1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
8 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
9 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.2 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU project C and C++ compiler
33 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
42 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
52 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
53 script to report bugs is recommended.
56 See the Info entry for @command{gcc}, or
57 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
58 for contributors to GCC@.
63 @chapter GCC Command Options
64 @cindex GCC command options
65 @cindex command options
66 @cindex options, GCC command
68 @c man begin DESCRIPTION
69 When you invoke GCC, it normally does preprocessing, compilation,
70 assembly and linking. The ``overall options'' allow you to stop this
71 process at an intermediate stage. For example, the @option{-c} option
72 says not to run the linker. Then the output consists of object files
73 output by the assembler.
75 Other options are passed on to one stage of processing. Some options
76 control the preprocessor and others the compiler itself. Yet other
77 options control the assembler and linker; most of these are not
78 documented here, since you rarely need to use any of them.
80 @cindex C compilation options
81 Most of the command line options that you can use with GCC are useful
82 for C programs; when an option is only useful with another language
83 (usually C++), the explanation says so explicitly. If the description
84 for a particular option does not mention a source language, you can use
85 that option with all supported languages.
87 @cindex C++ compilation options
88 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
89 options for compiling C++ programs.
91 @cindex grouping options
92 @cindex options, grouping
93 The @command{gcc} program accepts options and file names as operands. Many
94 options have multi-letter names; therefore multiple single-letter options
95 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
98 @cindex order of options
99 @cindex options, order
100 You can mix options and other arguments. For the most part, the order
101 you use doesn't matter. Order does matter when you use several options
102 of the same kind; for example, if you specify @option{-L} more than once,
103 the directories are searched in the order specified.
105 Many options have long names starting with @samp{-f} or with
106 @samp{-W}---for example, @option{-fforce-mem},
107 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
108 these have both positive and negative forms; the negative form of
109 @option{-ffoo} would be @option{-fno-foo}. This manual documents
110 only one of these two forms, whichever one is not the default.
114 @xref{Option Index}, for an index to GCC's options.
117 * Option Summary:: Brief list of all options, without explanations.
118 * Overall Options:: Controlling the kind of output:
119 an executable, object files, assembler files,
120 or preprocessed source.
121 * Invoking G++:: Compiling C++ programs.
122 * C Dialect Options:: Controlling the variant of C language compiled.
123 * C++ Dialect Options:: Variations on C++.
124 * Objective-C Dialect Options:: Variations on Objective-C.
125 * Language Independent Options:: Controlling how diagnostics should be
127 * Warning Options:: How picky should the compiler be?
128 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
129 * Optimize Options:: How much optimization?
130 * Preprocessor Options:: Controlling header files and macro definitions.
131 Also, getting dependency information for Make.
132 * Assembler Options:: Passing options to the assembler.
133 * Link Options:: Specifying libraries and so on.
134 * Directory Options:: Where to find header files and libraries.
135 Where to find the compiler executable files.
136 * Spec Files:: How to pass switches to sub-processes.
137 * Target Options:: Running a cross-compiler, or an old version of GCC.
138 * Submodel Options:: Specifying minor hardware or convention variations,
139 such as 68010 vs 68020.
140 * Code Gen Options:: Specifying conventions for function calls, data layout
142 * Environment Variables:: Env vars that affect GCC.
143 * Precompiled Headers:: Compiling a header once, and using it many times.
144 * Running Protoize:: Automatically adding or removing function prototypes.
150 @section Option Summary
152 Here is a summary of all the options, grouped by type. Explanations are
153 in the following sections.
156 @item Overall Options
157 @xref{Overall Options,,Options Controlling the Kind of Output}.
158 @gccoptlist{-c -S -E -o @var{file} -pipe -pass-exit-codes @gol
159 -x @var{language} -v -### --help --target-help --version}
161 @item C Language Options
162 @xref{C Dialect Options,,Options Controlling C Dialect}.
163 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
164 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
165 -fhosted -ffreestanding -fms-extensions @gol
166 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
167 -fallow-single-precision -fcond-mismatch @gol
168 -fsigned-bitfields -fsigned-char @gol
169 -funsigned-bitfields -funsigned-char @gol
172 @item C++ Language Options
173 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
174 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
175 -fconserve-space -fno-const-strings @gol
176 -fno-elide-constructors @gol
177 -fno-enforce-eh-specs -fexternal-templates @gol
178 -falt-external-templates @gol
179 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
180 -fno-implicit-templates @gol
181 -fno-implicit-inline-templates @gol
182 -fno-implement-inlines -fms-extensions @gol
183 -fno-nonansi-builtins -fno-operator-names @gol
184 -fno-optional-diags -fpermissive @gol
185 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
186 -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol
187 -fno-default-inline -Wabi -Wctor-dtor-privacy @gol
188 -Wnon-virtual-dtor -Wreorder @gol
189 -Weffc++ -Wno-deprecated @gol
190 -Wno-non-template-friend -Wold-style-cast @gol
191 -Woverloaded-virtual -Wno-pmf-conversions @gol
192 -Wsign-promo -Wsynth}
194 @item Objective-C Language Options
195 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
196 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
197 -fgnu-runtime -fnext-runtime -gen-decls @gol
198 -Wno-protocol -Wselector -Wundeclared-selector}
200 @item Language Independent Options
201 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
202 @gccoptlist{-fmessage-length=@var{n} @gol
203 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
205 @item Warning Options
206 @xref{Warning Options,,Options to Request or Suppress Warnings}.
207 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
208 -w -Wextra -Wall -Waggregate-return @gol
209 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
210 -Wconversion -Wno-deprecated-declarations @gol
211 -Wdisabled-optimization -Wno-div-by-zero -Werror @gol
212 -Wfloat-equal -Wformat -Wformat=2 @gol
213 -Wformat-nonliteral -Wformat-security @gol
214 -Wimplicit -Wimplicit-int @gol
215 -Wimplicit-function-declaration @gol
216 -Werror-implicit-function-declaration @gol
217 -Wimport -Winline -Winvalid-pch -Wno-endif-labels @gol
218 -Wno-invalid-offsetof @gol
219 -Wlarger-than-@var{len} -Wlong-long @gol
220 -Wmain -Wmissing-braces @gol
221 -Wmissing-format-attribute -Wmissing-noreturn @gol
222 -Wno-multichar -Wno-format-extra-args -Wno-format-y2k @gol
223 -Wno-import -Wnonnull -Wpacked -Wpadded @gol
224 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
225 -Wreturn-type -Wsequence-point -Wshadow @gol
226 -Wsign-compare -Wstrict-aliasing @gol
227 -Wswitch -Wswitch-default -Wswitch-enum @gol
228 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
229 -Wunknown-pragmas -Wunreachable-code @gol
230 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
231 -Wunused-value -Wunused-variable -Wwrite-strings}
233 @item C-only Warning Options
234 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
235 -Wmissing-prototypes -Wnested-externs @gol
236 -Wstrict-prototypes -Wtraditional}
238 @item Debugging Options
239 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
240 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
241 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
242 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
243 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
244 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
245 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
246 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
247 -fmem-report -fprofile-arcs @gol
248 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
249 -ftest-coverage -ftime-report @gol
250 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
251 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
252 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
253 -print-multi-directory -print-multi-lib @gol
254 -print-prog-name=@var{program} -print-search-dirs -Q @gol
257 @item Optimization Options
258 @xref{Optimize Options,,Options that Control Optimization}.
259 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
260 -falign-labels=@var{n} -falign-loops=@var{n} @gol
261 -fbranch-probabilities -fbranch-target-load-optimize @gol
262 -fbranch-target-load-optimize2 -fcaller-saves -fcprop-registers @gol
263 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
264 -fdelayed-branch -fdelete-null-pointer-checks @gol
265 -fexpensive-optimizations -ffast-math -ffloat-store @gol
266 -fforce-addr -fforce-mem -ffunction-sections @gol
267 -fgcse -fgcse-lm -fgcse-sm -floop-optimize -fcrossjumping @gol
268 -fif-conversion -fif-conversion2 @gol
269 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
270 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
271 -fmove-all-movables -fnew-ra -fno-branch-count-reg @gol
272 -fno-default-inline -fno-defer-pop @gol
273 -fno-function-cse -fno-guess-branch-probability @gol
274 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
275 -funsafe-math-optimizations -ffinite-math-only @gol
276 -fno-trapping-math -fno-zero-initialized-in-bss @gol
277 -fomit-frame-pointer -foptimize-register-move @gol
278 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
279 -freduce-all-givs -fregmove -frename-registers @gol
280 -freorder-blocks -freorder-functions @gol
281 -frerun-cse-after-loop -frerun-loop-opt @gol
282 -fschedule-insns -fschedule-insns2 @gol
283 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
284 -fsched-spec-load-dangerous -fsched2-use-superblocks @gol
285 -fsched2-use-traces -fsignaling-nans @gol
286 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
287 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
288 -funroll-all-loops -funroll-loops -fpeel-loops @gol
289 -funswitch-loops -fold-unroll-loops -fold-unroll-all-loops @gol
290 --param @var{name}=@var{value}
291 -O -O0 -O1 -O2 -O3 -Os}
293 @item Preprocessor Options
294 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
295 @gccoptlist{-A@var{question}=@var{answer} @gol
296 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
297 -C -dD -dI -dM -dN @gol
298 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
299 -idirafter @var{dir} @gol
300 -include @var{file} -imacros @var{file} @gol
301 -iprefix @var{file} -iwithprefix @var{dir} @gol
302 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
303 -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol
304 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
305 -Xpreprocessor @var{option}}
307 @item Assembler Option
308 @xref{Assembler Options,,Passing Options to the Assembler}.
309 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
312 @xref{Link Options,,Options for Linking}.
313 @gccoptlist{@var{object-file-name} -l@var{library} @gol
314 -nostartfiles -nodefaultlibs -nostdlib -pie @gol
315 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
316 -Wl,@var{option} -Xlinker @var{option} @gol
319 @item Directory Options
320 @xref{Directory Options,,Options for Directory Search}.
321 @gccoptlist{-B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
324 @c I wrote this xref this way to avoid overfull hbox. -- rms
325 @xref{Target Options}.
326 @gccoptlist{-V @var{version} -b @var{machine}}
328 @item Machine Dependent Options
329 @xref{Submodel Options,,Hardware Models and Configurations}.
331 @emph{M680x0 Options}
332 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
333 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
334 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
335 -malign-int -mstrict-align}
337 @emph{M68hc1x Options}
338 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
339 -mauto-incdec -minmax -mlong-calls -mshort @gol
340 -msoft-reg-count=@var{count}}
343 @gccoptlist{-mg -mgnu -munix}
346 @gccoptlist{-mcpu=@var{cpu-type} @gol
347 -mtune=@var{cpu-type} @gol
348 -mcmodel=@var{code-model} @gol
350 -mapp-regs -mbroken-saverestore -mcypress @gol
351 -mfaster-structs -mflat @gol
352 -mfpu -mhard-float -mhard-quad-float @gol
353 -mimpure-text -mlive-g0 -mno-app-regs @gol
354 -mno-faster-structs -mno-flat -mno-fpu @gol
355 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
356 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
357 -msupersparc -munaligned-doubles -mv8}
360 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
361 -mapcs-26 -mapcs-32 @gol
362 -mapcs-stack-check -mno-apcs-stack-check @gol
363 -mapcs-float -mno-apcs-float @gol
364 -mapcs-reentrant -mno-apcs-reentrant @gol
365 -msched-prolog -mno-sched-prolog @gol
366 -mlittle-endian -mbig-endian -mwords-little-endian @gol
367 -malignment-traps -mno-alignment-traps @gol
368 -msoft-float -mhard-float -mfpe @gol
369 -mthumb-interwork -mno-thumb-interwork @gol
370 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
371 -mstructure-size-boundary=@var{n} @gol
372 -mabort-on-noreturn @gol
373 -mlong-calls -mno-long-calls @gol
374 -msingle-pic-base -mno-single-pic-base @gol
375 -mpic-register=@var{reg} @gol
376 -mnop-fun-dllimport @gol
377 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
378 -mpoke-function-name @gol
380 -mtpcs-frame -mtpcs-leaf-frame @gol
381 -mcaller-super-interworking -mcallee-super-interworking}
383 @emph{MN10200 Options}
386 @emph{MN10300 Options}
387 @gccoptlist{-mmult-bug -mno-mult-bug @gol
388 -mam33 -mno-am33 @gol
391 @emph{M32R/D Options}
392 @gccoptlist{-m32rx -m32r -mcode-model=@var{model-type} @gol
393 -msdata=@var{sdata-type} -G @var{num}}
396 @gccoptlist{-m88000 -m88100 -m88110 -mbig-pic @gol
397 -mcheck-zero-division -mhandle-large-shift @gol
398 -midentify-revision -mno-check-zero-division @gol
399 -mno-ocs-debug-info -mno-ocs-frame-position @gol
400 -mno-optimize-arg-area -mno-serialize-volatile @gol
401 -mno-underscores -mocs-debug-info @gol
402 -mocs-frame-position -moptimize-arg-area @gol
403 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
404 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
405 -mversion-03.00 -mwarn-passed-structs}
407 @emph{RS/6000 and PowerPC Options}
408 @gccoptlist{-mcpu=@var{cpu-type} @gol
409 -mtune=@var{cpu-type} @gol
410 -mpower -mno-power -mpower2 -mno-power2 @gol
411 -mpowerpc -mpowerpc64 -mno-powerpc @gol
412 -maltivec -mno-altivec @gol
413 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
414 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
415 -mnew-mnemonics -mold-mnemonics @gol
416 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
417 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
418 -malign-power -malign-natural @gol
419 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
420 -mstring -mno-string -mupdate -mno-update @gol
421 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
422 -mstrict-align -mno-strict-align -mrelocatable @gol
423 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
424 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
425 -mdynamic-no-pic @gol
426 -mcall-sysv -mcall-netbsd @gol
427 -maix-struct-return -msvr4-struct-return @gol
428 -mabi=altivec -mabi=no-altivec @gol
429 -mabi=spe -mabi=no-spe @gol
430 -misel=yes -misel=no @gol
431 -mspe=yes -mspe=no @gol
432 -mfloat-gprs=yes -mfloat-gprs=no @gol
433 -mprototype -mno-prototype @gol
434 -msim -mmvme -mads -myellowknife -memb -msdata @gol
435 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
437 @emph{Darwin Options}
438 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
439 -arch_only -bind_at_load -bundle -bundle_loader @gol
440 -client_name -compatibility_version -current_version @gol
441 -dependency-file -dylib_file -dylinker_install_name @gol
442 -dynamic -dynamiclib -exported_symbols_list @gol
443 -filelist -flat_namespace -force_cpusubtype_ALL @gol
444 -force_flat_namespace -headerpad_max_install_names @gol
445 -image_base -init -install_name -keep_private_externs @gol
446 -multi_module -multiply_defined -multiply_defined_unused @gol
447 -noall_load -nomultidefs -noprebind -noseglinkedit @gol
448 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
449 -private_bundle -read_only_relocs -sectalign @gol
450 -sectobjectsymbols -whyload -seg1addr @gol
451 -sectcreate -sectobjectsymbols -sectorder @gol
452 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
453 -segprot -segs_read_only_addr -segs_read_write_addr @gol
454 -single_module -static -sub_library -sub_umbrella @gol
455 -twolevel_namespace -umbrella -undefined @gol
456 -unexported_symbols_list -weak_reference_mismatches @gol
460 @gccoptlist{-mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
461 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
462 -mminimum-fp-blocks -mnohc-struct-return}
465 @gccoptlist{-mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
466 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
467 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
468 -mgas -mgp32 -mgp64 @gol
469 -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol
470 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
471 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
472 -mmips-as -mmips-tfile -mno-abicalls @gol
473 -mno-embedded-data -mno-uninit-const-in-rodata @gol
474 -mno-embedded-pic -mno-gpopt -mno-long-calls @gol
475 -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol
476 -mrnames -msoft-float @gol
477 -m4650 -msingle-float -mmad @gol
478 -EL -EB -G @var{num} -nocpp @gol
479 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi -mabi-fake-default @gol
480 -mfix7000 -mno-crt0 -mflush-func=@var{func} -mno-flush-func @gol
481 -mbranch-likely -mno-branch-likely}
483 @emph{i386 and x86-64 Options}
484 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
485 -mfpmath=@var{unit} @gol
486 -masm=@var{dialect} -mno-fancy-math-387 @gol
487 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
488 -mno-wide-multiply -mrtd -malign-double @gol
489 -mpreferred-stack-boundary=@var{num} @gol
490 -mmmx -msse -msse2 -m3dnow @gol
491 -mthreads -mno-align-stringops -minline-all-stringops @gol
492 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
493 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
494 -mno-red-zone -mno-tls-direct-seg-refs @gol
495 -mcmodel=@var{code-model} @gol
499 @gccoptlist{-march=@var{architecture-type} @gol
500 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
501 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
502 -mjump-in-delay -mlinker-opt -mlong-calls @gol
503 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
504 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
505 -mno-jump-in-delay -mno-long-load-store @gol
506 -mno-portable-runtime -mno-soft-float @gol
507 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
508 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
509 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
510 -nolibdld -static -threads}
512 @emph{Intel 960 Options}
513 @gccoptlist{-m@var{cpu-type} -masm-compat -mclean-linkage @gol
514 -mcode-align -mcomplex-addr -mleaf-procedures @gol
515 -mic-compat -mic2.0-compat -mic3.0-compat @gol
516 -mintel-asm -mno-clean-linkage -mno-code-align @gol
517 -mno-complex-addr -mno-leaf-procedures @gol
518 -mno-old-align -mno-strict-align -mno-tail-call @gol
519 -mnumerics -mold-align -msoft-float -mstrict-align @gol
522 @emph{DEC Alpha Options}
523 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
524 -mieee -mieee-with-inexact -mieee-conformant @gol
525 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
526 -mtrap-precision=@var{mode} -mbuild-constants @gol
527 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
528 -mbwx -mmax -mfix -mcix @gol
529 -mfloat-vax -mfloat-ieee @gol
530 -mexplicit-relocs -msmall-data -mlarge-data @gol
531 -msmall-text -mlarge-text @gol
532 -mmemory-latency=@var{time}}
534 @emph{DEC Alpha/VMS Options}
535 @gccoptlist{-mvms-return-codes}
537 @emph{H8/300 Options}
538 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
541 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
542 -m4-nofpu -m4-single-only -m4-single -m4 @gol
543 -m5-64media -m5-64media-nofpu @gol
544 -m5-32media -m5-32media-nofpu @gol
545 -m5-compact -m5-compact-nofpu @gol
546 -mb -ml -mdalign -mrelax @gol
547 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
548 -mieee -misize -mpadstruct -mspace @gol
549 -mprefergot -musermode}
551 @emph{System V Options}
552 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
555 @gccoptlist{-EB -EL @gol
556 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
557 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
559 @emph{TMS320C3x/C4x Options}
560 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
561 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
562 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
563 -mparallel-insns -mparallel-mpy -mpreserve-float}
566 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
567 -mprolog-function -mno-prolog-function -mspace @gol
568 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
569 -mapp-regs -mno-app-regs @gol
570 -mdisable-callt -mno-disable-callt @gol
575 @gccoptlist{-m32032 -m32332 -m32532 -m32081 -m32381 @gol
576 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
577 -mregparam -mnoregparam -msb -mnosb @gol
578 -mbitfield -mnobitfield -mhimem -mnohimem}
581 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
582 -mcall-prologues -mno-tablejump -mtiny-stack}
585 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
586 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
587 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
588 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
589 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
592 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
593 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
594 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
595 -mno-base-addresses -msingle-exit -mno-single-exit}
598 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
599 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
600 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
601 -minline-float-divide-max-throughput @gol
602 -minline-int-divide-min-latency @gol
603 -minline-int-divide-max-throughput -mno-dwarf2-asm @gol
604 -mfixed-range=@var{register-range}}
607 @gccoptlist{-mextmem -mextmemory -monchip -mno-asm-optimize @gol
608 -masm-optimize -mbranch-cost=@var{n} -mcond-exec=@var{n}}
610 @emph{S/390 and zSeries Options}
611 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
612 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
613 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
614 -m64 -m31 -mdebug -mno-debug -mesa -mzarch}
617 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
618 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
619 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
620 -mstack-align -mdata-align -mconst-align @gol
621 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
622 -melf -maout -melinux -mlinux -sim -sim2}
624 @emph{PDP-11 Options}
625 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
626 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
627 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
628 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
629 -mbranch-expensive -mbranch-cheap @gol
630 -msplit -mno-split -munix-asm -mdec-asm}
632 @emph{Xstormy16 Options}
635 @emph{Xtensa Options}
636 @gccoptlist{-mbig-endian -mlittle-endian @gol
637 -mdensity -mno-density @gol
638 -mconst16 -mno-const16 @gol
640 -maddx -mno-addx @gol
641 -mmac16 -mno-mac16 @gol
642 -mmul16 -mno-mul16 @gol
643 -mmul32 -mno-mul32 @gol
645 -mminmax -mno-minmax @gol
646 -msext -mno-sext @gol
647 -mbooleans -mno-booleans @gol
648 -mhard-float -msoft-float @gol
649 -mfused-madd -mno-fused-madd @gol
650 -mtext-section-literals -mno-text-section-literals @gol
651 -mtarget-align -mno-target-align @gol
652 -mlongcalls -mno-longcalls}
655 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
656 -mhard-float -msoft-float @gol
657 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
658 -mdouble -mno-double @gol
659 -mmedia -mno-media -mmuladd -mno-muladd @gol
660 -mlibrary-pic -macc-4 -macc-8 @gol
661 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
662 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
663 -mvliw-branch -mno-vliw-branch @gol
664 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
665 -mno-nested-cond-exec -mtomcat-stats @gol
668 @item Code Generation Options
669 @xref{Code Gen Options,,Options for Code Generation Conventions}.
670 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
671 -ffixed-@var{reg} -fexceptions @gol
672 -fnon-call-exceptions -funwind-tables @gol
673 -fasynchronous-unwind-tables @gol
674 -finhibit-size-directive -finstrument-functions @gol
675 -fno-common -fno-ident -fno-gnu-linker @gol
676 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
677 -freg-struct-return -fshared-data -fshort-enums @gol
678 -fshort-double -fshort-wchar @gol
679 -fverbose-asm -fpack-struct -fstack-check @gol
680 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
681 -fargument-alias -fargument-noalias @gol
682 -fargument-noalias-global -fleading-underscore @gol
683 -ftls-model=@var{model} @gol
684 -ftrapv -fwrapv -fbounds-check}
688 * Overall Options:: Controlling the kind of output:
689 an executable, object files, assembler files,
690 or preprocessed source.
691 * C Dialect Options:: Controlling the variant of C language compiled.
692 * C++ Dialect Options:: Variations on C++.
693 * Objective-C Dialect Options:: Variations on Objective-C.
694 * Language Independent Options:: Controlling how diagnostics should be
696 * Warning Options:: How picky should the compiler be?
697 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
698 * Optimize Options:: How much optimization?
699 * Preprocessor Options:: Controlling header files and macro definitions.
700 Also, getting dependency information for Make.
701 * Assembler Options:: Passing options to the assembler.
702 * Link Options:: Specifying libraries and so on.
703 * Directory Options:: Where to find header files and libraries.
704 Where to find the compiler executable files.
705 * Spec Files:: How to pass switches to sub-processes.
706 * Target Options:: Running a cross-compiler, or an old version of GCC.
709 @node Overall Options
710 @section Options Controlling the Kind of Output
712 Compilation can involve up to four stages: preprocessing, compilation
713 proper, assembly and linking, always in that order. The first three
714 stages apply to an individual source file, and end by producing an
715 object file; linking combines all the object files (those newly
716 compiled, and those specified as input) into an executable file.
718 @cindex file name suffix
719 For any given input file, the file name suffix determines what kind of
724 C source code which must be preprocessed.
727 C source code which should not be preprocessed.
730 C++ source code which should not be preprocessed.
733 Objective-C source code. Note that you must link with the library
734 @file{libobjc.a} to make an Objective-C program work.
737 Objective-C source code which should not be preprocessed.
740 C or C++ header file to be turned into a precompiled header.
744 @itemx @var{file}.cxx
745 @itemx @var{file}.cpp
746 @itemx @var{file}.CPP
747 @itemx @var{file}.c++
749 C++ source code which must be preprocessed. Note that in @samp{.cxx},
750 the last two letters must both be literally @samp{x}. Likewise,
751 @samp{.C} refers to a literal capital C@.
755 C++ header file to be turned into a precompiled header.
758 @itemx @var{file}.for
759 @itemx @var{file}.FOR
760 Fortran source code which should not be preprocessed.
763 @itemx @var{file}.fpp
764 @itemx @var{file}.FPP
765 Fortran source code which must be preprocessed (with the traditional
769 Fortran source code which must be preprocessed with a RATFOR
770 preprocessor (not included with GCC)@.
772 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
773 Using and Porting GNU Fortran}, for more details of the handling of
776 @c FIXME: Descriptions of Java file types.
783 Ada source code file which contains a library unit declaration (a
784 declaration of a package, subprogram, or generic, or a generic
785 instantiation), or a library unit renaming declaration (a package,
786 generic, or subprogram renaming declaration). Such files are also
789 @itemx @var{file}.adb
790 Ada source code file containing a library unit body (a subprogram or
791 package body). Such files are also called @dfn{bodies}.
793 @c GCC also knows about some suffixes for languages not yet included:
802 Assembler code which must be preprocessed.
805 An object file to be fed straight into linking.
806 Any file name with no recognized suffix is treated this way.
810 You can specify the input language explicitly with the @option{-x} option:
813 @item -x @var{language}
814 Specify explicitly the @var{language} for the following input files
815 (rather than letting the compiler choose a default based on the file
816 name suffix). This option applies to all following input files until
817 the next @option{-x} option. Possible values for @var{language} are:
819 c c-header cpp-output
820 c++ c++-header c++-cpp-output
821 objective-c objective-c-header objc-cpp-output
822 assembler assembler-with-cpp
824 f77 f77-cpp-input ratfor
830 Turn off any specification of a language, so that subsequent files are
831 handled according to their file name suffixes (as they are if @option{-x}
832 has not been used at all).
834 @item -pass-exit-codes
835 @opindex pass-exit-codes
836 Normally the @command{gcc} program will exit with the code of 1 if any
837 phase of the compiler returns a non-success return code. If you specify
838 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
839 numerically highest error produced by any phase that returned an error
843 If you only want some of the stages of compilation, you can use
844 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
845 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
846 @command{gcc} is to stop. Note that some combinations (for example,
847 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
852 Compile or assemble the source files, but do not link. The linking
853 stage simply is not done. The ultimate output is in the form of an
854 object file for each source file.
856 By default, the object file name for a source file is made by replacing
857 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
859 Unrecognized input files, not requiring compilation or assembly, are
864 Stop after the stage of compilation proper; do not assemble. The output
865 is in the form of an assembler code file for each non-assembler input
868 By default, the assembler file name for a source file is made by
869 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
871 Input files that don't require compilation are ignored.
875 Stop after the preprocessing stage; do not run the compiler proper. The
876 output is in the form of preprocessed source code, which is sent to the
879 Input files which don't require preprocessing are ignored.
881 @cindex output file option
884 Place output in file @var{file}. This applies regardless to whatever
885 sort of output is being produced, whether it be an executable file,
886 an object file, an assembler file or preprocessed C code.
888 Since only one output file can be specified, it does not make sense to
889 use @option{-o} when compiling more than one input file, unless you are
890 producing an executable file as output.
892 If @option{-o} is not specified, the default is to put an executable file
893 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
894 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
895 all preprocessed C source on standard output.
899 Print (on standard error output) the commands executed to run the stages
900 of compilation. Also print the version number of the compiler driver
901 program and of the preprocessor and the compiler proper.
905 Like @option{-v} except the commands are not executed and all command
906 arguments are quoted. This is useful for shell scripts to capture the
907 driver-generated command lines.
911 Use pipes rather than temporary files for communication between the
912 various stages of compilation. This fails to work on some systems where
913 the assembler is unable to read from a pipe; but the GNU assembler has
918 Print (on the standard output) a description of the command line options
919 understood by @command{gcc}. If the @option{-v} option is also specified
920 then @option{--help} will also be passed on to the various processes
921 invoked by @command{gcc}, so that they can display the command line options
922 they accept. If the @option{-Wextra} option is also specified then command
923 line options which have no documentation associated with them will also
928 Print (on the standard output) a description of target specific command
929 line options for each tool.
933 Display the version number and copyrights of the invoked GCC.
937 @section Compiling C++ Programs
939 @cindex suffixes for C++ source
940 @cindex C++ source file suffixes
941 C++ source files conventionally use one of the suffixes @samp{.C},
942 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
943 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
944 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
945 files with these names and compiles them as C++ programs even if you
946 call the compiler the same way as for compiling C programs (usually
947 with the name @command{gcc}).
951 However, C++ programs often require class libraries as well as a
952 compiler that understands the C++ language---and under some
953 circumstances, you might want to compile programs or header files from
954 standard input, or otherwise without a suffix that flags them as C++
955 programs. You might also like to precompile a C header file with a
956 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
957 program that calls GCC with the default language set to C++, and
958 automatically specifies linking against the C++ library. On many
959 systems, @command{g++} is also installed with the name @command{c++}.
961 @cindex invoking @command{g++}
962 When you compile C++ programs, you may specify many of the same
963 command-line options that you use for compiling programs in any
964 language; or command-line options meaningful for C and related
965 languages; or options that are meaningful only for C++ programs.
966 @xref{C Dialect Options,,Options Controlling C Dialect}, for
967 explanations of options for languages related to C@.
968 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
969 explanations of options that are meaningful only for C++ programs.
971 @node C Dialect Options
972 @section Options Controlling C Dialect
973 @cindex dialect options
974 @cindex language dialect options
975 @cindex options, dialect
977 The following options control the dialect of C (or languages derived
978 from C, such as C++ and Objective-C) that the compiler accepts:
985 In C mode, support all ISO C90 programs. In C++ mode,
986 remove GNU extensions that conflict with ISO C++.
988 This turns off certain features of GCC that are incompatible with ISO
989 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
990 such as the @code{asm} and @code{typeof} keywords, and
991 predefined macros such as @code{unix} and @code{vax} that identify the
992 type of system you are using. It also enables the undesirable and
993 rarely used ISO trigraph feature. For the C compiler,
994 it disables recognition of C++ style @samp{//} comments as well as
995 the @code{inline} keyword.
997 The alternate keywords @code{__asm__}, @code{__extension__},
998 @code{__inline__} and @code{__typeof__} continue to work despite
999 @option{-ansi}. You would not want to use them in an ISO C program, of
1000 course, but it is useful to put them in header files that might be included
1001 in compilations done with @option{-ansi}. Alternate predefined macros
1002 such as @code{__unix__} and @code{__vax__} are also available, with or
1003 without @option{-ansi}.
1005 The @option{-ansi} option does not cause non-ISO programs to be
1006 rejected gratuitously. For that, @option{-pedantic} is required in
1007 addition to @option{-ansi}. @xref{Warning Options}.
1009 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1010 option is used. Some header files may notice this macro and refrain
1011 from declaring certain functions or defining certain macros that the
1012 ISO standard doesn't call for; this is to avoid interfering with any
1013 programs that might use these names for other things.
1015 Functions which would normally be built in but do not have semantics
1016 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1017 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1018 built-in functions provided by GCC}, for details of the functions
1023 Determine the language standard. This option is currently only
1024 supported when compiling C or C++. A value for this option must be
1025 provided; possible values are
1030 ISO C90 (same as @option{-ansi}).
1032 @item iso9899:199409
1033 ISO C90 as modified in amendment 1.
1039 ISO C99. Note that this standard is not yet fully supported; see
1040 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1041 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1044 Default, ISO C90 plus GNU extensions (including some C99 features).
1048 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1049 this will become the default. The name @samp{gnu9x} is deprecated.
1052 The 1998 ISO C++ standard plus amendments.
1055 The same as @option{-std=c++98} plus GNU extensions. This is the
1056 default for C++ code.
1059 Even when this option is not specified, you can still use some of the
1060 features of newer standards in so far as they do not conflict with
1061 previous C standards. For example, you may use @code{__restrict__} even
1062 when @option{-std=c99} is not specified.
1064 The @option{-std} options specifying some version of ISO C have the same
1065 effects as @option{-ansi}, except that features that were not in ISO C90
1066 but are in the specified version (for example, @samp{//} comments and
1067 the @code{inline} keyword in ISO C99) are not disabled.
1069 @xref{Standards,,Language Standards Supported by GCC}, for details of
1070 these standard versions.
1072 @item -aux-info @var{filename}
1074 Output to the given filename prototyped declarations for all functions
1075 declared and/or defined in a translation unit, including those in header
1076 files. This option is silently ignored in any language other than C@.
1078 Besides declarations, the file indicates, in comments, the origin of
1079 each declaration (source file and line), whether the declaration was
1080 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1081 @samp{O} for old, respectively, in the first character after the line
1082 number and the colon), and whether it came from a declaration or a
1083 definition (@samp{C} or @samp{F}, respectively, in the following
1084 character). In the case of function definitions, a K&R-style list of
1085 arguments followed by their declarations is also provided, inside
1086 comments, after the declaration.
1090 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1091 keyword, so that code can use these words as identifiers. You can use
1092 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1093 instead. @option{-ansi} implies @option{-fno-asm}.
1095 In C++, this switch only affects the @code{typeof} keyword, since
1096 @code{asm} and @code{inline} are standard keywords. You may want to
1097 use the @option{-fno-gnu-keywords} flag instead, which has the same
1098 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1099 switch only affects the @code{asm} and @code{typeof} keywords, since
1100 @code{inline} is a standard keyword in ISO C99.
1103 @itemx -fno-builtin-@var{function}
1104 @opindex fno-builtin
1105 @cindex built-in functions
1106 Don't recognize built-in functions that do not begin with
1107 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1108 functions provided by GCC}, for details of the functions affected,
1109 including those which are not built-in functions when @option{-ansi} or
1110 @option{-std} options for strict ISO C conformance are used because they
1111 do not have an ISO standard meaning.
1113 GCC normally generates special code to handle certain built-in functions
1114 more efficiently; for instance, calls to @code{alloca} may become single
1115 instructions that adjust the stack directly, and calls to @code{memcpy}
1116 may become inline copy loops. The resulting code is often both smaller
1117 and faster, but since the function calls no longer appear as such, you
1118 cannot set a breakpoint on those calls, nor can you change the behavior
1119 of the functions by linking with a different library.
1121 With the @option{-fno-builtin-@var{function}} option
1122 only the built-in function @var{function} is
1123 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1124 function is named this is not built-in in this version of GCC, this
1125 option is ignored. There is no corresponding
1126 @option{-fbuiltin-@var{function}} option; if you wish to enable
1127 built-in functions selectively when using @option{-fno-builtin} or
1128 @option{-ffreestanding}, you may define macros such as:
1131 #define abs(n) __builtin_abs ((n))
1132 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1137 @cindex hosted environment
1139 Assert that compilation takes place in a hosted environment. This implies
1140 @option{-fbuiltin}. A hosted environment is one in which the
1141 entire standard library is available, and in which @code{main} has a return
1142 type of @code{int}. Examples are nearly everything except a kernel.
1143 This is equivalent to @option{-fno-freestanding}.
1145 @item -ffreestanding
1146 @opindex ffreestanding
1147 @cindex hosted environment
1149 Assert that compilation takes place in a freestanding environment. This
1150 implies @option{-fno-builtin}. A freestanding environment
1151 is one in which the standard library may not exist, and program startup may
1152 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1153 This is equivalent to @option{-fno-hosted}.
1155 @xref{Standards,,Language Standards Supported by GCC}, for details of
1156 freestanding and hosted environments.
1158 @item -fms-extensions
1159 @opindex fms-extensions
1160 Accept some non-standard constructs used in Microsoft header files.
1164 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1165 options for strict ISO C conformance) implies @option{-trigraphs}.
1167 @item -no-integrated-cpp
1168 @opindex no-integrated-cpp
1169 Performs a compilation in two passes: preprocessing and compiling. This
1170 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1171 @option{-B} option. The user supplied compilation step can then add in
1172 an additional preprocessing step after normal preprocessing but before
1173 compiling. The default is to use the integrated cpp (internal cpp)
1175 The semantics of this option will change if "cc1", "cc1plus", and
1176 "cc1obj" are merged.
1178 @cindex traditional C language
1179 @cindex C language, traditional
1181 @itemx -traditional-cpp
1182 @opindex traditional-cpp
1183 @opindex traditional
1184 Formerly, these options caused GCC to attempt to emulate a pre-standard
1185 C compiler. They are now only supported with the @option{-E} switch.
1186 The preprocessor continues to support a pre-standard mode. See the GNU
1187 CPP manual for details.
1189 @item -fcond-mismatch
1190 @opindex fcond-mismatch
1191 Allow conditional expressions with mismatched types in the second and
1192 third arguments. The value of such an expression is void. This option
1193 is not supported for C++.
1195 @item -funsigned-char
1196 @opindex funsigned-char
1197 Let the type @code{char} be unsigned, like @code{unsigned char}.
1199 Each kind of machine has a default for what @code{char} should
1200 be. It is either like @code{unsigned char} by default or like
1201 @code{signed char} by default.
1203 Ideally, a portable program should always use @code{signed char} or
1204 @code{unsigned char} when it depends on the signedness of an object.
1205 But many programs have been written to use plain @code{char} and
1206 expect it to be signed, or expect it to be unsigned, depending on the
1207 machines they were written for. This option, and its inverse, let you
1208 make such a program work with the opposite default.
1210 The type @code{char} is always a distinct type from each of
1211 @code{signed char} or @code{unsigned char}, even though its behavior
1212 is always just like one of those two.
1215 @opindex fsigned-char
1216 Let the type @code{char} be signed, like @code{signed char}.
1218 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1219 the negative form of @option{-funsigned-char}. Likewise, the option
1220 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1222 @item -fsigned-bitfields
1223 @itemx -funsigned-bitfields
1224 @itemx -fno-signed-bitfields
1225 @itemx -fno-unsigned-bitfields
1226 @opindex fsigned-bitfields
1227 @opindex funsigned-bitfields
1228 @opindex fno-signed-bitfields
1229 @opindex fno-unsigned-bitfields
1230 These options control whether a bit-field is signed or unsigned, when the
1231 declaration does not use either @code{signed} or @code{unsigned}. By
1232 default, such a bit-field is signed, because this is consistent: the
1233 basic integer types such as @code{int} are signed types.
1235 @item -fwritable-strings
1236 @opindex fwritable-strings
1237 Store string constants in the writable data segment and don't uniquize
1238 them. This is for compatibility with old programs which assume they can
1239 write into string constants.
1241 Writing into string constants is a very bad idea; ``constants'' should
1245 @node C++ Dialect Options
1246 @section Options Controlling C++ Dialect
1248 @cindex compiler options, C++
1249 @cindex C++ options, command line
1250 @cindex options, C++
1251 This section describes the command-line options that are only meaningful
1252 for C++ programs; but you can also use most of the GNU compiler options
1253 regardless of what language your program is in. For example, you
1254 might compile a file @code{firstClass.C} like this:
1257 g++ -g -frepo -O -c firstClass.C
1261 In this example, only @option{-frepo} is an option meant
1262 only for C++ programs; you can use the other options with any
1263 language supported by GCC@.
1265 Here is a list of options that are @emph{only} for compiling C++ programs:
1269 @item -fabi-version=@var{n}
1270 @opindex fabi-version
1271 Use version @var{n} of the C++ ABI. Version 1 is the version of the C++
1272 ABI that first appeared in G++ 3.2. Version 0 will always be the
1273 version that conforms most closely to the C++ ABI specification.
1274 Therefore, the ABI obtained using version 0 will change as ABI bugs are
1277 The default is version 1.
1279 @item -fno-access-control
1280 @opindex fno-access-control
1281 Turn off all access checking. This switch is mainly useful for working
1282 around bugs in the access control code.
1286 Check that the pointer returned by @code{operator new} is non-null
1287 before attempting to modify the storage allocated. This check is
1288 normally unnecessary because the C++ standard specifies that
1289 @code{operator new} will only return @code{0} if it is declared
1290 @samp{throw()}, in which case the compiler will always check the
1291 return value even without this option. In all other cases, when
1292 @code{operator new} has a non-empty exception specification, memory
1293 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1294 @samp{new (nothrow)}.
1296 @item -fconserve-space
1297 @opindex fconserve-space
1298 Put uninitialized or runtime-initialized global variables into the
1299 common segment, as C does. This saves space in the executable at the
1300 cost of not diagnosing duplicate definitions. If you compile with this
1301 flag and your program mysteriously crashes after @code{main()} has
1302 completed, you may have an object that is being destroyed twice because
1303 two definitions were merged.
1305 This option is no longer useful on most targets, now that support has
1306 been added for putting variables into BSS without making them common.
1308 @item -fno-const-strings
1309 @opindex fno-const-strings
1310 Give string constants type @code{char *} instead of type @code{const
1311 char *}. By default, G++ uses type @code{const char *} as required by
1312 the standard. Even if you use @option{-fno-const-strings}, you cannot
1313 actually modify the value of a string constant, unless you also use
1314 @option{-fwritable-strings}.
1316 This option might be removed in a future release of G++. For maximum
1317 portability, you should structure your code so that it works with
1318 string constants that have type @code{const char *}.
1320 @item -fno-elide-constructors
1321 @opindex fno-elide-constructors
1322 The C++ standard allows an implementation to omit creating a temporary
1323 which is only used to initialize another object of the same type.
1324 Specifying this option disables that optimization, and forces G++ to
1325 call the copy constructor in all cases.
1327 @item -fno-enforce-eh-specs
1328 @opindex fno-enforce-eh-specs
1329 Don't check for violation of exception specifications at runtime. This
1330 option violates the C++ standard, but may be useful for reducing code
1331 size in production builds, much like defining @samp{NDEBUG}. The compiler
1332 will still optimize based on the exception specifications.
1334 @item -fexternal-templates
1335 @opindex fexternal-templates
1337 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1338 template instantiation; template instances are emitted or not according
1339 to the location of the template definition. @xref{Template
1340 Instantiation}, for more information.
1342 This option is deprecated.
1344 @item -falt-external-templates
1345 @opindex falt-external-templates
1346 Similar to @option{-fexternal-templates}, but template instances are
1347 emitted or not according to the place where they are first instantiated.
1348 @xref{Template Instantiation}, for more information.
1350 This option is deprecated.
1353 @itemx -fno-for-scope
1355 @opindex fno-for-scope
1356 If @option{-ffor-scope} is specified, the scope of variables declared in
1357 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1358 as specified by the C++ standard.
1359 If @option{-fno-for-scope} is specified, the scope of variables declared in
1360 a @i{for-init-statement} extends to the end of the enclosing scope,
1361 as was the case in old versions of G++, and other (traditional)
1362 implementations of C++.
1364 The default if neither flag is given to follow the standard,
1365 but to allow and give a warning for old-style code that would
1366 otherwise be invalid, or have different behavior.
1368 @item -fno-gnu-keywords
1369 @opindex fno-gnu-keywords
1370 Do not recognize @code{typeof} as a keyword, so that code can use this
1371 word as an identifier. You can use the keyword @code{__typeof__} instead.
1372 @option{-ansi} implies @option{-fno-gnu-keywords}.
1374 @item -fno-implicit-templates
1375 @opindex fno-implicit-templates
1376 Never emit code for non-inline templates which are instantiated
1377 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1378 @xref{Template Instantiation}, for more information.
1380 @item -fno-implicit-inline-templates
1381 @opindex fno-implicit-inline-templates
1382 Don't emit code for implicit instantiations of inline templates, either.
1383 The default is to handle inlines differently so that compiles with and
1384 without optimization will need the same set of explicit instantiations.
1386 @item -fno-implement-inlines
1387 @opindex fno-implement-inlines
1388 To save space, do not emit out-of-line copies of inline functions
1389 controlled by @samp{#pragma implementation}. This will cause linker
1390 errors if these functions are not inlined everywhere they are called.
1392 @item -fms-extensions
1393 @opindex fms-extensions
1394 Disable pedantic warnings about constructs used in MFC, such as implicit
1395 int and getting a pointer to member function via non-standard syntax.
1397 @item -fno-nonansi-builtins
1398 @opindex fno-nonansi-builtins
1399 Disable built-in declarations of functions that are not mandated by
1400 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1401 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1403 @item -fno-operator-names
1404 @opindex fno-operator-names
1405 Do not treat the operator name keywords @code{and}, @code{bitand},
1406 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1407 synonyms as keywords.
1409 @item -fno-optional-diags
1410 @opindex fno-optional-diags
1411 Disable diagnostics that the standard says a compiler does not need to
1412 issue. Currently, the only such diagnostic issued by G++ is the one for
1413 a name having multiple meanings within a class.
1416 @opindex fpermissive
1417 Downgrade messages about nonconformant code from errors to warnings. By
1418 default, G++ effectively sets @option{-pedantic-errors} without
1419 @option{-pedantic}; this option reverses that. This behavior and this
1420 option are superseded by @option{-pedantic}, which works as it does for GNU C@.
1424 Enable automatic template instantiation at link time. This option also
1425 implies @option{-fno-implicit-templates}. @xref{Template
1426 Instantiation}, for more information.
1430 Disable generation of information about every class with virtual
1431 functions for use by the C++ runtime type identification features
1432 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1433 of the language, you can save some space by using this flag. Note that
1434 exception handling uses the same information, but it will generate it as
1439 Emit statistics about front-end processing at the end of the compilation.
1440 This information is generally only useful to the G++ development team.
1442 @item -ftemplate-depth-@var{n}
1443 @opindex ftemplate-depth
1444 Set the maximum instantiation depth for template classes to @var{n}.
1445 A limit on the template instantiation depth is needed to detect
1446 endless recursions during template class instantiation. ANSI/ISO C++
1447 conforming programs must not rely on a maximum depth greater than 17.
1449 @item -fuse-cxa-atexit
1450 @opindex fuse-cxa-atexit
1451 Register destructors for objects with static storage duration with the
1452 @code{__cxa_atexit} function rather than the @code{atexit} function.
1453 This option is required for fully standards-compliant handling of static
1454 destructors, but will only work if your C library supports
1455 @code{__cxa_atexit}.
1459 Emit special relocations for vtables and virtual function references
1460 so that the linker can identify unused virtual functions and zero out
1461 vtable slots that refer to them. This is most useful with
1462 @option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to
1463 also discard the functions themselves.
1465 This optimization requires GNU as and GNU ld. Not all systems support
1466 this option. @option{-Wl,--gc-sections} is ignored without @option{-static}.
1470 Do not use weak symbol support, even if it is provided by the linker.
1471 By default, G++ will use weak symbols if they are available. This
1472 option exists only for testing, and should not be used by end-users;
1473 it will result in inferior code and has no benefits. This option may
1474 be removed in a future release of G++.
1478 Do not search for header files in the standard directories specific to
1479 C++, but do still search the other standard directories. (This option
1480 is used when building the C++ library.)
1483 In addition, these optimization, warning, and code generation options
1484 have meanings only for C++ programs:
1487 @item -fno-default-inline
1488 @opindex fno-default-inline
1489 Do not assume @samp{inline} for functions defined inside a class scope.
1490 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1491 functions will have linkage like inline functions; they just won't be
1494 @item -Wabi @r{(C++ only)}
1496 Warn when G++ generates code that is probably not compatible with the
1497 vendor-neutral C++ ABI. Although an effort has been made to warn about
1498 all such cases, there are probably some cases that are not warned about,
1499 even though G++ is generating incompatible code. There may also be
1500 cases where warnings are emitted even though the code that is generated
1503 You should rewrite your code to avoid these warnings if you are
1504 concerned about the fact that code generated by G++ may not be binary
1505 compatible with code generated by other compilers.
1507 The known incompatibilities at this point include:
1512 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1513 pack data into the same byte as a base class. For example:
1516 struct A @{ virtual void f(); int f1 : 1; @};
1517 struct B : public A @{ int f2 : 1; @};
1521 In this case, G++ will place @code{B::f2} into the same byte
1522 as@code{A::f1}; other compilers will not. You can avoid this problem
1523 by explicitly padding @code{A} so that its size is a multiple of the
1524 byte size on your platform; that will cause G++ and other compilers to
1525 layout @code{B} identically.
1528 Incorrect handling of tail-padding for virtual bases. G++ does not use
1529 tail padding when laying out virtual bases. For example:
1532 struct A @{ virtual void f(); char c1; @};
1533 struct B @{ B(); char c2; @};
1534 struct C : public A, public virtual B @{@};
1538 In this case, G++ will not place @code{B} into the tail-padding for
1539 @code{A}; other compilers will. You can avoid this problem by
1540 explicitly padding @code{A} so that its size is a multiple of its
1541 alignment (ignoring virtual base classes); that will cause G++ and other
1542 compilers to layout @code{C} identically.
1545 Incorrect handling of bit-fields with declared widths greater than that
1546 of their underlying types, when the bit-fields appear in a union. For
1550 union U @{ int i : 4096; @};
1554 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1555 union too small by the number of bits in an @code{int}.
1558 Empty classes can be placed at incorrect offsets. For example:
1568 struct C : public B, public A @{@};
1572 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1573 it should be placed at offset zero. G++ mistakenly believes that the
1574 @code{A} data member of @code{B} is already at offset zero.
1577 Names of template functions whose types involve @code{typename} or
1578 template template parameters can be mangled incorrectly.
1581 template <typename Q>
1582 void f(typename Q::X) @{@}
1584 template <template <typename> class Q>
1585 void f(typename Q<int>::X) @{@}
1589 Instantiations of these templates may be mangled incorrectly.
1593 @item -Wctor-dtor-privacy @r{(C++ only)}
1594 @opindex Wctor-dtor-privacy
1595 Warn when a class seems unusable, because all the constructors or
1596 destructors in a class are private and the class has no friends or
1597 public static member functions.
1599 @item -Wnon-virtual-dtor @r{(C++ only)}
1600 @opindex Wnon-virtual-dtor
1601 Warn when a class declares a non-virtual destructor that should probably
1602 be virtual, because it looks like the class will be used polymorphically.
1603 This warning is enabled by @option{-Wall}.
1605 @item -Wreorder @r{(C++ only)}
1607 @cindex reordering, warning
1608 @cindex warning for reordering of member initializers
1609 Warn when the order of member initializers given in the code does not
1610 match the order in which they must be executed. For instance:
1616 A(): j (0), i (1) @{ @}
1620 Here the compiler will warn that the member initializers for @samp{i}
1621 and @samp{j} will be rearranged to match the declaration order of the
1622 members. This warning is enabled by @option{-Wall}.
1625 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1628 @item -Weffc++ @r{(C++ only)}
1630 Warn about violations of the following style guidelines from Scott Meyers'
1631 @cite{Effective C++} book:
1635 Item 11: Define a copy constructor and an assignment operator for classes
1636 with dynamically allocated memory.
1639 Item 12: Prefer initialization to assignment in constructors.
1642 Item 14: Make destructors virtual in base classes.
1645 Item 15: Have @code{operator=} return a reference to @code{*this}.
1648 Item 23: Don't try to return a reference when you must return an object.
1652 and about violations of the following style guidelines from Scott Meyers'
1653 @cite{More Effective C++} book:
1657 Item 6: Distinguish between prefix and postfix forms of increment and
1658 decrement operators.
1661 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1665 If you use this option, you should be aware that the standard library
1666 headers do not obey all of these guidelines; you can use @samp{grep -v}
1667 to filter out those warnings.
1669 @item -Wno-deprecated @r{(C++ only)}
1670 @opindex Wno-deprecated
1671 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1673 @item -Wno-non-template-friend @r{(C++ only)}
1674 @opindex Wno-non-template-friend
1675 Disable warnings when non-templatized friend functions are declared
1676 within a template. With the advent of explicit template specification
1677 support in G++, if the name of the friend is an unqualified-id (i.e.,
1678 @samp{friend foo(int)}), the C++ language specification demands that the
1679 friend declare or define an ordinary, nontemplate function. (Section
1680 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1681 could be interpreted as a particular specialization of a templatized
1682 function. Because this non-conforming behavior is no longer the default
1683 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1684 check existing code for potential trouble spots, and is on by default.
1685 This new compiler behavior can be turned off with
1686 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1687 but disables the helpful warning.
1689 @item -Wold-style-cast @r{(C++ only)}
1690 @opindex Wold-style-cast
1691 Warn if an old-style (C-style) cast to a non-void type is used within
1692 a C++ program. The new-style casts (@samp{static_cast},
1693 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1694 unintended effects, and much easier to grep for.
1696 @item -Woverloaded-virtual @r{(C++ only)}
1697 @opindex Woverloaded-virtual
1698 @cindex overloaded virtual fn, warning
1699 @cindex warning for overloaded virtual fn
1700 Warn when a function declaration hides virtual functions from a
1701 base class. For example, in:
1708 struct B: public A @{
1713 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1721 will fail to compile.
1723 @item -Wno-pmf-conversions @r{(C++ only)}
1724 @opindex Wno-pmf-conversions
1725 Disable the diagnostic for converting a bound pointer to member function
1728 @item -Wsign-promo @r{(C++ only)}
1729 @opindex Wsign-promo
1730 Warn when overload resolution chooses a promotion from unsigned or
1731 enumeral type to a signed type over a conversion to an unsigned type of
1732 the same size. Previous versions of G++ would try to preserve
1733 unsignedness, but the standard mandates the current behavior.
1735 @item -Wsynth @r{(C++ only)}
1737 @cindex warning for synthesized methods
1738 @cindex synthesized methods, warning
1739 Warn when G++'s synthesis behavior does not match that of cfront. For
1745 A& operator = (int);
1755 In this example, G++ will synthesize a default @samp{A& operator =
1756 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1759 @node Objective-C Dialect Options
1760 @section Options Controlling Objective-C Dialect
1762 @cindex compiler options, Objective-C
1763 @cindex Objective-C options, command line
1764 @cindex options, Objective-C
1765 This section describes the command-line options that are only meaningful
1766 for Objective-C programs; but you can also use most of the GNU compiler
1767 options regardless of what language your program is in. For example,
1768 you might compile a file @code{some_class.m} like this:
1771 gcc -g -fgnu-runtime -O -c some_class.m
1775 In this example, only @option{-fgnu-runtime} is an option meant only for
1776 Objective-C programs; you can use the other options with any language
1779 Here is a list of options that are @emph{only} for compiling Objective-C
1783 @item -fconstant-string-class=@var{class-name}
1784 @opindex fconstant-string-class
1785 Use @var{class-name} as the name of the class to instantiate for each
1786 literal string specified with the syntax @code{@@"@dots{}"}. The default
1787 class name is @code{NXConstantString}.
1790 @opindex fgnu-runtime
1791 Generate object code compatible with the standard GNU Objective-C
1792 runtime. This is the default for most types of systems.
1794 @item -fnext-runtime
1795 @opindex fnext-runtime
1796 Generate output compatible with the NeXT runtime. This is the default
1797 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1798 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1803 Dump interface declarations for all classes seen in the source file to a
1804 file named @file{@var{sourcename}.decl}.
1807 @opindex Wno-protocol
1808 If a class is declared to implement a protocol, a warning is issued for
1809 every method in the protocol that is not implemented by the class. The
1810 default behavior is to issue a warning for every method not explicitly
1811 implemented in the class, even if a method implementation is inherited
1812 from the superclass. If you use the @code{-Wno-protocol} option, then
1813 methods inherited from the superclass are considered to be implemented,
1814 and no warning is issued for them.
1818 Warn if multiple methods of different types for the same selector are
1819 found during compilation. The check is performed on the list of methods
1820 in the final stage of compilation. Additionally, a check is performed
1821 that for each selector appearing in a @code{@@selector(@dots{})}
1822 expression, a corresponding method with that selector has been found
1823 during compilation. Because these checks scan the method table only at
1824 the end of compilation, these warnings are not produced if the final
1825 stage of compilation is not reached, for example because an error is
1826 found during compilation, or because the @code{-fsyntax-only} option is
1829 @item -Wundeclared-selector
1830 @opindex Wundeclared-selector
1831 Warn if a @code{@@selector(@dots{})} expression referring to an
1832 undeclared selector is found. A selector is considered undeclared if no
1833 method with that name has been declared (explicitly, in an
1834 @code{@@interface} or @code{@@protocol} declaration, or implicitly, in
1835 an @code{@@implementation} section) before the
1836 @code{@@selector(@dots{})} expression. This option always performs its
1837 checks as soon as a @code{@@selector(@dots{})} expression is found
1838 (while @code{-Wselector} only performs its checks in the final stage of
1839 compilation), and so additionally enforces the coding style convention
1840 that methods and selectors must be declared before being used.
1842 @c not documented because only avail via -Wp
1843 @c @item -print-objc-runtime-info
1847 @node Language Independent Options
1848 @section Options to Control Diagnostic Messages Formatting
1849 @cindex options to control diagnostics formatting
1850 @cindex diagnostic messages
1851 @cindex message formatting
1853 Traditionally, diagnostic messages have been formatted irrespective of
1854 the output device's aspect (e.g.@: its width, @dots{}). The options described
1855 below can be used to control the diagnostic messages formatting
1856 algorithm, e.g.@: how many characters per line, how often source location
1857 information should be reported. Right now, only the C++ front end can
1858 honor these options. However it is expected, in the near future, that
1859 the remaining front ends would be able to digest them correctly.
1862 @item -fmessage-length=@var{n}
1863 @opindex fmessage-length
1864 Try to format error messages so that they fit on lines of about @var{n}
1865 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1866 the front ends supported by GCC@. If @var{n} is zero, then no
1867 line-wrapping will be done; each error message will appear on a single
1870 @opindex fdiagnostics-show-location
1871 @item -fdiagnostics-show-location=once
1872 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1873 reporter to emit @emph{once} source location information; that is, in
1874 case the message is too long to fit on a single physical line and has to
1875 be wrapped, the source location won't be emitted (as prefix) again,
1876 over and over, in subsequent continuation lines. This is the default
1879 @item -fdiagnostics-show-location=every-line
1880 Only meaningful in line-wrapping mode. Instructs the diagnostic
1881 messages reporter to emit the same source location information (as
1882 prefix) for physical lines that result from the process of breaking
1883 a message which is too long to fit on a single line.
1887 @node Warning Options
1888 @section Options to Request or Suppress Warnings
1889 @cindex options to control warnings
1890 @cindex warning messages
1891 @cindex messages, warning
1892 @cindex suppressing warnings
1894 Warnings are diagnostic messages that report constructions which
1895 are not inherently erroneous but which are risky or suggest there
1896 may have been an error.
1898 You can request many specific warnings with options beginning @samp{-W},
1899 for example @option{-Wimplicit} to request warnings on implicit
1900 declarations. Each of these specific warning options also has a
1901 negative form beginning @samp{-Wno-} to turn off warnings;
1902 for example, @option{-Wno-implicit}. This manual lists only one of the
1903 two forms, whichever is not the default.
1905 The following options control the amount and kinds of warnings produced
1906 by GCC; for further, language-specific options also refer to
1907 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
1910 @cindex syntax checking
1912 @opindex fsyntax-only
1913 Check the code for syntax errors, but don't do anything beyond that.
1917 Issue all the warnings demanded by strict ISO C and ISO C++;
1918 reject all programs that use forbidden extensions, and some other
1919 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1920 version of the ISO C standard specified by any @option{-std} option used.
1922 Valid ISO C and ISO C++ programs should compile properly with or without
1923 this option (though a rare few will require @option{-ansi} or a
1924 @option{-std} option specifying the required version of ISO C)@. However,
1925 without this option, certain GNU extensions and traditional C and C++
1926 features are supported as well. With this option, they are rejected.
1928 @option{-pedantic} does not cause warning messages for use of the
1929 alternate keywords whose names begin and end with @samp{__}. Pedantic
1930 warnings are also disabled in the expression that follows
1931 @code{__extension__}. However, only system header files should use
1932 these escape routes; application programs should avoid them.
1933 @xref{Alternate Keywords}.
1935 Some users try to use @option{-pedantic} to check programs for strict ISO
1936 C conformance. They soon find that it does not do quite what they want:
1937 it finds some non-ISO practices, but not all---only those for which
1938 ISO C @emph{requires} a diagnostic, and some others for which
1939 diagnostics have been added.
1941 A feature to report any failure to conform to ISO C might be useful in
1942 some instances, but would require considerable additional work and would
1943 be quite different from @option{-pedantic}. We don't have plans to
1944 support such a feature in the near future.
1946 Where the standard specified with @option{-std} represents a GNU
1947 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1948 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1949 extended dialect is based. Warnings from @option{-pedantic} are given
1950 where they are required by the base standard. (It would not make sense
1951 for such warnings to be given only for features not in the specified GNU
1952 C dialect, since by definition the GNU dialects of C include all
1953 features the compiler supports with the given option, and there would be
1954 nothing to warn about.)
1956 @item -pedantic-errors
1957 @opindex pedantic-errors
1958 Like @option{-pedantic}, except that errors are produced rather than
1963 Inhibit all warning messages.
1967 Inhibit warning messages about the use of @samp{#import}.
1969 @item -Wchar-subscripts
1970 @opindex Wchar-subscripts
1971 Warn if an array subscript has type @code{char}. This is a common cause
1972 of error, as programmers often forget that this type is signed on some
1977 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1978 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1982 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1983 the arguments supplied have types appropriate to the format string
1984 specified, and that the conversions specified in the format string make
1985 sense. This includes standard functions, and others specified by format
1986 attributes (@pxref{Function Attributes}), in the @code{printf},
1987 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1988 not in the C standard) families.
1990 The formats are checked against the format features supported by GNU
1991 libc version 2.2. These include all ISO C90 and C99 features, as well
1992 as features from the Single Unix Specification and some BSD and GNU
1993 extensions. Other library implementations may not support all these
1994 features; GCC does not support warning about features that go beyond a
1995 particular library's limitations. However, if @option{-pedantic} is used
1996 with @option{-Wformat}, warnings will be given about format features not
1997 in the selected standard version (but not for @code{strfmon} formats,
1998 since those are not in any version of the C standard). @xref{C Dialect
1999 Options,,Options Controlling C Dialect}.
2001 Since @option{-Wformat} also checks for null format arguments for
2002 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2004 @option{-Wformat} is included in @option{-Wall}. For more control over some
2005 aspects of format checking, the options @option{-Wno-format-y2k},
2006 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2007 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2008 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2010 @item -Wno-format-y2k
2011 @opindex Wno-format-y2k
2012 If @option{-Wformat} is specified, do not warn about @code{strftime}
2013 formats which may yield only a two-digit year.
2015 @item -Wno-format-extra-args
2016 @opindex Wno-format-extra-args
2017 If @option{-Wformat} is specified, do not warn about excess arguments to a
2018 @code{printf} or @code{scanf} format function. The C standard specifies
2019 that such arguments are ignored.
2021 Where the unused arguments lie between used arguments that are
2022 specified with @samp{$} operand number specifications, normally
2023 warnings are still given, since the implementation could not know what
2024 type to pass to @code{va_arg} to skip the unused arguments. However,
2025 in the case of @code{scanf} formats, this option will suppress the
2026 warning if the unused arguments are all pointers, since the Single
2027 Unix Specification says that such unused arguments are allowed.
2029 @item -Wno-format-zero-length
2030 @opindex Wno-format-zero-length
2031 If @option{-Wformat} is specified, do not warn about zero-length formats.
2032 The C standard specifies that zero-length formats are allowed.
2034 @item -Wformat-nonliteral
2035 @opindex Wformat-nonliteral
2036 If @option{-Wformat} is specified, also warn if the format string is not a
2037 string literal and so cannot be checked, unless the format function
2038 takes its format arguments as a @code{va_list}.
2040 @item -Wformat-security
2041 @opindex Wformat-security
2042 If @option{-Wformat} is specified, also warn about uses of format
2043 functions that represent possible security problems. At present, this
2044 warns about calls to @code{printf} and @code{scanf} functions where the
2045 format string is not a string literal and there are no format arguments,
2046 as in @code{printf (foo);}. This may be a security hole if the format
2047 string came from untrusted input and contains @samp{%n}. (This is
2048 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2049 in future warnings may be added to @option{-Wformat-security} that are not
2050 included in @option{-Wformat-nonliteral}.)
2054 Enable @option{-Wformat} plus format checks not included in
2055 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2056 -Wformat-nonliteral -Wformat-security}.
2060 Enable warning about passing a null pointer for arguments marked as
2061 requiring a non-null value by the @code{nonnull} function attribute.
2063 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2064 can be disabled with the @option{-Wno-nonnull} option.
2066 @item -Wimplicit-int
2067 @opindex Wimplicit-int
2068 Warn when a declaration does not specify a type.
2070 @item -Wimplicit-function-declaration
2071 @itemx -Werror-implicit-function-declaration
2072 @opindex Wimplicit-function-declaration
2073 @opindex Werror-implicit-function-declaration
2074 Give a warning (or error) whenever a function is used before being
2079 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2083 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2084 function with external linkage, returning int, taking either zero
2085 arguments, two, or three arguments of appropriate types.
2087 @item -Wmissing-braces
2088 @opindex Wmissing-braces
2089 Warn if an aggregate or union initializer is not fully bracketed. In
2090 the following example, the initializer for @samp{a} is not fully
2091 bracketed, but that for @samp{b} is fully bracketed.
2094 int a[2][2] = @{ 0, 1, 2, 3 @};
2095 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2099 @opindex Wparentheses
2100 Warn if parentheses are omitted in certain contexts, such
2101 as when there is an assignment in a context where a truth value
2102 is expected, or when operators are nested whose precedence people
2103 often get confused about.
2105 Also warn about constructions where there may be confusion to which
2106 @code{if} statement an @code{else} branch belongs. Here is an example of
2121 In C, every @code{else} branch belongs to the innermost possible @code{if}
2122 statement, which in this example is @code{if (b)}. This is often not
2123 what the programmer expected, as illustrated in the above example by
2124 indentation the programmer chose. When there is the potential for this
2125 confusion, GCC will issue a warning when this flag is specified.
2126 To eliminate the warning, add explicit braces around the innermost
2127 @code{if} statement so there is no way the @code{else} could belong to
2128 the enclosing @code{if}. The resulting code would look like this:
2144 @item -Wsequence-point
2145 @opindex Wsequence-point
2146 Warn about code that may have undefined semantics because of violations
2147 of sequence point rules in the C standard.
2149 The C standard defines the order in which expressions in a C program are
2150 evaluated in terms of @dfn{sequence points}, which represent a partial
2151 ordering between the execution of parts of the program: those executed
2152 before the sequence point, and those executed after it. These occur
2153 after the evaluation of a full expression (one which is not part of a
2154 larger expression), after the evaluation of the first operand of a
2155 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2156 function is called (but after the evaluation of its arguments and the
2157 expression denoting the called function), and in certain other places.
2158 Other than as expressed by the sequence point rules, the order of
2159 evaluation of subexpressions of an expression is not specified. All
2160 these rules describe only a partial order rather than a total order,
2161 since, for example, if two functions are called within one expression
2162 with no sequence point between them, the order in which the functions
2163 are called is not specified. However, the standards committee have
2164 ruled that function calls do not overlap.
2166 It is not specified when between sequence points modifications to the
2167 values of objects take effect. Programs whose behavior depends on this
2168 have undefined behavior; the C standard specifies that ``Between the
2169 previous and next sequence point an object shall have its stored value
2170 modified at most once by the evaluation of an expression. Furthermore,
2171 the prior value shall be read only to determine the value to be
2172 stored.''. If a program breaks these rules, the results on any
2173 particular implementation are entirely unpredictable.
2175 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2176 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2177 diagnosed by this option, and it may give an occasional false positive
2178 result, but in general it has been found fairly effective at detecting
2179 this sort of problem in programs.
2181 The present implementation of this option only works for C programs. A
2182 future implementation may also work for C++ programs.
2184 The C standard is worded confusingly, therefore there is some debate
2185 over the precise meaning of the sequence point rules in subtle cases.
2186 Links to discussions of the problem, including proposed formal
2187 definitions, may be found on our readings page, at
2188 @w{@uref{http://gcc.gnu.org/readings.html}}.
2191 @opindex Wreturn-type
2192 Warn whenever a function is defined with a return-type that defaults to
2193 @code{int}. Also warn about any @code{return} statement with no
2194 return-value in a function whose return-type is not @code{void}.
2196 For C++, a function without return type always produces a diagnostic
2197 message, even when @option{-Wno-return-type} is specified. The only
2198 exceptions are @samp{main} and functions defined in system headers.
2202 Warn whenever a @code{switch} statement has an index of enumeral type
2203 and lacks a @code{case} for one or more of the named codes of that
2204 enumeration. (The presence of a @code{default} label prevents this
2205 warning.) @code{case} labels outside the enumeration range also
2206 provoke warnings when this option is used.
2208 @item -Wswitch-default
2209 @opindex Wswitch-switch
2210 Warn whenever a @code{switch} statement does not have a @code{default}
2214 @opindex Wswitch-enum
2215 Warn whenever a @code{switch} statement has an index of enumeral type
2216 and lacks a @code{case} for one or more of the named codes of that
2217 enumeration. @code{case} labels outside the enumeration range also
2218 provoke warnings when this option is used.
2222 Warn if any trigraphs are encountered that might change the meaning of
2223 the program (trigraphs within comments are not warned about).
2225 @item -Wunused-function
2226 @opindex Wunused-function
2227 Warn whenever a static function is declared but not defined or a
2228 non\-inline static function is unused.
2230 @item -Wunused-label
2231 @opindex Wunused-label
2232 Warn whenever a label is declared but not used.
2234 To suppress this warning use the @samp{unused} attribute
2235 (@pxref{Variable Attributes}).
2237 @item -Wunused-parameter
2238 @opindex Wunused-parameter
2239 Warn whenever a function parameter is unused aside from its declaration.
2241 To suppress this warning use the @samp{unused} attribute
2242 (@pxref{Variable Attributes}).
2244 @item -Wunused-variable
2245 @opindex Wunused-variable
2246 Warn whenever a local variable or non-constant static variable is unused
2247 aside from its declaration
2249 To suppress this warning use the @samp{unused} attribute
2250 (@pxref{Variable Attributes}).
2252 @item -Wunused-value
2253 @opindex Wunused-value
2254 Warn whenever a statement computes a result that is explicitly not used.
2256 To suppress this warning cast the expression to @samp{void}.
2260 All the above @option{-Wunused} options combined.
2262 In order to get a warning about an unused function parameter, you must
2263 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2264 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2266 @item -Wuninitialized
2267 @opindex Wuninitialized
2268 Warn if an automatic variable is used without first being initialized or
2269 if a variable may be clobbered by a @code{setjmp} call.
2271 These warnings are possible only in optimizing compilation,
2272 because they require data flow information that is computed only
2273 when optimizing. If you don't specify @option{-O}, you simply won't
2276 These warnings occur only for variables that are candidates for
2277 register allocation. Therefore, they do not occur for a variable that
2278 is declared @code{volatile}, or whose address is taken, or whose size
2279 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2280 structures, unions or arrays, even when they are in registers.
2282 Note that there may be no warning about a variable that is used only
2283 to compute a value that itself is never used, because such
2284 computations may be deleted by data flow analysis before the warnings
2287 These warnings are made optional because GCC is not smart
2288 enough to see all the reasons why the code might be correct
2289 despite appearing to have an error. Here is one example of how
2310 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2311 always initialized, but GCC doesn't know this. Here is
2312 another common case:
2317 if (change_y) save_y = y, y = new_y;
2319 if (change_y) y = save_y;
2324 This has no bug because @code{save_y} is used only if it is set.
2326 @cindex @code{longjmp} warnings
2327 This option also warns when a non-volatile automatic variable might be
2328 changed by a call to @code{longjmp}. These warnings as well are possible
2329 only in optimizing compilation.
2331 The compiler sees only the calls to @code{setjmp}. It cannot know
2332 where @code{longjmp} will be called; in fact, a signal handler could
2333 call it at any point in the code. As a result, you may get a warning
2334 even when there is in fact no problem because @code{longjmp} cannot
2335 in fact be called at the place which would cause a problem.
2337 Some spurious warnings can be avoided if you declare all the functions
2338 you use that never return as @code{noreturn}. @xref{Function
2341 @item -Wunknown-pragmas
2342 @opindex Wunknown-pragmas
2343 @cindex warning for unknown pragmas
2344 @cindex unknown pragmas, warning
2345 @cindex pragmas, warning of unknown
2346 Warn when a #pragma directive is encountered which is not understood by
2347 GCC@. If this command line option is used, warnings will even be issued
2348 for unknown pragmas in system header files. This is not the case if
2349 the warnings were only enabled by the @option{-Wall} command line option.
2351 @item -Wstrict-aliasing
2352 @opindex Wstrict-aliasing
2353 This option is only active when @option{-fstrict-aliasing} is active.
2354 It warns about code which might break the strict aliasing rules that the
2355 compiler is using for optimization. The warning does not catch all
2356 cases, but does attempt to catch the more common pitfalls. It is
2357 included in @option{-Wall}.
2361 All of the above @samp{-W} options combined. This enables all the
2362 warnings about constructions that some users consider questionable, and
2363 that are easy to avoid (or modify to prevent the warning), even in
2364 conjunction with macros. This also enables some language-specific
2365 warnings described in @ref{C++ Dialect Options} and
2366 @ref{Objective-C Dialect Options}.
2369 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2370 Some of them warn about constructions that users generally do not
2371 consider questionable, but which occasionally you might wish to check
2372 for; others warn about constructions that are necessary or hard to avoid
2373 in some cases, and there is no simple way to modify the code to suppress
2380 (This option used to be called @option{-W}. The older name is still
2381 supported, but the newer name is more descriptive.) Print extra warning
2382 messages for these events:
2386 A function can return either with or without a value. (Falling
2387 off the end of the function body is considered returning without
2388 a value.) For example, this function would evoke such a
2402 An expression-statement or the left-hand side of a comma expression
2403 contains no side effects.
2404 To suppress the warning, cast the unused expression to void.
2405 For example, an expression such as @samp{x[i,j]} will cause a warning,
2406 but @samp{x[(void)i,j]} will not.
2409 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2412 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2413 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2414 that of ordinary mathematical notation.
2417 Storage-class specifiers like @code{static} are not the first things in
2418 a declaration. According to the C Standard, this usage is obsolescent.
2421 The return type of a function has a type qualifier such as @code{const}.
2422 Such a type qualifier has no effect, since the value returned by a
2423 function is not an lvalue. (But don't warn about the GNU extension of
2424 @code{volatile void} return types. That extension will be warned about
2425 if @option{-pedantic} is specified.)
2428 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2432 A comparison between signed and unsigned values could produce an
2433 incorrect result when the signed value is converted to unsigned.
2434 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2437 An aggregate has an initializer which does not initialize all members.
2438 For example, the following code would cause such a warning, because
2439 @code{x.h} would be implicitly initialized to zero:
2442 struct s @{ int f, g, h; @};
2443 struct s x = @{ 3, 4 @};
2447 A function parameter is declared without a type specifier in K&R-style
2455 An empty body occurs in an @samp{if} or @samp{else} statement.
2458 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2459 @samp{>}, or @samp{>=}.
2462 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2465 Any of several floating-point events that often indicate errors, such as
2466 overflow, underflow, loss of precision, etc.
2468 @item @r{(C++ only)}
2469 An enumerator and a non-enumerator both appear in a conditional expression.
2471 @item @r{(C++ only)}
2472 A non-static reference or non-static @samp{const} member appears in a
2473 class without constructors.
2475 @item @r{(C++ only)}
2476 Ambiguous virtual bases.
2478 @item @r{(C++ only)}
2479 Subscripting an array which has been declared @samp{register}.
2481 @item @r{(C++ only)}
2482 Taking the address of a variable which has been declared @samp{register}.
2484 @item @r{(C++ only)}
2485 A base class is not initialized in a derived class' copy constructor.
2488 @item -Wno-div-by-zero
2489 @opindex Wno-div-by-zero
2490 @opindex Wdiv-by-zero
2491 Do not warn about compile-time integer division by zero. Floating point
2492 division by zero is not warned about, as it can be a legitimate way of
2493 obtaining infinities and NaNs.
2495 @item -Wsystem-headers
2496 @opindex Wsystem-headers
2497 @cindex warnings from system headers
2498 @cindex system headers, warnings from
2499 Print warning messages for constructs found in system header files.
2500 Warnings from system headers are normally suppressed, on the assumption
2501 that they usually do not indicate real problems and would only make the
2502 compiler output harder to read. Using this command line option tells
2503 GCC to emit warnings from system headers as if they occurred in user
2504 code. However, note that using @option{-Wall} in conjunction with this
2505 option will @emph{not} warn about unknown pragmas in system
2506 headers---for that, @option{-Wunknown-pragmas} must also be used.
2509 @opindex Wfloat-equal
2510 Warn if floating point values are used in equality comparisons.
2512 The idea behind this is that sometimes it is convenient (for the
2513 programmer) to consider floating-point values as approximations to
2514 infinitely precise real numbers. If you are doing this, then you need
2515 to compute (by analyzing the code, or in some other way) the maximum or
2516 likely maximum error that the computation introduces, and allow for it
2517 when performing comparisons (and when producing output, but that's a
2518 different problem). In particular, instead of testing for equality, you
2519 would check to see whether the two values have ranges that overlap; and
2520 this is done with the relational operators, so equality comparisons are
2523 @item -Wtraditional @r{(C only)}
2524 @opindex Wtraditional
2525 Warn about certain constructs that behave differently in traditional and
2526 ISO C@. Also warn about ISO C constructs that have no traditional C
2527 equivalent, and/or problematic constructs which should be avoided.
2531 Macro parameters that appear within string literals in the macro body.
2532 In traditional C macro replacement takes place within string literals,
2533 but does not in ISO C@.
2536 In traditional C, some preprocessor directives did not exist.
2537 Traditional preprocessors would only consider a line to be a directive
2538 if the @samp{#} appeared in column 1 on the line. Therefore
2539 @option{-Wtraditional} warns about directives that traditional C
2540 understands but would ignore because the @samp{#} does not appear as the
2541 first character on the line. It also suggests you hide directives like
2542 @samp{#pragma} not understood by traditional C by indenting them. Some
2543 traditional implementations would not recognize @samp{#elif}, so it
2544 suggests avoiding it altogether.
2547 A function-like macro that appears without arguments.
2550 The unary plus operator.
2553 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2554 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2555 constants.) Note, these suffixes appear in macros defined in the system
2556 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2557 Use of these macros in user code might normally lead to spurious
2558 warnings, however gcc's integrated preprocessor has enough context to
2559 avoid warning in these cases.
2562 A function declared external in one block and then used after the end of
2566 A @code{switch} statement has an operand of type @code{long}.
2569 A non-@code{static} function declaration follows a @code{static} one.
2570 This construct is not accepted by some traditional C compilers.
2573 The ISO type of an integer constant has a different width or
2574 signedness from its traditional type. This warning is only issued if
2575 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2576 typically represent bit patterns, are not warned about.
2579 Usage of ISO string concatenation is detected.
2582 Initialization of automatic aggregates.
2585 Identifier conflicts with labels. Traditional C lacks a separate
2586 namespace for labels.
2589 Initialization of unions. If the initializer is zero, the warning is
2590 omitted. This is done under the assumption that the zero initializer in
2591 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2592 initializer warnings and relies on default initialization to zero in the
2596 Conversions by prototypes between fixed/floating point values and vice
2597 versa. The absence of these prototypes when compiling with traditional
2598 C would cause serious problems. This is a subset of the possible
2599 conversion warnings, for the full set use @option{-Wconversion}.
2602 Use of ISO C style function definitions. This warning intentionally is
2603 @emph{not} issued for prototype declarations or variadic functions
2604 because these ISO C features will appear in your code when using
2605 libiberty's traditional C compatibility macros, @code{PARAMS} and
2606 @code{VPARAMS}. This warning is also bypassed for nested functions
2607 because that feature is already a gcc extension and thus not relevant to
2608 traditional C compatibility.
2613 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2615 @item -Wendif-labels
2616 @opindex Wendif-labels
2617 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2621 Warn whenever a local variable shadows another local variable, parameter or
2622 global variable or whenever a built-in function is shadowed.
2624 @item -Wlarger-than-@var{len}
2625 @opindex Wlarger-than
2626 Warn whenever an object of larger than @var{len} bytes is defined.
2628 @item -Wpointer-arith
2629 @opindex Wpointer-arith
2630 Warn about anything that depends on the ``size of'' a function type or
2631 of @code{void}. GNU C assigns these types a size of 1, for
2632 convenience in calculations with @code{void *} pointers and pointers
2635 @item -Wbad-function-cast @r{(C only)}
2636 @opindex Wbad-function-cast
2637 Warn whenever a function call is cast to a non-matching type.
2638 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2642 Warn whenever a pointer is cast so as to remove a type qualifier from
2643 the target type. For example, warn if a @code{const char *} is cast
2644 to an ordinary @code{char *}.
2647 @opindex Wcast-align
2648 Warn whenever a pointer is cast such that the required alignment of the
2649 target is increased. For example, warn if a @code{char *} is cast to
2650 an @code{int *} on machines where integers can only be accessed at
2651 two- or four-byte boundaries.
2653 @item -Wwrite-strings
2654 @opindex Wwrite-strings
2655 When compiling C, give string constants the type @code{const
2656 char[@var{length}]} so that
2657 copying the address of one into a non-@code{const} @code{char *}
2658 pointer will get a warning; when compiling C++, warn about the
2659 deprecated conversion from string constants to @code{char *}.
2660 These warnings will help you find at
2661 compile time code that can try to write into a string constant, but
2662 only if you have been very careful about using @code{const} in
2663 declarations and prototypes. Otherwise, it will just be a nuisance;
2664 this is why we did not make @option{-Wall} request these warnings.
2667 @opindex Wconversion
2668 Warn if a prototype causes a type conversion that is different from what
2669 would happen to the same argument in the absence of a prototype. This
2670 includes conversions of fixed point to floating and vice versa, and
2671 conversions changing the width or signedness of a fixed point argument
2672 except when the same as the default promotion.
2674 Also, warn if a negative integer constant expression is implicitly
2675 converted to an unsigned type. For example, warn about the assignment
2676 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2677 casts like @code{(unsigned) -1}.
2679 @item -Wsign-compare
2680 @opindex Wsign-compare
2681 @cindex warning for comparison of signed and unsigned values
2682 @cindex comparison of signed and unsigned values, warning
2683 @cindex signed and unsigned values, comparison warning
2684 Warn when a comparison between signed and unsigned values could produce
2685 an incorrect result when the signed value is converted to unsigned.
2686 This warning is also enabled by @option{-Wextra}; to get the other warnings
2687 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2689 @item -Waggregate-return
2690 @opindex Waggregate-return
2691 Warn if any functions that return structures or unions are defined or
2692 called. (In languages where you can return an array, this also elicits
2695 @item -Wstrict-prototypes @r{(C only)}
2696 @opindex Wstrict-prototypes
2697 Warn if a function is declared or defined without specifying the
2698 argument types. (An old-style function definition is permitted without
2699 a warning if preceded by a declaration which specifies the argument
2702 @item -Wmissing-prototypes @r{(C only)}
2703 @opindex Wmissing-prototypes
2704 Warn if a global function is defined without a previous prototype
2705 declaration. This warning is issued even if the definition itself
2706 provides a prototype. The aim is to detect global functions that fail
2707 to be declared in header files.
2709 @item -Wmissing-declarations @r{(C only)}
2710 @opindex Wmissing-declarations
2711 Warn if a global function is defined without a previous declaration.
2712 Do so even if the definition itself provides a prototype.
2713 Use this option to detect global functions that are not declared in
2716 @item -Wmissing-noreturn
2717 @opindex Wmissing-noreturn
2718 Warn about functions which might be candidates for attribute @code{noreturn}.
2719 Note these are only possible candidates, not absolute ones. Care should
2720 be taken to manually verify functions actually do not ever return before
2721 adding the @code{noreturn} attribute, otherwise subtle code generation
2722 bugs could be introduced. You will not get a warning for @code{main} in
2723 hosted C environments.
2725 @item -Wmissing-format-attribute
2726 @opindex Wmissing-format-attribute
2728 If @option{-Wformat} is enabled, also warn about functions which might be
2729 candidates for @code{format} attributes. Note these are only possible
2730 candidates, not absolute ones. GCC will guess that @code{format}
2731 attributes might be appropriate for any function that calls a function
2732 like @code{vprintf} or @code{vscanf}, but this might not always be the
2733 case, and some functions for which @code{format} attributes are
2734 appropriate may not be detected. This option has no effect unless
2735 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2737 @item -Wno-multichar
2738 @opindex Wno-multichar
2740 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2741 Usually they indicate a typo in the user's code, as they have
2742 implementation-defined values, and should not be used in portable code.
2744 @item -Wno-deprecated-declarations
2745 @opindex Wno-deprecated-declarations
2746 Do not warn about uses of functions, variables, and types marked as
2747 deprecated by using the @code{deprecated} attribute.
2748 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2749 @pxref{Type Attributes}.)
2753 Warn if a structure is given the packed attribute, but the packed
2754 attribute has no effect on the layout or size of the structure.
2755 Such structures may be mis-aligned for little benefit. For
2756 instance, in this code, the variable @code{f.x} in @code{struct bar}
2757 will be misaligned even though @code{struct bar} does not itself
2758 have the packed attribute:
2765 @} __attribute__((packed));
2775 Warn if padding is included in a structure, either to align an element
2776 of the structure or to align the whole structure. Sometimes when this
2777 happens it is possible to rearrange the fields of the structure to
2778 reduce the padding and so make the structure smaller.
2780 @item -Wredundant-decls
2781 @opindex Wredundant-decls
2782 Warn if anything is declared more than once in the same scope, even in
2783 cases where multiple declaration is valid and changes nothing.
2785 @item -Wnested-externs @r{(C only)}
2786 @opindex Wnested-externs
2787 Warn if an @code{extern} declaration is encountered within a function.
2789 @item -Wunreachable-code
2790 @opindex Wunreachable-code
2791 Warn if the compiler detects that code will never be executed.
2793 This option is intended to warn when the compiler detects that at
2794 least a whole line of source code will never be executed, because
2795 some condition is never satisfied or because it is after a
2796 procedure that never returns.
2798 It is possible for this option to produce a warning even though there
2799 are circumstances under which part of the affected line can be executed,
2800 so care should be taken when removing apparently-unreachable code.
2802 For instance, when a function is inlined, a warning may mean that the
2803 line is unreachable in only one inlined copy of the function.
2805 This option is not made part of @option{-Wall} because in a debugging
2806 version of a program there is often substantial code which checks
2807 correct functioning of the program and is, hopefully, unreachable
2808 because the program does work. Another common use of unreachable
2809 code is to provide behavior which is selectable at compile-time.
2813 Warn if a function can not be inlined and it was declared as inline.
2814 Even with this option, the compiler will not warn about failures to
2815 inline functions declared in system headers.
2817 The compiler uses a variety of heuristics to determine whether or not
2818 to inline a function. For example, the compiler takes into account
2819 the size of the function being inlined and the the amount of inlining
2820 that has already been done in the current function. Therefore,
2821 seemingly insignificant changes in the source program can cause the
2822 warnings produced by @option{-Winline} to appear or disappear.
2824 @item -Wno-invalid-offsetof @r{(C++ only)}
2825 @opindex Wno-invalid-offsetof
2826 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
2827 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
2828 to a non-POD type is undefined. In existing C++ implementations,
2829 however, @samp{offsetof} typically gives meaningful results even when
2830 applied to certain kinds of non-POD types. (Such as a simple
2831 @samp{struct} that fails to be a POD type only by virtue of having a
2832 constructor.) This flag is for users who are aware that they are
2833 writing nonportable code and who have deliberately chosen to ignore the
2836 The restrictions on @samp{offsetof} may be relaxed in a future version
2837 of the C++ standard.
2840 @opindex Winvalid-pch
2841 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
2842 the search path but can't be used.
2846 @opindex Wno-long-long
2847 Warn if @samp{long long} type is used. This is default. To inhibit
2848 the warning messages, use @option{-Wno-long-long}. Flags
2849 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2850 only when @option{-pedantic} flag is used.
2852 @item -Wdisabled-optimization
2853 @opindex Wdisabled-optimization
2854 Warn if a requested optimization pass is disabled. This warning does
2855 not generally indicate that there is anything wrong with your code; it
2856 merely indicates that GCC's optimizers were unable to handle the code
2857 effectively. Often, the problem is that your code is too big or too
2858 complex; GCC will refuse to optimize programs when the optimization
2859 itself is likely to take inordinate amounts of time.
2863 Make all warnings into errors.
2866 @node Debugging Options
2867 @section Options for Debugging Your Program or GCC
2868 @cindex options, debugging
2869 @cindex debugging information options
2871 GCC has various special options that are used for debugging
2872 either your program or GCC:
2877 Produce debugging information in the operating system's native format
2878 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2881 On most systems that use stabs format, @option{-g} enables use of extra
2882 debugging information that only GDB can use; this extra information
2883 makes debugging work better in GDB but will probably make other debuggers
2885 refuse to read the program. If you want to control for certain whether
2886 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2887 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
2888 or @option{-gvms} (see below).
2890 Unlike most other C compilers, GCC allows you to use @option{-g} with
2891 @option{-O}. The shortcuts taken by optimized code may occasionally
2892 produce surprising results: some variables you declared may not exist
2893 at all; flow of control may briefly move where you did not expect it;
2894 some statements may not be executed because they compute constant
2895 results or their values were already at hand; some statements may
2896 execute in different places because they were moved out of loops.
2898 Nevertheless it proves possible to debug optimized output. This makes
2899 it reasonable to use the optimizer for programs that might have bugs.
2901 The following options are useful when GCC is generated with the
2902 capability for more than one debugging format.
2906 Produce debugging information for use by GDB@. This means to use the
2907 most expressive format available (DWARF 2, stabs, or the native format
2908 if neither of those are supported), including GDB extensions if at all
2913 Produce debugging information in stabs format (if that is supported),
2914 without GDB extensions. This is the format used by DBX on most BSD
2915 systems. On MIPS, Alpha and System V Release 4 systems this option
2916 produces stabs debugging output which is not understood by DBX or SDB@.
2917 On System V Release 4 systems this option requires the GNU assembler.
2921 Produce debugging information in stabs format (if that is supported),
2922 using GNU extensions understood only by the GNU debugger (GDB)@. The
2923 use of these extensions is likely to make other debuggers crash or
2924 refuse to read the program.
2928 Produce debugging information in COFF format (if that is supported).
2929 This is the format used by SDB on most System V systems prior to
2934 Produce debugging information in XCOFF format (if that is supported).
2935 This is the format used by the DBX debugger on IBM RS/6000 systems.
2939 Produce debugging information in XCOFF format (if that is supported),
2940 using GNU extensions understood only by the GNU debugger (GDB)@. The
2941 use of these extensions is likely to make other debuggers crash or
2942 refuse to read the program, and may cause assemblers other than the GNU
2943 assembler (GAS) to fail with an error.
2947 Produce debugging information in DWARF version 1 format (if that is
2948 supported). This is the format used by SDB on most System V Release 4
2951 This option is deprecated.
2955 Produce debugging information in DWARF version 1 format (if that is
2956 supported), using GNU extensions understood only by the GNU debugger
2957 (GDB)@. The use of these extensions is likely to make other debuggers
2958 crash or refuse to read the program.
2960 This option is deprecated.
2964 Produce debugging information in DWARF version 2 format (if that is
2965 supported). This is the format used by DBX on IRIX 6.
2969 Produce debugging information in VMS debug format (if that is
2970 supported). This is the format used by DEBUG on VMS systems.
2973 @itemx -ggdb@var{level}
2974 @itemx -gstabs@var{level}
2975 @itemx -gcoff@var{level}
2976 @itemx -gxcoff@var{level}
2977 @itemx -gvms@var{level}
2978 Request debugging information and also use @var{level} to specify how
2979 much information. The default level is 2.
2981 Level 1 produces minimal information, enough for making backtraces in
2982 parts of the program that you don't plan to debug. This includes
2983 descriptions of functions and external variables, but no information
2984 about local variables and no line numbers.
2986 Level 3 includes extra information, such as all the macro definitions
2987 present in the program. Some debuggers support macro expansion when
2988 you use @option{-g3}.
2990 Note that in order to avoid confusion between DWARF1 debug level 2,
2991 and DWARF2, neither @option{-gdwarf} nor @option{-gdwarf-2} accept
2992 a concatenated debug level. Instead use an additional @option{-g@var{level}}
2993 option to change the debug level for DWARF1 or DWARF2.
2995 @item -feliminate-dwarf2-dups
2996 @opindex feliminate-dwarf2-dups
2997 Compress DWARF2 debugging information by eliminating duplicated
2998 information about each symbol. This option only makes sense when
2999 generating DWARF2 debugging information with @option{-gdwarf-2}.
3001 @cindex @command{prof}
3004 Generate extra code to write profile information suitable for the
3005 analysis program @command{prof}. You must use this option when compiling
3006 the source files you want data about, and you must also use it when
3009 @cindex @command{gprof}
3012 Generate extra code to write profile information suitable for the
3013 analysis program @command{gprof}. You must use this option when compiling
3014 the source files you want data about, and you must also use it when
3019 Makes the compiler print out each function name as it is compiled, and
3020 print some statistics about each pass when it finishes.
3023 @opindex ftime-report
3024 Makes the compiler print some statistics about the time consumed by each
3025 pass when it finishes.
3028 @opindex fmem-report
3029 Makes the compiler print some statistics about permanent memory
3030 allocation when it finishes.
3032 @item -fprofile-arcs
3033 @opindex fprofile-arcs
3034 Add code so that program flow @dfn{arcs} are instrumented. During
3035 execution the program records how many times each branch and call is
3036 executed and how many times it is taken or returns. When the compiled
3037 program exits it saves this data to a file called
3038 @file{@var{auxname}.da} for each source file. The data may be used for
3039 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3040 test coverage analysis (@option{-ftest-coverage}). Each object file's
3041 @var{auxname} is generated from the name of the output file, if
3042 explicitly specified and it is not the final executable, otherwise it is
3043 the basename of the source file. In both cases any suffix is removed
3044 (e.g. @file{foo.da} for input file @file{dir/foo.c}, or
3045 @file{dir/foo.da} for output file specified as @option{-o dir/foo.o}).
3050 Compile the source files with @option{-fprofile-arcs} plus optimization
3051 and code generation options. For test coverage analysis, use the
3052 additional @option{-ftest-coverage} option. You do not need to profile
3053 every source file in a program.
3056 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3057 (the latter implies the former).
3060 Run the program on a representative workload to generate the arc profile
3061 information. This may be repeated any number of times. You can run
3062 concurrent instances of your program, and provided that the file system
3063 supports locking, the data files will be correctly updated. Also
3064 @code{fork} calls are detected and correctly handled (double counting
3068 For profile-directed optimizations, compile the source files again with
3069 the same optimization and code generation options plus
3070 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3071 Control Optimization}).
3074 For test coverage analysis, use @command{gcov} to produce human readable
3075 information from the @file{.bbg} and @file{.da} files. Refer to the
3076 @command{gcov} documentation for further information.
3080 With @option{-fprofile-arcs}, for each function of your program GCC
3081 creates a program flow graph, then finds a spanning tree for the graph.
3082 Only arcs that are not on the spanning tree have to be instrumented: the
3083 compiler adds code to count the number of times that these arcs are
3084 executed. When an arc is the only exit or only entrance to a block, the
3085 instrumentation code can be added to the block; otherwise, a new basic
3086 block must be created to hold the instrumentation code.
3089 @item -ftest-coverage
3090 @opindex ftest-coverage
3091 Produce a graph file that the @command{gcov} code-coverage utility
3092 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3093 show program coverage. Each source file's data file is called
3094 @file{@var{auxname}.bbg}. Refer to the @option{-fprofile-arcs} option
3095 above for a description of @var{auxname} and instructions on how to
3096 generate test coverage data. Coverage data will match the source files
3097 more closely, if you do not optimize.
3099 @item -d@var{letters}
3101 Says to make debugging dumps during compilation at times specified by
3102 @var{letters}. This is used for debugging the compiler. The file names
3103 for most of the dumps are made by appending a pass number and a word to
3104 the @var{dumpname}. @var{dumpname} is generated from the name of the
3105 output file, if explicitly specified and it is not an executable,
3106 otherwise it is the basename of the source file. In both cases any
3107 suffix is removed (e.g. @file{foo.00.rtl} or @file{foo.01.sibling}).
3108 Here are the possible letters for use in @var{letters}, and their
3114 Annotate the assembler output with miscellaneous debugging information.
3117 Dump after computing branch probabilities, to @file{@var{file}.15.bp}.
3120 Dump after block reordering, to @file{@var{file}.31.bbro}.
3123 Dump after instruction combination, to the file @file{@var{file}.21.combine}.
3126 Dump after the first if conversion, to the file @file{@var{file}.16.ce1}.
3127 Also dump after the second if conversion, to the file @file{@var{file}.22.ce2}.
3130 Dump after branch target load optimization, to to @file{@var{file}.33.btl}.
3131 Also dump after delayed branch scheduling, to @file{@var{file}.36.dbr}.
3134 Dump all macro definitions, at the end of preprocessing, in addition to
3138 Dump after SSA optimizations, to @file{@var{file}.04.ssa} and
3139 @file{@var{file}.07.ussa}.
3142 Dump after the second if conversion, to @file{@var{file}.32.ce3}.
3145 Dump after control and data flow analysis, to @file{@var{file}.14.cfg}.
3146 Also dump after life analysis, to @file{@var{file}.20.life}.
3149 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.10.addressof}.
3152 Dump after global register allocation, to @file{@var{file}.26.greg}.
3155 Dump after GCSE, to @file{@var{file}.11.gcse}.
3156 Also dump after jump bypassing and control flow optimizations, to
3157 @file{@var{file}.13.bypass}.
3160 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3163 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3166 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3169 Dump after conversion from registers to stack, to @file{@var{file}.35.stack}.
3172 Dump after local register allocation, to @file{@var{file}.25.lreg}.
3175 Dump after loop optimization passes, to @file{@var{file}.12.loop} and
3176 @file{@var{file}.18.loop2}.
3179 Dump after performing the machine dependent reorganization pass, to
3180 @file{@var{file}.36.mach}.
3183 Dump after register renumbering, to @file{@var{file}.30.rnreg}.
3186 Dump after the register move pass, to @file{@var{file}.23.regmove}.
3189 Dump after post-reload optimizations, to @file{@var{file}.27.postreload}.
3192 Dump after RTL generation, to @file{@var{file}.00.rtl}.
3195 Dump after the second scheduling pass, to @file{@var{file}.34.sched2}.
3198 Dump after CSE (including the jump optimization that sometimes follows
3199 CSE), to @file{@var{file}.09.cse}.
3202 Dump after the first scheduling pass, to @file{@var{file}.24.sched}.
3205 Dump after the second CSE pass (including the jump optimization that
3206 sometimes follows CSE), to @file{@var{file}.19.cse2}.
3209 Dump after running tracer, to @file{@var{file}.17.tracer}.
3212 Dump after null pointer elimination pass to @file{@var{file}.08.null}.
3215 Dump after the second flow pass, to @file{@var{file}.28.flow2}.
3218 Dump after SSA conditional constant propagation, to
3219 @file{@var{file}.05.ssaccp}.
3222 Dump after SSA dead code elimination, to @file{@var{file}.06.ssadce}.
3225 Dump after the peephole pass, to @file{@var{file}.29.peephole2}.
3228 Produce all the dumps listed above.
3231 Produce a core dump whenever an error occurs.
3234 Print statistics on memory usage, at the end of the run, to
3238 Annotate the assembler output with a comment indicating which
3239 pattern and alternative was used. The length of each instruction is
3243 Dump the RTL in the assembler output as a comment before each instruction.
3244 Also turns on @option{-dp} annotation.
3247 For each of the other indicated dump files (except for
3248 @file{@var{file}.00.rtl}), dump a representation of the control flow graph
3249 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3252 Just generate RTL for a function instead of compiling it. Usually used
3256 Dump debugging information during parsing, to standard error.
3259 @item -fdump-unnumbered
3260 @opindex fdump-unnumbered
3261 When doing debugging dumps (see @option{-d} option above), suppress instruction
3262 numbers and line number note output. This makes it more feasible to
3263 use diff on debugging dumps for compiler invocations with different
3264 options, in particular with and without @option{-g}.
3266 @item -fdump-translation-unit @r{(C and C++ only)}
3267 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3268 @opindex fdump-translation-unit
3269 Dump a representation of the tree structure for the entire translation
3270 unit to a file. The file name is made by appending @file{.tu} to the
3271 source file name. If the @samp{-@var{options}} form is used, @var{options}
3272 controls the details of the dump as described for the
3273 @option{-fdump-tree} options.
3275 @item -fdump-class-hierarchy @r{(C++ only)}
3276 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3277 @opindex fdump-class-hierarchy
3278 Dump a representation of each class's hierarchy and virtual function
3279 table layout to a file. The file name is made by appending @file{.class}
3280 to the source file name. If the @samp{-@var{options}} form is used,
3281 @var{options} controls the details of the dump as described for the
3282 @option{-fdump-tree} options.
3284 @item -fdump-tree-@var{switch} @r{(C++ only)}
3285 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3287 Control the dumping at various stages of processing the intermediate
3288 language tree to a file. The file name is generated by appending a switch
3289 specific suffix to the source file name. If the @samp{-@var{options}}
3290 form is used, @var{options} is a list of @samp{-} separated options that
3291 control the details of the dump. Not all options are applicable to all
3292 dumps, those which are not meaningful will be ignored. The following
3293 options are available
3297 Print the address of each node. Usually this is not meaningful as it
3298 changes according to the environment and source file. Its primary use
3299 is for tying up a dump file with a debug environment.
3301 Inhibit dumping of members of a scope or body of a function merely
3302 because that scope has been reached. Only dump such items when they
3303 are directly reachable by some other path.
3305 Turn on all options.
3308 The following tree dumps are possible:
3311 Dump before any tree based optimization, to @file{@var{file}.original}.
3313 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3315 Dump after function inlining, to @file{@var{file}.inlined}.
3318 @item -frandom-seed=@var{string}
3319 @opindex frandom-string
3320 This option provides a seed that GCC uses when it would otherwise use
3321 random numbers. At present, this is used to generate certain symbol names
3322 that have to be different in every compiled file.
3324 The @var{string} should be different for every file you compile.
3326 @item -fsched-verbose=@var{n}
3327 @opindex fsched-verbose
3328 On targets that use instruction scheduling, this option controls the
3329 amount of debugging output the scheduler prints. This information is
3330 written to standard error, unless @option{-dS} or @option{-dR} is
3331 specified, in which case it is output to the usual dump
3332 listing file, @file{.sched} or @file{.sched2} respectively. However
3333 for @var{n} greater than nine, the output is always printed to standard
3336 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3337 same information as @option{-dRS}. For @var{n} greater than one, it
3338 also output basic block probabilities, detailed ready list information
3339 and unit/insn info. For @var{n} greater than two, it includes RTL
3340 at abort point, control-flow and regions info. And for @var{n} over
3341 four, @option{-fsched-verbose} also includes dependence info.
3345 Store the usual ``temporary'' intermediate files permanently; place them
3346 in the current directory and name them based on the source file. Thus,
3347 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3348 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3349 preprocessed @file{foo.i} output file even though the compiler now
3350 normally uses an integrated preprocessor.
3354 Report the CPU time taken by each subprocess in the compilation
3355 sequence. For C source files, this is the compiler proper and assembler
3356 (plus the linker if linking is done). The output looks like this:
3363 The first number on each line is the ``user time,'' that is time spent
3364 executing the program itself. The second number is ``system time,''
3365 time spent executing operating system routines on behalf of the program.
3366 Both numbers are in seconds.
3368 @item -print-file-name=@var{library}
3369 @opindex print-file-name
3370 Print the full absolute name of the library file @var{library} that
3371 would be used when linking---and don't do anything else. With this
3372 option, GCC does not compile or link anything; it just prints the
3375 @item -print-multi-directory
3376 @opindex print-multi-directory
3377 Print the directory name corresponding to the multilib selected by any
3378 other switches present in the command line. This directory is supposed
3379 to exist in @env{GCC_EXEC_PREFIX}.
3381 @item -print-multi-lib
3382 @opindex print-multi-lib
3383 Print the mapping from multilib directory names to compiler switches
3384 that enable them. The directory name is separated from the switches by
3385 @samp{;}, and each switch starts with an @samp{@@} instead of the
3386 @samp{-}, without spaces between multiple switches. This is supposed to
3387 ease shell-processing.
3389 @item -print-prog-name=@var{program}
3390 @opindex print-prog-name
3391 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3393 @item -print-libgcc-file-name
3394 @opindex print-libgcc-file-name
3395 Same as @option{-print-file-name=libgcc.a}.
3397 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3398 but you do want to link with @file{libgcc.a}. You can do
3401 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3404 @item -print-search-dirs
3405 @opindex print-search-dirs
3406 Print the name of the configured installation directory and a list of
3407 program and library directories gcc will search---and don't do anything else.
3409 This is useful when gcc prints the error message
3410 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3411 To resolve this you either need to put @file{cpp0} and the other compiler
3412 components where gcc expects to find them, or you can set the environment
3413 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3414 Don't forget the trailing '/'.
3415 @xref{Environment Variables}.
3418 @opindex dumpmachine
3419 Print the compiler's target machine (for example,
3420 @samp{i686-pc-linux-gnu})---and don't do anything else.
3423 @opindex dumpversion
3424 Print the compiler version (for example, @samp{3.0})---and don't do
3429 Print the compiler's built-in specs---and don't do anything else. (This
3430 is used when GCC itself is being built.) @xref{Spec Files}.
3432 @item -feliminate-unused-debug-types
3433 @opindex feliminate-unused-debug-types
3434 Normally, when producing DWARF2 output, GCC will emit debugging
3435 information for all types declared in a compilation
3436 unit, regardless of whether or not they are actually used
3437 in that compilation unit. Sometimes this is useful, such as
3438 if, in the debugger, you want to cast a value to a type that is
3439 not actually used in your program (but is declared). More often,
3440 however, this results in a significant amount of wasted space.
3441 With this option, GCC will avoid producing debug symbol output
3442 for types that are nowhere used in the source file being compiled.
3445 @node Optimize Options
3446 @section Options That Control Optimization
3447 @cindex optimize options
3448 @cindex options, optimization
3450 These options control various sorts of optimizations.
3452 Without any optimization option, the compiler's goal is to reduce the
3453 cost of compilation and to make debugging produce the expected
3454 results. Statements are independent: if you stop the program with a
3455 breakpoint between statements, you can then assign a new value to any
3456 variable or change the program counter to any other statement in the
3457 function and get exactly the results you would expect from the source
3460 Turning on optimization flags makes the compiler attempt to improve
3461 the performance and/or code size at the expense of compilation time
3462 and possibly the ability to debug the program.
3464 Not all optimizations are controlled directly by a flag. Only
3465 optimizations that have a flag are listed.
3472 Optimize. Optimizing compilation takes somewhat more time, and a lot
3473 more memory for a large function.
3475 With @option{-O}, the compiler tries to reduce code size and execution
3476 time, without performing any optimizations that take a great deal of
3479 @option{-O} turns on the following optimization flags:
3480 @gccoptlist{-fdefer-pop @gol
3481 -fmerge-constants @gol
3483 -floop-optimize @gol
3485 -fif-conversion @gol
3486 -fif-conversion2 @gol
3487 -fdelayed-branch @gol
3488 -fguess-branch-probability @gol
3491 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
3492 where doing so does not interfere with debugging.
3496 Optimize even more. GCC performs nearly all supported optimizations
3497 that do not involve a space-speed tradeoff. The compiler does not
3498 perform loop unrolling or function inlining when you specify @option{-O2}.
3499 As compared to @option{-O}, this option increases both compilation time
3500 and the performance of the generated code.
3502 @option{-O2} turns on all optimization flags specified by @option{-O}. It
3503 also turns on the following optimization flags:
3504 @gccoptlist{-fforce-mem @gol
3505 -foptimize-sibling-calls @gol
3506 -fstrength-reduce @gol
3507 -fcse-follow-jumps -fcse-skip-blocks @gol
3508 -frerun-cse-after-loop -frerun-loop-opt @gol
3509 -fgcse -fgcse-lm -fgcse-sm @gol
3510 -fdelete-null-pointer-checks @gol
3511 -fexpensive-optimizations @gol
3513 -fschedule-insns -fschedule-insns2 @gol
3514 -fsched-interblock -fsched-spec @gol
3517 -freorder-blocks -freorder-functions @gol
3518 -fstrict-aliasing @gol
3519 -falign-functions -falign-jumps @gol
3520 -falign-loops -falign-labels}
3522 Please note the warning under @option{-fgcse} about
3523 invoking @option{-O2} on programs that use computed gotos.
3527 Optimize yet more. @option{-O3} turns on all optimizations specified by
3528 @option{-O2} and also turns on the @option{-finline-functions},
3529 @option{-funit-at-a-time} and @option{-frename-registers} options.
3533 Do not optimize. This is the default.
3537 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3538 do not typically increase code size. It also performs further
3539 optimizations designed to reduce code size.
3541 @option{-Os} disables the following optimization flags:
3542 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
3543 -falign-labels -freorder-blocks -fprefetch-loop-arrays}
3545 If you use multiple @option{-O} options, with or without level numbers,
3546 the last such option is the one that is effective.
3549 Options of the form @option{-f@var{flag}} specify machine-independent
3550 flags. Most flags have both positive and negative forms; the negative
3551 form of @option{-ffoo} would be @option{-fno-foo}. In the table
3552 below, only one of the forms is listed---the one you typically will
3553 use. You can figure out the other form by either removing @samp{no-}
3556 The following options control specific optimizations. They are either
3557 activated by @option{-O} options or are related to ones that are. You
3558 can use the following flags in the rare cases when ``fine-tuning'' of
3559 optimizations to be performed is desired.
3562 @item -fno-default-inline
3563 @opindex fno-default-inline
3564 Do not make member functions inline by default merely because they are
3565 defined inside the class scope (C++ only). Otherwise, when you specify
3566 @w{@option{-O}}, member functions defined inside class scope are compiled
3567 inline by default; i.e., you don't need to add @samp{inline} in front of
3568 the member function name.
3570 @item -fno-defer-pop
3571 @opindex fno-defer-pop
3572 Always pop the arguments to each function call as soon as that function
3573 returns. For machines which must pop arguments after a function call,
3574 the compiler normally lets arguments accumulate on the stack for several
3575 function calls and pops them all at once.
3577 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3581 Force memory operands to be copied into registers before doing
3582 arithmetic on them. This produces better code by making all memory
3583 references potential common subexpressions. When they are not common
3584 subexpressions, instruction combination should eliminate the separate
3587 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3590 @opindex fforce-addr
3591 Force memory address constants to be copied into registers before
3592 doing arithmetic on them. This may produce better code just as
3593 @option{-fforce-mem} may.
3595 @item -fomit-frame-pointer
3596 @opindex fomit-frame-pointer
3597 Don't keep the frame pointer in a register for functions that
3598 don't need one. This avoids the instructions to save, set up and
3599 restore frame pointers; it also makes an extra register available
3600 in many functions. @strong{It also makes debugging impossible on
3603 On some machines, such as the VAX, this flag has no effect, because
3604 the standard calling sequence automatically handles the frame pointer
3605 and nothing is saved by pretending it doesn't exist. The
3606 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3607 whether a target machine supports this flag. @xref{Registers,,Register
3608 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3610 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3612 @item -foptimize-sibling-calls
3613 @opindex foptimize-sibling-calls
3614 Optimize sibling and tail recursive calls.
3616 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3620 Don't pay attention to the @code{inline} keyword. Normally this option
3621 is used to keep the compiler from expanding any functions inline.
3622 Note that if you are not optimizing, no functions can be expanded inline.
3624 @item -finline-functions
3625 @opindex finline-functions
3626 Integrate all simple functions into their callers. The compiler
3627 heuristically decides which functions are simple enough to be worth
3628 integrating in this way.
3630 If all calls to a given function are integrated, and the function is
3631 declared @code{static}, then the function is normally not output as
3632 assembler code in its own right.
3634 Enabled at level @option{-O3}.
3636 @item -finline-limit=@var{n}
3637 @opindex finline-limit
3638 By default, gcc limits the size of functions that can be inlined. This flag
3639 allows the control of this limit for functions that are explicitly marked as
3640 inline (i.e., marked with the inline keyword or defined within the class
3641 definition in c++). @var{n} is the size of functions that can be inlined in
3642 number of pseudo instructions (not counting parameter handling). The default
3643 value of @var{n} is 600.
3644 Increasing this value can result in more inlined code at
3645 the cost of compilation time and memory consumption. Decreasing usually makes
3646 the compilation faster and less code will be inlined (which presumably
3647 means slower programs). This option is particularly useful for programs that
3648 use inlining heavily such as those based on recursive templates with C++.
3650 Inlining is actually controlled by a number of parameters, which may be
3651 specified individually by using @option{--param @var{name}=@var{value}}.
3652 The @option{-finline-limit=@var{n}} option sets some of these parameters
3656 @item max-inline-insns
3658 @item max-inline-insns-single
3659 is set to @var{n}/2.
3660 @item max-inline-insns-auto
3661 is set to @var{n}/2.
3662 @item min-inline-insns
3663 is set to 130 or @var{n}/4, whichever is smaller.
3664 @item max-inline-insns-rtl
3668 Using @option{-finline-limit=600} thus results in the default settings
3669 for these parameters. See below for a documentation of the individual
3670 parameters controlling inlining.
3672 @emph{Note:} pseudo instruction represents, in this particular context, an
3673 abstract measurement of function's size. In no way, it represents a count
3674 of assembly instructions and as such its exact meaning might change from one
3675 release to an another.
3677 @item -fkeep-inline-functions
3678 @opindex fkeep-inline-functions
3679 Even if all calls to a given function are integrated, and the function
3680 is declared @code{static}, nevertheless output a separate run-time
3681 callable version of the function. This switch does not affect
3682 @code{extern inline} functions.
3684 @item -fkeep-static-consts
3685 @opindex fkeep-static-consts
3686 Emit variables declared @code{static const} when optimization isn't turned
3687 on, even if the variables aren't referenced.
3689 GCC enables this option by default. If you want to force the compiler to
3690 check if the variable was referenced, regardless of whether or not
3691 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3693 @item -fmerge-constants
3694 Attempt to merge identical constants (string constants and floating point
3695 constants) across compilation units.
3697 This option is the default for optimized compilation if the assembler and
3698 linker support it. Use @option{-fno-merge-constants} to inhibit this
3701 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3703 @item -fmerge-all-constants
3704 Attempt to merge identical constants and identical variables.
3706 This option implies @option{-fmerge-constants}. In addition to
3707 @option{-fmerge-constants} this considers e.g. even constant initialized
3708 arrays or initialized constant variables with integral or floating point
3709 types. Languages like C or C++ require each non-automatic variable to
3710 have distinct location, so using this option will result in non-conforming
3715 Use a graph coloring register allocator. Currently this option is meant
3716 for testing, so we are interested to hear about miscompilations with
3719 @item -fno-branch-count-reg
3720 @opindex fno-branch-count-reg
3721 Do not use ``decrement and branch'' instructions on a count register,
3722 but instead generate a sequence of instructions that decrement a
3723 register, compare it against zero, then branch based upon the result.
3724 This option is only meaningful on architectures that support such
3725 instructions, which include x86, PowerPC, IA-64 and S/390.
3727 The default is @option{-fbranch-count-reg}, enabled when
3728 @option{-fstrength-reduce} is enabled.
3730 @item -fno-function-cse
3731 @opindex fno-function-cse
3732 Do not put function addresses in registers; make each instruction that
3733 calls a constant function contain the function's address explicitly.
3735 This option results in less efficient code, but some strange hacks
3736 that alter the assembler output may be confused by the optimizations
3737 performed when this option is not used.
3739 The default is @option{-ffunction-cse}
3741 @item -fno-zero-initialized-in-bss
3742 @opindex fno-zero-initialized-in-bss
3743 If the target supports a BSS section, GCC by default puts variables that
3744 are initialized to zero into BSS@. This can save space in the resulting
3747 This option turns off this behavior because some programs explicitly
3748 rely on variables going to the data section. E.g., so that the
3749 resulting executable can find the beginning of that section and/or make
3750 assumptions based on that.
3752 The default is @option{-fzero-initialized-in-bss}.
3754 @item -fstrength-reduce
3755 @opindex fstrength-reduce
3756 Perform the optimizations of loop strength reduction and
3757 elimination of iteration variables.
3759 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3761 @item -fthread-jumps
3762 @opindex fthread-jumps
3763 Perform optimizations where we check to see if a jump branches to a
3764 location where another comparison subsumed by the first is found. If
3765 so, the first branch is redirected to either the destination of the
3766 second branch or a point immediately following it, depending on whether
3767 the condition is known to be true or false.
3769 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3771 @item -fcse-follow-jumps
3772 @opindex fcse-follow-jumps
3773 In common subexpression elimination, scan through jump instructions
3774 when the target of the jump is not reached by any other path. For
3775 example, when CSE encounters an @code{if} statement with an
3776 @code{else} clause, CSE will follow the jump when the condition
3779 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3781 @item -fcse-skip-blocks
3782 @opindex fcse-skip-blocks
3783 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3784 follow jumps which conditionally skip over blocks. When CSE
3785 encounters a simple @code{if} statement with no else clause,
3786 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3787 body of the @code{if}.
3789 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3791 @item -frerun-cse-after-loop
3792 @opindex frerun-cse-after-loop
3793 Re-run common subexpression elimination after loop optimizations has been
3796 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3798 @item -frerun-loop-opt
3799 @opindex frerun-loop-opt
3800 Run the loop optimizer twice.
3802 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3806 Perform a global common subexpression elimination pass.
3807 This pass also performs global constant and copy propagation.
3809 @emph{Note:} When compiling a program using computed gotos, a GCC
3810 extension, you may get better runtime performance if you disable
3811 the global common subexpression elimination pass by adding
3812 @option{-fno-gcse} to the command line.
3814 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3818 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3819 attempt to move loads which are only killed by stores into themselves. This
3820 allows a loop containing a load/store sequence to be changed to a load outside
3821 the loop, and a copy/store within the loop.
3823 Enabled by default when gcse is enabled.
3827 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3828 subexpression elimination. This pass will attempt to move stores out of loops.
3829 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3830 can be changed to a load before the loop and a store after the loop.
3832 Enabled by default when gcse is enabled.
3834 @item -floop-optimize
3835 @opindex floop-optimize
3836 Perform loop optimizations: move constant expressions out of loops, simplify
3837 exit test conditions and optionally do strength-reduction and loop unrolling as
3840 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3842 @item -fcrossjumping
3843 @opindex crossjumping
3844 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
3845 resulting code may or may not perform better than without cross-jumping.
3847 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3849 @item -fif-conversion
3850 @opindex if-conversion
3851 Attempt to transform conditional jumps into branch-less equivalents. This
3852 include use of conditional moves, min, max, set flags and abs instructions, and
3853 some tricks doable by standard arithmetics. The use of conditional execution
3854 on chips where it is available is controlled by @code{if-conversion2}.
3856 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3858 @item -fif-conversion2
3859 @opindex if-conversion2
3860 Use conditional execution (where available) to transform conditional jumps into
3861 branch-less equivalents.
3863 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3865 @item -fdelete-null-pointer-checks
3866 @opindex fdelete-null-pointer-checks
3867 Use global dataflow analysis to identify and eliminate useless checks
3868 for null pointers. The compiler assumes that dereferencing a null
3869 pointer would have halted the program. If a pointer is checked after
3870 it has already been dereferenced, it cannot be null.
3872 In some environments, this assumption is not true, and programs can
3873 safely dereference null pointers. Use
3874 @option{-fno-delete-null-pointer-checks} to disable this optimization
3875 for programs which depend on that behavior.
3877 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3879 @item -fexpensive-optimizations
3880 @opindex fexpensive-optimizations
3881 Perform a number of minor optimizations that are relatively expensive.
3883 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3885 @item -foptimize-register-move
3887 @opindex foptimize-register-move
3889 Attempt to reassign register numbers in move instructions and as
3890 operands of other simple instructions in order to maximize the amount of
3891 register tying. This is especially helpful on machines with two-operand
3894 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3897 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3899 @item -fdelayed-branch
3900 @opindex fdelayed-branch
3901 If supported for the target machine, attempt to reorder instructions
3902 to exploit instruction slots available after delayed branch
3905 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3907 @item -fschedule-insns
3908 @opindex fschedule-insns
3909 If supported for the target machine, attempt to reorder instructions to
3910 eliminate execution stalls due to required data being unavailable. This
3911 helps machines that have slow floating point or memory load instructions
3912 by allowing other instructions to be issued until the result of the load
3913 or floating point instruction is required.
3915 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3917 @item -fschedule-insns2
3918 @opindex fschedule-insns2
3919 Similar to @option{-fschedule-insns}, but requests an additional pass of
3920 instruction scheduling after register allocation has been done. This is
3921 especially useful on machines with a relatively small number of
3922 registers and where memory load instructions take more than one cycle.
3924 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3926 @item -fno-sched-interblock
3927 @opindex fno-sched-interblock
3928 Don't schedule instructions across basic blocks. This is normally
3929 enabled by default when scheduling before register allocation, i.e.@:
3930 with @option{-fschedule-insns} or at @option{-O2} or higher.
3932 @item -fno-sched-spec
3933 @opindex fno-sched-spec
3934 Don't allow speculative motion of non-load instructions. This is normally
3935 enabled by default when scheduling before register allocation, i.e.@:
3936 with @option{-fschedule-insns} or at @option{-O2} or higher.
3938 @item -fsched-spec-load
3939 @opindex fsched-spec-load
3940 Allow speculative motion of some load instructions. This only makes
3941 sense when scheduling before register allocation, i.e.@: with
3942 @option{-fschedule-insns} or at @option{-O2} or higher.
3944 @item -fsched-spec-load-dangerous
3945 @opindex fsched-spec-load-dangerous
3946 Allow speculative motion of more load instructions. This only makes
3947 sense when scheduling before register allocation, i.e.@: with
3948 @option{-fschedule-insns} or at @option{-O2} or higher.
3950 @item -fsched2-use-superblocks
3951 @opindex fsched2-use-superblocks
3952 When schedulilng after register allocation, do use superblock scheduling
3953 algorithm. Superblock scheduling allows motion across basic block boundaries
3954 resulting on faster schedules. This option is experimental, as not all machine
3955 descriptions used by GCC model the CPU closely enough to avoid unreliable
3956 results from the algorithm.
3958 This only makes sense when scheduling after register allocation, i.e.@: with
3959 @option{-fschedule-insns2} or at @option{-O2} or higher.
3961 @item -fsched2-use-traces
3962 @opindex fsched2-use-traces
3963 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
3964 allocation and additionally perform code duplication in order to increase the
3965 size of superblocks using tracer pass. See @option{-ftracer} for details on
3968 This mode should produce faster but significantly longer programs. Also
3969 without @code{-fbranch-probabilities} the traces constructed may not match the
3970 reality and hurt the performance. This only makes
3971 sense when scheduling after register allocation, i.e.@: with
3972 @option{-fschedule-insns2} or at @option{-O2} or higher.
3974 @item -fcaller-saves
3975 @opindex fcaller-saves
3976 Enable values to be allocated in registers that will be clobbered by
3977 function calls, by emitting extra instructions to save and restore the
3978 registers around such calls. Such allocation is done only when it
3979 seems to result in better code than would otherwise be produced.
3981 This option is always enabled by default on certain machines, usually
3982 those which have no call-preserved registers to use instead.
3984 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3986 @item -fmove-all-movables
3987 @opindex fmove-all-movables
3988 Forces all invariant computations in loops to be moved
3991 @item -freduce-all-givs
3992 @opindex freduce-all-givs
3993 Forces all general-induction variables in loops to be
3996 @emph{Note:} When compiling programs written in Fortran,
3997 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
3998 by default when you use the optimizer.
4000 These options may generate better or worse code; results are highly
4001 dependent on the structure of loops within the source code.
4003 These two options are intended to be removed someday, once
4004 they have helped determine the efficacy of various
4005 approaches to improving loop optimizations.
4007 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
4008 know how use of these options affects
4009 the performance of your production code.
4010 We're very interested in code that runs @emph{slower}
4011 when these options are @emph{enabled}.
4014 @itemx -fno-peephole2
4015 @opindex fno-peephole
4016 @opindex fno-peephole2
4017 Disable any machine-specific peephole optimizations. The difference
4018 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4019 are implemented in the compiler; some targets use one, some use the
4020 other, a few use both.
4022 @option{-fpeephole} is enabled by default.
4023 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4025 @item -fno-guess-branch-probability
4026 @opindex fno-guess-branch-probability
4027 Do not guess branch probabilities using a randomized model.
4029 Sometimes gcc will opt to use a randomized model to guess branch
4030 probabilities, when none are available from either profiling feedback
4031 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4032 different runs of the compiler on the same program may produce different
4035 In a hard real-time system, people don't want different runs of the
4036 compiler to produce code that has different behavior; minimizing
4037 non-determinism is of paramount import. This switch allows users to
4038 reduce non-determinism, possibly at the expense of inferior
4041 The default is @option{-fguess-branch-probability} at levels
4042 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4044 @item -freorder-blocks
4045 @opindex freorder-blocks
4046 Reorder basic blocks in the compiled function in order to reduce number of
4047 taken branches and improve code locality.
4049 Enabled at levels @option{-O2}, @option{-O3}.
4051 @item -freorder-functions
4052 @opindex freorder-functions
4053 Reorder basic blocks in the compiled function in order to reduce number of
4054 taken branches and improve code locality. This is implemented by using special
4055 subsections @code{text.hot} for most frequently executed functions and
4056 @code{text.unlikely} for unlikely executed functions. Reordering is done by
4057 the linker so object file format must support named sections and linker must
4058 place them in a reasonable way.
4060 Also profile feedback must be available in to make this option effective. See
4061 @option{-fprofile-arcs} for details.
4063 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4065 @item -fstrict-aliasing
4066 @opindex fstrict-aliasing
4067 Allows the compiler to assume the strictest aliasing rules applicable to
4068 the language being compiled. For C (and C++), this activates
4069 optimizations based on the type of expressions. In particular, an
4070 object of one type is assumed never to reside at the same address as an
4071 object of a different type, unless the types are almost the same. For
4072 example, an @code{unsigned int} can alias an @code{int}, but not a
4073 @code{void*} or a @code{double}. A character type may alias any other
4076 Pay special attention to code like this:
4089 The practice of reading from a different union member than the one most
4090 recently written to (called ``type-punning'') is common. Even with
4091 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4092 is accessed through the union type. So, the code above will work as
4093 expected. However, this code might not:
4104 Every language that wishes to perform language-specific alias analysis
4105 should define a function that computes, given an @code{tree}
4106 node, an alias set for the node. Nodes in different alias sets are not
4107 allowed to alias. For an example, see the C front-end function
4108 @code{c_get_alias_set}.
4110 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4112 @item -falign-functions
4113 @itemx -falign-functions=@var{n}
4114 @opindex falign-functions
4115 Align the start of functions to the next power-of-two greater than
4116 @var{n}, skipping up to @var{n} bytes. For instance,
4117 @option{-falign-functions=32} aligns functions to the next 32-byte
4118 boundary, but @option{-falign-functions=24} would align to the next
4119 32-byte boundary only if this can be done by skipping 23 bytes or less.
4121 @option{-fno-align-functions} and @option{-falign-functions=1} are
4122 equivalent and mean that functions will not be aligned.
4124 Some assemblers only support this flag when @var{n} is a power of two;
4125 in that case, it is rounded up.
4127 If @var{n} is not specified, use a machine-dependent default.
4129 Enabled at levels @option{-O2}, @option{-O3}.
4131 @item -falign-labels
4132 @itemx -falign-labels=@var{n}
4133 @opindex falign-labels
4134 Align all branch targets to a power-of-two boundary, skipping up to
4135 @var{n} bytes like @option{-falign-functions}. This option can easily
4136 make code slower, because it must insert dummy operations for when the
4137 branch target is reached in the usual flow of the code.
4139 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4140 are greater than this value, then their values are used instead.
4142 If @var{n} is not specified, use a machine-dependent default which is
4143 very likely to be @samp{1}, meaning no alignment.
4145 Enabled at levels @option{-O2}, @option{-O3}.
4148 @itemx -falign-loops=@var{n}
4149 @opindex falign-loops
4150 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4151 like @option{-falign-functions}. The hope is that the loop will be
4152 executed many times, which will make up for any execution of the dummy
4155 If @var{n} is not specified, use a machine-dependent default.
4157 Enabled at levels @option{-O2}, @option{-O3}.
4160 @itemx -falign-jumps=@var{n}
4161 @opindex falign-jumps
4162 Align branch targets to a power-of-two boundary, for branch targets
4163 where the targets can only be reached by jumping, skipping up to @var{n}
4164 bytes like @option{-falign-functions}. In this case, no dummy operations
4167 If @var{n} is not specified, use a machine-dependent default.
4169 Enabled at levels @option{-O2}, @option{-O3}.
4171 @item -frename-registers
4172 @opindex frename-registers
4173 Attempt to avoid false dependencies in scheduled code by making use
4174 of registers left over after register allocation. This optimization
4175 will most benefit processors with lots of registers. It can, however,
4176 make debugging impossible, since variables will no longer stay in
4177 a ``home register''.
4179 Enabled at levels @option{-O3}.
4181 @item -fno-cprop-registers
4182 @opindex fno-cprop-registers
4183 After register allocation and post-register allocation instruction splitting,
4184 we perform a copy-propagation pass to try to reduce scheduling dependencies
4185 and occasionally eliminate the copy.
4187 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4191 The following options control compiler behavior regarding floating
4192 point arithmetic. These options trade off between speed and
4193 correctness. All must be specifically enabled.
4197 @opindex ffloat-store
4198 Do not store floating point variables in registers, and inhibit other
4199 options that might change whether a floating point value is taken from a
4202 @cindex floating point precision
4203 This option prevents undesirable excess precision on machines such as
4204 the 68000 where the floating registers (of the 68881) keep more
4205 precision than a @code{double} is supposed to have. Similarly for the
4206 x86 architecture. For most programs, the excess precision does only
4207 good, but a few programs rely on the precise definition of IEEE floating
4208 point. Use @option{-ffloat-store} for such programs, after modifying
4209 them to store all pertinent intermediate computations into variables.
4213 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
4214 @option{-fno-trapping-math}, @option{-ffinite-math-only} and @*
4215 @option{-fno-signaling-nans}.
4217 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
4219 This option should never be turned on by any @option{-O} option since
4220 it can result in incorrect output for programs which depend on
4221 an exact implementation of IEEE or ISO rules/specifications for
4224 @item -fno-math-errno
4225 @opindex fno-math-errno
4226 Do not set ERRNO after calling math functions that are executed
4227 with a single instruction, e.g., sqrt. A program that relies on
4228 IEEE exceptions for math error handling may want to use this flag
4229 for speed while maintaining IEEE arithmetic compatibility.
4231 This option should never be turned on by any @option{-O} option since
4232 it can result in incorrect output for programs which depend on
4233 an exact implementation of IEEE or ISO rules/specifications for
4236 The default is @option{-fmath-errno}.
4238 @item -funsafe-math-optimizations
4239 @opindex funsafe-math-optimizations
4240 Allow optimizations for floating-point arithmetic that (a) assume
4241 that arguments and results are valid and (b) may violate IEEE or
4242 ANSI standards. When used at link-time, it may include libraries
4243 or startup files that change the default FPU control word or other
4244 similar optimizations.
4246 This option should never be turned on by any @option{-O} option since
4247 it can result in incorrect output for programs which depend on
4248 an exact implementation of IEEE or ISO rules/specifications for
4251 The default is @option{-fno-unsafe-math-optimizations}.
4253 @item -ffinite-math-only
4254 @opindex ffinite-math-only
4255 Allow optimizations for floating-point arithmetic that assume
4256 that arguments and results are not NaNs or +-Infs.
4258 This option should never be turned on by any @option{-O} option since
4259 it can result in incorrect output for programs which depend on
4260 an exact implementation of IEEE or ISO rules/specifications.
4262 The default is @option{-fno-finite-math-only}.
4264 @item -fno-trapping-math
4265 @opindex fno-trapping-math
4266 Compile code assuming that floating-point operations cannot generate
4267 user-visible traps. These traps include division by zero, overflow,
4268 underflow, inexact result and invalid operation. This option implies
4269 @option{-fno-signaling-nans}. Setting this option may allow faster
4270 code if one relies on ``non-stop'' IEEE arithmetic, for example.
4272 This option should never be turned on by any @option{-O} option since
4273 it can result in incorrect output for programs which depend on
4274 an exact implementation of IEEE or ISO rules/specifications for
4277 The default is @option{-ftrapping-math}.
4279 @item -fsignaling-nans
4280 @opindex fsignaling-nans
4281 Compile code assuming that IEEE signaling NaNs may generate user-visible
4282 traps during floating-point operations. Setting this option disables
4283 optimizations that may change the number of exceptions visible with
4284 signaling NaNs. This option implies @option{-ftrapping-math}.
4286 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
4289 The default is @option{-fno-signaling-nans}.
4291 This option is experimental and does not currently guarantee to
4292 disable all GCC optimizations that affect signaling NaN behavior.
4294 @item -fsingle-precision-constant
4295 @opindex fsingle-precision-constant
4296 Treat floating point constant as single precision constant instead of
4297 implicitly converting it to double precision constant.
4302 The following options control optimizations that may improve
4303 performance, but are not enabled by any @option{-O} options. This
4304 section includes experimental options that may produce broken code.
4307 @item -fbranch-probabilities
4308 @opindex fbranch-probabilities
4309 After running a program compiled with @option{-fprofile-arcs}
4310 (@pxref{Debugging Options,, Options for Debugging Your Program or
4311 @command{gcc}}), you can compile it a second time using
4312 @option{-fbranch-probabilities}, to improve optimizations based on
4313 the number of times each branch was taken. When the program
4314 compiled with @option{-fprofile-arcs} exits it saves arc execution
4315 counts to a file called @file{@var{sourcename}.da} for each source
4316 file The information in this data file is very dependent on the
4317 structure of the generated code, so you must use the same source code
4318 and the same optimization options for both compilations.
4320 With @option{-fbranch-probabilities}, GCC puts a
4321 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
4322 These can be used to improve optimization. Currently, they are only
4323 used in one place: in @file{reorg.c}, instead of guessing which path a
4324 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
4325 exactly determine which path is taken more often.
4329 Use a graph coloring register allocator. Currently this option is meant
4330 for testing, so we are interested to hear about miscompilations with
4335 Perform tail duplication to enlarge superblock size. This transformation
4336 simplifies the control flow of the function allowing other optimizations to do
4339 @item -funit-at-a-time
4340 @opindex funit-at-a-time
4341 Parse the whole compilation unit before starting to produce code. This allows some
4342 extra optimizations to take place but consumes more memory.
4344 @item -funroll-loops
4345 @opindex funroll-loops
4346 Unroll loops whose number of iterations can be determined at compile time or
4347 upon entry to the loop. @option{-funroll-loops} implies
4348 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
4349 (i.e. complete removal of loops with small constant number of iterations).
4350 This option makes code larger, and may or may not make it run faster.
4352 @item -funroll-all-loops
4353 @opindex funroll-all-loops
4354 Unroll all loops, even if their number of iterations is uncertain when
4355 the loop is entered. This usually makes programs run more slowly.
4356 @option{-funroll-all-loops} implies the same options as
4357 @option{-funroll-loops}.
4360 @opindex fpeel-loops
4361 Peels the loops for that there is enough information that they do not
4362 roll much (from profile feedback). It also turns on complete loop peeling
4363 (i.e. complete removal of loops with small constant number of iterations).
4365 @item -funswitch-loops
4366 @opindex funswitch-loops
4367 Move branches with loop invariant conditions out of the loop, with duplicates
4368 of the loop on both branches (modified according to result of the condition).
4370 @item -fold-unroll-loops
4371 @opindex fold-unroll-loops
4372 Unroll loops whose number of iterations can be determined at compile
4373 time or upon entry to the loop, using the old loop unroller whose loop
4374 recognition is based on notes from frontend. @option{-fold-unroll-loops} implies
4375 both @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4376 option makes code larger, and may or may not make it run faster.
4378 @item -fold-unroll-all-loops
4379 @opindex fold-unroll-all-loops
4380 Unroll all loops, even if their number of iterations is uncertain when
4381 the loop is entered. This is done using the old loop unroller whose loop
4382 recognition is based on notes from frontend. This usually makes programs run more slowly.
4383 @option{-fold-unroll-all-loops} implies the same options as
4384 @option{-fold-unroll-loops}.
4386 @item -funswitch-loops
4387 @opindex funswitch-loops
4388 Move branches with loop invariant conditions out of the loop, with duplicates
4389 of the loop on both branches (modified according to result of the condition).
4391 @item -funswitch-loops
4392 @opindex funswitch-loops
4393 Move branches with loop invariant conditions out of the loop, with duplicates
4394 of the loop on both branches (modified according to result of the condition).
4396 @item -fprefetch-loop-arrays
4397 @opindex fprefetch-loop-arrays
4398 If supported by the target machine, generate instructions to prefetch
4399 memory to improve the performance of loops that access large arrays.
4401 Disabled at level @option{-Os}.
4403 @item -ffunction-sections
4404 @itemx -fdata-sections
4405 @opindex ffunction-sections
4406 @opindex fdata-sections
4407 Place each function or data item into its own section in the output
4408 file if the target supports arbitrary sections. The name of the
4409 function or the name of the data item determines the section's name
4412 Use these options on systems where the linker can perform optimizations
4413 to improve locality of reference in the instruction space. Most systems
4414 using the ELF object format and SPARC processors running Solaris 2 have
4415 linkers with such optimizations. AIX may have these optimizations in
4418 Only use these options when there are significant benefits from doing
4419 so. When you specify these options, the assembler and linker will
4420 create larger object and executable files and will also be slower.
4421 You will not be able to use @code{gprof} on all systems if you
4422 specify this option and you may have problems with debugging if
4423 you specify both this option and @option{-g}.
4427 Perform optimizations in static single assignment form. Each function's
4428 flow graph is translated into SSA form, optimizations are performed, and
4429 the flow graph is translated back from SSA form. Users should not
4430 specify this option, since it is not yet ready for production use.
4434 Perform Sparse Conditional Constant Propagation in SSA form. Requires
4435 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
4439 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
4440 Like @option{-fssa}, this is an experimental feature.
4442 @item -fbranch-target-load-optimize
4443 @opindex fbranch-target-load-optimize
4444 Perform branch target register load optimization before prologue / epilogue
4446 The use of target registers can typically be exposed only during reload,
4447 thus hoisting loads out of loops and doing inter-block scheduling needs
4448 a separate optimization pass.
4450 @item -fbranch-target-load-optimize2
4451 @opindex fbranch-target-load-optimize2
4452 Perform branch target register load optimization after prologue / epilogue
4458 @item --param @var{name}=@var{value}
4460 In some places, GCC uses various constants to control the amount of
4461 optimization that is done. For example, GCC will not inline functions
4462 that contain more that a certain number of instructions. You can
4463 control some of these constants on the command-line using the
4464 @option{--param} option.
4466 In each case, the @var{value} is an integer. The allowable choices for
4467 @var{name} are given in the following table:
4470 @item max-crossjump-edges
4471 The maximum number of incoming edges to consider for crossjumping.
4472 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
4473 the number of edges incoming to each block. Increasing values mean
4474 more aggressive optimization, making the compile time increase with
4475 probably small improvement in executable size.
4477 @item max-delay-slot-insn-search
4478 The maximum number of instructions to consider when looking for an
4479 instruction to fill a delay slot. If more than this arbitrary number of
4480 instructions is searched, the time savings from filling the delay slot
4481 will be minimal so stop searching. Increasing values mean more
4482 aggressive optimization, making the compile time increase with probably
4483 small improvement in executable run time.
4485 @item max-delay-slot-live-search
4486 When trying to fill delay slots, the maximum number of instructions to
4487 consider when searching for a block with valid live register
4488 information. Increasing this arbitrarily chosen value means more
4489 aggressive optimization, increasing the compile time. This parameter
4490 should be removed when the delay slot code is rewritten to maintain the
4493 @item max-gcse-memory
4494 The approximate maximum amount of memory that will be allocated in
4495 order to perform the global common subexpression elimination
4496 optimization. If more memory than specified is required, the
4497 optimization will not be done.
4499 @item max-gcse-passes
4500 The maximum number of passes of GCSE to run.
4502 @item max-pending-list-length
4503 The maximum number of pending dependencies scheduling will allow
4504 before flushing the current state and starting over. Large functions
4505 with few branches or calls can create excessively large lists which
4506 needlessly consume memory and resources.
4508 @item max-inline-insns-single
4509 Several parameters control the tree inliner used in gcc.
4510 This number sets the maximum number of instructions (counted in gcc's
4511 internal representation) in a single function that the tree inliner
4512 will consider for inlining. This only affects functions declared
4513 inline and methods implemented in a class declaration (C++).
4514 The default value is 300.
4516 @item max-inline-insns-auto
4517 When you use @option{-finline-functions} (included in @option{-O3}),
4518 a lot of functions that would otherwise not be considered for inlining
4519 by the compiler will be investigated. To those functions, a different
4520 (more restrictive) limit compared to functions declared inline can
4522 The default value is 300.
4524 @item max-inline-insns
4525 The tree inliner does decrease the allowable size for single functions
4526 to be inlined after we already inlined the number of instructions
4527 given here by repeated inlining. This number should be a factor of
4528 two or more larger than the single function limit.
4529 Higher numbers result in better runtime performance, but incur higher
4530 compile-time resource (CPU time, memory) requirements and result in
4531 larger binaries. Very high values are not advisable, as too large
4532 binaries may adversely affect runtime performance.
4533 The default value is 600.
4535 @item max-inline-slope
4536 After exceeding the maximum number of inlined instructions by repeated
4537 inlining, a linear function is used to decrease the allowable size
4538 for single functions. The slope of that function is the negative
4539 reciprocal of the number specified here.
4540 The default value is 32.
4542 @item min-inline-insns
4543 The repeated inlining is throttled more and more by the linear function
4544 after exceeding the limit. To avoid too much throttling, a minimum for
4545 this function is specified here to allow repeated inlining for very small
4546 functions even when a lot of repeated inlining already has been done.
4547 The default value is 130.
4549 @item max-inline-insns-rtl
4550 For languages that use the RTL inliner (this happens at a later stage
4551 than tree inlining), you can set the maximum allowable size (counted
4552 in RTL instructions) for the RTL inliner with this parameter.
4553 The default value is 600.
4556 @item max-unrolled-insns
4557 The maximum number of instructions that a loop should have if that loop
4558 is unrolled, and if the loop is unrolled, it determines how many times
4559 the loop code is unrolled.
4561 @item max-average-unrolled-insns
4562 The maximum number of instructions biased by probabilities of their execution
4563 that a loop should have if that loop is unrolled, and if the loop is unrolled,
4564 it determines how many times the loop code is unrolled.
4566 @item max-unroll-times
4567 The maximum number of unrollings of a single loop.
4569 @item max-peeled-insns
4570 The maximum number of instructions that a loop should have if that loop
4571 is peeled, and if the loop is peeled, it determines how many times
4572 the loop code is peeled.
4574 @item max-peel-times
4575 The maximum number of peelings of a single loop.
4577 @item max-completely-peeled-insns
4578 The maximum number of insns of a completely peeled loop.
4580 @item max-completely-peel-times
4581 The maximum number of iterations of a loop to be suitable for complete peeling.
4583 @item max-unswitch-insns
4584 The maximum number of insns of an unswitched loop.
4586 @item max-unswitch-level
4587 The maximum number of branches unswitched in a single loop.
4589 @item hot-bb-count-fraction
4590 Select fraction of the maximal count of repetitions of basic block in program
4591 given basic block needs to have to be considered hot.
4593 @item hot-bb-frequency-fraction
4594 Select fraction of the maximal frequency of executions of basic block in
4595 function given basic block needs to have to be considered hot
4597 @item tracer-dynamic-coverage
4598 @itemx tracer-dynamic-coverage-feedback
4600 This value is used to limit superblock formation once the given percentage of
4601 executed instructions is covered. This limits unnecessary code size
4604 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4605 feedback is available. The real profiles (as opposed to statically estimated
4606 ones) are much less balanced allowing the threshold to be larger value.
4608 @item tracer-max-code-growth
4609 Stop tail duplication once code growth has reached given percentage. This is
4610 rather hokey argument, as most of the duplicates will be eliminated later in
4611 cross jumping, so it may be set to much higher values than is the desired code
4614 @item tracer-min-branch-ratio
4616 Stop reverse growth when the reverse probability of best edge is less than this
4617 threshold (in percent).
4619 @item tracer-min-branch-ratio
4620 @itemx tracer-min-branch-ratio-feedback
4622 Stop forward growth if the best edge do have probability lower than this
4625 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
4626 compilation for profile feedback and one for compilation without. The value
4627 for compilation with profile feedback needs to be more conservative (higher) in
4628 order to make tracer effective.
4630 @item max-cse-path-length
4632 Maximum number of basic blocks on path that cse considers.
4634 @item ggc-min-expand
4636 GCC uses a garbage collector to manage its own memory allocation. This
4637 parameter specifies the minimum percentage by which the garbage
4638 collector's heap should be allowed to expand between collections.
4639 Tuning this may improve compilation speed; it has no effect on code
4642 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
4643 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
4644 the smallest of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If
4645 GCC is not able to calculate RAM on a particular platform, the lower
4646 bound of 30% is used. Setting this parameter and
4647 @option{ggc-min-heapsize} to zero causes a full collection to occur at
4648 every opportunity. This is extremely slow, but can be useful for
4651 @item ggc-min-heapsize
4653 Minimum size of the garbage collector's heap before it begins bothering
4654 to collect garbage. The first collection occurs after the heap expands
4655 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
4656 tuning this may improve compilation speed, and has no effect on code
4659 The default is RAM/8, with a lower bound of 4096 (four megabytes) and an
4660 upper bound of 131072 (128 megabytes). If @code{getrlimit} is
4661 available, the notion of "RAM" is the smallest of actual RAM,
4662 RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If GCC is not able to calculate
4663 RAM on a particular platform, the lower bound is used. Setting this
4664 parameter very large effectively disables garbage collection. Setting
4665 this parameter and @option{ggc-min-expand} to zero causes a full
4666 collection to occur at every opportunity.
4668 @item reorder-blocks-duplicate
4669 @itemx reorder-blocks-duplicate-feedback
4671 Used by basic block reordering pass to decide whether to use unconditional
4672 branch or duplicate the code on it's destination. Code is duplicated when it's
4673 estimated size is smaller than this value multiplied by the estimated size of
4674 unconditional jump in the hot spots of the program.
4676 The @option{reorder-block-duplicate-feedback} is used only when profile
4677 feedback is available and may be set to higher values than
4678 @option{reorder-block-duplicate} since information about the hot spots is more
4683 @node Preprocessor Options
4684 @section Options Controlling the Preprocessor
4685 @cindex preprocessor options
4686 @cindex options, preprocessor
4688 These options control the C preprocessor, which is run on each C source
4689 file before actual compilation.
4691 If you use the @option{-E} option, nothing is done except preprocessing.
4692 Some of these options make sense only together with @option{-E} because
4693 they cause the preprocessor output to be unsuitable for actual
4698 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4699 and pass @var{option} directly through to the preprocessor. If
4700 @var{option} contains commas, it is split into multiple options at the
4701 commas. However, many options are modified, translated or interpreted
4702 by the compiler driver before being passed to the preprocessor, and
4703 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4704 interface is undocumented and subject to change, so whenever possible
4705 you should avoid using @option{-Wp} and let the driver handle the
4708 @item -Xpreprocessor @var{option}
4709 @opindex preprocessor
4710 Pass @var{option} as an option to the preprocessor. You can use this to
4711 supply system-specific preprocessor options which GCC does not know how to
4714 If you want to pass an option that takes an argument, you must use
4715 @option{-Xpreprocessor} twice, once for the option and once for the argument.
4718 @include cppopts.texi
4720 @node Assembler Options
4721 @section Passing Options to the Assembler
4723 @c prevent bad page break with this line
4724 You can pass options to the assembler.
4727 @item -Wa,@var{option}
4729 Pass @var{option} as an option to the assembler. If @var{option}
4730 contains commas, it is split into multiple options at the commas.
4732 @item -Xassembler @var{option}
4734 Pass @var{option} as an option to the assembler. You can use this to
4735 supply system-specific assembler options which GCC does not know how to
4738 If you want to pass an option that takes an argument, you must use
4739 @option{-Xassembler} twice, once for the option and once for the argument.
4744 @section Options for Linking
4745 @cindex link options
4746 @cindex options, linking
4748 These options come into play when the compiler links object files into
4749 an executable output file. They are meaningless if the compiler is
4750 not doing a link step.
4754 @item @var{object-file-name}
4755 A file name that does not end in a special recognized suffix is
4756 considered to name an object file or library. (Object files are
4757 distinguished from libraries by the linker according to the file
4758 contents.) If linking is done, these object files are used as input
4767 If any of these options is used, then the linker is not run, and
4768 object file names should not be used as arguments. @xref{Overall
4772 @item -l@var{library}
4773 @itemx -l @var{library}
4775 Search the library named @var{library} when linking. (The second
4776 alternative with the library as a separate argument is only for
4777 POSIX compliance and is not recommended.)
4779 It makes a difference where in the command you write this option; the
4780 linker searches and processes libraries and object files in the order they
4781 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4782 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4783 to functions in @samp{z}, those functions may not be loaded.
4785 The linker searches a standard list of directories for the library,
4786 which is actually a file named @file{lib@var{library}.a}. The linker
4787 then uses this file as if it had been specified precisely by name.
4789 The directories searched include several standard system directories
4790 plus any that you specify with @option{-L}.
4792 Normally the files found this way are library files---archive files
4793 whose members are object files. The linker handles an archive file by
4794 scanning through it for members which define symbols that have so far
4795 been referenced but not defined. But if the file that is found is an
4796 ordinary object file, it is linked in the usual fashion. The only
4797 difference between using an @option{-l} option and specifying a file name
4798 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4799 and searches several directories.
4803 You need this special case of the @option{-l} option in order to
4804 link an Objective-C program.
4807 @opindex nostartfiles
4808 Do not use the standard system startup files when linking.
4809 The standard system libraries are used normally, unless @option{-nostdlib}
4810 or @option{-nodefaultlibs} is used.
4812 @item -nodefaultlibs
4813 @opindex nodefaultlibs
4814 Do not use the standard system libraries when linking.
4815 Only the libraries you specify will be passed to the linker.
4816 The standard startup files are used normally, unless @option{-nostartfiles}
4817 is used. The compiler may generate calls to memcmp, memset, and memcpy
4818 for System V (and ISO C) environments or to bcopy and bzero for
4819 BSD environments. These entries are usually resolved by entries in
4820 libc. These entry points should be supplied through some other
4821 mechanism when this option is specified.
4825 Do not use the standard system startup files or libraries when linking.
4826 No startup files and only the libraries you specify will be passed to
4827 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4828 for System V (and ISO C) environments or to bcopy and bzero for
4829 BSD environments. These entries are usually resolved by entries in
4830 libc. These entry points should be supplied through some other
4831 mechanism when this option is specified.
4833 @cindex @option{-lgcc}, use with @option{-nostdlib}
4834 @cindex @option{-nostdlib} and unresolved references
4835 @cindex unresolved references and @option{-nostdlib}
4836 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4837 @cindex @option{-nodefaultlibs} and unresolved references
4838 @cindex unresolved references and @option{-nodefaultlibs}
4839 One of the standard libraries bypassed by @option{-nostdlib} and
4840 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4841 that GCC uses to overcome shortcomings of particular machines, or special
4842 needs for some languages.
4843 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
4844 Collection (GCC) Internals},
4845 for more discussion of @file{libgcc.a}.)
4846 In most cases, you need @file{libgcc.a} even when you want to avoid
4847 other standard libraries. In other words, when you specify @option{-nostdlib}
4848 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4849 This ensures that you have no unresolved references to internal GCC
4850 library subroutines. (For example, @samp{__main}, used to ensure C++
4851 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
4852 GNU Compiler Collection (GCC) Internals}.)
4856 Produce a position independent executable on targets which support it.
4857 For predictable results, you must also specify the same set of options
4858 that were used to generate code (@option{-fpie}, @option{-fPIE},
4859 or model suboptions) when you specify this option.
4863 Remove all symbol table and relocation information from the executable.
4867 On systems that support dynamic linking, this prevents linking with the shared
4868 libraries. On other systems, this option has no effect.
4872 Produce a shared object which can then be linked with other objects to
4873 form an executable. Not all systems support this option. For predictable
4874 results, you must also specify the same set of options that were used to
4875 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4876 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4877 needs to build supplementary stub code for constructors to work. On
4878 multi-libbed systems, @samp{gcc -shared} must select the correct support
4879 libraries to link against. Failing to supply the correct flags may lead
4880 to subtle defects. Supplying them in cases where they are not necessary
4883 @item -shared-libgcc
4884 @itemx -static-libgcc
4885 @opindex shared-libgcc
4886 @opindex static-libgcc
4887 On systems that provide @file{libgcc} as a shared library, these options
4888 force the use of either the shared or static version respectively.
4889 If no shared version of @file{libgcc} was built when the compiler was
4890 configured, these options have no effect.
4892 There are several situations in which an application should use the
4893 shared @file{libgcc} instead of the static version. The most common
4894 of these is when the application wishes to throw and catch exceptions
4895 across different shared libraries. In that case, each of the libraries
4896 as well as the application itself should use the shared @file{libgcc}.
4898 Therefore, the G++ and GCJ drivers automatically add
4899 @option{-shared-libgcc} whenever you build a shared library or a main
4900 executable, because C++ and Java programs typically use exceptions, so
4901 this is the right thing to do.
4903 If, instead, you use the GCC driver to create shared libraries, you may
4904 find that they will not always be linked with the shared @file{libgcc}.
4905 If GCC finds, at its configuration time, that you have a GNU linker that
4906 does not support option @option{--eh-frame-hdr}, it will link the shared
4907 version of @file{libgcc} into shared libraries by default. Otherwise,
4908 it will take advantage of the linker and optimize away the linking with
4909 the shared version of @file{libgcc}, linking with the static version of
4910 libgcc by default. This allows exceptions to propagate through such
4911 shared libraries, without incurring relocation costs at library load
4914 However, if a library or main executable is supposed to throw or catch
4915 exceptions, you must link it using the G++ or GCJ driver, as appropriate
4916 for the languages used in the program, or using the option
4917 @option{-shared-libgcc}, such that it is linked with the shared
4922 Bind references to global symbols when building a shared object. Warn
4923 about any unresolved references (unless overridden by the link editor
4924 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4927 @item -Xlinker @var{option}
4929 Pass @var{option} as an option to the linker. You can use this to
4930 supply system-specific linker options which GCC does not know how to
4933 If you want to pass an option that takes an argument, you must use
4934 @option{-Xlinker} twice, once for the option and once for the argument.
4935 For example, to pass @option{-assert definitions}, you must write
4936 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4937 @option{-Xlinker "-assert definitions"}, because this passes the entire
4938 string as a single argument, which is not what the linker expects.
4940 @item -Wl,@var{option}
4942 Pass @var{option} as an option to the linker. If @var{option} contains
4943 commas, it is split into multiple options at the commas.
4945 @item -u @var{symbol}
4947 Pretend the symbol @var{symbol} is undefined, to force linking of
4948 library modules to define it. You can use @option{-u} multiple times with
4949 different symbols to force loading of additional library modules.
4952 @node Directory Options
4953 @section Options for Directory Search
4954 @cindex directory options
4955 @cindex options, directory search
4958 These options specify directories to search for header files, for
4959 libraries and for parts of the compiler:
4964 Add the directory @var{dir} to the head of the list of directories to be
4965 searched for header files. This can be used to override a system header
4966 file, substituting your own version, since these directories are
4967 searched before the system header file directories. However, you should
4968 not use this option to add directories that contain vendor-supplied
4969 system header files (use @option{-isystem} for that). If you use more than
4970 one @option{-I} option, the directories are scanned in left-to-right
4971 order; the standard system directories come after.
4973 If a standard system include directory, or a directory specified with
4974 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
4975 option will be ignored. The directory will still be searched but as a
4976 system directory at its normal position in the system include chain.
4977 This is to ensure that GCC's procedure to fix buggy system headers and
4978 the ordering for the include_next directive are not inadvertently changed.
4979 If you really need to change the search order for system directories,
4980 use the @option{-nostdinc} and/or @option{-isystem} options.
4984 Any directories you specify with @option{-I} options before the @option{-I-}
4985 option are searched only for the case of @samp{#include "@var{file}"};
4986 they are not searched for @samp{#include <@var{file}>}.
4988 If additional directories are specified with @option{-I} options after
4989 the @option{-I-}, these directories are searched for all @samp{#include}
4990 directives. (Ordinarily @emph{all} @option{-I} directories are used
4993 In addition, the @option{-I-} option inhibits the use of the current
4994 directory (where the current input file came from) as the first search
4995 directory for @samp{#include "@var{file}"}. There is no way to
4996 override this effect of @option{-I-}. With @option{-I.} you can specify
4997 searching the directory which was current when the compiler was
4998 invoked. That is not exactly the same as what the preprocessor does
4999 by default, but it is often satisfactory.
5001 @option{-I-} does not inhibit the use of the standard system directories
5002 for header files. Thus, @option{-I-} and @option{-nostdinc} are
5007 Add directory @var{dir} to the list of directories to be searched
5010 @item -B@var{prefix}
5012 This option specifies where to find the executables, libraries,
5013 include files, and data files of the compiler itself.
5015 The compiler driver program runs one or more of the subprograms
5016 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5017 @var{prefix} as a prefix for each program it tries to run, both with and
5018 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5020 For each subprogram to be run, the compiler driver first tries the
5021 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5022 was not specified, the driver tries two standard prefixes, which are
5023 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of
5024 those results in a file name that is found, the unmodified program
5025 name is searched for using the directories specified in your
5026 @env{PATH} environment variable.
5028 The compiler will check to see if the path provided by the @option{-B}
5029 refers to a directory, and if necessary it will add a directory
5030 separator character at the end of the path.
5032 @option{-B} prefixes that effectively specify directory names also apply
5033 to libraries in the linker, because the compiler translates these
5034 options into @option{-L} options for the linker. They also apply to
5035 includes files in the preprocessor, because the compiler translates these
5036 options into @option{-isystem} options for the preprocessor. In this case,
5037 the compiler appends @samp{include} to the prefix.
5039 The run-time support file @file{libgcc.a} can also be searched for using
5040 the @option{-B} prefix, if needed. If it is not found there, the two
5041 standard prefixes above are tried, and that is all. The file is left
5042 out of the link if it is not found by those means.
5044 Another way to specify a prefix much like the @option{-B} prefix is to use
5045 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5048 As a special kludge, if the path provided by @option{-B} is
5049 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5050 9, then it will be replaced by @file{[dir/]include}. This is to help
5051 with boot-strapping the compiler.
5053 @item -specs=@var{file}
5055 Process @var{file} after the compiler reads in the standard @file{specs}
5056 file, in order to override the defaults that the @file{gcc} driver
5057 program uses when determining what switches to pass to @file{cc1},
5058 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5059 @option{-specs=@var{file}} can be specified on the command line, and they
5060 are processed in order, from left to right.
5066 @section Specifying subprocesses and the switches to pass to them
5069 @command{gcc} is a driver program. It performs its job by invoking a
5070 sequence of other programs to do the work of compiling, assembling and
5071 linking. GCC interprets its command-line parameters and uses these to
5072 deduce which programs it should invoke, and which command-line options
5073 it ought to place on their command lines. This behavior is controlled
5074 by @dfn{spec strings}. In most cases there is one spec string for each
5075 program that GCC can invoke, but a few programs have multiple spec
5076 strings to control their behavior. The spec strings built into GCC can
5077 be overridden by using the @option{-specs=} command-line switch to specify
5080 @dfn{Spec files} are plaintext files that are used to construct spec
5081 strings. They consist of a sequence of directives separated by blank
5082 lines. The type of directive is determined by the first non-whitespace
5083 character on the line and it can be one of the following:
5086 @item %@var{command}
5087 Issues a @var{command} to the spec file processor. The commands that can
5091 @item %include <@var{file}>
5093 Search for @var{file} and insert its text at the current point in the
5096 @item %include_noerr <@var{file}>
5097 @cindex %include_noerr
5098 Just like @samp{%include}, but do not generate an error message if the include
5099 file cannot be found.
5101 @item %rename @var{old_name} @var{new_name}
5103 Rename the spec string @var{old_name} to @var{new_name}.
5107 @item *[@var{spec_name}]:
5108 This tells the compiler to create, override or delete the named spec
5109 string. All lines after this directive up to the next directive or
5110 blank line are considered to be the text for the spec string. If this
5111 results in an empty string then the spec will be deleted. (Or, if the
5112 spec did not exist, then nothing will happened.) Otherwise, if the spec
5113 does not currently exist a new spec will be created. If the spec does
5114 exist then its contents will be overridden by the text of this
5115 directive, unless the first character of that text is the @samp{+}
5116 character, in which case the text will be appended to the spec.
5118 @item [@var{suffix}]:
5119 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
5120 and up to the next directive or blank line are considered to make up the
5121 spec string for the indicated suffix. When the compiler encounters an
5122 input file with the named suffix, it will processes the spec string in
5123 order to work out how to compile that file. For example:
5130 This says that any input file whose name ends in @samp{.ZZ} should be
5131 passed to the program @samp{z-compile}, which should be invoked with the
5132 command-line switch @option{-input} and with the result of performing the
5133 @samp{%i} substitution. (See below.)
5135 As an alternative to providing a spec string, the text that follows a
5136 suffix directive can be one of the following:
5139 @item @@@var{language}
5140 This says that the suffix is an alias for a known @var{language}. This is
5141 similar to using the @option{-x} command-line switch to GCC to specify a
5142 language explicitly. For example:
5149 Says that .ZZ files are, in fact, C++ source files.
5152 This causes an error messages saying:
5155 @var{name} compiler not installed on this system.
5159 GCC already has an extensive list of suffixes built into it.
5160 This directive will add an entry to the end of the list of suffixes, but
5161 since the list is searched from the end backwards, it is effectively
5162 possible to override earlier entries using this technique.
5166 GCC has the following spec strings built into it. Spec files can
5167 override these strings or create their own. Note that individual
5168 targets can also add their own spec strings to this list.
5171 asm Options to pass to the assembler
5172 asm_final Options to pass to the assembler post-processor
5173 cpp Options to pass to the C preprocessor
5174 cc1 Options to pass to the C compiler
5175 cc1plus Options to pass to the C++ compiler
5176 endfile Object files to include at the end of the link
5177 link Options to pass to the linker
5178 lib Libraries to include on the command line to the linker
5179 libgcc Decides which GCC support library to pass to the linker
5180 linker Sets the name of the linker
5181 predefines Defines to be passed to the C preprocessor
5182 signed_char Defines to pass to CPP to say whether @code{char} is signed
5184 startfile Object files to include at the start of the link
5187 Here is a small example of a spec file:
5193 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
5196 This example renames the spec called @samp{lib} to @samp{old_lib} and
5197 then overrides the previous definition of @samp{lib} with a new one.
5198 The new definition adds in some extra command-line options before
5199 including the text of the old definition.
5201 @dfn{Spec strings} are a list of command-line options to be passed to their
5202 corresponding program. In addition, the spec strings can contain
5203 @samp{%}-prefixed sequences to substitute variable text or to
5204 conditionally insert text into the command line. Using these constructs
5205 it is possible to generate quite complex command lines.
5207 Here is a table of all defined @samp{%}-sequences for spec
5208 strings. Note that spaces are not generated automatically around the
5209 results of expanding these sequences. Therefore you can concatenate them
5210 together or combine them with constant text in a single argument.
5214 Substitute one @samp{%} into the program name or argument.
5217 Substitute the name of the input file being processed.
5220 Substitute the basename of the input file being processed.
5221 This is the substring up to (and not including) the last period
5222 and not including the directory.
5225 This is the same as @samp{%b}, but include the file suffix (text after
5229 Marks the argument containing or following the @samp{%d} as a
5230 temporary file name, so that that file will be deleted if GCC exits
5231 successfully. Unlike @samp{%g}, this contributes no text to the
5234 @item %g@var{suffix}
5235 Substitute a file name that has suffix @var{suffix} and is chosen
5236 once per compilation, and mark the argument in the same way as
5237 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
5238 name is now chosen in a way that is hard to predict even when previously
5239 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
5240 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
5241 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
5242 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
5243 was simply substituted with a file name chosen once per compilation,
5244 without regard to any appended suffix (which was therefore treated
5245 just like ordinary text), making such attacks more likely to succeed.
5247 @item %u@var{suffix}
5248 Like @samp{%g}, but generates a new temporary file name even if
5249 @samp{%u@var{suffix}} was already seen.
5251 @item %U@var{suffix}
5252 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
5253 new one if there is no such last file name. In the absence of any
5254 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
5255 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
5256 would involve the generation of two distinct file names, one
5257 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
5258 simply substituted with a file name chosen for the previous @samp{%u},
5259 without regard to any appended suffix.
5261 @item %j@var{suffix}
5262 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
5263 writable, and if save-temps is off; otherwise, substitute the name
5264 of a temporary file, just like @samp{%u}. This temporary file is not
5265 meant for communication between processes, but rather as a junk
5268 @item %|@var{suffix}
5269 @itemx %m@var{suffix}
5270 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
5271 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
5272 all. These are the two most common ways to instruct a program that it
5273 should read from standard input or write to standard output. If you
5274 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
5275 construct: see for example @file{f/lang-specs.h}.
5277 @item %.@var{SUFFIX}
5278 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
5279 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
5280 terminated by the next space or %.
5283 Marks the argument containing or following the @samp{%w} as the
5284 designated output file of this compilation. This puts the argument
5285 into the sequence of arguments that @samp{%o} will substitute later.
5288 Substitutes the names of all the output files, with spaces
5289 automatically placed around them. You should write spaces
5290 around the @samp{%o} as well or the results are undefined.
5291 @samp{%o} is for use in the specs for running the linker.
5292 Input files whose names have no recognized suffix are not compiled
5293 at all, but they are included among the output files, so they will
5297 Substitutes the suffix for object files. Note that this is
5298 handled specially when it immediately follows @samp{%g, %u, or %U},
5299 because of the need for those to form complete file names. The
5300 handling is such that @samp{%O} is treated exactly as if it had already
5301 been substituted, except that @samp{%g, %u, and %U} do not currently
5302 support additional @var{suffix} characters following @samp{%O} as they would
5303 following, for example, @samp{.o}.
5306 Substitutes the standard macro predefinitions for the
5307 current target machine. Use this when running @code{cpp}.
5310 Like @samp{%p}, but puts @samp{__} before and after the name of each
5311 predefined macro, except for macros that start with @samp{__} or with
5312 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
5316 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
5317 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
5318 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
5322 Current argument is the name of a library or startup file of some sort.
5323 Search for that file in a standard list of directories and substitute
5324 the full name found.
5327 Print @var{str} as an error message. @var{str} is terminated by a newline.
5328 Use this when inconsistent options are detected.
5331 Substitute the contents of spec string @var{name} at this point.
5334 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
5336 @item %x@{@var{option}@}
5337 Accumulate an option for @samp{%X}.
5340 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
5344 Output the accumulated assembler options specified by @option{-Wa}.
5347 Output the accumulated preprocessor options specified by @option{-Wp}.
5350 Process the @code{asm} spec. This is used to compute the
5351 switches to be passed to the assembler.
5354 Process the @code{asm_final} spec. This is a spec string for
5355 passing switches to an assembler post-processor, if such a program is
5359 Process the @code{link} spec. This is the spec for computing the
5360 command line passed to the linker. Typically it will make use of the
5361 @samp{%L %G %S %D and %E} sequences.
5364 Dump out a @option{-L} option for each directory that GCC believes might
5365 contain startup files. If the target supports multilibs then the
5366 current multilib directory will be prepended to each of these paths.
5369 Output the multilib directory with directory separators replaced with
5370 @samp{_}. If multilib directories are not set, or the multilib directory is
5371 @file{.} then this option emits nothing.
5374 Process the @code{lib} spec. This is a spec string for deciding which
5375 libraries should be included on the command line to the linker.
5378 Process the @code{libgcc} spec. This is a spec string for deciding
5379 which GCC support library should be included on the command line to the linker.
5382 Process the @code{startfile} spec. This is a spec for deciding which
5383 object files should be the first ones passed to the linker. Typically
5384 this might be a file named @file{crt0.o}.
5387 Process the @code{endfile} spec. This is a spec string that specifies
5388 the last object files that will be passed to the linker.
5391 Process the @code{cpp} spec. This is used to construct the arguments
5392 to be passed to the C preprocessor.
5395 Process the @code{signed_char} spec. This is intended to be used
5396 to tell cpp whether a char is signed. It typically has the definition:
5398 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
5402 Process the @code{cc1} spec. This is used to construct the options to be
5403 passed to the actual C compiler (@samp{cc1}).
5406 Process the @code{cc1plus} spec. This is used to construct the options to be
5407 passed to the actual C++ compiler (@samp{cc1plus}).
5410 Substitute the variable part of a matched option. See below.
5411 Note that each comma in the substituted string is replaced by
5415 Remove all occurrences of @code{-S} from the command line. Note---this
5416 command is position dependent. @samp{%} commands in the spec string
5417 before this one will see @code{-S}, @samp{%} commands in the spec string
5418 after this one will not.
5420 @item %:@var{function}(@var{args})
5421 Call the named function @var{function}, passing it @var{args}.
5422 @var{args} is first processed as a nested spec string, then split
5423 into an argument vector in the usual fashion. The function returns
5424 a string which is processed as if it had appeared literally as part
5425 of the current spec.
5427 The following built-in spec functions are provided:
5430 @item @code{if-exists}
5431 The @code{if-exists} spec function takes one argument, an absolute
5432 pathname to a file. If the file exists, @code{if-exists} returns the
5433 pathname. Here is a small example of its usage:
5437 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
5440 @item @code{if-exists-else}
5441 The @code{if-exists-else} spec function is similar to the @code{if-exists}
5442 spec function, except that it takes two arguments. The first argument is
5443 an absolute pathname to a file. If the file exists, @code{if-exists-else}
5444 returns the pathname. If it does not exist, it returns the second argument.
5445 This way, @code{if-exists-else} can be used to select one file or another,
5446 based on the existence of the first. Here is a small example of its usage:
5450 crt0%O%s %:if-exists(crti%O%s) \
5451 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
5456 Substitutes the @code{-S} switch, if that switch was given to GCC@.
5457 If that switch was not specified, this substitutes nothing. Note that
5458 the leading dash is omitted when specifying this option, and it is
5459 automatically inserted if the substitution is performed. Thus the spec
5460 string @samp{%@{foo@}} would match the command-line option @option{-foo}
5461 and would output the command line option @option{-foo}.
5463 @item %W@{@code{S}@}
5464 Like %@{@code{S}@} but mark last argument supplied within as a file to be
5467 @item %@{@code{S}*@}
5468 Substitutes all the switches specified to GCC whose names start
5469 with @code{-S}, but which also take an argument. This is used for
5470 switches like @option{-o}, @option{-D}, @option{-I}, etc.
5471 GCC considers @option{-o foo} as being
5472 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
5473 text, including the space. Thus two arguments would be generated.
5475 @item %@{@code{S}*&@code{T}*@}
5476 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
5477 (the order of @code{S} and @code{T} in the spec is not significant).
5478 There can be any number of ampersand-separated variables; for each the
5479 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
5481 @item %@{@code{S}:@code{X}@}
5482 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
5484 @item %@{!@code{S}:@code{X}@}
5485 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
5487 @item %@{@code{S}*:@code{X}@}
5488 Substitutes @code{X} if one or more switches whose names start with
5489 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
5490 once, no matter how many such switches appeared. However, if @code{%*}
5491 appears somewhere in @code{X}, then @code{X} will be substituted once
5492 for each matching switch, with the @code{%*} replaced by the part of
5493 that switch that matched the @code{*}.
5495 @item %@{.@code{S}:@code{X}@}
5496 Substitutes @code{X}, if processing a file with suffix @code{S}.
5498 @item %@{!.@code{S}:@code{X}@}
5499 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
5501 @item %@{@code{S}|@code{P}:@code{X}@}
5502 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
5503 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
5504 although they have a stronger binding than the @samp{|}. If @code{%*}
5505 appears in @code{X}, all of the alternatives must be starred, and only
5506 the first matching alternative is substituted.
5508 For example, a spec string like this:
5511 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
5514 will output the following command-line options from the following input
5515 command-line options:
5520 -d fred.c -foo -baz -boggle
5521 -d jim.d -bar -baz -boggle
5524 @item %@{S:X; T:Y; :D@}
5526 If @code{S} was given to GCC, substitues @code{X}; else if @code{T} was
5527 given to GCC, substitues @code{Y}; else substitutes @code{D}. There can
5528 be as many clauses as you need. This may be combined with @code{.},
5529 @code{!}, @code{|}, and @code{*} as needed.
5534 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
5535 construct may contain other nested @samp{%} constructs or spaces, or
5536 even newlines. They are processed as usual, as described above.
5537 Trailing white space in @code{X} is ignored. White space may also
5538 appear anywhere on the left side of the colon in these constructs,
5539 except between @code{.} or @code{*} and the corresponding word.
5541 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
5542 handled specifically in these constructs. If another value of
5543 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
5544 @option{-W} switch is found later in the command line, the earlier
5545 switch value is ignored, except with @{@code{S}*@} where @code{S} is
5546 just one letter, which passes all matching options.
5548 The character @samp{|} at the beginning of the predicate text is used to
5549 indicate that a command should be piped to the following command, but
5550 only if @option{-pipe} is specified.
5552 It is built into GCC which switches take arguments and which do not.
5553 (You might think it would be useful to generalize this to allow each
5554 compiler's spec to say which switches take arguments. But this cannot
5555 be done in a consistent fashion. GCC cannot even decide which input
5556 files have been specified without knowing which switches take arguments,
5557 and it must know which input files to compile in order to tell which
5560 GCC also knows implicitly that arguments starting in @option{-l} are to be
5561 treated as compiler output files, and passed to the linker in their
5562 proper position among the other output files.
5564 @c man begin OPTIONS
5566 @node Target Options
5567 @section Specifying Target Machine and Compiler Version
5568 @cindex target options
5569 @cindex cross compiling
5570 @cindex specifying machine version
5571 @cindex specifying compiler version and target machine
5572 @cindex compiler version, specifying
5573 @cindex target machine, specifying
5575 The usual way to run GCC is to run the executable called @file{gcc}, or
5576 @file{<machine>-gcc} when cross-compiling, or
5577 @file{<machine>-gcc-<version>} to run a version other than the one that
5578 was installed last. Sometimes this is inconvenient, so GCC provides
5579 options that will switch to another cross-compiler or version.
5582 @item -b @var{machine}
5584 The argument @var{machine} specifies the target machine for compilation.
5586 The value to use for @var{machine} is the same as was specified as the
5587 machine type when configuring GCC as a cross-compiler. For
5588 example, if a cross-compiler was configured with @samp{configure
5589 i386v}, meaning to compile for an 80386 running System V, then you
5590 would specify @option{-b i386v} to run that cross compiler.
5592 @item -V @var{version}
5594 The argument @var{version} specifies which version of GCC to run.
5595 This is useful when multiple versions are installed. For example,
5596 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5599 The @option{-V} and @option{-b} options work by running the
5600 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5601 use them if you can just run that directly.
5603 @node Submodel Options
5604 @section Hardware Models and Configurations
5605 @cindex submodel options
5606 @cindex specifying hardware config
5607 @cindex hardware models and configurations, specifying
5608 @cindex machine dependent options
5610 Earlier we discussed the standard option @option{-b} which chooses among
5611 different installed compilers for completely different target
5612 machines, such as VAX vs.@: 68000 vs.@: 80386.
5614 In addition, each of these target machine types can have its own
5615 special options, starting with @samp{-m}, to choose among various
5616 hardware models or configurations---for example, 68010 vs 68020,
5617 floating coprocessor or none. A single installed version of the
5618 compiler can compile for any model or configuration, according to the
5621 Some configurations of the compiler also support additional special
5622 options, usually for compatibility with other compilers on the same
5625 These options are defined by the macro @code{TARGET_SWITCHES} in the
5626 machine description. The default for the options is also defined by
5627 that macro, which enables you to change the defaults.
5639 * RS/6000 and PowerPC Options::
5643 * i386 and x86-64 Options::
5645 * Intel 960 Options::
5646 * DEC Alpha Options::
5647 * DEC Alpha/VMS Options::
5650 * System V Options::
5651 * TMS320C3x/C4x Options::
5659 * S/390 and zSeries Options::
5663 * Xstormy16 Options::
5668 @node M680x0 Options
5669 @subsection M680x0 Options
5670 @cindex M680x0 options
5672 These are the @samp{-m} options defined for the 68000 series. The default
5673 values for these options depends on which style of 68000 was selected when
5674 the compiler was configured; the defaults for the most common choices are
5682 Generate output for a 68000. This is the default
5683 when the compiler is configured for 68000-based systems.
5685 Use this option for microcontrollers with a 68000 or EC000 core,
5686 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5692 Generate output for a 68020. This is the default
5693 when the compiler is configured for 68020-based systems.
5697 Generate output containing 68881 instructions for floating point.
5698 This is the default for most 68020 systems unless @option{--nfp} was
5699 specified when the compiler was configured.
5703 Generate output for a 68030. This is the default when the compiler is
5704 configured for 68030-based systems.
5708 Generate output for a 68040. This is the default when the compiler is
5709 configured for 68040-based systems.
5711 This option inhibits the use of 68881/68882 instructions that have to be
5712 emulated by software on the 68040. Use this option if your 68040 does not
5713 have code to emulate those instructions.
5717 Generate output for a 68060. This is the default when the compiler is
5718 configured for 68060-based systems.
5720 This option inhibits the use of 68020 and 68881/68882 instructions that
5721 have to be emulated by software on the 68060. Use this option if your 68060
5722 does not have code to emulate those instructions.
5726 Generate output for a CPU32. This is the default
5727 when the compiler is configured for CPU32-based systems.
5729 Use this option for microcontrollers with a
5730 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5731 68336, 68340, 68341, 68349 and 68360.
5735 Generate output for a 520X ``coldfire'' family cpu. This is the default
5736 when the compiler is configured for 520X-based systems.
5738 Use this option for microcontroller with a 5200 core, including
5739 the MCF5202, MCF5203, MCF5204 and MCF5202.
5744 Generate output for a 68040, without using any of the new instructions.
5745 This results in code which can run relatively efficiently on either a
5746 68020/68881 or a 68030 or a 68040. The generated code does use the
5747 68881 instructions that are emulated on the 68040.
5751 Generate output for a 68060, without using any of the new instructions.
5752 This results in code which can run relatively efficiently on either a
5753 68020/68881 or a 68030 or a 68040. The generated code does use the
5754 68881 instructions that are emulated on the 68060.
5757 @opindex msoft-float
5758 Generate output containing library calls for floating point.
5759 @strong{Warning:} the requisite libraries are not available for all m68k
5760 targets. Normally the facilities of the machine's usual C compiler are
5761 used, but this can't be done directly in cross-compilation. You must
5762 make your own arrangements to provide suitable library functions for
5763 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5764 @samp{m68k-*-coff} do provide software floating point support.
5768 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5771 @opindex mnobitfield
5772 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5773 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5777 Do use the bit-field instructions. The @option{-m68020} option implies
5778 @option{-mbitfield}. This is the default if you use a configuration
5779 designed for a 68020.
5783 Use a different function-calling convention, in which functions
5784 that take a fixed number of arguments return with the @code{rtd}
5785 instruction, which pops their arguments while returning. This
5786 saves one instruction in the caller since there is no need to pop
5787 the arguments there.
5789 This calling convention is incompatible with the one normally
5790 used on Unix, so you cannot use it if you need to call libraries
5791 compiled with the Unix compiler.
5793 Also, you must provide function prototypes for all functions that
5794 take variable numbers of arguments (including @code{printf});
5795 otherwise incorrect code will be generated for calls to those
5798 In addition, seriously incorrect code will result if you call a
5799 function with too many arguments. (Normally, extra arguments are
5800 harmlessly ignored.)
5802 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5803 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5806 @itemx -mno-align-int
5808 @opindex mno-align-int
5809 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5810 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5811 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5812 Aligning variables on 32-bit boundaries produces code that runs somewhat
5813 faster on processors with 32-bit busses at the expense of more memory.
5815 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5816 align structures containing the above types differently than
5817 most published application binary interface specifications for the m68k.
5821 Use the pc-relative addressing mode of the 68000 directly, instead of
5822 using a global offset table. At present, this option implies @option{-fpic},
5823 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5824 not presently supported with @option{-mpcrel}, though this could be supported for
5825 68020 and higher processors.
5827 @item -mno-strict-align
5828 @itemx -mstrict-align
5829 @opindex mno-strict-align
5830 @opindex mstrict-align
5831 Do not (do) assume that unaligned memory references will be handled by
5836 @node M68hc1x Options
5837 @subsection M68hc1x Options
5838 @cindex M68hc1x options
5840 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5841 microcontrollers. The default values for these options depends on
5842 which style of microcontroller was selected when the compiler was configured;
5843 the defaults for the most common choices are given below.
5850 Generate output for a 68HC11. This is the default
5851 when the compiler is configured for 68HC11-based systems.
5857 Generate output for a 68HC12. This is the default
5858 when the compiler is configured for 68HC12-based systems.
5864 Generate output for a 68HCS12.
5867 @opindex mauto-incdec
5868 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5875 Enable the use of 68HC12 min and max instructions.
5878 @itemx -mno-long-calls
5879 @opindex mlong-calls
5880 @opindex mno-long-calls
5881 Treat all calls as being far away (near). If calls are assumed to be
5882 far away, the compiler will use the @code{call} instruction to
5883 call a function and the @code{rtc} instruction for returning.
5887 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5889 @item -msoft-reg-count=@var{count}
5890 @opindex msoft-reg-count
5891 Specify the number of pseudo-soft registers which are used for the
5892 code generation. The maximum number is 32. Using more pseudo-soft
5893 register may or may not result in better code depending on the program.
5894 The default is 4 for 68HC11 and 2 for 68HC12.
5899 @subsection VAX Options
5902 These @samp{-m} options are defined for the VAX:
5907 Do not output certain jump instructions (@code{aobleq} and so on)
5908 that the Unix assembler for the VAX cannot handle across long
5913 Do output those jump instructions, on the assumption that you
5914 will assemble with the GNU assembler.
5918 Output code for g-format floating point numbers instead of d-format.
5922 @subsection SPARC Options
5923 @cindex SPARC options
5925 These @samp{-m} switches are supported on the SPARC:
5930 @opindex mno-app-regs
5932 Specify @option{-mapp-regs} to generate output using the global registers
5933 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5936 To be fully SVR4 ABI compliant at the cost of some performance loss,
5937 specify @option{-mno-app-regs}. You should compile libraries and system
5938 software with this option.
5943 @opindex mhard-float
5944 Generate output containing floating point instructions. This is the
5950 @opindex msoft-float
5951 Generate output containing library calls for floating point.
5952 @strong{Warning:} the requisite libraries are not available for all SPARC
5953 targets. Normally the facilities of the machine's usual C compiler are
5954 used, but this cannot be done directly in cross-compilation. You must make
5955 your own arrangements to provide suitable library functions for
5956 cross-compilation. The embedded targets @samp{sparc-*-aout} and
5957 @samp{sparclite-*-*} do provide software floating point support.
5959 @option{-msoft-float} changes the calling convention in the output file;
5960 therefore, it is only useful if you compile @emph{all} of a program with
5961 this option. In particular, you need to compile @file{libgcc.a}, the
5962 library that comes with GCC, with @option{-msoft-float} in order for
5965 @item -mhard-quad-float
5966 @opindex mhard-quad-float
5967 Generate output containing quad-word (long double) floating point
5971 @opindex mimpure-text
5972 @option{-mimpure-text}, used in addition to @option{-shared}, tells
5973 the compiler to not pass @option{-z text} to the linker when linking a
5974 shared object. Using this option, you can link position-dependent
5975 code into a shared object.
5977 @option{-mimpure-text} suppresses the ``relocations remain against
5978 allocatable but non-writable sections'' linker error message.
5979 However, the necessary relocations will trigger copy-on-write, and the
5980 shared object is not actually shared across processes. Instead of
5981 using @option{-mimpure-text}, you should compile all source code with
5982 @option{-fpic} or @option{-fPIC}.
5984 This option is only available on SunOS and Solaris.
5986 @item -msoft-quad-float
5987 @opindex msoft-quad-float
5988 Generate output containing library calls for quad-word (long double)
5989 floating point instructions. The functions called are those specified
5990 in the SPARC ABI@. This is the default.
5992 As of this writing, there are no sparc implementations that have hardware
5993 support for the quad-word floating point instructions. They all invoke
5994 a trap handler for one of these instructions, and then the trap handler
5995 emulates the effect of the instruction. Because of the trap handler overhead,
5996 this is much slower than calling the ABI library routines. Thus the
5997 @option{-msoft-quad-float} option is the default.
6003 With @option{-mflat}, the compiler does not generate save/restore instructions
6004 and will use a ``flat'' or single register window calling convention.
6005 This model uses %i7 as the frame pointer and is compatible with the normal
6006 register window model. Code from either may be intermixed.
6007 The local registers and the input registers (0--5) are still treated as
6008 ``call saved'' registers and will be saved on the stack as necessary.
6010 With @option{-mno-flat} (the default), the compiler emits save/restore
6011 instructions (except for leaf functions) and is the normal mode of operation.
6013 @item -mno-unaligned-doubles
6014 @itemx -munaligned-doubles
6015 @opindex mno-unaligned-doubles
6016 @opindex munaligned-doubles
6017 Assume that doubles have 8 byte alignment. This is the default.
6019 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
6020 alignment only if they are contained in another type, or if they have an
6021 absolute address. Otherwise, it assumes they have 4 byte alignment.
6022 Specifying this option avoids some rare compatibility problems with code
6023 generated by other compilers. It is not the default because it results
6024 in a performance loss, especially for floating point code.
6026 @item -mno-faster-structs
6027 @itemx -mfaster-structs
6028 @opindex mno-faster-structs
6029 @opindex mfaster-structs
6030 With @option{-mfaster-structs}, the compiler assumes that structures
6031 should have 8 byte alignment. This enables the use of pairs of
6032 @code{ldd} and @code{std} instructions for copies in structure
6033 assignment, in place of twice as many @code{ld} and @code{st} pairs.
6034 However, the use of this changed alignment directly violates the SPARC
6035 ABI@. Thus, it's intended only for use on targets where the developer
6036 acknowledges that their resulting code will not be directly in line with
6037 the rules of the ABI@.
6043 These two options select variations on the SPARC architecture.
6045 By default (unless specifically configured for the Fujitsu SPARClite),
6046 GCC generates code for the v7 variant of the SPARC architecture.
6048 @option{-mv8} will give you SPARC v8 code. The only difference from v7
6049 code is that the compiler emits the integer multiply and integer
6050 divide instructions which exist in SPARC v8 but not in SPARC v7.
6052 @option{-msparclite} will give you SPARClite code. This adds the integer
6053 multiply, integer divide step and scan (@code{ffs}) instructions which
6054 exist in SPARClite but not in SPARC v7.
6056 These options are deprecated and will be deleted in a future GCC release.
6057 They have been replaced with @option{-mcpu=xxx}.
6062 @opindex msupersparc
6063 These two options select the processor for which the code is optimized.
6065 With @option{-mcypress} (the default), the compiler optimizes code for the
6066 Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series.
6067 This is also appropriate for the older SPARCStation 1, 2, IPX etc.
6069 With @option{-msupersparc} the compiler optimizes code for the SuperSPARC cpu, as
6070 used in the SPARCStation 10, 1000 and 2000 series. This flag also enables use
6071 of the full SPARC v8 instruction set.
6073 These options are deprecated and will be deleted in a future GCC release.
6074 They have been replaced with @option{-mcpu=xxx}.
6076 @item -mcpu=@var{cpu_type}
6078 Set the instruction set, register set, and instruction scheduling parameters
6079 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
6080 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
6081 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
6082 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
6085 Default instruction scheduling parameters are used for values that select
6086 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
6087 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
6089 Here is a list of each supported architecture and their supported
6094 v8: supersparc, hypersparc
6095 sparclite: f930, f934, sparclite86x
6097 v9: ultrasparc, ultrasparc3
6100 @item -mtune=@var{cpu_type}
6102 Set the instruction scheduling parameters for machine type
6103 @var{cpu_type}, but do not set the instruction set or register set that the
6104 option @option{-mcpu=@var{cpu_type}} would.
6106 The same values for @option{-mcpu=@var{cpu_type}} can be used for
6107 @option{-mtune=@var{cpu_type}}, but the only useful values are those
6108 that select a particular cpu implementation. Those are @samp{cypress},
6109 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
6110 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
6115 These @samp{-m} switches are supported in addition to the above
6116 on the SPARCLET processor.
6119 @item -mlittle-endian
6120 @opindex mlittle-endian
6121 Generate code for a processor running in little-endian mode.
6125 Treat register @code{%g0} as a normal register.
6126 GCC will continue to clobber it as necessary but will not assume
6127 it always reads as 0.
6129 @item -mbroken-saverestore
6130 @opindex mbroken-saverestore
6131 Generate code that does not use non-trivial forms of the @code{save} and
6132 @code{restore} instructions. Early versions of the SPARCLET processor do
6133 not correctly handle @code{save} and @code{restore} instructions used with
6134 arguments. They correctly handle them used without arguments. A @code{save}
6135 instruction used without arguments increments the current window pointer
6136 but does not allocate a new stack frame. It is assumed that the window
6137 overflow trap handler will properly handle this case as will interrupt
6141 These @samp{-m} switches are supported in addition to the above
6142 on SPARC V9 processors in 64-bit environments.
6145 @item -mlittle-endian
6146 @opindex mlittle-endian
6147 Generate code for a processor running in little-endian mode.
6153 Generate code for a 32-bit or 64-bit environment.
6154 The 32-bit environment sets int, long and pointer to 32 bits.
6155 The 64-bit environment sets int to 32 bits and long and pointer
6158 @item -mcmodel=medlow
6159 @opindex mcmodel=medlow
6160 Generate code for the Medium/Low code model: the program must be linked
6161 in the low 32 bits of the address space. Pointers are 64 bits.
6162 Programs can be statically or dynamically linked.
6164 @item -mcmodel=medmid
6165 @opindex mcmodel=medmid
6166 Generate code for the Medium/Middle code model: the program must be linked
6167 in the low 44 bits of the address space, the text segment must be less than
6168 2G bytes, and data segment must be within 2G of the text segment.
6169 Pointers are 64 bits.
6171 @item -mcmodel=medany
6172 @opindex mcmodel=medany
6173 Generate code for the Medium/Anywhere code model: the program may be linked
6174 anywhere in the address space, the text segment must be less than
6175 2G bytes, and data segment must be within 2G of the text segment.
6176 Pointers are 64 bits.
6178 @item -mcmodel=embmedany
6179 @opindex mcmodel=embmedany
6180 Generate code for the Medium/Anywhere code model for embedded systems:
6181 assume a 32-bit text and a 32-bit data segment, both starting anywhere
6182 (determined at link time). Register %g4 points to the base of the
6183 data segment. Pointers are still 64 bits.
6184 Programs are statically linked, PIC is not supported.
6187 @itemx -mno-stack-bias
6188 @opindex mstack-bias
6189 @opindex mno-stack-bias
6190 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
6191 frame pointer if present, are offset by @minus{}2047 which must be added back
6192 when making stack frame references.
6193 Otherwise, assume no such offset is present.
6197 @subsection ARM Options
6200 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6205 @opindex mapcs-frame
6206 Generate a stack frame that is compliant with the ARM Procedure Call
6207 Standard for all functions, even if this is not strictly necessary for
6208 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6209 with this option will cause the stack frames not to be generated for
6210 leaf functions. The default is @option{-mno-apcs-frame}.
6214 This is a synonym for @option{-mapcs-frame}.
6218 Generate code for a processor running with a 26-bit program counter,
6219 and conforming to the function calling standards for the APCS 26-bit
6220 option. This option replaces the @option{-m2} and @option{-m3} options
6221 of previous releases of the compiler.
6225 Generate code for a processor running with a 32-bit program counter,
6226 and conforming to the function calling standards for the APCS 32-bit
6227 option. This option replaces the @option{-m6} option of previous releases
6231 @c not currently implemented
6232 @item -mapcs-stack-check
6233 @opindex mapcs-stack-check
6234 Generate code to check the amount of stack space available upon entry to
6235 every function (that actually uses some stack space). If there is
6236 insufficient space available then either the function
6237 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6238 called, depending upon the amount of stack space required. The run time
6239 system is required to provide these functions. The default is
6240 @option{-mno-apcs-stack-check}, since this produces smaller code.
6242 @c not currently implemented
6244 @opindex mapcs-float
6245 Pass floating point arguments using the float point registers. This is
6246 one of the variants of the APCS@. This option is recommended if the
6247 target hardware has a floating point unit or if a lot of floating point
6248 arithmetic is going to be performed by the code. The default is
6249 @option{-mno-apcs-float}, since integer only code is slightly increased in
6250 size if @option{-mapcs-float} is used.
6252 @c not currently implemented
6253 @item -mapcs-reentrant
6254 @opindex mapcs-reentrant
6255 Generate reentrant, position independent code. The default is
6256 @option{-mno-apcs-reentrant}.
6259 @item -mthumb-interwork
6260 @opindex mthumb-interwork
6261 Generate code which supports calling between the ARM and Thumb
6262 instruction sets. Without this option the two instruction sets cannot
6263 be reliably used inside one program. The default is
6264 @option{-mno-thumb-interwork}, since slightly larger code is generated
6265 when @option{-mthumb-interwork} is specified.
6267 @item -mno-sched-prolog
6268 @opindex mno-sched-prolog
6269 Prevent the reordering of instructions in the function prolog, or the
6270 merging of those instruction with the instructions in the function's
6271 body. This means that all functions will start with a recognizable set
6272 of instructions (or in fact one of a choice from a small set of
6273 different function prologues), and this information can be used to
6274 locate the start if functions inside an executable piece of code. The
6275 default is @option{-msched-prolog}.
6278 @opindex mhard-float
6279 Generate output containing floating point instructions. This is the
6283 @opindex msoft-float
6284 Generate output containing library calls for floating point.
6285 @strong{Warning:} the requisite libraries are not available for all ARM
6286 targets. Normally the facilities of the machine's usual C compiler are
6287 used, but this cannot be done directly in cross-compilation. You must make
6288 your own arrangements to provide suitable library functions for
6291 @option{-msoft-float} changes the calling convention in the output file;
6292 therefore, it is only useful if you compile @emph{all} of a program with
6293 this option. In particular, you need to compile @file{libgcc.a}, the
6294 library that comes with GCC, with @option{-msoft-float} in order for
6297 @item -mlittle-endian
6298 @opindex mlittle-endian
6299 Generate code for a processor running in little-endian mode. This is
6300 the default for all standard configurations.
6303 @opindex mbig-endian
6304 Generate code for a processor running in big-endian mode; the default is
6305 to compile code for a little-endian processor.
6307 @item -mwords-little-endian
6308 @opindex mwords-little-endian
6309 This option only applies when generating code for big-endian processors.
6310 Generate code for a little-endian word order but a big-endian byte
6311 order. That is, a byte order of the form @samp{32107654}. Note: this
6312 option should only be used if you require compatibility with code for
6313 big-endian ARM processors generated by versions of the compiler prior to
6316 @item -malignment-traps
6317 @opindex malignment-traps
6318 Generate code that will not trap if the MMU has alignment traps enabled.
6319 On ARM architectures prior to ARMv4, there were no instructions to
6320 access half-word objects stored in memory. However, when reading from
6321 memory a feature of the ARM architecture allows a word load to be used,
6322 even if the address is unaligned, and the processor core will rotate the
6323 data as it is being loaded. This option tells the compiler that such
6324 misaligned accesses will cause a MMU trap and that it should instead
6325 synthesize the access as a series of byte accesses. The compiler can
6326 still use word accesses to load half-word data if it knows that the
6327 address is aligned to a word boundary.
6329 This option is ignored when compiling for ARM architecture 4 or later,
6330 since these processors have instructions to directly access half-word
6333 @item -mno-alignment-traps
6334 @opindex mno-alignment-traps
6335 Generate code that assumes that the MMU will not trap unaligned
6336 accesses. This produces better code when the target instruction set
6337 does not have half-word memory operations (i.e.@: implementations prior to
6340 Note that you cannot use this option to access unaligned word objects,
6341 since the processor will only fetch one 32-bit aligned object from
6344 The default setting for most targets is @option{-mno-alignment-traps}, since
6345 this produces better code when there are no half-word memory
6346 instructions available.
6348 @item -mshort-load-bytes
6349 @itemx -mno-short-load-words
6350 @opindex mshort-load-bytes
6351 @opindex mno-short-load-words
6352 These are deprecated aliases for @option{-malignment-traps}.
6354 @item -mno-short-load-bytes
6355 @itemx -mshort-load-words
6356 @opindex mno-short-load-bytes
6357 @opindex mshort-load-words
6358 This are deprecated aliases for @option{-mno-alignment-traps}.
6360 @item -mcpu=@var{name}
6362 This specifies the name of the target ARM processor. GCC uses this name
6363 to determine what kind of instructions it can emit when generating
6364 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6365 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6366 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6367 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6368 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6369 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
6370 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6371 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6372 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
6373 @samp{arm1020t}, @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
6375 @itemx -mtune=@var{name}
6377 This option is very similar to the @option{-mcpu=} option, except that
6378 instead of specifying the actual target processor type, and hence
6379 restricting which instructions can be used, it specifies that GCC should
6380 tune the performance of the code as if the target were of the type
6381 specified in this option, but still choosing the instructions that it
6382 will generate based on the cpu specified by a @option{-mcpu=} option.
6383 For some ARM implementations better performance can be obtained by using
6386 @item -march=@var{name}
6388 This specifies the name of the target ARM architecture. GCC uses this
6389 name to determine what kind of instructions it can emit when generating
6390 assembly code. This option can be used in conjunction with or instead
6391 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6392 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6393 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{iwmmxt}, @samp{ep9312}.
6395 @item -mfpe=@var{number}
6396 @itemx -mfp=@var{number}
6399 This specifies the version of the floating point emulation available on
6400 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6401 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6403 @item -mstructure-size-boundary=@var{n}
6404 @opindex mstructure-size-boundary
6405 The size of all structures and unions will be rounded up to a multiple
6406 of the number of bits set by this option. Permissible values are 8 and
6407 32. The default value varies for different toolchains. For the COFF
6408 targeted toolchain the default value is 8. Specifying the larger number
6409 can produce faster, more efficient code, but can also increase the size
6410 of the program. The two values are potentially incompatible. Code
6411 compiled with one value cannot necessarily expect to work with code or
6412 libraries compiled with the other value, if they exchange information
6413 using structures or unions.
6415 @item -mabort-on-noreturn
6416 @opindex mabort-on-noreturn
6417 Generate a call to the function @code{abort} at the end of a
6418 @code{noreturn} function. It will be executed if the function tries to
6422 @itemx -mno-long-calls
6423 @opindex mlong-calls
6424 @opindex mno-long-calls
6425 Tells the compiler to perform function calls by first loading the
6426 address of the function into a register and then performing a subroutine
6427 call on this register. This switch is needed if the target function
6428 will lie outside of the 64 megabyte addressing range of the offset based
6429 version of subroutine call instruction.
6431 Even if this switch is enabled, not all function calls will be turned
6432 into long calls. The heuristic is that static functions, functions
6433 which have the @samp{short-call} attribute, functions that are inside
6434 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6435 definitions have already been compiled within the current compilation
6436 unit, will not be turned into long calls. The exception to this rule is
6437 that weak function definitions, functions with the @samp{long-call}
6438 attribute or the @samp{section} attribute, and functions that are within
6439 the scope of a @samp{#pragma long_calls} directive, will always be
6440 turned into long calls.
6442 This feature is not enabled by default. Specifying
6443 @option{-mno-long-calls} will restore the default behavior, as will
6444 placing the function calls within the scope of a @samp{#pragma
6445 long_calls_off} directive. Note these switches have no effect on how
6446 the compiler generates code to handle function calls via function
6449 @item -mnop-fun-dllimport
6450 @opindex mnop-fun-dllimport
6451 Disable support for the @code{dllimport} attribute.
6453 @item -msingle-pic-base
6454 @opindex msingle-pic-base
6455 Treat the register used for PIC addressing as read-only, rather than
6456 loading it in the prologue for each function. The run-time system is
6457 responsible for initializing this register with an appropriate value
6458 before execution begins.
6460 @item -mpic-register=@var{reg}
6461 @opindex mpic-register
6462 Specify the register to be used for PIC addressing. The default is R10
6463 unless stack-checking is enabled, when R9 is used.
6465 @item -mcirrus-fix-invalid-insns
6466 @opindex mcirrus-fix-invalid-insns
6467 @opindex mno-cirrus-fix-invalid-insns
6468 Insert NOPs into the instruction stream to in order to work around
6469 problems with invalid Maverick instruction combinations. This option
6470 is only valid if the @option{-mcpu=ep9312} option has been used to
6471 enable generation of instructions for the Cirrus Maverick floating
6472 point co-processor. This option is not enabled by default, since the
6473 problem is only present in older Maverick implementations. The default
6474 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6477 @item -mpoke-function-name
6478 @opindex mpoke-function-name
6479 Write the name of each function into the text section, directly
6480 preceding the function prologue. The generated code is similar to this:
6484 .ascii "arm_poke_function_name", 0
6487 .word 0xff000000 + (t1 - t0)
6488 arm_poke_function_name
6490 stmfd sp!, @{fp, ip, lr, pc@}
6494 When performing a stack backtrace, code can inspect the value of
6495 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6496 location @code{pc - 12} and the top 8 bits are set, then we know that
6497 there is a function name embedded immediately preceding this location
6498 and has length @code{((pc[-3]) & 0xff000000)}.
6502 Generate code for the 16-bit Thumb instruction set. The default is to
6503 use the 32-bit ARM instruction set.
6506 @opindex mtpcs-frame
6507 Generate a stack frame that is compliant with the Thumb Procedure Call
6508 Standard for all non-leaf functions. (A leaf function is one that does
6509 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6511 @item -mtpcs-leaf-frame
6512 @opindex mtpcs-leaf-frame
6513 Generate a stack frame that is compliant with the Thumb Procedure Call
6514 Standard for all leaf functions. (A leaf function is one that does
6515 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6517 @item -mcallee-super-interworking
6518 @opindex mcallee-super-interworking
6519 Gives all externally visible functions in the file being compiled an ARM
6520 instruction set header which switches to Thumb mode before executing the
6521 rest of the function. This allows these functions to be called from
6522 non-interworking code.
6524 @item -mcaller-super-interworking
6525 @opindex mcaller-super-interworking
6526 Allows calls via function pointers (including virtual functions) to
6527 execute correctly regardless of whether the target code has been
6528 compiled for interworking or not. There is a small overhead in the cost
6529 of executing a function pointer if this option is enabled.
6533 @node MN10200 Options
6534 @subsection MN10200 Options
6535 @cindex MN10200 options
6537 These @option{-m} options are defined for Matsushita MN10200 architectures:
6542 Indicate to the linker that it should perform a relaxation optimization pass
6543 to shorten branches, calls and absolute memory addresses. This option only
6544 has an effect when used on the command line for the final link step.
6546 This option makes symbolic debugging impossible.
6549 @node MN10300 Options
6550 @subsection MN10300 Options
6551 @cindex MN10300 options
6553 These @option{-m} options are defined for Matsushita MN10300 architectures:
6558 Generate code to avoid bugs in the multiply instructions for the MN10300
6559 processors. This is the default.
6562 @opindex mno-mult-bug
6563 Do not generate code to avoid bugs in the multiply instructions for the
6568 Generate code which uses features specific to the AM33 processor.
6572 Do not generate code which uses features specific to the AM33 processor. This
6577 Do not link in the C run-time initialization object file.
6581 Indicate to the linker that it should perform a relaxation optimization pass
6582 to shorten branches, calls and absolute memory addresses. This option only
6583 has an effect when used on the command line for the final link step.
6585 This option makes symbolic debugging impossible.
6589 @node M32R/D Options
6590 @subsection M32R/D Options
6591 @cindex M32R/D options
6593 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6598 Generate code for the M32R/X@.
6602 Generate code for the M32R@. This is the default.
6604 @item -mcode-model=small
6605 @opindex mcode-model=small
6606 Assume all objects live in the lower 16MB of memory (so that their addresses
6607 can be loaded with the @code{ld24} instruction), and assume all subroutines
6608 are reachable with the @code{bl} instruction.
6609 This is the default.
6611 The addressability of a particular object can be set with the
6612 @code{model} attribute.
6614 @item -mcode-model=medium
6615 @opindex mcode-model=medium
6616 Assume objects may be anywhere in the 32-bit address space (the compiler
6617 will generate @code{seth/add3} instructions to load their addresses), and
6618 assume all subroutines are reachable with the @code{bl} instruction.
6620 @item -mcode-model=large
6621 @opindex mcode-model=large
6622 Assume objects may be anywhere in the 32-bit address space (the compiler
6623 will generate @code{seth/add3} instructions to load their addresses), and
6624 assume subroutines may not be reachable with the @code{bl} instruction
6625 (the compiler will generate the much slower @code{seth/add3/jl}
6626 instruction sequence).
6629 @opindex msdata=none
6630 Disable use of the small data area. Variables will be put into
6631 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6632 @code{section} attribute has been specified).
6633 This is the default.
6635 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6636 Objects may be explicitly put in the small data area with the
6637 @code{section} attribute using one of these sections.
6640 @opindex msdata=sdata
6641 Put small global and static data in the small data area, but do not
6642 generate special code to reference them.
6646 Put small global and static data in the small data area, and generate
6647 special instructions to reference them.
6651 @cindex smaller data references
6652 Put global and static objects less than or equal to @var{num} bytes
6653 into the small data or bss sections instead of the normal data or bss
6654 sections. The default value of @var{num} is 8.
6655 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6656 for this option to have any effect.
6658 All modules should be compiled with the same @option{-G @var{num}} value.
6659 Compiling with different values of @var{num} may or may not work; if it
6660 doesn't the linker will give an error message---incorrect code will not be
6666 @subsection M88K Options
6667 @cindex M88k options
6669 These @samp{-m} options are defined for Motorola 88k architectures:
6674 Generate code that works well on both the m88100 and the
6679 Generate code that works best for the m88100, but that also
6684 Generate code that works best for the m88110, and may not run
6689 Obsolete option to be removed from the next revision.
6692 @item -midentify-revision
6693 @opindex midentify-revision
6694 @cindex identifying source, compiler (88k)
6695 Include an @code{ident} directive in the assembler output recording the
6696 source file name, compiler name and version, timestamp, and compilation
6699 @item -mno-underscores
6700 @opindex mno-underscores
6701 @cindex underscores, avoiding (88k)
6702 In assembler output, emit symbol names without adding an underscore
6703 character at the beginning of each name. The default is to use an
6704 underscore as prefix on each name.
6706 @item -mocs-debug-info
6707 @itemx -mno-ocs-debug-info
6708 @opindex mocs-debug-info
6709 @opindex mno-ocs-debug-info
6711 @cindex debugging, 88k OCS
6712 Include (or omit) additional debugging information (about registers used
6713 in each stack frame) as specified in the 88open Object Compatibility
6714 Standard, ``OCS''@. This extra information allows debugging of code that
6715 has had the frame pointer eliminated. The default for SVr4 and Delta 88
6716 SVr3.2 is to include this information; other 88k configurations omit this
6717 information by default.
6719 @item -mocs-frame-position
6720 @opindex mocs-frame-position
6721 @cindex register positions in frame (88k)
6722 When emitting COFF debugging information for automatic variables and
6723 parameters stored on the stack, use the offset from the canonical frame
6724 address, which is the stack pointer (register 31) on entry to the
6725 function. The SVr4 and Delta88 SVr3.2, and BCS configurations use
6726 @option{-mocs-frame-position}; other 88k configurations have the default
6727 @option{-mno-ocs-frame-position}.
6729 @item -mno-ocs-frame-position
6730 @opindex mno-ocs-frame-position
6731 @cindex register positions in frame (88k)
6732 When emitting COFF debugging information for automatic variables and
6733 parameters stored on the stack, use the offset from the frame pointer
6734 register (register 30). When this option is in effect, the frame
6735 pointer is not eliminated when debugging information is selected by the
6738 @item -moptimize-arg-area
6739 @opindex moptimize-arg-area
6740 @cindex arguments in frame (88k)
6741 Save space by reorganizing the stack frame. This option generates code
6742 that does not agree with the 88open specifications, but uses less
6745 @itemx -mno-optimize-arg-area
6746 @opindex mno-optimize-arg-area
6747 Do not reorganize the stack frame to save space. This is the default.
6748 The generated conforms to the specification, but uses more memory.
6750 @item -mshort-data-@var{num}
6751 @opindex mshort-data
6752 @cindex smaller data references (88k)
6753 @cindex r0-relative references (88k)
6754 Generate smaller data references by making them relative to @code{r0},
6755 which allows loading a value using a single instruction (rather than the
6756 usual two). You control which data references are affected by
6757 specifying @var{num} with this option. For example, if you specify
6758 @option{-mshort-data-512}, then the data references affected are those
6759 involving displacements of less than 512 bytes.
6760 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6763 @item -mserialize-volatile
6764 @opindex mserialize-volatile
6765 @itemx -mno-serialize-volatile
6766 @opindex mno-serialize-volatile
6767 @cindex sequential consistency on 88k
6768 Do, or don't, generate code to guarantee sequential consistency
6769 of volatile memory references. By default, consistency is
6772 The order of memory references made by the MC88110 processor does
6773 not always match the order of the instructions requesting those
6774 references. In particular, a load instruction may execute before
6775 a preceding store instruction. Such reordering violates
6776 sequential consistency of volatile memory references, when there
6777 are multiple processors. When consistency must be guaranteed,
6778 GCC generates special instructions, as needed, to force
6779 execution in the proper order.
6781 The MC88100 processor does not reorder memory references and so
6782 always provides sequential consistency. However, by default, GCC
6783 generates the special instructions to guarantee consistency
6784 even when you use @option{-m88100}, so that the code may be run on an
6785 MC88110 processor. If you intend to run your code only on the
6786 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6788 The extra code generated to guarantee consistency may affect the
6789 performance of your application. If you know that you can safely
6790 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6796 @cindex assembler syntax, 88k
6798 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6799 related to System V release 4 (SVr4). This controls the following:
6803 Which variant of the assembler syntax to emit.
6805 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6806 that is used on System V release 4.
6808 @option{-msvr4} makes GCC issue additional declaration directives used in
6812 @option{-msvr4} is the default for the m88k-motorola-sysv4 configuration.
6813 @option{-msvr3} is the default for all other m88k configurations.
6815 @item -mversion-03.00
6816 @opindex mversion-03.00
6817 This option is obsolete, and is ignored.
6818 @c ??? which asm syntax better for GAS? option there too?
6820 @item -mno-check-zero-division
6821 @itemx -mcheck-zero-division
6822 @opindex mno-check-zero-division
6823 @opindex mcheck-zero-division
6824 @cindex zero division on 88k
6825 Do, or don't, generate code to guarantee that integer division by
6826 zero will be detected. By default, detection is guaranteed.
6828 Some models of the MC88100 processor fail to trap upon integer
6829 division by zero under certain conditions. By default, when
6830 compiling code that might be run on such a processor, GCC
6831 generates code that explicitly checks for zero-valued divisors
6832 and traps with exception number 503 when one is detected. Use of
6833 @option{-mno-check-zero-division} suppresses such checking for code
6834 generated to run on an MC88100 processor.
6836 GCC assumes that the MC88110 processor correctly detects all instances
6837 of integer division by zero. When @option{-m88110} is specified, no
6838 explicit checks for zero-valued divisors are generated, and both
6839 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
6842 @item -muse-div-instruction
6843 @opindex muse-div-instruction
6844 @cindex divide instruction, 88k
6845 Use the div instruction for signed integer division on the
6846 MC88100 processor. By default, the div instruction is not used.
6848 On the MC88100 processor the signed integer division instruction
6849 div) traps to the operating system on a negative operand. The
6850 operating system transparently completes the operation, but at a
6851 large cost in execution time. By default, when compiling code
6852 that might be run on an MC88100 processor, GCC emulates signed
6853 integer division using the unsigned integer division instruction
6854 divu), thereby avoiding the large penalty of a trap to the
6855 operating system. Such emulation has its own, smaller, execution
6856 cost in both time and space. To the extent that your code's
6857 important signed integer division operations are performed on two
6858 nonnegative operands, it may be desirable to use the div
6859 instruction directly.
6861 On the MC88110 processor the div instruction (also known as the
6862 divs instruction) processes negative operands without trapping to
6863 the operating system. When @option{-m88110} is specified,
6864 @option{-muse-div-instruction} is ignored, and the div instruction is used
6865 for signed integer division.
6867 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6868 particular, the behavior of such a division with and without
6869 @option{-muse-div-instruction} may differ.
6871 @item -mtrap-large-shift
6872 @itemx -mhandle-large-shift
6873 @opindex mtrap-large-shift
6874 @opindex mhandle-large-shift
6875 @cindex bit shift overflow (88k)
6876 @cindex large bit shifts (88k)
6877 Include code to detect bit-shifts of more than 31 bits; respectively,
6878 trap such shifts or emit code to handle them properly. By default GCC
6879 makes no special provision for large bit shifts.
6881 @item -mwarn-passed-structs
6882 @opindex mwarn-passed-structs
6883 @cindex structure passing (88k)
6884 Warn when a function passes a struct as an argument or result.
6885 Structure-passing conventions have changed during the evolution of the C
6886 language, and are often the source of portability problems. By default,
6887 GCC issues no such warning.
6890 @c break page here to avoid unsightly interparagraph stretch.
6894 @node RS/6000 and PowerPC Options
6895 @subsection IBM RS/6000 and PowerPC Options
6896 @cindex RS/6000 and PowerPC Options
6897 @cindex IBM RS/6000 and PowerPC Options
6899 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6907 @itemx -mpowerpc-gpopt
6908 @itemx -mno-powerpc-gpopt
6909 @itemx -mpowerpc-gfxopt
6910 @itemx -mno-powerpc-gfxopt
6912 @itemx -mno-powerpc64
6918 @opindex mno-powerpc
6919 @opindex mpowerpc-gpopt
6920 @opindex mno-powerpc-gpopt
6921 @opindex mpowerpc-gfxopt
6922 @opindex mno-powerpc-gfxopt
6924 @opindex mno-powerpc64
6925 GCC supports two related instruction set architectures for the
6926 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6927 instructions supported by the @samp{rios} chip set used in the original
6928 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6929 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6930 the IBM 4xx microprocessors.
6932 Neither architecture is a subset of the other. However there is a
6933 large common subset of instructions supported by both. An MQ
6934 register is included in processors supporting the POWER architecture.
6936 You use these options to specify which instructions are available on the
6937 processor you are using. The default value of these options is
6938 determined when configuring GCC@. Specifying the
6939 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6940 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6941 rather than the options listed above.
6943 The @option{-mpower} option allows GCC to generate instructions that
6944 are found only in the POWER architecture and to use the MQ register.
6945 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
6946 to generate instructions that are present in the POWER2 architecture but
6947 not the original POWER architecture.
6949 The @option{-mpowerpc} option allows GCC to generate instructions that
6950 are found only in the 32-bit subset of the PowerPC architecture.
6951 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
6952 GCC to use the optional PowerPC architecture instructions in the
6953 General Purpose group, including floating-point square root. Specifying
6954 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
6955 use the optional PowerPC architecture instructions in the Graphics
6956 group, including floating-point select.
6958 The @option{-mpowerpc64} option allows GCC to generate the additional
6959 64-bit instructions that are found in the full PowerPC64 architecture
6960 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
6961 @option{-mno-powerpc64}.
6963 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
6964 will use only the instructions in the common subset of both
6965 architectures plus some special AIX common-mode calls, and will not use
6966 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
6967 permits GCC to use any instruction from either architecture and to
6968 allow use of the MQ register; specify this for the Motorola MPC601.
6970 @item -mnew-mnemonics
6971 @itemx -mold-mnemonics
6972 @opindex mnew-mnemonics
6973 @opindex mold-mnemonics
6974 Select which mnemonics to use in the generated assembler code. With
6975 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
6976 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
6977 assembler mnemonics defined for the POWER architecture. Instructions
6978 defined in only one architecture have only one mnemonic; GCC uses that
6979 mnemonic irrespective of which of these options is specified.
6981 GCC defaults to the mnemonics appropriate for the architecture in
6982 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
6983 value of these option. Unless you are building a cross-compiler, you
6984 should normally not specify either @option{-mnew-mnemonics} or
6985 @option{-mold-mnemonics}, but should instead accept the default.
6987 @item -mcpu=@var{cpu_type}
6989 Set architecture type, register usage, choice of mnemonics, and
6990 instruction scheduling parameters for machine type @var{cpu_type}.
6991 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
6992 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
6993 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
6994 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
6995 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
6996 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
6998 @option{-mcpu=common} selects a completely generic processor. Code
6999 generated under this option will run on any POWER or PowerPC processor.
7000 GCC will use only the instructions in the common subset of both
7001 architectures, and will not use the MQ register. GCC assumes a generic
7002 processor model for scheduling purposes.
7004 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
7005 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
7006 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
7007 types, with an appropriate, generic processor model assumed for
7008 scheduling purposes.
7010 The other options specify a specific processor. Code generated under
7011 those options will run best on that processor, and may not run at all on
7014 The @option{-mcpu} options automatically enable or disable other
7015 @option{-m} options as follows:
7019 @option{-mno-power}, @option{-mno-powerpc}
7026 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
7041 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7044 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7049 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
7052 @item -mtune=@var{cpu_type}
7054 Set the instruction scheduling parameters for machine type
7055 @var{cpu_type}, but do not set the architecture type, register usage, or
7056 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
7057 values for @var{cpu_type} are used for @option{-mtune} as for
7058 @option{-mcpu}. If both are specified, the code generated will use the
7059 architecture, registers, and mnemonics set by @option{-mcpu}, but the
7060 scheduling parameters set by @option{-mtune}.
7065 @opindex mno-altivec
7066 These switches enable or disable the use of built-in functions that
7067 allow access to the AltiVec instruction set. You may also need to set
7068 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
7073 Extend the current ABI with SPE ABI extensions. This does not change
7074 the default ABI, instead it adds the SPE ABI extensions to the current
7078 @opindex mabi=no-spe
7079 Disable Booke SPE ABI extensions for the current ABI.
7081 @item -misel=@var{yes/no}
7084 This switch enables or disables the generation of ISEL instructions.
7086 @item -mspe=@var{yes/no}
7089 This switch enables or disables the generation of SPE simd
7092 @item -mfloat-gprs=@var{yes/no}
7094 @opindex mfloat-gprs
7095 This switch enables or disables the generation of floating point
7096 operations on the general purpose registers for architectures that
7097 support it. This option is currently only available on the MPC8540.
7100 @itemx -mno-fp-in-toc
7101 @itemx -mno-sum-in-toc
7102 @itemx -mminimal-toc
7104 @opindex mno-fp-in-toc
7105 @opindex mno-sum-in-toc
7106 @opindex mminimal-toc
7107 Modify generation of the TOC (Table Of Contents), which is created for
7108 every executable file. The @option{-mfull-toc} option is selected by
7109 default. In that case, GCC will allocate at least one TOC entry for
7110 each unique non-automatic variable reference in your program. GCC
7111 will also place floating-point constants in the TOC@. However, only
7112 16,384 entries are available in the TOC@.
7114 If you receive a linker error message that saying you have overflowed
7115 the available TOC space, you can reduce the amount of TOC space used
7116 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
7117 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
7118 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
7119 generate code to calculate the sum of an address and a constant at
7120 run-time instead of putting that sum into the TOC@. You may specify one
7121 or both of these options. Each causes GCC to produce very slightly
7122 slower and larger code at the expense of conserving TOC space.
7124 If you still run out of space in the TOC even when you specify both of
7125 these options, specify @option{-mminimal-toc} instead. This option causes
7126 GCC to make only one TOC entry for every file. When you specify this
7127 option, GCC will produce code that is slower and larger but which
7128 uses extremely little TOC space. You may wish to use this option
7129 only on files that contain less frequently executed code.
7135 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
7136 @code{long} type, and the infrastructure needed to support them.
7137 Specifying @option{-maix64} implies @option{-mpowerpc64} and
7138 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
7139 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
7144 @opindex mno-xl-call
7145 On AIX, pass floating-point arguments to prototyped functions beyond the
7146 register save area (RSA) on the stack in addition to argument FPRs. The
7147 AIX calling convention was extended but not initially documented to
7148 handle an obscure K&R C case of calling a function that takes the
7149 address of its arguments with fewer arguments than declared. AIX XL
7150 compilers access floating point arguments which do not fit in the
7151 RSA from the stack when a subroutine is compiled without
7152 optimization. Because always storing floating-point arguments on the
7153 stack is inefficient and rarely needed, this option is not enabled by
7154 default and only is necessary when calling subroutines compiled by AIX
7155 XL compilers without optimization.
7159 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
7160 application written to use message passing with special startup code to
7161 enable the application to run. The system must have PE installed in the
7162 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
7163 must be overridden with the @option{-specs=} option to specify the
7164 appropriate directory location. The Parallel Environment does not
7165 support threads, so the @option{-mpe} option and the @option{-pthread}
7166 option are incompatible.
7168 @item -malign-natural
7169 @itemx -malign-power
7170 @opindex malign-natural
7171 @opindex malign-power
7172 On AIX, Darwin, and 64-bit PowerPC Linux, the option
7173 @option{-malign-natural} overrides the ABI-defined alignment of larger
7174 types, such as floating-point doubles, on their natural size-based boundary.
7175 The option @option{-malign-power} instructs GCC to follow the ABI-specified
7176 alignment rules. GCC defaults to the standard alignment defined in the ABI.
7180 @opindex msoft-float
7181 @opindex mhard-float
7182 Generate code that does not use (uses) the floating-point register set.
7183 Software floating point emulation is provided if you use the
7184 @option{-msoft-float} option, and pass the option to GCC when linking.
7187 @itemx -mno-multiple
7189 @opindex mno-multiple
7190 Generate code that uses (does not use) the load multiple word
7191 instructions and the store multiple word instructions. These
7192 instructions are generated by default on POWER systems, and not
7193 generated on PowerPC systems. Do not use @option{-mmultiple} on little
7194 endian PowerPC systems, since those instructions do not work when the
7195 processor is in little endian mode. The exceptions are PPC740 and
7196 PPC750 which permit the instructions usage in little endian mode.
7202 Generate code that uses (does not use) the load string instructions
7203 and the store string word instructions to save multiple registers and
7204 do small block moves. These instructions are generated by default on
7205 POWER systems, and not generated on PowerPC systems. Do not use
7206 @option{-mstring} on little endian PowerPC systems, since those
7207 instructions do not work when the processor is in little endian mode.
7208 The exceptions are PPC740 and PPC750 which permit the instructions
7209 usage in little endian mode.
7215 Generate code that uses (does not use) the load or store instructions
7216 that update the base register to the address of the calculated memory
7217 location. These instructions are generated by default. If you use
7218 @option{-mno-update}, there is a small window between the time that the
7219 stack pointer is updated and the address of the previous frame is
7220 stored, which means code that walks the stack frame across interrupts or
7221 signals may get corrupted data.
7224 @itemx -mno-fused-madd
7225 @opindex mfused-madd
7226 @opindex mno-fused-madd
7227 Generate code that uses (does not use) the floating point multiply and
7228 accumulate instructions. These instructions are generated by default if
7229 hardware floating is used.
7231 @item -mno-bit-align
7233 @opindex mno-bit-align
7235 On System V.4 and embedded PowerPC systems do not (do) force structures
7236 and unions that contain bit-fields to be aligned to the base type of the
7239 For example, by default a structure containing nothing but 8
7240 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
7241 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
7242 the structure would be aligned to a 1 byte boundary and be one byte in
7245 @item -mno-strict-align
7246 @itemx -mstrict-align
7247 @opindex mno-strict-align
7248 @opindex mstrict-align
7249 On System V.4 and embedded PowerPC systems do not (do) assume that
7250 unaligned memory references will be handled by the system.
7253 @itemx -mno-relocatable
7254 @opindex mrelocatable
7255 @opindex mno-relocatable
7256 On embedded PowerPC systems generate code that allows (does not allow)
7257 the program to be relocated to a different address at runtime. If you
7258 use @option{-mrelocatable} on any module, all objects linked together must
7259 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
7261 @item -mrelocatable-lib
7262 @itemx -mno-relocatable-lib
7263 @opindex mrelocatable-lib
7264 @opindex mno-relocatable-lib
7265 On embedded PowerPC systems generate code that allows (does not allow)
7266 the program to be relocated to a different address at runtime. Modules
7267 compiled with @option{-mrelocatable-lib} can be linked with either modules
7268 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
7269 with modules compiled with the @option{-mrelocatable} options.
7275 On System V.4 and embedded PowerPC systems do not (do) assume that
7276 register 2 contains a pointer to a global area pointing to the addresses
7277 used in the program.
7280 @itemx -mlittle-endian
7282 @opindex mlittle-endian
7283 On System V.4 and embedded PowerPC systems compile code for the
7284 processor in little endian mode. The @option{-mlittle-endian} option is
7285 the same as @option{-mlittle}.
7290 @opindex mbig-endian
7291 On System V.4 and embedded PowerPC systems compile code for the
7292 processor in big endian mode. The @option{-mbig-endian} option is
7293 the same as @option{-mbig}.
7295 @item -mdynamic-no-pic
7296 @opindex mdynamic-no-pic
7297 On Darwin and Mac OS X systems, compile code so that it is not
7298 relocatable, but that its external references are relocatable. The
7299 resulting code is suitable for applications, but not shared
7304 On System V.4 and embedded PowerPC systems compile code using calling
7305 conventions that adheres to the March 1995 draft of the System V
7306 Application Binary Interface, PowerPC processor supplement. This is the
7307 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
7309 @item -mcall-sysv-eabi
7310 @opindex mcall-sysv-eabi
7311 Specify both @option{-mcall-sysv} and @option{-meabi} options.
7313 @item -mcall-sysv-noeabi
7314 @opindex mcall-sysv-noeabi
7315 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
7317 @item -mcall-solaris
7318 @opindex mcall-solaris
7319 On System V.4 and embedded PowerPC systems compile code for the Solaris
7323 @opindex mcall-linux
7324 On System V.4 and embedded PowerPC systems compile code for the
7325 Linux-based GNU system.
7329 On System V.4 and embedded PowerPC systems compile code for the
7330 Hurd-based GNU system.
7333 @opindex mcall-netbsd
7334 On System V.4 and embedded PowerPC systems compile code for the
7335 NetBSD operating system.
7337 @item -maix-struct-return
7338 @opindex maix-struct-return
7339 Return all structures in memory (as specified by the AIX ABI)@.
7341 @item -msvr4-struct-return
7342 @opindex msvr4-struct-return
7343 Return structures smaller than 8 bytes in registers (as specified by the
7347 @opindex mabi=altivec
7348 Extend the current ABI with AltiVec ABI extensions. This does not
7349 change the default ABI, instead it adds the AltiVec ABI extensions to
7352 @item -mabi=no-altivec
7353 @opindex mabi=no-altivec
7354 Disable AltiVec ABI extensions for the current ABI.
7357 @itemx -mno-prototype
7359 @opindex mno-prototype
7360 On System V.4 and embedded PowerPC systems assume that all calls to
7361 variable argument functions are properly prototyped. Otherwise, the
7362 compiler must insert an instruction before every non prototyped call to
7363 set or clear bit 6 of the condition code register (@var{CR}) to
7364 indicate whether floating point values were passed in the floating point
7365 registers in case the function takes a variable arguments. With
7366 @option{-mprototype}, only calls to prototyped variable argument functions
7367 will set or clear the bit.
7371 On embedded PowerPC systems, assume that the startup module is called
7372 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
7373 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
7378 On embedded PowerPC systems, assume that the startup module is called
7379 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
7384 On embedded PowerPC systems, assume that the startup module is called
7385 @file{crt0.o} and the standard C libraries are @file{libads.a} and
7389 @opindex myellowknife
7390 On embedded PowerPC systems, assume that the startup module is called
7391 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
7396 On System V.4 and embedded PowerPC systems, specify that you are
7397 compiling for a VxWorks system.
7401 Specify that you are compiling for the WindISS simulation environment.
7405 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
7406 header to indicate that @samp{eabi} extended relocations are used.
7412 On System V.4 and embedded PowerPC systems do (do not) adhere to the
7413 Embedded Applications Binary Interface (eabi) which is a set of
7414 modifications to the System V.4 specifications. Selecting @option{-meabi}
7415 means that the stack is aligned to an 8 byte boundary, a function
7416 @code{__eabi} is called to from @code{main} to set up the eabi
7417 environment, and the @option{-msdata} option can use both @code{r2} and
7418 @code{r13} to point to two separate small data areas. Selecting
7419 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
7420 do not call an initialization function from @code{main}, and the
7421 @option{-msdata} option will only use @code{r13} to point to a single
7422 small data area. The @option{-meabi} option is on by default if you
7423 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
7426 @opindex msdata=eabi
7427 On System V.4 and embedded PowerPC systems, put small initialized
7428 @code{const} global and static data in the @samp{.sdata2} section, which
7429 is pointed to by register @code{r2}. Put small initialized
7430 non-@code{const} global and static data in the @samp{.sdata} section,
7431 which is pointed to by register @code{r13}. Put small uninitialized
7432 global and static data in the @samp{.sbss} section, which is adjacent to
7433 the @samp{.sdata} section. The @option{-msdata=eabi} option is
7434 incompatible with the @option{-mrelocatable} option. The
7435 @option{-msdata=eabi} option also sets the @option{-memb} option.
7438 @opindex msdata=sysv
7439 On System V.4 and embedded PowerPC systems, put small global and static
7440 data in the @samp{.sdata} section, which is pointed to by register
7441 @code{r13}. Put small uninitialized global and static data in the
7442 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7443 The @option{-msdata=sysv} option is incompatible with the
7444 @option{-mrelocatable} option.
7446 @item -msdata=default
7448 @opindex msdata=default
7450 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7451 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7452 same as @option{-msdata=sysv}.
7455 @opindex msdata-data
7456 On System V.4 and embedded PowerPC systems, put small global and static
7457 data in the @samp{.sdata} section. Put small uninitialized global and
7458 static data in the @samp{.sbss} section. Do not use register @code{r13}
7459 to address small data however. This is the default behavior unless
7460 other @option{-msdata} options are used.
7464 @opindex msdata=none
7466 On embedded PowerPC systems, put all initialized global and static data
7467 in the @samp{.data} section, and all uninitialized data in the
7468 @samp{.bss} section.
7472 @cindex smaller data references (PowerPC)
7473 @cindex .sdata/.sdata2 references (PowerPC)
7474 On embedded PowerPC systems, put global and static items less than or
7475 equal to @var{num} bytes into the small data or bss sections instead of
7476 the normal data or bss section. By default, @var{num} is 8. The
7477 @option{-G @var{num}} switch is also passed to the linker.
7478 All modules should be compiled with the same @option{-G @var{num}} value.
7481 @itemx -mno-regnames
7483 @opindex mno-regnames
7484 On System V.4 and embedded PowerPC systems do (do not) emit register
7485 names in the assembly language output using symbolic forms.
7488 @itemx -mno-longcall
7490 @opindex mno-longcall
7491 Default to making all function calls via pointers, so that functions
7492 which reside further than 64 megabytes (67,108,864 bytes) from the
7493 current location can be called. This setting can be overridden by the
7494 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7496 Some linkers are capable of detecting out-of-range calls and generating
7497 glue code on the fly. On these systems, long calls are unnecessary and
7498 generate slower code. As of this writing, the AIX linker can do this,
7499 as can the GNU linker for PowerPC/64. It is planned to add this feature
7500 to the GNU linker for 32-bit PowerPC systems as well.
7502 In the future, we may cause GCC to ignore all longcall specifications
7503 when the linker is known to generate glue.
7507 Adds support for multithreading with the @dfn{pthreads} library.
7508 This option sets flags for both the preprocessor and linker.
7512 @node Darwin Options
7513 @subsection Darwin Options
7514 @cindex Darwin options
7516 These options are defined for all architectures running the Darwin operating
7517 system. They are useful for compatibility with other Mac OS compilers.
7522 Loads all members of static archive libraries.
7523 See man ld(1) for more information.
7525 @item -arch_errors_fatal
7526 @opindex arch_errors_fatal
7527 Cause the errors having to do with files that have the wrong architecture
7531 @opindex bind_at_load
7532 Causes the output file to be marked such that the dynamic linker will
7533 bind all undefined references when the file is loaded or launched.
7537 Produce a Mach-o bundle format file.
7538 See man ld(1) for more information.
7540 @item -bundle_loader @var{executable}
7541 @opindex bundle_loader
7542 This specifies the @var{executable} that will be loading the build
7543 output file being linked. See man ld(1) for more information.
7545 @item -allowable_client @var{client_name}
7549 @item -compatibility_version
7550 @item -current_version
7551 @item -dependency-file
7553 @item -dylinker_install_name
7556 @item -exported_symbols_list
7558 @item -flat_namespace
7559 @item -force_cpusubtype_ALL
7560 @item -force_flat_namespace
7561 @item -headerpad_max_install_names
7565 @item -keep_private_externs
7567 @item -multiply_defined
7568 @item -multiply_defined_unused
7572 @item -noseglinkedit
7573 @item -pagezero_size
7575 @item -prebind_all_twolevel_modules
7576 @item -private_bundle
7577 @item -read_only_relocs
7579 @item -sectobjectsymbols
7583 @item -sectobjectsymbols
7585 @item -seg_addr_table
7586 @item -seg_addr_table_filename
7589 @item -segs_read_only_addr
7590 @item -segs_read_write_addr
7591 @item -single_module
7595 @item -twolevel_namespace
7598 @item -unexported_symbols_list
7599 @item -weak_reference_mismatches
7602 @opindex allowable_client
7604 @opindex client_name
7605 @opindex compatibility_version
7606 @opindex current_version
7607 @opindex dependency-file
7609 @opindex dylinker_install_name
7612 @opindex exported_symbols_list
7614 @opindex flat_namespace
7615 @opindex force_cpusubtype_ALL
7616 @opindex force_flat_namespace
7617 @opindex headerpad_max_install_names
7620 @opindex install_name
7621 @opindex keep_private_externs
7622 @opindex multi_module
7623 @opindex multiply_defined
7624 @opindex multiply_defined_unused
7626 @opindex nomultidefs
7628 @opindex noseglinkedit
7629 @opindex pagezero_size
7631 @opindex prebind_all_twolevel_modules
7632 @opindex private_bundle
7633 @opindex read_only_relocs
7635 @opindex sectobjectsymbols
7639 @opindex sectobjectsymbols
7641 @opindex seg_addr_table
7642 @opindex seg_addr_table_filename
7643 @opindex seglinkedit
7645 @opindex segs_read_only_addr
7646 @opindex segs_read_write_addr
7647 @opindex single_module
7649 @opindex sub_library
7650 @opindex sub_umbrella
7651 @opindex twolevel_namespace
7654 @opindex unexported_symbols_list
7655 @opindex weak_reference_mismatches
7656 @opindex whatsloaded
7658 This options are available for Darwin linker. Darwin linker man page
7659 describes them in detail.
7664 @subsection IBM RT Options
7666 @cindex IBM RT options
7668 These @samp{-m} options are defined for the IBM RT PC:
7672 @opindex min-line-mul
7673 Use an in-line code sequence for integer multiplies. This is the
7676 @item -mcall-lib-mul
7677 @opindex mcall-lib-mul
7678 Call @code{lmul$$} for integer multiples.
7680 @item -mfull-fp-blocks
7681 @opindex mfull-fp-blocks
7682 Generate full-size floating point data blocks, including the minimum
7683 amount of scratch space recommended by IBM@. This is the default.
7685 @item -mminimum-fp-blocks
7686 @opindex mminimum-fp-blocks
7687 Do not include extra scratch space in floating point data blocks. This
7688 results in smaller code, but slower execution, since scratch space must
7689 be allocated dynamically.
7691 @cindex @file{stdarg.h} and RT PC
7692 @item -mfp-arg-in-fpregs
7693 @opindex mfp-arg-in-fpregs
7694 Use a calling sequence incompatible with the IBM calling convention in
7695 which floating point arguments are passed in floating point registers.
7696 Note that @code{stdarg.h} will not work with floating point operands
7697 if this option is specified.
7699 @item -mfp-arg-in-gregs
7700 @opindex mfp-arg-in-gregs
7701 Use the normal calling convention for floating point arguments. This is
7704 @item -mhc-struct-return
7705 @opindex mhc-struct-return
7706 Return structures of more than one word in memory, rather than in a
7707 register. This provides compatibility with the MetaWare HighC (hc)
7708 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7709 with the Portable C Compiler (pcc).
7711 @item -mnohc-struct-return
7712 @opindex mnohc-struct-return
7713 Return some structures of more than one word in registers, when
7714 convenient. This is the default. For compatibility with the
7715 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7716 option @option{-mhc-struct-return}.
7720 @subsection MIPS Options
7721 @cindex MIPS options
7723 These @samp{-m} options are defined for the MIPS family of computers:
7727 @item -march=@var{arch}
7729 Generate code that will run on @var{arch}, which can be the name of a
7730 generic MIPS ISA, or the name of a particular processor.
7732 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
7733 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
7734 The processor names are:
7735 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
7737 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
7738 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
7741 @samp{vr4100}, @samp{vr4300}, and @samp{vr5000}.
7742 The special value @samp{from-abi} selects the
7743 most compatible architecture for the selected ABI (that is,
7744 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
7746 In processor names, a final @samp{000} can be abbreviated as @samp{k}
7747 (for example, @samp{-march=r2k}). Prefixes are optional, and
7748 @samp{vr} may be written @samp{r}.
7750 GCC defines two macros based on the value of this option. The first
7751 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
7752 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
7753 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
7754 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
7755 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
7757 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
7758 above. In other words, it will have the full prefix and will not
7759 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
7760 the macro names the resolved architecture (either @samp{"mips1"} or
7761 @samp{"mips3"}). It names the default architecture when no
7762 @option{-march} option is given.
7764 @item -mtune=@var{arch}
7766 Optimize for @var{arch}. Among other things, this option controls
7767 the way instructions are scheduled, and the perceived cost of arithmetic
7768 operations. The list of @var{arch} values is the same as for
7771 When this option is not used, GCC will optimize for the processor
7772 specified by @option{-march}. By using @option{-march} and
7773 @option{-mtune} together, it is possible to generate code that will
7774 run on a family of processors, but optimize the code for one
7775 particular member of that family.
7777 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
7778 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
7779 @samp{-march} ones described above.
7783 Equivalent to @samp{-march=mips1}.
7787 Equivalent to @samp{-march=mips2}.
7791 Equivalent to @samp{-march=mips3}.
7795 Equivalent to @samp{-march=mips4}.
7799 Equivalent to @samp{-march=mips32}.
7803 Equivalent to @samp{-march=mips32r2}.
7807 Equivalent to @samp{-march=mips64}.
7810 @itemx -mno-fused-madd
7811 @opindex mfused-madd
7812 @opindex mno-fused-madd
7813 Generate code that uses (does not use) the floating point multiply and
7814 accumulate instructions, when they are available. These instructions
7815 are generated by default if they are available, but this may be
7816 undesirable if the extra precision causes problems or on certain chips
7817 in the mode where denormals are rounded to zero where denormals
7818 generated by multiply and accumulate instructions cause exceptions
7823 Assume that floating point registers are 32 bits wide.
7827 Assume that floating point registers are 64 bits wide.
7831 Assume that general purpose registers are 32 bits wide.
7835 Assume that general purpose registers are 64 bits wide.
7839 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7840 explanation of the default, and the width of pointers.
7844 Force long types to be 64 bits wide. See @option{-mlong32} for an
7845 explanation of the default, and the width of pointers.
7849 Force long, int, and pointer types to be 32 bits wide.
7851 The default size of ints, longs and pointers depends on the ABI@. All
7852 the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as
7853 does the 64-bit Cygnus EABI; the others use 32-bit longs. Pointers
7854 are the same size as longs, or the same size as integer registers,
7855 whichever is smaller.
7869 Generate code for the given ABI@.
7871 Note that there are two embedded ABIs: @option{-mabi=eabi}
7872 selects the one defined by Cygnus while @option{-meabi=meabi}
7873 selects the one defined by MIPS@. Both these ABIs have
7874 32-bit and 64-bit variants. Normally, GCC will generate
7875 64-bit code when you select a 64-bit architecture, but you
7876 can use @option{-mgp32} to get 32-bit code instead.
7878 @item -mabi-fake-default
7879 @opindex mabi-fake-default
7880 You don't want to know what this option does. No, really. I mean
7881 it. Move on to the next option.
7883 What? You're still here? Oh, well@enddots{} Ok, here's the deal. GCC
7884 wants the default set of options to get the root of the multilib tree,
7885 and the shared library SONAMEs without any multilib-indicating
7886 suffixes. This is not convenience for @samp{mips64-linux-gnu}, since
7887 we want to default to the N32 ABI, while still being binary-compatible
7888 with @samp{mips-linux-gnu} if you stick to the O32 ABI@. Being
7889 binary-compatible means shared libraries should have the same SONAMEs,
7890 and libraries should live in the same location. Having O32 libraries
7891 in a sub-directory named say @file{o32} is not acceptable.
7893 So we trick GCC into believing that O32 is the default ABI, except
7894 that we override the default with some internal command-line
7895 processing magic. Problem is, if we stopped at that, and you then
7896 created a multilib-aware package that used the output of @command{gcc
7897 -print-multi-lib} to decide which multilibs to build, and how, and
7898 you'd find yourself in an awkward situation when you found out that
7899 some of the options listed ended up mapping to the same multilib, and
7900 none of your libraries was actually built for the multilib that
7901 @option{-print-multi-lib} claims to be the default. So we added this
7902 option that disables the default switcher, falling back to GCC's
7903 original notion of the default library. Confused yet?
7905 For short: don't ever use this option, unless you find it in the list
7906 of additional options to be used when building for multilibs, in the
7907 output of @option{gcc -print-multi-lib}.
7911 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7912 add normal debug information. This is the default for all
7913 platforms except for the OSF/1 reference platform, using the OSF/rose
7914 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7915 switches are used, the @file{mips-tfile} program will encapsulate the
7916 stabs within MIPS ECOFF@.
7920 Generate code for the GNU assembler. This is the default on the OSF/1
7921 reference platform, using the OSF/rose object format. Also, this is
7922 the default if the configure option @option{--with-gnu-as} is used.
7924 @item -msplit-addresses
7925 @itemx -mno-split-addresses
7926 @opindex msplit-addresses
7927 @opindex mno-split-addresses
7928 Generate code to load the high and low parts of address constants separately.
7929 This allows GCC to optimize away redundant loads of the high order
7930 bits of addresses. This optimization requires GNU as and GNU ld.
7931 This optimization is enabled by default for some embedded targets where
7932 GNU as and GNU ld are standard.
7938 The @option{-mrnames} switch says to output code using the MIPS software
7939 names for the registers, instead of the hardware names (ie, @var{a0}
7940 instead of @var{$4}). The only known assembler that supports this option
7941 is the Algorithmics assembler.
7947 The @option{-mgpopt} switch says to write all of the data declarations
7948 before the instructions in the text section, this allows the MIPS
7949 assembler to generate one word memory references instead of using two
7950 words for short global or static data items. This is on by default if
7951 optimization is selected.
7957 The @option{-mmemcpy} switch makes all block moves call the appropriate
7958 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
7959 generating inline code.
7962 @itemx -mno-mips-tfile
7963 @opindex mmips-tfile
7964 @opindex mno-mips-tfile
7965 The @option{-mno-mips-tfile} switch causes the compiler not
7966 postprocess the object file with the @file{mips-tfile} program,
7967 after the MIPS assembler has generated it to add debug support. If
7968 @file{mips-tfile} is not run, then no local variables will be
7969 available to the debugger. In addition, @file{stage2} and
7970 @file{stage3} objects will have the temporary file names passed to the
7971 assembler embedded in the object file, which means the objects will
7972 not compare the same. The @option{-mno-mips-tfile} switch should only
7973 be used when there are bugs in the @file{mips-tfile} program that
7974 prevents compilation.
7977 @opindex msoft-float
7978 Generate output containing library calls for floating point.
7979 @strong{Warning:} the requisite libraries are not part of GCC@.
7980 Normally the facilities of the machine's usual C compiler are used, but
7981 this can't be done directly in cross-compilation. You must make your
7982 own arrangements to provide suitable library functions for
7986 @opindex mhard-float
7987 Generate output containing floating point instructions. This is the
7988 default if you use the unmodified sources.
7991 @itemx -mno-abicalls
7993 @opindex mno-abicalls
7994 Emit (or do not emit) the pseudo operations @samp{.abicalls},
7995 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
7996 position independent code.
7999 @itemx -mno-long-calls
8000 @opindex mlong-calls
8001 @opindex mno-long-calls
8002 Do all calls with the @samp{JALR} instruction, which requires
8003 loading up a function's address into a register before the call.
8004 You need to use this switch, if you call outside of the current
8005 512 megabyte segment to functions that are not through pointers.
8008 @itemx -mno-half-pic
8010 @opindex mno-half-pic
8011 Put pointers to extern references into the data section and load them
8012 up, rather than put the references in the text section.
8014 @item -membedded-pic
8015 @itemx -mno-embedded-pic
8016 @opindex membedded-pic
8017 @opindex mno-embedded-pic
8018 Generate PIC code suitable for some embedded systems. All calls are
8019 made using PC relative address, and all data is addressed using the $gp
8020 register. No more than 65536 bytes of global data may be used. This
8021 requires GNU as and GNU ld which do most of the work. This currently
8022 only works on targets which use ECOFF; it does not work with ELF@.
8024 @item -membedded-data
8025 @itemx -mno-embedded-data
8026 @opindex membedded-data
8027 @opindex mno-embedded-data
8028 Allocate variables to the read-only data section first if possible, then
8029 next in the small data section if possible, otherwise in data. This gives
8030 slightly slower code than the default, but reduces the amount of RAM required
8031 when executing, and thus may be preferred for some embedded systems.
8033 @item -muninit-const-in-rodata
8034 @itemx -mno-uninit-const-in-rodata
8035 @opindex muninit-const-in-rodata
8036 @opindex mno-uninit-const-in-rodata
8037 When used together with @option{-membedded-data}, it will always store uninitialized
8038 const variables in the read-only data section.
8040 @item -msingle-float
8041 @itemx -mdouble-float
8042 @opindex msingle-float
8043 @opindex mdouble-float
8044 The @option{-msingle-float} switch tells gcc to assume that the floating
8045 point coprocessor only supports single precision operations, as on the
8046 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
8047 double precision operations. This is the default.
8053 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
8054 as on the @samp{r4650} chip.
8058 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
8059 @option{-mcpu=r4650}.
8065 Enable 16-bit instructions.
8069 Use the entry and exit pseudo ops. This option can only be used with
8074 Compile code for the processor in little endian mode.
8075 The requisite libraries are assumed to exist.
8079 Compile code for the processor in big endian mode.
8080 The requisite libraries are assumed to exist.
8084 @cindex smaller data references (MIPS)
8085 @cindex gp-relative references (MIPS)
8086 Put global and static items less than or equal to @var{num} bytes into
8087 the small data or bss sections instead of the normal data or bss
8088 section. This allows the assembler to emit one word memory reference
8089 instructions based on the global pointer (@var{gp} or @var{$28}),
8090 instead of the normal two words used. By default, @var{num} is 8 when
8091 the MIPS assembler is used, and 0 when the GNU assembler is used. The
8092 @option{-G @var{num}} switch is also passed to the assembler and linker.
8093 All modules should be compiled with the same @option{-G @var{num}}
8098 Tell the MIPS assembler to not run its preprocessor over user
8099 assembler files (with a @samp{.s} suffix) when assembling them.
8103 Pass an option to gas which will cause nops to be inserted if
8104 the read of the destination register of an mfhi or mflo instruction
8105 occurs in the following two instructions.
8109 Do not include the default crt0.
8111 @item -mflush-func=@var{func}
8112 @itemx -mno-flush-func
8113 @opindex mflush-func
8114 Specifies the function to call to flush the I and D caches, or to not
8115 call any such function. If called, the function must take the same
8116 arguments as the common @code{_flush_func()}, that is, the address of the
8117 memory range for which the cache is being flushed, the size of the
8118 memory range, and the number 3 (to flush both caches). The default
8119 depends on the target gcc was configured for, but commonly is either
8120 @samp{_flush_func} or @samp{__cpu_flush}.
8122 @item -mbranch-likely
8123 @itemx -mno-branch-likely
8124 @opindex mbranch-likely
8125 @opindex mno-branch-likely
8126 Enable or disable use of Branch Likely instructions, regardless of the
8127 default for the selected architecture. By default, Branch Likely
8128 instructions may be generated if they are supported by the selected
8129 architecture. An exception is for the MIPS32 and MIPS64 architectures
8130 and processors which implement those architectures; for those, Branch
8131 Likely instructions will not be generated by default because the MIPS32
8132 and MIPS64 architectures specifically deprecate their use.
8135 @node i386 and x86-64 Options
8136 @subsection Intel 386 and AMD x86-64 Options
8137 @cindex i386 Options
8138 @cindex x86-64 Options
8139 @cindex Intel 386 Options
8140 @cindex AMD x86-64 Options
8142 These @samp{-m} options are defined for the i386 and x86-64 family of
8146 @item -mtune=@var{cpu-type}
8148 Tune to @var{cpu-type} everything applicable about the generated code, except
8149 for the ABI and the set of available instructions. The choices for
8150 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
8151 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
8152 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
8153 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp},
8154 @samp{athlon-mp}, @samp{winchip-c6}, @samp{winchip2}, @samp{k8}, @samp{c3}
8157 While picking a specific @var{cpu-type} will schedule things appropriately
8158 for that particular chip, the compiler will not generate any code that
8159 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8160 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
8161 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
8162 AMD chips as opposed to the Intel ones.
8164 @item -march=@var{cpu-type}
8166 Generate instructions for the machine type @var{cpu-type}. The choices
8167 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8168 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8170 @item -mcpu=@var{cpu-type}
8172 A deprecated synonym for @option{-mtune}.
8181 @opindex mpentiumpro
8182 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8183 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8184 These synonyms are deprecated.
8186 @item -mfpmath=@var{unit}
8188 generate floating point arithmetics for selected unit @var{unit}. the choices
8193 Use the standard 387 floating point coprocessor present majority of chips and
8194 emulated otherwise. Code compiled with this option will run almost everywhere.
8195 The temporary results are computed in 80bit precision instead of precision
8196 specified by the type resulting in slightly different results compared to most
8197 of other chips. See @option{-ffloat-store} for more detailed description.
8199 This is the default choice for i386 compiler.
8202 Use scalar floating point instructions present in the SSE instruction set.
8203 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8204 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8205 instruction set supports only single precision arithmetics, thus the double and
8206 extended precision arithmetics is still done using 387. Later version, present
8207 only in Pentium4 and the future AMD x86-64 chips supports double precision
8210 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8211 @option{-msse2} switches to enable SSE extensions and make this option
8212 effective. For x86-64 compiler, these extensions are enabled by default.
8214 The resulting code should be considerably faster in majority of cases and avoid
8215 the numerical instability problems of 387 code, but may break some existing
8216 code that expects temporaries to be 80bit.
8218 This is the default choice for x86-64 compiler.
8221 Attempt to utilize both instruction sets at once. This effectively double the
8222 amount of available registers and on chips with separate execution units for
8223 387 and SSE the execution resources too. Use this option with care, as it is
8224 still experimental, because gcc register allocator does not model separate
8225 functional units well resulting in instable performance.
8228 @item -masm=@var{dialect}
8229 @opindex masm=@var{dialect}
8230 Output asm instructions using selected @var{dialect}. Supported choices are
8231 @samp{intel} or @samp{att} (the default one).
8236 @opindex mno-ieee-fp
8237 Control whether or not the compiler uses IEEE floating point
8238 comparisons. These handle correctly the case where the result of a
8239 comparison is unordered.
8242 @opindex msoft-float
8243 Generate output containing library calls for floating point.
8244 @strong{Warning:} the requisite libraries are not part of GCC@.
8245 Normally the facilities of the machine's usual C compiler are used, but
8246 this can't be done directly in cross-compilation. You must make your
8247 own arrangements to provide suitable library functions for
8250 On machines where a function returns floating point results in the 80387
8251 register stack, some floating point opcodes may be emitted even if
8252 @option{-msoft-float} is used.
8254 @item -mno-fp-ret-in-387
8255 @opindex mno-fp-ret-in-387
8256 Do not use the FPU registers for return values of functions.
8258 The usual calling convention has functions return values of types
8259 @code{float} and @code{double} in an FPU register, even if there
8260 is no FPU@. The idea is that the operating system should emulate
8263 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8264 in ordinary CPU registers instead.
8266 @item -mno-fancy-math-387
8267 @opindex mno-fancy-math-387
8268 Some 387 emulators do not support the @code{sin}, @code{cos} and
8269 @code{sqrt} instructions for the 387. Specify this option to avoid
8270 generating those instructions. This option is the default on FreeBSD,
8271 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8272 indicates that the target cpu will always have an FPU and so the
8273 instruction will not need emulation. As of revision 2.6.1, these
8274 instructions are not generated unless you also use the
8275 @option{-funsafe-math-optimizations} switch.
8277 @item -malign-double
8278 @itemx -mno-align-double
8279 @opindex malign-double
8280 @opindex mno-align-double
8281 Control whether GCC aligns @code{double}, @code{long double}, and
8282 @code{long long} variables on a two word boundary or a one word
8283 boundary. Aligning @code{double} variables on a two word boundary will
8284 produce code that runs somewhat faster on a @samp{Pentium} at the
8285 expense of more memory.
8287 @strong{Warning:} if you use the @option{-malign-double} switch,
8288 structures containing the above types will be aligned differently than
8289 the published application binary interface specifications for the 386
8290 and will not be binary compatible with structures in code compiled
8291 without that switch.
8293 @item -m96bit-long-double
8294 @item -m128bit-long-double
8295 @opindex m96bit-long-double
8296 @opindex m128bit-long-double
8297 These switches control the size of @code{long double} type. The i386
8298 application binary interface specifies the size to be 96 bits,
8299 so @option{-m96bit-long-double} is the default in 32 bit mode.
8301 Modern architectures (Pentium and newer) would prefer @code{long double}
8302 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8303 conforming to the ABI, this would not be possible. So specifying a
8304 @option{-m128bit-long-double} will align @code{long double}
8305 to a 16 byte boundary by padding the @code{long double} with an additional
8308 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8309 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8311 Notice that neither of these options enable any extra precision over the x87
8312 standard of 80 bits for a @code{long double}.
8314 @strong{Warning:} if you override the default value for your target ABI, the
8315 structures and arrays containing @code{long double} will change their size as
8316 well as function calling convention for function taking @code{long double}
8317 will be modified. Hence they will not be binary compatible with arrays or
8318 structures in code compiled without that switch.
8322 @itemx -mno-svr3-shlib
8323 @opindex msvr3-shlib
8324 @opindex mno-svr3-shlib
8325 Control whether GCC places uninitialized local variables into the
8326 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8327 into @code{bss}. These options are meaningful only on System V Release 3.
8331 Use a different function-calling convention, in which functions that
8332 take a fixed number of arguments return with the @code{ret} @var{num}
8333 instruction, which pops their arguments while returning. This saves one
8334 instruction in the caller since there is no need to pop the arguments
8337 You can specify that an individual function is called with this calling
8338 sequence with the function attribute @samp{stdcall}. You can also
8339 override the @option{-mrtd} option by using the function attribute
8340 @samp{cdecl}. @xref{Function Attributes}.
8342 @strong{Warning:} this calling convention is incompatible with the one
8343 normally used on Unix, so you cannot use it if you need to call
8344 libraries compiled with the Unix compiler.
8346 Also, you must provide function prototypes for all functions that
8347 take variable numbers of arguments (including @code{printf});
8348 otherwise incorrect code will be generated for calls to those
8351 In addition, seriously incorrect code will result if you call a
8352 function with too many arguments. (Normally, extra arguments are
8353 harmlessly ignored.)
8355 @item -mregparm=@var{num}
8357 Control how many registers are used to pass integer arguments. By
8358 default, no registers are used to pass arguments, and at most 3
8359 registers can be used. You can control this behavior for a specific
8360 function by using the function attribute @samp{regparm}.
8361 @xref{Function Attributes}.
8363 @strong{Warning:} if you use this switch, and
8364 @var{num} is nonzero, then you must build all modules with the same
8365 value, including any libraries. This includes the system libraries and
8368 @item -mpreferred-stack-boundary=@var{num}
8369 @opindex mpreferred-stack-boundary
8370 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8371 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8372 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8373 size (@option{-Os}), in which case the default is the minimum correct
8374 alignment (4 bytes for x86, and 8 bytes for x86-64).
8376 On Pentium and PentiumPro, @code{double} and @code{long double} values
8377 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8378 suffer significant run time performance penalties. On Pentium III, the
8379 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8380 penalties if it is not 16 byte aligned.
8382 To ensure proper alignment of this values on the stack, the stack boundary
8383 must be as aligned as that required by any value stored on the stack.
8384 Further, every function must be generated such that it keeps the stack
8385 aligned. Thus calling a function compiled with a higher preferred
8386 stack boundary from a function compiled with a lower preferred stack
8387 boundary will most likely misalign the stack. It is recommended that
8388 libraries that use callbacks always use the default setting.
8390 This extra alignment does consume extra stack space, and generally
8391 increases code size. Code that is sensitive to stack space usage, such
8392 as embedded systems and operating system kernels, may want to reduce the
8393 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8409 These switches enable or disable the use of built-in functions that allow
8410 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
8412 @xref{X86 Built-in Functions}, for details of the functions enabled
8413 and disabled by these switches.
8415 To have SSE/SSE2 instructions generated automatically from floating-point
8416 code, see @option{-mfpmath=sse}.
8419 @itemx -mno-push-args
8421 @opindex mno-push-args
8422 Use PUSH operations to store outgoing parameters. This method is shorter
8423 and usually equally fast as method using SUB/MOV operations and is enabled
8424 by default. In some cases disabling it may improve performance because of
8425 improved scheduling and reduced dependencies.
8427 @item -maccumulate-outgoing-args
8428 @opindex maccumulate-outgoing-args
8429 If enabled, the maximum amount of space required for outgoing arguments will be
8430 computed in the function prologue. This is faster on most modern CPUs
8431 because of reduced dependencies, improved scheduling and reduced stack usage
8432 when preferred stack boundary is not equal to 2. The drawback is a notable
8433 increase in code size. This switch implies @option{-mno-push-args}.
8437 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8438 on thread-safe exception handling must compile and link all code with the
8439 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8440 @option{-D_MT}; when linking, it links in a special thread helper library
8441 @option{-lmingwthrd} which cleans up per thread exception handling data.
8443 @item -mno-align-stringops
8444 @opindex mno-align-stringops
8445 Do not align destination of inlined string operations. This switch reduces
8446 code size and improves performance in case the destination is already aligned,
8447 but gcc don't know about it.
8449 @item -minline-all-stringops
8450 @opindex minline-all-stringops
8451 By default GCC inlines string operations only when destination is known to be
8452 aligned at least to 4 byte boundary. This enables more inlining, increase code
8453 size, but may improve performance of code that depends on fast memcpy, strlen
8454 and memset for short lengths.
8456 @item -momit-leaf-frame-pointer
8457 @opindex momit-leaf-frame-pointer
8458 Don't keep the frame pointer in a register for leaf functions. This
8459 avoids the instructions to save, set up and restore frame pointers and
8460 makes an extra register available in leaf functions. The option
8461 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8462 which might make debugging harder.
8464 @item -mtls-direct-seg-refs
8465 @itemx -mno-tls-direct-seg-refs
8466 @opindex mtls-direct-seg-refs
8467 Controls whether TLS variables may be accessed with offsets from the
8468 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8469 or whether the thread base pointer must be added. Whether or not this
8470 is legal depends on the operating system, and whether it maps the
8471 segment to cover the entire TLS area.
8473 For systems that use GNU libc, the default is on.
8476 These @samp{-m} switches are supported in addition to the above
8477 on AMD x86-64 processors in 64-bit environments.
8484 Generate code for a 32-bit or 64-bit environment.
8485 The 32-bit environment sets int, long and pointer to 32 bits and
8486 generates code that runs on any i386 system.
8487 The 64-bit environment sets int to 32 bits and long and pointer
8488 to 64 bits and generates code for AMD's x86-64 architecture.
8491 @opindex no-red-zone
8492 Do not use a so called red zone for x86-64 code. The red zone is mandated
8493 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8494 stack pointer that will not be modified by signal or interrupt handlers
8495 and therefore can be used for temporary data without adjusting the stack
8496 pointer. The flag @option{-mno-red-zone} disables this red zone.
8498 @item -mcmodel=small
8499 @opindex mcmodel=small
8500 Generate code for the small code model: the program and its symbols must
8501 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8502 Programs can be statically or dynamically linked. This is the default
8505 @item -mcmodel=kernel
8506 @opindex mcmodel=kernel
8507 Generate code for the kernel code model. The kernel runs in the
8508 negative 2 GB of the address space.
8509 This model has to be used for Linux kernel code.
8511 @item -mcmodel=medium
8512 @opindex mcmodel=medium
8513 Generate code for the medium model: The program is linked in the lower 2
8514 GB of the address space but symbols can be located anywhere in the
8515 address space. Programs can be statically or dynamically linked, but
8516 building of shared libraries are not supported with the medium model.
8518 @item -mcmodel=large
8519 @opindex mcmodel=large
8520 Generate code for the large model: This model makes no assumptions
8521 about addresses and sizes of sections. Currently GCC does not implement
8526 @subsection HPPA Options
8527 @cindex HPPA Options
8529 These @samp{-m} options are defined for the HPPA family of computers:
8532 @item -march=@var{architecture-type}
8534 Generate code for the specified architecture. The choices for
8535 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8536 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8537 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8538 architecture option for your machine. Code compiled for lower numbered
8539 architectures will run on higher numbered architectures, but not the
8542 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8543 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8547 @itemx -mpa-risc-1-1
8548 @itemx -mpa-risc-2-0
8549 @opindex mpa-risc-1-0
8550 @opindex mpa-risc-1-1
8551 @opindex mpa-risc-2-0
8552 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8555 @opindex mbig-switch
8556 Generate code suitable for big switch tables. Use this option only if
8557 the assembler/linker complain about out of range branches within a switch
8560 @item -mjump-in-delay
8561 @opindex mjump-in-delay
8562 Fill delay slots of function calls with unconditional jump instructions
8563 by modifying the return pointer for the function call to be the target
8564 of the conditional jump.
8566 @item -mdisable-fpregs
8567 @opindex mdisable-fpregs
8568 Prevent floating point registers from being used in any manner. This is
8569 necessary for compiling kernels which perform lazy context switching of
8570 floating point registers. If you use this option and attempt to perform
8571 floating point operations, the compiler will abort.
8573 @item -mdisable-indexing
8574 @opindex mdisable-indexing
8575 Prevent the compiler from using indexing address modes. This avoids some
8576 rather obscure problems when compiling MIG generated code under MACH@.
8578 @item -mno-space-regs
8579 @opindex mno-space-regs
8580 Generate code that assumes the target has no space registers. This allows
8581 GCC to generate faster indirect calls and use unscaled index address modes.
8583 Such code is suitable for level 0 PA systems and kernels.
8585 @item -mfast-indirect-calls
8586 @opindex mfast-indirect-calls
8587 Generate code that assumes calls never cross space boundaries. This
8588 allows GCC to emit code which performs faster indirect calls.
8590 This option will not work in the presence of shared libraries or nested
8593 @item -mlong-load-store
8594 @opindex mlong-load-store
8595 Generate 3-instruction load and store sequences as sometimes required by
8596 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8599 @item -mportable-runtime
8600 @opindex mportable-runtime
8601 Use the portable calling conventions proposed by HP for ELF systems.
8605 Enable the use of assembler directives only GAS understands.
8607 @item -mschedule=@var{cpu-type}
8609 Schedule code according to the constraints for the machine type
8610 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8611 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8612 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8613 proper scheduling option for your machine. The default scheduling is
8617 @opindex mlinker-opt
8618 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8619 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8620 linkers in which they give bogus error messages when linking some programs.
8623 @opindex msoft-float
8624 Generate output containing library calls for floating point.
8625 @strong{Warning:} the requisite libraries are not available for all HPPA
8626 targets. Normally the facilities of the machine's usual C compiler are
8627 used, but this cannot be done directly in cross-compilation. You must make
8628 your own arrangements to provide suitable library functions for
8629 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8630 does provide software floating point support.
8632 @option{-msoft-float} changes the calling convention in the output file;
8633 therefore, it is only useful if you compile @emph{all} of a program with
8634 this option. In particular, you need to compile @file{libgcc.a}, the
8635 library that comes with GCC, with @option{-msoft-float} in order for
8640 Generate the predefine, @code{_SIO}, for server IO. The default is
8641 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8642 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8643 options are available under HP-UX and HI-UX.
8647 Use GNU ld specific options. This passes @option{-shared} to ld when
8648 building a shared library. It is the default when GCC is configured,
8649 explicitly or implicitly, with the GNU linker. This option does not
8650 have any affect on which ld is called, it only changes what parameters
8651 are passed to that ld. The ld that is called is determined by the
8652 @option{--with-ld} configure option, gcc's program search path, and
8653 finally by the user's @env{PATH}. The linker used by GCC can be printed
8654 using @samp{which `gcc -print-prog-name=ld`}.
8658 Use HP ld specific options. This passes @option{-b} to ld when building
8659 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8660 links. It is the default when GCC is configured, explicitly or
8661 implicitly, with the HP linker. This option does not have any affect on
8662 which ld is called, it only changes what parameters are passed to that
8663 ld. The ld that is called is determined by the @option{--with-ld}
8664 configure option, gcc's program search path, and finally by the user's
8665 @env{PATH}. The linker used by GCC can be printed using @samp{which
8666 `gcc -print-prog-name=ld`}.
8669 @opindex mno-long-calls
8670 Generate code that uses long call sequences. This ensures that a call
8671 is always able to reach linker generated stubs. The default is to generate
8672 long calls only when the distance from the call site to the beginning
8673 of the function or translation unit, as the case may be, exceeds a
8674 predefined limit set by the branch type being used. The limits for
8675 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8676 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8679 Distances are measured from the beginning of functions when using the
8680 @option{-ffunction-sections} option, or when using the @option{-mgas}
8681 and @option{-mno-portable-runtime} options together under HP-UX with
8684 It is normally not desirable to use this option as it will degrade
8685 performance. However, it may be useful in large applications,
8686 particularly when partial linking is used to build the application.
8688 The types of long calls used depends on the capabilities of the
8689 assembler and linker, and the type of code being generated. The
8690 impact on systems that support long absolute calls, and long pic
8691 symbol-difference or pc-relative calls should be relatively small.
8692 However, an indirect call is used on 32-bit ELF systems in pic code
8693 and it is quite long.
8697 Suppress the generation of link options to search libdld.sl when the
8698 @option{-static} option is specified on HP-UX 10 and later.
8702 The HP-UX implementation of setlocale in libc has a dependency on
8703 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8704 when the @option{-static} option is specified, special link options
8705 are needed to resolve this dependency.
8707 On HP-UX 10 and later, the GCC driver adds the necessary options to
8708 link with libdld.sl when the @option{-static} option is specified.
8709 This causes the resulting binary to be dynamic. On the 64-bit port,
8710 the linkers generate dynamic binaries by default in any case. The
8711 @option{-nolibdld} option can be used to prevent the GCC driver from
8712 adding these link options.
8716 Add support for multithreading with the @dfn{dce thread} library
8717 under HP-UX. This option sets flags for both the preprocessor and
8721 @node Intel 960 Options
8722 @subsection Intel 960 Options
8724 These @samp{-m} options are defined for the Intel 960 implementations:
8727 @item -m@var{cpu-type}
8735 Assume the defaults for the machine type @var{cpu-type} for some of
8736 the other options, including instruction scheduling, floating point
8737 support, and addressing modes. The choices for @var{cpu-type} are
8738 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8739 @samp{sa}, and @samp{sb}.
8746 @opindex msoft-float
8747 The @option{-mnumerics} option indicates that the processor does support
8748 floating-point instructions. The @option{-msoft-float} option indicates
8749 that floating-point support should not be assumed.
8751 @item -mleaf-procedures
8752 @itemx -mno-leaf-procedures
8753 @opindex mleaf-procedures
8754 @opindex mno-leaf-procedures
8755 Do (or do not) attempt to alter leaf procedures to be callable with the
8756 @code{bal} instruction as well as @code{call}. This will result in more
8757 efficient code for explicit calls when the @code{bal} instruction can be
8758 substituted by the assembler or linker, but less efficient code in other
8759 cases, such as calls via function pointers, or using a linker that doesn't
8760 support this optimization.
8763 @itemx -mno-tail-call
8765 @opindex mno-tail-call
8766 Do (or do not) make additional attempts (beyond those of the
8767 machine-independent portions of the compiler) to optimize tail-recursive
8768 calls into branches. You may not want to do this because the detection of
8769 cases where this is not valid is not totally complete. The default is
8770 @option{-mno-tail-call}.
8772 @item -mcomplex-addr
8773 @itemx -mno-complex-addr
8774 @opindex mcomplex-addr
8775 @opindex mno-complex-addr
8776 Assume (or do not assume) that the use of a complex addressing mode is a
8777 win on this implementation of the i960. Complex addressing modes may not
8778 be worthwhile on the K-series, but they definitely are on the C-series.
8779 The default is currently @option{-mcomplex-addr} for all processors except
8783 @itemx -mno-code-align
8784 @opindex mcode-align
8785 @opindex mno-code-align
8786 Align code to 8-byte boundaries for faster fetching (or don't bother).
8787 Currently turned on by default for C-series implementations only.
8790 @item -mclean-linkage
8791 @itemx -mno-clean-linkage
8792 @opindex mclean-linkage
8793 @opindex mno-clean-linkage
8794 These options are not fully implemented.
8798 @itemx -mic2.0-compat
8799 @itemx -mic3.0-compat
8801 @opindex mic2.0-compat
8802 @opindex mic3.0-compat
8803 Enable compatibility with iC960 v2.0 or v3.0.
8807 @opindex masm-compat
8809 Enable compatibility with the iC960 assembler.
8811 @item -mstrict-align
8812 @itemx -mno-strict-align
8813 @opindex mstrict-align
8814 @opindex mno-strict-align
8815 Do not permit (do permit) unaligned accesses.
8819 Enable structure-alignment compatibility with Intel's gcc release version
8820 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8822 @item -mlong-double-64
8823 @opindex mlong-double-64
8824 Implement type @samp{long double} as 64-bit floating point numbers.
8825 Without the option @samp{long double} is implemented by 80-bit
8826 floating point numbers. The only reason we have it because there is
8827 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8828 is only useful for people using soft-float targets. Otherwise, we
8829 should recommend against use of it.
8833 @node DEC Alpha Options
8834 @subsection DEC Alpha Options
8836 These @samp{-m} options are defined for the DEC Alpha implementations:
8839 @item -mno-soft-float
8841 @opindex mno-soft-float
8842 @opindex msoft-float
8843 Use (do not use) the hardware floating-point instructions for
8844 floating-point operations. When @option{-msoft-float} is specified,
8845 functions in @file{libgcc.a} will be used to perform floating-point
8846 operations. Unless they are replaced by routines that emulate the
8847 floating-point operations, or compiled in such a way as to call such
8848 emulations routines, these routines will issue floating-point
8849 operations. If you are compiling for an Alpha without floating-point
8850 operations, you must ensure that the library is built so as not to call
8853 Note that Alpha implementations without floating-point operations are
8854 required to have floating-point registers.
8859 @opindex mno-fp-regs
8860 Generate code that uses (does not use) the floating-point register set.
8861 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8862 register set is not used, floating point operands are passed in integer
8863 registers as if they were integers and floating-point results are passed
8864 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8865 so any function with a floating-point argument or return value called by code
8866 compiled with @option{-mno-fp-regs} must also be compiled with that
8869 A typical use of this option is building a kernel that does not use,
8870 and hence need not save and restore, any floating-point registers.
8874 The Alpha architecture implements floating-point hardware optimized for
8875 maximum performance. It is mostly compliant with the IEEE floating
8876 point standard. However, for full compliance, software assistance is
8877 required. This option generates code fully IEEE compliant code
8878 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8879 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8880 defined during compilation. The resulting code is less efficient but is
8881 able to correctly support denormalized numbers and exceptional IEEE
8882 values such as not-a-number and plus/minus infinity. Other Alpha
8883 compilers call this option @option{-ieee_with_no_inexact}.
8885 @item -mieee-with-inexact
8886 @opindex mieee-with-inexact
8887 This is like @option{-mieee} except the generated code also maintains
8888 the IEEE @var{inexact-flag}. Turning on this option causes the
8889 generated code to implement fully-compliant IEEE math. In addition to
8890 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8891 macro. On some Alpha implementations the resulting code may execute
8892 significantly slower than the code generated by default. Since there is
8893 very little code that depends on the @var{inexact-flag}, you should
8894 normally not specify this option. Other Alpha compilers call this
8895 option @option{-ieee_with_inexact}.
8897 @item -mfp-trap-mode=@var{trap-mode}
8898 @opindex mfp-trap-mode
8899 This option controls what floating-point related traps are enabled.
8900 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8901 The trap mode can be set to one of four values:
8905 This is the default (normal) setting. The only traps that are enabled
8906 are the ones that cannot be disabled in software (e.g., division by zero
8910 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8914 Like @samp{su}, but the instructions are marked to be safe for software
8915 completion (see Alpha architecture manual for details).
8918 Like @samp{su}, but inexact traps are enabled as well.
8921 @item -mfp-rounding-mode=@var{rounding-mode}
8922 @opindex mfp-rounding-mode
8923 Selects the IEEE rounding mode. Other Alpha compilers call this option
8924 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8929 Normal IEEE rounding mode. Floating point numbers are rounded towards
8930 the nearest machine number or towards the even machine number in case
8934 Round towards minus infinity.
8937 Chopped rounding mode. Floating point numbers are rounded towards zero.
8940 Dynamic rounding mode. A field in the floating point control register
8941 (@var{fpcr}, see Alpha architecture reference manual) controls the
8942 rounding mode in effect. The C library initializes this register for
8943 rounding towards plus infinity. Thus, unless your program modifies the
8944 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8947 @item -mtrap-precision=@var{trap-precision}
8948 @opindex mtrap-precision
8949 In the Alpha architecture, floating point traps are imprecise. This
8950 means without software assistance it is impossible to recover from a
8951 floating trap and program execution normally needs to be terminated.
8952 GCC can generate code that can assist operating system trap handlers
8953 in determining the exact location that caused a floating point trap.
8954 Depending on the requirements of an application, different levels of
8955 precisions can be selected:
8959 Program precision. This option is the default and means a trap handler
8960 can only identify which program caused a floating point exception.
8963 Function precision. The trap handler can determine the function that
8964 caused a floating point exception.
8967 Instruction precision. The trap handler can determine the exact
8968 instruction that caused a floating point exception.
8971 Other Alpha compilers provide the equivalent options called
8972 @option{-scope_safe} and @option{-resumption_safe}.
8974 @item -mieee-conformant
8975 @opindex mieee-conformant
8976 This option marks the generated code as IEEE conformant. You must not
8977 use this option unless you also specify @option{-mtrap-precision=i} and either
8978 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8979 is to emit the line @samp{.eflag 48} in the function prologue of the
8980 generated assembly file. Under DEC Unix, this has the effect that
8981 IEEE-conformant math library routines will be linked in.
8983 @item -mbuild-constants
8984 @opindex mbuild-constants
8985 Normally GCC examines a 32- or 64-bit integer constant to
8986 see if it can construct it from smaller constants in two or three
8987 instructions. If it cannot, it will output the constant as a literal and
8988 generate code to load it from the data segment at runtime.
8990 Use this option to require GCC to construct @emph{all} integer constants
8991 using code, even if it takes more instructions (the maximum is six).
8993 You would typically use this option to build a shared library dynamic
8994 loader. Itself a shared library, it must relocate itself in memory
8995 before it can find the variables and constants in its own data segment.
9001 Select whether to generate code to be assembled by the vendor-supplied
9002 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9020 Indicate whether GCC should generate code to use the optional BWX,
9021 CIX, FIX and MAX instruction sets. The default is to use the instruction
9022 sets supported by the CPU type specified via @option{-mcpu=} option or that
9023 of the CPU on which GCC was built if none was specified.
9028 @opindex mfloat-ieee
9029 Generate code that uses (does not use) VAX F and G floating point
9030 arithmetic instead of IEEE single and double precision.
9032 @item -mexplicit-relocs
9033 @itemx -mno-explicit-relocs
9034 @opindex mexplicit-relocs
9035 @opindex mno-explicit-relocs
9036 Older Alpha assemblers provided no way to generate symbol relocations
9037 except via assembler macros. Use of these macros does not allow
9038 optimal instruction scheduling. GNU binutils as of version 2.12
9039 supports a new syntax that allows the compiler to explicitly mark
9040 which relocations should apply to which instructions. This option
9041 is mostly useful for debugging, as GCC detects the capabilities of
9042 the assembler when it is built and sets the default accordingly.
9046 @opindex msmall-data
9047 @opindex mlarge-data
9048 When @option{-mexplicit-relocs} is in effect, static data is
9049 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9050 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9051 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9052 16-bit relocations off of the @code{$gp} register. This limits the
9053 size of the small data area to 64KB, but allows the variables to be
9054 directly accessed via a single instruction.
9056 The default is @option{-mlarge-data}. With this option the data area
9057 is limited to just below 2GB. Programs that require more than 2GB of
9058 data must use @code{malloc} or @code{mmap} to allocate the data in the
9059 heap instead of in the program's data segment.
9061 When generating code for shared libraries, @option{-fpic} implies
9062 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9066 @opindex msmall-text
9067 @opindex mlarge-text
9068 When @option{-msmall-text} is used, the compiler assumes that the
9069 code of the entire program (or shared library) fits in 4MB, and is
9070 thus reachable with a branch instruction. When @option{-msmall-data}
9071 is used, the compiler can assume that all local symbols share the
9072 same @code{$gp} value, and thus reduce the number of instructions
9073 required for a function call from 4 to 1.
9075 The default is @option{-mlarge-text}.
9077 @item -mcpu=@var{cpu_type}
9079 Set the instruction set and instruction scheduling parameters for
9080 machine type @var{cpu_type}. You can specify either the @samp{EV}
9081 style name or the corresponding chip number. GCC supports scheduling
9082 parameters for the EV4, EV5 and EV6 family of processors and will
9083 choose the default values for the instruction set from the processor
9084 you specify. If you do not specify a processor type, GCC will default
9085 to the processor on which the compiler was built.
9087 Supported values for @var{cpu_type} are
9093 Schedules as an EV4 and has no instruction set extensions.
9097 Schedules as an EV5 and has no instruction set extensions.
9101 Schedules as an EV5 and supports the BWX extension.
9106 Schedules as an EV5 and supports the BWX and MAX extensions.
9110 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9114 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9117 @item -mtune=@var{cpu_type}
9119 Set only the instruction scheduling parameters for machine type
9120 @var{cpu_type}. The instruction set is not changed.
9122 @item -mmemory-latency=@var{time}
9123 @opindex mmemory-latency
9124 Sets the latency the scheduler should assume for typical memory
9125 references as seen by the application. This number is highly
9126 dependent on the memory access patterns used by the application
9127 and the size of the external cache on the machine.
9129 Valid options for @var{time} are
9133 A decimal number representing clock cycles.
9139 The compiler contains estimates of the number of clock cycles for
9140 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9141 (also called Dcache, Scache, and Bcache), as well as to main memory.
9142 Note that L3 is only valid for EV5.
9147 @node DEC Alpha/VMS Options
9148 @subsection DEC Alpha/VMS Options
9150 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9153 @item -mvms-return-codes
9154 @opindex mvms-return-codes
9155 Return VMS condition codes from main. The default is to return POSIX
9156 style condition (e.g.@ error) codes.
9159 @node H8/300 Options
9160 @subsection H8/300 Options
9162 These @samp{-m} options are defined for the H8/300 implementations:
9167 Shorten some address references at link time, when possible; uses the
9168 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9169 ld.info, Using ld}, for a fuller description.
9173 Generate code for the H8/300H@.
9177 Generate code for the H8S@.
9181 Generate code for the H8S and H8/300H in the normal mode. This switch
9182 must be used either with -mh or -ms.
9186 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9190 Make @code{int} data 32 bits by default.
9194 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9195 The default for the H8/300H and H8S is to align longs and floats on 4
9197 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9198 This option has no effect on the H8/300.
9202 @subsection SH Options
9204 These @samp{-m} options are defined for the SH implementations:
9209 Generate code for the SH1.
9213 Generate code for the SH2.
9216 Generate code for the SH2e.
9220 Generate code for the SH3.
9224 Generate code for the SH3e.
9228 Generate code for the SH4 without a floating-point unit.
9230 @item -m4-single-only
9231 @opindex m4-single-only
9232 Generate code for the SH4 with a floating-point unit that only
9233 supports single-precision arithmetic.
9237 Generate code for the SH4 assuming the floating-point unit is in
9238 single-precision mode by default.
9242 Generate code for the SH4.
9246 Compile code for the processor in big endian mode.
9250 Compile code for the processor in little endian mode.
9254 Align doubles at 64-bit boundaries. Note that this changes the calling
9255 conventions, and thus some functions from the standard C library will
9256 not work unless you recompile it first with @option{-mdalign}.
9260 Shorten some address references at link time, when possible; uses the
9261 linker option @option{-relax}.
9265 Use 32-bit offsets in @code{switch} tables. The default is to use
9270 Enable the use of the instruction @code{fmovd}.
9274 Comply with the calling conventions defined by Renesas.
9278 Mark the @code{MAC} register as call-clobbered, even if
9279 @option{-mhitachi} is given.
9283 Increase IEEE-compliance of floating-point code.
9287 Dump instruction size and location in the assembly code.
9291 This option is deprecated. It pads structures to multiple of 4 bytes,
9292 which is incompatible with the SH ABI@.
9296 Optimize for space instead of speed. Implied by @option{-Os}.
9300 When generating position-independent code, emit function calls using
9301 the Global Offset Table instead of the Procedure Linkage Table.
9305 Generate a library function call to invalidate instruction cache
9306 entries, after fixing up a trampoline. This library function call
9307 doesn't assume it can write to the whole memory address space. This
9308 is the default when the target is @code{sh-*-linux*}.
9311 @node System V Options
9312 @subsection Options for System V
9314 These additional options are available on System V Release 4 for
9315 compatibility with other compilers on those systems:
9320 Create a shared object.
9321 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
9325 Identify the versions of each tool used by the compiler, in a
9326 @code{.ident} assembler directive in the output.
9330 Refrain from adding @code{.ident} directives to the output file (this is
9333 @item -YP,@var{dirs}
9335 Search the directories @var{dirs}, and no others, for libraries
9336 specified with @option{-l}.
9340 Look in the directory @var{dir} to find the M4 preprocessor.
9341 The assembler uses this option.
9342 @c This is supposed to go with a -Yd for predefined M4 macro files, but
9343 @c the generic assembler that comes with Solaris takes just -Ym.
9346 @node TMS320C3x/C4x Options
9347 @subsection TMS320C3x/C4x Options
9348 @cindex TMS320C3x/C4x Options
9350 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
9354 @item -mcpu=@var{cpu_type}
9356 Set the instruction set, register set, and instruction scheduling
9357 parameters for machine type @var{cpu_type}. Supported values for
9358 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
9359 @samp{c44}. The default is @samp{c40} to generate code for the
9364 @itemx -msmall-memory
9366 @opindex mbig-memory
9368 @opindex msmall-memory
9370 Generates code for the big or small memory model. The small memory
9371 model assumed that all data fits into one 64K word page. At run-time
9372 the data page (DP) register must be set to point to the 64K page
9373 containing the .bss and .data program sections. The big memory model is
9374 the default and requires reloading of the DP register for every direct
9381 Allow (disallow) allocation of general integer operands into the block
9388 Enable (disable) generation of code using decrement and branch,
9389 DBcond(D), instructions. This is enabled by default for the C4x. To be
9390 on the safe side, this is disabled for the C3x, since the maximum
9391 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
9392 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
9393 that it can utilize the decrement and branch instruction, but will give
9394 up if there is more than one memory reference in the loop. Thus a loop
9395 where the loop counter is decremented can generate slightly more
9396 efficient code, in cases where the RPTB instruction cannot be utilized.
9398 @item -mdp-isr-reload
9400 @opindex mdp-isr-reload
9402 Force the DP register to be saved on entry to an interrupt service
9403 routine (ISR), reloaded to point to the data section, and restored on
9404 exit from the ISR@. This should not be required unless someone has
9405 violated the small memory model by modifying the DP register, say within
9412 For the C3x use the 24-bit MPYI instruction for integer multiplies
9413 instead of a library call to guarantee 32-bit results. Note that if one
9414 of the operands is a constant, then the multiplication will be performed
9415 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
9416 then squaring operations are performed inline instead of a library call.
9419 @itemx -mno-fast-fix
9421 @opindex mno-fast-fix
9422 The C3x/C4x FIX instruction to convert a floating point value to an
9423 integer value chooses the nearest integer less than or equal to the
9424 floating point value rather than to the nearest integer. Thus if the
9425 floating point number is negative, the result will be incorrectly
9426 truncated an additional code is necessary to detect and correct this
9427 case. This option can be used to disable generation of the additional
9428 code required to correct the result.
9434 Enable (disable) generation of repeat block sequences using the RPTB
9435 instruction for zero overhead looping. The RPTB construct is only used
9436 for innermost loops that do not call functions or jump across the loop
9437 boundaries. There is no advantage having nested RPTB loops due to the
9438 overhead required to save and restore the RC, RS, and RE registers.
9439 This is enabled by default with @option{-O2}.
9441 @item -mrpts=@var{count}
9445 Enable (disable) the use of the single instruction repeat instruction
9446 RPTS@. If a repeat block contains a single instruction, and the loop
9447 count can be guaranteed to be less than the value @var{count}, GCC will
9448 emit a RPTS instruction instead of a RPTB@. If no value is specified,
9449 then a RPTS will be emitted even if the loop count cannot be determined
9450 at compile time. Note that the repeated instruction following RPTS does
9451 not have to be reloaded from memory each iteration, thus freeing up the
9452 CPU buses for operands. However, since interrupts are blocked by this
9453 instruction, it is disabled by default.
9455 @item -mloop-unsigned
9456 @itemx -mno-loop-unsigned
9457 @opindex mloop-unsigned
9458 @opindex mno-loop-unsigned
9459 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
9460 is @math{2^{31} + 1} since these instructions test if the iteration count is
9461 negative to terminate the loop. If the iteration count is unsigned
9462 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
9463 exceeded. This switch allows an unsigned iteration count.
9467 Try to emit an assembler syntax that the TI assembler (asm30) is happy
9468 with. This also enforces compatibility with the API employed by the TI
9469 C3x C compiler. For example, long doubles are passed as structures
9470 rather than in floating point registers.
9476 Generate code that uses registers (stack) for passing arguments to functions.
9477 By default, arguments are passed in registers where possible rather
9478 than by pushing arguments on to the stack.
9480 @item -mparallel-insns
9481 @itemx -mno-parallel-insns
9482 @opindex mparallel-insns
9483 @opindex mno-parallel-insns
9484 Allow the generation of parallel instructions. This is enabled by
9485 default with @option{-O2}.
9487 @item -mparallel-mpy
9488 @itemx -mno-parallel-mpy
9489 @opindex mparallel-mpy
9490 @opindex mno-parallel-mpy
9491 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
9492 provided @option{-mparallel-insns} is also specified. These instructions have
9493 tight register constraints which can pessimize the code generation
9499 @subsection V850 Options
9500 @cindex V850 Options
9502 These @samp{-m} options are defined for V850 implementations:
9506 @itemx -mno-long-calls
9507 @opindex mlong-calls
9508 @opindex mno-long-calls
9509 Treat all calls as being far away (near). If calls are assumed to be
9510 far away, the compiler will always load the functions address up into a
9511 register, and call indirect through the pointer.
9517 Do not optimize (do optimize) basic blocks that use the same index
9518 pointer 4 or more times to copy pointer into the @code{ep} register, and
9519 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
9520 option is on by default if you optimize.
9522 @item -mno-prolog-function
9523 @itemx -mprolog-function
9524 @opindex mno-prolog-function
9525 @opindex mprolog-function
9526 Do not use (do use) external functions to save and restore registers at
9527 the prolog and epilog of a function. The external functions are slower,
9528 but use less code space if more than one function saves the same number
9529 of registers. The @option{-mprolog-function} option is on by default if
9534 Try to make the code as small as possible. At present, this just turns
9535 on the @option{-mep} and @option{-mprolog-function} options.
9539 Put static or global variables whose size is @var{n} bytes or less into
9540 the tiny data area that register @code{ep} points to. The tiny data
9541 area can hold up to 256 bytes in total (128 bytes for byte references).
9545 Put static or global variables whose size is @var{n} bytes or less into
9546 the small data area that register @code{gp} points to. The small data
9547 area can hold up to 64 kilobytes.
9551 Put static or global variables whose size is @var{n} bytes or less into
9552 the first 32 kilobytes of memory.
9556 Specify that the target processor is the V850.
9559 @opindex mbig-switch
9560 Generate code suitable for big switch tables. Use this option only if
9561 the assembler/linker complain about out of range branches within a switch
9566 This option will cause r2 and r5 to be used in the code generated by
9567 the compiler. This setting is the default.
9570 @opindex mno-app-regs
9571 This option will cause r2 and r5 to be treated as fixed registers.
9575 Specify that the target processor is the V850E. The preprocessor
9576 constant @samp{__v850e__} will be defined if this option is used.
9578 If neither @option{-mv850} nor @option{-mv850e} are defined
9579 then a default target processor will be chosen and the relevant
9580 @samp{__v850*__} preprocessor constant will be defined.
9582 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
9583 defined, regardless of which processor variant is the target.
9585 @item -mdisable-callt
9586 @opindex mdisable-callt
9587 This option will suppress generation of the CALLT instruction for the
9588 v850e flavors of the v850 architecture. The default is
9589 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
9594 @subsection ARC Options
9597 These options are defined for ARC implementations:
9602 Compile code for little endian mode. This is the default.
9606 Compile code for big endian mode.
9609 @opindex mmangle-cpu
9610 Prepend the name of the cpu to all public symbol names.
9611 In multiple-processor systems, there are many ARC variants with different
9612 instruction and register set characteristics. This flag prevents code
9613 compiled for one cpu to be linked with code compiled for another.
9614 No facility exists for handling variants that are ``almost identical''.
9615 This is an all or nothing option.
9617 @item -mcpu=@var{cpu}
9619 Compile code for ARC variant @var{cpu}.
9620 Which variants are supported depend on the configuration.
9621 All variants support @option{-mcpu=base}, this is the default.
9623 @item -mtext=@var{text-section}
9624 @itemx -mdata=@var{data-section}
9625 @itemx -mrodata=@var{readonly-data-section}
9629 Put functions, data, and readonly data in @var{text-section},
9630 @var{data-section}, and @var{readonly-data-section} respectively
9631 by default. This can be overridden with the @code{section} attribute.
9632 @xref{Variable Attributes}.
9637 @subsection NS32K Options
9638 @cindex NS32K options
9640 These are the @samp{-m} options defined for the 32000 series. The default
9641 values for these options depends on which style of 32000 was selected when
9642 the compiler was configured; the defaults for the most common choices are
9650 Generate output for a 32032. This is the default
9651 when the compiler is configured for 32032 and 32016 based systems.
9657 Generate output for a 32332. This is the default
9658 when the compiler is configured for 32332-based systems.
9664 Generate output for a 32532. This is the default
9665 when the compiler is configured for 32532-based systems.
9669 Generate output containing 32081 instructions for floating point.
9670 This is the default for all systems.
9674 Generate output containing 32381 instructions for floating point. This
9675 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9676 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9680 Try and generate multiply-add floating point instructions @code{polyF}
9681 and @code{dotF}. This option is only available if the @option{-m32381}
9682 option is in effect. Using these instructions requires changes to
9683 register allocation which generally has a negative impact on
9684 performance. This option should only be enabled when compiling code
9685 particularly likely to make heavy use of multiply-add instructions.
9688 @opindex mnomulti-add
9689 Do not try and generate multiply-add floating point instructions
9690 @code{polyF} and @code{dotF}. This is the default on all platforms.
9693 @opindex msoft-float
9694 Generate output containing library calls for floating point.
9695 @strong{Warning:} the requisite libraries may not be available.
9697 @item -mieee-compare
9698 @itemx -mno-ieee-compare
9699 @opindex mieee-compare
9700 @opindex mno-ieee-compare
9701 Control whether or not the compiler uses IEEE floating point
9702 comparisons. These handle correctly the case where the result of a
9703 comparison is unordered.
9704 @strong{Warning:} the requisite kernel support may not be available.
9707 @opindex mnobitfield
9708 Do not use the bit-field instructions. On some machines it is faster to
9709 use shifting and masking operations. This is the default for the pc532.
9713 Do use the bit-field instructions. This is the default for all platforms
9718 Use a different function-calling convention, in which functions
9719 that take a fixed number of arguments return pop their
9720 arguments on return with the @code{ret} instruction.
9722 This calling convention is incompatible with the one normally
9723 used on Unix, so you cannot use it if you need to call libraries
9724 compiled with the Unix compiler.
9726 Also, you must provide function prototypes for all functions that
9727 take variable numbers of arguments (including @code{printf});
9728 otherwise incorrect code will be generated for calls to those
9731 In addition, seriously incorrect code will result if you call a
9732 function with too many arguments. (Normally, extra arguments are
9733 harmlessly ignored.)
9735 This option takes its name from the 680x0 @code{rtd} instruction.
9740 Use a different function-calling convention where the first two arguments
9741 are passed in registers.
9743 This calling convention is incompatible with the one normally
9744 used on Unix, so you cannot use it if you need to call libraries
9745 compiled with the Unix compiler.
9748 @opindex mnoregparam
9749 Do not pass any arguments in registers. This is the default for all
9754 It is OK to use the sb as an index register which is always loaded with
9755 zero. This is the default for the pc532-netbsd target.
9759 The sb register is not available for use or has not been initialized to
9760 zero by the run time system. This is the default for all targets except
9761 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9762 @option{-fpic} is set.
9766 Many ns32000 series addressing modes use displacements of up to 512MB@.
9767 If an address is above 512MB then displacements from zero can not be used.
9768 This option causes code to be generated which can be loaded above 512MB@.
9769 This may be useful for operating systems or ROM code.
9773 Assume code will be loaded in the first 512MB of virtual address space.
9774 This is the default for all platforms.
9780 @subsection AVR Options
9783 These options are defined for AVR implementations:
9786 @item -mmcu=@var{mcu}
9788 Specify ATMEL AVR instruction set or MCU type.
9790 Instruction set avr1 is for the minimal AVR core, not supported by the C
9791 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9792 attiny11, attiny12, attiny15, attiny28).
9794 Instruction set avr2 (default) is for the classic AVR core with up to
9795 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9796 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9797 at90c8534, at90s8535).
9799 Instruction set avr3 is for the classic AVR core with up to 128K program
9800 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9802 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9803 memory space (MCU types: atmega8, atmega83, atmega85).
9805 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9806 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9807 atmega64, atmega128, at43usb355, at94k).
9811 Output instruction sizes to the asm file.
9813 @item -minit-stack=@var{N}
9814 @opindex minit-stack
9815 Specify the initial stack address, which may be a symbol or numeric value,
9816 @samp{__stack} is the default.
9818 @item -mno-interrupts
9819 @opindex mno-interrupts
9820 Generated code is not compatible with hardware interrupts.
9821 Code size will be smaller.
9823 @item -mcall-prologues
9824 @opindex mcall-prologues
9825 Functions prologues/epilogues expanded as call to appropriate
9826 subroutines. Code size will be smaller.
9828 @item -mno-tablejump
9829 @opindex mno-tablejump
9830 Do not generate tablejump insns which sometimes increase code size.
9833 @opindex mtiny-stack
9834 Change only the low 8 bits of the stack pointer.
9838 @subsection MCore Options
9839 @cindex MCore options
9841 These are the @samp{-m} options defined for the Motorola M*Core
9849 @opindex mno-hardlit
9850 Inline constants into the code stream if it can be done in two
9851 instructions or less.
9857 Use the divide instruction. (Enabled by default).
9859 @item -mrelax-immediate
9860 @itemx -mno-relax-immediate
9861 @opindex mrelax-immediate
9862 @opindex mno-relax-immediate
9863 Allow arbitrary sized immediates in bit operations.
9865 @item -mwide-bitfields
9866 @itemx -mno-wide-bitfields
9867 @opindex mwide-bitfields
9868 @opindex mno-wide-bitfields
9869 Always treat bit-fields as int-sized.
9871 @item -m4byte-functions
9872 @itemx -mno-4byte-functions
9873 @opindex m4byte-functions
9874 @opindex mno-4byte-functions
9875 Force all functions to be aligned to a four byte boundary.
9877 @item -mcallgraph-data
9878 @itemx -mno-callgraph-data
9879 @opindex mcallgraph-data
9880 @opindex mno-callgraph-data
9881 Emit callgraph information.
9884 @itemx -mno-slow-bytes
9885 @opindex mslow-bytes
9886 @opindex mno-slow-bytes
9887 Prefer word access when reading byte quantities.
9889 @item -mlittle-endian
9891 @opindex mlittle-endian
9892 @opindex mbig-endian
9893 Generate code for a little endian target.
9899 Generate code for the 210 processor.
9903 @subsection IA-64 Options
9904 @cindex IA-64 Options
9906 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9910 @opindex mbig-endian
9911 Generate code for a big endian target. This is the default for HP-UX@.
9913 @item -mlittle-endian
9914 @opindex mlittle-endian
9915 Generate code for a little endian target. This is the default for AIX5
9922 Generate (or don't) code for the GNU assembler. This is the default.
9923 @c Also, this is the default if the configure option @option{--with-gnu-as}
9930 Generate (or don't) code for the GNU linker. This is the default.
9931 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9936 Generate code that does not use a global pointer register. The result
9937 is not position independent code, and violates the IA-64 ABI@.
9939 @item -mvolatile-asm-stop
9940 @itemx -mno-volatile-asm-stop
9941 @opindex mvolatile-asm-stop
9942 @opindex mno-volatile-asm-stop
9943 Generate (or don't) a stop bit immediately before and after volatile asm
9948 Generate code that works around Itanium B step errata.
9950 @item -mregister-names
9951 @itemx -mno-register-names
9952 @opindex mregister-names
9953 @opindex mno-register-names
9954 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9955 the stacked registers. This may make assembler output more readable.
9961 Disable (or enable) optimizations that use the small data section. This may
9962 be useful for working around optimizer bugs.
9965 @opindex mconstant-gp
9966 Generate code that uses a single constant global pointer value. This is
9967 useful when compiling kernel code.
9971 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9972 This is useful when compiling firmware code.
9974 @item -minline-float-divide-min-latency
9975 @opindex minline-float-divide-min-latency
9976 Generate code for inline divides of floating point values
9977 using the minimum latency algorithm.
9979 @item -minline-float-divide-max-throughput
9980 @opindex minline-float-divide-max-throughput
9981 Generate code for inline divides of floating point values
9982 using the maximum throughput algorithm.
9984 @item -minline-int-divide-min-latency
9985 @opindex minline-int-divide-min-latency
9986 Generate code for inline divides of integer values
9987 using the minimum latency algorithm.
9989 @item -minline-int-divide-max-throughput
9990 @opindex minline-int-divide-max-throughput
9991 Generate code for inline divides of integer values
9992 using the maximum throughput algorithm.
9994 @item -mno-dwarf2-asm
9996 @opindex mno-dwarf2-asm
9997 @opindex mdwarf2-asm
9998 Don't (or do) generate assembler code for the DWARF2 line number debugging
9999 info. This may be useful when not using the GNU assembler.
10001 @item -mfixed-range=@var{register-range}
10002 @opindex mfixed-range
10003 Generate code treating the given register range as fixed registers.
10004 A fixed register is one that the register allocator can not use. This is
10005 useful when compiling kernel code. A register range is specified as
10006 two registers separated by a dash. Multiple register ranges can be
10007 specified separated by a comma.
10009 @item -mearly-stop-bits
10010 @itemx -mno-early-stop-bits
10011 @opindex mearly-stop-bits
10012 @opindex mno-early-stop-bits
10013 Allow stop bits to be placed earlier than immediately preceding the
10014 instruction that triggered the stop bit. This can improve instruction
10015 scheduling, but does not always do so.
10019 @subsection D30V Options
10020 @cindex D30V Options
10022 These @samp{-m} options are defined for D30V implementations:
10027 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
10028 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
10029 memory, which starts at location @code{0x80000000}.
10032 @opindex mextmemory
10033 Same as the @option{-mextmem} switch.
10037 Link the @samp{.text} section into onchip text memory, which starts at
10038 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
10039 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
10040 into onchip data memory, which starts at location @code{0x20000000}.
10042 @item -mno-asm-optimize
10043 @itemx -masm-optimize
10044 @opindex mno-asm-optimize
10045 @opindex masm-optimize
10046 Disable (enable) passing @option{-O} to the assembler when optimizing.
10047 The assembler uses the @option{-O} option to automatically parallelize
10048 adjacent short instructions where possible.
10050 @item -mbranch-cost=@var{n}
10051 @opindex mbranch-cost
10052 Increase the internal costs of branches to @var{n}. Higher costs means
10053 that the compiler will issue more instructions to avoid doing a branch.
10056 @item -mcond-exec=@var{n}
10057 @opindex mcond-exec
10058 Specify the maximum number of conditionally executed instructions that
10059 replace a branch. The default is 4.
10062 @node S/390 and zSeries Options
10063 @subsection S/390 and zSeries Options
10064 @cindex S/390 and zSeries Options
10066 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10070 @itemx -msoft-float
10071 @opindex mhard-float
10072 @opindex msoft-float
10073 Use (do not use) the hardware floating-point instructions and registers
10074 for floating-point operations. When @option{-msoft-float} is specified,
10075 functions in @file{libgcc.a} will be used to perform floating-point
10076 operations. When @option{-mhard-float} is specified, the compiler
10077 generates IEEE floating-point instructions. This is the default.
10080 @itemx -mno-backchain
10081 @opindex mbackchain
10082 @opindex mno-backchain
10083 Generate (or do not generate) code which maintains an explicit
10084 backchain within the stack frame that points to the caller's frame.
10085 This is currently needed to allow debugging. The default is to
10086 generate the backchain.
10089 @itemx -mno-small-exec
10090 @opindex msmall-exec
10091 @opindex mno-small-exec
10092 Generate (or do not generate) code using the @code{bras} instruction
10093 to do subroutine calls.
10094 This only works reliably if the total executable size does not
10095 exceed 64k. The default is to use the @code{basr} instruction instead,
10096 which does not have this limitation.
10102 When @option{-m31} is specified, generate code compliant to the
10103 Linux for S/390 ABI@. When @option{-m64} is specified, generate
10104 code compliant to the Linux for zSeries ABI@. This allows GCC in
10105 particular to generate 64-bit instructions. For the @samp{s390}
10106 targets, the default is @option{-m31}, while the @samp{s390x}
10107 targets default to @option{-m64}.
10113 When @option{-mzarch} is specified, generate code using the
10114 instructions available on z/Architecture.
10115 When @option{-mesa} is specified, generate code using the
10116 instructions available on ESA/390. Note that @option{-mesa} is
10117 not possible with @option{-m64}.
10118 For the @samp{s390} targets, the default is @option{-mesa},
10119 while the @samp{s390x} targets default to @option{-mzarch}.
10125 Generate (or do not generate) code using the @code{mvcle} instruction
10126 to perform block moves. When @option{-mno-mvcle} is specified,
10127 use a @code{mvc} loop instead. This is the default.
10133 Print (or do not print) additional debug information when compiling.
10134 The default is to not print debug information.
10136 @item -march=@var{arch}
10138 Generate code that will run on @var{arch}, which is the name of system
10139 representing a certain processor type. Possible values for
10140 @var{cpu-type} are @samp{g5}, @samp{g6} and @samp{z900}.
10142 @item -mtune=@var{arch}
10144 Tune to @var{cpu-type} everything applicable about the generated code,
10145 except for the ABI and the set of available instructions.
10146 The list of @var{arch} values is the same as for @option{-march}.
10151 @subsection CRIS Options
10152 @cindex CRIS Options
10154 These options are defined specifically for the CRIS ports.
10157 @item -march=@var{architecture-type}
10158 @itemx -mcpu=@var{architecture-type}
10161 Generate code for the specified architecture. The choices for
10162 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10163 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
10164 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10167 @item -mtune=@var{architecture-type}
10169 Tune to @var{architecture-type} everything applicable about the generated
10170 code, except for the ABI and the set of available instructions. The
10171 choices for @var{architecture-type} are the same as for
10172 @option{-march=@var{architecture-type}}.
10174 @item -mmax-stack-frame=@var{n}
10175 @opindex mmax-stack-frame
10176 Warn when the stack frame of a function exceeds @var{n} bytes.
10178 @item -melinux-stacksize=@var{n}
10179 @opindex melinux-stacksize
10180 Only available with the @samp{cris-axis-aout} target. Arranges for
10181 indications in the program to the kernel loader that the stack of the
10182 program should be set to @var{n} bytes.
10188 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10189 @option{-march=v3} and @option{-march=v8} respectively.
10193 Enable CRIS-specific verbose debug-related information in the assembly
10194 code. This option also has the effect to turn off the @samp{#NO_APP}
10195 formatted-code indicator to the assembler at the beginning of the
10200 Do not use condition-code results from previous instruction; always emit
10201 compare and test instructions before use of condition codes.
10203 @item -mno-side-effects
10204 @opindex mno-side-effects
10205 Do not emit instructions with side-effects in addressing modes other than
10208 @item -mstack-align
10209 @itemx -mno-stack-align
10210 @itemx -mdata-align
10211 @itemx -mno-data-align
10212 @itemx -mconst-align
10213 @itemx -mno-const-align
10214 @opindex mstack-align
10215 @opindex mno-stack-align
10216 @opindex mdata-align
10217 @opindex mno-data-align
10218 @opindex mconst-align
10219 @opindex mno-const-align
10220 These options (no-options) arranges (eliminate arrangements) for the
10221 stack-frame, individual data and constants to be aligned for the maximum
10222 single data access size for the chosen CPU model. The default is to
10223 arrange for 32-bit alignment. ABI details such as structure layout are
10224 not affected by these options.
10232 Similar to the stack- data- and const-align options above, these options
10233 arrange for stack-frame, writable data and constants to all be 32-bit,
10234 16-bit or 8-bit aligned. The default is 32-bit alignment.
10236 @item -mno-prologue-epilogue
10237 @itemx -mprologue-epilogue
10238 @opindex mno-prologue-epilogue
10239 @opindex mprologue-epilogue
10240 With @option{-mno-prologue-epilogue}, the normal function prologue and
10241 epilogue that sets up the stack-frame are omitted and no return
10242 instructions or return sequences are generated in the code. Use this
10243 option only together with visual inspection of the compiled code: no
10244 warnings or errors are generated when call-saved registers must be saved,
10245 or storage for local variable needs to be allocated.
10249 @opindex mno-gotplt
10251 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10252 instruction sequences that load addresses for functions from the PLT part
10253 of the GOT rather than (traditional on other architectures) calls to the
10254 PLT. The default is @option{-mgotplt}.
10258 Legacy no-op option only recognized with the cris-axis-aout target.
10262 Legacy no-op option only recognized with the cris-axis-elf and
10263 cris-axis-linux-gnu targets.
10267 Only recognized with the cris-axis-aout target, where it selects a
10268 GNU/linux-like multilib, include files and instruction set for
10269 @option{-march=v8}.
10273 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10277 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
10278 to link with input-output functions from a simulator library. Code,
10279 initialized data and zero-initialized data are allocated consecutively.
10283 Like @option{-sim}, but pass linker options to locate initialized data at
10284 0x40000000 and zero-initialized data at 0x80000000.
10288 @subsection MMIX Options
10289 @cindex MMIX Options
10291 These options are defined for the MMIX:
10295 @itemx -mno-libfuncs
10297 @opindex mno-libfuncs
10298 Specify that intrinsic library functions are being compiled, passing all
10299 values in registers, no matter the size.
10302 @itemx -mno-epsilon
10304 @opindex mno-epsilon
10305 Generate floating-point comparison instructions that compare with respect
10306 to the @code{rE} epsilon register.
10308 @item -mabi=mmixware
10310 @opindex mabi-mmixware
10312 Generate code that passes function parameters and return values that (in
10313 the called function) are seen as registers @code{$0} and up, as opposed to
10314 the GNU ABI which uses global registers @code{$231} and up.
10316 @item -mzero-extend
10317 @itemx -mno-zero-extend
10318 @opindex mzero-extend
10319 @opindex mno-zero-extend
10320 When reading data from memory in sizes shorter than 64 bits, use (do not
10321 use) zero-extending load instructions by default, rather than
10322 sign-extending ones.
10325 @itemx -mno-knuthdiv
10327 @opindex mno-knuthdiv
10328 Make the result of a division yielding a remainder have the same sign as
10329 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10330 remainder follows the sign of the dividend. Both methods are
10331 arithmetically valid, the latter being almost exclusively used.
10333 @item -mtoplevel-symbols
10334 @itemx -mno-toplevel-symbols
10335 @opindex mtoplevel-symbols
10336 @opindex mno-toplevel-symbols
10337 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10338 code can be used with the @code{PREFIX} assembly directive.
10342 Generate an executable in the ELF format, rather than the default
10343 @samp{mmo} format used by the @command{mmix} simulator.
10345 @item -mbranch-predict
10346 @itemx -mno-branch-predict
10347 @opindex mbranch-predict
10348 @opindex mno-branch-predict
10349 Use (do not use) the probable-branch instructions, when static branch
10350 prediction indicates a probable branch.
10352 @item -mbase-addresses
10353 @itemx -mno-base-addresses
10354 @opindex mbase-addresses
10355 @opindex mno-base-addresses
10356 Generate (do not generate) code that uses @emph{base addresses}. Using a
10357 base address automatically generates a request (handled by the assembler
10358 and the linker) for a constant to be set up in a global register. The
10359 register is used for one or more base address requests within the range 0
10360 to 255 from the value held in the register. The generally leads to short
10361 and fast code, but the number of different data items that can be
10362 addressed is limited. This means that a program that uses lots of static
10363 data may require @option{-mno-base-addresses}.
10365 @item -msingle-exit
10366 @itemx -mno-single-exit
10367 @opindex msingle-exit
10368 @opindex mno-single-exit
10369 Force (do not force) generated code to have a single exit point in each
10373 @node PDP-11 Options
10374 @subsection PDP-11 Options
10375 @cindex PDP-11 Options
10377 These options are defined for the PDP-11:
10382 Use hardware FPP floating point. This is the default. (FIS floating
10383 point on the PDP-11/40 is not supported.)
10386 @opindex msoft-float
10387 Do not use hardware floating point.
10391 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10395 Return floating-point results in memory. This is the default.
10399 Generate code for a PDP-11/40.
10403 Generate code for a PDP-11/45. This is the default.
10407 Generate code for a PDP-11/10.
10409 @item -mbcopy-builtin
10410 @opindex bcopy-builtin
10411 Use inline @code{movstrhi} patterns for copying memory. This is the
10416 Do not use inline @code{movstrhi} patterns for copying memory.
10422 Use 16-bit @code{int}. This is the default.
10428 Use 32-bit @code{int}.
10431 @itemx -mno-float32
10433 @opindex mno-float32
10434 Use 64-bit @code{float}. This is the default.
10439 @opindex mno-float64
10440 Use 32-bit @code{float}.
10444 Use @code{abshi2} pattern. This is the default.
10448 Do not use @code{abshi2} pattern.
10450 @item -mbranch-expensive
10451 @opindex mbranch-expensive
10452 Pretend that branches are expensive. This is for experimenting with
10453 code generation only.
10455 @item -mbranch-cheap
10456 @opindex mbranch-cheap
10457 Do not pretend that branches are expensive. This is the default.
10461 Generate code for a system with split I&D.
10465 Generate code for a system without split I&D. This is the default.
10469 Use Unix assembler syntax. This is the default when configured for
10470 @samp{pdp11-*-bsd}.
10474 Use DEC assembler syntax. This is the default when configured for any
10475 PDP-11 target other than @samp{pdp11-*-bsd}.
10478 @node Xstormy16 Options
10479 @subsection Xstormy16 Options
10480 @cindex Xstormy16 Options
10482 These options are defined for Xstormy16:
10487 Choose startup files and linker script suitable for the simulator.
10491 @subsection FRV Options
10492 @cindex FRV Options
10498 Only use the first 32 general purpose registers.
10503 Use all 64 general purpose registers.
10508 Use only the first 32 floating point registers.
10513 Use all 64 floating point registers
10516 @opindex mhard-float
10518 Use hardware instructions for floating point operations.
10521 @opindex msoft-float
10523 Use library routines for floating point operations.
10528 Dynamically allocate condition code registers.
10533 Do not try to dynamically allocate condition code registers, only
10534 use @code{icc0} and @code{fcc0}.
10539 Change ABI to use double word insns.
10544 Do not use double word instructions.
10549 Use floating point double instructions.
10552 @opindex mno-double
10554 Do not use floating point double instructions.
10559 Use media instructions.
10564 Do not use media instructions.
10569 Use multiply and add/subtract instructions.
10572 @opindex mno-muladd
10574 Do not use multiply and add/subtract instructions.
10576 @item -mlibrary-pic
10577 @opindex mlibrary-pic
10579 Enable PIC support for building libraries
10584 Use only the first four media accumulator registers.
10589 Use all eight media accumulator registers.
10594 Pack VLIW instructions.
10599 Do not pack VLIW instructions.
10602 @opindex mno-eflags
10604 Do not mark ABI switches in e_flags.
10607 @opindex mcond-move
10609 Enable the use of conditional-move instructions (default).
10611 This switch is mainly for debugging the compiler and will likely be removed
10612 in a future version.
10614 @item -mno-cond-move
10615 @opindex mno-cond-move
10617 Disable the use of conditional-move instructions.
10619 This switch is mainly for debugging the compiler and will likely be removed
10620 in a future version.
10625 Enable the use of conditional set instructions (default).
10627 This switch is mainly for debugging the compiler and will likely be removed
10628 in a future version.
10633 Disable the use of conditional set instructions.
10635 This switch is mainly for debugging the compiler and will likely be removed
10636 in a future version.
10639 @opindex mcond-exec
10641 Enable the use of conditional execution (default).
10643 This switch is mainly for debugging the compiler and will likely be removed
10644 in a future version.
10646 @item -mno-cond-exec
10647 @opindex mno-cond-exec
10649 Disable the use of conditional execution.
10651 This switch is mainly for debugging the compiler and will likely be removed
10652 in a future version.
10654 @item -mvliw-branch
10655 @opindex mvliw-branch
10657 Run a pass to pack branches into VLIW instructions (default).
10659 This switch is mainly for debugging the compiler and will likely be removed
10660 in a future version.
10662 @item -mno-vliw-branch
10663 @opindex mno-vliw-branch
10665 Do not run a pass to pack branches into VLIW instructions.
10667 This switch is mainly for debugging the compiler and will likely be removed
10668 in a future version.
10670 @item -mmulti-cond-exec
10671 @opindex mmulti-cond-exec
10673 Enable optimization of @code{&&} and @code{||} in conditional execution
10676 This switch is mainly for debugging the compiler and will likely be removed
10677 in a future version.
10679 @item -mno-multi-cond-exec
10680 @opindex mno-multi-cond-exec
10682 Disable optimization of @code{&&} and @code{||} in conditional execution.
10684 This switch is mainly for debugging the compiler and will likely be removed
10685 in a future version.
10687 @item -mnested-cond-exec
10688 @opindex mnested-cond-exec
10690 Enable nested conditional execution optimizations (default).
10692 This switch is mainly for debugging the compiler and will likely be removed
10693 in a future version.
10695 @item -mno-nested-cond-exec
10696 @opindex mno-nested-cond-exec
10698 Disable nested conditional execution optimizations.
10700 This switch is mainly for debugging the compiler and will likely be removed
10701 in a future version.
10703 @item -mtomcat-stats
10704 @opindex mtomcat-stats
10706 Cause gas to print out tomcat statistics.
10708 @item -mcpu=@var{cpu}
10711 Select the processor type for which to generate code. Possible values are
10712 @samp{simple}, @samp{tomcat}, @samp{fr500}, @samp{fr400}, @samp{fr300},
10717 @node Xtensa Options
10718 @subsection Xtensa Options
10719 @cindex Xtensa Options
10721 The Xtensa architecture is designed to support many different
10722 configurations. The compiler's default options can be set to match a
10723 particular Xtensa configuration by copying a configuration file into the
10724 GCC sources when building GCC@. The options below may be used to
10725 override the default options.
10729 @itemx -mlittle-endian
10730 @opindex mbig-endian
10731 @opindex mlittle-endian
10732 Specify big-endian or little-endian byte ordering for the target Xtensa
10736 @itemx -mno-density
10738 @opindex mno-density
10739 Enable or disable use of the optional Xtensa code density instructions.
10742 @itemx -mno-const16
10744 @opindex mno-const16
10745 Enable or disable use of @code{CONST16} instructions for loading
10746 constant values. The @code{CONST16} instruction is currently not a
10747 standard option from Tensilica. When enabled, @code{CONST16}
10748 instructions are always used in place of the standard @code{L32R}
10749 instructions. The use of @code{CONST16} is enabled by default only if
10750 the @code{L32R} instruction is not available.
10756 Enable or disable use of the Xtensa @code{ABS} instruction for absolute
10763 Enable or disable use of the Xtensa @code{ADDX} and @code{SUBX}
10770 Enable or disable use of the Xtensa MAC16 option. When enabled, GCC
10771 will generate MAC16 instructions from standard C code, with the
10772 limitation that it will use neither the MR register file nor any
10773 instruction that operates on the MR registers. When this option is
10774 disabled, GCC will translate 16-bit multiply/accumulate operations to a
10775 combination of core instructions and library calls, depending on whether
10776 any other multiplier options are enabled.
10782 Enable or disable use of the 16-bit integer multiplier option. When
10783 enabled, the compiler will generate 16-bit multiply instructions for
10784 multiplications of 16 bits or smaller in standard C code. When this
10785 option is disabled, the compiler will either use 32-bit multiply or
10786 MAC16 instructions if they are available or generate library calls to
10787 perform the multiply operations using shifts and adds.
10793 Enable or disable use of the 32-bit integer multiplier option. When
10794 enabled, the compiler will generate 32-bit multiply instructions for
10795 multiplications of 32 bits or smaller in standard C code. When this
10796 option is disabled, the compiler will generate library calls to perform
10797 the multiply operations using either shifts and adds or 16-bit multiply
10798 instructions if they are available.
10804 Enable or disable use of the optional normalization shift amount
10805 (@code{NSA}) instructions to implement the built-in @code{ffs} function.
10810 @opindex mno-minmax
10811 Enable or disable use of the optional minimum and maximum value
10818 Enable or disable use of the optional sign extend (@code{SEXT})
10822 @itemx -mno-booleans
10824 @opindex mno-booleans
10825 Enable or disable support for the boolean register file used by Xtensa
10826 coprocessors. This is not typically useful by itself but may be
10827 required for other options that make use of the boolean registers (e.g.,
10828 the floating-point option).
10831 @itemx -msoft-float
10832 @opindex mhard-float
10833 @opindex msoft-float
10834 Enable or disable use of the floating-point option. When enabled, GCC
10835 generates floating-point instructions for 32-bit @code{float}
10836 operations. When this option is disabled, GCC generates library calls
10837 to emulate 32-bit floating-point operations using integer instructions.
10838 Regardless of this option, 64-bit @code{double} operations are always
10839 emulated with calls to library functions.
10842 @itemx -mno-fused-madd
10843 @opindex mfused-madd
10844 @opindex mno-fused-madd
10845 Enable or disable use of fused multiply/add and multiply/subtract
10846 instructions in the floating-point option. This has no effect if the
10847 floating-point option is not also enabled. Disabling fused multiply/add
10848 and multiply/subtract instructions forces the compiler to use separate
10849 instructions for the multiply and add/subtract operations. This may be
10850 desirable in some cases where strict IEEE 754-compliant results are
10851 required: the fused multiply add/subtract instructions do not round the
10852 intermediate result, thereby producing results with @emph{more} bits of
10853 precision than specified by the IEEE standard. Disabling fused multiply
10854 add/subtract instructions also ensures that the program output is not
10855 sensitive to the compiler's ability to combine multiply and add/subtract
10858 @item -mtext-section-literals
10859 @itemx -mno-text-section-literals
10860 @opindex mtext-section-literals
10861 @opindex mno-text-section-literals
10862 Control the treatment of literal pools. The default is
10863 @option{-mno-text-section-literals}, which places literals in a separate
10864 section in the output file. This allows the literal pool to be placed
10865 in a data RAM/ROM, and it also allows the linker to combine literal
10866 pools from separate object files to remove redundant literals and
10867 improve code size. With @option{-mtext-section-literals}, the literals
10868 are interspersed in the text section in order to keep them as close as
10869 possible to their references. This may be necessary for large assembly
10872 @item -mtarget-align
10873 @itemx -mno-target-align
10874 @opindex mtarget-align
10875 @opindex mno-target-align
10876 When this option is enabled, GCC instructs the assembler to
10877 automatically align instructions to reduce branch penalties at the
10878 expense of some code density. The assembler attempts to widen density
10879 instructions to align branch targets and the instructions following call
10880 instructions. If there are not enough preceding safe density
10881 instructions to align a target, no widening will be performed. The
10882 default is @option{-mtarget-align}. These options do not affect the
10883 treatment of auto-aligned instructions like @code{LOOP}, which the
10884 assembler will always align, either by widening density instructions or
10885 by inserting no-op instructions.
10888 @itemx -mno-longcalls
10889 @opindex mlongcalls
10890 @opindex mno-longcalls
10891 When this option is enabled, GCC instructs the assembler to translate
10892 direct calls to indirect calls unless it can determine that the target
10893 of a direct call is in the range allowed by the call instruction. This
10894 translation typically occurs for calls to functions in other source
10895 files. Specifically, the assembler translates a direct @code{CALL}
10896 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
10897 The default is @option{-mno-longcalls}. This option should be used in
10898 programs where the call target can potentially be out of range. This
10899 option is implemented in the assembler, not the compiler, so the
10900 assembly code generated by GCC will still show direct call
10901 instructions---look at the disassembled object code to see the actual
10902 instructions. Note that the assembler will use an indirect call for
10903 every cross-file call, not just those that really will be out of range.
10906 @node Code Gen Options
10907 @section Options for Code Generation Conventions
10908 @cindex code generation conventions
10909 @cindex options, code generation
10910 @cindex run-time options
10912 These machine-independent options control the interface conventions
10913 used in code generation.
10915 Most of them have both positive and negative forms; the negative form
10916 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
10917 one of the forms is listed---the one which is not the default. You
10918 can figure out the other form by either removing @samp{no-} or adding
10922 @item -fbounds-check
10923 @opindex fbounds-check
10924 For front-ends that support it, generate additional code to check that
10925 indices used to access arrays are within the declared range. This is
10926 currently only supported by the Java and Fortran 77 front-ends, where
10927 this option defaults to true and false respectively.
10931 This option generates traps for signed overflow on addition, subtraction,
10932 multiplication operations.
10936 This option instructs the compiler to assume that signed arithmetic
10937 overflow of addition, subtraction and multiplication wraps around
10938 using twos-complement representation. This flag enables some optimzations
10939 and disables other. This option is enabled by default for the Java
10940 front-end, as required by the Java language specification.
10943 @opindex fexceptions
10944 Enable exception handling. Generates extra code needed to propagate
10945 exceptions. For some targets, this implies GCC will generate frame
10946 unwind information for all functions, which can produce significant data
10947 size overhead, although it does not affect execution. If you do not
10948 specify this option, GCC will enable it by default for languages like
10949 C++ which normally require exception handling, and disable it for
10950 languages like C that do not normally require it. However, you may need
10951 to enable this option when compiling C code that needs to interoperate
10952 properly with exception handlers written in C++. You may also wish to
10953 disable this option if you are compiling older C++ programs that don't
10954 use exception handling.
10956 @item -fnon-call-exceptions
10957 @opindex fnon-call-exceptions
10958 Generate code that allows trapping instructions to throw exceptions.
10959 Note that this requires platform-specific runtime support that does
10960 not exist everywhere. Moreover, it only allows @emph{trapping}
10961 instructions to throw exceptions, i.e.@: memory references or floating
10962 point instructions. It does not allow exceptions to be thrown from
10963 arbitrary signal handlers such as @code{SIGALRM}.
10965 @item -funwind-tables
10966 @opindex funwind-tables
10967 Similar to @option{-fexceptions}, except that it will just generate any needed
10968 static data, but will not affect the generated code in any other way.
10969 You will normally not enable this option; instead, a language processor
10970 that needs this handling would enable it on your behalf.
10972 @item -fasynchronous-unwind-tables
10973 @opindex funwind-tables
10974 Generate unwind table in dwarf2 format, if supported by target machine. The
10975 table is exact at each instruction boundary, so it can be used for stack
10976 unwinding from asynchronous events (such as debugger or garbage collector).
10978 @item -fpcc-struct-return
10979 @opindex fpcc-struct-return
10980 Return ``short'' @code{struct} and @code{union} values in memory like
10981 longer ones, rather than in registers. This convention is less
10982 efficient, but it has the advantage of allowing intercallability between
10983 GCC-compiled files and files compiled with other compilers, particularly
10984 the Portable C Compiler (pcc).
10986 The precise convention for returning structures in memory depends
10987 on the target configuration macros.
10989 Short structures and unions are those whose size and alignment match
10990 that of some integer type.
10992 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
10993 switch is not binary compatible with code compiled with the
10994 @option{-freg-struct-return} switch.
10995 Use it to conform to a non-default application binary interface.
10997 @item -freg-struct-return
10998 @opindex freg-struct-return
10999 Return @code{struct} and @code{union} values in registers when possible.
11000 This is more efficient for small structures than
11001 @option{-fpcc-struct-return}.
11003 If you specify neither @option{-fpcc-struct-return} nor
11004 @option{-freg-struct-return}, GCC defaults to whichever convention is
11005 standard for the target. If there is no standard convention, GCC
11006 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11007 the principal compiler. In those cases, we can choose the standard, and
11008 we chose the more efficient register return alternative.
11010 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11011 switch is not binary compatible with code compiled with the
11012 @option{-fpcc-struct-return} switch.
11013 Use it to conform to a non-default application binary interface.
11015 @item -fshort-enums
11016 @opindex fshort-enums
11017 Allocate to an @code{enum} type only as many bytes as it needs for the
11018 declared range of possible values. Specifically, the @code{enum} type
11019 will be equivalent to the smallest integer type which has enough room.
11021 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11022 code that is not binary compatible with code generated without that switch.
11023 Use it to conform to a non-default application binary interface.
11025 @item -fshort-double
11026 @opindex fshort-double
11027 Use the same size for @code{double} as for @code{float}.
11029 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11030 code that is not binary compatible with code generated without that switch.
11031 Use it to conform to a non-default application binary interface.
11033 @item -fshort-wchar
11034 @opindex fshort-wchar
11035 Override the underlying type for @samp{wchar_t} to be @samp{short
11036 unsigned int} instead of the default for the target. This option is
11037 useful for building programs to run under WINE@.
11039 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11040 code that is not binary compatible with code generated without that switch.
11041 Use it to conform to a non-default application binary interface.
11043 @item -fshared-data
11044 @opindex fshared-data
11045 Requests that the data and non-@code{const} variables of this
11046 compilation be shared data rather than private data. The distinction
11047 makes sense only on certain operating systems, where shared data is
11048 shared between processes running the same program, while private data
11049 exists in one copy per process.
11052 @opindex fno-common
11053 In C, allocate even uninitialized global variables in the data section of the
11054 object file, rather than generating them as common blocks. This has the
11055 effect that if the same variable is declared (without @code{extern}) in
11056 two different compilations, you will get an error when you link them.
11057 The only reason this might be useful is if you wish to verify that the
11058 program will work on other systems which always work this way.
11062 Ignore the @samp{#ident} directive.
11064 @item -fno-gnu-linker
11065 @opindex fno-gnu-linker
11066 Do not output global initializations (such as C++ constructors and
11067 destructors) in the form used by the GNU linker (on systems where the GNU
11068 linker is the standard method of handling them). Use this option when
11069 you want to use a non-GNU linker, which also requires using the
11070 @command{collect2} program to make sure the system linker includes
11071 constructors and destructors. (@command{collect2} is included in the GCC
11072 distribution.) For systems which @emph{must} use @command{collect2}, the
11073 compiler driver @command{gcc} is configured to do this automatically.
11075 @item -finhibit-size-directive
11076 @opindex finhibit-size-directive
11077 Don't output a @code{.size} assembler directive, or anything else that
11078 would cause trouble if the function is split in the middle, and the
11079 two halves are placed at locations far apart in memory. This option is
11080 used when compiling @file{crtstuff.c}; you should not need to use it
11083 @item -fverbose-asm
11084 @opindex fverbose-asm
11085 Put extra commentary information in the generated assembly code to
11086 make it more readable. This option is generally only of use to those
11087 who actually need to read the generated assembly code (perhaps while
11088 debugging the compiler itself).
11090 @option{-fno-verbose-asm}, the default, causes the
11091 extra information to be omitted and is useful when comparing two assembler
11096 @cindex global offset table
11098 Generate position-independent code (PIC) suitable for use in a shared
11099 library, if supported for the target machine. Such code accesses all
11100 constant addresses through a global offset table (GOT)@. The dynamic
11101 loader resolves the GOT entries when the program starts (the dynamic
11102 loader is not part of GCC; it is part of the operating system). If
11103 the GOT size for the linked executable exceeds a machine-specific
11104 maximum size, you get an error message from the linker indicating that
11105 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11106 instead. (These maximums are 16k on the m88k, 8k on the SPARC, and 32k
11107 on the m68k and RS/6000. The 386 has no such limit.)
11109 Position-independent code requires special support, and therefore works
11110 only on certain machines. For the 386, GCC supports PIC for System V
11111 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11112 position-independent.
11116 If supported for the target machine, emit position-independent code,
11117 suitable for dynamic linking and avoiding any limit on the size of the
11118 global offset table. This option makes a difference on the m68k, m88k,
11121 Position-independent code requires special support, and therefore works
11122 only on certain machines.
11128 These options are similar to @option{-fpic} and @option{-fPIC}, but
11129 generated position independent code can be only linked into executables.
11130 Usually these options are used when @option{-pie} GCC option will be
11131 used during linking.
11133 @item -ffixed-@var{reg}
11135 Treat the register named @var{reg} as a fixed register; generated code
11136 should never refer to it (except perhaps as a stack pointer, frame
11137 pointer or in some other fixed role).
11139 @var{reg} must be the name of a register. The register names accepted
11140 are machine-specific and are defined in the @code{REGISTER_NAMES}
11141 macro in the machine description macro file.
11143 This flag does not have a negative form, because it specifies a
11146 @item -fcall-used-@var{reg}
11147 @opindex fcall-used
11148 Treat the register named @var{reg} as an allocable register that is
11149 clobbered by function calls. It may be allocated for temporaries or
11150 variables that do not live across a call. Functions compiled this way
11151 will not save and restore the register @var{reg}.
11153 It is an error to used this flag with the frame pointer or stack pointer.
11154 Use of this flag for other registers that have fixed pervasive roles in
11155 the machine's execution model will produce disastrous results.
11157 This flag does not have a negative form, because it specifies a
11160 @item -fcall-saved-@var{reg}
11161 @opindex fcall-saved
11162 Treat the register named @var{reg} as an allocable register saved by
11163 functions. It may be allocated even for temporaries or variables that
11164 live across a call. Functions compiled this way will save and restore
11165 the register @var{reg} if they use it.
11167 It is an error to used this flag with the frame pointer or stack pointer.
11168 Use of this flag for other registers that have fixed pervasive roles in
11169 the machine's execution model will produce disastrous results.
11171 A different sort of disaster will result from the use of this flag for
11172 a register in which function values may be returned.
11174 This flag does not have a negative form, because it specifies a
11177 @item -fpack-struct
11178 @opindex fpack-struct
11179 Pack all structure members together without holes.
11181 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
11182 code that is not binary compatible with code generated without that switch.
11183 Additionally, it makes the code suboptimal.
11184 Use it to conform to a non-default application binary interface.
11186 @item -finstrument-functions
11187 @opindex finstrument-functions
11188 Generate instrumentation calls for entry and exit to functions. Just
11189 after function entry and just before function exit, the following
11190 profiling functions will be called with the address of the current
11191 function and its call site. (On some platforms,
11192 @code{__builtin_return_address} does not work beyond the current
11193 function, so the call site information may not be available to the
11194 profiling functions otherwise.)
11197 void __cyg_profile_func_enter (void *this_fn,
11199 void __cyg_profile_func_exit (void *this_fn,
11203 The first argument is the address of the start of the current function,
11204 which may be looked up exactly in the symbol table.
11206 This instrumentation is also done for functions expanded inline in other
11207 functions. The profiling calls will indicate where, conceptually, the
11208 inline function is entered and exited. This means that addressable
11209 versions of such functions must be available. If all your uses of a
11210 function are expanded inline, this may mean an additional expansion of
11211 code size. If you use @samp{extern inline} in your C code, an
11212 addressable version of such functions must be provided. (This is
11213 normally the case anyways, but if you get lucky and the optimizer always
11214 expands the functions inline, you might have gotten away without
11215 providing static copies.)
11217 A function may be given the attribute @code{no_instrument_function}, in
11218 which case this instrumentation will not be done. This can be used, for
11219 example, for the profiling functions listed above, high-priority
11220 interrupt routines, and any functions from which the profiling functions
11221 cannot safely be called (perhaps signal handlers, if the profiling
11222 routines generate output or allocate memory).
11224 @item -fstack-check
11225 @opindex fstack-check
11226 Generate code to verify that you do not go beyond the boundary of the
11227 stack. You should specify this flag if you are running in an
11228 environment with multiple threads, but only rarely need to specify it in
11229 a single-threaded environment since stack overflow is automatically
11230 detected on nearly all systems if there is only one stack.
11232 Note that this switch does not actually cause checking to be done; the
11233 operating system must do that. The switch causes generation of code
11234 to ensure that the operating system sees the stack being extended.
11236 @item -fstack-limit-register=@var{reg}
11237 @itemx -fstack-limit-symbol=@var{sym}
11238 @itemx -fno-stack-limit
11239 @opindex fstack-limit-register
11240 @opindex fstack-limit-symbol
11241 @opindex fno-stack-limit
11242 Generate code to ensure that the stack does not grow beyond a certain value,
11243 either the value of a register or the address of a symbol. If the stack
11244 would grow beyond the value, a signal is raised. For most targets,
11245 the signal is raised before the stack overruns the boundary, so
11246 it is possible to catch the signal without taking special precautions.
11248 For instance, if the stack starts at absolute address @samp{0x80000000}
11249 and grows downwards, you can use the flags
11250 @option{-fstack-limit-symbol=__stack_limit} and
11251 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
11252 of 128KB@. Note that this may only work with the GNU linker.
11254 @cindex aliasing of parameters
11255 @cindex parameters, aliased
11256 @item -fargument-alias
11257 @itemx -fargument-noalias
11258 @itemx -fargument-noalias-global
11259 @opindex fargument-alias
11260 @opindex fargument-noalias
11261 @opindex fargument-noalias-global
11262 Specify the possible relationships among parameters and between
11263 parameters and global data.
11265 @option{-fargument-alias} specifies that arguments (parameters) may
11266 alias each other and may alias global storage.@*
11267 @option{-fargument-noalias} specifies that arguments do not alias
11268 each other, but may alias global storage.@*
11269 @option{-fargument-noalias-global} specifies that arguments do not
11270 alias each other and do not alias global storage.
11272 Each language will automatically use whatever option is required by
11273 the language standard. You should not need to use these options yourself.
11275 @item -fleading-underscore
11276 @opindex fleading-underscore
11277 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
11278 change the way C symbols are represented in the object file. One use
11279 is to help link with legacy assembly code.
11281 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
11282 generate code that is not binary compatible with code generated without that
11283 switch. Use it to conform to a non-default application binary interface.
11284 Not all targets provide complete support for this switch.
11286 @item -ftls-model=@var{model}
11287 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
11288 The @var{model} argument should be one of @code{global-dynamic},
11289 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
11291 The default without @option{-fpic} is @code{initial-exec}; with
11292 @option{-fpic} the default is @code{global-dynamic}.
11297 @node Environment Variables
11298 @section Environment Variables Affecting GCC
11299 @cindex environment variables
11301 @c man begin ENVIRONMENT
11302 This section describes several environment variables that affect how GCC
11303 operates. Some of them work by specifying directories or prefixes to use
11304 when searching for various kinds of files. Some are used to specify other
11305 aspects of the compilation environment.
11307 Note that you can also specify places to search using options such as
11308 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
11309 take precedence over places specified using environment variables, which
11310 in turn take precedence over those specified by the configuration of GCC@.
11311 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
11312 GNU Compiler Collection (GCC) Internals}.
11317 @c @itemx LC_COLLATE
11319 @c @itemx LC_MONETARY
11320 @c @itemx LC_NUMERIC
11325 @c @findex LC_COLLATE
11326 @findex LC_MESSAGES
11327 @c @findex LC_MONETARY
11328 @c @findex LC_NUMERIC
11332 These environment variables control the way that GCC uses
11333 localization information that allow GCC to work with different
11334 national conventions. GCC inspects the locale categories
11335 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
11336 so. These locale categories can be set to any value supported by your
11337 installation. A typical value is @samp{en_UK} for English in the United
11340 The @env{LC_CTYPE} environment variable specifies character
11341 classification. GCC uses it to determine the character boundaries in
11342 a string; this is needed for some multibyte encodings that contain quote
11343 and escape characters that would otherwise be interpreted as a string
11346 The @env{LC_MESSAGES} environment variable specifies the language to
11347 use in diagnostic messages.
11349 If the @env{LC_ALL} environment variable is set, it overrides the value
11350 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
11351 and @env{LC_MESSAGES} default to the value of the @env{LANG}
11352 environment variable. If none of these variables are set, GCC
11353 defaults to traditional C English behavior.
11357 If @env{TMPDIR} is set, it specifies the directory to use for temporary
11358 files. GCC uses temporary files to hold the output of one stage of
11359 compilation which is to be used as input to the next stage: for example,
11360 the output of the preprocessor, which is the input to the compiler
11363 @item GCC_EXEC_PREFIX
11364 @findex GCC_EXEC_PREFIX
11365 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
11366 names of the subprograms executed by the compiler. No slash is added
11367 when this prefix is combined with the name of a subprogram, but you can
11368 specify a prefix that ends with a slash if you wish.
11370 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
11371 an appropriate prefix to use based on the pathname it was invoked with.
11373 If GCC cannot find the subprogram using the specified prefix, it
11374 tries looking in the usual places for the subprogram.
11376 The default value of @env{GCC_EXEC_PREFIX} is
11377 @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
11378 of @code{prefix} when you ran the @file{configure} script.
11380 Other prefixes specified with @option{-B} take precedence over this prefix.
11382 This prefix is also used for finding files such as @file{crt0.o} that are
11385 In addition, the prefix is used in an unusual way in finding the
11386 directories to search for header files. For each of the standard
11387 directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
11388 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
11389 replacing that beginning with the specified prefix to produce an
11390 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
11391 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
11392 These alternate directories are searched first; the standard directories
11395 @item COMPILER_PATH
11396 @findex COMPILER_PATH
11397 The value of @env{COMPILER_PATH} is a colon-separated list of
11398 directories, much like @env{PATH}. GCC tries the directories thus
11399 specified when searching for subprograms, if it can't find the
11400 subprograms using @env{GCC_EXEC_PREFIX}.
11403 @findex LIBRARY_PATH
11404 The value of @env{LIBRARY_PATH} is a colon-separated list of
11405 directories, much like @env{PATH}. When configured as a native compiler,
11406 GCC tries the directories thus specified when searching for special
11407 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
11408 using GCC also uses these directories when searching for ordinary
11409 libraries for the @option{-l} option (but directories specified with
11410 @option{-L} come first).
11414 @cindex locale definition
11415 This variable is used to pass locale information to the compiler. One way in
11416 which this information is used is to determine the character set to be used
11417 when character literals, string literals and comments are parsed in C and C++.
11418 When the compiler is configured to allow multibyte characters,
11419 the following values for @env{LANG} are recognized:
11423 Recognize JIS characters.
11425 Recognize SJIS characters.
11427 Recognize EUCJP characters.
11430 If @env{LANG} is not defined, or if it has some other value, then the
11431 compiler will use mblen and mbtowc as defined by the default locale to
11432 recognize and translate multibyte characters.
11436 Some additional environments variables affect the behavior of the
11439 @include cppenv.texi
11443 @node Precompiled Headers
11444 @section Using Precompiled Headers
11445 @cindex precompiled headers
11446 @cindex speed of compilation
11448 Often large projects have many header files that are included in every
11449 source file. The time the compiler takes to process these header files
11450 over and over again can account for nearly all of the time required to
11451 build the project. To make builds faster, GCC allows users to
11452 `precompile' a header file; then, if builds can use the precompiled
11453 header file they will be much faster.
11455 To create a precompiled header file, simply compile it as you would any
11456 other file, if necessary using the @option{-x} option to make the driver
11457 treat it as a C or C++ header file. You will probably want to use a
11458 tool like @command{make} to keep the precompiled header up-to-date when
11459 the headers it contains change.
11461 A precompiled header file will be searched for when @code{#include} is
11462 seen in the compilation. As it searches for the included file
11463 (@pxref{Search Path,,Search Path,cpp.info,The C Preprocessor}) the
11464 compiler looks for a precompiled header in each directory just before it
11465 looks for the include file in that directory. The name searched for is
11466 the name specified in the @code{#include} with @samp{.gch} appended. If
11467 the precompiled header file can't be used, it is ignored.
11469 For instance, if you have @code{#include "all.h"}, and you have
11470 @file{all.h.gch} in the same directory as @file{all.h}, then the
11471 precompiled header file will be used if possible, and the original
11472 header will be used otherwise.
11474 Alternatively, you might decide to put the precompiled header file in a
11475 directory and use @option{-I} to ensure that directory is searched
11476 before (or instead of) the directory containing the original header.
11477 Then, if you want to check that the precompiled header file is always
11478 used, you can put a file of the same name as the original header in this
11479 directory containing an @code{#error} command.
11481 This also works with @option{-include}. So yet another way to use
11482 precompiled headers, good for projects not designed with precompiled
11483 header files in mind, is to simply take most of the header files used by
11484 a project, include them from another header file, precompile that header
11485 file, and @option{-include} the precompiled header. If the header files
11486 have guards against multiple inclusion, they will be skipped because
11487 they've already been included (in the precompiled header).
11489 If you need to precompile the same header file for different
11490 languages, targets, or compiler options, you can instead make a
11491 @emph{directory} named like @file{all.h.gch}, and put each precompiled
11492 header in the directory. (It doesn't matter what you call the files
11493 in the directory, every precompiled header in the directory will be
11494 considered.) The first precompiled header encountered in the
11495 directory that is valid for this compilation will be used; they're
11496 searched in no particular order.
11498 There are many other possibilities, limited only by your imagination,
11499 good sense, and the constraints of your build system.
11501 A precompiled header file can be used only when these conditions apply:
11505 Only one precompiled header can be used in a particular compilation.
11507 A precompiled header can't be used once the first C token is seen. You
11508 can have preprocessor directives before a precompiled header; you can
11509 even include a precompiled header from inside another header, so long as
11510 there are no C tokens before the @code{#include}.
11512 The precompiled header file must be produced for the same language as
11513 the current compilation. You can't use a C precompiled header for a C++
11516 The precompiled header file must be produced by the same compiler
11517 version and configuration as the current compilation is using.
11518 The easiest way to guarantee this is to use the same compiler binary
11519 for creating and using precompiled headers.
11521 Any macros defined before the precompiled header (including with
11522 @option{-D}) must either be defined in the same way as when the
11523 precompiled header was generated, or must not affect the precompiled
11524 header, which usually means that the they don't appear in the
11525 precompiled header at all.
11527 Certain command-line options must be defined in the same way as when the
11528 precompiled header was generated. At present, it's not clear which
11529 options are safe to change and which are not; the safest choice is to
11530 use exactly the same options when generating and using the precompiled
11534 For all of these but the last, the compiler will automatically ignore
11535 the precompiled header if the conditions aren't met. For the last item,
11536 some option changes will cause the precompiled header to be rejected,
11537 but not all incompatible option combinations have yet been found. If
11538 you find a new incompatible combination, please consider filing a bug
11539 report, see @ref{Bugs}.
11541 @node Running Protoize
11542 @section Running Protoize
11544 The program @code{protoize} is an optional part of GCC@. You can use
11545 it to add prototypes to a program, thus converting the program to ISO
11546 C in one respect. The companion program @code{unprotoize} does the
11547 reverse: it removes argument types from any prototypes that are found.
11549 When you run these programs, you must specify a set of source files as
11550 command line arguments. The conversion programs start out by compiling
11551 these files to see what functions they define. The information gathered
11552 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
11554 After scanning comes actual conversion. The specified files are all
11555 eligible to be converted; any files they include (whether sources or
11556 just headers) are eligible as well.
11558 But not all the eligible files are converted. By default,
11559 @code{protoize} and @code{unprotoize} convert only source and header
11560 files in the current directory. You can specify additional directories
11561 whose files should be converted with the @option{-d @var{directory}}
11562 option. You can also specify particular files to exclude with the
11563 @option{-x @var{file}} option. A file is converted if it is eligible, its
11564 directory name matches one of the specified directory names, and its
11565 name within the directory has not been excluded.
11567 Basic conversion with @code{protoize} consists of rewriting most
11568 function definitions and function declarations to specify the types of
11569 the arguments. The only ones not rewritten are those for varargs
11572 @code{protoize} optionally inserts prototype declarations at the
11573 beginning of the source file, to make them available for any calls that
11574 precede the function's definition. Or it can insert prototype
11575 declarations with block scope in the blocks where undeclared functions
11578 Basic conversion with @code{unprotoize} consists of rewriting most
11579 function declarations to remove any argument types, and rewriting
11580 function definitions to the old-style pre-ISO form.
11582 Both conversion programs print a warning for any function declaration or
11583 definition that they can't convert. You can suppress these warnings
11586 The output from @code{protoize} or @code{unprotoize} replaces the
11587 original source file. The original file is renamed to a name ending
11588 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
11589 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
11590 for DOS) file already exists, then the source file is simply discarded.
11592 @code{protoize} and @code{unprotoize} both depend on GCC itself to
11593 scan the program and collect information about the functions it uses.
11594 So neither of these programs will work until GCC is installed.
11596 Here is a table of the options you can use with @code{protoize} and
11597 @code{unprotoize}. Each option works with both programs unless
11601 @item -B @var{directory}
11602 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
11603 usual directory (normally @file{/usr/local/lib}). This file contains
11604 prototype information about standard system functions. This option
11605 applies only to @code{protoize}.
11607 @item -c @var{compilation-options}
11608 Use @var{compilation-options} as the options when running @command{gcc} to
11609 produce the @samp{.X} files. The special option @option{-aux-info} is
11610 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
11612 Note that the compilation options must be given as a single argument to
11613 @code{protoize} or @code{unprotoize}. If you want to specify several
11614 @command{gcc} options, you must quote the entire set of compilation options
11615 to make them a single word in the shell.
11617 There are certain @command{gcc} arguments that you cannot use, because they
11618 would produce the wrong kind of output. These include @option{-g},
11619 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
11620 the @var{compilation-options}, they are ignored.
11623 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
11624 systems) instead of @samp{.c}. This is convenient if you are converting
11625 a C program to C++. This option applies only to @code{protoize}.
11628 Add explicit global declarations. This means inserting explicit
11629 declarations at the beginning of each source file for each function
11630 that is called in the file and was not declared. These declarations
11631 precede the first function definition that contains a call to an
11632 undeclared function. This option applies only to @code{protoize}.
11634 @item -i @var{string}
11635 Indent old-style parameter declarations with the string @var{string}.
11636 This option applies only to @code{protoize}.
11638 @code{unprotoize} converts prototyped function definitions to old-style
11639 function definitions, where the arguments are declared between the
11640 argument list and the initial @samp{@{}. By default, @code{unprotoize}
11641 uses five spaces as the indentation. If you want to indent with just
11642 one space instead, use @option{-i " "}.
11645 Keep the @samp{.X} files. Normally, they are deleted after conversion
11649 Add explicit local declarations. @code{protoize} with @option{-l} inserts
11650 a prototype declaration for each function in each block which calls the
11651 function without any declaration. This option applies only to
11655 Make no real changes. This mode just prints information about the conversions
11656 that would have been done without @option{-n}.
11659 Make no @samp{.save} files. The original files are simply deleted.
11660 Use this option with caution.
11662 @item -p @var{program}
11663 Use the program @var{program} as the compiler. Normally, the name
11664 @file{gcc} is used.
11667 Work quietly. Most warnings are suppressed.
11670 Print the version number, just like @option{-v} for @command{gcc}.
11673 If you need special compiler options to compile one of your program's
11674 source files, then you should generate that file's @samp{.X} file
11675 specially, by running @command{gcc} on that source file with the
11676 appropriate options and the option @option{-aux-info}. Then run
11677 @code{protoize} on the entire set of files. @code{protoize} will use
11678 the existing @samp{.X} file because it is newer than the source file.
11682 gcc -Dfoo=bar file1.c -aux-info file1.X
11687 You need to include the special files along with the rest in the
11688 @code{protoize} command, even though their @samp{.X} files already
11689 exist, because otherwise they won't get converted.
11691 @xref{Protoize Caveats}, for more information on how to use
11692 @code{protoize} successfully.