1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
11 @c man begin COPYRIGHT
12 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
13 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
15 Permission is granted to copy, distribute and/or modify this document
16 under the terms of the GNU Free Documentation License, Version 1.2 or
17 any later version published by the Free Software Foundation; with the
18 Invariant Sections being ``GNU General Public License'' and ``Funding
19 Free Software'', the Front-Cover texts being (a) (see below), and with
20 the Back-Cover Texts being (b) (see below). A copy of the license is
21 included in the gfdl(7) man page.
23 (a) The FSF's Front-Cover Text is:
27 (b) The FSF's Back-Cover Text is:
29 You have freedom to copy and modify this GNU Manual, like GNU
30 software. Copies published by the Free Software Foundation raise
31 funds for GNU development.
33 @c Set file name and title for the man page.
35 @settitle GNU project C and C++ compiler
37 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
38 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
39 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
40 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
41 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
42 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
43 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
45 Only the most useful options are listed here; see below for the
46 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
49 gpl(7), gfdl(7), fsf-funding(7),
50 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
51 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
52 @file{ld}, @file{binutils} and @file{gdb}.
55 For instructions on reporting bugs, see
56 @w{@uref{http://gcc.gnu.org/bugs.html}}.
59 See the Info entry for @command{gcc}, or
60 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
61 for contributors to GCC@.
66 @chapter GCC Command Options
67 @cindex GCC command options
68 @cindex command options
69 @cindex options, GCC command
71 @c man begin DESCRIPTION
72 When you invoke GCC, it normally does preprocessing, compilation,
73 assembly and linking. The ``overall options'' allow you to stop this
74 process at an intermediate stage. For example, the @option{-c} option
75 says not to run the linker. Then the output consists of object files
76 output by the assembler.
78 Other options are passed on to one stage of processing. Some options
79 control the preprocessor and others the compiler itself. Yet other
80 options control the assembler and linker; most of these are not
81 documented here, since you rarely need to use any of them.
83 @cindex C compilation options
84 Most of the command line options that you can use with GCC are useful
85 for C programs; when an option is only useful with another language
86 (usually C++), the explanation says so explicitly. If the description
87 for a particular option does not mention a source language, you can use
88 that option with all supported languages.
90 @cindex C++ compilation options
91 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
92 options for compiling C++ programs.
94 @cindex grouping options
95 @cindex options, grouping
96 The @command{gcc} program accepts options and file names as operands. Many
97 options have multi-letter names; therefore multiple single-letter options
98 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
101 @cindex order of options
102 @cindex options, order
103 You can mix options and other arguments. For the most part, the order
104 you use doesn't matter. Order does matter when you use several options
105 of the same kind; for example, if you specify @option{-L} more than once,
106 the directories are searched in the order specified.
108 Many options have long names starting with @samp{-f} or with
109 @samp{-W}---for example,
110 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
111 these have both positive and negative forms; the negative form of
112 @option{-ffoo} would be @option{-fno-foo}. This manual documents
113 only one of these two forms, whichever one is not the default.
117 @xref{Option Index}, for an index to GCC's options.
120 * Option Summary:: Brief list of all options, without explanations.
121 * Overall Options:: Controlling the kind of output:
122 an executable, object files, assembler files,
123 or preprocessed source.
124 * Invoking G++:: Compiling C++ programs.
125 * C Dialect Options:: Controlling the variant of C language compiled.
126 * C++ Dialect Options:: Variations on C++.
127 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
129 * Language Independent Options:: Controlling how diagnostics should be
131 * Warning Options:: How picky should the compiler be?
132 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
133 * Optimize Options:: How much optimization?
134 * Preprocessor Options:: Controlling header files and macro definitions.
135 Also, getting dependency information for Make.
136 * Assembler Options:: Passing options to the assembler.
137 * Link Options:: Specifying libraries and so on.
138 * Directory Options:: Where to find header files and libraries.
139 Where to find the compiler executable files.
140 * Spec Files:: How to pass switches to sub-processes.
141 * Target Options:: Running a cross-compiler, or an old version of GCC.
142 * Submodel Options:: Specifying minor hardware or convention variations,
143 such as 68010 vs 68020.
144 * Code Gen Options:: Specifying conventions for function calls, data layout
146 * Environment Variables:: Env vars that affect GCC.
147 * Precompiled Headers:: Compiling a header once, and using it many times.
148 * Running Protoize:: Automatically adding or removing function prototypes.
154 @section Option Summary
156 Here is a summary of all the options, grouped by type. Explanations are
157 in the following sections.
160 @item Overall Options
161 @xref{Overall Options,,Options Controlling the Kind of Output}.
162 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
163 -x @var{language} -v -### --help --target-help --version @@@var{file}}
165 @item C Language Options
166 @xref{C Dialect Options,,Options Controlling C Dialect}.
167 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
168 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
169 -fhosted -ffreestanding -fms-extensions @gol
170 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
171 -fallow-single-precision -fcond-mismatch @gol
172 -fsigned-bitfields -fsigned-char @gol
173 -funsigned-bitfields -funsigned-char}
175 @item C++ Language Options
176 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
177 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
178 -fconserve-space -ffriend-injection -fno-const-strings @gol
179 -fno-elide-constructors @gol
180 -fno-enforce-eh-specs @gol
181 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
182 -fno-implicit-templates @gol
183 -fno-implicit-inline-templates @gol
184 -fno-implement-inlines -fms-extensions @gol
185 -fno-nonansi-builtins -fno-operator-names @gol
186 -fno-optional-diags -fpermissive @gol
187 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
188 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
189 -fno-default-inline -fvisibility-inlines-hidden @gol
190 -Wabi -Wctor-dtor-privacy @gol
191 -Wnon-virtual-dtor -Wreorder @gol
192 -Weffc++ -Wno-deprecated -Wstrict-null-sentinel @gol
193 -Wno-non-template-friend -Wold-style-cast @gol
194 -Woverloaded-virtual -Wno-pmf-conversions @gol
197 @item Objective-C and Objective-C++ Language Options
198 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
199 Objective-C and Objective-C++ Dialects}.
201 -fconstant-string-class=@var{class-name} @gol
202 -fgnu-runtime -fnext-runtime @gol
203 -fno-nil-receivers @gol
204 -fobjc-call-cxx-cdtors @gol
205 -fobjc-direct-dispatch @gol
206 -fobjc-exceptions @gol
208 -freplace-objc-classes @gol
211 -Wassign-intercept @gol
212 -Wno-protocol -Wselector @gol
213 -Wstrict-selector-match @gol
214 -Wundeclared-selector}
216 @item Language Independent Options
217 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
218 @gccoptlist{-fmessage-length=@var{n} @gol
219 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}} @gol
220 -fdiagnostics-show-options
222 @item Warning Options
223 @xref{Warning Options,,Options to Request or Suppress Warnings}.
224 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
225 -w -Wextra -Wall -Waggregate-return -Walways-true -Wno-attributes @gol
226 -Wc++-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
227 -Wconversion -Wno-deprecated-declarations @gol
228 -Wdisabled-optimization -Wno-div-by-zero -Wno-endif-labels @gol
229 -Werror -Werror-* -Werror-implicit-function-declaration @gol
230 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
231 -Wno-format-extra-args -Wformat-nonliteral @gol
232 -Wformat-security -Wformat-y2k @gol
233 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
234 -Wimport -Wno-import -Winit-self -Winline @gol
235 -Wno-int-to-pointer-cast @gol
236 -Wno-invalid-offsetof -Winvalid-pch @gol
237 -Wlarger-than-@var{len} -Wunsafe-loop-optimizations -Wlong-long @gol
238 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
239 -Wmissing-format-attribute -Wmissing-include-dirs @gol
240 -Wmissing-noreturn @gol
241 -Wno-multichar -Wnonnull -Wpacked -Wpadded @gol
242 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
243 -Wredundant-decls @gol
244 -Wreturn-type -Wsequence-point -Wshadow @gol
245 -Wsign-compare -Wstack-protector @gol
246 -Wstrict-aliasing -Wstrict-aliasing=2 @gol
247 -Wstring-literal-comparison @gol
248 -Wswitch -Wswitch-default -Wswitch-enum @gol
249 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
250 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
251 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
252 -Wunused-value -Wunused-variable -Wvariadic-macros @gol
253 -Wvolatile-register-var -Wwrite-strings}
255 @item C-only Warning Options
256 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
257 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
258 -Wstrict-prototypes -Wtraditional @gol
259 -Wdeclaration-after-statement -Wno-pointer-sign}
261 @item Debugging Options
262 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
263 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
264 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
265 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
266 -fdump-ipa-all -fdump-ipa-cgraph @gol
268 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
269 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
270 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
271 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
273 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
274 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
275 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
276 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
277 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
278 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
279 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
280 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
281 -fdump-tree-nrv -fdump-tree-vect @gol
282 -fdump-tree-sink @gol
283 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
284 -fdump-tree-salias @gol
285 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
287 -ftree-vectorizer-verbose=@var{n} @gol
288 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
289 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
290 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
291 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
292 -ftest-coverage -ftime-report -fvar-tracking @gol
293 -g -g@var{level} -gcoff -gdwarf-2 @gol
294 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
295 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
296 -print-multi-directory -print-multi-lib @gol
297 -print-prog-name=@var{program} -print-search-dirs -Q @gol
300 @item Optimization Options
301 @xref{Optimize Options,,Options that Control Optimization}.
302 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
303 -falign-labels=@var{n} -falign-loops=@var{n} @gol
304 -fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
305 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
306 -fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
307 -fcaller-saves -fcprop-registers -fcse-follow-jumps @gol
308 -fcse-skip-blocks -fcx-limited-range -fdata-sections @gol
309 -fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining @gol
310 -fexpensive-optimizations -ffast-math -ffloat-store @gol
311 -fforce-addr -ffunction-sections @gol
312 -fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol
313 -floop-optimize -fcrossjumping -fif-conversion -fif-conversion2 @gol
314 -finline-functions -finline-functions-called-once @gol
315 -finline-limit=@var{n} -fkeep-inline-functions @gol
316 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
317 -fmodulo-sched -fno-branch-count-reg @gol
318 -fno-default-inline -fno-defer-pop -floop-optimize2 -fmove-loop-invariants @gol
319 -fno-function-cse -fno-guess-branch-probability @gol
320 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
321 -funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only @gol
322 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
323 -fomit-frame-pointer -foptimize-register-move @gol
324 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
325 -fprofile-generate -fprofile-use @gol
326 -fregmove -frename-registers @gol
327 -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
328 -frerun-cse-after-loop -frerun-loop-opt @gol
329 -frounding-math -frtl-abstract-sequences @gol
330 -fschedule-insns -fschedule-insns2 @gol
331 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
332 -fsched-spec-load-dangerous @gol
333 -fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol
334 -fsched2-use-superblocks @gol
335 -fsched2-use-traces -freschedule-modulo-scheduled-loops @gol
336 -fsignaling-nans -fsingle-precision-constant @gol
337 -fstack-protector -fstack-protector-all @gol
338 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
339 -funroll-all-loops -funroll-loops -fpeel-loops @gol
340 -fsplit-ivs-in-unroller -funswitch-loops @gol
341 -fvariable-expansion-in-unroller @gol
342 -ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol
343 -ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol
344 -ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
345 -ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol
346 -ftree-vect-loop-version -ftree-salias -fweb @gol
347 -ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
348 --param @var{name}=@var{value}
349 -O -O0 -O1 -O2 -O3 -Os}
351 @item Preprocessor Options
352 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
353 @gccoptlist{-A@var{question}=@var{answer} @gol
354 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
355 -C -dD -dI -dM -dN @gol
356 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
357 -idirafter @var{dir} @gol
358 -include @var{file} -imacros @var{file} @gol
359 -iprefix @var{file} -iwithprefix @var{dir} @gol
360 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
361 -imultilib @var{dir} -isysroot @var{dir} @gol
362 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
363 -P -fworking-directory -remap @gol
364 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
365 -Xpreprocessor @var{option}}
367 @item Assembler Option
368 @xref{Assembler Options,,Passing Options to the Assembler}.
369 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
372 @xref{Link Options,,Options for Linking}.
373 @gccoptlist{@var{object-file-name} -l@var{library} @gol
374 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
375 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
376 -Wl,@var{option} -Xlinker @var{option} @gol
379 @item Directory Options
380 @xref{Directory Options,,Options for Directory Search}.
381 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
382 -specs=@var{file} -I- --sysroot=@var{dir}}
385 @c I wrote this xref this way to avoid overfull hbox. -- rms
386 @xref{Target Options}.
387 @gccoptlist{-V @var{version} -b @var{machine}}
389 @item Machine Dependent Options
390 @xref{Submodel Options,,Hardware Models and Configurations}.
391 @c This list is ordered alphanumerically by subsection name.
392 @c Try and put the significant identifier (CPU or system) first,
393 @c so users have a clue at guessing where the ones they want will be.
396 @gccoptlist{-EB -EL @gol
397 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
398 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
401 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
402 -mabi=@var{name} @gol
403 -mapcs-stack-check -mno-apcs-stack-check @gol
404 -mapcs-float -mno-apcs-float @gol
405 -mapcs-reentrant -mno-apcs-reentrant @gol
406 -msched-prolog -mno-sched-prolog @gol
407 -mlittle-endian -mbig-endian -mwords-little-endian @gol
408 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
409 -mthumb-interwork -mno-thumb-interwork @gol
410 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
411 -mstructure-size-boundary=@var{n} @gol
412 -mabort-on-noreturn @gol
413 -mlong-calls -mno-long-calls @gol
414 -msingle-pic-base -mno-single-pic-base @gol
415 -mpic-register=@var{reg} @gol
416 -mnop-fun-dllimport @gol
417 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
418 -mpoke-function-name @gol
420 -mtpcs-frame -mtpcs-leaf-frame @gol
421 -mcaller-super-interworking -mcallee-super-interworking @gol
425 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
426 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
428 @emph{Blackfin Options}
429 @gccoptlist{-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
430 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
431 -mlow-64k -mno-low64k -mid-shared-library @gol
432 -mno-id-shared-library -mshared-library-id=@var{n} @gol
433 -mlong-calls -mno-long-calls}
436 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
437 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
438 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
439 -mstack-align -mdata-align -mconst-align @gol
440 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
441 -melf -maout -melinux -mlinux -sim -sim2 @gol
442 -mmul-bug-workaround -mno-mul-bug-workaround}
445 @gccoptlist{-mmac -mpush-args}
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
452 -dependency-file -dylib_file -dylinker_install_name @gol
453 -dynamic -dynamiclib -exported_symbols_list @gol
454 -filelist -flat_namespace -force_cpusubtype_ALL @gol
455 -force_flat_namespace -headerpad_max_install_names @gol
456 -image_base -init -install_name -keep_private_externs @gol
457 -multi_module -multiply_defined -multiply_defined_unused @gol
458 -noall_load -no_dead_strip_inits_and_terms @gol
459 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
460 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
461 -private_bundle -read_only_relocs -sectalign @gol
462 -sectobjectsymbols -whyload -seg1addr @gol
463 -sectcreate -sectobjectsymbols -sectorder @gol
464 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
465 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
466 -segprot -segs_read_only_addr -segs_read_write_addr @gol
467 -single_module -static -sub_library -sub_umbrella @gol
468 -twolevel_namespace -umbrella -undefined @gol
469 -unexported_symbols_list -weak_reference_mismatches @gol
470 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
473 @emph{DEC Alpha Options}
474 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
475 -mieee -mieee-with-inexact -mieee-conformant @gol
476 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
477 -mtrap-precision=@var{mode} -mbuild-constants @gol
478 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
479 -mbwx -mmax -mfix -mcix @gol
480 -mfloat-vax -mfloat-ieee @gol
481 -mexplicit-relocs -msmall-data -mlarge-data @gol
482 -msmall-text -mlarge-text @gol
483 -mmemory-latency=@var{time}}
485 @emph{DEC Alpha/VMS Options}
486 @gccoptlist{-mvms-return-codes}
489 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
490 -mhard-float -msoft-float @gol
491 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
492 -mdouble -mno-double @gol
493 -mmedia -mno-media -mmuladd -mno-muladd @gol
494 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
495 -mlinked-fp -mlong-calls -malign-labels @gol
496 -mlibrary-pic -macc-4 -macc-8 @gol
497 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
498 -moptimize-membar -mno-optimize-membar @gol
499 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
500 -mvliw-branch -mno-vliw-branch @gol
501 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
502 -mno-nested-cond-exec -mtomcat-stats @gol
506 @emph{H8/300 Options}
507 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
510 @gccoptlist{-march=@var{architecture-type} @gol
511 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
512 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
513 -mfixed-range=@var{register-range} @gol
514 -mjump-in-delay -mlinker-opt -mlong-calls @gol
515 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
516 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
517 -mno-jump-in-delay -mno-long-load-store @gol
518 -mno-portable-runtime -mno-soft-float @gol
519 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
520 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
521 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
522 -munix=@var{unix-std} -nolibdld -static -threads}
524 @emph{i386 and x86-64 Options}
525 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
526 -mfpmath=@var{unit} @gol
527 -masm=@var{dialect} -mno-fancy-math-387 @gol
528 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
529 -mno-wide-multiply -mrtd -malign-double @gol
530 -mpreferred-stack-boundary=@var{num} @gol
531 -mmmx -msse -msse2 -msse3 -m3dnow @gol
532 -mthreads -mno-align-stringops -minline-all-stringops @gol
533 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
534 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
535 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
536 -mcmodel=@var{code-model} @gol
537 -m32 -m64 -mlarge-data-threshold=@var{num}}
540 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
541 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
542 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
543 -minline-float-divide-max-throughput @gol
544 -minline-int-divide-min-latency @gol
545 -minline-int-divide-max-throughput @gol
546 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
547 -mno-dwarf2-asm -mearly-stop-bits @gol
548 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
549 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64}
551 @emph{M32R/D Options}
552 @gccoptlist{-m32r2 -m32rx -m32r @gol
554 -malign-loops -mno-align-loops @gol
555 -missue-rate=@var{number} @gol
556 -mbranch-cost=@var{number} @gol
557 -mmodel=@var{code-size-model-type} @gol
558 -msdata=@var{sdata-type} @gol
559 -mno-flush-func -mflush-func=@var{name} @gol
560 -mno-flush-trap -mflush-trap=@var{number} @gol
564 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
566 @emph{M680x0 Options}
567 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
568 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
569 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
570 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
571 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
573 @emph{M68hc1x Options}
574 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
575 -mauto-incdec -minmax -mlong-calls -mshort @gol
576 -msoft-reg-count=@var{count}}
579 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
580 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
581 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
582 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
583 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
586 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
587 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
588 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
589 -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 @gol
590 -mhard-float -msoft-float -msingle-float -mdouble-float @gol
591 -mdsp -mpaired-single -mips3d @gol
592 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
593 -G@var{num} -membedded-data -mno-embedded-data @gol
594 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
595 -msplit-addresses -mno-split-addresses @gol
596 -mexplicit-relocs -mno-explicit-relocs @gol
597 -mcheck-zero-division -mno-check-zero-division @gol
598 -mdivide-traps -mdivide-breaks @gol
599 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
600 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
601 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
602 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 @gol
603 -mfix-sb1 -mno-fix-sb1 @gol
604 -mflush-func=@var{func} -mno-flush-func @gol
605 -mbranch-likely -mno-branch-likely @gol
606 -mfp-exceptions -mno-fp-exceptions @gol
607 -mvr4130-align -mno-vr4130-align}
610 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
611 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
612 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
613 -mno-base-addresses -msingle-exit -mno-single-exit}
615 @emph{MN10300 Options}
616 @gccoptlist{-mmult-bug -mno-mult-bug @gol
617 -mam33 -mno-am33 @gol
618 -mam33-2 -mno-am33-2 @gol
619 -mreturn-pointer-on-d0 @gol
623 @gccoptlist{-mno-crt0 -mbacc -msim @gol
624 -march=@var{cpu-type} }
626 @emph{PDP-11 Options}
627 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
628 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
629 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
630 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
631 -mbranch-expensive -mbranch-cheap @gol
632 -msplit -mno-split -munix-asm -mdec-asm}
634 @emph{PowerPC Options}
635 See RS/6000 and PowerPC Options.
637 @emph{RS/6000 and PowerPC Options}
638 @gccoptlist{-mcpu=@var{cpu-type} @gol
639 -mtune=@var{cpu-type} @gol
640 -mpower -mno-power -mpower2 -mno-power2 @gol
641 -mpowerpc -mpowerpc64 -mno-powerpc @gol
642 -maltivec -mno-altivec @gol
643 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
644 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
645 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
646 -mnew-mnemonics -mold-mnemonics @gol
647 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
648 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
649 -malign-power -malign-natural @gol
650 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
651 -mstring -mno-string -mupdate -mno-update @gol
652 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
653 -mstrict-align -mno-strict-align -mrelocatable @gol
654 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
655 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
656 -mdynamic-no-pic -maltivec -mswdiv @gol
657 -mprioritize-restricted-insns=@var{priority} @gol
658 -msched-costly-dep=@var{dependence_type} @gol
659 -minsert-sched-nops=@var{scheme} @gol
660 -mcall-sysv -mcall-netbsd @gol
661 -maix-struct-return -msvr4-struct-return @gol
662 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
663 -misel -mno-isel @gol
664 -misel=yes -misel=no @gol
666 -mspe=yes -mspe=no @gol
667 -mvrsave -mno-vrsave @gol
668 -mmulhw -mno-mulhw @gol
669 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
670 -mprototype -mno-prototype @gol
671 -msim -mmvme -mads -myellowknife -memb -msdata @gol
672 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
674 @emph{S/390 and zSeries Options}
675 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
676 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
677 -mpacked-stack -mno-packed-stack @gol
678 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
679 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
680 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
681 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
684 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
685 -m4-nofpu -m4-single-only -m4-single -m4 @gol
686 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
687 -m5-64media -m5-64media-nofpu @gol
688 -m5-32media -m5-32media-nofpu @gol
689 -m5-compact -m5-compact-nofpu @gol
690 -mb -ml -mdalign -mrelax @gol
691 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
692 -mieee -misize -mpadstruct -mspace @gol
693 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
694 -mdivsi3_libfunc=@var{name} @gol
695 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
699 @gccoptlist{-mcpu=@var{cpu-type} @gol
700 -mtune=@var{cpu-type} @gol
701 -mcmodel=@var{code-model} @gol
702 -m32 -m64 -mapp-regs -mno-app-regs @gol
703 -mfaster-structs -mno-faster-structs @gol
704 -mfpu -mno-fpu -mhard-float -msoft-float @gol
705 -mhard-quad-float -msoft-quad-float @gol
706 -mimpure-text -mno-impure-text -mlittle-endian @gol
707 -mstack-bias -mno-stack-bias @gol
708 -munaligned-doubles -mno-unaligned-doubles @gol
709 -mv8plus -mno-v8plus -mvis -mno-vis
712 @emph{System V Options}
713 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
715 @emph{TMS320C3x/C4x Options}
716 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
717 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
718 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
719 -mparallel-insns -mparallel-mpy -mpreserve-float}
722 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
723 -mprolog-function -mno-prolog-function -mspace @gol
724 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
725 -mapp-regs -mno-app-regs @gol
726 -mdisable-callt -mno-disable-callt @gol
732 @gccoptlist{-mg -mgnu -munix}
734 @emph{x86-64 Options}
735 See i386 and x86-64 Options.
737 @emph{Xstormy16 Options}
740 @emph{Xtensa Options}
741 @gccoptlist{-mconst16 -mno-const16 @gol
742 -mfused-madd -mno-fused-madd @gol
743 -mtext-section-literals -mno-text-section-literals @gol
744 -mtarget-align -mno-target-align @gol
745 -mlongcalls -mno-longcalls}
747 @emph{zSeries Options}
748 See S/390 and zSeries Options.
750 @item Code Generation Options
751 @xref{Code Gen Options,,Options for Code Generation Conventions}.
752 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
753 -ffixed-@var{reg} -fexceptions @gol
754 -fnon-call-exceptions -funwind-tables @gol
755 -fasynchronous-unwind-tables @gol
756 -finhibit-size-directive -finstrument-functions @gol
757 -fno-common -fno-ident @gol
758 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
759 -fno-jump-tables @gol
760 -freg-struct-return -fshared-data -fshort-enums @gol
761 -fshort-double -fshort-wchar @gol
762 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
763 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
764 -fargument-alias -fargument-noalias @gol
765 -fargument-noalias-global -fleading-underscore @gol
766 -ftls-model=@var{model} @gol
767 -ftrapv -fwrapv -fbounds-check @gol
768 -fvisibility -fopenmp}
772 * Overall Options:: Controlling the kind of output:
773 an executable, object files, assembler files,
774 or preprocessed source.
775 * C Dialect Options:: Controlling the variant of C language compiled.
776 * C++ Dialect Options:: Variations on C++.
777 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
779 * Language Independent Options:: Controlling how diagnostics should be
781 * Warning Options:: How picky should the compiler be?
782 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
783 * Optimize Options:: How much optimization?
784 * Preprocessor Options:: Controlling header files and macro definitions.
785 Also, getting dependency information for Make.
786 * Assembler Options:: Passing options to the assembler.
787 * Link Options:: Specifying libraries and so on.
788 * Directory Options:: Where to find header files and libraries.
789 Where to find the compiler executable files.
790 * Spec Files:: How to pass switches to sub-processes.
791 * Target Options:: Running a cross-compiler, or an old version of GCC.
794 @node Overall Options
795 @section Options Controlling the Kind of Output
797 Compilation can involve up to four stages: preprocessing, compilation
798 proper, assembly and linking, always in that order. GCC is capable of
799 preprocessing and compiling several files either into several
800 assembler input files, or into one assembler input file; then each
801 assembler input file produces an object file, and linking combines all
802 the object files (those newly compiled, and those specified as input)
803 into an executable file.
805 @cindex file name suffix
806 For any given input file, the file name suffix determines what kind of
811 C source code which must be preprocessed.
814 C source code which should not be preprocessed.
817 C++ source code which should not be preprocessed.
820 Objective-C source code. Note that you must link with the @file{libobjc}
821 library to make an Objective-C program work.
824 Objective-C source code which should not be preprocessed.
828 Objective-C++ source code. Note that you must link with the @file{libobjc}
829 library to make an Objective-C++ program work. Note that @samp{.M} refers
830 to a literal capital M@.
833 Objective-C++ source code which should not be preprocessed.
836 C, C++, Objective-C or Objective-C++ header file to be turned into a
841 @itemx @var{file}.cxx
842 @itemx @var{file}.cpp
843 @itemx @var{file}.CPP
844 @itemx @var{file}.c++
846 C++ source code which must be preprocessed. Note that in @samp{.cxx},
847 the last two letters must both be literally @samp{x}. Likewise,
848 @samp{.C} refers to a literal capital C@.
852 Objective-C++ source code which must be preprocessed.
855 Objective-C++ source code which should not be preprocessed.
859 C++ header file to be turned into a precompiled header.
862 @itemx @var{file}.for
863 @itemx @var{file}.FOR
864 Fixed form Fortran source code which should not be preprocessed.
867 @itemx @var{file}.fpp
868 @itemx @var{file}.FPP
869 Fixed form Fortran source code which must be preprocessed (with the traditional
873 @itemx @var{file}.f95
874 Free form Fortran source code which should not be preprocessed.
877 @itemx @var{file}.F95
878 Free form Fortran source code which must be preprocessed (with the
879 traditional preprocessor).
881 @c FIXME: Descriptions of Java file types.
888 Ada source code file which contains a library unit declaration (a
889 declaration of a package, subprogram, or generic, or a generic
890 instantiation), or a library unit renaming declaration (a package,
891 generic, or subprogram renaming declaration). Such files are also
894 @itemx @var{file}.adb
895 Ada source code file containing a library unit body (a subprogram or
896 package body). Such files are also called @dfn{bodies}.
898 @c GCC also knows about some suffixes for languages not yet included:
909 Assembler code which must be preprocessed.
912 An object file to be fed straight into linking.
913 Any file name with no recognized suffix is treated this way.
917 You can specify the input language explicitly with the @option{-x} option:
920 @item -x @var{language}
921 Specify explicitly the @var{language} for the following input files
922 (rather than letting the compiler choose a default based on the file
923 name suffix). This option applies to all following input files until
924 the next @option{-x} option. Possible values for @var{language} are:
926 c c-header c-cpp-output
927 c++ c++-header c++-cpp-output
928 objective-c objective-c-header objective-c-cpp-output
929 objective-c++ objective-c++-header objective-c++-cpp-output
930 assembler assembler-with-cpp
939 Turn off any specification of a language, so that subsequent files are
940 handled according to their file name suffixes (as they are if @option{-x}
941 has not been used at all).
943 @item -pass-exit-codes
944 @opindex pass-exit-codes
945 Normally the @command{gcc} program will exit with the code of 1 if any
946 phase of the compiler returns a non-success return code. If you specify
947 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
948 numerically highest error produced by any phase that returned an error
952 If you only want some of the stages of compilation, you can use
953 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
954 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
955 @command{gcc} is to stop. Note that some combinations (for example,
956 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
961 Compile or assemble the source files, but do not link. The linking
962 stage simply is not done. The ultimate output is in the form of an
963 object file for each source file.
965 By default, the object file name for a source file is made by replacing
966 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
968 Unrecognized input files, not requiring compilation or assembly, are
973 Stop after the stage of compilation proper; do not assemble. The output
974 is in the form of an assembler code file for each non-assembler input
977 By default, the assembler file name for a source file is made by
978 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
980 Input files that don't require compilation are ignored.
984 Stop after the preprocessing stage; do not run the compiler proper. The
985 output is in the form of preprocessed source code, which is sent to the
988 Input files which don't require preprocessing are ignored.
990 @cindex output file option
993 Place output in file @var{file}. This applies regardless to whatever
994 sort of output is being produced, whether it be an executable file,
995 an object file, an assembler file or preprocessed C code.
997 If @option{-o} is not specified, the default is to put an executable
998 file in @file{a.out}, the object file for
999 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1000 assembler file in @file{@var{source}.s}, a precompiled header file in
1001 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1006 Print (on standard error output) the commands executed to run the stages
1007 of compilation. Also print the version number of the compiler driver
1008 program and of the preprocessor and the compiler proper.
1012 Like @option{-v} except the commands are not executed and all command
1013 arguments are quoted. This is useful for shell scripts to capture the
1014 driver-generated command lines.
1018 Use pipes rather than temporary files for communication between the
1019 various stages of compilation. This fails to work on some systems where
1020 the assembler is unable to read from a pipe; but the GNU assembler has
1025 If you are compiling multiple source files, this option tells the driver
1026 to pass all the source files to the compiler at once (for those
1027 languages for which the compiler can handle this). This will allow
1028 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1029 language for which this is supported is C@. If you pass source files for
1030 multiple languages to the driver, using this option, the driver will invoke
1031 the compiler(s) that support IMA once each, passing each compiler all the
1032 source files appropriate for it. For those languages that do not support
1033 IMA this option will be ignored, and the compiler will be invoked once for
1034 each source file in that language. If you use this option in conjunction
1035 with @option{-save-temps}, the compiler will generate multiple
1037 (one for each source file), but only one (combined) @file{.o} or
1042 Print (on the standard output) a description of the command line options
1043 understood by @command{gcc}. If the @option{-v} option is also specified
1044 then @option{--help} will also be passed on to the various processes
1045 invoked by @command{gcc}, so that they can display the command line options
1046 they accept. If the @option{-Wextra} option is also specified then command
1047 line options which have no documentation associated with them will also
1051 @opindex target-help
1052 Print (on the standard output) a description of target specific command
1053 line options for each tool.
1057 Display the version number and copyrights of the invoked GCC@.
1059 @include @value{srcdir}/../libiberty/at-file.texi
1063 @section Compiling C++ Programs
1065 @cindex suffixes for C++ source
1066 @cindex C++ source file suffixes
1067 C++ source files conventionally use one of the suffixes @samp{.C},
1068 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1069 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1070 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1071 files with these names and compiles them as C++ programs even if you
1072 call the compiler the same way as for compiling C programs (usually
1073 with the name @command{gcc}).
1077 However, C++ programs often require class libraries as well as a
1078 compiler that understands the C++ language---and under some
1079 circumstances, you might want to compile programs or header files from
1080 standard input, or otherwise without a suffix that flags them as C++
1081 programs. You might also like to precompile a C header file with a
1082 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
1083 program that calls GCC with the default language set to C++, and
1084 automatically specifies linking against the C++ library. On many
1085 systems, @command{g++} is also installed with the name @command{c++}.
1087 @cindex invoking @command{g++}
1088 When you compile C++ programs, you may specify many of the same
1089 command-line options that you use for compiling programs in any
1090 language; or command-line options meaningful for C and related
1091 languages; or options that are meaningful only for C++ programs.
1092 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1093 explanations of options for languages related to C@.
1094 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1095 explanations of options that are meaningful only for C++ programs.
1097 @node C Dialect Options
1098 @section Options Controlling C Dialect
1099 @cindex dialect options
1100 @cindex language dialect options
1101 @cindex options, dialect
1103 The following options control the dialect of C (or languages derived
1104 from C, such as C++, Objective-C and Objective-C++) that the compiler
1108 @cindex ANSI support
1112 In C mode, support all ISO C90 programs. In C++ mode,
1113 remove GNU extensions that conflict with ISO C++.
1115 This turns off certain features of GCC that are incompatible with ISO
1116 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1117 such as the @code{asm} and @code{typeof} keywords, and
1118 predefined macros such as @code{unix} and @code{vax} that identify the
1119 type of system you are using. It also enables the undesirable and
1120 rarely used ISO trigraph feature. For the C compiler,
1121 it disables recognition of C++ style @samp{//} comments as well as
1122 the @code{inline} keyword.
1124 The alternate keywords @code{__asm__}, @code{__extension__},
1125 @code{__inline__} and @code{__typeof__} continue to work despite
1126 @option{-ansi}. You would not want to use them in an ISO C program, of
1127 course, but it is useful to put them in header files that might be included
1128 in compilations done with @option{-ansi}. Alternate predefined macros
1129 such as @code{__unix__} and @code{__vax__} are also available, with or
1130 without @option{-ansi}.
1132 The @option{-ansi} option does not cause non-ISO programs to be
1133 rejected gratuitously. For that, @option{-pedantic} is required in
1134 addition to @option{-ansi}. @xref{Warning Options}.
1136 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1137 option is used. Some header files may notice this macro and refrain
1138 from declaring certain functions or defining certain macros that the
1139 ISO standard doesn't call for; this is to avoid interfering with any
1140 programs that might use these names for other things.
1142 Functions which would normally be built in but do not have semantics
1143 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1144 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1145 built-in functions provided by GCC}, for details of the functions
1150 Determine the language standard. This option is currently only
1151 supported when compiling C or C++. A value for this option must be
1152 provided; possible values are
1157 ISO C90 (same as @option{-ansi}).
1159 @item iso9899:199409
1160 ISO C90 as modified in amendment 1.
1166 ISO C99. Note that this standard is not yet fully supported; see
1167 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1168 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1171 Default, ISO C90 plus GNU extensions (including some C99 features).
1175 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1176 this will become the default. The name @samp{gnu9x} is deprecated.
1179 The 1998 ISO C++ standard plus amendments.
1182 The same as @option{-std=c++98} plus GNU extensions. This is the
1183 default for C++ code.
1186 Even when this option is not specified, you can still use some of the
1187 features of newer standards in so far as they do not conflict with
1188 previous C standards. For example, you may use @code{__restrict__} even
1189 when @option{-std=c99} is not specified.
1191 The @option{-std} options specifying some version of ISO C have the same
1192 effects as @option{-ansi}, except that features that were not in ISO C90
1193 but are in the specified version (for example, @samp{//} comments and
1194 the @code{inline} keyword in ISO C99) are not disabled.
1196 @xref{Standards,,Language Standards Supported by GCC}, for details of
1197 these standard versions.
1199 @item -aux-info @var{filename}
1201 Output to the given filename prototyped declarations for all functions
1202 declared and/or defined in a translation unit, including those in header
1203 files. This option is silently ignored in any language other than C@.
1205 Besides declarations, the file indicates, in comments, the origin of
1206 each declaration (source file and line), whether the declaration was
1207 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1208 @samp{O} for old, respectively, in the first character after the line
1209 number and the colon), and whether it came from a declaration or a
1210 definition (@samp{C} or @samp{F}, respectively, in the following
1211 character). In the case of function definitions, a K&R-style list of
1212 arguments followed by their declarations is also provided, inside
1213 comments, after the declaration.
1217 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1218 keyword, so that code can use these words as identifiers. You can use
1219 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1220 instead. @option{-ansi} implies @option{-fno-asm}.
1222 In C++, this switch only affects the @code{typeof} keyword, since
1223 @code{asm} and @code{inline} are standard keywords. You may want to
1224 use the @option{-fno-gnu-keywords} flag instead, which has the same
1225 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1226 switch only affects the @code{asm} and @code{typeof} keywords, since
1227 @code{inline} is a standard keyword in ISO C99.
1230 @itemx -fno-builtin-@var{function}
1231 @opindex fno-builtin
1232 @cindex built-in functions
1233 Don't recognize built-in functions that do not begin with
1234 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1235 functions provided by GCC}, for details of the functions affected,
1236 including those which are not built-in functions when @option{-ansi} or
1237 @option{-std} options for strict ISO C conformance are used because they
1238 do not have an ISO standard meaning.
1240 GCC normally generates special code to handle certain built-in functions
1241 more efficiently; for instance, calls to @code{alloca} may become single
1242 instructions that adjust the stack directly, and calls to @code{memcpy}
1243 may become inline copy loops. The resulting code is often both smaller
1244 and faster, but since the function calls no longer appear as such, you
1245 cannot set a breakpoint on those calls, nor can you change the behavior
1246 of the functions by linking with a different library. In addition,
1247 when a function is recognized as a built-in function, GCC may use
1248 information about that function to warn about problems with calls to
1249 that function, or to generate more efficient code, even if the
1250 resulting code still contains calls to that function. For example,
1251 warnings are given with @option{-Wformat} for bad calls to
1252 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1253 known not to modify global memory.
1255 With the @option{-fno-builtin-@var{function}} option
1256 only the built-in function @var{function} is
1257 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1258 function is named this is not built-in in this version of GCC, this
1259 option is ignored. There is no corresponding
1260 @option{-fbuiltin-@var{function}} option; if you wish to enable
1261 built-in functions selectively when using @option{-fno-builtin} or
1262 @option{-ffreestanding}, you may define macros such as:
1265 #define abs(n) __builtin_abs ((n))
1266 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1271 @cindex hosted environment
1273 Assert that compilation takes place in a hosted environment. This implies
1274 @option{-fbuiltin}. A hosted environment is one in which the
1275 entire standard library is available, and in which @code{main} has a return
1276 type of @code{int}. Examples are nearly everything except a kernel.
1277 This is equivalent to @option{-fno-freestanding}.
1279 @item -ffreestanding
1280 @opindex ffreestanding
1281 @cindex hosted environment
1283 Assert that compilation takes place in a freestanding environment. This
1284 implies @option{-fno-builtin}. A freestanding environment
1285 is one in which the standard library may not exist, and program startup may
1286 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1287 This is equivalent to @option{-fno-hosted}.
1289 @xref{Standards,,Language Standards Supported by GCC}, for details of
1290 freestanding and hosted environments.
1292 @item -fms-extensions
1293 @opindex fms-extensions
1294 Accept some non-standard constructs used in Microsoft header files.
1296 Some cases of unnamed fields in structures and unions are only
1297 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1298 fields within structs/unions}, for details.
1302 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1303 options for strict ISO C conformance) implies @option{-trigraphs}.
1305 @item -no-integrated-cpp
1306 @opindex no-integrated-cpp
1307 Performs a compilation in two passes: preprocessing and compiling. This
1308 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1309 @option{-B} option. The user supplied compilation step can then add in
1310 an additional preprocessing step after normal preprocessing but before
1311 compiling. The default is to use the integrated cpp (internal cpp)
1313 The semantics of this option will change if "cc1", "cc1plus", and
1314 "cc1obj" are merged.
1316 @cindex traditional C language
1317 @cindex C language, traditional
1319 @itemx -traditional-cpp
1320 @opindex traditional-cpp
1321 @opindex traditional
1322 Formerly, these options caused GCC to attempt to emulate a pre-standard
1323 C compiler. They are now only supported with the @option{-E} switch.
1324 The preprocessor continues to support a pre-standard mode. See the GNU
1325 CPP manual for details.
1327 @item -fcond-mismatch
1328 @opindex fcond-mismatch
1329 Allow conditional expressions with mismatched types in the second and
1330 third arguments. The value of such an expression is void. This option
1331 is not supported for C++.
1333 @item -funsigned-char
1334 @opindex funsigned-char
1335 Let the type @code{char} be unsigned, like @code{unsigned char}.
1337 Each kind of machine has a default for what @code{char} should
1338 be. It is either like @code{unsigned char} by default or like
1339 @code{signed char} by default.
1341 Ideally, a portable program should always use @code{signed char} or
1342 @code{unsigned char} when it depends on the signedness of an object.
1343 But many programs have been written to use plain @code{char} and
1344 expect it to be signed, or expect it to be unsigned, depending on the
1345 machines they were written for. This option, and its inverse, let you
1346 make such a program work with the opposite default.
1348 The type @code{char} is always a distinct type from each of
1349 @code{signed char} or @code{unsigned char}, even though its behavior
1350 is always just like one of those two.
1353 @opindex fsigned-char
1354 Let the type @code{char} be signed, like @code{signed char}.
1356 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1357 the negative form of @option{-funsigned-char}. Likewise, the option
1358 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1360 @item -fsigned-bitfields
1361 @itemx -funsigned-bitfields
1362 @itemx -fno-signed-bitfields
1363 @itemx -fno-unsigned-bitfields
1364 @opindex fsigned-bitfields
1365 @opindex funsigned-bitfields
1366 @opindex fno-signed-bitfields
1367 @opindex fno-unsigned-bitfields
1368 These options control whether a bit-field is signed or unsigned, when the
1369 declaration does not use either @code{signed} or @code{unsigned}. By
1370 default, such a bit-field is signed, because this is consistent: the
1371 basic integer types such as @code{int} are signed types.
1374 @node C++ Dialect Options
1375 @section Options Controlling C++ Dialect
1377 @cindex compiler options, C++
1378 @cindex C++ options, command line
1379 @cindex options, C++
1380 This section describes the command-line options that are only meaningful
1381 for C++ programs; but you can also use most of the GNU compiler options
1382 regardless of what language your program is in. For example, you
1383 might compile a file @code{firstClass.C} like this:
1386 g++ -g -frepo -O -c firstClass.C
1390 In this example, only @option{-frepo} is an option meant
1391 only for C++ programs; you can use the other options with any
1392 language supported by GCC@.
1394 Here is a list of options that are @emph{only} for compiling C++ programs:
1398 @item -fabi-version=@var{n}
1399 @opindex fabi-version
1400 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1401 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1402 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1403 the version that conforms most closely to the C++ ABI specification.
1404 Therefore, the ABI obtained using version 0 will change as ABI bugs
1407 The default is version 2.
1409 @item -fno-access-control
1410 @opindex fno-access-control
1411 Turn off all access checking. This switch is mainly useful for working
1412 around bugs in the access control code.
1416 Check that the pointer returned by @code{operator new} is non-null
1417 before attempting to modify the storage allocated. This check is
1418 normally unnecessary because the C++ standard specifies that
1419 @code{operator new} will only return @code{0} if it is declared
1420 @samp{throw()}, in which case the compiler will always check the
1421 return value even without this option. In all other cases, when
1422 @code{operator new} has a non-empty exception specification, memory
1423 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1424 @samp{new (nothrow)}.
1426 @item -fconserve-space
1427 @opindex fconserve-space
1428 Put uninitialized or runtime-initialized global variables into the
1429 common segment, as C does. This saves space in the executable at the
1430 cost of not diagnosing duplicate definitions. If you compile with this
1431 flag and your program mysteriously crashes after @code{main()} has
1432 completed, you may have an object that is being destroyed twice because
1433 two definitions were merged.
1435 This option is no longer useful on most targets, now that support has
1436 been added for putting variables into BSS without making them common.
1438 @item -ffriend-injection
1439 @opindex ffriend-injection
1440 Inject friend functions into the enclosing namespace, so that they are
1441 visible outside the scope of the class in which they are declared.
1442 Friend functions were documented to work this way in the old Annotated
1443 C++ Reference Manual, and versions of G++ before 4.1 always worked
1444 that way. However, in ISO C++ a friend function which is not declared
1445 in an enclosing scope can only be found using argument dependent
1446 lookup. This option causes friends to be injected as they were in
1449 This option is for compatibility, and may be removed in a future
1452 @item -fno-const-strings
1453 @opindex fno-const-strings
1454 Give string constants type @code{char *} instead of type @code{const
1455 char *}. By default, G++ uses type @code{const char *} as required by
1456 the standard. Even if you use @option{-fno-const-strings}, you cannot
1457 actually modify the value of a string constant.
1459 This option might be removed in a future release of G++. For maximum
1460 portability, you should structure your code so that it works with
1461 string constants that have type @code{const char *}.
1463 @item -fno-elide-constructors
1464 @opindex fno-elide-constructors
1465 The C++ standard allows an implementation to omit creating a temporary
1466 which is only used to initialize another object of the same type.
1467 Specifying this option disables that optimization, and forces G++ to
1468 call the copy constructor in all cases.
1470 @item -fno-enforce-eh-specs
1471 @opindex fno-enforce-eh-specs
1472 Don't generate code to check for violation of exception specifications
1473 at runtime. This option violates the C++ standard, but may be useful
1474 for reducing code size in production builds, much like defining
1475 @samp{NDEBUG}. This does not give user code permission to throw
1476 exceptions in violation of the exception specifications; the compiler
1477 will still optimize based on the specifications, so throwing an
1478 unexpected exception will result in undefined behavior.
1481 @itemx -fno-for-scope
1483 @opindex fno-for-scope
1484 If @option{-ffor-scope} is specified, the scope of variables declared in
1485 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1486 as specified by the C++ standard.
1487 If @option{-fno-for-scope} is specified, the scope of variables declared in
1488 a @i{for-init-statement} extends to the end of the enclosing scope,
1489 as was the case in old versions of G++, and other (traditional)
1490 implementations of C++.
1492 The default if neither flag is given to follow the standard,
1493 but to allow and give a warning for old-style code that would
1494 otherwise be invalid, or have different behavior.
1496 @item -fno-gnu-keywords
1497 @opindex fno-gnu-keywords
1498 Do not recognize @code{typeof} as a keyword, so that code can use this
1499 word as an identifier. You can use the keyword @code{__typeof__} instead.
1500 @option{-ansi} implies @option{-fno-gnu-keywords}.
1502 @item -fno-implicit-templates
1503 @opindex fno-implicit-templates
1504 Never emit code for non-inline templates which are instantiated
1505 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1506 @xref{Template Instantiation}, for more information.
1508 @item -fno-implicit-inline-templates
1509 @opindex fno-implicit-inline-templates
1510 Don't emit code for implicit instantiations of inline templates, either.
1511 The default is to handle inlines differently so that compiles with and
1512 without optimization will need the same set of explicit instantiations.
1514 @item -fno-implement-inlines
1515 @opindex fno-implement-inlines
1516 To save space, do not emit out-of-line copies of inline functions
1517 controlled by @samp{#pragma implementation}. This will cause linker
1518 errors if these functions are not inlined everywhere they are called.
1520 @item -fms-extensions
1521 @opindex fms-extensions
1522 Disable pedantic warnings about constructs used in MFC, such as implicit
1523 int and getting a pointer to member function via non-standard syntax.
1525 @item -fno-nonansi-builtins
1526 @opindex fno-nonansi-builtins
1527 Disable built-in declarations of functions that are not mandated by
1528 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1529 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1531 @item -fno-operator-names
1532 @opindex fno-operator-names
1533 Do not treat the operator name keywords @code{and}, @code{bitand},
1534 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1535 synonyms as keywords.
1537 @item -fno-optional-diags
1538 @opindex fno-optional-diags
1539 Disable diagnostics that the standard says a compiler does not need to
1540 issue. Currently, the only such diagnostic issued by G++ is the one for
1541 a name having multiple meanings within a class.
1544 @opindex fpermissive
1545 Downgrade some diagnostics about nonconformant code from errors to
1546 warnings. Thus, using @option{-fpermissive} will allow some
1547 nonconforming code to compile.
1551 Enable automatic template instantiation at link time. This option also
1552 implies @option{-fno-implicit-templates}. @xref{Template
1553 Instantiation}, for more information.
1557 Disable generation of information about every class with virtual
1558 functions for use by the C++ runtime type identification features
1559 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1560 of the language, you can save some space by using this flag. Note that
1561 exception handling uses the same information, but it will generate it as
1566 Emit statistics about front-end processing at the end of the compilation.
1567 This information is generally only useful to the G++ development team.
1569 @item -ftemplate-depth-@var{n}
1570 @opindex ftemplate-depth
1571 Set the maximum instantiation depth for template classes to @var{n}.
1572 A limit on the template instantiation depth is needed to detect
1573 endless recursions during template class instantiation. ANSI/ISO C++
1574 conforming programs must not rely on a maximum depth greater than 17.
1576 @item -fno-threadsafe-statics
1577 @opindex fno-threadsafe-statics
1578 Do not emit the extra code to use the routines specified in the C++
1579 ABI for thread-safe initialization of local statics. You can use this
1580 option to reduce code size slightly in code that doesn't need to be
1583 @item -fuse-cxa-atexit
1584 @opindex fuse-cxa-atexit
1585 Register destructors for objects with static storage duration with the
1586 @code{__cxa_atexit} function rather than the @code{atexit} function.
1587 This option is required for fully standards-compliant handling of static
1588 destructors, but will only work if your C library supports
1589 @code{__cxa_atexit}.
1591 @item -fvisibility-inlines-hidden
1592 @opindex fvisibility-inlines-hidden
1593 Causes all inlined methods to be marked with
1594 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1595 appear in the export table of a DSO and do not require a PLT indirection
1596 when used within the DSO@. Enabling this option can have a dramatic effect
1597 on load and link times of a DSO as it massively reduces the size of the
1598 dynamic export table when the library makes heavy use of templates. While
1599 it can cause bloating through duplication of code within each DSO where
1600 it is used, often the wastage is less than the considerable space occupied
1601 by a long symbol name in the export table which is typical when using
1602 templates and namespaces. For even more savings, combine with the
1603 @option{-fvisibility=hidden} switch.
1607 Do not use weak symbol support, even if it is provided by the linker.
1608 By default, G++ will use weak symbols if they are available. This
1609 option exists only for testing, and should not be used by end-users;
1610 it will result in inferior code and has no benefits. This option may
1611 be removed in a future release of G++.
1615 Do not search for header files in the standard directories specific to
1616 C++, but do still search the other standard directories. (This option
1617 is used when building the C++ library.)
1620 In addition, these optimization, warning, and code generation options
1621 have meanings only for C++ programs:
1624 @item -fno-default-inline
1625 @opindex fno-default-inline
1626 Do not assume @samp{inline} for functions defined inside a class scope.
1627 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1628 functions will have linkage like inline functions; they just won't be
1631 @item -Wabi @r{(C++ only)}
1633 Warn when G++ generates code that is probably not compatible with the
1634 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1635 all such cases, there are probably some cases that are not warned about,
1636 even though G++ is generating incompatible code. There may also be
1637 cases where warnings are emitted even though the code that is generated
1640 You should rewrite your code to avoid these warnings if you are
1641 concerned about the fact that code generated by G++ may not be binary
1642 compatible with code generated by other compilers.
1644 The known incompatibilities at this point include:
1649 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1650 pack data into the same byte as a base class. For example:
1653 struct A @{ virtual void f(); int f1 : 1; @};
1654 struct B : public A @{ int f2 : 1; @};
1658 In this case, G++ will place @code{B::f2} into the same byte
1659 as@code{A::f1}; other compilers will not. You can avoid this problem
1660 by explicitly padding @code{A} so that its size is a multiple of the
1661 byte size on your platform; that will cause G++ and other compilers to
1662 layout @code{B} identically.
1665 Incorrect handling of tail-padding for virtual bases. G++ does not use
1666 tail padding when laying out virtual bases. For example:
1669 struct A @{ virtual void f(); char c1; @};
1670 struct B @{ B(); char c2; @};
1671 struct C : public A, public virtual B @{@};
1675 In this case, G++ will not place @code{B} into the tail-padding for
1676 @code{A}; other compilers will. You can avoid this problem by
1677 explicitly padding @code{A} so that its size is a multiple of its
1678 alignment (ignoring virtual base classes); that will cause G++ and other
1679 compilers to layout @code{C} identically.
1682 Incorrect handling of bit-fields with declared widths greater than that
1683 of their underlying types, when the bit-fields appear in a union. For
1687 union U @{ int i : 4096; @};
1691 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1692 union too small by the number of bits in an @code{int}.
1695 Empty classes can be placed at incorrect offsets. For example:
1705 struct C : public B, public A @{@};
1709 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1710 it should be placed at offset zero. G++ mistakenly believes that the
1711 @code{A} data member of @code{B} is already at offset zero.
1714 Names of template functions whose types involve @code{typename} or
1715 template template parameters can be mangled incorrectly.
1718 template <typename Q>
1719 void f(typename Q::X) @{@}
1721 template <template <typename> class Q>
1722 void f(typename Q<int>::X) @{@}
1726 Instantiations of these templates may be mangled incorrectly.
1730 @item -Wctor-dtor-privacy @r{(C++ only)}
1731 @opindex Wctor-dtor-privacy
1732 Warn when a class seems unusable because all the constructors or
1733 destructors in that class are private, and it has neither friends nor
1734 public static member functions.
1736 @item -Wnon-virtual-dtor @r{(C++ only)}
1737 @opindex Wnon-virtual-dtor
1738 Warn when a class appears to be polymorphic, thereby requiring a virtual
1739 destructor, yet it declares a non-virtual one.
1740 This warning is enabled by @option{-Wall}.
1742 @item -Wreorder @r{(C++ only)}
1744 @cindex reordering, warning
1745 @cindex warning for reordering of member initializers
1746 Warn when the order of member initializers given in the code does not
1747 match the order in which they must be executed. For instance:
1753 A(): j (0), i (1) @{ @}
1757 The compiler will rearrange the member initializers for @samp{i}
1758 and @samp{j} to match the declaration order of the members, emitting
1759 a warning to that effect. This warning is enabled by @option{-Wall}.
1762 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1765 @item -Weffc++ @r{(C++ only)}
1767 Warn about violations of the following style guidelines from Scott Meyers'
1768 @cite{Effective C++} book:
1772 Item 11: Define a copy constructor and an assignment operator for classes
1773 with dynamically allocated memory.
1776 Item 12: Prefer initialization to assignment in constructors.
1779 Item 14: Make destructors virtual in base classes.
1782 Item 15: Have @code{operator=} return a reference to @code{*this}.
1785 Item 23: Don't try to return a reference when you must return an object.
1789 Also warn about violations of the following style guidelines from
1790 Scott Meyers' @cite{More Effective C++} book:
1794 Item 6: Distinguish between prefix and postfix forms of increment and
1795 decrement operators.
1798 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1802 When selecting this option, be aware that the standard library
1803 headers do not obey all of these guidelines; use @samp{grep -v}
1804 to filter out those warnings.
1806 @item -Wno-deprecated @r{(C++ only)}
1807 @opindex Wno-deprecated
1808 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1810 @item -Wstrict-null-sentinel @r{(C++ only)}
1811 @opindex Wstrict-null-sentinel
1812 Warn also about the use of an uncasted @code{NULL} as sentinel. When
1813 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
1814 to @code{__null}. Although it is a null pointer constant not a null pointer,
1815 it is guaranteed to of the same size as a pointer. But this use is
1816 not portable across different compilers.
1818 @item -Wno-non-template-friend @r{(C++ only)}
1819 @opindex Wno-non-template-friend
1820 Disable warnings when non-templatized friend functions are declared
1821 within a template. Since the advent of explicit template specification
1822 support in G++, if the name of the friend is an unqualified-id (i.e.,
1823 @samp{friend foo(int)}), the C++ language specification demands that the
1824 friend declare or define an ordinary, nontemplate function. (Section
1825 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1826 could be interpreted as a particular specialization of a templatized
1827 function. Because this non-conforming behavior is no longer the default
1828 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1829 check existing code for potential trouble spots and is on by default.
1830 This new compiler behavior can be turned off with
1831 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1832 but disables the helpful warning.
1834 @item -Wold-style-cast @r{(C++ only)}
1835 @opindex Wold-style-cast
1836 Warn if an old-style (C-style) cast to a non-void type is used within
1837 a C++ program. The new-style casts (@samp{dynamic_cast},
1838 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
1839 less vulnerable to unintended effects and much easier to search for.
1841 @item -Woverloaded-virtual @r{(C++ only)}
1842 @opindex Woverloaded-virtual
1843 @cindex overloaded virtual fn, warning
1844 @cindex warning for overloaded virtual fn
1845 Warn when a function declaration hides virtual functions from a
1846 base class. For example, in:
1853 struct B: public A @{
1858 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1866 will fail to compile.
1868 @item -Wno-pmf-conversions @r{(C++ only)}
1869 @opindex Wno-pmf-conversions
1870 Disable the diagnostic for converting a bound pointer to member function
1873 @item -Wsign-promo @r{(C++ only)}
1874 @opindex Wsign-promo
1875 Warn when overload resolution chooses a promotion from unsigned or
1876 enumerated type to a signed type, over a conversion to an unsigned type of
1877 the same size. Previous versions of G++ would try to preserve
1878 unsignedness, but the standard mandates the current behavior.
1883 A& operator = (int);
1893 In this example, G++ will synthesize a default @samp{A& operator =
1894 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1897 @node Objective-C and Objective-C++ Dialect Options
1898 @section Options Controlling Objective-C and Objective-C++ Dialects
1900 @cindex compiler options, Objective-C and Objective-C++
1901 @cindex Objective-C and Objective-C++ options, command line
1902 @cindex options, Objective-C and Objective-C++
1903 (NOTE: This manual does not describe the Objective-C and Objective-C++
1904 languages themselves. See @xref{Standards,,Language Standards
1905 Supported by GCC}, for references.)
1907 This section describes the command-line options that are only meaningful
1908 for Objective-C and Objective-C++ programs, but you can also use most of
1909 the language-independent GNU compiler options.
1910 For example, you might compile a file @code{some_class.m} like this:
1913 gcc -g -fgnu-runtime -O -c some_class.m
1917 In this example, @option{-fgnu-runtime} is an option meant only for
1918 Objective-C and Objective-C++ programs; you can use the other options with
1919 any language supported by GCC@.
1921 Note that since Objective-C is an extension of the C language, Objective-C
1922 compilations may also use options specific to the C front-end (e.g.,
1923 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1924 C++-specific options (e.g., @option{-Wabi}).
1926 Here is a list of options that are @emph{only} for compiling Objective-C
1927 and Objective-C++ programs:
1930 @item -fconstant-string-class=@var{class-name}
1931 @opindex fconstant-string-class
1932 Use @var{class-name} as the name of the class to instantiate for each
1933 literal string specified with the syntax @code{@@"@dots{}"}. The default
1934 class name is @code{NXConstantString} if the GNU runtime is being used, and
1935 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1936 @option{-fconstant-cfstrings} option, if also present, will override the
1937 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1938 to be laid out as constant CoreFoundation strings.
1941 @opindex fgnu-runtime
1942 Generate object code compatible with the standard GNU Objective-C
1943 runtime. This is the default for most types of systems.
1945 @item -fnext-runtime
1946 @opindex fnext-runtime
1947 Generate output compatible with the NeXT runtime. This is the default
1948 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1949 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1952 @item -fno-nil-receivers
1953 @opindex fno-nil-receivers
1954 Assume that all Objective-C message dispatches (e.g.,
1955 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1956 is not @code{nil}. This allows for more efficient entry points in the runtime
1957 to be used. Currently, this option is only available in conjunction with
1958 the NeXT runtime on Mac OS X 10.3 and later.
1960 @item -fobjc-call-cxx-cdtors
1961 @opindex fobjc-call-cxx-cdtors
1962 For each Objective-C class, check if any of its instance variables is a
1963 C++ object with a non-trivial default constructor. If so, synthesize a
1964 special @code{- (id) .cxx_construct} instance method that will run
1965 non-trivial default constructors on any such instance variables, in order,
1966 and then return @code{self}. Similarly, check if any instance variable
1967 is a C++ object with a non-trivial destructor, and if so, synthesize a
1968 special @code{- (void) .cxx_destruct} method that will run
1969 all such default destructors, in reverse order.
1971 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
1972 thusly generated will only operate on instance variables declared in the
1973 current Objective-C class, and not those inherited from superclasses. It
1974 is the responsibility of the Objective-C runtime to invoke all such methods
1975 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
1976 will be invoked by the runtime immediately after a new object
1977 instance is allocated; the @code{- (void) .cxx_destruct} methods will
1978 be invoked immediately before the runtime deallocates an object instance.
1980 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
1981 support for invoking the @code{- (id) .cxx_construct} and
1982 @code{- (void) .cxx_destruct} methods.
1984 @item -fobjc-direct-dispatch
1985 @opindex fobjc-direct-dispatch
1986 Allow fast jumps to the message dispatcher. On Darwin this is
1987 accomplished via the comm page.
1989 @item -fobjc-exceptions
1990 @opindex fobjc-exceptions
1991 Enable syntactic support for structured exception handling in Objective-C,
1992 similar to what is offered by C++ and Java. This option is
1993 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2002 @@catch (AnObjCClass *exc) @{
2009 @@catch (AnotherClass *exc) @{
2012 @@catch (id allOthers) @{
2022 The @code{@@throw} statement may appear anywhere in an Objective-C or
2023 Objective-C++ program; when used inside of a @code{@@catch} block, the
2024 @code{@@throw} may appear without an argument (as shown above), in which case
2025 the object caught by the @code{@@catch} will be rethrown.
2027 Note that only (pointers to) Objective-C objects may be thrown and
2028 caught using this scheme. When an object is thrown, it will be caught
2029 by the nearest @code{@@catch} clause capable of handling objects of that type,
2030 analogously to how @code{catch} blocks work in C++ and Java. A
2031 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2032 any and all Objective-C exceptions not caught by previous @code{@@catch}
2035 The @code{@@finally} clause, if present, will be executed upon exit from the
2036 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2037 regardless of whether any exceptions are thrown, caught or rethrown
2038 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2039 of the @code{finally} clause in Java.
2041 There are several caveats to using the new exception mechanism:
2045 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2046 idioms provided by the @code{NSException} class, the new
2047 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2048 systems, due to additional functionality needed in the (NeXT) Objective-C
2052 As mentioned above, the new exceptions do not support handling
2053 types other than Objective-C objects. Furthermore, when used from
2054 Objective-C++, the Objective-C exception model does not interoperate with C++
2055 exceptions at this time. This means you cannot @code{@@throw} an exception
2056 from Objective-C and @code{catch} it in C++, or vice versa
2057 (i.e., @code{throw @dots{} @@catch}).
2060 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2061 blocks for thread-safe execution:
2064 @@synchronized (ObjCClass *guard) @{
2069 Upon entering the @code{@@synchronized} block, a thread of execution shall
2070 first check whether a lock has been placed on the corresponding @code{guard}
2071 object by another thread. If it has, the current thread shall wait until
2072 the other thread relinquishes its lock. Once @code{guard} becomes available,
2073 the current thread will place its own lock on it, execute the code contained in
2074 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2075 making @code{guard} available to other threads).
2077 Unlike Java, Objective-C does not allow for entire methods to be marked
2078 @code{@@synchronized}. Note that throwing exceptions out of
2079 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2080 to be unlocked properly.
2084 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2086 @item -freplace-objc-classes
2087 @opindex freplace-objc-classes
2088 Emit a special marker instructing @command{ld(1)} not to statically link in
2089 the resulting object file, and allow @command{dyld(1)} to load it in at
2090 run time instead. This is used in conjunction with the Fix-and-Continue
2091 debugging mode, where the object file in question may be recompiled and
2092 dynamically reloaded in the course of program execution, without the need
2093 to restart the program itself. Currently, Fix-and-Continue functionality
2094 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2099 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2100 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2101 compile time) with static class references that get initialized at load time,
2102 which improves run-time performance. Specifying the @option{-fzero-link} flag
2103 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2104 to be retained. This is useful in Zero-Link debugging mode, since it allows
2105 for individual class implementations to be modified during program execution.
2109 Dump interface declarations for all classes seen in the source file to a
2110 file named @file{@var{sourcename}.decl}.
2112 @item -Wassign-intercept
2113 @opindex Wassign-intercept
2114 Warn whenever an Objective-C assignment is being intercepted by the
2118 @opindex Wno-protocol
2119 If a class is declared to implement a protocol, a warning is issued for
2120 every method in the protocol that is not implemented by the class. The
2121 default behavior is to issue a warning for every method not explicitly
2122 implemented in the class, even if a method implementation is inherited
2123 from the superclass. If you use the @option{-Wno-protocol} option, then
2124 methods inherited from the superclass are considered to be implemented,
2125 and no warning is issued for them.
2129 Warn if multiple methods of different types for the same selector are
2130 found during compilation. The check is performed on the list of methods
2131 in the final stage of compilation. Additionally, a check is performed
2132 for each selector appearing in a @code{@@selector(@dots{})}
2133 expression, and a corresponding method for that selector has been found
2134 during compilation. Because these checks scan the method table only at
2135 the end of compilation, these warnings are not produced if the final
2136 stage of compilation is not reached, for example because an error is
2137 found during compilation, or because the @option{-fsyntax-only} option is
2140 @item -Wstrict-selector-match
2141 @opindex Wstrict-selector-match
2142 Warn if multiple methods with differing argument and/or return types are
2143 found for a given selector when attempting to send a message using this
2144 selector to a receiver of type @code{id} or @code{Class}. When this flag
2145 is off (which is the default behavior), the compiler will omit such warnings
2146 if any differences found are confined to types which share the same size
2149 @item -Wundeclared-selector
2150 @opindex Wundeclared-selector
2151 Warn if a @code{@@selector(@dots{})} expression referring to an
2152 undeclared selector is found. A selector is considered undeclared if no
2153 method with that name has been declared before the
2154 @code{@@selector(@dots{})} expression, either explicitly in an
2155 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2156 an @code{@@implementation} section. This option always performs its
2157 checks as soon as a @code{@@selector(@dots{})} expression is found,
2158 while @option{-Wselector} only performs its checks in the final stage of
2159 compilation. This also enforces the coding style convention
2160 that methods and selectors must be declared before being used.
2162 @item -print-objc-runtime-info
2163 @opindex print-objc-runtime-info
2164 Generate C header describing the largest structure that is passed by
2169 @node Language Independent Options
2170 @section Options to Control Diagnostic Messages Formatting
2171 @cindex options to control diagnostics formatting
2172 @cindex diagnostic messages
2173 @cindex message formatting
2175 Traditionally, diagnostic messages have been formatted irrespective of
2176 the output device's aspect (e.g.@: its width, @dots{}). The options described
2177 below can be used to control the diagnostic messages formatting
2178 algorithm, e.g.@: how many characters per line, how often source location
2179 information should be reported. Right now, only the C++ front end can
2180 honor these options. However it is expected, in the near future, that
2181 the remaining front ends would be able to digest them correctly.
2184 @item -fmessage-length=@var{n}
2185 @opindex fmessage-length
2186 Try to format error messages so that they fit on lines of about @var{n}
2187 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2188 the front ends supported by GCC@. If @var{n} is zero, then no
2189 line-wrapping will be done; each error message will appear on a single
2192 @opindex fdiagnostics-show-location
2193 @item -fdiagnostics-show-location=once
2194 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2195 reporter to emit @emph{once} source location information; that is, in
2196 case the message is too long to fit on a single physical line and has to
2197 be wrapped, the source location won't be emitted (as prefix) again,
2198 over and over, in subsequent continuation lines. This is the default
2201 @item -fdiagnostics-show-location=every-line
2202 Only meaningful in line-wrapping mode. Instructs the diagnostic
2203 messages reporter to emit the same source location information (as
2204 prefix) for physical lines that result from the process of breaking
2205 a message which is too long to fit on a single line.
2207 @item -fdiagnostics-show-options
2208 @opindex fdiagnostics-show-options
2209 This option instructs the diagnostic machinery to add text to each
2210 diagnostic emitted, which indicates which command line option directly
2211 controls that diagnostic, when such an option is known to the
2212 diagnostic machinery.
2216 @node Warning Options
2217 @section Options to Request or Suppress Warnings
2218 @cindex options to control warnings
2219 @cindex warning messages
2220 @cindex messages, warning
2221 @cindex suppressing warnings
2223 Warnings are diagnostic messages that report constructions which
2224 are not inherently erroneous but which are risky or suggest there
2225 may have been an error.
2227 You can request many specific warnings with options beginning @samp{-W},
2228 for example @option{-Wimplicit} to request warnings on implicit
2229 declarations. Each of these specific warning options also has a
2230 negative form beginning @samp{-Wno-} to turn off warnings;
2231 for example, @option{-Wno-implicit}. This manual lists only one of the
2232 two forms, whichever is not the default.
2234 The following options control the amount and kinds of warnings produced
2235 by GCC; for further, language-specific options also refer to
2236 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2240 @cindex syntax checking
2242 @opindex fsyntax-only
2243 Check the code for syntax errors, but don't do anything beyond that.
2247 Issue all the warnings demanded by strict ISO C and ISO C++;
2248 reject all programs that use forbidden extensions, and some other
2249 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2250 version of the ISO C standard specified by any @option{-std} option used.
2252 Valid ISO C and ISO C++ programs should compile properly with or without
2253 this option (though a rare few will require @option{-ansi} or a
2254 @option{-std} option specifying the required version of ISO C)@. However,
2255 without this option, certain GNU extensions and traditional C and C++
2256 features are supported as well. With this option, they are rejected.
2258 @option{-pedantic} does not cause warning messages for use of the
2259 alternate keywords whose names begin and end with @samp{__}. Pedantic
2260 warnings are also disabled in the expression that follows
2261 @code{__extension__}. However, only system header files should use
2262 these escape routes; application programs should avoid them.
2263 @xref{Alternate Keywords}.
2265 Some users try to use @option{-pedantic} to check programs for strict ISO
2266 C conformance. They soon find that it does not do quite what they want:
2267 it finds some non-ISO practices, but not all---only those for which
2268 ISO C @emph{requires} a diagnostic, and some others for which
2269 diagnostics have been added.
2271 A feature to report any failure to conform to ISO C might be useful in
2272 some instances, but would require considerable additional work and would
2273 be quite different from @option{-pedantic}. We don't have plans to
2274 support such a feature in the near future.
2276 Where the standard specified with @option{-std} represents a GNU
2277 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2278 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2279 extended dialect is based. Warnings from @option{-pedantic} are given
2280 where they are required by the base standard. (It would not make sense
2281 for such warnings to be given only for features not in the specified GNU
2282 C dialect, since by definition the GNU dialects of C include all
2283 features the compiler supports with the given option, and there would be
2284 nothing to warn about.)
2286 @item -pedantic-errors
2287 @opindex pedantic-errors
2288 Like @option{-pedantic}, except that errors are produced rather than
2293 Inhibit all warning messages.
2297 Inhibit warning messages about the use of @samp{#import}.
2299 @item -Wchar-subscripts
2300 @opindex Wchar-subscripts
2301 Warn if an array subscript has type @code{char}. This is a common cause
2302 of error, as programmers often forget that this type is signed on some
2304 This warning is enabled by @option{-Wall}.
2308 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2309 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2310 This warning is enabled by @option{-Wall}.
2312 @item -Wfatal-errors
2313 @opindex Wfatal-errors
2314 This option causes the compiler to abort compilation on the first error
2315 occurred rather than trying to keep going and printing further error
2320 @opindex ffreestanding
2321 @opindex fno-builtin
2322 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2323 the arguments supplied have types appropriate to the format string
2324 specified, and that the conversions specified in the format string make
2325 sense. This includes standard functions, and others specified by format
2326 attributes (@pxref{Function Attributes}), in the @code{printf},
2327 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2328 not in the C standard) families (or other target-specific families).
2329 Which functions are checked without format attributes having been
2330 specified depends on the standard version selected, and such checks of
2331 functions without the attribute specified are disabled by
2332 @option{-ffreestanding} or @option{-fno-builtin}.
2334 The formats are checked against the format features supported by GNU
2335 libc version 2.2. These include all ISO C90 and C99 features, as well
2336 as features from the Single Unix Specification and some BSD and GNU
2337 extensions. Other library implementations may not support all these
2338 features; GCC does not support warning about features that go beyond a
2339 particular library's limitations. However, if @option{-pedantic} is used
2340 with @option{-Wformat}, warnings will be given about format features not
2341 in the selected standard version (but not for @code{strfmon} formats,
2342 since those are not in any version of the C standard). @xref{C Dialect
2343 Options,,Options Controlling C Dialect}.
2345 Since @option{-Wformat} also checks for null format arguments for
2346 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2348 @option{-Wformat} is included in @option{-Wall}. For more control over some
2349 aspects of format checking, the options @option{-Wformat-y2k},
2350 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2351 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2352 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2355 @opindex Wformat-y2k
2356 If @option{-Wformat} is specified, also warn about @code{strftime}
2357 formats which may yield only a two-digit year.
2359 @item -Wno-format-extra-args
2360 @opindex Wno-format-extra-args
2361 If @option{-Wformat} is specified, do not warn about excess arguments to a
2362 @code{printf} or @code{scanf} format function. The C standard specifies
2363 that such arguments are ignored.
2365 Where the unused arguments lie between used arguments that are
2366 specified with @samp{$} operand number specifications, normally
2367 warnings are still given, since the implementation could not know what
2368 type to pass to @code{va_arg} to skip the unused arguments. However,
2369 in the case of @code{scanf} formats, this option will suppress the
2370 warning if the unused arguments are all pointers, since the Single
2371 Unix Specification says that such unused arguments are allowed.
2373 @item -Wno-format-zero-length
2374 @opindex Wno-format-zero-length
2375 If @option{-Wformat} is specified, do not warn about zero-length formats.
2376 The C standard specifies that zero-length formats are allowed.
2378 @item -Wformat-nonliteral
2379 @opindex Wformat-nonliteral
2380 If @option{-Wformat} is specified, also warn if the format string is not a
2381 string literal and so cannot be checked, unless the format function
2382 takes its format arguments as a @code{va_list}.
2384 @item -Wformat-security
2385 @opindex Wformat-security
2386 If @option{-Wformat} is specified, also warn about uses of format
2387 functions that represent possible security problems. At present, this
2388 warns about calls to @code{printf} and @code{scanf} functions where the
2389 format string is not a string literal and there are no format arguments,
2390 as in @code{printf (foo);}. This may be a security hole if the format
2391 string came from untrusted input and contains @samp{%n}. (This is
2392 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2393 in future warnings may be added to @option{-Wformat-security} that are not
2394 included in @option{-Wformat-nonliteral}.)
2398 Enable @option{-Wformat} plus format checks not included in
2399 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2400 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2404 Warn about passing a null pointer for arguments marked as
2405 requiring a non-null value by the @code{nonnull} function attribute.
2407 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2408 can be disabled with the @option{-Wno-nonnull} option.
2410 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2412 Warn about uninitialized variables which are initialized with themselves.
2413 Note this option can only be used with the @option{-Wuninitialized} option,
2414 which in turn only works with @option{-O1} and above.
2416 For example, GCC will warn about @code{i} being uninitialized in the
2417 following snippet only when @option{-Winit-self} has been specified:
2428 @item -Wimplicit-int
2429 @opindex Wimplicit-int
2430 Warn when a declaration does not specify a type.
2431 This warning is enabled by @option{-Wall}.
2433 @item -Wimplicit-function-declaration
2434 @itemx -Werror-implicit-function-declaration
2435 @opindex Wimplicit-function-declaration
2436 @opindex Werror-implicit-function-declaration
2437 Give a warning (or error) whenever a function is used before being
2438 declared. The form @option{-Wno-error-implicit-function-declaration}
2440 This warning is enabled by @option{-Wall} (as a warning, not an error).
2444 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2445 This warning is enabled by @option{-Wall}.
2449 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2450 function with external linkage, returning int, taking either zero
2451 arguments, two, or three arguments of appropriate types.
2452 This warning is enabled by @option{-Wall}.
2454 @item -Wmissing-braces
2455 @opindex Wmissing-braces
2456 Warn if an aggregate or union initializer is not fully bracketed. In
2457 the following example, the initializer for @samp{a} is not fully
2458 bracketed, but that for @samp{b} is fully bracketed.
2461 int a[2][2] = @{ 0, 1, 2, 3 @};
2462 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2465 This warning is enabled by @option{-Wall}.
2467 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2468 @opindex Wmissing-include-dirs
2469 Warn if a user-supplied include directory does not exist.
2472 @opindex Wparentheses
2473 Warn if parentheses are omitted in certain contexts, such
2474 as when there is an assignment in a context where a truth value
2475 is expected, or when operators are nested whose precedence people
2476 often get confused about. Only the warning for an assignment used as
2477 a truth value is supported when compiling C++; the other warnings are
2478 only supported when compiling C@.
2480 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2481 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2482 interpretation from that of ordinary mathematical notation.
2484 Also warn about constructions where there may be confusion to which
2485 @code{if} statement an @code{else} branch belongs. Here is an example of
2500 In C, every @code{else} branch belongs to the innermost possible @code{if}
2501 statement, which in this example is @code{if (b)}. This is often not
2502 what the programmer expected, as illustrated in the above example by
2503 indentation the programmer chose. When there is the potential for this
2504 confusion, GCC will issue a warning when this flag is specified.
2505 To eliminate the warning, add explicit braces around the innermost
2506 @code{if} statement so there is no way the @code{else} could belong to
2507 the enclosing @code{if}. The resulting code would look like this:
2523 This warning is enabled by @option{-Wall}.
2525 @item -Wsequence-point
2526 @opindex Wsequence-point
2527 Warn about code that may have undefined semantics because of violations
2528 of sequence point rules in the C standard.
2530 The C standard defines the order in which expressions in a C program are
2531 evaluated in terms of @dfn{sequence points}, which represent a partial
2532 ordering between the execution of parts of the program: those executed
2533 before the sequence point, and those executed after it. These occur
2534 after the evaluation of a full expression (one which is not part of a
2535 larger expression), after the evaluation of the first operand of a
2536 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2537 function is called (but after the evaluation of its arguments and the
2538 expression denoting the called function), and in certain other places.
2539 Other than as expressed by the sequence point rules, the order of
2540 evaluation of subexpressions of an expression is not specified. All
2541 these rules describe only a partial order rather than a total order,
2542 since, for example, if two functions are called within one expression
2543 with no sequence point between them, the order in which the functions
2544 are called is not specified. However, the standards committee have
2545 ruled that function calls do not overlap.
2547 It is not specified when between sequence points modifications to the
2548 values of objects take effect. Programs whose behavior depends on this
2549 have undefined behavior; the C standard specifies that ``Between the
2550 previous and next sequence point an object shall have its stored value
2551 modified at most once by the evaluation of an expression. Furthermore,
2552 the prior value shall be read only to determine the value to be
2553 stored.''. If a program breaks these rules, the results on any
2554 particular implementation are entirely unpredictable.
2556 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2557 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2558 diagnosed by this option, and it may give an occasional false positive
2559 result, but in general it has been found fairly effective at detecting
2560 this sort of problem in programs.
2562 The present implementation of this option only works for C programs. A
2563 future implementation may also work for C++ programs.
2565 The C standard is worded confusingly, therefore there is some debate
2566 over the precise meaning of the sequence point rules in subtle cases.
2567 Links to discussions of the problem, including proposed formal
2568 definitions, may be found on the GCC readings page, at
2569 @w{@uref{http://gcc.gnu.org/readings.html}}.
2571 This warning is enabled by @option{-Wall}.
2574 @opindex Wreturn-type
2575 Warn whenever a function is defined with a return-type that defaults to
2576 @code{int}. Also warn about any @code{return} statement with no
2577 return-value in a function whose return-type is not @code{void}.
2579 For C, also warn if the return type of a function has a type qualifier
2580 such as @code{const}. Such a type qualifier has no effect, since the
2581 value returned by a function is not an lvalue. ISO C prohibits
2582 qualified @code{void} return types on function definitions, so such
2583 return types always receive a warning even without this option.
2585 For C++, a function without return type always produces a diagnostic
2586 message, even when @option{-Wno-return-type} is specified. The only
2587 exceptions are @samp{main} and functions defined in system headers.
2589 This warning is enabled by @option{-Wall}.
2593 Warn whenever a @code{switch} statement has an index of enumerated type
2594 and lacks a @code{case} for one or more of the named codes of that
2595 enumeration. (The presence of a @code{default} label prevents this
2596 warning.) @code{case} labels outside the enumeration range also
2597 provoke warnings when this option is used.
2598 This warning is enabled by @option{-Wall}.
2600 @item -Wswitch-default
2601 @opindex Wswitch-switch
2602 Warn whenever a @code{switch} statement does not have a @code{default}
2606 @opindex Wswitch-enum
2607 Warn whenever a @code{switch} statement has an index of enumerated type
2608 and lacks a @code{case} for one or more of the named codes of that
2609 enumeration. @code{case} labels outside the enumeration range also
2610 provoke warnings when this option is used.
2614 Warn if any trigraphs are encountered that might change the meaning of
2615 the program (trigraphs within comments are not warned about).
2616 This warning is enabled by @option{-Wall}.
2618 @item -Wunused-function
2619 @opindex Wunused-function
2620 Warn whenever a static function is declared but not defined or a
2621 non-inline static function is unused.
2622 This warning is enabled by @option{-Wall}.
2624 @item -Wunused-label
2625 @opindex Wunused-label
2626 Warn whenever a label is declared but not used.
2627 This warning is enabled by @option{-Wall}.
2629 To suppress this warning use the @samp{unused} attribute
2630 (@pxref{Variable Attributes}).
2632 @item -Wunused-parameter
2633 @opindex Wunused-parameter
2634 Warn whenever a function parameter is unused aside from its declaration.
2636 To suppress this warning use the @samp{unused} attribute
2637 (@pxref{Variable Attributes}).
2639 @item -Wunused-variable
2640 @opindex Wunused-variable
2641 Warn whenever a local variable or non-constant static variable is unused
2642 aside from its declaration
2643 This warning is enabled by @option{-Wall}.
2645 To suppress this warning use the @samp{unused} attribute
2646 (@pxref{Variable Attributes}).
2648 @item -Wunused-value
2649 @opindex Wunused-value
2650 Warn whenever a statement computes a result that is explicitly not used.
2651 This warning is enabled by @option{-Wall}.
2653 To suppress this warning cast the expression to @samp{void}.
2657 All the above @option{-Wunused} options combined.
2659 In order to get a warning about an unused function parameter, you must
2660 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2661 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2663 @item -Wuninitialized
2664 @opindex Wuninitialized
2665 Warn if an automatic variable is used without first being initialized or
2666 if a variable may be clobbered by a @code{setjmp} call.
2668 These warnings are possible only in optimizing compilation,
2669 because they require data flow information that is computed only
2670 when optimizing. If you don't specify @option{-O}, you simply won't
2673 If you want to warn about code which uses the uninitialized value of the
2674 variable in its own initializer, use the @option{-Winit-self} option.
2676 These warnings occur for individual uninitialized or clobbered
2677 elements of structure, union or array variables as well as for
2678 variables which are uninitialized or clobbered as a whole. They do
2679 not occur for variables or elements declared @code{volatile}. Because
2680 these warnings depend on optimization, the exact variables or elements
2681 for which there are warnings will depend on the precise optimization
2682 options and version of GCC used.
2684 Note that there may be no warning about a variable that is used only
2685 to compute a value that itself is never used, because such
2686 computations may be deleted by data flow analysis before the warnings
2689 These warnings are made optional because GCC is not smart
2690 enough to see all the reasons why the code might be correct
2691 despite appearing to have an error. Here is one example of how
2712 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2713 always initialized, but GCC doesn't know this. Here is
2714 another common case:
2719 if (change_y) save_y = y, y = new_y;
2721 if (change_y) y = save_y;
2726 This has no bug because @code{save_y} is used only if it is set.
2728 @cindex @code{longjmp} warnings
2729 This option also warns when a non-volatile automatic variable might be
2730 changed by a call to @code{longjmp}. These warnings as well are possible
2731 only in optimizing compilation.
2733 The compiler sees only the calls to @code{setjmp}. It cannot know
2734 where @code{longjmp} will be called; in fact, a signal handler could
2735 call it at any point in the code. As a result, you may get a warning
2736 even when there is in fact no problem because @code{longjmp} cannot
2737 in fact be called at the place which would cause a problem.
2739 Some spurious warnings can be avoided if you declare all the functions
2740 you use that never return as @code{noreturn}. @xref{Function
2743 This warning is enabled by @option{-Wall}.
2745 @item -Wunknown-pragmas
2746 @opindex Wunknown-pragmas
2747 @cindex warning for unknown pragmas
2748 @cindex unknown pragmas, warning
2749 @cindex pragmas, warning of unknown
2750 Warn when a #pragma directive is encountered which is not understood by
2751 GCC@. If this command line option is used, warnings will even be issued
2752 for unknown pragmas in system header files. This is not the case if
2753 the warnings were only enabled by the @option{-Wall} command line option.
2756 @opindex Wno-pragmas
2758 Do not warn about misuses of pragmas, such as incorrect parameters,
2759 invalid syntax, or conflicts between pragmas. See also
2760 @samp{-Wunknown-pragmas}.
2762 @item -Wstrict-aliasing
2763 @opindex Wstrict-aliasing
2764 This option is only active when @option{-fstrict-aliasing} is active.
2765 It warns about code which might break the strict aliasing rules that the
2766 compiler is using for optimization. The warning does not catch all
2767 cases, but does attempt to catch the more common pitfalls. It is
2768 included in @option{-Wall}.
2770 @item -Wstrict-aliasing=2
2771 @opindex Wstrict-aliasing=2
2772 This option is only active when @option{-fstrict-aliasing} is active.
2773 It warns about code which might break the strict aliasing rules that the
2774 compiler is using for optimization. This warning catches more cases than
2775 @option{-Wstrict-aliasing}, but it will also give a warning for some ambiguous
2776 cases that are safe.
2780 All of the above @samp{-W} options combined. This enables all the
2781 warnings about constructions that some users consider questionable, and
2782 that are easy to avoid (or modify to prevent the warning), even in
2783 conjunction with macros. This also enables some language-specific
2784 warnings described in @ref{C++ Dialect Options} and
2785 @ref{Objective-C and Objective-C++ Dialect Options}.
2788 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2789 Some of them warn about constructions that users generally do not
2790 consider questionable, but which occasionally you might wish to check
2791 for; others warn about constructions that are necessary or hard to avoid
2792 in some cases, and there is no simple way to modify the code to suppress
2799 (This option used to be called @option{-W}. The older name is still
2800 supported, but the newer name is more descriptive.) Print extra warning
2801 messages for these events:
2805 A function can return either with or without a value. (Falling
2806 off the end of the function body is considered returning without
2807 a value.) For example, this function would evoke such a
2821 An expression-statement or the left-hand side of a comma expression
2822 contains no side effects.
2823 To suppress the warning, cast the unused expression to void.
2824 For example, an expression such as @samp{x[i,j]} will cause a warning,
2825 but @samp{x[(void)i,j]} will not.
2828 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2831 Storage-class specifiers like @code{static} are not the first things in
2832 a declaration. According to the C Standard, this usage is obsolescent.
2835 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2839 A comparison between signed and unsigned values could produce an
2840 incorrect result when the signed value is converted to unsigned.
2841 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2844 An aggregate has an initializer which does not initialize all members.
2845 This warning can be independently controlled by
2846 @option{-Wmissing-field-initializers}.
2849 A function parameter is declared without a type specifier in K&R-style
2857 An empty body occurs in an @samp{if} or @samp{else} statement.
2860 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2861 @samp{>}, or @samp{>=}.
2864 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2867 Any of several floating-point events that often indicate errors, such as
2868 overflow, underflow, loss of precision, etc.
2870 @item @r{(C++ only)}
2871 An enumerator and a non-enumerator both appear in a conditional expression.
2873 @item @r{(C++ only)}
2874 A non-static reference or non-static @samp{const} member appears in a
2875 class without constructors.
2877 @item @r{(C++ only)}
2878 Ambiguous virtual bases.
2880 @item @r{(C++ only)}
2881 Subscripting an array which has been declared @samp{register}.
2883 @item @r{(C++ only)}
2884 Taking the address of a variable which has been declared @samp{register}.
2886 @item @r{(C++ only)}
2887 A base class is not initialized in a derived class' copy constructor.
2890 @item -Wno-div-by-zero
2891 @opindex Wno-div-by-zero
2892 @opindex Wdiv-by-zero
2893 Do not warn about compile-time integer division by zero. Floating point
2894 division by zero is not warned about, as it can be a legitimate way of
2895 obtaining infinities and NaNs.
2897 @item -Wsystem-headers
2898 @opindex Wsystem-headers
2899 @cindex warnings from system headers
2900 @cindex system headers, warnings from
2901 Print warning messages for constructs found in system header files.
2902 Warnings from system headers are normally suppressed, on the assumption
2903 that they usually do not indicate real problems and would only make the
2904 compiler output harder to read. Using this command line option tells
2905 GCC to emit warnings from system headers as if they occurred in user
2906 code. However, note that using @option{-Wall} in conjunction with this
2907 option will @emph{not} warn about unknown pragmas in system
2908 headers---for that, @option{-Wunknown-pragmas} must also be used.
2911 @opindex Wfloat-equal
2912 Warn if floating point values are used in equality comparisons.
2914 The idea behind this is that sometimes it is convenient (for the
2915 programmer) to consider floating-point values as approximations to
2916 infinitely precise real numbers. If you are doing this, then you need
2917 to compute (by analyzing the code, or in some other way) the maximum or
2918 likely maximum error that the computation introduces, and allow for it
2919 when performing comparisons (and when producing output, but that's a
2920 different problem). In particular, instead of testing for equality, you
2921 would check to see whether the two values have ranges that overlap; and
2922 this is done with the relational operators, so equality comparisons are
2925 @item -Wtraditional @r{(C only)}
2926 @opindex Wtraditional
2927 Warn about certain constructs that behave differently in traditional and
2928 ISO C@. Also warn about ISO C constructs that have no traditional C
2929 equivalent, and/or problematic constructs which should be avoided.
2933 Macro parameters that appear within string literals in the macro body.
2934 In traditional C macro replacement takes place within string literals,
2935 but does not in ISO C@.
2938 In traditional C, some preprocessor directives did not exist.
2939 Traditional preprocessors would only consider a line to be a directive
2940 if the @samp{#} appeared in column 1 on the line. Therefore
2941 @option{-Wtraditional} warns about directives that traditional C
2942 understands but would ignore because the @samp{#} does not appear as the
2943 first character on the line. It also suggests you hide directives like
2944 @samp{#pragma} not understood by traditional C by indenting them. Some
2945 traditional implementations would not recognize @samp{#elif}, so it
2946 suggests avoiding it altogether.
2949 A function-like macro that appears without arguments.
2952 The unary plus operator.
2955 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2956 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2957 constants.) Note, these suffixes appear in macros defined in the system
2958 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2959 Use of these macros in user code might normally lead to spurious
2960 warnings, however GCC's integrated preprocessor has enough context to
2961 avoid warning in these cases.
2964 A function declared external in one block and then used after the end of
2968 A @code{switch} statement has an operand of type @code{long}.
2971 A non-@code{static} function declaration follows a @code{static} one.
2972 This construct is not accepted by some traditional C compilers.
2975 The ISO type of an integer constant has a different width or
2976 signedness from its traditional type. This warning is only issued if
2977 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2978 typically represent bit patterns, are not warned about.
2981 Usage of ISO string concatenation is detected.
2984 Initialization of automatic aggregates.
2987 Identifier conflicts with labels. Traditional C lacks a separate
2988 namespace for labels.
2991 Initialization of unions. If the initializer is zero, the warning is
2992 omitted. This is done under the assumption that the zero initializer in
2993 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2994 initializer warnings and relies on default initialization to zero in the
2998 Conversions by prototypes between fixed/floating point values and vice
2999 versa. The absence of these prototypes when compiling with traditional
3000 C would cause serious problems. This is a subset of the possible
3001 conversion warnings, for the full set use @option{-Wconversion}.
3004 Use of ISO C style function definitions. This warning intentionally is
3005 @emph{not} issued for prototype declarations or variadic functions
3006 because these ISO C features will appear in your code when using
3007 libiberty's traditional C compatibility macros, @code{PARAMS} and
3008 @code{VPARAMS}. This warning is also bypassed for nested functions
3009 because that feature is already a GCC extension and thus not relevant to
3010 traditional C compatibility.
3013 @item -Wdeclaration-after-statement @r{(C only)}
3014 @opindex Wdeclaration-after-statement
3015 Warn when a declaration is found after a statement in a block. This
3016 construct, known from C++, was introduced with ISO C99 and is by default
3017 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3018 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3022 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3024 @item -Wno-endif-labels
3025 @opindex Wno-endif-labels
3026 @opindex Wendif-labels
3027 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3031 Warn whenever a local variable shadows another local variable, parameter or
3032 global variable or whenever a built-in function is shadowed.
3034 @item -Wlarger-than-@var{len}
3035 @opindex Wlarger-than
3036 Warn whenever an object of larger than @var{len} bytes is defined.
3038 @item -Wunsafe-loop-optimizations
3039 @opindex Wunsafe-loop-optimizations
3040 Warn if the loop cannot be optimized because the compiler could not
3041 assume anything on the bounds of the loop indices. With
3042 @option{-funsafe-loop-optimizations} warn if the compiler made
3045 @item -Wpointer-arith
3046 @opindex Wpointer-arith
3047 Warn about anything that depends on the ``size of'' a function type or
3048 of @code{void}. GNU C assigns these types a size of 1, for
3049 convenience in calculations with @code{void *} pointers and pointers
3052 @item -Wbad-function-cast @r{(C only)}
3053 @opindex Wbad-function-cast
3054 Warn whenever a function call is cast to a non-matching type.
3055 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3058 Warn about ISO C constructs that are outside of the common subset of
3059 ISO C and ISO C++, e.g.@: request for implicit conversion from
3060 @code{void *} to a pointer to non-@code{void} type.
3064 Warn whenever a pointer is cast so as to remove a type qualifier from
3065 the target type. For example, warn if a @code{const char *} is cast
3066 to an ordinary @code{char *}.
3069 @opindex Wcast-align
3070 Warn whenever a pointer is cast such that the required alignment of the
3071 target is increased. For example, warn if a @code{char *} is cast to
3072 an @code{int *} on machines where integers can only be accessed at
3073 two- or four-byte boundaries.
3075 @item -Wwrite-strings
3076 @opindex Wwrite-strings
3077 When compiling C, give string constants the type @code{const
3078 char[@var{length}]} so that
3079 copying the address of one into a non-@code{const} @code{char *}
3080 pointer will get a warning; when compiling C++, warn about the
3081 deprecated conversion from string constants to @code{char *}.
3082 These warnings will help you find at
3083 compile time code that can try to write into a string constant, but
3084 only if you have been very careful about using @code{const} in
3085 declarations and prototypes. Otherwise, it will just be a nuisance;
3086 this is why we did not make @option{-Wall} request these warnings.
3089 @opindex Wconversion
3090 Warn if a prototype causes a type conversion that is different from what
3091 would happen to the same argument in the absence of a prototype. This
3092 includes conversions of fixed point to floating and vice versa, and
3093 conversions changing the width or signedness of a fixed point argument
3094 except when the same as the default promotion.
3096 Also, warn if a negative integer constant expression is implicitly
3097 converted to an unsigned type. For example, warn about the assignment
3098 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
3099 casts like @code{(unsigned) -1}.
3101 @item -Wsign-compare
3102 @opindex Wsign-compare
3103 @cindex warning for comparison of signed and unsigned values
3104 @cindex comparison of signed and unsigned values, warning
3105 @cindex signed and unsigned values, comparison warning
3106 Warn when a comparison between signed and unsigned values could produce
3107 an incorrect result when the signed value is converted to unsigned.
3108 This warning is also enabled by @option{-Wextra}; to get the other warnings
3109 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3111 @item -Waggregate-return
3112 @opindex Waggregate-return
3113 Warn if any functions that return structures or unions are defined or
3114 called. (In languages where you can return an array, this also elicits
3118 @opindex Walways-true
3119 Warn about comparisons which are always true such as testing if
3120 unsigned values are greater than or equal to zero. This warning is
3121 enabled by @option{-Wall}.
3123 @item -Wno-attributes
3124 @opindex Wno-attributes
3125 @opindex Wattributes
3126 Do not warn if an unexpected @code{__attribute__} is used, such as
3127 unrecognized attributes, function attributes applied to variables,
3128 etc. This will not stop errors for incorrect use of supported
3131 @item -Wstrict-prototypes @r{(C only)}
3132 @opindex Wstrict-prototypes
3133 Warn if a function is declared or defined without specifying the
3134 argument types. (An old-style function definition is permitted without
3135 a warning if preceded by a declaration which specifies the argument
3138 @item -Wold-style-definition @r{(C only)}
3139 @opindex Wold-style-definition
3140 Warn if an old-style function definition is used. A warning is given
3141 even if there is a previous prototype.
3143 @item -Wmissing-prototypes @r{(C only)}
3144 @opindex Wmissing-prototypes
3145 Warn if a global function is defined without a previous prototype
3146 declaration. This warning is issued even if the definition itself
3147 provides a prototype. The aim is to detect global functions that fail
3148 to be declared in header files.
3150 @item -Wmissing-declarations @r{(C only)}
3151 @opindex Wmissing-declarations
3152 Warn if a global function is defined without a previous declaration.
3153 Do so even if the definition itself provides a prototype.
3154 Use this option to detect global functions that are not declared in
3157 @item -Wmissing-field-initializers
3158 @opindex Wmissing-field-initializers
3161 Warn if a structure's initializer has some fields missing. For
3162 example, the following code would cause such a warning, because
3163 @code{x.h} is implicitly zero:
3166 struct s @{ int f, g, h; @};
3167 struct s x = @{ 3, 4 @};
3170 This option does not warn about designated initializers, so the following
3171 modification would not trigger a warning:
3174 struct s @{ int f, g, h; @};
3175 struct s x = @{ .f = 3, .g = 4 @};
3178 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3179 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3181 @item -Wmissing-noreturn
3182 @opindex Wmissing-noreturn
3183 Warn about functions which might be candidates for attribute @code{noreturn}.
3184 Note these are only possible candidates, not absolute ones. Care should
3185 be taken to manually verify functions actually do not ever return before
3186 adding the @code{noreturn} attribute, otherwise subtle code generation
3187 bugs could be introduced. You will not get a warning for @code{main} in
3188 hosted C environments.
3190 @item -Wmissing-format-attribute
3191 @opindex Wmissing-format-attribute
3193 Warn about function pointers which might be candidates for @code{format}
3194 attributes. Note these are only possible candidates, not absolute ones.
3195 GCC will guess that function pointers with @code{format} attributes that
3196 are used in assignment, initialization, parameter passing or return
3197 statements should have a corresponding @code{format} attribute in the
3198 resulting type. I.e.@: the left-hand side of the assignment or
3199 initialization, the type of the parameter variable, or the return type
3200 of the containing function respectively should also have a @code{format}
3201 attribute to avoid the warning.
3203 GCC will also warn about function definitions which might be
3204 candidates for @code{format} attributes. Again, these are only
3205 possible candidates. GCC will guess that @code{format} attributes
3206 might be appropriate for any function that calls a function like
3207 @code{vprintf} or @code{vscanf}, but this might not always be the
3208 case, and some functions for which @code{format} attributes are
3209 appropriate may not be detected.
3211 @item -Wno-multichar
3212 @opindex Wno-multichar
3214 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3215 Usually they indicate a typo in the user's code, as they have
3216 implementation-defined values, and should not be used in portable code.
3218 @item -Wnormalized=<none|id|nfc|nfkc>
3219 @opindex Wnormalized
3222 @cindex character set, input normalization
3223 In ISO C and ISO C++, two identifiers are different if they are
3224 different sequences of characters. However, sometimes when characters
3225 outside the basic ASCII character set are used, you can have two
3226 different character sequences that look the same. To avoid confusion,
3227 the ISO 10646 standard sets out some @dfn{normalization rules} which
3228 when applied ensure that two sequences that look the same are turned into
3229 the same sequence. GCC can warn you if you are using identifiers which
3230 have not been normalized; this option controls that warning.
3232 There are four levels of warning that GCC supports. The default is
3233 @option{-Wnormalized=nfc}, which warns about any identifier which is
3234 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3235 recommended form for most uses.
3237 Unfortunately, there are some characters which ISO C and ISO C++ allow
3238 in identifiers that when turned into NFC aren't allowable as
3239 identifiers. That is, there's no way to use these symbols in portable
3240 ISO C or C++ and have all your identifiers in NFC.
3241 @option{-Wnormalized=id} suppresses the warning for these characters.
3242 It is hoped that future versions of the standards involved will correct
3243 this, which is why this option is not the default.
3245 You can switch the warning off for all characters by writing
3246 @option{-Wnormalized=none}. You would only want to do this if you
3247 were using some other normalization scheme (like ``D''), because
3248 otherwise you can easily create bugs that are literally impossible to see.
3250 Some characters in ISO 10646 have distinct meanings but look identical
3251 in some fonts or display methodologies, especially once formatting has
3252 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3253 LETTER N'', will display just like a regular @code{n} which has been
3254 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3255 normalisation scheme to convert all these into a standard form as
3256 well, and GCC will warn if your code is not in NFKC if you use
3257 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3258 about every identifier that contains the letter O because it might be
3259 confused with the digit 0, and so is not the default, but may be
3260 useful as a local coding convention if the programming environment is
3261 unable to be fixed to display these characters distinctly.
3263 @item -Wno-deprecated-declarations
3264 @opindex Wno-deprecated-declarations
3265 Do not warn about uses of functions, variables, and types marked as
3266 deprecated by using the @code{deprecated} attribute.
3267 (@pxref{Function Attributes}, @pxref{Variable Attributes},
3268 @pxref{Type Attributes}.)
3272 Warn if a structure is given the packed attribute, but the packed
3273 attribute has no effect on the layout or size of the structure.
3274 Such structures may be mis-aligned for little benefit. For
3275 instance, in this code, the variable @code{f.x} in @code{struct bar}
3276 will be misaligned even though @code{struct bar} does not itself
3277 have the packed attribute:
3284 @} __attribute__((packed));
3294 Warn if padding is included in a structure, either to align an element
3295 of the structure or to align the whole structure. Sometimes when this
3296 happens it is possible to rearrange the fields of the structure to
3297 reduce the padding and so make the structure smaller.
3299 @item -Wredundant-decls
3300 @opindex Wredundant-decls
3301 Warn if anything is declared more than once in the same scope, even in
3302 cases where multiple declaration is valid and changes nothing.
3304 @item -Wnested-externs @r{(C only)}
3305 @opindex Wnested-externs
3306 Warn if an @code{extern} declaration is encountered within a function.
3308 @item -Wunreachable-code
3309 @opindex Wunreachable-code
3310 Warn if the compiler detects that code will never be executed.
3312 This option is intended to warn when the compiler detects that at
3313 least a whole line of source code will never be executed, because
3314 some condition is never satisfied or because it is after a
3315 procedure that never returns.
3317 It is possible for this option to produce a warning even though there
3318 are circumstances under which part of the affected line can be executed,
3319 so care should be taken when removing apparently-unreachable code.
3321 For instance, when a function is inlined, a warning may mean that the
3322 line is unreachable in only one inlined copy of the function.
3324 This option is not made part of @option{-Wall} because in a debugging
3325 version of a program there is often substantial code which checks
3326 correct functioning of the program and is, hopefully, unreachable
3327 because the program does work. Another common use of unreachable
3328 code is to provide behavior which is selectable at compile-time.
3332 Warn if a function can not be inlined and it was declared as inline.
3333 Even with this option, the compiler will not warn about failures to
3334 inline functions declared in system headers.
3336 The compiler uses a variety of heuristics to determine whether or not
3337 to inline a function. For example, the compiler takes into account
3338 the size of the function being inlined and the amount of inlining
3339 that has already been done in the current function. Therefore,
3340 seemingly insignificant changes in the source program can cause the
3341 warnings produced by @option{-Winline} to appear or disappear.
3343 @item -Wno-invalid-offsetof @r{(C++ only)}
3344 @opindex Wno-invalid-offsetof
3345 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3346 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3347 to a non-POD type is undefined. In existing C++ implementations,
3348 however, @samp{offsetof} typically gives meaningful results even when
3349 applied to certain kinds of non-POD types. (Such as a simple
3350 @samp{struct} that fails to be a POD type only by virtue of having a
3351 constructor.) This flag is for users who are aware that they are
3352 writing nonportable code and who have deliberately chosen to ignore the
3355 The restrictions on @samp{offsetof} may be relaxed in a future version
3356 of the C++ standard.
3358 @item -Wno-int-to-pointer-cast @r{(C only)}
3359 @opindex Wno-int-to-pointer-cast
3360 Suppress warnings from casts to pointer type of an integer of a
3363 @item -Wno-pointer-to-int-cast @r{(C only)}
3364 @opindex Wno-pointer-to-int-cast
3365 Suppress warnings from casts from a pointer to an integer type of a
3369 @opindex Winvalid-pch
3370 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3371 the search path but can't be used.
3375 @opindex Wno-long-long
3376 Warn if @samp{long long} type is used. This is default. To inhibit
3377 the warning messages, use @option{-Wno-long-long}. Flags
3378 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3379 only when @option{-pedantic} flag is used.
3381 @item -Wvariadic-macros
3382 @opindex Wvariadic-macros
3383 @opindex Wno-variadic-macros
3384 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3385 alternate syntax when in pedantic ISO C99 mode. This is default.
3386 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3388 @item -Wvolatile-register-var
3389 @opindex Wvolatile-register-var
3390 @opindex Wno-volatile-register-var
3391 Warn if a register variable is declared volatile. The volatile
3392 modifier does not inhibit all optimizations that may eliminate reads
3393 and/or writes to register variables.
3395 @item -Wdisabled-optimization
3396 @opindex Wdisabled-optimization
3397 Warn if a requested optimization pass is disabled. This warning does
3398 not generally indicate that there is anything wrong with your code; it
3399 merely indicates that GCC's optimizers were unable to handle the code
3400 effectively. Often, the problem is that your code is too big or too
3401 complex; GCC will refuse to optimize programs when the optimization
3402 itself is likely to take inordinate amounts of time.
3404 @item -Wno-pointer-sign
3405 @opindex Wno-pointer-sign
3406 Don't warn for pointer argument passing or assignment with different signedness.
3407 Only useful in the negative form since this warning is enabled by default.
3408 This option is only supported for C and Objective-C@.
3412 Make all warnings into errors.
3416 Make the specified warning into an errors. The specifier for a
3417 warning is appended, for example @option{-Werror=switch} turns the
3418 warnings controlled by @option{-Wswitch} into errors. This switch
3419 takes a negative form, to be used to negate @option{-Werror} for
3420 specific warnings, for example @option{-Wno-error=switch} makes
3421 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
3422 is in effect. You can use the @option{-fdiagnostics-show-option}
3423 option to have each controllable warning amended with the option which
3424 controls it, to determine what to use with this option.
3426 Note that specifying @option{-Werror=}@var{foo} automatically implies
3427 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
3430 @item -Wstack-protector
3431 @opindex Wstack-protector
3432 This option is only active when @option{-fstack-protector} is active. It
3433 warns about functions that will not be protected against stack smashing.
3435 @item -Wstring-literal-comparison
3436 @opindex Wstring-literal-comparison
3437 Warn about suspicious comparisons to string literal constants. In C,
3438 direct comparisons against the memory address of a string literal, such
3439 as @code{if (x == "abc")}, typically indicate a programmer error, and
3440 even when intentional, result in unspecified behavior and are not portable.
3441 Usually these warnings alert that the programmer intended to use
3442 @code{strcmp}. This warning is enabled by @option{-Wall}.
3446 @node Debugging Options
3447 @section Options for Debugging Your Program or GCC
3448 @cindex options, debugging
3449 @cindex debugging information options
3451 GCC has various special options that are used for debugging
3452 either your program or GCC:
3457 Produce debugging information in the operating system's native format
3458 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3461 On most systems that use stabs format, @option{-g} enables use of extra
3462 debugging information that only GDB can use; this extra information
3463 makes debugging work better in GDB but will probably make other debuggers
3465 refuse to read the program. If you want to control for certain whether
3466 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3467 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3469 GCC allows you to use @option{-g} with
3470 @option{-O}. The shortcuts taken by optimized code may occasionally
3471 produce surprising results: some variables you declared may not exist
3472 at all; flow of control may briefly move where you did not expect it;
3473 some statements may not be executed because they compute constant
3474 results or their values were already at hand; some statements may
3475 execute in different places because they were moved out of loops.
3477 Nevertheless it proves possible to debug optimized output. This makes
3478 it reasonable to use the optimizer for programs that might have bugs.
3480 The following options are useful when GCC is generated with the
3481 capability for more than one debugging format.
3485 Produce debugging information for use by GDB@. This means to use the
3486 most expressive format available (DWARF 2, stabs, or the native format
3487 if neither of those are supported), including GDB extensions if at all
3492 Produce debugging information in stabs format (if that is supported),
3493 without GDB extensions. This is the format used by DBX on most BSD
3494 systems. On MIPS, Alpha and System V Release 4 systems this option
3495 produces stabs debugging output which is not understood by DBX or SDB@.
3496 On System V Release 4 systems this option requires the GNU assembler.
3498 @item -feliminate-unused-debug-symbols
3499 @opindex feliminate-unused-debug-symbols
3500 Produce debugging information in stabs format (if that is supported),
3501 for only symbols that are actually used.
3505 Produce debugging information in stabs format (if that is supported),
3506 using GNU extensions understood only by the GNU debugger (GDB)@. The
3507 use of these extensions is likely to make other debuggers crash or
3508 refuse to read the program.
3512 Produce debugging information in COFF format (if that is supported).
3513 This is the format used by SDB on most System V systems prior to
3518 Produce debugging information in XCOFF format (if that is supported).
3519 This is the format used by the DBX debugger on IBM RS/6000 systems.
3523 Produce debugging information in XCOFF format (if that is supported),
3524 using GNU extensions understood only by the GNU debugger (GDB)@. The
3525 use of these extensions is likely to make other debuggers crash or
3526 refuse to read the program, and may cause assemblers other than the GNU
3527 assembler (GAS) to fail with an error.
3531 Produce debugging information in DWARF version 2 format (if that is
3532 supported). This is the format used by DBX on IRIX 6. With this
3533 option, GCC uses features of DWARF version 3 when they are useful;
3534 version 3 is upward compatible with version 2, but may still cause
3535 problems for older debuggers.
3539 Produce debugging information in VMS debug format (if that is
3540 supported). This is the format used by DEBUG on VMS systems.
3543 @itemx -ggdb@var{level}
3544 @itemx -gstabs@var{level}
3545 @itemx -gcoff@var{level}
3546 @itemx -gxcoff@var{level}
3547 @itemx -gvms@var{level}
3548 Request debugging information and also use @var{level} to specify how
3549 much information. The default level is 2.
3551 Level 1 produces minimal information, enough for making backtraces in
3552 parts of the program that you don't plan to debug. This includes
3553 descriptions of functions and external variables, but no information
3554 about local variables and no line numbers.
3556 Level 3 includes extra information, such as all the macro definitions
3557 present in the program. Some debuggers support macro expansion when
3558 you use @option{-g3}.
3560 @option{-gdwarf-2} does not accept a concatenated debug level, because
3561 GCC used to support an option @option{-gdwarf} that meant to generate
3562 debug information in version 1 of the DWARF format (which is very
3563 different from version 2), and it would have been too confusing. That
3564 debug format is long obsolete, but the option cannot be changed now.
3565 Instead use an additional @option{-g@var{level}} option to change the
3566 debug level for DWARF2.
3568 @item -feliminate-dwarf2-dups
3569 @opindex feliminate-dwarf2-dups
3570 Compress DWARF2 debugging information by eliminating duplicated
3571 information about each symbol. This option only makes sense when
3572 generating DWARF2 debugging information with @option{-gdwarf-2}.
3574 @cindex @command{prof}
3577 Generate extra code to write profile information suitable for the
3578 analysis program @command{prof}. You must use this option when compiling
3579 the source files you want data about, and you must also use it when
3582 @cindex @command{gprof}
3585 Generate extra code to write profile information suitable for the
3586 analysis program @command{gprof}. You must use this option when compiling
3587 the source files you want data about, and you must also use it when
3592 Makes the compiler print out each function name as it is compiled, and
3593 print some statistics about each pass when it finishes.
3596 @opindex ftime-report
3597 Makes the compiler print some statistics about the time consumed by each
3598 pass when it finishes.
3601 @opindex fmem-report
3602 Makes the compiler print some statistics about permanent memory
3603 allocation when it finishes.
3605 @item -fprofile-arcs
3606 @opindex fprofile-arcs
3607 Add code so that program flow @dfn{arcs} are instrumented. During
3608 execution the program records how many times each branch and call is
3609 executed and how many times it is taken or returns. When the compiled
3610 program exits it saves this data to a file called
3611 @file{@var{auxname}.gcda} for each source file. The data may be used for
3612 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3613 test coverage analysis (@option{-ftest-coverage}). Each object file's
3614 @var{auxname} is generated from the name of the output file, if
3615 explicitly specified and it is not the final executable, otherwise it is
3616 the basename of the source file. In both cases any suffix is removed
3617 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3618 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3619 @xref{Cross-profiling}.
3621 @cindex @command{gcov}
3625 This option is used to compile and link code instrumented for coverage
3626 analysis. The option is a synonym for @option{-fprofile-arcs}
3627 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
3628 linking). See the documentation for those options for more details.
3633 Compile the source files with @option{-fprofile-arcs} plus optimization
3634 and code generation options. For test coverage analysis, use the
3635 additional @option{-ftest-coverage} option. You do not need to profile
3636 every source file in a program.
3639 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3640 (the latter implies the former).
3643 Run the program on a representative workload to generate the arc profile
3644 information. This may be repeated any number of times. You can run
3645 concurrent instances of your program, and provided that the file system
3646 supports locking, the data files will be correctly updated. Also
3647 @code{fork} calls are detected and correctly handled (double counting
3651 For profile-directed optimizations, compile the source files again with
3652 the same optimization and code generation options plus
3653 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3654 Control Optimization}).
3657 For test coverage analysis, use @command{gcov} to produce human readable
3658 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3659 @command{gcov} documentation for further information.
3663 With @option{-fprofile-arcs}, for each function of your program GCC
3664 creates a program flow graph, then finds a spanning tree for the graph.
3665 Only arcs that are not on the spanning tree have to be instrumented: the
3666 compiler adds code to count the number of times that these arcs are
3667 executed. When an arc is the only exit or only entrance to a block, the
3668 instrumentation code can be added to the block; otherwise, a new basic
3669 block must be created to hold the instrumentation code.
3672 @item -ftest-coverage
3673 @opindex ftest-coverage
3674 Produce a notes file that the @command{gcov} code-coverage utility
3675 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3676 show program coverage. Each source file's note file is called
3677 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3678 above for a description of @var{auxname} and instructions on how to
3679 generate test coverage data. Coverage data will match the source files
3680 more closely, if you do not optimize.
3682 @item -d@var{letters}
3683 @item -fdump-rtl-@var{pass}
3685 Says to make debugging dumps during compilation at times specified by
3686 @var{letters}. This is used for debugging the RTL-based passes of the
3687 compiler. The file names for most of the dumps are made by appending a
3688 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3689 from the name of the output file, if explicitly specified and it is not
3690 an executable, otherwise it is the basename of the source file.
3692 Most debug dumps can be enabled either passing a letter to the @option{-d}
3693 option, or with a long @option{-fdump-rtl} switch; here are the possible
3694 letters for use in @var{letters} and @var{pass}, and their meanings:
3699 Annotate the assembler output with miscellaneous debugging information.
3702 @itemx -fdump-rtl-bp
3704 @opindex fdump-rtl-bp
3705 Dump after computing branch probabilities, to @file{@var{file}.09.bp}.
3708 @itemx -fdump-rtl-bbro
3710 @opindex fdump-rtl-bbro
3711 Dump after block reordering, to @file{@var{file}.30.bbro}.
3714 @itemx -fdump-rtl-combine
3716 @opindex fdump-rtl-combine
3717 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3720 @itemx -fdump-rtl-ce1
3721 @itemx -fdump-rtl-ce2
3723 @opindex fdump-rtl-ce1
3724 @opindex fdump-rtl-ce2
3725 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3726 first if conversion, to the file @file{@var{file}.11.ce1}. @option{-dC}
3727 and @option{-fdump-rtl-ce2} enable dumping after the second if
3728 conversion, to the file @file{@var{file}.18.ce2}.
3731 @itemx -fdump-rtl-btl
3732 @itemx -fdump-rtl-dbr
3734 @opindex fdump-rtl-btl
3735 @opindex fdump-rtl-dbr
3736 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3737 target load optimization, to @file{@var{file}.31.btl}. @option{-dd}
3738 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3739 scheduling, to @file{@var{file}.36.dbr}.
3743 Dump all macro definitions, at the end of preprocessing, in addition to
3747 @itemx -fdump-rtl-ce3
3749 @opindex fdump-rtl-ce3
3750 Dump after the third if conversion, to @file{@var{file}.28.ce3}.
3753 @itemx -fdump-rtl-cfg
3754 @itemx -fdump-rtl-life
3756 @opindex fdump-rtl-cfg
3757 @opindex fdump-rtl-life
3758 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3759 and data flow analysis, to @file{@var{file}.08.cfg}. @option{-df}
3760 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3761 to @file{@var{file}.16.life}.
3764 @itemx -fdump-rtl-greg
3766 @opindex fdump-rtl-greg
3767 Dump after global register allocation, to @file{@var{file}.23.greg}.
3770 @itemx -fdump-rtl-gcse
3771 @itemx -fdump-rtl-bypass
3773 @opindex fdump-rtl-gcse
3774 @opindex fdump-rtl-bypass
3775 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3776 @file{@var{file}.05.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3777 enable dumping after jump bypassing and control flow optimizations, to
3778 @file{@var{file}.07.bypass}.
3781 @itemx -fdump-rtl-eh
3783 @opindex fdump-rtl-eh
3784 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3787 @itemx -fdump-rtl-sibling
3789 @opindex fdump-rtl-sibling
3790 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3793 @itemx -fdump-rtl-jump
3795 @opindex fdump-rtl-jump
3796 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3799 @itemx -fdump-rtl-stack
3801 @opindex fdump-rtl-stack
3802 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3805 @itemx -fdump-rtl-lreg
3807 @opindex fdump-rtl-lreg
3808 Dump after local register allocation, to @file{@var{file}.22.lreg}.
3811 @itemx -fdump-rtl-loop
3812 @itemx -fdump-rtl-loop2
3814 @opindex fdump-rtl-loop
3815 @opindex fdump-rtl-loop2
3816 @option{-dL} and @option{-fdump-rtl-loop} enable dumping after the first
3817 loop optimization pass, to @file{@var{file}.06.loop}. @option{-dL} and
3818 @option{-fdump-rtl-loop2} enable dumping after the second pass, to
3819 @file{@var{file}.13.loop2}.
3822 @itemx -fdump-rtl-sms
3824 @opindex fdump-rtl-sms
3825 Dump after modulo scheduling, to @file{@var{file}.20.sms}.
3828 @itemx -fdump-rtl-mach
3830 @opindex fdump-rtl-mach
3831 Dump after performing the machine dependent reorganization pass, to
3832 @file{@var{file}.35.mach}.
3835 @itemx -fdump-rtl-rnreg
3837 @opindex fdump-rtl-rnreg
3838 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3841 @itemx -fdump-rtl-regmove
3843 @opindex fdump-rtl-regmove
3844 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3847 @itemx -fdump-rtl-postreload
3849 @opindex fdump-rtl-postreload
3850 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3853 @itemx -fdump-rtl-expand
3855 @opindex fdump-rtl-expand
3856 Dump after RTL generation, to @file{@var{file}.00.expand}.
3859 @itemx -fdump-rtl-sched2
3861 @opindex fdump-rtl-sched2
3862 Dump after the second scheduling pass, to @file{@var{file}.32.sched2}.
3865 @itemx -fdump-rtl-cse
3867 @opindex fdump-rtl-cse
3868 Dump after CSE (including the jump optimization that sometimes follows
3869 CSE), to @file{@var{file}.04.cse}.
3872 @itemx -fdump-rtl-sched
3874 @opindex fdump-rtl-sched
3875 Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
3878 @itemx -fdump-rtl-cse2
3880 @opindex fdump-rtl-cse2
3881 Dump after the second CSE pass (including the jump optimization that
3882 sometimes follows CSE), to @file{@var{file}.15.cse2}.
3885 @itemx -fdump-rtl-tracer
3887 @opindex fdump-rtl-tracer
3888 Dump after running tracer, to @file{@var{file}.12.tracer}.
3891 @itemx -fdump-rtl-vpt
3892 @itemx -fdump-rtl-vartrack
3894 @opindex fdump-rtl-vpt
3895 @opindex fdump-rtl-vartrack
3896 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
3897 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
3898 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
3899 to @file{@var{file}.34.vartrack}.
3902 @itemx -fdump-rtl-flow2
3904 @opindex fdump-rtl-flow2
3905 Dump after the second flow pass, to @file{@var{file}.26.flow2}.
3908 @itemx -fdump-rtl-peephole2
3910 @opindex fdump-rtl-peephole2
3911 Dump after the peephole pass, to @file{@var{file}.27.peephole2}.
3914 @itemx -fdump-rtl-web
3916 @opindex fdump-rtl-web
3917 Dump after live range splitting, to @file{@var{file}.14.web}.
3920 @itemx -fdump-rtl-all
3922 @opindex fdump-rtl-all
3923 Produce all the dumps listed above.
3927 Produce a core dump whenever an error occurs.
3931 Print statistics on memory usage, at the end of the run, to
3936 Annotate the assembler output with a comment indicating which
3937 pattern and alternative was used. The length of each instruction is
3942 Dump the RTL in the assembler output as a comment before each instruction.
3943 Also turns on @option{-dp} annotation.
3947 For each of the other indicated dump files (either with @option{-d} or
3948 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
3949 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3953 Just generate RTL for a function instead of compiling it. Usually used
3954 with @samp{r} (@option{-fdump-rtl-expand}).
3958 Dump debugging information during parsing, to standard error.
3961 @item -fdump-unnumbered
3962 @opindex fdump-unnumbered
3963 When doing debugging dumps (see @option{-d} option above), suppress instruction
3964 numbers and line number note output. This makes it more feasible to
3965 use diff on debugging dumps for compiler invocations with different
3966 options, in particular with and without @option{-g}.
3968 @item -fdump-translation-unit @r{(C++ only)}
3969 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
3970 @opindex fdump-translation-unit
3971 Dump a representation of the tree structure for the entire translation
3972 unit to a file. The file name is made by appending @file{.tu} to the
3973 source file name. If the @samp{-@var{options}} form is used, @var{options}
3974 controls the details of the dump as described for the
3975 @option{-fdump-tree} options.
3977 @item -fdump-class-hierarchy @r{(C++ only)}
3978 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3979 @opindex fdump-class-hierarchy
3980 Dump a representation of each class's hierarchy and virtual function
3981 table layout to a file. The file name is made by appending @file{.class}
3982 to the source file name. If the @samp{-@var{options}} form is used,
3983 @var{options} controls the details of the dump as described for the
3984 @option{-fdump-tree} options.
3986 @item -fdump-ipa-@var{switch}
3988 Control the dumping at various stages of inter-procedural analysis
3989 language tree to a file. The file name is generated by appending a switch
3990 specific suffix to the source file name. The following dumps are possible:
3994 Enables all inter-procedural analysis dumps; currently the only produced
3995 dump is the @samp{cgraph} dump.
3998 Dumps information about call-graph optimization, unused function removal,
3999 and inlining decisions.
4002 @item -fdump-tree-@var{switch}
4003 @itemx -fdump-tree-@var{switch}-@var{options}
4005 Control the dumping at various stages of processing the intermediate
4006 language tree to a file. The file name is generated by appending a switch
4007 specific suffix to the source file name. If the @samp{-@var{options}}
4008 form is used, @var{options} is a list of @samp{-} separated options that
4009 control the details of the dump. Not all options are applicable to all
4010 dumps, those which are not meaningful will be ignored. The following
4011 options are available
4015 Print the address of each node. Usually this is not meaningful as it
4016 changes according to the environment and source file. Its primary use
4017 is for tying up a dump file with a debug environment.
4019 Inhibit dumping of members of a scope or body of a function merely
4020 because that scope has been reached. Only dump such items when they
4021 are directly reachable by some other path. When dumping pretty-printed
4022 trees, this option inhibits dumping the bodies of control structures.
4024 Print a raw representation of the tree. By default, trees are
4025 pretty-printed into a C-like representation.
4027 Enable more detailed dumps (not honored by every dump option).
4029 Enable dumping various statistics about the pass (not honored by every dump
4032 Enable showing basic block boundaries (disabled in raw dumps).
4034 Enable showing virtual operands for every statement.
4036 Enable showing line numbers for statements.
4038 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4040 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
4043 The following tree dumps are possible:
4047 Dump before any tree based optimization, to @file{@var{file}.original}.
4050 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4053 Dump after function inlining, to @file{@var{file}.inlined}.
4056 @opindex fdump-tree-gimple
4057 Dump each function before and after the gimplification pass to a file. The
4058 file name is made by appending @file{.gimple} to the source file name.
4061 @opindex fdump-tree-cfg
4062 Dump the control flow graph of each function to a file. The file name is
4063 made by appending @file{.cfg} to the source file name.
4066 @opindex fdump-tree-vcg
4067 Dump the control flow graph of each function to a file in VCG format. The
4068 file name is made by appending @file{.vcg} to the source file name. Note
4069 that if the file contains more than one function, the generated file cannot
4070 be used directly by VCG@. You will need to cut and paste each function's
4071 graph into its own separate file first.
4074 @opindex fdump-tree-ch
4075 Dump each function after copying loop headers. The file name is made by
4076 appending @file{.ch} to the source file name.
4079 @opindex fdump-tree-ssa
4080 Dump SSA related information to a file. The file name is made by appending
4081 @file{.ssa} to the source file name.
4084 @opindex fdump-tree-salias
4085 Dump structure aliasing variable information to a file. This file name
4086 is made by appending @file{.salias} to the source file name.
4089 @opindex fdump-tree-alias
4090 Dump aliasing information for each function. The file name is made by
4091 appending @file{.alias} to the source file name.
4094 @opindex fdump-tree-ccp
4095 Dump each function after CCP@. The file name is made by appending
4096 @file{.ccp} to the source file name.
4099 @opindex fdump-tree-storeccp
4100 Dump each function after STORE-CCP. The file name is made by appending
4101 @file{.storeccp} to the source file name.
4104 @opindex fdump-tree-pre
4105 Dump trees after partial redundancy elimination. The file name is made
4106 by appending @file{.pre} to the source file name.
4109 @opindex fdump-tree-fre
4110 Dump trees after full redundancy elimination. The file name is made
4111 by appending @file{.fre} to the source file name.
4114 @opindex fdump-tree-copyprop
4115 Dump trees after copy propagation. The file name is made
4116 by appending @file{.copyprop} to the source file name.
4118 @item store_copyprop
4119 @opindex fdump-tree-store_copyprop
4120 Dump trees after store copy-propagation. The file name is made
4121 by appending @file{.store_copyprop} to the source file name.
4124 @opindex fdump-tree-dce
4125 Dump each function after dead code elimination. The file name is made by
4126 appending @file{.dce} to the source file name.
4129 @opindex fdump-tree-mudflap
4130 Dump each function after adding mudflap instrumentation. The file name is
4131 made by appending @file{.mudflap} to the source file name.
4134 @opindex fdump-tree-sra
4135 Dump each function after performing scalar replacement of aggregates. The
4136 file name is made by appending @file{.sra} to the source file name.
4139 @opindex fdump-tree-sink
4140 Dump each function after performing code sinking. The file name is made
4141 by appending @file{.sink} to the source file name.
4144 @opindex fdump-tree-dom
4145 Dump each function after applying dominator tree optimizations. The file
4146 name is made by appending @file{.dom} to the source file name.
4149 @opindex fdump-tree-dse
4150 Dump each function after applying dead store elimination. The file
4151 name is made by appending @file{.dse} to the source file name.
4154 @opindex fdump-tree-phiopt
4155 Dump each function after optimizing PHI nodes into straightline code. The file
4156 name is made by appending @file{.phiopt} to the source file name.
4159 @opindex fdump-tree-forwprop
4160 Dump each function after forward propagating single use variables. The file
4161 name is made by appending @file{.forwprop} to the source file name.
4164 @opindex fdump-tree-copyrename
4165 Dump each function after applying the copy rename optimization. The file
4166 name is made by appending @file{.copyrename} to the source file name.
4169 @opindex fdump-tree-nrv
4170 Dump each function after applying the named return value optimization on
4171 generic trees. The file name is made by appending @file{.nrv} to the source
4175 @opindex fdump-tree-vect
4176 Dump each function after applying vectorization of loops. The file name is
4177 made by appending @file{.vect} to the source file name.
4180 @opindex fdump-tree-vrp
4181 Dump each function after Value Range Propagation (VRP). The file name
4182 is made by appending @file{.vrp} to the source file name.
4185 @opindex fdump-tree-all
4186 Enable all the available tree dumps with the flags provided in this option.
4189 @item -ftree-vectorizer-verbose=@var{n}
4190 @opindex ftree-vectorizer-verbose
4191 This option controls the amount of debugging output the vectorizer prints.
4192 This information is written to standard error, unless @option{-fdump-tree-all}
4193 or @option{-fdump-tree-vect} is specified, in which case it is output to the
4194 usual dump listing file, @file{.vect}.
4196 @item -frandom-seed=@var{string}
4197 @opindex frandom-string
4198 This option provides a seed that GCC uses when it would otherwise use
4199 random numbers. It is used to generate certain symbol names
4200 that have to be different in every compiled file. It is also used to
4201 place unique stamps in coverage data files and the object files that
4202 produce them. You can use the @option{-frandom-seed} option to produce
4203 reproducibly identical object files.
4205 The @var{string} should be different for every file you compile.
4207 @item -fsched-verbose=@var{n}
4208 @opindex fsched-verbose
4209 On targets that use instruction scheduling, this option controls the
4210 amount of debugging output the scheduler prints. This information is
4211 written to standard error, unless @option{-dS} or @option{-dR} is
4212 specified, in which case it is output to the usual dump
4213 listing file, @file{.sched} or @file{.sched2} respectively. However
4214 for @var{n} greater than nine, the output is always printed to standard
4217 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4218 same information as @option{-dRS}. For @var{n} greater than one, it
4219 also output basic block probabilities, detailed ready list information
4220 and unit/insn info. For @var{n} greater than two, it includes RTL
4221 at abort point, control-flow and regions info. And for @var{n} over
4222 four, @option{-fsched-verbose} also includes dependence info.
4226 Store the usual ``temporary'' intermediate files permanently; place them
4227 in the current directory and name them based on the source file. Thus,
4228 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4229 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4230 preprocessed @file{foo.i} output file even though the compiler now
4231 normally uses an integrated preprocessor.
4233 When used in combination with the @option{-x} command line option,
4234 @option{-save-temps} is sensible enough to avoid over writing an
4235 input source file with the same extension as an intermediate file.
4236 The corresponding intermediate file may be obtained by renaming the
4237 source file before using @option{-save-temps}.
4241 Report the CPU time taken by each subprocess in the compilation
4242 sequence. For C source files, this is the compiler proper and assembler
4243 (plus the linker if linking is done). The output looks like this:
4250 The first number on each line is the ``user time'', that is time spent
4251 executing the program itself. The second number is ``system time'',
4252 time spent executing operating system routines on behalf of the program.
4253 Both numbers are in seconds.
4255 @item -fvar-tracking
4256 @opindex fvar-tracking
4257 Run variable tracking pass. It computes where variables are stored at each
4258 position in code. Better debugging information is then generated
4259 (if the debugging information format supports this information).
4261 It is enabled by default when compiling with optimization (@option{-Os},
4262 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
4263 the debug info format supports it.
4265 @item -print-file-name=@var{library}
4266 @opindex print-file-name
4267 Print the full absolute name of the library file @var{library} that
4268 would be used when linking---and don't do anything else. With this
4269 option, GCC does not compile or link anything; it just prints the
4272 @item -print-multi-directory
4273 @opindex print-multi-directory
4274 Print the directory name corresponding to the multilib selected by any
4275 other switches present in the command line. This directory is supposed
4276 to exist in @env{GCC_EXEC_PREFIX}.
4278 @item -print-multi-lib
4279 @opindex print-multi-lib
4280 Print the mapping from multilib directory names to compiler switches
4281 that enable them. The directory name is separated from the switches by
4282 @samp{;}, and each switch starts with an @samp{@@} instead of the
4283 @samp{-}, without spaces between multiple switches. This is supposed to
4284 ease shell-processing.
4286 @item -print-prog-name=@var{program}
4287 @opindex print-prog-name
4288 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
4290 @item -print-libgcc-file-name
4291 @opindex print-libgcc-file-name
4292 Same as @option{-print-file-name=libgcc.a}.
4294 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
4295 but you do want to link with @file{libgcc.a}. You can do
4298 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
4301 @item -print-search-dirs
4302 @opindex print-search-dirs
4303 Print the name of the configured installation directory and a list of
4304 program and library directories @command{gcc} will search---and don't do anything else.
4306 This is useful when @command{gcc} prints the error message
4307 @samp{installation problem, cannot exec cpp0: No such file or directory}.
4308 To resolve this you either need to put @file{cpp0} and the other compiler
4309 components where @command{gcc} expects to find them, or you can set the environment
4310 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
4311 Don't forget the trailing @samp{/}.
4312 @xref{Environment Variables}.
4315 @opindex dumpmachine
4316 Print the compiler's target machine (for example,
4317 @samp{i686-pc-linux-gnu})---and don't do anything else.
4320 @opindex dumpversion
4321 Print the compiler version (for example, @samp{3.0})---and don't do
4326 Print the compiler's built-in specs---and don't do anything else. (This
4327 is used when GCC itself is being built.) @xref{Spec Files}.
4329 @item -feliminate-unused-debug-types
4330 @opindex feliminate-unused-debug-types
4331 Normally, when producing DWARF2 output, GCC will emit debugging
4332 information for all types declared in a compilation
4333 unit, regardless of whether or not they are actually used
4334 in that compilation unit. Sometimes this is useful, such as
4335 if, in the debugger, you want to cast a value to a type that is
4336 not actually used in your program (but is declared). More often,
4337 however, this results in a significant amount of wasted space.
4338 With this option, GCC will avoid producing debug symbol output
4339 for types that are nowhere used in the source file being compiled.
4342 @node Optimize Options
4343 @section Options That Control Optimization
4344 @cindex optimize options
4345 @cindex options, optimization
4347 These options control various sorts of optimizations.
4349 Without any optimization option, the compiler's goal is to reduce the
4350 cost of compilation and to make debugging produce the expected
4351 results. Statements are independent: if you stop the program with a
4352 breakpoint between statements, you can then assign a new value to any
4353 variable or change the program counter to any other statement in the
4354 function and get exactly the results you would expect from the source
4357 Turning on optimization flags makes the compiler attempt to improve
4358 the performance and/or code size at the expense of compilation time
4359 and possibly the ability to debug the program.
4361 The compiler performs optimization based on the knowledge it has of
4362 the program. Optimization levels @option{-O2} and above, in
4363 particular, enable @emph{unit-at-a-time} mode, which allows the
4364 compiler to consider information gained from later functions in
4365 the file when compiling a function. Compiling multiple files at
4366 once to a single output file in @emph{unit-at-a-time} mode allows
4367 the compiler to use information gained from all of the files when
4368 compiling each of them.
4370 Not all optimizations are controlled directly by a flag. Only
4371 optimizations that have a flag are listed.
4378 Optimize. Optimizing compilation takes somewhat more time, and a lot
4379 more memory for a large function.
4381 With @option{-O}, the compiler tries to reduce code size and execution
4382 time, without performing any optimizations that take a great deal of
4385 @option{-O} turns on the following optimization flags:
4386 @gccoptlist{-fdefer-pop @gol
4387 -fdelayed-branch @gol
4388 -fguess-branch-probability @gol
4389 -fcprop-registers @gol
4390 -floop-optimize @gol
4391 -fif-conversion @gol
4392 -fif-conversion2 @gol
4395 -ftree-dominator-opts @gol
4400 -ftree-copyrename @gol
4405 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4406 where doing so does not interfere with debugging.
4410 Optimize even more. GCC performs nearly all supported optimizations
4411 that do not involve a space-speed tradeoff. The compiler does not
4412 perform loop unrolling or function inlining when you specify @option{-O2}.
4413 As compared to @option{-O}, this option increases both compilation time
4414 and the performance of the generated code.
4416 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4417 also turns on the following optimization flags:
4418 @gccoptlist{-fthread-jumps @gol
4420 -foptimize-sibling-calls @gol
4421 -fcse-follow-jumps -fcse-skip-blocks @gol
4422 -fgcse -fgcse-lm @gol
4423 -fexpensive-optimizations @gol
4424 -fstrength-reduce @gol
4425 -frerun-cse-after-loop -frerun-loop-opt @gol
4428 -fschedule-insns -fschedule-insns2 @gol
4429 -fsched-interblock -fsched-spec @gol
4431 -fstrict-aliasing @gol
4432 -fdelete-null-pointer-checks @gol
4433 -freorder-blocks -freorder-functions @gol
4434 -funit-at-a-time @gol
4435 -falign-functions -falign-jumps @gol
4436 -falign-loops -falign-labels @gol
4440 Please note the warning under @option{-fgcse} about
4441 invoking @option{-O2} on programs that use computed gotos.
4445 Optimize yet more. @option{-O3} turns on all optimizations specified by
4446 @option{-O2} and also turns on the @option{-finline-functions},
4447 @option{-funswitch-loops} and @option{-fgcse-after-reload} options.
4451 Do not optimize. This is the default.
4455 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4456 do not typically increase code size. It also performs further
4457 optimizations designed to reduce code size.
4459 @option{-Os} disables the following optimization flags:
4460 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4461 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
4462 -fprefetch-loop-arrays -ftree-vect-loop-version}
4464 If you use multiple @option{-O} options, with or without level numbers,
4465 the last such option is the one that is effective.
4468 Options of the form @option{-f@var{flag}} specify machine-independent
4469 flags. Most flags have both positive and negative forms; the negative
4470 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4471 below, only one of the forms is listed---the one you typically will
4472 use. You can figure out the other form by either removing @samp{no-}
4475 The following options control specific optimizations. They are either
4476 activated by @option{-O} options or are related to ones that are. You
4477 can use the following flags in the rare cases when ``fine-tuning'' of
4478 optimizations to be performed is desired.
4481 @item -fno-default-inline
4482 @opindex fno-default-inline
4483 Do not make member functions inline by default merely because they are
4484 defined inside the class scope (C++ only). Otherwise, when you specify
4485 @w{@option{-O}}, member functions defined inside class scope are compiled
4486 inline by default; i.e., you don't need to add @samp{inline} in front of
4487 the member function name.
4489 @item -fno-defer-pop
4490 @opindex fno-defer-pop
4491 Always pop the arguments to each function call as soon as that function
4492 returns. For machines which must pop arguments after a function call,
4493 the compiler normally lets arguments accumulate on the stack for several
4494 function calls and pops them all at once.
4496 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4500 Force memory operands to be copied into registers before doing
4501 arithmetic on them. This produces better code by making all memory
4502 references potential common subexpressions. When they are not common
4503 subexpressions, instruction combination should eliminate the separate
4504 register-load. This option is now a nop and will be removed in 4.2.
4507 @opindex fforce-addr
4508 Force memory address constants to be copied into registers before
4509 doing arithmetic on them.
4511 @item -fomit-frame-pointer
4512 @opindex fomit-frame-pointer
4513 Don't keep the frame pointer in a register for functions that
4514 don't need one. This avoids the instructions to save, set up and
4515 restore frame pointers; it also makes an extra register available
4516 in many functions. @strong{It also makes debugging impossible on
4519 On some machines, such as the VAX, this flag has no effect, because
4520 the standard calling sequence automatically handles the frame pointer
4521 and nothing is saved by pretending it doesn't exist. The
4522 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4523 whether a target machine supports this flag. @xref{Registers,,Register
4524 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4526 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4528 @item -foptimize-sibling-calls
4529 @opindex foptimize-sibling-calls
4530 Optimize sibling and tail recursive calls.
4532 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4536 Don't pay attention to the @code{inline} keyword. Normally this option
4537 is used to keep the compiler from expanding any functions inline.
4538 Note that if you are not optimizing, no functions can be expanded inline.
4540 @item -finline-functions
4541 @opindex finline-functions
4542 Integrate all simple functions into their callers. The compiler
4543 heuristically decides which functions are simple enough to be worth
4544 integrating in this way.
4546 If all calls to a given function are integrated, and the function is
4547 declared @code{static}, then the function is normally not output as
4548 assembler code in its own right.
4550 Enabled at level @option{-O3}.
4552 @item -finline-functions-called-once
4553 @opindex finline-functions-called-once
4554 Consider all @code{static} functions called once for inlining into their
4555 caller even if they are not marked @code{inline}. If a call to a given
4556 function is integrated, then the function is not output as assembler code
4559 Enabled if @option{-funit-at-a-time} is enabled.
4561 @item -fearly-inlining
4562 @opindex fearly-inlining
4563 Inline functions marked by @code{always_inline} and functions whose body seems
4564 smaller than the function call overhead early before doing
4565 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
4566 makes profiling significantly cheaper and usually inlining faster on programs
4567 having large chains of nested wrapper functions.
4571 @item -finline-limit=@var{n}
4572 @opindex finline-limit
4573 By default, GCC limits the size of functions that can be inlined. This flag
4574 allows the control of this limit for functions that are explicitly marked as
4575 inline (i.e., marked with the inline keyword or defined within the class
4576 definition in c++). @var{n} is the size of functions that can be inlined in
4577 number of pseudo instructions (not counting parameter handling). The default
4578 value of @var{n} is 600.
4579 Increasing this value can result in more inlined code at
4580 the cost of compilation time and memory consumption. Decreasing usually makes
4581 the compilation faster and less code will be inlined (which presumably
4582 means slower programs). This option is particularly useful for programs that
4583 use inlining heavily such as those based on recursive templates with C++.
4585 Inlining is actually controlled by a number of parameters, which may be
4586 specified individually by using @option{--param @var{name}=@var{value}}.
4587 The @option{-finline-limit=@var{n}} option sets some of these parameters
4591 @item max-inline-insns-single
4592 is set to @var{n}/2.
4593 @item max-inline-insns-auto
4594 is set to @var{n}/2.
4595 @item min-inline-insns
4596 is set to 130 or @var{n}/4, whichever is smaller.
4597 @item max-inline-insns-rtl
4601 See below for a documentation of the individual
4602 parameters controlling inlining.
4604 @emph{Note:} pseudo instruction represents, in this particular context, an
4605 abstract measurement of function's size. In no way does it represent a count
4606 of assembly instructions and as such its exact meaning might change from one
4607 release to an another.
4609 @item -fkeep-inline-functions
4610 @opindex fkeep-inline-functions
4611 In C, emit @code{static} functions that are declared @code{inline}
4612 into the object file, even if the function has been inlined into all
4613 of its callers. This switch does not affect functions using the
4614 @code{extern inline} extension in GNU C@. In C++, emit any and all
4615 inline functions into the object file.
4617 @item -fkeep-static-consts
4618 @opindex fkeep-static-consts
4619 Emit variables declared @code{static const} when optimization isn't turned
4620 on, even if the variables aren't referenced.
4622 GCC enables this option by default. If you want to force the compiler to
4623 check if the variable was referenced, regardless of whether or not
4624 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4626 @item -fmerge-constants
4627 Attempt to merge identical constants (string constants and floating point
4628 constants) across compilation units.
4630 This option is the default for optimized compilation if the assembler and
4631 linker support it. Use @option{-fno-merge-constants} to inhibit this
4634 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4636 @item -fmerge-all-constants
4637 Attempt to merge identical constants and identical variables.
4639 This option implies @option{-fmerge-constants}. In addition to
4640 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4641 arrays or initialized constant variables with integral or floating point
4642 types. Languages like C or C++ require each non-automatic variable to
4643 have distinct location, so using this option will result in non-conforming
4646 @item -fmodulo-sched
4647 @opindex fmodulo-sched
4648 Perform swing modulo scheduling immediately before the first scheduling
4649 pass. This pass looks at innermost loops and reorders their
4650 instructions by overlapping different iterations.
4652 @item -fno-branch-count-reg
4653 @opindex fno-branch-count-reg
4654 Do not use ``decrement and branch'' instructions on a count register,
4655 but instead generate a sequence of instructions that decrement a
4656 register, compare it against zero, then branch based upon the result.
4657 This option is only meaningful on architectures that support such
4658 instructions, which include x86, PowerPC, IA-64 and S/390.
4660 The default is @option{-fbranch-count-reg}, enabled when
4661 @option{-fstrength-reduce} is enabled.
4663 @item -fno-function-cse
4664 @opindex fno-function-cse
4665 Do not put function addresses in registers; make each instruction that
4666 calls a constant function contain the function's address explicitly.
4668 This option results in less efficient code, but some strange hacks
4669 that alter the assembler output may be confused by the optimizations
4670 performed when this option is not used.
4672 The default is @option{-ffunction-cse}
4674 @item -fno-zero-initialized-in-bss
4675 @opindex fno-zero-initialized-in-bss
4676 If the target supports a BSS section, GCC by default puts variables that
4677 are initialized to zero into BSS@. This can save space in the resulting
4680 This option turns off this behavior because some programs explicitly
4681 rely on variables going to the data section. E.g., so that the
4682 resulting executable can find the beginning of that section and/or make
4683 assumptions based on that.
4685 The default is @option{-fzero-initialized-in-bss}.
4687 @item -fbounds-check
4688 @opindex fbounds-check
4689 For front-ends that support it, generate additional code to check that
4690 indices used to access arrays are within the declared range. This is
4691 currently only supported by the Java and Fortran front-ends, where
4692 this option defaults to true and false respectively.
4694 @item -fmudflap -fmudflapth -fmudflapir
4698 @cindex bounds checking
4700 For front-ends that support it (C and C++), instrument all risky
4701 pointer/array dereferencing operations, some standard library
4702 string/heap functions, and some other associated constructs with
4703 range/validity tests. Modules so instrumented should be immune to
4704 buffer overflows, invalid heap use, and some other classes of C/C++
4705 programming errors. The instrumentation relies on a separate runtime
4706 library (@file{libmudflap}), which will be linked into a program if
4707 @option{-fmudflap} is given at link time. Run-time behavior of the
4708 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4709 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4712 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4713 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4714 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4715 instrumentation should ignore pointer reads. This produces less
4716 instrumentation (and therefore faster execution) and still provides
4717 some protection against outright memory corrupting writes, but allows
4718 erroneously read data to propagate within a program.
4722 @cindex openmp parallel
4723 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
4724 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
4725 compiler generates parallel code according to the OpenMP Application
4726 Program Interface v2.5. To generate the final exectuable, the runtime
4727 library @code{libgomp} must be linked in using @option{-lgomp}.
4729 @item -fstrength-reduce
4730 @opindex fstrength-reduce
4731 Perform the optimizations of loop strength reduction and
4732 elimination of iteration variables.
4734 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4736 @item -fthread-jumps
4737 @opindex fthread-jumps
4738 Perform optimizations where we check to see if a jump branches to a
4739 location where another comparison subsumed by the first is found. If
4740 so, the first branch is redirected to either the destination of the
4741 second branch or a point immediately following it, depending on whether
4742 the condition is known to be true or false.
4744 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4746 @item -fcse-follow-jumps
4747 @opindex fcse-follow-jumps
4748 In common subexpression elimination, scan through jump instructions
4749 when the target of the jump is not reached by any other path. For
4750 example, when CSE encounters an @code{if} statement with an
4751 @code{else} clause, CSE will follow the jump when the condition
4754 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4756 @item -fcse-skip-blocks
4757 @opindex fcse-skip-blocks
4758 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4759 follow jumps which conditionally skip over blocks. When CSE
4760 encounters a simple @code{if} statement with no else clause,
4761 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4762 body of the @code{if}.
4764 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4766 @item -frerun-cse-after-loop
4767 @opindex frerun-cse-after-loop
4768 Re-run common subexpression elimination after loop optimizations has been
4771 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4773 @item -frerun-loop-opt
4774 @opindex frerun-loop-opt
4775 Run the loop optimizer twice.
4777 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4781 Perform a global common subexpression elimination pass.
4782 This pass also performs global constant and copy propagation.
4784 @emph{Note:} When compiling a program using computed gotos, a GCC
4785 extension, you may get better runtime performance if you disable
4786 the global common subexpression elimination pass by adding
4787 @option{-fno-gcse} to the command line.
4789 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4793 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4794 attempt to move loads which are only killed by stores into themselves. This
4795 allows a loop containing a load/store sequence to be changed to a load outside
4796 the loop, and a copy/store within the loop.
4798 Enabled by default when gcse is enabled.
4802 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4803 global common subexpression elimination. This pass will attempt to move
4804 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4805 loops containing a load/store sequence can be changed to a load before
4806 the loop and a store after the loop.
4808 Not enabled at any optimization level.
4812 When @option{-fgcse-las} is enabled, the global common subexpression
4813 elimination pass eliminates redundant loads that come after stores to the
4814 same memory location (both partial and full redundancies).
4816 Not enabled at any optimization level.
4818 @item -fgcse-after-reload
4819 @opindex fgcse-after-reload
4820 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4821 pass is performed after reload. The purpose of this pass is to cleanup
4824 @item -floop-optimize
4825 @opindex floop-optimize
4826 Perform loop optimizations: move constant expressions out of loops, simplify
4827 exit test conditions and optionally do strength-reduction as well.
4829 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4831 @item -floop-optimize2
4832 @opindex floop-optimize2
4833 Perform loop optimizations using the new loop optimizer. The optimizations
4834 (loop unrolling, peeling and unswitching, loop invariant motion) are enabled
4837 @item -funsafe-loop-optimizations
4838 @opindex funsafe-loop-optimizations
4839 If given, the loop optimizer will assume that loop indices do not
4840 overflow, and that the loops with nontrivial exit condition are not
4841 infinite. This enables a wider range of loop optimizations even if
4842 the loop optimizer itself cannot prove that these assumptions are valid.
4843 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
4844 if it finds this kind of loop.
4846 @item -fcrossjumping
4847 @opindex crossjumping
4848 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4849 resulting code may or may not perform better than without cross-jumping.
4851 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4853 @item -fif-conversion
4854 @opindex if-conversion
4855 Attempt to transform conditional jumps into branch-less equivalents. This
4856 include use of conditional moves, min, max, set flags and abs instructions, and
4857 some tricks doable by standard arithmetics. The use of conditional execution
4858 on chips where it is available is controlled by @code{if-conversion2}.
4860 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4862 @item -fif-conversion2
4863 @opindex if-conversion2
4864 Use conditional execution (where available) to transform conditional jumps into
4865 branch-less equivalents.
4867 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4869 @item -fdelete-null-pointer-checks
4870 @opindex fdelete-null-pointer-checks
4871 Use global dataflow analysis to identify and eliminate useless checks
4872 for null pointers. The compiler assumes that dereferencing a null
4873 pointer would have halted the program. If a pointer is checked after
4874 it has already been dereferenced, it cannot be null.
4876 In some environments, this assumption is not true, and programs can
4877 safely dereference null pointers. Use
4878 @option{-fno-delete-null-pointer-checks} to disable this optimization
4879 for programs which depend on that behavior.
4881 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4883 @item -fexpensive-optimizations
4884 @opindex fexpensive-optimizations
4885 Perform a number of minor optimizations that are relatively expensive.
4887 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4889 @item -foptimize-register-move
4891 @opindex foptimize-register-move
4893 Attempt to reassign register numbers in move instructions and as
4894 operands of other simple instructions in order to maximize the amount of
4895 register tying. This is especially helpful on machines with two-operand
4898 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4901 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4903 @item -fdelayed-branch
4904 @opindex fdelayed-branch
4905 If supported for the target machine, attempt to reorder instructions
4906 to exploit instruction slots available after delayed branch
4909 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4911 @item -fschedule-insns
4912 @opindex fschedule-insns
4913 If supported for the target machine, attempt to reorder instructions to
4914 eliminate execution stalls due to required data being unavailable. This
4915 helps machines that have slow floating point or memory load instructions
4916 by allowing other instructions to be issued until the result of the load
4917 or floating point instruction is required.
4919 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4921 @item -fschedule-insns2
4922 @opindex fschedule-insns2
4923 Similar to @option{-fschedule-insns}, but requests an additional pass of
4924 instruction scheduling after register allocation has been done. This is
4925 especially useful on machines with a relatively small number of
4926 registers and where memory load instructions take more than one cycle.
4928 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4930 @item -fno-sched-interblock
4931 @opindex fno-sched-interblock
4932 Don't schedule instructions across basic blocks. This is normally
4933 enabled by default when scheduling before register allocation, i.e.@:
4934 with @option{-fschedule-insns} or at @option{-O2} or higher.
4936 @item -fno-sched-spec
4937 @opindex fno-sched-spec
4938 Don't allow speculative motion of non-load instructions. This is normally
4939 enabled by default when scheduling before register allocation, i.e.@:
4940 with @option{-fschedule-insns} or at @option{-O2} or higher.
4942 @item -fsched-spec-load
4943 @opindex fsched-spec-load
4944 Allow speculative motion of some load instructions. This only makes
4945 sense when scheduling before register allocation, i.e.@: with
4946 @option{-fschedule-insns} or at @option{-O2} or higher.
4948 @item -fsched-spec-load-dangerous
4949 @opindex fsched-spec-load-dangerous
4950 Allow speculative motion of more load instructions. This only makes
4951 sense when scheduling before register allocation, i.e.@: with
4952 @option{-fschedule-insns} or at @option{-O2} or higher.
4954 @item -fsched-stalled-insns=@var{n}
4955 @opindex fsched-stalled-insns
4956 Define how many insns (if any) can be moved prematurely from the queue
4957 of stalled insns into the ready list, during the second scheduling pass.
4959 @item -fsched-stalled-insns-dep=@var{n}
4960 @opindex fsched-stalled-insns-dep
4961 Define how many insn groups (cycles) will be examined for a dependency
4962 on a stalled insn that is candidate for premature removal from the queue
4963 of stalled insns. Has an effect only during the second scheduling pass,
4964 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4966 @item -fsched2-use-superblocks
4967 @opindex fsched2-use-superblocks
4968 When scheduling after register allocation, do use superblock scheduling
4969 algorithm. Superblock scheduling allows motion across basic block boundaries
4970 resulting on faster schedules. This option is experimental, as not all machine
4971 descriptions used by GCC model the CPU closely enough to avoid unreliable
4972 results from the algorithm.
4974 This only makes sense when scheduling after register allocation, i.e.@: with
4975 @option{-fschedule-insns2} or at @option{-O2} or higher.
4977 @item -fsched2-use-traces
4978 @opindex fsched2-use-traces
4979 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4980 allocation and additionally perform code duplication in order to increase the
4981 size of superblocks using tracer pass. See @option{-ftracer} for details on
4984 This mode should produce faster but significantly longer programs. Also
4985 without @option{-fbranch-probabilities} the traces constructed may not
4986 match the reality and hurt the performance. This only makes
4987 sense when scheduling after register allocation, i.e.@: with
4988 @option{-fschedule-insns2} or at @option{-O2} or higher.
4990 @item -freschedule-modulo-scheduled-loops
4991 @opindex fscheduling-in-modulo-scheduled-loops
4992 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
4993 we may want to prevent the later scheduling passes from changing its schedule, we use this
4994 option to control that.
4996 @item -fcaller-saves
4997 @opindex fcaller-saves
4998 Enable values to be allocated in registers that will be clobbered by
4999 function calls, by emitting extra instructions to save and restore the
5000 registers around such calls. Such allocation is done only when it
5001 seems to result in better code than would otherwise be produced.
5003 This option is always enabled by default on certain machines, usually
5004 those which have no call-preserved registers to use instead.
5006 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5009 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
5010 enabled by default at @option{-O2} and @option{-O3}.
5013 Perform Full Redundancy Elimination (FRE) on trees. The difference
5014 between FRE and PRE is that FRE only considers expressions
5015 that are computed on all paths leading to the redundant computation.
5016 This analysis faster than PRE, though it exposes fewer redundancies.
5017 This flag is enabled by default at @option{-O} and higher.
5019 @item -ftree-copy-prop
5020 Perform copy propagation on trees. This pass eliminates unnecessary
5021 copy operations. This flag is enabled by default at @option{-O} and
5024 @item -ftree-store-copy-prop
5025 Perform copy propagation of memory loads and stores. This pass
5026 eliminates unnecessary copy operations in memory references
5027 (structures, global variables, arrays, etc). This flag is enabled by
5028 default at @option{-O2} and higher.
5031 Perform structural alias analysis on trees. This flag
5032 is enabled by default at @option{-O} and higher.
5035 Perform forward store motion on trees. This flag is
5036 enabled by default at @option{-O} and higher.
5039 Perform sparse conditional constant propagation (CCP) on trees. This
5040 pass only operates on local scalar variables and is enabled by default
5041 at @option{-O} and higher.
5043 @item -ftree-store-ccp
5044 Perform sparse conditional constant propagation (CCP) on trees. This
5045 pass operates on both local scalar variables and memory stores and
5046 loads (global variables, structures, arrays, etc). This flag is
5047 enabled by default at @option{-O2} and higher.
5050 Perform dead code elimination (DCE) on trees. This flag is enabled by
5051 default at @option{-O} and higher.
5053 @item -ftree-dominator-opts
5054 Perform a variety of simple scalar cleanups (constant/copy
5055 propagation, redundancy elimination, range propagation and expression
5056 simplification) based on a dominator tree traversal. This also
5057 performs jump threading (to reduce jumps to jumps). This flag is
5058 enabled by default at @option{-O} and higher.
5061 Perform loop header copying on trees. This is beneficial since it increases
5062 effectiveness of code motion optimizations. It also saves one jump. This flag
5063 is enabled by default at @option{-O} and higher. It is not enabled
5064 for @option{-Os}, since it usually increases code size.
5066 @item -ftree-loop-optimize
5067 Perform loop optimizations on trees. This flag is enabled by default
5068 at @option{-O} and higher.
5070 @item -ftree-loop-linear
5071 Perform linear loop transformations on tree. This flag can improve cache
5072 performance and allow further loop optimizations to take place.
5074 @item -ftree-loop-im
5075 Perform loop invariant motion on trees. This pass moves only invariants that
5076 would be hard to handle at RTL level (function calls, operations that expand to
5077 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5078 operands of conditions that are invariant out of the loop, so that we can use
5079 just trivial invariantness analysis in loop unswitching. The pass also includes
5082 @item -ftree-loop-ivcanon
5083 Create a canonical counter for number of iterations in the loop for that
5084 determining number of iterations requires complicated analysis. Later
5085 optimizations then may determine the number easily. Useful especially
5086 in connection with unrolling.
5089 Perform induction variable optimizations (strength reduction, induction
5090 variable merging and induction variable elimination) on trees.
5093 Perform scalar replacement of aggregates. This pass replaces structure
5094 references with scalars to prevent committing structures to memory too
5095 early. This flag is enabled by default at @option{-O} and higher.
5097 @item -ftree-copyrename
5098 Perform copy renaming on trees. This pass attempts to rename compiler
5099 temporaries to other variables at copy locations, usually resulting in
5100 variable names which more closely resemble the original variables. This flag
5101 is enabled by default at @option{-O} and higher.
5104 Perform temporary expression replacement during the SSA->normal phase. Single
5105 use/single def temporaries are replaced at their use location with their
5106 defining expression. This results in non-GIMPLE code, but gives the expanders
5107 much more complex trees to work on resulting in better RTL generation. This is
5108 enabled by default at @option{-O} and higher.
5111 Perform live range splitting during the SSA->normal phase. Distinct live
5112 ranges of a variable are split into unique variables, allowing for better
5113 optimization later. This is enabled by default at @option{-O} and higher.
5115 @item -ftree-vectorize
5116 Perform loop vectorization on trees.
5118 @item -ftree-vect-loop-version
5119 @opindex ftree-vect-loop-version
5120 Perform loop versioning when doing loop vectorization on trees. When a loop
5121 appears to be vectorizable except that data alignment or data dependence cannot
5122 be determined at compile time then vectorized and non-vectorized versions of
5123 the loop are generated along with runtime checks for alignment or dependence
5124 to control which version is executed. This option is enabled by default
5125 except at level @option{-Os} where it is disabled.
5128 Perform Value Range Propagation on trees. This is similar to the
5129 constant propagation pass, but instead of values, ranges of values are
5130 propagated. This allows the optimizers to remove unnecessary range
5131 checks like array bound checks and null pointer checks. This is
5132 enabled by default at @option{-O2} and higher. Null pointer check
5133 elimination is only done if @option{-fdelete-null-pointer-checks} is
5138 Perform tail duplication to enlarge superblock size. This transformation
5139 simplifies the control flow of the function allowing other optimizations to do
5142 @item -funroll-loops
5143 @opindex funroll-loops
5144 Unroll loops whose number of iterations can be determined at compile
5145 time or upon entry to the loop. @option{-funroll-loops} implies both
5146 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
5147 option makes code larger, and may or may not make it run faster.
5149 @item -funroll-all-loops
5150 @opindex funroll-all-loops
5151 Unroll all loops, even if their number of iterations is uncertain when
5152 the loop is entered. This usually makes programs run more slowly.
5153 @option{-funroll-all-loops} implies the same options as
5154 @option{-funroll-loops},
5156 @item -fsplit-ivs-in-unroller
5157 @opindex -fsplit-ivs-in-unroller
5158 Enables expressing of values of induction variables in later iterations
5159 of the unrolled loop using the value in the first iteration. This breaks
5160 long dependency chains, thus improving efficiency of the scheduling passes.
5162 Combination of @option{-fweb} and CSE is often sufficient to obtain the
5163 same effect. However in cases the loop body is more complicated than
5164 a single basic block, this is not reliable. It also does not work at all
5165 on some of the architectures due to restrictions in the CSE pass.
5167 This optimization is enabled by default.
5169 @item -fvariable-expansion-in-unroller
5170 @opindex -fvariable-expansion-in-unroller
5171 With this option, the compiler will create multiple copies of some
5172 local variables when unrolling a loop which can result in superior code.
5174 @item -fprefetch-loop-arrays
5175 @opindex fprefetch-loop-arrays
5176 If supported by the target machine, generate instructions to prefetch
5177 memory to improve the performance of loops that access large arrays.
5179 These options may generate better or worse code; results are highly
5180 dependent on the structure of loops within the source code.
5183 @itemx -fno-peephole2
5184 @opindex fno-peephole
5185 @opindex fno-peephole2
5186 Disable any machine-specific peephole optimizations. The difference
5187 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
5188 are implemented in the compiler; some targets use one, some use the
5189 other, a few use both.
5191 @option{-fpeephole} is enabled by default.
5192 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5194 @item -fno-guess-branch-probability
5195 @opindex fno-guess-branch-probability
5196 Do not guess branch probabilities using heuristics.
5198 GCC will use heuristics to guess branch probabilities if they are
5199 not provided by profiling feedback (@option{-fprofile-arcs}). These
5200 heuristics are based on the control flow graph. If some branch probabilities
5201 are specified by @samp{__builtin_expect}, then the heuristics will be
5202 used to guess branch probabilities for the rest of the control flow graph,
5203 taking the @samp{__builtin_expect} info into account. The interactions
5204 between the heuristics and @samp{__builtin_expect} can be complex, and in
5205 some cases, it may be useful to disable the heuristics so that the effects
5206 of @samp{__builtin_expect} are easier to understand.
5208 The default is @option{-fguess-branch-probability} at levels
5209 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5211 @item -freorder-blocks
5212 @opindex freorder-blocks
5213 Reorder basic blocks in the compiled function in order to reduce number of
5214 taken branches and improve code locality.
5216 Enabled at levels @option{-O2}, @option{-O3}.
5218 @item -freorder-blocks-and-partition
5219 @opindex freorder-blocks-and-partition
5220 In addition to reordering basic blocks in the compiled function, in order
5221 to reduce number of taken branches, partitions hot and cold basic blocks
5222 into separate sections of the assembly and .o files, to improve
5223 paging and cache locality performance.
5225 This optimization is automatically turned off in the presence of
5226 exception handling, for linkonce sections, for functions with a user-defined
5227 section attribute and on any architecture that does not support named
5230 @item -freorder-functions
5231 @opindex freorder-functions
5232 Reorder functions in the object file in order to
5233 improve code locality. This is implemented by using special
5234 subsections @code{.text.hot} for most frequently executed functions and
5235 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
5236 the linker so object file format must support named sections and linker must
5237 place them in a reasonable way.
5239 Also profile feedback must be available in to make this option effective. See
5240 @option{-fprofile-arcs} for details.
5242 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5244 @item -fstrict-aliasing
5245 @opindex fstrict-aliasing
5246 Allows the compiler to assume the strictest aliasing rules applicable to
5247 the language being compiled. For C (and C++), this activates
5248 optimizations based on the type of expressions. In particular, an
5249 object of one type is assumed never to reside at the same address as an
5250 object of a different type, unless the types are almost the same. For
5251 example, an @code{unsigned int} can alias an @code{int}, but not a
5252 @code{void*} or a @code{double}. A character type may alias any other
5255 Pay special attention to code like this:
5268 The practice of reading from a different union member than the one most
5269 recently written to (called ``type-punning'') is common. Even with
5270 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
5271 is accessed through the union type. So, the code above will work as
5272 expected. However, this code might not:
5283 Every language that wishes to perform language-specific alias analysis
5284 should define a function that computes, given an @code{tree}
5285 node, an alias set for the node. Nodes in different alias sets are not
5286 allowed to alias. For an example, see the C front-end function
5287 @code{c_get_alias_set}.
5289 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5291 @item -falign-functions
5292 @itemx -falign-functions=@var{n}
5293 @opindex falign-functions
5294 Align the start of functions to the next power-of-two greater than
5295 @var{n}, skipping up to @var{n} bytes. For instance,
5296 @option{-falign-functions=32} aligns functions to the next 32-byte
5297 boundary, but @option{-falign-functions=24} would align to the next
5298 32-byte boundary only if this can be done by skipping 23 bytes or less.
5300 @option{-fno-align-functions} and @option{-falign-functions=1} are
5301 equivalent and mean that functions will not be aligned.
5303 Some assemblers only support this flag when @var{n} is a power of two;
5304 in that case, it is rounded up.
5306 If @var{n} is not specified or is zero, use a machine-dependent default.
5308 Enabled at levels @option{-O2}, @option{-O3}.
5310 @item -falign-labels
5311 @itemx -falign-labels=@var{n}
5312 @opindex falign-labels
5313 Align all branch targets to a power-of-two boundary, skipping up to
5314 @var{n} bytes like @option{-falign-functions}. This option can easily
5315 make code slower, because it must insert dummy operations for when the
5316 branch target is reached in the usual flow of the code.
5318 @option{-fno-align-labels} and @option{-falign-labels=1} are
5319 equivalent and mean that labels will not be aligned.
5321 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
5322 are greater than this value, then their values are used instead.
5324 If @var{n} is not specified or is zero, use a machine-dependent default
5325 which is very likely to be @samp{1}, meaning no alignment.
5327 Enabled at levels @option{-O2}, @option{-O3}.
5330 @itemx -falign-loops=@var{n}
5331 @opindex falign-loops
5332 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
5333 like @option{-falign-functions}. The hope is that the loop will be
5334 executed many times, which will make up for any execution of the dummy
5337 @option{-fno-align-loops} and @option{-falign-loops=1} are
5338 equivalent and mean that loops will not be aligned.
5340 If @var{n} is not specified or is zero, use a machine-dependent default.
5342 Enabled at levels @option{-O2}, @option{-O3}.
5345 @itemx -falign-jumps=@var{n}
5346 @opindex falign-jumps
5347 Align branch targets to a power-of-two boundary, for branch targets
5348 where the targets can only be reached by jumping, skipping up to @var{n}
5349 bytes like @option{-falign-functions}. In this case, no dummy operations
5352 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
5353 equivalent and mean that loops will not be aligned.
5355 If @var{n} is not specified or is zero, use a machine-dependent default.
5357 Enabled at levels @option{-O2}, @option{-O3}.
5359 @item -funit-at-a-time
5360 @opindex funit-at-a-time
5361 Parse the whole compilation unit before starting to produce code.
5362 This allows some extra optimizations to take place but consumes
5363 more memory (in general). There are some compatibility issues
5364 with @emph{unit-at-a-time} mode:
5367 enabling @emph{unit-at-a-time} mode may change the order
5368 in which functions, variables, and top-level @code{asm} statements
5369 are emitted, and will likely break code relying on some particular
5370 ordering. The majority of such top-level @code{asm} statements,
5371 though, can be replaced by @code{section} attributes. The
5372 @option{fno-toplevel-reorder} option may be used to keep the ordering
5373 used in the input file, at the cost of some optimizations.
5376 @emph{unit-at-a-time} mode removes unreferenced static variables
5377 and functions. This may result in undefined references
5378 when an @code{asm} statement refers directly to variables or functions
5379 that are otherwise unused. In that case either the variable/function
5380 shall be listed as an operand of the @code{asm} statement operand or,
5381 in the case of top-level @code{asm} statements the attribute @code{used}
5382 shall be used on the declaration.
5385 Static functions now can use non-standard passing conventions that
5386 may break @code{asm} statements calling functions directly. Again,
5387 attribute @code{used} will prevent this behavior.
5390 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
5391 but this scheme may not be supported by future releases of GCC@.
5393 Enabled at levels @option{-O2}, @option{-O3}.
5395 @item -fno-toplevel-reorder
5396 Do not reorder top-level functions, variables, and @code{asm}
5397 statements. Output them in the same order that they appear in the
5398 input file. When this option is used, unreferenced static variables
5399 will not be removed. This option is intended to support existing code
5400 which relies on a particular ordering. For new code, it is better to
5405 Constructs webs as commonly used for register allocation purposes and assign
5406 each web individual pseudo register. This allows the register allocation pass
5407 to operate on pseudos directly, but also strengthens several other optimization
5408 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
5409 however, make debugging impossible, since variables will no longer stay in a
5412 Enabled by default with @option{-funroll-loops}.
5414 @item -fwhole-program
5415 @opindex fwhole-program
5416 Assume that the current compilation unit represents whole program being
5417 compiled. All public functions and variables with the exception of @code{main}
5418 and those merged by attribute @code{externally_visible} become static functions
5419 and in a affect gets more aggressively optimized by interprocedural optimizers.
5420 While this option is equivalent to proper use of @code{static} keyword for
5421 programs consisting of single file, in combination with option
5422 @option{--combine} this flag can be used to compile most of smaller scale C
5423 programs since the functions and variables become local for the whole combined
5424 compilation unit, not for the single source file itself.
5427 @item -fno-cprop-registers
5428 @opindex fno-cprop-registers
5429 After register allocation and post-register allocation instruction splitting,
5430 we perform a copy-propagation pass to try to reduce scheduling dependencies
5431 and occasionally eliminate the copy.
5433 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5435 @item -fprofile-generate
5436 @opindex fprofile-generate
5438 Enable options usually used for instrumenting application to produce
5439 profile useful for later recompilation with profile feedback based
5440 optimization. You must use @option{-fprofile-generate} both when
5441 compiling and when linking your program.
5443 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
5446 @opindex fprofile-use
5447 Enable profile feedback directed optimizations, and optimizations
5448 generally profitable only with profile feedback available.
5450 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
5451 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer},
5452 @code{-fno-loop-optimize}.
5456 The following options control compiler behavior regarding floating
5457 point arithmetic. These options trade off between speed and
5458 correctness. All must be specifically enabled.
5462 @opindex ffloat-store
5463 Do not store floating point variables in registers, and inhibit other
5464 options that might change whether a floating point value is taken from a
5467 @cindex floating point precision
5468 This option prevents undesirable excess precision on machines such as
5469 the 68000 where the floating registers (of the 68881) keep more
5470 precision than a @code{double} is supposed to have. Similarly for the
5471 x86 architecture. For most programs, the excess precision does only
5472 good, but a few programs rely on the precise definition of IEEE floating
5473 point. Use @option{-ffloat-store} for such programs, after modifying
5474 them to store all pertinent intermediate computations into variables.
5478 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5479 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5480 @option{-fno-rounding-math}, @option{-fno-signaling-nans}
5481 and @option{fcx-limited-range}.
5483 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5485 This option should never be turned on by any @option{-O} option since
5486 it can result in incorrect output for programs which depend on
5487 an exact implementation of IEEE or ISO rules/specifications for
5490 @item -fno-math-errno
5491 @opindex fno-math-errno
5492 Do not set ERRNO after calling math functions that are executed
5493 with a single instruction, e.g., sqrt. A program that relies on
5494 IEEE exceptions for math error handling may want to use this flag
5495 for speed while maintaining IEEE arithmetic compatibility.
5497 This option should never be turned on by any @option{-O} option since
5498 it can result in incorrect output for programs which depend on
5499 an exact implementation of IEEE or ISO rules/specifications for
5502 The default is @option{-fmath-errno}.
5504 On Darwin systems, the math library never sets @code{errno}. There is therefore
5505 no reason for the compiler to consider the possibility that it might,
5506 and @option{-fno-math-errno} is the default.
5508 @item -funsafe-math-optimizations
5509 @opindex funsafe-math-optimizations
5510 Allow optimizations for floating-point arithmetic that (a) assume
5511 that arguments and results are valid and (b) may violate IEEE or
5512 ANSI standards. When used at link-time, it may include libraries
5513 or startup files that change the default FPU control word or other
5514 similar optimizations.
5516 This option should never be turned on by any @option{-O} option since
5517 it can result in incorrect output for programs which depend on
5518 an exact implementation of IEEE or ISO rules/specifications for
5521 The default is @option{-fno-unsafe-math-optimizations}.
5523 @item -ffinite-math-only
5524 @opindex ffinite-math-only
5525 Allow optimizations for floating-point arithmetic that assume
5526 that arguments and results are not NaNs or +-Infs.
5528 This option should never be turned on by any @option{-O} option since
5529 it can result in incorrect output for programs which depend on
5530 an exact implementation of IEEE or ISO rules/specifications.
5532 The default is @option{-fno-finite-math-only}.
5534 @item -fno-trapping-math
5535 @opindex fno-trapping-math
5536 Compile code assuming that floating-point operations cannot generate
5537 user-visible traps. These traps include division by zero, overflow,
5538 underflow, inexact result and invalid operation. This option implies
5539 @option{-fno-signaling-nans}. Setting this option may allow faster
5540 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5542 This option should never be turned on by any @option{-O} option since
5543 it can result in incorrect output for programs which depend on
5544 an exact implementation of IEEE or ISO rules/specifications for
5547 The default is @option{-ftrapping-math}.
5549 @item -frounding-math
5550 @opindex frounding-math
5551 Disable transformations and optimizations that assume default floating
5552 point rounding behavior. This is round-to-zero for all floating point
5553 to integer conversions, and round-to-nearest for all other arithmetic
5554 truncations. This option should be specified for programs that change
5555 the FP rounding mode dynamically, or that may be executed with a
5556 non-default rounding mode. This option disables constant folding of
5557 floating point expressions at compile-time (which may be affected by
5558 rounding mode) and arithmetic transformations that are unsafe in the
5559 presence of sign-dependent rounding modes.
5561 The default is @option{-fno-rounding-math}.
5563 This option is experimental and does not currently guarantee to
5564 disable all GCC optimizations that are affected by rounding mode.
5565 Future versions of GCC may provide finer control of this setting
5566 using C99's @code{FENV_ACCESS} pragma. This command line option
5567 will be used to specify the default state for @code{FENV_ACCESS}.
5569 @item -frtl-abstract-sequences
5570 @opindex frtl-abstract-sequences
5571 It is a size optimization method. This option is to find identical
5572 sequences of code, which can be turned into pseudo-procedures and
5573 then replace all occurrences with calls to the newly created
5574 subroutine. It is kind of an opposite of @option{-finline-functions}.
5575 This optimization runs at RTL level.
5577 @item -fsignaling-nans
5578 @opindex fsignaling-nans
5579 Compile code assuming that IEEE signaling NaNs may generate user-visible
5580 traps during floating-point operations. Setting this option disables
5581 optimizations that may change the number of exceptions visible with
5582 signaling NaNs. This option implies @option{-ftrapping-math}.
5584 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5587 The default is @option{-fno-signaling-nans}.
5589 This option is experimental and does not currently guarantee to
5590 disable all GCC optimizations that affect signaling NaN behavior.
5592 @item -fsingle-precision-constant
5593 @opindex fsingle-precision-constant
5594 Treat floating point constant as single precision constant instead of
5595 implicitly converting it to double precision constant.
5597 @item -fcx-limited-range
5598 @itemx -fno-cx-limited-range
5599 @opindex fcx-limited-range
5600 @opindex fno-cx-limited-range
5601 When enabled, this option states that a range reduction step is not
5602 needed when performing complex division. The default is
5603 @option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}.
5605 This option controls the default setting of the ISO C99
5606 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
5611 The following options control optimizations that may improve
5612 performance, but are not enabled by any @option{-O} options. This
5613 section includes experimental options that may produce broken code.
5616 @item -fbranch-probabilities
5617 @opindex fbranch-probabilities
5618 After running a program compiled with @option{-fprofile-arcs}
5619 (@pxref{Debugging Options,, Options for Debugging Your Program or
5620 @command{gcc}}), you can compile it a second time using
5621 @option{-fbranch-probabilities}, to improve optimizations based on
5622 the number of times each branch was taken. When the program
5623 compiled with @option{-fprofile-arcs} exits it saves arc execution
5624 counts to a file called @file{@var{sourcename}.gcda} for each source
5625 file The information in this data file is very dependent on the
5626 structure of the generated code, so you must use the same source code
5627 and the same optimization options for both compilations.
5629 With @option{-fbranch-probabilities}, GCC puts a
5630 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5631 These can be used to improve optimization. Currently, they are only
5632 used in one place: in @file{reorg.c}, instead of guessing which path a
5633 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5634 exactly determine which path is taken more often.
5636 @item -fprofile-values
5637 @opindex fprofile-values
5638 If combined with @option{-fprofile-arcs}, it adds code so that some
5639 data about values of expressions in the program is gathered.
5641 With @option{-fbranch-probabilities}, it reads back the data gathered
5642 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5643 notes to instructions for their later usage in optimizations.
5645 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5649 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5650 a code to gather information about values of expressions.
5652 With @option{-fbranch-probabilities}, it reads back the data gathered
5653 and actually performs the optimizations based on them.
5654 Currently the optimizations include specialization of division operation
5655 using the knowledge about the value of the denominator.
5657 @item -frename-registers
5658 @opindex frename-registers
5659 Attempt to avoid false dependencies in scheduled code by making use
5660 of registers left over after register allocation. This optimization
5661 will most benefit processors with lots of registers. Depending on the
5662 debug information format adopted by the target, however, it can
5663 make debugging impossible, since variables will no longer stay in
5664 a ``home register''.
5666 Enabled by default with @option{-funroll-loops}.
5670 Perform tail duplication to enlarge superblock size. This transformation
5671 simplifies the control flow of the function allowing other optimizations to do
5674 Enabled with @option{-fprofile-use}.
5676 @item -funroll-loops
5677 @opindex funroll-loops
5678 Unroll loops whose number of iterations can be determined at compile time or
5679 upon entry to the loop. @option{-funroll-loops} implies
5680 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
5681 It also turns on complete loop peeling (i.e.@: complete removal of loops with
5682 small constant number of iterations). This option makes code larger, and may
5683 or may not make it run faster.
5685 Enabled with @option{-fprofile-use}.
5687 @item -funroll-all-loops
5688 @opindex funroll-all-loops
5689 Unroll all loops, even if their number of iterations is uncertain when
5690 the loop is entered. This usually makes programs run more slowly.
5691 @option{-funroll-all-loops} implies the same options as
5692 @option{-funroll-loops}.
5695 @opindex fpeel-loops
5696 Peels the loops for that there is enough information that they do not
5697 roll much (from profile feedback). It also turns on complete loop peeling
5698 (i.e.@: complete removal of loops with small constant number of iterations).
5700 Enabled with @option{-fprofile-use}.
5702 @item -fmove-loop-invariants
5703 @opindex fmove-loop-invariants
5704 Enables the loop invariant motion pass in the new loop optimizer. Enabled
5705 at level @option{-O1}
5707 @item -funswitch-loops
5708 @opindex funswitch-loops
5709 Move branches with loop invariant conditions out of the loop, with duplicates
5710 of the loop on both branches (modified according to result of the condition).
5712 @item -fprefetch-loop-arrays
5713 @opindex fprefetch-loop-arrays
5714 If supported by the target machine, generate instructions to prefetch
5715 memory to improve the performance of loops that access large arrays.
5717 Disabled at level @option{-Os}.
5719 @item -ffunction-sections
5720 @itemx -fdata-sections
5721 @opindex ffunction-sections
5722 @opindex fdata-sections
5723 Place each function or data item into its own section in the output
5724 file if the target supports arbitrary sections. The name of the
5725 function or the name of the data item determines the section's name
5728 Use these options on systems where the linker can perform optimizations
5729 to improve locality of reference in the instruction space. Most systems
5730 using the ELF object format and SPARC processors running Solaris 2 have
5731 linkers with such optimizations. AIX may have these optimizations in
5734 Only use these options when there are significant benefits from doing
5735 so. When you specify these options, the assembler and linker will
5736 create larger object and executable files and will also be slower.
5737 You will not be able to use @code{gprof} on all systems if you
5738 specify this option and you may have problems with debugging if
5739 you specify both this option and @option{-g}.
5741 @item -fbranch-target-load-optimize
5742 @opindex fbranch-target-load-optimize
5743 Perform branch target register load optimization before prologue / epilogue
5745 The use of target registers can typically be exposed only during reload,
5746 thus hoisting loads out of loops and doing inter-block scheduling needs
5747 a separate optimization pass.
5749 @item -fbranch-target-load-optimize2
5750 @opindex fbranch-target-load-optimize2
5751 Perform branch target register load optimization after prologue / epilogue
5754 @item -fbtr-bb-exclusive
5755 @opindex fbtr-bb-exclusive
5756 When performing branch target register load optimization, don't reuse
5757 branch target registers in within any basic block.
5759 @item -fstack-protector
5760 Emit extra code to check for buffer overflows, such as stack smashing
5761 attacks. This is done by adding a guard variable to functions with
5762 vulnerable objects. This includes functions that call alloca, and
5763 functions with buffers larger than 8 bytes. The guards are initialized
5764 when a function is entered and then checked when the function exits.
5765 If a guard check fails, an error message is printed and the program exits.
5767 @item -fstack-protector-all
5768 Like @option{-fstack-protector} except that all functions are protected.
5770 @item --param @var{name}=@var{value}
5772 In some places, GCC uses various constants to control the amount of
5773 optimization that is done. For example, GCC will not inline functions
5774 that contain more that a certain number of instructions. You can
5775 control some of these constants on the command-line using the
5776 @option{--param} option.
5778 The names of specific parameters, and the meaning of the values, are
5779 tied to the internals of the compiler, and are subject to change
5780 without notice in future releases.
5782 In each case, the @var{value} is an integer. The allowable choices for
5783 @var{name} are given in the following table:
5786 @item salias-max-implicit-fields
5787 The maximum number of fields in a variable without direct
5788 structure accesses for which structure aliasing will consider trying
5789 to track each field. The default is 5
5791 @item salias-max-array-elements
5792 The maximum number of elements an array can have and its elements
5793 still be tracked individually by structure aliasing. The default is 4
5795 @item sra-max-structure-size
5796 The maximum structure size, in bytes, at which the scalar replacement
5797 of aggregates (SRA) optimization will perform block copies. The
5798 default value, 0, implies that GCC will select the most appropriate
5801 @item sra-field-structure-ratio
5802 The threshold ratio (as a percentage) between instantiated fields and
5803 the complete structure size. We say that if the ratio of the number
5804 of bytes in instantiated fields to the number of bytes in the complete
5805 structure exceeds this parameter, then block copies are not used. The
5808 @item max-crossjump-edges
5809 The maximum number of incoming edges to consider for crossjumping.
5810 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5811 the number of edges incoming to each block. Increasing values mean
5812 more aggressive optimization, making the compile time increase with
5813 probably small improvement in executable size.
5815 @item min-crossjump-insns
5816 The minimum number of instructions which must be matched at the end
5817 of two blocks before crossjumping will be performed on them. This
5818 value is ignored in the case where all instructions in the block being
5819 crossjumped from are matched. The default value is 5.
5821 @item max-grow-copy-bb-insns
5822 The maximum code size expansion factor when copying basic blocks
5823 instead of jumping. The expansion is relative to a jump instruction.
5824 The default value is 8.
5826 @item max-goto-duplication-insns
5827 The maximum number of instructions to duplicate to a block that jumps
5828 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
5829 passes, GCC factors computed gotos early in the compilation process,
5830 and unfactors them as late as possible. Only computed jumps at the
5831 end of a basic blocks with no more than max-goto-duplication-insns are
5832 unfactored. The default value is 8.
5834 @item max-delay-slot-insn-search
5835 The maximum number of instructions to consider when looking for an
5836 instruction to fill a delay slot. If more than this arbitrary number of
5837 instructions is searched, the time savings from filling the delay slot
5838 will be minimal so stop searching. Increasing values mean more
5839 aggressive optimization, making the compile time increase with probably
5840 small improvement in executable run time.
5842 @item max-delay-slot-live-search
5843 When trying to fill delay slots, the maximum number of instructions to
5844 consider when searching for a block with valid live register
5845 information. Increasing this arbitrarily chosen value means more
5846 aggressive optimization, increasing the compile time. This parameter
5847 should be removed when the delay slot code is rewritten to maintain the
5850 @item max-gcse-memory
5851 The approximate maximum amount of memory that will be allocated in
5852 order to perform the global common subexpression elimination
5853 optimization. If more memory than specified is required, the
5854 optimization will not be done.
5856 @item max-gcse-passes
5857 The maximum number of passes of GCSE to run. The default is 1.
5859 @item max-pending-list-length
5860 The maximum number of pending dependencies scheduling will allow
5861 before flushing the current state and starting over. Large functions
5862 with few branches or calls can create excessively large lists which
5863 needlessly consume memory and resources.
5865 @item max-inline-insns-single
5866 Several parameters control the tree inliner used in gcc.
5867 This number sets the maximum number of instructions (counted in GCC's
5868 internal representation) in a single function that the tree inliner
5869 will consider for inlining. This only affects functions declared
5870 inline and methods implemented in a class declaration (C++).
5871 The default value is 450.
5873 @item max-inline-insns-auto
5874 When you use @option{-finline-functions} (included in @option{-O3}),
5875 a lot of functions that would otherwise not be considered for inlining
5876 by the compiler will be investigated. To those functions, a different
5877 (more restrictive) limit compared to functions declared inline can
5879 The default value is 90.
5881 @item large-function-insns
5882 The limit specifying really large functions. For functions larger than this
5883 limit after inlining inlining is constrained by
5884 @option{--param large-function-growth}. This parameter is useful primarily
5885 to avoid extreme compilation time caused by non-linear algorithms used by the
5887 This parameter is ignored when @option{-funit-at-a-time} is not used.
5888 The default value is 2700.
5890 @item large-function-growth
5891 Specifies maximal growth of large function caused by inlining in percents.
5892 This parameter is ignored when @option{-funit-at-a-time} is not used.
5893 The default value is 100 which limits large function growth to 2.0 times
5896 @item large-unit-insns
5897 The limit specifying large translation unit. Growth caused by inlining of
5898 units larger than this limit is limited by @option{--param inline-unit-growth}.
5899 For small units this might be too tight (consider unit consisting of function A
5900 that is inline and B that just calls A three time. If B is small relative to
5901 A, the growth of unit is 300\% and yet such inlining is very sane. For very
5902 large units consisting of small inlininable functions however the overall unit
5903 growth limit is needed to avoid exponential explosion of code size. Thus for
5904 smaller units, the size is increased to @option{--param large-unit-insns}
5905 before applying @option{--param inline-unit-growth}. The default is 10000
5907 @item inline-unit-growth
5908 Specifies maximal overall growth of the compilation unit caused by inlining.
5909 This parameter is ignored when @option{-funit-at-a-time} is not used.
5910 The default value is 50 which limits unit growth to 1.5 times the original
5913 @item max-inline-insns-recursive
5914 @itemx max-inline-insns-recursive-auto
5915 Specifies maximum number of instructions out-of-line copy of self recursive inline
5916 function can grow into by performing recursive inlining.
5918 For functions declared inline @option{--param max-inline-insns-recursive} is
5919 taken into acount. For function not declared inline, recursive inlining
5920 happens only when @option{-finline-functions} (included in @option{-O3}) is
5921 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
5922 default value is 450.
5924 @item max-inline-recursive-depth
5925 @itemx max-inline-recursive-depth-auto
5926 Specifies maximum recursion depth used by the recursive inlining.
5928 For functions declared inline @option{--param max-inline-recursive-depth} is
5929 taken into acount. For function not declared inline, recursive inlining
5930 happens only when @option{-finline-functions} (included in @option{-O3}) is
5931 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
5932 default value is 450.
5934 @item min-inline-recursive-probability
5935 Recursive inlining is profitable only for function having deep recursion
5936 in average and can hurt for function having little recursion depth by
5937 increasing the prologue size or complexity of function body to other
5940 When profile feedback is available (see @option{-fprofile-generate}) the actual
5941 recursion depth can be guessed from probability that function will recurse via
5942 given call expression. This parameter limits inlining only to call expression
5943 whose probability exceeds given threshold (in percents). The default value is
5946 @item inline-call-cost
5947 Specify cost of call instruction relative to simple arithmetics operations
5948 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
5949 functions and at the same time increases size of leaf function that is believed to
5950 reduce function size by being inlined. In effect it increases amount of
5951 inlining for code having large abstraction penalty (many functions that just
5952 pass the arguments to other functions) and decrease inlining for code with low
5953 abstraction penalty. The default value is 16.
5955 @item max-unrolled-insns
5956 The maximum number of instructions that a loop should have if that loop
5957 is unrolled, and if the loop is unrolled, it determines how many times
5958 the loop code is unrolled.
5960 @item max-average-unrolled-insns
5961 The maximum number of instructions biased by probabilities of their execution
5962 that a loop should have if that loop is unrolled, and if the loop is unrolled,
5963 it determines how many times the loop code is unrolled.
5965 @item max-unroll-times
5966 The maximum number of unrollings of a single loop.
5968 @item max-peeled-insns
5969 The maximum number of instructions that a loop should have if that loop
5970 is peeled, and if the loop is peeled, it determines how many times
5971 the loop code is peeled.
5973 @item max-peel-times
5974 The maximum number of peelings of a single loop.
5976 @item max-completely-peeled-insns
5977 The maximum number of insns of a completely peeled loop.
5979 @item max-completely-peel-times
5980 The maximum number of iterations of a loop to be suitable for complete peeling.
5982 @item max-unswitch-insns
5983 The maximum number of insns of an unswitched loop.
5985 @item max-unswitch-level
5986 The maximum number of branches unswitched in a single loop.
5989 The minimum cost of an expensive expression in the loop invariant motion.
5991 @item iv-consider-all-candidates-bound
5992 Bound on number of candidates for induction variables below that
5993 all candidates are considered for each use in induction variable
5994 optimizations. Only the most relevant candidates are considered
5995 if there are more candidates, to avoid quadratic time complexity.
5997 @item iv-max-considered-uses
5998 The induction variable optimizations give up on loops that contain more
5999 induction variable uses.
6001 @item iv-always-prune-cand-set-bound
6002 If number of candidates in the set is smaller than this value,
6003 we always try to remove unnecessary ivs from the set during its
6004 optimization when a new iv is added to the set.
6006 @item scev-max-expr-size
6007 Bound on size of expressions used in the scalar evolutions analyzer.
6008 Large expressions slow the analyzer.
6010 @item vect-max-version-checks
6011 The maximum number of runtime checks that can be performed when doing
6012 loop versioning in the vectorizer. See option ftree-vect-loop-version
6013 for more information.
6015 @item max-iterations-to-track
6017 The maximum number of iterations of a loop the brute force algorithm
6018 for analysis of # of iterations of the loop tries to evaluate.
6020 @item hot-bb-count-fraction
6021 Select fraction of the maximal count of repetitions of basic block in program
6022 given basic block needs to have to be considered hot.
6024 @item hot-bb-frequency-fraction
6025 Select fraction of the maximal frequency of executions of basic block in
6026 function given basic block needs to have to be considered hot
6028 @item max-predicted-iterations
6029 The maximum number of loop iterations we predict statically. This is useful
6030 in cases where function contain single loop with known bound and other loop
6031 with unknown. We predict the known number of iterations correctly, while
6032 the unknown number of iterations average to roughly 10. This means that the
6033 loop without bounds would appear artificially cold relative to the other one.
6035 @item tracer-dynamic-coverage
6036 @itemx tracer-dynamic-coverage-feedback
6038 This value is used to limit superblock formation once the given percentage of
6039 executed instructions is covered. This limits unnecessary code size
6042 The @option{tracer-dynamic-coverage-feedback} is used only when profile
6043 feedback is available. The real profiles (as opposed to statically estimated
6044 ones) are much less balanced allowing the threshold to be larger value.
6046 @item tracer-max-code-growth
6047 Stop tail duplication once code growth has reached given percentage. This is
6048 rather hokey argument, as most of the duplicates will be eliminated later in
6049 cross jumping, so it may be set to much higher values than is the desired code
6052 @item tracer-min-branch-ratio
6054 Stop reverse growth when the reverse probability of best edge is less than this
6055 threshold (in percent).
6057 @item tracer-min-branch-ratio
6058 @itemx tracer-min-branch-ratio-feedback
6060 Stop forward growth if the best edge do have probability lower than this
6063 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
6064 compilation for profile feedback and one for compilation without. The value
6065 for compilation with profile feedback needs to be more conservative (higher) in
6066 order to make tracer effective.
6068 @item max-cse-path-length
6070 Maximum number of basic blocks on path that cse considers. The default is 10.
6073 The maximum instructions CSE process before flushing. The default is 1000.
6075 @item global-var-threshold
6077 Counts the number of function calls (@var{n}) and the number of
6078 call-clobbered variables (@var{v}). If @var{n}x@var{v} is larger than this limit, a
6079 single artificial variable will be created to represent all the
6080 call-clobbered variables at function call sites. This artificial
6081 variable will then be made to alias every call-clobbered variable.
6082 (done as @code{int * size_t} on the host machine; beware overflow).
6084 @item max-aliased-vops
6086 Maximum number of virtual operands allowed to represent aliases
6087 before triggering the alias grouping heuristic. Alias grouping
6088 reduces compile times and memory consumption needed for aliasing at
6089 the expense of precision loss in alias information.
6091 @item ggc-min-expand
6093 GCC uses a garbage collector to manage its own memory allocation. This
6094 parameter specifies the minimum percentage by which the garbage
6095 collector's heap should be allowed to expand between collections.
6096 Tuning this may improve compilation speed; it has no effect on code
6099 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
6100 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
6101 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
6102 GCC is not able to calculate RAM on a particular platform, the lower
6103 bound of 30% is used. Setting this parameter and
6104 @option{ggc-min-heapsize} to zero causes a full collection to occur at
6105 every opportunity. This is extremely slow, but can be useful for
6108 @item ggc-min-heapsize
6110 Minimum size of the garbage collector's heap before it begins bothering
6111 to collect garbage. The first collection occurs after the heap expands
6112 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
6113 tuning this may improve compilation speed, and has no effect on code
6116 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
6117 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
6118 with a lower bound of 4096 (four megabytes) and an upper bound of
6119 131072 (128 megabytes). If GCC is not able to calculate RAM on a
6120 particular platform, the lower bound is used. Setting this parameter
6121 very large effectively disables garbage collection. Setting this
6122 parameter and @option{ggc-min-expand} to zero causes a full collection
6123 to occur at every opportunity.
6125 @item max-reload-search-insns
6126 The maximum number of instruction reload should look backward for equivalent
6127 register. Increasing values mean more aggressive optimization, making the
6128 compile time increase with probably slightly better performance. The default
6131 @item max-cselib-memory-location
6132 The maximum number of memory locations cselib should take into acount.
6133 Increasing values mean more aggressive optimization, making the compile time
6134 increase with probably slightly better performance. The default value is 500.
6136 @item max-flow-memory-location
6137 Similar as @option{max-cselib-memory-location} but for dataflow liveness.
6138 The default value is 100.
6140 @item reorder-blocks-duplicate
6141 @itemx reorder-blocks-duplicate-feedback
6143 Used by basic block reordering pass to decide whether to use unconditional
6144 branch or duplicate the code on its destination. Code is duplicated when its
6145 estimated size is smaller than this value multiplied by the estimated size of
6146 unconditional jump in the hot spots of the program.
6148 The @option{reorder-block-duplicate-feedback} is used only when profile
6149 feedback is available and may be set to higher values than
6150 @option{reorder-block-duplicate} since information about the hot spots is more
6153 @item max-sched-region-blocks
6154 The maximum number of blocks in a region to be considered for
6155 interblock scheduling. The default value is 10.
6157 @item max-sched-region-insns
6158 The maximum number of insns in a region to be considered for
6159 interblock scheduling. The default value is 100.
6161 @item min-sched-prob
6162 The minimum probability of reaching a source block for interblock
6163 speculative scheduling. The default value is 40.
6165 @item max-last-value-rtl
6167 The maximum size measured as number of RTLs that can be recorded in an expression
6168 in combiner for a pseudo register as last known value of that register. The default
6171 @item integer-share-limit
6172 Small integer constants can use a shared data structure, reducing the
6173 compiler's memory usage and increasing its speed. This sets the maximum
6174 value of a shared integer constant's. The default value is 256.
6176 @item min-virtual-mappings
6177 Specifies the minimum number of virtual mappings in the incremental
6178 SSA updater that should be registered to trigger the virtual mappings
6179 heuristic defined by virtual-mappings-ratio. The default value is
6182 @item virtual-mappings-ratio
6183 If the number of virtual mappings is virtual-mappings-ratio bigger
6184 than the number of virtual symbols to be updated, then the incremental
6185 SSA updater switches to a full update for those symbols. The default
6188 @item ssp-buffer-size
6189 The minimum size of buffers (i.e. arrays) that will receive stack smashing
6190 protection when @option{-fstack-protection} is used.
6192 @item max-jump-thread-duplication-stmts
6193 Maximum number of statements allowed in a block that needs to be
6194 duplicated when threading jumps.
6198 @node Preprocessor Options
6199 @section Options Controlling the Preprocessor
6200 @cindex preprocessor options
6201 @cindex options, preprocessor
6203 These options control the C preprocessor, which is run on each C source
6204 file before actual compilation.
6206 If you use the @option{-E} option, nothing is done except preprocessing.
6207 Some of these options make sense only together with @option{-E} because
6208 they cause the preprocessor output to be unsuitable for actual
6213 You can use @option{-Wp,@var{option}} to bypass the compiler driver
6214 and pass @var{option} directly through to the preprocessor. If
6215 @var{option} contains commas, it is split into multiple options at the
6216 commas. However, many options are modified, translated or interpreted
6217 by the compiler driver before being passed to the preprocessor, and
6218 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
6219 interface is undocumented and subject to change, so whenever possible
6220 you should avoid using @option{-Wp} and let the driver handle the
6223 @item -Xpreprocessor @var{option}
6224 @opindex preprocessor
6225 Pass @var{option} as an option to the preprocessor. You can use this to
6226 supply system-specific preprocessor options which GCC does not know how to
6229 If you want to pass an option that takes an argument, you must use
6230 @option{-Xpreprocessor} twice, once for the option and once for the argument.
6233 @include cppopts.texi
6235 @node Assembler Options
6236 @section Passing Options to the Assembler
6238 @c prevent bad page break with this line
6239 You can pass options to the assembler.
6242 @item -Wa,@var{option}
6244 Pass @var{option} as an option to the assembler. If @var{option}
6245 contains commas, it is split into multiple options at the commas.
6247 @item -Xassembler @var{option}
6249 Pass @var{option} as an option to the assembler. You can use this to
6250 supply system-specific assembler options which GCC does not know how to
6253 If you want to pass an option that takes an argument, you must use
6254 @option{-Xassembler} twice, once for the option and once for the argument.
6259 @section Options for Linking
6260 @cindex link options
6261 @cindex options, linking
6263 These options come into play when the compiler links object files into
6264 an executable output file. They are meaningless if the compiler is
6265 not doing a link step.
6269 @item @var{object-file-name}
6270 A file name that does not end in a special recognized suffix is
6271 considered to name an object file or library. (Object files are
6272 distinguished from libraries by the linker according to the file
6273 contents.) If linking is done, these object files are used as input
6282 If any of these options is used, then the linker is not run, and
6283 object file names should not be used as arguments. @xref{Overall
6287 @item -l@var{library}
6288 @itemx -l @var{library}
6290 Search the library named @var{library} when linking. (The second
6291 alternative with the library as a separate argument is only for
6292 POSIX compliance and is not recommended.)
6294 It makes a difference where in the command you write this option; the
6295 linker searches and processes libraries and object files in the order they
6296 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
6297 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
6298 to functions in @samp{z}, those functions may not be loaded.
6300 The linker searches a standard list of directories for the library,
6301 which is actually a file named @file{lib@var{library}.a}. The linker
6302 then uses this file as if it had been specified precisely by name.
6304 The directories searched include several standard system directories
6305 plus any that you specify with @option{-L}.
6307 Normally the files found this way are library files---archive files
6308 whose members are object files. The linker handles an archive file by
6309 scanning through it for members which define symbols that have so far
6310 been referenced but not defined. But if the file that is found is an
6311 ordinary object file, it is linked in the usual fashion. The only
6312 difference between using an @option{-l} option and specifying a file name
6313 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
6314 and searches several directories.
6318 You need this special case of the @option{-l} option in order to
6319 link an Objective-C or Objective-C++ program.
6322 @opindex nostartfiles
6323 Do not use the standard system startup files when linking.
6324 The standard system libraries are used normally, unless @option{-nostdlib}
6325 or @option{-nodefaultlibs} is used.
6327 @item -nodefaultlibs
6328 @opindex nodefaultlibs
6329 Do not use the standard system libraries when linking.
6330 Only the libraries you specify will be passed to the linker.
6331 The standard startup files are used normally, unless @option{-nostartfiles}
6332 is used. The compiler may generate calls to @code{memcmp},
6333 @code{memset}, @code{memcpy} and @code{memmove}.
6334 These entries are usually resolved by entries in
6335 libc. These entry points should be supplied through some other
6336 mechanism when this option is specified.
6340 Do not use the standard system startup files or libraries when linking.
6341 No startup files and only the libraries you specify will be passed to
6342 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
6343 @code{memcpy} and @code{memmove}.
6344 These entries are usually resolved by entries in
6345 libc. These entry points should be supplied through some other
6346 mechanism when this option is specified.
6348 @cindex @option{-lgcc}, use with @option{-nostdlib}
6349 @cindex @option{-nostdlib} and unresolved references
6350 @cindex unresolved references and @option{-nostdlib}
6351 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
6352 @cindex @option{-nodefaultlibs} and unresolved references
6353 @cindex unresolved references and @option{-nodefaultlibs}
6354 One of the standard libraries bypassed by @option{-nostdlib} and
6355 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
6356 that GCC uses to overcome shortcomings of particular machines, or special
6357 needs for some languages.
6358 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
6359 Collection (GCC) Internals},
6360 for more discussion of @file{libgcc.a}.)
6361 In most cases, you need @file{libgcc.a} even when you want to avoid
6362 other standard libraries. In other words, when you specify @option{-nostdlib}
6363 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
6364 This ensures that you have no unresolved references to internal GCC
6365 library subroutines. (For example, @samp{__main}, used to ensure C++
6366 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
6367 GNU Compiler Collection (GCC) Internals}.)
6371 Produce a position independent executable on targets which support it.
6372 For predictable results, you must also specify the same set of options
6373 that were used to generate code (@option{-fpie}, @option{-fPIE},
6374 or model suboptions) when you specify this option.
6378 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
6379 that support it. This instructs the linker to add all symbols, not
6380 only used ones, to the dynamic symbol table. This option is needed
6381 for some uses of @code{dlopen} or to allow obtaining backtraces
6382 from within a program.
6386 Remove all symbol table and relocation information from the executable.
6390 On systems that support dynamic linking, this prevents linking with the shared
6391 libraries. On other systems, this option has no effect.
6395 Produce a shared object which can then be linked with other objects to
6396 form an executable. Not all systems support this option. For predictable
6397 results, you must also specify the same set of options that were used to
6398 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
6399 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
6400 needs to build supplementary stub code for constructors to work. On
6401 multi-libbed systems, @samp{gcc -shared} must select the correct support
6402 libraries to link against. Failing to supply the correct flags may lead
6403 to subtle defects. Supplying them in cases where they are not necessary
6406 @item -shared-libgcc
6407 @itemx -static-libgcc
6408 @opindex shared-libgcc
6409 @opindex static-libgcc
6410 On systems that provide @file{libgcc} as a shared library, these options
6411 force the use of either the shared or static version respectively.
6412 If no shared version of @file{libgcc} was built when the compiler was
6413 configured, these options have no effect.
6415 There are several situations in which an application should use the
6416 shared @file{libgcc} instead of the static version. The most common
6417 of these is when the application wishes to throw and catch exceptions
6418 across different shared libraries. In that case, each of the libraries
6419 as well as the application itself should use the shared @file{libgcc}.
6421 Therefore, the G++ and GCJ drivers automatically add
6422 @option{-shared-libgcc} whenever you build a shared library or a main
6423 executable, because C++ and Java programs typically use exceptions, so
6424 this is the right thing to do.
6426 If, instead, you use the GCC driver to create shared libraries, you may
6427 find that they will not always be linked with the shared @file{libgcc}.
6428 If GCC finds, at its configuration time, that you have a non-GNU linker
6429 or a GNU linker that does not support option @option{--eh-frame-hdr},
6430 it will link the shared version of @file{libgcc} into shared libraries
6431 by default. Otherwise, it will take advantage of the linker and optimize
6432 away the linking with the shared version of @file{libgcc}, linking with
6433 the static version of libgcc by default. This allows exceptions to
6434 propagate through such shared libraries, without incurring relocation
6435 costs at library load time.
6437 However, if a library or main executable is supposed to throw or catch
6438 exceptions, you must link it using the G++ or GCJ driver, as appropriate
6439 for the languages used in the program, or using the option
6440 @option{-shared-libgcc}, such that it is linked with the shared
6445 Bind references to global symbols when building a shared object. Warn
6446 about any unresolved references (unless overridden by the link editor
6447 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
6450 @item -Xlinker @var{option}
6452 Pass @var{option} as an option to the linker. You can use this to
6453 supply system-specific linker options which GCC does not know how to
6456 If you want to pass an option that takes an argument, you must use
6457 @option{-Xlinker} twice, once for the option and once for the argument.
6458 For example, to pass @option{-assert definitions}, you must write
6459 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
6460 @option{-Xlinker "-assert definitions"}, because this passes the entire
6461 string as a single argument, which is not what the linker expects.
6463 @item -Wl,@var{option}
6465 Pass @var{option} as an option to the linker. If @var{option} contains
6466 commas, it is split into multiple options at the commas.
6468 @item -u @var{symbol}
6470 Pretend the symbol @var{symbol} is undefined, to force linking of
6471 library modules to define it. You can use @option{-u} multiple times with
6472 different symbols to force loading of additional library modules.
6475 @node Directory Options
6476 @section Options for Directory Search
6477 @cindex directory options
6478 @cindex options, directory search
6481 These options specify directories to search for header files, for
6482 libraries and for parts of the compiler:
6487 Add the directory @var{dir} to the head of the list of directories to be
6488 searched for header files. This can be used to override a system header
6489 file, substituting your own version, since these directories are
6490 searched before the system header file directories. However, you should
6491 not use this option to add directories that contain vendor-supplied
6492 system header files (use @option{-isystem} for that). If you use more than
6493 one @option{-I} option, the directories are scanned in left-to-right
6494 order; the standard system directories come after.
6496 If a standard system include directory, or a directory specified with
6497 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
6498 option will be ignored. The directory will still be searched but as a
6499 system directory at its normal position in the system include chain.
6500 This is to ensure that GCC's procedure to fix buggy system headers and
6501 the ordering for the include_next directive are not inadvertently changed.
6502 If you really need to change the search order for system directories,
6503 use the @option{-nostdinc} and/or @option{-isystem} options.
6505 @item -iquote@var{dir}
6507 Add the directory @var{dir} to the head of the list of directories to
6508 be searched for header files only for the case of @samp{#include
6509 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
6510 otherwise just like @option{-I}.
6514 Add directory @var{dir} to the list of directories to be searched
6517 @item -B@var{prefix}
6519 This option specifies where to find the executables, libraries,
6520 include files, and data files of the compiler itself.
6522 The compiler driver program runs one or more of the subprograms
6523 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
6524 @var{prefix} as a prefix for each program it tries to run, both with and
6525 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
6527 For each subprogram to be run, the compiler driver first tries the
6528 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
6529 was not specified, the driver tries two standard prefixes, which are
6530 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
6531 those results in a file name that is found, the unmodified program
6532 name is searched for using the directories specified in your
6533 @env{PATH} environment variable.
6535 The compiler will check to see if the path provided by the @option{-B}
6536 refers to a directory, and if necessary it will add a directory
6537 separator character at the end of the path.
6539 @option{-B} prefixes that effectively specify directory names also apply
6540 to libraries in the linker, because the compiler translates these
6541 options into @option{-L} options for the linker. They also apply to
6542 includes files in the preprocessor, because the compiler translates these
6543 options into @option{-isystem} options for the preprocessor. In this case,
6544 the compiler appends @samp{include} to the prefix.
6546 The run-time support file @file{libgcc.a} can also be searched for using
6547 the @option{-B} prefix, if needed. If it is not found there, the two
6548 standard prefixes above are tried, and that is all. The file is left
6549 out of the link if it is not found by those means.
6551 Another way to specify a prefix much like the @option{-B} prefix is to use
6552 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
6555 As a special kludge, if the path provided by @option{-B} is
6556 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
6557 9, then it will be replaced by @file{[dir/]include}. This is to help
6558 with boot-strapping the compiler.
6560 @item -specs=@var{file}
6562 Process @var{file} after the compiler reads in the standard @file{specs}
6563 file, in order to override the defaults that the @file{gcc} driver
6564 program uses when determining what switches to pass to @file{cc1},
6565 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
6566 @option{-specs=@var{file}} can be specified on the command line, and they
6567 are processed in order, from left to right.
6569 @item --sysroot=@var{dir}
6571 Use @var{dir} as the logical root directory for headers and libraries.
6572 For example, if the compiler would normally search for headers in
6573 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
6574 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
6576 If you use both this option and the @option{-isysroot} option, then
6577 the @option{--sysroot} option will apply to libraries, but the
6578 @option{-isysroot} option will apply to header files.
6580 The GNU linker (beginning with version 2.16) has the necessary support
6581 for this option. If your linker does not support this option, the
6582 header file aspect of @option{--sysroot} will still work, but the
6583 library aspect will not.
6587 This option has been deprecated. Please use @option{-iquote} instead for
6588 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
6589 Any directories you specify with @option{-I} options before the @option{-I-}
6590 option are searched only for the case of @samp{#include "@var{file}"};
6591 they are not searched for @samp{#include <@var{file}>}.
6593 If additional directories are specified with @option{-I} options after
6594 the @option{-I-}, these directories are searched for all @samp{#include}
6595 directives. (Ordinarily @emph{all} @option{-I} directories are used
6598 In addition, the @option{-I-} option inhibits the use of the current
6599 directory (where the current input file came from) as the first search
6600 directory for @samp{#include "@var{file}"}. There is no way to
6601 override this effect of @option{-I-}. With @option{-I.} you can specify
6602 searching the directory which was current when the compiler was
6603 invoked. That is not exactly the same as what the preprocessor does
6604 by default, but it is often satisfactory.
6606 @option{-I-} does not inhibit the use of the standard system directories
6607 for header files. Thus, @option{-I-} and @option{-nostdinc} are
6614 @section Specifying subprocesses and the switches to pass to them
6617 @command{gcc} is a driver program. It performs its job by invoking a
6618 sequence of other programs to do the work of compiling, assembling and
6619 linking. GCC interprets its command-line parameters and uses these to
6620 deduce which programs it should invoke, and which command-line options
6621 it ought to place on their command lines. This behavior is controlled
6622 by @dfn{spec strings}. In most cases there is one spec string for each
6623 program that GCC can invoke, but a few programs have multiple spec
6624 strings to control their behavior. The spec strings built into GCC can
6625 be overridden by using the @option{-specs=} command-line switch to specify
6628 @dfn{Spec files} are plaintext files that are used to construct spec
6629 strings. They consist of a sequence of directives separated by blank
6630 lines. The type of directive is determined by the first non-whitespace
6631 character on the line and it can be one of the following:
6634 @item %@var{command}
6635 Issues a @var{command} to the spec file processor. The commands that can
6639 @item %include <@var{file}>
6641 Search for @var{file} and insert its text at the current point in the
6644 @item %include_noerr <@var{file}>
6645 @cindex %include_noerr
6646 Just like @samp{%include}, but do not generate an error message if the include
6647 file cannot be found.
6649 @item %rename @var{old_name} @var{new_name}
6651 Rename the spec string @var{old_name} to @var{new_name}.
6655 @item *[@var{spec_name}]:
6656 This tells the compiler to create, override or delete the named spec
6657 string. All lines after this directive up to the next directive or
6658 blank line are considered to be the text for the spec string. If this
6659 results in an empty string then the spec will be deleted. (Or, if the
6660 spec did not exist, then nothing will happened.) Otherwise, if the spec
6661 does not currently exist a new spec will be created. If the spec does
6662 exist then its contents will be overridden by the text of this
6663 directive, unless the first character of that text is the @samp{+}
6664 character, in which case the text will be appended to the spec.
6666 @item [@var{suffix}]:
6667 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6668 and up to the next directive or blank line are considered to make up the
6669 spec string for the indicated suffix. When the compiler encounters an
6670 input file with the named suffix, it will processes the spec string in
6671 order to work out how to compile that file. For example:
6678 This says that any input file whose name ends in @samp{.ZZ} should be
6679 passed to the program @samp{z-compile}, which should be invoked with the
6680 command-line switch @option{-input} and with the result of performing the
6681 @samp{%i} substitution. (See below.)
6683 As an alternative to providing a spec string, the text that follows a
6684 suffix directive can be one of the following:
6687 @item @@@var{language}
6688 This says that the suffix is an alias for a known @var{language}. This is
6689 similar to using the @option{-x} command-line switch to GCC to specify a
6690 language explicitly. For example:
6697 Says that .ZZ files are, in fact, C++ source files.
6700 This causes an error messages saying:
6703 @var{name} compiler not installed on this system.
6707 GCC already has an extensive list of suffixes built into it.
6708 This directive will add an entry to the end of the list of suffixes, but
6709 since the list is searched from the end backwards, it is effectively
6710 possible to override earlier entries using this technique.
6714 GCC has the following spec strings built into it. Spec files can
6715 override these strings or create their own. Note that individual
6716 targets can also add their own spec strings to this list.
6719 asm Options to pass to the assembler
6720 asm_final Options to pass to the assembler post-processor
6721 cpp Options to pass to the C preprocessor
6722 cc1 Options to pass to the C compiler
6723 cc1plus Options to pass to the C++ compiler
6724 endfile Object files to include at the end of the link
6725 link Options to pass to the linker
6726 lib Libraries to include on the command line to the linker
6727 libgcc Decides which GCC support library to pass to the linker
6728 linker Sets the name of the linker
6729 predefines Defines to be passed to the C preprocessor
6730 signed_char Defines to pass to CPP to say whether @code{char} is signed
6732 startfile Object files to include at the start of the link
6735 Here is a small example of a spec file:
6741 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6744 This example renames the spec called @samp{lib} to @samp{old_lib} and
6745 then overrides the previous definition of @samp{lib} with a new one.
6746 The new definition adds in some extra command-line options before
6747 including the text of the old definition.
6749 @dfn{Spec strings} are a list of command-line options to be passed to their
6750 corresponding program. In addition, the spec strings can contain
6751 @samp{%}-prefixed sequences to substitute variable text or to
6752 conditionally insert text into the command line. Using these constructs
6753 it is possible to generate quite complex command lines.
6755 Here is a table of all defined @samp{%}-sequences for spec
6756 strings. Note that spaces are not generated automatically around the
6757 results of expanding these sequences. Therefore you can concatenate them
6758 together or combine them with constant text in a single argument.
6762 Substitute one @samp{%} into the program name or argument.
6765 Substitute the name of the input file being processed.
6768 Substitute the basename of the input file being processed.
6769 This is the substring up to (and not including) the last period
6770 and not including the directory.
6773 This is the same as @samp{%b}, but include the file suffix (text after
6777 Marks the argument containing or following the @samp{%d} as a
6778 temporary file name, so that that file will be deleted if GCC exits
6779 successfully. Unlike @samp{%g}, this contributes no text to the
6782 @item %g@var{suffix}
6783 Substitute a file name that has suffix @var{suffix} and is chosen
6784 once per compilation, and mark the argument in the same way as
6785 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6786 name is now chosen in a way that is hard to predict even when previously
6787 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6788 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6789 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6790 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6791 was simply substituted with a file name chosen once per compilation,
6792 without regard to any appended suffix (which was therefore treated
6793 just like ordinary text), making such attacks more likely to succeed.
6795 @item %u@var{suffix}
6796 Like @samp{%g}, but generates a new temporary file name even if
6797 @samp{%u@var{suffix}} was already seen.
6799 @item %U@var{suffix}
6800 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6801 new one if there is no such last file name. In the absence of any
6802 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6803 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6804 would involve the generation of two distinct file names, one
6805 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6806 simply substituted with a file name chosen for the previous @samp{%u},
6807 without regard to any appended suffix.
6809 @item %j@var{suffix}
6810 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6811 writable, and if save-temps is off; otherwise, substitute the name
6812 of a temporary file, just like @samp{%u}. This temporary file is not
6813 meant for communication between processes, but rather as a junk
6816 @item %|@var{suffix}
6817 @itemx %m@var{suffix}
6818 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6819 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6820 all. These are the two most common ways to instruct a program that it
6821 should read from standard input or write to standard output. If you
6822 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6823 construct: see for example @file{f/lang-specs.h}.
6825 @item %.@var{SUFFIX}
6826 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
6827 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
6828 terminated by the next space or %.
6831 Marks the argument containing or following the @samp{%w} as the
6832 designated output file of this compilation. This puts the argument
6833 into the sequence of arguments that @samp{%o} will substitute later.
6836 Substitutes the names of all the output files, with spaces
6837 automatically placed around them. You should write spaces
6838 around the @samp{%o} as well or the results are undefined.
6839 @samp{%o} is for use in the specs for running the linker.
6840 Input files whose names have no recognized suffix are not compiled
6841 at all, but they are included among the output files, so they will
6845 Substitutes the suffix for object files. Note that this is
6846 handled specially when it immediately follows @samp{%g, %u, or %U},
6847 because of the need for those to form complete file names. The
6848 handling is such that @samp{%O} is treated exactly as if it had already
6849 been substituted, except that @samp{%g, %u, and %U} do not currently
6850 support additional @var{suffix} characters following @samp{%O} as they would
6851 following, for example, @samp{.o}.
6854 Substitutes the standard macro predefinitions for the
6855 current target machine. Use this when running @code{cpp}.
6858 Like @samp{%p}, but puts @samp{__} before and after the name of each
6859 predefined macro, except for macros that start with @samp{__} or with
6860 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
6864 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
6865 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
6866 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
6867 and @option{-imultilib} as necessary.
6870 Current argument is the name of a library or startup file of some sort.
6871 Search for that file in a standard list of directories and substitute
6872 the full name found.
6875 Print @var{str} as an error message. @var{str} is terminated by a newline.
6876 Use this when inconsistent options are detected.
6879 Substitute the contents of spec string @var{name} at this point.
6882 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
6884 @item %x@{@var{option}@}
6885 Accumulate an option for @samp{%X}.
6888 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
6892 Output the accumulated assembler options specified by @option{-Wa}.
6895 Output the accumulated preprocessor options specified by @option{-Wp}.
6898 Process the @code{asm} spec. This is used to compute the
6899 switches to be passed to the assembler.
6902 Process the @code{asm_final} spec. This is a spec string for
6903 passing switches to an assembler post-processor, if such a program is
6907 Process the @code{link} spec. This is the spec for computing the
6908 command line passed to the linker. Typically it will make use of the
6909 @samp{%L %G %S %D and %E} sequences.
6912 Dump out a @option{-L} option for each directory that GCC believes might
6913 contain startup files. If the target supports multilibs then the
6914 current multilib directory will be prepended to each of these paths.
6917 Process the @code{lib} spec. This is a spec string for deciding which
6918 libraries should be included on the command line to the linker.
6921 Process the @code{libgcc} spec. This is a spec string for deciding
6922 which GCC support library should be included on the command line to the linker.
6925 Process the @code{startfile} spec. This is a spec for deciding which
6926 object files should be the first ones passed to the linker. Typically
6927 this might be a file named @file{crt0.o}.
6930 Process the @code{endfile} spec. This is a spec string that specifies
6931 the last object files that will be passed to the linker.
6934 Process the @code{cpp} spec. This is used to construct the arguments
6935 to be passed to the C preprocessor.
6938 Process the @code{cc1} spec. This is used to construct the options to be
6939 passed to the actual C compiler (@samp{cc1}).
6942 Process the @code{cc1plus} spec. This is used to construct the options to be
6943 passed to the actual C++ compiler (@samp{cc1plus}).
6946 Substitute the variable part of a matched option. See below.
6947 Note that each comma in the substituted string is replaced by
6951 Remove all occurrences of @code{-S} from the command line. Note---this
6952 command is position dependent. @samp{%} commands in the spec string
6953 before this one will see @code{-S}, @samp{%} commands in the spec string
6954 after this one will not.
6956 @item %:@var{function}(@var{args})
6957 Call the named function @var{function}, passing it @var{args}.
6958 @var{args} is first processed as a nested spec string, then split
6959 into an argument vector in the usual fashion. The function returns
6960 a string which is processed as if it had appeared literally as part
6961 of the current spec.
6963 The following built-in spec functions are provided:
6966 @item @code{if-exists}
6967 The @code{if-exists} spec function takes one argument, an absolute
6968 pathname to a file. If the file exists, @code{if-exists} returns the
6969 pathname. Here is a small example of its usage:
6973 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
6976 @item @code{if-exists-else}
6977 The @code{if-exists-else} spec function is similar to the @code{if-exists}
6978 spec function, except that it takes two arguments. The first argument is
6979 an absolute pathname to a file. If the file exists, @code{if-exists-else}
6980 returns the pathname. If it does not exist, it returns the second argument.
6981 This way, @code{if-exists-else} can be used to select one file or another,
6982 based on the existence of the first. Here is a small example of its usage:
6986 crt0%O%s %:if-exists(crti%O%s) \
6987 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
6990 @item @code{replace-outfile}
6991 The @code{replace-outfile} spec function takes two arguments. It looks for the
6992 first argument in the outfiles array and replaces it with the second argument. Here
6993 is a small example of its usage:
6996 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
7002 Substitutes the @code{-S} switch, if that switch was given to GCC@.
7003 If that switch was not specified, this substitutes nothing. Note that
7004 the leading dash is omitted when specifying this option, and it is
7005 automatically inserted if the substitution is performed. Thus the spec
7006 string @samp{%@{foo@}} would match the command-line option @option{-foo}
7007 and would output the command line option @option{-foo}.
7009 @item %W@{@code{S}@}
7010 Like %@{@code{S}@} but mark last argument supplied within as a file to be
7013 @item %@{@code{S}*@}
7014 Substitutes all the switches specified to GCC whose names start
7015 with @code{-S}, but which also take an argument. This is used for
7016 switches like @option{-o}, @option{-D}, @option{-I}, etc.
7017 GCC considers @option{-o foo} as being
7018 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
7019 text, including the space. Thus two arguments would be generated.
7021 @item %@{@code{S}*&@code{T}*@}
7022 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
7023 (the order of @code{S} and @code{T} in the spec is not significant).
7024 There can be any number of ampersand-separated variables; for each the
7025 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
7027 @item %@{@code{S}:@code{X}@}
7028 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
7030 @item %@{!@code{S}:@code{X}@}
7031 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
7033 @item %@{@code{S}*:@code{X}@}
7034 Substitutes @code{X} if one or more switches whose names start with
7035 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
7036 once, no matter how many such switches appeared. However, if @code{%*}
7037 appears somewhere in @code{X}, then @code{X} will be substituted once
7038 for each matching switch, with the @code{%*} replaced by the part of
7039 that switch that matched the @code{*}.
7041 @item %@{.@code{S}:@code{X}@}
7042 Substitutes @code{X}, if processing a file with suffix @code{S}.
7044 @item %@{!.@code{S}:@code{X}@}
7045 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
7047 @item %@{@code{S}|@code{P}:@code{X}@}
7048 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
7049 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
7050 although they have a stronger binding than the @samp{|}. If @code{%*}
7051 appears in @code{X}, all of the alternatives must be starred, and only
7052 the first matching alternative is substituted.
7054 For example, a spec string like this:
7057 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
7060 will output the following command-line options from the following input
7061 command-line options:
7066 -d fred.c -foo -baz -boggle
7067 -d jim.d -bar -baz -boggle
7070 @item %@{S:X; T:Y; :D@}
7072 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
7073 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
7074 be as many clauses as you need. This may be combined with @code{.},
7075 @code{!}, @code{|}, and @code{*} as needed.
7080 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
7081 construct may contain other nested @samp{%} constructs or spaces, or
7082 even newlines. They are processed as usual, as described above.
7083 Trailing white space in @code{X} is ignored. White space may also
7084 appear anywhere on the left side of the colon in these constructs,
7085 except between @code{.} or @code{*} and the corresponding word.
7087 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
7088 handled specifically in these constructs. If another value of
7089 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
7090 @option{-W} switch is found later in the command line, the earlier
7091 switch value is ignored, except with @{@code{S}*@} where @code{S} is
7092 just one letter, which passes all matching options.
7094 The character @samp{|} at the beginning of the predicate text is used to
7095 indicate that a command should be piped to the following command, but
7096 only if @option{-pipe} is specified.
7098 It is built into GCC which switches take arguments and which do not.
7099 (You might think it would be useful to generalize this to allow each
7100 compiler's spec to say which switches take arguments. But this cannot
7101 be done in a consistent fashion. GCC cannot even decide which input
7102 files have been specified without knowing which switches take arguments,
7103 and it must know which input files to compile in order to tell which
7106 GCC also knows implicitly that arguments starting in @option{-l} are to be
7107 treated as compiler output files, and passed to the linker in their
7108 proper position among the other output files.
7110 @c man begin OPTIONS
7112 @node Target Options
7113 @section Specifying Target Machine and Compiler Version
7114 @cindex target options
7115 @cindex cross compiling
7116 @cindex specifying machine version
7117 @cindex specifying compiler version and target machine
7118 @cindex compiler version, specifying
7119 @cindex target machine, specifying
7121 The usual way to run GCC is to run the executable called @file{gcc}, or
7122 @file{<machine>-gcc} when cross-compiling, or
7123 @file{<machine>-gcc-<version>} to run a version other than the one that
7124 was installed last. Sometimes this is inconvenient, so GCC provides
7125 options that will switch to another cross-compiler or version.
7128 @item -b @var{machine}
7130 The argument @var{machine} specifies the target machine for compilation.
7132 The value to use for @var{machine} is the same as was specified as the
7133 machine type when configuring GCC as a cross-compiler. For
7134 example, if a cross-compiler was configured with @samp{configure
7135 arm-elf}, meaning to compile for an arm processor with elf binaries,
7136 then you would specify @option{-b arm-elf} to run that cross compiler.
7137 Because there are other options beginning with @option{-b}, the
7138 configuration must contain a hyphen.
7140 @item -V @var{version}
7142 The argument @var{version} specifies which version of GCC to run.
7143 This is useful when multiple versions are installed. For example,
7144 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
7147 The @option{-V} and @option{-b} options work by running the
7148 @file{<machine>-gcc-<version>} executable, so there's no real reason to
7149 use them if you can just run that directly.
7151 @node Submodel Options
7152 @section Hardware Models and Configurations
7153 @cindex submodel options
7154 @cindex specifying hardware config
7155 @cindex hardware models and configurations, specifying
7156 @cindex machine dependent options
7158 Earlier we discussed the standard option @option{-b} which chooses among
7159 different installed compilers for completely different target
7160 machines, such as VAX vs.@: 68000 vs.@: 80386.
7162 In addition, each of these target machine types can have its own
7163 special options, starting with @samp{-m}, to choose among various
7164 hardware models or configurations---for example, 68010 vs 68020,
7165 floating coprocessor or none. A single installed version of the
7166 compiler can compile for any model or configuration, according to the
7169 Some configurations of the compiler also support additional special
7170 options, usually for compatibility with other compilers on the same
7173 @c This list is ordered alphanumerically by subsection name.
7174 @c It should be the same order and spelling as these options are listed
7175 @c in Machine Dependent Options
7181 * Blackfin Options::
7185 * DEC Alpha Options::
7186 * DEC Alpha/VMS Options::
7190 * i386 and x86-64 Options::
7203 * RS/6000 and PowerPC Options::
7204 * S/390 and zSeries Options::
7207 * System V Options::
7208 * TMS320C3x/C4x Options::
7212 * Xstormy16 Options::
7218 @subsection ARC Options
7221 These options are defined for ARC implementations:
7226 Compile code for little endian mode. This is the default.
7230 Compile code for big endian mode.
7233 @opindex mmangle-cpu
7234 Prepend the name of the cpu to all public symbol names.
7235 In multiple-processor systems, there are many ARC variants with different
7236 instruction and register set characteristics. This flag prevents code
7237 compiled for one cpu to be linked with code compiled for another.
7238 No facility exists for handling variants that are ``almost identical''.
7239 This is an all or nothing option.
7241 @item -mcpu=@var{cpu}
7243 Compile code for ARC variant @var{cpu}.
7244 Which variants are supported depend on the configuration.
7245 All variants support @option{-mcpu=base}, this is the default.
7247 @item -mtext=@var{text-section}
7248 @itemx -mdata=@var{data-section}
7249 @itemx -mrodata=@var{readonly-data-section}
7253 Put functions, data, and readonly data in @var{text-section},
7254 @var{data-section}, and @var{readonly-data-section} respectively
7255 by default. This can be overridden with the @code{section} attribute.
7256 @xref{Variable Attributes}.
7261 @subsection ARM Options
7264 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
7268 @item -mabi=@var{name}
7270 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
7271 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
7274 @opindex mapcs-frame
7275 Generate a stack frame that is compliant with the ARM Procedure Call
7276 Standard for all functions, even if this is not strictly necessary for
7277 correct execution of the code. Specifying @option{-fomit-frame-pointer}
7278 with this option will cause the stack frames not to be generated for
7279 leaf functions. The default is @option{-mno-apcs-frame}.
7283 This is a synonym for @option{-mapcs-frame}.
7286 @c not currently implemented
7287 @item -mapcs-stack-check
7288 @opindex mapcs-stack-check
7289 Generate code to check the amount of stack space available upon entry to
7290 every function (that actually uses some stack space). If there is
7291 insufficient space available then either the function
7292 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
7293 called, depending upon the amount of stack space required. The run time
7294 system is required to provide these functions. The default is
7295 @option{-mno-apcs-stack-check}, since this produces smaller code.
7297 @c not currently implemented
7299 @opindex mapcs-float
7300 Pass floating point arguments using the float point registers. This is
7301 one of the variants of the APCS@. This option is recommended if the
7302 target hardware has a floating point unit or if a lot of floating point
7303 arithmetic is going to be performed by the code. The default is
7304 @option{-mno-apcs-float}, since integer only code is slightly increased in
7305 size if @option{-mapcs-float} is used.
7307 @c not currently implemented
7308 @item -mapcs-reentrant
7309 @opindex mapcs-reentrant
7310 Generate reentrant, position independent code. The default is
7311 @option{-mno-apcs-reentrant}.
7314 @item -mthumb-interwork
7315 @opindex mthumb-interwork
7316 Generate code which supports calling between the ARM and Thumb
7317 instruction sets. Without this option the two instruction sets cannot
7318 be reliably used inside one program. The default is
7319 @option{-mno-thumb-interwork}, since slightly larger code is generated
7320 when @option{-mthumb-interwork} is specified.
7322 @item -mno-sched-prolog
7323 @opindex mno-sched-prolog
7324 Prevent the reordering of instructions in the function prolog, or the
7325 merging of those instruction with the instructions in the function's
7326 body. This means that all functions will start with a recognizable set
7327 of instructions (or in fact one of a choice from a small set of
7328 different function prologues), and this information can be used to
7329 locate the start if functions inside an executable piece of code. The
7330 default is @option{-msched-prolog}.
7333 @opindex mhard-float
7334 Generate output containing floating point instructions. This is the
7338 @opindex msoft-float
7339 Generate output containing library calls for floating point.
7340 @strong{Warning:} the requisite libraries are not available for all ARM
7341 targets. Normally the facilities of the machine's usual C compiler are
7342 used, but this cannot be done directly in cross-compilation. You must make
7343 your own arrangements to provide suitable library functions for
7346 @option{-msoft-float} changes the calling convention in the output file;
7347 therefore, it is only useful if you compile @emph{all} of a program with
7348 this option. In particular, you need to compile @file{libgcc.a}, the
7349 library that comes with GCC, with @option{-msoft-float} in order for
7352 @item -mfloat-abi=@var{name}
7354 Specifies which ABI to use for floating point values. Permissible values
7355 are: @samp{soft}, @samp{softfp} and @samp{hard}.
7357 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
7358 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
7359 of floating point instructions, but still uses the soft-float calling
7362 @item -mlittle-endian
7363 @opindex mlittle-endian
7364 Generate code for a processor running in little-endian mode. This is
7365 the default for all standard configurations.
7368 @opindex mbig-endian
7369 Generate code for a processor running in big-endian mode; the default is
7370 to compile code for a little-endian processor.
7372 @item -mwords-little-endian
7373 @opindex mwords-little-endian
7374 This option only applies when generating code for big-endian processors.
7375 Generate code for a little-endian word order but a big-endian byte
7376 order. That is, a byte order of the form @samp{32107654}. Note: this
7377 option should only be used if you require compatibility with code for
7378 big-endian ARM processors generated by versions of the compiler prior to
7381 @item -mcpu=@var{name}
7383 This specifies the name of the target ARM processor. GCC uses this name
7384 to determine what kind of instructions it can emit when generating
7385 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
7386 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
7387 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
7388 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
7389 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
7390 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
7391 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
7392 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
7393 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
7394 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
7395 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
7396 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
7397 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
7398 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
7401 @itemx -mtune=@var{name}
7403 This option is very similar to the @option{-mcpu=} option, except that
7404 instead of specifying the actual target processor type, and hence
7405 restricting which instructions can be used, it specifies that GCC should
7406 tune the performance of the code as if the target were of the type
7407 specified in this option, but still choosing the instructions that it
7408 will generate based on the cpu specified by a @option{-mcpu=} option.
7409 For some ARM implementations better performance can be obtained by using
7412 @item -march=@var{name}
7414 This specifies the name of the target ARM architecture. GCC uses this
7415 name to determine what kind of instructions it can emit when generating
7416 assembly code. This option can be used in conjunction with or instead
7417 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
7418 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
7419 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
7420 @samp{iwmmxt}, @samp{ep9312}.
7422 @item -mfpu=@var{name}
7423 @itemx -mfpe=@var{number}
7424 @itemx -mfp=@var{number}
7428 This specifies what floating point hardware (or hardware emulation) is
7429 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
7430 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
7431 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
7432 with older versions of GCC@.
7434 If @option{-msoft-float} is specified this specifies the format of
7435 floating point values.
7437 @item -mstructure-size-boundary=@var{n}
7438 @opindex mstructure-size-boundary
7439 The size of all structures and unions will be rounded up to a multiple
7440 of the number of bits set by this option. Permissible values are 8, 32
7441 and 64. The default value varies for different toolchains. For the COFF
7442 targeted toolchain the default value is 8. A value of 64 is only allowed
7443 if the underlying ABI supports it.
7445 Specifying the larger number can produce faster, more efficient code, but
7446 can also increase the size of the program. Different values are potentially
7447 incompatible. Code compiled with one value cannot necessarily expect to
7448 work with code or libraries compiled with another value, if they exchange
7449 information using structures or unions.
7451 @item -mabort-on-noreturn
7452 @opindex mabort-on-noreturn
7453 Generate a call to the function @code{abort} at the end of a
7454 @code{noreturn} function. It will be executed if the function tries to
7458 @itemx -mno-long-calls
7459 @opindex mlong-calls
7460 @opindex mno-long-calls
7461 Tells the compiler to perform function calls by first loading the
7462 address of the function into a register and then performing a subroutine
7463 call on this register. This switch is needed if the target function
7464 will lie outside of the 64 megabyte addressing range of the offset based
7465 version of subroutine call instruction.
7467 Even if this switch is enabled, not all function calls will be turned
7468 into long calls. The heuristic is that static functions, functions
7469 which have the @samp{short-call} attribute, functions that are inside
7470 the scope of a @samp{#pragma no_long_calls} directive and functions whose
7471 definitions have already been compiled within the current compilation
7472 unit, will not be turned into long calls. The exception to this rule is
7473 that weak function definitions, functions with the @samp{long-call}
7474 attribute or the @samp{section} attribute, and functions that are within
7475 the scope of a @samp{#pragma long_calls} directive, will always be
7476 turned into long calls.
7478 This feature is not enabled by default. Specifying
7479 @option{-mno-long-calls} will restore the default behavior, as will
7480 placing the function calls within the scope of a @samp{#pragma
7481 long_calls_off} directive. Note these switches have no effect on how
7482 the compiler generates code to handle function calls via function
7485 @item -mnop-fun-dllimport
7486 @opindex mnop-fun-dllimport
7487 Disable support for the @code{dllimport} attribute.
7489 @item -msingle-pic-base
7490 @opindex msingle-pic-base
7491 Treat the register used for PIC addressing as read-only, rather than
7492 loading it in the prologue for each function. The run-time system is
7493 responsible for initializing this register with an appropriate value
7494 before execution begins.
7496 @item -mpic-register=@var{reg}
7497 @opindex mpic-register
7498 Specify the register to be used for PIC addressing. The default is R10
7499 unless stack-checking is enabled, when R9 is used.
7501 @item -mcirrus-fix-invalid-insns
7502 @opindex mcirrus-fix-invalid-insns
7503 @opindex mno-cirrus-fix-invalid-insns
7504 Insert NOPs into the instruction stream to in order to work around
7505 problems with invalid Maverick instruction combinations. This option
7506 is only valid if the @option{-mcpu=ep9312} option has been used to
7507 enable generation of instructions for the Cirrus Maverick floating
7508 point co-processor. This option is not enabled by default, since the
7509 problem is only present in older Maverick implementations. The default
7510 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
7513 @item -mpoke-function-name
7514 @opindex mpoke-function-name
7515 Write the name of each function into the text section, directly
7516 preceding the function prologue. The generated code is similar to this:
7520 .ascii "arm_poke_function_name", 0
7523 .word 0xff000000 + (t1 - t0)
7524 arm_poke_function_name
7526 stmfd sp!, @{fp, ip, lr, pc@}
7530 When performing a stack backtrace, code can inspect the value of
7531 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
7532 location @code{pc - 12} and the top 8 bits are set, then we know that
7533 there is a function name embedded immediately preceding this location
7534 and has length @code{((pc[-3]) & 0xff000000)}.
7538 Generate code for the 16-bit Thumb instruction set. The default is to
7539 use the 32-bit ARM instruction set.
7542 @opindex mtpcs-frame
7543 Generate a stack frame that is compliant with the Thumb Procedure Call
7544 Standard for all non-leaf functions. (A leaf function is one that does
7545 not call any other functions.) The default is @option{-mno-tpcs-frame}.
7547 @item -mtpcs-leaf-frame
7548 @opindex mtpcs-leaf-frame
7549 Generate a stack frame that is compliant with the Thumb Procedure Call
7550 Standard for all leaf functions. (A leaf function is one that does
7551 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
7553 @item -mcallee-super-interworking
7554 @opindex mcallee-super-interworking
7555 Gives all externally visible functions in the file being compiled an ARM
7556 instruction set header which switches to Thumb mode before executing the
7557 rest of the function. This allows these functions to be called from
7558 non-interworking code.
7560 @item -mcaller-super-interworking
7561 @opindex mcaller-super-interworking
7562 Allows calls via function pointers (including virtual functions) to
7563 execute correctly regardless of whether the target code has been
7564 compiled for interworking or not. There is a small overhead in the cost
7565 of executing a function pointer if this option is enabled.
7567 @item -mtp=@var{name}
7569 Specify the access model for the thread local storage pointer. The valid
7570 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
7571 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
7572 (supported in the arm6k architecture), and @option{auto}, which uses the
7573 best available method for the selected processor. The default setting is
7579 @subsection AVR Options
7582 These options are defined for AVR implementations:
7585 @item -mmcu=@var{mcu}
7587 Specify ATMEL AVR instruction set or MCU type.
7589 Instruction set avr1 is for the minimal AVR core, not supported by the C
7590 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
7591 attiny11, attiny12, attiny15, attiny28).
7593 Instruction set avr2 (default) is for the classic AVR core with up to
7594 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
7595 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
7596 at90c8534, at90s8535).
7598 Instruction set avr3 is for the classic AVR core with up to 128K program
7599 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
7601 Instruction set avr4 is for the enhanced AVR core with up to 8K program
7602 memory space (MCU types: atmega8, atmega83, atmega85).
7604 Instruction set avr5 is for the enhanced AVR core with up to 128K program
7605 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
7606 atmega64, atmega128, at43usb355, at94k).
7610 Output instruction sizes to the asm file.
7612 @item -minit-stack=@var{N}
7613 @opindex minit-stack
7614 Specify the initial stack address, which may be a symbol or numeric value,
7615 @samp{__stack} is the default.
7617 @item -mno-interrupts
7618 @opindex mno-interrupts
7619 Generated code is not compatible with hardware interrupts.
7620 Code size will be smaller.
7622 @item -mcall-prologues
7623 @opindex mcall-prologues
7624 Functions prologues/epilogues expanded as call to appropriate
7625 subroutines. Code size will be smaller.
7627 @item -mno-tablejump
7628 @opindex mno-tablejump
7629 Do not generate tablejump insns which sometimes increase code size.
7632 @opindex mtiny-stack
7633 Change only the low 8 bits of the stack pointer.
7637 Assume int to be 8 bit integer. This affects the sizes of all types: A
7638 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7639 and long long will be 4 bytes. Please note that this option does not
7640 comply to the C standards, but it will provide you with smaller code
7644 @node Blackfin Options
7645 @subsection Blackfin Options
7646 @cindex Blackfin Options
7649 @item -momit-leaf-frame-pointer
7650 @opindex momit-leaf-frame-pointer
7651 Don't keep the frame pointer in a register for leaf functions. This
7652 avoids the instructions to save, set up and restore frame pointers and
7653 makes an extra register available in leaf functions. The option
7654 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7655 which might make debugging harder.
7657 @item -mspecld-anomaly
7658 @opindex mspecld-anomaly
7659 When enabled, the compiler will ensure that the generated code does not
7660 contain speculative loads after jump instructions. This option is enabled
7663 @item -mno-specld-anomaly
7664 @opindex mno-specld-anomaly
7665 Don't generate extra code to prevent speculative loads from occurring.
7667 @item -mcsync-anomaly
7668 @opindex mcsync-anomaly
7669 When enabled, the compiler will ensure that the generated code does not
7670 contain CSYNC or SSYNC instructions too soon after conditional branches.
7671 This option is enabled by default.
7673 @item -mno-csync-anomaly
7674 @opindex mno-csync-anomaly
7675 Don't generate extra code to prevent CSYNC or SSYNC instructions from
7676 occurring too soon after a conditional branch.
7680 When enabled, the compiler is free to take advantage of the knowledge that
7681 the entire program fits into the low 64k of memory.
7684 @opindex mno-low-64k
7685 Assume that the program is arbitrarily large. This is the default.
7687 @item -mid-shared-library
7688 @opindex mid-shared-library
7689 Generate code that supports shared libraries via the library ID method.
7690 This allows for execute in place and shared libraries in an environment
7691 without virtual memory management. This option implies @option{-fPIC}.
7693 @item -mno-id-shared-library
7694 @opindex mno-id-shared-library
7695 Generate code that doesn't assume ID based shared libraries are being used.
7696 This is the default.
7698 @item -mshared-library-id=n
7699 @opindex mshared-library-id
7700 Specified the identification number of the ID based shared library being
7701 compiled. Specifying a value of 0 will generate more compact code, specifying
7702 other values will force the allocation of that number to the current
7703 library but is no more space or time efficient than omitting this option.
7706 @itemx -mno-long-calls
7707 @opindex mlong-calls
7708 @opindex mno-long-calls
7709 Tells the compiler to perform function calls by first loading the
7710 address of the function into a register and then performing a subroutine
7711 call on this register. This switch is needed if the target function
7712 will lie outside of the 24 bit addressing range of the offset based
7713 version of subroutine call instruction.
7715 This feature is not enabled by default. Specifying
7716 @option{-mno-long-calls} will restore the default behavior. Note these
7717 switches have no effect on how the compiler generates code to handle
7718 function calls via function pointers.
7722 @subsection CRIS Options
7723 @cindex CRIS Options
7725 These options are defined specifically for the CRIS ports.
7728 @item -march=@var{architecture-type}
7729 @itemx -mcpu=@var{architecture-type}
7732 Generate code for the specified architecture. The choices for
7733 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7734 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
7735 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7738 @item -mtune=@var{architecture-type}
7740 Tune to @var{architecture-type} everything applicable about the generated
7741 code, except for the ABI and the set of available instructions. The
7742 choices for @var{architecture-type} are the same as for
7743 @option{-march=@var{architecture-type}}.
7745 @item -mmax-stack-frame=@var{n}
7746 @opindex mmax-stack-frame
7747 Warn when the stack frame of a function exceeds @var{n} bytes.
7749 @item -melinux-stacksize=@var{n}
7750 @opindex melinux-stacksize
7751 Only available with the @samp{cris-axis-aout} target. Arranges for
7752 indications in the program to the kernel loader that the stack of the
7753 program should be set to @var{n} bytes.
7759 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7760 @option{-march=v3} and @option{-march=v8} respectively.
7762 @item -mmul-bug-workaround
7763 @itemx -mno-mul-bug-workaround
7764 @opindex mmul-bug-workaround
7765 @opindex mno-mul-bug-workaround
7766 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7767 models where it applies. This option is active by default.
7771 Enable CRIS-specific verbose debug-related information in the assembly
7772 code. This option also has the effect to turn off the @samp{#NO_APP}
7773 formatted-code indicator to the assembler at the beginning of the
7778 Do not use condition-code results from previous instruction; always emit
7779 compare and test instructions before use of condition codes.
7781 @item -mno-side-effects
7782 @opindex mno-side-effects
7783 Do not emit instructions with side-effects in addressing modes other than
7787 @itemx -mno-stack-align
7789 @itemx -mno-data-align
7790 @itemx -mconst-align
7791 @itemx -mno-const-align
7792 @opindex mstack-align
7793 @opindex mno-stack-align
7794 @opindex mdata-align
7795 @opindex mno-data-align
7796 @opindex mconst-align
7797 @opindex mno-const-align
7798 These options (no-options) arranges (eliminate arrangements) for the
7799 stack-frame, individual data and constants to be aligned for the maximum
7800 single data access size for the chosen CPU model. The default is to
7801 arrange for 32-bit alignment. ABI details such as structure layout are
7802 not affected by these options.
7810 Similar to the stack- data- and const-align options above, these options
7811 arrange for stack-frame, writable data and constants to all be 32-bit,
7812 16-bit or 8-bit aligned. The default is 32-bit alignment.
7814 @item -mno-prologue-epilogue
7815 @itemx -mprologue-epilogue
7816 @opindex mno-prologue-epilogue
7817 @opindex mprologue-epilogue
7818 With @option{-mno-prologue-epilogue}, the normal function prologue and
7819 epilogue that sets up the stack-frame are omitted and no return
7820 instructions or return sequences are generated in the code. Use this
7821 option only together with visual inspection of the compiled code: no
7822 warnings or errors are generated when call-saved registers must be saved,
7823 or storage for local variable needs to be allocated.
7829 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
7830 instruction sequences that load addresses for functions from the PLT part
7831 of the GOT rather than (traditional on other architectures) calls to the
7832 PLT@. The default is @option{-mgotplt}.
7836 Legacy no-op option only recognized with the cris-axis-aout target.
7840 Legacy no-op option only recognized with the cris-axis-elf and
7841 cris-axis-linux-gnu targets.
7845 Only recognized with the cris-axis-aout target, where it selects a
7846 GNU/linux-like multilib, include files and instruction set for
7851 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
7855 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
7856 to link with input-output functions from a simulator library. Code,
7857 initialized data and zero-initialized data are allocated consecutively.
7861 Like @option{-sim}, but pass linker options to locate initialized data at
7862 0x40000000 and zero-initialized data at 0x80000000.
7866 @subsection CRX Options
7869 These options are defined specifically for the CRX ports.
7875 Enable the use of multiply-accumulate instructions. Disabled by default.
7879 Push instructions will be used to pass outgoing arguments when functions
7880 are called. Enabled by default.
7883 @node Darwin Options
7884 @subsection Darwin Options
7885 @cindex Darwin options
7887 These options are defined for all architectures running the Darwin operating
7890 FSF GCC on Darwin does not create ``fat'' object files; it will create
7891 an object file for the single architecture that it was built to
7892 target. Apple's GCC on Darwin does create ``fat'' files if multiple
7893 @option{-arch} options are used; it does so by running the compiler or
7894 linker multiple times and joining the results together with
7897 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
7898 @samp{i686}) is determined by the flags that specify the ISA
7899 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
7900 @option{-force_cpusubtype_ALL} option can be used to override this.
7902 The Darwin tools vary in their behavior when presented with an ISA
7903 mismatch. The assembler, @file{as}, will only permit instructions to
7904 be used that are valid for the subtype of the file it is generating,
7905 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
7906 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
7907 and print an error if asked to create a shared library with a less
7908 restrictive subtype than its input files (for instance, trying to put
7909 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
7910 for executables, @file{ld}, will quietly give the executable the most
7911 restrictive subtype of any of its input files.
7916 Add the framework directory @var{dir} to the head of the list of
7917 directories to be searched for header files. These directories are
7918 interleaved with those specified by @option{-I} options and are
7919 scanned in a left-to-right order.
7921 A framework directory is a directory with frameworks in it. A
7922 framework is a directory with a @samp{"Headers"} and/or
7923 @samp{"PrivateHeaders"} directory contained directly in it that ends
7924 in @samp{".framework"}. The name of a framework is the name of this
7925 directory excluding the @samp{".framework"}. Headers associated with
7926 the framework are found in one of those two directories, with
7927 @samp{"Headers"} being searched first. A subframework is a framework
7928 directory that is in a framework's @samp{"Frameworks"} directory.
7929 Includes of subframework headers can only appear in a header of a
7930 framework that contains the subframework, or in a sibling subframework
7931 header. Two subframeworks are siblings if they occur in the same
7932 framework. A subframework should not have the same name as a
7933 framework, a warning will be issued if this is violated. Currently a
7934 subframework cannot have subframeworks, in the future, the mechanism
7935 may be extended to support this. The standard frameworks can be found
7936 in @samp{"/System/Library/Frameworks"} and
7937 @samp{"/Library/Frameworks"}. An example include looks like
7938 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
7939 the name of the framework and header.h is found in the
7940 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
7944 Emit debugging information for symbols that are used. For STABS
7945 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
7946 This is by default ON@.
7950 Emit debugging information for all symbols and types.
7952 @item -mmacosx-version-min=@var{version}
7953 The earliest version of MacOS X that this executable will run on
7954 is @var{version}. Typical values of @var{version} include @code{10.1},
7955 @code{10.2}, and @code{10.3.9}.
7957 The default for this option is to make choices that seem to be most
7960 @item -mone-byte-bool
7961 @opindex -mone-byte-bool
7962 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
7963 By default @samp{sizeof(bool)} is @samp{4} when compiling for
7964 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
7965 option has no effect on x86.
7967 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
7968 to generate code that is not binary compatible with code generated
7969 without that switch. Using this switch may require recompiling all
7970 other modules in a program, including system libraries. Use this
7971 switch to conform to a non-default data model.
7973 @item -mfix-and-continue
7974 @itemx -ffix-and-continue
7975 @itemx -findirect-data
7976 @opindex mfix-and-continue
7977 @opindex ffix-and-continue
7978 @opindex findirect-data
7979 Generate code suitable for fast turn around development. Needed to
7980 enable gdb to dynamically load @code{.o} files into already running
7981 programs. @option{-findirect-data} and @option{-ffix-and-continue}
7982 are provided for backwards compatibility.
7986 Loads all members of static archive libraries.
7987 See man ld(1) for more information.
7989 @item -arch_errors_fatal
7990 @opindex arch_errors_fatal
7991 Cause the errors having to do with files that have the wrong architecture
7995 @opindex bind_at_load
7996 Causes the output file to be marked such that the dynamic linker will
7997 bind all undefined references when the file is loaded or launched.
8001 Produce a Mach-o bundle format file.
8002 See man ld(1) for more information.
8004 @item -bundle_loader @var{executable}
8005 @opindex bundle_loader
8006 This option specifies the @var{executable} that will be loading the build
8007 output file being linked. See man ld(1) for more information.
8010 @opindex -dynamiclib
8011 When passed this option, GCC will produce a dynamic library instead of
8012 an executable when linking, using the Darwin @file{libtool} command.
8014 @item -force_cpusubtype_ALL
8015 @opindex -force_cpusubtype_ALL
8016 This causes GCC's output file to have the @var{ALL} subtype, instead of
8017 one controlled by the @option{-mcpu} or @option{-march} option.
8019 @item -allowable_client @var{client_name}
8021 @itemx -compatibility_version
8022 @itemx -current_version
8024 @itemx -dependency-file
8026 @itemx -dylinker_install_name
8028 @itemx -exported_symbols_list
8030 @itemx -flat_namespace
8031 @itemx -force_flat_namespace
8032 @itemx -headerpad_max_install_names
8035 @itemx -install_name
8036 @itemx -keep_private_externs
8037 @itemx -multi_module
8038 @itemx -multiply_defined
8039 @itemx -multiply_defined_unused
8041 @itemx -no_dead_strip_inits_and_terms
8042 @itemx -nofixprebinding
8045 @itemx -noseglinkedit
8046 @itemx -pagezero_size
8048 @itemx -prebind_all_twolevel_modules
8049 @itemx -private_bundle
8050 @itemx -read_only_relocs
8052 @itemx -sectobjectsymbols
8056 @itemx -sectobjectsymbols
8059 @itemx -segs_read_only_addr
8060 @itemx -segs_read_write_addr
8061 @itemx -seg_addr_table
8062 @itemx -seg_addr_table_filename
8065 @itemx -segs_read_only_addr
8066 @itemx -segs_read_write_addr
8067 @itemx -single_module
8070 @itemx -sub_umbrella
8071 @itemx -twolevel_namespace
8074 @itemx -unexported_symbols_list
8075 @itemx -weak_reference_mismatches
8078 @opindex allowable_client
8079 @opindex client_name
8080 @opindex compatibility_version
8081 @opindex current_version
8083 @opindex dependency-file
8085 @opindex dylinker_install_name
8087 @opindex exported_symbols_list
8089 @opindex flat_namespace
8090 @opindex force_flat_namespace
8091 @opindex headerpad_max_install_names
8094 @opindex install_name
8095 @opindex keep_private_externs
8096 @opindex multi_module
8097 @opindex multiply_defined
8098 @opindex multiply_defined_unused
8100 @opindex no_dead_strip_inits_and_terms
8101 @opindex nofixprebinding
8102 @opindex nomultidefs
8104 @opindex noseglinkedit
8105 @opindex pagezero_size
8107 @opindex prebind_all_twolevel_modules
8108 @opindex private_bundle
8109 @opindex read_only_relocs
8111 @opindex sectobjectsymbols
8115 @opindex sectobjectsymbols
8118 @opindex segs_read_only_addr
8119 @opindex segs_read_write_addr
8120 @opindex seg_addr_table
8121 @opindex seg_addr_table_filename
8122 @opindex seglinkedit
8124 @opindex segs_read_only_addr
8125 @opindex segs_read_write_addr
8126 @opindex single_module
8128 @opindex sub_library
8129 @opindex sub_umbrella
8130 @opindex twolevel_namespace
8133 @opindex unexported_symbols_list
8134 @opindex weak_reference_mismatches
8135 @opindex whatsloaded
8137 These options are passed to the Darwin linker. The Darwin linker man page
8138 describes them in detail.
8141 @node DEC Alpha Options
8142 @subsection DEC Alpha Options
8144 These @samp{-m} options are defined for the DEC Alpha implementations:
8147 @item -mno-soft-float
8149 @opindex mno-soft-float
8150 @opindex msoft-float
8151 Use (do not use) the hardware floating-point instructions for
8152 floating-point operations. When @option{-msoft-float} is specified,
8153 functions in @file{libgcc.a} will be used to perform floating-point
8154 operations. Unless they are replaced by routines that emulate the
8155 floating-point operations, or compiled in such a way as to call such
8156 emulations routines, these routines will issue floating-point
8157 operations. If you are compiling for an Alpha without floating-point
8158 operations, you must ensure that the library is built so as not to call
8161 Note that Alpha implementations without floating-point operations are
8162 required to have floating-point registers.
8167 @opindex mno-fp-regs
8168 Generate code that uses (does not use) the floating-point register set.
8169 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8170 register set is not used, floating point operands are passed in integer
8171 registers as if they were integers and floating-point results are passed
8172 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8173 so any function with a floating-point argument or return value called by code
8174 compiled with @option{-mno-fp-regs} must also be compiled with that
8177 A typical use of this option is building a kernel that does not use,
8178 and hence need not save and restore, any floating-point registers.
8182 The Alpha architecture implements floating-point hardware optimized for
8183 maximum performance. It is mostly compliant with the IEEE floating
8184 point standard. However, for full compliance, software assistance is
8185 required. This option generates code fully IEEE compliant code
8186 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8187 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8188 defined during compilation. The resulting code is less efficient but is
8189 able to correctly support denormalized numbers and exceptional IEEE
8190 values such as not-a-number and plus/minus infinity. Other Alpha
8191 compilers call this option @option{-ieee_with_no_inexact}.
8193 @item -mieee-with-inexact
8194 @opindex mieee-with-inexact
8195 This is like @option{-mieee} except the generated code also maintains
8196 the IEEE @var{inexact-flag}. Turning on this option causes the
8197 generated code to implement fully-compliant IEEE math. In addition to
8198 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8199 macro. On some Alpha implementations the resulting code may execute
8200 significantly slower than the code generated by default. Since there is
8201 very little code that depends on the @var{inexact-flag}, you should
8202 normally not specify this option. Other Alpha compilers call this
8203 option @option{-ieee_with_inexact}.
8205 @item -mfp-trap-mode=@var{trap-mode}
8206 @opindex mfp-trap-mode
8207 This option controls what floating-point related traps are enabled.
8208 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8209 The trap mode can be set to one of four values:
8213 This is the default (normal) setting. The only traps that are enabled
8214 are the ones that cannot be disabled in software (e.g., division by zero
8218 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8222 Like @samp{su}, but the instructions are marked to be safe for software
8223 completion (see Alpha architecture manual for details).
8226 Like @samp{su}, but inexact traps are enabled as well.
8229 @item -mfp-rounding-mode=@var{rounding-mode}
8230 @opindex mfp-rounding-mode
8231 Selects the IEEE rounding mode. Other Alpha compilers call this option
8232 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8237 Normal IEEE rounding mode. Floating point numbers are rounded towards
8238 the nearest machine number or towards the even machine number in case
8242 Round towards minus infinity.
8245 Chopped rounding mode. Floating point numbers are rounded towards zero.
8248 Dynamic rounding mode. A field in the floating point control register
8249 (@var{fpcr}, see Alpha architecture reference manual) controls the
8250 rounding mode in effect. The C library initializes this register for
8251 rounding towards plus infinity. Thus, unless your program modifies the
8252 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8255 @item -mtrap-precision=@var{trap-precision}
8256 @opindex mtrap-precision
8257 In the Alpha architecture, floating point traps are imprecise. This
8258 means without software assistance it is impossible to recover from a
8259 floating trap and program execution normally needs to be terminated.
8260 GCC can generate code that can assist operating system trap handlers
8261 in determining the exact location that caused a floating point trap.
8262 Depending on the requirements of an application, different levels of
8263 precisions can be selected:
8267 Program precision. This option is the default and means a trap handler
8268 can only identify which program caused a floating point exception.
8271 Function precision. The trap handler can determine the function that
8272 caused a floating point exception.
8275 Instruction precision. The trap handler can determine the exact
8276 instruction that caused a floating point exception.
8279 Other Alpha compilers provide the equivalent options called
8280 @option{-scope_safe} and @option{-resumption_safe}.
8282 @item -mieee-conformant
8283 @opindex mieee-conformant
8284 This option marks the generated code as IEEE conformant. You must not
8285 use this option unless you also specify @option{-mtrap-precision=i} and either
8286 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8287 is to emit the line @samp{.eflag 48} in the function prologue of the
8288 generated assembly file. Under DEC Unix, this has the effect that
8289 IEEE-conformant math library routines will be linked in.
8291 @item -mbuild-constants
8292 @opindex mbuild-constants
8293 Normally GCC examines a 32- or 64-bit integer constant to
8294 see if it can construct it from smaller constants in two or three
8295 instructions. If it cannot, it will output the constant as a literal and
8296 generate code to load it from the data segment at runtime.
8298 Use this option to require GCC to construct @emph{all} integer constants
8299 using code, even if it takes more instructions (the maximum is six).
8301 You would typically use this option to build a shared library dynamic
8302 loader. Itself a shared library, it must relocate itself in memory
8303 before it can find the variables and constants in its own data segment.
8309 Select whether to generate code to be assembled by the vendor-supplied
8310 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8328 Indicate whether GCC should generate code to use the optional BWX,
8329 CIX, FIX and MAX instruction sets. The default is to use the instruction
8330 sets supported by the CPU type specified via @option{-mcpu=} option or that
8331 of the CPU on which GCC was built if none was specified.
8336 @opindex mfloat-ieee
8337 Generate code that uses (does not use) VAX F and G floating point
8338 arithmetic instead of IEEE single and double precision.
8340 @item -mexplicit-relocs
8341 @itemx -mno-explicit-relocs
8342 @opindex mexplicit-relocs
8343 @opindex mno-explicit-relocs
8344 Older Alpha assemblers provided no way to generate symbol relocations
8345 except via assembler macros. Use of these macros does not allow
8346 optimal instruction scheduling. GNU binutils as of version 2.12
8347 supports a new syntax that allows the compiler to explicitly mark
8348 which relocations should apply to which instructions. This option
8349 is mostly useful for debugging, as GCC detects the capabilities of
8350 the assembler when it is built and sets the default accordingly.
8354 @opindex msmall-data
8355 @opindex mlarge-data
8356 When @option{-mexplicit-relocs} is in effect, static data is
8357 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
8358 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
8359 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
8360 16-bit relocations off of the @code{$gp} register. This limits the
8361 size of the small data area to 64KB, but allows the variables to be
8362 directly accessed via a single instruction.
8364 The default is @option{-mlarge-data}. With this option the data area
8365 is limited to just below 2GB@. Programs that require more than 2GB of
8366 data must use @code{malloc} or @code{mmap} to allocate the data in the
8367 heap instead of in the program's data segment.
8369 When generating code for shared libraries, @option{-fpic} implies
8370 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
8374 @opindex msmall-text
8375 @opindex mlarge-text
8376 When @option{-msmall-text} is used, the compiler assumes that the
8377 code of the entire program (or shared library) fits in 4MB, and is
8378 thus reachable with a branch instruction. When @option{-msmall-data}
8379 is used, the compiler can assume that all local symbols share the
8380 same @code{$gp} value, and thus reduce the number of instructions
8381 required for a function call from 4 to 1.
8383 The default is @option{-mlarge-text}.
8385 @item -mcpu=@var{cpu_type}
8387 Set the instruction set and instruction scheduling parameters for
8388 machine type @var{cpu_type}. You can specify either the @samp{EV}
8389 style name or the corresponding chip number. GCC supports scheduling
8390 parameters for the EV4, EV5 and EV6 family of processors and will
8391 choose the default values for the instruction set from the processor
8392 you specify. If you do not specify a processor type, GCC will default
8393 to the processor on which the compiler was built.
8395 Supported values for @var{cpu_type} are
8401 Schedules as an EV4 and has no instruction set extensions.
8405 Schedules as an EV5 and has no instruction set extensions.
8409 Schedules as an EV5 and supports the BWX extension.
8414 Schedules as an EV5 and supports the BWX and MAX extensions.
8418 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
8422 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
8425 @item -mtune=@var{cpu_type}
8427 Set only the instruction scheduling parameters for machine type
8428 @var{cpu_type}. The instruction set is not changed.
8430 @item -mmemory-latency=@var{time}
8431 @opindex mmemory-latency
8432 Sets the latency the scheduler should assume for typical memory
8433 references as seen by the application. This number is highly
8434 dependent on the memory access patterns used by the application
8435 and the size of the external cache on the machine.
8437 Valid options for @var{time} are
8441 A decimal number representing clock cycles.
8447 The compiler contains estimates of the number of clock cycles for
8448 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8449 (also called Dcache, Scache, and Bcache), as well as to main memory.
8450 Note that L3 is only valid for EV5.
8455 @node DEC Alpha/VMS Options
8456 @subsection DEC Alpha/VMS Options
8458 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
8461 @item -mvms-return-codes
8462 @opindex mvms-return-codes
8463 Return VMS condition codes from main. The default is to return POSIX
8464 style condition (e.g.@ error) codes.
8468 @subsection FRV Options
8475 Only use the first 32 general purpose registers.
8480 Use all 64 general purpose registers.
8485 Use only the first 32 floating point registers.
8490 Use all 64 floating point registers
8493 @opindex mhard-float
8495 Use hardware instructions for floating point operations.
8498 @opindex msoft-float
8500 Use library routines for floating point operations.
8505 Dynamically allocate condition code registers.
8510 Do not try to dynamically allocate condition code registers, only
8511 use @code{icc0} and @code{fcc0}.
8516 Change ABI to use double word insns.
8521 Do not use double word instructions.
8526 Use floating point double instructions.
8531 Do not use floating point double instructions.
8536 Use media instructions.
8541 Do not use media instructions.
8546 Use multiply and add/subtract instructions.
8551 Do not use multiply and add/subtract instructions.
8556 Select the FDPIC ABI, that uses function descriptors to represent
8557 pointers to functions. Without any PIC/PIE-related options, it
8558 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
8559 assumes GOT entries and small data are within a 12-bit range from the
8560 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
8561 are computed with 32 bits.
8564 @opindex minline-plt
8566 Enable inlining of PLT entries in function calls to functions that are
8567 not known to bind locally. It has no effect without @option{-mfdpic}.
8568 It's enabled by default if optimizing for speed and compiling for
8569 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
8570 optimization option such as @option{-O3} or above is present in the
8576 Assume a large TLS segment when generating thread-local code.
8581 Do not assume a large TLS segment when generating thread-local code.
8586 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
8587 that is known to be in read-only sections. It's enabled by default,
8588 except for @option{-fpic} or @option{-fpie}: even though it may help
8589 make the global offset table smaller, it trades 1 instruction for 4.
8590 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
8591 one of which may be shared by multiple symbols, and it avoids the need
8592 for a GOT entry for the referenced symbol, so it's more likely to be a
8593 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
8595 @item -multilib-library-pic
8596 @opindex multilib-library-pic
8598 Link with the (library, not FD) pic libraries. It's implied by
8599 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
8600 @option{-fpic} without @option{-mfdpic}. You should never have to use
8606 Follow the EABI requirement of always creating a frame pointer whenever
8607 a stack frame is allocated. This option is enabled by default and can
8608 be disabled with @option{-mno-linked-fp}.
8611 @opindex mlong-calls
8613 Use indirect addressing to call functions outside the current
8614 compilation unit. This allows the functions to be placed anywhere
8615 within the 32-bit address space.
8617 @item -malign-labels
8618 @opindex malign-labels
8620 Try to align labels to an 8-byte boundary by inserting nops into the
8621 previous packet. This option only has an effect when VLIW packing
8622 is enabled. It doesn't create new packets; it merely adds nops to
8626 @opindex mlibrary-pic
8628 Generate position-independent EABI code.
8633 Use only the first four media accumulator registers.
8638 Use all eight media accumulator registers.
8643 Pack VLIW instructions.
8648 Do not pack VLIW instructions.
8653 Do not mark ABI switches in e_flags.
8658 Enable the use of conditional-move instructions (default).
8660 This switch is mainly for debugging the compiler and will likely be removed
8661 in a future version.
8663 @item -mno-cond-move
8664 @opindex mno-cond-move
8666 Disable the use of conditional-move instructions.
8668 This switch is mainly for debugging the compiler and will likely be removed
8669 in a future version.
8674 Enable the use of conditional set instructions (default).
8676 This switch is mainly for debugging the compiler and will likely be removed
8677 in a future version.
8682 Disable the use of conditional set instructions.
8684 This switch is mainly for debugging the compiler and will likely be removed
8685 in a future version.
8690 Enable the use of conditional execution (default).
8692 This switch is mainly for debugging the compiler and will likely be removed
8693 in a future version.
8695 @item -mno-cond-exec
8696 @opindex mno-cond-exec
8698 Disable the use of conditional execution.
8700 This switch is mainly for debugging the compiler and will likely be removed
8701 in a future version.
8704 @opindex mvliw-branch
8706 Run a pass to pack branches into VLIW instructions (default).
8708 This switch is mainly for debugging the compiler and will likely be removed
8709 in a future version.
8711 @item -mno-vliw-branch
8712 @opindex mno-vliw-branch
8714 Do not run a pass to pack branches into VLIW instructions.
8716 This switch is mainly for debugging the compiler and will likely be removed
8717 in a future version.
8719 @item -mmulti-cond-exec
8720 @opindex mmulti-cond-exec
8722 Enable optimization of @code{&&} and @code{||} in conditional execution
8725 This switch is mainly for debugging the compiler and will likely be removed
8726 in a future version.
8728 @item -mno-multi-cond-exec
8729 @opindex mno-multi-cond-exec
8731 Disable optimization of @code{&&} and @code{||} in conditional execution.
8733 This switch is mainly for debugging the compiler and will likely be removed
8734 in a future version.
8736 @item -mnested-cond-exec
8737 @opindex mnested-cond-exec
8739 Enable nested conditional execution optimizations (default).
8741 This switch is mainly for debugging the compiler and will likely be removed
8742 in a future version.
8744 @item -mno-nested-cond-exec
8745 @opindex mno-nested-cond-exec
8747 Disable nested conditional execution optimizations.
8749 This switch is mainly for debugging the compiler and will likely be removed
8750 in a future version.
8752 @item -moptimize-membar
8753 @opindex moptimize-membar
8755 This switch removes redundant @code{membar} instructions from the
8756 compiler generated code. It is enabled by default.
8758 @item -mno-optimize-membar
8759 @opindex mno-optimize-membar
8761 This switch disables the automatic removal of redundant @code{membar}
8762 instructions from the generated code.
8764 @item -mtomcat-stats
8765 @opindex mtomcat-stats
8767 Cause gas to print out tomcat statistics.
8769 @item -mcpu=@var{cpu}
8772 Select the processor type for which to generate code. Possible values are
8773 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8774 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8778 @node H8/300 Options
8779 @subsection H8/300 Options
8781 These @samp{-m} options are defined for the H8/300 implementations:
8786 Shorten some address references at link time, when possible; uses the
8787 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8788 ld, Using ld}, for a fuller description.
8792 Generate code for the H8/300H@.
8796 Generate code for the H8S@.
8800 Generate code for the H8S and H8/300H in the normal mode. This switch
8801 must be used either with @option{-mh} or @option{-ms}.
8805 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8809 Make @code{int} data 32 bits by default.
8813 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8814 The default for the H8/300H and H8S is to align longs and floats on 4
8816 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8817 This option has no effect on the H8/300.
8821 @subsection HPPA Options
8822 @cindex HPPA Options
8824 These @samp{-m} options are defined for the HPPA family of computers:
8827 @item -march=@var{architecture-type}
8829 Generate code for the specified architecture. The choices for
8830 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8831 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8832 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8833 architecture option for your machine. Code compiled for lower numbered
8834 architectures will run on higher numbered architectures, but not the
8838 @itemx -mpa-risc-1-1
8839 @itemx -mpa-risc-2-0
8840 @opindex mpa-risc-1-0
8841 @opindex mpa-risc-1-1
8842 @opindex mpa-risc-2-0
8843 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8846 @opindex mbig-switch
8847 Generate code suitable for big switch tables. Use this option only if
8848 the assembler/linker complain about out of range branches within a switch
8851 @item -mjump-in-delay
8852 @opindex mjump-in-delay
8853 Fill delay slots of function calls with unconditional jump instructions
8854 by modifying the return pointer for the function call to be the target
8855 of the conditional jump.
8857 @item -mdisable-fpregs
8858 @opindex mdisable-fpregs
8859 Prevent floating point registers from being used in any manner. This is
8860 necessary for compiling kernels which perform lazy context switching of
8861 floating point registers. If you use this option and attempt to perform
8862 floating point operations, the compiler will abort.
8864 @item -mdisable-indexing
8865 @opindex mdisable-indexing
8866 Prevent the compiler from using indexing address modes. This avoids some
8867 rather obscure problems when compiling MIG generated code under MACH@.
8869 @item -mno-space-regs
8870 @opindex mno-space-regs
8871 Generate code that assumes the target has no space registers. This allows
8872 GCC to generate faster indirect calls and use unscaled index address modes.
8874 Such code is suitable for level 0 PA systems and kernels.
8876 @item -mfast-indirect-calls
8877 @opindex mfast-indirect-calls
8878 Generate code that assumes calls never cross space boundaries. This
8879 allows GCC to emit code which performs faster indirect calls.
8881 This option will not work in the presence of shared libraries or nested
8884 @item -mfixed-range=@var{register-range}
8885 @opindex mfixed-range
8886 Generate code treating the given register range as fixed registers.
8887 A fixed register is one that the register allocator can not use. This is
8888 useful when compiling kernel code. A register range is specified as
8889 two registers separated by a dash. Multiple register ranges can be
8890 specified separated by a comma.
8892 @item -mlong-load-store
8893 @opindex mlong-load-store
8894 Generate 3-instruction load and store sequences as sometimes required by
8895 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8898 @item -mportable-runtime
8899 @opindex mportable-runtime
8900 Use the portable calling conventions proposed by HP for ELF systems.
8904 Enable the use of assembler directives only GAS understands.
8906 @item -mschedule=@var{cpu-type}
8908 Schedule code according to the constraints for the machine type
8909 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8910 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8911 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8912 proper scheduling option for your machine. The default scheduling is
8916 @opindex mlinker-opt
8917 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8918 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8919 linkers in which they give bogus error messages when linking some programs.
8922 @opindex msoft-float
8923 Generate output containing library calls for floating point.
8924 @strong{Warning:} the requisite libraries are not available for all HPPA
8925 targets. Normally the facilities of the machine's usual C compiler are
8926 used, but this cannot be done directly in cross-compilation. You must make
8927 your own arrangements to provide suitable library functions for
8928 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8929 does provide software floating point support.
8931 @option{-msoft-float} changes the calling convention in the output file;
8932 therefore, it is only useful if you compile @emph{all} of a program with
8933 this option. In particular, you need to compile @file{libgcc.a}, the
8934 library that comes with GCC, with @option{-msoft-float} in order for
8939 Generate the predefine, @code{_SIO}, for server IO@. The default is
8940 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8941 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
8942 options are available under HP-UX and HI-UX@.
8946 Use GNU ld specific options. This passes @option{-shared} to ld when
8947 building a shared library. It is the default when GCC is configured,
8948 explicitly or implicitly, with the GNU linker. This option does not
8949 have any affect on which ld is called, it only changes what parameters
8950 are passed to that ld. The ld that is called is determined by the
8951 @option{--with-ld} configure option, GCC's program search path, and
8952 finally by the user's @env{PATH}. The linker used by GCC can be printed
8953 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
8954 on the 64 bit HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
8958 Use HP ld specific options. This passes @option{-b} to ld when building
8959 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8960 links. It is the default when GCC is configured, explicitly or
8961 implicitly, with the HP linker. This option does not have any affect on
8962 which ld is called, it only changes what parameters are passed to that
8963 ld. The ld that is called is determined by the @option{--with-ld}
8964 configure option, GCC's program search path, and finally by the user's
8965 @env{PATH}. The linker used by GCC can be printed using @samp{which
8966 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
8967 HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
8970 @opindex mno-long-calls
8971 Generate code that uses long call sequences. This ensures that a call
8972 is always able to reach linker generated stubs. The default is to generate
8973 long calls only when the distance from the call site to the beginning
8974 of the function or translation unit, as the case may be, exceeds a
8975 predefined limit set by the branch type being used. The limits for
8976 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8977 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8980 Distances are measured from the beginning of functions when using the
8981 @option{-ffunction-sections} option, or when using the @option{-mgas}
8982 and @option{-mno-portable-runtime} options together under HP-UX with
8985 It is normally not desirable to use this option as it will degrade
8986 performance. However, it may be useful in large applications,
8987 particularly when partial linking is used to build the application.
8989 The types of long calls used depends on the capabilities of the
8990 assembler and linker, and the type of code being generated. The
8991 impact on systems that support long absolute calls, and long pic
8992 symbol-difference or pc-relative calls should be relatively small.
8993 However, an indirect call is used on 32-bit ELF systems in pic code
8994 and it is quite long.
8996 @item -munix=@var{unix-std}
8998 Generate compiler predefines and select a startfile for the specified
8999 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
9000 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
9001 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
9002 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
9003 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
9006 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
9007 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
9008 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
9009 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
9010 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
9011 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
9013 It is @emph{important} to note that this option changes the interfaces
9014 for various library routines. It also affects the operational behavior
9015 of the C library. Thus, @emph{extreme} care is needed in using this
9018 Library code that is intended to operate with more than one UNIX
9019 standard must test, set and restore the variable @var{__xpg4_extended_mask}
9020 as appropriate. Most GNU software doesn't provide this capability.
9024 Suppress the generation of link options to search libdld.sl when the
9025 @option{-static} option is specified on HP-UX 10 and later.
9029 The HP-UX implementation of setlocale in libc has a dependency on
9030 libdld.sl. There isn't an archive version of libdld.sl. Thus,
9031 when the @option{-static} option is specified, special link options
9032 are needed to resolve this dependency.
9034 On HP-UX 10 and later, the GCC driver adds the necessary options to
9035 link with libdld.sl when the @option{-static} option is specified.
9036 This causes the resulting binary to be dynamic. On the 64-bit port,
9037 the linkers generate dynamic binaries by default in any case. The
9038 @option{-nolibdld} option can be used to prevent the GCC driver from
9039 adding these link options.
9043 Add support for multithreading with the @dfn{dce thread} library
9044 under HP-UX@. This option sets flags for both the preprocessor and
9048 @node i386 and x86-64 Options
9049 @subsection Intel 386 and AMD x86-64 Options
9050 @cindex i386 Options
9051 @cindex x86-64 Options
9052 @cindex Intel 386 Options
9053 @cindex AMD x86-64 Options
9055 These @samp{-m} options are defined for the i386 and x86-64 family of
9059 @item -mtune=@var{cpu-type}
9061 Tune to @var{cpu-type} everything applicable about the generated code, except
9062 for the ABI and the set of available instructions. The choices for
9066 Produce code optimized for the most common IA32/AMD64/EM64T processors.
9067 If you know the CPU on which your code will run, then you should use
9068 the corresponding @option{-mtune} option instead of
9069 @option{-mtune=generic}. But, if you do not know exactly what CPU users
9070 of your application will have, then you should use this option.
9072 As new processors are deployed in the marketplace, the behavior of this
9073 option will change. Therefore, if you upgrade to a newer version of
9074 GCC, the code generated option will change to reflect the processors
9075 that were most common when that version of GCC was released.
9077 There is no @option{-march=generic} option because @option{-march}
9078 indicates the instruction set the compiler can use, and there is no
9079 generic instruction set applicable to all processors. In contrast,
9080 @option{-mtune} indicates the processor (or, in this case, collection of
9081 processors) for which the code is optimized.
9083 Original Intel's i386 CPU@.
9085 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
9087 Intel Pentium CPU with no MMX support.
9089 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
9091 Intel PentiumPro CPU@.
9093 Same as @code{generic}, but when used as @code{march} option, PentiumPro
9094 instruction set will be used, so the code will run on all i686 familly chips.
9096 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
9097 @item pentium3, pentium3m
9098 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
9101 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
9102 support. Used by Centrino notebooks.
9103 @item pentium4, pentium4m
9104 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
9106 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
9109 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
9110 SSE2 and SSE3 instruction set support.
9112 AMD K6 CPU with MMX instruction set support.
9114 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
9115 @item athlon, athlon-tbird
9116 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
9118 @item athlon-4, athlon-xp, athlon-mp
9119 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
9120 instruction set support.
9121 @item k8, opteron, athlon64, athlon-fx
9122 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
9123 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
9125 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
9128 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
9129 instruction set support.
9131 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
9132 implemented for this chip.)
9134 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
9135 implemented for this chip.)
9138 While picking a specific @var{cpu-type} will schedule things appropriately
9139 for that particular chip, the compiler will not generate any code that
9140 does not run on the i386 without the @option{-march=@var{cpu-type}} option
9143 @item -march=@var{cpu-type}
9145 Generate instructions for the machine type @var{cpu-type}. The choices
9146 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
9147 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
9149 @item -mcpu=@var{cpu-type}
9151 A deprecated synonym for @option{-mtune}.
9160 @opindex mpentiumpro
9161 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
9162 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
9163 These synonyms are deprecated.
9165 @item -mfpmath=@var{unit}
9167 Generate floating point arithmetics for selected unit @var{unit}. The choices
9172 Use the standard 387 floating point coprocessor present majority of chips and
9173 emulated otherwise. Code compiled with this option will run almost everywhere.
9174 The temporary results are computed in 80bit precision instead of precision
9175 specified by the type resulting in slightly different results compared to most
9176 of other chips. See @option{-ffloat-store} for more detailed description.
9178 This is the default choice for i386 compiler.
9181 Use scalar floating point instructions present in the SSE instruction set.
9182 This instruction set is supported by Pentium3 and newer chips, in the AMD line
9183 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
9184 instruction set supports only single precision arithmetics, thus the double and
9185 extended precision arithmetics is still done using 387. Later version, present
9186 only in Pentium4 and the future AMD x86-64 chips supports double precision
9189 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
9190 or @option{-msse2} switches to enable SSE extensions and make this option
9191 effective. For the x86-64 compiler, these extensions are enabled by default.
9193 The resulting code should be considerably faster in the majority of cases and avoid
9194 the numerical instability problems of 387 code, but may break some existing
9195 code that expects temporaries to be 80bit.
9197 This is the default choice for the x86-64 compiler.
9200 Attempt to utilize both instruction sets at once. This effectively double the
9201 amount of available registers and on chips with separate execution units for
9202 387 and SSE the execution resources too. Use this option with care, as it is
9203 still experimental, because the GCC register allocator does not model separate
9204 functional units well resulting in instable performance.
9207 @item -masm=@var{dialect}
9208 @opindex masm=@var{dialect}
9209 Output asm instructions using selected @var{dialect}. Supported
9210 choices are @samp{intel} or @samp{att} (the default one). Darwin does
9211 not support @samp{intel}.
9216 @opindex mno-ieee-fp
9217 Control whether or not the compiler uses IEEE floating point
9218 comparisons. These handle correctly the case where the result of a
9219 comparison is unordered.
9222 @opindex msoft-float
9223 Generate output containing library calls for floating point.
9224 @strong{Warning:} the requisite libraries are not part of GCC@.
9225 Normally the facilities of the machine's usual C compiler are used, but
9226 this can't be done directly in cross-compilation. You must make your
9227 own arrangements to provide suitable library functions for
9230 On machines where a function returns floating point results in the 80387
9231 register stack, some floating point opcodes may be emitted even if
9232 @option{-msoft-float} is used.
9234 @item -mno-fp-ret-in-387
9235 @opindex mno-fp-ret-in-387
9236 Do not use the FPU registers for return values of functions.
9238 The usual calling convention has functions return values of types
9239 @code{float} and @code{double} in an FPU register, even if there
9240 is no FPU@. The idea is that the operating system should emulate
9243 The option @option{-mno-fp-ret-in-387} causes such values to be returned
9244 in ordinary CPU registers instead.
9246 @item -mno-fancy-math-387
9247 @opindex mno-fancy-math-387
9248 Some 387 emulators do not support the @code{sin}, @code{cos} and
9249 @code{sqrt} instructions for the 387. Specify this option to avoid
9250 generating those instructions. This option is the default on FreeBSD,
9251 OpenBSD and NetBSD@. This option is overridden when @option{-march}
9252 indicates that the target cpu will always have an FPU and so the
9253 instruction will not need emulation. As of revision 2.6.1, these
9254 instructions are not generated unless you also use the
9255 @option{-funsafe-math-optimizations} switch.
9257 @item -malign-double
9258 @itemx -mno-align-double
9259 @opindex malign-double
9260 @opindex mno-align-double
9261 Control whether GCC aligns @code{double}, @code{long double}, and
9262 @code{long long} variables on a two word boundary or a one word
9263 boundary. Aligning @code{double} variables on a two word boundary will
9264 produce code that runs somewhat faster on a @samp{Pentium} at the
9265 expense of more memory.
9267 @strong{Warning:} if you use the @option{-malign-double} switch,
9268 structures containing the above types will be aligned differently than
9269 the published application binary interface specifications for the 386
9270 and will not be binary compatible with structures in code compiled
9271 without that switch.
9273 @item -m96bit-long-double
9274 @itemx -m128bit-long-double
9275 @opindex m96bit-long-double
9276 @opindex m128bit-long-double
9277 These switches control the size of @code{long double} type. The i386
9278 application binary interface specifies the size to be 96 bits,
9279 so @option{-m96bit-long-double} is the default in 32 bit mode.
9281 Modern architectures (Pentium and newer) would prefer @code{long double}
9282 to be aligned to an 8 or 16 byte boundary. In arrays or structures
9283 conforming to the ABI, this would not be possible. So specifying a
9284 @option{-m128bit-long-double} will align @code{long double}
9285 to a 16 byte boundary by padding the @code{long double} with an additional
9288 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
9289 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
9291 Notice that neither of these options enable any extra precision over the x87
9292 standard of 80 bits for a @code{long double}.
9294 @strong{Warning:} if you override the default value for your target ABI, the
9295 structures and arrays containing @code{long double} variables will change
9296 their size as well as function calling convention for function taking
9297 @code{long double} will be modified. Hence they will not be binary
9298 compatible with arrays or structures in code compiled without that switch.
9300 @item -mmlarge-data-threshold=@var{number}
9301 @opindex mlarge-data-threshold=@var{number}
9302 When @option{-mcmodel=medium} is specified, the data greater than
9303 @var{threshold} are placed in large data section. This value must be the
9304 same across all object linked into the binary and defaults to 65535.
9307 @itemx -mno-svr3-shlib
9308 @opindex msvr3-shlib
9309 @opindex mno-svr3-shlib
9310 Control whether GCC places uninitialized local variables into the
9311 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
9312 into @code{bss}. These options are meaningful only on System V Release 3.
9316 Use a different function-calling convention, in which functions that
9317 take a fixed number of arguments return with the @code{ret} @var{num}
9318 instruction, which pops their arguments while returning. This saves one
9319 instruction in the caller since there is no need to pop the arguments
9322 You can specify that an individual function is called with this calling
9323 sequence with the function attribute @samp{stdcall}. You can also
9324 override the @option{-mrtd} option by using the function attribute
9325 @samp{cdecl}. @xref{Function Attributes}.
9327 @strong{Warning:} this calling convention is incompatible with the one
9328 normally used on Unix, so you cannot use it if you need to call
9329 libraries compiled with the Unix compiler.
9331 Also, you must provide function prototypes for all functions that
9332 take variable numbers of arguments (including @code{printf});
9333 otherwise incorrect code will be generated for calls to those
9336 In addition, seriously incorrect code will result if you call a
9337 function with too many arguments. (Normally, extra arguments are
9338 harmlessly ignored.)
9340 @item -mregparm=@var{num}
9342 Control how many registers are used to pass integer arguments. By
9343 default, no registers are used to pass arguments, and at most 3
9344 registers can be used. You can control this behavior for a specific
9345 function by using the function attribute @samp{regparm}.
9346 @xref{Function Attributes}.
9348 @strong{Warning:} if you use this switch, and
9349 @var{num} is nonzero, then you must build all modules with the same
9350 value, including any libraries. This includes the system libraries and
9354 @opindex msseregparm
9355 Use SSE register passing conventions for float and double arguments
9356 and return values. You can control this behavior for a specific
9357 function by using the function attribute @samp{sseregparm}.
9358 @xref{Function Attributes}.
9360 @strong{Warning:} if you use this switch then you must build all
9361 modules with the same value, including any libraries. This includes
9362 the system libraries and startup modules.
9364 @item -mpreferred-stack-boundary=@var{num}
9365 @opindex mpreferred-stack-boundary
9366 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
9367 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
9368 the default is 4 (16 bytes or 128 bits), except when optimizing for code
9369 size (@option{-Os}), in which case the default is the minimum correct
9370 alignment (4 bytes for x86, and 8 bytes for x86-64).
9372 On Pentium and PentiumPro, @code{double} and @code{long double} values
9373 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
9374 suffer significant run time performance penalties. On Pentium III, the
9375 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
9376 penalties if it is not 16 byte aligned.
9378 To ensure proper alignment of this values on the stack, the stack boundary
9379 must be as aligned as that required by any value stored on the stack.
9380 Further, every function must be generated such that it keeps the stack
9381 aligned. Thus calling a function compiled with a higher preferred
9382 stack boundary from a function compiled with a lower preferred stack
9383 boundary will most likely misalign the stack. It is recommended that
9384 libraries that use callbacks always use the default setting.
9386 This extra alignment does consume extra stack space, and generally
9387 increases code size. Code that is sensitive to stack space usage, such
9388 as embedded systems and operating system kernels, may want to reduce the
9389 preferred alignment to @option{-mpreferred-stack-boundary=2}.
9407 These switches enable or disable the use of instructions in the MMX,
9408 SSE, SSE2 or 3DNow! extended instruction sets. These extensions are
9409 also available as built-in functions: see @ref{X86 Built-in Functions},
9410 for details of the functions enabled and disabled by these switches.
9412 To have SSE/SSE2 instructions generated automatically from floating-point
9413 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
9415 These options will enable GCC to use these extended instructions in
9416 generated code, even without @option{-mfpmath=sse}. Applications which
9417 perform runtime CPU detection must compile separate files for each
9418 supported architecture, using the appropriate flags. In particular,
9419 the file containing the CPU detection code should be compiled without
9423 @itemx -mno-push-args
9425 @opindex mno-push-args
9426 Use PUSH operations to store outgoing parameters. This method is shorter
9427 and usually equally fast as method using SUB/MOV operations and is enabled
9428 by default. In some cases disabling it may improve performance because of
9429 improved scheduling and reduced dependencies.
9431 @item -maccumulate-outgoing-args
9432 @opindex maccumulate-outgoing-args
9433 If enabled, the maximum amount of space required for outgoing arguments will be
9434 computed in the function prologue. This is faster on most modern CPUs
9435 because of reduced dependencies, improved scheduling and reduced stack usage
9436 when preferred stack boundary is not equal to 2. The drawback is a notable
9437 increase in code size. This switch implies @option{-mno-push-args}.
9441 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
9442 on thread-safe exception handling must compile and link all code with the
9443 @option{-mthreads} option. When compiling, @option{-mthreads} defines
9444 @option{-D_MT}; when linking, it links in a special thread helper library
9445 @option{-lmingwthrd} which cleans up per thread exception handling data.
9447 @item -mno-align-stringops
9448 @opindex mno-align-stringops
9449 Do not align destination of inlined string operations. This switch reduces
9450 code size and improves performance in case the destination is already aligned,
9451 but GCC doesn't know about it.
9453 @item -minline-all-stringops
9454 @opindex minline-all-stringops
9455 By default GCC inlines string operations only when destination is known to be
9456 aligned at least to 4 byte boundary. This enables more inlining, increase code
9457 size, but may improve performance of code that depends on fast memcpy, strlen
9458 and memset for short lengths.
9460 @item -momit-leaf-frame-pointer
9461 @opindex momit-leaf-frame-pointer
9462 Don't keep the frame pointer in a register for leaf functions. This
9463 avoids the instructions to save, set up and restore frame pointers and
9464 makes an extra register available in leaf functions. The option
9465 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9466 which might make debugging harder.
9468 @item -mtls-direct-seg-refs
9469 @itemx -mno-tls-direct-seg-refs
9470 @opindex mtls-direct-seg-refs
9471 Controls whether TLS variables may be accessed with offsets from the
9472 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
9473 or whether the thread base pointer must be added. Whether or not this
9474 is legal depends on the operating system, and whether it maps the
9475 segment to cover the entire TLS area.
9477 For systems that use GNU libc, the default is on.
9480 These @samp{-m} switches are supported in addition to the above
9481 on AMD x86-64 processors in 64-bit environments.
9488 Generate code for a 32-bit or 64-bit environment.
9489 The 32-bit environment sets int, long and pointer to 32 bits and
9490 generates code that runs on any i386 system.
9491 The 64-bit environment sets int to 32 bits and long and pointer
9492 to 64 bits and generates code for AMD's x86-64 architecture.
9495 @opindex no-red-zone
9496 Do not use a so called red zone for x86-64 code. The red zone is mandated
9497 by the x86-64 ABI, it is a 128-byte area beyond the location of the
9498 stack pointer that will not be modified by signal or interrupt handlers
9499 and therefore can be used for temporary data without adjusting the stack
9500 pointer. The flag @option{-mno-red-zone} disables this red zone.
9502 @item -mcmodel=small
9503 @opindex mcmodel=small
9504 Generate code for the small code model: the program and its symbols must
9505 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
9506 Programs can be statically or dynamically linked. This is the default
9509 @item -mcmodel=kernel
9510 @opindex mcmodel=kernel
9511 Generate code for the kernel code model. The kernel runs in the
9512 negative 2 GB of the address space.
9513 This model has to be used for Linux kernel code.
9515 @item -mcmodel=medium
9516 @opindex mcmodel=medium
9517 Generate code for the medium model: The program is linked in the lower 2
9518 GB of the address space but symbols can be located anywhere in the
9519 address space. Programs can be statically or dynamically linked, but
9520 building of shared libraries are not supported with the medium model.
9522 @item -mcmodel=large
9523 @opindex mcmodel=large
9524 Generate code for the large model: This model makes no assumptions
9525 about addresses and sizes of sections. Currently GCC does not implement
9530 @subsection IA-64 Options
9531 @cindex IA-64 Options
9533 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9537 @opindex mbig-endian
9538 Generate code for a big endian target. This is the default for HP-UX@.
9540 @item -mlittle-endian
9541 @opindex mlittle-endian
9542 Generate code for a little endian target. This is the default for AIX5
9549 Generate (or don't) code for the GNU assembler. This is the default.
9550 @c Also, this is the default if the configure option @option{--with-gnu-as}
9557 Generate (or don't) code for the GNU linker. This is the default.
9558 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9563 Generate code that does not use a global pointer register. The result
9564 is not position independent code, and violates the IA-64 ABI@.
9566 @item -mvolatile-asm-stop
9567 @itemx -mno-volatile-asm-stop
9568 @opindex mvolatile-asm-stop
9569 @opindex mno-volatile-asm-stop
9570 Generate (or don't) a stop bit immediately before and after volatile asm
9573 @item -mregister-names
9574 @itemx -mno-register-names
9575 @opindex mregister-names
9576 @opindex mno-register-names
9577 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9578 the stacked registers. This may make assembler output more readable.
9584 Disable (or enable) optimizations that use the small data section. This may
9585 be useful for working around optimizer bugs.
9588 @opindex mconstant-gp
9589 Generate code that uses a single constant global pointer value. This is
9590 useful when compiling kernel code.
9594 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9595 This is useful when compiling firmware code.
9597 @item -minline-float-divide-min-latency
9598 @opindex minline-float-divide-min-latency
9599 Generate code for inline divides of floating point values
9600 using the minimum latency algorithm.
9602 @item -minline-float-divide-max-throughput
9603 @opindex minline-float-divide-max-throughput
9604 Generate code for inline divides of floating point values
9605 using the maximum throughput algorithm.
9607 @item -minline-int-divide-min-latency
9608 @opindex minline-int-divide-min-latency
9609 Generate code for inline divides of integer values
9610 using the minimum latency algorithm.
9612 @item -minline-int-divide-max-throughput
9613 @opindex minline-int-divide-max-throughput
9614 Generate code for inline divides of integer values
9615 using the maximum throughput algorithm.
9617 @item -minline-sqrt-min-latency
9618 @opindex minline-sqrt-min-latency
9619 Generate code for inline square roots
9620 using the minimum latency algorithm.
9622 @item -minline-sqrt-max-throughput
9623 @opindex minline-sqrt-max-throughput
9624 Generate code for inline square roots
9625 using the maximum throughput algorithm.
9627 @item -mno-dwarf2-asm
9629 @opindex mno-dwarf2-asm
9630 @opindex mdwarf2-asm
9631 Don't (or do) generate assembler code for the DWARF2 line number debugging
9632 info. This may be useful when not using the GNU assembler.
9634 @item -mearly-stop-bits
9635 @itemx -mno-early-stop-bits
9636 @opindex mearly-stop-bits
9637 @opindex mno-early-stop-bits
9638 Allow stop bits to be placed earlier than immediately preceding the
9639 instruction that triggered the stop bit. This can improve instruction
9640 scheduling, but does not always do so.
9642 @item -mfixed-range=@var{register-range}
9643 @opindex mfixed-range
9644 Generate code treating the given register range as fixed registers.
9645 A fixed register is one that the register allocator can not use. This is
9646 useful when compiling kernel code. A register range is specified as
9647 two registers separated by a dash. Multiple register ranges can be
9648 specified separated by a comma.
9650 @item -mtls-size=@var{tls-size}
9652 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
9655 @item -mtune=@var{cpu-type}
9657 Tune the instruction scheduling for a particular CPU, Valid values are
9658 itanium, itanium1, merced, itanium2, and mckinley.
9664 Add support for multithreading using the POSIX threads library. This
9665 option sets flags for both the preprocessor and linker. It does
9666 not affect the thread safety of object code produced by the compiler or
9667 that of libraries supplied with it. These are HP-UX specific flags.
9673 Generate code for a 32-bit or 64-bit environment.
9674 The 32-bit environment sets int, long and pointer to 32 bits.
9675 The 64-bit environment sets int to 32 bits and long and pointer
9676 to 64 bits. These are HP-UX specific flags.
9681 @subsection M32C Options
9682 @cindex M32C options
9685 @item -mcpu=@var{name}
9687 Select the CPU for which code is generated. @var{name} may be one of
9688 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
9689 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
9694 Specifies that the program will be run on the simulator. This causes
9695 an alternate runtime library to be linked in which supports, for
9696 example, file I/O. You must not use this option when generating
9697 programs that will run on real hardware; you must provide your own
9698 runtime library for whatever I/O functions are needed.
9700 @item -memregs=@var{number}
9702 Specifies the number of memory-based pseudo-registers GCC will use
9703 during code generation. These pseudo-registers will be used like real
9704 registers, so there is a tradeoff between GCC's ability to fit the
9705 code into available registers, and the performance penalty of using
9706 memory instead of registers. Note that all modules in a program must
9707 be compiled with the same value for this option. Because of that, you
9708 must not use this option with the default runtime libraries gcc
9713 @node M32R/D Options
9714 @subsection M32R/D Options
9715 @cindex M32R/D options
9717 These @option{-m} options are defined for Renesas M32R/D architectures:
9722 Generate code for the M32R/2@.
9726 Generate code for the M32R/X@.
9730 Generate code for the M32R@. This is the default.
9733 @opindex mmodel=small
9734 Assume all objects live in the lower 16MB of memory (so that their addresses
9735 can be loaded with the @code{ld24} instruction), and assume all subroutines
9736 are reachable with the @code{bl} instruction.
9737 This is the default.
9739 The addressability of a particular object can be set with the
9740 @code{model} attribute.
9742 @item -mmodel=medium
9743 @opindex mmodel=medium
9744 Assume objects may be anywhere in the 32-bit address space (the compiler
9745 will generate @code{seth/add3} instructions to load their addresses), and
9746 assume all subroutines are reachable with the @code{bl} instruction.
9749 @opindex mmodel=large
9750 Assume objects may be anywhere in the 32-bit address space (the compiler
9751 will generate @code{seth/add3} instructions to load their addresses), and
9752 assume subroutines may not be reachable with the @code{bl} instruction
9753 (the compiler will generate the much slower @code{seth/add3/jl}
9754 instruction sequence).
9757 @opindex msdata=none
9758 Disable use of the small data area. Variables will be put into
9759 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
9760 @code{section} attribute has been specified).
9761 This is the default.
9763 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
9764 Objects may be explicitly put in the small data area with the
9765 @code{section} attribute using one of these sections.
9768 @opindex msdata=sdata
9769 Put small global and static data in the small data area, but do not
9770 generate special code to reference them.
9774 Put small global and static data in the small data area, and generate
9775 special instructions to reference them.
9779 @cindex smaller data references
9780 Put global and static objects less than or equal to @var{num} bytes
9781 into the small data or bss sections instead of the normal data or bss
9782 sections. The default value of @var{num} is 8.
9783 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
9784 for this option to have any effect.
9786 All modules should be compiled with the same @option{-G @var{num}} value.
9787 Compiling with different values of @var{num} may or may not work; if it
9788 doesn't the linker will give an error message---incorrect code will not be
9793 Makes the M32R specific code in the compiler display some statistics
9794 that might help in debugging programs.
9797 @opindex malign-loops
9798 Align all loops to a 32-byte boundary.
9800 @item -mno-align-loops
9801 @opindex mno-align-loops
9802 Do not enforce a 32-byte alignment for loops. This is the default.
9804 @item -missue-rate=@var{number}
9805 @opindex missue-rate=@var{number}
9806 Issue @var{number} instructions per cycle. @var{number} can only be 1
9809 @item -mbranch-cost=@var{number}
9810 @opindex mbranch-cost=@var{number}
9811 @var{number} can only be 1 or 2. If it is 1 then branches will be
9812 preferred over conditional code, if it is 2, then the opposite will
9815 @item -mflush-trap=@var{number}
9816 @opindex mflush-trap=@var{number}
9817 Specifies the trap number to use to flush the cache. The default is
9818 12. Valid numbers are between 0 and 15 inclusive.
9820 @item -mno-flush-trap
9821 @opindex mno-flush-trap
9822 Specifies that the cache cannot be flushed by using a trap.
9824 @item -mflush-func=@var{name}
9825 @opindex mflush-func=@var{name}
9826 Specifies the name of the operating system function to call to flush
9827 the cache. The default is @emph{_flush_cache}, but a function call
9828 will only be used if a trap is not available.
9830 @item -mno-flush-func
9831 @opindex mno-flush-func
9832 Indicates that there is no OS function for flushing the cache.
9836 @node M680x0 Options
9837 @subsection M680x0 Options
9838 @cindex M680x0 options
9840 These are the @samp{-m} options defined for the 68000 series. The default
9841 values for these options depends on which style of 68000 was selected when
9842 the compiler was configured; the defaults for the most common choices are
9850 Generate output for a 68000. This is the default
9851 when the compiler is configured for 68000-based systems.
9853 Use this option for microcontrollers with a 68000 or EC000 core,
9854 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
9860 Generate output for a 68020. This is the default
9861 when the compiler is configured for 68020-based systems.
9865 Generate output containing 68881 instructions for floating point.
9866 This is the default for most 68020 systems unless @option{--nfp} was
9867 specified when the compiler was configured.
9871 Generate output for a 68030. This is the default when the compiler is
9872 configured for 68030-based systems.
9876 Generate output for a 68040. This is the default when the compiler is
9877 configured for 68040-based systems.
9879 This option inhibits the use of 68881/68882 instructions that have to be
9880 emulated by software on the 68040. Use this option if your 68040 does not
9881 have code to emulate those instructions.
9885 Generate output for a 68060. This is the default when the compiler is
9886 configured for 68060-based systems.
9888 This option inhibits the use of 68020 and 68881/68882 instructions that
9889 have to be emulated by software on the 68060. Use this option if your 68060
9890 does not have code to emulate those instructions.
9894 Generate output for a CPU32. This is the default
9895 when the compiler is configured for CPU32-based systems.
9897 Use this option for microcontrollers with a
9898 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
9899 68336, 68340, 68341, 68349 and 68360.
9903 Generate output for a 520X ``coldfire'' family cpu. This is the default
9904 when the compiler is configured for 520X-based systems.
9906 Use this option for microcontroller with a 5200 core, including
9907 the MCF5202, MCF5203, MCF5204 and MCF5202.
9912 Generate output for a 68040, without using any of the new instructions.
9913 This results in code which can run relatively efficiently on either a
9914 68020/68881 or a 68030 or a 68040. The generated code does use the
9915 68881 instructions that are emulated on the 68040.
9919 Generate output for a 68060, without using any of the new instructions.
9920 This results in code which can run relatively efficiently on either a
9921 68020/68881 or a 68030 or a 68040. The generated code does use the
9922 68881 instructions that are emulated on the 68060.
9925 @opindex msoft-float
9926 Generate output containing library calls for floating point.
9927 @strong{Warning:} the requisite libraries are not available for all m68k
9928 targets. Normally the facilities of the machine's usual C compiler are
9929 used, but this can't be done directly in cross-compilation. You must
9930 make your own arrangements to provide suitable library functions for
9931 cross-compilation. The embedded targets @samp{m68k-*-aout} and
9932 @samp{m68k-*-coff} do provide software floating point support.
9936 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9937 Additionally, parameters passed on the stack are also aligned to a
9938 16-bit boundary even on targets whose API mandates promotion to 32-bit.
9941 @opindex mnobitfield
9942 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
9943 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
9947 Do use the bit-field instructions. The @option{-m68020} option implies
9948 @option{-mbitfield}. This is the default if you use a configuration
9949 designed for a 68020.
9953 Use a different function-calling convention, in which functions
9954 that take a fixed number of arguments return with the @code{rtd}
9955 instruction, which pops their arguments while returning. This
9956 saves one instruction in the caller since there is no need to pop
9957 the arguments there.
9959 This calling convention is incompatible with the one normally
9960 used on Unix, so you cannot use it if you need to call libraries
9961 compiled with the Unix compiler.
9963 Also, you must provide function prototypes for all functions that
9964 take variable numbers of arguments (including @code{printf});
9965 otherwise incorrect code will be generated for calls to those
9968 In addition, seriously incorrect code will result if you call a
9969 function with too many arguments. (Normally, extra arguments are
9970 harmlessly ignored.)
9972 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
9973 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
9976 @itemx -mno-align-int
9978 @opindex mno-align-int
9979 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
9980 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
9981 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
9982 Aligning variables on 32-bit boundaries produces code that runs somewhat
9983 faster on processors with 32-bit busses at the expense of more memory.
9985 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
9986 align structures containing the above types differently than
9987 most published application binary interface specifications for the m68k.
9991 Use the pc-relative addressing mode of the 68000 directly, instead of
9992 using a global offset table. At present, this option implies @option{-fpic},
9993 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
9994 not presently supported with @option{-mpcrel}, though this could be supported for
9995 68020 and higher processors.
9997 @item -mno-strict-align
9998 @itemx -mstrict-align
9999 @opindex mno-strict-align
10000 @opindex mstrict-align
10001 Do not (do) assume that unaligned memory references will be handled by
10005 Generate code that allows the data segment to be located in a different
10006 area of memory from the text segment. This allows for execute in place in
10007 an environment without virtual memory management. This option implies
10010 @item -mno-sep-data
10011 Generate code that assumes that the data segment follows the text segment.
10012 This is the default.
10014 @item -mid-shared-library
10015 Generate code that supports shared libraries via the library ID method.
10016 This allows for execute in place and shared libraries in an environment
10017 without virtual memory management. This option implies @option{-fPIC}.
10019 @item -mno-id-shared-library
10020 Generate code that doesn't assume ID based shared libraries are being used.
10021 This is the default.
10023 @item -mshared-library-id=n
10024 Specified the identification number of the ID based shared library being
10025 compiled. Specifying a value of 0 will generate more compact code, specifying
10026 other values will force the allocation of that number to the current
10027 library but is no more space or time efficient than omitting this option.
10031 @node M68hc1x Options
10032 @subsection M68hc1x Options
10033 @cindex M68hc1x options
10035 These are the @samp{-m} options defined for the 68hc11 and 68hc12
10036 microcontrollers. The default values for these options depends on
10037 which style of microcontroller was selected when the compiler was configured;
10038 the defaults for the most common choices are given below.
10045 Generate output for a 68HC11. This is the default
10046 when the compiler is configured for 68HC11-based systems.
10052 Generate output for a 68HC12. This is the default
10053 when the compiler is configured for 68HC12-based systems.
10059 Generate output for a 68HCS12.
10061 @item -mauto-incdec
10062 @opindex mauto-incdec
10063 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
10070 Enable the use of 68HC12 min and max instructions.
10073 @itemx -mno-long-calls
10074 @opindex mlong-calls
10075 @opindex mno-long-calls
10076 Treat all calls as being far away (near). If calls are assumed to be
10077 far away, the compiler will use the @code{call} instruction to
10078 call a function and the @code{rtc} instruction for returning.
10082 Consider type @code{int} to be 16 bits wide, like @code{short int}.
10084 @item -msoft-reg-count=@var{count}
10085 @opindex msoft-reg-count
10086 Specify the number of pseudo-soft registers which are used for the
10087 code generation. The maximum number is 32. Using more pseudo-soft
10088 register may or may not result in better code depending on the program.
10089 The default is 4 for 68HC11 and 2 for 68HC12.
10093 @node MCore Options
10094 @subsection MCore Options
10095 @cindex MCore options
10097 These are the @samp{-m} options defined for the Motorola M*Core
10103 @itemx -mno-hardlit
10105 @opindex mno-hardlit
10106 Inline constants into the code stream if it can be done in two
10107 instructions or less.
10113 Use the divide instruction. (Enabled by default).
10115 @item -mrelax-immediate
10116 @itemx -mno-relax-immediate
10117 @opindex mrelax-immediate
10118 @opindex mno-relax-immediate
10119 Allow arbitrary sized immediates in bit operations.
10121 @item -mwide-bitfields
10122 @itemx -mno-wide-bitfields
10123 @opindex mwide-bitfields
10124 @opindex mno-wide-bitfields
10125 Always treat bit-fields as int-sized.
10127 @item -m4byte-functions
10128 @itemx -mno-4byte-functions
10129 @opindex m4byte-functions
10130 @opindex mno-4byte-functions
10131 Force all functions to be aligned to a four byte boundary.
10133 @item -mcallgraph-data
10134 @itemx -mno-callgraph-data
10135 @opindex mcallgraph-data
10136 @opindex mno-callgraph-data
10137 Emit callgraph information.
10140 @itemx -mno-slow-bytes
10141 @opindex mslow-bytes
10142 @opindex mno-slow-bytes
10143 Prefer word access when reading byte quantities.
10145 @item -mlittle-endian
10146 @itemx -mbig-endian
10147 @opindex mlittle-endian
10148 @opindex mbig-endian
10149 Generate code for a little endian target.
10155 Generate code for the 210 processor.
10159 @subsection MIPS Options
10160 @cindex MIPS options
10166 Generate big-endian code.
10170 Generate little-endian code. This is the default for @samp{mips*el-*-*}
10173 @item -march=@var{arch}
10175 Generate code that will run on @var{arch}, which can be the name of a
10176 generic MIPS ISA, or the name of a particular processor.
10178 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
10179 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
10180 The processor names are:
10181 @samp{4kc}, @samp{4km}, @samp{4kp},
10182 @samp{5kc}, @samp{5kf},
10184 @samp{24k}, @samp{24kc}, @samp{24kf}, @samp{24kx},
10187 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
10188 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
10189 @samp{rm7000}, @samp{rm9000},
10192 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
10193 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
10194 The special value @samp{from-abi} selects the
10195 most compatible architecture for the selected ABI (that is,
10196 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
10198 In processor names, a final @samp{000} can be abbreviated as @samp{k}
10199 (for example, @samp{-march=r2k}). Prefixes are optional, and
10200 @samp{vr} may be written @samp{r}.
10202 GCC defines two macros based on the value of this option. The first
10203 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
10204 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
10205 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
10206 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
10207 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
10209 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
10210 above. In other words, it will have the full prefix and will not
10211 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
10212 the macro names the resolved architecture (either @samp{"mips1"} or
10213 @samp{"mips3"}). It names the default architecture when no
10214 @option{-march} option is given.
10216 @item -mtune=@var{arch}
10218 Optimize for @var{arch}. Among other things, this option controls
10219 the way instructions are scheduled, and the perceived cost of arithmetic
10220 operations. The list of @var{arch} values is the same as for
10223 When this option is not used, GCC will optimize for the processor
10224 specified by @option{-march}. By using @option{-march} and
10225 @option{-mtune} together, it is possible to generate code that will
10226 run on a family of processors, but optimize the code for one
10227 particular member of that family.
10229 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
10230 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
10231 @samp{-march} ones described above.
10235 Equivalent to @samp{-march=mips1}.
10239 Equivalent to @samp{-march=mips2}.
10243 Equivalent to @samp{-march=mips3}.
10247 Equivalent to @samp{-march=mips4}.
10251 Equivalent to @samp{-march=mips32}.
10255 Equivalent to @samp{-march=mips32r2}.
10259 Equivalent to @samp{-march=mips64}.
10264 @opindex mno-mips16
10265 Generate (do not generate) MIPS16 code. If GCC is targetting a
10266 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
10278 Generate code for the given ABI@.
10280 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
10281 generates 64-bit code when you select a 64-bit architecture, but you
10282 can use @option{-mgp32} to get 32-bit code instead.
10284 For information about the O64 ABI, see
10285 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
10288 @itemx -mno-abicalls
10290 @opindex mno-abicalls
10291 Generate (do not generate) SVR4-style position-independent code.
10292 @option{-mabicalls} is the default for SVR4-based systems.
10298 Lift (do not lift) the usual restrictions on the size of the global
10301 GCC normally uses a single instruction to load values from the GOT@.
10302 While this is relatively efficient, it will only work if the GOT
10303 is smaller than about 64k. Anything larger will cause the linker
10304 to report an error such as:
10306 @cindex relocation truncated to fit (MIPS)
10308 relocation truncated to fit: R_MIPS_GOT16 foobar
10311 If this happens, you should recompile your code with @option{-mxgot}.
10312 It should then work with very large GOTs, although it will also be
10313 less efficient, since it will take three instructions to fetch the
10314 value of a global symbol.
10316 Note that some linkers can create multiple GOTs. If you have such a
10317 linker, you should only need to use @option{-mxgot} when a single object
10318 file accesses more than 64k's worth of GOT entries. Very few do.
10320 These options have no effect unless GCC is generating position
10325 Assume that general-purpose registers are 32 bits wide.
10329 Assume that general-purpose registers are 64 bits wide.
10333 Assume that floating-point registers are 32 bits wide.
10337 Assume that floating-point registers are 64 bits wide.
10340 @opindex mhard-float
10341 Use floating-point coprocessor instructions.
10344 @opindex msoft-float
10345 Do not use floating-point coprocessor instructions. Implement
10346 floating-point calculations using library calls instead.
10348 @item -msingle-float
10349 @opindex msingle-float
10350 Assume that the floating-point coprocessor only supports single-precision
10353 @itemx -mdouble-float
10354 @opindex mdouble-float
10355 Assume that the floating-point coprocessor supports double-precision
10356 operations. This is the default.
10362 Use (do not use) the MIPS DSP ASE. @xref{MIPS DSP Built-in Functions}.
10364 @itemx -mpaired-single
10365 @itemx -mno-paired-single
10366 @opindex mpaired-single
10367 @opindex mno-paired-single
10368 Use (do not use) paired-single floating-point instructions.
10369 @xref{MIPS Paired-Single Support}. This option can only be used
10370 when generating 64-bit code and requires hardware floating-point
10371 support to be enabled.
10376 @opindex mno-mips3d
10377 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
10378 The option @option{-mips3d} implies @option{-mpaired-single}.
10382 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
10383 an explanation of the default and the way that the pointer size is
10388 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
10390 The default size of @code{int}s, @code{long}s and pointers depends on
10391 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
10392 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
10393 32-bit @code{long}s. Pointers are the same size as @code{long}s,
10394 or the same size as integer registers, whichever is smaller.
10400 Assume (do not assume) that all symbols have 32-bit values, regardless
10401 of the selected ABI@. This option is useful in combination with
10402 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
10403 to generate shorter and faster references to symbolic addresses.
10407 @cindex smaller data references (MIPS)
10408 @cindex gp-relative references (MIPS)
10409 Put global and static items less than or equal to @var{num} bytes into
10410 the small data or bss section instead of the normal data or bss section.
10411 This allows the data to be accessed using a single instruction.
10413 All modules should be compiled with the same @option{-G @var{num}}
10416 @item -membedded-data
10417 @itemx -mno-embedded-data
10418 @opindex membedded-data
10419 @opindex mno-embedded-data
10420 Allocate variables to the read-only data section first if possible, then
10421 next in the small data section if possible, otherwise in data. This gives
10422 slightly slower code than the default, but reduces the amount of RAM required
10423 when executing, and thus may be preferred for some embedded systems.
10425 @item -muninit-const-in-rodata
10426 @itemx -mno-uninit-const-in-rodata
10427 @opindex muninit-const-in-rodata
10428 @opindex mno-uninit-const-in-rodata
10429 Put uninitialized @code{const} variables in the read-only data section.
10430 This option is only meaningful in conjunction with @option{-membedded-data}.
10432 @item -msplit-addresses
10433 @itemx -mno-split-addresses
10434 @opindex msplit-addresses
10435 @opindex mno-split-addresses
10436 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
10437 relocation operators. This option has been superseded by
10438 @option{-mexplicit-relocs} but is retained for backwards compatibility.
10440 @item -mexplicit-relocs
10441 @itemx -mno-explicit-relocs
10442 @opindex mexplicit-relocs
10443 @opindex mno-explicit-relocs
10444 Use (do not use) assembler relocation operators when dealing with symbolic
10445 addresses. The alternative, selected by @option{-mno-explicit-relocs},
10446 is to use assembler macros instead.
10448 @option{-mexplicit-relocs} is the default if GCC was configured
10449 to use an assembler that supports relocation operators.
10451 @item -mcheck-zero-division
10452 @itemx -mno-check-zero-division
10453 @opindex mcheck-zero-division
10454 @opindex mno-check-zero-division
10455 Trap (do not trap) on integer division by zero. The default is
10456 @option{-mcheck-zero-division}.
10458 @item -mdivide-traps
10459 @itemx -mdivide-breaks
10460 @opindex mdivide-traps
10461 @opindex mdivide-breaks
10462 MIPS systems check for division by zero by generating either a
10463 conditional trap or a break instruction. Using traps results in
10464 smaller code, but is only supported on MIPS II and later. Also, some
10465 versions of the Linux kernel have a bug that prevents trap from
10466 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
10467 allow conditional traps on architectures that support them and
10468 @option{-mdivide-breaks} to force the use of breaks.
10470 The default is usually @option{-mdivide-traps}, but this can be
10471 overridden at configure time using @option{--with-divide=breaks}.
10472 Divide-by-zero checks can be completely disabled using
10473 @option{-mno-check-zero-division}.
10478 @opindex mno-memcpy
10479 Force (do not force) the use of @code{memcpy()} for non-trivial block
10480 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
10481 most constant-sized copies.
10484 @itemx -mno-long-calls
10485 @opindex mlong-calls
10486 @opindex mno-long-calls
10487 Disable (do not disable) use of the @code{jal} instruction. Calling
10488 functions using @code{jal} is more efficient but requires the caller
10489 and callee to be in the same 256 megabyte segment.
10491 This option has no effect on abicalls code. The default is
10492 @option{-mno-long-calls}.
10498 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
10499 instructions, as provided by the R4650 ISA@.
10502 @itemx -mno-fused-madd
10503 @opindex mfused-madd
10504 @opindex mno-fused-madd
10505 Enable (disable) use of the floating point multiply-accumulate
10506 instructions, when they are available. The default is
10507 @option{-mfused-madd}.
10509 When multiply-accumulate instructions are used, the intermediate
10510 product is calculated to infinite precision and is not subject to
10511 the FCSR Flush to Zero bit. This may be undesirable in some
10516 Tell the MIPS assembler to not run its preprocessor over user
10517 assembler files (with a @samp{.s} suffix) when assembling them.
10520 @itemx -mno-fix-r4000
10521 @opindex mfix-r4000
10522 @opindex mno-fix-r4000
10523 Work around certain R4000 CPU errata:
10526 A double-word or a variable shift may give an incorrect result if executed
10527 immediately after starting an integer division.
10529 A double-word or a variable shift may give an incorrect result if executed
10530 while an integer multiplication is in progress.
10532 An integer division may give an incorrect result if started in a delay slot
10533 of a taken branch or a jump.
10537 @itemx -mno-fix-r4400
10538 @opindex mfix-r4400
10539 @opindex mno-fix-r4400
10540 Work around certain R4400 CPU errata:
10543 A double-word or a variable shift may give an incorrect result if executed
10544 immediately after starting an integer division.
10548 @itemx -mno-fix-vr4120
10549 @opindex mfix-vr4120
10550 Work around certain VR4120 errata:
10553 @code{dmultu} does not always produce the correct result.
10555 @code{div} and @code{ddiv} do not always produce the correct result if one
10556 of the operands is negative.
10558 The workarounds for the division errata rely on special functions in
10559 @file{libgcc.a}. At present, these functions are only provided by
10560 the @code{mips64vr*-elf} configurations.
10562 Other VR4120 errata require a nop to be inserted between certain pairs of
10563 instructions. These errata are handled by the assembler, not by GCC itself.
10566 @opindex mfix-vr4130
10567 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
10568 workarounds are implemented by the assembler rather than by GCC,
10569 although GCC will avoid using @code{mflo} and @code{mfhi} if the
10570 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
10571 instructions are available instead.
10574 @itemx -mno-fix-sb1
10576 Work around certain SB-1 CPU core errata.
10577 (This flag currently works around the SB-1 revision 2
10578 ``F1'' and ``F2'' floating point errata.)
10580 @item -mflush-func=@var{func}
10581 @itemx -mno-flush-func
10582 @opindex mflush-func
10583 Specifies the function to call to flush the I and D caches, or to not
10584 call any such function. If called, the function must take the same
10585 arguments as the common @code{_flush_func()}, that is, the address of the
10586 memory range for which the cache is being flushed, the size of the
10587 memory range, and the number 3 (to flush both caches). The default
10588 depends on the target GCC was configured for, but commonly is either
10589 @samp{_flush_func} or @samp{__cpu_flush}.
10591 @item -mbranch-likely
10592 @itemx -mno-branch-likely
10593 @opindex mbranch-likely
10594 @opindex mno-branch-likely
10595 Enable or disable use of Branch Likely instructions, regardless of the
10596 default for the selected architecture. By default, Branch Likely
10597 instructions may be generated if they are supported by the selected
10598 architecture. An exception is for the MIPS32 and MIPS64 architectures
10599 and processors which implement those architectures; for those, Branch
10600 Likely instructions will not be generated by default because the MIPS32
10601 and MIPS64 architectures specifically deprecate their use.
10603 @item -mfp-exceptions
10604 @itemx -mno-fp-exceptions
10605 @opindex mfp-exceptions
10606 Specifies whether FP exceptions are enabled. This affects how we schedule
10607 FP instructions for some processors. The default is that FP exceptions are
10610 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
10611 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
10614 @item -mvr4130-align
10615 @itemx -mno-vr4130-align
10616 @opindex mvr4130-align
10617 The VR4130 pipeline is two-way superscalar, but can only issue two
10618 instructions together if the first one is 8-byte aligned. When this
10619 option is enabled, GCC will align pairs of instructions that it
10620 thinks should execute in parallel.
10622 This option only has an effect when optimizing for the VR4130.
10623 It normally makes code faster, but at the expense of making it bigger.
10624 It is enabled by default at optimization level @option{-O3}.
10628 @subsection MMIX Options
10629 @cindex MMIX Options
10631 These options are defined for the MMIX:
10635 @itemx -mno-libfuncs
10637 @opindex mno-libfuncs
10638 Specify that intrinsic library functions are being compiled, passing all
10639 values in registers, no matter the size.
10642 @itemx -mno-epsilon
10644 @opindex mno-epsilon
10645 Generate floating-point comparison instructions that compare with respect
10646 to the @code{rE} epsilon register.
10648 @item -mabi=mmixware
10650 @opindex mabi-mmixware
10652 Generate code that passes function parameters and return values that (in
10653 the called function) are seen as registers @code{$0} and up, as opposed to
10654 the GNU ABI which uses global registers @code{$231} and up.
10656 @item -mzero-extend
10657 @itemx -mno-zero-extend
10658 @opindex mzero-extend
10659 @opindex mno-zero-extend
10660 When reading data from memory in sizes shorter than 64 bits, use (do not
10661 use) zero-extending load instructions by default, rather than
10662 sign-extending ones.
10665 @itemx -mno-knuthdiv
10667 @opindex mno-knuthdiv
10668 Make the result of a division yielding a remainder have the same sign as
10669 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10670 remainder follows the sign of the dividend. Both methods are
10671 arithmetically valid, the latter being almost exclusively used.
10673 @item -mtoplevel-symbols
10674 @itemx -mno-toplevel-symbols
10675 @opindex mtoplevel-symbols
10676 @opindex mno-toplevel-symbols
10677 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10678 code can be used with the @code{PREFIX} assembly directive.
10682 Generate an executable in the ELF format, rather than the default
10683 @samp{mmo} format used by the @command{mmix} simulator.
10685 @item -mbranch-predict
10686 @itemx -mno-branch-predict
10687 @opindex mbranch-predict
10688 @opindex mno-branch-predict
10689 Use (do not use) the probable-branch instructions, when static branch
10690 prediction indicates a probable branch.
10692 @item -mbase-addresses
10693 @itemx -mno-base-addresses
10694 @opindex mbase-addresses
10695 @opindex mno-base-addresses
10696 Generate (do not generate) code that uses @emph{base addresses}. Using a
10697 base address automatically generates a request (handled by the assembler
10698 and the linker) for a constant to be set up in a global register. The
10699 register is used for one or more base address requests within the range 0
10700 to 255 from the value held in the register. The generally leads to short
10701 and fast code, but the number of different data items that can be
10702 addressed is limited. This means that a program that uses lots of static
10703 data may require @option{-mno-base-addresses}.
10705 @item -msingle-exit
10706 @itemx -mno-single-exit
10707 @opindex msingle-exit
10708 @opindex mno-single-exit
10709 Force (do not force) generated code to have a single exit point in each
10713 @node MN10300 Options
10714 @subsection MN10300 Options
10715 @cindex MN10300 options
10717 These @option{-m} options are defined for Matsushita MN10300 architectures:
10722 Generate code to avoid bugs in the multiply instructions for the MN10300
10723 processors. This is the default.
10725 @item -mno-mult-bug
10726 @opindex mno-mult-bug
10727 Do not generate code to avoid bugs in the multiply instructions for the
10728 MN10300 processors.
10732 Generate code which uses features specific to the AM33 processor.
10736 Do not generate code which uses features specific to the AM33 processor. This
10739 @item -mreturn-pointer-on-d0
10740 @opindex mreturn-pointer-on-d0
10741 When generating a function which returns a pointer, return the pointer
10742 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
10743 only in a0, and attempts to call such functions without a prototype
10744 would result in errors. Note that this option is on by default; use
10745 @option{-mno-return-pointer-on-d0} to disable it.
10749 Do not link in the C run-time initialization object file.
10753 Indicate to the linker that it should perform a relaxation optimization pass
10754 to shorten branches, calls and absolute memory addresses. This option only
10755 has an effect when used on the command line for the final link step.
10757 This option makes symbolic debugging impossible.
10761 @subsection MT Options
10764 These @option{-m} options are defined for Morpho MT architectures:
10768 @item -march=@var{cpu-type}
10770 Generate code that will run on @var{cpu-type}, which is the name of a system
10771 representing a certain processor type. Possible values for
10772 @var{cpu-type} are @samp{ms1-64-001}, @samp{ms1-16-002},
10773 @samp{ms1-16-003} and @samp{ms2}.
10775 When this option is not used, the default is @option{-march=ms1-16-002}.
10779 Use byte loads and stores when generating code.
10783 Do not use byte loads and stores when generating code.
10787 Use simulator runtime
10791 Do not link in the C run-time initialization object file
10792 @file{crti.o}. Other run-time initialization and termination files
10793 such as @file{startup.o} and @file{exit.o} are still included on the
10794 linker command line.
10798 @node PDP-11 Options
10799 @subsection PDP-11 Options
10800 @cindex PDP-11 Options
10802 These options are defined for the PDP-11:
10807 Use hardware FPP floating point. This is the default. (FIS floating
10808 point on the PDP-11/40 is not supported.)
10811 @opindex msoft-float
10812 Do not use hardware floating point.
10816 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10820 Return floating-point results in memory. This is the default.
10824 Generate code for a PDP-11/40.
10828 Generate code for a PDP-11/45. This is the default.
10832 Generate code for a PDP-11/10.
10834 @item -mbcopy-builtin
10835 @opindex bcopy-builtin
10836 Use inline @code{movmemhi} patterns for copying memory. This is the
10841 Do not use inline @code{movmemhi} patterns for copying memory.
10847 Use 16-bit @code{int}. This is the default.
10853 Use 32-bit @code{int}.
10856 @itemx -mno-float32
10858 @opindex mno-float32
10859 Use 64-bit @code{float}. This is the default.
10862 @itemx -mno-float64
10864 @opindex mno-float64
10865 Use 32-bit @code{float}.
10869 Use @code{abshi2} pattern. This is the default.
10873 Do not use @code{abshi2} pattern.
10875 @item -mbranch-expensive
10876 @opindex mbranch-expensive
10877 Pretend that branches are expensive. This is for experimenting with
10878 code generation only.
10880 @item -mbranch-cheap
10881 @opindex mbranch-cheap
10882 Do not pretend that branches are expensive. This is the default.
10886 Generate code for a system with split I&D@.
10890 Generate code for a system without split I&D@. This is the default.
10894 Use Unix assembler syntax. This is the default when configured for
10895 @samp{pdp11-*-bsd}.
10899 Use DEC assembler syntax. This is the default when configured for any
10900 PDP-11 target other than @samp{pdp11-*-bsd}.
10903 @node PowerPC Options
10904 @subsection PowerPC Options
10905 @cindex PowerPC options
10907 These are listed under @xref{RS/6000 and PowerPC Options}.
10909 @node RS/6000 and PowerPC Options
10910 @subsection IBM RS/6000 and PowerPC Options
10911 @cindex RS/6000 and PowerPC Options
10912 @cindex IBM RS/6000 and PowerPC Options
10914 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
10921 @itemx -mno-powerpc
10922 @itemx -mpowerpc-gpopt
10923 @itemx -mno-powerpc-gpopt
10924 @itemx -mpowerpc-gfxopt
10925 @itemx -mno-powerpc-gfxopt
10927 @itemx -mno-powerpc64
10931 @itemx -mno-popcntb
10937 @opindex mno-power2
10939 @opindex mno-powerpc
10940 @opindex mpowerpc-gpopt
10941 @opindex mno-powerpc-gpopt
10942 @opindex mpowerpc-gfxopt
10943 @opindex mno-powerpc-gfxopt
10944 @opindex mpowerpc64
10945 @opindex mno-powerpc64
10949 @opindex mno-popcntb
10952 GCC supports two related instruction set architectures for the
10953 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
10954 instructions supported by the @samp{rios} chip set used in the original
10955 RS/6000 systems and the @dfn{PowerPC} instruction set is the
10956 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
10957 the IBM 4xx, 6xx, and follow-on microprocessors.
10959 Neither architecture is a subset of the other. However there is a
10960 large common subset of instructions supported by both. An MQ
10961 register is included in processors supporting the POWER architecture.
10963 You use these options to specify which instructions are available on the
10964 processor you are using. The default value of these options is
10965 determined when configuring GCC@. Specifying the
10966 @option{-mcpu=@var{cpu_type}} overrides the specification of these
10967 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
10968 rather than the options listed above.
10970 The @option{-mpower} option allows GCC to generate instructions that
10971 are found only in the POWER architecture and to use the MQ register.
10972 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
10973 to generate instructions that are present in the POWER2 architecture but
10974 not the original POWER architecture.
10976 The @option{-mpowerpc} option allows GCC to generate instructions that
10977 are found only in the 32-bit subset of the PowerPC architecture.
10978 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
10979 GCC to use the optional PowerPC architecture instructions in the
10980 General Purpose group, including floating-point square root. Specifying
10981 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
10982 use the optional PowerPC architecture instructions in the Graphics
10983 group, including floating-point select.
10985 The @option{-mmfcrf} option allows GCC to generate the move from
10986 condition register field instruction implemented on the POWER4
10987 processor and other processors that support the PowerPC V2.01
10989 The @option{-mpopcntb} option allows GCC to generate the popcount and
10990 double precision FP reciprocal estimate instruction implemented on the
10991 POWER5 processor and other processors that support the PowerPC V2.02
10993 The @option{-mfprnd} option allows GCC to generate the FP round to
10994 integer instructions implemented on the POWER5+ processor and other
10995 processors that support the PowerPC V2.03 architecture.
10997 The @option{-mpowerpc64} option allows GCC to generate the additional
10998 64-bit instructions that are found in the full PowerPC64 architecture
10999 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
11000 @option{-mno-powerpc64}.
11002 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
11003 will use only the instructions in the common subset of both
11004 architectures plus some special AIX common-mode calls, and will not use
11005 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
11006 permits GCC to use any instruction from either architecture and to
11007 allow use of the MQ register; specify this for the Motorola MPC601.
11009 @item -mnew-mnemonics
11010 @itemx -mold-mnemonics
11011 @opindex mnew-mnemonics
11012 @opindex mold-mnemonics
11013 Select which mnemonics to use in the generated assembler code. With
11014 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
11015 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
11016 assembler mnemonics defined for the POWER architecture. Instructions
11017 defined in only one architecture have only one mnemonic; GCC uses that
11018 mnemonic irrespective of which of these options is specified.
11020 GCC defaults to the mnemonics appropriate for the architecture in
11021 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
11022 value of these option. Unless you are building a cross-compiler, you
11023 should normally not specify either @option{-mnew-mnemonics} or
11024 @option{-mold-mnemonics}, but should instead accept the default.
11026 @item -mcpu=@var{cpu_type}
11028 Set architecture type, register usage, choice of mnemonics, and
11029 instruction scheduling parameters for machine type @var{cpu_type}.
11030 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
11031 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
11032 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
11033 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
11034 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
11035 @samp{860}, @samp{970}, @samp{8540}, @samp{ec603e}, @samp{G3},
11036 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
11037 @samp{power4}, @samp{power5}, @samp{power5+},
11038 @samp{common}, @samp{powerpc}, @samp{powerpc64},
11039 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
11041 @option{-mcpu=common} selects a completely generic processor. Code
11042 generated under this option will run on any POWER or PowerPC processor.
11043 GCC will use only the instructions in the common subset of both
11044 architectures, and will not use the MQ register. GCC assumes a generic
11045 processor model for scheduling purposes.
11047 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
11048 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
11049 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
11050 types, with an appropriate, generic processor model assumed for
11051 scheduling purposes.
11053 The other options specify a specific processor. Code generated under
11054 those options will run best on that processor, and may not run at all on
11057 The @option{-mcpu} options automatically enable or disable the
11058 following options: @option{-maltivec}, @option{-mfprnd},
11059 @option{-mhard-float}, @option{-mmfcrf}, @option{-mmultiple},
11060 @option{-mnew-mnemonics}, @option{-mpopcntb}, @option{-mpower},
11061 @option{-mpower2}, @option{-mpowerpc64}, @option{-mpowerpc-gpopt},
11062 @option{-mpowerpc-gfxopt}, @option{-mstring}, @option{-mmulhw}.
11063 The particular options
11064 set for any particular CPU will vary between compiler versions,
11065 depending on what setting seems to produce optimal code for that CPU;
11066 it doesn't necessarily reflect the actual hardware's capabilities. If
11067 you wish to set an individual option to a particular value, you may
11068 specify it after the @option{-mcpu} option, like @samp{-mcpu=970
11071 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
11072 not enabled or disabled by the @option{-mcpu} option at present because
11073 AIX does not have full support for these options. You may still
11074 enable or disable them individually if you're sure it'll work in your
11077 @item -mtune=@var{cpu_type}
11079 Set the instruction scheduling parameters for machine type
11080 @var{cpu_type}, but do not set the architecture type, register usage, or
11081 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
11082 values for @var{cpu_type} are used for @option{-mtune} as for
11083 @option{-mcpu}. If both are specified, the code generated will use the
11084 architecture, registers, and mnemonics set by @option{-mcpu}, but the
11085 scheduling parameters set by @option{-mtune}.
11091 Generate code to compute division as reciprocal estimate and iterative
11092 refinement, creating opportunities for increased throughput. This
11093 feature requires: optional PowerPC Graphics instruction set for single
11094 precision and FRE instruction for double precision, assuming divides
11095 cannot generate user-visible traps, and the domain values not include
11096 Infinities, denormals or zero denominator.
11099 @itemx -mno-altivec
11101 @opindex mno-altivec
11102 Generate code that uses (does not use) AltiVec instructions, and also
11103 enable the use of built-in functions that allow more direct access to
11104 the AltiVec instruction set. You may also need to set
11105 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
11111 @opindex mno-vrsave
11112 Generate VRSAVE instructions when generating AltiVec code.
11116 Extend the current ABI with SPE ABI extensions. This does not change
11117 the default ABI, instead it adds the SPE ABI extensions to the current
11121 @opindex mabi=no-spe
11122 Disable Booke SPE ABI extensions for the current ABI@.
11125 @opindex msecure-plt
11126 Generate code that allows ld and ld.so to build executables and shared
11127 libraries with non-exec .plt and .got sections. This is a PowerPC
11128 32-bit SYSV ABI option.
11132 Generate code that uses a BSS .plt section that ld.so fills in, and
11133 requires .plt and .got sections that are both writable and executable.
11134 This is a PowerPC 32-bit SYSV ABI option.
11140 This switch enables or disables the generation of ISEL instructions.
11142 @item -misel=@var{yes/no}
11143 This switch has been deprecated. Use @option{-misel} and
11144 @option{-mno-isel} instead.
11150 This switch enables or disables the generation of SPE simd
11153 @item -mspe=@var{yes/no}
11154 This option has been deprecated. Use @option{-mspe} and
11155 @option{-mno-spe} instead.
11157 @item -mfloat-gprs=@var{yes/single/double/no}
11158 @itemx -mfloat-gprs
11159 @opindex mfloat-gprs
11160 This switch enables or disables the generation of floating point
11161 operations on the general purpose registers for architectures that
11164 The argument @var{yes} or @var{single} enables the use of
11165 single-precision floating point operations.
11167 The argument @var{double} enables the use of single and
11168 double-precision floating point operations.
11170 The argument @var{no} disables floating point operations on the
11171 general purpose registers.
11173 This option is currently only available on the MPC854x.
11179 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
11180 targets (including GNU/Linux). The 32-bit environment sets int, long
11181 and pointer to 32 bits and generates code that runs on any PowerPC
11182 variant. The 64-bit environment sets int to 32 bits and long and
11183 pointer to 64 bits, and generates code for PowerPC64, as for
11184 @option{-mpowerpc64}.
11187 @itemx -mno-fp-in-toc
11188 @itemx -mno-sum-in-toc
11189 @itemx -mminimal-toc
11191 @opindex mno-fp-in-toc
11192 @opindex mno-sum-in-toc
11193 @opindex mminimal-toc
11194 Modify generation of the TOC (Table Of Contents), which is created for
11195 every executable file. The @option{-mfull-toc} option is selected by
11196 default. In that case, GCC will allocate at least one TOC entry for
11197 each unique non-automatic variable reference in your program. GCC
11198 will also place floating-point constants in the TOC@. However, only
11199 16,384 entries are available in the TOC@.
11201 If you receive a linker error message that saying you have overflowed
11202 the available TOC space, you can reduce the amount of TOC space used
11203 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
11204 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
11205 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
11206 generate code to calculate the sum of an address and a constant at
11207 run-time instead of putting that sum into the TOC@. You may specify one
11208 or both of these options. Each causes GCC to produce very slightly
11209 slower and larger code at the expense of conserving TOC space.
11211 If you still run out of space in the TOC even when you specify both of
11212 these options, specify @option{-mminimal-toc} instead. This option causes
11213 GCC to make only one TOC entry for every file. When you specify this
11214 option, GCC will produce code that is slower and larger but which
11215 uses extremely little TOC space. You may wish to use this option
11216 only on files that contain less frequently executed code.
11222 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
11223 @code{long} type, and the infrastructure needed to support them.
11224 Specifying @option{-maix64} implies @option{-mpowerpc64} and
11225 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
11226 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
11229 @itemx -mno-xl-compat
11230 @opindex mxl-compat
11231 @opindex mno-xl-compat
11232 Produce code that conforms more closely to IBM XLC semantics when using
11233 AIX-compatible ABI. Pass floating-point arguments to prototyped
11234 functions beyond the register save area (RSA) on the stack in addition
11235 to argument FPRs. Do not assume that most significant double in 128
11236 bit long double value is properly rounded when comparing values.
11238 The AIX calling convention was extended but not initially documented to
11239 handle an obscure K&R C case of calling a function that takes the
11240 address of its arguments with fewer arguments than declared. AIX XL
11241 compilers access floating point arguments which do not fit in the
11242 RSA from the stack when a subroutine is compiled without
11243 optimization. Because always storing floating-point arguments on the
11244 stack is inefficient and rarely needed, this option is not enabled by
11245 default and only is necessary when calling subroutines compiled by AIX
11246 XL compilers without optimization.
11250 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
11251 application written to use message passing with special startup code to
11252 enable the application to run. The system must have PE installed in the
11253 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
11254 must be overridden with the @option{-specs=} option to specify the
11255 appropriate directory location. The Parallel Environment does not
11256 support threads, so the @option{-mpe} option and the @option{-pthread}
11257 option are incompatible.
11259 @item -malign-natural
11260 @itemx -malign-power
11261 @opindex malign-natural
11262 @opindex malign-power
11263 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
11264 @option{-malign-natural} overrides the ABI-defined alignment of larger
11265 types, such as floating-point doubles, on their natural size-based boundary.
11266 The option @option{-malign-power} instructs GCC to follow the ABI-specified
11267 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
11269 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
11273 @itemx -mhard-float
11274 @opindex msoft-float
11275 @opindex mhard-float
11276 Generate code that does not use (uses) the floating-point register set.
11277 Software floating point emulation is provided if you use the
11278 @option{-msoft-float} option, and pass the option to GCC when linking.
11281 @itemx -mno-multiple
11283 @opindex mno-multiple
11284 Generate code that uses (does not use) the load multiple word
11285 instructions and the store multiple word instructions. These
11286 instructions are generated by default on POWER systems, and not
11287 generated on PowerPC systems. Do not use @option{-mmultiple} on little
11288 endian PowerPC systems, since those instructions do not work when the
11289 processor is in little endian mode. The exceptions are PPC740 and
11290 PPC750 which permit the instructions usage in little endian mode.
11295 @opindex mno-string
11296 Generate code that uses (does not use) the load string instructions
11297 and the store string word instructions to save multiple registers and
11298 do small block moves. These instructions are generated by default on
11299 POWER systems, and not generated on PowerPC systems. Do not use
11300 @option{-mstring} on little endian PowerPC systems, since those
11301 instructions do not work when the processor is in little endian mode.
11302 The exceptions are PPC740 and PPC750 which permit the instructions
11303 usage in little endian mode.
11308 @opindex mno-update
11309 Generate code that uses (does not use) the load or store instructions
11310 that update the base register to the address of the calculated memory
11311 location. These instructions are generated by default. If you use
11312 @option{-mno-update}, there is a small window between the time that the
11313 stack pointer is updated and the address of the previous frame is
11314 stored, which means code that walks the stack frame across interrupts or
11315 signals may get corrupted data.
11318 @itemx -mno-fused-madd
11319 @opindex mfused-madd
11320 @opindex mno-fused-madd
11321 Generate code that uses (does not use) the floating point multiply and
11322 accumulate instructions. These instructions are generated by default if
11323 hardware floating is used.
11329 Generate code that uses (does not use) the half-word multiply and
11330 multiply-accumulate instructions on the IBM 405 and 440 processors.
11331 These instructions are generated by default when targetting those
11334 @item -mno-bit-align
11336 @opindex mno-bit-align
11337 @opindex mbit-align
11338 On System V.4 and embedded PowerPC systems do not (do) force structures
11339 and unions that contain bit-fields to be aligned to the base type of the
11342 For example, by default a structure containing nothing but 8
11343 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
11344 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
11345 the structure would be aligned to a 1 byte boundary and be one byte in
11348 @item -mno-strict-align
11349 @itemx -mstrict-align
11350 @opindex mno-strict-align
11351 @opindex mstrict-align
11352 On System V.4 and embedded PowerPC systems do not (do) assume that
11353 unaligned memory references will be handled by the system.
11355 @item -mrelocatable
11356 @itemx -mno-relocatable
11357 @opindex mrelocatable
11358 @opindex mno-relocatable
11359 On embedded PowerPC systems generate code that allows (does not allow)
11360 the program to be relocated to a different address at runtime. If you
11361 use @option{-mrelocatable} on any module, all objects linked together must
11362 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
11364 @item -mrelocatable-lib
11365 @itemx -mno-relocatable-lib
11366 @opindex mrelocatable-lib
11367 @opindex mno-relocatable-lib
11368 On embedded PowerPC systems generate code that allows (does not allow)
11369 the program to be relocated to a different address at runtime. Modules
11370 compiled with @option{-mrelocatable-lib} can be linked with either modules
11371 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
11372 with modules compiled with the @option{-mrelocatable} options.
11378 On System V.4 and embedded PowerPC systems do not (do) assume that
11379 register 2 contains a pointer to a global area pointing to the addresses
11380 used in the program.
11383 @itemx -mlittle-endian
11385 @opindex mlittle-endian
11386 On System V.4 and embedded PowerPC systems compile code for the
11387 processor in little endian mode. The @option{-mlittle-endian} option is
11388 the same as @option{-mlittle}.
11391 @itemx -mbig-endian
11393 @opindex mbig-endian
11394 On System V.4 and embedded PowerPC systems compile code for the
11395 processor in big endian mode. The @option{-mbig-endian} option is
11396 the same as @option{-mbig}.
11398 @item -mdynamic-no-pic
11399 @opindex mdynamic-no-pic
11400 On Darwin and Mac OS X systems, compile code so that it is not
11401 relocatable, but that its external references are relocatable. The
11402 resulting code is suitable for applications, but not shared
11405 @item -mprioritize-restricted-insns=@var{priority}
11406 @opindex mprioritize-restricted-insns
11407 This option controls the priority that is assigned to
11408 dispatch-slot restricted instructions during the second scheduling
11409 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
11410 @var{no/highest/second-highest} priority to dispatch slot restricted
11413 @item -msched-costly-dep=@var{dependence_type}
11414 @opindex msched-costly-dep
11415 This option controls which dependences are considered costly
11416 by the target during instruction scheduling. The argument
11417 @var{dependence_type} takes one of the following values:
11418 @var{no}: no dependence is costly,
11419 @var{all}: all dependences are costly,
11420 @var{true_store_to_load}: a true dependence from store to load is costly,
11421 @var{store_to_load}: any dependence from store to load is costly,
11422 @var{number}: any dependence which latency >= @var{number} is costly.
11424 @item -minsert-sched-nops=@var{scheme}
11425 @opindex minsert-sched-nops
11426 This option controls which nop insertion scheme will be used during
11427 the second scheduling pass. The argument @var{scheme} takes one of the
11429 @var{no}: Don't insert nops.
11430 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
11431 according to the scheduler's grouping.
11432 @var{regroup_exact}: Insert nops to force costly dependent insns into
11433 separate groups. Insert exactly as many nops as needed to force an insn
11434 to a new group, according to the estimated processor grouping.
11435 @var{number}: Insert nops to force costly dependent insns into
11436 separate groups. Insert @var{number} nops to force an insn to a new group.
11439 @opindex mcall-sysv
11440 On System V.4 and embedded PowerPC systems compile code using calling
11441 conventions that adheres to the March 1995 draft of the System V
11442 Application Binary Interface, PowerPC processor supplement. This is the
11443 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
11445 @item -mcall-sysv-eabi
11446 @opindex mcall-sysv-eabi
11447 Specify both @option{-mcall-sysv} and @option{-meabi} options.
11449 @item -mcall-sysv-noeabi
11450 @opindex mcall-sysv-noeabi
11451 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
11453 @item -mcall-solaris
11454 @opindex mcall-solaris
11455 On System V.4 and embedded PowerPC systems compile code for the Solaris
11459 @opindex mcall-linux
11460 On System V.4 and embedded PowerPC systems compile code for the
11461 Linux-based GNU system.
11465 On System V.4 and embedded PowerPC systems compile code for the
11466 Hurd-based GNU system.
11468 @item -mcall-netbsd
11469 @opindex mcall-netbsd
11470 On System V.4 and embedded PowerPC systems compile code for the
11471 NetBSD operating system.
11473 @item -maix-struct-return
11474 @opindex maix-struct-return
11475 Return all structures in memory (as specified by the AIX ABI)@.
11477 @item -msvr4-struct-return
11478 @opindex msvr4-struct-return
11479 Return structures smaller than 8 bytes in registers (as specified by the
11482 @item -mabi=@var{abi-type}
11484 Extend the current ABI with a particular extension, or remove such extension.
11485 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
11489 @itemx -mno-prototype
11490 @opindex mprototype
11491 @opindex mno-prototype
11492 On System V.4 and embedded PowerPC systems assume that all calls to
11493 variable argument functions are properly prototyped. Otherwise, the
11494 compiler must insert an instruction before every non prototyped call to
11495 set or clear bit 6 of the condition code register (@var{CR}) to
11496 indicate whether floating point values were passed in the floating point
11497 registers in case the function takes a variable arguments. With
11498 @option{-mprototype}, only calls to prototyped variable argument functions
11499 will set or clear the bit.
11503 On embedded PowerPC systems, assume that the startup module is called
11504 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
11505 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
11510 On embedded PowerPC systems, assume that the startup module is called
11511 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
11516 On embedded PowerPC systems, assume that the startup module is called
11517 @file{crt0.o} and the standard C libraries are @file{libads.a} and
11520 @item -myellowknife
11521 @opindex myellowknife
11522 On embedded PowerPC systems, assume that the startup module is called
11523 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
11528 On System V.4 and embedded PowerPC systems, specify that you are
11529 compiling for a VxWorks system.
11533 Specify that you are compiling for the WindISS simulation environment.
11537 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
11538 header to indicate that @samp{eabi} extended relocations are used.
11544 On System V.4 and embedded PowerPC systems do (do not) adhere to the
11545 Embedded Applications Binary Interface (eabi) which is a set of
11546 modifications to the System V.4 specifications. Selecting @option{-meabi}
11547 means that the stack is aligned to an 8 byte boundary, a function
11548 @code{__eabi} is called to from @code{main} to set up the eabi
11549 environment, and the @option{-msdata} option can use both @code{r2} and
11550 @code{r13} to point to two separate small data areas. Selecting
11551 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
11552 do not call an initialization function from @code{main}, and the
11553 @option{-msdata} option will only use @code{r13} to point to a single
11554 small data area. The @option{-meabi} option is on by default if you
11555 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
11558 @opindex msdata=eabi
11559 On System V.4 and embedded PowerPC systems, put small initialized
11560 @code{const} global and static data in the @samp{.sdata2} section, which
11561 is pointed to by register @code{r2}. Put small initialized
11562 non-@code{const} global and static data in the @samp{.sdata} section,
11563 which is pointed to by register @code{r13}. Put small uninitialized
11564 global and static data in the @samp{.sbss} section, which is adjacent to
11565 the @samp{.sdata} section. The @option{-msdata=eabi} option is
11566 incompatible with the @option{-mrelocatable} option. The
11567 @option{-msdata=eabi} option also sets the @option{-memb} option.
11570 @opindex msdata=sysv
11571 On System V.4 and embedded PowerPC systems, put small global and static
11572 data in the @samp{.sdata} section, which is pointed to by register
11573 @code{r13}. Put small uninitialized global and static data in the
11574 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
11575 The @option{-msdata=sysv} option is incompatible with the
11576 @option{-mrelocatable} option.
11578 @item -msdata=default
11580 @opindex msdata=default
11582 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
11583 compile code the same as @option{-msdata=eabi}, otherwise compile code the
11584 same as @option{-msdata=sysv}.
11587 @opindex msdata-data
11588 On System V.4 and embedded PowerPC systems, put small global
11589 data in the @samp{.sdata} section. Put small uninitialized global
11590 data in the @samp{.sbss} section. Do not use register @code{r13}
11591 to address small data however. This is the default behavior unless
11592 other @option{-msdata} options are used.
11596 @opindex msdata=none
11598 On embedded PowerPC systems, put all initialized global and static data
11599 in the @samp{.data} section, and all uninitialized data in the
11600 @samp{.bss} section.
11604 @cindex smaller data references (PowerPC)
11605 @cindex .sdata/.sdata2 references (PowerPC)
11606 On embedded PowerPC systems, put global and static items less than or
11607 equal to @var{num} bytes into the small data or bss sections instead of
11608 the normal data or bss section. By default, @var{num} is 8. The
11609 @option{-G @var{num}} switch is also passed to the linker.
11610 All modules should be compiled with the same @option{-G @var{num}} value.
11613 @itemx -mno-regnames
11615 @opindex mno-regnames
11616 On System V.4 and embedded PowerPC systems do (do not) emit register
11617 names in the assembly language output using symbolic forms.
11620 @itemx -mno-longcall
11622 @opindex mno-longcall
11623 Default to making all function calls indirectly, using a register, so
11624 that functions which reside further than 32 megabytes (33,554,432
11625 bytes) from the current location can be called. This setting can be
11626 overridden by the @code{shortcall} function attribute, or by
11627 @code{#pragma longcall(0)}.
11629 Some linkers are capable of detecting out-of-range calls and generating
11630 glue code on the fly. On these systems, long calls are unnecessary and
11631 generate slower code. As of this writing, the AIX linker can do this,
11632 as can the GNU linker for PowerPC/64. It is planned to add this feature
11633 to the GNU linker for 32-bit PowerPC systems as well.
11635 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
11636 callee, L42'', plus a ``branch island'' (glue code). The two target
11637 addresses represent the callee and the ``branch island''. The
11638 Darwin/PPC linker will prefer the first address and generate a ``bl
11639 callee'' if the PPC ``bl'' instruction will reach the callee directly;
11640 otherwise, the linker will generate ``bl L42'' to call the ``branch
11641 island''. The ``branch island'' is appended to the body of the
11642 calling function; it computes the full 32-bit address of the callee
11645 On Mach-O (Darwin) systems, this option directs the compiler emit to
11646 the glue for every direct call, and the Darwin linker decides whether
11647 to use or discard it.
11649 In the future, we may cause GCC to ignore all longcall specifications
11650 when the linker is known to generate glue.
11654 Adds support for multithreading with the @dfn{pthreads} library.
11655 This option sets flags for both the preprocessor and linker.
11659 @node S/390 and zSeries Options
11660 @subsection S/390 and zSeries Options
11661 @cindex S/390 and zSeries Options
11663 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
11667 @itemx -msoft-float
11668 @opindex mhard-float
11669 @opindex msoft-float
11670 Use (do not use) the hardware floating-point instructions and registers
11671 for floating-point operations. When @option{-msoft-float} is specified,
11672 functions in @file{libgcc.a} will be used to perform floating-point
11673 operations. When @option{-mhard-float} is specified, the compiler
11674 generates IEEE floating-point instructions. This is the default.
11677 @itemx -mno-backchain
11678 @opindex mbackchain
11679 @opindex mno-backchain
11680 Store (do not store) the address of the caller's frame as backchain pointer
11681 into the callee's stack frame.
11682 A backchain may be needed to allow debugging using tools that do not understand
11683 DWARF-2 call frame information.
11684 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
11685 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
11686 the backchain is placed into the topmost word of the 96/160 byte register
11689 In general, code compiled with @option{-mbackchain} is call-compatible with
11690 code compiled with @option{-mmo-backchain}; however, use of the backchain
11691 for debugging purposes usually requires that the whole binary is built with
11692 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
11693 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11694 to build a linux kernel use @option{-msoft-float}.
11696 The default is to not maintain the backchain.
11698 @item -mpacked-stack
11699 @item -mno-packed-stack
11700 @opindex mpacked-stack
11701 @opindex mno-packed-stack
11702 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
11703 specified, the compiler uses the all fields of the 96/160 byte register save
11704 area only for their default purpose; unused fields still take up stack space.
11705 When @option{-mpacked-stack} is specified, register save slots are densely
11706 packed at the top of the register save area; unused space is reused for other
11707 purposes, allowing for more efficient use of the available stack space.
11708 However, when @option{-mbackchain} is also in effect, the topmost word of
11709 the save area is always used to store the backchain, and the return address
11710 register is always saved two words below the backchain.
11712 As long as the stack frame backchain is not used, code generated with
11713 @option{-mpacked-stack} is call-compatible with code generated with
11714 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
11715 S/390 or zSeries generated code that uses the stack frame backchain at run
11716 time, not just for debugging purposes. Such code is not call-compatible
11717 with code compiled with @option{-mpacked-stack}. Also, note that the
11718 combination of @option{-mbackchain},
11719 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11720 to build a linux kernel use @option{-msoft-float}.
11722 The default is to not use the packed stack layout.
11725 @itemx -mno-small-exec
11726 @opindex msmall-exec
11727 @opindex mno-small-exec
11728 Generate (or do not generate) code using the @code{bras} instruction
11729 to do subroutine calls.
11730 This only works reliably if the total executable size does not
11731 exceed 64k. The default is to use the @code{basr} instruction instead,
11732 which does not have this limitation.
11738 When @option{-m31} is specified, generate code compliant to the
11739 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
11740 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
11741 particular to generate 64-bit instructions. For the @samp{s390}
11742 targets, the default is @option{-m31}, while the @samp{s390x}
11743 targets default to @option{-m64}.
11749 When @option{-mzarch} is specified, generate code using the
11750 instructions available on z/Architecture.
11751 When @option{-mesa} is specified, generate code using the
11752 instructions available on ESA/390. Note that @option{-mesa} is
11753 not possible with @option{-m64}.
11754 When generating code compliant to the GNU/Linux for S/390 ABI,
11755 the default is @option{-mesa}. When generating code compliant
11756 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
11762 Generate (or do not generate) code using the @code{mvcle} instruction
11763 to perform block moves. When @option{-mno-mvcle} is specified,
11764 use a @code{mvc} loop instead. This is the default unless optimizing for
11771 Print (or do not print) additional debug information when compiling.
11772 The default is to not print debug information.
11774 @item -march=@var{cpu-type}
11776 Generate code that will run on @var{cpu-type}, which is the name of a system
11777 representing a certain processor type. Possible values for
11778 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
11779 When generating code using the instructions available on z/Architecture,
11780 the default is @option{-march=z900}. Otherwise, the default is
11781 @option{-march=g5}.
11783 @item -mtune=@var{cpu-type}
11785 Tune to @var{cpu-type} everything applicable about the generated code,
11786 except for the ABI and the set of available instructions.
11787 The list of @var{cpu-type} values is the same as for @option{-march}.
11788 The default is the value used for @option{-march}.
11791 @itemx -mno-tpf-trace
11792 @opindex mtpf-trace
11793 @opindex mno-tpf-trace
11794 Generate code that adds (does not add) in TPF OS specific branches to trace
11795 routines in the operating system. This option is off by default, even
11796 when compiling for the TPF OS@.
11799 @itemx -mno-fused-madd
11800 @opindex mfused-madd
11801 @opindex mno-fused-madd
11802 Generate code that uses (does not use) the floating point multiply and
11803 accumulate instructions. These instructions are generated by default if
11804 hardware floating point is used.
11806 @item -mwarn-framesize=@var{framesize}
11807 @opindex mwarn-framesize
11808 Emit a warning if the current function exceeds the given frame size. Because
11809 this is a compile time check it doesn't need to be a real problem when the program
11810 runs. It is intended to identify functions which most probably cause
11811 a stack overflow. It is useful to be used in an environment with limited stack
11812 size e.g.@: the linux kernel.
11814 @item -mwarn-dynamicstack
11815 @opindex mwarn-dynamicstack
11816 Emit a warning if the function calls alloca or uses dynamically
11817 sized arrays. This is generally a bad idea with a limited stack size.
11819 @item -mstack-guard=@var{stack-guard}
11820 @item -mstack-size=@var{stack-size}
11821 @opindex mstack-guard
11822 @opindex mstack-size
11823 These arguments always have to be used in conjunction. If they are present the s390
11824 back end emits additional instructions in the function prologue which trigger a trap
11825 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
11826 (remember that the stack on s390 grows downward). These options are intended to
11827 be used to help debugging stack overflow problems. The additionally emitted code
11828 causes only little overhead and hence can also be used in production like systems
11829 without greater performance degradation. The given values have to be exact
11830 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard} without
11832 In order to be efficient the extra code makes the assumption that the stack starts
11833 at an address aligned to the value given by @var{stack-size}.
11837 @subsection SH Options
11839 These @samp{-m} options are defined for the SH implementations:
11844 Generate code for the SH1.
11848 Generate code for the SH2.
11851 Generate code for the SH2e.
11855 Generate code for the SH3.
11859 Generate code for the SH3e.
11863 Generate code for the SH4 without a floating-point unit.
11865 @item -m4-single-only
11866 @opindex m4-single-only
11867 Generate code for the SH4 with a floating-point unit that only
11868 supports single-precision arithmetic.
11872 Generate code for the SH4 assuming the floating-point unit is in
11873 single-precision mode by default.
11877 Generate code for the SH4.
11881 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
11882 floating-point unit is not used.
11884 @item -m4a-single-only
11885 @opindex m4a-single-only
11886 Generate code for the SH4a, in such a way that no double-precision
11887 floating point operations are used.
11890 @opindex m4a-single
11891 Generate code for the SH4a assuming the floating-point unit is in
11892 single-precision mode by default.
11896 Generate code for the SH4a.
11900 Same as @option{-m4a-nofpu}, except that it implicitly passes
11901 @option{-dsp} to the assembler. GCC doesn't generate any DSP
11902 instructions at the moment.
11906 Compile code for the processor in big endian mode.
11910 Compile code for the processor in little endian mode.
11914 Align doubles at 64-bit boundaries. Note that this changes the calling
11915 conventions, and thus some functions from the standard C library will
11916 not work unless you recompile it first with @option{-mdalign}.
11920 Shorten some address references at link time, when possible; uses the
11921 linker option @option{-relax}.
11925 Use 32-bit offsets in @code{switch} tables. The default is to use
11930 Enable the use of the instruction @code{fmovd}.
11934 Comply with the calling conventions defined by Renesas.
11938 Comply with the calling conventions defined by Renesas.
11942 Comply with the calling conventions defined for GCC before the Renesas
11943 conventions were available. This option is the default for all
11944 targets of the SH toolchain except for @samp{sh-symbianelf}.
11947 @opindex mnomacsave
11948 Mark the @code{MAC} register as call-clobbered, even if
11949 @option{-mhitachi} is given.
11953 Increase IEEE-compliance of floating-point code.
11954 At the moment, this is equivalent to @option{-fno-finite-math-only}.
11955 When generating 16 bit SH opcodes, getting IEEE-conforming results for
11956 comparisons of NANs / infinities incurs extra overhead in every
11957 floating point comparison, therefore the default is set to
11958 @option{-ffinite-math-only}.
11962 Dump instruction size and location in the assembly code.
11965 @opindex mpadstruct
11966 This option is deprecated. It pads structures to multiple of 4 bytes,
11967 which is incompatible with the SH ABI@.
11971 Optimize for space instead of speed. Implied by @option{-Os}.
11974 @opindex mprefergot
11975 When generating position-independent code, emit function calls using
11976 the Global Offset Table instead of the Procedure Linkage Table.
11980 Generate a library function call to invalidate instruction cache
11981 entries, after fixing up a trampoline. This library function call
11982 doesn't assume it can write to the whole memory address space. This
11983 is the default when the target is @code{sh-*-linux*}.
11985 @item -multcost=@var{number}
11986 @opindex multcost=@var{number}
11987 Set the cost to assume for a multiply insn.
11989 @item -mdiv=@var{strategy}
11990 @opindex mdiv=@var{strategy}
11991 Set the division strategy to use for SHmedia code. @var{strategy} must be
11992 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
11993 inv:call2, inv:fp .
11994 "fp" performs the operation in floating point. This has a very high latency,
11995 but needs only a few instructions, so it might be a good choice if
11996 your code has enough easily exploitable ILP to allow the compiler to
11997 schedule the floating point instructions together with other instructions.
11998 Division by zero causes a floating point exception.
11999 "inv" uses integer operations to calculate the inverse of the divisor,
12000 and then multiplies the dividend with the inverse. This strategy allows
12001 cse and hoisting of the inverse calculation. Division by zero calculates
12002 an unspecified result, but does not trap.
12003 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
12004 have been found, or if the entire operation has been hoisted to the same
12005 place, the last stages of the inverse calculation are intertwined with the
12006 final multiply to reduce the overall latency, at the expense of using a few
12007 more instructions, and thus offering fewer scheduling opportunities with
12009 "call" calls a library function that usually implements the inv:minlat
12011 This gives high code density for m5-*media-nofpu compilations.
12012 "call2" uses a different entry point of the same library function, where it
12013 assumes that a pointer to a lookup table has already been set up, which
12014 exposes the pointer load to cse / code hoisting optimizations.
12015 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
12016 code generation, but if the code stays unoptimized, revert to the "call",
12017 "call2", or "fp" strategies, respectively. Note that the
12018 potentially-trapping side effect of division by zero is carried by a
12019 separate instruction, so it is possible that all the integer instructions
12020 are hoisted out, but the marker for the side effect stays where it is.
12021 A recombination to fp operations or a call is not possible in that case.
12022 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
12023 that the inverse calculation was nor separated from the multiply, they speed
12024 up division where the dividend fits into 20 bits (plus sign where applicable),
12025 by inserting a test to skip a number of operations in this case; this test
12026 slows down the case of larger dividends. inv20u assumes the case of a such
12027 a small dividend to be unlikely, and inv20l assumes it to be likely.
12029 @item -mdivsi3_libfunc=@var{name}
12030 @opindex mdivsi3_libfunc=@var{name}
12031 Set the name of the library function used for 32 bit signed division to
12032 @var{name}. This only affect the name used in the call and inv:call
12033 division strategies, and the compiler will still expect the same
12034 sets of input/output/clobbered registers as if this option was not present.
12036 @item -madjust-unroll
12037 @opindex madjust-unroll
12038 Throttle unrolling to avoid thrashing target registers.
12039 This option only has an effect if the gcc code base supports the
12040 TARGET_ADJUST_UNROLL_MAX target hook.
12042 @item -mindexed-addressing
12043 @opindex mindexed-addressing
12044 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
12045 This is only safe if the hardware and/or OS implement 32 bit wrap-around
12046 semantics for the indexed addressing mode. The architecture allows the
12047 implementation of processors with 64 bit MMU, which the OS could use to
12048 get 32 bit addressing, but since no current hardware implementation supports
12049 this or any other way to make the indexed addressing mode safe to use in
12050 the 32 bit ABI, the default is -mno-indexed-addressing.
12052 @item -mgettrcost=@var{number}
12053 @opindex mgettrcost=@var{number}
12054 Set the cost assumed for the gettr instruction to @var{number}.
12055 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
12059 Assume pt* instructions won't trap. This will generally generate better
12060 scheduled code, but is unsafe on current hardware. The current architecture
12061 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
12062 This has the unintentional effect of making it unsafe to schedule ptabs /
12063 ptrel before a branch, or hoist it out of a loop. For example,
12064 __do_global_ctors, a part of libgcc that runs constructors at program
12065 startup, calls functions in a list which is delimited by -1. With the
12066 -mpt-fixed option, the ptabs will be done before testing against -1.
12067 That means that all the constructors will be run a bit quicker, but when
12068 the loop comes to the end of the list, the program crashes because ptabs
12069 loads -1 into a target register. Since this option is unsafe for any
12070 hardware implementing the current architecture specification, the default
12071 is -mno-pt-fixed. Unless the user specifies a specific cost with
12072 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
12073 this deters register allocation using target registers for storing
12076 @item -minvalid-symbols
12077 @opindex minvalid-symbols
12078 Assume symbols might be invalid. Ordinary function symbols generated by
12079 the compiler will always be valid to load with movi/shori/ptabs or
12080 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
12081 to generate symbols that will cause ptabs / ptrel to trap.
12082 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
12083 It will then prevent cross-basic-block cse, hoisting and most scheduling
12084 of symbol loads. The default is @option{-mno-invalid-symbols}.
12087 @node SPARC Options
12088 @subsection SPARC Options
12089 @cindex SPARC options
12091 These @samp{-m} options are supported on the SPARC:
12094 @item -mno-app-regs
12096 @opindex mno-app-regs
12098 Specify @option{-mapp-regs} to generate output using the global registers
12099 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
12102 To be fully SVR4 ABI compliant at the cost of some performance loss,
12103 specify @option{-mno-app-regs}. You should compile libraries and system
12104 software with this option.
12107 @itemx -mhard-float
12109 @opindex mhard-float
12110 Generate output containing floating point instructions. This is the
12114 @itemx -msoft-float
12116 @opindex msoft-float
12117 Generate output containing library calls for floating point.
12118 @strong{Warning:} the requisite libraries are not available for all SPARC
12119 targets. Normally the facilities of the machine's usual C compiler are
12120 used, but this cannot be done directly in cross-compilation. You must make
12121 your own arrangements to provide suitable library functions for
12122 cross-compilation. The embedded targets @samp{sparc-*-aout} and
12123 @samp{sparclite-*-*} do provide software floating point support.
12125 @option{-msoft-float} changes the calling convention in the output file;
12126 therefore, it is only useful if you compile @emph{all} of a program with
12127 this option. In particular, you need to compile @file{libgcc.a}, the
12128 library that comes with GCC, with @option{-msoft-float} in order for
12131 @item -mhard-quad-float
12132 @opindex mhard-quad-float
12133 Generate output containing quad-word (long double) floating point
12136 @item -msoft-quad-float
12137 @opindex msoft-quad-float
12138 Generate output containing library calls for quad-word (long double)
12139 floating point instructions. The functions called are those specified
12140 in the SPARC ABI@. This is the default.
12142 As of this writing, there are no SPARC implementations that have hardware
12143 support for the quad-word floating point instructions. They all invoke
12144 a trap handler for one of these instructions, and then the trap handler
12145 emulates the effect of the instruction. Because of the trap handler overhead,
12146 this is much slower than calling the ABI library routines. Thus the
12147 @option{-msoft-quad-float} option is the default.
12149 @item -mno-unaligned-doubles
12150 @itemx -munaligned-doubles
12151 @opindex mno-unaligned-doubles
12152 @opindex munaligned-doubles
12153 Assume that doubles have 8 byte alignment. This is the default.
12155 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
12156 alignment only if they are contained in another type, or if they have an
12157 absolute address. Otherwise, it assumes they have 4 byte alignment.
12158 Specifying this option avoids some rare compatibility problems with code
12159 generated by other compilers. It is not the default because it results
12160 in a performance loss, especially for floating point code.
12162 @item -mno-faster-structs
12163 @itemx -mfaster-structs
12164 @opindex mno-faster-structs
12165 @opindex mfaster-structs
12166 With @option{-mfaster-structs}, the compiler assumes that structures
12167 should have 8 byte alignment. This enables the use of pairs of
12168 @code{ldd} and @code{std} instructions for copies in structure
12169 assignment, in place of twice as many @code{ld} and @code{st} pairs.
12170 However, the use of this changed alignment directly violates the SPARC
12171 ABI@. Thus, it's intended only for use on targets where the developer
12172 acknowledges that their resulting code will not be directly in line with
12173 the rules of the ABI@.
12175 @item -mimpure-text
12176 @opindex mimpure-text
12177 @option{-mimpure-text}, used in addition to @option{-shared}, tells
12178 the compiler to not pass @option{-z text} to the linker when linking a
12179 shared object. Using this option, you can link position-dependent
12180 code into a shared object.
12182 @option{-mimpure-text} suppresses the ``relocations remain against
12183 allocatable but non-writable sections'' linker error message.
12184 However, the necessary relocations will trigger copy-on-write, and the
12185 shared object is not actually shared across processes. Instead of
12186 using @option{-mimpure-text}, you should compile all source code with
12187 @option{-fpic} or @option{-fPIC}.
12189 This option is only available on SunOS and Solaris.
12191 @item -mcpu=@var{cpu_type}
12193 Set the instruction set, register set, and instruction scheduling parameters
12194 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
12195 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
12196 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
12197 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
12198 @samp{ultrasparc3}.
12200 Default instruction scheduling parameters are used for values that select
12201 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
12202 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
12204 Here is a list of each supported architecture and their supported
12209 v8: supersparc, hypersparc
12210 sparclite: f930, f934, sparclite86x
12212 v9: ultrasparc, ultrasparc3
12215 By default (unless configured otherwise), GCC generates code for the V7
12216 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
12217 additionally optimizes it for the Cypress CY7C602 chip, as used in the
12218 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
12219 SPARCStation 1, 2, IPX etc.
12221 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
12222 architecture. The only difference from V7 code is that the compiler emits
12223 the integer multiply and integer divide instructions which exist in SPARC-V8
12224 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
12225 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
12228 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
12229 the SPARC architecture. This adds the integer multiply, integer divide step
12230 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
12231 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
12232 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
12233 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
12234 MB86934 chip, which is the more recent SPARClite with FPU@.
12236 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
12237 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
12238 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
12239 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
12240 optimizes it for the TEMIC SPARClet chip.
12242 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
12243 architecture. This adds 64-bit integer and floating-point move instructions,
12244 3 additional floating-point condition code registers and conditional move
12245 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
12246 optimizes it for the Sun UltraSPARC I/II chips. With
12247 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
12248 Sun UltraSPARC III chip.
12250 @item -mtune=@var{cpu_type}
12252 Set the instruction scheduling parameters for machine type
12253 @var{cpu_type}, but do not set the instruction set or register set that the
12254 option @option{-mcpu=@var{cpu_type}} would.
12256 The same values for @option{-mcpu=@var{cpu_type}} can be used for
12257 @option{-mtune=@var{cpu_type}}, but the only useful values are those
12258 that select a particular cpu implementation. Those are @samp{cypress},
12259 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
12260 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
12261 @samp{ultrasparc3}.
12266 @opindex mno-v8plus
12267 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
12268 difference from the V8 ABI is that the global and out registers are
12269 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
12270 mode for all SPARC-V9 processors.
12276 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
12277 Visual Instruction Set extensions. The default is @option{-mno-vis}.
12280 These @samp{-m} options are supported in addition to the above
12281 on SPARC-V9 processors in 64-bit environments:
12284 @item -mlittle-endian
12285 @opindex mlittle-endian
12286 Generate code for a processor running in little-endian mode. It is only
12287 available for a few configurations and most notably not on Solaris and Linux.
12293 Generate code for a 32-bit or 64-bit environment.
12294 The 32-bit environment sets int, long and pointer to 32 bits.
12295 The 64-bit environment sets int to 32 bits and long and pointer
12298 @item -mcmodel=medlow
12299 @opindex mcmodel=medlow
12300 Generate code for the Medium/Low code model: 64-bit addresses, programs
12301 must be linked in the low 32 bits of memory. Programs can be statically
12302 or dynamically linked.
12304 @item -mcmodel=medmid
12305 @opindex mcmodel=medmid
12306 Generate code for the Medium/Middle code model: 64-bit addresses, programs
12307 must be linked in the low 44 bits of memory, the text and data segments must
12308 be less than 2GB in size and the data segment must be located within 2GB of
12311 @item -mcmodel=medany
12312 @opindex mcmodel=medany
12313 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
12314 may be linked anywhere in memory, the text and data segments must be less
12315 than 2GB in size and the data segment must be located within 2GB of the
12318 @item -mcmodel=embmedany
12319 @opindex mcmodel=embmedany
12320 Generate code for the Medium/Anywhere code model for embedded systems:
12321 64-bit addresses, the text and data segments must be less than 2GB in
12322 size, both starting anywhere in memory (determined at link time). The
12323 global register %g4 points to the base of the data segment. Programs
12324 are statically linked and PIC is not supported.
12327 @itemx -mno-stack-bias
12328 @opindex mstack-bias
12329 @opindex mno-stack-bias
12330 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
12331 frame pointer if present, are offset by @minus{}2047 which must be added back
12332 when making stack frame references. This is the default in 64-bit mode.
12333 Otherwise, assume no such offset is present.
12336 These switches are supported in addition to the above on Solaris:
12341 Add support for multithreading using the Solaris threads library. This
12342 option sets flags for both the preprocessor and linker. This option does
12343 not affect the thread safety of object code produced by the compiler or
12344 that of libraries supplied with it.
12348 Add support for multithreading using the POSIX threads library. This
12349 option sets flags for both the preprocessor and linker. This option does
12350 not affect the thread safety of object code produced by the compiler or
12351 that of libraries supplied with it.
12354 @node System V Options
12355 @subsection Options for System V
12357 These additional options are available on System V Release 4 for
12358 compatibility with other compilers on those systems:
12363 Create a shared object.
12364 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
12368 Identify the versions of each tool used by the compiler, in a
12369 @code{.ident} assembler directive in the output.
12373 Refrain from adding @code{.ident} directives to the output file (this is
12376 @item -YP,@var{dirs}
12378 Search the directories @var{dirs}, and no others, for libraries
12379 specified with @option{-l}.
12381 @item -Ym,@var{dir}
12383 Look in the directory @var{dir} to find the M4 preprocessor.
12384 The assembler uses this option.
12385 @c This is supposed to go with a -Yd for predefined M4 macro files, but
12386 @c the generic assembler that comes with Solaris takes just -Ym.
12389 @node TMS320C3x/C4x Options
12390 @subsection TMS320C3x/C4x Options
12391 @cindex TMS320C3x/C4x Options
12393 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
12397 @item -mcpu=@var{cpu_type}
12399 Set the instruction set, register set, and instruction scheduling
12400 parameters for machine type @var{cpu_type}. Supported values for
12401 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
12402 @samp{c44}. The default is @samp{c40} to generate code for the
12407 @itemx -msmall-memory
12409 @opindex mbig-memory
12411 @opindex msmall-memory
12413 Generates code for the big or small memory model. The small memory
12414 model assumed that all data fits into one 64K word page. At run-time
12415 the data page (DP) register must be set to point to the 64K page
12416 containing the .bss and .data program sections. The big memory model is
12417 the default and requires reloading of the DP register for every direct
12424 Allow (disallow) allocation of general integer operands into the block
12425 count register BK@.
12431 Enable (disable) generation of code using decrement and branch,
12432 DBcond(D), instructions. This is enabled by default for the C4x. To be
12433 on the safe side, this is disabled for the C3x, since the maximum
12434 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
12435 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
12436 that it can utilize the decrement and branch instruction, but will give
12437 up if there is more than one memory reference in the loop. Thus a loop
12438 where the loop counter is decremented can generate slightly more
12439 efficient code, in cases where the RPTB instruction cannot be utilized.
12441 @item -mdp-isr-reload
12443 @opindex mdp-isr-reload
12445 Force the DP register to be saved on entry to an interrupt service
12446 routine (ISR), reloaded to point to the data section, and restored on
12447 exit from the ISR@. This should not be required unless someone has
12448 violated the small memory model by modifying the DP register, say within
12455 For the C3x use the 24-bit MPYI instruction for integer multiplies
12456 instead of a library call to guarantee 32-bit results. Note that if one
12457 of the operands is a constant, then the multiplication will be performed
12458 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
12459 then squaring operations are performed inline instead of a library call.
12462 @itemx -mno-fast-fix
12464 @opindex mno-fast-fix
12465 The C3x/C4x FIX instruction to convert a floating point value to an
12466 integer value chooses the nearest integer less than or equal to the
12467 floating point value rather than to the nearest integer. Thus if the
12468 floating point number is negative, the result will be incorrectly
12469 truncated an additional code is necessary to detect and correct this
12470 case. This option can be used to disable generation of the additional
12471 code required to correct the result.
12477 Enable (disable) generation of repeat block sequences using the RPTB
12478 instruction for zero overhead looping. The RPTB construct is only used
12479 for innermost loops that do not call functions or jump across the loop
12480 boundaries. There is no advantage having nested RPTB loops due to the
12481 overhead required to save and restore the RC, RS, and RE registers.
12482 This is enabled by default with @option{-O2}.
12484 @item -mrpts=@var{count}
12488 Enable (disable) the use of the single instruction repeat instruction
12489 RPTS@. If a repeat block contains a single instruction, and the loop
12490 count can be guaranteed to be less than the value @var{count}, GCC will
12491 emit a RPTS instruction instead of a RPTB@. If no value is specified,
12492 then a RPTS will be emitted even if the loop count cannot be determined
12493 at compile time. Note that the repeated instruction following RPTS does
12494 not have to be reloaded from memory each iteration, thus freeing up the
12495 CPU buses for operands. However, since interrupts are blocked by this
12496 instruction, it is disabled by default.
12498 @item -mloop-unsigned
12499 @itemx -mno-loop-unsigned
12500 @opindex mloop-unsigned
12501 @opindex mno-loop-unsigned
12502 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
12503 is @math{2^{31} + 1} since these instructions test if the iteration count is
12504 negative to terminate the loop. If the iteration count is unsigned
12505 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
12506 exceeded. This switch allows an unsigned iteration count.
12510 Try to emit an assembler syntax that the TI assembler (asm30) is happy
12511 with. This also enforces compatibility with the API employed by the TI
12512 C3x C compiler. For example, long doubles are passed as structures
12513 rather than in floating point registers.
12519 Generate code that uses registers (stack) for passing arguments to functions.
12520 By default, arguments are passed in registers where possible rather
12521 than by pushing arguments on to the stack.
12523 @item -mparallel-insns
12524 @itemx -mno-parallel-insns
12525 @opindex mparallel-insns
12526 @opindex mno-parallel-insns
12527 Allow the generation of parallel instructions. This is enabled by
12528 default with @option{-O2}.
12530 @item -mparallel-mpy
12531 @itemx -mno-parallel-mpy
12532 @opindex mparallel-mpy
12533 @opindex mno-parallel-mpy
12534 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
12535 provided @option{-mparallel-insns} is also specified. These instructions have
12536 tight register constraints which can pessimize the code generation
12537 of large functions.
12542 @subsection V850 Options
12543 @cindex V850 Options
12545 These @samp{-m} options are defined for V850 implementations:
12549 @itemx -mno-long-calls
12550 @opindex mlong-calls
12551 @opindex mno-long-calls
12552 Treat all calls as being far away (near). If calls are assumed to be
12553 far away, the compiler will always load the functions address up into a
12554 register, and call indirect through the pointer.
12560 Do not optimize (do optimize) basic blocks that use the same index
12561 pointer 4 or more times to copy pointer into the @code{ep} register, and
12562 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
12563 option is on by default if you optimize.
12565 @item -mno-prolog-function
12566 @itemx -mprolog-function
12567 @opindex mno-prolog-function
12568 @opindex mprolog-function
12569 Do not use (do use) external functions to save and restore registers
12570 at the prologue and epilogue of a function. The external functions
12571 are slower, but use less code space if more than one function saves
12572 the same number of registers. The @option{-mprolog-function} option
12573 is on by default if you optimize.
12577 Try to make the code as small as possible. At present, this just turns
12578 on the @option{-mep} and @option{-mprolog-function} options.
12580 @item -mtda=@var{n}
12582 Put static or global variables whose size is @var{n} bytes or less into
12583 the tiny data area that register @code{ep} points to. The tiny data
12584 area can hold up to 256 bytes in total (128 bytes for byte references).
12586 @item -msda=@var{n}
12588 Put static or global variables whose size is @var{n} bytes or less into
12589 the small data area that register @code{gp} points to. The small data
12590 area can hold up to 64 kilobytes.
12592 @item -mzda=@var{n}
12594 Put static or global variables whose size is @var{n} bytes or less into
12595 the first 32 kilobytes of memory.
12599 Specify that the target processor is the V850.
12602 @opindex mbig-switch
12603 Generate code suitable for big switch tables. Use this option only if
12604 the assembler/linker complain about out of range branches within a switch
12609 This option will cause r2 and r5 to be used in the code generated by
12610 the compiler. This setting is the default.
12612 @item -mno-app-regs
12613 @opindex mno-app-regs
12614 This option will cause r2 and r5 to be treated as fixed registers.
12618 Specify that the target processor is the V850E1. The preprocessor
12619 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
12620 this option is used.
12624 Specify that the target processor is the V850E@. The preprocessor
12625 constant @samp{__v850e__} will be defined if this option is used.
12627 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
12628 are defined then a default target processor will be chosen and the
12629 relevant @samp{__v850*__} preprocessor constant will be defined.
12631 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
12632 defined, regardless of which processor variant is the target.
12634 @item -mdisable-callt
12635 @opindex mdisable-callt
12636 This option will suppress generation of the CALLT instruction for the
12637 v850e and v850e1 flavors of the v850 architecture. The default is
12638 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
12643 @subsection VAX Options
12644 @cindex VAX options
12646 These @samp{-m} options are defined for the VAX:
12651 Do not output certain jump instructions (@code{aobleq} and so on)
12652 that the Unix assembler for the VAX cannot handle across long
12657 Do output those jump instructions, on the assumption that you
12658 will assemble with the GNU assembler.
12662 Output code for g-format floating point numbers instead of d-format.
12665 @node x86-64 Options
12666 @subsection x86-64 Options
12667 @cindex x86-64 options
12669 These are listed under @xref{i386 and x86-64 Options}.
12671 @node Xstormy16 Options
12672 @subsection Xstormy16 Options
12673 @cindex Xstormy16 Options
12675 These options are defined for Xstormy16:
12680 Choose startup files and linker script suitable for the simulator.
12683 @node Xtensa Options
12684 @subsection Xtensa Options
12685 @cindex Xtensa Options
12687 These options are supported for Xtensa targets:
12691 @itemx -mno-const16
12693 @opindex mno-const16
12694 Enable or disable use of @code{CONST16} instructions for loading
12695 constant values. The @code{CONST16} instruction is currently not a
12696 standard option from Tensilica. When enabled, @code{CONST16}
12697 instructions are always used in place of the standard @code{L32R}
12698 instructions. The use of @code{CONST16} is enabled by default only if
12699 the @code{L32R} instruction is not available.
12702 @itemx -mno-fused-madd
12703 @opindex mfused-madd
12704 @opindex mno-fused-madd
12705 Enable or disable use of fused multiply/add and multiply/subtract
12706 instructions in the floating-point option. This has no effect if the
12707 floating-point option is not also enabled. Disabling fused multiply/add
12708 and multiply/subtract instructions forces the compiler to use separate
12709 instructions for the multiply and add/subtract operations. This may be
12710 desirable in some cases where strict IEEE 754-compliant results are
12711 required: the fused multiply add/subtract instructions do not round the
12712 intermediate result, thereby producing results with @emph{more} bits of
12713 precision than specified by the IEEE standard. Disabling fused multiply
12714 add/subtract instructions also ensures that the program output is not
12715 sensitive to the compiler's ability to combine multiply and add/subtract
12718 @item -mtext-section-literals
12719 @itemx -mno-text-section-literals
12720 @opindex mtext-section-literals
12721 @opindex mno-text-section-literals
12722 Control the treatment of literal pools. The default is
12723 @option{-mno-text-section-literals}, which places literals in a separate
12724 section in the output file. This allows the literal pool to be placed
12725 in a data RAM/ROM, and it also allows the linker to combine literal
12726 pools from separate object files to remove redundant literals and
12727 improve code size. With @option{-mtext-section-literals}, the literals
12728 are interspersed in the text section in order to keep them as close as
12729 possible to their references. This may be necessary for large assembly
12732 @item -mtarget-align
12733 @itemx -mno-target-align
12734 @opindex mtarget-align
12735 @opindex mno-target-align
12736 When this option is enabled, GCC instructs the assembler to
12737 automatically align instructions to reduce branch penalties at the
12738 expense of some code density. The assembler attempts to widen density
12739 instructions to align branch targets and the instructions following call
12740 instructions. If there are not enough preceding safe density
12741 instructions to align a target, no widening will be performed. The
12742 default is @option{-mtarget-align}. These options do not affect the
12743 treatment of auto-aligned instructions like @code{LOOP}, which the
12744 assembler will always align, either by widening density instructions or
12745 by inserting no-op instructions.
12748 @itemx -mno-longcalls
12749 @opindex mlongcalls
12750 @opindex mno-longcalls
12751 When this option is enabled, GCC instructs the assembler to translate
12752 direct calls to indirect calls unless it can determine that the target
12753 of a direct call is in the range allowed by the call instruction. This
12754 translation typically occurs for calls to functions in other source
12755 files. Specifically, the assembler translates a direct @code{CALL}
12756 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
12757 The default is @option{-mno-longcalls}. This option should be used in
12758 programs where the call target can potentially be out of range. This
12759 option is implemented in the assembler, not the compiler, so the
12760 assembly code generated by GCC will still show direct call
12761 instructions---look at the disassembled object code to see the actual
12762 instructions. Note that the assembler will use an indirect call for
12763 every cross-file call, not just those that really will be out of range.
12766 @node zSeries Options
12767 @subsection zSeries Options
12768 @cindex zSeries options
12770 These are listed under @xref{S/390 and zSeries Options}.
12772 @node Code Gen Options
12773 @section Options for Code Generation Conventions
12774 @cindex code generation conventions
12775 @cindex options, code generation
12776 @cindex run-time options
12778 These machine-independent options control the interface conventions
12779 used in code generation.
12781 Most of them have both positive and negative forms; the negative form
12782 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
12783 one of the forms is listed---the one which is not the default. You
12784 can figure out the other form by either removing @samp{no-} or adding
12788 @item -fbounds-check
12789 @opindex fbounds-check
12790 For front-ends that support it, generate additional code to check that
12791 indices used to access arrays are within the declared range. This is
12792 currently only supported by the Java and Fortran 77 front-ends, where
12793 this option defaults to true and false respectively.
12797 This option generates traps for signed overflow on addition, subtraction,
12798 multiplication operations.
12802 This option instructs the compiler to assume that signed arithmetic
12803 overflow of addition, subtraction and multiplication wraps around
12804 using twos-complement representation. This flag enables some optimizations
12805 and disables others. This option is enabled by default for the Java
12806 front-end, as required by the Java language specification.
12809 @opindex fexceptions
12810 Enable exception handling. Generates extra code needed to propagate
12811 exceptions. For some targets, this implies GCC will generate frame
12812 unwind information for all functions, which can produce significant data
12813 size overhead, although it does not affect execution. If you do not
12814 specify this option, GCC will enable it by default for languages like
12815 C++ which normally require exception handling, and disable it for
12816 languages like C that do not normally require it. However, you may need
12817 to enable this option when compiling C code that needs to interoperate
12818 properly with exception handlers written in C++. You may also wish to
12819 disable this option if you are compiling older C++ programs that don't
12820 use exception handling.
12822 @item -fnon-call-exceptions
12823 @opindex fnon-call-exceptions
12824 Generate code that allows trapping instructions to throw exceptions.
12825 Note that this requires platform-specific runtime support that does
12826 not exist everywhere. Moreover, it only allows @emph{trapping}
12827 instructions to throw exceptions, i.e.@: memory references or floating
12828 point instructions. It does not allow exceptions to be thrown from
12829 arbitrary signal handlers such as @code{SIGALRM}.
12831 @item -funwind-tables
12832 @opindex funwind-tables
12833 Similar to @option{-fexceptions}, except that it will just generate any needed
12834 static data, but will not affect the generated code in any other way.
12835 You will normally not enable this option; instead, a language processor
12836 that needs this handling would enable it on your behalf.
12838 @item -fasynchronous-unwind-tables
12839 @opindex fasynchronous-unwind-tables
12840 Generate unwind table in dwarf2 format, if supported by target machine. The
12841 table is exact at each instruction boundary, so it can be used for stack
12842 unwinding from asynchronous events (such as debugger or garbage collector).
12844 @item -fpcc-struct-return
12845 @opindex fpcc-struct-return
12846 Return ``short'' @code{struct} and @code{union} values in memory like
12847 longer ones, rather than in registers. This convention is less
12848 efficient, but it has the advantage of allowing intercallability between
12849 GCC-compiled files and files compiled with other compilers, particularly
12850 the Portable C Compiler (pcc).
12852 The precise convention for returning structures in memory depends
12853 on the target configuration macros.
12855 Short structures and unions are those whose size and alignment match
12856 that of some integer type.
12858 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
12859 switch is not binary compatible with code compiled with the
12860 @option{-freg-struct-return} switch.
12861 Use it to conform to a non-default application binary interface.
12863 @item -freg-struct-return
12864 @opindex freg-struct-return
12865 Return @code{struct} and @code{union} values in registers when possible.
12866 This is more efficient for small structures than
12867 @option{-fpcc-struct-return}.
12869 If you specify neither @option{-fpcc-struct-return} nor
12870 @option{-freg-struct-return}, GCC defaults to whichever convention is
12871 standard for the target. If there is no standard convention, GCC
12872 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
12873 the principal compiler. In those cases, we can choose the standard, and
12874 we chose the more efficient register return alternative.
12876 @strong{Warning:} code compiled with the @option{-freg-struct-return}
12877 switch is not binary compatible with code compiled with the
12878 @option{-fpcc-struct-return} switch.
12879 Use it to conform to a non-default application binary interface.
12881 @item -fshort-enums
12882 @opindex fshort-enums
12883 Allocate to an @code{enum} type only as many bytes as it needs for the
12884 declared range of possible values. Specifically, the @code{enum} type
12885 will be equivalent to the smallest integer type which has enough room.
12887 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
12888 code that is not binary compatible with code generated without that switch.
12889 Use it to conform to a non-default application binary interface.
12891 @item -fshort-double
12892 @opindex fshort-double
12893 Use the same size for @code{double} as for @code{float}.
12895 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
12896 code that is not binary compatible with code generated without that switch.
12897 Use it to conform to a non-default application binary interface.
12899 @item -fshort-wchar
12900 @opindex fshort-wchar
12901 Override the underlying type for @samp{wchar_t} to be @samp{short
12902 unsigned int} instead of the default for the target. This option is
12903 useful for building programs to run under WINE@.
12905 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
12906 code that is not binary compatible with code generated without that switch.
12907 Use it to conform to a non-default application binary interface.
12909 @item -fshared-data
12910 @opindex fshared-data
12911 Requests that the data and non-@code{const} variables of this
12912 compilation be shared data rather than private data. The distinction
12913 makes sense only on certain operating systems, where shared data is
12914 shared between processes running the same program, while private data
12915 exists in one copy per process.
12918 @opindex fno-common
12919 In C, allocate even uninitialized global variables in the data section of the
12920 object file, rather than generating them as common blocks. This has the
12921 effect that if the same variable is declared (without @code{extern}) in
12922 two different compilations, you will get an error when you link them.
12923 The only reason this might be useful is if you wish to verify that the
12924 program will work on other systems which always work this way.
12928 Ignore the @samp{#ident} directive.
12930 @item -finhibit-size-directive
12931 @opindex finhibit-size-directive
12932 Don't output a @code{.size} assembler directive, or anything else that
12933 would cause trouble if the function is split in the middle, and the
12934 two halves are placed at locations far apart in memory. This option is
12935 used when compiling @file{crtstuff.c}; you should not need to use it
12938 @item -fverbose-asm
12939 @opindex fverbose-asm
12940 Put extra commentary information in the generated assembly code to
12941 make it more readable. This option is generally only of use to those
12942 who actually need to read the generated assembly code (perhaps while
12943 debugging the compiler itself).
12945 @option{-fno-verbose-asm}, the default, causes the
12946 extra information to be omitted and is useful when comparing two assembler
12951 @cindex global offset table
12953 Generate position-independent code (PIC) suitable for use in a shared
12954 library, if supported for the target machine. Such code accesses all
12955 constant addresses through a global offset table (GOT)@. The dynamic
12956 loader resolves the GOT entries when the program starts (the dynamic
12957 loader is not part of GCC; it is part of the operating system). If
12958 the GOT size for the linked executable exceeds a machine-specific
12959 maximum size, you get an error message from the linker indicating that
12960 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
12961 instead. (These maximums are 8k on the SPARC and 32k
12962 on the m68k and RS/6000. The 386 has no such limit.)
12964 Position-independent code requires special support, and therefore works
12965 only on certain machines. For the 386, GCC supports PIC for System V
12966 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
12967 position-independent.
12969 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
12974 If supported for the target machine, emit position-independent code,
12975 suitable for dynamic linking and avoiding any limit on the size of the
12976 global offset table. This option makes a difference on the m68k,
12977 PowerPC and SPARC@.
12979 Position-independent code requires special support, and therefore works
12980 only on certain machines.
12982 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
12989 These options are similar to @option{-fpic} and @option{-fPIC}, but
12990 generated position independent code can be only linked into executables.
12991 Usually these options are used when @option{-pie} GCC option will be
12992 used during linking.
12994 @item -fno-jump-tables
12995 @opindex fno-jump-tables
12996 Do not use jump tables for switch statements even where it would be
12997 more efficient than other code generation strategies. This option is
12998 of use in conjunction with @option{-fpic} or @option{-fPIC} for
12999 building code which forms part of a dynamic linker and cannot
13000 reference the address of a jump table. On some targets, jump tables
13001 do not require a GOT and this option is not needed.
13003 @item -ffixed-@var{reg}
13005 Treat the register named @var{reg} as a fixed register; generated code
13006 should never refer to it (except perhaps as a stack pointer, frame
13007 pointer or in some other fixed role).
13009 @var{reg} must be the name of a register. The register names accepted
13010 are machine-specific and are defined in the @code{REGISTER_NAMES}
13011 macro in the machine description macro file.
13013 This flag does not have a negative form, because it specifies a
13016 @item -fcall-used-@var{reg}
13017 @opindex fcall-used
13018 Treat the register named @var{reg} as an allocable register that is
13019 clobbered by function calls. It may be allocated for temporaries or
13020 variables that do not live across a call. Functions compiled this way
13021 will not save and restore the register @var{reg}.
13023 It is an error to used this flag with the frame pointer or stack pointer.
13024 Use of this flag for other registers that have fixed pervasive roles in
13025 the machine's execution model will produce disastrous results.
13027 This flag does not have a negative form, because it specifies a
13030 @item -fcall-saved-@var{reg}
13031 @opindex fcall-saved
13032 Treat the register named @var{reg} as an allocable register saved by
13033 functions. It may be allocated even for temporaries or variables that
13034 live across a call. Functions compiled this way will save and restore
13035 the register @var{reg} if they use it.
13037 It is an error to used this flag with the frame pointer or stack pointer.
13038 Use of this flag for other registers that have fixed pervasive roles in
13039 the machine's execution model will produce disastrous results.
13041 A different sort of disaster will result from the use of this flag for
13042 a register in which function values may be returned.
13044 This flag does not have a negative form, because it specifies a
13047 @item -fpack-struct[=@var{n}]
13048 @opindex fpack-struct
13049 Without a value specified, pack all structure members together without
13050 holes. When a value is specified (which must be a small power of two), pack
13051 structure members according to this value, representing the maximum
13052 alignment (that is, objects with default alignment requirements larger than
13053 this will be output potentially unaligned at the next fitting location.
13055 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
13056 code that is not binary compatible with code generated without that switch.
13057 Additionally, it makes the code suboptimal.
13058 Use it to conform to a non-default application binary interface.
13060 @item -finstrument-functions
13061 @opindex finstrument-functions
13062 Generate instrumentation calls for entry and exit to functions. Just
13063 after function entry and just before function exit, the following
13064 profiling functions will be called with the address of the current
13065 function and its call site. (On some platforms,
13066 @code{__builtin_return_address} does not work beyond the current
13067 function, so the call site information may not be available to the
13068 profiling functions otherwise.)
13071 void __cyg_profile_func_enter (void *this_fn,
13073 void __cyg_profile_func_exit (void *this_fn,
13077 The first argument is the address of the start of the current function,
13078 which may be looked up exactly in the symbol table.
13080 This instrumentation is also done for functions expanded inline in other
13081 functions. The profiling calls will indicate where, conceptually, the
13082 inline function is entered and exited. This means that addressable
13083 versions of such functions must be available. If all your uses of a
13084 function are expanded inline, this may mean an additional expansion of
13085 code size. If you use @samp{extern inline} in your C code, an
13086 addressable version of such functions must be provided. (This is
13087 normally the case anyways, but if you get lucky and the optimizer always
13088 expands the functions inline, you might have gotten away without
13089 providing static copies.)
13091 A function may be given the attribute @code{no_instrument_function}, in
13092 which case this instrumentation will not be done. This can be used, for
13093 example, for the profiling functions listed above, high-priority
13094 interrupt routines, and any functions from which the profiling functions
13095 cannot safely be called (perhaps signal handlers, if the profiling
13096 routines generate output or allocate memory).
13098 @item -fstack-check
13099 @opindex fstack-check
13100 Generate code to verify that you do not go beyond the boundary of the
13101 stack. You should specify this flag if you are running in an
13102 environment with multiple threads, but only rarely need to specify it in
13103 a single-threaded environment since stack overflow is automatically
13104 detected on nearly all systems if there is only one stack.
13106 Note that this switch does not actually cause checking to be done; the
13107 operating system must do that. The switch causes generation of code
13108 to ensure that the operating system sees the stack being extended.
13110 @item -fstack-limit-register=@var{reg}
13111 @itemx -fstack-limit-symbol=@var{sym}
13112 @itemx -fno-stack-limit
13113 @opindex fstack-limit-register
13114 @opindex fstack-limit-symbol
13115 @opindex fno-stack-limit
13116 Generate code to ensure that the stack does not grow beyond a certain value,
13117 either the value of a register or the address of a symbol. If the stack
13118 would grow beyond the value, a signal is raised. For most targets,
13119 the signal is raised before the stack overruns the boundary, so
13120 it is possible to catch the signal without taking special precautions.
13122 For instance, if the stack starts at absolute address @samp{0x80000000}
13123 and grows downwards, you can use the flags
13124 @option{-fstack-limit-symbol=__stack_limit} and
13125 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
13126 of 128KB@. Note that this may only work with the GNU linker.
13128 @cindex aliasing of parameters
13129 @cindex parameters, aliased
13130 @item -fargument-alias
13131 @itemx -fargument-noalias
13132 @itemx -fargument-noalias-global
13133 @opindex fargument-alias
13134 @opindex fargument-noalias
13135 @opindex fargument-noalias-global
13136 Specify the possible relationships among parameters and between
13137 parameters and global data.
13139 @option{-fargument-alias} specifies that arguments (parameters) may
13140 alias each other and may alias global storage.@*
13141 @option{-fargument-noalias} specifies that arguments do not alias
13142 each other, but may alias global storage.@*
13143 @option{-fargument-noalias-global} specifies that arguments do not
13144 alias each other and do not alias global storage.
13146 Each language will automatically use whatever option is required by
13147 the language standard. You should not need to use these options yourself.
13149 @item -fleading-underscore
13150 @opindex fleading-underscore
13151 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
13152 change the way C symbols are represented in the object file. One use
13153 is to help link with legacy assembly code.
13155 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
13156 generate code that is not binary compatible with code generated without that
13157 switch. Use it to conform to a non-default application binary interface.
13158 Not all targets provide complete support for this switch.
13160 @item -ftls-model=@var{model}
13161 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
13162 The @var{model} argument should be one of @code{global-dynamic},
13163 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
13165 The default without @option{-fpic} is @code{initial-exec}; with
13166 @option{-fpic} the default is @code{global-dynamic}.
13168 @item -fvisibility=@var{default|internal|hidden|protected}
13169 @opindex fvisibility
13170 Set the default ELF image symbol visibility to the specified option---all
13171 symbols will be marked with this unless overridden within the code.
13172 Using this feature can very substantially improve linking and
13173 load times of shared object libraries, produce more optimized
13174 code, provide near-perfect API export and prevent symbol clashes.
13175 It is @strong{strongly} recommended that you use this in any shared objects
13178 Despite the nomenclature, @code{default} always means public ie;
13179 available to be linked against from outside the shared object.
13180 @code{protected} and @code{internal} are pretty useless in real-world
13181 usage so the only other commonly used option will be @code{hidden}.
13182 The default if @option{-fvisibility} isn't specified is
13183 @code{default}, i.e., make every
13184 symbol public---this causes the same behavior as previous versions of
13187 A good explanation of the benefits offered by ensuring ELF
13188 symbols have the correct visibility is given by ``How To Write
13189 Shared Libraries'' by Ulrich Drepper (which can be found at
13190 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
13191 solution made possible by this option to marking things hidden when
13192 the default is public is to make the default hidden and mark things
13193 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
13194 and @code{__attribute__ ((visibility("default")))} instead of
13195 @code{__declspec(dllexport)} you get almost identical semantics with
13196 identical syntax. This is a great boon to those working with
13197 cross-platform projects.
13199 For those adding visibility support to existing code, you may find
13200 @samp{#pragma GCC visibility} of use. This works by you enclosing
13201 the declarations you wish to set visibility for with (for example)
13202 @samp{#pragma GCC visibility push(hidden)} and
13203 @samp{#pragma GCC visibility pop}.
13204 Bear in mind that symbol visibility should be viewed @strong{as
13205 part of the API interface contract} and thus all new code should
13206 always specify visibility when it is not the default ie; declarations
13207 only for use within the local DSO should @strong{always} be marked explicitly
13208 as hidden as so to avoid PLT indirection overheads---making this
13209 abundantly clear also aids readability and self-documentation of the code.
13210 Note that due to ISO C++ specification requirements, operator new and
13211 operator delete must always be of default visibility.
13213 An overview of these techniques, their benefits and how to use them
13214 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
13220 @node Environment Variables
13221 @section Environment Variables Affecting GCC
13222 @cindex environment variables
13224 @c man begin ENVIRONMENT
13225 This section describes several environment variables that affect how GCC
13226 operates. Some of them work by specifying directories or prefixes to use
13227 when searching for various kinds of files. Some are used to specify other
13228 aspects of the compilation environment.
13230 Note that you can also specify places to search using options such as
13231 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
13232 take precedence over places specified using environment variables, which
13233 in turn take precedence over those specified by the configuration of GCC@.
13234 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
13235 GNU Compiler Collection (GCC) Internals}.
13240 @c @itemx LC_COLLATE
13242 @c @itemx LC_MONETARY
13243 @c @itemx LC_NUMERIC
13248 @c @findex LC_COLLATE
13249 @findex LC_MESSAGES
13250 @c @findex LC_MONETARY
13251 @c @findex LC_NUMERIC
13255 These environment variables control the way that GCC uses
13256 localization information that allow GCC to work with different
13257 national conventions. GCC inspects the locale categories
13258 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
13259 so. These locale categories can be set to any value supported by your
13260 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
13261 Kingdom encoded in UTF-8.
13263 The @env{LC_CTYPE} environment variable specifies character
13264 classification. GCC uses it to determine the character boundaries in
13265 a string; this is needed for some multibyte encodings that contain quote
13266 and escape characters that would otherwise be interpreted as a string
13269 The @env{LC_MESSAGES} environment variable specifies the language to
13270 use in diagnostic messages.
13272 If the @env{LC_ALL} environment variable is set, it overrides the value
13273 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
13274 and @env{LC_MESSAGES} default to the value of the @env{LANG}
13275 environment variable. If none of these variables are set, GCC
13276 defaults to traditional C English behavior.
13280 If @env{TMPDIR} is set, it specifies the directory to use for temporary
13281 files. GCC uses temporary files to hold the output of one stage of
13282 compilation which is to be used as input to the next stage: for example,
13283 the output of the preprocessor, which is the input to the compiler
13286 @item GCC_EXEC_PREFIX
13287 @findex GCC_EXEC_PREFIX
13288 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
13289 names of the subprograms executed by the compiler. No slash is added
13290 when this prefix is combined with the name of a subprogram, but you can
13291 specify a prefix that ends with a slash if you wish.
13293 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
13294 an appropriate prefix to use based on the pathname it was invoked with.
13296 If GCC cannot find the subprogram using the specified prefix, it
13297 tries looking in the usual places for the subprogram.
13299 The default value of @env{GCC_EXEC_PREFIX} is
13300 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
13301 of @code{prefix} when you ran the @file{configure} script.
13303 Other prefixes specified with @option{-B} take precedence over this prefix.
13305 This prefix is also used for finding files such as @file{crt0.o} that are
13308 In addition, the prefix is used in an unusual way in finding the
13309 directories to search for header files. For each of the standard
13310 directories whose name normally begins with @samp{/usr/local/lib/gcc}
13311 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
13312 replacing that beginning with the specified prefix to produce an
13313 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
13314 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
13315 These alternate directories are searched first; the standard directories
13318 @item COMPILER_PATH
13319 @findex COMPILER_PATH
13320 The value of @env{COMPILER_PATH} is a colon-separated list of
13321 directories, much like @env{PATH}. GCC tries the directories thus
13322 specified when searching for subprograms, if it can't find the
13323 subprograms using @env{GCC_EXEC_PREFIX}.
13326 @findex LIBRARY_PATH
13327 The value of @env{LIBRARY_PATH} is a colon-separated list of
13328 directories, much like @env{PATH}. When configured as a native compiler,
13329 GCC tries the directories thus specified when searching for special
13330 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
13331 using GCC also uses these directories when searching for ordinary
13332 libraries for the @option{-l} option (but directories specified with
13333 @option{-L} come first).
13337 @cindex locale definition
13338 This variable is used to pass locale information to the compiler. One way in
13339 which this information is used is to determine the character set to be used
13340 when character literals, string literals and comments are parsed in C and C++.
13341 When the compiler is configured to allow multibyte characters,
13342 the following values for @env{LANG} are recognized:
13346 Recognize JIS characters.
13348 Recognize SJIS characters.
13350 Recognize EUCJP characters.
13353 If @env{LANG} is not defined, or if it has some other value, then the
13354 compiler will use mblen and mbtowc as defined by the default locale to
13355 recognize and translate multibyte characters.
13359 Some additional environments variables affect the behavior of the
13362 @include cppenv.texi
13366 @node Precompiled Headers
13367 @section Using Precompiled Headers
13368 @cindex precompiled headers
13369 @cindex speed of compilation
13371 Often large projects have many header files that are included in every
13372 source file. The time the compiler takes to process these header files
13373 over and over again can account for nearly all of the time required to
13374 build the project. To make builds faster, GCC allows users to
13375 `precompile' a header file; then, if builds can use the precompiled
13376 header file they will be much faster.
13378 To create a precompiled header file, simply compile it as you would any
13379 other file, if necessary using the @option{-x} option to make the driver
13380 treat it as a C or C++ header file. You will probably want to use a
13381 tool like @command{make} to keep the precompiled header up-to-date when
13382 the headers it contains change.
13384 A precompiled header file will be searched for when @code{#include} is
13385 seen in the compilation. As it searches for the included file
13386 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
13387 compiler looks for a precompiled header in each directory just before it
13388 looks for the include file in that directory. The name searched for is
13389 the name specified in the @code{#include} with @samp{.gch} appended. If
13390 the precompiled header file can't be used, it is ignored.
13392 For instance, if you have @code{#include "all.h"}, and you have
13393 @file{all.h.gch} in the same directory as @file{all.h}, then the
13394 precompiled header file will be used if possible, and the original
13395 header will be used otherwise.
13397 Alternatively, you might decide to put the precompiled header file in a
13398 directory and use @option{-I} to ensure that directory is searched
13399 before (or instead of) the directory containing the original header.
13400 Then, if you want to check that the precompiled header file is always
13401 used, you can put a file of the same name as the original header in this
13402 directory containing an @code{#error} command.
13404 This also works with @option{-include}. So yet another way to use
13405 precompiled headers, good for projects not designed with precompiled
13406 header files in mind, is to simply take most of the header files used by
13407 a project, include them from another header file, precompile that header
13408 file, and @option{-include} the precompiled header. If the header files
13409 have guards against multiple inclusion, they will be skipped because
13410 they've already been included (in the precompiled header).
13412 If you need to precompile the same header file for different
13413 languages, targets, or compiler options, you can instead make a
13414 @emph{directory} named like @file{all.h.gch}, and put each precompiled
13415 header in the directory, perhaps using @option{-o}. It doesn't matter
13416 what you call the files in the directory, every precompiled header in
13417 the directory will be considered. The first precompiled header
13418 encountered in the directory that is valid for this compilation will
13419 be used; they're searched in no particular order.
13421 There are many other possibilities, limited only by your imagination,
13422 good sense, and the constraints of your build system.
13424 A precompiled header file can be used only when these conditions apply:
13428 Only one precompiled header can be used in a particular compilation.
13431 A precompiled header can't be used once the first C token is seen. You
13432 can have preprocessor directives before a precompiled header; you can
13433 even include a precompiled header from inside another header, so long as
13434 there are no C tokens before the @code{#include}.
13437 The precompiled header file must be produced for the same language as
13438 the current compilation. You can't use a C precompiled header for a C++
13442 The precompiled header file must have been produced by the same compiler
13443 binary as the current compilation is using.
13446 Any macros defined before the precompiled header is included must
13447 either be defined in the same way as when the precompiled header was
13448 generated, or must not affect the precompiled header, which usually
13449 means that they don't appear in the precompiled header at all.
13451 The @option{-D} option is one way to define a macro before a
13452 precompiled header is included; using a @code{#define} can also do it.
13453 There are also some options that define macros implicitly, like
13454 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
13457 @item If debugging information is output when using the precompiled
13458 header, using @option{-g} or similar, the same kind of debugging information
13459 must have been output when building the precompiled header. However,
13460 a precompiled header built using @option{-g} can be used in a compilation
13461 when no debugging information is being output.
13463 @item The same @option{-m} options must generally be used when building
13464 and using the precompiled header. @xref{Submodel Options},
13465 for any cases where this rule is relaxed.
13467 @item Each of the following options must be the same when building and using
13468 the precompiled header:
13470 @gccoptlist{-fexceptions -funit-at-a-time}
13473 Some other command-line options starting with @option{-f},
13474 @option{-p}, or @option{-O} must be defined in the same way as when
13475 the precompiled header was generated. At present, it's not clear
13476 which options are safe to change and which are not; the safest choice
13477 is to use exactly the same options when generating and using the
13478 precompiled header. The following are known to be safe:
13480 @gccoptlist{-fmessage-length= -fpreprocessed
13481 -fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous
13482 -fsched-verbose=<number> -fschedule-insns -fvisibility=
13487 For all of these except the last, the compiler will automatically
13488 ignore the precompiled header if the conditions aren't met. If you
13489 find an option combination that doesn't work and doesn't cause the
13490 precompiled header to be ignored, please consider filing a bug report,
13493 If you do use differing options when generating and using the
13494 precompiled header, the actual behavior will be a mixture of the
13495 behavior for the options. For instance, if you use @option{-g} to
13496 generate the precompiled header but not when using it, you may or may
13497 not get debugging information for routines in the precompiled header.
13499 @node Running Protoize
13500 @section Running Protoize
13502 The program @code{protoize} is an optional part of GCC@. You can use
13503 it to add prototypes to a program, thus converting the program to ISO
13504 C in one respect. The companion program @code{unprotoize} does the
13505 reverse: it removes argument types from any prototypes that are found.
13507 When you run these programs, you must specify a set of source files as
13508 command line arguments. The conversion programs start out by compiling
13509 these files to see what functions they define. The information gathered
13510 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
13512 After scanning comes actual conversion. The specified files are all
13513 eligible to be converted; any files they include (whether sources or
13514 just headers) are eligible as well.
13516 But not all the eligible files are converted. By default,
13517 @code{protoize} and @code{unprotoize} convert only source and header
13518 files in the current directory. You can specify additional directories
13519 whose files should be converted with the @option{-d @var{directory}}
13520 option. You can also specify particular files to exclude with the
13521 @option{-x @var{file}} option. A file is converted if it is eligible, its
13522 directory name matches one of the specified directory names, and its
13523 name within the directory has not been excluded.
13525 Basic conversion with @code{protoize} consists of rewriting most
13526 function definitions and function declarations to specify the types of
13527 the arguments. The only ones not rewritten are those for varargs
13530 @code{protoize} optionally inserts prototype declarations at the
13531 beginning of the source file, to make them available for any calls that
13532 precede the function's definition. Or it can insert prototype
13533 declarations with block scope in the blocks where undeclared functions
13536 Basic conversion with @code{unprotoize} consists of rewriting most
13537 function declarations to remove any argument types, and rewriting
13538 function definitions to the old-style pre-ISO form.
13540 Both conversion programs print a warning for any function declaration or
13541 definition that they can't convert. You can suppress these warnings
13544 The output from @code{protoize} or @code{unprotoize} replaces the
13545 original source file. The original file is renamed to a name ending
13546 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
13547 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
13548 for DOS) file already exists, then the source file is simply discarded.
13550 @code{protoize} and @code{unprotoize} both depend on GCC itself to
13551 scan the program and collect information about the functions it uses.
13552 So neither of these programs will work until GCC is installed.
13554 Here is a table of the options you can use with @code{protoize} and
13555 @code{unprotoize}. Each option works with both programs unless
13559 @item -B @var{directory}
13560 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
13561 usual directory (normally @file{/usr/local/lib}). This file contains
13562 prototype information about standard system functions. This option
13563 applies only to @code{protoize}.
13565 @item -c @var{compilation-options}
13566 Use @var{compilation-options} as the options when running @command{gcc} to
13567 produce the @samp{.X} files. The special option @option{-aux-info} is
13568 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
13570 Note that the compilation options must be given as a single argument to
13571 @code{protoize} or @code{unprotoize}. If you want to specify several
13572 @command{gcc} options, you must quote the entire set of compilation options
13573 to make them a single word in the shell.
13575 There are certain @command{gcc} arguments that you cannot use, because they
13576 would produce the wrong kind of output. These include @option{-g},
13577 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
13578 the @var{compilation-options}, they are ignored.
13581 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
13582 systems) instead of @samp{.c}. This is convenient if you are converting
13583 a C program to C++. This option applies only to @code{protoize}.
13586 Add explicit global declarations. This means inserting explicit
13587 declarations at the beginning of each source file for each function
13588 that is called in the file and was not declared. These declarations
13589 precede the first function definition that contains a call to an
13590 undeclared function. This option applies only to @code{protoize}.
13592 @item -i @var{string}
13593 Indent old-style parameter declarations with the string @var{string}.
13594 This option applies only to @code{protoize}.
13596 @code{unprotoize} converts prototyped function definitions to old-style
13597 function definitions, where the arguments are declared between the
13598 argument list and the initial @samp{@{}. By default, @code{unprotoize}
13599 uses five spaces as the indentation. If you want to indent with just
13600 one space instead, use @option{-i " "}.
13603 Keep the @samp{.X} files. Normally, they are deleted after conversion
13607 Add explicit local declarations. @code{protoize} with @option{-l} inserts
13608 a prototype declaration for each function in each block which calls the
13609 function without any declaration. This option applies only to
13613 Make no real changes. This mode just prints information about the conversions
13614 that would have been done without @option{-n}.
13617 Make no @samp{.save} files. The original files are simply deleted.
13618 Use this option with caution.
13620 @item -p @var{program}
13621 Use the program @var{program} as the compiler. Normally, the name
13622 @file{gcc} is used.
13625 Work quietly. Most warnings are suppressed.
13628 Print the version number, just like @option{-v} for @command{gcc}.
13631 If you need special compiler options to compile one of your program's
13632 source files, then you should generate that file's @samp{.X} file
13633 specially, by running @command{gcc} on that source file with the
13634 appropriate options and the option @option{-aux-info}. Then run
13635 @code{protoize} on the entire set of files. @code{protoize} will use
13636 the existing @samp{.X} file because it is newer than the source file.
13640 gcc -Dfoo=bar file1.c -aux-info file1.X
13645 You need to include the special files along with the rest in the
13646 @code{protoize} command, even though their @samp{.X} files already
13647 exist, because otherwise they won't get converted.
13649 @xref{Protoize Caveats}, for more information on how to use
13650 @code{protoize} successfully.