequence).

`-msdata=none'
     Disable use of the small data area.  Variables will be put into
     one of `.data', `bss', or `.rodata' (unless the `section'
     attribute has been specified).  This is the default.

     The small data area consists of sections `.sdata' and `.sbss'.
     Objects may be explicitly put in the small data area with the
     `section' attribute using one of these sections.

`-msdata=sdata'
     Put small global and static data in the small data area, but do not
     generate special code to reference them.

`-msdata=use'
     Put small global and static data in the small data area, and
     generate special instructions to reference them.

`-G NUM'
     Put global and static objects less than or equal to NUM bytes into
     the small data or bss sections instead of the normal data or bss
     sections.  The default value of NUM is 8.  The `-msdata' option
     must be set to one of `sdata' or `use' for this option to have any
     effect.

     All modules should be compiled with the same `-G NUM' value.
     Compiling with different values of NUM may or may not work; if it
     doesn't the linker will give an error message--incorrect code will
     not be generated.



File: gcc.info,  Node: M88K Options,  Next: RS/6000 and PowerPC Options,  Prev: M32R/D Options,  Up: Submodel Options

3.17.11 M88K Options
--------------------

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'
     Save space by reorganizing the stack frame.  This option generates
     code that does not agree with the 88open specifications, but uses
     less memory.

`-mno-optimize-arg-area'
     Do not reorganize the stack frame to save space.  This is the
     default.  The generated conforms to the specification, but uses
     more memory.

`-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,
     GCC 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, GCC
     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:

       1. Which variant of the assembler syntax to emit.

       2. `-msvr4' makes the C preprocessor recognize `#pragma weak'
          that is used on System V release 4.

       3. `-msvr4' makes GCC 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, GCC
     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.

     GCC assumes that the MC88110 processor correctly detects all
     instances of integer division by zero.  When `-m88110' is
     specified, no explicit checks for zero-valued divisors are
     generated, and both `-mcheck-zero-division' and
     `-mno-check-zero-division' are ignored.

`-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, GCC 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 GCC 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, GCC issues no such warning.


File: gcc.info,  Node: RS/6000 and PowerPC Options,  Next: RT Options,  Prev: M88K Options,  Up: Submodel Options

3.17.12 IBM RS/6000 and PowerPC Options
---------------------------------------

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'
`-mpowerpc64'
`-mno-powerpc64'
     GCC 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 MPC5xx, MPC6xx, MPC8xx
     microprocessors, and the IBM 4xx microprocessors.

     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 GCC.  Specifying the
     `-mcpu=CPU_TYPE' overrides the specification of these options.  We
     recommend you use the `-mcpu=CPU_TYPE' option rather than the
     options listed above.

     The `-mpower' option allows GCC to generate instructions that are
     found only in the POWER architecture and to use the MQ register.
     Specifying `-mpower2' implies `-power' and also allows GCC to
     generate instructions that are present in the POWER2 architecture
     but not the original POWER architecture.

     The `-mpowerpc' option allows GCC to generate instructions that
     are found only in the 32-bit subset of the PowerPC architecture.
     Specifying `-mpowerpc-gpopt' implies `-mpowerpc' and also allows
     GCC 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
     GCC to use the optional PowerPC architecture instructions in the
     Graphics group, including floating-point select.

     The `-mpowerpc64' option allows GCC to generate the additional
     64-bit instructions that are found in the full PowerPC64
     architecture and to treat GPRs as 64-bit, doubleword quantities.
     GCC defaults to `-mno-powerpc64'.

     If you specify both `-mno-power' and `-mno-powerpc', GCC 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 GCC
     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.
     With `-mnew-mnemonics', GCC uses the assembler mnemonics defined
     for the PowerPC architecture.  With `-mold-mnemonics' it uses the
     assembler mnemonics defined for the POWER architecture.
     Instructions defined in only one architecture have only one
     mnemonic; GCC uses that mnemonic irrespective of which of these
     options is specified.

     GCC defaults to the mnemonics appropriate for the architecture in
     use.  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.
     Supported values for CPU_TYPE are `rios', `rios1', `rsc', `rios2',
     `rs64a', `601', `602', `603', `603e', `604', `604e', `620', `630',
     `740', `7400', `7450', `750', `power', `power2', `powerpc', `403',
     `505', `801', `821', `823', and `860' and `common'.

     `-mcpu=common' selects a completely generic processor.  Code
     generated under this option will run on any POWER or PowerPC
     processor.  GCC will use only the instructions in the common
     subset of both architectures, and will not use the MQ register.
     GCC assumes a generic processor model for scheduling purposes.

     `-mcpu=power', `-mcpu=power2', `-mcpu=powerpc', and
     `-mcpu=powerpc64' specify generic POWER, POWER2, pure 32-bit
     PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
     types, with an appropriate, generic processor model assumed for
     scheduling purposes.

     The other options specify a specific processor.  Code generated
     under those options will run best on that processor, and may not
     run at all on others.

     The `-mcpu' options automatically enable or disable other `-m'
     options as follows:

    `common'
          `-mno-power', `-mno-powerc'

    `power'
    `power2'
    `rios1'
    `rios2'
    `rsc'
          `-mpower', `-mno-powerpc', `-mno-new-mnemonics'

    `powerpc'
    `rs64a'
    `602'
    `603'
    `603e'
    `604'
    `620'
    `630'
    `740'
    `7400'
    `7450'
    `750'
    `505'
          `-mno-power', `-mpowerpc', `-mnew-mnemonics'

    `601'
          `-mpower', `-mpowerpc', `-mnew-mnemonics'

    `403'
    `821'
    `860'
          `-mno-power', `-mpowerpc', `-mnew-mnemonics', `-msoft-float'

`-mtune=CPU_TYPE'
     Set the instruction scheduling parameters for machine type
     CPU_TYPE, but do not set the architecture type, register usage, or
     choice of mnemonics, as `-mcpu=CPU_TYPE' would.  The same values
     for CPU_TYPE are used for `-mtune' as for `-mcpu'.  If both are
     specified, the code generated will use the architecture,
     registers, and mnemonics set by `-mcpu', but the scheduling
     parameters set by `-mtune'.

`-maltivec'
`-mno-altivec'
     These switches enable or disable the use of built-in functions that
     allow access to the AltiVec instruction set.  You may also need to
     set `-mabi=altivec' to adjust the current ABI with AltiVec ABI
     enhancements.

`-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, GCC will allocate at least one TOC entry
     for each unique non-automatic variable reference in your program.
     GCC 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 GCC from putting floating-point
     constants in the TOC and `-mno-sum-in-toc' forces GCC 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 GCC 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 GCC to make only one TOC entry for every file.  When
     you specify this option, GCC 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.

`-maix64'
`-maix32'
     Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
     64-bit `long' type, and the infrastructure needed to support them.
     Specifying `-maix64' implies `-mpowerpc64' and `-mpowerpc', while
     `-maix32' disables the 64-bit ABI and implies `-mno-powerpc64'.
     GCC defaults to `-maix32'.

`-mxl-call'
`-mno-xl-call'
     On AIX, pass floating-point arguments to prototyped functions
     beyond the register save area (RSA) on the stack in addition to
     argument FPRs.  The AIX calling convention was extended but not
     initially documented to handle an obscure K&R C case of calling a
     function that takes the address of its arguments with fewer
     arguments than declared.  AIX XL compilers access floating point
     arguments which do not fit in the RSA from the stack when a
     subroutine is compiled without optimization.  Because always
     storing floating-point arguments on the stack is inefficient and
     rarely needed, this option is not enabled by default and only is
     necessary when calling subroutines compiled by AIX XL compilers
     without optimization.

`-mpe'
     Support "IBM RS/6000 SP" "Parallel Environment" (PE).  Link an
     application written to use message passing with special startup
     code to enable the application to run.  The system must have PE
     installed in the standard location (`/usr/lpp/ppe.poe/'), or the
     `specs' file must be overridden with the `-specs=' option to
     specify the appropriate directory location.  The Parallel
     Environment does not support threads, so the `-mpe' option and the
     `-pthread' option are incompatible.

`-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 GCC 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.  The exceptions are PPC740
     and PPC750 which permit the instructions usage 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, and 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.  The exceptions are PPC740 and PPC750 which permit the
     instructions usage in little endian mode.

`-mupdate'
`-mno-update'
     Generate code that uses (does not use) the load or store
     instructions that update the base register to the address of the
     calculated memory location.  These instructions are generated by
     default.  If you use `-mno-update', there is a small window
     between the time that the stack pointer is updated and the address
     of the previous frame is stored, which means code that walks the
     stack frame across interrupts or signals may get corrupted data.

`-mfused-madd'
`-mno-fused-madd'
     Generate code that uses (does not use) the floating point multiply
     and accumulate instructions.  These instructions are generated by
     default if hardware floating is used.

`-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' bit-fields 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.  If you use `-mrelocatable' on any module, all objects
     linked together must be compiled with `-mrelocatable' or
     `-mrelocatable-lib'.

`-mrelocatable-lib'
`-mno-relocatable-lib'
     On embedded PowerPC systems generate code that allows (does not
     allow) the program to be relocated to a different address at
     runtime.  Modules compiled with `-mrelocatable-lib' can be linked
     with either modules compiled without `-mrelocatable' and
     `-mrelocatable-lib' or with modules compiled with the
     `-mrelocatable' options.

`-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.

`-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-sysv-eabi'
     Specify both `-mcall-sysv' and `-meabi' options.

`-mcall-sysv-noeabi'
     Specify both `-mcall-sysv' and `-mno-eabi' options.

`-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'.

`-mcall-solaris'
     On System V.4 and embedded PowerPC systems compile code for the
     Solaris operating system.

`-mcall-linux'
     On System V.4 and embedded PowerPC systems compile code for the
     Linux-based GNU system.

`-mcall-gnu'
     On System V.4 and embedded PowerPC systems compile code for the
     Hurd-based GNU system.

`-mcall-netbsd'
     On System V.4 and embedded PowerPC systems compile code for the
     NetBSD operating system.

`-maix-struct-return'
     Return all structures in memory (as specified by the AIX ABI).

`-msvr4-struct-return'
     Return structures smaller than 8 bytes in registers (as specified
     by the SVR4 ABI).

`-mabi=altivec'
     Extend the current ABI with AltiVec ABI extensions.  This does not
     change the default ABI, instead it adds the AltiVec ABI extensions
     to the current ABI.

`-mabi=no-altivec'
     Disable AltiVec ABI extensions for the current ABI.

`-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.

`-msim'
     On embedded PowerPC systems, assume that the startup module is
     called `sim-crt0.o' and that the standard C libraries are
     `libsim.a' and `libc.a'.  This is the default for
     `powerpc-*-eabisim'.  configurations.

`-mmvme'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libmvme.a' and
     `libc.a'.

`-mads'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libads.a' and
     `libc.a'.

`-myellowknife'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libyk.a' and
     `libc.a'.

`-mvxworks'
     On System V.4 and embedded PowerPC systems, specify that you are
     compiling for a VxWorks system.

`-memb'
     On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags
     header to indicate that `eabi' extended relocations are used.

`-meabi'
`-mno-eabi'
     On System V.4 and embedded PowerPC systems do (do not) adhere to
     the Embedded Applications Binary Interface (eabi) which is a set of
     modifications to the System V.4 specifications.  Selecting `-meabi'
     means that the stack is aligned to an 8 byte boundary, a function
     `__eabi' is called to from `main' to set up the eabi environment,
     and the `-msdata' option can use both `r2' and `r13' to point to
     two separate small data areas.  Selecting `-mno-eabi' means that
     the stack is aligned to a 16 byte boundary, do not call an
     initialization function from `main', and the `-msdata' option will
     only use `r13' to point to a single small data area.  The `-meabi'
     option is on by default if you configured GCC using one of the
     `powerpc*-*-eabi*' options.

`-msdata=eabi'
     On System V.4 and embedded PowerPC systems, put small initialized
     `const' global and static data in the `.sdata2' section, which is
     pointed to by register `r2'.  Put small initialized non-`const'
     global and static data in the `.sdata' section, which is pointed
     to by register `r13'.  Put small uninitialized global and static
     data in the `.sbss' section, which is adjacent to the `.sdata'
     section.  The `-msdata=eabi' option is incompatible with the
     `-mrelocatable' option.  The `-msdata=eabi' option also sets the
     `-memb' option.

`-msdata=sysv'
     On System V.4 and embedded PowerPC systems, put small global and
     static data in the `.sdata' section, which is pointed to by
     register `r13'.  Put small uninitialized global and static data in
     the `.sbss' section, which is adjacent to the `.sdata' section.
     The `-msdata=sysv' option is incompatible with the `-mrelocatable'
     option.

`-msdata=default'
`-msdata'
     On System V.4 and embedded PowerPC systems, if `-meabi' is used,
     compile code the same as `-msdata=eabi', otherwise compile code the
     same as `-msdata=sysv'.

`-msdata-data'
     On System V.4 and embedded PowerPC systems, put small global and
     static data in the `.sdata' section.  Put small uninitialized
     global and static data in the `.sbss' section.  Do not use
     register `r13' to address small data however.  This is the default
     behavior unless other `-msdata' options are used.

`-msdata=none'
`-mno-sdata'
     On embedded PowerPC systems, put all initialized global and static
     data in the `.data' section, and all uninitialized data in the
     `.bss' section.

`-G NUM'
     On embedded PowerPC systems, 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.  By default, NUM is 8.  The `-G
     NUM' switch is also passed to the linker.  All modules should be
     compiled with the same `-G NUM' value.

`-mregnames'
`-mno-regnames'
     On System V.4 and embedded PowerPC systems do (do not) emit
     register names in the assembly language output using symbolic
     forms.

`-pthread'
     Adds support for multithreading with the "pthreads" library.  This
     option sets flags for both the preprocessor and linker.



File: gcc.info,  Node: RT Options,  Next: MIPS Options,  Prev: RS/6000 and PowerPC Options,  Up: Submodel Options

3.17.13 IBM RT Options
----------------------

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 `stdarg.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'.


File: gcc.info,  Node: MIPS Options,  Next: i386 and x86-64 Options,  Prev: RT Options,  Up: Submodel Options

3.17.14 MIPS Options
--------------------

These `-m' options are defined for the MIPS family of computers:

`-march=CPU-TYPE'
     Assume the defaults for the machine type CPU-TYPE when generating
     instructions.  The choices for CPU-TYPE are  `r2000', `r3000',
     `r3900', `r4000', `r4100', `r4300', `r4400', `r4600', `r4650',
     `r5000', `r6000', `r8000', and `orion'.  Additionally, the
     `r2000', `r3000', `r4000', `r5000', and `r6000' can be abbreviated
     as `r2k' (or `r2K'), `r3k', etc.

`-mtune=CPU-TYPE'
     Assume the defaults for the machine type CPU-TYPE when scheduling
     instructions.  The choices for CPU-TYPE are `r2000', `r3000',
     `r3900', `r4000', `r4100', `r4300', `r4400', `r4600', `r4650',
     `r5000', `r6000', `r8000', and `orion'.  Additionally, the
     `r2000', `r3000', `r4000', `r5000', and `r6000' can be abbreviated
     as `r2k' (or `r2K'), `r3k', etc.  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 a
     `-mipsX' or `-mabi' switch being used.

`-mcpu=CPU-TYPE'
     This is identical to specifying both `-march' and `-mtune'.

`-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.

`-mips4'
     Issue instructions from level 4 of the MIPS ISA (conditional move,
     prefetch, enhanced FPU instructions).  `r8000' is the default
     CPU-TYPE at this ISA level.

`-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.

`-mfused-madd'
`-mno-fused-madd'
     Generate code that uses (does not use) the floating point multiply
     and accumulate instructions, when they are available.  These
     instructions are generated by default if they are available, but
     this may be undesirable if the extra precision causes problems or
     on certain chips in the mode where denormals are rounded to zero
     where denormals generated by multiply and accumulate instructions
     cause exceptions anyway.

`-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'
     Force int and long types to be 64 bits wide.  See `-mlong32' for an
     explanation of the default, and the width of pointers.

`-mlong64'
     Force long types to be 64 bits wide.  See `-mlong32' for an
     explanation of the default, and the width of pointers.

`-mlong32'
     Force long, int, and pointer types to be 32 bits wide.

     If none of `-mlong32', `-mlong64', or `-mint64' are set, the size
     of ints, longs, and pointers depends on the ABI and ISA chosen.
     For `-mabi=32', and `-mabi=n32', ints and longs are 32 bits wide.
     For `-mabi=64', ints are 32 bits, and longs are 64 bits wide.  For
     `-mabi=eabi' and either `-mips1' or `-mips2', ints and longs are
     32 bits wide.  For `-mabi=eabi' and higher ISAs, ints are 32 bits,
     and longs are 64 bits wide.  The width of pointer types is the
     smaller of the width of longs or the width of general purpose
     registers (which in turn depends on the ISA).

`-mabi=32'
`-mabi=o64'
`-mabi=n32'
`-mabi=64'
`-mabi=eabi'
     Generate code for the indicated ABI.  The default instruction
     level is `-mips1' for `32', `-mips3' for `n32', and `-mips4'
     otherwise.  Conversely, with `-mips1' or `-mips2', the default ABI
     is `32'; otherwise, the default ABI is `64'.

`-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.  Also,
     this is the default if the configure option `--with-gnu-as' is
     used.

`-msplit-addresses'
`-mno-split-addresses'
     Generate code to load the high and low parts of address constants
     separately.  This allows GCC to optimize away redundant loads of
     the high order bits of addresses.  This optimization requires GNU
     as and GNU ld.  This optimization is enabled by default for some
     embedded targets where GNU as and GNU ld are standard.

`-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 GCC.  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.  No more than 65536 bytes of global data
     may be used.  This requires GNU as and GNU ld which do most of the
     work.  This currently only works on targets which use ECOFF; it
     does not work with ELF.

`-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.

`-muninit-const-in-rodata'
`-mno-uninit-const-in-rodata'
     When used together with `-membedded-data', it will always store
     uninitialized const variables in the read-only data section.

`-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'.

`-mips16'
`-mno-mips16'
     Enable 16-bit instructions.

`-mentry'
     Use the entry and exit pseudo ops.  This option can only be used
     with `-mips16'.

`-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 its preprocessor over user
     assembler files (with a `.s' suffix) when assembling them.

`-mfix7000'
     Pass an option to gas which will cause nops to be inserted if the
     read of the destination register of an mfhi or mflo instruction
     occurs in the following two instructions.

`-no-crt0'
     Do not include the default crt0.

`-mflush-func=FUNC'
`-mno-flush-func'
     Specifies the function to call to flush the I and D caches, or to
     not call any such function.  If called, the function must take the
     same arguments as the common `_flush_func()', that is, the address
     of the memory range for which the cache is being flushed, the size
     of the memory range, and the number 3 (to flush both caches).  The
     default depends on the target gcc was configured for, but commonly
     is either `_flush_func' or `__cpu_flush'.

   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.

