1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005 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, 2004, 2005 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 @gol
178 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
179 -fno-implicit-templates @gol
180 -fno-implicit-inline-templates @gol
181 -fno-implement-inlines -fms-extensions @gol
182 -fno-nonansi-builtins -fno-operator-names @gol
183 -fno-optional-diags -fpermissive @gol
184 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
185 -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
186 -fno-default-inline -Wabi -Wctor-dtor-privacy @gol
187 -Wnon-virtual-dtor -Wreorder @gol
188 -Weffc++ -Wno-deprecated @gol
189 -Wno-non-template-friend -Wold-style-cast @gol
190 -Woverloaded-virtual -Wno-pmf-conversions @gol
193 @item Objective-C Language Options
194 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
196 -fconstant-string-class=@var{class-name} @gol
197 -fgnu-runtime -fnext-runtime @gol
198 -fno-nil-receivers @gol
199 -fobjc-exceptions @gol
200 -freplace-objc-classes @gol
203 -Wno-protocol -Wselector -Wundeclared-selector}
205 @item Language Independent Options
206 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
207 @gccoptlist{-fmessage-length=@var{n} @gol
208 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
210 @item Warning Options
211 @xref{Warning Options,,Options to Request or Suppress Warnings}.
212 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
213 -w -Wextra -Wall -Waggregate-return @gol
214 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
215 -Wconversion -Wno-deprecated-declarations @gol
216 -Wdisabled-optimization -Wno-div-by-zero -Wendif-labels @gol
217 -Werror -Werror-implicit-function-declaration @gol
218 -Wfloat-equal -Wformat -Wformat=2 @gol
219 -Wno-format-extra-args -Wformat-nonliteral @gol
220 -Wformat-security -Wformat-y2k @gol
221 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
222 -Wimport -Wno-import -Winit-self -Winline @gol
223 -Wno-invalid-offsetof -Winvalid-pch @gol
224 -Wlarger-than-@var{len} -Wlong-long @gol
225 -Wmain -Wmissing-braces @gol
226 -Wmissing-format-attribute -Wmissing-noreturn @gol
227 -Wno-multichar -Wnonnull -Wpacked -Wpadded @gol
228 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
229 -Wreturn-type -Wsequence-point -Wshadow @gol
230 -Wsign-compare -Wstrict-aliasing @gol
231 -Wswitch -Wswitch-default -Wswitch-enum @gol
232 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
233 -Wunknown-pragmas -Wunreachable-code @gol
234 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
235 -Wunused-value -Wunused-variable -Wwrite-strings}
237 @item C-only Warning Options
238 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
239 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
240 -Wstrict-prototypes -Wtraditional @gol
241 -Wdeclaration-after-statement}
243 @item Debugging Options
244 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
245 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
246 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
247 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
248 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
249 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
250 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
251 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
252 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
253 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
254 -ftest-coverage -ftime-report @gol
255 -g -g@var{level} -gcoff -gdwarf-2 @gol
256 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
257 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
258 -print-multi-directory -print-multi-lib @gol
259 -print-prog-name=@var{program} -print-search-dirs -Q @gol
262 @item Optimization Options
263 @xref{Optimize Options,,Options that Control Optimization}.
264 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
265 -falign-labels=@var{n} -falign-loops=@var{n} @gol
266 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
267 -fbranch-target-load-optimize2 -fcaller-saves -fcprop-registers @gol
268 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
269 -fdelayed-branch -fdelete-null-pointer-checks @gol
270 -fexpensive-optimizations -ffast-math -ffloat-store @gol
271 -fforce-addr -fforce-mem -ffunction-sections @gol
272 -fgcse -fgcse-lm -fgcse-sm -fgcse-las -floop-optimize @gol
273 -fcrossjumping -fif-conversion -fif-conversion2 @gol
274 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
275 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
276 -fmove-all-movables -fnew-ra -fno-branch-count-reg @gol
277 -fno-default-inline -fno-defer-pop @gol
278 -fno-function-cse -fno-guess-branch-probability @gol
279 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
280 -funsafe-math-optimizations -ffinite-math-only @gol
281 -fno-trapping-math -fno-zero-initialized-in-bss @gol
282 -fomit-frame-pointer -foptimize-register-move @gol
283 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
284 -fprofile-generate -fprofile-use @gol
285 -freduce-all-givs -fregmove -frename-registers @gol
286 -freorder-blocks -freorder-functions @gol
287 -frerun-cse-after-loop -frerun-loop-opt @gol
288 -frounding-math -fschedule-insns -fschedule-insns2 @gol
289 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
290 -fsched-spec-load-dangerous @gol
291 -fsched-stalled-insns=@var{n} -sched-stalled-insns-dep=@var{n} @gol
292 -fsched2-use-superblocks @gol
293 -fsched2-use-traces -fsignaling-nans @gol
294 -fsingle-precision-constant @gol
295 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
296 -funroll-all-loops -funroll-loops -fpeel-loops @gol
297 -funswitch-loops -fold-unroll-loops -fold-unroll-all-loops @gol
298 --param @var{name}=@var{value}
299 -O -O0 -O1 -O2 -O3 -Os}
301 @item Preprocessor Options
302 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
303 @gccoptlist{-A@var{question}=@var{answer} @gol
304 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
305 -C -dD -dI -dM -dN @gol
306 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
307 -idirafter @var{dir} @gol
308 -include @var{file} -imacros @var{file} @gol
309 -iprefix @var{file} -iwithprefix @var{dir} @gol
310 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
311 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
312 -P -fworking-directory -remap @gol
313 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
314 -Xpreprocessor @var{option}}
316 @item Assembler Option
317 @xref{Assembler Options,,Passing Options to the Assembler}.
318 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
321 @xref{Link Options,,Options for Linking}.
322 @gccoptlist{@var{object-file-name} -l@var{library} @gol
323 -nostartfiles -nodefaultlibs -nostdlib -pie @gol
324 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
325 -Wl,@var{option} -Xlinker @var{option} @gol
328 @item Directory Options
329 @xref{Directory Options,,Options for Directory Search}.
330 @gccoptlist{-B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
333 @c I wrote this xref this way to avoid overfull hbox. -- rms
334 @xref{Target Options}.
335 @gccoptlist{-V @var{version} -b @var{machine}}
337 @item Machine Dependent Options
338 @xref{Submodel Options,,Hardware Models and Configurations}.
340 @emph{M680x0 Options}
341 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
342 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
343 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
344 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
345 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
347 @emph{M68hc1x Options}
348 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
349 -mauto-incdec -minmax -mlong-calls -mshort @gol
350 -msoft-reg-count=@var{count}}
353 @gccoptlist{-mg -mgnu -munix}
356 @gccoptlist{-mcpu=@var{cpu-type} @gol
357 -mtune=@var{cpu-type} @gol
358 -mcmodel=@var{code-model} @gol
359 -m32 -m64 -mapp-regs -mno-app-regs @gol
360 -mfaster-structs -mno-faster-structs @gol
361 -mflat -mno-flat -mfpu -mno-fpu @gol
362 -mhard-float -msoft-float @gol
363 -mhard-quad-float -msoft-quad-float @gol
364 -mimpure-text -mno-impure-text -mlittle-endian @gol
365 -mstack-bias -mno-stack-bias @gol
366 -munaligned-doubles -mno-unaligned-doubles @gol
367 -mv8plus -mno-v8plus -mvis -mno-vis @gol
368 -mcypress -mf930 -mf934 @gol
369 -msparclite -msupersparc -mv8
373 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
374 -mapcs-26 -mapcs-32 @gol
375 -mapcs-stack-check -mno-apcs-stack-check @gol
376 -mapcs-float -mno-apcs-float @gol
377 -mapcs-reentrant -mno-apcs-reentrant @gol
378 -msched-prolog -mno-sched-prolog @gol
379 -mlittle-endian -mbig-endian -mwords-little-endian @gol
380 -malignment-traps -mno-alignment-traps @gol
381 -msoft-float -mhard-float -mfpe @gol
382 -mthumb-interwork -mno-thumb-interwork @gol
383 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
384 -mstructure-size-boundary=@var{n} @gol
385 -mabort-on-noreturn @gol
386 -mlong-calls -mno-long-calls @gol
387 -msingle-pic-base -mno-single-pic-base @gol
388 -mpic-register=@var{reg} @gol
389 -mnop-fun-dllimport @gol
390 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
391 -mpoke-function-name @gol
393 -mtpcs-frame -mtpcs-leaf-frame @gol
394 -mcaller-super-interworking -mcallee-super-interworking}
396 @emph{MN10300 Options}
397 @gccoptlist{-mmult-bug -mno-mult-bug @gol
398 -mam33 -mno-am33 @gol
399 -mam33-2 -mno-am33-2 @gol
402 @emph{M32R/D Options}
403 @gccoptlist{-m32r2 -m32rx -m32r @gol
405 -malign-loops -mno-align-loops @gol
406 -missue-rate=@var{number} @gol
407 -mbranch-cost=@var{number} @gol
408 -mmodel=@var{code-size-model-type} @gol
409 -msdata=@var{sdata-type} @gol
410 -mno-flush-func -mflush-func=@var{name} @gol
411 -mno-flush-trap -mflush-trap=@var{number} @gol
414 @emph{RS/6000 and PowerPC Options}
415 @gccoptlist{-mcpu=@var{cpu-type} @gol
416 -mtune=@var{cpu-type} @gol
417 -mpower -mno-power -mpower2 -mno-power2 @gol
418 -mpowerpc -mpowerpc64 -mno-powerpc @gol
419 -maltivec -mno-altivec @gol
420 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
421 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
422 -mnew-mnemonics -mold-mnemonics @gol
423 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
424 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
425 -malign-power -malign-natural @gol
426 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
427 -mstring -mno-string -mupdate -mno-update @gol
428 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
429 -mstrict-align -mno-strict-align -mrelocatable @gol
430 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
431 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
432 -mdynamic-no-pic @gol
433 -mprioritize-restricted-insns=@var{priority} @gol
434 -msched-costly-dep=@var{dependence_type} @gol
435 -minsert-sched-nops=@var{scheme} @gol
436 -mcall-sysv -mcall-netbsd @gol
437 -maix-struct-return -msvr4-struct-return @gol
438 -mabi=altivec -mabi=no-altivec @gol
439 -mabi=spe -mabi=no-spe @gol
440 -misel=yes -misel=no @gol
441 -mspe=yes -mspe=no @gol
442 -mfloat-gprs=yes -mfloat-gprs=no @gol
443 -mprototype -mno-prototype @gol
444 -msim -mmvme -mads -myellowknife -memb -msdata @gol
445 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
447 @emph{Darwin Options}
448 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
449 -arch_only -bind_at_load -bundle -bundle_loader @gol
450 -client_name -compatibility_version -current_version @gol
451 -dependency-file -dylib_file -dylinker_install_name @gol
452 -dynamic -dynamiclib -exported_symbols_list @gol
453 -filelist -flat_namespace -force_cpusubtype_ALL @gol
454 -force_flat_namespace -headerpad_max_install_names @gol
455 -image_base -init -install_name -keep_private_externs @gol
456 -multi_module -multiply_defined -multiply_defined_unused @gol
457 -noall_load -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
458 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
459 -private_bundle -read_only_relocs -sectalign @gol
460 -sectobjectsymbols -whyload -seg1addr @gol
461 -sectcreate -sectobjectsymbols -sectorder @gol
462 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
463 -segprot -segs_read_only_addr -segs_read_write_addr @gol
464 -single_module -static -sub_library -sub_umbrella @gol
465 -twolevel_namespace -umbrella -undefined @gol
466 -unexported_symbols_list -weak_reference_mismatches @gol
470 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
471 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
472 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
473 -mxgot -mno-xgot -membedded-pic -mno-embedded-pic @gol
474 -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol
475 -msingle-float -mdouble-float -mint64 -mlong64 -mlong32 @gol
476 -G@var{num} -membedded-data -mno-embedded-data @gol
477 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
478 -msplit-addresses -mno-split-addresses @gol
479 -mexplicit-relocs -mno-explicit-relocs @gol
480 -mrnames -mno-rnames @gol
481 -mcheck-zero-division -mno-check-zero-division @gol
482 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
483 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
484 -mfix-sb1 -mno-fix-sb1 -mflush-func=@var{func} @gol
485 -mno-flush-func -mbranch-likely -mno-branch-likely}
487 @emph{i386 and x86-64 Options}
488 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
489 -mfpmath=@var{unit} @gol
490 -masm=@var{dialect} -mno-fancy-math-387 @gol
491 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
492 -mno-wide-multiply -mrtd -malign-double @gol
493 -mpreferred-stack-boundary=@var{num} @gol
494 -mmmx -msse -msse2 -msse3 -m3dnow @gol
495 -mthreads -mno-align-stringops -minline-all-stringops @gol
496 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
497 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
498 -mno-red-zone -mno-tls-direct-seg-refs @gol
499 -mcmodel=@var{code-model} @gol
503 @gccoptlist{-march=@var{architecture-type} @gol
504 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
505 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
506 -mjump-in-delay -mlinker-opt -mlong-calls @gol
507 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
508 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
509 -mno-jump-in-delay -mno-long-load-store @gol
510 -mno-portable-runtime -mno-soft-float @gol
511 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
512 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
513 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
514 -nolibdld -static -threads}
516 @emph{Intel 960 Options}
517 @gccoptlist{-m@var{cpu-type} -masm-compat -mclean-linkage @gol
518 -mcode-align -mcomplex-addr -mleaf-procedures @gol
519 -mic-compat -mic2.0-compat -mic3.0-compat @gol
520 -mintel-asm -mno-clean-linkage -mno-code-align @gol
521 -mno-complex-addr -mno-leaf-procedures @gol
522 -mno-old-align -mno-strict-align -mno-tail-call @gol
523 -mnumerics -mold-align -msoft-float -mstrict-align @gol
526 @emph{DEC Alpha Options}
527 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
528 -mieee -mieee-with-inexact -mieee-conformant @gol
529 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
530 -mtrap-precision=@var{mode} -mbuild-constants @gol
531 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
532 -mbwx -mmax -mfix -mcix @gol
533 -mfloat-vax -mfloat-ieee @gol
534 -mexplicit-relocs -msmall-data -mlarge-data @gol
535 -msmall-text -mlarge-text @gol
536 -mmemory-latency=@var{time}}
538 @emph{DEC Alpha/VMS Options}
539 @gccoptlist{-mvms-return-codes}
541 @emph{H8/300 Options}
542 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
545 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
546 -m4-nofpu -m4-single-only -m4-single -m4 @gol
547 -m5-64media -m5-64media-nofpu @gol
548 -m5-32media -m5-32media-nofpu @gol
549 -m5-compact -m5-compact-nofpu @gol
550 -mb -ml -mdalign -mrelax @gol
551 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
552 -mieee -misize -mpadstruct -mspace @gol
553 -mprefergot -musermode}
555 @emph{System V Options}
556 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
559 @gccoptlist{-EB -EL @gol
560 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
561 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
563 @emph{TMS320C3x/C4x Options}
564 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
565 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
566 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
567 -mparallel-insns -mparallel-mpy -mpreserve-float}
570 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
571 -mprolog-function -mno-prolog-function -mspace @gol
572 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
573 -mapp-regs -mno-app-regs @gol
574 -mdisable-callt -mno-disable-callt @gol
580 @gccoptlist{-m32032 -m32332 -m32532 -m32081 -m32381 @gol
581 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
582 -mregparam -mnoregparam -msb -mnosb @gol
583 -mbitfield -mnobitfield -mhimem -mnohimem}
586 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
587 -mcall-prologues -mno-tablejump -mtiny-stack}
590 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
591 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
592 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
593 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
594 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
597 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
598 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
599 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
600 -mno-base-addresses -msingle-exit -mno-single-exit}
603 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
604 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
605 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
606 -minline-float-divide-max-throughput @gol
607 -minline-int-divide-min-latency @gol
608 -minline-int-divide-max-throughput @gol
609 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
610 -mno-dwarf2-asm -mearly-stop-bits @gol
611 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
612 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64}
615 @gccoptlist{-mextmem -mextmemory -monchip -mno-asm-optimize @gol
616 -masm-optimize -mbranch-cost=@var{n} -mcond-exec=@var{n}}
618 @emph{S/390 and zSeries Options}
619 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
620 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
621 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
622 -m64 -m31 -mdebug -mno-debug -mesa -mzarch -mfused-madd -mno-fused-madd}
625 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
626 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
627 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
628 -mstack-align -mdata-align -mconst-align @gol
629 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
630 -melf -maout -melinux -mlinux -sim -sim2 @gol
631 -mmul-bug-workaround -mno-mul-bug-workaround}
633 @emph{PDP-11 Options}
634 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
635 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
636 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
637 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
638 -mbranch-expensive -mbranch-cheap @gol
639 -msplit -mno-split -munix-asm -mdec-asm}
641 @emph{Xstormy16 Options}
644 @emph{Xtensa Options}
645 @gccoptlist{-mconst16 -mno-const16 @gol
646 -mfused-madd -mno-fused-madd @gol
647 -mtext-section-literals -mno-text-section-literals @gol
648 -mtarget-align -mno-target-align @gol
649 -mlongcalls -mno-longcalls}
652 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
653 -mhard-float -msoft-float @gol
654 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
655 -mdouble -mno-double @gol
656 -mmedia -mno-media -mmuladd -mno-muladd @gol
657 -mlibrary-pic -macc-4 -macc-8 @gol
658 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
659 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
660 -mvliw-branch -mno-vliw-branch @gol
661 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
662 -mno-nested-cond-exec -mtomcat-stats @gol
665 @item Code Generation Options
666 @xref{Code Gen Options,,Options for Code Generation Conventions}.
667 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
668 -ffixed-@var{reg} -fexceptions @gol
669 -fnon-call-exceptions -funwind-tables @gol
670 -fasynchronous-unwind-tables @gol
671 -finhibit-size-directive -finstrument-functions @gol
672 -fno-common -fno-ident @gol
673 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
674 -freg-struct-return -fshared-data -fshort-enums @gol
675 -fshort-double -fshort-wchar @gol
676 -fverbose-asm -fpack-struct -fstack-check @gol
677 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
678 -fargument-alias -fargument-noalias @gol
679 -fargument-noalias-global -fleading-underscore @gol
680 -ftls-model=@var{model} @gol
681 -ftrapv -fwrapv -fbounds-check}
685 * Overall Options:: Controlling the kind of output:
686 an executable, object files, assembler files,
687 or preprocessed source.
688 * C Dialect Options:: Controlling the variant of C language compiled.
689 * C++ Dialect Options:: Variations on C++.
690 * Objective-C Dialect Options:: Variations on Objective-C.
691 * Language Independent Options:: Controlling how diagnostics should be
693 * Warning Options:: How picky should the compiler be?
694 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
695 * Optimize Options:: How much optimization?
696 * Preprocessor Options:: Controlling header files and macro definitions.
697 Also, getting dependency information for Make.
698 * Assembler Options:: Passing options to the assembler.
699 * Link Options:: Specifying libraries and so on.
700 * Directory Options:: Where to find header files and libraries.
701 Where to find the compiler executable files.
702 * Spec Files:: How to pass switches to sub-processes.
703 * Target Options:: Running a cross-compiler, or an old version of GCC.
706 @node Overall Options
707 @section Options Controlling the Kind of Output
709 Compilation can involve up to four stages: preprocessing, compilation
710 proper, assembly and linking, always in that order. GCC is capable of
711 preprocessing and compiling several files either into several
712 assembler input files, or into one assembler input file; then each
713 assembler input file produces an object file, and linking combines all
714 the object files (those newly compiled, and those specified as input)
715 into an executable file.
717 @cindex file name suffix
718 For any given input file, the file name suffix determines what kind of
723 C source code which must be preprocessed.
726 C source code which should not be preprocessed.
729 C++ source code which should not be preprocessed.
732 Objective-C source code. Note that you must link with the library
733 @file{libobjc.a} to make an Objective-C program work.
736 Objective-C source code which should not be preprocessed.
739 C or C++ header file to be turned into a precompiled header.
743 @itemx @var{file}.cxx
744 @itemx @var{file}.cpp
745 @itemx @var{file}.CPP
746 @itemx @var{file}.c++
748 C++ source code which must be preprocessed. Note that in @samp{.cxx},
749 the last two letters must both be literally @samp{x}. Likewise,
750 @samp{.C} refers to a literal capital C@.
754 C++ header file to be turned into a precompiled header.
757 @itemx @var{file}.for
758 @itemx @var{file}.FOR
759 Fortran source code which should not be preprocessed.
762 @itemx @var{file}.fpp
763 @itemx @var{file}.FPP
764 Fortran source code which must be preprocessed (with the traditional
768 Fortran source code which must be preprocessed with a RATFOR
769 preprocessor (not included with GCC)@.
771 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
772 Using and Porting GNU Fortran}, for more details of the handling of
775 @c FIXME: Descriptions of Java file types.
782 Ada source code file which contains a library unit declaration (a
783 declaration of a package, subprogram, or generic, or a generic
784 instantiation), or a library unit renaming declaration (a package,
785 generic, or subprogram renaming declaration). Such files are also
788 @itemx @var{file}.adb
789 Ada source code file containing a library unit body (a subprogram or
790 package body). Such files are also called @dfn{bodies}.
792 @c GCC also knows about some suffixes for languages not yet included:
801 Assembler code which must be preprocessed.
804 An object file to be fed straight into linking.
805 Any file name with no recognized suffix is treated this way.
809 You can specify the input language explicitly with the @option{-x} option:
812 @item -x @var{language}
813 Specify explicitly the @var{language} for the following input files
814 (rather than letting the compiler choose a default based on the file
815 name suffix). This option applies to all following input files until
816 the next @option{-x} option. Possible values for @var{language} are:
818 c c-header cpp-output
819 c++ c++-header c++-cpp-output
820 objective-c objective-c-header objc-cpp-output
821 assembler assembler-with-cpp
823 f77 f77-cpp-input ratfor
829 Turn off any specification of a language, so that subsequent files are
830 handled according to their file name suffixes (as they are if @option{-x}
831 has not been used at all).
833 @item -pass-exit-codes
834 @opindex pass-exit-codes
835 Normally the @command{gcc} program will exit with the code of 1 if any
836 phase of the compiler returns a non-success return code. If you specify
837 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
838 numerically highest error produced by any phase that returned an error
842 If you only want some of the stages of compilation, you can use
843 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
844 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
845 @command{gcc} is to stop. Note that some combinations (for example,
846 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
851 Compile or assemble the source files, but do not link. The linking
852 stage simply is not done. The ultimate output is in the form of an
853 object file for each source file.
855 By default, the object file name for a source file is made by replacing
856 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
858 Unrecognized input files, not requiring compilation or assembly, are
863 Stop after the stage of compilation proper; do not assemble. The output
864 is in the form of an assembler code file for each non-assembler input
867 By default, the assembler file name for a source file is made by
868 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
870 Input files that don't require compilation are ignored.
874 Stop after the preprocessing stage; do not run the compiler proper. The
875 output is in the form of preprocessed source code, which is sent to the
878 Input files which don't require preprocessing are ignored.
880 @cindex output file option
883 Place output in file @var{file}. This applies regardless to whatever
884 sort of output is being produced, whether it be an executable file,
885 an object file, an assembler file or preprocessed C code.
887 If you specify @option{-o} when compiling more than one input file, or
888 you are producing an executable file as output, all the source files
889 on the command line will be compiled at once.
891 If @option{-o} is not specified, the default is to put an executable file
892 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
893 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
894 all preprocessed C source on standard output.
898 Print (on standard error output) the commands executed to run the stages
899 of compilation. Also print the version number of the compiler driver
900 program and of the preprocessor and the compiler proper.
904 Like @option{-v} except the commands are not executed and all command
905 arguments are quoted. This is useful for shell scripts to capture the
906 driver-generated command lines.
910 Use pipes rather than temporary files for communication between the
911 various stages of compilation. This fails to work on some systems where
912 the assembler is unable to read from a pipe; but the GNU assembler has
917 Print (on the standard output) a description of the command line options
918 understood by @command{gcc}. If the @option{-v} option is also specified
919 then @option{--help} will also be passed on to the various processes
920 invoked by @command{gcc}, so that they can display the command line options
921 they accept. If the @option{-Wextra} option is also specified then command
922 line options which have no documentation associated with them will also
927 Print (on the standard output) a description of target specific command
928 line options for each tool.
932 Display the version number and copyrights of the invoked GCC.
936 @section Compiling C++ Programs
938 @cindex suffixes for C++ source
939 @cindex C++ source file suffixes
940 C++ source files conventionally use one of the suffixes @samp{.C},
941 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
942 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
943 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
944 files with these names and compiles them as C++ programs even if you
945 call the compiler the same way as for compiling C programs (usually
946 with the name @command{gcc}).
950 However, C++ programs often require class libraries as well as a
951 compiler that understands the C++ language---and under some
952 circumstances, you might want to compile programs or header files from
953 standard input, or otherwise without a suffix that flags them as C++
954 programs. You might also like to precompile a C header file with a
955 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
956 program that calls GCC with the default language set to C++, and
957 automatically specifies linking against the C++ library. On many
958 systems, @command{g++} is also installed with the name @command{c++}.
960 @cindex invoking @command{g++}
961 When you compile C++ programs, you may specify many of the same
962 command-line options that you use for compiling programs in any
963 language; or command-line options meaningful for C and related
964 languages; or options that are meaningful only for C++ programs.
965 @xref{C Dialect Options,,Options Controlling C Dialect}, for
966 explanations of options for languages related to C@.
967 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
968 explanations of options that are meaningful only for C++ programs.
970 @node C Dialect Options
971 @section Options Controlling C Dialect
972 @cindex dialect options
973 @cindex language dialect options
974 @cindex options, dialect
976 The following options control the dialect of C (or languages derived
977 from C, such as C++ and Objective-C) that the compiler accepts:
984 In C mode, support all ISO C90 programs. In C++ mode,
985 remove GNU extensions that conflict with ISO C++.
987 This turns off certain features of GCC that are incompatible with ISO
988 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
989 such as the @code{asm} and @code{typeof} keywords, and
990 predefined macros such as @code{unix} and @code{vax} that identify the
991 type of system you are using. It also enables the undesirable and
992 rarely used ISO trigraph feature. For the C compiler,
993 it disables recognition of C++ style @samp{//} comments as well as
994 the @code{inline} keyword.
996 The alternate keywords @code{__asm__}, @code{__extension__},
997 @code{__inline__} and @code{__typeof__} continue to work despite
998 @option{-ansi}. You would not want to use them in an ISO C program, of
999 course, but it is useful to put them in header files that might be included
1000 in compilations done with @option{-ansi}. Alternate predefined macros
1001 such as @code{__unix__} and @code{__vax__} are also available, with or
1002 without @option{-ansi}.
1004 The @option{-ansi} option does not cause non-ISO programs to be
1005 rejected gratuitously. For that, @option{-pedantic} is required in
1006 addition to @option{-ansi}. @xref{Warning Options}.
1008 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1009 option is used. Some header files may notice this macro and refrain
1010 from declaring certain functions or defining certain macros that the
1011 ISO standard doesn't call for; this is to avoid interfering with any
1012 programs that might use these names for other things.
1014 Functions which would normally be built in but do not have semantics
1015 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1016 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1017 built-in functions provided by GCC}, for details of the functions
1022 Determine the language standard. This option is currently only
1023 supported when compiling C or C++. A value for this option must be
1024 provided; possible values are
1029 ISO C90 (same as @option{-ansi}).
1031 @item iso9899:199409
1032 ISO C90 as modified in amendment 1.
1038 ISO C99. Note that this standard is not yet fully supported; see
1039 @w{@uref{http://gcc.gnu.org/gcc-3.4/c99status.html}} for more information. The
1040 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1043 Default, ISO C90 plus GNU extensions (including some C99 features).
1047 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1048 this will become the default. The name @samp{gnu9x} is deprecated.
1051 The 1998 ISO C++ standard plus amendments.
1054 The same as @option{-std=c++98} plus GNU extensions. This is the
1055 default for C++ code.
1058 Even when this option is not specified, you can still use some of the
1059 features of newer standards in so far as they do not conflict with
1060 previous C standards. For example, you may use @code{__restrict__} even
1061 when @option{-std=c99} is not specified.
1063 The @option{-std} options specifying some version of ISO C have the same
1064 effects as @option{-ansi}, except that features that were not in ISO C90
1065 but are in the specified version (for example, @samp{//} comments and
1066 the @code{inline} keyword in ISO C99) are not disabled.
1068 @xref{Standards,,Language Standards Supported by GCC}, for details of
1069 these standard versions.
1071 @item -aux-info @var{filename}
1073 Output to the given filename prototyped declarations for all functions
1074 declared and/or defined in a translation unit, including those in header
1075 files. This option is silently ignored in any language other than C@.
1077 Besides declarations, the file indicates, in comments, the origin of
1078 each declaration (source file and line), whether the declaration was
1079 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1080 @samp{O} for old, respectively, in the first character after the line
1081 number and the colon), and whether it came from a declaration or a
1082 definition (@samp{C} or @samp{F}, respectively, in the following
1083 character). In the case of function definitions, a K&R-style list of
1084 arguments followed by their declarations is also provided, inside
1085 comments, after the declaration.
1089 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1090 keyword, so that code can use these words as identifiers. You can use
1091 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1092 instead. @option{-ansi} implies @option{-fno-asm}.
1094 In C++, this switch only affects the @code{typeof} keyword, since
1095 @code{asm} and @code{inline} are standard keywords. You may want to
1096 use the @option{-fno-gnu-keywords} flag instead, which has the same
1097 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1098 switch only affects the @code{asm} and @code{typeof} keywords, since
1099 @code{inline} is a standard keyword in ISO C99.
1102 @itemx -fno-builtin-@var{function}
1103 @opindex fno-builtin
1104 @cindex built-in functions
1105 Don't recognize built-in functions that do not begin with
1106 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1107 functions provided by GCC}, for details of the functions affected,
1108 including those which are not built-in functions when @option{-ansi} or
1109 @option{-std} options for strict ISO C conformance are used because they
1110 do not have an ISO standard meaning.
1112 GCC normally generates special code to handle certain built-in functions
1113 more efficiently; for instance, calls to @code{alloca} may become single
1114 instructions that adjust the stack directly, and calls to @code{memcpy}
1115 may become inline copy loops. The resulting code is often both smaller
1116 and faster, but since the function calls no longer appear as such, you
1117 cannot set a breakpoint on those calls, nor can you change the behavior
1118 of the functions by linking with a different library.
1120 With the @option{-fno-builtin-@var{function}} option
1121 only the built-in function @var{function} is
1122 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1123 function is named this is not built-in in this version of GCC, this
1124 option is ignored. There is no corresponding
1125 @option{-fbuiltin-@var{function}} option; if you wish to enable
1126 built-in functions selectively when using @option{-fno-builtin} or
1127 @option{-ffreestanding}, you may define macros such as:
1130 #define abs(n) __builtin_abs ((n))
1131 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1136 @cindex hosted environment
1138 Assert that compilation takes place in a hosted environment. This implies
1139 @option{-fbuiltin}. A hosted environment is one in which the
1140 entire standard library is available, and in which @code{main} has a return
1141 type of @code{int}. Examples are nearly everything except a kernel.
1142 This is equivalent to @option{-fno-freestanding}.
1144 @item -ffreestanding
1145 @opindex ffreestanding
1146 @cindex hosted environment
1148 Assert that compilation takes place in a freestanding environment. This
1149 implies @option{-fno-builtin}. A freestanding environment
1150 is one in which the standard library may not exist, and program startup may
1151 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1152 This is equivalent to @option{-fno-hosted}.
1154 @xref{Standards,,Language Standards Supported by GCC}, for details of
1155 freestanding and hosted environments.
1157 @item -fms-extensions
1158 @opindex fms-extensions
1159 Accept some non-standard constructs used in Microsoft header files.
1163 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1164 options for strict ISO C conformance) implies @option{-trigraphs}.
1166 @item -no-integrated-cpp
1167 @opindex no-integrated-cpp
1168 Performs a compilation in two passes: preprocessing and compiling. This
1169 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1170 @option{-B} option. The user supplied compilation step can then add in
1171 an additional preprocessing step after normal preprocessing but before
1172 compiling. The default is to use the integrated cpp (internal cpp)
1174 The semantics of this option will change if "cc1", "cc1plus", and
1175 "cc1obj" are merged.
1177 @cindex traditional C language
1178 @cindex C language, traditional
1180 @itemx -traditional-cpp
1181 @opindex traditional-cpp
1182 @opindex traditional
1183 Formerly, these options caused GCC to attempt to emulate a pre-standard
1184 C compiler. They are now only supported with the @option{-E} switch.
1185 The preprocessor continues to support a pre-standard mode. See the GNU
1186 CPP manual for details.
1188 @item -fcond-mismatch
1189 @opindex fcond-mismatch
1190 Allow conditional expressions with mismatched types in the second and
1191 third arguments. The value of such an expression is void. This option
1192 is not supported for C++.
1194 @item -funsigned-char
1195 @opindex funsigned-char
1196 Let the type @code{char} be unsigned, like @code{unsigned char}.
1198 Each kind of machine has a default for what @code{char} should
1199 be. It is either like @code{unsigned char} by default or like
1200 @code{signed char} by default.
1202 Ideally, a portable program should always use @code{signed char} or
1203 @code{unsigned char} when it depends on the signedness of an object.
1204 But many programs have been written to use plain @code{char} and
1205 expect it to be signed, or expect it to be unsigned, depending on the
1206 machines they were written for. This option, and its inverse, let you
1207 make such a program work with the opposite default.
1209 The type @code{char} is always a distinct type from each of
1210 @code{signed char} or @code{unsigned char}, even though its behavior
1211 is always just like one of those two.
1214 @opindex fsigned-char
1215 Let the type @code{char} be signed, like @code{signed char}.
1217 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1218 the negative form of @option{-funsigned-char}. Likewise, the option
1219 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1221 @item -fsigned-bitfields
1222 @itemx -funsigned-bitfields
1223 @itemx -fno-signed-bitfields
1224 @itemx -fno-unsigned-bitfields
1225 @opindex fsigned-bitfields
1226 @opindex funsigned-bitfields
1227 @opindex fno-signed-bitfields
1228 @opindex fno-unsigned-bitfields
1229 These options control whether a bit-field is signed or unsigned, when the
1230 declaration does not use either @code{signed} or @code{unsigned}. By
1231 default, such a bit-field is signed, because this is consistent: the
1232 basic integer types such as @code{int} are signed types.
1234 @item -fwritable-strings
1235 @opindex fwritable-strings
1236 Store string constants in the writable data segment and don't uniquize
1237 them. This is for compatibility with old programs which assume they can
1238 write into string constants.
1240 Writing into string constants is a very bad idea; ``constants'' should
1243 This option is deprecated.
1246 @node C++ Dialect Options
1247 @section Options Controlling C++ Dialect
1249 @cindex compiler options, C++
1250 @cindex C++ options, command line
1251 @cindex options, C++
1252 This section describes the command-line options that are only meaningful
1253 for C++ programs; but you can also use most of the GNU compiler options
1254 regardless of what language your program is in. For example, you
1255 might compile a file @code{firstClass.C} like this:
1258 g++ -g -frepo -O -c firstClass.C
1262 In this example, only @option{-frepo} is an option meant
1263 only for C++ programs; you can use the other options with any
1264 language supported by GCC@.
1266 Here is a list of options that are @emph{only} for compiling C++ programs:
1270 @item -fabi-version=@var{n}
1271 @opindex fabi-version
1272 Use version @var{n} of the C++ ABI. Version 2 is the version of the
1273 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1274 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1275 the version that conforms most closely to the C++ ABI specification.
1276 Therefore, the ABI obtained using version 0 will change as ABI bugs
1279 The default is version 2.
1281 @item -fno-access-control
1282 @opindex fno-access-control
1283 Turn off all access checking. This switch is mainly useful for working
1284 around bugs in the access control code.
1288 Check that the pointer returned by @code{operator new} is non-null
1289 before attempting to modify the storage allocated. This check is
1290 normally unnecessary because the C++ standard specifies that
1291 @code{operator new} will only return @code{0} if it is declared
1292 @samp{throw()}, in which case the compiler will always check the
1293 return value even without this option. In all other cases, when
1294 @code{operator new} has a non-empty exception specification, memory
1295 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1296 @samp{new (nothrow)}.
1298 @item -fconserve-space
1299 @opindex fconserve-space
1300 Put uninitialized or runtime-initialized global variables into the
1301 common segment, as C does. This saves space in the executable at the
1302 cost of not diagnosing duplicate definitions. If you compile with this
1303 flag and your program mysteriously crashes after @code{main()} has
1304 completed, you may have an object that is being destroyed twice because
1305 two definitions were merged.
1307 This option is no longer useful on most targets, now that support has
1308 been added for putting variables into BSS without making them common.
1310 @item -fno-const-strings
1311 @opindex fno-const-strings
1312 Give string constants type @code{char *} instead of type @code{const
1313 char *}. By default, G++ uses type @code{const char *} as required by
1314 the standard. Even if you use @option{-fno-const-strings}, you cannot
1315 actually modify the value of a string constant, unless you also use
1316 @option{-fwritable-strings}.
1318 This option might be removed in a future release of G++. For maximum
1319 portability, you should structure your code so that it works with
1320 string constants that have type @code{const char *}.
1322 @item -fno-elide-constructors
1323 @opindex fno-elide-constructors
1324 The C++ standard allows an implementation to omit creating a temporary
1325 which is only used to initialize another object of the same type.
1326 Specifying this option disables that optimization, and forces G++ to
1327 call the copy constructor in all cases.
1329 @item -fno-enforce-eh-specs
1330 @opindex fno-enforce-eh-specs
1331 Don't check for violation of exception specifications at runtime. This
1332 option violates the C++ standard, but may be useful for reducing code
1333 size in production builds, much like defining @samp{NDEBUG}. The compiler
1334 will still optimize based on the exception specifications.
1337 @itemx -fno-for-scope
1339 @opindex fno-for-scope
1340 If @option{-ffor-scope} is specified, the scope of variables declared in
1341 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1342 as specified by the C++ standard.
1343 If @option{-fno-for-scope} is specified, the scope of variables declared in
1344 a @i{for-init-statement} extends to the end of the enclosing scope,
1345 as was the case in old versions of G++, and other (traditional)
1346 implementations of C++.
1348 The default if neither flag is given to follow the standard,
1349 but to allow and give a warning for old-style code that would
1350 otherwise be invalid, or have different behavior.
1352 @item -fno-gnu-keywords
1353 @opindex fno-gnu-keywords
1354 Do not recognize @code{typeof} as a keyword, so that code can use this
1355 word as an identifier. You can use the keyword @code{__typeof__} instead.
1356 @option{-ansi} implies @option{-fno-gnu-keywords}.
1358 @item -fno-implicit-templates
1359 @opindex fno-implicit-templates
1360 Never emit code for non-inline templates which are instantiated
1361 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1362 @xref{Template Instantiation}, for more information.
1364 @item -fno-implicit-inline-templates
1365 @opindex fno-implicit-inline-templates
1366 Don't emit code for implicit instantiations of inline templates, either.
1367 The default is to handle inlines differently so that compiles with and
1368 without optimization will need the same set of explicit instantiations.
1370 @item -fno-implement-inlines
1371 @opindex fno-implement-inlines
1372 To save space, do not emit out-of-line copies of inline functions
1373 controlled by @samp{#pragma implementation}. This will cause linker
1374 errors if these functions are not inlined everywhere they are called.
1376 @item -fms-extensions
1377 @opindex fms-extensions
1378 Disable pedantic warnings about constructs used in MFC, such as implicit
1379 int and getting a pointer to member function via non-standard syntax.
1381 @item -fno-nonansi-builtins
1382 @opindex fno-nonansi-builtins
1383 Disable built-in declarations of functions that are not mandated by
1384 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1385 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1387 @item -fno-operator-names
1388 @opindex fno-operator-names
1389 Do not treat the operator name keywords @code{and}, @code{bitand},
1390 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1391 synonyms as keywords.
1393 @item -fno-optional-diags
1394 @opindex fno-optional-diags
1395 Disable diagnostics that the standard says a compiler does not need to
1396 issue. Currently, the only such diagnostic issued by G++ is the one for
1397 a name having multiple meanings within a class.
1400 @opindex fpermissive
1401 Downgrade some diagnostics about nonconformant code from errors to
1402 warnings. Thus, using @option{-fpermissive} will allow some
1403 nonconforming code to compile.
1407 Enable automatic template instantiation at link time. This option also
1408 implies @option{-fno-implicit-templates}. @xref{Template
1409 Instantiation}, for more information.
1413 Disable generation of information about every class with virtual
1414 functions for use by the C++ runtime type identification features
1415 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1416 of the language, you can save some space by using this flag. Note that
1417 exception handling uses the same information, but it will generate it as
1422 Emit statistics about front-end processing at the end of the compilation.
1423 This information is generally only useful to the G++ development team.
1425 @item -ftemplate-depth-@var{n}
1426 @opindex ftemplate-depth
1427 Set the maximum instantiation depth for template classes to @var{n}.
1428 A limit on the template instantiation depth is needed to detect
1429 endless recursions during template class instantiation. ANSI/ISO C++
1430 conforming programs must not rely on a maximum depth greater than 17.
1432 @item -fuse-cxa-atexit
1433 @opindex fuse-cxa-atexit
1434 Register destructors for objects with static storage duration with the
1435 @code{__cxa_atexit} function rather than the @code{atexit} function.
1436 This option is required for fully standards-compliant handling of static
1437 destructors, but will only work if your C library supports
1438 @code{__cxa_atexit}.
1442 Do not use weak symbol support, even if it is provided by the linker.
1443 By default, G++ will use weak symbols if they are available. This
1444 option exists only for testing, and should not be used by end-users;
1445 it will result in inferior code and has no benefits. This option may
1446 be removed in a future release of G++.
1450 Do not search for header files in the standard directories specific to
1451 C++, but do still search the other standard directories. (This option
1452 is used when building the C++ library.)
1455 In addition, these optimization, warning, and code generation options
1456 have meanings only for C++ programs:
1459 @item -fno-default-inline
1460 @opindex fno-default-inline
1461 Do not assume @samp{inline} for functions defined inside a class scope.
1462 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1463 functions will have linkage like inline functions; they just won't be
1466 @item -Wabi @r{(C++ only)}
1468 Warn when G++ generates code that is probably not compatible with the
1469 vendor-neutral C++ ABI. Although an effort has been made to warn about
1470 all such cases, there are probably some cases that are not warned about,
1471 even though G++ is generating incompatible code. There may also be
1472 cases where warnings are emitted even though the code that is generated
1475 You should rewrite your code to avoid these warnings if you are
1476 concerned about the fact that code generated by G++ may not be binary
1477 compatible with code generated by other compilers.
1479 The known incompatibilities at this point include:
1484 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1485 pack data into the same byte as a base class. For example:
1488 struct A @{ virtual void f(); int f1 : 1; @};
1489 struct B : public A @{ int f2 : 1; @};
1493 In this case, G++ will place @code{B::f2} into the same byte
1494 as@code{A::f1}; other compilers will not. You can avoid this problem
1495 by explicitly padding @code{A} so that its size is a multiple of the
1496 byte size on your platform; that will cause G++ and other compilers to
1497 layout @code{B} identically.
1500 Incorrect handling of tail-padding for virtual bases. G++ does not use
1501 tail padding when laying out virtual bases. For example:
1504 struct A @{ virtual void f(); char c1; @};
1505 struct B @{ B(); char c2; @};
1506 struct C : public A, public virtual B @{@};
1510 In this case, G++ will not place @code{B} into the tail-padding for
1511 @code{A}; other compilers will. You can avoid this problem by
1512 explicitly padding @code{A} so that its size is a multiple of its
1513 alignment (ignoring virtual base classes); that will cause G++ and other
1514 compilers to layout @code{C} identically.
1517 Incorrect handling of bit-fields with declared widths greater than that
1518 of their underlying types, when the bit-fields appear in a union. For
1522 union U @{ int i : 4096; @};
1526 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1527 union too small by the number of bits in an @code{int}.
1530 Empty classes can be placed at incorrect offsets. For example:
1540 struct C : public B, public A @{@};
1544 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1545 it should be placed at offset zero. G++ mistakenly believes that the
1546 @code{A} data member of @code{B} is already at offset zero.
1549 Names of template functions whose types involve @code{typename} or
1550 template template parameters can be mangled incorrectly.
1553 template <typename Q>
1554 void f(typename Q::X) @{@}
1556 template <template <typename> class Q>
1557 void f(typename Q<int>::X) @{@}
1561 Instantiations of these templates may be mangled incorrectly.
1565 @item -Wctor-dtor-privacy @r{(C++ only)}
1566 @opindex Wctor-dtor-privacy
1567 Warn when a class seems unusable because all the constructors or
1568 destructors in that class are private, and it has neither friends nor
1569 public static member functions.
1571 @item -Wnon-virtual-dtor @r{(C++ only)}
1572 @opindex Wnon-virtual-dtor
1573 Warn when a class appears to be polymorphic, thereby requiring a virtual
1574 destructor, yet it declares a non-virtual one.
1575 This warning is enabled by @option{-Wall}.
1577 @item -Wreorder @r{(C++ only)}
1579 @cindex reordering, warning
1580 @cindex warning for reordering of member initializers
1581 Warn when the order of member initializers given in the code does not
1582 match the order in which they must be executed. For instance:
1588 A(): j (0), i (1) @{ @}
1592 The compiler will rearrange the member initializers for @samp{i}
1593 and @samp{j} to match the declaration order of the members, emitting
1594 a warning to that effect. This warning is enabled by @option{-Wall}.
1597 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1600 @item -Weffc++ @r{(C++ only)}
1602 Warn about violations of the following style guidelines from Scott Meyers'
1603 @cite{Effective C++} book:
1607 Item 11: Define a copy constructor and an assignment operator for classes
1608 with dynamically allocated memory.
1611 Item 12: Prefer initialization to assignment in constructors.
1614 Item 14: Make destructors virtual in base classes.
1617 Item 15: Have @code{operator=} return a reference to @code{*this}.
1620 Item 23: Don't try to return a reference when you must return an object.
1624 Also warn about violations of the following style guidelines from
1625 Scott Meyers' @cite{More Effective C++} book:
1629 Item 6: Distinguish between prefix and postfix forms of increment and
1630 decrement operators.
1633 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1637 When selecting this option, be aware that the standard library
1638 headers do not obey all of these guidelines; use @samp{grep -v}
1639 to filter out those warnings.
1641 @item -Wno-deprecated @r{(C++ only)}
1642 @opindex Wno-deprecated
1643 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1645 @item -Wno-non-template-friend @r{(C++ only)}
1646 @opindex Wno-non-template-friend
1647 Disable warnings when non-templatized friend functions are declared
1648 within a template. Since the advent of explicit template specification
1649 support in G++, if the name of the friend is an unqualified-id (i.e.,
1650 @samp{friend foo(int)}), the C++ language specification demands that the
1651 friend declare or define an ordinary, nontemplate function. (Section
1652 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1653 could be interpreted as a particular specialization of a templatized
1654 function. Because this non-conforming behavior is no longer the default
1655 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1656 check existing code for potential trouble spots and is on by default.
1657 This new compiler behavior can be turned off with
1658 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1659 but disables the helpful warning.
1661 @item -Wold-style-cast @r{(C++ only)}
1662 @opindex Wold-style-cast
1663 Warn if an old-style (C-style) cast to a non-void type is used within
1664 a C++ program. The new-style casts (@samp{static_cast},
1665 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1666 unintended effects and much easier to search for.
1668 @item -Woverloaded-virtual @r{(C++ only)}
1669 @opindex Woverloaded-virtual
1670 @cindex overloaded virtual fn, warning
1671 @cindex warning for overloaded virtual fn
1672 Warn when a function declaration hides virtual functions from a
1673 base class. For example, in:
1680 struct B: public A @{
1685 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1693 will fail to compile.
1695 @item -Wno-pmf-conversions @r{(C++ only)}
1696 @opindex Wno-pmf-conversions
1697 Disable the diagnostic for converting a bound pointer to member function
1700 @item -Wsign-promo @r{(C++ only)}
1701 @opindex Wsign-promo
1702 Warn when overload resolution chooses a promotion from unsigned or
1703 enumerated type to a signed type, over a conversion to an unsigned type of
1704 the same size. Previous versions of G++ would try to preserve
1705 unsignedness, but the standard mandates the current behavior.
1710 A& operator = (int);
1720 In this example, G++ will synthesize a default @samp{A& operator =
1721 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1724 @node Objective-C Dialect Options
1725 @section Options Controlling Objective-C Dialect
1727 @cindex compiler options, Objective-C
1728 @cindex Objective-C options, command line
1729 @cindex options, Objective-C
1730 (NOTE: This manual does not describe the Objective-C language itself. See
1731 @w{@uref{http://gcc.gnu.org/readings.html}} for references.)
1733 This section describes the command-line options that are only meaningful
1734 for Objective-C programs, but you can also use most of the GNU compiler
1735 options regardless of what language your program is in. For example,
1736 you might compile a file @code{some_class.m} like this:
1739 gcc -g -fgnu-runtime -O -c some_class.m
1743 In this example, @option{-fgnu-runtime} is an option meant only for
1744 Objective-C programs; you can use the other options with any language
1747 Here is a list of options that are @emph{only} for compiling Objective-C
1751 @item -fconstant-string-class=@var{class-name}
1752 @opindex fconstant-string-class
1753 Use @var{class-name} as the name of the class to instantiate for each
1754 literal string specified with the syntax @code{@@"@dots{}"}. The default
1755 class name is @code{NXConstantString} if the GNU runtime is being used, and
1756 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1757 @option{-fconstant-cfstrings} option, if also present, will override the
1758 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1759 to be laid out as constant CoreFoundation strings.
1762 @opindex fgnu-runtime
1763 Generate object code compatible with the standard GNU Objective-C
1764 runtime. This is the default for most types of systems.
1766 @item -fnext-runtime
1767 @opindex fnext-runtime
1768 Generate output compatible with the NeXT runtime. This is the default
1769 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1770 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1773 @item -fno-nil-receivers
1774 @opindex fno-nil-receivers
1775 Assume that all Objective-C message dispatches (e.g.,
1776 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1777 is not @code{nil}. This allows for more efficient entry points in the runtime to be
1778 used. Currently, this option is only available in conjunction with
1779 the NeXT runtime on Mac OS X 10.3 and later.
1781 @item -fobjc-exceptions
1782 @opindex fobjc-exceptions
1783 Enable syntactic support for structured exception handling in Objective-C,
1784 similar to what is offered by C++ and Java. Currently, this option is only
1785 available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1793 @@catch (AnObjCClass *exc) @{
1800 @@catch (AnotherClass *exc) @{
1803 @@catch (id allOthers) @{
1813 The @code{@@throw} statement may appear anywhere in an Objective-C or
1814 Objective-C++ program; when used inside of a @code{@@catch} block, the
1815 @code{@@throw} may appear without an argument (as shown above), in which case
1816 the object caught by the @code{@@catch} will be rethrown.
1818 Note that only (pointers to) Objective-C objects may be thrown and
1819 caught using this scheme. When an object is thrown, it will be caught
1820 by the nearest @code{@@catch} clause capable of handling objects of that type,
1821 analogously to how @code{catch} blocks work in C++ and Java. A
1822 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
1823 any and all Objective-C exceptions not caught by previous @code{@@catch}
1826 The @code{@@finally} clause, if present, will be executed upon exit from the
1827 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
1828 regardless of whether any exceptions are thrown, caught or rethrown
1829 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
1830 of the @code{finally} clause in Java.
1832 There are several caveats to using the new exception mechanism:
1836 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
1837 idioms provided by the @code{NSException} class, the new
1838 exceptions can only be used on Mac OS X 10.3 (Panther) and later
1839 systems, due to additional functionality needed in the (NeXT) Objective-C
1843 As mentioned above, the new exceptions do not support handling
1844 types other than Objective-C objects. Furthermore, when used from
1845 Objective-C++, the Objective-C exception model does not interoperate with C++
1846 exceptions at this time. This means you cannot @code{@@throw} an exception
1847 from Objective-C and @code{catch} it in C++, or vice versa
1848 (i.e., @code{throw @dots{} @@catch}).
1851 The @option{-fobjc-exceptions} switch also enables the use of synchronization
1852 blocks for thread-safe execution:
1855 @@synchronized (ObjCClass *guard) @{
1860 Upon entering the @code{@@synchronized} block, a thread of execution shall
1861 first check whether a lock has been placed on the corresponding @code{guard}
1862 object by another thread. If it has, the current thread shall wait until
1863 the other thread relinquishes its lock. Once @code{guard} becomes available,
1864 the current thread will place its own lock on it, execute the code contained in
1865 the @code{@@synchronized} block, and finally relinquish the lock (thereby
1866 making @code{guard} available to other threads).
1868 Unlike Java, Objective-C does not allow for entire methods to be marked
1869 @code{@@synchronized}. Note that throwing exceptions out of
1870 @code{@@synchronized} blocks is allowed, and will cause the guarding object
1871 to be unlocked properly.
1873 @item -freplace-objc-classes
1874 @opindex freplace-objc-classes
1875 Emit a special marker instructing @command{ld(1)} not to statically link in
1876 the resulting object file, and allow @command{dyld(1)} to load it in at
1877 run time instead. This is used in conjunction with the Fix-and-Continue
1878 debugging mode, where the object file in question may be recompiled and
1879 dynamically reloaded in the course of program execution, without the need
1880 to restart the program itself. Currently, Fix-and-Continue functionality
1881 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
1886 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
1887 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
1888 compile time) with static class references that get initialized at load time,
1889 which improves run-time performance. Specifying the @option{-fzero-link} flag
1890 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
1891 to be retained. This is useful in Zero-Link debugging mode, since it allows
1892 for individual class implementations to be modified during program execution.
1896 Dump interface declarations for all classes seen in the source file to a
1897 file named @file{@var{sourcename}.decl}.
1900 @opindex Wno-protocol
1901 If a class is declared to implement a protocol, a warning is issued for
1902 every method in the protocol that is not implemented by the class. The
1903 default behavior is to issue a warning for every method not explicitly
1904 implemented in the class, even if a method implementation is inherited
1905 from the superclass. If you use the @code{-Wno-protocol} option, then
1906 methods inherited from the superclass are considered to be implemented,
1907 and no warning is issued for them.
1911 Warn if multiple methods of different types for the same selector are
1912 found during compilation. The check is performed on the list of methods
1913 in the final stage of compilation. Additionally, a check is performed
1914 for each selector appearing in a @code{@@selector(@dots{})}
1915 expression, and a corresponding method for that selector has been found
1916 during compilation. Because these checks scan the method table only at
1917 the end of compilation, these warnings are not produced if the final
1918 stage of compilation is not reached, for example because an error is
1919 found during compilation, or because the @code{-fsyntax-only} option is
1922 @item -Wundeclared-selector
1923 @opindex Wundeclared-selector
1924 Warn if a @code{@@selector(@dots{})} expression referring to an
1925 undeclared selector is found. A selector is considered undeclared if no
1926 method with that name has been declared before the
1927 @code{@@selector(@dots{})} expression, either explicitly in an
1928 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
1929 an @code{@@implementation} section. This option always performs its
1930 checks as soon as a @code{@@selector(@dots{})} expression is found,
1931 while @code{-Wselector} only performs its checks in the final stage of
1932 compilation. This also enforces the coding style convention
1933 that methods and selectors must be declared before being used.
1935 @item -print-objc-runtime-info
1936 @opindex print-objc-runtime-info
1937 Generate C header describing the largest structure that is passed by
1942 @node Language Independent Options
1943 @section Options to Control Diagnostic Messages Formatting
1944 @cindex options to control diagnostics formatting
1945 @cindex diagnostic messages
1946 @cindex message formatting
1948 Traditionally, diagnostic messages have been formatted irrespective of
1949 the output device's aspect (e.g.@: its width, @dots{}). The options described
1950 below can be used to control the diagnostic messages formatting
1951 algorithm, e.g.@: how many characters per line, how often source location
1952 information should be reported. Right now, only the C++ front end can
1953 honor these options. However it is expected, in the near future, that
1954 the remaining front ends would be able to digest them correctly.
1957 @item -fmessage-length=@var{n}
1958 @opindex fmessage-length
1959 Try to format error messages so that they fit on lines of about @var{n}
1960 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1961 the front ends supported by GCC@. If @var{n} is zero, then no
1962 line-wrapping will be done; each error message will appear on a single
1965 @opindex fdiagnostics-show-location
1966 @item -fdiagnostics-show-location=once
1967 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1968 reporter to emit @emph{once} source location information; that is, in
1969 case the message is too long to fit on a single physical line and has to
1970 be wrapped, the source location won't be emitted (as prefix) again,
1971 over and over, in subsequent continuation lines. This is the default
1974 @item -fdiagnostics-show-location=every-line
1975 Only meaningful in line-wrapping mode. Instructs the diagnostic
1976 messages reporter to emit the same source location information (as
1977 prefix) for physical lines that result from the process of breaking
1978 a message which is too long to fit on a single line.
1982 @node Warning Options
1983 @section Options to Request or Suppress Warnings
1984 @cindex options to control warnings
1985 @cindex warning messages
1986 @cindex messages, warning
1987 @cindex suppressing warnings
1989 Warnings are diagnostic messages that report constructions which
1990 are not inherently erroneous but which are risky or suggest there
1991 may have been an error.
1993 You can request many specific warnings with options beginning @samp{-W},
1994 for example @option{-Wimplicit} to request warnings on implicit
1995 declarations. Each of these specific warning options also has a
1996 negative form beginning @samp{-Wno-} to turn off warnings;
1997 for example, @option{-Wno-implicit}. This manual lists only one of the
1998 two forms, whichever is not the default.
2000 The following options control the amount and kinds of warnings produced
2001 by GCC; for further, language-specific options also refer to
2002 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
2005 @cindex syntax checking
2007 @opindex fsyntax-only
2008 Check the code for syntax errors, but don't do anything beyond that.
2012 Issue all the warnings demanded by strict ISO C and ISO C++;
2013 reject all programs that use forbidden extensions, and some other
2014 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2015 version of the ISO C standard specified by any @option{-std} option used.
2017 Valid ISO C and ISO C++ programs should compile properly with or without
2018 this option (though a rare few will require @option{-ansi} or a
2019 @option{-std} option specifying the required version of ISO C)@. However,
2020 without this option, certain GNU extensions and traditional C and C++
2021 features are supported as well. With this option, they are rejected.
2023 @option{-pedantic} does not cause warning messages for use of the
2024 alternate keywords whose names begin and end with @samp{__}. Pedantic
2025 warnings are also disabled in the expression that follows
2026 @code{__extension__}. However, only system header files should use
2027 these escape routes; application programs should avoid them.
2028 @xref{Alternate Keywords}.
2030 Some users try to use @option{-pedantic} to check programs for strict ISO
2031 C conformance. They soon find that it does not do quite what they want:
2032 it finds some non-ISO practices, but not all---only those for which
2033 ISO C @emph{requires} a diagnostic, and some others for which
2034 diagnostics have been added.
2036 A feature to report any failure to conform to ISO C might be useful in
2037 some instances, but would require considerable additional work and would
2038 be quite different from @option{-pedantic}. We don't have plans to
2039 support such a feature in the near future.
2041 Where the standard specified with @option{-std} represents a GNU
2042 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2043 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2044 extended dialect is based. Warnings from @option{-pedantic} are given
2045 where they are required by the base standard. (It would not make sense
2046 for such warnings to be given only for features not in the specified GNU
2047 C dialect, since by definition the GNU dialects of C include all
2048 features the compiler supports with the given option, and there would be
2049 nothing to warn about.)
2051 @item -pedantic-errors
2052 @opindex pedantic-errors
2053 Like @option{-pedantic}, except that errors are produced rather than
2058 Inhibit all warning messages.
2062 Inhibit warning messages about the use of @samp{#import}.
2064 @item -Wchar-subscripts
2065 @opindex Wchar-subscripts
2066 Warn if an array subscript has type @code{char}. This is a common cause
2067 of error, as programmers often forget that this type is signed on some
2072 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2073 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2077 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2078 the arguments supplied have types appropriate to the format string
2079 specified, and that the conversions specified in the format string make
2080 sense. This includes standard functions, and others specified by format
2081 attributes (@pxref{Function Attributes}), in the @code{printf},
2082 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2083 not in the C standard) families.
2085 The formats are checked against the format features supported by GNU
2086 libc version 2.2. These include all ISO C90 and C99 features, as well
2087 as features from the Single Unix Specification and some BSD and GNU
2088 extensions. Other library implementations may not support all these
2089 features; GCC does not support warning about features that go beyond a
2090 particular library's limitations. However, if @option{-pedantic} is used
2091 with @option{-Wformat}, warnings will be given about format features not
2092 in the selected standard version (but not for @code{strfmon} formats,
2093 since those are not in any version of the C standard). @xref{C Dialect
2094 Options,,Options Controlling C Dialect}.
2096 Since @option{-Wformat} also checks for null format arguments for
2097 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2099 @option{-Wformat} is included in @option{-Wall}. For more control over some
2100 aspects of format checking, the options @option{-Wformat-y2k},
2101 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2102 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2103 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2106 @opindex Wformat-y2k
2107 If @option{-Wformat} is specified, also warn about @code{strftime}
2108 formats which may yield only a two-digit year.
2110 @item -Wno-format-extra-args
2111 @opindex Wno-format-extra-args
2112 If @option{-Wformat} is specified, do not warn about excess arguments to a
2113 @code{printf} or @code{scanf} format function. The C standard specifies
2114 that such arguments are ignored.
2116 Where the unused arguments lie between used arguments that are
2117 specified with @samp{$} operand number specifications, normally
2118 warnings are still given, since the implementation could not know what
2119 type to pass to @code{va_arg} to skip the unused arguments. However,
2120 in the case of @code{scanf} formats, this option will suppress the
2121 warning if the unused arguments are all pointers, since the Single
2122 Unix Specification says that such unused arguments are allowed.
2124 @item -Wno-format-zero-length
2125 @opindex Wno-format-zero-length
2126 If @option{-Wformat} is specified, do not warn about zero-length formats.
2127 The C standard specifies that zero-length formats are allowed.
2129 @item -Wformat-nonliteral
2130 @opindex Wformat-nonliteral
2131 If @option{-Wformat} is specified, also warn if the format string is not a
2132 string literal and so cannot be checked, unless the format function
2133 takes its format arguments as a @code{va_list}.
2135 @item -Wformat-security
2136 @opindex Wformat-security
2137 If @option{-Wformat} is specified, also warn about uses of format
2138 functions that represent possible security problems. At present, this
2139 warns about calls to @code{printf} and @code{scanf} functions where the
2140 format string is not a string literal and there are no format arguments,
2141 as in @code{printf (foo);}. This may be a security hole if the format
2142 string came from untrusted input and contains @samp{%n}. (This is
2143 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2144 in future warnings may be added to @option{-Wformat-security} that are not
2145 included in @option{-Wformat-nonliteral}.)
2149 Enable @option{-Wformat} plus format checks not included in
2150 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2151 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2155 Warn about passing a null pointer for arguments marked as
2156 requiring a non-null value by the @code{nonnull} function attribute.
2158 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2159 can be disabled with the @option{-Wno-nonnull} option.
2161 @item -Winit-self @r{(C, C++, and Objective-C only)}
2163 Warn about uninitialized variables which are initialized with themselves.
2164 Note this option can only be used with the @option{-Wuninitialized} option,
2165 which in turn only works with @option{-O1} and above.
2167 For example, GCC will warn about @code{i} being uninitialized in the
2168 following snippet only when @option{-Winit-self} has been specified:
2179 @item -Wimplicit-int
2180 @opindex Wimplicit-int
2181 Warn when a declaration does not specify a type.
2183 @item -Wimplicit-function-declaration
2184 @itemx -Werror-implicit-function-declaration
2185 @opindex Wimplicit-function-declaration
2186 @opindex Werror-implicit-function-declaration
2187 Give a warning (or error) whenever a function is used before being
2192 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2196 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2197 function with external linkage, returning int, taking either zero
2198 arguments, two, or three arguments of appropriate types.
2200 @item -Wmissing-braces
2201 @opindex Wmissing-braces
2202 Warn if an aggregate or union initializer is not fully bracketed. In
2203 the following example, the initializer for @samp{a} is not fully
2204 bracketed, but that for @samp{b} is fully bracketed.
2207 int a[2][2] = @{ 0, 1, 2, 3 @};
2208 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2212 @opindex Wparentheses
2213 Warn if parentheses are omitted in certain contexts, such
2214 as when there is an assignment in a context where a truth value
2215 is expected, or when operators are nested whose precedence people
2216 often get confused about.
2218 Also warn about constructions where there may be confusion to which
2219 @code{if} statement an @code{else} branch belongs. Here is an example of
2234 In C, every @code{else} branch belongs to the innermost possible @code{if}
2235 statement, which in this example is @code{if (b)}. This is often not
2236 what the programmer expected, as illustrated in the above example by
2237 indentation the programmer chose. When there is the potential for this
2238 confusion, GCC will issue a warning when this flag is specified.
2239 To eliminate the warning, add explicit braces around the innermost
2240 @code{if} statement so there is no way the @code{else} could belong to
2241 the enclosing @code{if}. The resulting code would look like this:
2257 @item -Wsequence-point
2258 @opindex Wsequence-point
2259 Warn about code that may have undefined semantics because of violations
2260 of sequence point rules in the C standard.
2262 The C standard defines the order in which expressions in a C program are
2263 evaluated in terms of @dfn{sequence points}, which represent a partial
2264 ordering between the execution of parts of the program: those executed
2265 before the sequence point, and those executed after it. These occur
2266 after the evaluation of a full expression (one which is not part of a
2267 larger expression), after the evaluation of the first operand of a
2268 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2269 function is called (but after the evaluation of its arguments and the
2270 expression denoting the called function), and in certain other places.
2271 Other than as expressed by the sequence point rules, the order of
2272 evaluation of subexpressions of an expression is not specified. All
2273 these rules describe only a partial order rather than a total order,
2274 since, for example, if two functions are called within one expression
2275 with no sequence point between them, the order in which the functions
2276 are called is not specified. However, the standards committee have
2277 ruled that function calls do not overlap.
2279 It is not specified when between sequence points modifications to the
2280 values of objects take effect. Programs whose behavior depends on this
2281 have undefined behavior; the C standard specifies that ``Between the
2282 previous and next sequence point an object shall have its stored value
2283 modified at most once by the evaluation of an expression. Furthermore,
2284 the prior value shall be read only to determine the value to be
2285 stored.''. If a program breaks these rules, the results on any
2286 particular implementation are entirely unpredictable.
2288 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2289 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2290 diagnosed by this option, and it may give an occasional false positive
2291 result, but in general it has been found fairly effective at detecting
2292 this sort of problem in programs.
2294 The present implementation of this option only works for C programs. A
2295 future implementation may also work for C++ programs.
2297 The C standard is worded confusingly, therefore there is some debate
2298 over the precise meaning of the sequence point rules in subtle cases.
2299 Links to discussions of the problem, including proposed formal
2300 definitions, may be found on the GCC readings page, at
2301 @w{@uref{http://gcc.gnu.org/readings.html}}.
2304 @opindex Wreturn-type
2305 Warn whenever a function is defined with a return-type that defaults to
2306 @code{int}. Also warn about any @code{return} statement with no
2307 return-value in a function whose return-type is not @code{void}.
2309 For C++, a function without return type always produces a diagnostic
2310 message, even when @option{-Wno-return-type} is specified. The only
2311 exceptions are @samp{main} and functions defined in system headers.
2315 Warn whenever a @code{switch} statement has an index of enumerated type
2316 and lacks a @code{case} for one or more of the named codes of that
2317 enumeration. (The presence of a @code{default} label prevents this
2318 warning.) @code{case} labels outside the enumeration range also
2319 provoke warnings when this option is used.
2321 @item -Wswitch-default
2322 @opindex Wswitch-switch
2323 Warn whenever a @code{switch} statement does not have a @code{default}
2327 @opindex Wswitch-enum
2328 Warn whenever a @code{switch} statement has an index of enumerated type
2329 and lacks a @code{case} for one or more of the named codes of that
2330 enumeration. @code{case} labels outside the enumeration range also
2331 provoke warnings when this option is used.
2335 Warn if any trigraphs are encountered that might change the meaning of
2336 the program (trigraphs within comments are not warned about).
2338 @item -Wunused-function
2339 @opindex Wunused-function
2340 Warn whenever a static function is declared but not defined or a
2341 non\-inline static function is unused.
2343 @item -Wunused-label
2344 @opindex Wunused-label
2345 Warn whenever a label is declared but not used.
2347 To suppress this warning use the @samp{unused} attribute
2348 (@pxref{Variable Attributes}).
2350 @item -Wunused-parameter
2351 @opindex Wunused-parameter
2352 Warn whenever a function parameter is unused aside from its declaration.
2354 To suppress this warning use the @samp{unused} attribute
2355 (@pxref{Variable Attributes}).
2357 @item -Wunused-variable
2358 @opindex Wunused-variable
2359 Warn whenever a local variable or non-constant static variable is unused
2360 aside from its declaration
2362 To suppress this warning use the @samp{unused} attribute
2363 (@pxref{Variable Attributes}).
2365 @item -Wunused-value
2366 @opindex Wunused-value
2367 Warn whenever a statement computes a result that is explicitly not used.
2369 To suppress this warning cast the expression to @samp{void}.
2373 All the above @option{-Wunused} options combined.
2375 In order to get a warning about an unused function parameter, you must
2376 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2377 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2379 @item -Wuninitialized
2380 @opindex Wuninitialized
2381 Warn if an automatic variable is used without first being initialized or
2382 if a variable may be clobbered by a @code{setjmp} call.
2384 These warnings are possible only in optimizing compilation,
2385 because they require data flow information that is computed only
2386 when optimizing. If you don't specify @option{-O}, you simply won't
2389 If you want to warn about code which uses the uninitialized value of the
2390 variable in its own initializer, use the @option{-Winit-self} option.
2392 These warnings occur only for variables that are candidates for
2393 register allocation. Therefore, they do not occur for a variable that
2394 is declared @code{volatile}, or whose address is taken, or whose size
2395 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2396 structures, unions or arrays, even when they are in registers.
2398 Note that there may be no warning about a variable that is used only
2399 to compute a value that itself is never used, because such
2400 computations may be deleted by data flow analysis before the warnings
2403 These warnings are made optional because GCC is not smart
2404 enough to see all the reasons why the code might be correct
2405 despite appearing to have an error. Here is one example of how
2426 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2427 always initialized, but GCC doesn't know this. Here is
2428 another common case:
2433 if (change_y) save_y = y, y = new_y;
2435 if (change_y) y = save_y;
2440 This has no bug because @code{save_y} is used only if it is set.
2442 @cindex @code{longjmp} warnings
2443 This option also warns when a non-volatile automatic variable might be
2444 changed by a call to @code{longjmp}. These warnings as well are possible
2445 only in optimizing compilation.
2447 The compiler sees only the calls to @code{setjmp}. It cannot know
2448 where @code{longjmp} will be called; in fact, a signal handler could
2449 call it at any point in the code. As a result, you may get a warning
2450 even when there is in fact no problem because @code{longjmp} cannot
2451 in fact be called at the place which would cause a problem.
2453 Some spurious warnings can be avoided if you declare all the functions
2454 you use that never return as @code{noreturn}. @xref{Function
2457 @item -Wunknown-pragmas
2458 @opindex Wunknown-pragmas
2459 @cindex warning for unknown pragmas
2460 @cindex unknown pragmas, warning
2461 @cindex pragmas, warning of unknown
2462 Warn when a #pragma directive is encountered which is not understood by
2463 GCC@. If this command line option is used, warnings will even be issued
2464 for unknown pragmas in system header files. This is not the case if
2465 the warnings were only enabled by the @option{-Wall} command line option.
2467 @item -Wstrict-aliasing
2468 @opindex Wstrict-aliasing
2469 This option is only active when @option{-fstrict-aliasing} is active.
2470 It warns about code which might break the strict aliasing rules that the
2471 compiler is using for optimization. The warning does not catch all
2472 cases, but does attempt to catch the more common pitfalls. It is
2473 included in @option{-Wall}.
2477 All of the above @samp{-W} options combined. This enables all the
2478 warnings about constructions that some users consider questionable, and
2479 that are easy to avoid (or modify to prevent the warning), even in
2480 conjunction with macros. This also enables some language-specific
2481 warnings described in @ref{C++ Dialect Options} and
2482 @ref{Objective-C Dialect Options}.
2485 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2486 Some of them warn about constructions that users generally do not
2487 consider questionable, but which occasionally you might wish to check
2488 for; others warn about constructions that are necessary or hard to avoid
2489 in some cases, and there is no simple way to modify the code to suppress
2496 (This option used to be called @option{-W}. The older name is still
2497 supported, but the newer name is more descriptive.) Print extra warning
2498 messages for these events:
2502 A function can return either with or without a value. (Falling
2503 off the end of the function body is considered returning without
2504 a value.) For example, this function would evoke such a
2518 An expression-statement or the left-hand side of a comma expression
2519 contains no side effects.
2520 To suppress the warning, cast the unused expression to void.
2521 For example, an expression such as @samp{x[i,j]} will cause a warning,
2522 but @samp{x[(void)i,j]} will not.
2525 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2528 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2529 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2530 that of ordinary mathematical notation.
2533 Storage-class specifiers like @code{static} are not the first things in
2534 a declaration. According to the C Standard, this usage is obsolescent.
2537 The return type of a function has a type qualifier such as @code{const}.
2538 Such a type qualifier has no effect, since the value returned by a
2539 function is not an lvalue. (But don't warn about the GNU extension of
2540 @code{volatile void} return types. That extension will be warned about
2541 if @option{-pedantic} is specified.)
2544 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2548 A comparison between signed and unsigned values could produce an
2549 incorrect result when the signed value is converted to unsigned.
2550 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2553 An aggregate has an initializer which does not initialize all members.
2554 For example, the following code would cause such a warning, because
2555 @code{x.h} would be implicitly initialized to zero:
2558 struct s @{ int f, g, h; @};
2559 struct s x = @{ 3, 4 @};
2563 A function parameter is declared without a type specifier in K&R-style
2571 An empty body occurs in an @samp{if} or @samp{else} statement.
2574 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2575 @samp{>}, or @samp{>=}.
2578 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2581 Any of several floating-point events that often indicate errors, such as
2582 overflow, underflow, loss of precision, etc.
2584 @item @r{(C++ only)}
2585 An enumerator and a non-enumerator both appear in a conditional expression.
2587 @item @r{(C++ only)}
2588 A non-static reference or non-static @samp{const} member appears in a
2589 class without constructors.
2591 @item @r{(C++ only)}
2592 Ambiguous virtual bases.
2594 @item @r{(C++ only)}
2595 Subscripting an array which has been declared @samp{register}.
2597 @item @r{(C++ only)}
2598 Taking the address of a variable which has been declared @samp{register}.
2600 @item @r{(C++ only)}
2601 A base class is not initialized in a derived class' copy constructor.
2604 @item -Wno-div-by-zero
2605 @opindex Wno-div-by-zero
2606 @opindex Wdiv-by-zero
2607 Do not warn about compile-time integer division by zero. Floating point
2608 division by zero is not warned about, as it can be a legitimate way of
2609 obtaining infinities and NaNs.
2611 @item -Wsystem-headers
2612 @opindex Wsystem-headers
2613 @cindex warnings from system headers
2614 @cindex system headers, warnings from
2615 Print warning messages for constructs found in system header files.
2616 Warnings from system headers are normally suppressed, on the assumption
2617 that they usually do not indicate real problems and would only make the
2618 compiler output harder to read. Using this command line option tells
2619 GCC to emit warnings from system headers as if they occurred in user
2620 code. However, note that using @option{-Wall} in conjunction with this
2621 option will @emph{not} warn about unknown pragmas in system
2622 headers---for that, @option{-Wunknown-pragmas} must also be used.
2625 @opindex Wfloat-equal
2626 Warn if floating point values are used in equality comparisons.
2628 The idea behind this is that sometimes it is convenient (for the
2629 programmer) to consider floating-point values as approximations to
2630 infinitely precise real numbers. If you are doing this, then you need
2631 to compute (by analyzing the code, or in some other way) the maximum or
2632 likely maximum error that the computation introduces, and allow for it
2633 when performing comparisons (and when producing output, but that's a
2634 different problem). In particular, instead of testing for equality, you
2635 would check to see whether the two values have ranges that overlap; and
2636 this is done with the relational operators, so equality comparisons are
2639 @item -Wtraditional @r{(C only)}
2640 @opindex Wtraditional
2641 Warn about certain constructs that behave differently in traditional and
2642 ISO C@. Also warn about ISO C constructs that have no traditional C
2643 equivalent, and/or problematic constructs which should be avoided.
2647 Macro parameters that appear within string literals in the macro body.
2648 In traditional C macro replacement takes place within string literals,
2649 but does not in ISO C@.
2652 In traditional C, some preprocessor directives did not exist.
2653 Traditional preprocessors would only consider a line to be a directive
2654 if the @samp{#} appeared in column 1 on the line. Therefore
2655 @option{-Wtraditional} warns about directives that traditional C
2656 understands but would ignore because the @samp{#} does not appear as the
2657 first character on the line. It also suggests you hide directives like
2658 @samp{#pragma} not understood by traditional C by indenting them. Some
2659 traditional implementations would not recognize @samp{#elif}, so it
2660 suggests avoiding it altogether.
2663 A function-like macro that appears without arguments.
2666 The unary plus operator.
2669 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2670 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2671 constants.) Note, these suffixes appear in macros defined in the system
2672 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2673 Use of these macros in user code might normally lead to spurious
2674 warnings, however GCC's integrated preprocessor has enough context to
2675 avoid warning in these cases.
2678 A function declared external in one block and then used after the end of
2682 A @code{switch} statement has an operand of type @code{long}.
2685 A non-@code{static} function declaration follows a @code{static} one.
2686 This construct is not accepted by some traditional C compilers.
2689 The ISO type of an integer constant has a different width or
2690 signedness from its traditional type. This warning is only issued if
2691 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2692 typically represent bit patterns, are not warned about.
2695 Usage of ISO string concatenation is detected.
2698 Initialization of automatic aggregates.
2701 Identifier conflicts with labels. Traditional C lacks a separate
2702 namespace for labels.
2705 Initialization of unions. If the initializer is zero, the warning is
2706 omitted. This is done under the assumption that the zero initializer in
2707 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2708 initializer warnings and relies on default initialization to zero in the
2712 Conversions by prototypes between fixed/floating point values and vice
2713 versa. The absence of these prototypes when compiling with traditional
2714 C would cause serious problems. This is a subset of the possible
2715 conversion warnings, for the full set use @option{-Wconversion}.
2718 Use of ISO C style function definitions. This warning intentionally is
2719 @emph{not} issued for prototype declarations or variadic functions
2720 because these ISO C features will appear in your code when using
2721 libiberty's traditional C compatibility macros, @code{PARAMS} and
2722 @code{VPARAMS}. This warning is also bypassed for nested functions
2723 because that feature is already a GCC extension and thus not relevant to
2724 traditional C compatibility.
2727 @item -Wdeclaration-after-statement @r{(C only)}
2728 @opindex Wdeclaration-after-statement
2729 Warn when a declaration is found after a statement in a block. This
2730 construct, known from C++, was introduced with ISO C99 and is by default
2731 allowed in GCC@. It is not supported by ISO C90 and was not supported by
2732 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
2736 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2738 @item -Wendif-labels
2739 @opindex Wendif-labels
2740 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2744 Warn whenever a local variable shadows another local variable, parameter or
2745 global variable or whenever a built-in function is shadowed.
2747 @item -Wlarger-than-@var{len}
2748 @opindex Wlarger-than
2749 Warn whenever an object of larger than @var{len} bytes is defined.
2751 @item -Wpointer-arith
2752 @opindex Wpointer-arith
2753 Warn about anything that depends on the ``size of'' a function type or
2754 of @code{void}. GNU C assigns these types a size of 1, for
2755 convenience in calculations with @code{void *} pointers and pointers
2758 @item -Wbad-function-cast @r{(C only)}
2759 @opindex Wbad-function-cast
2760 Warn whenever a function call is cast to a non-matching type.
2761 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2765 Warn whenever a pointer is cast so as to remove a type qualifier from
2766 the target type. For example, warn if a @code{const char *} is cast
2767 to an ordinary @code{char *}.
2770 @opindex Wcast-align
2771 Warn whenever a pointer is cast such that the required alignment of the
2772 target is increased. For example, warn if a @code{char *} is cast to
2773 an @code{int *} on machines where integers can only be accessed at
2774 two- or four-byte boundaries.
2776 @item -Wwrite-strings
2777 @opindex Wwrite-strings
2778 When compiling C, give string constants the type @code{const
2779 char[@var{length}]} so that
2780 copying the address of one into a non-@code{const} @code{char *}
2781 pointer will get a warning; when compiling C++, warn about the
2782 deprecated conversion from string constants to @code{char *}.
2783 These warnings will help you find at
2784 compile time code that can try to write into a string constant, but
2785 only if you have been very careful about using @code{const} in
2786 declarations and prototypes. Otherwise, it will just be a nuisance;
2787 this is why we did not make @option{-Wall} request these warnings.
2790 @opindex Wconversion
2791 Warn if a prototype causes a type conversion that is different from what
2792 would happen to the same argument in the absence of a prototype. This
2793 includes conversions of fixed point to floating and vice versa, and
2794 conversions changing the width or signedness of a fixed point argument
2795 except when the same as the default promotion.
2797 Also, warn if a negative integer constant expression is implicitly
2798 converted to an unsigned type. For example, warn about the assignment
2799 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2800 casts like @code{(unsigned) -1}.
2802 @item -Wsign-compare
2803 @opindex Wsign-compare
2804 @cindex warning for comparison of signed and unsigned values
2805 @cindex comparison of signed and unsigned values, warning
2806 @cindex signed and unsigned values, comparison warning
2807 Warn when a comparison between signed and unsigned values could produce
2808 an incorrect result when the signed value is converted to unsigned.
2809 This warning is also enabled by @option{-Wextra}; to get the other warnings
2810 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2812 @item -Waggregate-return
2813 @opindex Waggregate-return
2814 Warn if any functions that return structures or unions are defined or
2815 called. (In languages where you can return an array, this also elicits
2818 @item -Wstrict-prototypes @r{(C only)}
2819 @opindex Wstrict-prototypes
2820 Warn if a function is declared or defined without specifying the
2821 argument types. (An old-style function definition is permitted without
2822 a warning if preceded by a declaration which specifies the argument
2825 @item -Wold-style-definition @r{(C only)}
2826 @opindex Wold-style-definition
2827 Warn if an old-style function definition is used. A warning is given
2828 even if there is a previous prototype.
2830 @item -Wmissing-prototypes @r{(C only)}
2831 @opindex Wmissing-prototypes
2832 Warn if a global function is defined without a previous prototype
2833 declaration. This warning is issued even if the definition itself
2834 provides a prototype. The aim is to detect global functions that fail
2835 to be declared in header files.
2837 @item -Wmissing-declarations @r{(C only)}
2838 @opindex Wmissing-declarations
2839 Warn if a global function is defined without a previous declaration.
2840 Do so even if the definition itself provides a prototype.
2841 Use this option to detect global functions that are not declared in
2844 @item -Wmissing-noreturn
2845 @opindex Wmissing-noreturn
2846 Warn about functions which might be candidates for attribute @code{noreturn}.
2847 Note these are only possible candidates, not absolute ones. Care should
2848 be taken to manually verify functions actually do not ever return before
2849 adding the @code{noreturn} attribute, otherwise subtle code generation
2850 bugs could be introduced. You will not get a warning for @code{main} in
2851 hosted C environments.
2853 @item -Wmissing-format-attribute
2854 @opindex Wmissing-format-attribute
2856 If @option{-Wformat} is enabled, also warn about functions which might be
2857 candidates for @code{format} attributes. Note these are only possible
2858 candidates, not absolute ones. GCC will guess that @code{format}
2859 attributes might be appropriate for any function that calls a function
2860 like @code{vprintf} or @code{vscanf}, but this might not always be the
2861 case, and some functions for which @code{format} attributes are
2862 appropriate may not be detected. This option has no effect unless
2863 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2865 @item -Wno-multichar
2866 @opindex Wno-multichar
2868 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2869 Usually they indicate a typo in the user's code, as they have
2870 implementation-defined values, and should not be used in portable code.
2872 @item -Wno-deprecated-declarations
2873 @opindex Wno-deprecated-declarations
2874 Do not warn about uses of functions, variables, and types marked as
2875 deprecated by using the @code{deprecated} attribute.
2876 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2877 @pxref{Type Attributes}.)
2881 Warn if a structure is given the packed attribute, but the packed
2882 attribute has no effect on the layout or size of the structure.
2883 Such structures may be mis-aligned for little benefit. For
2884 instance, in this code, the variable @code{f.x} in @code{struct bar}
2885 will be misaligned even though @code{struct bar} does not itself
2886 have the packed attribute:
2893 @} __attribute__((packed));
2903 Warn if padding is included in a structure, either to align an element
2904 of the structure or to align the whole structure. Sometimes when this
2905 happens it is possible to rearrange the fields of the structure to
2906 reduce the padding and so make the structure smaller.
2908 @item -Wredundant-decls
2909 @opindex Wredundant-decls
2910 Warn if anything is declared more than once in the same scope, even in
2911 cases where multiple declaration is valid and changes nothing.
2913 @item -Wnested-externs @r{(C only)}
2914 @opindex Wnested-externs
2915 Warn if an @code{extern} declaration is encountered within a function.
2917 @item -Wunreachable-code
2918 @opindex Wunreachable-code
2919 Warn if the compiler detects that code will never be executed.
2921 This option is intended to warn when the compiler detects that at
2922 least a whole line of source code will never be executed, because
2923 some condition is never satisfied or because it is after a
2924 procedure that never returns.
2926 It is possible for this option to produce a warning even though there
2927 are circumstances under which part of the affected line can be executed,
2928 so care should be taken when removing apparently-unreachable code.
2930 For instance, when a function is inlined, a warning may mean that the
2931 line is unreachable in only one inlined copy of the function.
2933 This option is not made part of @option{-Wall} because in a debugging
2934 version of a program there is often substantial code which checks
2935 correct functioning of the program and is, hopefully, unreachable
2936 because the program does work. Another common use of unreachable
2937 code is to provide behavior which is selectable at compile-time.
2941 Warn if a function can not be inlined and it was declared as inline.
2942 Even with this option, the compiler will not warn about failures to
2943 inline functions declared in system headers.
2945 The compiler uses a variety of heuristics to determine whether or not
2946 to inline a function. For example, the compiler takes into account
2947 the size of the function being inlined and the the amount of inlining
2948 that has already been done in the current function. Therefore,
2949 seemingly insignificant changes in the source program can cause the
2950 warnings produced by @option{-Winline} to appear or disappear.
2952 @item -Wno-invalid-offsetof @r{(C++ only)}
2953 @opindex Wno-invalid-offsetof
2954 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
2955 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
2956 to a non-POD type is undefined. In existing C++ implementations,
2957 however, @samp{offsetof} typically gives meaningful results even when
2958 applied to certain kinds of non-POD types. (Such as a simple
2959 @samp{struct} that fails to be a POD type only by virtue of having a
2960 constructor.) This flag is for users who are aware that they are
2961 writing nonportable code and who have deliberately chosen to ignore the
2964 The restrictions on @samp{offsetof} may be relaxed in a future version
2965 of the C++ standard.
2968 @opindex Winvalid-pch
2969 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
2970 the search path but can't be used.
2974 @opindex Wno-long-long
2975 Warn if @samp{long long} type is used. This is default. To inhibit
2976 the warning messages, use @option{-Wno-long-long}. Flags
2977 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2978 only when @option{-pedantic} flag is used.
2980 @item -Wdisabled-optimization
2981 @opindex Wdisabled-optimization
2982 Warn if a requested optimization pass is disabled. This warning does
2983 not generally indicate that there is anything wrong with your code; it
2984 merely indicates that GCC's optimizers were unable to handle the code
2985 effectively. Often, the problem is that your code is too big or too
2986 complex; GCC will refuse to optimize programs when the optimization
2987 itself is likely to take inordinate amounts of time.
2991 Make all warnings into errors.
2994 @node Debugging Options
2995 @section Options for Debugging Your Program or GCC
2996 @cindex options, debugging
2997 @cindex debugging information options
2999 GCC has various special options that are used for debugging
3000 either your program or GCC:
3005 Produce debugging information in the operating system's native format
3006 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
3009 On most systems that use stabs format, @option{-g} enables use of extra
3010 debugging information that only GDB can use; this extra information
3011 makes debugging work better in GDB but will probably make other debuggers
3013 refuse to read the program. If you want to control for certain whether
3014 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3015 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3017 Unlike most other C compilers, GCC allows you to use @option{-g} with
3018 @option{-O}. The shortcuts taken by optimized code may occasionally
3019 produce surprising results: some variables you declared may not exist
3020 at all; flow of control may briefly move where you did not expect it;
3021 some statements may not be executed because they compute constant
3022 results or their values were already at hand; some statements may
3023 execute in different places because they were moved out of loops.
3025 Nevertheless it proves possible to debug optimized output. This makes
3026 it reasonable to use the optimizer for programs that might have bugs.
3028 The following options are useful when GCC is generated with the
3029 capability for more than one debugging format.
3033 Produce debugging information for use by GDB@. This means to use the
3034 most expressive format available (DWARF 2, stabs, or the native format
3035 if neither of those are supported), including GDB extensions if at all
3040 Produce debugging information in stabs format (if that is supported),
3041 without GDB extensions. This is the format used by DBX on most BSD
3042 systems. On MIPS, Alpha and System V Release 4 systems this option
3043 produces stabs debugging output which is not understood by DBX or SDB@.
3044 On System V Release 4 systems this option requires the GNU assembler.
3046 @item -feliminate-unused-debug-symbols
3047 @opindex feliminate-unused-debug-symbols
3048 Produce debugging information in stabs format (if that is supported),
3049 for only symbols that are actually used.
3053 Produce debugging information in stabs format (if that is supported),
3054 using GNU extensions understood only by the GNU debugger (GDB)@. The
3055 use of these extensions is likely to make other debuggers crash or
3056 refuse to read the program.
3060 Produce debugging information in COFF format (if that is supported).
3061 This is the format used by SDB on most System V systems prior to
3066 Produce debugging information in XCOFF format (if that is supported).
3067 This is the format used by the DBX debugger on IBM RS/6000 systems.
3071 Produce debugging information in XCOFF format (if that is supported),
3072 using GNU extensions understood only by the GNU debugger (GDB)@. The
3073 use of these extensions is likely to make other debuggers crash or
3074 refuse to read the program, and may cause assemblers other than the GNU
3075 assembler (GAS) to fail with an error.
3079 Produce debugging information in DWARF version 2 format (if that is
3080 supported). This is the format used by DBX on IRIX 6.
3084 Produce debugging information in VMS debug format (if that is
3085 supported). This is the format used by DEBUG on VMS systems.
3088 @itemx -ggdb@var{level}
3089 @itemx -gstabs@var{level}
3090 @itemx -gcoff@var{level}
3091 @itemx -gxcoff@var{level}
3092 @itemx -gvms@var{level}
3093 Request debugging information and also use @var{level} to specify how
3094 much information. The default level is 2.
3096 Level 1 produces minimal information, enough for making backtraces in
3097 parts of the program that you don't plan to debug. This includes
3098 descriptions of functions and external variables, but no information
3099 about local variables and no line numbers.
3101 Level 3 includes extra information, such as all the macro definitions
3102 present in the program. Some debuggers support macro expansion when
3103 you use @option{-g3}.
3105 Note that in order to avoid confusion between DWARF1 debug level 2,
3106 and DWARF2 @option{-gdwarf-2} does not accept a concatenated debug
3107 level. Instead use an additional @option{-g@var{level}} option to
3108 change the debug level for DWARF2.
3110 @item -feliminate-dwarf2-dups
3111 @opindex feliminate-dwarf2-dups
3112 Compress DWARF2 debugging information by eliminating duplicated
3113 information about each symbol. This option only makes sense when
3114 generating DWARF2 debugging information with @option{-gdwarf-2}.
3116 @cindex @command{prof}
3119 Generate extra code to write profile information suitable for the
3120 analysis program @command{prof}. You must use this option when compiling
3121 the source files you want data about, and you must also use it when
3124 @cindex @command{gprof}
3127 Generate extra code to write profile information suitable for the
3128 analysis program @command{gprof}. You must use this option when compiling
3129 the source files you want data about, and you must also use it when
3134 Makes the compiler print out each function name as it is compiled, and
3135 print some statistics about each pass when it finishes.
3138 @opindex ftime-report
3139 Makes the compiler print some statistics about the time consumed by each
3140 pass when it finishes.
3143 @opindex fmem-report
3144 Makes the compiler print some statistics about permanent memory
3145 allocation when it finishes.
3147 @item -fprofile-arcs
3148 @opindex fprofile-arcs
3149 Add code so that program flow @dfn{arcs} are instrumented. During
3150 execution the program records how many times each branch and call is
3151 executed and how many times it is taken or returns. When the compiled
3152 program exits it saves this data to a file called
3153 @file{@var{auxname}.gcda} for each source file. The data may be used for
3154 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3155 test coverage analysis (@option{-ftest-coverage}). Each object file's
3156 @var{auxname} is generated from the name of the output file, if
3157 explicitly specified and it is not the final executable, otherwise it is
3158 the basename of the source file. In both cases any suffix is removed
3159 (e.g. @file{foo.gcda} for input file @file{dir/foo.c}, or
3160 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3165 Compile the source files with @option{-fprofile-arcs} plus optimization
3166 and code generation options. For test coverage analysis, use the
3167 additional @option{-ftest-coverage} option. You do not need to profile
3168 every source file in a program.
3171 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3172 (the latter implies the former).
3175 Run the program on a representative workload to generate the arc profile
3176 information. This may be repeated any number of times. You can run
3177 concurrent instances of your program, and provided that the file system
3178 supports locking, the data files will be correctly updated. Also
3179 @code{fork} calls are detected and correctly handled (double counting
3183 For profile-directed optimizations, compile the source files again with
3184 the same optimization and code generation options plus
3185 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3186 Control Optimization}).
3189 For test coverage analysis, use @command{gcov} to produce human readable
3190 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3191 @command{gcov} documentation for further information.
3195 With @option{-fprofile-arcs}, for each function of your program GCC
3196 creates a program flow graph, then finds a spanning tree for the graph.
3197 Only arcs that are not on the spanning tree have to be instrumented: the
3198 compiler adds code to count the number of times that these arcs are
3199 executed. When an arc is the only exit or only entrance to a block, the
3200 instrumentation code can be added to the block; otherwise, a new basic
3201 block must be created to hold the instrumentation code.
3204 @item -ftest-coverage
3205 @opindex ftest-coverage
3206 Produce a notes file that the @command{gcov} code-coverage utility
3207 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3208 show program coverage. Each source file's note file is called
3209 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3210 above for a description of @var{auxname} and instructions on how to
3211 generate test coverage data. Coverage data will match the source files
3212 more closely, if you do not optimize.
3214 @item -d@var{letters}
3216 Says to make debugging dumps during compilation at times specified by
3217 @var{letters}. This is used for debugging the compiler. The file names
3218 for most of the dumps are made by appending a pass number and a word to
3219 the @var{dumpname}. @var{dumpname} is generated from the name of the
3220 output file, if explicitly specified and it is not an executable,
3221 otherwise it is the basename of the source file. In both cases any
3222 suffix is removed (e.g. @file{foo.01.rtl} or @file{foo.02.sibling}).
3223 Here are the possible letters for use in @var{letters}, and their
3229 Annotate the assembler output with miscellaneous debugging information.
3232 Dump after computing branch probabilities, to @file{@var{file}.12.bp}.
3235 Dump after block reordering, to @file{@var{file}.31.bbro}.
3238 Dump after instruction combination, to the file @file{@var{file}.20.combine}.
3241 Dump after the first if conversion, to the file @file{@var{file}.14.ce1}.
3242 Also dump after the second if conversion, to the file @file{@var{file}.21.ce2}.
3245 Dump after branch target load optimization, to to @file{@var{file}.32.btl}.
3246 Also dump after delayed branch scheduling, to @file{@var{file}.36.dbr}.
3249 Dump all macro definitions, at the end of preprocessing, in addition to
3253 Dump after the third if conversion, to @file{@var{file}.30.ce3}.
3256 Dump after control and data flow analysis, to @file{@var{file}.11.cfg}.
3257 Also dump after life analysis, to @file{@var{file}.19.life}.
3260 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.07.addressof}.
3263 Dump after global register allocation, to @file{@var{file}.25.greg}.
3266 Dump after GCSE, to @file{@var{file}.08.gcse}.
3267 Also dump after jump bypassing and control flow optimizations, to
3268 @file{@var{file}.10.bypass}.
3271 Dump after finalization of EH handling code, to @file{@var{file}.03.eh}.
3274 Dump after sibling call optimizations, to @file{@var{file}.02.sibling}.
3277 Dump after the first jump optimization, to @file{@var{file}.04.jump}.
3280 Dump after conversion from registers to stack, to @file{@var{file}.34.stack}.
3283 Dump after local register allocation, to @file{@var{file}.24.lreg}.
3286 Dump after loop optimization passes, to @file{@var{file}.09.loop} and
3287 @file{@var{file}.16.loop2}.
3290 Dump after performing the machine dependent reorganization pass, to
3291 @file{@var{file}.35.mach}.
3294 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3297 Dump after the register move pass, to @file{@var{file}.22.regmove}.
3300 Dump after post-reload optimizations, to @file{@var{file}.26.postreload}.
3303 Dump after RTL generation, to @file{@var{file}.01.rtl}.
3306 Dump after the second scheduling pass, to @file{@var{file}.33.sched2}.
3309 Dump after CSE (including the jump optimization that sometimes follows
3310 CSE), to @file{@var{file}.06.cse}.
3313 Dump after the first scheduling pass, to @file{@var{file}.23.sched}.
3316 Dump after the second CSE pass (including the jump optimization that
3317 sometimes follows CSE), to @file{@var{file}.18.cse2}.
3320 Dump after running tracer, to @file{@var{file}.15.tracer}.
3323 Dump after null pointer elimination pass to @file{@var{file}.05.null}.
3326 Dump callgraph and unit-at-a-time optimization @file{@var{file}.00.unit}.
3329 Dump after the value profile transformations, to @file{@var{file}.13.vpt}.
3332 Dump after the second flow pass, to @file{@var{file}.27.flow2}.
3335 Dump after the peephole pass, to @file{@var{file}.28.peephole2}.
3338 Dump after constructing the web, to @file{@var{file}.17.web}.
3341 Produce all the dumps listed above.
3344 Produce a core dump whenever an error occurs.
3347 Print statistics on memory usage, at the end of the run, to
3351 Annotate the assembler output with a comment indicating which
3352 pattern and alternative was used. The length of each instruction is
3356 Dump the RTL in the assembler output as a comment before each instruction.
3357 Also turns on @option{-dp} annotation.
3360 For each of the other indicated dump files (except for
3361 @file{@var{file}.01.rtl}), dump a representation of the control flow graph
3362 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3365 Just generate RTL for a function instead of compiling it. Usually used
3369 Dump debugging information during parsing, to standard error.
3372 @item -fdump-unnumbered
3373 @opindex fdump-unnumbered
3374 When doing debugging dumps (see @option{-d} option above), suppress instruction
3375 numbers and line number note output. This makes it more feasible to
3376 use diff on debugging dumps for compiler invocations with different
3377 options, in particular with and without @option{-g}.
3379 @item -fdump-translation-unit @r{(C and C++ only)}
3380 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3381 @opindex fdump-translation-unit
3382 Dump a representation of the tree structure for the entire translation
3383 unit to a file. The file name is made by appending @file{.tu} to the
3384 source file name. If the @samp{-@var{options}} form is used, @var{options}
3385 controls the details of the dump as described for the
3386 @option{-fdump-tree} options.
3388 @item -fdump-class-hierarchy @r{(C++ only)}
3389 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3390 @opindex fdump-class-hierarchy
3391 Dump a representation of each class's hierarchy and virtual function
3392 table layout to a file. The file name is made by appending @file{.class}
3393 to the source file name. If the @samp{-@var{options}} form is used,
3394 @var{options} controls the details of the dump as described for the
3395 @option{-fdump-tree} options.
3397 @item -fdump-tree-@var{switch} @r{(C++ only)}
3398 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3400 Control the dumping at various stages of processing the intermediate
3401 language tree to a file. The file name is generated by appending a switch
3402 specific suffix to the source file name. If the @samp{-@var{options}}
3403 form is used, @var{options} is a list of @samp{-} separated options that
3404 control the details of the dump. Not all options are applicable to all
3405 dumps, those which are not meaningful will be ignored. The following
3406 options are available
3410 Print the address of each node. Usually this is not meaningful as it
3411 changes according to the environment and source file. Its primary use
3412 is for tying up a dump file with a debug environment.
3414 Inhibit dumping of members of a scope or body of a function merely
3415 because that scope has been reached. Only dump such items when they
3416 are directly reachable by some other path.
3418 Turn on all options.
3421 The following tree dumps are possible:
3424 Dump before any tree based optimization, to @file{@var{file}.original}.
3426 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3428 Dump after function inlining, to @file{@var{file}.inlined}.
3431 @item -frandom-seed=@var{string}
3432 @opindex frandom-string
3433 This option provides a seed that GCC uses when it would otherwise use
3434 random numbers. It is used to generate certain symbol names
3435 that have to be different in every compiled file. It is also used to
3436 place unique stamps in coverage data files and the object files that
3437 produce them. You can use the @option{-frandom-seed} option to produce
3438 reproducibly identical object files.
3440 The @var{string} should be different for every file you compile.
3442 @item -fsched-verbose=@var{n}
3443 @opindex fsched-verbose
3444 On targets that use instruction scheduling, this option controls the
3445 amount of debugging output the scheduler prints. This information is
3446 written to standard error, unless @option{-dS} or @option{-dR} is
3447 specified, in which case it is output to the usual dump
3448 listing file, @file{.sched} or @file{.sched2} respectively. However
3449 for @var{n} greater than nine, the output is always printed to standard
3452 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3453 same information as @option{-dRS}. For @var{n} greater than one, it
3454 also output basic block probabilities, detailed ready list information
3455 and unit/insn info. For @var{n} greater than two, it includes RTL
3456 at abort point, control-flow and regions info. And for @var{n} over
3457 four, @option{-fsched-verbose} also includes dependence info.
3461 Store the usual ``temporary'' intermediate files permanently; place them
3462 in the current directory and name them based on the source file. Thus,
3463 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3464 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3465 preprocessed @file{foo.i} output file even though the compiler now
3466 normally uses an integrated preprocessor.
3470 Report the CPU time taken by each subprocess in the compilation
3471 sequence. For C source files, this is the compiler proper and assembler
3472 (plus the linker if linking is done). The output looks like this:
3479 The first number on each line is the ``user time,'' that is time spent
3480 executing the program itself. The second number is ``system time,''
3481 time spent executing operating system routines on behalf of the program.
3482 Both numbers are in seconds.
3484 @item -print-file-name=@var{library}
3485 @opindex print-file-name
3486 Print the full absolute name of the library file @var{library} that
3487 would be used when linking---and don't do anything else. With this
3488 option, GCC does not compile or link anything; it just prints the
3491 @item -print-multi-directory
3492 @opindex print-multi-directory
3493 Print the directory name corresponding to the multilib selected by any
3494 other switches present in the command line. This directory is supposed
3495 to exist in @env{GCC_EXEC_PREFIX}.
3497 @item -print-multi-lib
3498 @opindex print-multi-lib
3499 Print the mapping from multilib directory names to compiler switches
3500 that enable them. The directory name is separated from the switches by
3501 @samp{;}, and each switch starts with an @samp{@@} instead of the
3502 @samp{-}, without spaces between multiple switches. This is supposed to
3503 ease shell-processing.
3505 @item -print-prog-name=@var{program}
3506 @opindex print-prog-name
3507 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3509 @item -print-libgcc-file-name
3510 @opindex print-libgcc-file-name
3511 Same as @option{-print-file-name=libgcc.a}.
3513 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3514 but you do want to link with @file{libgcc.a}. You can do
3517 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3520 @item -print-search-dirs
3521 @opindex print-search-dirs
3522 Print the name of the configured installation directory and a list of
3523 program and library directories @command{gcc} will search---and don't do anything else.
3525 This is useful when @command{gcc} prints the error message
3526 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3527 To resolve this you either need to put @file{cpp0} and the other compiler
3528 components where @command{gcc} expects to find them, or you can set the environment
3529 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3530 Don't forget the trailing '/'.
3531 @xref{Environment Variables}.
3534 @opindex dumpmachine
3535 Print the compiler's target machine (for example,
3536 @samp{i686-pc-linux-gnu})---and don't do anything else.
3539 @opindex dumpversion
3540 Print the compiler version (for example, @samp{3.0})---and don't do
3545 Print the compiler's built-in specs---and don't do anything else. (This
3546 is used when GCC itself is being built.) @xref{Spec Files}.
3548 @item -feliminate-unused-debug-types
3549 @opindex feliminate-unused-debug-types
3550 Normally, when producing DWARF2 output, GCC will emit debugging
3551 information for all types declared in a compilation
3552 unit, regardless of whether or not they are actually used
3553 in that compilation unit. Sometimes this is useful, such as
3554 if, in the debugger, you want to cast a value to a type that is
3555 not actually used in your program (but is declared). More often,
3556 however, this results in a significant amount of wasted space.
3557 With this option, GCC will avoid producing debug symbol output
3558 for types that are nowhere used in the source file being compiled.
3561 @node Optimize Options
3562 @section Options That Control Optimization
3563 @cindex optimize options
3564 @cindex options, optimization
3566 These options control various sorts of optimizations.
3568 Without any optimization option, the compiler's goal is to reduce the
3569 cost of compilation and to make debugging produce the expected
3570 results. Statements are independent: if you stop the program with a
3571 breakpoint between statements, you can then assign a new value to any
3572 variable or change the program counter to any other statement in the
3573 function and get exactly the results you would expect from the source
3576 Turning on optimization flags makes the compiler attempt to improve
3577 the performance and/or code size at the expense of compilation time
3578 and possibly the ability to debug the program.
3580 The compiler performs optimization based on the knowledge it has of
3581 the program. Using the @option{-funit-at-a-time} flag will allow the
3582 compiler to consider information gained from later functions in the
3583 file when compiling a function. Compiling multiple files at once to a
3584 single output file (and using @option{-funit-at-a-time}) will allow
3585 the compiler to use information gained from all of the files when
3586 compiling each of them.
3588 Not all optimizations are controlled directly by a flag. Only
3589 optimizations that have a flag are listed.
3596 Optimize. Optimizing compilation takes somewhat more time, and a lot
3597 more memory for a large function.
3599 With @option{-O}, the compiler tries to reduce code size and execution
3600 time, without performing any optimizations that take a great deal of
3603 @option{-O} turns on the following optimization flags:
3604 @gccoptlist{-fdefer-pop @gol
3605 -fmerge-constants @gol
3607 -floop-optimize @gol
3608 -fif-conversion @gol
3609 -fif-conversion2 @gol
3610 -fdelayed-branch @gol
3611 -fguess-branch-probability @gol
3614 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
3615 where doing so does not interfere with debugging.
3619 Optimize even more. GCC performs nearly all supported optimizations
3620 that do not involve a space-speed tradeoff. The compiler does not
3621 perform loop unrolling or function inlining when you specify @option{-O2}.
3622 As compared to @option{-O}, this option increases both compilation time
3623 and the performance of the generated code.
3625 @option{-O2} turns on all optimization flags specified by @option{-O}. It
3626 also turns on the following optimization flags:
3627 @gccoptlist{-fforce-mem @gol
3628 -foptimize-sibling-calls @gol
3629 -fstrength-reduce @gol
3630 -fcse-follow-jumps -fcse-skip-blocks @gol
3631 -frerun-cse-after-loop -frerun-loop-opt @gol
3632 -fgcse -fgcse-lm -fgcse-sm -fgcse-las @gol
3633 -fdelete-null-pointer-checks @gol
3634 -fexpensive-optimizations @gol
3636 -fschedule-insns -fschedule-insns2 @gol
3637 -fsched-interblock -fsched-spec @gol
3640 -freorder-blocks -freorder-functions @gol
3641 -fstrict-aliasing @gol
3642 -funit-at-a-time @gol
3643 -falign-functions -falign-jumps @gol
3644 -falign-loops -falign-labels @gol
3647 Please note the warning under @option{-fgcse} about
3648 invoking @option{-O2} on programs that use computed gotos.
3652 Optimize yet more. @option{-O3} turns on all optimizations specified by
3653 @option{-O2} and also turns on the @option{-finline-functions},
3654 @option{-fweb}, @option{-frename-registers} and @option{-funswitch-loops}
3659 Do not optimize. This is the default.
3663 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3664 do not typically increase code size. It also performs further
3665 optimizations designed to reduce code size.
3667 @option{-Os} disables the following optimization flags:
3668 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
3669 -falign-labels -freorder-blocks -fprefetch-loop-arrays}
3671 If you use multiple @option{-O} options, with or without level numbers,
3672 the last such option is the one that is effective.
3675 Options of the form @option{-f@var{flag}} specify machine-independent
3676 flags. Most flags have both positive and negative forms; the negative
3677 form of @option{-ffoo} would be @option{-fno-foo}. In the table
3678 below, only one of the forms is listed---the one you typically will
3679 use. You can figure out the other form by either removing @samp{no-}
3682 The following options control specific optimizations. They are either
3683 activated by @option{-O} options or are related to ones that are. You
3684 can use the following flags in the rare cases when ``fine-tuning'' of
3685 optimizations to be performed is desired.
3688 @item -fno-default-inline
3689 @opindex fno-default-inline
3690 Do not make member functions inline by default merely because they are
3691 defined inside the class scope (C++ only). Otherwise, when you specify
3692 @w{@option{-O}}, member functions defined inside class scope are compiled
3693 inline by default; i.e., you don't need to add @samp{inline} in front of
3694 the member function name.
3696 @item -fno-defer-pop
3697 @opindex fno-defer-pop
3698 Always pop the arguments to each function call as soon as that function
3699 returns. For machines which must pop arguments after a function call,
3700 the compiler normally lets arguments accumulate on the stack for several
3701 function calls and pops them all at once.
3703 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3707 Force memory operands to be copied into registers before doing
3708 arithmetic on them. This produces better code by making all memory
3709 references potential common subexpressions. When they are not common
3710 subexpressions, instruction combination should eliminate the separate
3713 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3716 @opindex fforce-addr
3717 Force memory address constants to be copied into registers before
3718 doing arithmetic on them. This may produce better code just as
3719 @option{-fforce-mem} may.
3721 @item -fomit-frame-pointer
3722 @opindex fomit-frame-pointer
3723 Don't keep the frame pointer in a register for functions that
3724 don't need one. This avoids the instructions to save, set up and
3725 restore frame pointers; it also makes an extra register available
3726 in many functions. @strong{It also makes debugging impossible on
3729 On some machines, such as the VAX, this flag has no effect, because
3730 the standard calling sequence automatically handles the frame pointer
3731 and nothing is saved by pretending it doesn't exist. The
3732 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3733 whether a target machine supports this flag. @xref{Registers,,Register
3734 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3736 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3738 @item -foptimize-sibling-calls
3739 @opindex foptimize-sibling-calls
3740 Optimize sibling and tail recursive calls.
3742 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3746 Don't pay attention to the @code{inline} keyword. Normally this option
3747 is used to keep the compiler from expanding any functions inline.
3748 Note that if you are not optimizing, no functions can be expanded inline.
3750 @item -finline-functions
3751 @opindex finline-functions
3752 Integrate all simple functions into their callers. The compiler
3753 heuristically decides which functions are simple enough to be worth
3754 integrating in this way.
3756 If all calls to a given function are integrated, and the function is
3757 declared @code{static}, then the function is normally not output as
3758 assembler code in its own right.
3760 Enabled at level @option{-O3}.
3762 @item -finline-limit=@var{n}
3763 @opindex finline-limit
3764 By default, GCC limits the size of functions that can be inlined. This flag
3765 allows the control of this limit for functions that are explicitly marked as
3766 inline (i.e., marked with the inline keyword or defined within the class
3767 definition in c++). @var{n} is the size of functions that can be inlined in
3768 number of pseudo instructions (not counting parameter handling). The default
3769 value of @var{n} is 600.
3770 Increasing this value can result in more inlined code at
3771 the cost of compilation time and memory consumption. Decreasing usually makes
3772 the compilation faster and less code will be inlined (which presumably
3773 means slower programs). This option is particularly useful for programs that
3774 use inlining heavily such as those based on recursive templates with C++.
3776 Inlining is actually controlled by a number of parameters, which may be
3777 specified individually by using @option{--param @var{name}=@var{value}}.
3778 The @option{-finline-limit=@var{n}} option sets some of these parameters
3782 @item max-inline-insns-single
3783 is set to @var{n}/2.
3784 @item max-inline-insns-auto
3785 is set to @var{n}/2.
3786 @item min-inline-insns
3787 is set to 130 or @var{n}/4, whichever is smaller.
3788 @item max-inline-insns-rtl
3792 See below for a documentation of the individual
3793 parameters controlling inlining.
3795 @emph{Note:} pseudo instruction represents, in this particular context, an
3796 abstract measurement of function's size. In no way, it represents a count
3797 of assembly instructions and as such its exact meaning might change from one
3798 release to an another.
3800 @item -fkeep-inline-functions
3801 @opindex fkeep-inline-functions
3802 Even if all calls to a given function are integrated, and the function
3803 is declared @code{static}, nevertheless output a separate run-time
3804 callable version of the function. This switch does not affect
3805 @code{extern inline} functions.
3807 @item -fkeep-static-consts
3808 @opindex fkeep-static-consts
3809 Emit variables declared @code{static const} when optimization isn't turned
3810 on, even if the variables aren't referenced.
3812 GCC enables this option by default. If you want to force the compiler to
3813 check if the variable was referenced, regardless of whether or not
3814 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3816 @item -fmerge-constants
3817 Attempt to merge identical constants (string constants and floating point
3818 constants) across compilation units.
3820 This option is the default for optimized compilation if the assembler and
3821 linker support it. Use @option{-fno-merge-constants} to inhibit this
3824 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3826 @item -fmerge-all-constants
3827 Attempt to merge identical constants and identical variables.
3829 This option implies @option{-fmerge-constants}. In addition to
3830 @option{-fmerge-constants} this considers e.g. even constant initialized
3831 arrays or initialized constant variables with integral or floating point
3832 types. Languages like C or C++ require each non-automatic variable to
3833 have distinct location, so using this option will result in non-conforming
3838 Use a graph coloring register allocator. Currently this option is meant
3839 only for testing. Users should not specify this option, since it is not
3840 yet ready for production use.
3842 @item -fno-branch-count-reg
3843 @opindex fno-branch-count-reg
3844 Do not use ``decrement and branch'' instructions on a count register,
3845 but instead generate a sequence of instructions that decrement a
3846 register, compare it against zero, then branch based upon the result.
3847 This option is only meaningful on architectures that support such
3848 instructions, which include x86, PowerPC, IA-64 and S/390.
3850 The default is @option{-fbranch-count-reg}, enabled when
3851 @option{-fstrength-reduce} is enabled.
3853 @item -fno-function-cse
3854 @opindex fno-function-cse
3855 Do not put function addresses in registers; make each instruction that
3856 calls a constant function contain the function's address explicitly.
3858 This option results in less efficient code, but some strange hacks
3859 that alter the assembler output may be confused by the optimizations
3860 performed when this option is not used.
3862 The default is @option{-ffunction-cse}
3864 @item -fno-zero-initialized-in-bss
3865 @opindex fno-zero-initialized-in-bss
3866 If the target supports a BSS section, GCC by default puts variables that
3867 are initialized to zero into BSS@. This can save space in the resulting
3870 This option turns off this behavior because some programs explicitly
3871 rely on variables going to the data section. E.g., so that the
3872 resulting executable can find the beginning of that section and/or make
3873 assumptions based on that.
3875 The default is @option{-fzero-initialized-in-bss}.
3877 @item -fstrength-reduce
3878 @opindex fstrength-reduce
3879 Perform the optimizations of loop strength reduction and
3880 elimination of iteration variables.
3882 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3884 @item -fthread-jumps
3885 @opindex fthread-jumps
3886 Perform optimizations where we check to see if a jump branches to a
3887 location where another comparison subsumed by the first is found. If
3888 so, the first branch is redirected to either the destination of the
3889 second branch or a point immediately following it, depending on whether
3890 the condition is known to be true or false.
3892 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3894 @item -fcse-follow-jumps
3895 @opindex fcse-follow-jumps
3896 In common subexpression elimination, scan through jump instructions
3897 when the target of the jump is not reached by any other path. For
3898 example, when CSE encounters an @code{if} statement with an
3899 @code{else} clause, CSE will follow the jump when the condition
3902 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3904 @item -fcse-skip-blocks
3905 @opindex fcse-skip-blocks
3906 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3907 follow jumps which conditionally skip over blocks. When CSE
3908 encounters a simple @code{if} statement with no else clause,
3909 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3910 body of the @code{if}.
3912 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3914 @item -frerun-cse-after-loop
3915 @opindex frerun-cse-after-loop
3916 Re-run common subexpression elimination after loop optimizations has been
3919 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3921 @item -frerun-loop-opt
3922 @opindex frerun-loop-opt
3923 Run the loop optimizer twice.
3925 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3929 Perform a global common subexpression elimination pass.
3930 This pass also performs global constant and copy propagation.
3932 @emph{Note:} When compiling a program using computed gotos, a GCC
3933 extension, you may get better runtime performance if you disable
3934 the global common subexpression elimination pass by adding
3935 @option{-fno-gcse} to the command line.
3937 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3941 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3942 attempt to move loads which are only killed by stores into themselves. This
3943 allows a loop containing a load/store sequence to be changed to a load outside
3944 the loop, and a copy/store within the loop.
3946 Enabled by default when gcse is enabled.
3950 When @option{-fgcse-sm} is enabled, a store motion pass is run after
3951 global common subexpression elimination. This pass will attempt to move
3952 stores out of loops. When used in conjunction with @option{-fgcse-lm},
3953 loops containing a load/store sequence can be changed to a load before
3954 the loop and a store after the loop.
3956 Enabled by default when gcse is enabled.
3960 When @option{-fgcse-las} is enabled, the global common subexpression
3961 elimination pass eliminates redundant loads that come after stores to the
3962 same memory location (both partial and full redundancies).
3964 Enabled by default when gcse is enabled.
3966 @item -floop-optimize
3967 @opindex floop-optimize
3968 Perform loop optimizations: move constant expressions out of loops, simplify
3969 exit test conditions and optionally do strength-reduction and loop unrolling as
3972 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3974 @item -fcrossjumping
3975 @opindex crossjumping
3976 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
3977 resulting code may or may not perform better than without cross-jumping.
3979 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3981 @item -fif-conversion
3982 @opindex if-conversion
3983 Attempt to transform conditional jumps into branch-less equivalents. This
3984 include use of conditional moves, min, max, set flags and abs instructions, and
3985 some tricks doable by standard arithmetics. The use of conditional execution
3986 on chips where it is available is controlled by @code{if-conversion2}.
3988 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3990 @item -fif-conversion2
3991 @opindex if-conversion2
3992 Use conditional execution (where available) to transform conditional jumps into
3993 branch-less equivalents.
3995 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3997 @item -fdelete-null-pointer-checks
3998 @opindex fdelete-null-pointer-checks
3999 Use global dataflow analysis to identify and eliminate useless checks
4000 for null pointers. The compiler assumes that dereferencing a null
4001 pointer would have halted the program. If a pointer is checked after
4002 it has already been dereferenced, it cannot be null.
4004 In some environments, this assumption is not true, and programs can
4005 safely dereference null pointers. Use
4006 @option{-fno-delete-null-pointer-checks} to disable this optimization
4007 for programs which depend on that behavior.
4009 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4011 @item -fexpensive-optimizations
4012 @opindex fexpensive-optimizations
4013 Perform a number of minor optimizations that are relatively expensive.
4015 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4017 @item -foptimize-register-move
4019 @opindex foptimize-register-move
4021 Attempt to reassign register numbers in move instructions and as
4022 operands of other simple instructions in order to maximize the amount of
4023 register tying. This is especially helpful on machines with two-operand
4026 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4029 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4031 @item -fdelayed-branch
4032 @opindex fdelayed-branch
4033 If supported for the target machine, attempt to reorder instructions
4034 to exploit instruction slots available after delayed branch
4037 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4039 @item -fschedule-insns
4040 @opindex fschedule-insns
4041 If supported for the target machine, attempt to reorder instructions to
4042 eliminate execution stalls due to required data being unavailable. This
4043 helps machines that have slow floating point or memory load instructions
4044 by allowing other instructions to be issued until the result of the load
4045 or floating point instruction is required.
4047 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4049 @item -fschedule-insns2
4050 @opindex fschedule-insns2
4051 Similar to @option{-fschedule-insns}, but requests an additional pass of
4052 instruction scheduling after register allocation has been done. This is
4053 especially useful on machines with a relatively small number of
4054 registers and where memory load instructions take more than one cycle.
4056 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4058 @item -fno-sched-interblock
4059 @opindex fno-sched-interblock
4060 Don't schedule instructions across basic blocks. This is normally
4061 enabled by default when scheduling before register allocation, i.e.@:
4062 with @option{-fschedule-insns} or at @option{-O2} or higher.
4064 @item -fno-sched-spec
4065 @opindex fno-sched-spec
4066 Don't allow speculative motion of non-load instructions. This is normally
4067 enabled by default when scheduling before register allocation, i.e.@:
4068 with @option{-fschedule-insns} or at @option{-O2} or higher.
4070 @item -fsched-spec-load
4071 @opindex fsched-spec-load
4072 Allow speculative motion of some load instructions. This only makes
4073 sense when scheduling before register allocation, i.e.@: with
4074 @option{-fschedule-insns} or at @option{-O2} or higher.
4076 @item -fsched-spec-load-dangerous
4077 @opindex fsched-spec-load-dangerous
4078 Allow speculative motion of more load instructions. This only makes
4079 sense when scheduling before register allocation, i.e.@: with
4080 @option{-fschedule-insns} or at @option{-O2} or higher.
4082 @item -fsched-stalled-insns=@var{n}
4083 @opindex fsched-stalled-insns
4084 Define how many insns (if any) can be moved prematurely from the queue
4085 of stalled insns into the ready list, during the second scheduling pass.
4087 @item -fsched-stalled-insns-dep=@var{n}
4088 @opindex fsched-stalled-insns-dep
4089 Define how many insn groups (cycles) will be examined for a dependency
4090 on a stalled insn that is candidate for premature removal from the queue
4091 of stalled insns. Has an effect only during the second scheduling pass,
4092 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4094 @item -fsched2-use-superblocks
4095 @opindex fsched2-use-superblocks
4096 When scheduling after register allocation, do use superblock scheduling
4097 algorithm. Superblock scheduling allows motion across basic block boundaries
4098 resulting on faster schedules. This option is experimental, as not all machine
4099 descriptions used by GCC model the CPU closely enough to avoid unreliable
4100 results from the algorithm.
4102 This only makes sense when scheduling after register allocation, i.e.@: with
4103 @option{-fschedule-insns2} or at @option{-O2} or higher.
4105 @item -fsched2-use-traces
4106 @opindex fsched2-use-traces
4107 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4108 allocation and additionally perform code duplication in order to increase the
4109 size of superblocks using tracer pass. See @option{-ftracer} for details on
4112 This mode should produce faster but significantly longer programs. Also
4113 without @code{-fbranch-probabilities} the traces constructed may not match the
4114 reality and hurt the performance. This only makes
4115 sense when scheduling after register allocation, i.e.@: with
4116 @option{-fschedule-insns2} or at @option{-O2} or higher.
4118 @item -fcaller-saves
4119 @opindex fcaller-saves
4120 Enable values to be allocated in registers that will be clobbered by
4121 function calls, by emitting extra instructions to save and restore the
4122 registers around such calls. Such allocation is done only when it
4123 seems to result in better code than would otherwise be produced.
4125 This option is always enabled by default on certain machines, usually
4126 those which have no call-preserved registers to use instead.
4128 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4130 @item -fmove-all-movables
4131 @opindex fmove-all-movables
4132 Forces all invariant computations in loops to be moved
4135 @item -freduce-all-givs
4136 @opindex freduce-all-givs
4137 Forces all general-induction variables in loops to be
4140 @emph{Note:} When compiling programs written in Fortran,
4141 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
4142 by default when you use the optimizer.
4144 These options may generate better or worse code; results are highly
4145 dependent on the structure of loops within the source code.
4147 These two options are intended to be removed someday, once
4148 they have helped determine the efficacy of various
4149 approaches to improving loop optimizations.
4151 Please contact @w{@email{gcc@@gcc.gnu.org}}, and describe how use of
4152 these options affects the performance of your production code.
4153 Examples of code that runs @emph{slower} when these options are
4154 @emph{enabled} are very valuable.
4157 @itemx -fno-peephole2
4158 @opindex fno-peephole
4159 @opindex fno-peephole2
4160 Disable any machine-specific peephole optimizations. The difference
4161 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4162 are implemented in the compiler; some targets use one, some use the
4163 other, a few use both.
4165 @option{-fpeephole} is enabled by default.
4166 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4168 @item -fno-guess-branch-probability
4169 @opindex fno-guess-branch-probability
4170 Do not guess branch probabilities using a randomized model.
4172 Sometimes GCC will opt to use a randomized model to guess branch
4173 probabilities, when none are available from either profiling feedback
4174 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4175 different runs of the compiler on the same program may produce different
4178 In a hard real-time system, people don't want different runs of the
4179 compiler to produce code that has different behavior; minimizing
4180 non-determinism is of paramount import. This switch allows users to
4181 reduce non-determinism, possibly at the expense of inferior
4184 The default is @option{-fguess-branch-probability} at levels
4185 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4187 @item -freorder-blocks
4188 @opindex freorder-blocks
4189 Reorder basic blocks in the compiled function in order to reduce number of
4190 taken branches and improve code locality.
4192 Enabled at levels @option{-O2}, @option{-O3}.
4194 @item -freorder-functions
4195 @opindex freorder-functions
4196 Reorder basic blocks in the compiled function in order to reduce number of
4197 taken branches and improve code locality. This is implemented by using special
4198 subsections @code{.text.hot} for most frequently executed functions and
4199 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
4200 the linker so object file format must support named sections and linker must
4201 place them in a reasonable way.
4203 Also profile feedback must be available in to make this option effective. See
4204 @option{-fprofile-arcs} for details.
4206 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4208 @item -fstrict-aliasing
4209 @opindex fstrict-aliasing
4210 Allows the compiler to assume the strictest aliasing rules applicable to
4211 the language being compiled. For C (and C++), this activates
4212 optimizations based on the type of expressions. In particular, an
4213 object of one type is assumed never to reside at the same address as an
4214 object of a different type, unless the types are almost the same. For
4215 example, an @code{unsigned int} can alias an @code{int}, but not a
4216 @code{void*} or a @code{double}. A character type may alias any other
4219 Pay special attention to code like this:
4232 The practice of reading from a different union member than the one most
4233 recently written to (called ``type-punning'') is common. Even with
4234 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4235 is accessed through the union type. So, the code above will work as
4236 expected. However, this code might not:
4247 Every language that wishes to perform language-specific alias analysis
4248 should define a function that computes, given an @code{tree}
4249 node, an alias set for the node. Nodes in different alias sets are not
4250 allowed to alias. For an example, see the C front-end function
4251 @code{c_get_alias_set}.
4253 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4255 @item -falign-functions
4256 @itemx -falign-functions=@var{n}
4257 @opindex falign-functions
4258 Align the start of functions to the next power-of-two greater than
4259 @var{n}, skipping up to @var{n} bytes. For instance,
4260 @option{-falign-functions=32} aligns functions to the next 32-byte
4261 boundary, but @option{-falign-functions=24} would align to the next
4262 32-byte boundary only if this can be done by skipping 23 bytes or less.
4264 @option{-fno-align-functions} and @option{-falign-functions=1} are
4265 equivalent and mean that functions will not be aligned.
4267 Some assemblers only support this flag when @var{n} is a power of two;
4268 in that case, it is rounded up.
4270 If @var{n} is not specified or is zero, use a machine-dependent default.
4272 Enabled at levels @option{-O2}, @option{-O3}.
4274 @item -falign-labels
4275 @itemx -falign-labels=@var{n}
4276 @opindex falign-labels
4277 Align all branch targets to a power-of-two boundary, skipping up to
4278 @var{n} bytes like @option{-falign-functions}. This option can easily
4279 make code slower, because it must insert dummy operations for when the
4280 branch target is reached in the usual flow of the code.
4282 @option{-fno-align-labels} and @option{-falign-labels=1} are
4283 equivalent and mean that labels will not be aligned.
4285 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4286 are greater than this value, then their values are used instead.
4288 If @var{n} is not specified or is zero, use a machine-dependent default
4289 which is very likely to be @samp{1}, meaning no alignment.
4291 Enabled at levels @option{-O2}, @option{-O3}.
4294 @itemx -falign-loops=@var{n}
4295 @opindex falign-loops
4296 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4297 like @option{-falign-functions}. The hope is that the loop will be
4298 executed many times, which will make up for any execution of the dummy
4301 @option{-fno-align-loops} and @option{-falign-loops=1} are
4302 equivalent and mean that loops will not be aligned.
4304 If @var{n} is not specified or is zero, use a machine-dependent default.
4306 Enabled at levels @option{-O2}, @option{-O3}.
4309 @itemx -falign-jumps=@var{n}
4310 @opindex falign-jumps
4311 Align branch targets to a power-of-two boundary, for branch targets
4312 where the targets can only be reached by jumping, skipping up to @var{n}
4313 bytes like @option{-falign-functions}. In this case, no dummy operations
4316 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4317 equivalent and mean that loops will not be aligned.
4319 If @var{n} is not specified or is zero, use a machine-dependent default.
4321 Enabled at levels @option{-O2}, @option{-O3}.
4323 @item -frename-registers
4324 @opindex frename-registers
4325 Attempt to avoid false dependencies in scheduled code by making use
4326 of registers left over after register allocation. This optimization
4327 will most benefit processors with lots of registers. It can, however,
4328 make debugging impossible, since variables will no longer stay in
4329 a ``home register''.
4333 Constructs webs as commonly used for register allocation purposes and assign
4334 each web individual pseudo register. This allows the register allocation pass
4335 to operate on pseudos directly, but also strengthens several other optimization
4336 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
4337 however, make debugging impossible, since variables will no longer stay in a
4340 Enabled at levels @option{-O3}.
4342 @item -fno-cprop-registers
4343 @opindex fno-cprop-registers
4344 After register allocation and post-register allocation instruction splitting,
4345 we perform a copy-propagation pass to try to reduce scheduling dependencies
4346 and occasionally eliminate the copy.
4348 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4350 @item -fprofile-generate
4351 @opindex fprofile-generate
4353 Enable options usually used for instrumenting application to produce
4354 profile useful for later recompilation with profile feedback based
4355 optimization. You must use @code{-fprofile-generate} both when
4356 compiling and when linking your program.
4358 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
4361 @opindex fprofile-use
4362 Enable profile feedback directed optimizations, and optimizations
4363 generally profitable only with profile feedback available.
4365 The following options are enabled: @code{-fbranch-probabilities},
4366 @code{-fvpt}, @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}.
4370 The following options control compiler behavior regarding floating
4371 point arithmetic. These options trade off between speed and
4372 correctness. All must be specifically enabled.
4376 @opindex ffloat-store
4377 Do not store floating point variables in registers, and inhibit other
4378 options that might change whether a floating point value is taken from a
4381 @cindex floating point precision
4382 This option prevents undesirable excess precision on machines such as
4383 the 68000 where the floating registers (of the 68881) keep more
4384 precision than a @code{double} is supposed to have. Similarly for the
4385 x86 architecture. For most programs, the excess precision does only
4386 good, but a few programs rely on the precise definition of IEEE floating
4387 point. Use @option{-ffloat-store} for such programs, after modifying
4388 them to store all pertinent intermediate computations into variables.
4392 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
4393 @option{-fno-trapping-math}, @option{-ffinite-math-only},
4394 @option{-fno-rounding-math} and @option{-fno-signaling-nans}.
4396 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
4398 This option should never be turned on by any @option{-O} option since
4399 it can result in incorrect output for programs which depend on
4400 an exact implementation of IEEE or ISO rules/specifications for
4403 @item -fno-math-errno
4404 @opindex fno-math-errno
4405 Do not set ERRNO after calling math functions that are executed
4406 with a single instruction, e.g., sqrt. A program that relies on
4407 IEEE exceptions for math error handling may want to use this flag
4408 for speed while maintaining IEEE arithmetic compatibility.
4410 This option should never be turned on by any @option{-O} option since
4411 it can result in incorrect output for programs which depend on
4412 an exact implementation of IEEE or ISO rules/specifications for
4415 The default is @option{-fmath-errno}.
4417 @item -funsafe-math-optimizations
4418 @opindex funsafe-math-optimizations
4419 Allow optimizations for floating-point arithmetic that (a) assume
4420 that arguments and results are valid and (b) may violate IEEE or
4421 ANSI standards. When used at link-time, it may include libraries
4422 or startup files that change the default FPU control word or other
4423 similar optimizations.
4425 This option should never be turned on by any @option{-O} option since
4426 it can result in incorrect output for programs which depend on
4427 an exact implementation of IEEE or ISO rules/specifications for
4430 The default is @option{-fno-unsafe-math-optimizations}.
4432 @item -ffinite-math-only
4433 @opindex ffinite-math-only
4434 Allow optimizations for floating-point arithmetic that assume
4435 that arguments and results are not NaNs or +-Infs.
4437 This option should never be turned on by any @option{-O} option since
4438 it can result in incorrect output for programs which depend on
4439 an exact implementation of IEEE or ISO rules/specifications.
4441 The default is @option{-fno-finite-math-only}.
4443 @item -fno-trapping-math
4444 @opindex fno-trapping-math
4445 Compile code assuming that floating-point operations cannot generate
4446 user-visible traps. These traps include division by zero, overflow,
4447 underflow, inexact result and invalid operation. This option implies
4448 @option{-fno-signaling-nans}. Setting this option may allow faster
4449 code if one relies on ``non-stop'' IEEE arithmetic, for example.
4451 This option should never be turned on by any @option{-O} option since
4452 it can result in incorrect output for programs which depend on
4453 an exact implementation of IEEE or ISO rules/specifications for
4456 The default is @option{-ftrapping-math}.
4458 @item -frounding-math
4459 @opindex frounding-math
4460 Disable transformations and optimizations that assume default floating
4461 point rounding behavior. This is round-to-zero for all floating point
4462 to integer conversions, and round-to-nearest for all other arithmetic
4463 truncations. This option should be specified for programs that change
4464 the FP rounding mode dynamically, or that may be executed with a
4465 non-default rounding mode. This option disables constant folding of
4466 floating point expressions at compile-time (which may be affected by
4467 rounding mode) and arithmetic transformations that are unsafe in the
4468 presence of sign-dependent rounding modes.
4470 The default is @option{-fno-rounding-math}.
4472 This option is experimental and does not currently guarantee to
4473 disable all GCC optimizations that are affected by rounding mode.
4474 Future versions of GCC may provide finer control of this setting
4475 using C99's @code{FENV_ACCESS} pragma. This command line option
4476 will be used to specify the default state for @code{FENV_ACCESS}.
4478 @item -fsignaling-nans
4479 @opindex fsignaling-nans
4480 Compile code assuming that IEEE signaling NaNs may generate user-visible
4481 traps during floating-point operations. Setting this option disables
4482 optimizations that may change the number of exceptions visible with
4483 signaling NaNs. This option implies @option{-ftrapping-math}.
4485 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
4488 The default is @option{-fno-signaling-nans}.
4490 This option is experimental and does not currently guarantee to
4491 disable all GCC optimizations that affect signaling NaN behavior.
4493 @item -fsingle-precision-constant
4494 @opindex fsingle-precision-constant
4495 Treat floating point constant as single precision constant instead of
4496 implicitly converting it to double precision constant.
4501 The following options control optimizations that may improve
4502 performance, but are not enabled by any @option{-O} options. This
4503 section includes experimental options that may produce broken code.
4506 @item -fbranch-probabilities
4507 @opindex fbranch-probabilities
4508 After running a program compiled with @option{-fprofile-arcs}
4509 (@pxref{Debugging Options,, Options for Debugging Your Program or
4510 @command{gcc}}), you can compile it a second time using
4511 @option{-fbranch-probabilities}, to improve optimizations based on
4512 the number of times each branch was taken. When the program
4513 compiled with @option{-fprofile-arcs} exits it saves arc execution
4514 counts to a file called @file{@var{sourcename}.gcda} for each source
4515 file The information in this data file is very dependent on the
4516 structure of the generated code, so you must use the same source code
4517 and the same optimization options for both compilations.
4519 With @option{-fbranch-probabilities}, GCC puts a
4520 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
4521 These can be used to improve optimization. Currently, they are only
4522 used in one place: in @file{reorg.c}, instead of guessing which path a
4523 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
4524 exactly determine which path is taken more often.
4526 @item -fprofile-values
4527 @opindex fprofile-values
4528 If combined with @option{-fprofile-arcs}, it adds code so that some
4529 data about values of expressions in the program is gathered.
4531 With @option{-fbranch-probabilities}, it reads back the data gathered
4532 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
4533 notes to instructions for their later usage in optimizations.
4537 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
4538 a code to gather information about values of expressions.
4540 With @option{-fbranch-probabilities}, it reads back the data gathered
4541 and actually performs the optimizations based on them.
4542 Currently the optimizations include specialization of division operation
4543 using the knowledge about the value of the denominator.
4547 Use a graph coloring register allocator. Currently this option is meant
4548 for testing, so we are interested to hear about miscompilations with
4553 Perform tail duplication to enlarge superblock size. This transformation
4554 simplifies the control flow of the function allowing other optimizations to do
4557 @item -funit-at-a-time
4558 @opindex funit-at-a-time
4559 Parse the whole compilation unit before starting to produce code.
4560 This allows some extra optimizations to take place but consumes more
4563 @item -funroll-loops
4564 @opindex funroll-loops
4565 Unroll loops whose number of iterations can be determined at compile time or
4566 upon entry to the loop. @option{-funroll-loops} implies
4567 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
4568 (i.e. complete removal of loops with small constant number of iterations).
4569 This option makes code larger, and may or may not make it run faster.
4571 @item -funroll-all-loops
4572 @opindex funroll-all-loops
4573 Unroll all loops, even if their number of iterations is uncertain when
4574 the loop is entered. This usually makes programs run more slowly.
4575 @option{-funroll-all-loops} implies the same options as
4576 @option{-funroll-loops}.
4579 @opindex fpeel-loops
4580 Peels the loops for that there is enough information that they do not
4581 roll much (from profile feedback). It also turns on complete loop peeling
4582 (i.e. complete removal of loops with small constant number of iterations).
4584 @item -funswitch-loops
4585 @opindex funswitch-loops
4586 Move branches with loop invariant conditions out of the loop, with duplicates
4587 of the loop on both branches (modified according to result of the condition).
4589 @item -fold-unroll-loops
4590 @opindex fold-unroll-loops
4591 Unroll loops whose number of iterations can be determined at compile
4592 time or upon entry to the loop, using the old loop unroller whose loop
4593 recognition is based on notes from frontend. @option{-fold-unroll-loops} implies
4594 both @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4595 option makes code larger, and may or may not make it run faster.
4597 @item -fold-unroll-all-loops
4598 @opindex fold-unroll-all-loops
4599 Unroll all loops, even if their number of iterations is uncertain when
4600 the loop is entered. This is done using the old loop unroller whose loop
4601 recognition is based on notes from frontend. This usually makes programs run more slowly.
4602 @option{-fold-unroll-all-loops} implies the same options as
4603 @option{-fold-unroll-loops}.
4605 @item -funswitch-loops
4606 @opindex funswitch-loops
4607 Move branches with loop invariant conditions out of the loop, with duplicates
4608 of the loop on both branches (modified according to result of the condition).
4610 @item -funswitch-loops
4611 @opindex funswitch-loops
4612 Move branches with loop invariant conditions out of the loop, with duplicates
4613 of the loop on both branches (modified according to result of the condition).
4615 @item -fprefetch-loop-arrays
4616 @opindex fprefetch-loop-arrays
4617 If supported by the target machine, generate instructions to prefetch
4618 memory to improve the performance of loops that access large arrays.
4620 Disabled at level @option{-Os}.
4622 @item -ffunction-sections
4623 @itemx -fdata-sections
4624 @opindex ffunction-sections
4625 @opindex fdata-sections
4626 Place each function or data item into its own section in the output
4627 file if the target supports arbitrary sections. The name of the
4628 function or the name of the data item determines the section's name
4631 Use these options on systems where the linker can perform optimizations
4632 to improve locality of reference in the instruction space. Most systems
4633 using the ELF object format and SPARC processors running Solaris 2 have
4634 linkers with such optimizations. AIX may have these optimizations in
4637 Only use these options when there are significant benefits from doing
4638 so. When you specify these options, the assembler and linker will
4639 create larger object and executable files and will also be slower.
4640 You will not be able to use @code{gprof} on all systems if you
4641 specify this option and you may have problems with debugging if
4642 you specify both this option and @option{-g}.
4644 @item -fbranch-target-load-optimize
4645 @opindex fbranch-target-load-optimize
4646 Perform branch target register load optimization before prologue / epilogue
4648 The use of target registers can typically be exposed only during reload,
4649 thus hoisting loads out of loops and doing inter-block scheduling needs
4650 a separate optimization pass.
4652 @item -fbranch-target-load-optimize2
4653 @opindex fbranch-target-load-optimize2
4654 Perform branch target register load optimization after prologue / epilogue
4657 @item --param @var{name}=@var{value}
4659 In some places, GCC uses various constants to control the amount of
4660 optimization that is done. For example, GCC will not inline functions
4661 that contain more that a certain number of instructions. You can
4662 control some of these constants on the command-line using the
4663 @option{--param} option.
4665 The names of specific parameters, and the meaning of the values, are
4666 tied to the internals of the compiler, and are subject to change
4667 without notice in future releases.
4669 In each case, the @var{value} is an integer. The allowable choices for
4670 @var{name} are given in the following table:
4673 @item max-crossjump-edges
4674 The maximum number of incoming edges to consider for crossjumping.
4675 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
4676 the number of edges incoming to each block. Increasing values mean
4677 more aggressive optimization, making the compile time increase with
4678 probably small improvement in executable size.
4680 @item max-delay-slot-insn-search
4681 The maximum number of instructions to consider when looking for an
4682 instruction to fill a delay slot. If more than this arbitrary number of
4683 instructions is searched, the time savings from filling the delay slot
4684 will be minimal so stop searching. Increasing values mean more
4685 aggressive optimization, making the compile time increase with probably
4686 small improvement in executable run time.
4688 @item max-delay-slot-live-search
4689 When trying to fill delay slots, the maximum number of instructions to
4690 consider when searching for a block with valid live register
4691 information. Increasing this arbitrarily chosen value means more
4692 aggressive optimization, increasing the compile time. This parameter
4693 should be removed when the delay slot code is rewritten to maintain the
4696 @item max-gcse-memory
4697 The approximate maximum amount of memory that will be allocated in
4698 order to perform the global common subexpression elimination
4699 optimization. If more memory than specified is required, the
4700 optimization will not be done.
4702 @item max-gcse-passes
4703 The maximum number of passes of GCSE to run.
4705 @item max-pending-list-length
4706 The maximum number of pending dependencies scheduling will allow
4707 before flushing the current state and starting over. Large functions
4708 with few branches or calls can create excessively large lists which
4709 needlessly consume memory and resources.
4711 @item max-inline-insns-single
4712 Several parameters control the tree inliner used in gcc.
4713 This number sets the maximum number of instructions (counted in GCC's
4714 internal representation) in a single function that the tree inliner
4715 will consider for inlining. This only affects functions declared
4716 inline and methods implemented in a class declaration (C++).
4717 The default value is 500.
4719 @item max-inline-insns-auto
4720 When you use @option{-finline-functions} (included in @option{-O3}),
4721 a lot of functions that would otherwise not be considered for inlining
4722 by the compiler will be investigated. To those functions, a different
4723 (more restrictive) limit compared to functions declared inline can
4725 The default value is 100.
4727 @item large-function-insns
4728 The limit specifying really large functions. For functions greater than this
4729 limit inlining is constrained by @option{--param large-function-growth}.
4730 This parameter is useful primarily to avoid extreme compilation time caused by non-linear
4731 algorithms used by the backend.
4732 This parameter is ignored when @option{-funit-at-a-time} is not used.
4733 The default value is 3000.
4735 @item large-function-growth
4736 Specifies maximal growth of large function caused by inlining in percents.
4737 This parameter is ignored when @option{-funit-at-a-time} is not used.
4738 The default value is 200.
4740 @item inline-unit-growth
4741 Specifies maximal overall growth of the compilation unit caused by inlining.
4742 This parameter is ignored when @option{-funit-at-a-time} is not used.
4743 The default value is 150.
4745 @item max-inline-insns-rtl
4746 For languages that use the RTL inliner (this happens at a later stage
4747 than tree inlining), you can set the maximum allowable size (counted
4748 in RTL instructions) for the RTL inliner with this parameter.
4749 The default value is 600.
4751 @item max-unrolled-insns
4752 The maximum number of instructions that a loop should have if that loop
4753 is unrolled, and if the loop is unrolled, it determines how many times
4754 the loop code is unrolled.
4756 @item max-average-unrolled-insns
4757 The maximum number of instructions biased by probabilities of their execution
4758 that a loop should have if that loop is unrolled, and if the loop is unrolled,
4759 it determines how many times the loop code is unrolled.
4761 @item max-unroll-times
4762 The maximum number of unrollings of a single loop.
4764 @item max-peeled-insns
4765 The maximum number of instructions that a loop should have if that loop
4766 is peeled, and if the loop is peeled, it determines how many times
4767 the loop code is peeled.
4769 @item max-peel-times
4770 The maximum number of peelings of a single loop.
4772 @item max-completely-peeled-insns
4773 The maximum number of insns of a completely peeled loop.
4775 @item max-completely-peel-times
4776 The maximum number of iterations of a loop to be suitable for complete peeling.
4778 @item max-unswitch-insns
4779 The maximum number of insns of an unswitched loop.
4781 @item max-unswitch-level
4782 The maximum number of branches unswitched in a single loop.
4784 @item hot-bb-count-fraction
4785 Select fraction of the maximal count of repetitions of basic block in program
4786 given basic block needs to have to be considered hot.
4788 @item hot-bb-frequency-fraction
4789 Select fraction of the maximal frequency of executions of basic block in
4790 function given basic block needs to have to be considered hot
4792 @item tracer-dynamic-coverage
4793 @itemx tracer-dynamic-coverage-feedback
4795 This value is used to limit superblock formation once the given percentage of
4796 executed instructions is covered. This limits unnecessary code size
4799 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4800 feedback is available. The real profiles (as opposed to statically estimated
4801 ones) are much less balanced allowing the threshold to be larger value.
4803 @item tracer-max-code-growth
4804 Stop tail duplication once code growth has reached given percentage. This is
4805 rather hokey argument, as most of the duplicates will be eliminated later in
4806 cross jumping, so it may be set to much higher values than is the desired code
4809 @item tracer-min-branch-ratio
4811 Stop reverse growth when the reverse probability of best edge is less than this
4812 threshold (in percent).
4814 @item tracer-min-branch-ratio
4815 @itemx tracer-min-branch-ratio-feedback
4817 Stop forward growth if the best edge do have probability lower than this
4820 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
4821 compilation for profile feedback and one for compilation without. The value
4822 for compilation with profile feedback needs to be more conservative (higher) in
4823 order to make tracer effective.
4825 @item max-cse-path-length
4827 Maximum number of basic blocks on path that cse considers.
4829 @item max-last-value-rtl
4831 The maximum size measured as number of RTLs that can be recorded in an
4832 expression in combiner for a pseudo register as last known value of that
4833 register. The default is 10000.
4835 @item ggc-min-expand
4837 GCC uses a garbage collector to manage its own memory allocation. This
4838 parameter specifies the minimum percentage by which the garbage
4839 collector's heap should be allowed to expand between collections.
4840 Tuning this may improve compilation speed; it has no effect on code
4843 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
4844 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
4845 the smallest of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If
4846 GCC is not able to calculate RAM on a particular platform, the lower
4847 bound of 30% is used. Setting this parameter and
4848 @option{ggc-min-heapsize} to zero causes a full collection to occur at
4849 every opportunity. This is extremely slow, but can be useful for
4852 @item ggc-min-heapsize
4854 Minimum size of the garbage collector's heap before it begins bothering
4855 to collect garbage. The first collection occurs after the heap expands
4856 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
4857 tuning this may improve compilation speed, and has no effect on code
4860 The default is RAM/8, with a lower bound of 4096 (four megabytes) and an
4861 upper bound of 131072 (128 megabytes). If @code{getrlimit} is
4862 available, the notion of "RAM" is the smallest of actual RAM,
4863 RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If GCC is not able to calculate
4864 RAM on a particular platform, the lower bound is used. Setting this
4865 parameter very large effectively disables garbage collection. Setting
4866 this parameter and @option{ggc-min-expand} to zero causes a full
4867 collection to occur at every opportunity.
4869 @item max-reload-search-insns
4870 The maximum number of instruction reload should look backward for equivalent
4871 register. Increasing values mean more aggressive optimization, making the
4872 compile time increase with probably slightly better performance. The default
4875 @item max-cselib-memory-location
4876 The maximum number of memory locations cselib should take into acount.
4877 Increasing values mean more aggressive optimization, making the compile time
4878 increase with probably slightly better performance. The default value is 500.
4880 @item reorder-blocks-duplicate
4881 @itemx reorder-blocks-duplicate-feedback
4883 Used by basic block reordering pass to decide whether to use unconditional
4884 branch or duplicate the code on its destination. Code is duplicated when its
4885 estimated size is smaller than this value multiplied by the estimated size of
4886 unconditional jump in the hot spots of the program.
4888 The @option{reorder-block-duplicate-feedback} is used only when profile
4889 feedback is available and may be set to higher values than
4890 @option{reorder-block-duplicate} since information about the hot spots is more
4895 @node Preprocessor Options
4896 @section Options Controlling the Preprocessor
4897 @cindex preprocessor options
4898 @cindex options, preprocessor
4900 These options control the C preprocessor, which is run on each C source
4901 file before actual compilation.
4903 If you use the @option{-E} option, nothing is done except preprocessing.
4904 Some of these options make sense only together with @option{-E} because
4905 they cause the preprocessor output to be unsuitable for actual
4910 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4911 and pass @var{option} directly through to the preprocessor. If
4912 @var{option} contains commas, it is split into multiple options at the
4913 commas. However, many options are modified, translated or interpreted
4914 by the compiler driver before being passed to the preprocessor, and
4915 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4916 interface is undocumented and subject to change, so whenever possible
4917 you should avoid using @option{-Wp} and let the driver handle the
4920 @item -Xpreprocessor @var{option}
4921 @opindex preprocessor
4922 Pass @var{option} as an option to the preprocessor. You can use this to
4923 supply system-specific preprocessor options which GCC does not know how to
4926 If you want to pass an option that takes an argument, you must use
4927 @option{-Xpreprocessor} twice, once for the option and once for the argument.
4930 @include cppopts.texi
4932 @node Assembler Options
4933 @section Passing Options to the Assembler
4935 @c prevent bad page break with this line
4936 You can pass options to the assembler.
4939 @item -Wa,@var{option}
4941 Pass @var{option} as an option to the assembler. If @var{option}
4942 contains commas, it is split into multiple options at the commas.
4944 @item -Xassembler @var{option}
4946 Pass @var{option} as an option to the assembler. You can use this to
4947 supply system-specific assembler options which GCC does not know how to
4950 If you want to pass an option that takes an argument, you must use
4951 @option{-Xassembler} twice, once for the option and once for the argument.
4956 @section Options for Linking
4957 @cindex link options
4958 @cindex options, linking
4960 These options come into play when the compiler links object files into
4961 an executable output file. They are meaningless if the compiler is
4962 not doing a link step.
4966 @item @var{object-file-name}
4967 A file name that does not end in a special recognized suffix is
4968 considered to name an object file or library. (Object files are
4969 distinguished from libraries by the linker according to the file
4970 contents.) If linking is done, these object files are used as input
4979 If any of these options is used, then the linker is not run, and
4980 object file names should not be used as arguments. @xref{Overall
4984 @item -l@var{library}
4985 @itemx -l @var{library}
4987 Search the library named @var{library} when linking. (The second
4988 alternative with the library as a separate argument is only for
4989 POSIX compliance and is not recommended.)
4991 It makes a difference where in the command you write this option; the
4992 linker searches and processes libraries and object files in the order they
4993 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4994 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4995 to functions in @samp{z}, those functions may not be loaded.
4997 The linker searches a standard list of directories for the library,
4998 which is actually a file named @file{lib@var{library}.a}. The linker
4999 then uses this file as if it had been specified precisely by name.
5001 The directories searched include several standard system directories
5002 plus any that you specify with @option{-L}.
5004 Normally the files found this way are library files---archive files
5005 whose members are object files. The linker handles an archive file by
5006 scanning through it for members which define symbols that have so far
5007 been referenced but not defined. But if the file that is found is an
5008 ordinary object file, it is linked in the usual fashion. The only
5009 difference between using an @option{-l} option and specifying a file name
5010 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
5011 and searches several directories.
5015 You need this special case of the @option{-l} option in order to
5016 link an Objective-C program.
5019 @opindex nostartfiles
5020 Do not use the standard system startup files when linking.
5021 The standard system libraries are used normally, unless @option{-nostdlib}
5022 or @option{-nodefaultlibs} is used.
5024 @item -nodefaultlibs
5025 @opindex nodefaultlibs
5026 Do not use the standard system libraries when linking.
5027 Only the libraries you specify will be passed to the linker.
5028 The standard startup files are used normally, unless @option{-nostartfiles}
5029 is used. The compiler may generate calls to memcmp, memset, and memcpy
5030 for System V (and ISO C) environments or to bcopy and bzero for
5031 BSD environments. These entries are usually resolved by entries in
5032 libc. These entry points should be supplied through some other
5033 mechanism when this option is specified.
5037 Do not use the standard system startup files or libraries when linking.
5038 No startup files and only the libraries you specify will be passed to
5039 the linker. The compiler may generate calls to memcmp, memset, and memcpy
5040 for System V (and ISO C) environments or to bcopy and bzero for
5041 BSD environments. These entries are usually resolved by entries in
5042 libc. These entry points should be supplied through some other
5043 mechanism when this option is specified.
5045 @cindex @option{-lgcc}, use with @option{-nostdlib}
5046 @cindex @option{-nostdlib} and unresolved references
5047 @cindex unresolved references and @option{-nostdlib}
5048 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
5049 @cindex @option{-nodefaultlibs} and unresolved references
5050 @cindex unresolved references and @option{-nodefaultlibs}
5051 One of the standard libraries bypassed by @option{-nostdlib} and
5052 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
5053 that GCC uses to overcome shortcomings of particular machines, or special
5054 needs for some languages.
5055 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
5056 Collection (GCC) Internals},
5057 for more discussion of @file{libgcc.a}.)
5058 In most cases, you need @file{libgcc.a} even when you want to avoid
5059 other standard libraries. In other words, when you specify @option{-nostdlib}
5060 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
5061 This ensures that you have no unresolved references to internal GCC
5062 library subroutines. (For example, @samp{__main}, used to ensure C++
5063 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
5064 GNU Compiler Collection (GCC) Internals}.)
5068 Produce a position independent executable on targets which support it.
5069 For predictable results, you must also specify the same set of options
5070 that were used to generate code (@option{-fpie}, @option{-fPIE},
5071 or model suboptions) when you specify this option.
5075 Remove all symbol table and relocation information from the executable.
5079 On systems that support dynamic linking, this prevents linking with the shared
5080 libraries. On other systems, this option has no effect.
5084 Produce a shared object which can then be linked with other objects to
5085 form an executable. Not all systems support this option. For predictable
5086 results, you must also specify the same set of options that were used to
5087 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
5088 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
5089 needs to build supplementary stub code for constructors to work. On
5090 multi-libbed systems, @samp{gcc -shared} must select the correct support
5091 libraries to link against. Failing to supply the correct flags may lead
5092 to subtle defects. Supplying them in cases where they are not necessary
5095 @item -shared-libgcc
5096 @itemx -static-libgcc
5097 @opindex shared-libgcc
5098 @opindex static-libgcc
5099 On systems that provide @file{libgcc} as a shared library, these options
5100 force the use of either the shared or static version respectively.
5101 If no shared version of @file{libgcc} was built when the compiler was
5102 configured, these options have no effect.
5104 There are several situations in which an application should use the
5105 shared @file{libgcc} instead of the static version. The most common
5106 of these is when the application wishes to throw and catch exceptions
5107 across different shared libraries. In that case, each of the libraries
5108 as well as the application itself should use the shared @file{libgcc}.
5110 Therefore, the G++ and GCJ drivers automatically add
5111 @option{-shared-libgcc} whenever you build a shared library or a main
5112 executable, because C++ and Java programs typically use exceptions, so
5113 this is the right thing to do.
5115 If, instead, you use the GCC driver to create shared libraries, you may
5116 find that they will not always be linked with the shared @file{libgcc}.
5117 If GCC finds, at its configuration time, that you have a non-GNU linker
5118 or a GNU linker that does not support option @option{--eh-frame-hdr},
5119 it will link the shared version of @file{libgcc} into shared libraries
5120 by default. Otherwise, it will take advantage of the linker and optimize
5121 away the linking with the shared version of @file{libgcc}, linking with
5122 the static version of libgcc by default. This allows exceptions to
5123 propagate through such shared libraries, without incurring relocation
5124 costs at library load time.
5126 However, if a library or main executable is supposed to throw or catch
5127 exceptions, you must link it using the G++ or GCJ driver, as appropriate
5128 for the languages used in the program, or using the option
5129 @option{-shared-libgcc}, such that it is linked with the shared
5134 Bind references to global symbols when building a shared object. Warn
5135 about any unresolved references (unless overridden by the link editor
5136 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
5139 @item -Xlinker @var{option}
5141 Pass @var{option} as an option to the linker. You can use this to
5142 supply system-specific linker options which GCC does not know how to
5145 If you want to pass an option that takes an argument, you must use
5146 @option{-Xlinker} twice, once for the option and once for the argument.
5147 For example, to pass @option{-assert definitions}, you must write
5148 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
5149 @option{-Xlinker "-assert definitions"}, because this passes the entire
5150 string as a single argument, which is not what the linker expects.
5152 @item -Wl,@var{option}
5154 Pass @var{option} as an option to the linker. If @var{option} contains
5155 commas, it is split into multiple options at the commas.
5157 @item -u @var{symbol}
5159 Pretend the symbol @var{symbol} is undefined, to force linking of
5160 library modules to define it. You can use @option{-u} multiple times with
5161 different symbols to force loading of additional library modules.
5164 @node Directory Options
5165 @section Options for Directory Search
5166 @cindex directory options
5167 @cindex options, directory search
5170 These options specify directories to search for header files, for
5171 libraries and for parts of the compiler:
5176 Add the directory @var{dir} to the head of the list of directories to be
5177 searched for header files. This can be used to override a system header
5178 file, substituting your own version, since these directories are
5179 searched before the system header file directories. However, you should
5180 not use this option to add directories that contain vendor-supplied
5181 system header files (use @option{-isystem} for that). If you use more than
5182 one @option{-I} option, the directories are scanned in left-to-right
5183 order; the standard system directories come after.
5185 If a standard system include directory, or a directory specified with
5186 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5187 option will be ignored. The directory will still be searched but as a
5188 system directory at its normal position in the system include chain.
5189 This is to ensure that GCC's procedure to fix buggy system headers and
5190 the ordering for the include_next directive are not inadvertently changed.
5191 If you really need to change the search order for system directories,
5192 use the @option{-nostdinc} and/or @option{-isystem} options.
5196 Any directories you specify with @option{-I} options before the @option{-I-}
5197 option are searched only for the case of @samp{#include "@var{file}"};
5198 they are not searched for @samp{#include <@var{file}>}.
5200 If additional directories are specified with @option{-I} options after
5201 the @option{-I-}, these directories are searched for all @samp{#include}
5202 directives. (Ordinarily @emph{all} @option{-I} directories are used
5205 In addition, the @option{-I-} option inhibits the use of the current
5206 directory (where the current input file came from) as the first search
5207 directory for @samp{#include "@var{file}"}. There is no way to
5208 override this effect of @option{-I-}. With @option{-I.} you can specify
5209 searching the directory which was current when the compiler was
5210 invoked. That is not exactly the same as what the preprocessor does
5211 by default, but it is often satisfactory.
5213 @option{-I-} does not inhibit the use of the standard system directories
5214 for header files. Thus, @option{-I-} and @option{-nostdinc} are
5219 Add directory @var{dir} to the list of directories to be searched
5222 @item -B@var{prefix}
5224 This option specifies where to find the executables, libraries,
5225 include files, and data files of the compiler itself.
5227 The compiler driver program runs one or more of the subprograms
5228 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5229 @var{prefix} as a prefix for each program it tries to run, both with and
5230 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5232 For each subprogram to be run, the compiler driver first tries the
5233 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5234 was not specified, the driver tries two standard prefixes, which are
5235 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
5236 those results in a file name that is found, the unmodified program
5237 name is searched for using the directories specified in your
5238 @env{PATH} environment variable.
5240 The compiler will check to see if the path provided by the @option{-B}
5241 refers to a directory, and if necessary it will add a directory
5242 separator character at the end of the path.
5244 @option{-B} prefixes that effectively specify directory names also apply
5245 to libraries in the linker, because the compiler translates these
5246 options into @option{-L} options for the linker. They also apply to
5247 includes files in the preprocessor, because the compiler translates these
5248 options into @option{-isystem} options for the preprocessor. In this case,
5249 the compiler appends @samp{include} to the prefix.
5251 The run-time support file @file{libgcc.a} can also be searched for using
5252 the @option{-B} prefix, if needed. If it is not found there, the two
5253 standard prefixes above are tried, and that is all. The file is left
5254 out of the link if it is not found by those means.
5256 Another way to specify a prefix much like the @option{-B} prefix is to use
5257 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5260 As a special kludge, if the path provided by @option{-B} is
5261 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5262 9, then it will be replaced by @file{[dir/]include}. This is to help
5263 with boot-strapping the compiler.
5265 @item -specs=@var{file}
5267 Process @var{file} after the compiler reads in the standard @file{specs}
5268 file, in order to override the defaults that the @file{gcc} driver
5269 program uses when determining what switches to pass to @file{cc1},
5270 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5271 @option{-specs=@var{file}} can be specified on the command line, and they
5272 are processed in order, from left to right.
5278 @section Specifying subprocesses and the switches to pass to them
5281 @command{gcc} is a driver program. It performs its job by invoking a
5282 sequence of other programs to do the work of compiling, assembling and
5283 linking. GCC interprets its command-line parameters and uses these to
5284 deduce which programs it should invoke, and which command-line options
5285 it ought to place on their command lines. This behavior is controlled
5286 by @dfn{spec strings}. In most cases there is one spec string for each
5287 program that GCC can invoke, but a few programs have multiple spec
5288 strings to control their behavior. The spec strings built into GCC can
5289 be overridden by using the @option{-specs=} command-line switch to specify
5292 @dfn{Spec files} are plaintext files that are used to construct spec
5293 strings. They consist of a sequence of directives separated by blank
5294 lines. The type of directive is determined by the first non-whitespace
5295 character on the line and it can be one of the following:
5298 @item %@var{command}
5299 Issues a @var{command} to the spec file processor. The commands that can
5303 @item %include <@var{file}>
5305 Search for @var{file} and insert its text at the current point in the
5308 @item %include_noerr <@var{file}>
5309 @cindex %include_noerr
5310 Just like @samp{%include}, but do not generate an error message if the include
5311 file cannot be found.
5313 @item %rename @var{old_name} @var{new_name}
5315 Rename the spec string @var{old_name} to @var{new_name}.
5319 @item *[@var{spec_name}]:
5320 This tells the compiler to create, override or delete the named spec
5321 string. All lines after this directive up to the next directive or
5322 blank line are considered to be the text for the spec string. If this
5323 results in an empty string then the spec will be deleted. (Or, if the
5324 spec did not exist, then nothing will happened.) Otherwise, if the spec
5325 does not currently exist a new spec will be created. If the spec does
5326 exist then its contents will be overridden by the text of this
5327 directive, unless the first character of that text is the @samp{+}
5328 character, in which case the text will be appended to the spec.
5330 @item [@var{suffix}]:
5331 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
5332 and up to the next directive or blank line are considered to make up the
5333 spec string for the indicated suffix. When the compiler encounters an
5334 input file with the named suffix, it will processes the spec string in
5335 order to work out how to compile that file. For example:
5342 This says that any input file whose name ends in @samp{.ZZ} should be
5343 passed to the program @samp{z-compile}, which should be invoked with the
5344 command-line switch @option{-input} and with the result of performing the
5345 @samp{%i} substitution. (See below.)
5347 As an alternative to providing a spec string, the text that follows a
5348 suffix directive can be one of the following:
5351 @item @@@var{language}
5352 This says that the suffix is an alias for a known @var{language}. This is
5353 similar to using the @option{-x} command-line switch to GCC to specify a
5354 language explicitly. For example:
5361 Says that .ZZ files are, in fact, C++ source files.
5364 This causes an error messages saying:
5367 @var{name} compiler not installed on this system.
5371 GCC already has an extensive list of suffixes built into it.
5372 This directive will add an entry to the end of the list of suffixes, but
5373 since the list is searched from the end backwards, it is effectively
5374 possible to override earlier entries using this technique.
5378 GCC has the following spec strings built into it. Spec files can
5379 override these strings or create their own. Note that individual
5380 targets can also add their own spec strings to this list.
5383 asm Options to pass to the assembler
5384 asm_final Options to pass to the assembler post-processor
5385 cpp Options to pass to the C preprocessor
5386 cc1 Options to pass to the C compiler
5387 cc1plus Options to pass to the C++ compiler
5388 endfile Object files to include at the end of the link
5389 link Options to pass to the linker
5390 lib Libraries to include on the command line to the linker
5391 libgcc Decides which GCC support library to pass to the linker
5392 linker Sets the name of the linker
5393 predefines Defines to be passed to the C preprocessor
5394 signed_char Defines to pass to CPP to say whether @code{char} is signed
5396 startfile Object files to include at the start of the link
5399 Here is a small example of a spec file:
5405 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
5408 This example renames the spec called @samp{lib} to @samp{old_lib} and
5409 then overrides the previous definition of @samp{lib} with a new one.
5410 The new definition adds in some extra command-line options before
5411 including the text of the old definition.
5413 @dfn{Spec strings} are a list of command-line options to be passed to their
5414 corresponding program. In addition, the spec strings can contain
5415 @samp{%}-prefixed sequences to substitute variable text or to
5416 conditionally insert text into the command line. Using these constructs
5417 it is possible to generate quite complex command lines.
5419 Here is a table of all defined @samp{%}-sequences for spec
5420 strings. Note that spaces are not generated automatically around the
5421 results of expanding these sequences. Therefore you can concatenate them
5422 together or combine them with constant text in a single argument.
5426 Substitute one @samp{%} into the program name or argument.
5429 Substitute the name of the input file being processed.
5432 Substitute the basename of the input file being processed.
5433 This is the substring up to (and not including) the last period
5434 and not including the directory.
5437 This is the same as @samp{%b}, but include the file suffix (text after
5441 Marks the argument containing or following the @samp{%d} as a
5442 temporary file name, so that that file will be deleted if GCC exits
5443 successfully. Unlike @samp{%g}, this contributes no text to the
5446 @item %g@var{suffix}
5447 Substitute a file name that has suffix @var{suffix} and is chosen
5448 once per compilation, and mark the argument in the same way as
5449 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
5450 name is now chosen in a way that is hard to predict even when previously
5451 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
5452 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
5453 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
5454 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
5455 was simply substituted with a file name chosen once per compilation,
5456 without regard to any appended suffix (which was therefore treated
5457 just like ordinary text), making such attacks more likely to succeed.
5459 @item %u@var{suffix}
5460 Like @samp{%g}, but generates a new temporary file name even if
5461 @samp{%u@var{suffix}} was already seen.
5463 @item %U@var{suffix}
5464 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
5465 new one if there is no such last file name. In the absence of any
5466 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
5467 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
5468 would involve the generation of two distinct file names, one
5469 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
5470 simply substituted with a file name chosen for the previous @samp{%u},
5471 without regard to any appended suffix.
5473 @item %j@var{suffix}
5474 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
5475 writable, and if save-temps is off; otherwise, substitute the name
5476 of a temporary file, just like @samp{%u}. This temporary file is not
5477 meant for communication between processes, but rather as a junk
5480 @item %|@var{suffix}
5481 @itemx %m@var{suffix}
5482 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
5483 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
5484 all. These are the two most common ways to instruct a program that it
5485 should read from standard input or write to standard output. If you
5486 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
5487 construct: see for example @file{f/lang-specs.h}.
5489 @item %.@var{SUFFIX}
5490 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
5491 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
5492 terminated by the next space or %.
5495 Marks the argument containing or following the @samp{%w} as the
5496 designated output file of this compilation. This puts the argument
5497 into the sequence of arguments that @samp{%o} will substitute later.
5500 Substitutes the names of all the output files, with spaces
5501 automatically placed around them. You should write spaces
5502 around the @samp{%o} as well or the results are undefined.
5503 @samp{%o} is for use in the specs for running the linker.
5504 Input files whose names have no recognized suffix are not compiled
5505 at all, but they are included among the output files, so they will
5509 Substitutes the suffix for object files. Note that this is
5510 handled specially when it immediately follows @samp{%g, %u, or %U},
5511 because of the need for those to form complete file names. The
5512 handling is such that @samp{%O} is treated exactly as if it had already
5513 been substituted, except that @samp{%g, %u, and %U} do not currently
5514 support additional @var{suffix} characters following @samp{%O} as they would
5515 following, for example, @samp{.o}.
5518 Substitutes the standard macro predefinitions for the
5519 current target machine. Use this when running @code{cpp}.
5522 Like @samp{%p}, but puts @samp{__} before and after the name of each
5523 predefined macro, except for macros that start with @samp{__} or with
5524 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
5528 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
5529 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
5530 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
5534 Current argument is the name of a library or startup file of some sort.
5535 Search for that file in a standard list of directories and substitute
5536 the full name found.
5539 Print @var{str} as an error message. @var{str} is terminated by a newline.
5540 Use this when inconsistent options are detected.
5543 Substitute the contents of spec string @var{name} at this point.
5546 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
5548 @item %x@{@var{option}@}
5549 Accumulate an option for @samp{%X}.
5552 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
5556 Output the accumulated assembler options specified by @option{-Wa}.
5559 Output the accumulated preprocessor options specified by @option{-Wp}.
5562 Process the @code{asm} spec. This is used to compute the
5563 switches to be passed to the assembler.
5566 Process the @code{asm_final} spec. This is a spec string for
5567 passing switches to an assembler post-processor, if such a program is
5571 Process the @code{link} spec. This is the spec for computing the
5572 command line passed to the linker. Typically it will make use of the
5573 @samp{%L %G %S %D and %E} sequences.
5576 Dump out a @option{-L} option for each directory that GCC believes might
5577 contain startup files. If the target supports multilibs then the
5578 current multilib directory will be prepended to each of these paths.
5581 Output the multilib directory with directory separators replaced with
5582 @samp{_}. If multilib directories are not set, or the multilib directory is
5583 @file{.} then this option emits nothing.
5586 Process the @code{lib} spec. This is a spec string for deciding which
5587 libraries should be included on the command line to the linker.
5590 Process the @code{libgcc} spec. This is a spec string for deciding
5591 which GCC support library should be included on the command line to the linker.
5594 Process the @code{startfile} spec. This is a spec for deciding which
5595 object files should be the first ones passed to the linker. Typically
5596 this might be a file named @file{crt0.o}.
5599 Process the @code{endfile} spec. This is a spec string that specifies
5600 the last object files that will be passed to the linker.
5603 Process the @code{cpp} spec. This is used to construct the arguments
5604 to be passed to the C preprocessor.
5607 Process the @code{signed_char} spec. This is intended to be used
5608 to tell cpp whether a char is signed. It typically has the definition:
5610 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
5614 Process the @code{cc1} spec. This is used to construct the options to be
5615 passed to the actual C compiler (@samp{cc1}).
5618 Process the @code{cc1plus} spec. This is used to construct the options to be
5619 passed to the actual C++ compiler (@samp{cc1plus}).
5622 Substitute the variable part of a matched option. See below.
5623 Note that each comma in the substituted string is replaced by
5627 Remove all occurrences of @code{-S} from the command line. Note---this
5628 command is position dependent. @samp{%} commands in the spec string
5629 before this one will see @code{-S}, @samp{%} commands in the spec string
5630 after this one will not.
5632 @item %:@var{function}(@var{args})
5633 Call the named function @var{function}, passing it @var{args}.
5634 @var{args} is first processed as a nested spec string, then split
5635 into an argument vector in the usual fashion. The function returns
5636 a string which is processed as if it had appeared literally as part
5637 of the current spec.
5639 The following built-in spec functions are provided:
5642 @item @code{if-exists}
5643 The @code{if-exists} spec function takes one argument, an absolute
5644 pathname to a file. If the file exists, @code{if-exists} returns the
5645 pathname. Here is a small example of its usage:
5649 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
5652 @item @code{if-exists-else}
5653 The @code{if-exists-else} spec function is similar to the @code{if-exists}
5654 spec function, except that it takes two arguments. The first argument is
5655 an absolute pathname to a file. If the file exists, @code{if-exists-else}
5656 returns the pathname. If it does not exist, it returns the second argument.
5657 This way, @code{if-exists-else} can be used to select one file or another,
5658 based on the existence of the first. Here is a small example of its usage:
5662 crt0%O%s %:if-exists(crti%O%s) \
5663 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
5668 Substitutes the @code{-S} switch, if that switch was given to GCC@.
5669 If that switch was not specified, this substitutes nothing. Note that
5670 the leading dash is omitted when specifying this option, and it is
5671 automatically inserted if the substitution is performed. Thus the spec
5672 string @samp{%@{foo@}} would match the command-line option @option{-foo}
5673 and would output the command line option @option{-foo}.
5675 @item %W@{@code{S}@}
5676 Like %@{@code{S}@} but mark last argument supplied within as a file to be
5679 @item %@{@code{S}*@}
5680 Substitutes all the switches specified to GCC whose names start
5681 with @code{-S}, but which also take an argument. This is used for
5682 switches like @option{-o}, @option{-D}, @option{-I}, etc.
5683 GCC considers @option{-o foo} as being
5684 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
5685 text, including the space. Thus two arguments would be generated.
5687 @item %@{@code{S}*&@code{T}*@}
5688 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
5689 (the order of @code{S} and @code{T} in the spec is not significant).
5690 There can be any number of ampersand-separated variables; for each the
5691 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
5693 @item %@{@code{S}:@code{X}@}
5694 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
5696 @item %@{!@code{S}:@code{X}@}
5697 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
5699 @item %@{@code{S}*:@code{X}@}
5700 Substitutes @code{X} if one or more switches whose names start with
5701 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
5702 once, no matter how many such switches appeared. However, if @code{%*}
5703 appears somewhere in @code{X}, then @code{X} will be substituted once
5704 for each matching switch, with the @code{%*} replaced by the part of
5705 that switch that matched the @code{*}.
5707 @item %@{.@code{S}:@code{X}@}
5708 Substitutes @code{X}, if processing a file with suffix @code{S}.
5710 @item %@{!.@code{S}:@code{X}@}
5711 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
5713 @item %@{@code{S}|@code{P}:@code{X}@}
5714 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
5715 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
5716 although they have a stronger binding than the @samp{|}. If @code{%*}
5717 appears in @code{X}, all of the alternatives must be starred, and only
5718 the first matching alternative is substituted.
5720 For example, a spec string like this:
5723 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
5726 will output the following command-line options from the following input
5727 command-line options:
5732 -d fred.c -foo -baz -boggle
5733 -d jim.d -bar -baz -boggle
5736 @item %@{S:X; T:Y; :D@}
5738 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
5739 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
5740 be as many clauses as you need. This may be combined with @code{.},
5741 @code{!}, @code{|}, and @code{*} as needed.
5746 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
5747 construct may contain other nested @samp{%} constructs or spaces, or
5748 even newlines. They are processed as usual, as described above.
5749 Trailing white space in @code{X} is ignored. White space may also
5750 appear anywhere on the left side of the colon in these constructs,
5751 except between @code{.} or @code{*} and the corresponding word.
5753 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
5754 handled specifically in these constructs. If another value of
5755 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
5756 @option{-W} switch is found later in the command line, the earlier
5757 switch value is ignored, except with @{@code{S}*@} where @code{S} is
5758 just one letter, which passes all matching options.
5760 The character @samp{|} at the beginning of the predicate text is used to
5761 indicate that a command should be piped to the following command, but
5762 only if @option{-pipe} is specified.
5764 It is built into GCC which switches take arguments and which do not.
5765 (You might think it would be useful to generalize this to allow each
5766 compiler's spec to say which switches take arguments. But this cannot
5767 be done in a consistent fashion. GCC cannot even decide which input
5768 files have been specified without knowing which switches take arguments,
5769 and it must know which input files to compile in order to tell which
5772 GCC also knows implicitly that arguments starting in @option{-l} are to be
5773 treated as compiler output files, and passed to the linker in their
5774 proper position among the other output files.
5776 @c man begin OPTIONS
5778 @node Target Options
5779 @section Specifying Target Machine and Compiler Version
5780 @cindex target options
5781 @cindex cross compiling
5782 @cindex specifying machine version
5783 @cindex specifying compiler version and target machine
5784 @cindex compiler version, specifying
5785 @cindex target machine, specifying
5787 The usual way to run GCC is to run the executable called @file{gcc}, or
5788 @file{<machine>-gcc} when cross-compiling, or
5789 @file{<machine>-gcc-<version>} to run a version other than the one that
5790 was installed last. Sometimes this is inconvenient, so GCC provides
5791 options that will switch to another cross-compiler or version.
5794 @item -b @var{machine}
5796 The argument @var{machine} specifies the target machine for compilation.
5798 The value to use for @var{machine} is the same as was specified as the
5799 machine type when configuring GCC as a cross-compiler. For
5800 example, if a cross-compiler was configured with @samp{configure
5801 i386v}, meaning to compile for an 80386 running System V, then you
5802 would specify @option{-b i386v} to run that cross compiler.
5804 @item -V @var{version}
5806 The argument @var{version} specifies which version of GCC to run.
5807 This is useful when multiple versions are installed. For example,
5808 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5811 The @option{-V} and @option{-b} options work by running the
5812 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5813 use them if you can just run that directly.
5815 @node Submodel Options
5816 @section Hardware Models and Configurations
5817 @cindex submodel options
5818 @cindex specifying hardware config
5819 @cindex hardware models and configurations, specifying
5820 @cindex machine dependent options
5822 Earlier we discussed the standard option @option{-b} which chooses among
5823 different installed compilers for completely different target
5824 machines, such as VAX vs.@: 68000 vs.@: 80386.
5826 In addition, each of these target machine types can have its own
5827 special options, starting with @samp{-m}, to choose among various
5828 hardware models or configurations---for example, 68010 vs 68020,
5829 floating coprocessor or none. A single installed version of the
5830 compiler can compile for any model or configuration, according to the
5833 Some configurations of the compiler also support additional special
5834 options, usually for compatibility with other compilers on the same
5837 These options are defined by the macro @code{TARGET_SWITCHES} in the
5838 machine description. The default for the options is also defined by
5839 that macro, which enables you to change the defaults.
5849 * RS/6000 and PowerPC Options::
5852 * i386 and x86-64 Options::
5854 * Intel 960 Options::
5855 * DEC Alpha Options::
5856 * DEC Alpha/VMS Options::
5859 * System V Options::
5860 * TMS320C3x/C4x Options::
5868 * S/390 and zSeries Options::
5872 * Xstormy16 Options::
5877 @node M680x0 Options
5878 @subsection M680x0 Options
5879 @cindex M680x0 options
5881 These are the @samp{-m} options defined for the 68000 series. The default
5882 values for these options depends on which style of 68000 was selected when
5883 the compiler was configured; the defaults for the most common choices are
5891 Generate output for a 68000. This is the default
5892 when the compiler is configured for 68000-based systems.
5894 Use this option for microcontrollers with a 68000 or EC000 core,
5895 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5901 Generate output for a 68020. This is the default
5902 when the compiler is configured for 68020-based systems.
5906 Generate output containing 68881 instructions for floating point.
5907 This is the default for most 68020 systems unless @option{--nfp} was
5908 specified when the compiler was configured.
5912 Generate output for a 68030. This is the default when the compiler is
5913 configured for 68030-based systems.
5917 Generate output for a 68040. This is the default when the compiler is
5918 configured for 68040-based systems.
5920 This option inhibits the use of 68881/68882 instructions that have to be
5921 emulated by software on the 68040. Use this option if your 68040 does not
5922 have code to emulate those instructions.
5926 Generate output for a 68060. This is the default when the compiler is
5927 configured for 68060-based systems.
5929 This option inhibits the use of 68020 and 68881/68882 instructions that
5930 have to be emulated by software on the 68060. Use this option if your 68060
5931 does not have code to emulate those instructions.
5935 Generate output for a CPU32. This is the default
5936 when the compiler is configured for CPU32-based systems.
5938 Use this option for microcontrollers with a
5939 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5940 68336, 68340, 68341, 68349 and 68360.
5944 Generate output for a 520X ``coldfire'' family cpu. This is the default
5945 when the compiler is configured for 520X-based systems.
5947 Use this option for microcontroller with a 5200 core, including
5948 the MCF5202, MCF5203, MCF5204 and MCF5202.
5953 Generate output for a 68040, without using any of the new instructions.
5954 This results in code which can run relatively efficiently on either a
5955 68020/68881 or a 68030 or a 68040. The generated code does use the
5956 68881 instructions that are emulated on the 68040.
5960 Generate output for a 68060, without using any of the new instructions.
5961 This results in code which can run relatively efficiently on either a
5962 68020/68881 or a 68030 or a 68040. The generated code does use the
5963 68881 instructions that are emulated on the 68060.
5966 @opindex msoft-float
5967 Generate output containing library calls for floating point.
5968 @strong{Warning:} the requisite libraries are not available for all m68k
5969 targets. Normally the facilities of the machine's usual C compiler are
5970 used, but this can't be done directly in cross-compilation. You must
5971 make your own arrangements to provide suitable library functions for
5972 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5973 @samp{m68k-*-coff} do provide software floating point support.
5977 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5980 @opindex mnobitfield
5981 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5982 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5986 Do use the bit-field instructions. The @option{-m68020} option implies
5987 @option{-mbitfield}. This is the default if you use a configuration
5988 designed for a 68020.
5992 Use a different function-calling convention, in which functions
5993 that take a fixed number of arguments return with the @code{rtd}
5994 instruction, which pops their arguments while returning. This
5995 saves one instruction in the caller since there is no need to pop
5996 the arguments there.
5998 This calling convention is incompatible with the one normally
5999 used on Unix, so you cannot use it if you need to call libraries
6000 compiled with the Unix compiler.
6002 Also, you must provide function prototypes for all functions that
6003 take variable numbers of arguments (including @code{printf});
6004 otherwise incorrect code will be generated for calls to those
6007 In addition, seriously incorrect code will result if you call a
6008 function with too many arguments. (Normally, extra arguments are
6009 harmlessly ignored.)
6011 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
6012 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
6015 @itemx -mno-align-int
6017 @opindex mno-align-int
6018 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
6019 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
6020 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
6021 Aligning variables on 32-bit boundaries produces code that runs somewhat
6022 faster on processors with 32-bit busses at the expense of more memory.
6024 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
6025 align structures containing the above types differently than
6026 most published application binary interface specifications for the m68k.
6030 Use the pc-relative addressing mode of the 68000 directly, instead of
6031 using a global offset table. At present, this option implies @option{-fpic},
6032 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
6033 not presently supported with @option{-mpcrel}, though this could be supported for
6034 68020 and higher processors.
6036 @item -mno-strict-align
6037 @itemx -mstrict-align
6038 @opindex mno-strict-align
6039 @opindex mstrict-align
6040 Do not (do) assume that unaligned memory references will be handled by
6044 Generate code that allows the data segment to be located in a different
6045 area of memory from the text segment. This allows for execute in place in
6046 an environment without virtual memory management. This option implies -fPIC.
6049 Generate code that assumes that the data segment follows the text segment.
6050 This is the default.
6052 @item -mid-shared-library
6053 Generate code that supports shared libraries via the library ID method.
6054 This allows for execute in place and shared libraries in an environment
6055 without virtual memory management. This option implies -fPIC.
6057 @item -mno-id-shared-library
6058 Generate code that doesn't assume ID based shared libraries are being used.
6059 This is the default.
6061 @item -mshared-library-id=n
6062 Specified the identification number of the ID based shared library being
6063 compiled. Specifying a value of 0 will generate more compact code, specifying
6064 other values will force the allocation of that number to the current
6065 library but is no more space or time efficient than omitting this option.
6069 @node M68hc1x Options
6070 @subsection M68hc1x Options
6071 @cindex M68hc1x options
6073 These are the @samp{-m} options defined for the 68hc11 and 68hc12
6074 microcontrollers. The default values for these options depends on
6075 which style of microcontroller was selected when the compiler was configured;
6076 the defaults for the most common choices are given below.
6083 Generate output for a 68HC11. This is the default
6084 when the compiler is configured for 68HC11-based systems.
6090 Generate output for a 68HC12. This is the default
6091 when the compiler is configured for 68HC12-based systems.
6097 Generate output for a 68HCS12.
6100 @opindex mauto-incdec
6101 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
6108 Enable the use of 68HC12 min and max instructions.
6111 @itemx -mno-long-calls
6112 @opindex mlong-calls
6113 @opindex mno-long-calls
6114 Treat all calls as being far away (near). If calls are assumed to be
6115 far away, the compiler will use the @code{call} instruction to
6116 call a function and the @code{rtc} instruction for returning.
6120 Consider type @code{int} to be 16 bits wide, like @code{short int}.
6122 @item -msoft-reg-count=@var{count}
6123 @opindex msoft-reg-count
6124 Specify the number of pseudo-soft registers which are used for the
6125 code generation. The maximum number is 32. Using more pseudo-soft
6126 register may or may not result in better code depending on the program.
6127 The default is 4 for 68HC11 and 2 for 68HC12.
6132 @subsection VAX Options
6135 These @samp{-m} options are defined for the VAX:
6140 Do not output certain jump instructions (@code{aobleq} and so on)
6141 that the Unix assembler for the VAX cannot handle across long
6146 Do output those jump instructions, on the assumption that you
6147 will assemble with the GNU assembler.
6151 Output code for g-format floating point numbers instead of d-format.
6155 @subsection SPARC Options
6156 @cindex SPARC options
6158 These @samp{-m} options are supported on the SPARC:
6163 @opindex mno-app-regs
6165 Specify @option{-mapp-regs} to generate output using the global registers
6166 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
6167 is the default, except on Solaris.
6169 To be fully SVR4 ABI compliant at the cost of some performance loss,
6170 specify @option{-mno-app-regs}. You should compile libraries and system
6171 software with this option.
6176 @opindex mhard-float
6177 Generate output containing floating point instructions. This is the
6183 @opindex msoft-float
6184 Generate output containing library calls for floating point.
6185 @strong{Warning:} the requisite libraries are not available for all SPARC
6186 targets. Normally the facilities of the machine's usual C compiler are
6187 used, but this cannot be done directly in cross-compilation. You must make
6188 your own arrangements to provide suitable library functions for
6189 cross-compilation. The embedded targets @samp{sparc-*-aout} and
6190 @samp{sparclite-*-*} do provide software floating point support.
6192 @option{-msoft-float} changes the calling convention in the output file;
6193 therefore, it is only useful if you compile @emph{all} of a program with
6194 this option. In particular, you need to compile @file{libgcc.a}, the
6195 library that comes with GCC, with @option{-msoft-float} in order for
6198 @item -mhard-quad-float
6199 @opindex mhard-quad-float
6200 Generate output containing quad-word (long double) floating point
6203 @item -msoft-quad-float
6204 @opindex msoft-quad-float
6205 Generate output containing library calls for quad-word (long double)
6206 floating point instructions. The functions called are those specified
6207 in the SPARC ABI@. This is the default.
6209 As of this writing, there are no SPARC implementations that have hardware
6210 support for the quad-word floating point instructions. They all invoke
6211 a trap handler for one of these instructions, and then the trap handler
6212 emulates the effect of the instruction. Because of the trap handler overhead,
6213 this is much slower than calling the ABI library routines. Thus the
6214 @option{-msoft-quad-float} option is the default.
6220 With @option{-mflat}, the compiler does not generate save/restore instructions
6221 and will use a ``flat'' or single register window calling convention.
6222 This model uses %i7 as the frame pointer and is compatible with the normal
6223 register window model. Code from either may be intermixed.
6224 The local registers and the input registers (0--5) are still treated as
6225 ``call saved'' registers and will be saved on the stack as necessary.
6227 With @option{-mno-flat} (the default), the compiler emits save/restore
6228 instructions (except for leaf functions) and is the normal mode of operation.
6230 These options are deprecated and will be deleted in a future GCC release.
6232 @item -mno-unaligned-doubles
6233 @itemx -munaligned-doubles
6234 @opindex mno-unaligned-doubles
6235 @opindex munaligned-doubles
6236 Assume that doubles have 8 byte alignment. This is the default.
6238 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
6239 alignment only if they are contained in another type, or if they have an
6240 absolute address. Otherwise, it assumes they have 4 byte alignment.
6241 Specifying this option avoids some rare compatibility problems with code
6242 generated by other compilers. It is not the default because it results
6243 in a performance loss, especially for floating point code.
6245 @item -mno-faster-structs
6246 @itemx -mfaster-structs
6247 @opindex mno-faster-structs
6248 @opindex mfaster-structs
6249 With @option{-mfaster-structs}, the compiler assumes that structures
6250 should have 8 byte alignment. This enables the use of pairs of
6251 @code{ldd} and @code{std} instructions for copies in structure
6252 assignment, in place of twice as many @code{ld} and @code{st} pairs.
6253 However, the use of this changed alignment directly violates the SPARC
6254 ABI@. Thus, it's intended only for use on targets where the developer
6255 acknowledges that their resulting code will not be directly in line with
6256 the rules of the ABI@.
6259 @opindex mimpure-text
6260 @option{-mimpure-text}, used in addition to @option{-shared}, tells
6261 the compiler to not pass @option{-z text} to the linker when linking a
6262 shared object. Using this option, you can link position-dependent
6263 code into a shared object.
6265 @option{-mimpure-text} suppresses the ``relocations remain against
6266 allocatable but non-writable sections'' linker error message.
6267 However, the necessary relocations will trigger copy-on-write, and the
6268 shared object is not actually shared across processes. Instead of
6269 using @option{-mimpure-text}, you should compile all source code with
6270 @option{-fpic} or @option{-fPIC}.
6272 This option is only available on SunOS and Solaris.
6278 These two options select variations on the SPARC architecture.
6279 These options are deprecated and will be deleted in a future GCC release.
6280 They have been replaced with @option{-mcpu=xxx}.
6287 @opindex msupersparc
6290 These four options select the processor for which the code is optimized.
6291 These options are deprecated and will be deleted in a future GCC release.
6292 They have been replaced with @option{-mcpu=xxx}.
6294 @item -mcpu=@var{cpu_type}
6296 Set the instruction set, register set, and instruction scheduling parameters
6297 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
6298 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
6299 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
6300 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
6303 Default instruction scheduling parameters are used for values that select
6304 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
6305 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
6307 Here is a list of each supported architecture and their supported
6312 v8: supersparc, hypersparc
6313 sparclite: f930, f934, sparclite86x
6315 v9: ultrasparc, ultrasparc3
6318 By default (unless configured otherwise), GCC generates code for the V7
6319 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
6320 additionally optimizes it for the Cypress CY7C602 chip, as used in the
6321 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
6322 SPARCStation 1, 2, IPX etc.
6324 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
6325 architecture. The only difference from V7 code is that the compiler emits
6326 the integer multiply and integer divide instructions which exist in SPARC-V8
6327 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
6328 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
6331 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
6332 the SPARC architecture. This adds the integer multiply, integer divide step
6333 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
6334 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
6335 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU. With
6336 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
6337 MB86934 chip, which is the more recent SPARClite with FPU.
6339 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
6340 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
6341 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
6342 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
6343 optimizes it for the TEMIC SPARClet chip.
6345 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
6346 architecture. This adds 64-bit integer and floating-point move instructions,
6347 3 additional floating-point condition code registers and conditional move
6348 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
6349 optimizes it for the Sun UltraSPARC I/II chips. With
6350 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
6351 Sun UltraSPARC III chip.
6353 @item -mtune=@var{cpu_type}
6355 Set the instruction scheduling parameters for machine type
6356 @var{cpu_type}, but do not set the instruction set or register set that the
6357 option @option{-mcpu=@var{cpu_type}} would.
6359 The same values for @option{-mcpu=@var{cpu_type}} can be used for
6360 @option{-mtune=@var{cpu_type}}, but the only useful values are those
6361 that select a particular cpu implementation. Those are @samp{cypress},
6362 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
6363 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
6370 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI. The
6371 difference from the V8 ABI is that the global and out registers are
6372 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
6373 mode for all SPARC-V9 processors.
6379 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
6380 Visual Instruction Set extensions. The default is @option{-mno-vis}.
6383 These @samp{-m} options are supported in addition to the above
6384 on SPARC-V9 processors in 64-bit environments:
6387 @item -mlittle-endian
6388 @opindex mlittle-endian
6389 Generate code for a processor running in little-endian mode. It is only
6390 available for a few configurations and most notably not on Solaris and Linux.
6396 Generate code for a 32-bit or 64-bit environment.
6397 The 32-bit environment sets int, long and pointer to 32 bits.
6398 The 64-bit environment sets int to 32 bits and long and pointer
6401 @item -mcmodel=medlow
6402 @opindex mcmodel=medlow
6403 Generate code for the Medium/Low code model: 64-bit addresses, programs
6404 must be linked in the low 32 bits of memory. Programs can be statically
6405 or dynamically linked.
6407 @item -mcmodel=medmid
6408 @opindex mcmodel=medmid
6409 Generate code for the Medium/Middle code model: 64-bit addresses, programs
6410 must be linked in the low 44 bits of memory, the text and data segments must
6411 be less than 2GB in size and the data segment must be located within 2GB of
6414 @item -mcmodel=medany
6415 @opindex mcmodel=medany
6416 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
6417 may be linked anywhere in memory, the text and data segments must be less
6418 than 2GB in size and the data segment must be located within 2GB of the
6421 @item -mcmodel=embmedany
6422 @opindex mcmodel=embmedany
6423 Generate code for the Medium/Anywhere code model for embedded systems:
6424 64-bit addresses, the text and data segments must be less than 2GB in
6425 size, both starting anywhere in memory (determined at link time). The
6426 global register %g4 points to the base of the data segment. Programs
6427 are statically linked and PIC is not supported.
6430 @itemx -mno-stack-bias
6431 @opindex mstack-bias
6432 @opindex mno-stack-bias
6433 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
6434 frame pointer if present, are offset by @minus{}2047 which must be added back
6435 when making stack frame references. This is the default in 64-bit mode.
6436 Otherwise, assume no such offset is present.
6439 These switches are supported in addition to the above on Solaris:
6444 Add support for multithreading using the Solaris threads library. This
6445 option sets flags for both the preprocessor and linker. This option does
6446 not affect the thread safety of object code produced by the compiler or
6447 that of libraries supplied with it.
6451 Add support for multithreading using the POSIX threads library. This
6452 option sets flags for both the preprocessor and linker. This option does
6453 not affect the thread safety of object code produced by the compiler or
6454 that of libraries supplied with it.
6458 @subsection ARM Options
6461 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6466 @opindex mapcs-frame
6467 Generate a stack frame that is compliant with the ARM Procedure Call
6468 Standard for all functions, even if this is not strictly necessary for
6469 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6470 with this option will cause the stack frames not to be generated for
6471 leaf functions. The default is @option{-mno-apcs-frame}.
6475 This is a synonym for @option{-mapcs-frame}.
6479 Generate code for a processor running with a 26-bit program counter,
6480 and conforming to the function calling standards for the APCS 26-bit
6483 This option is deprecated. Future releases of the GCC will only support
6484 generating code that runs in apcs-32 mode.
6488 Generate code for a processor running with a 32-bit program counter,
6489 and conforming to the function calling standards for the APCS 32-bit
6492 This flag is deprecated. Future releases of GCC will make this flag
6496 @c not currently implemented
6497 @item -mapcs-stack-check
6498 @opindex mapcs-stack-check
6499 Generate code to check the amount of stack space available upon entry to
6500 every function (that actually uses some stack space). If there is
6501 insufficient space available then either the function
6502 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6503 called, depending upon the amount of stack space required. The run time
6504 system is required to provide these functions. The default is
6505 @option{-mno-apcs-stack-check}, since this produces smaller code.
6507 @c not currently implemented
6509 @opindex mapcs-float
6510 Pass floating point arguments using the float point registers. This is
6511 one of the variants of the APCS@. This option is recommended if the
6512 target hardware has a floating point unit or if a lot of floating point
6513 arithmetic is going to be performed by the code. The default is
6514 @option{-mno-apcs-float}, since integer only code is slightly increased in
6515 size if @option{-mapcs-float} is used.
6517 @c not currently implemented
6518 @item -mapcs-reentrant
6519 @opindex mapcs-reentrant
6520 Generate reentrant, position independent code. The default is
6521 @option{-mno-apcs-reentrant}.
6524 @item -mthumb-interwork
6525 @opindex mthumb-interwork
6526 Generate code which supports calling between the ARM and Thumb
6527 instruction sets. Without this option the two instruction sets cannot
6528 be reliably used inside one program. The default is
6529 @option{-mno-thumb-interwork}, since slightly larger code is generated
6530 when @option{-mthumb-interwork} is specified.
6532 @item -mno-sched-prolog
6533 @opindex mno-sched-prolog
6534 Prevent the reordering of instructions in the function prolog, or the
6535 merging of those instruction with the instructions in the function's
6536 body. This means that all functions will start with a recognizable set
6537 of instructions (or in fact one of a choice from a small set of
6538 different function prologues), and this information can be used to
6539 locate the start if functions inside an executable piece of code. The
6540 default is @option{-msched-prolog}.
6543 @opindex mhard-float
6544 Generate output containing floating point instructions. This is the
6548 @opindex msoft-float
6549 Generate output containing library calls for floating point.
6550 @strong{Warning:} the requisite libraries are not available for all ARM
6551 targets. Normally the facilities of the machine's usual C compiler are
6552 used, but this cannot be done directly in cross-compilation. You must make
6553 your own arrangements to provide suitable library functions for
6556 @option{-msoft-float} changes the calling convention in the output file;
6557 therefore, it is only useful if you compile @emph{all} of a program with
6558 this option. In particular, you need to compile @file{libgcc.a}, the
6559 library that comes with GCC, with @option{-msoft-float} in order for
6562 @item -mlittle-endian
6563 @opindex mlittle-endian
6564 Generate code for a processor running in little-endian mode. This is
6565 the default for all standard configurations.
6568 @opindex mbig-endian
6569 Generate code for a processor running in big-endian mode; the default is
6570 to compile code for a little-endian processor.
6572 @item -mwords-little-endian
6573 @opindex mwords-little-endian
6574 This option only applies when generating code for big-endian processors.
6575 Generate code for a little-endian word order but a big-endian byte
6576 order. That is, a byte order of the form @samp{32107654}. Note: this
6577 option should only be used if you require compatibility with code for
6578 big-endian ARM processors generated by versions of the compiler prior to
6581 @item -malignment-traps
6582 @opindex malignment-traps
6583 Generate code that will not trap if the MMU has alignment traps enabled.
6584 On ARM architectures prior to ARMv4, there were no instructions to
6585 access half-word objects stored in memory. However, when reading from
6586 memory a feature of the ARM architecture allows a word load to be used,
6587 even if the address is unaligned, and the processor core will rotate the
6588 data as it is being loaded. This option tells the compiler that such
6589 misaligned accesses will cause a MMU trap and that it should instead
6590 synthesize the access as a series of byte accesses. The compiler can
6591 still use word accesses to load half-word data if it knows that the
6592 address is aligned to a word boundary.
6594 This option has no effect when compiling for ARM architecture 4 or later,
6595 since these processors have instructions to directly access half-word
6598 @item -mno-alignment-traps
6599 @opindex mno-alignment-traps
6600 Generate code that assumes that the MMU will not trap unaligned
6601 accesses. This produces better code when the target instruction set
6602 does not have half-word memory operations (i.e.@: implementations prior to
6605 Note that you cannot use this option to access unaligned word objects,
6606 since the processor will only fetch one 32-bit aligned object from
6609 The default setting is @option{-malignment-traps}, since this produces
6610 code that will also run on processors implementing ARM architecture
6613 This option is deprecated and will be removed in the next release of GCC.
6615 @item -mcpu=@var{name}
6617 This specifies the name of the target ARM processor. GCC uses this name
6618 to determine what kind of instructions it can emit when generating
6619 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6620 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6621 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6622 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6623 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6624 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
6625 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6626 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6627 @samp{arm920t}, @samp{arm926ejs}, @samp{arm940t}, @samp{arm9tdmi},
6628 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ejs},
6629 @samp{arm1136js}, @samp{arm1136jfs} ,@samp{xscale}, @samp{iwmmxt},
6632 @itemx -mtune=@var{name}
6634 This option is very similar to the @option{-mcpu=} option, except that
6635 instead of specifying the actual target processor type, and hence
6636 restricting which instructions can be used, it specifies that GCC should
6637 tune the performance of the code as if the target were of the type
6638 specified in this option, but still choosing the instructions that it
6639 will generate based on the cpu specified by a @option{-mcpu=} option.
6640 For some ARM implementations better performance can be obtained by using
6643 @item -march=@var{name}
6645 This specifies the name of the target ARM architecture. GCC uses this
6646 name to determine what kind of instructions it can emit when generating
6647 assembly code. This option can be used in conjunction with or instead
6648 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6649 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6650 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6j},
6651 @samp{iwmmxt}, @samp{ep9312}.
6653 @item -mfpe=@var{number}
6654 @itemx -mfp=@var{number}
6657 This specifies the version of the floating point emulation available on
6658 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6659 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6661 @item -mstructure-size-boundary=@var{n}
6662 @opindex mstructure-size-boundary
6663 The size of all structures and unions will be rounded up to a multiple
6664 of the number of bits set by this option. Permissible values are 8 and
6665 32. The default value varies for different toolchains. For the COFF
6666 targeted toolchain the default value is 8. Specifying the larger number
6667 can produce faster, more efficient code, but can also increase the size
6668 of the program. The two values are potentially incompatible. Code
6669 compiled with one value cannot necessarily expect to work with code or
6670 libraries compiled with the other value, if they exchange information
6671 using structures or unions.
6673 @item -mabort-on-noreturn
6674 @opindex mabort-on-noreturn
6675 Generate a call to the function @code{abort} at the end of a
6676 @code{noreturn} function. It will be executed if the function tries to
6680 @itemx -mno-long-calls
6681 @opindex mlong-calls
6682 @opindex mno-long-calls
6683 Tells the compiler to perform function calls by first loading the
6684 address of the function into a register and then performing a subroutine
6685 call on this register. This switch is needed if the target function
6686 will lie outside of the 64 megabyte addressing range of the offset based
6687 version of subroutine call instruction.
6689 Even if this switch is enabled, not all function calls will be turned
6690 into long calls. The heuristic is that static functions, functions
6691 which have the @samp{short-call} attribute, functions that are inside
6692 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6693 definitions have already been compiled within the current compilation
6694 unit, will not be turned into long calls. The exception to this rule is
6695 that weak function definitions, functions with the @samp{long-call}
6696 attribute or the @samp{section} attribute, and functions that are within
6697 the scope of a @samp{#pragma long_calls} directive, will always be
6698 turned into long calls.
6700 This feature is not enabled by default. Specifying
6701 @option{-mno-long-calls} will restore the default behavior, as will
6702 placing the function calls within the scope of a @samp{#pragma
6703 long_calls_off} directive. Note these switches have no effect on how
6704 the compiler generates code to handle function calls via function
6707 @item -mnop-fun-dllimport
6708 @opindex mnop-fun-dllimport
6709 Disable support for the @code{dllimport} attribute.
6711 @item -msingle-pic-base
6712 @opindex msingle-pic-base
6713 Treat the register used for PIC addressing as read-only, rather than
6714 loading it in the prologue for each function. The run-time system is
6715 responsible for initializing this register with an appropriate value
6716 before execution begins.
6718 @item -mpic-register=@var{reg}
6719 @opindex mpic-register
6720 Specify the register to be used for PIC addressing. The default is R10
6721 unless stack-checking is enabled, when R9 is used.
6723 @item -mcirrus-fix-invalid-insns
6724 @opindex mcirrus-fix-invalid-insns
6725 @opindex mno-cirrus-fix-invalid-insns
6726 Insert NOPs into the instruction stream to in order to work around
6727 problems with invalid Maverick instruction combinations. This option
6728 is only valid if the @option{-mcpu=ep9312} option has been used to
6729 enable generation of instructions for the Cirrus Maverick floating
6730 point co-processor. This option is not enabled by default, since the
6731 problem is only present in older Maverick implementations. The default
6732 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6735 @item -mpoke-function-name
6736 @opindex mpoke-function-name
6737 Write the name of each function into the text section, directly
6738 preceding the function prologue. The generated code is similar to this:
6742 .ascii "arm_poke_function_name", 0
6745 .word 0xff000000 + (t1 - t0)
6746 arm_poke_function_name
6748 stmfd sp!, @{fp, ip, lr, pc@}
6752 When performing a stack backtrace, code can inspect the value of
6753 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6754 location @code{pc - 12} and the top 8 bits are set, then we know that
6755 there is a function name embedded immediately preceding this location
6756 and has length @code{((pc[-3]) & 0xff000000)}.
6760 Generate code for the 16-bit Thumb instruction set. The default is to
6761 use the 32-bit ARM instruction set.
6764 @opindex mtpcs-frame
6765 Generate a stack frame that is compliant with the Thumb Procedure Call
6766 Standard for all non-leaf functions. (A leaf function is one that does
6767 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6769 @item -mtpcs-leaf-frame
6770 @opindex mtpcs-leaf-frame
6771 Generate a stack frame that is compliant with the Thumb Procedure Call
6772 Standard for all leaf functions. (A leaf function is one that does
6773 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6775 @item -mcallee-super-interworking
6776 @opindex mcallee-super-interworking
6777 Gives all externally visible functions in the file being compiled an ARM
6778 instruction set header which switches to Thumb mode before executing the
6779 rest of the function. This allows these functions to be called from
6780 non-interworking code.
6782 @item -mcaller-super-interworking
6783 @opindex mcaller-super-interworking
6784 Allows calls via function pointers (including virtual functions) to
6785 execute correctly regardless of whether the target code has been
6786 compiled for interworking or not. There is a small overhead in the cost
6787 of executing a function pointer if this option is enabled.
6791 @node MN10300 Options
6792 @subsection MN10300 Options
6793 @cindex MN10300 options
6795 These @option{-m} options are defined for Matsushita MN10300 architectures:
6800 Generate code to avoid bugs in the multiply instructions for the MN10300
6801 processors. This is the default.
6804 @opindex mno-mult-bug
6805 Do not generate code to avoid bugs in the multiply instructions for the
6810 Generate code which uses features specific to the AM33 processor.
6814 Do not generate code which uses features specific to the AM33 processor. This
6819 Do not link in the C run-time initialization object file.
6823 Indicate to the linker that it should perform a relaxation optimization pass
6824 to shorten branches, calls and absolute memory addresses. This option only
6825 has an effect when used on the command line for the final link step.
6827 This option makes symbolic debugging impossible.
6831 @node M32R/D Options
6832 @subsection M32R/D Options
6833 @cindex M32R/D options
6835 These @option{-m} options are defined for Renesas M32R/D architectures:
6840 Generate code for the M32R/2@.
6844 Generate code for the M32R/X@.
6848 Generate code for the M32R@. This is the default.
6851 @opindex mmodel=small
6852 Assume all objects live in the lower 16MB of memory (so that their addresses
6853 can be loaded with the @code{ld24} instruction), and assume all subroutines
6854 are reachable with the @code{bl} instruction.
6855 This is the default.
6857 The addressability of a particular object can be set with the
6858 @code{model} attribute.
6860 @item -mmodel=medium
6861 @opindex mmodel=medium
6862 Assume objects may be anywhere in the 32-bit address space (the compiler
6863 will generate @code{seth/add3} instructions to load their addresses), and
6864 assume all subroutines are reachable with the @code{bl} instruction.
6867 @opindex mmodel=large
6868 Assume objects may be anywhere in the 32-bit address space (the compiler
6869 will generate @code{seth/add3} instructions to load their addresses), and
6870 assume subroutines may not be reachable with the @code{bl} instruction
6871 (the compiler will generate the much slower @code{seth/add3/jl}
6872 instruction sequence).
6875 @opindex msdata=none
6876 Disable use of the small data area. Variables will be put into
6877 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6878 @code{section} attribute has been specified).
6879 This is the default.
6881 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6882 Objects may be explicitly put in the small data area with the
6883 @code{section} attribute using one of these sections.
6886 @opindex msdata=sdata
6887 Put small global and static data in the small data area, but do not
6888 generate special code to reference them.
6892 Put small global and static data in the small data area, and generate
6893 special instructions to reference them.
6897 @cindex smaller data references
6898 Put global and static objects less than or equal to @var{num} bytes
6899 into the small data or bss sections instead of the normal data or bss
6900 sections. The default value of @var{num} is 8.
6901 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6902 for this option to have any effect.
6904 All modules should be compiled with the same @option{-G @var{num}} value.
6905 Compiling with different values of @var{num} may or may not work; if it
6906 doesn't the linker will give an error message---incorrect code will not be
6911 Makes the M32R specific code in the compiler display some statistics
6912 that might help in debugging programs.
6915 @opindex malign-loops
6916 Align all loops to a 32-byte boundary.
6918 @item -mno-align-loops
6919 @opindex mno-align-loops
6920 Do not enforce a 32-byte alignment for loops. This is the default.
6922 @item -missue-rate=@var{number}
6923 @opindex missue-rate=@var{number}
6924 Issue @var{number} instructions per cycle. @var{number} can only be 1
6927 @item -mbranch-cost=@var{number}
6928 @opindex mbranch-cost=@var{number}
6929 @var{number} can only be 1 or 2. If it is 1 then branches will be
6930 preferred over conditional code, if it is 2, then the opposite will
6933 @item -mflush-trap=@var{number}
6934 @opindex mflush-trap=@var{number}
6935 Specifies the trap number to use to flush the cache. The default is
6936 12. Valid numbers are between 0 and 15 inclusive.
6938 @item -mno-flush-trap
6939 @opindex mno-flush-trap
6940 Specifies that the cache cannot be flushed by using a trap.
6942 @item -mflush-func=@var{name}
6943 @opindex mflush-func=@var{name}
6944 Specifies the name of the operating system function to call to flush
6945 the cache. The default is @emph{_flush_cache}, but a function call
6946 will only be used if a trap is not available.
6948 @item -mno-flush-func
6949 @opindex mno-flush-func
6950 Indicates that there is no OS function for flushing the cache.
6954 @node RS/6000 and PowerPC Options
6955 @subsection IBM RS/6000 and PowerPC Options
6956 @cindex RS/6000 and PowerPC Options
6957 @cindex IBM RS/6000 and PowerPC Options
6959 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6967 @itemx -mpowerpc-gpopt
6968 @itemx -mno-powerpc-gpopt
6969 @itemx -mpowerpc-gfxopt
6970 @itemx -mno-powerpc-gfxopt
6972 @itemx -mno-powerpc64
6978 @opindex mno-powerpc
6979 @opindex mpowerpc-gpopt
6980 @opindex mno-powerpc-gpopt
6981 @opindex mpowerpc-gfxopt
6982 @opindex mno-powerpc-gfxopt
6984 @opindex mno-powerpc64
6985 GCC supports two related instruction set architectures for the
6986 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6987 instructions supported by the @samp{rios} chip set used in the original
6988 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6989 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6990 the IBM 4xx microprocessors.
6992 Neither architecture is a subset of the other. However there is a
6993 large common subset of instructions supported by both. An MQ
6994 register is included in processors supporting the POWER architecture.
6996 You use these options to specify which instructions are available on the
6997 processor you are using. The default value of these options is
6998 determined when configuring GCC@. Specifying the
6999 @option{-mcpu=@var{cpu_type}} overrides the specification of these
7000 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
7001 rather than the options listed above.
7003 The @option{-mpower} option allows GCC to generate instructions that
7004 are found only in the POWER architecture and to use the MQ register.
7005 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
7006 to generate instructions that are present in the POWER2 architecture but
7007 not the original POWER architecture.
7009 The @option{-mpowerpc} option allows GCC to generate instructions that
7010 are found only in the 32-bit subset of the PowerPC architecture.
7011 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
7012 GCC to use the optional PowerPC architecture instructions in the
7013 General Purpose group, including floating-point square root. Specifying
7014 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
7015 use the optional PowerPC architecture instructions in the Graphics
7016 group, including floating-point select.
7018 The @option{-mpowerpc64} option allows GCC to generate the additional
7019 64-bit instructions that are found in the full PowerPC64 architecture
7020 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
7021 @option{-mno-powerpc64}.
7023 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
7024 will use only the instructions in the common subset of both
7025 architectures plus some special AIX common-mode calls, and will not use
7026 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
7027 permits GCC to use any instruction from either architecture and to
7028 allow use of the MQ register; specify this for the Motorola MPC601.
7030 @item -mnew-mnemonics
7031 @itemx -mold-mnemonics
7032 @opindex mnew-mnemonics
7033 @opindex mold-mnemonics
7034 Select which mnemonics to use in the generated assembler code. With
7035 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
7036 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
7037 assembler mnemonics defined for the POWER architecture. Instructions
7038 defined in only one architecture have only one mnemonic; GCC uses that
7039 mnemonic irrespective of which of these options is specified.
7041 GCC defaults to the mnemonics appropriate for the architecture in
7042 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
7043 value of these option. Unless you are building a cross-compiler, you
7044 should normally not specify either @option{-mnew-mnemonics} or
7045 @option{-mold-mnemonics}, but should instead accept the default.
7047 @item -mcpu=@var{cpu_type}
7049 Set architecture type, register usage, choice of mnemonics, and
7050 instruction scheduling parameters for machine type @var{cpu_type}.
7051 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
7052 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
7053 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
7054 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
7055 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
7056 @samp{860}, @samp{970}, @samp{8540}, @samp{common}, @samp{ec603e}, @samp{G3},
7057 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
7058 @samp{power4}, @samp{power5}, @samp{powerpc}, @samp{powerpc64},
7059 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64a}.
7061 @option{-mcpu=common} selects a completely generic processor. Code
7062 generated under this option will run on any POWER or PowerPC processor.
7063 GCC will use only the instructions in the common subset of both
7064 architectures, and will not use the MQ register. GCC assumes a generic
7065 processor model for scheduling purposes.
7067 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
7068 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
7069 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
7070 types, with an appropriate, generic processor model assumed for
7071 scheduling purposes.
7073 The other options specify a specific processor. Code generated under
7074 those options will run best on that processor, and may not run at all on
7077 The @option{-mcpu} options automatically enable or disable the
7078 following options: @option{-maltivec}, @option{-mhard-float},
7079 @option{-mmfcrf}, @option{-mmultiple}, @option{-mnew-mnemonics},
7080 @option{-mpower}, @option{-mpower2}, @option{-mpowerpc64},
7081 @option{-mpowerpc-gpopt}, @option{-mpowerpc-gfxopt},
7082 @option{-mstring}. The particular options set for any particular CPU
7083 will vary between compiler versions, depending on what setting seems
7084 to produce optimal code for that CPU; it doesn't necessarily reflect
7085 the actual hardware's capabilities. If you wish to set an individual
7086 option to a particular value, you may specify it after the
7087 @option{-mcpu} option, like @samp{-mcpu=970 -mno-altivec}.
7089 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
7090 not enabled or disabled by the @option{-mcpu} option at present, since
7091 AIX does not have full support for these options. You may still
7092 enable or disable them individually if you're sure it'll work in your
7095 @item -mtune=@var{cpu_type}
7097 Set the instruction scheduling parameters for machine type
7098 @var{cpu_type}, but do not set the architecture type, register usage, or
7099 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
7100 values for @var{cpu_type} are used for @option{-mtune} as for
7101 @option{-mcpu}. If both are specified, the code generated will use the
7102 architecture, registers, and mnemonics set by @option{-mcpu}, but the
7103 scheduling parameters set by @option{-mtune}.
7108 @opindex mno-altivec
7109 These switches enable or disable the use of built-in functions that
7110 allow access to the AltiVec instruction set. You may also need to set
7111 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
7116 Extend the current ABI with SPE ABI extensions. This does not change
7117 the default ABI, instead it adds the SPE ABI extensions to the current
7121 @opindex mabi=no-spe
7122 Disable Booke SPE ABI extensions for the current ABI.
7124 @item -misel=@var{yes/no}
7127 This switch enables or disables the generation of ISEL instructions.
7129 @item -mspe=@var{yes/no}
7132 This switch enables or disables the generation of SPE simd
7135 @item -mfloat-gprs=@var{yes/no}
7137 @opindex mfloat-gprs
7138 This switch enables or disables the generation of floating point
7139 operations on the general purpose registers for architectures that
7140 support it. This option is currently only available on the MPC8540.
7143 @itemx -mno-fp-in-toc
7144 @itemx -mno-sum-in-toc
7145 @itemx -mminimal-toc
7147 @opindex mno-fp-in-toc
7148 @opindex mno-sum-in-toc
7149 @opindex mminimal-toc
7150 Modify generation of the TOC (Table Of Contents), which is created for
7151 every executable file. The @option{-mfull-toc} option is selected by
7152 default. In that case, GCC will allocate at least one TOC entry for
7153 each unique non-automatic variable reference in your program. GCC
7154 will also place floating-point constants in the TOC@. However, only
7155 16,384 entries are available in the TOC@.
7157 If you receive a linker error message that saying you have overflowed
7158 the available TOC space, you can reduce the amount of TOC space used
7159 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
7160 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
7161 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
7162 generate code to calculate the sum of an address and a constant at
7163 run-time instead of putting that sum into the TOC@. You may specify one
7164 or both of these options. Each causes GCC to produce very slightly
7165 slower and larger code at the expense of conserving TOC space.
7167 If you still run out of space in the TOC even when you specify both of
7168 these options, specify @option{-mminimal-toc} instead. This option causes
7169 GCC to make only one TOC entry for every file. When you specify this
7170 option, GCC will produce code that is slower and larger but which
7171 uses extremely little TOC space. You may wish to use this option
7172 only on files that contain less frequently executed code.
7178 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
7179 @code{long} type, and the infrastructure needed to support them.
7180 Specifying @option{-maix64} implies @option{-mpowerpc64} and
7181 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
7182 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
7185 @itemx -mno-xl-compat
7187 @opindex mno-xl-compat
7188 Produce code that conforms more closely to IBM XLC semantics when using
7189 AIX-compatible ABI. Pass floating-point arguments to prototyped
7190 functions beyond the register save area (RSA) on the stack in addition
7191 to argument FPRs. Do not assume that most significant double in 128
7192 bit long double value is properly rounded when comparing values.
7194 The AIX calling convention was extended but not initially documented to
7195 handle an obscure K&R C case of calling a function that takes the
7196 address of its arguments with fewer arguments than declared. AIX XL
7197 compilers access floating point arguments which do not fit in the
7198 RSA from the stack when a subroutine is compiled without
7199 optimization. Because always storing floating-point arguments on the
7200 stack is inefficient and rarely needed, this option is not enabled by
7201 default and only is necessary when calling subroutines compiled by AIX
7202 XL compilers without optimization.
7206 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
7207 application written to use message passing with special startup code to
7208 enable the application to run. The system must have PE installed in the
7209 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
7210 must be overridden with the @option{-specs=} option to specify the
7211 appropriate directory location. The Parallel Environment does not
7212 support threads, so the @option{-mpe} option and the @option{-pthread}
7213 option are incompatible.
7215 @item -malign-natural
7216 @itemx -malign-power
7217 @opindex malign-natural
7218 @opindex malign-power
7219 On AIX, Darwin, and 64-bit PowerPC GNU/Linux, the option
7220 @option{-malign-natural} overrides the ABI-defined alignment of larger
7221 types, such as floating-point doubles, on their natural size-based boundary.
7222 The option @option{-malign-power} instructs GCC to follow the ABI-specified
7223 alignment rules. GCC defaults to the standard alignment defined in the ABI.
7227 @opindex msoft-float
7228 @opindex mhard-float
7229 Generate code that does not use (uses) the floating-point register set.
7230 Software floating point emulation is provided if you use the
7231 @option{-msoft-float} option, and pass the option to GCC when linking.
7234 @itemx -mno-multiple
7236 @opindex mno-multiple
7237 Generate code that uses (does not use) the load multiple word
7238 instructions and the store multiple word instructions. These
7239 instructions are generated by default on POWER systems, and not
7240 generated on PowerPC systems. Do not use @option{-mmultiple} on little
7241 endian PowerPC systems, since those instructions do not work when the
7242 processor is in little endian mode. The exceptions are PPC740 and
7243 PPC750 which permit the instructions usage in little endian mode.
7249 Generate code that uses (does not use) the load string instructions
7250 and the store string word instructions to save multiple registers and
7251 do small block moves. These instructions are generated by default on
7252 POWER systems, and not generated on PowerPC systems. Do not use
7253 @option{-mstring} on little endian PowerPC systems, since those
7254 instructions do not work when the processor is in little endian mode.
7255 The exceptions are PPC740 and PPC750 which permit the instructions
7256 usage in little endian mode.
7262 Generate code that uses (does not use) the load or store instructions
7263 that update the base register to the address of the calculated memory
7264 location. These instructions are generated by default. If you use
7265 @option{-mno-update}, there is a small window between the time that the
7266 stack pointer is updated and the address of the previous frame is
7267 stored, which means code that walks the stack frame across interrupts or
7268 signals may get corrupted data.
7271 @itemx -mno-fused-madd
7272 @opindex mfused-madd
7273 @opindex mno-fused-madd
7274 Generate code that uses (does not use) the floating point multiply and
7275 accumulate instructions. These instructions are generated by default if
7276 hardware floating is used.
7278 @item -mno-bit-align
7280 @opindex mno-bit-align
7282 On System V.4 and embedded PowerPC systems do not (do) force structures
7283 and unions that contain bit-fields to be aligned to the base type of the
7286 For example, by default a structure containing nothing but 8
7287 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
7288 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
7289 the structure would be aligned to a 1 byte boundary and be one byte in
7292 @item -mno-strict-align
7293 @itemx -mstrict-align
7294 @opindex mno-strict-align
7295 @opindex mstrict-align
7296 On System V.4 and embedded PowerPC systems do not (do) assume that
7297 unaligned memory references will be handled by the system.
7300 @itemx -mno-relocatable
7301 @opindex mrelocatable
7302 @opindex mno-relocatable
7303 On embedded PowerPC systems generate code that allows (does not allow)
7304 the program to be relocated to a different address at runtime. If you
7305 use @option{-mrelocatable} on any module, all objects linked together must
7306 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
7308 @item -mrelocatable-lib
7309 @itemx -mno-relocatable-lib
7310 @opindex mrelocatable-lib
7311 @opindex mno-relocatable-lib
7312 On embedded PowerPC systems generate code that allows (does not allow)
7313 the program to be relocated to a different address at runtime. Modules
7314 compiled with @option{-mrelocatable-lib} can be linked with either modules
7315 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
7316 with modules compiled with the @option{-mrelocatable} options.
7322 On System V.4 and embedded PowerPC systems do not (do) assume that
7323 register 2 contains a pointer to a global area pointing to the addresses
7324 used in the program.
7327 @itemx -mlittle-endian
7329 @opindex mlittle-endian
7330 On System V.4 and embedded PowerPC systems compile code for the
7331 processor in little endian mode. The @option{-mlittle-endian} option is
7332 the same as @option{-mlittle}.
7337 @opindex mbig-endian
7338 On System V.4 and embedded PowerPC systems compile code for the
7339 processor in big endian mode. The @option{-mbig-endian} option is
7340 the same as @option{-mbig}.
7342 @item -mdynamic-no-pic
7343 @opindex mdynamic-no-pic
7344 On Darwin and Mac OS X systems, compile code so that it is not
7345 relocatable, but that its external references are relocatable. The
7346 resulting code is suitable for applications, but not shared
7349 @item -mprioritize-restricted-insns=@var{priority}
7350 @opindex mprioritize-restricted-insns
7351 This option controls the priority that is assigned to
7352 dispatch-slot restricted instructions during the second scheduling
7353 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
7354 @var{no/highest/second-highest} priority to dispatch slot restricted
7357 @item -msched-costly-dep=@var{dependence_type}
7358 @opindex msched-costly-dep
7359 This option controls which dependences are considered costly
7360 by the target during instruction scheduling. The argument
7361 @var{dependence_type} takes one of the following values:
7362 @var{no}: no dependence is costly,
7363 @var{all}: all dependences are costly,
7364 @var{true_store_to_load}: a true dependence from store to load is costly,
7365 @var{store_to_load}: any dependence from store to load is costly,
7366 @var{number}: any dependence which latency >= @var{number} is costly.
7368 @item -minsert-sched-nops=@var{scheme}
7369 @opindex minsert-sched-nops
7370 This option controls which nop insertion scheme will be used during
7371 the second scheduling pass. The argument @var{scheme} takes one of the
7373 @var{no}: Don't insert nops.
7374 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
7375 according to the scheduler's grouping.
7376 @var{regroup_exact}: Insert nops to force costly dependent insns into
7377 separate groups. Insert exactly as many nops as needed to force an insn
7378 to a new group, according to the estimated processor grouping.
7379 @var{number}: Insert nops to force costly dependent insns into
7380 separate groups. Insert @var{number} nops to force an insn to a new group.
7384 On System V.4 and embedded PowerPC systems compile code using calling
7385 conventions that adheres to the March 1995 draft of the System V
7386 Application Binary Interface, PowerPC processor supplement. This is the
7387 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
7389 @item -mcall-sysv-eabi
7390 @opindex mcall-sysv-eabi
7391 Specify both @option{-mcall-sysv} and @option{-meabi} options.
7393 @item -mcall-sysv-noeabi
7394 @opindex mcall-sysv-noeabi
7395 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
7397 @item -mcall-solaris
7398 @opindex mcall-solaris
7399 On System V.4 and embedded PowerPC systems compile code for the Solaris
7403 @opindex mcall-linux
7404 On System V.4 and embedded PowerPC systems compile code for the
7405 Linux-based GNU system.
7409 On System V.4 and embedded PowerPC systems compile code for the
7410 Hurd-based GNU system.
7413 @opindex mcall-netbsd
7414 On System V.4 and embedded PowerPC systems compile code for the
7415 NetBSD operating system.
7417 @item -maix-struct-return
7418 @opindex maix-struct-return
7419 Return all structures in memory (as specified by the AIX ABI)@.
7421 @item -msvr4-struct-return
7422 @opindex msvr4-struct-return
7423 Return structures smaller than 8 bytes in registers (as specified by the
7427 @opindex mabi=altivec
7428 Extend the current ABI with AltiVec ABI extensions. This does not
7429 change the default ABI, instead it adds the AltiVec ABI extensions to
7432 @item -mabi=no-altivec
7433 @opindex mabi=no-altivec
7434 Disable AltiVec ABI extensions for the current ABI.
7437 @itemx -mno-prototype
7439 @opindex mno-prototype
7440 On System V.4 and embedded PowerPC systems assume that all calls to
7441 variable argument functions are properly prototyped. Otherwise, the
7442 compiler must insert an instruction before every non prototyped call to
7443 set or clear bit 6 of the condition code register (@var{CR}) to
7444 indicate whether floating point values were passed in the floating point
7445 registers in case the function takes a variable arguments. With
7446 @option{-mprototype}, only calls to prototyped variable argument functions
7447 will set or clear the bit.
7451 On embedded PowerPC systems, assume that the startup module is called
7452 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
7453 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
7458 On embedded PowerPC systems, assume that the startup module is called
7459 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
7464 On embedded PowerPC systems, assume that the startup module is called
7465 @file{crt0.o} and the standard C libraries are @file{libads.a} and
7469 @opindex myellowknife
7470 On embedded PowerPC systems, assume that the startup module is called
7471 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
7476 On System V.4 and embedded PowerPC systems, specify that you are
7477 compiling for a VxWorks system.
7481 Specify that you are compiling for the WindISS simulation environment.
7485 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
7486 header to indicate that @samp{eabi} extended relocations are used.
7492 On System V.4 and embedded PowerPC systems do (do not) adhere to the
7493 Embedded Applications Binary Interface (eabi) which is a set of
7494 modifications to the System V.4 specifications. Selecting @option{-meabi}
7495 means that the stack is aligned to an 8 byte boundary, a function
7496 @code{__eabi} is called to from @code{main} to set up the eabi
7497 environment, and the @option{-msdata} option can use both @code{r2} and
7498 @code{r13} to point to two separate small data areas. Selecting
7499 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
7500 do not call an initialization function from @code{main}, and the
7501 @option{-msdata} option will only use @code{r13} to point to a single
7502 small data area. The @option{-meabi} option is on by default if you
7503 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
7506 @opindex msdata=eabi
7507 On System V.4 and embedded PowerPC systems, put small initialized
7508 @code{const} global and static data in the @samp{.sdata2} section, which
7509 is pointed to by register @code{r2}. Put small initialized
7510 non-@code{const} global and static data in the @samp{.sdata} section,
7511 which is pointed to by register @code{r13}. Put small uninitialized
7512 global and static data in the @samp{.sbss} section, which is adjacent to
7513 the @samp{.sdata} section. The @option{-msdata=eabi} option is
7514 incompatible with the @option{-mrelocatable} option. The
7515 @option{-msdata=eabi} option also sets the @option{-memb} option.
7518 @opindex msdata=sysv
7519 On System V.4 and embedded PowerPC systems, put small global and static
7520 data in the @samp{.sdata} section, which is pointed to by register
7521 @code{r13}. Put small uninitialized global and static data in the
7522 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7523 The @option{-msdata=sysv} option is incompatible with the
7524 @option{-mrelocatable} option.
7526 @item -msdata=default
7528 @opindex msdata=default
7530 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7531 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7532 same as @option{-msdata=sysv}.
7535 @opindex msdata-data
7536 On System V.4 and embedded PowerPC systems, put small global and static
7537 data in the @samp{.sdata} section. Put small uninitialized global and
7538 static data in the @samp{.sbss} section. Do not use register @code{r13}
7539 to address small data however. This is the default behavior unless
7540 other @option{-msdata} options are used.
7544 @opindex msdata=none
7546 On embedded PowerPC systems, put all initialized global and static data
7547 in the @samp{.data} section, and all uninitialized data in the
7548 @samp{.bss} section.
7552 @cindex smaller data references (PowerPC)
7553 @cindex .sdata/.sdata2 references (PowerPC)
7554 On embedded PowerPC systems, put global and static items less than or
7555 equal to @var{num} bytes into the small data or bss sections instead of
7556 the normal data or bss section. By default, @var{num} is 8. The
7557 @option{-G @var{num}} switch is also passed to the linker.
7558 All modules should be compiled with the same @option{-G @var{num}} value.
7561 @itemx -mno-regnames
7563 @opindex mno-regnames
7564 On System V.4 and embedded PowerPC systems do (do not) emit register
7565 names in the assembly language output using symbolic forms.
7568 @itemx -mno-longcall
7570 @opindex mno-longcall
7571 Default to making all function calls via pointers, so that functions
7572 which reside further than 64 megabytes (67,108,864 bytes) from the
7573 current location can be called. This setting can be overridden by the
7574 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7576 Some linkers are capable of detecting out-of-range calls and generating
7577 glue code on the fly. On these systems, long calls are unnecessary and
7578 generate slower code. As of this writing, the AIX linker can do this,
7579 as can the GNU linker for PowerPC/64. It is planned to add this feature
7580 to the GNU linker for 32-bit PowerPC systems as well.
7582 On Mach-O (Darwin) systems, this option directs the compiler emit to
7583 the glue for every direct call, and the Darwin linker decides whether
7584 to use or discard it.
7586 In the future, we may cause GCC to ignore all longcall specifications
7587 when the linker is known to generate glue.
7591 Adds support for multithreading with the @dfn{pthreads} library.
7592 This option sets flags for both the preprocessor and linker.
7596 @node Darwin Options
7597 @subsection Darwin Options
7598 @cindex Darwin options
7600 These options are defined for all architectures running the Darwin operating
7601 system. They are useful for compatibility with other Mac OS compilers.
7606 Loads all members of static archive libraries.
7607 See man ld(1) for more information.
7609 @item -arch_errors_fatal
7610 @opindex arch_errors_fatal
7611 Cause the errors having to do with files that have the wrong architecture
7615 @opindex bind_at_load
7616 Causes the output file to be marked such that the dynamic linker will
7617 bind all undefined references when the file is loaded or launched.
7621 Produce a Mach-o bundle format file.
7622 See man ld(1) for more information.
7624 @item -bundle_loader @var{executable}
7625 @opindex bundle_loader
7626 This specifies the @var{executable} that will be loading the build
7627 output file being linked. See man ld(1) for more information.
7629 @item -allowable_client @var{client_name}
7633 @itemx -compatibility_version
7634 @itemx -current_version
7635 @itemx -dependency-file
7637 @itemx -dylinker_install_name
7640 @itemx -exported_symbols_list
7642 @itemx -flat_namespace
7643 @itemx -force_cpusubtype_ALL
7644 @itemx -force_flat_namespace
7645 @itemx -headerpad_max_install_names
7648 @itemx -install_name
7649 @itemx -keep_private_externs
7650 @itemx -multi_module
7651 @itemx -multiply_defined
7652 @itemx -multiply_defined_unused
7654 @itemx -nofixprebinding
7657 @itemx -noseglinkedit
7658 @itemx -pagezero_size
7660 @itemx -prebind_all_twolevel_modules
7661 @itemx -private_bundle
7662 @itemx -read_only_relocs
7664 @itemx -sectobjectsymbols
7668 @itemx -sectobjectsymbols
7670 @itemx -seg_addr_table
7671 @itemx -seg_addr_table_filename
7674 @itemx -segs_read_only_addr
7675 @itemx -segs_read_write_addr
7676 @itemx -single_module
7679 @itemx -sub_umbrella
7680 @itemx -twolevel_namespace
7683 @itemx -unexported_symbols_list
7684 @itemx -weak_reference_mismatches
7687 @opindex allowable_client
7689 @opindex client_name
7690 @opindex compatibility_version
7691 @opindex current_version
7692 @opindex dependency-file
7694 @opindex dylinker_install_name
7697 @opindex exported_symbols_list
7699 @opindex flat_namespace
7700 @opindex force_cpusubtype_ALL
7701 @opindex force_flat_namespace
7702 @opindex headerpad_max_install_names
7705 @opindex install_name
7706 @opindex keep_private_externs
7707 @opindex multi_module
7708 @opindex multiply_defined
7709 @opindex multiply_defined_unused
7711 @opindex nofixprebinding
7712 @opindex nomultidefs
7714 @opindex noseglinkedit
7715 @opindex pagezero_size
7717 @opindex prebind_all_twolevel_modules
7718 @opindex private_bundle
7719 @opindex read_only_relocs
7721 @opindex sectobjectsymbols
7725 @opindex sectobjectsymbols
7727 @opindex seg_addr_table
7728 @opindex seg_addr_table_filename
7729 @opindex seglinkedit
7731 @opindex segs_read_only_addr
7732 @opindex segs_read_write_addr
7733 @opindex single_module
7735 @opindex sub_library
7736 @opindex sub_umbrella
7737 @opindex twolevel_namespace
7740 @opindex unexported_symbols_list
7741 @opindex weak_reference_mismatches
7742 @opindex whatsloaded
7744 These options are available for Darwin linker. Darwin linker man page
7745 describes them in detail.
7750 @subsection MIPS Options
7751 @cindex MIPS options
7757 Generate big-endian code.
7761 Generate little-endian code. This is the default for @samp{mips*el-*-*}
7764 @item -march=@var{arch}
7766 Generate code that will run on @var{arch}, which can be the name of a
7767 generic MIPS ISA, or the name of a particular processor.
7769 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
7770 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
7771 The processor names are:
7772 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
7774 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
7775 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, @samp{rm7000},
7779 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4300},
7780 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
7781 The special value @samp{from-abi} selects the
7782 most compatible architecture for the selected ABI (that is,
7783 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
7785 In processor names, a final @samp{000} can be abbreviated as @samp{k}
7786 (for example, @samp{-march=r2k}). Prefixes are optional, and
7787 @samp{vr} may be written @samp{r}.
7789 GCC defines two macros based on the value of this option. The first
7790 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
7791 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
7792 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
7793 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
7794 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
7796 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
7797 above. In other words, it will have the full prefix and will not
7798 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
7799 the macro names the resolved architecture (either @samp{"mips1"} or
7800 @samp{"mips3"}). It names the default architecture when no
7801 @option{-march} option is given.
7803 @item -mtune=@var{arch}
7805 Optimize for @var{arch}. Among other things, this option controls
7806 the way instructions are scheduled, and the perceived cost of arithmetic
7807 operations. The list of @var{arch} values is the same as for
7810 When this option is not used, GCC will optimize for the processor
7811 specified by @option{-march}. By using @option{-march} and
7812 @option{-mtune} together, it is possible to generate code that will
7813 run on a family of processors, but optimize the code for one
7814 particular member of that family.
7816 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
7817 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
7818 @samp{-march} ones described above.
7822 Equivalent to @samp{-march=mips1}.
7826 Equivalent to @samp{-march=mips2}.
7830 Equivalent to @samp{-march=mips3}.
7834 Equivalent to @samp{-march=mips4}.
7838 Equivalent to @samp{-march=mips32}.
7842 Equivalent to @samp{-march=mips32r2}.
7846 Equivalent to @samp{-march=mips64}.
7852 Use (do not use) the MIPS16 ISA.
7864 Generate code for the given ABI@.
7866 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
7867 generates 64-bit code when you select a 64-bit architecture, but you
7868 can use @option{-mgp32} to get 32-bit code instead.
7871 @itemx -mno-abicalls
7873 @opindex mno-abicalls
7874 Generate (do not generate) SVR4-style position-independent code.
7875 @option{-mabicalls} is the default for SVR4-based systems.
7881 Lift (do not lift) the usual restrictions on the size of the global
7884 GCC normally uses a single instruction to load values from the GOT.
7885 While this is relatively efficient, it will only work if the GOT
7886 is smaller than about 64k. Anything larger will cause the linker
7887 to report an error such as:
7889 @cindex relocation truncated to fit (MIPS)
7891 relocation truncated to fit: R_MIPS_GOT16 foobar
7894 If this happens, you should recompile your code with @option{-mxgot}.
7895 It should then work with very large GOTs, although it will also be
7896 less efficient, since it will take three instructions to fetch the
7897 value of a global symbol.
7899 Note that some linkers can create multiple GOTs. If you have such a
7900 linker, you should only need to use @option{-mxgot} when a single object
7901 file accesses more than 64k's worth of GOT entries. Very few do.
7903 These options have no effect unless GCC is generating position
7906 @item -membedded-pic
7907 @itemx -mno-embedded-pic
7908 @opindex membedded-pic
7909 @opindex mno-embedded-pic
7910 Generate (do not generate) position-independent code suitable for some
7911 embedded systems. All calls are made using PC relative addresses, and
7912 all data is addressed using the $gp register. No more than 65536
7913 bytes of global data may be used. This requires GNU as and GNU ld,
7914 which do most of the work.
7918 Assume that general-purpose registers are 32 bits wide.
7922 Assume that general-purpose registers are 64 bits wide.
7926 Assume that floating-point registers are 32 bits wide.
7930 Assume that floating-point registers are 64 bits wide.
7933 @opindex mhard-float
7934 Use floating-point coprocessor instructions.
7937 @opindex msoft-float
7938 Do not use floating-point coprocessor instructions. Implement
7939 floating-point calculations using library calls instead.
7941 @item -msingle-float
7942 @opindex msingle-float
7943 Assume that the floating-point coprocessor only supports single-precision
7946 @itemx -mdouble-float
7947 @opindex mdouble-float
7948 Assume that the floating-point coprocessor supports double-precision
7949 operations. This is the default.
7953 Force @code{int} and @code{long} types to be 64 bits wide. See
7954 @option{-mlong32} for an explanation of the default and the way
7955 that the pointer size is determined.
7959 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
7960 an explanation of the default and the way that the pointer size is
7965 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
7967 The default size of @code{int}s, @code{long}s and pointers depends on
7968 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
7969 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
7970 32-bit @code{long}s. Pointers are the same size as @code{long}s,
7971 or the same size as integer registers, whichever is smaller.
7975 @cindex smaller data references (MIPS)
7976 @cindex gp-relative references (MIPS)
7977 Put global and static items less than or equal to @var{num} bytes into
7978 the small data or bss section instead of the normal data or bss section.
7979 This allows the data to be accessed using a single instruction.
7981 All modules should be compiled with the same @option{-G @var{num}}
7984 @item -membedded-data
7985 @itemx -mno-embedded-data
7986 @opindex membedded-data
7987 @opindex mno-embedded-data
7988 Allocate variables to the read-only data section first if possible, then
7989 next in the small data section if possible, otherwise in data. This gives
7990 slightly slower code than the default, but reduces the amount of RAM required
7991 when executing, and thus may be preferred for some embedded systems.
7993 @item -muninit-const-in-rodata
7994 @itemx -mno-uninit-const-in-rodata
7995 @opindex muninit-const-in-rodata
7996 @opindex mno-uninit-const-in-rodata
7997 Put uninitialized @code{const} variables in the read-only data section.
7998 This option is only meaningful in conjunction with @option{-membedded-data}.
8000 @item -msplit-addresses
8001 @itemx -mno-split-addresses
8002 @opindex msplit-addresses
8003 @opindex mno-split-addresses
8004 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
8005 relocation operators. This option has been superceded by
8006 @option{-mexplicit-relocs} but is retained for backwards compatibility.
8008 @item -mexplicit-relocs
8009 @itemx -mno-explicit-relocs
8010 @opindex mexplicit-relocs
8011 @opindex mno-explicit-relocs
8012 Use (do not use) assembler relocation operators when dealing with symbolic
8013 addresses. The alternative, selected by @option{-mno-explicit-relocs},
8014 is to use assembler macros instead.
8016 @option{-mexplicit-relocs} is usually the default if GCC was
8017 configured to use an assembler that supports relocation operators.
8018 However, there are two exceptions:
8022 GCC is not yet able to generate explicit relocations for the combination
8023 of @option{-mabi=64} and @option{-mno-abicalls}. This will be addressed
8024 in a future release.
8027 The combination of @option{-mabicalls} and @option{-fno-unit-at-a-time}
8028 implies @option{-mno-explicit-relocs} unless explicitly overridden.
8029 This is because, when generating abicalls, the choice of relocation
8030 depends on whether a symbol is local or global. In some rare cases,
8031 GCC will not be able to decide this until the whole compilation unit
8039 Generate (do not generate) code that refers to registers using their
8040 software names. The default is @option{-mno-rnames}, which tells GCC
8041 to use hardware names like @samp{$4} instead of software names like
8042 @samp{a0}. The only assembler known to support @option{-rnames} is
8043 the Algorithmics assembler.
8045 @item -mcheck-zero-division
8046 @itemx -mno-check-zero-division
8047 @opindex mcheck-zero-division
8048 @opindex mno-check-zero-division
8049 Trap (do not trap) on integer division by zero. The default is
8050 @option{-mcheck-zero-division}.
8056 Force (do not force) the use of @code{memcpy()} for non-trivial block
8057 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
8058 most constant-sized copies.
8061 @itemx -mno-long-calls
8062 @opindex mlong-calls
8063 @opindex mno-long-calls
8064 Disable (do not disable) use of the @code{jal} instruction. Calling
8065 functions using @code{jal} is more efficient but requires the caller
8066 and callee to be in the same 256 megabyte segment.
8068 This option has no effect on abicalls code. The default is
8069 @option{-mno-long-calls}.
8075 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
8076 instructions, as provided by the R4650 ISA.
8079 @itemx -mno-fused-madd
8080 @opindex mfused-madd
8081 @opindex mno-fused-madd
8082 Enable (disable) use of the floating point multiply-accumulate
8083 instructions, when they are available. The default is
8084 @option{-mfused-madd}.
8086 When multiply-accumulate instructions are used, the intermediate
8087 product is calculated to infinite precision and is not subject to
8088 the FCSR Flush to Zero bit. This may be undesirable in some
8093 Tell the MIPS assembler to not run its preprocessor over user
8094 assembler files (with a @samp{.s} suffix) when assembling them.
8099 Work around certain SB-1 CPU core errata.
8100 (This flag currently works around the SB-1 revision 2
8101 ``F1'' and ``F2'' floating point errata.)
8103 @item -mflush-func=@var{func}
8104 @itemx -mno-flush-func
8105 @opindex mflush-func
8106 Specifies the function to call to flush the I and D caches, or to not
8107 call any such function. If called, the function must take the same
8108 arguments as the common @code{_flush_func()}, that is, the address of the
8109 memory range for which the cache is being flushed, the size of the
8110 memory range, and the number 3 (to flush both caches). The default
8111 depends on the target GCC was configured for, but commonly is either
8112 @samp{_flush_func} or @samp{__cpu_flush}.
8114 @item -mbranch-likely
8115 @itemx -mno-branch-likely
8116 @opindex mbranch-likely
8117 @opindex mno-branch-likely
8118 Enable or disable use of Branch Likely instructions, regardless of the
8119 default for the selected architecture. By default, Branch Likely
8120 instructions may be generated if they are supported by the selected
8121 architecture. An exception is for the MIPS32 and MIPS64 architectures
8122 and processors which implement those architectures; for those, Branch
8123 Likely instructions will not be generated by default because the MIPS32
8124 and MIPS64 architectures specifically deprecate their use.
8127 @node i386 and x86-64 Options
8128 @subsection Intel 386 and AMD x86-64 Options
8129 @cindex i386 Options
8130 @cindex x86-64 Options
8131 @cindex Intel 386 Options
8132 @cindex AMD x86-64 Options
8134 These @samp{-m} options are defined for the i386 and x86-64 family of
8138 @item -mtune=@var{cpu-type}
8140 Tune to @var{cpu-type} everything applicable about the generated code, except
8141 for the ABI and the set of available instructions. The choices for
8145 Original Intel's i386 CPU.
8147 Intel's i486 CPU. (No scheduling is implemented for this chip.)
8149 Intel Pentium CPU with no MMX support.
8151 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
8152 @item i686, pentiumpro
8153 Intel PentiumPro CPU.
8155 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
8156 @item pentium3, pentium3m
8157 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
8160 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
8161 support. Used by Centrino notebooks.
8162 @item pentium4, pentium4m
8163 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
8165 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
8168 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
8169 SSE2 and SSE3 instruction set support.
8171 AMD K6 CPU with MMX instruction set support.
8173 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
8174 @item athlon, athlon-tbird
8175 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
8177 @item athlon-4, athlon-xp, athlon-mp
8178 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
8179 instruction set support.
8180 @item k8, opteron, athlon64, athlon-fx
8181 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
8182 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
8184 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
8187 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
8188 instruction set support.
8190 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
8191 implemented for this chip.)
8193 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
8194 implemented for this chip.)
8197 While picking a specific @var{cpu-type} will schedule things appropriately
8198 for that particular chip, the compiler will not generate any code that
8199 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8202 @item -march=@var{cpu-type}
8204 Generate instructions for the machine type @var{cpu-type}. The choices
8205 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8206 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8208 @item -mcpu=@var{cpu-type}
8210 A deprecated synonym for @option{-mtune}.
8219 @opindex mpentiumpro
8220 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8221 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8222 These synonyms are deprecated.
8224 @item -mfpmath=@var{unit}
8226 Generate floating point arithmetics for selected unit @var{unit}. The choices
8231 Use the standard 387 floating point coprocessor present majority of chips and
8232 emulated otherwise. Code compiled with this option will run almost everywhere.
8233 The temporary results are computed in 80bit precision instead of precision
8234 specified by the type resulting in slightly different results compared to most
8235 of other chips. See @option{-ffloat-store} for more detailed description.
8237 This is the default choice for i386 compiler.
8240 Use scalar floating point instructions present in the SSE instruction set.
8241 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8242 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8243 instruction set supports only single precision arithmetics, thus the double and
8244 extended precision arithmetics is still done using 387. Later version, present
8245 only in Pentium4 and the future AMD x86-64 chips supports double precision
8248 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8249 @option{-msse2} switches to enable SSE extensions and make this option
8250 effective. For x86-64 compiler, these extensions are enabled by default.
8252 The resulting code should be considerably faster in the majority of cases and avoid
8253 the numerical instability problems of 387 code, but may break some existing
8254 code that expects temporaries to be 80bit.
8256 This is the default choice for the x86-64 compiler.
8259 Attempt to utilize both instruction sets at once. This effectively double the
8260 amount of available registers and on chips with separate execution units for
8261 387 and SSE the execution resources too. Use this option with care, as it is
8262 still experimental, because the GCC register allocator does not model separate
8263 functional units well resulting in instable performance.
8266 @item -masm=@var{dialect}
8267 @opindex masm=@var{dialect}
8268 Output asm instructions using selected @var{dialect}. Supported choices are
8269 @samp{intel} or @samp{att} (the default one).
8274 @opindex mno-ieee-fp
8275 Control whether or not the compiler uses IEEE floating point
8276 comparisons. These handle correctly the case where the result of a
8277 comparison is unordered.
8280 @opindex msoft-float
8281 Generate output containing library calls for floating point.
8282 @strong{Warning:} the requisite libraries are not part of GCC@.
8283 Normally the facilities of the machine's usual C compiler are used, but
8284 this can't be done directly in cross-compilation. You must make your
8285 own arrangements to provide suitable library functions for
8288 On machines where a function returns floating point results in the 80387
8289 register stack, some floating point opcodes may be emitted even if
8290 @option{-msoft-float} is used.
8292 @item -mno-fp-ret-in-387
8293 @opindex mno-fp-ret-in-387
8294 Do not use the FPU registers for return values of functions.
8296 The usual calling convention has functions return values of types
8297 @code{float} and @code{double} in an FPU register, even if there
8298 is no FPU@. The idea is that the operating system should emulate
8301 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8302 in ordinary CPU registers instead.
8304 @item -mno-fancy-math-387
8305 @opindex mno-fancy-math-387
8306 Some 387 emulators do not support the @code{sin}, @code{cos} and
8307 @code{sqrt} instructions for the 387. Specify this option to avoid
8308 generating those instructions. This option is the default on FreeBSD,
8309 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8310 indicates that the target cpu will always have an FPU and so the
8311 instruction will not need emulation. As of revision 2.6.1, these
8312 instructions are not generated unless you also use the
8313 @option{-funsafe-math-optimizations} switch.
8315 @item -malign-double
8316 @itemx -mno-align-double
8317 @opindex malign-double
8318 @opindex mno-align-double
8319 Control whether GCC aligns @code{double}, @code{long double}, and
8320 @code{long long} variables on a two word boundary or a one word
8321 boundary. Aligning @code{double} variables on a two word boundary will
8322 produce code that runs somewhat faster on a @samp{Pentium} at the
8323 expense of more memory.
8325 @strong{Warning:} if you use the @option{-malign-double} switch,
8326 structures containing the above types will be aligned differently than
8327 the published application binary interface specifications for the 386
8328 and will not be binary compatible with structures in code compiled
8329 without that switch.
8331 @item -m96bit-long-double
8332 @itemx -m128bit-long-double
8333 @opindex m96bit-long-double
8334 @opindex m128bit-long-double
8335 These switches control the size of @code{long double} type. The i386
8336 application binary interface specifies the size to be 96 bits,
8337 so @option{-m96bit-long-double} is the default in 32 bit mode.
8339 Modern architectures (Pentium and newer) would prefer @code{long double}
8340 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8341 conforming to the ABI, this would not be possible. So specifying a
8342 @option{-m128bit-long-double} will align @code{long double}
8343 to a 16 byte boundary by padding the @code{long double} with an additional
8346 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8347 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8349 Notice that neither of these options enable any extra precision over the x87
8350 standard of 80 bits for a @code{long double}.
8352 @strong{Warning:} if you override the default value for your target ABI, the
8353 structures and arrays containing @code{long double} variables will change
8354 their size as well as function calling convention for function taking
8355 @code{long double} will be modified. Hence they will not be binary
8356 compatible with arrays or structures in code compiled without that switch.
8360 @itemx -mno-svr3-shlib
8361 @opindex msvr3-shlib
8362 @opindex mno-svr3-shlib
8363 Control whether GCC places uninitialized local variables into the
8364 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8365 into @code{bss}. These options are meaningful only on System V Release 3.
8369 Use a different function-calling convention, in which functions that
8370 take a fixed number of arguments return with the @code{ret} @var{num}
8371 instruction, which pops their arguments while returning. This saves one
8372 instruction in the caller since there is no need to pop the arguments
8375 You can specify that an individual function is called with this calling
8376 sequence with the function attribute @samp{stdcall}. You can also
8377 override the @option{-mrtd} option by using the function attribute
8378 @samp{cdecl}. @xref{Function Attributes}.
8380 @strong{Warning:} this calling convention is incompatible with the one
8381 normally used on Unix, so you cannot use it if you need to call
8382 libraries compiled with the Unix compiler.
8384 Also, you must provide function prototypes for all functions that
8385 take variable numbers of arguments (including @code{printf});
8386 otherwise incorrect code will be generated for calls to those
8389 In addition, seriously incorrect code will result if you call a
8390 function with too many arguments. (Normally, extra arguments are
8391 harmlessly ignored.)
8393 @item -mregparm=@var{num}
8395 Control how many registers are used to pass integer arguments. By
8396 default, no registers are used to pass arguments, and at most 3
8397 registers can be used. You can control this behavior for a specific
8398 function by using the function attribute @samp{regparm}.
8399 @xref{Function Attributes}.
8401 @strong{Warning:} if you use this switch, and
8402 @var{num} is nonzero, then you must build all modules with the same
8403 value, including any libraries. This includes the system libraries and
8406 @item -mpreferred-stack-boundary=@var{num}
8407 @opindex mpreferred-stack-boundary
8408 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8409 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8410 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8411 size (@option{-Os}), in which case the default is the minimum correct
8412 alignment (4 bytes for x86, and 8 bytes for x86-64).
8414 On Pentium and PentiumPro, @code{double} and @code{long double} values
8415 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8416 suffer significant run time performance penalties. On Pentium III, the
8417 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8418 penalties if it is not 16 byte aligned.
8420 To ensure proper alignment of this values on the stack, the stack boundary
8421 must be as aligned as that required by any value stored on the stack.
8422 Further, every function must be generated such that it keeps the stack
8423 aligned. Thus calling a function compiled with a higher preferred
8424 stack boundary from a function compiled with a lower preferred stack
8425 boundary will most likely misalign the stack. It is recommended that
8426 libraries that use callbacks always use the default setting.
8428 This extra alignment does consume extra stack space, and generally
8429 increases code size. Code that is sensitive to stack space usage, such
8430 as embedded systems and operating system kernels, may want to reduce the
8431 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8449 These switches enable or disable the use of built-in functions that allow
8450 direct access to the MMX, SSE, SSE2, SSE3 and 3Dnow extensions of the
8453 @xref{X86 Built-in Functions}, for details of the functions enabled
8454 and disabled by these switches.
8456 To have SSE/SSE2 instructions generated automatically from floating-point
8457 code, see @option{-mfpmath=sse}.
8460 @itemx -mno-push-args
8462 @opindex mno-push-args
8463 Use PUSH operations to store outgoing parameters. This method is shorter
8464 and usually equally fast as method using SUB/MOV operations and is enabled
8465 by default. In some cases disabling it may improve performance because of
8466 improved scheduling and reduced dependencies.
8468 @item -maccumulate-outgoing-args
8469 @opindex maccumulate-outgoing-args
8470 If enabled, the maximum amount of space required for outgoing arguments will be
8471 computed in the function prologue. This is faster on most modern CPUs
8472 because of reduced dependencies, improved scheduling and reduced stack usage
8473 when preferred stack boundary is not equal to 2. The drawback is a notable
8474 increase in code size. This switch implies @option{-mno-push-args}.
8478 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8479 on thread-safe exception handling must compile and link all code with the
8480 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8481 @option{-D_MT}; when linking, it links in a special thread helper library
8482 @option{-lmingwthrd} which cleans up per thread exception handling data.
8484 @item -mno-align-stringops
8485 @opindex mno-align-stringops
8486 Do not align destination of inlined string operations. This switch reduces
8487 code size and improves performance in case the destination is already aligned,
8488 but GCC doesn't know about it.
8490 @item -minline-all-stringops
8491 @opindex minline-all-stringops
8492 By default GCC inlines string operations only when destination is known to be
8493 aligned at least to 4 byte boundary. This enables more inlining, increase code
8494 size, but may improve performance of code that depends on fast memcpy, strlen
8495 and memset for short lengths.
8497 @item -momit-leaf-frame-pointer
8498 @opindex momit-leaf-frame-pointer
8499 Don't keep the frame pointer in a register for leaf functions. This
8500 avoids the instructions to save, set up and restore frame pointers and
8501 makes an extra register available in leaf functions. The option
8502 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8503 which might make debugging harder.
8505 @item -mtls-direct-seg-refs
8506 @itemx -mno-tls-direct-seg-refs
8507 @opindex mtls-direct-seg-refs
8508 Controls whether TLS variables may be accessed with offsets from the
8509 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8510 or whether the thread base pointer must be added. Whether or not this
8511 is legal depends on the operating system, and whether it maps the
8512 segment to cover the entire TLS area.
8514 For systems that use GNU libc, the default is on.
8517 These @samp{-m} switches are supported in addition to the above
8518 on AMD x86-64 processors in 64-bit environments.
8525 Generate code for a 32-bit or 64-bit environment.
8526 The 32-bit environment sets int, long and pointer to 32 bits and
8527 generates code that runs on any i386 system.
8528 The 64-bit environment sets int to 32 bits and long and pointer
8529 to 64 bits and generates code for AMD's x86-64 architecture.
8532 @opindex no-red-zone
8533 Do not use a so called red zone for x86-64 code. The red zone is mandated
8534 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8535 stack pointer that will not be modified by signal or interrupt handlers
8536 and therefore can be used for temporary data without adjusting the stack
8537 pointer. The flag @option{-mno-red-zone} disables this red zone.
8539 @item -mcmodel=small
8540 @opindex mcmodel=small
8541 Generate code for the small code model: the program and its symbols must
8542 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8543 Programs can be statically or dynamically linked. This is the default
8546 @item -mcmodel=kernel
8547 @opindex mcmodel=kernel
8548 Generate code for the kernel code model. The kernel runs in the
8549 negative 2 GB of the address space.
8550 This model has to be used for Linux kernel code.
8552 @item -mcmodel=medium
8553 @opindex mcmodel=medium
8554 Generate code for the medium model: The program is linked in the lower 2
8555 GB of the address space but symbols can be located anywhere in the
8556 address space. Programs can be statically or dynamically linked, but
8557 building of shared libraries are not supported with the medium model.
8559 @item -mcmodel=large
8560 @opindex mcmodel=large
8561 Generate code for the large model: This model makes no assumptions
8562 about addresses and sizes of sections. Currently GCC does not implement
8567 @subsection HPPA Options
8568 @cindex HPPA Options
8570 These @samp{-m} options are defined for the HPPA family of computers:
8573 @item -march=@var{architecture-type}
8575 Generate code for the specified architecture. The choices for
8576 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8577 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8578 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8579 architecture option for your machine. Code compiled for lower numbered
8580 architectures will run on higher numbered architectures, but not the
8583 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8584 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8588 @itemx -mpa-risc-1-1
8589 @itemx -mpa-risc-2-0
8590 @opindex mpa-risc-1-0
8591 @opindex mpa-risc-1-1
8592 @opindex mpa-risc-2-0
8593 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8596 @opindex mbig-switch
8597 Generate code suitable for big switch tables. Use this option only if
8598 the assembler/linker complain about out of range branches within a switch
8601 @item -mjump-in-delay
8602 @opindex mjump-in-delay
8603 Fill delay slots of function calls with unconditional jump instructions
8604 by modifying the return pointer for the function call to be the target
8605 of the conditional jump.
8607 @item -mdisable-fpregs
8608 @opindex mdisable-fpregs
8609 Prevent floating point registers from being used in any manner. This is
8610 necessary for compiling kernels which perform lazy context switching of
8611 floating point registers. If you use this option and attempt to perform
8612 floating point operations, the compiler will abort.
8614 @item -mdisable-indexing
8615 @opindex mdisable-indexing
8616 Prevent the compiler from using indexing address modes. This avoids some
8617 rather obscure problems when compiling MIG generated code under MACH@.
8619 @item -mno-space-regs
8620 @opindex mno-space-regs
8621 Generate code that assumes the target has no space registers. This allows
8622 GCC to generate faster indirect calls and use unscaled index address modes.
8624 Such code is suitable for level 0 PA systems and kernels.
8626 @item -mfast-indirect-calls
8627 @opindex mfast-indirect-calls
8628 Generate code that assumes calls never cross space boundaries. This
8629 allows GCC to emit code which performs faster indirect calls.
8631 This option will not work in the presence of shared libraries or nested
8634 @item -mlong-load-store
8635 @opindex mlong-load-store
8636 Generate 3-instruction load and store sequences as sometimes required by
8637 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8640 @item -mportable-runtime
8641 @opindex mportable-runtime
8642 Use the portable calling conventions proposed by HP for ELF systems.
8646 Enable the use of assembler directives only GAS understands.
8648 @item -mschedule=@var{cpu-type}
8650 Schedule code according to the constraints for the machine type
8651 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8652 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8653 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8654 proper scheduling option for your machine. The default scheduling is
8658 @opindex mlinker-opt
8659 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8660 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8661 linkers in which they give bogus error messages when linking some programs.
8664 @opindex msoft-float
8665 Generate output containing library calls for floating point.
8666 @strong{Warning:} the requisite libraries are not available for all HPPA
8667 targets. Normally the facilities of the machine's usual C compiler are
8668 used, but this cannot be done directly in cross-compilation. You must make
8669 your own arrangements to provide suitable library functions for
8670 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8671 does provide software floating point support.
8673 @option{-msoft-float} changes the calling convention in the output file;
8674 therefore, it is only useful if you compile @emph{all} of a program with
8675 this option. In particular, you need to compile @file{libgcc.a}, the
8676 library that comes with GCC, with @option{-msoft-float} in order for
8681 Generate the predefine, @code{_SIO}, for server IO. The default is
8682 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8683 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8684 options are available under HP-UX and HI-UX.
8688 Use GNU ld specific options. This passes @option{-shared} to ld when
8689 building a shared library. It is the default when GCC is configured,
8690 explicitly or implicitly, with the GNU linker. This option does not
8691 have any affect on which ld is called, it only changes what parameters
8692 are passed to that ld. The ld that is called is determined by the
8693 @option{--with-ld} configure option, GCC's program search path, and
8694 finally by the user's @env{PATH}. The linker used by GCC can be printed
8695 using @samp{which `gcc -print-prog-name=ld`}.
8699 Use HP ld specific options. This passes @option{-b} to ld when building
8700 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8701 links. It is the default when GCC is configured, explicitly or
8702 implicitly, with the HP linker. This option does not have any affect on
8703 which ld is called, it only changes what parameters are passed to that
8704 ld. The ld that is called is determined by the @option{--with-ld}
8705 configure option, GCC's program search path, and finally by the user's
8706 @env{PATH}. The linker used by GCC can be printed using @samp{which
8707 `gcc -print-prog-name=ld`}.
8710 @opindex mno-long-calls
8711 Generate code that uses long call sequences. This ensures that a call
8712 is always able to reach linker generated stubs. The default is to generate
8713 long calls only when the distance from the call site to the beginning
8714 of the function or translation unit, as the case may be, exceeds a
8715 predefined limit set by the branch type being used. The limits for
8716 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8717 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8720 Distances are measured from the beginning of functions when using the
8721 @option{-ffunction-sections} option, or when using the @option{-mgas}
8722 and @option{-mno-portable-runtime} options together under HP-UX with
8725 It is normally not desirable to use this option as it will degrade
8726 performance. However, it may be useful in large applications,
8727 particularly when partial linking is used to build the application.
8729 The types of long calls used depends on the capabilities of the
8730 assembler and linker, and the type of code being generated. The
8731 impact on systems that support long absolute calls, and long pic
8732 symbol-difference or pc-relative calls should be relatively small.
8733 However, an indirect call is used on 32-bit ELF systems in pic code
8734 and it is quite long.
8738 Suppress the generation of link options to search libdld.sl when the
8739 @option{-static} option is specified on HP-UX 10 and later.
8743 The HP-UX implementation of setlocale in libc has a dependency on
8744 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8745 when the @option{-static} option is specified, special link options
8746 are needed to resolve this dependency.
8748 On HP-UX 10 and later, the GCC driver adds the necessary options to
8749 link with libdld.sl when the @option{-static} option is specified.
8750 This causes the resulting binary to be dynamic. On the 64-bit port,
8751 the linkers generate dynamic binaries by default in any case. The
8752 @option{-nolibdld} option can be used to prevent the GCC driver from
8753 adding these link options.
8757 Add support for multithreading with the @dfn{dce thread} library
8758 under HP-UX. This option sets flags for both the preprocessor and
8762 @node Intel 960 Options
8763 @subsection Intel 960 Options
8765 These @samp{-m} options are defined for the Intel 960 implementations:
8768 @item -m@var{cpu-type}
8776 Assume the defaults for the machine type @var{cpu-type} for some of
8777 the other options, including instruction scheduling, floating point
8778 support, and addressing modes. The choices for @var{cpu-type} are
8779 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8780 @samp{sa}, and @samp{sb}.
8787 @opindex msoft-float
8788 The @option{-mnumerics} option indicates that the processor does support
8789 floating-point instructions. The @option{-msoft-float} option indicates
8790 that floating-point support should not be assumed.
8792 @item -mleaf-procedures
8793 @itemx -mno-leaf-procedures
8794 @opindex mleaf-procedures
8795 @opindex mno-leaf-procedures
8796 Do (or do not) attempt to alter leaf procedures to be callable with the
8797 @code{bal} instruction as well as @code{call}. This will result in more
8798 efficient code for explicit calls when the @code{bal} instruction can be
8799 substituted by the assembler or linker, but less efficient code in other
8800 cases, such as calls via function pointers, or using a linker that doesn't
8801 support this optimization.
8804 @itemx -mno-tail-call
8806 @opindex mno-tail-call
8807 Do (or do not) make additional attempts (beyond those of the
8808 machine-independent portions of the compiler) to optimize tail-recursive
8809 calls into branches. You may not want to do this because the detection of
8810 cases where this is not valid is not totally complete. The default is
8811 @option{-mno-tail-call}.
8813 @item -mcomplex-addr
8814 @itemx -mno-complex-addr
8815 @opindex mcomplex-addr
8816 @opindex mno-complex-addr
8817 Assume (or do not assume) that the use of a complex addressing mode is a
8818 win on this implementation of the i960. Complex addressing modes may not
8819 be worthwhile on the K-series, but they definitely are on the C-series.
8820 The default is currently @option{-mcomplex-addr} for all processors except
8824 @itemx -mno-code-align
8825 @opindex mcode-align
8826 @opindex mno-code-align
8827 Align code to 8-byte boundaries for faster fetching (or don't bother).
8828 Currently turned on by default for C-series implementations only.
8831 @item -mclean-linkage
8832 @itemx -mno-clean-linkage
8833 @opindex mclean-linkage
8834 @opindex mno-clean-linkage
8835 These options are not fully implemented.
8839 @itemx -mic2.0-compat
8840 @itemx -mic3.0-compat
8842 @opindex mic2.0-compat
8843 @opindex mic3.0-compat
8844 Enable compatibility with iC960 v2.0 or v3.0.
8848 @opindex masm-compat
8850 Enable compatibility with the iC960 assembler.
8852 @item -mstrict-align
8853 @itemx -mno-strict-align
8854 @opindex mstrict-align
8855 @opindex mno-strict-align
8856 Do not permit (do permit) unaligned accesses.
8860 Enable structure-alignment compatibility with Intel's gcc release version
8861 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8863 @item -mlong-double-64
8864 @opindex mlong-double-64
8865 Implement type @samp{long double} as 64-bit floating point numbers.
8866 Without the option @samp{long double} is implemented by 80-bit
8867 floating point numbers. The only reason we have it because there is
8868 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8869 is only useful for people using soft-float targets. Otherwise, we
8870 should recommend against use of it.
8874 @node DEC Alpha Options
8875 @subsection DEC Alpha Options
8877 These @samp{-m} options are defined for the DEC Alpha implementations:
8880 @item -mno-soft-float
8882 @opindex mno-soft-float
8883 @opindex msoft-float
8884 Use (do not use) the hardware floating-point instructions for
8885 floating-point operations. When @option{-msoft-float} is specified,
8886 functions in @file{libgcc.a} will be used to perform floating-point
8887 operations. Unless they are replaced by routines that emulate the
8888 floating-point operations, or compiled in such a way as to call such
8889 emulations routines, these routines will issue floating-point
8890 operations. If you are compiling for an Alpha without floating-point
8891 operations, you must ensure that the library is built so as not to call
8894 Note that Alpha implementations without floating-point operations are
8895 required to have floating-point registers.
8900 @opindex mno-fp-regs
8901 Generate code that uses (does not use) the floating-point register set.
8902 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8903 register set is not used, floating point operands are passed in integer
8904 registers as if they were integers and floating-point results are passed
8905 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8906 so any function with a floating-point argument or return value called by code
8907 compiled with @option{-mno-fp-regs} must also be compiled with that
8910 A typical use of this option is building a kernel that does not use,
8911 and hence need not save and restore, any floating-point registers.
8915 The Alpha architecture implements floating-point hardware optimized for
8916 maximum performance. It is mostly compliant with the IEEE floating
8917 point standard. However, for full compliance, software assistance is
8918 required. This option generates code fully IEEE compliant code
8919 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8920 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8921 defined during compilation. The resulting code is less efficient but is
8922 able to correctly support denormalized numbers and exceptional IEEE
8923 values such as not-a-number and plus/minus infinity. Other Alpha
8924 compilers call this option @option{-ieee_with_no_inexact}.
8926 @item -mieee-with-inexact
8927 @opindex mieee-with-inexact
8928 This is like @option{-mieee} except the generated code also maintains
8929 the IEEE @var{inexact-flag}. Turning on this option causes the
8930 generated code to implement fully-compliant IEEE math. In addition to
8931 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8932 macro. On some Alpha implementations the resulting code may execute
8933 significantly slower than the code generated by default. Since there is
8934 very little code that depends on the @var{inexact-flag}, you should
8935 normally not specify this option. Other Alpha compilers call this
8936 option @option{-ieee_with_inexact}.
8938 @item -mfp-trap-mode=@var{trap-mode}
8939 @opindex mfp-trap-mode
8940 This option controls what floating-point related traps are enabled.
8941 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8942 The trap mode can be set to one of four values:
8946 This is the default (normal) setting. The only traps that are enabled
8947 are the ones that cannot be disabled in software (e.g., division by zero
8951 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8955 Like @samp{su}, but the instructions are marked to be safe for software
8956 completion (see Alpha architecture manual for details).
8959 Like @samp{su}, but inexact traps are enabled as well.
8962 @item -mfp-rounding-mode=@var{rounding-mode}
8963 @opindex mfp-rounding-mode
8964 Selects the IEEE rounding mode. Other Alpha compilers call this option
8965 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8970 Normal IEEE rounding mode. Floating point numbers are rounded towards
8971 the nearest machine number or towards the even machine number in case
8975 Round towards minus infinity.
8978 Chopped rounding mode. Floating point numbers are rounded towards zero.
8981 Dynamic rounding mode. A field in the floating point control register
8982 (@var{fpcr}, see Alpha architecture reference manual) controls the
8983 rounding mode in effect. The C library initializes this register for
8984 rounding towards plus infinity. Thus, unless your program modifies the
8985 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8988 @item -mtrap-precision=@var{trap-precision}
8989 @opindex mtrap-precision
8990 In the Alpha architecture, floating point traps are imprecise. This
8991 means without software assistance it is impossible to recover from a
8992 floating trap and program execution normally needs to be terminated.
8993 GCC can generate code that can assist operating system trap handlers
8994 in determining the exact location that caused a floating point trap.
8995 Depending on the requirements of an application, different levels of
8996 precisions can be selected:
9000 Program precision. This option is the default and means a trap handler
9001 can only identify which program caused a floating point exception.
9004 Function precision. The trap handler can determine the function that
9005 caused a floating point exception.
9008 Instruction precision. The trap handler can determine the exact
9009 instruction that caused a floating point exception.
9012 Other Alpha compilers provide the equivalent options called
9013 @option{-scope_safe} and @option{-resumption_safe}.
9015 @item -mieee-conformant
9016 @opindex mieee-conformant
9017 This option marks the generated code as IEEE conformant. You must not
9018 use this option unless you also specify @option{-mtrap-precision=i} and either
9019 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9020 is to emit the line @samp{.eflag 48} in the function prologue of the
9021 generated assembly file. Under DEC Unix, this has the effect that
9022 IEEE-conformant math library routines will be linked in.
9024 @item -mbuild-constants
9025 @opindex mbuild-constants
9026 Normally GCC examines a 32- or 64-bit integer constant to
9027 see if it can construct it from smaller constants in two or three
9028 instructions. If it cannot, it will output the constant as a literal and
9029 generate code to load it from the data segment at runtime.
9031 Use this option to require GCC to construct @emph{all} integer constants
9032 using code, even if it takes more instructions (the maximum is six).
9034 You would typically use this option to build a shared library dynamic
9035 loader. Itself a shared library, it must relocate itself in memory
9036 before it can find the variables and constants in its own data segment.
9042 Select whether to generate code to be assembled by the vendor-supplied
9043 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9061 Indicate whether GCC should generate code to use the optional BWX,
9062 CIX, FIX and MAX instruction sets. The default is to use the instruction
9063 sets supported by the CPU type specified via @option{-mcpu=} option or that
9064 of the CPU on which GCC was built if none was specified.
9069 @opindex mfloat-ieee
9070 Generate code that uses (does not use) VAX F and G floating point
9071 arithmetic instead of IEEE single and double precision.
9073 @item -mexplicit-relocs
9074 @itemx -mno-explicit-relocs
9075 @opindex mexplicit-relocs
9076 @opindex mno-explicit-relocs
9077 Older Alpha assemblers provided no way to generate symbol relocations
9078 except via assembler macros. Use of these macros does not allow
9079 optimal instruction scheduling. GNU binutils as of version 2.12
9080 supports a new syntax that allows the compiler to explicitly mark
9081 which relocations should apply to which instructions. This option
9082 is mostly useful for debugging, as GCC detects the capabilities of
9083 the assembler when it is built and sets the default accordingly.
9087 @opindex msmall-data
9088 @opindex mlarge-data
9089 When @option{-mexplicit-relocs} is in effect, static data is
9090 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9091 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9092 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9093 16-bit relocations off of the @code{$gp} register. This limits the
9094 size of the small data area to 64KB, but allows the variables to be
9095 directly accessed via a single instruction.
9097 The default is @option{-mlarge-data}. With this option the data area
9098 is limited to just below 2GB. Programs that require more than 2GB of
9099 data must use @code{malloc} or @code{mmap} to allocate the data in the
9100 heap instead of in the program's data segment.
9102 When generating code for shared libraries, @option{-fpic} implies
9103 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9107 @opindex msmall-text
9108 @opindex mlarge-text
9109 When @option{-msmall-text} is used, the compiler assumes that the
9110 code of the entire program (or shared library) fits in 4MB, and is
9111 thus reachable with a branch instruction. When @option{-msmall-data}
9112 is used, the compiler can assume that all local symbols share the
9113 same @code{$gp} value, and thus reduce the number of instructions
9114 required for a function call from 4 to 1.
9116 The default is @option{-mlarge-text}.
9118 @item -mcpu=@var{cpu_type}
9120 Set the instruction set and instruction scheduling parameters for
9121 machine type @var{cpu_type}. You can specify either the @samp{EV}
9122 style name or the corresponding chip number. GCC supports scheduling
9123 parameters for the EV4, EV5 and EV6 family of processors and will
9124 choose the default values for the instruction set from the processor
9125 you specify. If you do not specify a processor type, GCC will default
9126 to the processor on which the compiler was built.
9128 Supported values for @var{cpu_type} are
9134 Schedules as an EV4 and has no instruction set extensions.
9138 Schedules as an EV5 and has no instruction set extensions.
9142 Schedules as an EV5 and supports the BWX extension.
9147 Schedules as an EV5 and supports the BWX and MAX extensions.
9151 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9155 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9158 @item -mtune=@var{cpu_type}
9160 Set only the instruction scheduling parameters for machine type
9161 @var{cpu_type}. The instruction set is not changed.
9163 @item -mmemory-latency=@var{time}
9164 @opindex mmemory-latency
9165 Sets the latency the scheduler should assume for typical memory
9166 references as seen by the application. This number is highly
9167 dependent on the memory access patterns used by the application
9168 and the size of the external cache on the machine.
9170 Valid options for @var{time} are
9174 A decimal number representing clock cycles.
9180 The compiler contains estimates of the number of clock cycles for
9181 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9182 (also called Dcache, Scache, and Bcache), as well as to main memory.
9183 Note that L3 is only valid for EV5.
9188 @node DEC Alpha/VMS Options
9189 @subsection DEC Alpha/VMS Options
9191 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9194 @item -mvms-return-codes
9195 @opindex mvms-return-codes
9196 Return VMS condition codes from main. The default is to return POSIX
9197 style condition (e.g.@ error) codes.
9200 @node H8/300 Options
9201 @subsection H8/300 Options
9203 These @samp{-m} options are defined for the H8/300 implementations:
9208 Shorten some address references at link time, when possible; uses the
9209 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9210 ld, Using ld}, for a fuller description.
9214 Generate code for the H8/300H@.
9218 Generate code for the H8S@.
9222 Generate code for the H8S and H8/300H in the normal mode. This switch
9223 must be used either with -mh or -ms.
9227 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9231 Make @code{int} data 32 bits by default.
9235 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9236 The default for the H8/300H and H8S is to align longs and floats on 4
9238 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9239 This option has no effect on the H8/300.
9243 @subsection SH Options
9245 These @samp{-m} options are defined for the SH implementations:
9250 Generate code for the SH1.
9254 Generate code for the SH2.
9257 Generate code for the SH2e.
9261 Generate code for the SH3.
9265 Generate code for the SH3e.
9269 Generate code for the SH4 without a floating-point unit.
9271 @item -m4-single-only
9272 @opindex m4-single-only
9273 Generate code for the SH4 with a floating-point unit that only
9274 supports single-precision arithmetic.
9278 Generate code for the SH4 assuming the floating-point unit is in
9279 single-precision mode by default.
9283 Generate code for the SH4.
9287 Compile code for the processor in big endian mode.
9291 Compile code for the processor in little endian mode.
9295 Align doubles at 64-bit boundaries. Note that this changes the calling
9296 conventions, and thus some functions from the standard C library will
9297 not work unless you recompile it first with @option{-mdalign}.
9301 Shorten some address references at link time, when possible; uses the
9302 linker option @option{-relax}.
9306 Use 32-bit offsets in @code{switch} tables. The default is to use
9311 Enable the use of the instruction @code{fmovd}.
9315 Comply with the calling conventions defined by Renesas.
9319 Mark the @code{MAC} register as call-clobbered, even if
9320 @option{-mhitachi} is given.
9324 Increase IEEE-compliance of floating-point code.
9328 Dump instruction size and location in the assembly code.
9332 This option is deprecated. It pads structures to multiple of 4 bytes,
9333 which is incompatible with the SH ABI@.
9337 Optimize for space instead of speed. Implied by @option{-Os}.
9341 When generating position-independent code, emit function calls using
9342 the Global Offset Table instead of the Procedure Linkage Table.
9346 Generate a library function call to invalidate instruction cache
9347 entries, after fixing up a trampoline. This library function call
9348 doesn't assume it can write to the whole memory address space. This
9349 is the default when the target is @code{sh-*-linux*}.
9352 @node System V Options
9353 @subsection Options for System V
9355 These additional options are available on System V Release 4 for
9356 compatibility with other compilers on those systems:
9361 Create a shared object.
9362 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
9366 Identify the versions of each tool used by the compiler, in a
9367 @code{.ident} assembler directive in the output.
9371 Refrain from adding @code{.ident} directives to the output file (this is
9374 @item -YP,@var{dirs}
9376 Search the directories @var{dirs}, and no others, for libraries
9377 specified with @option{-l}.
9381 Look in the directory @var{dir} to find the M4 preprocessor.
9382 The assembler uses this option.
9383 @c This is supposed to go with a -Yd for predefined M4 macro files, but
9384 @c the generic assembler that comes with Solaris takes just -Ym.
9387 @node TMS320C3x/C4x Options
9388 @subsection TMS320C3x/C4x Options
9389 @cindex TMS320C3x/C4x Options
9391 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
9395 @item -mcpu=@var{cpu_type}
9397 Set the instruction set, register set, and instruction scheduling
9398 parameters for machine type @var{cpu_type}. Supported values for
9399 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
9400 @samp{c44}. The default is @samp{c40} to generate code for the
9405 @itemx -msmall-memory
9407 @opindex mbig-memory
9409 @opindex msmall-memory
9411 Generates code for the big or small memory model. The small memory
9412 model assumed that all data fits into one 64K word page. At run-time
9413 the data page (DP) register must be set to point to the 64K page
9414 containing the .bss and .data program sections. The big memory model is
9415 the default and requires reloading of the DP register for every direct
9422 Allow (disallow) allocation of general integer operands into the block
9429 Enable (disable) generation of code using decrement and branch,
9430 DBcond(D), instructions. This is enabled by default for the C4x. To be
9431 on the safe side, this is disabled for the C3x, since the maximum
9432 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
9433 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
9434 that it can utilize the decrement and branch instruction, but will give
9435 up if there is more than one memory reference in the loop. Thus a loop
9436 where the loop counter is decremented can generate slightly more
9437 efficient code, in cases where the RPTB instruction cannot be utilized.
9439 @item -mdp-isr-reload
9441 @opindex mdp-isr-reload
9443 Force the DP register to be saved on entry to an interrupt service
9444 routine (ISR), reloaded to point to the data section, and restored on
9445 exit from the ISR@. This should not be required unless someone has
9446 violated the small memory model by modifying the DP register, say within
9453 For the C3x use the 24-bit MPYI instruction for integer multiplies
9454 instead of a library call to guarantee 32-bit results. Note that if one
9455 of the operands is a constant, then the multiplication will be performed
9456 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
9457 then squaring operations are performed inline instead of a library call.
9460 @itemx -mno-fast-fix
9462 @opindex mno-fast-fix
9463 The C3x/C4x FIX instruction to convert a floating point value to an
9464 integer value chooses the nearest integer less than or equal to the
9465 floating point value rather than to the nearest integer. Thus if the
9466 floating point number is negative, the result will be incorrectly
9467 truncated an additional code is necessary to detect and correct this
9468 case. This option can be used to disable generation of the additional
9469 code required to correct the result.
9475 Enable (disable) generation of repeat block sequences using the RPTB
9476 instruction for zero overhead looping. The RPTB construct is only used
9477 for innermost loops that do not call functions or jump across the loop
9478 boundaries. There is no advantage having nested RPTB loops due to the
9479 overhead required to save and restore the RC, RS, and RE registers.
9480 This is enabled by default with @option{-O2}.
9482 @item -mrpts=@var{count}
9486 Enable (disable) the use of the single instruction repeat instruction
9487 RPTS@. If a repeat block contains a single instruction, and the loop
9488 count can be guaranteed to be less than the value @var{count}, GCC will
9489 emit a RPTS instruction instead of a RPTB@. If no value is specified,
9490 then a RPTS will be emitted even if the loop count cannot be determined
9491 at compile time. Note that the repeated instruction following RPTS does
9492 not have to be reloaded from memory each iteration, thus freeing up the
9493 CPU buses for operands. However, since interrupts are blocked by this
9494 instruction, it is disabled by default.
9496 @item -mloop-unsigned
9497 @itemx -mno-loop-unsigned
9498 @opindex mloop-unsigned
9499 @opindex mno-loop-unsigned
9500 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
9501 is @math{2^{31} + 1} since these instructions test if the iteration count is
9502 negative to terminate the loop. If the iteration count is unsigned
9503 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
9504 exceeded. This switch allows an unsigned iteration count.
9508 Try to emit an assembler syntax that the TI assembler (asm30) is happy
9509 with. This also enforces compatibility with the API employed by the TI
9510 C3x C compiler. For example, long doubles are passed as structures
9511 rather than in floating point registers.
9517 Generate code that uses registers (stack) for passing arguments to functions.
9518 By default, arguments are passed in registers where possible rather
9519 than by pushing arguments on to the stack.
9521 @item -mparallel-insns
9522 @itemx -mno-parallel-insns
9523 @opindex mparallel-insns
9524 @opindex mno-parallel-insns
9525 Allow the generation of parallel instructions. This is enabled by
9526 default with @option{-O2}.
9528 @item -mparallel-mpy
9529 @itemx -mno-parallel-mpy
9530 @opindex mparallel-mpy
9531 @opindex mno-parallel-mpy
9532 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
9533 provided @option{-mparallel-insns} is also specified. These instructions have
9534 tight register constraints which can pessimize the code generation
9540 @subsection V850 Options
9541 @cindex V850 Options
9543 These @samp{-m} options are defined for V850 implementations:
9547 @itemx -mno-long-calls
9548 @opindex mlong-calls
9549 @opindex mno-long-calls
9550 Treat all calls as being far away (near). If calls are assumed to be
9551 far away, the compiler will always load the functions address up into a
9552 register, and call indirect through the pointer.
9558 Do not optimize (do optimize) basic blocks that use the same index
9559 pointer 4 or more times to copy pointer into the @code{ep} register, and
9560 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
9561 option is on by default if you optimize.
9563 @item -mno-prolog-function
9564 @itemx -mprolog-function
9565 @opindex mno-prolog-function
9566 @opindex mprolog-function
9567 Do not use (do use) external functions to save and restore registers
9568 at the prologue and epilogue of a function. The external functions
9569 are slower, but use less code space if more than one function saves
9570 the same number of registers. The @option{-mprolog-function} option
9571 is on by default if you optimize.
9575 Try to make the code as small as possible. At present, this just turns
9576 on the @option{-mep} and @option{-mprolog-function} options.
9580 Put static or global variables whose size is @var{n} bytes or less into
9581 the tiny data area that register @code{ep} points to. The tiny data
9582 area can hold up to 256 bytes in total (128 bytes for byte references).
9586 Put static or global variables whose size is @var{n} bytes or less into
9587 the small data area that register @code{gp} points to. The small data
9588 area can hold up to 64 kilobytes.
9592 Put static or global variables whose size is @var{n} bytes or less into
9593 the first 32 kilobytes of memory.
9597 Specify that the target processor is the V850.
9600 @opindex mbig-switch
9601 Generate code suitable for big switch tables. Use this option only if
9602 the assembler/linker complain about out of range branches within a switch
9607 This option will cause r2 and r5 to be used in the code generated by
9608 the compiler. This setting is the default.
9611 @opindex mno-app-regs
9612 This option will cause r2 and r5 to be treated as fixed registers.
9616 Specify that the target processor is the V850E1. The preprocessor
9617 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
9618 this option is used.
9622 Specify that the target processor is the V850E. The preprocessor
9623 constant @samp{__v850e__} will be defined if this option is used.
9625 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
9626 are defined then a default target processor will be chosen and the
9627 relevant @samp{__v850*__} preprocessor constant will be defined.
9629 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
9630 defined, regardless of which processor variant is the target.
9632 @item -mdisable-callt
9633 @opindex mdisable-callt
9634 This option will suppress generation of the CALLT instruction for the
9635 v850e and v850e1 flavors of the v850 architecture. The default is
9636 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
9641 @subsection ARC Options
9644 These options are defined for ARC implementations:
9649 Compile code for little endian mode. This is the default.
9653 Compile code for big endian mode.
9656 @opindex mmangle-cpu
9657 Prepend the name of the cpu to all public symbol names.
9658 In multiple-processor systems, there are many ARC variants with different
9659 instruction and register set characteristics. This flag prevents code
9660 compiled for one cpu to be linked with code compiled for another.
9661 No facility exists for handling variants that are ``almost identical''.
9662 This is an all or nothing option.
9664 @item -mcpu=@var{cpu}
9666 Compile code for ARC variant @var{cpu}.
9667 Which variants are supported depend on the configuration.
9668 All variants support @option{-mcpu=base}, this is the default.
9670 @item -mtext=@var{text-section}
9671 @itemx -mdata=@var{data-section}
9672 @itemx -mrodata=@var{readonly-data-section}
9676 Put functions, data, and readonly data in @var{text-section},
9677 @var{data-section}, and @var{readonly-data-section} respectively
9678 by default. This can be overridden with the @code{section} attribute.
9679 @xref{Variable Attributes}.
9684 @subsection NS32K Options
9685 @cindex NS32K options
9687 These are the @samp{-m} options defined for the 32000 series. The default
9688 values for these options depends on which style of 32000 was selected when
9689 the compiler was configured; the defaults for the most common choices are
9697 Generate output for a 32032. This is the default
9698 when the compiler is configured for 32032 and 32016 based systems.
9704 Generate output for a 32332. This is the default
9705 when the compiler is configured for 32332-based systems.
9711 Generate output for a 32532. This is the default
9712 when the compiler is configured for 32532-based systems.
9716 Generate output containing 32081 instructions for floating point.
9717 This is the default for all systems.
9721 Generate output containing 32381 instructions for floating point. This
9722 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9723 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9727 Try and generate multiply-add floating point instructions @code{polyF}
9728 and @code{dotF}. This option is only available if the @option{-m32381}
9729 option is in effect. Using these instructions requires changes to
9730 register allocation which generally has a negative impact on
9731 performance. This option should only be enabled when compiling code
9732 particularly likely to make heavy use of multiply-add instructions.
9735 @opindex mnomulti-add
9736 Do not try and generate multiply-add floating point instructions
9737 @code{polyF} and @code{dotF}. This is the default on all platforms.
9740 @opindex msoft-float
9741 Generate output containing library calls for floating point.
9742 @strong{Warning:} the requisite libraries may not be available.
9744 @item -mieee-compare
9745 @itemx -mno-ieee-compare
9746 @opindex mieee-compare
9747 @opindex mno-ieee-compare
9748 Control whether or not the compiler uses IEEE floating point
9749 comparisons. These handle correctly the case where the result of a
9750 comparison is unordered.
9751 @strong{Warning:} the requisite kernel support may not be available.
9754 @opindex mnobitfield
9755 Do not use the bit-field instructions. On some machines it is faster to
9756 use shifting and masking operations. This is the default for the pc532.
9760 Do use the bit-field instructions. This is the default for all platforms
9765 Use a different function-calling convention, in which functions
9766 that take a fixed number of arguments return pop their
9767 arguments on return with the @code{ret} instruction.
9769 This calling convention is incompatible with the one normally
9770 used on Unix, so you cannot use it if you need to call libraries
9771 compiled with the Unix compiler.
9773 Also, you must provide function prototypes for all functions that
9774 take variable numbers of arguments (including @code{printf});
9775 otherwise incorrect code will be generated for calls to those
9778 In addition, seriously incorrect code will result if you call a
9779 function with too many arguments. (Normally, extra arguments are
9780 harmlessly ignored.)
9782 This option takes its name from the 680x0 @code{rtd} instruction.
9787 Use a different function-calling convention where the first two arguments
9788 are passed in registers.
9790 This calling convention is incompatible with the one normally
9791 used on Unix, so you cannot use it if you need to call libraries
9792 compiled with the Unix compiler.
9795 @opindex mnoregparam
9796 Do not pass any arguments in registers. This is the default for all
9801 It is OK to use the sb as an index register which is always loaded with
9802 zero. This is the default for the pc532-netbsd target.
9806 The sb register is not available for use or has not been initialized to
9807 zero by the run time system. This is the default for all targets except
9808 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9809 @option{-fpic} is set.
9813 Many ns32000 series addressing modes use displacements of up to 512MB@.
9814 If an address is above 512MB then displacements from zero can not be used.
9815 This option causes code to be generated which can be loaded above 512MB@.
9816 This may be useful for operating systems or ROM code.
9820 Assume code will be loaded in the first 512MB of virtual address space.
9821 This is the default for all platforms.
9827 @subsection AVR Options
9830 These options are defined for AVR implementations:
9833 @item -mmcu=@var{mcu}
9835 Specify ATMEL AVR instruction set or MCU type.
9837 Instruction set avr1 is for the minimal AVR core, not supported by the C
9838 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9839 attiny11, attiny12, attiny15, attiny28).
9841 Instruction set avr2 (default) is for the classic AVR core with up to
9842 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9843 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9844 at90c8534, at90s8535).
9846 Instruction set avr3 is for the classic AVR core with up to 128K program
9847 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9849 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9850 memory space (MCU types: atmega8, atmega83, atmega85).
9852 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9853 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9854 atmega64, atmega128, at43usb355, at94k).
9858 Output instruction sizes to the asm file.
9860 @item -minit-stack=@var{N}
9861 @opindex minit-stack
9862 Specify the initial stack address, which may be a symbol or numeric value,
9863 @samp{__stack} is the default.
9865 @item -mno-interrupts
9866 @opindex mno-interrupts
9867 Generated code is not compatible with hardware interrupts.
9868 Code size will be smaller.
9870 @item -mcall-prologues
9871 @opindex mcall-prologues
9872 Functions prologues/epilogues expanded as call to appropriate
9873 subroutines. Code size will be smaller.
9875 @item -mno-tablejump
9876 @opindex mno-tablejump
9877 Do not generate tablejump insns which sometimes increase code size.
9880 @opindex mtiny-stack
9881 Change only the low 8 bits of the stack pointer.
9885 @subsection MCore Options
9886 @cindex MCore options
9888 These are the @samp{-m} options defined for the Motorola M*Core
9896 @opindex mno-hardlit
9897 Inline constants into the code stream if it can be done in two
9898 instructions or less.
9904 Use the divide instruction. (Enabled by default).
9906 @item -mrelax-immediate
9907 @itemx -mno-relax-immediate
9908 @opindex mrelax-immediate
9909 @opindex mno-relax-immediate
9910 Allow arbitrary sized immediates in bit operations.
9912 @item -mwide-bitfields
9913 @itemx -mno-wide-bitfields
9914 @opindex mwide-bitfields
9915 @opindex mno-wide-bitfields
9916 Always treat bit-fields as int-sized.
9918 @item -m4byte-functions
9919 @itemx -mno-4byte-functions
9920 @opindex m4byte-functions
9921 @opindex mno-4byte-functions
9922 Force all functions to be aligned to a four byte boundary.
9924 @item -mcallgraph-data
9925 @itemx -mno-callgraph-data
9926 @opindex mcallgraph-data
9927 @opindex mno-callgraph-data
9928 Emit callgraph information.
9931 @itemx -mno-slow-bytes
9932 @opindex mslow-bytes
9933 @opindex mno-slow-bytes
9934 Prefer word access when reading byte quantities.
9936 @item -mlittle-endian
9938 @opindex mlittle-endian
9939 @opindex mbig-endian
9940 Generate code for a little endian target.
9946 Generate code for the 210 processor.
9950 @subsection IA-64 Options
9951 @cindex IA-64 Options
9953 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9957 @opindex mbig-endian
9958 Generate code for a big endian target. This is the default for HP-UX@.
9960 @item -mlittle-endian
9961 @opindex mlittle-endian
9962 Generate code for a little endian target. This is the default for AIX5
9969 Generate (or don't) code for the GNU assembler. This is the default.
9970 @c Also, this is the default if the configure option @option{--with-gnu-as}
9977 Generate (or don't) code for the GNU linker. This is the default.
9978 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9983 Generate code that does not use a global pointer register. The result
9984 is not position independent code, and violates the IA-64 ABI@.
9986 @item -mvolatile-asm-stop
9987 @itemx -mno-volatile-asm-stop
9988 @opindex mvolatile-asm-stop
9989 @opindex mno-volatile-asm-stop
9990 Generate (or don't) a stop bit immediately before and after volatile asm
9995 Generate code that works around Itanium B step errata.
9997 @item -mregister-names
9998 @itemx -mno-register-names
9999 @opindex mregister-names
10000 @opindex mno-register-names
10001 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
10002 the stacked registers. This may make assembler output more readable.
10008 Disable (or enable) optimizations that use the small data section. This may
10009 be useful for working around optimizer bugs.
10011 @item -mconstant-gp
10012 @opindex mconstant-gp
10013 Generate code that uses a single constant global pointer value. This is
10014 useful when compiling kernel code.
10018 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
10019 This is useful when compiling firmware code.
10021 @item -minline-float-divide-min-latency
10022 @opindex minline-float-divide-min-latency
10023 Generate code for inline divides of floating point values
10024 using the minimum latency algorithm.
10026 @item -minline-float-divide-max-throughput
10027 @opindex minline-float-divide-max-throughput
10028 Generate code for inline divides of floating point values
10029 using the maximum throughput algorithm.
10031 @item -minline-int-divide-min-latency
10032 @opindex minline-int-divide-min-latency
10033 Generate code for inline divides of integer values
10034 using the minimum latency algorithm.
10036 @item -minline-int-divide-max-throughput
10037 @opindex minline-int-divide-max-throughput
10038 Generate code for inline divides of integer values
10039 using the maximum throughput algorithm.
10041 @item -minline-sqrt-min-latency
10042 @opindex minline-sqrt-min-latency
10043 Generate code for inline square roots
10044 using the minimum latency algorithm.
10046 @item -minline-sqrt-max-throughput
10047 @opindex minline-sqrt-max-throughput
10048 Generate code for inline square roots
10049 using the maximum throughput algorithm.
10051 @item -mno-dwarf2-asm
10052 @itemx -mdwarf2-asm
10053 @opindex mno-dwarf2-asm
10054 @opindex mdwarf2-asm
10055 Don't (or do) generate assembler code for the DWARF2 line number debugging
10056 info. This may be useful when not using the GNU assembler.
10058 @item -mearly-stop-bits
10059 @itemx -mno-early-stop-bits
10060 @opindex mearly-stop-bits
10061 @opindex mno-early-stop-bits
10062 Allow stop bits to be placed earlier than immediately preceding the
10063 instruction that triggered the stop bit. This can improve instruction
10064 scheduling, but does not always do so.
10066 @item -mfixed-range=@var{register-range}
10067 @opindex mfixed-range
10068 Generate code treating the given register range as fixed registers.
10069 A fixed register is one that the register allocator can not use. This is
10070 useful when compiling kernel code. A register range is specified as
10071 two registers separated by a dash. Multiple register ranges can be
10072 specified separated by a comma.
10074 @item -mtls-size=@var{tls-size}
10076 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
10079 @item -mtune-arch=@var{cpu-type}
10080 @opindex mtune-arch
10081 Tune the instruction scheduling for a particular CPU, Valid values are
10082 itanium, itanium1, merced, itanium2, and mckinley.
10088 Add support for multithreading using the POSIX threads library. This
10089 option sets flags for both the preprocessor and linker. It does
10090 not affect the thread safety of object code produced by the compiler or
10091 that of libraries supplied with it. These are HP-UX specific flags.
10097 Generate code for a 32-bit or 64-bit environment.
10098 The 32-bit environment sets int, long and pointer to 32 bits.
10099 The 64-bit environment sets int to 32 bits and long and pointer
10100 to 64 bits. These are HP-UX specific flags.
10105 @subsection D30V Options
10106 @cindex D30V Options
10108 These @samp{-m} options are defined for D30V implementations:
10113 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
10114 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
10115 memory, which starts at location @code{0x80000000}.
10118 @opindex mextmemory
10119 Same as the @option{-mextmem} switch.
10123 Link the @samp{.text} section into onchip text memory, which starts at
10124 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
10125 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
10126 into onchip data memory, which starts at location @code{0x20000000}.
10128 @item -mno-asm-optimize
10129 @itemx -masm-optimize
10130 @opindex mno-asm-optimize
10131 @opindex masm-optimize
10132 Disable (enable) passing @option{-O} to the assembler when optimizing.
10133 The assembler uses the @option{-O} option to automatically parallelize
10134 adjacent short instructions where possible.
10136 @item -mbranch-cost=@var{n}
10137 @opindex mbranch-cost
10138 Increase the internal costs of branches to @var{n}. Higher costs means
10139 that the compiler will issue more instructions to avoid doing a branch.
10142 @item -mcond-exec=@var{n}
10143 @opindex mcond-exec
10144 Specify the maximum number of conditionally executed instructions that
10145 replace a branch. The default is 4.
10148 @node S/390 and zSeries Options
10149 @subsection S/390 and zSeries Options
10150 @cindex S/390 and zSeries Options
10152 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10156 @itemx -msoft-float
10157 @opindex mhard-float
10158 @opindex msoft-float
10159 Use (do not use) the hardware floating-point instructions and registers
10160 for floating-point operations. When @option{-msoft-float} is specified,
10161 functions in @file{libgcc.a} will be used to perform floating-point
10162 operations. When @option{-mhard-float} is specified, the compiler
10163 generates IEEE floating-point instructions. This is the default.
10166 @itemx -mno-backchain
10167 @opindex mbackchain
10168 @opindex mno-backchain
10169 Generate (or do not generate) code which maintains an explicit
10170 backchain within the stack frame that points to the caller's frame.
10171 This may be needed to allow debugging using tools that do not understand
10172 DWARF-2 call frame information. The default is not to generate the
10176 @itemx -mno-small-exec
10177 @opindex msmall-exec
10178 @opindex mno-small-exec
10179 Generate (or do not generate) code using the @code{bras} instruction
10180 to do subroutine calls.
10181 This only works reliably if the total executable size does not
10182 exceed 64k. The default is to use the @code{basr} instruction instead,
10183 which does not have this limitation.
10189 When @option{-m31} is specified, generate code compliant to the
10190 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
10191 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
10192 particular to generate 64-bit instructions. For the @samp{s390}
10193 targets, the default is @option{-m31}, while the @samp{s390x}
10194 targets default to @option{-m64}.
10200 When @option{-mzarch} is specified, generate code using the
10201 instructions available on z/Architecture.
10202 When @option{-mesa} is specified, generate code using the
10203 instructions available on ESA/390. Note that @option{-mesa} is
10204 not possible with @option{-m64}.
10205 When generating code compliant to the GNU/Linux for S/390 ABI,
10206 the default is @option{-mesa}. When generating code compliant
10207 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
10213 Generate (or do not generate) code using the @code{mvcle} instruction
10214 to perform block moves. When @option{-mno-mvcle} is specified,
10215 use a @code{mvc} loop instead. This is the default.
10221 Print (or do not print) additional debug information when compiling.
10222 The default is to not print debug information.
10224 @item -march=@var{cpu-type}
10226 Generate code that will run on @var{cpu-type}, which is the name of a system
10227 representing a certain processor type. Possible values for
10228 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10229 When generating code using the instructions available on z/Architecture,
10230 the default is @option{-march=z900}. Otherwise, the default is
10231 @option{-march=g5}.
10233 @item -mtune=@var{cpu-type}
10235 Tune to @var{cpu-type} everything applicable about the generated code,
10236 except for the ABI and the set of available instructions.
10237 The list of @var{cpu-type} values is the same as for @option{-march}.
10238 The default is the value used for @option{-march}.
10241 @itemx -mno-fused-madd
10242 @opindex mfused-madd
10243 @opindex mno-fused-madd
10244 Generate code that uses (does not use) the floating point multiply and
10245 accumulate instructions. These instructions are generated by default if
10246 hardware floating point is used.
10250 @subsection CRIS Options
10251 @cindex CRIS Options
10253 These options are defined specifically for the CRIS ports.
10256 @item -march=@var{architecture-type}
10257 @itemx -mcpu=@var{architecture-type}
10260 Generate code for the specified architecture. The choices for
10261 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10262 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
10263 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10266 @item -mtune=@var{architecture-type}
10268 Tune to @var{architecture-type} everything applicable about the generated
10269 code, except for the ABI and the set of available instructions. The
10270 choices for @var{architecture-type} are the same as for
10271 @option{-march=@var{architecture-type}}.
10273 @item -mmax-stack-frame=@var{n}
10274 @opindex mmax-stack-frame
10275 Warn when the stack frame of a function exceeds @var{n} bytes.
10277 @item -melinux-stacksize=@var{n}
10278 @opindex melinux-stacksize
10279 Only available with the @samp{cris-axis-aout} target. Arranges for
10280 indications in the program to the kernel loader that the stack of the
10281 program should be set to @var{n} bytes.
10287 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10288 @option{-march=v3} and @option{-march=v8} respectively.
10290 @item -mmul-bug-workaround
10291 @itemx -mno-mul-bug-workaround
10292 @opindex mmul-bug-workaround
10293 @opindex mno-mul-bug-workaround
10294 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
10295 models where it applies. This option is active by default.
10299 Enable CRIS-specific verbose debug-related information in the assembly
10300 code. This option also has the effect to turn off the @samp{#NO_APP}
10301 formatted-code indicator to the assembler at the beginning of the
10306 Do not use condition-code results from previous instruction; always emit
10307 compare and test instructions before use of condition codes.
10309 @item -mno-side-effects
10310 @opindex mno-side-effects
10311 Do not emit instructions with side-effects in addressing modes other than
10314 @item -mstack-align
10315 @itemx -mno-stack-align
10316 @itemx -mdata-align
10317 @itemx -mno-data-align
10318 @itemx -mconst-align
10319 @itemx -mno-const-align
10320 @opindex mstack-align
10321 @opindex mno-stack-align
10322 @opindex mdata-align
10323 @opindex mno-data-align
10324 @opindex mconst-align
10325 @opindex mno-const-align
10326 These options (no-options) arranges (eliminate arrangements) for the
10327 stack-frame, individual data and constants to be aligned for the maximum
10328 single data access size for the chosen CPU model. The default is to
10329 arrange for 32-bit alignment. ABI details such as structure layout are
10330 not affected by these options.
10338 Similar to the stack- data- and const-align options above, these options
10339 arrange for stack-frame, writable data and constants to all be 32-bit,
10340 16-bit or 8-bit aligned. The default is 32-bit alignment.
10342 @item -mno-prologue-epilogue
10343 @itemx -mprologue-epilogue
10344 @opindex mno-prologue-epilogue
10345 @opindex mprologue-epilogue
10346 With @option{-mno-prologue-epilogue}, the normal function prologue and
10347 epilogue that sets up the stack-frame are omitted and no return
10348 instructions or return sequences are generated in the code. Use this
10349 option only together with visual inspection of the compiled code: no
10350 warnings or errors are generated when call-saved registers must be saved,
10351 or storage for local variable needs to be allocated.
10355 @opindex mno-gotplt
10357 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10358 instruction sequences that load addresses for functions from the PLT part
10359 of the GOT rather than (traditional on other architectures) calls to the
10360 PLT. The default is @option{-mgotplt}.
10364 Legacy no-op option only recognized with the cris-axis-aout target.
10368 Legacy no-op option only recognized with the cris-axis-elf and
10369 cris-axis-linux-gnu targets.
10373 Only recognized with the cris-axis-aout target, where it selects a
10374 GNU/linux-like multilib, include files and instruction set for
10375 @option{-march=v8}.
10379 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10383 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
10384 to link with input-output functions from a simulator library. Code,
10385 initialized data and zero-initialized data are allocated consecutively.
10389 Like @option{-sim}, but pass linker options to locate initialized data at
10390 0x40000000 and zero-initialized data at 0x80000000.
10394 @subsection MMIX Options
10395 @cindex MMIX Options
10397 These options are defined for the MMIX:
10401 @itemx -mno-libfuncs
10403 @opindex mno-libfuncs
10404 Specify that intrinsic library functions are being compiled, passing all
10405 values in registers, no matter the size.
10408 @itemx -mno-epsilon
10410 @opindex mno-epsilon
10411 Generate floating-point comparison instructions that compare with respect
10412 to the @code{rE} epsilon register.
10414 @item -mabi=mmixware
10416 @opindex mabi-mmixware
10418 Generate code that passes function parameters and return values that (in
10419 the called function) are seen as registers @code{$0} and up, as opposed to
10420 the GNU ABI which uses global registers @code{$231} and up.
10422 @item -mzero-extend
10423 @itemx -mno-zero-extend
10424 @opindex mzero-extend
10425 @opindex mno-zero-extend
10426 When reading data from memory in sizes shorter than 64 bits, use (do not
10427 use) zero-extending load instructions by default, rather than
10428 sign-extending ones.
10431 @itemx -mno-knuthdiv
10433 @opindex mno-knuthdiv
10434 Make the result of a division yielding a remainder have the same sign as
10435 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10436 remainder follows the sign of the dividend. Both methods are
10437 arithmetically valid, the latter being almost exclusively used.
10439 @item -mtoplevel-symbols
10440 @itemx -mno-toplevel-symbols
10441 @opindex mtoplevel-symbols
10442 @opindex mno-toplevel-symbols
10443 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10444 code can be used with the @code{PREFIX} assembly directive.
10448 Generate an executable in the ELF format, rather than the default
10449 @samp{mmo} format used by the @command{mmix} simulator.
10451 @item -mbranch-predict
10452 @itemx -mno-branch-predict
10453 @opindex mbranch-predict
10454 @opindex mno-branch-predict
10455 Use (do not use) the probable-branch instructions, when static branch
10456 prediction indicates a probable branch.
10458 @item -mbase-addresses
10459 @itemx -mno-base-addresses
10460 @opindex mbase-addresses
10461 @opindex mno-base-addresses
10462 Generate (do not generate) code that uses @emph{base addresses}. Using a
10463 base address automatically generates a request (handled by the assembler
10464 and the linker) for a constant to be set up in a global register. The
10465 register is used for one or more base address requests within the range 0
10466 to 255 from the value held in the register. The generally leads to short
10467 and fast code, but the number of different data items that can be
10468 addressed is limited. This means that a program that uses lots of static
10469 data may require @option{-mno-base-addresses}.
10471 @item -msingle-exit
10472 @itemx -mno-single-exit
10473 @opindex msingle-exit
10474 @opindex mno-single-exit
10475 Force (do not force) generated code to have a single exit point in each
10479 @node PDP-11 Options
10480 @subsection PDP-11 Options
10481 @cindex PDP-11 Options
10483 These options are defined for the PDP-11:
10488 Use hardware FPP floating point. This is the default. (FIS floating
10489 point on the PDP-11/40 is not supported.)
10492 @opindex msoft-float
10493 Do not use hardware floating point.
10497 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10501 Return floating-point results in memory. This is the default.
10505 Generate code for a PDP-11/40.
10509 Generate code for a PDP-11/45. This is the default.
10513 Generate code for a PDP-11/10.
10515 @item -mbcopy-builtin
10516 @opindex bcopy-builtin
10517 Use inline @code{movstrhi} patterns for copying memory. This is the
10522 Do not use inline @code{movstrhi} patterns for copying memory.
10528 Use 16-bit @code{int}. This is the default.
10534 Use 32-bit @code{int}.
10537 @itemx -mno-float32
10539 @opindex mno-float32
10540 Use 64-bit @code{float}. This is the default.
10543 @itemx -mno-float64
10545 @opindex mno-float64
10546 Use 32-bit @code{float}.
10550 Use @code{abshi2} pattern. This is the default.
10554 Do not use @code{abshi2} pattern.
10556 @item -mbranch-expensive
10557 @opindex mbranch-expensive
10558 Pretend that branches are expensive. This is for experimenting with
10559 code generation only.
10561 @item -mbranch-cheap
10562 @opindex mbranch-cheap
10563 Do not pretend that branches are expensive. This is the default.
10567 Generate code for a system with split I&D.
10571 Generate code for a system without split I&D. This is the default.
10575 Use Unix assembler syntax. This is the default when configured for
10576 @samp{pdp11-*-bsd}.
10580 Use DEC assembler syntax. This is the default when configured for any
10581 PDP-11 target other than @samp{pdp11-*-bsd}.
10584 @node Xstormy16 Options
10585 @subsection Xstormy16 Options
10586 @cindex Xstormy16 Options
10588 These options are defined for Xstormy16:
10593 Choose startup files and linker script suitable for the simulator.
10597 @subsection FRV Options
10598 @cindex FRV Options
10604 Only use the first 32 general purpose registers.
10609 Use all 64 general purpose registers.
10614 Use only the first 32 floating point registers.
10619 Use all 64 floating point registers
10622 @opindex mhard-float
10624 Use hardware instructions for floating point operations.
10627 @opindex msoft-float
10629 Use library routines for floating point operations.
10634 Dynamically allocate condition code registers.
10639 Do not try to dynamically allocate condition code registers, only
10640 use @code{icc0} and @code{fcc0}.
10645 Change ABI to use double word insns.
10650 Do not use double word instructions.
10655 Use floating point double instructions.
10658 @opindex mno-double
10660 Do not use floating point double instructions.
10665 Use media instructions.
10670 Do not use media instructions.
10675 Use multiply and add/subtract instructions.
10678 @opindex mno-muladd
10680 Do not use multiply and add/subtract instructions.
10682 @item -mlibrary-pic
10683 @opindex mlibrary-pic
10685 Enable PIC support for building libraries
10690 Use only the first four media accumulator registers.
10695 Use all eight media accumulator registers.
10700 Pack VLIW instructions.
10705 Do not pack VLIW instructions.
10708 @opindex mno-eflags
10710 Do not mark ABI switches in e_flags.
10713 @opindex mcond-move
10715 Enable the use of conditional-move instructions (default).
10717 This switch is mainly for debugging the compiler and will likely be removed
10718 in a future version.
10720 @item -mno-cond-move
10721 @opindex mno-cond-move
10723 Disable the use of conditional-move instructions.
10725 This switch is mainly for debugging the compiler and will likely be removed
10726 in a future version.
10731 Enable the use of conditional set instructions (default).
10733 This switch is mainly for debugging the compiler and will likely be removed
10734 in a future version.
10739 Disable the use of conditional set instructions.
10741 This switch is mainly for debugging the compiler and will likely be removed
10742 in a future version.
10745 @opindex mcond-exec
10747 Enable the use of conditional execution (default).
10749 This switch is mainly for debugging the compiler and will likely be removed
10750 in a future version.
10752 @item -mno-cond-exec
10753 @opindex mno-cond-exec
10755 Disable the use of conditional execution.
10757 This switch is mainly for debugging the compiler and will likely be removed
10758 in a future version.
10760 @item -mvliw-branch
10761 @opindex mvliw-branch
10763 Run a pass to pack branches into VLIW instructions (default).
10765 This switch is mainly for debugging the compiler and will likely be removed
10766 in a future version.
10768 @item -mno-vliw-branch
10769 @opindex mno-vliw-branch
10771 Do not run a pass to pack branches into VLIW instructions.
10773 This switch is mainly for debugging the compiler and will likely be removed
10774 in a future version.
10776 @item -mmulti-cond-exec
10777 @opindex mmulti-cond-exec
10779 Enable optimization of @code{&&} and @code{||} in conditional execution
10782 This switch is mainly for debugging the compiler and will likely be removed
10783 in a future version.
10785 @item -mno-multi-cond-exec
10786 @opindex mno-multi-cond-exec
10788 Disable optimization of @code{&&} and @code{||} in conditional execution.
10790 This switch is mainly for debugging the compiler and will likely be removed
10791 in a future version.
10793 @item -mnested-cond-exec
10794 @opindex mnested-cond-exec
10796 Enable nested conditional execution optimizations (default).
10798 This switch is mainly for debugging the compiler and will likely be removed
10799 in a future version.
10801 @item -mno-nested-cond-exec
10802 @opindex mno-nested-cond-exec
10804 Disable nested conditional execution optimizations.
10806 This switch is mainly for debugging the compiler and will likely be removed
10807 in a future version.
10809 @item -mtomcat-stats
10810 @opindex mtomcat-stats
10812 Cause gas to print out tomcat statistics.
10814 @item -mcpu=@var{cpu}
10817 Select the processor type for which to generate code. Possible values are
10818 @samp{simple}, @samp{tomcat}, @samp{fr500}, @samp{fr400}, @samp{fr300},
10823 @node Xtensa Options
10824 @subsection Xtensa Options
10825 @cindex Xtensa Options
10827 These options are supported for Xtensa targets:
10831 @itemx -mno-const16
10833 @opindex mno-const16
10834 Enable or disable use of @code{CONST16} instructions for loading
10835 constant values. The @code{CONST16} instruction is currently not a
10836 standard option from Tensilica. When enabled, @code{CONST16}
10837 instructions are always used in place of the standard @code{L32R}
10838 instructions. The use of @code{CONST16} is enabled by default only if
10839 the @code{L32R} instruction is not available.
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 optimizations
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 -finhibit-size-directive
11065 @opindex finhibit-size-directive
11066 Don't output a @code{.size} assembler directive, or anything else that
11067 would cause trouble if the function is split in the middle, and the
11068 two halves are placed at locations far apart in memory. This option is
11069 used when compiling @file{crtstuff.c}; you should not need to use it
11072 @item -fverbose-asm
11073 @opindex fverbose-asm
11074 Put extra commentary information in the generated assembly code to
11075 make it more readable. This option is generally only of use to those
11076 who actually need to read the generated assembly code (perhaps while
11077 debugging the compiler itself).
11079 @option{-fno-verbose-asm}, the default, causes the
11080 extra information to be omitted and is useful when comparing two assembler
11085 @cindex global offset table
11087 Generate position-independent code (PIC) suitable for use in a shared
11088 library, if supported for the target machine. Such code accesses all
11089 constant addresses through a global offset table (GOT)@. The dynamic
11090 loader resolves the GOT entries when the program starts (the dynamic
11091 loader is not part of GCC; it is part of the operating system). If
11092 the GOT size for the linked executable exceeds a machine-specific
11093 maximum size, you get an error message from the linker indicating that
11094 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11095 instead. (These maximums are 8k on the SPARC and 32k
11096 on the m68k and RS/6000. The 386 has no such limit.)
11098 Position-independent code requires special support, and therefore works
11099 only on certain machines. For the 386, GCC supports PIC for System V
11100 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11101 position-independent.
11105 If supported for the target machine, emit position-independent code,
11106 suitable for dynamic linking and avoiding any limit on the size of the
11107 global offset table. This option makes a difference on the m68k
11110 Position-independent code requires special support, and therefore works
11111 only on certain machines.
11117 These options are similar to @option{-fpic} and @option{-fPIC}, but
11118 generated position independent code can be only linked into executables.
11119 Usually these options are used when @option{-pie} GCC option will be
11120 used during linking.
11122 @item -ffixed-@var{reg}
11124 Treat the register named @var{reg} as a fixed register; generated code
11125 should never refer to it (except perhaps as a stack pointer, frame
11126 pointer or in some other fixed role).
11128 @var{reg} must be the name of a register. The register names accepted
11129 are machine-specific and are defined in the @code{REGISTER_NAMES}
11130 macro in the machine description macro file.
11132 This flag does not have a negative form, because it specifies a
11135 @item -fcall-used-@var{reg}
11136 @opindex fcall-used
11137 Treat the register named @var{reg} as an allocable register that is
11138 clobbered by function calls. It may be allocated for temporaries or
11139 variables that do not live across a call. Functions compiled this way
11140 will not save and restore the register @var{reg}.
11142 It is an error to used this flag with the frame pointer or stack pointer.
11143 Use of this flag for other registers that have fixed pervasive roles in
11144 the machine's execution model will produce disastrous results.
11146 This flag does not have a negative form, because it specifies a
11149 @item -fcall-saved-@var{reg}
11150 @opindex fcall-saved
11151 Treat the register named @var{reg} as an allocable register saved by
11152 functions. It may be allocated even for temporaries or variables that
11153 live across a call. Functions compiled this way will save and restore
11154 the register @var{reg} if they use it.
11156 It is an error to used this flag with the frame pointer or stack pointer.
11157 Use of this flag for other registers that have fixed pervasive roles in
11158 the machine's execution model will produce disastrous results.
11160 A different sort of disaster will result from the use of this flag for
11161 a register in which function values may be returned.
11163 This flag does not have a negative form, because it specifies a
11166 @item -fpack-struct
11167 @opindex fpack-struct
11168 Pack all structure members together without holes.
11170 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
11171 code that is not binary compatible with code generated without that switch.
11172 Additionally, it makes the code suboptimal.
11173 Use it to conform to a non-default application binary interface.
11175 @item -finstrument-functions
11176 @opindex finstrument-functions
11177 Generate instrumentation calls for entry and exit to functions. Just
11178 after function entry and just before function exit, the following
11179 profiling functions will be called with the address of the current
11180 function and its call site. (On some platforms,
11181 @code{__builtin_return_address} does not work beyond the current
11182 function, so the call site information may not be available to the
11183 profiling functions otherwise.)
11186 void __cyg_profile_func_enter (void *this_fn,
11188 void __cyg_profile_func_exit (void *this_fn,
11192 The first argument is the address of the start of the current function,
11193 which may be looked up exactly in the symbol table.
11195 This currently disables function inlining. This restriction is
11196 expected to be removed in future releases.
11198 A function may be given the attribute @code{no_instrument_function}, in
11199 which case this instrumentation will not be done. This can be used, for
11200 example, for the profiling functions listed above, high-priority
11201 interrupt routines, and any functions from which the profiling functions
11202 cannot safely be called (perhaps signal handlers, if the profiling
11203 routines generate output or allocate memory).
11205 @item -fstack-check
11206 @opindex fstack-check
11207 Generate code to verify that you do not go beyond the boundary of the
11208 stack. You should specify this flag if you are running in an
11209 environment with multiple threads, but only rarely need to specify it in
11210 a single-threaded environment since stack overflow is automatically
11211 detected on nearly all systems if there is only one stack.
11213 Note that this switch does not actually cause checking to be done; the
11214 operating system must do that. The switch causes generation of code
11215 to ensure that the operating system sees the stack being extended.
11217 @item -fstack-limit-register=@var{reg}
11218 @itemx -fstack-limit-symbol=@var{sym}
11219 @itemx -fno-stack-limit
11220 @opindex fstack-limit-register
11221 @opindex fstack-limit-symbol
11222 @opindex fno-stack-limit
11223 Generate code to ensure that the stack does not grow beyond a certain value,
11224 either the value of a register or the address of a symbol. If the stack
11225 would grow beyond the value, a signal is raised. For most targets,
11226 the signal is raised before the stack overruns the boundary, so
11227 it is possible to catch the signal without taking special precautions.
11229 For instance, if the stack starts at absolute address @samp{0x80000000}
11230 and grows downwards, you can use the flags
11231 @option{-fstack-limit-symbol=__stack_limit} and
11232 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
11233 of 128KB@. Note that this may only work with the GNU linker.
11235 @cindex aliasing of parameters
11236 @cindex parameters, aliased
11237 @item -fargument-alias
11238 @itemx -fargument-noalias
11239 @itemx -fargument-noalias-global
11240 @opindex fargument-alias
11241 @opindex fargument-noalias
11242 @opindex fargument-noalias-global
11243 Specify the possible relationships among parameters and between
11244 parameters and global data.
11246 @option{-fargument-alias} specifies that arguments (parameters) may
11247 alias each other and may alias global storage.@*
11248 @option{-fargument-noalias} specifies that arguments do not alias
11249 each other, but may alias global storage.@*
11250 @option{-fargument-noalias-global} specifies that arguments do not
11251 alias each other and do not alias global storage.
11253 Each language will automatically use whatever option is required by
11254 the language standard. You should not need to use these options yourself.
11256 @item -fleading-underscore
11257 @opindex fleading-underscore
11258 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
11259 change the way C symbols are represented in the object file. One use
11260 is to help link with legacy assembly code.
11262 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
11263 generate code that is not binary compatible with code generated without that
11264 switch. Use it to conform to a non-default application binary interface.
11265 Not all targets provide complete support for this switch.
11267 @item -ftls-model=@var{model}
11268 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
11269 The @var{model} argument should be one of @code{global-dynamic},
11270 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
11272 The default without @option{-fpic} is @code{initial-exec}; with
11273 @option{-fpic} the default is @code{global-dynamic}.
11278 @node Environment Variables
11279 @section Environment Variables Affecting GCC
11280 @cindex environment variables
11282 @c man begin ENVIRONMENT
11283 This section describes several environment variables that affect how GCC
11284 operates. Some of them work by specifying directories or prefixes to use
11285 when searching for various kinds of files. Some are used to specify other
11286 aspects of the compilation environment.
11288 Note that you can also specify places to search using options such as
11289 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
11290 take precedence over places specified using environment variables, which
11291 in turn take precedence over those specified by the configuration of GCC@.
11292 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
11293 GNU Compiler Collection (GCC) Internals}.
11298 @c @itemx LC_COLLATE
11300 @c @itemx LC_MONETARY
11301 @c @itemx LC_NUMERIC
11306 @c @findex LC_COLLATE
11307 @findex LC_MESSAGES
11308 @c @findex LC_MONETARY
11309 @c @findex LC_NUMERIC
11313 These environment variables control the way that GCC uses
11314 localization information that allow GCC to work with different
11315 national conventions. GCC inspects the locale categories
11316 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
11317 so. These locale categories can be set to any value supported by your
11318 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
11319 Kingdom encoded in UTF-8.
11321 The @env{LC_CTYPE} environment variable specifies character
11322 classification. GCC uses it to determine the character boundaries in
11323 a string; this is needed for some multibyte encodings that contain quote
11324 and escape characters that would otherwise be interpreted as a string
11327 The @env{LC_MESSAGES} environment variable specifies the language to
11328 use in diagnostic messages.
11330 If the @env{LC_ALL} environment variable is set, it overrides the value
11331 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
11332 and @env{LC_MESSAGES} default to the value of the @env{LANG}
11333 environment variable. If none of these variables are set, GCC
11334 defaults to traditional C English behavior.
11338 If @env{TMPDIR} is set, it specifies the directory to use for temporary
11339 files. GCC uses temporary files to hold the output of one stage of
11340 compilation which is to be used as input to the next stage: for example,
11341 the output of the preprocessor, which is the input to the compiler
11344 @item GCC_EXEC_PREFIX
11345 @findex GCC_EXEC_PREFIX
11346 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
11347 names of the subprograms executed by the compiler. No slash is added
11348 when this prefix is combined with the name of a subprogram, but you can
11349 specify a prefix that ends with a slash if you wish.
11351 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
11352 an appropriate prefix to use based on the pathname it was invoked with.
11354 If GCC cannot find the subprogram using the specified prefix, it
11355 tries looking in the usual places for the subprogram.
11357 The default value of @env{GCC_EXEC_PREFIX} is
11358 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
11359 of @code{prefix} when you ran the @file{configure} script.
11361 Other prefixes specified with @option{-B} take precedence over this prefix.
11363 This prefix is also used for finding files such as @file{crt0.o} that are
11366 In addition, the prefix is used in an unusual way in finding the
11367 directories to search for header files. For each of the standard
11368 directories whose name normally begins with @samp{/usr/local/lib/gcc}
11369 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
11370 replacing that beginning with the specified prefix to produce an
11371 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
11372 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
11373 These alternate directories are searched first; the standard directories
11376 @item COMPILER_PATH
11377 @findex COMPILER_PATH
11378 The value of @env{COMPILER_PATH} is a colon-separated list of
11379 directories, much like @env{PATH}. GCC tries the directories thus
11380 specified when searching for subprograms, if it can't find the
11381 subprograms using @env{GCC_EXEC_PREFIX}.
11384 @findex LIBRARY_PATH
11385 The value of @env{LIBRARY_PATH} is a colon-separated list of
11386 directories, much like @env{PATH}. When configured as a native compiler,
11387 GCC tries the directories thus specified when searching for special
11388 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
11389 using GCC also uses these directories when searching for ordinary
11390 libraries for the @option{-l} option (but directories specified with
11391 @option{-L} come first).
11395 @cindex locale definition
11396 This variable is used to pass locale information to the compiler. One way in
11397 which this information is used is to determine the character set to be used
11398 when character literals, string literals and comments are parsed in C and C++.
11399 When the compiler is configured to allow multibyte characters,
11400 the following values for @env{LANG} are recognized:
11404 Recognize JIS characters.
11406 Recognize SJIS characters.
11408 Recognize EUCJP characters.
11411 If @env{LANG} is not defined, or if it has some other value, then the
11412 compiler will use mblen and mbtowc as defined by the default locale to
11413 recognize and translate multibyte characters.
11417 Some additional environments variables affect the behavior of the
11420 @include cppenv.texi
11424 @node Precompiled Headers
11425 @section Using Precompiled Headers
11426 @cindex precompiled headers
11427 @cindex speed of compilation
11429 Often large projects have many header files that are included in every
11430 source file. The time the compiler takes to process these header files
11431 over and over again can account for nearly all of the time required to
11432 build the project. To make builds faster, GCC allows users to
11433 `precompile' a header file; then, if builds can use the precompiled
11434 header file they will be much faster.
11436 @strong{Caution:} There are a few known situations where GCC will
11437 crash when trying to use a precompiled header. If you have trouble
11438 with a precompiled header, you should remove the precompiled header
11439 and compile without it. In addition, please use GCC's on-line
11440 defect-tracking system to report any problems you encounter with
11441 precompiled headers. @xref{Bugs}.
11443 To create a precompiled header file, simply compile it as you would any
11444 other file, if necessary using the @option{-x} option to make the driver
11445 treat it as a C or C++ header file. You will probably want to use a
11446 tool like @command{make} to keep the precompiled header up-to-date when
11447 the headers it contains change.
11449 A precompiled header file will be searched for when @code{#include} is
11450 seen in the compilation. As it searches for the included file
11451 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
11452 compiler looks for a precompiled header in each directory just before it
11453 looks for the include file in that directory. The name searched for is
11454 the name specified in the @code{#include} with @samp{.gch} appended. If
11455 the precompiled header file can't be used, it is ignored.
11457 For instance, if you have @code{#include "all.h"}, and you have
11458 @file{all.h.gch} in the same directory as @file{all.h}, then the
11459 precompiled header file will be used if possible, and the original
11460 header will be used otherwise.
11462 Alternatively, you might decide to put the precompiled header file in a
11463 directory and use @option{-I} to ensure that directory is searched
11464 before (or instead of) the directory containing the original header.
11465 Then, if you want to check that the precompiled header file is always
11466 used, you can put a file of the same name as the original header in this
11467 directory containing an @code{#error} command.
11469 This also works with @option{-include}. So yet another way to use
11470 precompiled headers, good for projects not designed with precompiled
11471 header files in mind, is to simply take most of the header files used by
11472 a project, include them from another header file, precompile that header
11473 file, and @option{-include} the precompiled header. If the header files
11474 have guards against multiple inclusion, they will be skipped because
11475 they've already been included (in the precompiled header).
11477 If you need to precompile the same header file for different
11478 languages, targets, or compiler options, you can instead make a
11479 @emph{directory} named like @file{all.h.gch}, and put each precompiled
11480 header in the directory. (It doesn't matter what you call the files
11481 in the directory, every precompiled header in the directory will be
11482 considered.) The first precompiled header encountered in the
11483 directory that is valid for this compilation will be used; they're
11484 searched in no particular order.
11486 There are many other possibilities, limited only by your imagination,
11487 good sense, and the constraints of your build system.
11489 A precompiled header file can be used only when these conditions apply:
11493 Only one precompiled header can be used in a particular compilation.
11495 A precompiled header can't be used once the first C token is seen. You
11496 can have preprocessor directives before a precompiled header; you can
11497 even include a precompiled header from inside another header, so long as
11498 there are no C tokens before the @code{#include}.
11500 The precompiled header file must be produced for the same language as
11501 the current compilation. You can't use a C precompiled header for a C++
11504 The precompiled header file must be produced by the same compiler
11505 version and configuration as the current compilation is using.
11506 The easiest way to guarantee this is to use the same compiler binary
11507 for creating and using precompiled headers.
11509 Any macros defined before the precompiled header (including with
11510 @option{-D}) must either be defined in the same way as when the
11511 precompiled header was generated, or must not affect the precompiled
11512 header, which usually means that the they don't appear in the
11513 precompiled header at all.
11515 Certain command-line options must be defined in the same way as when the
11516 precompiled header was generated. At present, it's not clear which
11517 options are safe to change and which are not; the safest choice is to
11518 use exactly the same options when generating and using the precompiled
11522 For all of these but the last, the compiler will automatically ignore
11523 the precompiled header if the conditions aren't met. For the last item,
11524 some option changes will cause the precompiled header to be rejected,
11525 but not all incompatible option combinations have yet been found. If
11526 you find a new incompatible combination, please consider filing a bug
11527 report, see @ref{Bugs}.
11529 @node Running Protoize
11530 @section Running Protoize
11532 The program @code{protoize} is an optional part of GCC@. You can use
11533 it to add prototypes to a program, thus converting the program to ISO
11534 C in one respect. The companion program @code{unprotoize} does the
11535 reverse: it removes argument types from any prototypes that are found.
11537 When you run these programs, you must specify a set of source files as
11538 command line arguments. The conversion programs start out by compiling
11539 these files to see what functions they define. The information gathered
11540 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
11542 After scanning comes actual conversion. The specified files are all
11543 eligible to be converted; any files they include (whether sources or
11544 just headers) are eligible as well.
11546 But not all the eligible files are converted. By default,
11547 @code{protoize} and @code{unprotoize} convert only source and header
11548 files in the current directory. You can specify additional directories
11549 whose files should be converted with the @option{-d @var{directory}}
11550 option. You can also specify particular files to exclude with the
11551 @option{-x @var{file}} option. A file is converted if it is eligible, its
11552 directory name matches one of the specified directory names, and its
11553 name within the directory has not been excluded.
11555 Basic conversion with @code{protoize} consists of rewriting most
11556 function definitions and function declarations to specify the types of
11557 the arguments. The only ones not rewritten are those for varargs
11560 @code{protoize} optionally inserts prototype declarations at the
11561 beginning of the source file, to make them available for any calls that
11562 precede the function's definition. Or it can insert prototype
11563 declarations with block scope in the blocks where undeclared functions
11566 Basic conversion with @code{unprotoize} consists of rewriting most
11567 function declarations to remove any argument types, and rewriting
11568 function definitions to the old-style pre-ISO form.
11570 Both conversion programs print a warning for any function declaration or
11571 definition that they can't convert. You can suppress these warnings
11574 The output from @code{protoize} or @code{unprotoize} replaces the
11575 original source file. The original file is renamed to a name ending
11576 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
11577 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
11578 for DOS) file already exists, then the source file is simply discarded.
11580 @code{protoize} and @code{unprotoize} both depend on GCC itself to
11581 scan the program and collect information about the functions it uses.
11582 So neither of these programs will work until GCC is installed.
11584 Here is a table of the options you can use with @code{protoize} and
11585 @code{unprotoize}. Each option works with both programs unless
11589 @item -B @var{directory}
11590 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
11591 usual directory (normally @file{/usr/local/lib}). This file contains
11592 prototype information about standard system functions. This option
11593 applies only to @code{protoize}.
11595 @item -c @var{compilation-options}
11596 Use @var{compilation-options} as the options when running @command{gcc} to
11597 produce the @samp{.X} files. The special option @option{-aux-info} is
11598 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
11600 Note that the compilation options must be given as a single argument to
11601 @code{protoize} or @code{unprotoize}. If you want to specify several
11602 @command{gcc} options, you must quote the entire set of compilation options
11603 to make them a single word in the shell.
11605 There are certain @command{gcc} arguments that you cannot use, because they
11606 would produce the wrong kind of output. These include @option{-g},
11607 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
11608 the @var{compilation-options}, they are ignored.
11611 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
11612 systems) instead of @samp{.c}. This is convenient if you are converting
11613 a C program to C++. This option applies only to @code{protoize}.
11616 Add explicit global declarations. This means inserting explicit
11617 declarations at the beginning of each source file for each function
11618 that is called in the file and was not declared. These declarations
11619 precede the first function definition that contains a call to an
11620 undeclared function. This option applies only to @code{protoize}.
11622 @item -i @var{string}
11623 Indent old-style parameter declarations with the string @var{string}.
11624 This option applies only to @code{protoize}.
11626 @code{unprotoize} converts prototyped function definitions to old-style
11627 function definitions, where the arguments are declared between the
11628 argument list and the initial @samp{@{}. By default, @code{unprotoize}
11629 uses five spaces as the indentation. If you want to indent with just
11630 one space instead, use @option{-i " "}.
11633 Keep the @samp{.X} files. Normally, they are deleted after conversion
11637 Add explicit local declarations. @code{protoize} with @option{-l} inserts
11638 a prototype declaration for each function in each block which calls the
11639 function without any declaration. This option applies only to
11643 Make no real changes. This mode just prints information about the conversions
11644 that would have been done without @option{-n}.
11647 Make no @samp{.save} files. The original files are simply deleted.
11648 Use this option with caution.
11650 @item -p @var{program}
11651 Use the program @var{program} as the compiler. Normally, the name
11652 @file{gcc} is used.
11655 Work quietly. Most warnings are suppressed.
11658 Print the version number, just like @option{-v} for @command{gcc}.
11661 If you need special compiler options to compile one of your program's
11662 source files, then you should generate that file's @samp{.X} file
11663 specially, by running @command{gcc} on that source file with the
11664 appropriate options and the option @option{-aux-info}. Then run
11665 @code{protoize} on the entire set of files. @code{protoize} will use
11666 the existing @samp{.X} file because it is newer than the source file.
11670 gcc -Dfoo=bar file1.c -aux-info file1.X
11675 You need to include the special files along with the rest in the
11676 @code{protoize} command, even though their @samp{.X} files already
11677 exist, because otherwise they won't get converted.
11679 @xref{Protoize Caveats}, for more information on how to use
11680 @code{protoize} successfully.