1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
12 @c man begin COPYRIGHT
13 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
14 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
15 Free Software Foundation, Inc.
17 Permission is granted to copy, distribute and/or modify this document
18 under the terms of the GNU Free Documentation License, Version 1.2 or
19 any later version published by the Free Software Foundation; with the
20 Invariant Sections being ``GNU General Public License'' and ``Funding
21 Free Software'', the Front-Cover texts being (a) (see below), and with
22 the Back-Cover Texts being (b) (see below). A copy of the license is
23 included in the gfdl(7) man page.
25 (a) The FSF's Front-Cover Text is:
29 (b) The FSF's Back-Cover Text is:
31 You have freedom to copy and modify this GNU Manual, like GNU
32 software. Copies published by the Free Software Foundation raise
33 funds for GNU development.
35 @c Set file name and title for the man page.
37 @settitle GNU project C and C++ compiler
39 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
40 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
41 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
42 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
43 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
44 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
45 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
47 Only the most useful options are listed here; see below for the
48 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
51 gpl(7), gfdl(7), fsf-funding(7),
52 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
53 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
54 @file{ld}, @file{binutils} and @file{gdb}.
57 For instructions on reporting bugs, see
61 See the Info entry for @command{gcc}, or
62 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
63 for contributors to GCC@.
68 @chapter GCC Command Options
69 @cindex GCC command options
70 @cindex command options
71 @cindex options, GCC command
73 @c man begin DESCRIPTION
74 When you invoke GCC, it normally does preprocessing, compilation,
75 assembly and linking. The ``overall options'' allow you to stop this
76 process at an intermediate stage. For example, the @option{-c} option
77 says not to run the linker. Then the output consists of object files
78 output by the assembler.
80 Other options are passed on to one stage of processing. Some options
81 control the preprocessor and others the compiler itself. Yet other
82 options control the assembler and linker; most of these are not
83 documented here, since you rarely need to use any of them.
85 @cindex C compilation options
86 Most of the command line options that you can use with GCC are useful
87 for C programs; when an option is only useful with another language
88 (usually C++), the explanation says so explicitly. If the description
89 for a particular option does not mention a source language, you can use
90 that option with all supported languages.
92 @cindex C++ compilation options
93 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
94 options for compiling C++ programs.
96 @cindex grouping options
97 @cindex options, grouping
98 The @command{gcc} program accepts options and file names as operands. Many
99 options have multi-letter names; therefore multiple single-letter options
100 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
103 @cindex order of options
104 @cindex options, order
105 You can mix options and other arguments. For the most part, the order
106 you use doesn't matter. Order does matter when you use several
107 options of the same kind; for example, if you specify @option{-L} more
108 than once, the directories are searched in the order specified. Also,
109 the placement of the @option{-l} option is significant.
111 Many options have long names starting with @samp{-f} or with
112 @samp{-W}---for example,
113 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
114 these have both positive and negative forms; the negative form of
115 @option{-ffoo} would be @option{-fno-foo}. This manual documents
116 only one of these two forms, whichever one is not the default.
120 @xref{Option Index}, for an index to GCC's options.
123 * Option Summary:: Brief list of all options, without explanations.
124 * Overall Options:: Controlling the kind of output:
125 an executable, object files, assembler files,
126 or preprocessed source.
127 * Invoking G++:: Compiling C++ programs.
128 * C Dialect Options:: Controlling the variant of C language compiled.
129 * C++ Dialect Options:: Variations on C++.
130 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
132 * Language Independent Options:: Controlling how diagnostics should be
134 * Warning Options:: How picky should the compiler be?
135 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
136 * Optimize Options:: How much optimization?
137 * Preprocessor Options:: Controlling header files and macro definitions.
138 Also, getting dependency information for Make.
139 * Assembler Options:: Passing options to the assembler.
140 * Link Options:: Specifying libraries and so on.
141 * Directory Options:: Where to find header files and libraries.
142 Where to find the compiler executable files.
143 * Spec Files:: How to pass switches to sub-processes.
144 * Target Options:: Running a cross-compiler, or an old version of GCC.
145 * Submodel Options:: Specifying minor hardware or convention variations,
146 such as 68010 vs 68020.
147 * Code Gen Options:: Specifying conventions for function calls, data layout
149 * Environment Variables:: Env vars that affect GCC.
150 * Precompiled Headers:: Compiling a header once, and using it many times.
151 * Running Protoize:: Automatically adding or removing function prototypes.
157 @section Option Summary
159 Here is a summary of all the options, grouped by type. Explanations are
160 in the following sections.
163 @item Overall Options
164 @xref{Overall Options,,Options Controlling the Kind of Output}.
165 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
166 -x @var{language} -v -### --help@r{[}=@var{class}@r{]} --target-help @gol
167 --version -wrapper@@@var{file}}
169 @item C Language Options
170 @xref{C Dialect Options,,Options Controlling C Dialect}.
171 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
172 -aux-info @var{filename} @gol
173 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
174 -fhosted -ffreestanding -fopenmp -fms-extensions @gol
175 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
176 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
177 -fsigned-bitfields -fsigned-char @gol
178 -funsigned-bitfields -funsigned-char}
180 @item C++ Language Options
181 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
182 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
183 -fconserve-space -ffriend-injection @gol
184 -fno-elide-constructors @gol
185 -fno-enforce-eh-specs @gol
186 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
187 -fno-implicit-templates @gol
188 -fno-implicit-inline-templates @gol
189 -fno-implement-inlines -fms-extensions @gol
190 -fno-nonansi-builtins -fno-operator-names @gol
191 -fno-optional-diags -fpermissive @gol
192 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
193 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
194 -fno-default-inline -fvisibility-inlines-hidden @gol
195 -fvisibility-ms-compat @gol
196 -Wabi -Wctor-dtor-privacy @gol
197 -Wnon-virtual-dtor -Wreorder @gol
198 -Weffc++ -Wstrict-null-sentinel @gol
199 -Wno-non-template-friend -Wold-style-cast @gol
200 -Woverloaded-virtual -Wno-pmf-conversions @gol
203 @item Objective-C and Objective-C++ Language Options
204 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
205 Objective-C and Objective-C++ Dialects}.
206 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
207 -fgnu-runtime -fnext-runtime @gol
208 -fno-nil-receivers @gol
209 -fobjc-call-cxx-cdtors @gol
210 -fobjc-direct-dispatch @gol
211 -fobjc-exceptions @gol
213 -freplace-objc-classes @gol
216 -Wassign-intercept @gol
217 -Wno-protocol -Wselector @gol
218 -Wstrict-selector-match @gol
219 -Wundeclared-selector}
221 @item Language Independent Options
222 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
223 @gccoptlist{-fmessage-length=@var{n} @gol
224 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
225 -fdiagnostics-show-option}
227 @item Warning Options
228 @xref{Warning Options,,Options to Request or Suppress Warnings}.
229 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
230 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
231 -Wno-attributes -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
232 -Wchar-subscripts -Wclobbered -Wcomment @gol
233 -Wconversion -Wcoverage-mismatch -Wno-deprecated @gol
234 -Wno-deprecated-declarations -Wdisabled-optimization @gol
235 -Wdisallowed-function-list=@var{sym},@var{sym},@dots{} @gol
236 -Wno-div-by-zero -Wempty-body -Wenum-compare -Wno-endif-labels @gol
237 -Werror -Werror=* @gol
238 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
239 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
240 -Wformat-security -Wformat-y2k @gol
241 -Wframe-larger-than=@var{len} -Wignored-qualifiers @gol
242 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
243 -Winit-self -Winline @gol
244 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
245 -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
246 -Wlogical-op -Wlong-long @gol
247 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
248 -Wmissing-format-attribute -Wmissing-include-dirs @gol
249 -Wmissing-noreturn -Wno-mudflap @gol
250 -Wno-multichar -Wnonnull -Wno-overflow @gol
251 -Woverlength-strings -Wpacked -Wpadded @gol
252 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
253 -Wredundant-decls @gol
254 -Wreturn-type -Wsequence-point -Wshadow @gol
255 -Wsign-compare -Wsign-conversion -Wstack-protector @gol
256 -Wstrict-aliasing -Wstrict-aliasing=n @gol
257 -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
258 -Wswitch -Wswitch-default -Wswitch-enum @gol
259 -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
260 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
261 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
262 -Wunused-value -Wunused-variable @gol
263 -Wvariadic-macros -Wvla @gol
264 -Wvolatile-register-var -Wwrite-strings}
266 @item C and Objective-C-only Warning Options
267 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
268 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
269 -Wold-style-declaration -Wold-style-definition @gol
270 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
271 -Wdeclaration-after-statement -Wpointer-sign}
273 @item Debugging Options
274 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
275 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
276 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
277 -fdump-noaddr -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
278 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
279 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
280 -fdump-statistics @gol
282 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
283 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
284 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
286 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
287 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
288 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
289 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
290 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
291 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
292 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
293 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
294 -fdump-tree-nrv -fdump-tree-vect @gol
295 -fdump-tree-sink @gol
296 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
297 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
298 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
299 -ftree-vectorizer-verbose=@var{n} @gol
300 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
301 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
302 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
303 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
304 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
305 -ftest-coverage -ftime-report -fvar-tracking @gol
306 -g -g@var{level} -gcoff -gdwarf-2 @gol
307 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
308 -fno-merge-debug-strings -fdebug-prefix-map=@var{old}=@var{new} @gol
309 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
310 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
311 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
312 -print-multi-directory -print-multi-lib @gol
313 -print-prog-name=@var{program} -print-search-dirs -Q @gol
314 -print-sysroot -print-sysroot-headers-suffix @gol
317 @item Optimization Options
318 @xref{Optimize Options,,Options that Control Optimization}.
320 -falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
321 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
322 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
323 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
324 -fcheck-data-deps -fcprop-registers -fcrossjumping -fcse-follow-jumps @gol
325 -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range @gol
326 -fdata-sections -fdce -fdce @gol
327 -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse @gol
328 -fearly-inlining -fexpensive-optimizations -ffast-math @gol
329 -ffinite-math-only -ffloat-store -fforward-propagate @gol
330 -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm @gol
331 -fgcse-sm -fif-conversion -fif-conversion2 -finline-functions @gol
332 -finline-functions-called-once -finline-limit=@var{n} @gol
333 -finline-small-functions -fipa-cp -fipa-marix-reorg -fipa-pta @gol
334 -fipa-pure-const -fipa-reference -fipa-struct-reorg @gol
335 -fipa-type-escape -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
336 -fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
337 -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap @gol
338 -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline @gol
339 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
340 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
341 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
342 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
343 -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol
344 -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays @gol
345 -fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol
346 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
347 -freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
348 -freorder-blocks-and-partition -freorder-functions @gol
349 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
350 -frounding-math -frtl-abstract-sequences -fsched2-use-superblocks @gol
351 -fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous @gol
352 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
353 -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee @gol
354 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
355 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
356 -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
357 -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
358 -ftree-copyrename -ftree-dce @gol
359 -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im @gol
360 -ftree-loop-distribution @gol
361 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
362 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-reassoc @gol
363 -ftree-sink -ftree-sra -ftree-store-ccp -ftree-switch-conversion @gol
364 -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol
365 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
366 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
367 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
369 --param @var{name}=@var{value}
370 -O -O0 -O1 -O2 -O3 -Os}
372 @item Preprocessor Options
373 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
374 @gccoptlist{-A@var{question}=@var{answer} @gol
375 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
376 -C -dD -dI -dM -dN @gol
377 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
378 -idirafter @var{dir} @gol
379 -include @var{file} -imacros @var{file} @gol
380 -iprefix @var{file} -iwithprefix @var{dir} @gol
381 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
382 -imultilib @var{dir} -isysroot @var{dir} @gol
383 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
384 -P -fworking-directory -remap @gol
385 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
386 -Xpreprocessor @var{option}}
388 @item Assembler Option
389 @xref{Assembler Options,,Passing Options to the Assembler}.
390 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
393 @xref{Link Options,,Options for Linking}.
394 @gccoptlist{@var{object-file-name} -l@var{library} @gol
395 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
396 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
397 -Wl,@var{option} -Xlinker @var{option} @gol
400 @item Directory Options
401 @xref{Directory Options,,Options for Directory Search}.
402 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
403 -specs=@var{file} -I- --sysroot=@var{dir}}
406 @c I wrote this xref this way to avoid overfull hbox. -- rms
407 @xref{Target Options}.
408 @gccoptlist{-V @var{version} -b @var{machine}}
410 @item Machine Dependent Options
411 @xref{Submodel Options,,Hardware Models and Configurations}.
412 @c This list is ordered alphanumerically by subsection name.
413 @c Try and put the significant identifier (CPU or system) first,
414 @c so users have a clue at guessing where the ones they want will be.
417 @gccoptlist{-EB -EL @gol
418 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
419 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
422 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
423 -mabi=@var{name} @gol
424 -mapcs-stack-check -mno-apcs-stack-check @gol
425 -mapcs-float -mno-apcs-float @gol
426 -mapcs-reentrant -mno-apcs-reentrant @gol
427 -msched-prolog -mno-sched-prolog @gol
428 -mlittle-endian -mbig-endian -mwords-little-endian @gol
429 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
430 -mthumb-interwork -mno-thumb-interwork @gol
431 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
432 -mstructure-size-boundary=@var{n} @gol
433 -mabort-on-noreturn @gol
434 -mlong-calls -mno-long-calls @gol
435 -msingle-pic-base -mno-single-pic-base @gol
436 -mpic-register=@var{reg} @gol
437 -mnop-fun-dllimport @gol
438 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
439 -mpoke-function-name @gol
441 -mtpcs-frame -mtpcs-leaf-frame @gol
442 -mcaller-super-interworking -mcallee-super-interworking @gol
446 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
447 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
449 @emph{Blackfin Options}
450 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
451 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
452 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
453 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
454 -mno-id-shared-library -mshared-library-id=@var{n} @gol
455 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
456 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
457 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram}
460 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
461 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
462 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
463 -mstack-align -mdata-align -mconst-align @gol
464 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
465 -melf -maout -melinux -mlinux -sim -sim2 @gol
466 -mmul-bug-workaround -mno-mul-bug-workaround}
469 @gccoptlist{-mmac -mpush-args}
471 @emph{Darwin Options}
472 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
473 -arch_only -bind_at_load -bundle -bundle_loader @gol
474 -client_name -compatibility_version -current_version @gol
476 -dependency-file -dylib_file -dylinker_install_name @gol
477 -dynamic -dynamiclib -exported_symbols_list @gol
478 -filelist -flat_namespace -force_cpusubtype_ALL @gol
479 -force_flat_namespace -headerpad_max_install_names @gol
481 -image_base -init -install_name -keep_private_externs @gol
482 -multi_module -multiply_defined -multiply_defined_unused @gol
483 -noall_load -no_dead_strip_inits_and_terms @gol
484 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
485 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
486 -private_bundle -read_only_relocs -sectalign @gol
487 -sectobjectsymbols -whyload -seg1addr @gol
488 -sectcreate -sectobjectsymbols -sectorder @gol
489 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
490 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
491 -segprot -segs_read_only_addr -segs_read_write_addr @gol
492 -single_module -static -sub_library -sub_umbrella @gol
493 -twolevel_namespace -umbrella -undefined @gol
494 -unexported_symbols_list -weak_reference_mismatches @gol
495 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
496 -mkernel -mone-byte-bool}
498 @emph{DEC Alpha Options}
499 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
500 -mieee -mieee-with-inexact -mieee-conformant @gol
501 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
502 -mtrap-precision=@var{mode} -mbuild-constants @gol
503 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
504 -mbwx -mmax -mfix -mcix @gol
505 -mfloat-vax -mfloat-ieee @gol
506 -mexplicit-relocs -msmall-data -mlarge-data @gol
507 -msmall-text -mlarge-text @gol
508 -mmemory-latency=@var{time}}
510 @emph{DEC Alpha/VMS Options}
511 @gccoptlist{-mvms-return-codes}
514 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
515 -mhard-float -msoft-float @gol
516 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
517 -mdouble -mno-double @gol
518 -mmedia -mno-media -mmuladd -mno-muladd @gol
519 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
520 -mlinked-fp -mlong-calls -malign-labels @gol
521 -mlibrary-pic -macc-4 -macc-8 @gol
522 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
523 -moptimize-membar -mno-optimize-membar @gol
524 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
525 -mvliw-branch -mno-vliw-branch @gol
526 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
527 -mno-nested-cond-exec -mtomcat-stats @gol
531 @emph{GNU/Linux Options}
532 @gccoptlist{-muclibc}
534 @emph{H8/300 Options}
535 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
538 @gccoptlist{-march=@var{architecture-type} @gol
539 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
540 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
541 -mfixed-range=@var{register-range} @gol
542 -mjump-in-delay -mlinker-opt -mlong-calls @gol
543 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
544 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
545 -mno-jump-in-delay -mno-long-load-store @gol
546 -mno-portable-runtime -mno-soft-float @gol
547 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
548 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
549 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
550 -munix=@var{unix-std} -nolibdld -static -threads}
552 @emph{i386 and x86-64 Options}
553 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
554 -mfpmath=@var{unit} @gol
555 -masm=@var{dialect} -mno-fancy-math-387 @gol
556 -mno-fp-ret-in-387 -msoft-float @gol
557 -mno-wide-multiply -mrtd -malign-double @gol
558 -mpreferred-stack-boundary=@var{num} -mcld -mcx16 -msahf -mrecip @gol
559 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 @gol
561 -msse4a -m3dnow -mpopcnt -mabm -msse5 @gol
562 -mthreads -mno-align-stringops -minline-all-stringops @gol
563 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
564 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
565 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
566 -mveclibabi=@var{type} -mpc32 -mpc64 -mpc80 -mstackrealign @gol
567 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
568 -mcmodel=@var{code-model} @gol
569 -m32 -m64 -mlarge-data-threshold=@var{num} @gol
570 -mfused-madd -mno-fused-madd}
573 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
574 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
575 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
576 -minline-float-divide-max-throughput @gol
577 -minline-int-divide-min-latency @gol
578 -minline-int-divide-max-throughput @gol
579 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
580 -mno-dwarf2-asm -mearly-stop-bits @gol
581 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
582 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol
583 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol
584 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
585 -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol
586 -mno-sched-prefer-non-data-spec-insns @gol
587 -mno-sched-prefer-non-control-spec-insns @gol
588 -mno-sched-count-spec-in-critical-path}
590 @emph{M32R/D Options}
591 @gccoptlist{-m32r2 -m32rx -m32r @gol
593 -malign-loops -mno-align-loops @gol
594 -missue-rate=@var{number} @gol
595 -mbranch-cost=@var{number} @gol
596 -mmodel=@var{code-size-model-type} @gol
597 -msdata=@var{sdata-type} @gol
598 -mno-flush-func -mflush-func=@var{name} @gol
599 -mno-flush-trap -mflush-trap=@var{number} @gol
603 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
605 @emph{M680x0 Options}
606 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
607 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
608 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
609 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
610 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
611 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
612 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
613 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
616 @emph{M68hc1x Options}
617 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
618 -mauto-incdec -minmax -mlong-calls -mshort @gol
619 -msoft-reg-count=@var{count}}
622 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
623 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
624 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
625 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
626 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
629 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
630 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
631 -mips16 -mno-mips16 -mflip-mips16 @gol
632 -minterlink-mips16 -mno-interlink-mips16 @gol
633 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
634 -mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64 @gol
635 -mfp32 -mfp64 -mhard-float -msoft-float @gol
636 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
637 -msmartmips -mno-smartmips @gol
638 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
639 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
640 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
641 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
642 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
643 -membedded-data -mno-embedded-data @gol
644 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
645 -mcode-readable=@var{setting} @gol
646 -msplit-addresses -mno-split-addresses @gol
647 -mexplicit-relocs -mno-explicit-relocs @gol
648 -mcheck-zero-division -mno-check-zero-division @gol
649 -mdivide-traps -mdivide-breaks @gol
650 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
651 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
652 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
653 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 @gol
654 -mfix-sb1 -mno-fix-sb1 @gol
655 -mflush-func=@var{func} -mno-flush-func @gol
656 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
657 -mfp-exceptions -mno-fp-exceptions @gol
658 -mvr4130-align -mno-vr4130-align}
661 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
662 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
663 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
664 -mno-base-addresses -msingle-exit -mno-single-exit}
666 @emph{MN10300 Options}
667 @gccoptlist{-mmult-bug -mno-mult-bug @gol
668 -mam33 -mno-am33 @gol
669 -mam33-2 -mno-am33-2 @gol
670 -mreturn-pointer-on-d0 @gol
673 @emph{PDP-11 Options}
674 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
675 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
676 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
677 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
678 -mbranch-expensive -mbranch-cheap @gol
679 -msplit -mno-split -munix-asm -mdec-asm}
681 @emph{PowerPC Options}
682 See RS/6000 and PowerPC Options.
684 @emph{RS/6000 and PowerPC Options}
685 @gccoptlist{-mcpu=@var{cpu-type} @gol
686 -mtune=@var{cpu-type} @gol
687 -mpower -mno-power -mpower2 -mno-power2 @gol
688 -mpowerpc -mpowerpc64 -mno-powerpc @gol
689 -maltivec -mno-altivec @gol
690 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
691 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
692 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
693 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
694 -mnew-mnemonics -mold-mnemonics @gol
695 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
696 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
697 -malign-power -malign-natural @gol
698 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
699 -mstring -mno-string -mupdate -mno-update @gol
700 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
701 -mstrict-align -mno-strict-align -mrelocatable @gol
702 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
703 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
704 -mdynamic-no-pic -maltivec -mswdiv @gol
705 -mprioritize-restricted-insns=@var{priority} @gol
706 -msched-costly-dep=@var{dependence_type} @gol
707 -minsert-sched-nops=@var{scheme} @gol
708 -mcall-sysv -mcall-netbsd @gol
709 -maix-struct-return -msvr4-struct-return @gol
710 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
711 -misel -mno-isel @gol
712 -misel=yes -misel=no @gol
714 -mspe=yes -mspe=no @gol
716 -mvrsave -mno-vrsave @gol
717 -mmulhw -mno-mulhw @gol
718 -mdlmzb -mno-dlmzb @gol
719 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
720 -mprototype -mno-prototype @gol
721 -msim -mmvme -mads -myellowknife -memb -msdata @gol
722 -msdata=@var{opt} -mvxworks -G @var{num} -pthread}
724 @emph{S/390 and zSeries Options}
725 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
726 -mhard-float -msoft-float -mlong-double-64 -mlong-double-128 @gol
727 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
728 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
729 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
730 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
731 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
734 @gccoptlist{-meb -mel @gol
738 -mscore5 -mscore5u -mscore7 -mscore7d}
741 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
742 -m4-nofpu -m4-single-only -m4-single -m4 @gol
743 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
744 -m5-64media -m5-64media-nofpu @gol
745 -m5-32media -m5-32media-nofpu @gol
746 -m5-compact -m5-compact-nofpu @gol
747 -mb -ml -mdalign -mrelax @gol
748 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
749 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
750 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
751 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
752 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
756 @gccoptlist{-mcpu=@var{cpu-type} @gol
757 -mtune=@var{cpu-type} @gol
758 -mcmodel=@var{code-model} @gol
759 -m32 -m64 -mapp-regs -mno-app-regs @gol
760 -mfaster-structs -mno-faster-structs @gol
761 -mfpu -mno-fpu -mhard-float -msoft-float @gol
762 -mhard-quad-float -msoft-quad-float @gol
763 -mimpure-text -mno-impure-text -mlittle-endian @gol
764 -mstack-bias -mno-stack-bias @gol
765 -munaligned-doubles -mno-unaligned-doubles @gol
766 -mv8plus -mno-v8plus -mvis -mno-vis
767 -threads -pthreads -pthread}
770 @gccoptlist{-mwarn-reloc -merror-reloc @gol
771 -msafe-dma -munsafe-dma @gol
773 -msmall-mem -mlarge-mem -mstdmain @gol
774 -mfixed-range=@var{register-range}}
776 @emph{System V Options}
777 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
780 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
781 -mprolog-function -mno-prolog-function -mspace @gol
782 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
783 -mapp-regs -mno-app-regs @gol
784 -mdisable-callt -mno-disable-callt @gol
790 @gccoptlist{-mg -mgnu -munix}
792 @emph{VxWorks Options}
793 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
794 -Xbind-lazy -Xbind-now}
796 @emph{x86-64 Options}
797 See i386 and x86-64 Options.
799 @emph{Xstormy16 Options}
802 @emph{Xtensa Options}
803 @gccoptlist{-mconst16 -mno-const16 @gol
804 -mfused-madd -mno-fused-madd @gol
805 -mserialize-volatile -mno-serialize-volatile @gol
806 -mtext-section-literals -mno-text-section-literals @gol
807 -mtarget-align -mno-target-align @gol
808 -mlongcalls -mno-longcalls}
810 @emph{zSeries Options}
811 See S/390 and zSeries Options.
813 @item Code Generation Options
814 @xref{Code Gen Options,,Options for Code Generation Conventions}.
815 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
816 -ffixed-@var{reg} -fexceptions @gol
817 -fnon-call-exceptions -funwind-tables @gol
818 -fasynchronous-unwind-tables @gol
819 -finhibit-size-directive -finstrument-functions @gol
820 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
821 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
822 -fno-common -fno-ident @gol
823 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
824 -fno-jump-tables @gol
825 -frecord-gcc-switches @gol
826 -freg-struct-return -fshort-enums @gol
827 -fshort-double -fshort-wchar @gol
828 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
829 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
830 -fno-stack-limit -fargument-alias -fargument-noalias @gol
831 -fargument-noalias-global -fargument-noalias-anything @gol
832 -fleading-underscore -ftls-model=@var{model} @gol
833 -ftrapv -fwrapv -fbounds-check @gol
838 * Overall Options:: Controlling the kind of output:
839 an executable, object files, assembler files,
840 or preprocessed source.
841 * C Dialect Options:: Controlling the variant of C language compiled.
842 * C++ Dialect Options:: Variations on C++.
843 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
845 * Language Independent Options:: Controlling how diagnostics should be
847 * Warning Options:: How picky should the compiler be?
848 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
849 * Optimize Options:: How much optimization?
850 * Preprocessor Options:: Controlling header files and macro definitions.
851 Also, getting dependency information for Make.
852 * Assembler Options:: Passing options to the assembler.
853 * Link Options:: Specifying libraries and so on.
854 * Directory Options:: Where to find header files and libraries.
855 Where to find the compiler executable files.
856 * Spec Files:: How to pass switches to sub-processes.
857 * Target Options:: Running a cross-compiler, or an old version of GCC.
860 @node Overall Options
861 @section Options Controlling the Kind of Output
863 Compilation can involve up to four stages: preprocessing, compilation
864 proper, assembly and linking, always in that order. GCC is capable of
865 preprocessing and compiling several files either into several
866 assembler input files, or into one assembler input file; then each
867 assembler input file produces an object file, and linking combines all
868 the object files (those newly compiled, and those specified as input)
869 into an executable file.
871 @cindex file name suffix
872 For any given input file, the file name suffix determines what kind of
877 C source code which must be preprocessed.
880 C source code which should not be preprocessed.
883 C++ source code which should not be preprocessed.
886 Objective-C source code. Note that you must link with the @file{libobjc}
887 library to make an Objective-C program work.
890 Objective-C source code which should not be preprocessed.
894 Objective-C++ source code. Note that you must link with the @file{libobjc}
895 library to make an Objective-C++ program work. Note that @samp{.M} refers
896 to a literal capital M@.
899 Objective-C++ source code which should not be preprocessed.
902 C, C++, Objective-C or Objective-C++ header file to be turned into a
907 @itemx @var{file}.cxx
908 @itemx @var{file}.cpp
909 @itemx @var{file}.CPP
910 @itemx @var{file}.c++
912 C++ source code which must be preprocessed. Note that in @samp{.cxx},
913 the last two letters must both be literally @samp{x}. Likewise,
914 @samp{.C} refers to a literal capital C@.
918 Objective-C++ source code which must be preprocessed.
921 Objective-C++ source code which should not be preprocessed.
926 @itemx @var{file}.hxx
927 @itemx @var{file}.hpp
928 @itemx @var{file}.HPP
929 @itemx @var{file}.h++
930 @itemx @var{file}.tcc
931 C++ header file to be turned into a precompiled header.
934 @itemx @var{file}.for
935 @itemx @var{file}.ftn
936 Fixed form Fortran source code which should not be preprocessed.
939 @itemx @var{file}.FOR
940 @itemx @var{file}.fpp
941 @itemx @var{file}.FPP
942 @itemx @var{file}.FTN
943 Fixed form Fortran source code which must be preprocessed (with the traditional
947 @itemx @var{file}.f95
948 @itemx @var{file}.f03
949 @itemx @var{file}.f08
950 Free form Fortran source code which should not be preprocessed.
953 @itemx @var{file}.F95
954 @itemx @var{file}.F03
955 @itemx @var{file}.F08
956 Free form Fortran source code which must be preprocessed (with the
957 traditional preprocessor).
959 @c FIXME: Descriptions of Java file types.
966 Ada source code file which contains a library unit declaration (a
967 declaration of a package, subprogram, or generic, or a generic
968 instantiation), or a library unit renaming declaration (a package,
969 generic, or subprogram renaming declaration). Such files are also
973 Ada source code file containing a library unit body (a subprogram or
974 package body). Such files are also called @dfn{bodies}.
976 @c GCC also knows about some suffixes for languages not yet included:
988 Assembler code which must be preprocessed.
991 An object file to be fed straight into linking.
992 Any file name with no recognized suffix is treated this way.
996 You can specify the input language explicitly with the @option{-x} option:
999 @item -x @var{language}
1000 Specify explicitly the @var{language} for the following input files
1001 (rather than letting the compiler choose a default based on the file
1002 name suffix). This option applies to all following input files until
1003 the next @option{-x} option. Possible values for @var{language} are:
1005 c c-header c-cpp-output
1006 c++ c++-header c++-cpp-output
1007 objective-c objective-c-header objective-c-cpp-output
1008 objective-c++ objective-c++-header objective-c++-cpp-output
1009 assembler assembler-with-cpp
1011 f77 f77-cpp-input f95 f95-cpp-input
1016 Turn off any specification of a language, so that subsequent files are
1017 handled according to their file name suffixes (as they are if @option{-x}
1018 has not been used at all).
1020 @item -pass-exit-codes
1021 @opindex pass-exit-codes
1022 Normally the @command{gcc} program will exit with the code of 1 if any
1023 phase of the compiler returns a non-success return code. If you specify
1024 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1025 numerically highest error produced by any phase that returned an error
1026 indication. The C, C++, and Fortran frontends return 4, if an internal
1027 compiler error is encountered.
1030 If you only want some of the stages of compilation, you can use
1031 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1032 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1033 @command{gcc} is to stop. Note that some combinations (for example,
1034 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1039 Compile or assemble the source files, but do not link. The linking
1040 stage simply is not done. The ultimate output is in the form of an
1041 object file for each source file.
1043 By default, the object file name for a source file is made by replacing
1044 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1046 Unrecognized input files, not requiring compilation or assembly, are
1051 Stop after the stage of compilation proper; do not assemble. The output
1052 is in the form of an assembler code file for each non-assembler input
1055 By default, the assembler file name for a source file is made by
1056 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1058 Input files that don't require compilation are ignored.
1062 Stop after the preprocessing stage; do not run the compiler proper. The
1063 output is in the form of preprocessed source code, which is sent to the
1066 Input files which don't require preprocessing are ignored.
1068 @cindex output file option
1071 Place output in file @var{file}. This applies regardless to whatever
1072 sort of output is being produced, whether it be an executable file,
1073 an object file, an assembler file or preprocessed C code.
1075 If @option{-o} is not specified, the default is to put an executable
1076 file in @file{a.out}, the object file for
1077 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1078 assembler file in @file{@var{source}.s}, a precompiled header file in
1079 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1084 Print (on standard error output) the commands executed to run the stages
1085 of compilation. Also print the version number of the compiler driver
1086 program and of the preprocessor and the compiler proper.
1090 Like @option{-v} except the commands are not executed and all command
1091 arguments are quoted. This is useful for shell scripts to capture the
1092 driver-generated command lines.
1096 Use pipes rather than temporary files for communication between the
1097 various stages of compilation. This fails to work on some systems where
1098 the assembler is unable to read from a pipe; but the GNU assembler has
1103 If you are compiling multiple source files, this option tells the driver
1104 to pass all the source files to the compiler at once (for those
1105 languages for which the compiler can handle this). This will allow
1106 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1107 language for which this is supported is C@. If you pass source files for
1108 multiple languages to the driver, using this option, the driver will invoke
1109 the compiler(s) that support IMA once each, passing each compiler all the
1110 source files appropriate for it. For those languages that do not support
1111 IMA this option will be ignored, and the compiler will be invoked once for
1112 each source file in that language. If you use this option in conjunction
1113 with @option{-save-temps}, the compiler will generate multiple
1115 (one for each source file), but only one (combined) @file{.o} or
1120 Print (on the standard output) a description of the command line options
1121 understood by @command{gcc}. If the @option{-v} option is also specified
1122 then @option{--help} will also be passed on to the various processes
1123 invoked by @command{gcc}, so that they can display the command line options
1124 they accept. If the @option{-Wextra} option has also been specified
1125 (prior to the @option{--help} option), then command line options which
1126 have no documentation associated with them will also be displayed.
1129 @opindex target-help
1130 Print (on the standard output) a description of target-specific command
1131 line options for each tool. For some targets extra target-specific
1132 information may also be printed.
1134 @item --help=@var{class}@r{[},@var{qualifier}@r{]}
1135 Print (on the standard output) a description of the command line
1136 options understood by the compiler that fit into a specific class.
1137 The class can be one of @samp{optimizers}, @samp{warnings}, @samp{target},
1138 @samp{params}, or @var{language}:
1141 @item @samp{optimizers}
1142 This will display all of the optimization options supported by the
1145 @item @samp{warnings}
1146 This will display all of the options controlling warning messages
1147 produced by the compiler.
1150 This will display target-specific options. Unlike the
1151 @option{--target-help} option however, target-specific options of the
1152 linker and assembler will not be displayed. This is because those
1153 tools do not currently support the extended @option{--help=} syntax.
1156 This will display the values recognized by the @option{--param}
1159 @item @var{language}
1160 This will display the options supported for @var{language}, where
1161 @var{language} is the name of one of the languages supported in this
1165 This will display the options that are common to all languages.
1168 It is possible to further refine the output of the @option{--help=}
1169 option by adding a comma separated list of qualifiers after the
1170 class. These can be any from the following list:
1173 @item @samp{undocumented}
1174 Display only those options which are undocumented.
1177 Display options which take an argument that appears after an equal
1178 sign in the same continuous piece of text, such as:
1179 @samp{--help=target}.
1181 @item @samp{separate}
1182 Display options which take an argument that appears as a separate word
1183 following the original option, such as: @samp{-o output-file}.
1186 Thus for example to display all the undocumented target-specific
1187 switches supported by the compiler the following can be used:
1190 --help=target,undocumented
1193 The sense of a qualifier can be inverted by prefixing it with the
1194 @var{^} character, so for example to display all binary warning
1195 options (i.e., ones that are either on or off and that do not take an
1196 argument), which have a description the following can be used:
1199 --help=warnings,^joined,^undocumented
1202 A class can also be used as a qualifier, although this usually
1203 restricts the output by so much that there is nothing to display. One
1204 case where it does work however is when one of the classes is
1205 @var{target}. So for example to display all the target-specific
1206 optimization options the following can be used:
1209 --help=target,optimizers
1212 The @option{--help=} option can be repeated on the command line. Each
1213 successive use will display its requested class of options, skipping
1214 those that have already been displayed.
1216 If the @option{-Q} option appears on the command line before the
1217 @option{--help=} option, then the descriptive text displayed by
1218 @option{--help=} is changed. Instead of describing the displayed
1219 options, an indication is given as to whether the option is enabled,
1220 disabled or set to a specific value (assuming that the compiler
1221 knows this at the point where the @option{--help=} option is used).
1223 Here is a truncated example from the ARM port of @command{gcc}:
1226 % gcc -Q -mabi=2 --help=target -c
1227 The following options are target specific:
1229 -mabort-on-noreturn [disabled]
1233 The output is sensitive to the effects of previous command line
1234 options, so for example it is possible to find out which optimizations
1235 are enabled at @option{-O2} by using:
1238 -O2 --help=optimizers
1241 Alternatively you can discover which binary optimizations are enabled
1242 by @option{-O3} by using:
1245 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1246 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1247 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1252 Display the version number and copyrights of the invoked GCC@.
1256 Invoke all subcommands under a wrapper program. It takes a single
1257 comma separated list as an argument, which will be used to invoke
1261 gcc -c t.c -wrapper gdb,--args
1264 This will invoke all subprograms of gcc under "gdb --args",
1265 thus cc1 invocation will be "gdb --args cc1 ...".
1267 @include @value{srcdir}/../libiberty/at-file.texi
1271 @section Compiling C++ Programs
1273 @cindex suffixes for C++ source
1274 @cindex C++ source file suffixes
1275 C++ source files conventionally use one of the suffixes @samp{.C},
1276 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1277 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1278 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1279 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1280 files with these names and compiles them as C++ programs even if you
1281 call the compiler the same way as for compiling C programs (usually
1282 with the name @command{gcc}).
1286 However, the use of @command{gcc} does not add the C++ library.
1287 @command{g++} is a program that calls GCC and treats @samp{.c},
1288 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1289 files unless @option{-x} is used, and automatically specifies linking
1290 against the C++ library. This program is also useful when
1291 precompiling a C header file with a @samp{.h} extension for use in C++
1292 compilations. On many systems, @command{g++} is also installed with
1293 the name @command{c++}.
1295 @cindex invoking @command{g++}
1296 When you compile C++ programs, you may specify many of the same
1297 command-line options that you use for compiling programs in any
1298 language; or command-line options meaningful for C and related
1299 languages; or options that are meaningful only for C++ programs.
1300 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1301 explanations of options for languages related to C@.
1302 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1303 explanations of options that are meaningful only for C++ programs.
1305 @node C Dialect Options
1306 @section Options Controlling C Dialect
1307 @cindex dialect options
1308 @cindex language dialect options
1309 @cindex options, dialect
1311 The following options control the dialect of C (or languages derived
1312 from C, such as C++, Objective-C and Objective-C++) that the compiler
1316 @cindex ANSI support
1320 In C mode, this is equivalent to @samp{-std=c89}. In C++ mode, it is
1321 equivalent to @samp{-std=c++98}.
1323 This turns off certain features of GCC that are incompatible with ISO
1324 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1325 such as the @code{asm} and @code{typeof} keywords, and
1326 predefined macros such as @code{unix} and @code{vax} that identify the
1327 type of system you are using. It also enables the undesirable and
1328 rarely used ISO trigraph feature. For the C compiler,
1329 it disables recognition of C++ style @samp{//} comments as well as
1330 the @code{inline} keyword.
1332 The alternate keywords @code{__asm__}, @code{__extension__},
1333 @code{__inline__} and @code{__typeof__} continue to work despite
1334 @option{-ansi}. You would not want to use them in an ISO C program, of
1335 course, but it is useful to put them in header files that might be included
1336 in compilations done with @option{-ansi}. Alternate predefined macros
1337 such as @code{__unix__} and @code{__vax__} are also available, with or
1338 without @option{-ansi}.
1340 The @option{-ansi} option does not cause non-ISO programs to be
1341 rejected gratuitously. For that, @option{-pedantic} is required in
1342 addition to @option{-ansi}. @xref{Warning Options}.
1344 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1345 option is used. Some header files may notice this macro and refrain
1346 from declaring certain functions or defining certain macros that the
1347 ISO standard doesn't call for; this is to avoid interfering with any
1348 programs that might use these names for other things.
1350 Functions that would normally be built in but do not have semantics
1351 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1352 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1353 built-in functions provided by GCC}, for details of the functions
1358 Determine the language standard. @xref{Standards,,Language Standards
1359 Supported by GCC}, for details of these standard versions. This option
1360 is currently only supported when compiling C or C++.
1362 The compiler can accept several base standards, such as @samp{c89} or
1363 @samp{c++98}, and GNU dialects of those standards, such as
1364 @samp{gnu89} or @samp{gnu++98}. By specifing a base standard, the
1365 compiler will accept all programs following that standard and those
1366 using GNU extensions that do not contradict it. For example,
1367 @samp{-std=c89} turns off certain features of GCC that are
1368 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1369 keywords, but not other GNU extensions that do not have a meaning in
1370 ISO C90, such as omitting the middle term of a @code{?:}
1371 expression. On the other hand, by specifing a GNU dialect of a
1372 standard, all features the compiler support are enabled, even when
1373 those features change the meaning of the base standard and some
1374 strict-conforming programs may be rejected. The particular standard
1375 is used by @option{-pedantic} to identify which features are GNU
1376 extensions given that version of the standard. For example
1377 @samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
1378 comments, while @samp{-std=gnu99 -pedantic} would not.
1380 A value for this option must be provided; possible values are
1385 Support all ISO C90 programs (certain GNU extensions that conflict
1386 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1388 @item iso9899:199409
1389 ISO C90 as modified in amendment 1.
1395 ISO C99. Note that this standard is not yet fully supported; see
1396 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1397 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1400 GNU dialect of ISO C90 (including some C99 features). This
1401 is the default for C code.
1405 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1406 this will become the default. The name @samp{gnu9x} is deprecated.
1409 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1413 GNU dialect of @option{-std=c++98}. This is the default for
1417 The working draft of the upcoming ISO C++0x standard. This option
1418 enables experimental features that are likely to be included in
1419 C++0x. The working draft is constantly changing, and any feature that is
1420 enabled by this flag may be removed from future versions of GCC if it is
1421 not part of the C++0x standard.
1424 GNU dialect of @option{-std=c++0x}. This option enables
1425 experimental features that may be removed in future versions of GCC.
1428 @item -fgnu89-inline
1429 @opindex fgnu89-inline
1430 The option @option{-fgnu89-inline} tells GCC to use the traditional
1431 GNU semantics for @code{inline} functions when in C99 mode.
1432 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1433 is accepted and ignored by GCC versions 4.1.3 up to but not including
1434 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1435 C99 mode. Using this option is roughly equivalent to adding the
1436 @code{gnu_inline} function attribute to all inline functions
1437 (@pxref{Function Attributes}).
1439 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1440 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1441 specifies the default behavior). This option was first supported in
1442 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1444 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1445 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1446 in effect for @code{inline} functions. @xref{Common Predefined
1447 Macros,,,cpp,The C Preprocessor}.
1449 @item -aux-info @var{filename}
1451 Output to the given filename prototyped declarations for all functions
1452 declared and/or defined in a translation unit, including those in header
1453 files. This option is silently ignored in any language other than C@.
1455 Besides declarations, the file indicates, in comments, the origin of
1456 each declaration (source file and line), whether the declaration was
1457 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1458 @samp{O} for old, respectively, in the first character after the line
1459 number and the colon), and whether it came from a declaration or a
1460 definition (@samp{C} or @samp{F}, respectively, in the following
1461 character). In the case of function definitions, a K&R-style list of
1462 arguments followed by their declarations is also provided, inside
1463 comments, after the declaration.
1467 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1468 keyword, so that code can use these words as identifiers. You can use
1469 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1470 instead. @option{-ansi} implies @option{-fno-asm}.
1472 In C++, this switch only affects the @code{typeof} keyword, since
1473 @code{asm} and @code{inline} are standard keywords. You may want to
1474 use the @option{-fno-gnu-keywords} flag instead, which has the same
1475 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1476 switch only affects the @code{asm} and @code{typeof} keywords, since
1477 @code{inline} is a standard keyword in ISO C99.
1480 @itemx -fno-builtin-@var{function}
1481 @opindex fno-builtin
1482 @cindex built-in functions
1483 Don't recognize built-in functions that do not begin with
1484 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1485 functions provided by GCC}, for details of the functions affected,
1486 including those which are not built-in functions when @option{-ansi} or
1487 @option{-std} options for strict ISO C conformance are used because they
1488 do not have an ISO standard meaning.
1490 GCC normally generates special code to handle certain built-in functions
1491 more efficiently; for instance, calls to @code{alloca} may become single
1492 instructions that adjust the stack directly, and calls to @code{memcpy}
1493 may become inline copy loops. The resulting code is often both smaller
1494 and faster, but since the function calls no longer appear as such, you
1495 cannot set a breakpoint on those calls, nor can you change the behavior
1496 of the functions by linking with a different library. In addition,
1497 when a function is recognized as a built-in function, GCC may use
1498 information about that function to warn about problems with calls to
1499 that function, or to generate more efficient code, even if the
1500 resulting code still contains calls to that function. For example,
1501 warnings are given with @option{-Wformat} for bad calls to
1502 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1503 known not to modify global memory.
1505 With the @option{-fno-builtin-@var{function}} option
1506 only the built-in function @var{function} is
1507 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1508 function is named this is not built-in in this version of GCC, this
1509 option is ignored. There is no corresponding
1510 @option{-fbuiltin-@var{function}} option; if you wish to enable
1511 built-in functions selectively when using @option{-fno-builtin} or
1512 @option{-ffreestanding}, you may define macros such as:
1515 #define abs(n) __builtin_abs ((n))
1516 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1521 @cindex hosted environment
1523 Assert that compilation takes place in a hosted environment. This implies
1524 @option{-fbuiltin}. A hosted environment is one in which the
1525 entire standard library is available, and in which @code{main} has a return
1526 type of @code{int}. Examples are nearly everything except a kernel.
1527 This is equivalent to @option{-fno-freestanding}.
1529 @item -ffreestanding
1530 @opindex ffreestanding
1531 @cindex hosted environment
1533 Assert that compilation takes place in a freestanding environment. This
1534 implies @option{-fno-builtin}. A freestanding environment
1535 is one in which the standard library may not exist, and program startup may
1536 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1537 This is equivalent to @option{-fno-hosted}.
1539 @xref{Standards,,Language Standards Supported by GCC}, for details of
1540 freestanding and hosted environments.
1544 @cindex openmp parallel
1545 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1546 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1547 compiler generates parallel code according to the OpenMP Application
1548 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}. This option
1549 implies @option{-pthread}, and thus is only supported on targets that
1550 have support for @option{-pthread}.
1552 @item -fms-extensions
1553 @opindex fms-extensions
1554 Accept some non-standard constructs used in Microsoft header files.
1556 Some cases of unnamed fields in structures and unions are only
1557 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1558 fields within structs/unions}, for details.
1562 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1563 options for strict ISO C conformance) implies @option{-trigraphs}.
1565 @item -no-integrated-cpp
1566 @opindex no-integrated-cpp
1567 Performs a compilation in two passes: preprocessing and compiling. This
1568 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1569 @option{-B} option. The user supplied compilation step can then add in
1570 an additional preprocessing step after normal preprocessing but before
1571 compiling. The default is to use the integrated cpp (internal cpp)
1573 The semantics of this option will change if "cc1", "cc1plus", and
1574 "cc1obj" are merged.
1576 @cindex traditional C language
1577 @cindex C language, traditional
1579 @itemx -traditional-cpp
1580 @opindex traditional-cpp
1581 @opindex traditional
1582 Formerly, these options caused GCC to attempt to emulate a pre-standard
1583 C compiler. They are now only supported with the @option{-E} switch.
1584 The preprocessor continues to support a pre-standard mode. See the GNU
1585 CPP manual for details.
1587 @item -fcond-mismatch
1588 @opindex fcond-mismatch
1589 Allow conditional expressions with mismatched types in the second and
1590 third arguments. The value of such an expression is void. This option
1591 is not supported for C++.
1593 @item -flax-vector-conversions
1594 @opindex flax-vector-conversions
1595 Allow implicit conversions between vectors with differing numbers of
1596 elements and/or incompatible element types. This option should not be
1599 @item -funsigned-char
1600 @opindex funsigned-char
1601 Let the type @code{char} be unsigned, like @code{unsigned char}.
1603 Each kind of machine has a default for what @code{char} should
1604 be. It is either like @code{unsigned char} by default or like
1605 @code{signed char} by default.
1607 Ideally, a portable program should always use @code{signed char} or
1608 @code{unsigned char} when it depends on the signedness of an object.
1609 But many programs have been written to use plain @code{char} and
1610 expect it to be signed, or expect it to be unsigned, depending on the
1611 machines they were written for. This option, and its inverse, let you
1612 make such a program work with the opposite default.
1614 The type @code{char} is always a distinct type from each of
1615 @code{signed char} or @code{unsigned char}, even though its behavior
1616 is always just like one of those two.
1619 @opindex fsigned-char
1620 Let the type @code{char} be signed, like @code{signed char}.
1622 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1623 the negative form of @option{-funsigned-char}. Likewise, the option
1624 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1626 @item -fsigned-bitfields
1627 @itemx -funsigned-bitfields
1628 @itemx -fno-signed-bitfields
1629 @itemx -fno-unsigned-bitfields
1630 @opindex fsigned-bitfields
1631 @opindex funsigned-bitfields
1632 @opindex fno-signed-bitfields
1633 @opindex fno-unsigned-bitfields
1634 These options control whether a bit-field is signed or unsigned, when the
1635 declaration does not use either @code{signed} or @code{unsigned}. By
1636 default, such a bit-field is signed, because this is consistent: the
1637 basic integer types such as @code{int} are signed types.
1640 @node C++ Dialect Options
1641 @section Options Controlling C++ Dialect
1643 @cindex compiler options, C++
1644 @cindex C++ options, command line
1645 @cindex options, C++
1646 This section describes the command-line options that are only meaningful
1647 for C++ programs; but you can also use most of the GNU compiler options
1648 regardless of what language your program is in. For example, you
1649 might compile a file @code{firstClass.C} like this:
1652 g++ -g -frepo -O -c firstClass.C
1656 In this example, only @option{-frepo} is an option meant
1657 only for C++ programs; you can use the other options with any
1658 language supported by GCC@.
1660 Here is a list of options that are @emph{only} for compiling C++ programs:
1664 @item -fabi-version=@var{n}
1665 @opindex fabi-version
1666 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1667 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1668 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1669 the version that conforms most closely to the C++ ABI specification.
1670 Therefore, the ABI obtained using version 0 will change as ABI bugs
1673 The default is version 2.
1675 @item -fno-access-control
1676 @opindex fno-access-control
1677 Turn off all access checking. This switch is mainly useful for working
1678 around bugs in the access control code.
1682 Check that the pointer returned by @code{operator new} is non-null
1683 before attempting to modify the storage allocated. This check is
1684 normally unnecessary because the C++ standard specifies that
1685 @code{operator new} will only return @code{0} if it is declared
1686 @samp{throw()}, in which case the compiler will always check the
1687 return value even without this option. In all other cases, when
1688 @code{operator new} has a non-empty exception specification, memory
1689 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1690 @samp{new (nothrow)}.
1692 @item -fconserve-space
1693 @opindex fconserve-space
1694 Put uninitialized or runtime-initialized global variables into the
1695 common segment, as C does. This saves space in the executable at the
1696 cost of not diagnosing duplicate definitions. If you compile with this
1697 flag and your program mysteriously crashes after @code{main()} has
1698 completed, you may have an object that is being destroyed twice because
1699 two definitions were merged.
1701 This option is no longer useful on most targets, now that support has
1702 been added for putting variables into BSS without making them common.
1704 @item -ffriend-injection
1705 @opindex ffriend-injection
1706 Inject friend functions into the enclosing namespace, so that they are
1707 visible outside the scope of the class in which they are declared.
1708 Friend functions were documented to work this way in the old Annotated
1709 C++ Reference Manual, and versions of G++ before 4.1 always worked
1710 that way. However, in ISO C++ a friend function which is not declared
1711 in an enclosing scope can only be found using argument dependent
1712 lookup. This option causes friends to be injected as they were in
1715 This option is for compatibility, and may be removed in a future
1718 @item -fno-elide-constructors
1719 @opindex fno-elide-constructors
1720 The C++ standard allows an implementation to omit creating a temporary
1721 which is only used to initialize another object of the same type.
1722 Specifying this option disables that optimization, and forces G++ to
1723 call the copy constructor in all cases.
1725 @item -fno-enforce-eh-specs
1726 @opindex fno-enforce-eh-specs
1727 Don't generate code to check for violation of exception specifications
1728 at runtime. This option violates the C++ standard, but may be useful
1729 for reducing code size in production builds, much like defining
1730 @samp{NDEBUG}. This does not give user code permission to throw
1731 exceptions in violation of the exception specifications; the compiler
1732 will still optimize based on the specifications, so throwing an
1733 unexpected exception will result in undefined behavior.
1736 @itemx -fno-for-scope
1738 @opindex fno-for-scope
1739 If @option{-ffor-scope} is specified, the scope of variables declared in
1740 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1741 as specified by the C++ standard.
1742 If @option{-fno-for-scope} is specified, the scope of variables declared in
1743 a @i{for-init-statement} extends to the end of the enclosing scope,
1744 as was the case in old versions of G++, and other (traditional)
1745 implementations of C++.
1747 The default if neither flag is given to follow the standard,
1748 but to allow and give a warning for old-style code that would
1749 otherwise be invalid, or have different behavior.
1751 @item -fno-gnu-keywords
1752 @opindex fno-gnu-keywords
1753 Do not recognize @code{typeof} as a keyword, so that code can use this
1754 word as an identifier. You can use the keyword @code{__typeof__} instead.
1755 @option{-ansi} implies @option{-fno-gnu-keywords}.
1757 @item -fno-implicit-templates
1758 @opindex fno-implicit-templates
1759 Never emit code for non-inline templates which are instantiated
1760 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1761 @xref{Template Instantiation}, for more information.
1763 @item -fno-implicit-inline-templates
1764 @opindex fno-implicit-inline-templates
1765 Don't emit code for implicit instantiations of inline templates, either.
1766 The default is to handle inlines differently so that compiles with and
1767 without optimization will need the same set of explicit instantiations.
1769 @item -fno-implement-inlines
1770 @opindex fno-implement-inlines
1771 To save space, do not emit out-of-line copies of inline functions
1772 controlled by @samp{#pragma implementation}. This will cause linker
1773 errors if these functions are not inlined everywhere they are called.
1775 @item -fms-extensions
1776 @opindex fms-extensions
1777 Disable pedantic warnings about constructs used in MFC, such as implicit
1778 int and getting a pointer to member function via non-standard syntax.
1780 @item -fno-nonansi-builtins
1781 @opindex fno-nonansi-builtins
1782 Disable built-in declarations of functions that are not mandated by
1783 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1784 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1786 @item -fno-operator-names
1787 @opindex fno-operator-names
1788 Do not treat the operator name keywords @code{and}, @code{bitand},
1789 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1790 synonyms as keywords.
1792 @item -fno-optional-diags
1793 @opindex fno-optional-diags
1794 Disable diagnostics that the standard says a compiler does not need to
1795 issue. Currently, the only such diagnostic issued by G++ is the one for
1796 a name having multiple meanings within a class.
1799 @opindex fpermissive
1800 Downgrade some diagnostics about nonconformant code from errors to
1801 warnings. Thus, using @option{-fpermissive} will allow some
1802 nonconforming code to compile.
1806 Enable automatic template instantiation at link time. This option also
1807 implies @option{-fno-implicit-templates}. @xref{Template
1808 Instantiation}, for more information.
1812 Disable generation of information about every class with virtual
1813 functions for use by the C++ runtime type identification features
1814 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1815 of the language, you can save some space by using this flag. Note that
1816 exception handling uses the same information, but it will generate it as
1817 needed. The @samp{dynamic_cast} operator can still be used for casts that
1818 do not require runtime type information, i.e.@: casts to @code{void *} or to
1819 unambiguous base classes.
1823 Emit statistics about front-end processing at the end of the compilation.
1824 This information is generally only useful to the G++ development team.
1826 @item -ftemplate-depth-@var{n}
1827 @opindex ftemplate-depth
1828 Set the maximum instantiation depth for template classes to @var{n}.
1829 A limit on the template instantiation depth is needed to detect
1830 endless recursions during template class instantiation. ANSI/ISO C++
1831 conforming programs must not rely on a maximum depth greater than 17.
1833 @item -fno-threadsafe-statics
1834 @opindex fno-threadsafe-statics
1835 Do not emit the extra code to use the routines specified in the C++
1836 ABI for thread-safe initialization of local statics. You can use this
1837 option to reduce code size slightly in code that doesn't need to be
1840 @item -fuse-cxa-atexit
1841 @opindex fuse-cxa-atexit
1842 Register destructors for objects with static storage duration with the
1843 @code{__cxa_atexit} function rather than the @code{atexit} function.
1844 This option is required for fully standards-compliant handling of static
1845 destructors, but will only work if your C library supports
1846 @code{__cxa_atexit}.
1848 @item -fno-use-cxa-get-exception-ptr
1849 @opindex fno-use-cxa-get-exception-ptr
1850 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1851 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1852 if the runtime routine is not available.
1854 @item -fvisibility-inlines-hidden
1855 @opindex fvisibility-inlines-hidden
1856 This switch declares that the user does not attempt to compare
1857 pointers to inline methods where the addresses of the two functions
1858 were taken in different shared objects.
1860 The effect of this is that GCC may, effectively, mark inline methods with
1861 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1862 appear in the export table of a DSO and do not require a PLT indirection
1863 when used within the DSO@. Enabling this option can have a dramatic effect
1864 on load and link times of a DSO as it massively reduces the size of the
1865 dynamic export table when the library makes heavy use of templates.
1867 The behavior of this switch is not quite the same as marking the
1868 methods as hidden directly, because it does not affect static variables
1869 local to the function or cause the compiler to deduce that
1870 the function is defined in only one shared object.
1872 You may mark a method as having a visibility explicitly to negate the
1873 effect of the switch for that method. For example, if you do want to
1874 compare pointers to a particular inline method, you might mark it as
1875 having default visibility. Marking the enclosing class with explicit
1876 visibility will have no effect.
1878 Explicitly instantiated inline methods are unaffected by this option
1879 as their linkage might otherwise cross a shared library boundary.
1880 @xref{Template Instantiation}.
1882 @item -fvisibility-ms-compat
1883 @opindex fvisibility-ms-compat
1884 This flag attempts to use visibility settings to make GCC's C++
1885 linkage model compatible with that of Microsoft Visual Studio.
1887 The flag makes these changes to GCC's linkage model:
1891 It sets the default visibility to @code{hidden}, like
1892 @option{-fvisibility=hidden}.
1895 Types, but not their members, are not hidden by default.
1898 The One Definition Rule is relaxed for types without explicit
1899 visibility specifications which are defined in more than one different
1900 shared object: those declarations are permitted if they would have
1901 been permitted when this option was not used.
1904 In new code it is better to use @option{-fvisibility=hidden} and
1905 export those classes which are intended to be externally visible.
1906 Unfortunately it is possible for code to rely, perhaps accidentally,
1907 on the Visual Studio behavior.
1909 Among the consequences of these changes are that static data members
1910 of the same type with the same name but defined in different shared
1911 objects will be different, so changing one will not change the other;
1912 and that pointers to function members defined in different shared
1913 objects may not compare equal. When this flag is given, it is a
1914 violation of the ODR to define types with the same name differently.
1918 Do not use weak symbol support, even if it is provided by the linker.
1919 By default, G++ will use weak symbols if they are available. This
1920 option exists only for testing, and should not be used by end-users;
1921 it will result in inferior code and has no benefits. This option may
1922 be removed in a future release of G++.
1926 Do not search for header files in the standard directories specific to
1927 C++, but do still search the other standard directories. (This option
1928 is used when building the C++ library.)
1931 In addition, these optimization, warning, and code generation options
1932 have meanings only for C++ programs:
1935 @item -fno-default-inline
1936 @opindex fno-default-inline
1937 Do not assume @samp{inline} for functions defined inside a class scope.
1938 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1939 functions will have linkage like inline functions; they just won't be
1942 @item -Wabi @r{(C++ and Objective-C++ only)}
1945 Warn when G++ generates code that is probably not compatible with the
1946 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1947 all such cases, there are probably some cases that are not warned about,
1948 even though G++ is generating incompatible code. There may also be
1949 cases where warnings are emitted even though the code that is generated
1952 You should rewrite your code to avoid these warnings if you are
1953 concerned about the fact that code generated by G++ may not be binary
1954 compatible with code generated by other compilers.
1956 The known incompatibilities at this point include:
1961 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1962 pack data into the same byte as a base class. For example:
1965 struct A @{ virtual void f(); int f1 : 1; @};
1966 struct B : public A @{ int f2 : 1; @};
1970 In this case, G++ will place @code{B::f2} into the same byte
1971 as@code{A::f1}; other compilers will not. You can avoid this problem
1972 by explicitly padding @code{A} so that its size is a multiple of the
1973 byte size on your platform; that will cause G++ and other compilers to
1974 layout @code{B} identically.
1977 Incorrect handling of tail-padding for virtual bases. G++ does not use
1978 tail padding when laying out virtual bases. For example:
1981 struct A @{ virtual void f(); char c1; @};
1982 struct B @{ B(); char c2; @};
1983 struct C : public A, public virtual B @{@};
1987 In this case, G++ will not place @code{B} into the tail-padding for
1988 @code{A}; other compilers will. You can avoid this problem by
1989 explicitly padding @code{A} so that its size is a multiple of its
1990 alignment (ignoring virtual base classes); that will cause G++ and other
1991 compilers to layout @code{C} identically.
1994 Incorrect handling of bit-fields with declared widths greater than that
1995 of their underlying types, when the bit-fields appear in a union. For
1999 union U @{ int i : 4096; @};
2003 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2004 union too small by the number of bits in an @code{int}.
2007 Empty classes can be placed at incorrect offsets. For example:
2017 struct C : public B, public A @{@};
2021 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2022 it should be placed at offset zero. G++ mistakenly believes that the
2023 @code{A} data member of @code{B} is already at offset zero.
2026 Names of template functions whose types involve @code{typename} or
2027 template template parameters can be mangled incorrectly.
2030 template <typename Q>
2031 void f(typename Q::X) @{@}
2033 template <template <typename> class Q>
2034 void f(typename Q<int>::X) @{@}
2038 Instantiations of these templates may be mangled incorrectly.
2042 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2043 @opindex Wctor-dtor-privacy
2044 @opindex Wno-ctor-dtor-privacy
2045 Warn when a class seems unusable because all the constructors or
2046 destructors in that class are private, and it has neither friends nor
2047 public static member functions.
2049 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2050 @opindex Wnon-virtual-dtor
2051 @opindex Wno-non-virtual-dtor
2052 Warn when a class has virtual functions and accessible non-virtual
2053 destructor, in which case it would be possible but unsafe to delete
2054 an instance of a derived class through a pointer to the base class.
2055 This warning is also enabled if -Weffc++ is specified.
2057 @item -Wreorder @r{(C++ and Objective-C++ only)}
2059 @opindex Wno-reorder
2060 @cindex reordering, warning
2061 @cindex warning for reordering of member initializers
2062 Warn when the order of member initializers given in the code does not
2063 match the order in which they must be executed. For instance:
2069 A(): j (0), i (1) @{ @}
2073 The compiler will rearrange the member initializers for @samp{i}
2074 and @samp{j} to match the declaration order of the members, emitting
2075 a warning to that effect. This warning is enabled by @option{-Wall}.
2078 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2081 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2084 Warn about violations of the following style guidelines from Scott Meyers'
2085 @cite{Effective C++} book:
2089 Item 11: Define a copy constructor and an assignment operator for classes
2090 with dynamically allocated memory.
2093 Item 12: Prefer initialization to assignment in constructors.
2096 Item 14: Make destructors virtual in base classes.
2099 Item 15: Have @code{operator=} return a reference to @code{*this}.
2102 Item 23: Don't try to return a reference when you must return an object.
2106 Also warn about violations of the following style guidelines from
2107 Scott Meyers' @cite{More Effective C++} book:
2111 Item 6: Distinguish between prefix and postfix forms of increment and
2112 decrement operators.
2115 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2119 When selecting this option, be aware that the standard library
2120 headers do not obey all of these guidelines; use @samp{grep -v}
2121 to filter out those warnings.
2123 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2124 @opindex Wstrict-null-sentinel
2125 @opindex Wno-strict-null-sentinel
2126 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2127 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2128 to @code{__null}. Although it is a null pointer constant not a null pointer,
2129 it is guaranteed to of the same size as a pointer. But this use is
2130 not portable across different compilers.
2132 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2133 @opindex Wno-non-template-friend
2134 @opindex Wnon-template-friend
2135 Disable warnings when non-templatized friend functions are declared
2136 within a template. Since the advent of explicit template specification
2137 support in G++, if the name of the friend is an unqualified-id (i.e.,
2138 @samp{friend foo(int)}), the C++ language specification demands that the
2139 friend declare or define an ordinary, nontemplate function. (Section
2140 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2141 could be interpreted as a particular specialization of a templatized
2142 function. Because this non-conforming behavior is no longer the default
2143 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2144 check existing code for potential trouble spots and is on by default.
2145 This new compiler behavior can be turned off with
2146 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2147 but disables the helpful warning.
2149 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2150 @opindex Wold-style-cast
2151 @opindex Wno-old-style-cast
2152 Warn if an old-style (C-style) cast to a non-void type is used within
2153 a C++ program. The new-style casts (@samp{dynamic_cast},
2154 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2155 less vulnerable to unintended effects and much easier to search for.
2157 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2158 @opindex Woverloaded-virtual
2159 @opindex Wno-overloaded-virtual
2160 @cindex overloaded virtual fn, warning
2161 @cindex warning for overloaded virtual fn
2162 Warn when a function declaration hides virtual functions from a
2163 base class. For example, in:
2170 struct B: public A @{
2175 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2183 will fail to compile.
2185 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2186 @opindex Wno-pmf-conversions
2187 @opindex Wpmf-conversions
2188 Disable the diagnostic for converting a bound pointer to member function
2191 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2192 @opindex Wsign-promo
2193 @opindex Wno-sign-promo
2194 Warn when overload resolution chooses a promotion from unsigned or
2195 enumerated type to a signed type, over a conversion to an unsigned type of
2196 the same size. Previous versions of G++ would try to preserve
2197 unsignedness, but the standard mandates the current behavior.
2202 A& operator = (int);
2212 In this example, G++ will synthesize a default @samp{A& operator =
2213 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2216 @node Objective-C and Objective-C++ Dialect Options
2217 @section Options Controlling Objective-C and Objective-C++ Dialects
2219 @cindex compiler options, Objective-C and Objective-C++
2220 @cindex Objective-C and Objective-C++ options, command line
2221 @cindex options, Objective-C and Objective-C++
2222 (NOTE: This manual does not describe the Objective-C and Objective-C++
2223 languages themselves. See @xref{Standards,,Language Standards
2224 Supported by GCC}, for references.)
2226 This section describes the command-line options that are only meaningful
2227 for Objective-C and Objective-C++ programs, but you can also use most of
2228 the language-independent GNU compiler options.
2229 For example, you might compile a file @code{some_class.m} like this:
2232 gcc -g -fgnu-runtime -O -c some_class.m
2236 In this example, @option{-fgnu-runtime} is an option meant only for
2237 Objective-C and Objective-C++ programs; you can use the other options with
2238 any language supported by GCC@.
2240 Note that since Objective-C is an extension of the C language, Objective-C
2241 compilations may also use options specific to the C front-end (e.g.,
2242 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2243 C++-specific options (e.g., @option{-Wabi}).
2245 Here is a list of options that are @emph{only} for compiling Objective-C
2246 and Objective-C++ programs:
2249 @item -fconstant-string-class=@var{class-name}
2250 @opindex fconstant-string-class
2251 Use @var{class-name} as the name of the class to instantiate for each
2252 literal string specified with the syntax @code{@@"@dots{}"}. The default
2253 class name is @code{NXConstantString} if the GNU runtime is being used, and
2254 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2255 @option{-fconstant-cfstrings} option, if also present, will override the
2256 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2257 to be laid out as constant CoreFoundation strings.
2260 @opindex fgnu-runtime
2261 Generate object code compatible with the standard GNU Objective-C
2262 runtime. This is the default for most types of systems.
2264 @item -fnext-runtime
2265 @opindex fnext-runtime
2266 Generate output compatible with the NeXT runtime. This is the default
2267 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2268 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2271 @item -fno-nil-receivers
2272 @opindex fno-nil-receivers
2273 Assume that all Objective-C message dispatches (e.g.,
2274 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2275 is not @code{nil}. This allows for more efficient entry points in the runtime
2276 to be used. Currently, this option is only available in conjunction with
2277 the NeXT runtime on Mac OS X 10.3 and later.
2279 @item -fobjc-call-cxx-cdtors
2280 @opindex fobjc-call-cxx-cdtors
2281 For each Objective-C class, check if any of its instance variables is a
2282 C++ object with a non-trivial default constructor. If so, synthesize a
2283 special @code{- (id) .cxx_construct} instance method that will run
2284 non-trivial default constructors on any such instance variables, in order,
2285 and then return @code{self}. Similarly, check if any instance variable
2286 is a C++ object with a non-trivial destructor, and if so, synthesize a
2287 special @code{- (void) .cxx_destruct} method that will run
2288 all such default destructors, in reverse order.
2290 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2291 thusly generated will only operate on instance variables declared in the
2292 current Objective-C class, and not those inherited from superclasses. It
2293 is the responsibility of the Objective-C runtime to invoke all such methods
2294 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2295 will be invoked by the runtime immediately after a new object
2296 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2297 be invoked immediately before the runtime deallocates an object instance.
2299 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2300 support for invoking the @code{- (id) .cxx_construct} and
2301 @code{- (void) .cxx_destruct} methods.
2303 @item -fobjc-direct-dispatch
2304 @opindex fobjc-direct-dispatch
2305 Allow fast jumps to the message dispatcher. On Darwin this is
2306 accomplished via the comm page.
2308 @item -fobjc-exceptions
2309 @opindex fobjc-exceptions
2310 Enable syntactic support for structured exception handling in Objective-C,
2311 similar to what is offered by C++ and Java. This option is
2312 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2321 @@catch (AnObjCClass *exc) @{
2328 @@catch (AnotherClass *exc) @{
2331 @@catch (id allOthers) @{
2341 The @code{@@throw} statement may appear anywhere in an Objective-C or
2342 Objective-C++ program; when used inside of a @code{@@catch} block, the
2343 @code{@@throw} may appear without an argument (as shown above), in which case
2344 the object caught by the @code{@@catch} will be rethrown.
2346 Note that only (pointers to) Objective-C objects may be thrown and
2347 caught using this scheme. When an object is thrown, it will be caught
2348 by the nearest @code{@@catch} clause capable of handling objects of that type,
2349 analogously to how @code{catch} blocks work in C++ and Java. A
2350 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2351 any and all Objective-C exceptions not caught by previous @code{@@catch}
2354 The @code{@@finally} clause, if present, will be executed upon exit from the
2355 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2356 regardless of whether any exceptions are thrown, caught or rethrown
2357 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2358 of the @code{finally} clause in Java.
2360 There are several caveats to using the new exception mechanism:
2364 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2365 idioms provided by the @code{NSException} class, the new
2366 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2367 systems, due to additional functionality needed in the (NeXT) Objective-C
2371 As mentioned above, the new exceptions do not support handling
2372 types other than Objective-C objects. Furthermore, when used from
2373 Objective-C++, the Objective-C exception model does not interoperate with C++
2374 exceptions at this time. This means you cannot @code{@@throw} an exception
2375 from Objective-C and @code{catch} it in C++, or vice versa
2376 (i.e., @code{throw @dots{} @@catch}).
2379 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2380 blocks for thread-safe execution:
2383 @@synchronized (ObjCClass *guard) @{
2388 Upon entering the @code{@@synchronized} block, a thread of execution shall
2389 first check whether a lock has been placed on the corresponding @code{guard}
2390 object by another thread. If it has, the current thread shall wait until
2391 the other thread relinquishes its lock. Once @code{guard} becomes available,
2392 the current thread will place its own lock on it, execute the code contained in
2393 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2394 making @code{guard} available to other threads).
2396 Unlike Java, Objective-C does not allow for entire methods to be marked
2397 @code{@@synchronized}. Note that throwing exceptions out of
2398 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2399 to be unlocked properly.
2403 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2405 @item -freplace-objc-classes
2406 @opindex freplace-objc-classes
2407 Emit a special marker instructing @command{ld(1)} not to statically link in
2408 the resulting object file, and allow @command{dyld(1)} to load it in at
2409 run time instead. This is used in conjunction with the Fix-and-Continue
2410 debugging mode, where the object file in question may be recompiled and
2411 dynamically reloaded in the course of program execution, without the need
2412 to restart the program itself. Currently, Fix-and-Continue functionality
2413 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2418 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2419 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2420 compile time) with static class references that get initialized at load time,
2421 which improves run-time performance. Specifying the @option{-fzero-link} flag
2422 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2423 to be retained. This is useful in Zero-Link debugging mode, since it allows
2424 for individual class implementations to be modified during program execution.
2428 Dump interface declarations for all classes seen in the source file to a
2429 file named @file{@var{sourcename}.decl}.
2431 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2432 @opindex Wassign-intercept
2433 @opindex Wno-assign-intercept
2434 Warn whenever an Objective-C assignment is being intercepted by the
2437 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2438 @opindex Wno-protocol
2440 If a class is declared to implement a protocol, a warning is issued for
2441 every method in the protocol that is not implemented by the class. The
2442 default behavior is to issue a warning for every method not explicitly
2443 implemented in the class, even if a method implementation is inherited
2444 from the superclass. If you use the @option{-Wno-protocol} option, then
2445 methods inherited from the superclass are considered to be implemented,
2446 and no warning is issued for them.
2448 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2450 @opindex Wno-selector
2451 Warn if multiple methods of different types for the same selector are
2452 found during compilation. The check is performed on the list of methods
2453 in the final stage of compilation. Additionally, a check is performed
2454 for each selector appearing in a @code{@@selector(@dots{})}
2455 expression, and a corresponding method for that selector has been found
2456 during compilation. Because these checks scan the method table only at
2457 the end of compilation, these warnings are not produced if the final
2458 stage of compilation is not reached, for example because an error is
2459 found during compilation, or because the @option{-fsyntax-only} option is
2462 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2463 @opindex Wstrict-selector-match
2464 @opindex Wno-strict-selector-match
2465 Warn if multiple methods with differing argument and/or return types are
2466 found for a given selector when attempting to send a message using this
2467 selector to a receiver of type @code{id} or @code{Class}. When this flag
2468 is off (which is the default behavior), the compiler will omit such warnings
2469 if any differences found are confined to types which share the same size
2472 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2473 @opindex Wundeclared-selector
2474 @opindex Wno-undeclared-selector
2475 Warn if a @code{@@selector(@dots{})} expression referring to an
2476 undeclared selector is found. A selector is considered undeclared if no
2477 method with that name has been declared before the
2478 @code{@@selector(@dots{})} expression, either explicitly in an
2479 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2480 an @code{@@implementation} section. This option always performs its
2481 checks as soon as a @code{@@selector(@dots{})} expression is found,
2482 while @option{-Wselector} only performs its checks in the final stage of
2483 compilation. This also enforces the coding style convention
2484 that methods and selectors must be declared before being used.
2486 @item -print-objc-runtime-info
2487 @opindex print-objc-runtime-info
2488 Generate C header describing the largest structure that is passed by
2493 @node Language Independent Options
2494 @section Options to Control Diagnostic Messages Formatting
2495 @cindex options to control diagnostics formatting
2496 @cindex diagnostic messages
2497 @cindex message formatting
2499 Traditionally, diagnostic messages have been formatted irrespective of
2500 the output device's aspect (e.g.@: its width, @dots{}). The options described
2501 below can be used to control the diagnostic messages formatting
2502 algorithm, e.g.@: how many characters per line, how often source location
2503 information should be reported. Right now, only the C++ front end can
2504 honor these options. However it is expected, in the near future, that
2505 the remaining front ends would be able to digest them correctly.
2508 @item -fmessage-length=@var{n}
2509 @opindex fmessage-length
2510 Try to format error messages so that they fit on lines of about @var{n}
2511 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2512 the front ends supported by GCC@. If @var{n} is zero, then no
2513 line-wrapping will be done; each error message will appear on a single
2516 @opindex fdiagnostics-show-location
2517 @item -fdiagnostics-show-location=once
2518 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2519 reporter to emit @emph{once} source location information; that is, in
2520 case the message is too long to fit on a single physical line and has to
2521 be wrapped, the source location won't be emitted (as prefix) again,
2522 over and over, in subsequent continuation lines. This is the default
2525 @item -fdiagnostics-show-location=every-line
2526 Only meaningful in line-wrapping mode. Instructs the diagnostic
2527 messages reporter to emit the same source location information (as
2528 prefix) for physical lines that result from the process of breaking
2529 a message which is too long to fit on a single line.
2531 @item -fdiagnostics-show-option
2532 @opindex fdiagnostics-show-option
2533 This option instructs the diagnostic machinery to add text to each
2534 diagnostic emitted, which indicates which command line option directly
2535 controls that diagnostic, when such an option is known to the
2536 diagnostic machinery.
2538 @item -Wcoverage-mismatch
2539 @opindex Wcoverage-mismatch
2540 Warn if feedback profiles do not match when using the
2541 @option{-fprofile-use} option.
2542 If a source file was changed between @option{-fprofile-gen} and
2543 @option{-fprofile-use}, the files with the profile feedback can fail
2544 to match the source file and GCC can not use the profile feedback
2545 information. By default, GCC emits an error message in this case.
2546 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2547 error. GCC does not use appropriate feedback profiles, so using this
2548 option can result in poorly optimized code. This option is useful
2549 only in the case of very minor changes such as bug fixes to an
2554 @node Warning Options
2555 @section Options to Request or Suppress Warnings
2556 @cindex options to control warnings
2557 @cindex warning messages
2558 @cindex messages, warning
2559 @cindex suppressing warnings
2561 Warnings are diagnostic messages that report constructions which
2562 are not inherently erroneous but which are risky or suggest there
2563 may have been an error.
2565 The following language-independent options do not enable specific
2566 warnings but control the kinds of diagnostics produced by GCC.
2569 @cindex syntax checking
2571 @opindex fsyntax-only
2572 Check the code for syntax errors, but don't do anything beyond that.
2576 Inhibit all warning messages.
2581 Make all warnings into errors.
2586 Make the specified warning into an error. The specifier for a warning
2587 is appended, for example @option{-Werror=switch} turns the warnings
2588 controlled by @option{-Wswitch} into errors. This switch takes a
2589 negative form, to be used to negate @option{-Werror} for specific
2590 warnings, for example @option{-Wno-error=switch} makes
2591 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2592 is in effect. You can use the @option{-fdiagnostics-show-option}
2593 option to have each controllable warning amended with the option which
2594 controls it, to determine what to use with this option.
2596 Note that specifying @option{-Werror=}@var{foo} automatically implies
2597 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2600 @item -Wfatal-errors
2601 @opindex Wfatal-errors
2602 @opindex Wno-fatal-errors
2603 This option causes the compiler to abort compilation on the first error
2604 occurred rather than trying to keep going and printing further error
2609 You can request many specific warnings with options beginning
2610 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2611 implicit declarations. Each of these specific warning options also
2612 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2613 example, @option{-Wno-implicit}. This manual lists only one of the
2614 two forms, whichever is not the default. For further,
2615 language-specific options also refer to @ref{C++ Dialect Options} and
2616 @ref{Objective-C and Objective-C++ Dialect Options}.
2621 Issue all the warnings demanded by strict ISO C and ISO C++;
2622 reject all programs that use forbidden extensions, and some other
2623 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2624 version of the ISO C standard specified by any @option{-std} option used.
2626 Valid ISO C and ISO C++ programs should compile properly with or without
2627 this option (though a rare few will require @option{-ansi} or a
2628 @option{-std} option specifying the required version of ISO C)@. However,
2629 without this option, certain GNU extensions and traditional C and C++
2630 features are supported as well. With this option, they are rejected.
2632 @option{-pedantic} does not cause warning messages for use of the
2633 alternate keywords whose names begin and end with @samp{__}. Pedantic
2634 warnings are also disabled in the expression that follows
2635 @code{__extension__}. However, only system header files should use
2636 these escape routes; application programs should avoid them.
2637 @xref{Alternate Keywords}.
2639 Some users try to use @option{-pedantic} to check programs for strict ISO
2640 C conformance. They soon find that it does not do quite what they want:
2641 it finds some non-ISO practices, but not all---only those for which
2642 ISO C @emph{requires} a diagnostic, and some others for which
2643 diagnostics have been added.
2645 A feature to report any failure to conform to ISO C might be useful in
2646 some instances, but would require considerable additional work and would
2647 be quite different from @option{-pedantic}. We don't have plans to
2648 support such a feature in the near future.
2650 Where the standard specified with @option{-std} represents a GNU
2651 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2652 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2653 extended dialect is based. Warnings from @option{-pedantic} are given
2654 where they are required by the base standard. (It would not make sense
2655 for such warnings to be given only for features not in the specified GNU
2656 C dialect, since by definition the GNU dialects of C include all
2657 features the compiler supports with the given option, and there would be
2658 nothing to warn about.)
2660 @item -pedantic-errors
2661 @opindex pedantic-errors
2662 Like @option{-pedantic}, except that errors are produced rather than
2668 This enables all the warnings about constructions that some users
2669 consider questionable, and that are easy to avoid (or modify to
2670 prevent the warning), even in conjunction with macros. This also
2671 enables some language-specific warnings described in @ref{C++ Dialect
2672 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2674 @option{-Wall} turns on the following warning flags:
2676 @gccoptlist{-Waddress @gol
2677 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2679 -Wchar-subscripts @gol
2681 -Wimplicit-function-declaration @gol
2684 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2685 -Wmissing-braces @gol
2691 -Wsequence-point @gol
2692 -Wsign-compare @r{(only in C++)} @gol
2693 -Wstrict-aliasing @gol
2694 -Wstrict-overflow=1 @gol
2697 -Wuninitialized @r{(only with} @option{-O1} @r{and above)} @gol
2698 -Wunknown-pragmas @gol
2699 -Wunused-function @gol
2702 -Wunused-variable @gol
2703 -Wvolatile-register-var @gol
2706 Note that some warning flags are not implied by @option{-Wall}. Some of
2707 them warn about constructions that users generally do not consider
2708 questionable, but which occasionally you might wish to check for;
2709 others warn about constructions that are necessary or hard to avoid in
2710 some cases, and there is no simple way to modify the code to suppress
2711 the warning. Some of them are enabled by @option{-Wextra} but many of
2712 them must be enabled individually.
2718 This enables some extra warning flags that are not enabled by
2719 @option{-Wall}. (This option used to be called @option{-W}. The older
2720 name is still supported, but the newer name is more descriptive.)
2722 @gccoptlist{-Wclobbered @gol
2724 -Wignored-qualifiers @gol
2725 -Wmissing-field-initializers @gol
2726 -Wmissing-parameter-type @r{(C only)} @gol
2727 -Wold-style-declaration @r{(C only)} @gol
2728 -Woverride-init @gol
2731 -Wuninitialized @r{(only with} @option{-O1} @r{and above)} @gol
2732 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2735 The option @option{-Wextra} also prints warning messages for the
2741 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2742 @samp{>}, or @samp{>=}.
2745 (C++ only) An enumerator and a non-enumerator both appear in a
2746 conditional expression.
2749 (C++ only) A non-static reference or non-static @samp{const} member
2750 appears in a class without constructors.
2753 (C++ only) Ambiguous virtual bases.
2756 (C++ only) Subscripting an array which has been declared @samp{register}.
2759 (C++ only) Taking the address of a variable which has been declared
2763 (C++ only) A base class is not initialized in a derived class' copy
2768 @item -Wchar-subscripts
2769 @opindex Wchar-subscripts
2770 @opindex Wno-char-subscripts
2771 Warn if an array subscript has type @code{char}. This is a common cause
2772 of error, as programmers often forget that this type is signed on some
2774 This warning is enabled by @option{-Wall}.
2778 @opindex Wno-comment
2779 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2780 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2781 This warning is enabled by @option{-Wall}.
2786 @opindex ffreestanding
2787 @opindex fno-builtin
2788 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2789 the arguments supplied have types appropriate to the format string
2790 specified, and that the conversions specified in the format string make
2791 sense. This includes standard functions, and others specified by format
2792 attributes (@pxref{Function Attributes}), in the @code{printf},
2793 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2794 not in the C standard) families (or other target-specific families).
2795 Which functions are checked without format attributes having been
2796 specified depends on the standard version selected, and such checks of
2797 functions without the attribute specified are disabled by
2798 @option{-ffreestanding} or @option{-fno-builtin}.
2800 The formats are checked against the format features supported by GNU
2801 libc version 2.2. These include all ISO C90 and C99 features, as well
2802 as features from the Single Unix Specification and some BSD and GNU
2803 extensions. Other library implementations may not support all these
2804 features; GCC does not support warning about features that go beyond a
2805 particular library's limitations. However, if @option{-pedantic} is used
2806 with @option{-Wformat}, warnings will be given about format features not
2807 in the selected standard version (but not for @code{strfmon} formats,
2808 since those are not in any version of the C standard). @xref{C Dialect
2809 Options,,Options Controlling C Dialect}.
2811 Since @option{-Wformat} also checks for null format arguments for
2812 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2814 @option{-Wformat} is included in @option{-Wall}. For more control over some
2815 aspects of format checking, the options @option{-Wformat-y2k},
2816 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2817 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2818 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2821 @opindex Wformat-y2k
2822 @opindex Wno-format-y2k
2823 If @option{-Wformat} is specified, also warn about @code{strftime}
2824 formats which may yield only a two-digit year.
2826 @item -Wno-format-contains-nul
2827 @opindex Wno-format-contains-nul
2828 @opindex Wformat-contains-nul
2829 If @option{-Wformat} is specified, do not warn about format strings that
2832 @item -Wno-format-extra-args
2833 @opindex Wno-format-extra-args
2834 @opindex Wformat-extra-args
2835 If @option{-Wformat} is specified, do not warn about excess arguments to a
2836 @code{printf} or @code{scanf} format function. The C standard specifies
2837 that such arguments are ignored.
2839 Where the unused arguments lie between used arguments that are
2840 specified with @samp{$} operand number specifications, normally
2841 warnings are still given, since the implementation could not know what
2842 type to pass to @code{va_arg} to skip the unused arguments. However,
2843 in the case of @code{scanf} formats, this option will suppress the
2844 warning if the unused arguments are all pointers, since the Single
2845 Unix Specification says that such unused arguments are allowed.
2847 @item -Wno-format-zero-length @r{(C and Objective-C only)}
2848 @opindex Wno-format-zero-length
2849 @opindex Wformat-zero-length
2850 If @option{-Wformat} is specified, do not warn about zero-length formats.
2851 The C standard specifies that zero-length formats are allowed.
2853 @item -Wformat-nonliteral
2854 @opindex Wformat-nonliteral
2855 @opindex Wno-format-nonliteral
2856 If @option{-Wformat} is specified, also warn if the format string is not a
2857 string literal and so cannot be checked, unless the format function
2858 takes its format arguments as a @code{va_list}.
2860 @item -Wformat-security
2861 @opindex Wformat-security
2862 @opindex Wno-format-security
2863 If @option{-Wformat} is specified, also warn about uses of format
2864 functions that represent possible security problems. At present, this
2865 warns about calls to @code{printf} and @code{scanf} functions where the
2866 format string is not a string literal and there are no format arguments,
2867 as in @code{printf (foo);}. This may be a security hole if the format
2868 string came from untrusted input and contains @samp{%n}. (This is
2869 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2870 in future warnings may be added to @option{-Wformat-security} that are not
2871 included in @option{-Wformat-nonliteral}.)
2875 @opindex Wno-format=2
2876 Enable @option{-Wformat} plus format checks not included in
2877 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2878 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2880 @item -Wnonnull @r{(C and Objective-C only)}
2882 @opindex Wno-nonnull
2883 Warn about passing a null pointer for arguments marked as
2884 requiring a non-null value by the @code{nonnull} function attribute.
2886 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2887 can be disabled with the @option{-Wno-nonnull} option.
2889 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2891 @opindex Wno-init-self
2892 Warn about uninitialized variables which are initialized with themselves.
2893 Note this option can only be used with the @option{-Wuninitialized} option,
2894 which in turn only works with @option{-O1} and above.
2896 For example, GCC will warn about @code{i} being uninitialized in the
2897 following snippet only when @option{-Winit-self} has been specified:
2908 @item -Wimplicit-int @r{(C and Objective-C only)}
2909 @opindex Wimplicit-int
2910 @opindex Wno-implicit-int
2911 Warn when a declaration does not specify a type.
2912 This warning is enabled by @option{-Wall}.
2914 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
2915 @opindex Wimplicit-function-declaration
2916 @opindex Wno-implicit-function-declaration
2917 Give a warning whenever a function is used before being declared. In
2918 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
2919 enabled by default and it is made into an error by
2920 @option{-pedantic-errors}. This warning is also enabled by
2925 @opindex Wno-implicit
2926 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2927 This warning is enabled by @option{-Wall}.
2929 @item -Wignored-qualifiers @r{(C and C++ only)}
2930 @opindex Wignored-qualifiers
2931 @opindex Wno-ignored-qualifiers
2932 Warn if the return type of a function has a type qualifier
2933 such as @code{const}. For ISO C such a type qualifier has no effect,
2934 since the value returned by a function is not an lvalue.
2935 For C++, the warning is only emitted for scalar types or @code{void}.
2936 ISO C prohibits qualified @code{void} return types on function
2937 definitions, so such return types always receive a warning
2938 even without this option.
2940 This warning is also enabled by @option{-Wextra}.
2945 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2946 function with external linkage, returning int, taking either zero
2947 arguments, two, or three arguments of appropriate types.
2948 This warning is enabled by @option{-Wall}.
2950 @item -Wmissing-braces
2951 @opindex Wmissing-braces
2952 @opindex Wno-missing-braces
2953 Warn if an aggregate or union initializer is not fully bracketed. In
2954 the following example, the initializer for @samp{a} is not fully
2955 bracketed, but that for @samp{b} is fully bracketed.
2958 int a[2][2] = @{ 0, 1, 2, 3 @};
2959 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2962 This warning is enabled by @option{-Wall}.
2964 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2965 @opindex Wmissing-include-dirs
2966 @opindex Wno-missing-include-dirs
2967 Warn if a user-supplied include directory does not exist.
2970 @opindex Wparentheses
2971 @opindex Wno-parentheses
2972 Warn if parentheses are omitted in certain contexts, such
2973 as when there is an assignment in a context where a truth value
2974 is expected, or when operators are nested whose precedence people
2975 often get confused about.
2977 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2978 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2979 interpretation from that of ordinary mathematical notation.
2981 Also warn about constructions where there may be confusion to which
2982 @code{if} statement an @code{else} branch belongs. Here is an example of
2997 In C/C++, every @code{else} branch belongs to the innermost possible
2998 @code{if} statement, which in this example is @code{if (b)}. This is
2999 often not what the programmer expected, as illustrated in the above
3000 example by indentation the programmer chose. When there is the
3001 potential for this confusion, GCC will issue a warning when this flag
3002 is specified. To eliminate the warning, add explicit braces around
3003 the innermost @code{if} statement so there is no way the @code{else}
3004 could belong to the enclosing @code{if}. The resulting code would
3021 This warning is enabled by @option{-Wall}.
3023 @item -Wsequence-point
3024 @opindex Wsequence-point
3025 @opindex Wno-sequence-point
3026 Warn about code that may have undefined semantics because of violations
3027 of sequence point rules in the C and C++ standards.
3029 The C and C++ standards defines the order in which expressions in a C/C++
3030 program are evaluated in terms of @dfn{sequence points}, which represent
3031 a partial ordering between the execution of parts of the program: those
3032 executed before the sequence point, and those executed after it. These
3033 occur after the evaluation of a full expression (one which is not part
3034 of a larger expression), after the evaluation of the first operand of a
3035 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3036 function is called (but after the evaluation of its arguments and the
3037 expression denoting the called function), and in certain other places.
3038 Other than as expressed by the sequence point rules, the order of
3039 evaluation of subexpressions of an expression is not specified. All
3040 these rules describe only a partial order rather than a total order,
3041 since, for example, if two functions are called within one expression
3042 with no sequence point between them, the order in which the functions
3043 are called is not specified. However, the standards committee have
3044 ruled that function calls do not overlap.
3046 It is not specified when between sequence points modifications to the
3047 values of objects take effect. Programs whose behavior depends on this
3048 have undefined behavior; the C and C++ standards specify that ``Between
3049 the previous and next sequence point an object shall have its stored
3050 value modified at most once by the evaluation of an expression.
3051 Furthermore, the prior value shall be read only to determine the value
3052 to be stored.''. If a program breaks these rules, the results on any
3053 particular implementation are entirely unpredictable.
3055 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3056 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3057 diagnosed by this option, and it may give an occasional false positive
3058 result, but in general it has been found fairly effective at detecting
3059 this sort of problem in programs.
3061 The standard is worded confusingly, therefore there is some debate
3062 over the precise meaning of the sequence point rules in subtle cases.
3063 Links to discussions of the problem, including proposed formal
3064 definitions, may be found on the GCC readings page, at
3065 @w{@uref{http://gcc.gnu.org/readings.html}}.
3067 This warning is enabled by @option{-Wall} for C and C++.
3070 @opindex Wreturn-type
3071 @opindex Wno-return-type
3072 Warn whenever a function is defined with a return-type that defaults
3073 to @code{int}. Also warn about any @code{return} statement with no
3074 return-value in a function whose return-type is not @code{void}
3075 (falling off the end of the function body is considered returning
3076 without a value), and about a @code{return} statement with a
3077 expression in a function whose return-type is @code{void}.
3079 For C++, a function without return type always produces a diagnostic
3080 message, even when @option{-Wno-return-type} is specified. The only
3081 exceptions are @samp{main} and functions defined in system headers.
3083 This warning is enabled by @option{-Wall}.
3088 Warn whenever a @code{switch} statement has an index of enumerated type
3089 and lacks a @code{case} for one or more of the named codes of that
3090 enumeration. (The presence of a @code{default} label prevents this
3091 warning.) @code{case} labels outside the enumeration range also
3092 provoke warnings when this option is used.
3093 This warning is enabled by @option{-Wall}.
3095 @item -Wswitch-default
3096 @opindex Wswitch-default
3097 @opindex Wno-switch-default
3098 Warn whenever a @code{switch} statement does not have a @code{default}
3102 @opindex Wswitch-enum
3103 @opindex Wno-switch-enum
3104 Warn whenever a @code{switch} statement has an index of enumerated type
3105 and lacks a @code{case} for one or more of the named codes of that
3106 enumeration. @code{case} labels outside the enumeration range also
3107 provoke warnings when this option is used.
3111 @opindex Wno-trigraphs
3112 Warn if any trigraphs are encountered that might change the meaning of
3113 the program (trigraphs within comments are not warned about).
3114 This warning is enabled by @option{-Wall}.
3116 @item -Wunused-function
3117 @opindex Wunused-function
3118 @opindex Wno-unused-function
3119 Warn whenever a static function is declared but not defined or a
3120 non-inline static function is unused.
3121 This warning is enabled by @option{-Wall}.
3123 @item -Wunused-label
3124 @opindex Wunused-label
3125 @opindex Wno-unused-label
3126 Warn whenever a label is declared but not used.
3127 This warning is enabled by @option{-Wall}.
3129 To suppress this warning use the @samp{unused} attribute
3130 (@pxref{Variable Attributes}).
3132 @item -Wunused-parameter
3133 @opindex Wunused-parameter
3134 @opindex Wno-unused-parameter
3135 Warn whenever a function parameter is unused aside from its declaration.
3137 To suppress this warning use the @samp{unused} attribute
3138 (@pxref{Variable Attributes}).
3140 @item -Wunused-variable
3141 @opindex Wunused-variable
3142 @opindex Wno-unused-variable
3143 Warn whenever a local variable or non-constant static variable is unused
3144 aside from its declaration.
3145 This warning is enabled by @option{-Wall}.
3147 To suppress this warning use the @samp{unused} attribute
3148 (@pxref{Variable Attributes}).
3150 @item -Wunused-value
3151 @opindex Wunused-value
3152 @opindex Wno-unused-value
3153 Warn whenever a statement computes a result that is explicitly not
3154 used. To suppress this warning cast the unused expression to
3155 @samp{void}. This includes an expression-statement or the left-hand
3156 side of a comma expression that contains no side effects. For example,
3157 an expression such as @samp{x[i,j]} will cause a warning, while
3158 @samp{x[(void)i,j]} will not.
3160 This warning is enabled by @option{-Wall}.
3165 All the above @option{-Wunused} options combined.
3167 In order to get a warning about an unused function parameter, you must
3168 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3169 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3171 @item -Wuninitialized
3172 @opindex Wuninitialized
3173 @opindex Wno-uninitialized
3174 Warn if an automatic variable is used without first being initialized or
3175 if a variable may be clobbered by a @code{setjmp} call.
3177 These warnings are possible only in optimizing compilation,
3178 because they require data flow information that is computed only
3179 when optimizing. If you do not specify @option{-O}, you will not get
3180 these warnings. Instead, GCC will issue a warning about @option{-Wuninitialized}
3181 requiring @option{-O}.
3183 If you want to warn about code which uses the uninitialized value of the
3184 variable in its own initializer, use the @option{-Winit-self} option.
3186 These warnings occur for individual uninitialized or clobbered
3187 elements of structure, union or array variables as well as for
3188 variables which are uninitialized or clobbered as a whole. They do
3189 not occur for variables or elements declared @code{volatile}. Because
3190 these warnings depend on optimization, the exact variables or elements
3191 for which there are warnings will depend on the precise optimization
3192 options and version of GCC used.
3194 Note that there may be no warning about a variable that is used only
3195 to compute a value that itself is never used, because such
3196 computations may be deleted by data flow analysis before the warnings
3199 These warnings are made optional because GCC is not smart
3200 enough to see all the reasons why the code might be correct
3201 despite appearing to have an error. Here is one example of how
3222 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3223 always initialized, but GCC doesn't know this. Here is
3224 another common case:
3229 if (change_y) save_y = y, y = new_y;
3231 if (change_y) y = save_y;
3236 This has no bug because @code{save_y} is used only if it is set.
3238 @cindex @code{longjmp} warnings
3239 This option also warns when a non-volatile automatic variable might be
3240 changed by a call to @code{longjmp}. These warnings as well are possible
3241 only in optimizing compilation.
3243 The compiler sees only the calls to @code{setjmp}. It cannot know
3244 where @code{longjmp} will be called; in fact, a signal handler could
3245 call it at any point in the code. As a result, you may get a warning
3246 even when there is in fact no problem because @code{longjmp} cannot
3247 in fact be called at the place which would cause a problem.
3249 Some spurious warnings can be avoided if you declare all the functions
3250 you use that never return as @code{noreturn}. @xref{Function
3253 This warning is enabled by @option{-Wall} or @option{-Wextra} in
3254 optimizing compilations (@option{-O1} and above).
3256 @item -Wunknown-pragmas
3257 @opindex Wunknown-pragmas
3258 @opindex Wno-unknown-pragmas
3259 @cindex warning for unknown pragmas
3260 @cindex unknown pragmas, warning
3261 @cindex pragmas, warning of unknown
3262 Warn when a #pragma directive is encountered which is not understood by
3263 GCC@. If this command line option is used, warnings will even be issued
3264 for unknown pragmas in system header files. This is not the case if
3265 the warnings were only enabled by the @option{-Wall} command line option.
3268 @opindex Wno-pragmas
3270 Do not warn about misuses of pragmas, such as incorrect parameters,
3271 invalid syntax, or conflicts between pragmas. See also
3272 @samp{-Wunknown-pragmas}.
3274 @item -Wstrict-aliasing
3275 @opindex Wstrict-aliasing
3276 @opindex Wno-strict-aliasing
3277 This option is only active when @option{-fstrict-aliasing} is active.
3278 It warns about code which might break the strict aliasing rules that the
3279 compiler is using for optimization. The warning does not catch all
3280 cases, but does attempt to catch the more common pitfalls. It is
3281 included in @option{-Wall}.
3282 It is equivalent to @option{-Wstrict-aliasing=3}
3284 @item -Wstrict-aliasing=n
3285 @opindex Wstrict-aliasing=n
3286 @opindex Wno-strict-aliasing=n
3287 This option is only active when @option{-fstrict-aliasing} is active.
3288 It warns about code which might break the strict aliasing rules that the
3289 compiler is using for optimization.
3290 Higher levels correspond to higher accuracy (fewer false positives).
3291 Higher levels also correspond to more effort, similar to the way -O works.
3292 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3295 Level 1: Most aggressive, quick, least accurate.
3296 Possibly useful when higher levels
3297 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3298 false negatives. However, it has many false positives.
3299 Warns for all pointer conversions between possibly incompatible types,
3300 even if never dereferenced. Runs in the frontend only.
3302 Level 2: Aggressive, quick, not too precise.
3303 May still have many false positives (not as many as level 1 though),
3304 and few false negatives (but possibly more than level 1).
3305 Unlike level 1, it only warns when an address is taken. Warns about
3306 incomplete types. Runs in the frontend only.
3308 Level 3 (default for @option{-Wstrict-aliasing}):
3309 Should have very few false positives and few false
3310 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3311 Takes care of the common punn+dereference pattern in the frontend:
3312 @code{*(int*)&some_float}.
3313 If optimization is enabled, it also runs in the backend, where it deals
3314 with multiple statement cases using flow-sensitive points-to information.
3315 Only warns when the converted pointer is dereferenced.
3316 Does not warn about incomplete types.
3318 @item -Wstrict-overflow
3319 @itemx -Wstrict-overflow=@var{n}
3320 @opindex Wstrict-overflow
3321 @opindex Wno-strict-overflow
3322 This option is only active when @option{-fstrict-overflow} is active.
3323 It warns about cases where the compiler optimizes based on the
3324 assumption that signed overflow does not occur. Note that it does not
3325 warn about all cases where the code might overflow: it only warns
3326 about cases where the compiler implements some optimization. Thus
3327 this warning depends on the optimization level.
3329 An optimization which assumes that signed overflow does not occur is
3330 perfectly safe if the values of the variables involved are such that
3331 overflow never does, in fact, occur. Therefore this warning can
3332 easily give a false positive: a warning about code which is not
3333 actually a problem. To help focus on important issues, several
3334 warning levels are defined. No warnings are issued for the use of
3335 undefined signed overflow when estimating how many iterations a loop
3336 will require, in particular when determining whether a loop will be
3340 @item -Wstrict-overflow=1
3341 Warn about cases which are both questionable and easy to avoid. For
3342 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3343 compiler will simplify this to @code{1}. This level of
3344 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3345 are not, and must be explicitly requested.
3347 @item -Wstrict-overflow=2
3348 Also warn about other cases where a comparison is simplified to a
3349 constant. For example: @code{abs (x) >= 0}. This can only be
3350 simplified when @option{-fstrict-overflow} is in effect, because
3351 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3352 zero. @option{-Wstrict-overflow} (with no level) is the same as
3353 @option{-Wstrict-overflow=2}.
3355 @item -Wstrict-overflow=3
3356 Also warn about other cases where a comparison is simplified. For
3357 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3359 @item -Wstrict-overflow=4
3360 Also warn about other simplifications not covered by the above cases.
3361 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3363 @item -Wstrict-overflow=5
3364 Also warn about cases where the compiler reduces the magnitude of a
3365 constant involved in a comparison. For example: @code{x + 2 > y} will
3366 be simplified to @code{x + 1 >= y}. This is reported only at the
3367 highest warning level because this simplification applies to many
3368 comparisons, so this warning level will give a very large number of
3372 @item -Warray-bounds
3373 @opindex Wno-array-bounds
3374 @opindex Warray-bounds
3375 This option is only active when @option{-ftree-vrp} is active
3376 (default for -O2 and above). It warns about subscripts to arrays
3377 that are always out of bounds. This warning is enabled by @option{-Wall}.
3379 @item -Wno-div-by-zero
3380 @opindex Wno-div-by-zero
3381 @opindex Wdiv-by-zero
3382 Do not warn about compile-time integer division by zero. Floating point
3383 division by zero is not warned about, as it can be a legitimate way of
3384 obtaining infinities and NaNs.
3386 @item -Wsystem-headers
3387 @opindex Wsystem-headers
3388 @opindex Wno-system-headers
3389 @cindex warnings from system headers
3390 @cindex system headers, warnings from
3391 Print warning messages for constructs found in system header files.
3392 Warnings from system headers are normally suppressed, on the assumption
3393 that they usually do not indicate real problems and would only make the
3394 compiler output harder to read. Using this command line option tells
3395 GCC to emit warnings from system headers as if they occurred in user
3396 code. However, note that using @option{-Wall} in conjunction with this
3397 option will @emph{not} warn about unknown pragmas in system
3398 headers---for that, @option{-Wunknown-pragmas} must also be used.
3401 @opindex Wfloat-equal
3402 @opindex Wno-float-equal
3403 Warn if floating point values are used in equality comparisons.
3405 The idea behind this is that sometimes it is convenient (for the
3406 programmer) to consider floating-point values as approximations to
3407 infinitely precise real numbers. If you are doing this, then you need
3408 to compute (by analyzing the code, or in some other way) the maximum or
3409 likely maximum error that the computation introduces, and allow for it
3410 when performing comparisons (and when producing output, but that's a
3411 different problem). In particular, instead of testing for equality, you
3412 would check to see whether the two values have ranges that overlap; and
3413 this is done with the relational operators, so equality comparisons are
3416 @item -Wtraditional @r{(C and Objective-C only)}
3417 @opindex Wtraditional
3418 @opindex Wno-traditional
3419 Warn about certain constructs that behave differently in traditional and
3420 ISO C@. Also warn about ISO C constructs that have no traditional C
3421 equivalent, and/or problematic constructs which should be avoided.
3425 Macro parameters that appear within string literals in the macro body.
3426 In traditional C macro replacement takes place within string literals,
3427 but does not in ISO C@.
3430 In traditional C, some preprocessor directives did not exist.
3431 Traditional preprocessors would only consider a line to be a directive
3432 if the @samp{#} appeared in column 1 on the line. Therefore
3433 @option{-Wtraditional} warns about directives that traditional C
3434 understands but would ignore because the @samp{#} does not appear as the
3435 first character on the line. It also suggests you hide directives like
3436 @samp{#pragma} not understood by traditional C by indenting them. Some
3437 traditional implementations would not recognize @samp{#elif}, so it
3438 suggests avoiding it altogether.
3441 A function-like macro that appears without arguments.
3444 The unary plus operator.
3447 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3448 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3449 constants.) Note, these suffixes appear in macros defined in the system
3450 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3451 Use of these macros in user code might normally lead to spurious
3452 warnings, however GCC's integrated preprocessor has enough context to
3453 avoid warning in these cases.
3456 A function declared external in one block and then used after the end of
3460 A @code{switch} statement has an operand of type @code{long}.
3463 A non-@code{static} function declaration follows a @code{static} one.
3464 This construct is not accepted by some traditional C compilers.
3467 The ISO type of an integer constant has a different width or
3468 signedness from its traditional type. This warning is only issued if
3469 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3470 typically represent bit patterns, are not warned about.
3473 Usage of ISO string concatenation is detected.
3476 Initialization of automatic aggregates.
3479 Identifier conflicts with labels. Traditional C lacks a separate
3480 namespace for labels.
3483 Initialization of unions. If the initializer is zero, the warning is
3484 omitted. This is done under the assumption that the zero initializer in
3485 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3486 initializer warnings and relies on default initialization to zero in the
3490 Conversions by prototypes between fixed/floating point values and vice
3491 versa. The absence of these prototypes when compiling with traditional
3492 C would cause serious problems. This is a subset of the possible
3493 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3496 Use of ISO C style function definitions. This warning intentionally is
3497 @emph{not} issued for prototype declarations or variadic functions
3498 because these ISO C features will appear in your code when using
3499 libiberty's traditional C compatibility macros, @code{PARAMS} and
3500 @code{VPARAMS}. This warning is also bypassed for nested functions
3501 because that feature is already a GCC extension and thus not relevant to
3502 traditional C compatibility.
3505 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3506 @opindex Wtraditional-conversion
3507 @opindex Wno-traditional-conversion
3508 Warn if a prototype causes a type conversion that is different from what
3509 would happen to the same argument in the absence of a prototype. This
3510 includes conversions of fixed point to floating and vice versa, and
3511 conversions changing the width or signedness of a fixed point argument
3512 except when the same as the default promotion.
3514 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3515 @opindex Wdeclaration-after-statement
3516 @opindex Wno-declaration-after-statement
3517 Warn when a declaration is found after a statement in a block. This
3518 construct, known from C++, was introduced with ISO C99 and is by default
3519 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3520 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3525 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3527 @item -Wno-endif-labels
3528 @opindex Wno-endif-labels
3529 @opindex Wendif-labels
3530 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3535 Warn whenever a local variable shadows another local variable, parameter or
3536 global variable or whenever a built-in function is shadowed.
3538 @item -Wlarger-than=@var{len}
3539 @opindex Wlarger-than=@var{len}
3540 @opindex Wlarger-than-@var{len}
3541 Warn whenever an object of larger than @var{len} bytes is defined.
3543 @item -Wframe-larger-than=@var{len}
3544 @opindex Wframe-larger-than
3545 Warn if the size of a function frame is larger than @var{len} bytes.
3546 The computation done to determine the stack frame size is approximate
3547 and not conservative.
3548 The actual requirements may be somewhat greater than @var{len}
3549 even if you do not get a warning. In addition, any space allocated
3550 via @code{alloca}, variable-length arrays, or related constructs
3551 is not included by the compiler when determining
3552 whether or not to issue a warning.
3554 @item -Wunsafe-loop-optimizations
3555 @opindex Wunsafe-loop-optimizations
3556 @opindex Wno-unsafe-loop-optimizations
3557 Warn if the loop cannot be optimized because the compiler could not
3558 assume anything on the bounds of the loop indices. With
3559 @option{-funsafe-loop-optimizations} warn if the compiler made
3562 @item -Wpointer-arith
3563 @opindex Wpointer-arith
3564 @opindex Wno-pointer-arith
3565 Warn about anything that depends on the ``size of'' a function type or
3566 of @code{void}. GNU C assigns these types a size of 1, for
3567 convenience in calculations with @code{void *} pointers and pointers
3568 to functions. In C++, warn also when an arithmetic operation involves
3569 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3572 @opindex Wtype-limits
3573 @opindex Wno-type-limits
3574 Warn if a comparison is always true or always false due to the limited
3575 range of the data type, but do not warn for constant expressions. For
3576 example, warn if an unsigned variable is compared against zero with
3577 @samp{<} or @samp{>=}. This warning is also enabled by
3580 @item -Wbad-function-cast @r{(C and Objective-C only)}
3581 @opindex Wbad-function-cast
3582 @opindex Wno-bad-function-cast
3583 Warn whenever a function call is cast to a non-matching type.
3584 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3586 @item -Wc++-compat @r{(C and Objective-C only)}
3587 Warn about ISO C constructs that are outside of the common subset of
3588 ISO C and ISO C++, e.g.@: request for implicit conversion from
3589 @code{void *} to a pointer to non-@code{void} type.
3591 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3592 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3593 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3594 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3598 @opindex Wno-cast-qual
3599 Warn whenever a pointer is cast so as to remove a type qualifier from
3600 the target type. For example, warn if a @code{const char *} is cast
3601 to an ordinary @code{char *}.
3604 @opindex Wcast-align
3605 @opindex Wno-cast-align
3606 Warn whenever a pointer is cast such that the required alignment of the
3607 target is increased. For example, warn if a @code{char *} is cast to
3608 an @code{int *} on machines where integers can only be accessed at
3609 two- or four-byte boundaries.
3611 @item -Wwrite-strings
3612 @opindex Wwrite-strings
3613 @opindex Wno-write-strings
3614 When compiling C, give string constants the type @code{const
3615 char[@var{length}]} so that
3616 copying the address of one into a non-@code{const} @code{char *}
3617 pointer will get a warning; when compiling C++, warn about the
3618 deprecated conversion from string literals to @code{char *}. This
3619 warning, by default, is enabled for C++ programs.
3620 These warnings will help you find at
3621 compile time code that can try to write into a string constant, but
3622 only if you have been very careful about using @code{const} in
3623 declarations and prototypes. Otherwise, it will just be a nuisance;
3624 this is why we did not make @option{-Wall} request these warnings.
3628 @opindex Wno-clobbered
3629 Warn for variables that might be changed by @samp{longjmp} or
3630 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3633 @opindex Wconversion
3634 @opindex Wno-conversion
3635 Warn for implicit conversions that may alter a value. This includes
3636 conversions between real and integer, like @code{abs (x)} when
3637 @code{x} is @code{double}; conversions between signed and unsigned,
3638 like @code{unsigned ui = -1}; and conversions to smaller types, like
3639 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3640 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3641 changed by the conversion like in @code{abs (2.0)}. Warnings about
3642 conversions between signed and unsigned integers can be disabled by
3643 using @option{-Wno-sign-conversion}.
3645 For C++, also warn for conversions between @code{NULL} and non-pointer
3646 types; confusing overload resolution for user-defined conversions; and
3647 conversions that will never use a type conversion operator:
3648 conversions to @code{void}, the same type, a base class or a reference
3649 to them. Warnings about conversions between signed and unsigned
3650 integers are disabled by default in C++ unless
3651 @option{-Wsign-conversion} is explicitly enabled.
3654 @opindex Wempty-body
3655 @opindex Wno-empty-body
3656 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3657 while} statement. Additionally, in C++, warn when an empty body occurs
3658 in a @samp{while} or @samp{for} statement with no whitespacing before
3659 the semicolon. This warning is also enabled by @option{-Wextra}.
3661 @item -Wenum-compare @r{(C++ and Objective-C++ only)}
3662 @opindex Wenum-compare
3663 @opindex Wno-enum-compare
3664 Warn about a comparison between values of different enum types. This
3665 warning is enabled by default.
3667 @item -Wsign-compare
3668 @opindex Wsign-compare
3669 @opindex Wno-sign-compare
3670 @cindex warning for comparison of signed and unsigned values
3671 @cindex comparison of signed and unsigned values, warning
3672 @cindex signed and unsigned values, comparison warning
3673 Warn when a comparison between signed and unsigned values could produce
3674 an incorrect result when the signed value is converted to unsigned.
3675 This warning is also enabled by @option{-Wextra}; to get the other warnings
3676 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3678 @item -Wsign-conversion
3679 @opindex Wsign-conversion
3680 @opindex Wno-sign-conversion
3681 Warn for implicit conversions that may change the sign of an integer
3682 value, like assigning a signed integer expression to an unsigned
3683 integer variable. An explicit cast silences the warning. In C, this
3684 option is enabled also by @option{-Wconversion}.
3688 @opindex Wno-address
3689 Warn about suspicious uses of memory addresses. These include using
3690 the address of a function in a conditional expression, such as
3691 @code{void func(void); if (func)}, and comparisons against the memory
3692 address of a string literal, such as @code{if (x == "abc")}. Such
3693 uses typically indicate a programmer error: the address of a function
3694 always evaluates to true, so their use in a conditional usually
3695 indicate that the programmer forgot the parentheses in a function
3696 call; and comparisons against string literals result in unspecified
3697 behavior and are not portable in C, so they usually indicate that the
3698 programmer intended to use @code{strcmp}. This warning is enabled by
3702 @opindex Wlogical-op
3703 @opindex Wno-logical-op
3704 Warn about suspicious uses of logical operators in expressions.
3705 This includes using logical operators in contexts where a
3706 bit-wise operator is likely to be expected.
3708 @item -Waggregate-return
3709 @opindex Waggregate-return
3710 @opindex Wno-aggregate-return
3711 Warn if any functions that return structures or unions are defined or
3712 called. (In languages where you can return an array, this also elicits
3715 @item -Wno-attributes
3716 @opindex Wno-attributes
3717 @opindex Wattributes
3718 Do not warn if an unexpected @code{__attribute__} is used, such as
3719 unrecognized attributes, function attributes applied to variables,
3720 etc. This will not stop errors for incorrect use of supported
3723 @item -Wstrict-prototypes @r{(C and Objective-C only)}
3724 @opindex Wstrict-prototypes
3725 @opindex Wno-strict-prototypes
3726 Warn if a function is declared or defined without specifying the
3727 argument types. (An old-style function definition is permitted without
3728 a warning if preceded by a declaration which specifies the argument
3731 @item -Wold-style-declaration @r{(C and Objective-C only)}
3732 @opindex Wold-style-declaration
3733 @opindex Wno-old-style-declaration
3734 Warn for obsolescent usages, according to the C Standard, in a
3735 declaration. For example, warn if storage-class specifiers like
3736 @code{static} are not the first things in a declaration. This warning
3737 is also enabled by @option{-Wextra}.
3739 @item -Wold-style-definition @r{(C and Objective-C only)}
3740 @opindex Wold-style-definition
3741 @opindex Wno-old-style-definition
3742 Warn if an old-style function definition is used. A warning is given
3743 even if there is a previous prototype.
3745 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
3746 @opindex Wmissing-parameter-type
3747 @opindex Wno-missing-parameter-type
3748 A function parameter is declared without a type specifier in K&R-style
3755 This warning is also enabled by @option{-Wextra}.
3757 @item -Wmissing-prototypes @r{(C and Objective-C only)}
3758 @opindex Wmissing-prototypes
3759 @opindex Wno-missing-prototypes
3760 Warn if a global function is defined without a previous prototype
3761 declaration. This warning is issued even if the definition itself
3762 provides a prototype. The aim is to detect global functions that fail
3763 to be declared in header files.
3765 @item -Wmissing-declarations
3766 @opindex Wmissing-declarations
3767 @opindex Wno-missing-declarations
3768 Warn if a global function is defined without a previous declaration.
3769 Do so even if the definition itself provides a prototype.
3770 Use this option to detect global functions that are not declared in
3771 header files. In C++, no warnings are issued for function templates,
3772 or for inline functions, or for functions in anonymous namespaces.
3774 @item -Wmissing-field-initializers
3775 @opindex Wmissing-field-initializers
3776 @opindex Wno-missing-field-initializers
3780 Warn if a structure's initializer has some fields missing. For
3781 example, the following code would cause such a warning, because
3782 @code{x.h} is implicitly zero:
3785 struct s @{ int f, g, h; @};
3786 struct s x = @{ 3, 4 @};
3789 This option does not warn about designated initializers, so the following
3790 modification would not trigger a warning:
3793 struct s @{ int f, g, h; @};
3794 struct s x = @{ .f = 3, .g = 4 @};
3797 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3798 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3800 @item -Wmissing-noreturn
3801 @opindex Wmissing-noreturn
3802 @opindex Wno-missing-noreturn
3803 Warn about functions which might be candidates for attribute @code{noreturn}.
3804 Note these are only possible candidates, not absolute ones. Care should
3805 be taken to manually verify functions actually do not ever return before
3806 adding the @code{noreturn} attribute, otherwise subtle code generation
3807 bugs could be introduced. You will not get a warning for @code{main} in
3808 hosted C environments.
3810 @item -Wmissing-format-attribute
3811 @opindex Wmissing-format-attribute
3812 @opindex Wno-missing-format-attribute
3815 Warn about function pointers which might be candidates for @code{format}
3816 attributes. Note these are only possible candidates, not absolute ones.
3817 GCC will guess that function pointers with @code{format} attributes that
3818 are used in assignment, initialization, parameter passing or return
3819 statements should have a corresponding @code{format} attribute in the
3820 resulting type. I.e.@: the left-hand side of the assignment or
3821 initialization, the type of the parameter variable, or the return type
3822 of the containing function respectively should also have a @code{format}
3823 attribute to avoid the warning.
3825 GCC will also warn about function definitions which might be
3826 candidates for @code{format} attributes. Again, these are only
3827 possible candidates. GCC will guess that @code{format} attributes
3828 might be appropriate for any function that calls a function like
3829 @code{vprintf} or @code{vscanf}, but this might not always be the
3830 case, and some functions for which @code{format} attributes are
3831 appropriate may not be detected.
3833 @item -Wno-multichar
3834 @opindex Wno-multichar
3836 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3837 Usually they indicate a typo in the user's code, as they have
3838 implementation-defined values, and should not be used in portable code.
3840 @item -Wnormalized=<none|id|nfc|nfkc>
3841 @opindex Wnormalized=
3844 @cindex character set, input normalization
3845 In ISO C and ISO C++, two identifiers are different if they are
3846 different sequences of characters. However, sometimes when characters
3847 outside the basic ASCII character set are used, you can have two
3848 different character sequences that look the same. To avoid confusion,
3849 the ISO 10646 standard sets out some @dfn{normalization rules} which
3850 when applied ensure that two sequences that look the same are turned into
3851 the same sequence. GCC can warn you if you are using identifiers which
3852 have not been normalized; this option controls that warning.
3854 There are four levels of warning that GCC supports. The default is
3855 @option{-Wnormalized=nfc}, which warns about any identifier which is
3856 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3857 recommended form for most uses.
3859 Unfortunately, there are some characters which ISO C and ISO C++ allow
3860 in identifiers that when turned into NFC aren't allowable as
3861 identifiers. That is, there's no way to use these symbols in portable
3862 ISO C or C++ and have all your identifiers in NFC@.
3863 @option{-Wnormalized=id} suppresses the warning for these characters.
3864 It is hoped that future versions of the standards involved will correct
3865 this, which is why this option is not the default.
3867 You can switch the warning off for all characters by writing
3868 @option{-Wnormalized=none}. You would only want to do this if you
3869 were using some other normalization scheme (like ``D''), because
3870 otherwise you can easily create bugs that are literally impossible to see.
3872 Some characters in ISO 10646 have distinct meanings but look identical
3873 in some fonts or display methodologies, especially once formatting has
3874 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3875 LETTER N'', will display just like a regular @code{n} which has been
3876 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3877 normalization scheme to convert all these into a standard form as
3878 well, and GCC will warn if your code is not in NFKC if you use
3879 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3880 about every identifier that contains the letter O because it might be
3881 confused with the digit 0, and so is not the default, but may be
3882 useful as a local coding convention if the programming environment is
3883 unable to be fixed to display these characters distinctly.
3885 @item -Wno-deprecated
3886 @opindex Wno-deprecated
3887 @opindex Wdeprecated
3888 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
3890 @item -Wno-deprecated-declarations
3891 @opindex Wno-deprecated-declarations
3892 @opindex Wdeprecated-declarations
3893 Do not warn about uses of functions (@pxref{Function Attributes}),
3894 variables (@pxref{Variable Attributes}), and types (@pxref{Type
3895 Attributes}) marked as deprecated by using the @code{deprecated}
3899 @opindex Wno-overflow
3901 Do not warn about compile-time overflow in constant expressions.
3903 @item -Woverride-init @r{(C and Objective-C only)}
3904 @opindex Woverride-init
3905 @opindex Wno-override-init
3909 Warn if an initialized field without side effects is overridden when
3910 using designated initializers (@pxref{Designated Inits, , Designated
3913 This warning is included in @option{-Wextra}. To get other
3914 @option{-Wextra} warnings without this one, use @samp{-Wextra
3915 -Wno-override-init}.
3920 Warn if a structure is given the packed attribute, but the packed
3921 attribute has no effect on the layout or size of the structure.
3922 Such structures may be mis-aligned for little benefit. For
3923 instance, in this code, the variable @code{f.x} in @code{struct bar}
3924 will be misaligned even though @code{struct bar} does not itself
3925 have the packed attribute:
3932 @} __attribute__((packed));
3943 Warn if padding is included in a structure, either to align an element
3944 of the structure or to align the whole structure. Sometimes when this
3945 happens it is possible to rearrange the fields of the structure to
3946 reduce the padding and so make the structure smaller.
3948 @item -Wredundant-decls
3949 @opindex Wredundant-decls
3950 @opindex Wno-redundant-decls
3951 Warn if anything is declared more than once in the same scope, even in
3952 cases where multiple declaration is valid and changes nothing.
3954 @item -Wnested-externs @r{(C and Objective-C only)}
3955 @opindex Wnested-externs
3956 @opindex Wno-nested-externs
3957 Warn if an @code{extern} declaration is encountered within a function.
3959 @item -Wunreachable-code
3960 @opindex Wunreachable-code
3961 @opindex Wno-unreachable-code
3962 Warn if the compiler detects that code will never be executed.
3964 This option is intended to warn when the compiler detects that at
3965 least a whole line of source code will never be executed, because
3966 some condition is never satisfied or because it is after a
3967 procedure that never returns.
3969 It is possible for this option to produce a warning even though there
3970 are circumstances under which part of the affected line can be executed,
3971 so care should be taken when removing apparently-unreachable code.
3973 For instance, when a function is inlined, a warning may mean that the
3974 line is unreachable in only one inlined copy of the function.
3976 This option is not made part of @option{-Wall} because in a debugging
3977 version of a program there is often substantial code which checks
3978 correct functioning of the program and is, hopefully, unreachable
3979 because the program does work. Another common use of unreachable
3980 code is to provide behavior which is selectable at compile-time.
3985 Warn if a function can not be inlined and it was declared as inline.
3986 Even with this option, the compiler will not warn about failures to
3987 inline functions declared in system headers.
3989 The compiler uses a variety of heuristics to determine whether or not
3990 to inline a function. For example, the compiler takes into account
3991 the size of the function being inlined and the amount of inlining
3992 that has already been done in the current function. Therefore,
3993 seemingly insignificant changes in the source program can cause the
3994 warnings produced by @option{-Winline} to appear or disappear.
3996 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
3997 @opindex Wno-invalid-offsetof
3998 @opindex Winvalid-offsetof
3999 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
4000 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
4001 to a non-POD type is undefined. In existing C++ implementations,
4002 however, @samp{offsetof} typically gives meaningful results even when
4003 applied to certain kinds of non-POD types. (Such as a simple
4004 @samp{struct} that fails to be a POD type only by virtue of having a
4005 constructor.) This flag is for users who are aware that they are
4006 writing nonportable code and who have deliberately chosen to ignore the
4009 The restrictions on @samp{offsetof} may be relaxed in a future version
4010 of the C++ standard.
4012 @item -Wno-int-to-pointer-cast @r{(C and Objective-C only)}
4013 @opindex Wno-int-to-pointer-cast
4014 @opindex Wint-to-pointer-cast
4015 Suppress warnings from casts to pointer type of an integer of a
4018 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4019 @opindex Wno-pointer-to-int-cast
4020 @opindex Wpointer-to-int-cast
4021 Suppress warnings from casts from a pointer to an integer type of a
4025 @opindex Winvalid-pch
4026 @opindex Wno-invalid-pch
4027 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4028 the search path but can't be used.
4032 @opindex Wno-long-long
4033 Warn if @samp{long long} type is used. This is default. To inhibit
4034 the warning messages, use @option{-Wno-long-long}. Flags
4035 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
4036 only when @option{-pedantic} flag is used.
4038 @item -Wvariadic-macros
4039 @opindex Wvariadic-macros
4040 @opindex Wno-variadic-macros
4041 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4042 alternate syntax when in pedantic ISO C99 mode. This is default.
4043 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4048 Warn if variable length array is used in the code.
4049 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4050 the variable length array.
4052 @item -Wvolatile-register-var
4053 @opindex Wvolatile-register-var
4054 @opindex Wno-volatile-register-var
4055 Warn if a register variable is declared volatile. The volatile
4056 modifier does not inhibit all optimizations that may eliminate reads
4057 and/or writes to register variables. This warning is enabled by
4060 @item -Wdisabled-optimization
4061 @opindex Wdisabled-optimization
4062 @opindex Wno-disabled-optimization
4063 Warn if a requested optimization pass is disabled. This warning does
4064 not generally indicate that there is anything wrong with your code; it
4065 merely indicates that GCC's optimizers were unable to handle the code
4066 effectively. Often, the problem is that your code is too big or too
4067 complex; GCC will refuse to optimize programs when the optimization
4068 itself is likely to take inordinate amounts of time.
4070 @item -Wpointer-sign @r{(C and Objective-C only)}
4071 @opindex Wpointer-sign
4072 @opindex Wno-pointer-sign
4073 Warn for pointer argument passing or assignment with different signedness.
4074 This option is only supported for C and Objective-C@. It is implied by
4075 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4076 @option{-Wno-pointer-sign}.
4078 @item -Wstack-protector
4079 @opindex Wstack-protector
4080 @opindex Wno-stack-protector
4081 This option is only active when @option{-fstack-protector} is active. It
4082 warns about functions that will not be protected against stack smashing.
4085 @opindex Wno-mudflap
4086 Suppress warnings about constructs that cannot be instrumented by
4089 @item -Woverlength-strings
4090 @opindex Woverlength-strings
4091 @opindex Wno-overlength-strings
4092 Warn about string constants which are longer than the ``minimum
4093 maximum'' length specified in the C standard. Modern compilers
4094 generally allow string constants which are much longer than the
4095 standard's minimum limit, but very portable programs should avoid
4096 using longer strings.
4098 The limit applies @emph{after} string constant concatenation, and does
4099 not count the trailing NUL@. In C89, the limit was 509 characters; in
4100 C99, it was raised to 4095. C++98 does not specify a normative
4101 minimum maximum, so we do not diagnose overlength strings in C++@.
4103 This option is implied by @option{-pedantic}, and can be disabled with
4104 @option{-Wno-overlength-strings}.
4106 @item -Wdisallowed-function-list=@var{sym},@var{sym},@dots{}
4107 @opindex Wdisallowed-function-list
4109 If any of @var{sym} is called, GCC will issue a warning. This can be useful
4110 in enforcing coding conventions that ban calls to certain functions, for
4111 example, @code{alloca}, @code{malloc}, etc.
4114 @node Debugging Options
4115 @section Options for Debugging Your Program or GCC
4116 @cindex options, debugging
4117 @cindex debugging information options
4119 GCC has various special options that are used for debugging
4120 either your program or GCC:
4125 Produce debugging information in the operating system's native format
4126 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4129 On most systems that use stabs format, @option{-g} enables use of extra
4130 debugging information that only GDB can use; this extra information
4131 makes debugging work better in GDB but will probably make other debuggers
4133 refuse to read the program. If you want to control for certain whether
4134 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4135 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4137 GCC allows you to use @option{-g} with
4138 @option{-O}. The shortcuts taken by optimized code may occasionally
4139 produce surprising results: some variables you declared may not exist
4140 at all; flow of control may briefly move where you did not expect it;
4141 some statements may not be executed because they compute constant
4142 results or their values were already at hand; some statements may
4143 execute in different places because they were moved out of loops.
4145 Nevertheless it proves possible to debug optimized output. This makes
4146 it reasonable to use the optimizer for programs that might have bugs.
4148 The following options are useful when GCC is generated with the
4149 capability for more than one debugging format.
4153 Produce debugging information for use by GDB@. This means to use the
4154 most expressive format available (DWARF 2, stabs, or the native format
4155 if neither of those are supported), including GDB extensions if at all
4160 Produce debugging information in stabs format (if that is supported),
4161 without GDB extensions. This is the format used by DBX on most BSD
4162 systems. On MIPS, Alpha and System V Release 4 systems this option
4163 produces stabs debugging output which is not understood by DBX or SDB@.
4164 On System V Release 4 systems this option requires the GNU assembler.
4166 @item -feliminate-unused-debug-symbols
4167 @opindex feliminate-unused-debug-symbols
4168 Produce debugging information in stabs format (if that is supported),
4169 for only symbols that are actually used.
4171 @item -femit-class-debug-always
4172 Instead of emitting debugging information for a C++ class in only one
4173 object file, emit it in all object files using the class. This option
4174 should be used only with debuggers that are unable to handle the way GCC
4175 normally emits debugging information for classes because using this
4176 option will increase the size of debugging information by as much as a
4181 Produce debugging information in stabs format (if that is supported),
4182 using GNU extensions understood only by the GNU debugger (GDB)@. The
4183 use of these extensions is likely to make other debuggers crash or
4184 refuse to read the program.
4188 Produce debugging information in COFF format (if that is supported).
4189 This is the format used by SDB on most System V systems prior to
4194 Produce debugging information in XCOFF format (if that is supported).
4195 This is the format used by the DBX debugger on IBM RS/6000 systems.
4199 Produce debugging information in XCOFF format (if that is supported),
4200 using GNU extensions understood only by the GNU debugger (GDB)@. The
4201 use of these extensions is likely to make other debuggers crash or
4202 refuse to read the program, and may cause assemblers other than the GNU
4203 assembler (GAS) to fail with an error.
4207 Produce debugging information in DWARF version 2 format (if that is
4208 supported). This is the format used by DBX on IRIX 6. With this
4209 option, GCC uses features of DWARF version 3 when they are useful;
4210 version 3 is upward compatible with version 2, but may still cause
4211 problems for older debuggers.
4215 Produce debugging information in VMS debug format (if that is
4216 supported). This is the format used by DEBUG on VMS systems.
4219 @itemx -ggdb@var{level}
4220 @itemx -gstabs@var{level}
4221 @itemx -gcoff@var{level}
4222 @itemx -gxcoff@var{level}
4223 @itemx -gvms@var{level}
4224 Request debugging information and also use @var{level} to specify how
4225 much information. The default level is 2.
4227 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4230 Level 1 produces minimal information, enough for making backtraces in
4231 parts of the program that you don't plan to debug. This includes
4232 descriptions of functions and external variables, but no information
4233 about local variables and no line numbers.
4235 Level 3 includes extra information, such as all the macro definitions
4236 present in the program. Some debuggers support macro expansion when
4237 you use @option{-g3}.
4239 @option{-gdwarf-2} does not accept a concatenated debug level, because
4240 GCC used to support an option @option{-gdwarf} that meant to generate
4241 debug information in version 1 of the DWARF format (which is very
4242 different from version 2), and it would have been too confusing. That
4243 debug format is long obsolete, but the option cannot be changed now.
4244 Instead use an additional @option{-g@var{level}} option to change the
4245 debug level for DWARF2.
4247 @item -feliminate-dwarf2-dups
4248 @opindex feliminate-dwarf2-dups
4249 Compress DWARF2 debugging information by eliminating duplicated
4250 information about each symbol. This option only makes sense when
4251 generating DWARF2 debugging information with @option{-gdwarf-2}.
4253 @item -femit-struct-debug-baseonly
4254 Emit debug information for struct-like types
4255 only when the base name of the compilation source file
4256 matches the base name of file in which the struct was defined.
4258 This option substantially reduces the size of debugging information,
4259 but at significant potential loss in type information to the debugger.
4260 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4261 See @option{-femit-struct-debug-detailed} for more detailed control.
4263 This option works only with DWARF 2.
4265 @item -femit-struct-debug-reduced
4266 Emit debug information for struct-like types
4267 only when the base name of the compilation source file
4268 matches the base name of file in which the type was defined,
4269 unless the struct is a template or defined in a system header.
4271 This option significantly reduces the size of debugging information,
4272 with some potential loss in type information to the debugger.
4273 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4274 See @option{-femit-struct-debug-detailed} for more detailed control.
4276 This option works only with DWARF 2.
4278 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4279 Specify the struct-like types
4280 for which the compiler will generate debug information.
4281 The intent is to reduce duplicate struct debug information
4282 between different object files within the same program.
4284 This option is a detailed version of
4285 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4286 which will serve for most needs.
4288 A specification has the syntax
4289 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4291 The optional first word limits the specification to
4292 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4293 A struct type is used directly when it is the type of a variable, member.
4294 Indirect uses arise through pointers to structs.
4295 That is, when use of an incomplete struct would be legal, the use is indirect.
4297 @samp{struct one direct; struct two * indirect;}.
4299 The optional second word limits the specification to
4300 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4301 Generic structs are a bit complicated to explain.
4302 For C++, these are non-explicit specializations of template classes,
4303 or non-template classes within the above.
4304 Other programming languages have generics,
4305 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4307 The third word specifies the source files for those
4308 structs for which the compiler will emit debug information.
4309 The values @samp{none} and @samp{any} have the normal meaning.
4310 The value @samp{base} means that
4311 the base of name of the file in which the type declaration appears
4312 must match the base of the name of the main compilation file.
4313 In practice, this means that
4314 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4315 but types declared in other header will not.
4316 The value @samp{sys} means those types satisfying @samp{base}
4317 or declared in system or compiler headers.
4319 You may need to experiment to determine the best settings for your application.
4321 The default is @samp{-femit-struct-debug-detailed=all}.
4323 This option works only with DWARF 2.
4325 @item -fno-merge-debug-strings
4326 @opindex fmerge-debug-strings
4327 @opindex fno-merge-debug-strings
4328 Direct the linker to merge together strings which are identical in
4329 different object files. This is not supported by all assemblers or
4330 linker. This decreases the size of the debug information in the
4331 output file at the cost of increasing link processing time. This is
4334 @item -fdebug-prefix-map=@var{old}=@var{new}
4335 @opindex fdebug-prefix-map
4336 When compiling files in directory @file{@var{old}}, record debugging
4337 information describing them as in @file{@var{new}} instead.
4339 @cindex @command{prof}
4342 Generate extra code to write profile information suitable for the
4343 analysis program @command{prof}. You must use this option when compiling
4344 the source files you want data about, and you must also use it when
4347 @cindex @command{gprof}
4350 Generate extra code to write profile information suitable for the
4351 analysis program @command{gprof}. You must use this option when compiling
4352 the source files you want data about, and you must also use it when
4357 Makes the compiler print out each function name as it is compiled, and
4358 print some statistics about each pass when it finishes.
4361 @opindex ftime-report
4362 Makes the compiler print some statistics about the time consumed by each
4363 pass when it finishes.
4366 @opindex fmem-report
4367 Makes the compiler print some statistics about permanent memory
4368 allocation when it finishes.
4370 @item -fpre-ipa-mem-report
4371 @opindex fpre-ipa-mem-report
4372 @item -fpost-ipa-mem-report
4373 @opindex fpost-ipa-mem-report
4374 Makes the compiler print some statistics about permanent memory
4375 allocation before or after interprocedural optimization.
4377 @item -fprofile-arcs
4378 @opindex fprofile-arcs
4379 Add code so that program flow @dfn{arcs} are instrumented. During
4380 execution the program records how many times each branch and call is
4381 executed and how many times it is taken or returns. When the compiled
4382 program exits it saves this data to a file called
4383 @file{@var{auxname}.gcda} for each source file. The data may be used for
4384 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4385 test coverage analysis (@option{-ftest-coverage}). Each object file's
4386 @var{auxname} is generated from the name of the output file, if
4387 explicitly specified and it is not the final executable, otherwise it is
4388 the basename of the source file. In both cases any suffix is removed
4389 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4390 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4391 @xref{Cross-profiling}.
4393 @cindex @command{gcov}
4397 This option is used to compile and link code instrumented for coverage
4398 analysis. The option is a synonym for @option{-fprofile-arcs}
4399 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4400 linking). See the documentation for those options for more details.
4405 Compile the source files with @option{-fprofile-arcs} plus optimization
4406 and code generation options. For test coverage analysis, use the
4407 additional @option{-ftest-coverage} option. You do not need to profile
4408 every source file in a program.
4411 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4412 (the latter implies the former).
4415 Run the program on a representative workload to generate the arc profile
4416 information. This may be repeated any number of times. You can run
4417 concurrent instances of your program, and provided that the file system
4418 supports locking, the data files will be correctly updated. Also
4419 @code{fork} calls are detected and correctly handled (double counting
4423 For profile-directed optimizations, compile the source files again with
4424 the same optimization and code generation options plus
4425 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4426 Control Optimization}).
4429 For test coverage analysis, use @command{gcov} to produce human readable
4430 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4431 @command{gcov} documentation for further information.
4435 With @option{-fprofile-arcs}, for each function of your program GCC
4436 creates a program flow graph, then finds a spanning tree for the graph.
4437 Only arcs that are not on the spanning tree have to be instrumented: the
4438 compiler adds code to count the number of times that these arcs are
4439 executed. When an arc is the only exit or only entrance to a block, the
4440 instrumentation code can be added to the block; otherwise, a new basic
4441 block must be created to hold the instrumentation code.
4444 @item -ftest-coverage
4445 @opindex ftest-coverage
4446 Produce a notes file that the @command{gcov} code-coverage utility
4447 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4448 show program coverage. Each source file's note file is called
4449 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4450 above for a description of @var{auxname} and instructions on how to
4451 generate test coverage data. Coverage data will match the source files
4452 more closely, if you do not optimize.
4454 @item -fdbg-cnt-list
4455 @opindex fdbg-cnt-list
4456 Print the name and the counter upperbound for all debug counters.
4458 @item -fdbg-cnt=@var{counter-value-list}
4460 Set the internal debug counter upperbound. @var{counter-value-list}
4461 is a comma-separated list of @var{name}:@var{value} pairs
4462 which sets the upperbound of each debug counter @var{name} to @var{value}.
4463 All debug counters have the initial upperbound of @var{UINT_MAX},
4464 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4465 e.g. With -fdbg-cnt=dce:10,tail_call:0
4466 dbg_cnt(dce) will return true only for first 10 invocations
4467 and dbg_cnt(tail_call) will return false always.
4469 @item -d@var{letters}
4470 @itemx -fdump-rtl-@var{pass}
4472 Says to make debugging dumps during compilation at times specified by
4473 @var{letters}. This is used for debugging the RTL-based passes of the
4474 compiler. The file names for most of the dumps are made by appending a
4475 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
4476 from the name of the output file, if explicitly specified and it is not
4477 an executable, otherwise it is the basename of the source file. These
4478 switches may have different effects when @option{-E} is used for
4481 Most debug dumps can be enabled either passing a letter to the @option{-d}
4482 option, or with a long @option{-fdump-rtl} switch; here are the possible
4483 letters for use in @var{letters} and @var{pass}, and their meanings:
4488 Annotate the assembler output with miscellaneous debugging information.
4490 @item -fdump-rtl-bbro
4491 @opindex fdump-rtl-bbro
4492 Dump after block reordering, to @file{@var{file}.148r.bbro}.
4494 @item -fdump-rtl-combine
4495 @opindex fdump-rtl-combine
4496 Dump after the RTL instruction combination pass, to the file
4497 @file{@var{file}.129r.combine}.
4499 @item -fdump-rtl-ce1
4500 @itemx -fdump-rtl-ce2
4501 @opindex fdump-rtl-ce1
4502 @opindex fdump-rtl-ce2
4503 @option{-fdump-rtl-ce1} enable dumping after the
4504 first if conversion, to the file @file{@var{file}.117r.ce1}.
4505 @option{-fdump-rtl-ce2} enable dumping after the second if
4506 conversion, to the file @file{@var{file}.130r.ce2}.
4508 @item -fdump-rtl-btl
4509 @itemx -fdump-rtl-dbr
4510 @opindex fdump-rtl-btl
4511 @opindex fdump-rtl-dbr
4512 @option{-fdump-rtl-btl} enable dumping after branch
4513 target load optimization, to @file{@var{file}.31.btl}.
4514 @option{-fdump-rtl-dbr} enable dumping after delayed branch
4515 scheduling, to @file{@var{file}.36.dbr}.
4519 Dump all macro definitions, at the end of preprocessing, in addition to
4522 @item -fdump-rtl-ce3
4523 @opindex fdump-rtl-ce3
4524 Dump after the third if conversion, to @file{@var{file}.146r.ce3}.
4526 @item -fdump-rtl-cfg
4527 @itemx -fdump-rtl-life
4528 @opindex fdump-rtl-cfg
4529 @opindex fdump-rtl-life
4530 @option{-fdump-rtl-cfg} enable dumping after control
4531 and data flow analysis, to @file{@var{file}.116r.cfg}.
4532 @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
4533 to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}.
4535 @item -fdump-rtl-greg
4536 @opindex fdump-rtl-greg
4537 Dump after global register allocation, to @file{@var{file}.139r.greg}.
4539 @item -fdump-rtl-gcse
4540 @itemx -fdump-rtl-bypass
4541 @opindex fdump-rtl-gcse
4542 @opindex fdump-rtl-bypass
4543 @option{-fdump-rtl-gcse} enable dumping after GCSE, to
4544 @file{@var{file}.114r.gcse}. @option{-fdump-rtl-bypass}
4545 enable dumping after jump bypassing and control flow optimizations, to
4546 @file{@var{file}.115r.bypass}.
4549 @opindex fdump-rtl-eh
4550 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
4552 @item -fdump-rtl-sibling
4553 @opindex fdump-rtl-sibling
4554 Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}.
4556 @item -fdump-rtl-jump
4557 @opindex fdump-rtl-jump
4558 Dump after the first jump optimization, to @file{@var{file}.112r.jump}.
4560 @item -fdump-rtl-stack
4561 @opindex fdump-rtl-stack
4562 Dump after conversion from GCC's "flat register file" registers to the
4563 x87's stack-like registers, to @file{@var{file}.152r.stack}.
4565 @item -fdump-rtl-lreg
4566 @opindex fdump-rtl-lreg
4567 Dump after local register allocation, to @file{@var{file}.138r.lreg}.
4569 @item -fdump-rtl-loop2
4570 @opindex fdump-rtl-loop2
4571 @option{-dL} and @option{-fdump-rtl-loop2} enable dumping after the
4572 loop optimization pass, to @file{@var{file}.119r.loop2},
4573 @file{@var{file}.120r.loop2_init},
4574 @file{@var{file}.121r.loop2_invariant}, and
4575 @file{@var{file}.125r.loop2_done}.
4577 @item -fdump-rtl-sms
4578 @opindex fdump-rtl-sms
4579 Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
4581 @item -fdump-rtl-mach
4582 @opindex fdump-rtl-mach
4583 Dump after performing the machine dependent reorganization pass, to
4584 @file{@var{file}.155r.mach} if that pass exists.
4586 @item -fdump-rtl-rnreg
4587 @opindex fdump-rtl-rnreg
4588 Dump after register renumbering, to @file{@var{file}.147r.rnreg}.
4590 @item -fdump-rtl-regmove
4591 @opindex fdump-rtl-regmove
4592 Dump after the register move pass, to @file{@var{file}.132r.regmove}.
4594 @item -fdump-rtl-postreload
4595 @opindex fdump-rtl-postreload
4596 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
4598 @item -fdump-rtl-expand
4599 @opindex fdump-rtl-expand
4600 Dump after RTL generation, to @file{@var{file}.104r.expand}.
4602 @item -fdump-rtl-sched2
4603 @opindex fdump-rtl-sched2
4604 Dump after the second scheduling pass, to @file{@var{file}.149r.sched2}.
4606 @item -fdump-rtl-cse
4607 @opindex fdump-rtl-cse
4608 Dump after CSE (including the jump optimization that sometimes follows
4609 CSE), to @file{@var{file}.113r.cse}.
4611 @item -fdump-rtl-sched1
4612 @opindex fdump-rtl-sched1
4613 Dump after the first scheduling pass, to @file{@var{file}.136r.sched1}.
4615 @item -fdump-rtl-cse2
4616 @opindex fdump-rtl-cse2
4617 Dump after the second CSE pass (including the jump optimization that
4618 sometimes follows CSE), to @file{@var{file}.127r.cse2}.
4620 @item -fdump-rtl-tracer
4621 @opindex fdump-rtl-tracer
4622 Dump after running tracer, to @file{@var{file}.118r.tracer}.
4624 @item -fdump-rtl-vpt
4625 @itemx -fdump-rtl-vartrack
4626 @opindex fdump-rtl-vpt
4627 @opindex fdump-rtl-vartrack
4628 @option{-fdump-rtl-vpt} enable dumping after the value
4629 profile transformations, to @file{@var{file}.10.vpt}.
4630 @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
4631 to @file{@var{file}.154r.vartrack}.
4633 @item -fdump-rtl-flow2
4634 @opindex fdump-rtl-flow2
4635 Dump after the second flow pass, to @file{@var{file}.142r.flow2}.
4637 @item -fdump-rtl-peephole2
4638 @opindex fdump-rtl-peephole2
4639 Dump after the peephole pass, to @file{@var{file}.145r.peephole2}.
4641 @item -fdump-rtl-web
4642 @opindex fdump-rtl-web
4643 Dump after live range splitting, to @file{@var{file}.126r.web}.
4645 @item -fdump-rtl-all
4646 @opindex fdump-rtl-all
4647 Produce all the dumps listed above.
4651 Produce a core dump whenever an error occurs.
4655 Print statistics on memory usage, at the end of the run, to
4660 Annotate the assembler output with a comment indicating which
4661 pattern and alternative was used. The length of each instruction is
4666 Dump the RTL in the assembler output as a comment before each instruction.
4667 Also turns on @option{-dp} annotation.
4671 For each of the other indicated dump files (either with @option{-d} or
4672 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
4673 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
4677 Just generate RTL for a function instead of compiling it. Usually used
4678 with @samp{r} (@option{-fdump-rtl-expand}).
4682 Dump debugging information during parsing, to standard error.
4686 @opindex fdump-noaddr
4687 When doing debugging dumps (see @option{-d} option above), suppress
4688 address output. This makes it more feasible to use diff on debugging
4689 dumps for compiler invocations with different compiler binaries and/or
4690 different text / bss / data / heap / stack / dso start locations.
4692 @item -fdump-unnumbered
4693 @opindex fdump-unnumbered
4694 When doing debugging dumps (see @option{-d} option above), suppress instruction
4695 numbers and address output. This makes it more feasible to
4696 use diff on debugging dumps for compiler invocations with different
4697 options, in particular with and without @option{-g}.
4699 @item -fdump-translation-unit @r{(C++ only)}
4700 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
4701 @opindex fdump-translation-unit
4702 Dump a representation of the tree structure for the entire translation
4703 unit to a file. The file name is made by appending @file{.tu} to the
4704 source file name. If the @samp{-@var{options}} form is used, @var{options}
4705 controls the details of the dump as described for the
4706 @option{-fdump-tree} options.
4708 @item -fdump-class-hierarchy @r{(C++ only)}
4709 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
4710 @opindex fdump-class-hierarchy
4711 Dump a representation of each class's hierarchy and virtual function
4712 table layout to a file. The file name is made by appending @file{.class}
4713 to the source file name. If the @samp{-@var{options}} form is used,
4714 @var{options} controls the details of the dump as described for the
4715 @option{-fdump-tree} options.
4717 @item -fdump-ipa-@var{switch}
4719 Control the dumping at various stages of inter-procedural analysis
4720 language tree to a file. The file name is generated by appending a switch
4721 specific suffix to the source file name. The following dumps are possible:
4725 Enables all inter-procedural analysis dumps.
4728 Dumps information about call-graph optimization, unused function removal,
4729 and inlining decisions.
4732 Dump after function inlining.
4736 @item -fdump-statistics-@var{option}
4737 @opindex -fdump-statistics
4738 Enable and control dumping of pass statistics in a separate file. The
4739 file name is generated by appending a suffix ending in @samp{.statistics}
4740 to the source file name. If the @samp{-@var{option}} form is used,
4741 @samp{-stats} will cause counters to be summed over the whole compilation unit
4742 while @samp{-details} will dump every event as the passes generate them.
4743 The default with no option is to sum counters for each function compiled.
4745 @item -fdump-tree-@var{switch}
4746 @itemx -fdump-tree-@var{switch}-@var{options}
4748 Control the dumping at various stages of processing the intermediate
4749 language tree to a file. The file name is generated by appending a switch
4750 specific suffix to the source file name. If the @samp{-@var{options}}
4751 form is used, @var{options} is a list of @samp{-} separated options that
4752 control the details of the dump. Not all options are applicable to all
4753 dumps, those which are not meaningful will be ignored. The following
4754 options are available
4758 Print the address of each node. Usually this is not meaningful as it
4759 changes according to the environment and source file. Its primary use
4760 is for tying up a dump file with a debug environment.
4762 Inhibit dumping of members of a scope or body of a function merely
4763 because that scope has been reached. Only dump such items when they
4764 are directly reachable by some other path. When dumping pretty-printed
4765 trees, this option inhibits dumping the bodies of control structures.
4767 Print a raw representation of the tree. By default, trees are
4768 pretty-printed into a C-like representation.
4770 Enable more detailed dumps (not honored by every dump option).
4772 Enable dumping various statistics about the pass (not honored by every dump
4775 Enable showing basic block boundaries (disabled in raw dumps).
4777 Enable showing virtual operands for every statement.
4779 Enable showing line numbers for statements.
4781 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4783 Enable showing the tree dump for each statement.
4785 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
4786 and @option{lineno}.
4789 The following tree dumps are possible:
4793 Dump before any tree based optimization, to @file{@var{file}.original}.
4796 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4799 @opindex fdump-tree-gimple
4800 Dump each function before and after the gimplification pass to a file. The
4801 file name is made by appending @file{.gimple} to the source file name.
4804 @opindex fdump-tree-cfg
4805 Dump the control flow graph of each function to a file. The file name is
4806 made by appending @file{.cfg} to the source file name.
4809 @opindex fdump-tree-vcg
4810 Dump the control flow graph of each function to a file in VCG format. The
4811 file name is made by appending @file{.vcg} to the source file name. Note
4812 that if the file contains more than one function, the generated file cannot
4813 be used directly by VCG@. You will need to cut and paste each function's
4814 graph into its own separate file first.
4817 @opindex fdump-tree-ch
4818 Dump each function after copying loop headers. The file name is made by
4819 appending @file{.ch} to the source file name.
4822 @opindex fdump-tree-ssa
4823 Dump SSA related information to a file. The file name is made by appending
4824 @file{.ssa} to the source file name.
4827 @opindex fdump-tree-alias
4828 Dump aliasing information for each function. The file name is made by
4829 appending @file{.alias} to the source file name.
4832 @opindex fdump-tree-ccp
4833 Dump each function after CCP@. The file name is made by appending
4834 @file{.ccp} to the source file name.
4837 @opindex fdump-tree-storeccp
4838 Dump each function after STORE-CCP@. The file name is made by appending
4839 @file{.storeccp} to the source file name.
4842 @opindex fdump-tree-pre
4843 Dump trees after partial redundancy elimination. The file name is made
4844 by appending @file{.pre} to the source file name.
4847 @opindex fdump-tree-fre
4848 Dump trees after full redundancy elimination. The file name is made
4849 by appending @file{.fre} to the source file name.
4852 @opindex fdump-tree-copyprop
4853 Dump trees after copy propagation. The file name is made
4854 by appending @file{.copyprop} to the source file name.
4856 @item store_copyprop
4857 @opindex fdump-tree-store_copyprop
4858 Dump trees after store copy-propagation. The file name is made
4859 by appending @file{.store_copyprop} to the source file name.
4862 @opindex fdump-tree-dce
4863 Dump each function after dead code elimination. The file name is made by
4864 appending @file{.dce} to the source file name.
4867 @opindex fdump-tree-mudflap
4868 Dump each function after adding mudflap instrumentation. The file name is
4869 made by appending @file{.mudflap} to the source file name.
4872 @opindex fdump-tree-sra
4873 Dump each function after performing scalar replacement of aggregates. The
4874 file name is made by appending @file{.sra} to the source file name.
4877 @opindex fdump-tree-sink
4878 Dump each function after performing code sinking. The file name is made
4879 by appending @file{.sink} to the source file name.
4882 @opindex fdump-tree-dom
4883 Dump each function after applying dominator tree optimizations. The file
4884 name is made by appending @file{.dom} to the source file name.
4887 @opindex fdump-tree-dse
4888 Dump each function after applying dead store elimination. The file
4889 name is made by appending @file{.dse} to the source file name.
4892 @opindex fdump-tree-phiopt
4893 Dump each function after optimizing PHI nodes into straightline code. The file
4894 name is made by appending @file{.phiopt} to the source file name.
4897 @opindex fdump-tree-forwprop
4898 Dump each function after forward propagating single use variables. The file
4899 name is made by appending @file{.forwprop} to the source file name.
4902 @opindex fdump-tree-copyrename
4903 Dump each function after applying the copy rename optimization. The file
4904 name is made by appending @file{.copyrename} to the source file name.
4907 @opindex fdump-tree-nrv
4908 Dump each function after applying the named return value optimization on
4909 generic trees. The file name is made by appending @file{.nrv} to the source
4913 @opindex fdump-tree-vect
4914 Dump each function after applying vectorization of loops. The file name is
4915 made by appending @file{.vect} to the source file name.
4918 @opindex fdump-tree-vrp
4919 Dump each function after Value Range Propagation (VRP). The file name
4920 is made by appending @file{.vrp} to the source file name.
4923 @opindex fdump-tree-all
4924 Enable all the available tree dumps with the flags provided in this option.
4927 @item -ftree-vectorizer-verbose=@var{n}
4928 @opindex ftree-vectorizer-verbose
4929 This option controls the amount of debugging output the vectorizer prints.
4930 This information is written to standard error, unless
4931 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
4932 in which case it is output to the usual dump listing file, @file{.vect}.
4933 For @var{n}=0 no diagnostic information is reported.
4934 If @var{n}=1 the vectorizer reports each loop that got vectorized,
4935 and the total number of loops that got vectorized.
4936 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
4937 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
4938 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
4939 level that @option{-fdump-tree-vect-stats} uses.
4940 Higher verbosity levels mean either more information dumped for each
4941 reported loop, or same amount of information reported for more loops:
4942 If @var{n}=3, alignment related information is added to the reports.
4943 If @var{n}=4, data-references related information (e.g.@: memory dependences,
4944 memory access-patterns) is added to the reports.
4945 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
4946 that did not pass the first analysis phase (i.e., may not be countable, or
4947 may have complicated control-flow).
4948 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
4949 For @var{n}=7, all the information the vectorizer generates during its
4950 analysis and transformation is reported. This is the same verbosity level
4951 that @option{-fdump-tree-vect-details} uses.
4953 @item -frandom-seed=@var{string}
4954 @opindex frandom-string
4955 This option provides a seed that GCC uses when it would otherwise use
4956 random numbers. It is used to generate certain symbol names
4957 that have to be different in every compiled file. It is also used to
4958 place unique stamps in coverage data files and the object files that
4959 produce them. You can use the @option{-frandom-seed} option to produce
4960 reproducibly identical object files.
4962 The @var{string} should be different for every file you compile.
4964 @item -fsched-verbose=@var{n}
4965 @opindex fsched-verbose
4966 On targets that use instruction scheduling, this option controls the
4967 amount of debugging output the scheduler prints. This information is
4968 written to standard error, unless @option{-dS} or @option{-dR} is
4969 specified, in which case it is output to the usual dump
4970 listing file, @file{.sched} or @file{.sched2} respectively. However
4971 for @var{n} greater than nine, the output is always printed to standard
4974 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4975 same information as @option{-dRS}. For @var{n} greater than one, it
4976 also output basic block probabilities, detailed ready list information
4977 and unit/insn info. For @var{n} greater than two, it includes RTL
4978 at abort point, control-flow and regions info. And for @var{n} over
4979 four, @option{-fsched-verbose} also includes dependence info.
4983 Store the usual ``temporary'' intermediate files permanently; place them
4984 in the current directory and name them based on the source file. Thus,
4985 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4986 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4987 preprocessed @file{foo.i} output file even though the compiler now
4988 normally uses an integrated preprocessor.
4990 When used in combination with the @option{-x} command line option,
4991 @option{-save-temps} is sensible enough to avoid over writing an
4992 input source file with the same extension as an intermediate file.
4993 The corresponding intermediate file may be obtained by renaming the
4994 source file before using @option{-save-temps}.
4998 Report the CPU time taken by each subprocess in the compilation
4999 sequence. For C source files, this is the compiler proper and assembler
5000 (plus the linker if linking is done). The output looks like this:
5007 The first number on each line is the ``user time'', that is time spent
5008 executing the program itself. The second number is ``system time'',
5009 time spent executing operating system routines on behalf of the program.
5010 Both numbers are in seconds.
5012 @item -fvar-tracking
5013 @opindex fvar-tracking
5014 Run variable tracking pass. It computes where variables are stored at each
5015 position in code. Better debugging information is then generated
5016 (if the debugging information format supports this information).
5018 It is enabled by default when compiling with optimization (@option{-Os},
5019 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5020 the debug info format supports it.
5022 @item -print-file-name=@var{library}
5023 @opindex print-file-name
5024 Print the full absolute name of the library file @var{library} that
5025 would be used when linking---and don't do anything else. With this
5026 option, GCC does not compile or link anything; it just prints the
5029 @item -print-multi-directory
5030 @opindex print-multi-directory
5031 Print the directory name corresponding to the multilib selected by any
5032 other switches present in the command line. This directory is supposed
5033 to exist in @env{GCC_EXEC_PREFIX}.
5035 @item -print-multi-lib
5036 @opindex print-multi-lib
5037 Print the mapping from multilib directory names to compiler switches
5038 that enable them. The directory name is separated from the switches by
5039 @samp{;}, and each switch starts with an @samp{@@} instead of the
5040 @samp{-}, without spaces between multiple switches. This is supposed to
5041 ease shell-processing.
5043 @item -print-prog-name=@var{program}
5044 @opindex print-prog-name
5045 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5047 @item -print-libgcc-file-name
5048 @opindex print-libgcc-file-name
5049 Same as @option{-print-file-name=libgcc.a}.
5051 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5052 but you do want to link with @file{libgcc.a}. You can do
5055 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5058 @item -print-search-dirs
5059 @opindex print-search-dirs
5060 Print the name of the configured installation directory and a list of
5061 program and library directories @command{gcc} will search---and don't do anything else.
5063 This is useful when @command{gcc} prints the error message
5064 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5065 To resolve this you either need to put @file{cpp0} and the other compiler
5066 components where @command{gcc} expects to find them, or you can set the environment
5067 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5068 Don't forget the trailing @samp{/}.
5069 @xref{Environment Variables}.
5071 @item -print-sysroot
5072 @opindex print-sysroot
5073 Print the target sysroot directory that will be used during
5074 compilation. This is the target sysroot specified either at configure
5075 time or or using the @option{--sysroot} option, possibly with an extra
5076 suffix that depends on compilation options. If no target sysroot is
5077 specified, the option prints nothing.
5079 @item -print-sysroot-headers-suffix
5080 @opindex print-sysroot-headers-suffix
5081 Print the suffix added to the target sysroot when searching for
5082 headers, or give an error if the compiler is not configured with such
5083 a suffix---and don't do anything else.
5086 @opindex dumpmachine
5087 Print the compiler's target machine (for example,
5088 @samp{i686-pc-linux-gnu})---and don't do anything else.
5091 @opindex dumpversion
5092 Print the compiler version (for example, @samp{3.0})---and don't do
5097 Print the compiler's built-in specs---and don't do anything else. (This
5098 is used when GCC itself is being built.) @xref{Spec Files}.
5100 @item -feliminate-unused-debug-types
5101 @opindex feliminate-unused-debug-types
5102 Normally, when producing DWARF2 output, GCC will emit debugging
5103 information for all types declared in a compilation
5104 unit, regardless of whether or not they are actually used
5105 in that compilation unit. Sometimes this is useful, such as
5106 if, in the debugger, you want to cast a value to a type that is
5107 not actually used in your program (but is declared). More often,
5108 however, this results in a significant amount of wasted space.
5109 With this option, GCC will avoid producing debug symbol output
5110 for types that are nowhere used in the source file being compiled.
5113 @node Optimize Options
5114 @section Options That Control Optimization
5115 @cindex optimize options
5116 @cindex options, optimization
5118 These options control various sorts of optimizations.
5120 Without any optimization option, the compiler's goal is to reduce the
5121 cost of compilation and to make debugging produce the expected
5122 results. Statements are independent: if you stop the program with a
5123 breakpoint between statements, you can then assign a new value to any
5124 variable or change the program counter to any other statement in the
5125 function and get exactly the results you would expect from the source
5128 Turning on optimization flags makes the compiler attempt to improve
5129 the performance and/or code size at the expense of compilation time
5130 and possibly the ability to debug the program.
5132 The compiler performs optimization based on the knowledge it has of the
5133 program. Compiling multiple files at once to a single output file mode allows
5134 the compiler to use information gained from all of the files when compiling
5137 Not all optimizations are controlled directly by a flag. Only
5138 optimizations that have a flag are listed.
5145 Optimize. Optimizing compilation takes somewhat more time, and a lot
5146 more memory for a large function.
5148 With @option{-O}, the compiler tries to reduce code size and execution
5149 time, without performing any optimizations that take a great deal of
5152 @option{-O} turns on the following optimization flags:
5155 -fcprop-registers @gol
5158 -fdelayed-branch @gol
5160 -fguess-branch-probability @gol
5161 -fif-conversion2 @gol
5162 -fif-conversion @gol
5163 -finline-small-functions @gol
5164 -fipa-pure-const @gol
5165 -fipa-reference @gol
5167 -fsplit-wide-types @gol
5168 -ftree-builtin-call-dce @gol
5171 -ftree-copyrename @gol
5173 -ftree-dominator-opts @gol
5180 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5181 where doing so does not interfere with debugging.
5185 Optimize even more. GCC performs nearly all supported optimizations
5186 that do not involve a space-speed tradeoff. The compiler does not
5187 perform loop unrolling or function inlining when you specify @option{-O2}.
5188 As compared to @option{-O}, this option increases both compilation time
5189 and the performance of the generated code.
5191 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5192 also turns on the following optimization flags:
5193 @gccoptlist{-fthread-jumps @gol
5194 -falign-functions -falign-jumps @gol
5195 -falign-loops -falign-labels @gol
5198 -fcse-follow-jumps -fcse-skip-blocks @gol
5199 -fdelete-null-pointer-checks @gol
5200 -fexpensive-optimizations @gol
5201 -fgcse -fgcse-lm @gol
5202 -foptimize-sibling-calls @gol
5205 -freorder-blocks -freorder-functions @gol
5206 -frerun-cse-after-loop @gol
5207 -fsched-interblock -fsched-spec @gol
5208 -fschedule-insns -fschedule-insns2 @gol
5209 -fstrict-aliasing -fstrict-overflow @gol
5210 -ftree-switch-conversion @gol
5214 Please note the warning under @option{-fgcse} about
5215 invoking @option{-O2} on programs that use computed gotos.
5219 Optimize yet more. @option{-O3} turns on all optimizations specified by
5220 @option{-O2} and also turns on the @option{-finline-functions},
5221 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5222 @option{-fgcse-after-reload} and @option{-ftree-vectorize} options.
5226 Reduce compilation time and make debugging produce the expected
5227 results. This is the default.
5231 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5232 do not typically increase code size. It also performs further
5233 optimizations designed to reduce code size.
5235 @option{-Os} disables the following optimization flags:
5236 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5237 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5238 -fprefetch-loop-arrays -ftree-vect-loop-version}
5240 If you use multiple @option{-O} options, with or without level numbers,
5241 the last such option is the one that is effective.
5244 Options of the form @option{-f@var{flag}} specify machine-independent
5245 flags. Most flags have both positive and negative forms; the negative
5246 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5247 below, only one of the forms is listed---the one you typically will
5248 use. You can figure out the other form by either removing @samp{no-}
5251 The following options control specific optimizations. They are either
5252 activated by @option{-O} options or are related to ones that are. You
5253 can use the following flags in the rare cases when ``fine-tuning'' of
5254 optimizations to be performed is desired.
5257 @item -fno-default-inline
5258 @opindex fno-default-inline
5259 Do not make member functions inline by default merely because they are
5260 defined inside the class scope (C++ only). Otherwise, when you specify
5261 @w{@option{-O}}, member functions defined inside class scope are compiled
5262 inline by default; i.e., you don't need to add @samp{inline} in front of
5263 the member function name.
5265 @item -fno-defer-pop
5266 @opindex fno-defer-pop
5267 Always pop the arguments to each function call as soon as that function
5268 returns. For machines which must pop arguments after a function call,
5269 the compiler normally lets arguments accumulate on the stack for several
5270 function calls and pops them all at once.
5272 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5274 @item -fforward-propagate
5275 @opindex fforward-propagate
5276 Perform a forward propagation pass on RTL@. The pass tries to combine two
5277 instructions and checks if the result can be simplified. If loop unrolling
5278 is active, two passes are performed and the second is scheduled after
5281 This option is enabled by default at optimization levels @option{-O2},
5282 @option{-O3}, @option{-Os}.
5284 @item -fomit-frame-pointer
5285 @opindex fomit-frame-pointer
5286 Don't keep the frame pointer in a register for functions that
5287 don't need one. This avoids the instructions to save, set up and
5288 restore frame pointers; it also makes an extra register available
5289 in many functions. @strong{It also makes debugging impossible on
5292 On some machines, such as the VAX, this flag has no effect, because
5293 the standard calling sequence automatically handles the frame pointer
5294 and nothing is saved by pretending it doesn't exist. The
5295 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5296 whether a target machine supports this flag. @xref{Registers,,Register
5297 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5299 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5301 @item -foptimize-sibling-calls
5302 @opindex foptimize-sibling-calls
5303 Optimize sibling and tail recursive calls.
5305 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5309 Don't pay attention to the @code{inline} keyword. Normally this option
5310 is used to keep the compiler from expanding any functions inline.
5311 Note that if you are not optimizing, no functions can be expanded inline.
5313 @item -finline-small-functions
5314 @opindex finline-small-functions
5315 Integrate functions into their callers when their body is smaller than expected
5316 function call code (so overall size of program gets smaller). The compiler
5317 heuristically decides which functions are simple enough to be worth integrating
5320 Enabled at level @option{-O2}.
5322 @item -finline-functions
5323 @opindex finline-functions
5324 Integrate all simple functions into their callers. The compiler
5325 heuristically decides which functions are simple enough to be worth
5326 integrating in this way.
5328 If all calls to a given function are integrated, and the function is
5329 declared @code{static}, then the function is normally not output as
5330 assembler code in its own right.
5332 Enabled at level @option{-O3}.
5334 @item -finline-functions-called-once
5335 @opindex finline-functions-called-once
5336 Consider all @code{static} functions called once for inlining into their
5337 caller even if they are not marked @code{inline}. If a call to a given
5338 function is integrated, then the function is not output as assembler code
5341 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
5343 @item -fearly-inlining
5344 @opindex fearly-inlining
5345 Inline functions marked by @code{always_inline} and functions whose body seems
5346 smaller than the function call overhead early before doing
5347 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5348 makes profiling significantly cheaper and usually inlining faster on programs
5349 having large chains of nested wrapper functions.
5353 @item -finline-limit=@var{n}
5354 @opindex finline-limit
5355 By default, GCC limits the size of functions that can be inlined. This flag
5356 allows coarse control of this limit. @var{n} is the size of functions that
5357 can be inlined in number of pseudo instructions.
5359 Inlining is actually controlled by a number of parameters, which may be
5360 specified individually by using @option{--param @var{name}=@var{value}}.
5361 The @option{-finline-limit=@var{n}} option sets some of these parameters
5365 @item max-inline-insns-single
5366 is set to @var{n}/2.
5367 @item max-inline-insns-auto
5368 is set to @var{n}/2.
5371 See below for a documentation of the individual
5372 parameters controlling inlining and for the defaults of these parameters.
5374 @emph{Note:} there may be no value to @option{-finline-limit} that results
5375 in default behavior.
5377 @emph{Note:} pseudo instruction represents, in this particular context, an
5378 abstract measurement of function's size. In no way does it represent a count
5379 of assembly instructions and as such its exact meaning might change from one
5380 release to an another.
5382 @item -fkeep-inline-functions
5383 @opindex fkeep-inline-functions
5384 In C, emit @code{static} functions that are declared @code{inline}
5385 into the object file, even if the function has been inlined into all
5386 of its callers. This switch does not affect functions using the
5387 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5388 inline functions into the object file.
5390 @item -fkeep-static-consts
5391 @opindex fkeep-static-consts
5392 Emit variables declared @code{static const} when optimization isn't turned
5393 on, even if the variables aren't referenced.
5395 GCC enables this option by default. If you want to force the compiler to
5396 check if the variable was referenced, regardless of whether or not
5397 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5399 @item -fmerge-constants
5400 @opindex fmerge-constants
5401 Attempt to merge identical constants (string constants and floating point
5402 constants) across compilation units.
5404 This option is the default for optimized compilation if the assembler and
5405 linker support it. Use @option{-fno-merge-constants} to inhibit this
5408 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5410 @item -fmerge-all-constants
5411 @opindex fmerge-all-constants
5412 Attempt to merge identical constants and identical variables.
5414 This option implies @option{-fmerge-constants}. In addition to
5415 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5416 arrays or initialized constant variables with integral or floating point
5417 types. Languages like C or C++ require each non-automatic variable to
5418 have distinct location, so using this option will result in non-conforming
5421 @item -fmodulo-sched
5422 @opindex fmodulo-sched
5423 Perform swing modulo scheduling immediately before the first scheduling
5424 pass. This pass looks at innermost loops and reorders their
5425 instructions by overlapping different iterations.
5427 @item -fmodulo-sched-allow-regmoves
5428 @opindex fmodulo-sched-allow-regmoves
5429 Perform more aggressive SMS based modulo scheduling with register moves
5430 allowed. By setting this flag certain anti-dependences edges will be
5431 deleted which will trigger the generation of reg-moves based on the
5432 life-range analysis. This option is effective only with
5433 @option{-fmodulo-sched} enabled.
5435 @item -fno-branch-count-reg
5436 @opindex fno-branch-count-reg
5437 Do not use ``decrement and branch'' instructions on a count register,
5438 but instead generate a sequence of instructions that decrement a
5439 register, compare it against zero, then branch based upon the result.
5440 This option is only meaningful on architectures that support such
5441 instructions, which include x86, PowerPC, IA-64 and S/390.
5443 The default is @option{-fbranch-count-reg}.
5445 @item -fno-function-cse
5446 @opindex fno-function-cse
5447 Do not put function addresses in registers; make each instruction that
5448 calls a constant function contain the function's address explicitly.
5450 This option results in less efficient code, but some strange hacks
5451 that alter the assembler output may be confused by the optimizations
5452 performed when this option is not used.
5454 The default is @option{-ffunction-cse}
5456 @item -fno-zero-initialized-in-bss
5457 @opindex fno-zero-initialized-in-bss
5458 If the target supports a BSS section, GCC by default puts variables that
5459 are initialized to zero into BSS@. This can save space in the resulting
5462 This option turns off this behavior because some programs explicitly
5463 rely on variables going to the data section. E.g., so that the
5464 resulting executable can find the beginning of that section and/or make
5465 assumptions based on that.
5467 The default is @option{-fzero-initialized-in-bss}.
5469 @item -fmudflap -fmudflapth -fmudflapir
5473 @cindex bounds checking
5475 For front-ends that support it (C and C++), instrument all risky
5476 pointer/array dereferencing operations, some standard library
5477 string/heap functions, and some other associated constructs with
5478 range/validity tests. Modules so instrumented should be immune to
5479 buffer overflows, invalid heap use, and some other classes of C/C++
5480 programming errors. The instrumentation relies on a separate runtime
5481 library (@file{libmudflap}), which will be linked into a program if
5482 @option{-fmudflap} is given at link time. Run-time behavior of the
5483 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
5484 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
5487 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
5488 link if your program is multi-threaded. Use @option{-fmudflapir}, in
5489 addition to @option{-fmudflap} or @option{-fmudflapth}, if
5490 instrumentation should ignore pointer reads. This produces less
5491 instrumentation (and therefore faster execution) and still provides
5492 some protection against outright memory corrupting writes, but allows
5493 erroneously read data to propagate within a program.
5495 @item -fthread-jumps
5496 @opindex fthread-jumps
5497 Perform optimizations where we check to see if a jump branches to a
5498 location where another comparison subsumed by the first is found. If
5499 so, the first branch is redirected to either the destination of the
5500 second branch or a point immediately following it, depending on whether
5501 the condition is known to be true or false.
5503 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5505 @item -fsplit-wide-types
5506 @opindex fsplit-wide-types
5507 When using a type that occupies multiple registers, such as @code{long
5508 long} on a 32-bit system, split the registers apart and allocate them
5509 independently. This normally generates better code for those types,
5510 but may make debugging more difficult.
5512 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
5515 @item -fcse-follow-jumps
5516 @opindex fcse-follow-jumps
5517 In common subexpression elimination (CSE), scan through jump instructions
5518 when the target of the jump is not reached by any other path. For
5519 example, when CSE encounters an @code{if} statement with an
5520 @code{else} clause, CSE will follow the jump when the condition
5523 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5525 @item -fcse-skip-blocks
5526 @opindex fcse-skip-blocks
5527 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
5528 follow jumps which conditionally skip over blocks. When CSE
5529 encounters a simple @code{if} statement with no else clause,
5530 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
5531 body of the @code{if}.
5533 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5535 @item -frerun-cse-after-loop
5536 @opindex frerun-cse-after-loop
5537 Re-run common subexpression elimination after loop optimizations has been
5540 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5544 Perform a global common subexpression elimination pass.
5545 This pass also performs global constant and copy propagation.
5547 @emph{Note:} When compiling a program using computed gotos, a GCC
5548 extension, you may get better runtime performance if you disable
5549 the global common subexpression elimination pass by adding
5550 @option{-fno-gcse} to the command line.
5552 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5556 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
5557 attempt to move loads which are only killed by stores into themselves. This
5558 allows a loop containing a load/store sequence to be changed to a load outside
5559 the loop, and a copy/store within the loop.
5561 Enabled by default when gcse is enabled.
5565 When @option{-fgcse-sm} is enabled, a store motion pass is run after
5566 global common subexpression elimination. This pass will attempt to move
5567 stores out of loops. When used in conjunction with @option{-fgcse-lm},
5568 loops containing a load/store sequence can be changed to a load before
5569 the loop and a store after the loop.
5571 Not enabled at any optimization level.
5575 When @option{-fgcse-las} is enabled, the global common subexpression
5576 elimination pass eliminates redundant loads that come after stores to the
5577 same memory location (both partial and full redundancies).
5579 Not enabled at any optimization level.
5581 @item -fgcse-after-reload
5582 @opindex fgcse-after-reload
5583 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
5584 pass is performed after reload. The purpose of this pass is to cleanup
5587 @item -funsafe-loop-optimizations
5588 @opindex funsafe-loop-optimizations
5589 If given, the loop optimizer will assume that loop indices do not
5590 overflow, and that the loops with nontrivial exit condition are not
5591 infinite. This enables a wider range of loop optimizations even if
5592 the loop optimizer itself cannot prove that these assumptions are valid.
5593 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
5594 if it finds this kind of loop.
5596 @item -fcrossjumping
5597 @opindex fcrossjumping
5598 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
5599 resulting code may or may not perform better than without cross-jumping.
5601 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5603 @item -fauto-inc-dec
5604 @opindex fauto-inc-dec
5605 Combine increments or decrements of addresses with memory accesses.
5606 This pass is always skipped on architectures that do not have
5607 instructions to support this. Enabled by default at @option{-O} and
5608 higher on architectures that support this.
5612 Perform dead code elimination (DCE) on RTL@.
5613 Enabled by default at @option{-O} and higher.
5617 Perform dead store elimination (DSE) on RTL@.
5618 Enabled by default at @option{-O} and higher.
5620 @item -fif-conversion
5621 @opindex fif-conversion
5622 Attempt to transform conditional jumps into branch-less equivalents. This
5623 include use of conditional moves, min, max, set flags and abs instructions, and
5624 some tricks doable by standard arithmetics. The use of conditional execution
5625 on chips where it is available is controlled by @code{if-conversion2}.
5627 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5629 @item -fif-conversion2
5630 @opindex fif-conversion2
5631 Use conditional execution (where available) to transform conditional jumps into
5632 branch-less equivalents.
5634 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5636 @item -fdelete-null-pointer-checks
5637 @opindex fdelete-null-pointer-checks
5638 Use global dataflow analysis to identify and eliminate useless checks
5639 for null pointers. The compiler assumes that dereferencing a null
5640 pointer would have halted the program. If a pointer is checked after
5641 it has already been dereferenced, it cannot be null.
5643 In some environments, this assumption is not true, and programs can
5644 safely dereference null pointers. Use
5645 @option{-fno-delete-null-pointer-checks} to disable this optimization
5646 for programs which depend on that behavior.
5648 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5650 @item -fexpensive-optimizations
5651 @opindex fexpensive-optimizations
5652 Perform a number of minor optimizations that are relatively expensive.
5654 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5656 @item -foptimize-register-move
5658 @opindex foptimize-register-move
5660 Attempt to reassign register numbers in move instructions and as
5661 operands of other simple instructions in order to maximize the amount of
5662 register tying. This is especially helpful on machines with two-operand
5665 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
5668 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5670 @item -fdelayed-branch
5671 @opindex fdelayed-branch
5672 If supported for the target machine, attempt to reorder instructions
5673 to exploit instruction slots available after delayed branch
5676 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5678 @item -fschedule-insns
5679 @opindex fschedule-insns
5680 If supported for the target machine, attempt to reorder instructions to
5681 eliminate execution stalls due to required data being unavailable. This
5682 helps machines that have slow floating point or memory load instructions
5683 by allowing other instructions to be issued until the result of the load
5684 or floating point instruction is required.
5686 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5688 @item -fschedule-insns2
5689 @opindex fschedule-insns2
5690 Similar to @option{-fschedule-insns}, but requests an additional pass of
5691 instruction scheduling after register allocation has been done. This is
5692 especially useful on machines with a relatively small number of
5693 registers and where memory load instructions take more than one cycle.
5695 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5697 @item -fno-sched-interblock
5698 @opindex fno-sched-interblock
5699 Don't schedule instructions across basic blocks. This is normally
5700 enabled by default when scheduling before register allocation, i.e.@:
5701 with @option{-fschedule-insns} or at @option{-O2} or higher.
5703 @item -fno-sched-spec
5704 @opindex fno-sched-spec
5705 Don't allow speculative motion of non-load instructions. This is normally
5706 enabled by default when scheduling before register allocation, i.e.@:
5707 with @option{-fschedule-insns} or at @option{-O2} or higher.
5709 @item -fsched-spec-load
5710 @opindex fsched-spec-load
5711 Allow speculative motion of some load instructions. This only makes
5712 sense when scheduling before register allocation, i.e.@: with
5713 @option{-fschedule-insns} or at @option{-O2} or higher.
5715 @item -fsched-spec-load-dangerous
5716 @opindex fsched-spec-load-dangerous
5717 Allow speculative motion of more load instructions. This only makes
5718 sense when scheduling before register allocation, i.e.@: with
5719 @option{-fschedule-insns} or at @option{-O2} or higher.
5721 @item -fsched-stalled-insns
5722 @itemx -fsched-stalled-insns=@var{n}
5723 @opindex fsched-stalled-insns
5724 Define how many insns (if any) can be moved prematurely from the queue
5725 of stalled insns into the ready list, during the second scheduling pass.
5726 @option{-fno-sched-stalled-insns} means that no insns will be moved
5727 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
5728 on how many queued insns can be moved prematurely.
5729 @option{-fsched-stalled-insns} without a value is equivalent to
5730 @option{-fsched-stalled-insns=1}.
5732 @item -fsched-stalled-insns-dep
5733 @itemx -fsched-stalled-insns-dep=@var{n}
5734 @opindex fsched-stalled-insns-dep
5735 Define how many insn groups (cycles) will be examined for a dependency
5736 on a stalled insn that is candidate for premature removal from the queue
5737 of stalled insns. This has an effect only during the second scheduling pass,
5738 and only if @option{-fsched-stalled-insns} is used.
5739 @option{-fno-sched-stalled-insns-dep} is equivalent to
5740 @option{-fsched-stalled-insns-dep=0}.
5741 @option{-fsched-stalled-insns-dep} without a value is equivalent to
5742 @option{-fsched-stalled-insns-dep=1}.
5744 @item -fsched2-use-superblocks
5745 @opindex fsched2-use-superblocks
5746 When scheduling after register allocation, do use superblock scheduling
5747 algorithm. Superblock scheduling allows motion across basic block boundaries
5748 resulting on faster schedules. This option is experimental, as not all machine
5749 descriptions used by GCC model the CPU closely enough to avoid unreliable
5750 results from the algorithm.
5752 This only makes sense when scheduling after register allocation, i.e.@: with
5753 @option{-fschedule-insns2} or at @option{-O2} or higher.
5755 @item -fsched2-use-traces
5756 @opindex fsched2-use-traces
5757 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
5758 allocation and additionally perform code duplication in order to increase the
5759 size of superblocks using tracer pass. See @option{-ftracer} for details on
5762 This mode should produce faster but significantly longer programs. Also
5763 without @option{-fbranch-probabilities} the traces constructed may not
5764 match the reality and hurt the performance. This only makes
5765 sense when scheduling after register allocation, i.e.@: with
5766 @option{-fschedule-insns2} or at @option{-O2} or higher.
5770 Eliminate redundant sign extension instructions and move the non-redundant
5771 ones to optimal placement using lazy code motion (LCM).
5773 @item -freschedule-modulo-scheduled-loops
5774 @opindex freschedule-modulo-scheduled-loops
5775 The modulo scheduling comes before the traditional scheduling, if a loop
5776 was modulo scheduled we may want to prevent the later scheduling passes
5777 from changing its schedule, we use this option to control that.
5779 @item -fcaller-saves
5780 @opindex fcaller-saves
5781 Enable values to be allocated in registers that will be clobbered by
5782 function calls, by emitting extra instructions to save and restore the
5783 registers around such calls. Such allocation is done only when it
5784 seems to result in better code than would otherwise be produced.
5786 This option is always enabled by default on certain machines, usually
5787 those which have no call-preserved registers to use instead.
5789 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5791 @item -ftree-reassoc
5792 @opindex ftree-reassoc
5793 Perform reassociation on trees. This flag is enabled by default
5794 at @option{-O} and higher.
5798 Perform partial redundancy elimination (PRE) on trees. This flag is
5799 enabled by default at @option{-O2} and @option{-O3}.
5803 Perform full redundancy elimination (FRE) on trees. The difference
5804 between FRE and PRE is that FRE only considers expressions
5805 that are computed on all paths leading to the redundant computation.
5806 This analysis is faster than PRE, though it exposes fewer redundancies.
5807 This flag is enabled by default at @option{-O} and higher.
5809 @item -ftree-copy-prop
5810 @opindex ftree-copy-prop
5811 Perform copy propagation on trees. This pass eliminates unnecessary
5812 copy operations. This flag is enabled by default at @option{-O} and
5815 @item -fipa-pure-const
5816 @opindex fipa-pure-const
5817 Discover which functions are pure or constant.
5818 Enabled by default at @option{-O} and higher.
5820 @item -fipa-reference
5821 @opindex fipa-reference
5822 Discover which static variables do not escape cannot escape the
5824 Enabled by default at @option{-O} and higher.
5826 @item -fipa-struct-reorg
5827 @opindex fipa-struct-reorg
5828 Perform structure reorganization optimization, that change C-like structures
5829 layout in order to better utilize spatial locality. This transformation is
5830 affective for programs containing arrays of structures. Available in two
5831 compilation modes: profile-based (enabled with @option{-fprofile-generate})
5832 or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
5833 to provide the safety of this transformation. It works only in whole program
5834 mode, so it requires @option{-fwhole-program} and @option{-combine} to be
5835 enabled. Structures considered @samp{cold} by this transformation are not
5836 affected (see @option{--param struct-reorg-cold-struct-ratio=@var{value}}).
5838 With this flag, the program debug info reflects a new structure layout.
5842 Perform interprocedural pointer analysis.
5846 Perform interprocedural constant propagation.
5847 This optimization analyzes the program to determine when values passed
5848 to functions are constants and then optimizes accordingly.
5849 This optimization can substantially increase performance
5850 if the application has constants passed to functions, but
5851 because this optimization can create multiple copies of functions,
5852 it may significantly increase code size.
5854 @item -fipa-matrix-reorg
5855 @opindex fipa-matrix-reorg
5856 Perform matrix flattening and transposing.
5857 Matrix flattening tries to replace a m-dimensional matrix
5858 with its equivalent n-dimensional matrix, where n < m.
5859 This reduces the level of indirection needed for accessing the elements
5860 of the matrix. The second optimization is matrix transposing that
5861 attemps to change the order of the matrix's dimensions in order to
5862 improve cache locality.
5863 Both optimizations need fwhole-program flag.
5864 Transposing is enabled only if profiling information is avaliable.
5869 Perform forward store motion on trees. This flag is
5870 enabled by default at @option{-O} and higher.
5874 Perform sparse conditional constant propagation (CCP) on trees. This
5875 pass only operates on local scalar variables and is enabled by default
5876 at @option{-O} and higher.
5878 @item -ftree-store-ccp
5879 @opindex ftree-store-ccp
5880 Perform sparse conditional constant propagation (CCP) on trees. This
5881 pass operates on both local scalar variables and memory stores and
5882 loads (global variables, structures, arrays, etc). This flag is
5883 enabled by default at @option{-O2} and higher.
5885 @item -ftree-switch-conversion
5886 Perform conversion of simple initializations in a switch to
5887 initializations from a scalar array. This flag is enabled by default
5888 at @option{-O2} and higher.
5892 Perform dead code elimination (DCE) on trees. This flag is enabled by
5893 default at @option{-O} and higher.
5895 @item -ftree-builtin-call-dce
5896 @opindex ftree-builtin-call-dce
5897 Perform conditional dead code elimination (DCE) for calls to builtin functions
5898 that may set @code{errno} but are otherwise side-effect free. This flag is
5899 enabled by default at @option{-O2} and higher if @option{-Os} is not also
5902 @item -ftree-dominator-opts
5903 @opindex ftree-dominator-opts
5904 Perform a variety of simple scalar cleanups (constant/copy
5905 propagation, redundancy elimination, range propagation and expression
5906 simplification) based on a dominator tree traversal. This also
5907 performs jump threading (to reduce jumps to jumps). This flag is
5908 enabled by default at @option{-O} and higher.
5912 Perform dead store elimination (DSE) on trees. A dead store is a store into
5913 a memory location which will later be overwritten by another store without
5914 any intervening loads. In this case the earlier store can be deleted. This
5915 flag is enabled by default at @option{-O} and higher.
5919 Perform loop header copying on trees. This is beneficial since it increases
5920 effectiveness of code motion optimizations. It also saves one jump. This flag
5921 is enabled by default at @option{-O} and higher. It is not enabled
5922 for @option{-Os}, since it usually increases code size.
5924 @item -ftree-loop-optimize
5925 @opindex ftree-loop-optimize
5926 Perform loop optimizations on trees. This flag is enabled by default
5927 at @option{-O} and higher.
5929 @item -ftree-loop-linear
5930 @opindex ftree-loop-linear
5931 Perform linear loop transformations on tree. This flag can improve cache
5932 performance and allow further loop optimizations to take place.
5934 @item -fcheck-data-deps
5935 @opindex fcheck-data-deps
5936 Compare the results of several data dependence analyzers. This option
5937 is used for debugging the data dependence analyzers.
5939 @item -ftree-loop-distribution
5940 Perform loop distribution. This flag can improve cache performance on
5941 big loop bodies and allow further loop optimizations, like
5942 parallelization or vectorization, to take place. For example, the loop
5959 @item -ftree-loop-im
5960 @opindex ftree-loop-im
5961 Perform loop invariant motion on trees. This pass moves only invariants that
5962 would be hard to handle at RTL level (function calls, operations that expand to
5963 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5964 operands of conditions that are invariant out of the loop, so that we can use
5965 just trivial invariantness analysis in loop unswitching. The pass also includes
5968 @item -ftree-loop-ivcanon
5969 @opindex ftree-loop-ivcanon
5970 Create a canonical counter for number of iterations in the loop for that
5971 determining number of iterations requires complicated analysis. Later
5972 optimizations then may determine the number easily. Useful especially
5973 in connection with unrolling.
5977 Perform induction variable optimizations (strength reduction, induction
5978 variable merging and induction variable elimination) on trees.
5980 @item -ftree-parallelize-loops=n
5981 @opindex ftree-parallelize-loops
5982 Parallelize loops, i.e., split their iteration space to run in n threads.
5983 This is only possible for loops whose iterations are independent
5984 and can be arbitrarily reordered. The optimization is only
5985 profitable on multiprocessor machines, for loops that are CPU-intensive,
5986 rather than constrained e.g.@: by memory bandwidth. This option
5987 implies @option{-pthread}, and thus is only supported on targets
5988 that have support for @option{-pthread}.
5992 Perform scalar replacement of aggregates. This pass replaces structure
5993 references with scalars to prevent committing structures to memory too
5994 early. This flag is enabled by default at @option{-O} and higher.
5996 @item -ftree-copyrename
5997 @opindex ftree-copyrename
5998 Perform copy renaming on trees. This pass attempts to rename compiler
5999 temporaries to other variables at copy locations, usually resulting in
6000 variable names which more closely resemble the original variables. This flag
6001 is enabled by default at @option{-O} and higher.
6005 Perform temporary expression replacement during the SSA->normal phase. Single
6006 use/single def temporaries are replaced at their use location with their
6007 defining expression. This results in non-GIMPLE code, but gives the expanders
6008 much more complex trees to work on resulting in better RTL generation. This is
6009 enabled by default at @option{-O} and higher.
6011 @item -ftree-vectorize
6012 @opindex ftree-vectorize
6013 Perform loop vectorization on trees. This flag is enabled by default at
6016 @item -ftree-vect-loop-version
6017 @opindex ftree-vect-loop-version
6018 Perform loop versioning when doing loop vectorization on trees. When a loop
6019 appears to be vectorizable except that data alignment or data dependence cannot
6020 be determined at compile time then vectorized and non-vectorized versions of
6021 the loop are generated along with runtime checks for alignment or dependence
6022 to control which version is executed. This option is enabled by default
6023 except at level @option{-Os} where it is disabled.
6025 @item -fvect-cost-model
6026 @opindex fvect-cost-model
6027 Enable cost model for vectorization.
6031 Perform Value Range Propagation on trees. This is similar to the
6032 constant propagation pass, but instead of values, ranges of values are
6033 propagated. This allows the optimizers to remove unnecessary range
6034 checks like array bound checks and null pointer checks. This is
6035 enabled by default at @option{-O2} and higher. Null pointer check
6036 elimination is only done if @option{-fdelete-null-pointer-checks} is
6041 Perform tail duplication to enlarge superblock size. This transformation
6042 simplifies the control flow of the function allowing other optimizations to do
6045 @item -funroll-loops
6046 @opindex funroll-loops
6047 Unroll loops whose number of iterations can be determined at compile
6048 time or upon entry to the loop. @option{-funroll-loops} implies
6049 @option{-frerun-cse-after-loop}. This option makes code larger,
6050 and may or may not make it run faster.
6052 @item -funroll-all-loops
6053 @opindex funroll-all-loops
6054 Unroll all loops, even if their number of iterations is uncertain when
6055 the loop is entered. This usually makes programs run more slowly.
6056 @option{-funroll-all-loops} implies the same options as
6057 @option{-funroll-loops},
6059 @item -fsplit-ivs-in-unroller
6060 @opindex fsplit-ivs-in-unroller
6061 Enables expressing of values of induction variables in later iterations
6062 of the unrolled loop using the value in the first iteration. This breaks
6063 long dependency chains, thus improving efficiency of the scheduling passes.
6065 Combination of @option{-fweb} and CSE is often sufficient to obtain the
6066 same effect. However in cases the loop body is more complicated than
6067 a single basic block, this is not reliable. It also does not work at all
6068 on some of the architectures due to restrictions in the CSE pass.
6070 This optimization is enabled by default.
6072 @item -fvariable-expansion-in-unroller
6073 @opindex fvariable-expansion-in-unroller
6074 With this option, the compiler will create multiple copies of some
6075 local variables when unrolling a loop which can result in superior code.
6077 @item -fpredictive-commoning
6078 @opindex fpredictive-commoning
6079 Perform predictive commoning optimization, i.e., reusing computations
6080 (especially memory loads and stores) performed in previous
6081 iterations of loops.
6083 This option is enabled at level @option{-O3}.
6085 @item -fprefetch-loop-arrays
6086 @opindex fprefetch-loop-arrays
6087 If supported by the target machine, generate instructions to prefetch
6088 memory to improve the performance of loops that access large arrays.
6090 This option may generate better or worse code; results are highly
6091 dependent on the structure of loops within the source code.
6093 Disabled at level @option{-Os}.
6096 @itemx -fno-peephole2
6097 @opindex fno-peephole
6098 @opindex fno-peephole2
6099 Disable any machine-specific peephole optimizations. The difference
6100 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
6101 are implemented in the compiler; some targets use one, some use the
6102 other, a few use both.
6104 @option{-fpeephole} is enabled by default.
6105 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6107 @item -fno-guess-branch-probability
6108 @opindex fno-guess-branch-probability
6109 Do not guess branch probabilities using heuristics.
6111 GCC will use heuristics to guess branch probabilities if they are
6112 not provided by profiling feedback (@option{-fprofile-arcs}). These
6113 heuristics are based on the control flow graph. If some branch probabilities
6114 are specified by @samp{__builtin_expect}, then the heuristics will be
6115 used to guess branch probabilities for the rest of the control flow graph,
6116 taking the @samp{__builtin_expect} info into account. The interactions
6117 between the heuristics and @samp{__builtin_expect} can be complex, and in
6118 some cases, it may be useful to disable the heuristics so that the effects
6119 of @samp{__builtin_expect} are easier to understand.
6121 The default is @option{-fguess-branch-probability} at levels
6122 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6124 @item -freorder-blocks
6125 @opindex freorder-blocks
6126 Reorder basic blocks in the compiled function in order to reduce number of
6127 taken branches and improve code locality.
6129 Enabled at levels @option{-O2}, @option{-O3}.
6131 @item -freorder-blocks-and-partition
6132 @opindex freorder-blocks-and-partition
6133 In addition to reordering basic blocks in the compiled function, in order
6134 to reduce number of taken branches, partitions hot and cold basic blocks
6135 into separate sections of the assembly and .o files, to improve
6136 paging and cache locality performance.
6138 This optimization is automatically turned off in the presence of
6139 exception handling, for linkonce sections, for functions with a user-defined
6140 section attribute and on any architecture that does not support named
6143 @item -freorder-functions
6144 @opindex freorder-functions
6145 Reorder functions in the object file in order to
6146 improve code locality. This is implemented by using special
6147 subsections @code{.text.hot} for most frequently executed functions and
6148 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
6149 the linker so object file format must support named sections and linker must
6150 place them in a reasonable way.
6152 Also profile feedback must be available in to make this option effective. See
6153 @option{-fprofile-arcs} for details.
6155 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6157 @item -fstrict-aliasing
6158 @opindex fstrict-aliasing
6159 Allows the compiler to assume the strictest aliasing rules applicable to
6160 the language being compiled. For C (and C++), this activates
6161 optimizations based on the type of expressions. In particular, an
6162 object of one type is assumed never to reside at the same address as an
6163 object of a different type, unless the types are almost the same. For
6164 example, an @code{unsigned int} can alias an @code{int}, but not a
6165 @code{void*} or a @code{double}. A character type may alias any other
6168 @anchor{Type-punning}Pay special attention to code like this:
6181 The practice of reading from a different union member than the one most
6182 recently written to (called ``type-punning'') is common. Even with
6183 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
6184 is accessed through the union type. So, the code above will work as
6185 expected. @xref{Structures unions enumerations and bit-fields
6186 implementation}. However, this code might not:
6197 Similarly, access by taking the address, casting the resulting pointer
6198 and dereferencing the result has undefined behavior, even if the cast
6199 uses a union type, e.g.:
6203 return ((union a_union *) &d)->i;
6207 The @option{-fstrict-aliasing} option is enabled at levels
6208 @option{-O2}, @option{-O3}, @option{-Os}.
6210 @item -fstrict-overflow
6211 @opindex fstrict-overflow
6212 Allow the compiler to assume strict signed overflow rules, depending
6213 on the language being compiled. For C (and C++) this means that
6214 overflow when doing arithmetic with signed numbers is undefined, which
6215 means that the compiler may assume that it will not happen. This
6216 permits various optimizations. For example, the compiler will assume
6217 that an expression like @code{i + 10 > i} will always be true for
6218 signed @code{i}. This assumption is only valid if signed overflow is
6219 undefined, as the expression is false if @code{i + 10} overflows when
6220 using twos complement arithmetic. When this option is in effect any
6221 attempt to determine whether an operation on signed numbers will
6222 overflow must be written carefully to not actually involve overflow.
6224 This option also allows the compiler to assume strict pointer
6225 semantics: given a pointer to an object, if adding an offset to that
6226 pointer does not produce a pointer to the same object, the addition is
6227 undefined. This permits the compiler to conclude that @code{p + u >
6228 p} is always true for a pointer @code{p} and unsigned integer
6229 @code{u}. This assumption is only valid because pointer wraparound is
6230 undefined, as the expression is false if @code{p + u} overflows using
6231 twos complement arithmetic.
6233 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
6234 that integer signed overflow is fully defined: it wraps. When
6235 @option{-fwrapv} is used, there is no difference between
6236 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
6237 integers. With @option{-fwrapv} certain types of overflow are
6238 permitted. For example, if the compiler gets an overflow when doing
6239 arithmetic on constants, the overflowed value can still be used with
6240 @option{-fwrapv}, but not otherwise.
6242 The @option{-fstrict-overflow} option is enabled at levels
6243 @option{-O2}, @option{-O3}, @option{-Os}.
6245 @item -falign-functions
6246 @itemx -falign-functions=@var{n}
6247 @opindex falign-functions
6248 Align the start of functions to the next power-of-two greater than
6249 @var{n}, skipping up to @var{n} bytes. For instance,
6250 @option{-falign-functions=32} aligns functions to the next 32-byte
6251 boundary, but @option{-falign-functions=24} would align to the next
6252 32-byte boundary only if this can be done by skipping 23 bytes or less.
6254 @option{-fno-align-functions} and @option{-falign-functions=1} are
6255 equivalent and mean that functions will not be aligned.
6257 Some assemblers only support this flag when @var{n} is a power of two;
6258 in that case, it is rounded up.
6260 If @var{n} is not specified or is zero, use a machine-dependent default.
6262 Enabled at levels @option{-O2}, @option{-O3}.
6264 @item -falign-labels
6265 @itemx -falign-labels=@var{n}
6266 @opindex falign-labels
6267 Align all branch targets to a power-of-two boundary, skipping up to
6268 @var{n} bytes like @option{-falign-functions}. This option can easily
6269 make code slower, because it must insert dummy operations for when the
6270 branch target is reached in the usual flow of the code.
6272 @option{-fno-align-labels} and @option{-falign-labels=1} are
6273 equivalent and mean that labels will not be aligned.
6275 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
6276 are greater than this value, then their values are used instead.
6278 If @var{n} is not specified or is zero, use a machine-dependent default
6279 which is very likely to be @samp{1}, meaning no alignment.
6281 Enabled at levels @option{-O2}, @option{-O3}.
6284 @itemx -falign-loops=@var{n}
6285 @opindex falign-loops
6286 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
6287 like @option{-falign-functions}. The hope is that the loop will be
6288 executed many times, which will make up for any execution of the dummy
6291 @option{-fno-align-loops} and @option{-falign-loops=1} are
6292 equivalent and mean that loops will not be aligned.
6294 If @var{n} is not specified or is zero, use a machine-dependent default.
6296 Enabled at levels @option{-O2}, @option{-O3}.
6299 @itemx -falign-jumps=@var{n}
6300 @opindex falign-jumps
6301 Align branch targets to a power-of-two boundary, for branch targets
6302 where the targets can only be reached by jumping, skipping up to @var{n}
6303 bytes like @option{-falign-functions}. In this case, no dummy operations
6306 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
6307 equivalent and mean that loops will not be aligned.
6309 If @var{n} is not specified or is zero, use a machine-dependent default.
6311 Enabled at levels @option{-O2}, @option{-O3}.
6313 @item -funit-at-a-time
6314 @opindex funit-at-a-time
6315 This option is left for compatibility reasons. @option{-funit-at-a-time}
6316 has no effect, while @option{-fno-unit-at-a-time} implies
6317 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
6321 @item -fno-toplevel-reorder
6322 @opindex fno-toplevel-reorder
6323 Do not reorder top-level functions, variables, and @code{asm}
6324 statements. Output them in the same order that they appear in the
6325 input file. When this option is used, unreferenced static variables
6326 will not be removed. This option is intended to support existing code
6327 which relies on a particular ordering. For new code, it is better to
6330 Enabled at level @option{-O0}. When disabled explicitly, it also imply
6331 @option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some
6336 Constructs webs as commonly used for register allocation purposes and assign
6337 each web individual pseudo register. This allows the register allocation pass
6338 to operate on pseudos directly, but also strengthens several other optimization
6339 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
6340 however, make debugging impossible, since variables will no longer stay in a
6343 Enabled by default with @option{-funroll-loops}.
6345 @item -fwhole-program
6346 @opindex fwhole-program
6347 Assume that the current compilation unit represents whole program being
6348 compiled. All public functions and variables with the exception of @code{main}
6349 and those merged by attribute @code{externally_visible} become static functions
6350 and in a affect gets more aggressively optimized by interprocedural optimizers.
6351 While this option is equivalent to proper use of @code{static} keyword for
6352 programs consisting of single file, in combination with option
6353 @option{--combine} this flag can be used to compile most of smaller scale C
6354 programs since the functions and variables become local for the whole combined
6355 compilation unit, not for the single source file itself.
6357 This option is not supported for Fortran programs.
6359 @item -fcprop-registers
6360 @opindex fcprop-registers
6361 After register allocation and post-register allocation instruction splitting,
6362 we perform a copy-propagation pass to try to reduce scheduling dependencies
6363 and occasionally eliminate the copy.
6365 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6367 @item -fprofile-dir=@var{path}
6368 @opindex fprofile-dir
6370 Set the directory to search the profile data files in to @var{path}.
6371 This option affects only the profile data generated by
6372 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
6373 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
6374 and its related options.
6375 By default, GCC will use the current directory as @var{path}
6376 thus the profile data file will appear in the same directory as the object file.
6378 @item -fprofile-generate
6379 @itemx -fprofile-generate=@var{path}
6380 @opindex fprofile-generate
6382 Enable options usually used for instrumenting application to produce
6383 profile useful for later recompilation with profile feedback based
6384 optimization. You must use @option{-fprofile-generate} both when
6385 compiling and when linking your program.
6387 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
6389 If @var{path} is specified, GCC will look at the @var{path} to find
6390 the profile feeedback data files. See @option{-fprofile-dir}.
6393 @itemx -fprofile-use=@var{path}
6394 @opindex fprofile-use
6395 Enable profile feedback directed optimizations, and optimizations
6396 generally profitable only with profile feedback available.
6398 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
6399 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
6401 By default, GCC emits an error message if the feedback profiles do not
6402 match the source code. This error can be turned into a warning by using
6403 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
6406 If @var{path} is specified, GCC will look at the @var{path} to find
6407 the profile feedback data files. See @option{-fprofile-dir}.
6410 The following options control compiler behavior regarding floating
6411 point arithmetic. These options trade off between speed and
6412 correctness. All must be specifically enabled.
6416 @opindex ffloat-store
6417 Do not store floating point variables in registers, and inhibit other
6418 options that might change whether a floating point value is taken from a
6421 @cindex floating point precision
6422 This option prevents undesirable excess precision on machines such as
6423 the 68000 where the floating registers (of the 68881) keep more
6424 precision than a @code{double} is supposed to have. Similarly for the
6425 x86 architecture. For most programs, the excess precision does only
6426 good, but a few programs rely on the precise definition of IEEE floating
6427 point. Use @option{-ffloat-store} for such programs, after modifying
6428 them to store all pertinent intermediate computations into variables.
6432 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
6433 @option{-ffinite-math-only}, @option{-fno-rounding-math},
6434 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
6436 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
6438 This option is not turned on by any @option{-O} option since
6439 it can result in incorrect output for programs which depend on
6440 an exact implementation of IEEE or ISO rules/specifications for
6441 math functions. It may, however, yield faster code for programs
6442 that do not require the guarantees of these specifications.
6444 @item -fno-math-errno
6445 @opindex fno-math-errno
6446 Do not set ERRNO after calling math functions that are executed
6447 with a single instruction, e.g., sqrt. A program that relies on
6448 IEEE exceptions for math error handling may want to use this flag
6449 for speed while maintaining IEEE arithmetic compatibility.
6451 This option is not turned on by any @option{-O} option since
6452 it can result in incorrect output for programs which depend on
6453 an exact implementation of IEEE or ISO rules/specifications for
6454 math functions. It may, however, yield faster code for programs
6455 that do not require the guarantees of these specifications.
6457 The default is @option{-fmath-errno}.
6459 On Darwin systems, the math library never sets @code{errno}. There is
6460 therefore no reason for the compiler to consider the possibility that
6461 it might, and @option{-fno-math-errno} is the default.
6463 @item -funsafe-math-optimizations
6464 @opindex funsafe-math-optimizations
6466 Allow optimizations for floating-point arithmetic that (a) assume
6467 that arguments and results are valid and (b) may violate IEEE or
6468 ANSI standards. When used at link-time, it may include libraries
6469 or startup files that change the default FPU control word or other
6470 similar optimizations.
6472 This option is not turned on by any @option{-O} option since
6473 it can result in incorrect output for programs which depend on
6474 an exact implementation of IEEE or ISO rules/specifications for
6475 math functions. It may, however, yield faster code for programs
6476 that do not require the guarantees of these specifications.
6477 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
6478 @option{-fassociative-math} and @option{-freciprocal-math}.
6480 The default is @option{-fno-unsafe-math-optimizations}.
6482 @item -fassociative-math
6483 @opindex fassociative-math
6485 Allow re-association of operands in series of floating-point operations.
6486 This violates the ISO C and C++ language standard by possibly changing
6487 computation result. NOTE: re-ordering may change the sign of zero as
6488 well as ignore NaNs and inhibit or create underflow or overflow (and
6489 thus cannot be used on a code which relies on rounding behavior like
6490 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
6491 and thus may not be used when ordered comparisons are required.
6492 This option requires that both @option{-fno-signed-zeros} and
6493 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
6494 much sense with @option{-frounding-math}.
6496 The default is @option{-fno-associative-math}.
6498 @item -freciprocal-math
6499 @opindex freciprocal-math
6501 Allow the reciprocal of a value to be used instead of dividing by
6502 the value if this enables optimizations. For example @code{x / y}
6503 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
6504 is subject to common subexpression elimination. Note that this loses
6505 precision and increases the number of flops operating on the value.
6507 The default is @option{-fno-reciprocal-math}.
6509 @item -ffinite-math-only
6510 @opindex ffinite-math-only
6511 Allow optimizations for floating-point arithmetic that assume
6512 that arguments and results are not NaNs or +-Infs.
6514 This option is not turned on by any @option{-O} option since
6515 it can result in incorrect output for programs which depend on
6516 an exact implementation of IEEE or ISO rules/specifications for
6517 math functions. It may, however, yield faster code for programs
6518 that do not require the guarantees of these specifications.
6520 The default is @option{-fno-finite-math-only}.
6522 @item -fno-signed-zeros
6523 @opindex fno-signed-zeros
6524 Allow optimizations for floating point arithmetic that ignore the
6525 signedness of zero. IEEE arithmetic specifies the behavior of
6526 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
6527 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
6528 This option implies that the sign of a zero result isn't significant.
6530 The default is @option{-fsigned-zeros}.
6532 @item -fno-trapping-math
6533 @opindex fno-trapping-math
6534 Compile code assuming that floating-point operations cannot generate
6535 user-visible traps. These traps include division by zero, overflow,
6536 underflow, inexact result and invalid operation. This option requires
6537 that @option{-fno-signaling-nans} be in effect. Setting this option may
6538 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
6540 This option should never be turned on by any @option{-O} option since
6541 it can result in incorrect output for programs which depend on
6542 an exact implementation of IEEE or ISO rules/specifications for
6545 The default is @option{-ftrapping-math}.
6547 @item -frounding-math
6548 @opindex frounding-math
6549 Disable transformations and optimizations that assume default floating
6550 point rounding behavior. This is round-to-zero for all floating point
6551 to integer conversions, and round-to-nearest for all other arithmetic
6552 truncations. This option should be specified for programs that change
6553 the FP rounding mode dynamically, or that may be executed with a
6554 non-default rounding mode. This option disables constant folding of
6555 floating point expressions at compile-time (which may be affected by
6556 rounding mode) and arithmetic transformations that are unsafe in the
6557 presence of sign-dependent rounding modes.
6559 The default is @option{-fno-rounding-math}.
6561 This option is experimental and does not currently guarantee to
6562 disable all GCC optimizations that are affected by rounding mode.
6563 Future versions of GCC may provide finer control of this setting
6564 using C99's @code{FENV_ACCESS} pragma. This command line option
6565 will be used to specify the default state for @code{FENV_ACCESS}.
6567 @item -frtl-abstract-sequences
6568 @opindex frtl-abstract-sequences
6569 It is a size optimization method. This option is to find identical
6570 sequences of code, which can be turned into pseudo-procedures and
6571 then replace all occurrences with calls to the newly created
6572 subroutine. It is kind of an opposite of @option{-finline-functions}.
6573 This optimization runs at RTL level.
6575 @item -fsignaling-nans
6576 @opindex fsignaling-nans
6577 Compile code assuming that IEEE signaling NaNs may generate user-visible
6578 traps during floating-point operations. Setting this option disables
6579 optimizations that may change the number of exceptions visible with
6580 signaling NaNs. This option implies @option{-ftrapping-math}.
6582 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
6585 The default is @option{-fno-signaling-nans}.
6587 This option is experimental and does not currently guarantee to
6588 disable all GCC optimizations that affect signaling NaN behavior.
6590 @item -fsingle-precision-constant
6591 @opindex fsingle-precision-constant
6592 Treat floating point constant as single precision constant instead of
6593 implicitly converting it to double precision constant.
6595 @item -fcx-limited-range
6596 @opindex fcx-limited-range
6597 When enabled, this option states that a range reduction step is not
6598 needed when performing complex division. Also, there is no checking
6599 whether the result of a complex multiplication or division is @code{NaN
6600 + I*NaN}, with an attempt to rescue the situation in that case. The
6601 default is @option{-fno-cx-limited-range}, but is enabled by
6602 @option{-ffast-math}.
6604 This option controls the default setting of the ISO C99
6605 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
6608 @item -fcx-fortran-rules
6609 @opindex fcx-fortran-rules
6610 Complex multiplication and division follow Fortran rules. Range
6611 reduction is done as part of complex division, but there is no checking
6612 whether the result of a complex multiplication or division is @code{NaN
6613 + I*NaN}, with an attempt to rescue the situation in that case.
6615 The default is @option{-fno-cx-fortran-rules}.
6619 The following options control optimizations that may improve
6620 performance, but are not enabled by any @option{-O} options. This
6621 section includes experimental options that may produce broken code.
6624 @item -fbranch-probabilities
6625 @opindex fbranch-probabilities
6626 After running a program compiled with @option{-fprofile-arcs}
6627 (@pxref{Debugging Options,, Options for Debugging Your Program or
6628 @command{gcc}}), you can compile it a second time using
6629 @option{-fbranch-probabilities}, to improve optimizations based on
6630 the number of times each branch was taken. When the program
6631 compiled with @option{-fprofile-arcs} exits it saves arc execution
6632 counts to a file called @file{@var{sourcename}.gcda} for each source
6633 file. The information in this data file is very dependent on the
6634 structure of the generated code, so you must use the same source code
6635 and the same optimization options for both compilations.
6637 With @option{-fbranch-probabilities}, GCC puts a
6638 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
6639 These can be used to improve optimization. Currently, they are only
6640 used in one place: in @file{reorg.c}, instead of guessing which path a
6641 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
6642 exactly determine which path is taken more often.
6644 @item -fprofile-values
6645 @opindex fprofile-values
6646 If combined with @option{-fprofile-arcs}, it adds code so that some
6647 data about values of expressions in the program is gathered.
6649 With @option{-fbranch-probabilities}, it reads back the data gathered
6650 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
6651 notes to instructions for their later usage in optimizations.
6653 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
6657 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
6658 a code to gather information about values of expressions.
6660 With @option{-fbranch-probabilities}, it reads back the data gathered
6661 and actually performs the optimizations based on them.
6662 Currently the optimizations include specialization of division operation
6663 using the knowledge about the value of the denominator.
6665 @item -frename-registers
6666 @opindex frename-registers
6667 Attempt to avoid false dependencies in scheduled code by making use
6668 of registers left over after register allocation. This optimization
6669 will most benefit processors with lots of registers. Depending on the
6670 debug information format adopted by the target, however, it can
6671 make debugging impossible, since variables will no longer stay in
6672 a ``home register''.
6674 Enabled by default with @option{-funroll-loops}.
6678 Perform tail duplication to enlarge superblock size. This transformation
6679 simplifies the control flow of the function allowing other optimizations to do
6682 Enabled with @option{-fprofile-use}.
6684 @item -funroll-loops
6685 @opindex funroll-loops
6686 Unroll loops whose number of iterations can be determined at compile time or
6687 upon entry to the loop. @option{-funroll-loops} implies
6688 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
6689 It also turns on complete loop peeling (i.e.@: complete removal of loops with
6690 small constant number of iterations). This option makes code larger, and may
6691 or may not make it run faster.
6693 Enabled with @option{-fprofile-use}.
6695 @item -funroll-all-loops
6696 @opindex funroll-all-loops
6697 Unroll all loops, even if their number of iterations is uncertain when
6698 the loop is entered. This usually makes programs run more slowly.
6699 @option{-funroll-all-loops} implies the same options as
6700 @option{-funroll-loops}.
6703 @opindex fpeel-loops
6704 Peels the loops for that there is enough information that they do not
6705 roll much (from profile feedback). It also turns on complete loop peeling
6706 (i.e.@: complete removal of loops with small constant number of iterations).
6708 Enabled with @option{-fprofile-use}.
6710 @item -fmove-loop-invariants
6711 @opindex fmove-loop-invariants
6712 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
6713 at level @option{-O1}
6715 @item -funswitch-loops
6716 @opindex funswitch-loops
6717 Move branches with loop invariant conditions out of the loop, with duplicates
6718 of the loop on both branches (modified according to result of the condition).
6720 @item -ffunction-sections
6721 @itemx -fdata-sections
6722 @opindex ffunction-sections
6723 @opindex fdata-sections
6724 Place each function or data item into its own section in the output
6725 file if the target supports arbitrary sections. The name of the
6726 function or the name of the data item determines the section's name
6729 Use these options on systems where the linker can perform optimizations
6730 to improve locality of reference in the instruction space. Most systems
6731 using the ELF object format and SPARC processors running Solaris 2 have
6732 linkers with such optimizations. AIX may have these optimizations in
6735 Only use these options when there are significant benefits from doing
6736 so. When you specify these options, the assembler and linker will
6737 create larger object and executable files and will also be slower.
6738 You will not be able to use @code{gprof} on all systems if you
6739 specify this option and you may have problems with debugging if
6740 you specify both this option and @option{-g}.
6742 @item -fbranch-target-load-optimize
6743 @opindex fbranch-target-load-optimize
6744 Perform branch target register load optimization before prologue / epilogue
6746 The use of target registers can typically be exposed only during reload,
6747 thus hoisting loads out of loops and doing inter-block scheduling needs
6748 a separate optimization pass.
6750 @item -fbranch-target-load-optimize2
6751 @opindex fbranch-target-load-optimize2
6752 Perform branch target register load optimization after prologue / epilogue
6755 @item -fbtr-bb-exclusive
6756 @opindex fbtr-bb-exclusive
6757 When performing branch target register load optimization, don't reuse
6758 branch target registers in within any basic block.
6760 @item -fstack-protector
6761 @opindex fstack-protector
6762 Emit extra code to check for buffer overflows, such as stack smashing
6763 attacks. This is done by adding a guard variable to functions with
6764 vulnerable objects. This includes functions that call alloca, and
6765 functions with buffers larger than 8 bytes. The guards are initialized
6766 when a function is entered and then checked when the function exits.
6767 If a guard check fails, an error message is printed and the program exits.
6769 @item -fstack-protector-all
6770 @opindex fstack-protector-all
6771 Like @option{-fstack-protector} except that all functions are protected.
6773 @item -fsection-anchors
6774 @opindex fsection-anchors
6775 Try to reduce the number of symbolic address calculations by using
6776 shared ``anchor'' symbols to address nearby objects. This transformation
6777 can help to reduce the number of GOT entries and GOT accesses on some
6780 For example, the implementation of the following function @code{foo}:
6784 int foo (void) @{ return a + b + c; @}
6787 would usually calculate the addresses of all three variables, but if you
6788 compile it with @option{-fsection-anchors}, it will access the variables
6789 from a common anchor point instead. The effect is similar to the
6790 following pseudocode (which isn't valid C):
6795 register int *xr = &x;
6796 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
6800 Not all targets support this option.
6802 @item --param @var{name}=@var{value}
6804 In some places, GCC uses various constants to control the amount of
6805 optimization that is done. For example, GCC will not inline functions
6806 that contain more that a certain number of instructions. You can
6807 control some of these constants on the command-line using the
6808 @option{--param} option.
6810 The names of specific parameters, and the meaning of the values, are
6811 tied to the internals of the compiler, and are subject to change
6812 without notice in future releases.
6814 In each case, the @var{value} is an integer. The allowable choices for
6815 @var{name} are given in the following table:
6818 @item sra-max-structure-size
6819 The maximum structure size, in bytes, at which the scalar replacement
6820 of aggregates (SRA) optimization will perform block copies. The
6821 default value, 0, implies that GCC will select the most appropriate
6824 @item sra-field-structure-ratio
6825 The threshold ratio (as a percentage) between instantiated fields and
6826 the complete structure size. We say that if the ratio of the number
6827 of bytes in instantiated fields to the number of bytes in the complete
6828 structure exceeds this parameter, then block copies are not used. The
6831 @item struct-reorg-cold-struct-ratio
6832 The threshold ratio (as a percentage) between a structure frequency
6833 and the frequency of the hottest structure in the program. This parameter
6834 is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
6835 We say that if the ratio of a structure frequency, calculated by profiling,
6836 to the hottest structure frequency in the program is less than this
6837 parameter, then structure reorganization is not applied to this structure.
6840 @item max-crossjump-edges
6841 The maximum number of incoming edges to consider for crossjumping.
6842 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
6843 the number of edges incoming to each block. Increasing values mean
6844 more aggressive optimization, making the compile time increase with
6845 probably small improvement in executable size.
6847 @item min-crossjump-insns
6848 The minimum number of instructions which must be matched at the end
6849 of two blocks before crossjumping will be performed on them. This
6850 value is ignored in the case where all instructions in the block being
6851 crossjumped from are matched. The default value is 5.
6853 @item max-grow-copy-bb-insns
6854 The maximum code size expansion factor when copying basic blocks
6855 instead of jumping. The expansion is relative to a jump instruction.
6856 The default value is 8.
6858 @item max-goto-duplication-insns
6859 The maximum number of instructions to duplicate to a block that jumps
6860 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
6861 passes, GCC factors computed gotos early in the compilation process,
6862 and unfactors them as late as possible. Only computed jumps at the
6863 end of a basic blocks with no more than max-goto-duplication-insns are
6864 unfactored. The default value is 8.
6866 @item max-delay-slot-insn-search
6867 The maximum number of instructions to consider when looking for an
6868 instruction to fill a delay slot. If more than this arbitrary number of
6869 instructions is searched, the time savings from filling the delay slot
6870 will be minimal so stop searching. Increasing values mean more
6871 aggressive optimization, making the compile time increase with probably
6872 small improvement in executable run time.
6874 @item max-delay-slot-live-search
6875 When trying to fill delay slots, the maximum number of instructions to
6876 consider when searching for a block with valid live register
6877 information. Increasing this arbitrarily chosen value means more
6878 aggressive optimization, increasing the compile time. This parameter
6879 should be removed when the delay slot code is rewritten to maintain the
6882 @item max-gcse-memory
6883 The approximate maximum amount of memory that will be allocated in
6884 order to perform the global common subexpression elimination
6885 optimization. If more memory than specified is required, the
6886 optimization will not be done.
6888 @item max-gcse-passes
6889 The maximum number of passes of GCSE to run. The default is 1.
6891 @item max-pending-list-length
6892 The maximum number of pending dependencies scheduling will allow
6893 before flushing the current state and starting over. Large functions
6894 with few branches or calls can create excessively large lists which
6895 needlessly consume memory and resources.
6897 @item max-inline-insns-single
6898 Several parameters control the tree inliner used in gcc.
6899 This number sets the maximum number of instructions (counted in GCC's
6900 internal representation) in a single function that the tree inliner
6901 will consider for inlining. This only affects functions declared
6902 inline and methods implemented in a class declaration (C++).
6903 The default value is 450.
6905 @item max-inline-insns-auto
6906 When you use @option{-finline-functions} (included in @option{-O3}),
6907 a lot of functions that would otherwise not be considered for inlining
6908 by the compiler will be investigated. To those functions, a different
6909 (more restrictive) limit compared to functions declared inline can
6911 The default value is 90.
6913 @item large-function-insns
6914 The limit specifying really large functions. For functions larger than this
6915 limit after inlining inlining is constrained by
6916 @option{--param large-function-growth}. This parameter is useful primarily
6917 to avoid extreme compilation time caused by non-linear algorithms used by the
6919 The default value is 2700.
6921 @item large-function-growth
6922 Specifies maximal growth of large function caused by inlining in percents.
6923 The default value is 100 which limits large function growth to 2.0 times
6926 @item large-unit-insns
6927 The limit specifying large translation unit. Growth caused by inlining of
6928 units larger than this limit is limited by @option{--param inline-unit-growth}.
6929 For small units this might be too tight (consider unit consisting of function A
6930 that is inline and B that just calls A three time. If B is small relative to
6931 A, the growth of unit is 300\% and yet such inlining is very sane. For very
6932 large units consisting of small inlineable functions however the overall unit
6933 growth limit is needed to avoid exponential explosion of code size. Thus for
6934 smaller units, the size is increased to @option{--param large-unit-insns}
6935 before applying @option{--param inline-unit-growth}. The default is 10000
6937 @item inline-unit-growth
6938 Specifies maximal overall growth of the compilation unit caused by inlining.
6939 The default value is 30 which limits unit growth to 1.3 times the original
6942 @item large-stack-frame
6943 The limit specifying large stack frames. While inlining the algorithm is trying
6944 to not grow past this limit too much. Default value is 256 bytes.
6946 @item large-stack-frame-growth
6947 Specifies maximal growth of large stack frames caused by inlining in percents.
6948 The default value is 1000 which limits large stack frame growth to 11 times
6951 @item max-inline-insns-recursive
6952 @itemx max-inline-insns-recursive-auto
6953 Specifies maximum number of instructions out-of-line copy of self recursive inline
6954 function can grow into by performing recursive inlining.
6956 For functions declared inline @option{--param max-inline-insns-recursive} is
6957 taken into account. For function not declared inline, recursive inlining
6958 happens only when @option{-finline-functions} (included in @option{-O3}) is
6959 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
6960 default value is 450.
6962 @item max-inline-recursive-depth
6963 @itemx max-inline-recursive-depth-auto
6964 Specifies maximum recursion depth used by the recursive inlining.
6966 For functions declared inline @option{--param max-inline-recursive-depth} is
6967 taken into account. For function not declared inline, recursive inlining
6968 happens only when @option{-finline-functions} (included in @option{-O3}) is
6969 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
6972 @item min-inline-recursive-probability
6973 Recursive inlining is profitable only for function having deep recursion
6974 in average and can hurt for function having little recursion depth by
6975 increasing the prologue size or complexity of function body to other
6978 When profile feedback is available (see @option{-fprofile-generate}) the actual
6979 recursion depth can be guessed from probability that function will recurse via
6980 given call expression. This parameter limits inlining only to call expression
6981 whose probability exceeds given threshold (in percents). The default value is
6984 @item inline-call-cost
6985 Specify cost of call instruction relative to simple arithmetics operations
6986 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
6987 functions and at the same time increases size of leaf function that is believed to
6988 reduce function size by being inlined. In effect it increases amount of
6989 inlining for code having large abstraction penalty (many functions that just
6990 pass the arguments to other functions) and decrease inlining for code with low
6991 abstraction penalty. The default value is 12.
6993 @item min-vect-loop-bound
6994 The minimum number of iterations under which a loop will not get vectorized
6995 when @option{-ftree-vectorize} is used. The number of iterations after
6996 vectorization needs to be greater than the value specified by this option
6997 to allow vectorization. The default value is 0.
6999 @item max-unrolled-insns
7000 The maximum number of instructions that a loop should have if that loop
7001 is unrolled, and if the loop is unrolled, it determines how many times
7002 the loop code is unrolled.
7004 @item max-average-unrolled-insns
7005 The maximum number of instructions biased by probabilities of their execution
7006 that a loop should have if that loop is unrolled, and if the loop is unrolled,
7007 it determines how many times the loop code is unrolled.
7009 @item max-unroll-times
7010 The maximum number of unrollings of a single loop.
7012 @item max-peeled-insns
7013 The maximum number of instructions that a loop should have if that loop
7014 is peeled, and if the loop is peeled, it determines how many times
7015 the loop code is peeled.
7017 @item max-peel-times
7018 The maximum number of peelings of a single loop.
7020 @item max-completely-peeled-insns
7021 The maximum number of insns of a completely peeled loop.
7023 @item max-completely-peel-times
7024 The maximum number of iterations of a loop to be suitable for complete peeling.
7026 @item max-unswitch-insns
7027 The maximum number of insns of an unswitched loop.
7029 @item max-unswitch-level
7030 The maximum number of branches unswitched in a single loop.
7033 The minimum cost of an expensive expression in the loop invariant motion.
7035 @item iv-consider-all-candidates-bound
7036 Bound on number of candidates for induction variables below that
7037 all candidates are considered for each use in induction variable
7038 optimizations. Only the most relevant candidates are considered
7039 if there are more candidates, to avoid quadratic time complexity.
7041 @item iv-max-considered-uses
7042 The induction variable optimizations give up on loops that contain more
7043 induction variable uses.
7045 @item iv-always-prune-cand-set-bound
7046 If number of candidates in the set is smaller than this value,
7047 we always try to remove unnecessary ivs from the set during its
7048 optimization when a new iv is added to the set.
7050 @item scev-max-expr-size
7051 Bound on size of expressions used in the scalar evolutions analyzer.
7052 Large expressions slow the analyzer.
7054 @item omega-max-vars
7055 The maximum number of variables in an Omega constraint system.
7056 The default value is 128.
7058 @item omega-max-geqs
7059 The maximum number of inequalities in an Omega constraint system.
7060 The default value is 256.
7063 The maximum number of equalities in an Omega constraint system.
7064 The default value is 128.
7066 @item omega-max-wild-cards
7067 The maximum number of wildcard variables that the Omega solver will
7068 be able to insert. The default value is 18.
7070 @item omega-hash-table-size
7071 The size of the hash table in the Omega solver. The default value is
7074 @item omega-max-keys
7075 The maximal number of keys used by the Omega solver. The default
7078 @item omega-eliminate-redundant-constraints
7079 When set to 1, use expensive methods to eliminate all redundant
7080 constraints. The default value is 0.
7082 @item vect-max-version-for-alignment-checks
7083 The maximum number of runtime checks that can be performed when
7084 doing loop versioning for alignment in the vectorizer. See option
7085 ftree-vect-loop-version for more information.
7087 @item vect-max-version-for-alias-checks
7088 The maximum number of runtime checks that can be performed when
7089 doing loop versioning for alias in the vectorizer. See option
7090 ftree-vect-loop-version for more information.
7092 @item max-iterations-to-track
7094 The maximum number of iterations of a loop the brute force algorithm
7095 for analysis of # of iterations of the loop tries to evaluate.
7097 @item hot-bb-count-fraction
7098 Select fraction of the maximal count of repetitions of basic block in program
7099 given basic block needs to have to be considered hot.
7101 @item hot-bb-frequency-fraction
7102 Select fraction of the maximal frequency of executions of basic block in
7103 function given basic block needs to have to be considered hot
7105 @item max-predicted-iterations
7106 The maximum number of loop iterations we predict statically. This is useful
7107 in cases where function contain single loop with known bound and other loop
7108 with unknown. We predict the known number of iterations correctly, while
7109 the unknown number of iterations average to roughly 10. This means that the
7110 loop without bounds would appear artificially cold relative to the other one.
7112 @item align-threshold
7114 Select fraction of the maximal frequency of executions of basic block in
7115 function given basic block will get aligned.
7117 @item align-loop-iterations
7119 A loop expected to iterate at lest the selected number of iterations will get
7122 @item tracer-dynamic-coverage
7123 @itemx tracer-dynamic-coverage-feedback
7125 This value is used to limit superblock formation once the given percentage of
7126 executed instructions is covered. This limits unnecessary code size
7129 The @option{tracer-dynamic-coverage-feedback} is used only when profile
7130 feedback is available. The real profiles (as opposed to statically estimated
7131 ones) are much less balanced allowing the threshold to be larger value.
7133 @item tracer-max-code-growth
7134 Stop tail duplication once code growth has reached given percentage. This is
7135 rather hokey argument, as most of the duplicates will be eliminated later in
7136 cross jumping, so it may be set to much higher values than is the desired code
7139 @item tracer-min-branch-ratio
7141 Stop reverse growth when the reverse probability of best edge is less than this
7142 threshold (in percent).
7144 @item tracer-min-branch-ratio
7145 @itemx tracer-min-branch-ratio-feedback
7147 Stop forward growth if the best edge do have probability lower than this
7150 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
7151 compilation for profile feedback and one for compilation without. The value
7152 for compilation with profile feedback needs to be more conservative (higher) in
7153 order to make tracer effective.
7155 @item max-cse-path-length
7157 Maximum number of basic blocks on path that cse considers. The default is 10.
7160 The maximum instructions CSE process before flushing. The default is 1000.
7162 @item max-aliased-vops
7164 Maximum number of virtual operands per function allowed to represent
7165 aliases before triggering the alias partitioning heuristic. Alias
7166 partitioning reduces compile times and memory consumption needed for
7167 aliasing at the expense of precision loss in alias information. The
7168 default value for this parameter is 100 for -O1, 500 for -O2 and 1000
7171 Notice that if a function contains more memory statements than the
7172 value of this parameter, it is not really possible to achieve this
7173 reduction. In this case, the compiler will use the number of memory
7174 statements as the value for @option{max-aliased-vops}.
7176 @item avg-aliased-vops
7178 Average number of virtual operands per statement allowed to represent
7179 aliases before triggering the alias partitioning heuristic. This
7180 works in conjunction with @option{max-aliased-vops}. If a function
7181 contains more than @option{max-aliased-vops} virtual operators, then
7182 memory symbols will be grouped into memory partitions until either the
7183 total number of virtual operators is below @option{max-aliased-vops}
7184 or the average number of virtual operators per memory statement is
7185 below @option{avg-aliased-vops}. The default value for this parameter
7186 is 1 for -O1 and -O2, and 3 for -O3.
7188 @item ggc-min-expand
7190 GCC uses a garbage collector to manage its own memory allocation. This
7191 parameter specifies the minimum percentage by which the garbage
7192 collector's heap should be allowed to expand between collections.
7193 Tuning this may improve compilation speed; it has no effect on code
7196 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
7197 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
7198 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
7199 GCC is not able to calculate RAM on a particular platform, the lower
7200 bound of 30% is used. Setting this parameter and
7201 @option{ggc-min-heapsize} to zero causes a full collection to occur at
7202 every opportunity. This is extremely slow, but can be useful for
7205 @item ggc-min-heapsize
7207 Minimum size of the garbage collector's heap before it begins bothering
7208 to collect garbage. The first collection occurs after the heap expands
7209 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
7210 tuning this may improve compilation speed, and has no effect on code
7213 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
7214 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
7215 with a lower bound of 4096 (four megabytes) and an upper bound of
7216 131072 (128 megabytes). If GCC is not able to calculate RAM on a
7217 particular platform, the lower bound is used. Setting this parameter
7218 very large effectively disables garbage collection. Setting this
7219 parameter and @option{ggc-min-expand} to zero causes a full collection
7220 to occur at every opportunity.
7222 @item max-reload-search-insns
7223 The maximum number of instruction reload should look backward for equivalent
7224 register. Increasing values mean more aggressive optimization, making the
7225 compile time increase with probably slightly better performance. The default
7228 @item max-cselib-memory-locations
7229 The maximum number of memory locations cselib should take into account.
7230 Increasing values mean more aggressive optimization, making the compile time
7231 increase with probably slightly better performance. The default value is 500.
7233 @item reorder-blocks-duplicate
7234 @itemx reorder-blocks-duplicate-feedback
7236 Used by basic block reordering pass to decide whether to use unconditional
7237 branch or duplicate the code on its destination. Code is duplicated when its
7238 estimated size is smaller than this value multiplied by the estimated size of
7239 unconditional jump in the hot spots of the program.
7241 The @option{reorder-block-duplicate-feedback} is used only when profile
7242 feedback is available and may be set to higher values than
7243 @option{reorder-block-duplicate} since information about the hot spots is more
7246 @item max-sched-ready-insns
7247 The maximum number of instructions ready to be issued the scheduler should
7248 consider at any given time during the first scheduling pass. Increasing
7249 values mean more thorough searches, making the compilation time increase
7250 with probably little benefit. The default value is 100.
7252 @item max-sched-region-blocks
7253 The maximum number of blocks in a region to be considered for
7254 interblock scheduling. The default value is 10.
7256 @item max-sched-region-insns
7257 The maximum number of insns in a region to be considered for
7258 interblock scheduling. The default value is 100.
7261 The minimum probability (in percents) of reaching a source block
7262 for interblock speculative scheduling. The default value is 40.
7264 @item max-sched-extend-regions-iters
7265 The maximum number of iterations through CFG to extend regions.
7266 0 - disable region extension,
7267 N - do at most N iterations.
7268 The default value is 0.
7270 @item max-sched-insn-conflict-delay
7271 The maximum conflict delay for an insn to be considered for speculative motion.
7272 The default value is 3.
7274 @item sched-spec-prob-cutoff
7275 The minimal probability of speculation success (in percents), so that
7276 speculative insn will be scheduled.
7277 The default value is 40.
7279 @item max-last-value-rtl
7281 The maximum size measured as number of RTLs that can be recorded in an expression
7282 in combiner for a pseudo register as last known value of that register. The default
7285 @item integer-share-limit
7286 Small integer constants can use a shared data structure, reducing the
7287 compiler's memory usage and increasing its speed. This sets the maximum
7288 value of a shared integer constant. The default value is 256.
7290 @item min-virtual-mappings
7291 Specifies the minimum number of virtual mappings in the incremental
7292 SSA updater that should be registered to trigger the virtual mappings
7293 heuristic defined by virtual-mappings-ratio. The default value is
7296 @item virtual-mappings-ratio
7297 If the number of virtual mappings is virtual-mappings-ratio bigger
7298 than the number of virtual symbols to be updated, then the incremental
7299 SSA updater switches to a full update for those symbols. The default
7302 @item ssp-buffer-size
7303 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
7304 protection when @option{-fstack-protection} is used.
7306 @item max-jump-thread-duplication-stmts
7307 Maximum number of statements allowed in a block that needs to be
7308 duplicated when threading jumps.
7310 @item max-fields-for-field-sensitive
7311 Maximum number of fields in a structure we will treat in
7312 a field sensitive manner during pointer analysis. The default is zero
7313 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
7315 @item prefetch-latency
7316 Estimate on average number of instructions that are executed before
7317 prefetch finishes. The distance we prefetch ahead is proportional
7318 to this constant. Increasing this number may also lead to less
7319 streams being prefetched (see @option{simultaneous-prefetches}).
7321 @item simultaneous-prefetches
7322 Maximum number of prefetches that can run at the same time.
7324 @item l1-cache-line-size
7325 The size of cache line in L1 cache, in bytes.
7328 The size of L1 cache, in kilobytes.
7331 The size of L2 cache, in kilobytes.
7333 @item use-canonical-types
7334 Whether the compiler should use the ``canonical'' type system. By
7335 default, this should always be 1, which uses a more efficient internal
7336 mechanism for comparing types in C++ and Objective-C++. However, if
7337 bugs in the canonical type system are causing compilation failures,
7338 set this value to 0 to disable canonical types.
7340 @item switch-conversion-max-branch-ratio
7341 Switch initialization conversion will refuse to create arrays that are
7342 bigger than @option{switch-conversion-max-branch-ratio} times the number of
7343 branches in the switch.
7345 @item max-partial-antic-length
7346 Maximum length of the partial antic set computed during the tree
7347 partial redundancy elimination optimization (@option{-ftree-pre}) when
7348 optimizing at @option{-O3} and above. For some sorts of source code
7349 the enhanced partial redundancy elimination optimization can run away,
7350 consuming all of the memory available on the host machine. This
7351 parameter sets a limit on the length of the sets that are computed,
7352 which prevents the runaway behaviour. Setting a value of 0 for
7353 this paramter will allow an unlimited set length.
7355 @item sccvn-max-scc-size
7356 Maximum size of a strongly connected component (SCC) during SCCVN
7357 processing. If this limit is hit, SCCVN processing for the whole
7358 function will not be done and optimizations depending on it will
7359 be disabled. The default maximum SCC size is 10000.
7364 @node Preprocessor Options
7365 @section Options Controlling the Preprocessor
7366 @cindex preprocessor options
7367 @cindex options, preprocessor
7369 These options control the C preprocessor, which is run on each C source
7370 file before actual compilation.
7372 If you use the @option{-E} option, nothing is done except preprocessing.
7373 Some of these options make sense only together with @option{-E} because
7374 they cause the preprocessor output to be unsuitable for actual
7379 You can use @option{-Wp,@var{option}} to bypass the compiler driver
7380 and pass @var{option} directly through to the preprocessor. If
7381 @var{option} contains commas, it is split into multiple options at the
7382 commas. However, many options are modified, translated or interpreted
7383 by the compiler driver before being passed to the preprocessor, and
7384 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
7385 interface is undocumented and subject to change, so whenever possible
7386 you should avoid using @option{-Wp} and let the driver handle the
7389 @item -Xpreprocessor @var{option}
7390 @opindex preprocessor
7391 Pass @var{option} as an option to the preprocessor. You can use this to
7392 supply system-specific preprocessor options which GCC does not know how to
7395 If you want to pass an option that takes an argument, you must use
7396 @option{-Xpreprocessor} twice, once for the option and once for the argument.
7399 @include cppopts.texi
7401 @node Assembler Options
7402 @section Passing Options to the Assembler
7404 @c prevent bad page break with this line
7405 You can pass options to the assembler.
7408 @item -Wa,@var{option}
7410 Pass @var{option} as an option to the assembler. If @var{option}
7411 contains commas, it is split into multiple options at the commas.
7413 @item -Xassembler @var{option}
7415 Pass @var{option} as an option to the assembler. You can use this to
7416 supply system-specific assembler options which GCC does not know how to
7419 If you want to pass an option that takes an argument, you must use
7420 @option{-Xassembler} twice, once for the option and once for the argument.
7425 @section Options for Linking
7426 @cindex link options
7427 @cindex options, linking
7429 These options come into play when the compiler links object files into
7430 an executable output file. They are meaningless if the compiler is
7431 not doing a link step.
7435 @item @var{object-file-name}
7436 A file name that does not end in a special recognized suffix is
7437 considered to name an object file or library. (Object files are
7438 distinguished from libraries by the linker according to the file
7439 contents.) If linking is done, these object files are used as input
7448 If any of these options is used, then the linker is not run, and
7449 object file names should not be used as arguments. @xref{Overall
7453 @item -l@var{library}
7454 @itemx -l @var{library}
7456 Search the library named @var{library} when linking. (The second
7457 alternative with the library as a separate argument is only for
7458 POSIX compliance and is not recommended.)
7460 It makes a difference where in the command you write this option; the
7461 linker searches and processes libraries and object files in the order they
7462 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
7463 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
7464 to functions in @samp{z}, those functions may not be loaded.
7466 The linker searches a standard list of directories for the library,
7467 which is actually a file named @file{lib@var{library}.a}. The linker
7468 then uses this file as if it had been specified precisely by name.
7470 The directories searched include several standard system directories
7471 plus any that you specify with @option{-L}.
7473 Normally the files found this way are library files---archive files
7474 whose members are object files. The linker handles an archive file by
7475 scanning through it for members which define symbols that have so far
7476 been referenced but not defined. But if the file that is found is an
7477 ordinary object file, it is linked in the usual fashion. The only
7478 difference between using an @option{-l} option and specifying a file name
7479 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
7480 and searches several directories.
7484 You need this special case of the @option{-l} option in order to
7485 link an Objective-C or Objective-C++ program.
7488 @opindex nostartfiles
7489 Do not use the standard system startup files when linking.
7490 The standard system libraries are used normally, unless @option{-nostdlib}
7491 or @option{-nodefaultlibs} is used.
7493 @item -nodefaultlibs
7494 @opindex nodefaultlibs
7495 Do not use the standard system libraries when linking.
7496 Only the libraries you specify will be passed to the linker.
7497 The standard startup files are used normally, unless @option{-nostartfiles}
7498 is used. The compiler may generate calls to @code{memcmp},
7499 @code{memset}, @code{memcpy} and @code{memmove}.
7500 These entries are usually resolved by entries in
7501 libc. These entry points should be supplied through some other
7502 mechanism when this option is specified.
7506 Do not use the standard system startup files or libraries when linking.
7507 No startup files and only the libraries you specify will be passed to
7508 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
7509 @code{memcpy} and @code{memmove}.
7510 These entries are usually resolved by entries in
7511 libc. These entry points should be supplied through some other
7512 mechanism when this option is specified.
7514 @cindex @option{-lgcc}, use with @option{-nostdlib}
7515 @cindex @option{-nostdlib} and unresolved references
7516 @cindex unresolved references and @option{-nostdlib}
7517 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
7518 @cindex @option{-nodefaultlibs} and unresolved references
7519 @cindex unresolved references and @option{-nodefaultlibs}
7520 One of the standard libraries bypassed by @option{-nostdlib} and
7521 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
7522 that GCC uses to overcome shortcomings of particular machines, or special
7523 needs for some languages.
7524 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
7525 Collection (GCC) Internals},
7526 for more discussion of @file{libgcc.a}.)
7527 In most cases, you need @file{libgcc.a} even when you want to avoid
7528 other standard libraries. In other words, when you specify @option{-nostdlib}
7529 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
7530 This ensures that you have no unresolved references to internal GCC
7531 library subroutines. (For example, @samp{__main}, used to ensure C++
7532 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
7533 GNU Compiler Collection (GCC) Internals}.)
7537 Produce a position independent executable on targets which support it.
7538 For predictable results, you must also specify the same set of options
7539 that were used to generate code (@option{-fpie}, @option{-fPIE},
7540 or model suboptions) when you specify this option.
7544 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
7545 that support it. This instructs the linker to add all symbols, not
7546 only used ones, to the dynamic symbol table. This option is needed
7547 for some uses of @code{dlopen} or to allow obtaining backtraces
7548 from within a program.
7552 Remove all symbol table and relocation information from the executable.
7556 On systems that support dynamic linking, this prevents linking with the shared
7557 libraries. On other systems, this option has no effect.
7561 Produce a shared object which can then be linked with other objects to
7562 form an executable. Not all systems support this option. For predictable
7563 results, you must also specify the same set of options that were used to
7564 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
7565 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
7566 needs to build supplementary stub code for constructors to work. On
7567 multi-libbed systems, @samp{gcc -shared} must select the correct support
7568 libraries to link against. Failing to supply the correct flags may lead
7569 to subtle defects. Supplying them in cases where they are not necessary
7572 @item -shared-libgcc
7573 @itemx -static-libgcc
7574 @opindex shared-libgcc
7575 @opindex static-libgcc
7576 On systems that provide @file{libgcc} as a shared library, these options
7577 force the use of either the shared or static version respectively.
7578 If no shared version of @file{libgcc} was built when the compiler was
7579 configured, these options have no effect.
7581 There are several situations in which an application should use the
7582 shared @file{libgcc} instead of the static version. The most common
7583 of these is when the application wishes to throw and catch exceptions
7584 across different shared libraries. In that case, each of the libraries
7585 as well as the application itself should use the shared @file{libgcc}.
7587 Therefore, the G++ and GCJ drivers automatically add
7588 @option{-shared-libgcc} whenever you build a shared library or a main
7589 executable, because C++ and Java programs typically use exceptions, so
7590 this is the right thing to do.
7592 If, instead, you use the GCC driver to create shared libraries, you may
7593 find that they will not always be linked with the shared @file{libgcc}.
7594 If GCC finds, at its configuration time, that you have a non-GNU linker
7595 or a GNU linker that does not support option @option{--eh-frame-hdr},
7596 it will link the shared version of @file{libgcc} into shared libraries
7597 by default. Otherwise, it will take advantage of the linker and optimize
7598 away the linking with the shared version of @file{libgcc}, linking with
7599 the static version of libgcc by default. This allows exceptions to
7600 propagate through such shared libraries, without incurring relocation
7601 costs at library load time.
7603 However, if a library or main executable is supposed to throw or catch
7604 exceptions, you must link it using the G++ or GCJ driver, as appropriate
7605 for the languages used in the program, or using the option
7606 @option{-shared-libgcc}, such that it is linked with the shared
7611 Bind references to global symbols when building a shared object. Warn
7612 about any unresolved references (unless overridden by the link editor
7613 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
7616 @item -Xlinker @var{option}
7618 Pass @var{option} as an option to the linker. You can use this to
7619 supply system-specific linker options which GCC does not know how to
7622 If you want to pass an option that takes an argument, you must use
7623 @option{-Xlinker} twice, once for the option and once for the argument.
7624 For example, to pass @option{-assert definitions}, you must write
7625 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
7626 @option{-Xlinker "-assert definitions"}, because this passes the entire
7627 string as a single argument, which is not what the linker expects.
7629 @item -Wl,@var{option}
7631 Pass @var{option} as an option to the linker. If @var{option} contains
7632 commas, it is split into multiple options at the commas.
7634 @item -u @var{symbol}
7636 Pretend the symbol @var{symbol} is undefined, to force linking of
7637 library modules to define it. You can use @option{-u} multiple times with
7638 different symbols to force loading of additional library modules.
7641 @node Directory Options
7642 @section Options for Directory Search
7643 @cindex directory options
7644 @cindex options, directory search
7647 These options specify directories to search for header files, for
7648 libraries and for parts of the compiler:
7653 Add the directory @var{dir} to the head of the list of directories to be
7654 searched for header files. This can be used to override a system header
7655 file, substituting your own version, since these directories are
7656 searched before the system header file directories. However, you should
7657 not use this option to add directories that contain vendor-supplied
7658 system header files (use @option{-isystem} for that). If you use more than
7659 one @option{-I} option, the directories are scanned in left-to-right
7660 order; the standard system directories come after.
7662 If a standard system include directory, or a directory specified with
7663 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
7664 option will be ignored. The directory will still be searched but as a
7665 system directory at its normal position in the system include chain.
7666 This is to ensure that GCC's procedure to fix buggy system headers and
7667 the ordering for the include_next directive are not inadvertently changed.
7668 If you really need to change the search order for system directories,
7669 use the @option{-nostdinc} and/or @option{-isystem} options.
7671 @item -iquote@var{dir}
7673 Add the directory @var{dir} to the head of the list of directories to
7674 be searched for header files only for the case of @samp{#include
7675 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
7676 otherwise just like @option{-I}.
7680 Add directory @var{dir} to the list of directories to be searched
7683 @item -B@var{prefix}
7685 This option specifies where to find the executables, libraries,
7686 include files, and data files of the compiler itself.
7688 The compiler driver program runs one or more of the subprograms
7689 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
7690 @var{prefix} as a prefix for each program it tries to run, both with and
7691 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
7693 For each subprogram to be run, the compiler driver first tries the
7694 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
7695 was not specified, the driver tries two standard prefixes, which are
7696 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
7697 those results in a file name that is found, the unmodified program
7698 name is searched for using the directories specified in your
7699 @env{PATH} environment variable.
7701 The compiler will check to see if the path provided by the @option{-B}
7702 refers to a directory, and if necessary it will add a directory
7703 separator character at the end of the path.
7705 @option{-B} prefixes that effectively specify directory names also apply
7706 to libraries in the linker, because the compiler translates these
7707 options into @option{-L} options for the linker. They also apply to
7708 includes files in the preprocessor, because the compiler translates these
7709 options into @option{-isystem} options for the preprocessor. In this case,
7710 the compiler appends @samp{include} to the prefix.
7712 The run-time support file @file{libgcc.a} can also be searched for using
7713 the @option{-B} prefix, if needed. If it is not found there, the two
7714 standard prefixes above are tried, and that is all. The file is left
7715 out of the link if it is not found by those means.
7717 Another way to specify a prefix much like the @option{-B} prefix is to use
7718 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
7721 As a special kludge, if the path provided by @option{-B} is
7722 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
7723 9, then it will be replaced by @file{[dir/]include}. This is to help
7724 with boot-strapping the compiler.
7726 @item -specs=@var{file}
7728 Process @var{file} after the compiler reads in the standard @file{specs}
7729 file, in order to override the defaults that the @file{gcc} driver
7730 program uses when determining what switches to pass to @file{cc1},
7731 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
7732 @option{-specs=@var{file}} can be specified on the command line, and they
7733 are processed in order, from left to right.
7735 @item --sysroot=@var{dir}
7737 Use @var{dir} as the logical root directory for headers and libraries.
7738 For example, if the compiler would normally search for headers in
7739 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
7740 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
7742 If you use both this option and the @option{-isysroot} option, then
7743 the @option{--sysroot} option will apply to libraries, but the
7744 @option{-isysroot} option will apply to header files.
7746 The GNU linker (beginning with version 2.16) has the necessary support
7747 for this option. If your linker does not support this option, the
7748 header file aspect of @option{--sysroot} will still work, but the
7749 library aspect will not.
7753 This option has been deprecated. Please use @option{-iquote} instead for
7754 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
7755 Any directories you specify with @option{-I} options before the @option{-I-}
7756 option are searched only for the case of @samp{#include "@var{file}"};
7757 they are not searched for @samp{#include <@var{file}>}.
7759 If additional directories are specified with @option{-I} options after
7760 the @option{-I-}, these directories are searched for all @samp{#include}
7761 directives. (Ordinarily @emph{all} @option{-I} directories are used
7764 In addition, the @option{-I-} option inhibits the use of the current
7765 directory (where the current input file came from) as the first search
7766 directory for @samp{#include "@var{file}"}. There is no way to
7767 override this effect of @option{-I-}. With @option{-I.} you can specify
7768 searching the directory which was current when the compiler was
7769 invoked. That is not exactly the same as what the preprocessor does
7770 by default, but it is often satisfactory.
7772 @option{-I-} does not inhibit the use of the standard system directories
7773 for header files. Thus, @option{-I-} and @option{-nostdinc} are
7780 @section Specifying subprocesses and the switches to pass to them
7783 @command{gcc} is a driver program. It performs its job by invoking a
7784 sequence of other programs to do the work of compiling, assembling and
7785 linking. GCC interprets its command-line parameters and uses these to
7786 deduce which programs it should invoke, and which command-line options
7787 it ought to place on their command lines. This behavior is controlled
7788 by @dfn{spec strings}. In most cases there is one spec string for each
7789 program that GCC can invoke, but a few programs have multiple spec
7790 strings to control their behavior. The spec strings built into GCC can
7791 be overridden by using the @option{-specs=} command-line switch to specify
7794 @dfn{Spec files} are plaintext files that are used to construct spec
7795 strings. They consist of a sequence of directives separated by blank
7796 lines. The type of directive is determined by the first non-whitespace
7797 character on the line and it can be one of the following:
7800 @item %@var{command}
7801 Issues a @var{command} to the spec file processor. The commands that can
7805 @item %include <@var{file}>
7807 Search for @var{file} and insert its text at the current point in the
7810 @item %include_noerr <@var{file}>
7811 @cindex %include_noerr
7812 Just like @samp{%include}, but do not generate an error message if the include
7813 file cannot be found.
7815 @item %rename @var{old_name} @var{new_name}
7817 Rename the spec string @var{old_name} to @var{new_name}.
7821 @item *[@var{spec_name}]:
7822 This tells the compiler to create, override or delete the named spec
7823 string. All lines after this directive up to the next directive or
7824 blank line are considered to be the text for the spec string. If this
7825 results in an empty string then the spec will be deleted. (Or, if the
7826 spec did not exist, then nothing will happened.) Otherwise, if the spec
7827 does not currently exist a new spec will be created. If the spec does
7828 exist then its contents will be overridden by the text of this
7829 directive, unless the first character of that text is the @samp{+}
7830 character, in which case the text will be appended to the spec.
7832 @item [@var{suffix}]:
7833 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
7834 and up to the next directive or blank line are considered to make up the
7835 spec string for the indicated suffix. When the compiler encounters an
7836 input file with the named suffix, it will processes the spec string in
7837 order to work out how to compile that file. For example:
7844 This says that any input file whose name ends in @samp{.ZZ} should be
7845 passed to the program @samp{z-compile}, which should be invoked with the
7846 command-line switch @option{-input} and with the result of performing the
7847 @samp{%i} substitution. (See below.)
7849 As an alternative to providing a spec string, the text that follows a
7850 suffix directive can be one of the following:
7853 @item @@@var{language}
7854 This says that the suffix is an alias for a known @var{language}. This is
7855 similar to using the @option{-x} command-line switch to GCC to specify a
7856 language explicitly. For example:
7863 Says that .ZZ files are, in fact, C++ source files.
7866 This causes an error messages saying:
7869 @var{name} compiler not installed on this system.
7873 GCC already has an extensive list of suffixes built into it.
7874 This directive will add an entry to the end of the list of suffixes, but
7875 since the list is searched from the end backwards, it is effectively
7876 possible to override earlier entries using this technique.
7880 GCC has the following spec strings built into it. Spec files can
7881 override these strings or create their own. Note that individual
7882 targets can also add their own spec strings to this list.
7885 asm Options to pass to the assembler
7886 asm_final Options to pass to the assembler post-processor
7887 cpp Options to pass to the C preprocessor
7888 cc1 Options to pass to the C compiler
7889 cc1plus Options to pass to the C++ compiler
7890 endfile Object files to include at the end of the link
7891 link Options to pass to the linker
7892 lib Libraries to include on the command line to the linker
7893 libgcc Decides which GCC support library to pass to the linker
7894 linker Sets the name of the linker
7895 predefines Defines to be passed to the C preprocessor
7896 signed_char Defines to pass to CPP to say whether @code{char} is signed
7898 startfile Object files to include at the start of the link
7901 Here is a small example of a spec file:
7907 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
7910 This example renames the spec called @samp{lib} to @samp{old_lib} and
7911 then overrides the previous definition of @samp{lib} with a new one.
7912 The new definition adds in some extra command-line options before
7913 including the text of the old definition.
7915 @dfn{Spec strings} are a list of command-line options to be passed to their
7916 corresponding program. In addition, the spec strings can contain
7917 @samp{%}-prefixed sequences to substitute variable text or to
7918 conditionally insert text into the command line. Using these constructs
7919 it is possible to generate quite complex command lines.
7921 Here is a table of all defined @samp{%}-sequences for spec
7922 strings. Note that spaces are not generated automatically around the
7923 results of expanding these sequences. Therefore you can concatenate them
7924 together or combine them with constant text in a single argument.
7928 Substitute one @samp{%} into the program name or argument.
7931 Substitute the name of the input file being processed.
7934 Substitute the basename of the input file being processed.
7935 This is the substring up to (and not including) the last period
7936 and not including the directory.
7939 This is the same as @samp{%b}, but include the file suffix (text after
7943 Marks the argument containing or following the @samp{%d} as a
7944 temporary file name, so that that file will be deleted if GCC exits
7945 successfully. Unlike @samp{%g}, this contributes no text to the
7948 @item %g@var{suffix}
7949 Substitute a file name that has suffix @var{suffix} and is chosen
7950 once per compilation, and mark the argument in the same way as
7951 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
7952 name is now chosen in a way that is hard to predict even when previously
7953 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
7954 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
7955 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
7956 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
7957 was simply substituted with a file name chosen once per compilation,
7958 without regard to any appended suffix (which was therefore treated
7959 just like ordinary text), making such attacks more likely to succeed.
7961 @item %u@var{suffix}
7962 Like @samp{%g}, but generates a new temporary file name even if
7963 @samp{%u@var{suffix}} was already seen.
7965 @item %U@var{suffix}
7966 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
7967 new one if there is no such last file name. In the absence of any
7968 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
7969 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
7970 would involve the generation of two distinct file names, one
7971 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
7972 simply substituted with a file name chosen for the previous @samp{%u},
7973 without regard to any appended suffix.
7975 @item %j@var{suffix}
7976 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
7977 writable, and if save-temps is off; otherwise, substitute the name
7978 of a temporary file, just like @samp{%u}. This temporary file is not
7979 meant for communication between processes, but rather as a junk
7982 @item %|@var{suffix}
7983 @itemx %m@var{suffix}
7984 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
7985 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
7986 all. These are the two most common ways to instruct a program that it
7987 should read from standard input or write to standard output. If you
7988 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
7989 construct: see for example @file{f/lang-specs.h}.
7991 @item %.@var{SUFFIX}
7992 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
7993 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
7994 terminated by the next space or %.
7997 Marks the argument containing or following the @samp{%w} as the
7998 designated output file of this compilation. This puts the argument
7999 into the sequence of arguments that @samp{%o} will substitute later.
8002 Substitutes the names of all the output files, with spaces
8003 automatically placed around them. You should write spaces
8004 around the @samp{%o} as well or the results are undefined.
8005 @samp{%o} is for use in the specs for running the linker.
8006 Input files whose names have no recognized suffix are not compiled
8007 at all, but they are included among the output files, so they will
8011 Substitutes the suffix for object files. Note that this is
8012 handled specially when it immediately follows @samp{%g, %u, or %U},
8013 because of the need for those to form complete file names. The
8014 handling is such that @samp{%O} is treated exactly as if it had already
8015 been substituted, except that @samp{%g, %u, and %U} do not currently
8016 support additional @var{suffix} characters following @samp{%O} as they would
8017 following, for example, @samp{.o}.
8020 Substitutes the standard macro predefinitions for the
8021 current target machine. Use this when running @code{cpp}.
8024 Like @samp{%p}, but puts @samp{__} before and after the name of each
8025 predefined macro, except for macros that start with @samp{__} or with
8026 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
8030 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
8031 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
8032 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
8033 and @option{-imultilib} as necessary.
8036 Current argument is the name of a library or startup file of some sort.
8037 Search for that file in a standard list of directories and substitute
8038 the full name found.
8041 Print @var{str} as an error message. @var{str} is terminated by a newline.
8042 Use this when inconsistent options are detected.
8045 Substitute the contents of spec string @var{name} at this point.
8048 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
8050 @item %x@{@var{option}@}
8051 Accumulate an option for @samp{%X}.
8054 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
8058 Output the accumulated assembler options specified by @option{-Wa}.
8061 Output the accumulated preprocessor options specified by @option{-Wp}.
8064 Process the @code{asm} spec. This is used to compute the
8065 switches to be passed to the assembler.
8068 Process the @code{asm_final} spec. This is a spec string for
8069 passing switches to an assembler post-processor, if such a program is
8073 Process the @code{link} spec. This is the spec for computing the
8074 command line passed to the linker. Typically it will make use of the
8075 @samp{%L %G %S %D and %E} sequences.
8078 Dump out a @option{-L} option for each directory that GCC believes might
8079 contain startup files. If the target supports multilibs then the
8080 current multilib directory will be prepended to each of these paths.
8083 Process the @code{lib} spec. This is a spec string for deciding which
8084 libraries should be included on the command line to the linker.
8087 Process the @code{libgcc} spec. This is a spec string for deciding
8088 which GCC support library should be included on the command line to the linker.
8091 Process the @code{startfile} spec. This is a spec for deciding which
8092 object files should be the first ones passed to the linker. Typically
8093 this might be a file named @file{crt0.o}.
8096 Process the @code{endfile} spec. This is a spec string that specifies
8097 the last object files that will be passed to the linker.
8100 Process the @code{cpp} spec. This is used to construct the arguments
8101 to be passed to the C preprocessor.
8104 Process the @code{cc1} spec. This is used to construct the options to be
8105 passed to the actual C compiler (@samp{cc1}).
8108 Process the @code{cc1plus} spec. This is used to construct the options to be
8109 passed to the actual C++ compiler (@samp{cc1plus}).
8112 Substitute the variable part of a matched option. See below.
8113 Note that each comma in the substituted string is replaced by
8117 Remove all occurrences of @code{-S} from the command line. Note---this
8118 command is position dependent. @samp{%} commands in the spec string
8119 before this one will see @code{-S}, @samp{%} commands in the spec string
8120 after this one will not.
8122 @item %:@var{function}(@var{args})
8123 Call the named function @var{function}, passing it @var{args}.
8124 @var{args} is first processed as a nested spec string, then split
8125 into an argument vector in the usual fashion. The function returns
8126 a string which is processed as if it had appeared literally as part
8127 of the current spec.
8129 The following built-in spec functions are provided:
8133 The @code{getenv} spec function takes two arguments: an environment
8134 variable name and a string. If the environment variable is not
8135 defined, a fatal error is issued. Otherwise, the return value is the
8136 value of the environment variable concatenated with the string. For
8137 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
8140 %:getenv(TOPDIR /include)
8143 expands to @file{/path/to/top/include}.
8145 @item @code{if-exists}
8146 The @code{if-exists} spec function takes one argument, an absolute
8147 pathname to a file. If the file exists, @code{if-exists} returns the
8148 pathname. Here is a small example of its usage:
8152 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
8155 @item @code{if-exists-else}
8156 The @code{if-exists-else} spec function is similar to the @code{if-exists}
8157 spec function, except that it takes two arguments. The first argument is
8158 an absolute pathname to a file. If the file exists, @code{if-exists-else}
8159 returns the pathname. If it does not exist, it returns the second argument.
8160 This way, @code{if-exists-else} can be used to select one file or another,
8161 based on the existence of the first. Here is a small example of its usage:
8165 crt0%O%s %:if-exists(crti%O%s) \
8166 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
8169 @item @code{replace-outfile}
8170 The @code{replace-outfile} spec function takes two arguments. It looks for the
8171 first argument in the outfiles array and replaces it with the second argument. Here
8172 is a small example of its usage:
8175 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
8178 @item @code{print-asm-header}
8179 The @code{print-asm-header} function takes no arguments and simply
8180 prints a banner like:
8186 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
8189 It is used to separate compiler options from assembler options
8190 in the @option{--target-help} output.
8194 Substitutes the @code{-S} switch, if that switch was given to GCC@.
8195 If that switch was not specified, this substitutes nothing. Note that
8196 the leading dash is omitted when specifying this option, and it is
8197 automatically inserted if the substitution is performed. Thus the spec
8198 string @samp{%@{foo@}} would match the command-line option @option{-foo}
8199 and would output the command line option @option{-foo}.
8201 @item %W@{@code{S}@}
8202 Like %@{@code{S}@} but mark last argument supplied within as a file to be
8205 @item %@{@code{S}*@}
8206 Substitutes all the switches specified to GCC whose names start
8207 with @code{-S}, but which also take an argument. This is used for
8208 switches like @option{-o}, @option{-D}, @option{-I}, etc.
8209 GCC considers @option{-o foo} as being
8210 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
8211 text, including the space. Thus two arguments would be generated.
8213 @item %@{@code{S}*&@code{T}*@}
8214 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
8215 (the order of @code{S} and @code{T} in the spec is not significant).
8216 There can be any number of ampersand-separated variables; for each the
8217 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
8219 @item %@{@code{S}:@code{X}@}
8220 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
8222 @item %@{!@code{S}:@code{X}@}
8223 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
8225 @item %@{@code{S}*:@code{X}@}
8226 Substitutes @code{X} if one or more switches whose names start with
8227 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
8228 once, no matter how many such switches appeared. However, if @code{%*}
8229 appears somewhere in @code{X}, then @code{X} will be substituted once
8230 for each matching switch, with the @code{%*} replaced by the part of
8231 that switch that matched the @code{*}.
8233 @item %@{.@code{S}:@code{X}@}
8234 Substitutes @code{X}, if processing a file with suffix @code{S}.
8236 @item %@{!.@code{S}:@code{X}@}
8237 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
8239 @item %@{,@code{S}:@code{X}@}
8240 Substitutes @code{X}, if processing a file for language @code{S}.
8242 @item %@{!,@code{S}:@code{X}@}
8243 Substitutes @code{X}, if not processing a file for language @code{S}.
8245 @item %@{@code{S}|@code{P}:@code{X}@}
8246 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
8247 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
8248 @code{*} sequences as well, although they have a stronger binding than
8249 the @samp{|}. If @code{%*} appears in @code{X}, all of the
8250 alternatives must be starred, and only the first matching alternative
8253 For example, a spec string like this:
8256 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
8259 will output the following command-line options from the following input
8260 command-line options:
8265 -d fred.c -foo -baz -boggle
8266 -d jim.d -bar -baz -boggle
8269 @item %@{S:X; T:Y; :D@}
8271 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
8272 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
8273 be as many clauses as you need. This may be combined with @code{.},
8274 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
8279 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
8280 construct may contain other nested @samp{%} constructs or spaces, or
8281 even newlines. They are processed as usual, as described above.
8282 Trailing white space in @code{X} is ignored. White space may also
8283 appear anywhere on the left side of the colon in these constructs,
8284 except between @code{.} or @code{*} and the corresponding word.
8286 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
8287 handled specifically in these constructs. If another value of
8288 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
8289 @option{-W} switch is found later in the command line, the earlier
8290 switch value is ignored, except with @{@code{S}*@} where @code{S} is
8291 just one letter, which passes all matching options.
8293 The character @samp{|} at the beginning of the predicate text is used to
8294 indicate that a command should be piped to the following command, but
8295 only if @option{-pipe} is specified.
8297 It is built into GCC which switches take arguments and which do not.
8298 (You might think it would be useful to generalize this to allow each
8299 compiler's spec to say which switches take arguments. But this cannot
8300 be done in a consistent fashion. GCC cannot even decide which input
8301 files have been specified without knowing which switches take arguments,
8302 and it must know which input files to compile in order to tell which
8305 GCC also knows implicitly that arguments starting in @option{-l} are to be
8306 treated as compiler output files, and passed to the linker in their
8307 proper position among the other output files.
8309 @c man begin OPTIONS
8311 @node Target Options
8312 @section Specifying Target Machine and Compiler Version
8313 @cindex target options
8314 @cindex cross compiling
8315 @cindex specifying machine version
8316 @cindex specifying compiler version and target machine
8317 @cindex compiler version, specifying
8318 @cindex target machine, specifying
8320 The usual way to run GCC is to run the executable called @file{gcc}, or
8321 @file{<machine>-gcc} when cross-compiling, or
8322 @file{<machine>-gcc-<version>} to run a version other than the one that
8323 was installed last. Sometimes this is inconvenient, so GCC provides
8324 options that will switch to another cross-compiler or version.
8327 @item -b @var{machine}
8329 The argument @var{machine} specifies the target machine for compilation.
8331 The value to use for @var{machine} is the same as was specified as the
8332 machine type when configuring GCC as a cross-compiler. For
8333 example, if a cross-compiler was configured with @samp{configure
8334 arm-elf}, meaning to compile for an arm processor with elf binaries,
8335 then you would specify @option{-b arm-elf} to run that cross compiler.
8336 Because there are other options beginning with @option{-b}, the
8337 configuration must contain a hyphen.
8339 @item -V @var{version}
8341 The argument @var{version} specifies which version of GCC to run.
8342 This is useful when multiple versions are installed. For example,
8343 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
8346 The @option{-V} and @option{-b} options work by running the
8347 @file{<machine>-gcc-<version>} executable, so there's no real reason to
8348 use them if you can just run that directly.
8350 @node Submodel Options
8351 @section Hardware Models and Configurations
8352 @cindex submodel options
8353 @cindex specifying hardware config
8354 @cindex hardware models and configurations, specifying
8355 @cindex machine dependent options
8357 Earlier we discussed the standard option @option{-b} which chooses among
8358 different installed compilers for completely different target
8359 machines, such as VAX vs.@: 68000 vs.@: 80386.
8361 In addition, each of these target machine types can have its own
8362 special options, starting with @samp{-m}, to choose among various
8363 hardware models or configurations---for example, 68010 vs 68020,
8364 floating coprocessor or none. A single installed version of the
8365 compiler can compile for any model or configuration, according to the
8368 Some configurations of the compiler also support additional special
8369 options, usually for compatibility with other compilers on the same
8372 @c This list is ordered alphanumerically by subsection name.
8373 @c It should be the same order and spelling as these options are listed
8374 @c in Machine Dependent Options
8380 * Blackfin Options::
8384 * DEC Alpha Options::
8385 * DEC Alpha/VMS Options::
8387 * GNU/Linux Options::
8390 * i386 and x86-64 Options::
8402 * RS/6000 and PowerPC Options::
8403 * S/390 and zSeries Options::
8408 * System V Options::
8413 * Xstormy16 Options::
8419 @subsection ARC Options
8422 These options are defined for ARC implementations:
8427 Compile code for little endian mode. This is the default.
8431 Compile code for big endian mode.
8434 @opindex mmangle-cpu
8435 Prepend the name of the cpu to all public symbol names.
8436 In multiple-processor systems, there are many ARC variants with different
8437 instruction and register set characteristics. This flag prevents code
8438 compiled for one cpu to be linked with code compiled for another.
8439 No facility exists for handling variants that are ``almost identical''.
8440 This is an all or nothing option.
8442 @item -mcpu=@var{cpu}
8444 Compile code for ARC variant @var{cpu}.
8445 Which variants are supported depend on the configuration.
8446 All variants support @option{-mcpu=base}, this is the default.
8448 @item -mtext=@var{text-section}
8449 @itemx -mdata=@var{data-section}
8450 @itemx -mrodata=@var{readonly-data-section}
8454 Put functions, data, and readonly data in @var{text-section},
8455 @var{data-section}, and @var{readonly-data-section} respectively
8456 by default. This can be overridden with the @code{section} attribute.
8457 @xref{Variable Attributes}.
8462 @subsection ARM Options
8465 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
8469 @item -mabi=@var{name}
8471 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
8472 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
8475 @opindex mapcs-frame
8476 Generate a stack frame that is compliant with the ARM Procedure Call
8477 Standard for all functions, even if this is not strictly necessary for
8478 correct execution of the code. Specifying @option{-fomit-frame-pointer}
8479 with this option will cause the stack frames not to be generated for
8480 leaf functions. The default is @option{-mno-apcs-frame}.
8484 This is a synonym for @option{-mapcs-frame}.
8487 @c not currently implemented
8488 @item -mapcs-stack-check
8489 @opindex mapcs-stack-check
8490 Generate code to check the amount of stack space available upon entry to
8491 every function (that actually uses some stack space). If there is
8492 insufficient space available then either the function
8493 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
8494 called, depending upon the amount of stack space required. The run time
8495 system is required to provide these functions. The default is
8496 @option{-mno-apcs-stack-check}, since this produces smaller code.
8498 @c not currently implemented
8500 @opindex mapcs-float
8501 Pass floating point arguments using the float point registers. This is
8502 one of the variants of the APCS@. This option is recommended if the
8503 target hardware has a floating point unit or if a lot of floating point
8504 arithmetic is going to be performed by the code. The default is
8505 @option{-mno-apcs-float}, since integer only code is slightly increased in
8506 size if @option{-mapcs-float} is used.
8508 @c not currently implemented
8509 @item -mapcs-reentrant
8510 @opindex mapcs-reentrant
8511 Generate reentrant, position independent code. The default is
8512 @option{-mno-apcs-reentrant}.
8515 @item -mthumb-interwork
8516 @opindex mthumb-interwork
8517 Generate code which supports calling between the ARM and Thumb
8518 instruction sets. Without this option the two instruction sets cannot
8519 be reliably used inside one program. The default is
8520 @option{-mno-thumb-interwork}, since slightly larger code is generated
8521 when @option{-mthumb-interwork} is specified.
8523 @item -mno-sched-prolog
8524 @opindex mno-sched-prolog
8525 Prevent the reordering of instructions in the function prolog, or the
8526 merging of those instruction with the instructions in the function's
8527 body. This means that all functions will start with a recognizable set
8528 of instructions (or in fact one of a choice from a small set of
8529 different function prologues), and this information can be used to
8530 locate the start if functions inside an executable piece of code. The
8531 default is @option{-msched-prolog}.
8534 @opindex mhard-float
8535 Generate output containing floating point instructions. This is the
8539 @opindex msoft-float
8540 Generate output containing library calls for floating point.
8541 @strong{Warning:} the requisite libraries are not available for all ARM
8542 targets. Normally the facilities of the machine's usual C compiler are
8543 used, but this cannot be done directly in cross-compilation. You must make
8544 your own arrangements to provide suitable library functions for
8547 @option{-msoft-float} changes the calling convention in the output file;
8548 therefore, it is only useful if you compile @emph{all} of a program with
8549 this option. In particular, you need to compile @file{libgcc.a}, the
8550 library that comes with GCC, with @option{-msoft-float} in order for
8553 @item -mfloat-abi=@var{name}
8555 Specifies which ABI to use for floating point values. Permissible values
8556 are: @samp{soft}, @samp{softfp} and @samp{hard}.
8558 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
8559 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
8560 of floating point instructions, but still uses the soft-float calling
8563 @item -mlittle-endian
8564 @opindex mlittle-endian
8565 Generate code for a processor running in little-endian mode. This is
8566 the default for all standard configurations.
8569 @opindex mbig-endian
8570 Generate code for a processor running in big-endian mode; the default is
8571 to compile code for a little-endian processor.
8573 @item -mwords-little-endian
8574 @opindex mwords-little-endian
8575 This option only applies when generating code for big-endian processors.
8576 Generate code for a little-endian word order but a big-endian byte
8577 order. That is, a byte order of the form @samp{32107654}. Note: this
8578 option should only be used if you require compatibility with code for
8579 big-endian ARM processors generated by versions of the compiler prior to
8582 @item -mcpu=@var{name}
8584 This specifies the name of the target ARM processor. GCC uses this name
8585 to determine what kind of instructions it can emit when generating
8586 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
8587 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
8588 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
8589 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
8590 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
8591 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
8592 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
8593 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
8594 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
8595 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
8596 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
8597 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
8598 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
8599 @samp{arm1156t2-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
8600 @samp{cortex-a8}, @samp{cortex-r4}, @samp{cortex-m3}, @samp{cortex-m1},
8601 @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
8603 @item -mtune=@var{name}
8605 This option is very similar to the @option{-mcpu=} option, except that
8606 instead of specifying the actual target processor type, and hence
8607 restricting which instructions can be used, it specifies that GCC should
8608 tune the performance of the code as if the target were of the type
8609 specified in this option, but still choosing the instructions that it
8610 will generate based on the cpu specified by a @option{-mcpu=} option.
8611 For some ARM implementations better performance can be obtained by using
8614 @item -march=@var{name}
8616 This specifies the name of the target ARM architecture. GCC uses this
8617 name to determine what kind of instructions it can emit when generating
8618 assembly code. This option can be used in conjunction with or instead
8619 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
8620 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
8621 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
8622 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
8623 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
8624 @samp{iwmmxt}, @samp{ep9312}.
8626 @item -mfpu=@var{name}
8627 @itemx -mfpe=@var{number}
8628 @itemx -mfp=@var{number}
8632 This specifies what floating point hardware (or hardware emulation) is
8633 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
8634 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
8635 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
8636 with older versions of GCC@.
8638 If @option{-msoft-float} is specified this specifies the format of
8639 floating point values.
8641 @item -mstructure-size-boundary=@var{n}
8642 @opindex mstructure-size-boundary
8643 The size of all structures and unions will be rounded up to a multiple
8644 of the number of bits set by this option. Permissible values are 8, 32
8645 and 64. The default value varies for different toolchains. For the COFF
8646 targeted toolchain the default value is 8. A value of 64 is only allowed
8647 if the underlying ABI supports it.
8649 Specifying the larger number can produce faster, more efficient code, but
8650 can also increase the size of the program. Different values are potentially
8651 incompatible. Code compiled with one value cannot necessarily expect to
8652 work with code or libraries compiled with another value, if they exchange
8653 information using structures or unions.
8655 @item -mabort-on-noreturn
8656 @opindex mabort-on-noreturn
8657 Generate a call to the function @code{abort} at the end of a
8658 @code{noreturn} function. It will be executed if the function tries to
8662 @itemx -mno-long-calls
8663 @opindex mlong-calls
8664 @opindex mno-long-calls
8665 Tells the compiler to perform function calls by first loading the
8666 address of the function into a register and then performing a subroutine
8667 call on this register. This switch is needed if the target function
8668 will lie outside of the 64 megabyte addressing range of the offset based
8669 version of subroutine call instruction.
8671 Even if this switch is enabled, not all function calls will be turned
8672 into long calls. The heuristic is that static functions, functions
8673 which have the @samp{short-call} attribute, functions that are inside
8674 the scope of a @samp{#pragma no_long_calls} directive and functions whose
8675 definitions have already been compiled within the current compilation
8676 unit, will not be turned into long calls. The exception to this rule is
8677 that weak function definitions, functions with the @samp{long-call}
8678 attribute or the @samp{section} attribute, and functions that are within
8679 the scope of a @samp{#pragma long_calls} directive, will always be
8680 turned into long calls.
8682 This feature is not enabled by default. Specifying
8683 @option{-mno-long-calls} will restore the default behavior, as will
8684 placing the function calls within the scope of a @samp{#pragma
8685 long_calls_off} directive. Note these switches have no effect on how
8686 the compiler generates code to handle function calls via function
8689 @item -mnop-fun-dllimport
8690 @opindex mnop-fun-dllimport
8691 Disable support for the @code{dllimport} attribute.
8693 @item -msingle-pic-base
8694 @opindex msingle-pic-base
8695 Treat the register used for PIC addressing as read-only, rather than
8696 loading it in the prologue for each function. The run-time system is
8697 responsible for initializing this register with an appropriate value
8698 before execution begins.
8700 @item -mpic-register=@var{reg}
8701 @opindex mpic-register
8702 Specify the register to be used for PIC addressing. The default is R10
8703 unless stack-checking is enabled, when R9 is used.
8705 @item -mcirrus-fix-invalid-insns
8706 @opindex mcirrus-fix-invalid-insns
8707 @opindex mno-cirrus-fix-invalid-insns
8708 Insert NOPs into the instruction stream to in order to work around
8709 problems with invalid Maverick instruction combinations. This option
8710 is only valid if the @option{-mcpu=ep9312} option has been used to
8711 enable generation of instructions for the Cirrus Maverick floating
8712 point co-processor. This option is not enabled by default, since the
8713 problem is only present in older Maverick implementations. The default
8714 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
8717 @item -mpoke-function-name
8718 @opindex mpoke-function-name
8719 Write the name of each function into the text section, directly
8720 preceding the function prologue. The generated code is similar to this:
8724 .ascii "arm_poke_function_name", 0
8727 .word 0xff000000 + (t1 - t0)
8728 arm_poke_function_name
8730 stmfd sp!, @{fp, ip, lr, pc@}
8734 When performing a stack backtrace, code can inspect the value of
8735 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
8736 location @code{pc - 12} and the top 8 bits are set, then we know that
8737 there is a function name embedded immediately preceding this location
8738 and has length @code{((pc[-3]) & 0xff000000)}.
8742 Generate code for the Thumb instruction set. The default is to
8743 use the 32-bit ARM instruction set.
8744 This option automatically enables either 16-bit Thumb-1 or
8745 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
8746 and @option{-march=@var{name}} options.
8749 @opindex mtpcs-frame
8750 Generate a stack frame that is compliant with the Thumb Procedure Call
8751 Standard for all non-leaf functions. (A leaf function is one that does
8752 not call any other functions.) The default is @option{-mno-tpcs-frame}.
8754 @item -mtpcs-leaf-frame
8755 @opindex mtpcs-leaf-frame
8756 Generate a stack frame that is compliant with the Thumb Procedure Call
8757 Standard for all leaf functions. (A leaf function is one that does
8758 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
8760 @item -mcallee-super-interworking
8761 @opindex mcallee-super-interworking
8762 Gives all externally visible functions in the file being compiled an ARM
8763 instruction set header which switches to Thumb mode before executing the
8764 rest of the function. This allows these functions to be called from
8765 non-interworking code.
8767 @item -mcaller-super-interworking
8768 @opindex mcaller-super-interworking
8769 Allows calls via function pointers (including virtual functions) to
8770 execute correctly regardless of whether the target code has been
8771 compiled for interworking or not. There is a small overhead in the cost
8772 of executing a function pointer if this option is enabled.
8774 @item -mtp=@var{name}
8776 Specify the access model for the thread local storage pointer. The valid
8777 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
8778 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
8779 (supported in the arm6k architecture), and @option{auto}, which uses the
8780 best available method for the selected processor. The default setting is
8786 @subsection AVR Options
8789 These options are defined for AVR implementations:
8792 @item -mmcu=@var{mcu}
8794 Specify ATMEL AVR instruction set or MCU type.
8796 Instruction set avr1 is for the minimal AVR core, not supported by the C
8797 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
8798 attiny11, attiny12, attiny15, attiny28).
8800 Instruction set avr2 (default) is for the classic AVR core with up to
8801 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
8802 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
8803 at90c8534, at90s8535).
8805 Instruction set avr3 is for the classic AVR core with up to 128K program
8806 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
8808 Instruction set avr4 is for the enhanced AVR core with up to 8K program
8809 memory space (MCU types: atmega8, atmega83, atmega85).
8811 Instruction set avr5 is for the enhanced AVR core with up to 128K program
8812 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
8813 atmega64, atmega128, at43usb355, at94k).
8817 Output instruction sizes to the asm file.
8819 @item -minit-stack=@var{N}
8820 @opindex minit-stack
8821 Specify the initial stack address, which may be a symbol or numeric value,
8822 @samp{__stack} is the default.
8824 @item -mno-interrupts
8825 @opindex mno-interrupts
8826 Generated code is not compatible with hardware interrupts.
8827 Code size will be smaller.
8829 @item -mcall-prologues
8830 @opindex mcall-prologues
8831 Functions prologues/epilogues expanded as call to appropriate
8832 subroutines. Code size will be smaller.
8834 @item -mno-tablejump
8835 @opindex mno-tablejump
8836 Do not generate tablejump insns which sometimes increase code size.
8839 @opindex mtiny-stack
8840 Change only the low 8 bits of the stack pointer.
8844 Assume int to be 8 bit integer. This affects the sizes of all types: A
8845 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
8846 and long long will be 4 bytes. Please note that this option does not
8847 comply to the C standards, but it will provide you with smaller code
8851 @node Blackfin Options
8852 @subsection Blackfin Options
8853 @cindex Blackfin Options
8856 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
8858 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
8859 can be one of @samp{bf522}, @samp{bf523}, @samp{bf524},
8860 @samp{bf525}, @samp{bf526}, @samp{bf527},
8861 @samp{bf531}, @samp{bf532}, @samp{bf533}, @samp{bf534},
8862 @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
8863 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
8865 The optional @var{sirevision} specifies the silicon revision of the target
8866 Blackfin processor. Any workarounds available for the targeted silicon revision
8867 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
8868 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
8869 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
8870 hexadecimal digits representing the major and minor numbers in the silicon
8871 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
8872 is not defined. If @var{sirevision} is @samp{any}, the
8873 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
8874 If this optional @var{sirevision} is not used, GCC assumes the latest known
8875 silicon revision of the targeted Blackfin processor.
8877 Support for @samp{bf561} is incomplete. For @samp{bf561},
8878 Only the processor macro is defined.
8879 Without this option, @samp{bf532} is used as the processor by default.
8880 The corresponding predefined processor macros for @var{cpu} is to
8881 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
8882 provided by libgloss to be linked in if @option{-msim} is not given.
8886 Specifies that the program will be run on the simulator. This causes
8887 the simulator BSP provided by libgloss to be linked in. This option
8888 has effect only for @samp{bfin-elf} toolchain.
8889 Certain other options, such as @option{-mid-shared-library} and
8890 @option{-mfdpic}, imply @option{-msim}.
8892 @item -momit-leaf-frame-pointer
8893 @opindex momit-leaf-frame-pointer
8894 Don't keep the frame pointer in a register for leaf functions. This
8895 avoids the instructions to save, set up and restore frame pointers and
8896 makes an extra register available in leaf functions. The option
8897 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8898 which might make debugging harder.
8900 @item -mspecld-anomaly
8901 @opindex mspecld-anomaly
8902 When enabled, the compiler will ensure that the generated code does not
8903 contain speculative loads after jump instructions. If this option is used,
8904 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
8906 @item -mno-specld-anomaly
8907 @opindex mno-specld-anomaly
8908 Don't generate extra code to prevent speculative loads from occurring.
8910 @item -mcsync-anomaly
8911 @opindex mcsync-anomaly
8912 When enabled, the compiler will ensure that the generated code does not
8913 contain CSYNC or SSYNC instructions too soon after conditional branches.
8914 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
8916 @item -mno-csync-anomaly
8917 @opindex mno-csync-anomaly
8918 Don't generate extra code to prevent CSYNC or SSYNC instructions from
8919 occurring too soon after a conditional branch.
8923 When enabled, the compiler is free to take advantage of the knowledge that
8924 the entire program fits into the low 64k of memory.
8927 @opindex mno-low-64k
8928 Assume that the program is arbitrarily large. This is the default.
8930 @item -mstack-check-l1
8931 @opindex mstack-check-l1
8932 Do stack checking using information placed into L1 scratchpad memory by the
8935 @item -mid-shared-library
8936 @opindex mid-shared-library
8937 Generate code that supports shared libraries via the library ID method.
8938 This allows for execute in place and shared libraries in an environment
8939 without virtual memory management. This option implies @option{-fPIC}.
8940 With a @samp{bfin-elf} target, this option implies @option{-msim}.
8942 @item -mno-id-shared-library
8943 @opindex mno-id-shared-library
8944 Generate code that doesn't assume ID based shared libraries are being used.
8945 This is the default.
8947 @item -mleaf-id-shared-library
8948 @opindex mleaf-id-shared-library
8949 Generate code that supports shared libraries via the library ID method,
8950 but assumes that this library or executable won't link against any other
8951 ID shared libraries. That allows the compiler to use faster code for jumps
8954 @item -mno-leaf-id-shared-library
8955 @opindex mno-leaf-id-shared-library
8956 Do not assume that the code being compiled won't link against any ID shared
8957 libraries. Slower code will be generated for jump and call insns.
8959 @item -mshared-library-id=n
8960 @opindex mshared-library-id
8961 Specified the identification number of the ID based shared library being
8962 compiled. Specifying a value of 0 will generate more compact code, specifying
8963 other values will force the allocation of that number to the current
8964 library but is no more space or time efficient than omitting this option.
8968 Generate code that allows the data segment to be located in a different
8969 area of memory from the text segment. This allows for execute in place in
8970 an environment without virtual memory management by eliminating relocations
8971 against the text section.
8974 @opindex mno-sep-data
8975 Generate code that assumes that the data segment follows the text segment.
8976 This is the default.
8979 @itemx -mno-long-calls
8980 @opindex mlong-calls
8981 @opindex mno-long-calls
8982 Tells the compiler to perform function calls by first loading the
8983 address of the function into a register and then performing a subroutine
8984 call on this register. This switch is needed if the target function
8985 will lie outside of the 24 bit addressing range of the offset based
8986 version of subroutine call instruction.
8988 This feature is not enabled by default. Specifying
8989 @option{-mno-long-calls} will restore the default behavior. Note these
8990 switches have no effect on how the compiler generates code to handle
8991 function calls via function pointers.
8995 Link with the fast floating-point library. This library relaxes some of
8996 the IEEE floating-point standard's rules for checking inputs against
8997 Not-a-Number (NAN), in the interest of performance.
9000 @opindex minline-plt
9001 Enable inlining of PLT entries in function calls to functions that are
9002 not known to bind locally. It has no effect without @option{-mfdpic}.
9006 Build standalone application for multicore Blackfin processor. Proper
9007 start files and link scripts will be used to support multicore.
9008 This option defines @code{__BFIN_MULTICORE}. It can only be used with
9009 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
9010 @option{-mcorea} or @option{-mcoreb}. If it's used without
9011 @option{-mcorea} or @option{-mcoreb}, single application/dual core
9012 programming model is used. In this model, the main function of Core B
9013 should be named as coreb_main. If it's used with @option{-mcorea} or
9014 @option{-mcoreb}, one application per core programming model is used.
9015 If this option is not used, single core application programming
9020 Build standalone application for Core A of BF561 when using
9021 one application per core programming model. Proper start files
9022 and link scripts will be used to support Core A. This option
9023 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
9027 Build standalone application for Core B of BF561 when using
9028 one application per core programming model. Proper start files
9029 and link scripts will be used to support Core B. This option
9030 defines @code{__BFIN_COREB}. When this option is used, coreb_main
9031 should be used instead of main. It must be used with
9032 @option{-mmulticore}.
9036 Build standalone application for SDRAM. Proper start files and
9037 link scripts will be used to put the application into SDRAM.
9038 Loader should initialize SDRAM before loading the application
9039 into SDRAM. This option defines @code{__BFIN_SDRAM}.
9043 @subsection CRIS Options
9044 @cindex CRIS Options
9046 These options are defined specifically for the CRIS ports.
9049 @item -march=@var{architecture-type}
9050 @itemx -mcpu=@var{architecture-type}
9053 Generate code for the specified architecture. The choices for
9054 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9055 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
9056 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9059 @item -mtune=@var{architecture-type}
9061 Tune to @var{architecture-type} everything applicable about the generated
9062 code, except for the ABI and the set of available instructions. The
9063 choices for @var{architecture-type} are the same as for
9064 @option{-march=@var{architecture-type}}.
9066 @item -mmax-stack-frame=@var{n}
9067 @opindex mmax-stack-frame
9068 Warn when the stack frame of a function exceeds @var{n} bytes.
9074 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9075 @option{-march=v3} and @option{-march=v8} respectively.
9077 @item -mmul-bug-workaround
9078 @itemx -mno-mul-bug-workaround
9079 @opindex mmul-bug-workaround
9080 @opindex mno-mul-bug-workaround
9081 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
9082 models where it applies. This option is active by default.
9086 Enable CRIS-specific verbose debug-related information in the assembly
9087 code. This option also has the effect to turn off the @samp{#NO_APP}
9088 formatted-code indicator to the assembler at the beginning of the
9093 Do not use condition-code results from previous instruction; always emit
9094 compare and test instructions before use of condition codes.
9096 @item -mno-side-effects
9097 @opindex mno-side-effects
9098 Do not emit instructions with side-effects in addressing modes other than
9102 @itemx -mno-stack-align
9104 @itemx -mno-data-align
9105 @itemx -mconst-align
9106 @itemx -mno-const-align
9107 @opindex mstack-align
9108 @opindex mno-stack-align
9109 @opindex mdata-align
9110 @opindex mno-data-align
9111 @opindex mconst-align
9112 @opindex mno-const-align
9113 These options (no-options) arranges (eliminate arrangements) for the
9114 stack-frame, individual data and constants to be aligned for the maximum
9115 single data access size for the chosen CPU model. The default is to
9116 arrange for 32-bit alignment. ABI details such as structure layout are
9117 not affected by these options.
9125 Similar to the stack- data- and const-align options above, these options
9126 arrange for stack-frame, writable data and constants to all be 32-bit,
9127 16-bit or 8-bit aligned. The default is 32-bit alignment.
9129 @item -mno-prologue-epilogue
9130 @itemx -mprologue-epilogue
9131 @opindex mno-prologue-epilogue
9132 @opindex mprologue-epilogue
9133 With @option{-mno-prologue-epilogue}, the normal function prologue and
9134 epilogue that sets up the stack-frame are omitted and no return
9135 instructions or return sequences are generated in the code. Use this
9136 option only together with visual inspection of the compiled code: no
9137 warnings or errors are generated when call-saved registers must be saved,
9138 or storage for local variable needs to be allocated.
9144 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9145 instruction sequences that load addresses for functions from the PLT part
9146 of the GOT rather than (traditional on other architectures) calls to the
9147 PLT@. The default is @option{-mgotplt}.
9151 Legacy no-op option only recognized with the cris-axis-elf and
9152 cris-axis-linux-gnu targets.
9156 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9160 This option, recognized for the cris-axis-elf arranges
9161 to link with input-output functions from a simulator library. Code,
9162 initialized data and zero-initialized data are allocated consecutively.
9166 Like @option{-sim}, but pass linker options to locate initialized data at
9167 0x40000000 and zero-initialized data at 0x80000000.
9171 @subsection CRX Options
9174 These options are defined specifically for the CRX ports.
9180 Enable the use of multiply-accumulate instructions. Disabled by default.
9184 Push instructions will be used to pass outgoing arguments when functions
9185 are called. Enabled by default.
9188 @node Darwin Options
9189 @subsection Darwin Options
9190 @cindex Darwin options
9192 These options are defined for all architectures running the Darwin operating
9195 FSF GCC on Darwin does not create ``fat'' object files; it will create
9196 an object file for the single architecture that it was built to
9197 target. Apple's GCC on Darwin does create ``fat'' files if multiple
9198 @option{-arch} options are used; it does so by running the compiler or
9199 linker multiple times and joining the results together with
9202 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
9203 @samp{i686}) is determined by the flags that specify the ISA
9204 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
9205 @option{-force_cpusubtype_ALL} option can be used to override this.
9207 The Darwin tools vary in their behavior when presented with an ISA
9208 mismatch. The assembler, @file{as}, will only permit instructions to
9209 be used that are valid for the subtype of the file it is generating,
9210 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
9211 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
9212 and print an error if asked to create a shared library with a less
9213 restrictive subtype than its input files (for instance, trying to put
9214 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
9215 for executables, @file{ld}, will quietly give the executable the most
9216 restrictive subtype of any of its input files.
9221 Add the framework directory @var{dir} to the head of the list of
9222 directories to be searched for header files. These directories are
9223 interleaved with those specified by @option{-I} options and are
9224 scanned in a left-to-right order.
9226 A framework directory is a directory with frameworks in it. A
9227 framework is a directory with a @samp{"Headers"} and/or
9228 @samp{"PrivateHeaders"} directory contained directly in it that ends
9229 in @samp{".framework"}. The name of a framework is the name of this
9230 directory excluding the @samp{".framework"}. Headers associated with
9231 the framework are found in one of those two directories, with
9232 @samp{"Headers"} being searched first. A subframework is a framework
9233 directory that is in a framework's @samp{"Frameworks"} directory.
9234 Includes of subframework headers can only appear in a header of a
9235 framework that contains the subframework, or in a sibling subframework
9236 header. Two subframeworks are siblings if they occur in the same
9237 framework. A subframework should not have the same name as a
9238 framework, a warning will be issued if this is violated. Currently a
9239 subframework cannot have subframeworks, in the future, the mechanism
9240 may be extended to support this. The standard frameworks can be found
9241 in @samp{"/System/Library/Frameworks"} and
9242 @samp{"/Library/Frameworks"}. An example include looks like
9243 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
9244 the name of the framework and header.h is found in the
9245 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
9247 @item -iframework@var{dir}
9249 Like @option{-F} except the directory is a treated as a system
9250 directory. The main difference between this @option{-iframework} and
9251 @option{-F} is that with @option{-iframework} the compiler does not
9252 warn about constructs contained within header files found via
9253 @var{dir}. This option is valid only for the C family of languages.
9257 Emit debugging information for symbols that are used. For STABS
9258 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
9259 This is by default ON@.
9263 Emit debugging information for all symbols and types.
9265 @item -mmacosx-version-min=@var{version}
9266 The earliest version of MacOS X that this executable will run on
9267 is @var{version}. Typical values of @var{version} include @code{10.1},
9268 @code{10.2}, and @code{10.3.9}.
9270 If the compiler was built to use the system's headers by default,
9271 then the default for this option is the system version on which the
9272 compiler is running, otherwise the default is to make choices which
9273 are compatible with as many systems and code bases as possible.
9277 Enable kernel development mode. The @option{-mkernel} option sets
9278 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
9279 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
9280 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
9281 applicable. This mode also sets @option{-mno-altivec},
9282 @option{-msoft-float}, @option{-fno-builtin} and
9283 @option{-mlong-branch} for PowerPC targets.
9285 @item -mone-byte-bool
9286 @opindex mone-byte-bool
9287 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
9288 By default @samp{sizeof(bool)} is @samp{4} when compiling for
9289 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
9290 option has no effect on x86.
9292 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
9293 to generate code that is not binary compatible with code generated
9294 without that switch. Using this switch may require recompiling all
9295 other modules in a program, including system libraries. Use this
9296 switch to conform to a non-default data model.
9298 @item -mfix-and-continue
9299 @itemx -ffix-and-continue
9300 @itemx -findirect-data
9301 @opindex mfix-and-continue
9302 @opindex ffix-and-continue
9303 @opindex findirect-data
9304 Generate code suitable for fast turn around development. Needed to
9305 enable gdb to dynamically load @code{.o} files into already running
9306 programs. @option{-findirect-data} and @option{-ffix-and-continue}
9307 are provided for backwards compatibility.
9311 Loads all members of static archive libraries.
9312 See man ld(1) for more information.
9314 @item -arch_errors_fatal
9315 @opindex arch_errors_fatal
9316 Cause the errors having to do with files that have the wrong architecture
9320 @opindex bind_at_load
9321 Causes the output file to be marked such that the dynamic linker will
9322 bind all undefined references when the file is loaded or launched.
9326 Produce a Mach-o bundle format file.
9327 See man ld(1) for more information.
9329 @item -bundle_loader @var{executable}
9330 @opindex bundle_loader
9331 This option specifies the @var{executable} that will be loading the build
9332 output file being linked. See man ld(1) for more information.
9336 When passed this option, GCC will produce a dynamic library instead of
9337 an executable when linking, using the Darwin @file{libtool} command.
9339 @item -force_cpusubtype_ALL
9340 @opindex force_cpusubtype_ALL
9341 This causes GCC's output file to have the @var{ALL} subtype, instead of
9342 one controlled by the @option{-mcpu} or @option{-march} option.
9344 @item -allowable_client @var{client_name}
9346 @itemx -compatibility_version
9347 @itemx -current_version
9349 @itemx -dependency-file
9351 @itemx -dylinker_install_name
9353 @itemx -exported_symbols_list
9355 @itemx -flat_namespace
9356 @itemx -force_flat_namespace
9357 @itemx -headerpad_max_install_names
9360 @itemx -install_name
9361 @itemx -keep_private_externs
9362 @itemx -multi_module
9363 @itemx -multiply_defined
9364 @itemx -multiply_defined_unused
9366 @itemx -no_dead_strip_inits_and_terms
9367 @itemx -nofixprebinding
9370 @itemx -noseglinkedit
9371 @itemx -pagezero_size
9373 @itemx -prebind_all_twolevel_modules
9374 @itemx -private_bundle
9375 @itemx -read_only_relocs
9377 @itemx -sectobjectsymbols
9381 @itemx -sectobjectsymbols
9384 @itemx -segs_read_only_addr
9385 @itemx -segs_read_write_addr
9386 @itemx -seg_addr_table
9387 @itemx -seg_addr_table_filename
9390 @itemx -segs_read_only_addr
9391 @itemx -segs_read_write_addr
9392 @itemx -single_module
9395 @itemx -sub_umbrella
9396 @itemx -twolevel_namespace
9399 @itemx -unexported_symbols_list
9400 @itemx -weak_reference_mismatches
9402 @opindex allowable_client
9403 @opindex client_name
9404 @opindex compatibility_version
9405 @opindex current_version
9407 @opindex dependency-file
9409 @opindex dylinker_install_name
9411 @opindex exported_symbols_list
9413 @opindex flat_namespace
9414 @opindex force_flat_namespace
9415 @opindex headerpad_max_install_names
9418 @opindex install_name
9419 @opindex keep_private_externs
9420 @opindex multi_module
9421 @opindex multiply_defined
9422 @opindex multiply_defined_unused
9424 @opindex no_dead_strip_inits_and_terms
9425 @opindex nofixprebinding
9426 @opindex nomultidefs
9428 @opindex noseglinkedit
9429 @opindex pagezero_size
9431 @opindex prebind_all_twolevel_modules
9432 @opindex private_bundle
9433 @opindex read_only_relocs
9435 @opindex sectobjectsymbols
9439 @opindex sectobjectsymbols
9442 @opindex segs_read_only_addr
9443 @opindex segs_read_write_addr
9444 @opindex seg_addr_table
9445 @opindex seg_addr_table_filename
9446 @opindex seglinkedit
9448 @opindex segs_read_only_addr
9449 @opindex segs_read_write_addr
9450 @opindex single_module
9452 @opindex sub_library
9453 @opindex sub_umbrella
9454 @opindex twolevel_namespace
9457 @opindex unexported_symbols_list
9458 @opindex weak_reference_mismatches
9459 @opindex whatsloaded
9460 These options are passed to the Darwin linker. The Darwin linker man page
9461 describes them in detail.
9464 @node DEC Alpha Options
9465 @subsection DEC Alpha Options
9467 These @samp{-m} options are defined for the DEC Alpha implementations:
9470 @item -mno-soft-float
9472 @opindex mno-soft-float
9473 @opindex msoft-float
9474 Use (do not use) the hardware floating-point instructions for
9475 floating-point operations. When @option{-msoft-float} is specified,
9476 functions in @file{libgcc.a} will be used to perform floating-point
9477 operations. Unless they are replaced by routines that emulate the
9478 floating-point operations, or compiled in such a way as to call such
9479 emulations routines, these routines will issue floating-point
9480 operations. If you are compiling for an Alpha without floating-point
9481 operations, you must ensure that the library is built so as not to call
9484 Note that Alpha implementations without floating-point operations are
9485 required to have floating-point registers.
9490 @opindex mno-fp-regs
9491 Generate code that uses (does not use) the floating-point register set.
9492 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9493 register set is not used, floating point operands are passed in integer
9494 registers as if they were integers and floating-point results are passed
9495 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9496 so any function with a floating-point argument or return value called by code
9497 compiled with @option{-mno-fp-regs} must also be compiled with that
9500 A typical use of this option is building a kernel that does not use,
9501 and hence need not save and restore, any floating-point registers.
9505 The Alpha architecture implements floating-point hardware optimized for
9506 maximum performance. It is mostly compliant with the IEEE floating
9507 point standard. However, for full compliance, software assistance is
9508 required. This option generates code fully IEEE compliant code
9509 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9510 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9511 defined during compilation. The resulting code is less efficient but is
9512 able to correctly support denormalized numbers and exceptional IEEE
9513 values such as not-a-number and plus/minus infinity. Other Alpha
9514 compilers call this option @option{-ieee_with_no_inexact}.
9516 @item -mieee-with-inexact
9517 @opindex mieee-with-inexact
9518 This is like @option{-mieee} except the generated code also maintains
9519 the IEEE @var{inexact-flag}. Turning on this option causes the
9520 generated code to implement fully-compliant IEEE math. In addition to
9521 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9522 macro. On some Alpha implementations the resulting code may execute
9523 significantly slower than the code generated by default. Since there is
9524 very little code that depends on the @var{inexact-flag}, you should
9525 normally not specify this option. Other Alpha compilers call this
9526 option @option{-ieee_with_inexact}.
9528 @item -mfp-trap-mode=@var{trap-mode}
9529 @opindex mfp-trap-mode
9530 This option controls what floating-point related traps are enabled.
9531 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9532 The trap mode can be set to one of four values:
9536 This is the default (normal) setting. The only traps that are enabled
9537 are the ones that cannot be disabled in software (e.g., division by zero
9541 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9545 Like @samp{u}, but the instructions are marked to be safe for software
9546 completion (see Alpha architecture manual for details).
9549 Like @samp{su}, but inexact traps are enabled as well.
9552 @item -mfp-rounding-mode=@var{rounding-mode}
9553 @opindex mfp-rounding-mode
9554 Selects the IEEE rounding mode. Other Alpha compilers call this option
9555 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9560 Normal IEEE rounding mode. Floating point numbers are rounded towards
9561 the nearest machine number or towards the even machine number in case
9565 Round towards minus infinity.
9568 Chopped rounding mode. Floating point numbers are rounded towards zero.
9571 Dynamic rounding mode. A field in the floating point control register
9572 (@var{fpcr}, see Alpha architecture reference manual) controls the
9573 rounding mode in effect. The C library initializes this register for
9574 rounding towards plus infinity. Thus, unless your program modifies the
9575 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9578 @item -mtrap-precision=@var{trap-precision}
9579 @opindex mtrap-precision
9580 In the Alpha architecture, floating point traps are imprecise. This
9581 means without software assistance it is impossible to recover from a
9582 floating trap and program execution normally needs to be terminated.
9583 GCC can generate code that can assist operating system trap handlers
9584 in determining the exact location that caused a floating point trap.
9585 Depending on the requirements of an application, different levels of
9586 precisions can be selected:
9590 Program precision. This option is the default and means a trap handler
9591 can only identify which program caused a floating point exception.
9594 Function precision. The trap handler can determine the function that
9595 caused a floating point exception.
9598 Instruction precision. The trap handler can determine the exact
9599 instruction that caused a floating point exception.
9602 Other Alpha compilers provide the equivalent options called
9603 @option{-scope_safe} and @option{-resumption_safe}.
9605 @item -mieee-conformant
9606 @opindex mieee-conformant
9607 This option marks the generated code as IEEE conformant. You must not
9608 use this option unless you also specify @option{-mtrap-precision=i} and either
9609 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9610 is to emit the line @samp{.eflag 48} in the function prologue of the
9611 generated assembly file. Under DEC Unix, this has the effect that
9612 IEEE-conformant math library routines will be linked in.
9614 @item -mbuild-constants
9615 @opindex mbuild-constants
9616 Normally GCC examines a 32- or 64-bit integer constant to
9617 see if it can construct it from smaller constants in two or three
9618 instructions. If it cannot, it will output the constant as a literal and
9619 generate code to load it from the data segment at runtime.
9621 Use this option to require GCC to construct @emph{all} integer constants
9622 using code, even if it takes more instructions (the maximum is six).
9624 You would typically use this option to build a shared library dynamic
9625 loader. Itself a shared library, it must relocate itself in memory
9626 before it can find the variables and constants in its own data segment.
9632 Select whether to generate code to be assembled by the vendor-supplied
9633 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9651 Indicate whether GCC should generate code to use the optional BWX,
9652 CIX, FIX and MAX instruction sets. The default is to use the instruction
9653 sets supported by the CPU type specified via @option{-mcpu=} option or that
9654 of the CPU on which GCC was built if none was specified.
9659 @opindex mfloat-ieee
9660 Generate code that uses (does not use) VAX F and G floating point
9661 arithmetic instead of IEEE single and double precision.
9663 @item -mexplicit-relocs
9664 @itemx -mno-explicit-relocs
9665 @opindex mexplicit-relocs
9666 @opindex mno-explicit-relocs
9667 Older Alpha assemblers provided no way to generate symbol relocations
9668 except via assembler macros. Use of these macros does not allow
9669 optimal instruction scheduling. GNU binutils as of version 2.12
9670 supports a new syntax that allows the compiler to explicitly mark
9671 which relocations should apply to which instructions. This option
9672 is mostly useful for debugging, as GCC detects the capabilities of
9673 the assembler when it is built and sets the default accordingly.
9677 @opindex msmall-data
9678 @opindex mlarge-data
9679 When @option{-mexplicit-relocs} is in effect, static data is
9680 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9681 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9682 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9683 16-bit relocations off of the @code{$gp} register. This limits the
9684 size of the small data area to 64KB, but allows the variables to be
9685 directly accessed via a single instruction.
9687 The default is @option{-mlarge-data}. With this option the data area
9688 is limited to just below 2GB@. Programs that require more than 2GB of
9689 data must use @code{malloc} or @code{mmap} to allocate the data in the
9690 heap instead of in the program's data segment.
9692 When generating code for shared libraries, @option{-fpic} implies
9693 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9697 @opindex msmall-text
9698 @opindex mlarge-text
9699 When @option{-msmall-text} is used, the compiler assumes that the
9700 code of the entire program (or shared library) fits in 4MB, and is
9701 thus reachable with a branch instruction. When @option{-msmall-data}
9702 is used, the compiler can assume that all local symbols share the
9703 same @code{$gp} value, and thus reduce the number of instructions
9704 required for a function call from 4 to 1.
9706 The default is @option{-mlarge-text}.
9708 @item -mcpu=@var{cpu_type}
9710 Set the instruction set and instruction scheduling parameters for
9711 machine type @var{cpu_type}. You can specify either the @samp{EV}
9712 style name or the corresponding chip number. GCC supports scheduling
9713 parameters for the EV4, EV5 and EV6 family of processors and will
9714 choose the default values for the instruction set from the processor
9715 you specify. If you do not specify a processor type, GCC will default
9716 to the processor on which the compiler was built.
9718 Supported values for @var{cpu_type} are
9724 Schedules as an EV4 and has no instruction set extensions.
9728 Schedules as an EV5 and has no instruction set extensions.
9732 Schedules as an EV5 and supports the BWX extension.
9737 Schedules as an EV5 and supports the BWX and MAX extensions.
9741 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9745 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9748 @item -mtune=@var{cpu_type}
9750 Set only the instruction scheduling parameters for machine type
9751 @var{cpu_type}. The instruction set is not changed.
9753 @item -mmemory-latency=@var{time}
9754 @opindex mmemory-latency
9755 Sets the latency the scheduler should assume for typical memory
9756 references as seen by the application. This number is highly
9757 dependent on the memory access patterns used by the application
9758 and the size of the external cache on the machine.
9760 Valid options for @var{time} are
9764 A decimal number representing clock cycles.
9770 The compiler contains estimates of the number of clock cycles for
9771 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9772 (also called Dcache, Scache, and Bcache), as well as to main memory.
9773 Note that L3 is only valid for EV5.
9778 @node DEC Alpha/VMS Options
9779 @subsection DEC Alpha/VMS Options
9781 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9784 @item -mvms-return-codes
9785 @opindex mvms-return-codes
9786 Return VMS condition codes from main. The default is to return POSIX
9787 style condition (e.g.@: error) codes.
9791 @subsection FRV Options
9798 Only use the first 32 general purpose registers.
9803 Use all 64 general purpose registers.
9808 Use only the first 32 floating point registers.
9813 Use all 64 floating point registers
9816 @opindex mhard-float
9818 Use hardware instructions for floating point operations.
9821 @opindex msoft-float
9823 Use library routines for floating point operations.
9828 Dynamically allocate condition code registers.
9833 Do not try to dynamically allocate condition code registers, only
9834 use @code{icc0} and @code{fcc0}.
9839 Change ABI to use double word insns.
9844 Do not use double word instructions.
9849 Use floating point double instructions.
9854 Do not use floating point double instructions.
9859 Use media instructions.
9864 Do not use media instructions.
9869 Use multiply and add/subtract instructions.
9874 Do not use multiply and add/subtract instructions.
9879 Select the FDPIC ABI, that uses function descriptors to represent
9880 pointers to functions. Without any PIC/PIE-related options, it
9881 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
9882 assumes GOT entries and small data are within a 12-bit range from the
9883 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
9884 are computed with 32 bits.
9885 With a @samp{bfin-elf} target, this option implies @option{-msim}.
9888 @opindex minline-plt
9890 Enable inlining of PLT entries in function calls to functions that are
9891 not known to bind locally. It has no effect without @option{-mfdpic}.
9892 It's enabled by default if optimizing for speed and compiling for
9893 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
9894 optimization option such as @option{-O3} or above is present in the
9900 Assume a large TLS segment when generating thread-local code.
9905 Do not assume a large TLS segment when generating thread-local code.
9910 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
9911 that is known to be in read-only sections. It's enabled by default,
9912 except for @option{-fpic} or @option{-fpie}: even though it may help
9913 make the global offset table smaller, it trades 1 instruction for 4.
9914 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
9915 one of which may be shared by multiple symbols, and it avoids the need
9916 for a GOT entry for the referenced symbol, so it's more likely to be a
9917 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
9919 @item -multilib-library-pic
9920 @opindex multilib-library-pic
9922 Link with the (library, not FD) pic libraries. It's implied by
9923 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
9924 @option{-fpic} without @option{-mfdpic}. You should never have to use
9930 Follow the EABI requirement of always creating a frame pointer whenever
9931 a stack frame is allocated. This option is enabled by default and can
9932 be disabled with @option{-mno-linked-fp}.
9935 @opindex mlong-calls
9937 Use indirect addressing to call functions outside the current
9938 compilation unit. This allows the functions to be placed anywhere
9939 within the 32-bit address space.
9941 @item -malign-labels
9942 @opindex malign-labels
9944 Try to align labels to an 8-byte boundary by inserting nops into the
9945 previous packet. This option only has an effect when VLIW packing
9946 is enabled. It doesn't create new packets; it merely adds nops to
9950 @opindex mlibrary-pic
9952 Generate position-independent EABI code.
9957 Use only the first four media accumulator registers.
9962 Use all eight media accumulator registers.
9967 Pack VLIW instructions.
9972 Do not pack VLIW instructions.
9977 Do not mark ABI switches in e_flags.
9982 Enable the use of conditional-move instructions (default).
9984 This switch is mainly for debugging the compiler and will likely be removed
9985 in a future version.
9987 @item -mno-cond-move
9988 @opindex mno-cond-move
9990 Disable the use of conditional-move instructions.
9992 This switch is mainly for debugging the compiler and will likely be removed
9993 in a future version.
9998 Enable the use of conditional set instructions (default).
10000 This switch is mainly for debugging the compiler and will likely be removed
10001 in a future version.
10006 Disable the use of conditional set instructions.
10008 This switch is mainly for debugging the compiler and will likely be removed
10009 in a future version.
10012 @opindex mcond-exec
10014 Enable the use of conditional execution (default).
10016 This switch is mainly for debugging the compiler and will likely be removed
10017 in a future version.
10019 @item -mno-cond-exec
10020 @opindex mno-cond-exec
10022 Disable the use of conditional execution.
10024 This switch is mainly for debugging the compiler and will likely be removed
10025 in a future version.
10027 @item -mvliw-branch
10028 @opindex mvliw-branch
10030 Run a pass to pack branches into VLIW instructions (default).
10032 This switch is mainly for debugging the compiler and will likely be removed
10033 in a future version.
10035 @item -mno-vliw-branch
10036 @opindex mno-vliw-branch
10038 Do not run a pass to pack branches into VLIW instructions.
10040 This switch is mainly for debugging the compiler and will likely be removed
10041 in a future version.
10043 @item -mmulti-cond-exec
10044 @opindex mmulti-cond-exec
10046 Enable optimization of @code{&&} and @code{||} in conditional execution
10049 This switch is mainly for debugging the compiler and will likely be removed
10050 in a future version.
10052 @item -mno-multi-cond-exec
10053 @opindex mno-multi-cond-exec
10055 Disable optimization of @code{&&} and @code{||} in conditional execution.
10057 This switch is mainly for debugging the compiler and will likely be removed
10058 in a future version.
10060 @item -mnested-cond-exec
10061 @opindex mnested-cond-exec
10063 Enable nested conditional execution optimizations (default).
10065 This switch is mainly for debugging the compiler and will likely be removed
10066 in a future version.
10068 @item -mno-nested-cond-exec
10069 @opindex mno-nested-cond-exec
10071 Disable nested conditional execution optimizations.
10073 This switch is mainly for debugging the compiler and will likely be removed
10074 in a future version.
10076 @item -moptimize-membar
10077 @opindex moptimize-membar
10079 This switch removes redundant @code{membar} instructions from the
10080 compiler generated code. It is enabled by default.
10082 @item -mno-optimize-membar
10083 @opindex mno-optimize-membar
10085 This switch disables the automatic removal of redundant @code{membar}
10086 instructions from the generated code.
10088 @item -mtomcat-stats
10089 @opindex mtomcat-stats
10091 Cause gas to print out tomcat statistics.
10093 @item -mcpu=@var{cpu}
10096 Select the processor type for which to generate code. Possible values are
10097 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
10098 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
10102 @node GNU/Linux Options
10103 @subsection GNU/Linux Options
10105 These @samp{-m} options are defined for GNU/Linux targets:
10110 Use the GNU C library instead of uClibc. This is the default except
10111 on @samp{*-*-linux-*uclibc*} targets.
10115 Use uClibc instead of the GNU C library. This is the default on
10116 @samp{*-*-linux-*uclibc*} targets.
10119 @node H8/300 Options
10120 @subsection H8/300 Options
10122 These @samp{-m} options are defined for the H8/300 implementations:
10127 Shorten some address references at link time, when possible; uses the
10128 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
10129 ld, Using ld}, for a fuller description.
10133 Generate code for the H8/300H@.
10137 Generate code for the H8S@.
10141 Generate code for the H8S and H8/300H in the normal mode. This switch
10142 must be used either with @option{-mh} or @option{-ms}.
10146 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
10150 Make @code{int} data 32 bits by default.
10153 @opindex malign-300
10154 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
10155 The default for the H8/300H and H8S is to align longs and floats on 4
10157 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
10158 This option has no effect on the H8/300.
10162 @subsection HPPA Options
10163 @cindex HPPA Options
10165 These @samp{-m} options are defined for the HPPA family of computers:
10168 @item -march=@var{architecture-type}
10170 Generate code for the specified architecture. The choices for
10171 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
10172 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
10173 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
10174 architecture option for your machine. Code compiled for lower numbered
10175 architectures will run on higher numbered architectures, but not the
10178 @item -mpa-risc-1-0
10179 @itemx -mpa-risc-1-1
10180 @itemx -mpa-risc-2-0
10181 @opindex mpa-risc-1-0
10182 @opindex mpa-risc-1-1
10183 @opindex mpa-risc-2-0
10184 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
10187 @opindex mbig-switch
10188 Generate code suitable for big switch tables. Use this option only if
10189 the assembler/linker complain about out of range branches within a switch
10192 @item -mjump-in-delay
10193 @opindex mjump-in-delay
10194 Fill delay slots of function calls with unconditional jump instructions
10195 by modifying the return pointer for the function call to be the target
10196 of the conditional jump.
10198 @item -mdisable-fpregs
10199 @opindex mdisable-fpregs
10200 Prevent floating point registers from being used in any manner. This is
10201 necessary for compiling kernels which perform lazy context switching of
10202 floating point registers. If you use this option and attempt to perform
10203 floating point operations, the compiler will abort.
10205 @item -mdisable-indexing
10206 @opindex mdisable-indexing
10207 Prevent the compiler from using indexing address modes. This avoids some
10208 rather obscure problems when compiling MIG generated code under MACH@.
10210 @item -mno-space-regs
10211 @opindex mno-space-regs
10212 Generate code that assumes the target has no space registers. This allows
10213 GCC to generate faster indirect calls and use unscaled index address modes.
10215 Such code is suitable for level 0 PA systems and kernels.
10217 @item -mfast-indirect-calls
10218 @opindex mfast-indirect-calls
10219 Generate code that assumes calls never cross space boundaries. This
10220 allows GCC to emit code which performs faster indirect calls.
10222 This option will not work in the presence of shared libraries or nested
10225 @item -mfixed-range=@var{register-range}
10226 @opindex mfixed-range
10227 Generate code treating the given register range as fixed registers.
10228 A fixed register is one that the register allocator can not use. This is
10229 useful when compiling kernel code. A register range is specified as
10230 two registers separated by a dash. Multiple register ranges can be
10231 specified separated by a comma.
10233 @item -mlong-load-store
10234 @opindex mlong-load-store
10235 Generate 3-instruction load and store sequences as sometimes required by
10236 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
10239 @item -mportable-runtime
10240 @opindex mportable-runtime
10241 Use the portable calling conventions proposed by HP for ELF systems.
10245 Enable the use of assembler directives only GAS understands.
10247 @item -mschedule=@var{cpu-type}
10249 Schedule code according to the constraints for the machine type
10250 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
10251 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
10252 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
10253 proper scheduling option for your machine. The default scheduling is
10257 @opindex mlinker-opt
10258 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
10259 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
10260 linkers in which they give bogus error messages when linking some programs.
10263 @opindex msoft-float
10264 Generate output containing library calls for floating point.
10265 @strong{Warning:} the requisite libraries are not available for all HPPA
10266 targets. Normally the facilities of the machine's usual C compiler are
10267 used, but this cannot be done directly in cross-compilation. You must make
10268 your own arrangements to provide suitable library functions for
10271 @option{-msoft-float} changes the calling convention in the output file;
10272 therefore, it is only useful if you compile @emph{all} of a program with
10273 this option. In particular, you need to compile @file{libgcc.a}, the
10274 library that comes with GCC, with @option{-msoft-float} in order for
10279 Generate the predefine, @code{_SIO}, for server IO@. The default is
10280 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
10281 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
10282 options are available under HP-UX and HI-UX@.
10286 Use GNU ld specific options. This passes @option{-shared} to ld when
10287 building a shared library. It is the default when GCC is configured,
10288 explicitly or implicitly, with the GNU linker. This option does not
10289 have any affect on which ld is called, it only changes what parameters
10290 are passed to that ld. The ld that is called is determined by the
10291 @option{--with-ld} configure option, GCC's program search path, and
10292 finally by the user's @env{PATH}. The linker used by GCC can be printed
10293 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
10294 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10298 Use HP ld specific options. This passes @option{-b} to ld when building
10299 a shared library and passes @option{+Accept TypeMismatch} to ld on all
10300 links. It is the default when GCC is configured, explicitly or
10301 implicitly, with the HP linker. This option does not have any affect on
10302 which ld is called, it only changes what parameters are passed to that
10303 ld. The ld that is called is determined by the @option{--with-ld}
10304 configure option, GCC's program search path, and finally by the user's
10305 @env{PATH}. The linker used by GCC can be printed using @samp{which
10306 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
10307 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10310 @opindex mno-long-calls
10311 Generate code that uses long call sequences. This ensures that a call
10312 is always able to reach linker generated stubs. The default is to generate
10313 long calls only when the distance from the call site to the beginning
10314 of the function or translation unit, as the case may be, exceeds a
10315 predefined limit set by the branch type being used. The limits for
10316 normal calls are 7,600,000 and 240,000 bytes, respectively for the
10317 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
10320 Distances are measured from the beginning of functions when using the
10321 @option{-ffunction-sections} option, or when using the @option{-mgas}
10322 and @option{-mno-portable-runtime} options together under HP-UX with
10325 It is normally not desirable to use this option as it will degrade
10326 performance. However, it may be useful in large applications,
10327 particularly when partial linking is used to build the application.
10329 The types of long calls used depends on the capabilities of the
10330 assembler and linker, and the type of code being generated. The
10331 impact on systems that support long absolute calls, and long pic
10332 symbol-difference or pc-relative calls should be relatively small.
10333 However, an indirect call is used on 32-bit ELF systems in pic code
10334 and it is quite long.
10336 @item -munix=@var{unix-std}
10338 Generate compiler predefines and select a startfile for the specified
10339 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
10340 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
10341 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
10342 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
10343 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
10346 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
10347 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
10348 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
10349 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
10350 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
10351 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
10353 It is @emph{important} to note that this option changes the interfaces
10354 for various library routines. It also affects the operational behavior
10355 of the C library. Thus, @emph{extreme} care is needed in using this
10358 Library code that is intended to operate with more than one UNIX
10359 standard must test, set and restore the variable @var{__xpg4_extended_mask}
10360 as appropriate. Most GNU software doesn't provide this capability.
10364 Suppress the generation of link options to search libdld.sl when the
10365 @option{-static} option is specified on HP-UX 10 and later.
10369 The HP-UX implementation of setlocale in libc has a dependency on
10370 libdld.sl. There isn't an archive version of libdld.sl. Thus,
10371 when the @option{-static} option is specified, special link options
10372 are needed to resolve this dependency.
10374 On HP-UX 10 and later, the GCC driver adds the necessary options to
10375 link with libdld.sl when the @option{-static} option is specified.
10376 This causes the resulting binary to be dynamic. On the 64-bit port,
10377 the linkers generate dynamic binaries by default in any case. The
10378 @option{-nolibdld} option can be used to prevent the GCC driver from
10379 adding these link options.
10383 Add support for multithreading with the @dfn{dce thread} library
10384 under HP-UX@. This option sets flags for both the preprocessor and
10388 @node i386 and x86-64 Options
10389 @subsection Intel 386 and AMD x86-64 Options
10390 @cindex i386 Options
10391 @cindex x86-64 Options
10392 @cindex Intel 386 Options
10393 @cindex AMD x86-64 Options
10395 These @samp{-m} options are defined for the i386 and x86-64 family of
10399 @item -mtune=@var{cpu-type}
10401 Tune to @var{cpu-type} everything applicable about the generated code, except
10402 for the ABI and the set of available instructions. The choices for
10403 @var{cpu-type} are:
10406 Produce code optimized for the most common IA32/AMD64/EM64T processors.
10407 If you know the CPU on which your code will run, then you should use
10408 the corresponding @option{-mtune} option instead of
10409 @option{-mtune=generic}. But, if you do not know exactly what CPU users
10410 of your application will have, then you should use this option.
10412 As new processors are deployed in the marketplace, the behavior of this
10413 option will change. Therefore, if you upgrade to a newer version of
10414 GCC, the code generated option will change to reflect the processors
10415 that were most common when that version of GCC was released.
10417 There is no @option{-march=generic} option because @option{-march}
10418 indicates the instruction set the compiler can use, and there is no
10419 generic instruction set applicable to all processors. In contrast,
10420 @option{-mtune} indicates the processor (or, in this case, collection of
10421 processors) for which the code is optimized.
10423 This selects the CPU to tune for at compilation time by determining
10424 the processor type of the compiling machine. Using @option{-mtune=native}
10425 will produce code optimized for the local machine under the constraints
10426 of the selected instruction set. Using @option{-march=native} will
10427 enable all instruction subsets supported by the local machine (hence
10428 the result might not run on different machines).
10430 Original Intel's i386 CPU@.
10432 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
10433 @item i586, pentium
10434 Intel Pentium CPU with no MMX support.
10436 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
10438 Intel PentiumPro CPU@.
10440 Same as @code{generic}, but when used as @code{march} option, PentiumPro
10441 instruction set will be used, so the code will run on all i686 family chips.
10443 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
10444 @item pentium3, pentium3m
10445 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
10448 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
10449 support. Used by Centrino notebooks.
10450 @item pentium4, pentium4m
10451 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
10453 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
10456 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
10457 SSE2 and SSE3 instruction set support.
10459 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
10460 instruction set support.
10462 AMD K6 CPU with MMX instruction set support.
10464 Improved versions of AMD K6 CPU with MMX and 3dNOW!@: instruction set support.
10465 @item athlon, athlon-tbird
10466 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and SSE prefetch instructions
10468 @item athlon-4, athlon-xp, athlon-mp
10469 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and full SSE
10470 instruction set support.
10471 @item k8, opteron, athlon64, athlon-fx
10472 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
10473 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW!@: and 64-bit instruction set extensions.)
10474 @item k8-sse3, opteron-sse3, athlon64-sse3
10475 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
10476 @item amdfam10, barcelona
10477 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
10478 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
10479 instruction set extensions.)
10481 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
10484 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!@:
10485 instruction set support.
10487 Via C3 CPU with MMX and 3dNOW!@: instruction set support. (No scheduling is
10488 implemented for this chip.)
10490 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
10491 implemented for this chip.)
10493 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
10496 While picking a specific @var{cpu-type} will schedule things appropriately
10497 for that particular chip, the compiler will not generate any code that
10498 does not run on the i386 without the @option{-march=@var{cpu-type}} option
10501 @item -march=@var{cpu-type}
10503 Generate instructions for the machine type @var{cpu-type}. The choices
10504 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
10505 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
10507 @item -mcpu=@var{cpu-type}
10509 A deprecated synonym for @option{-mtune}.
10511 @item -mfpmath=@var{unit}
10513 Generate floating point arithmetics for selected unit @var{unit}. The choices
10514 for @var{unit} are:
10518 Use the standard 387 floating point coprocessor present majority of chips and
10519 emulated otherwise. Code compiled with this option will run almost everywhere.
10520 The temporary results are computed in 80bit precision instead of precision
10521 specified by the type resulting in slightly different results compared to most
10522 of other chips. See @option{-ffloat-store} for more detailed description.
10524 This is the default choice for i386 compiler.
10527 Use scalar floating point instructions present in the SSE instruction set.
10528 This instruction set is supported by Pentium3 and newer chips, in the AMD line
10529 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
10530 instruction set supports only single precision arithmetics, thus the double and
10531 extended precision arithmetics is still done using 387. Later version, present
10532 only in Pentium4 and the future AMD x86-64 chips supports double precision
10535 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
10536 or @option{-msse2} switches to enable SSE extensions and make this option
10537 effective. For the x86-64 compiler, these extensions are enabled by default.
10539 The resulting code should be considerably faster in the majority of cases and avoid
10540 the numerical instability problems of 387 code, but may break some existing
10541 code that expects temporaries to be 80bit.
10543 This is the default choice for the x86-64 compiler.
10546 Attempt to utilize both instruction sets at once. This effectively double the
10547 amount of available registers and on chips with separate execution units for
10548 387 and SSE the execution resources too. Use this option with care, as it is
10549 still experimental, because the GCC register allocator does not model separate
10550 functional units well resulting in instable performance.
10553 @item -masm=@var{dialect}
10554 @opindex masm=@var{dialect}
10555 Output asm instructions using selected @var{dialect}. Supported
10556 choices are @samp{intel} or @samp{att} (the default one). Darwin does
10557 not support @samp{intel}.
10560 @itemx -mno-ieee-fp
10562 @opindex mno-ieee-fp
10563 Control whether or not the compiler uses IEEE floating point
10564 comparisons. These handle correctly the case where the result of a
10565 comparison is unordered.
10568 @opindex msoft-float
10569 Generate output containing library calls for floating point.
10570 @strong{Warning:} the requisite libraries are not part of GCC@.
10571 Normally the facilities of the machine's usual C compiler are used, but
10572 this can't be done directly in cross-compilation. You must make your
10573 own arrangements to provide suitable library functions for
10576 On machines where a function returns floating point results in the 80387
10577 register stack, some floating point opcodes may be emitted even if
10578 @option{-msoft-float} is used.
10580 @item -mno-fp-ret-in-387
10581 @opindex mno-fp-ret-in-387
10582 Do not use the FPU registers for return values of functions.
10584 The usual calling convention has functions return values of types
10585 @code{float} and @code{double} in an FPU register, even if there
10586 is no FPU@. The idea is that the operating system should emulate
10589 The option @option{-mno-fp-ret-in-387} causes such values to be returned
10590 in ordinary CPU registers instead.
10592 @item -mno-fancy-math-387
10593 @opindex mno-fancy-math-387
10594 Some 387 emulators do not support the @code{sin}, @code{cos} and
10595 @code{sqrt} instructions for the 387. Specify this option to avoid
10596 generating those instructions. This option is the default on FreeBSD,
10597 OpenBSD and NetBSD@. This option is overridden when @option{-march}
10598 indicates that the target cpu will always have an FPU and so the
10599 instruction will not need emulation. As of revision 2.6.1, these
10600 instructions are not generated unless you also use the
10601 @option{-funsafe-math-optimizations} switch.
10603 @item -malign-double
10604 @itemx -mno-align-double
10605 @opindex malign-double
10606 @opindex mno-align-double
10607 Control whether GCC aligns @code{double}, @code{long double}, and
10608 @code{long long} variables on a two word boundary or a one word
10609 boundary. Aligning @code{double} variables on a two word boundary will
10610 produce code that runs somewhat faster on a @samp{Pentium} at the
10611 expense of more memory.
10613 On x86-64, @option{-malign-double} is enabled by default.
10615 @strong{Warning:} if you use the @option{-malign-double} switch,
10616 structures containing the above types will be aligned differently than
10617 the published application binary interface specifications for the 386
10618 and will not be binary compatible with structures in code compiled
10619 without that switch.
10621 @item -m96bit-long-double
10622 @itemx -m128bit-long-double
10623 @opindex m96bit-long-double
10624 @opindex m128bit-long-double
10625 These switches control the size of @code{long double} type. The i386
10626 application binary interface specifies the size to be 96 bits,
10627 so @option{-m96bit-long-double} is the default in 32 bit mode.
10629 Modern architectures (Pentium and newer) would prefer @code{long double}
10630 to be aligned to an 8 or 16 byte boundary. In arrays or structures
10631 conforming to the ABI, this would not be possible. So specifying a
10632 @option{-m128bit-long-double} will align @code{long double}
10633 to a 16 byte boundary by padding the @code{long double} with an additional
10636 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
10637 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
10639 Notice that neither of these options enable any extra precision over the x87
10640 standard of 80 bits for a @code{long double}.
10642 @strong{Warning:} if you override the default value for your target ABI, the
10643 structures and arrays containing @code{long double} variables will change
10644 their size as well as function calling convention for function taking
10645 @code{long double} will be modified. Hence they will not be binary
10646 compatible with arrays or structures in code compiled without that switch.
10648 @item -mmlarge-data-threshold=@var{number}
10649 @opindex mlarge-data-threshold=@var{number}
10650 When @option{-mcmodel=medium} is specified, the data greater than
10651 @var{threshold} are placed in large data section. This value must be the
10652 same across all object linked into the binary and defaults to 65535.
10656 Use a different function-calling convention, in which functions that
10657 take a fixed number of arguments return with the @code{ret} @var{num}
10658 instruction, which pops their arguments while returning. This saves one
10659 instruction in the caller since there is no need to pop the arguments
10662 You can specify that an individual function is called with this calling
10663 sequence with the function attribute @samp{stdcall}. You can also
10664 override the @option{-mrtd} option by using the function attribute
10665 @samp{cdecl}. @xref{Function Attributes}.
10667 @strong{Warning:} this calling convention is incompatible with the one
10668 normally used on Unix, so you cannot use it if you need to call
10669 libraries compiled with the Unix compiler.
10671 Also, you must provide function prototypes for all functions that
10672 take variable numbers of arguments (including @code{printf});
10673 otherwise incorrect code will be generated for calls to those
10676 In addition, seriously incorrect code will result if you call a
10677 function with too many arguments. (Normally, extra arguments are
10678 harmlessly ignored.)
10680 @item -mregparm=@var{num}
10682 Control how many registers are used to pass integer arguments. By
10683 default, no registers are used to pass arguments, and at most 3
10684 registers can be used. You can control this behavior for a specific
10685 function by using the function attribute @samp{regparm}.
10686 @xref{Function Attributes}.
10688 @strong{Warning:} if you use this switch, and
10689 @var{num} is nonzero, then you must build all modules with the same
10690 value, including any libraries. This includes the system libraries and
10694 @opindex msseregparm
10695 Use SSE register passing conventions for float and double arguments
10696 and return values. You can control this behavior for a specific
10697 function by using the function attribute @samp{sseregparm}.
10698 @xref{Function Attributes}.
10700 @strong{Warning:} if you use this switch then you must build all
10701 modules with the same value, including any libraries. This includes
10702 the system libraries and startup modules.
10711 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
10712 is specified, the significands of results of floating-point operations are
10713 rounded to 24 bits (single precision); @option{-mpc64} rounds the the
10714 significands of results of floating-point operations to 53 bits (double
10715 precision) and @option{-mpc80} rounds the significands of results of
10716 floating-point operations to 64 bits (extended double precision), which is
10717 the default. When this option is used, floating-point operations in higher
10718 precisions are not available to the programmer without setting the FPU
10719 control word explicitly.
10721 Setting the rounding of floating-point operations to less than the default
10722 80 bits can speed some programs by 2% or more. Note that some mathematical
10723 libraries assume that extended precision (80 bit) floating-point operations
10724 are enabled by default; routines in such libraries could suffer significant
10725 loss of accuracy, typically through so-called "catastrophic cancellation",
10726 when this option is used to set the precision to less than extended precision.
10728 @item -mstackrealign
10729 @opindex mstackrealign
10730 Realign the stack at entry. On the Intel x86, the
10731 @option{-mstackrealign} option will generate an alternate prologue and
10732 epilogue that realigns the runtime stack. This supports mixing legacy
10733 codes that keep a 4-byte aligned stack with modern codes that keep a
10734 16-byte stack for SSE compatibility. The alternate prologue and
10735 epilogue are slower and bigger than the regular ones, and the
10736 alternate prologue requires an extra scratch register; this lowers the
10737 number of registers available if used in conjunction with the
10738 @code{regparm} attribute. The @option{-mstackrealign} option is
10739 incompatible with the nested function prologue; this is considered a
10740 hard error. See also the attribute @code{force_align_arg_pointer},
10741 applicable to individual functions.
10743 @item -mpreferred-stack-boundary=@var{num}
10744 @opindex mpreferred-stack-boundary
10745 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
10746 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
10747 the default is 4 (16 bytes or 128 bits).
10749 On Pentium and PentiumPro, @code{double} and @code{long double} values
10750 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
10751 suffer significant run time performance penalties. On Pentium III, the
10752 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
10753 properly if it is not 16 byte aligned.
10755 To ensure proper alignment of this values on the stack, the stack boundary
10756 must be as aligned as that required by any value stored on the stack.
10757 Further, every function must be generated such that it keeps the stack
10758 aligned. Thus calling a function compiled with a higher preferred
10759 stack boundary from a function compiled with a lower preferred stack
10760 boundary will most likely misalign the stack. It is recommended that
10761 libraries that use callbacks always use the default setting.
10763 This extra alignment does consume extra stack space, and generally
10764 increases code size. Code that is sensitive to stack space usage, such
10765 as embedded systems and operating system kernels, may want to reduce the
10766 preferred alignment to @option{-mpreferred-stack-boundary=2}.
10804 These switches enable or disable the use of instructions in the MMX,
10805 SSE, SSE2, SSE3, SSSE3, SSE4.1, AES, PCLMUL, SSE4A, SSE5, ABM or
10806 3DNow!@: extended instruction sets.
10807 These extensions are also available as built-in functions: see
10808 @ref{X86 Built-in Functions}, for details of the functions enabled and
10809 disabled by these switches.
10811 To have SSE/SSE2 instructions generated automatically from floating-point
10812 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
10814 These options will enable GCC to use these extended instructions in
10815 generated code, even without @option{-mfpmath=sse}. Applications which
10816 perform runtime CPU detection must compile separate files for each
10817 supported architecture, using the appropriate flags. In particular,
10818 the file containing the CPU detection code should be compiled without
10823 This option instructs GCC to emit a @code{cld} instruction in the prologue
10824 of functions that use string instructions. String instructions depend on
10825 the DF flag to select between autoincrement or autodecrement mode. While the
10826 ABI specifies the DF flag to be cleared on function entry, some operating
10827 systems violate this specification by not clearing the DF flag in their
10828 exception dispatchers. The exception handler can be invoked with the DF flag
10829 set which leads to wrong direction mode, when string instructions are used.
10830 This option can be enabled by default on 32-bit x86 targets by configuring
10831 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
10832 instructions can be suppressed with the @option{-mno-cld} compiler option
10837 This option will enable GCC to use CMPXCHG16B instruction in generated code.
10838 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
10839 data types. This is useful for high resolution counters that could be updated
10840 by multiple processors (or cores). This instruction is generated as part of
10841 atomic built-in functions: see @ref{Atomic Builtins} for details.
10845 This option will enable GCC to use SAHF instruction in generated 64-bit code.
10846 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
10847 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
10848 SAHF are load and store instructions, respectively, for certain status flags.
10849 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
10850 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
10854 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
10855 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Rhapson step
10856 to increase precision instead of DIVSS and SQRTSS (and their vectorized
10857 variants) for single precision floating point arguments. These instructions
10858 are generated only when @option{-funsafe-math-optimizations} is enabled
10859 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
10860 Note that while the throughput of the sequence is higher than the throughput
10861 of the non-reciprocal instruction, the precision of the sequence can be
10862 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
10864 @item -mveclibabi=@var{type}
10865 @opindex mveclibabi
10866 Specifies the ABI type to use for vectorizing intrinsics using an
10867 external library. Supported types are @code{svml} for the Intel short
10868 vector math library and @code{acml} for the AMD math core library style
10869 of interfacing. GCC will currently emit calls to @code{vmldExp2},
10870 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
10871 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
10872 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
10873 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
10874 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
10875 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
10876 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
10877 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
10878 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
10879 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
10880 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
10881 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
10882 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
10883 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
10884 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
10885 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
10886 compatible library will have to be specified at link time.
10889 @itemx -mno-push-args
10890 @opindex mpush-args
10891 @opindex mno-push-args
10892 Use PUSH operations to store outgoing parameters. This method is shorter
10893 and usually equally fast as method using SUB/MOV operations and is enabled
10894 by default. In some cases disabling it may improve performance because of
10895 improved scheduling and reduced dependencies.
10897 @item -maccumulate-outgoing-args
10898 @opindex maccumulate-outgoing-args
10899 If enabled, the maximum amount of space required for outgoing arguments will be
10900 computed in the function prologue. This is faster on most modern CPUs
10901 because of reduced dependencies, improved scheduling and reduced stack usage
10902 when preferred stack boundary is not equal to 2. The drawback is a notable
10903 increase in code size. This switch implies @option{-mno-push-args}.
10907 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
10908 on thread-safe exception handling must compile and link all code with the
10909 @option{-mthreads} option. When compiling, @option{-mthreads} defines
10910 @option{-D_MT}; when linking, it links in a special thread helper library
10911 @option{-lmingwthrd} which cleans up per thread exception handling data.
10913 @item -mno-align-stringops
10914 @opindex mno-align-stringops
10915 Do not align destination of inlined string operations. This switch reduces
10916 code size and improves performance in case the destination is already aligned,
10917 but GCC doesn't know about it.
10919 @item -minline-all-stringops
10920 @opindex minline-all-stringops
10921 By default GCC inlines string operations only when destination is known to be
10922 aligned at least to 4 byte boundary. This enables more inlining, increase code
10923 size, but may improve performance of code that depends on fast memcpy, strlen
10924 and memset for short lengths.
10926 @item -minline-stringops-dynamically
10927 @opindex minline-stringops-dynamically
10928 For string operation of unknown size, inline runtime checks so for small
10929 blocks inline code is used, while for large blocks library call is used.
10931 @item -mstringop-strategy=@var{alg}
10932 @opindex mstringop-strategy=@var{alg}
10933 Overwrite internal decision heuristic about particular algorithm to inline
10934 string operation with. The allowed values are @code{rep_byte},
10935 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
10936 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
10937 expanding inline loop, @code{libcall} for always expanding library call.
10939 @item -momit-leaf-frame-pointer
10940 @opindex momit-leaf-frame-pointer
10941 Don't keep the frame pointer in a register for leaf functions. This
10942 avoids the instructions to save, set up and restore frame pointers and
10943 makes an extra register available in leaf functions. The option
10944 @option{-fomit-frame-pointer} removes the frame pointer for all functions
10945 which might make debugging harder.
10947 @item -mtls-direct-seg-refs
10948 @itemx -mno-tls-direct-seg-refs
10949 @opindex mtls-direct-seg-refs
10950 Controls whether TLS variables may be accessed with offsets from the
10951 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
10952 or whether the thread base pointer must be added. Whether or not this
10953 is legal depends on the operating system, and whether it maps the
10954 segment to cover the entire TLS area.
10956 For systems that use GNU libc, the default is on.
10959 @itemx -mno-fused-madd
10960 @opindex mfused-madd
10961 Enable automatic generation of fused floating point multiply-add instructions
10962 if the ISA supports such instructions. The -mfused-madd option is on by
10963 default. The fused multiply-add instructions have a different
10964 rounding behavior compared to executing a multiply followed by an add.
10967 These @samp{-m} switches are supported in addition to the above
10968 on AMD x86-64 processors in 64-bit environments.
10975 Generate code for a 32-bit or 64-bit environment.
10976 The 32-bit environment sets int, long and pointer to 32 bits and
10977 generates code that runs on any i386 system.
10978 The 64-bit environment sets int to 32 bits and long and pointer
10979 to 64 bits and generates code for AMD's x86-64 architecture. For
10980 darwin only the -m64 option turns off the @option{-fno-pic} and
10981 @option{-mdynamic-no-pic} options.
10983 @item -mno-red-zone
10984 @opindex no-red-zone
10985 Do not use a so called red zone for x86-64 code. The red zone is mandated
10986 by the x86-64 ABI, it is a 128-byte area beyond the location of the
10987 stack pointer that will not be modified by signal or interrupt handlers
10988 and therefore can be used for temporary data without adjusting the stack
10989 pointer. The flag @option{-mno-red-zone} disables this red zone.
10991 @item -mcmodel=small
10992 @opindex mcmodel=small
10993 Generate code for the small code model: the program and its symbols must
10994 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
10995 Programs can be statically or dynamically linked. This is the default
10998 @item -mcmodel=kernel
10999 @opindex mcmodel=kernel
11000 Generate code for the kernel code model. The kernel runs in the
11001 negative 2 GB of the address space.
11002 This model has to be used for Linux kernel code.
11004 @item -mcmodel=medium
11005 @opindex mcmodel=medium
11006 Generate code for the medium model: The program is linked in the lower 2
11007 GB of the address space but symbols can be located anywhere in the
11008 address space. Programs can be statically or dynamically linked, but
11009 building of shared libraries are not supported with the medium model.
11011 @item -mcmodel=large
11012 @opindex mcmodel=large
11013 Generate code for the large model: This model makes no assumptions
11014 about addresses and sizes of sections.
11017 @node IA-64 Options
11018 @subsection IA-64 Options
11019 @cindex IA-64 Options
11021 These are the @samp{-m} options defined for the Intel IA-64 architecture.
11025 @opindex mbig-endian
11026 Generate code for a big endian target. This is the default for HP-UX@.
11028 @item -mlittle-endian
11029 @opindex mlittle-endian
11030 Generate code for a little endian target. This is the default for AIX5
11036 @opindex mno-gnu-as
11037 Generate (or don't) code for the GNU assembler. This is the default.
11038 @c Also, this is the default if the configure option @option{--with-gnu-as}
11044 @opindex mno-gnu-ld
11045 Generate (or don't) code for the GNU linker. This is the default.
11046 @c Also, this is the default if the configure option @option{--with-gnu-ld}
11051 Generate code that does not use a global pointer register. The result
11052 is not position independent code, and violates the IA-64 ABI@.
11054 @item -mvolatile-asm-stop
11055 @itemx -mno-volatile-asm-stop
11056 @opindex mvolatile-asm-stop
11057 @opindex mno-volatile-asm-stop
11058 Generate (or don't) a stop bit immediately before and after volatile asm
11061 @item -mregister-names
11062 @itemx -mno-register-names
11063 @opindex mregister-names
11064 @opindex mno-register-names
11065 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
11066 the stacked registers. This may make assembler output more readable.
11072 Disable (or enable) optimizations that use the small data section. This may
11073 be useful for working around optimizer bugs.
11075 @item -mconstant-gp
11076 @opindex mconstant-gp
11077 Generate code that uses a single constant global pointer value. This is
11078 useful when compiling kernel code.
11082 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
11083 This is useful when compiling firmware code.
11085 @item -minline-float-divide-min-latency
11086 @opindex minline-float-divide-min-latency
11087 Generate code for inline divides of floating point values
11088 using the minimum latency algorithm.
11090 @item -minline-float-divide-max-throughput
11091 @opindex minline-float-divide-max-throughput
11092 Generate code for inline divides of floating point values
11093 using the maximum throughput algorithm.
11095 @item -minline-int-divide-min-latency
11096 @opindex minline-int-divide-min-latency
11097 Generate code for inline divides of integer values
11098 using the minimum latency algorithm.
11100 @item -minline-int-divide-max-throughput
11101 @opindex minline-int-divide-max-throughput
11102 Generate code for inline divides of integer values
11103 using the maximum throughput algorithm.
11105 @item -minline-sqrt-min-latency
11106 @opindex minline-sqrt-min-latency
11107 Generate code for inline square roots
11108 using the minimum latency algorithm.
11110 @item -minline-sqrt-max-throughput
11111 @opindex minline-sqrt-max-throughput
11112 Generate code for inline square roots
11113 using the maximum throughput algorithm.
11115 @item -mno-dwarf2-asm
11116 @itemx -mdwarf2-asm
11117 @opindex mno-dwarf2-asm
11118 @opindex mdwarf2-asm
11119 Don't (or do) generate assembler code for the DWARF2 line number debugging
11120 info. This may be useful when not using the GNU assembler.
11122 @item -mearly-stop-bits
11123 @itemx -mno-early-stop-bits
11124 @opindex mearly-stop-bits
11125 @opindex mno-early-stop-bits
11126 Allow stop bits to be placed earlier than immediately preceding the
11127 instruction that triggered the stop bit. This can improve instruction
11128 scheduling, but does not always do so.
11130 @item -mfixed-range=@var{register-range}
11131 @opindex mfixed-range
11132 Generate code treating the given register range as fixed registers.
11133 A fixed register is one that the register allocator can not use. This is
11134 useful when compiling kernel code. A register range is specified as
11135 two registers separated by a dash. Multiple register ranges can be
11136 specified separated by a comma.
11138 @item -mtls-size=@var{tls-size}
11140 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
11143 @item -mtune=@var{cpu-type}
11145 Tune the instruction scheduling for a particular CPU, Valid values are
11146 itanium, itanium1, merced, itanium2, and mckinley.
11152 Add support for multithreading using the POSIX threads library. This
11153 option sets flags for both the preprocessor and linker. It does
11154 not affect the thread safety of object code produced by the compiler or
11155 that of libraries supplied with it. These are HP-UX specific flags.
11161 Generate code for a 32-bit or 64-bit environment.
11162 The 32-bit environment sets int, long and pointer to 32 bits.
11163 The 64-bit environment sets int to 32 bits and long and pointer
11164 to 64 bits. These are HP-UX specific flags.
11166 @item -mno-sched-br-data-spec
11167 @itemx -msched-br-data-spec
11168 @opindex mno-sched-br-data-spec
11169 @opindex msched-br-data-spec
11170 (Dis/En)able data speculative scheduling before reload.
11171 This will result in generation of the ld.a instructions and
11172 the corresponding check instructions (ld.c / chk.a).
11173 The default is 'disable'.
11175 @item -msched-ar-data-spec
11176 @itemx -mno-sched-ar-data-spec
11177 @opindex msched-ar-data-spec
11178 @opindex mno-sched-ar-data-spec
11179 (En/Dis)able data speculative scheduling after reload.
11180 This will result in generation of the ld.a instructions and
11181 the corresponding check instructions (ld.c / chk.a).
11182 The default is 'enable'.
11184 @item -mno-sched-control-spec
11185 @itemx -msched-control-spec
11186 @opindex mno-sched-control-spec
11187 @opindex msched-control-spec
11188 (Dis/En)able control speculative scheduling. This feature is
11189 available only during region scheduling (i.e.@: before reload).
11190 This will result in generation of the ld.s instructions and
11191 the corresponding check instructions chk.s .
11192 The default is 'disable'.
11194 @item -msched-br-in-data-spec
11195 @itemx -mno-sched-br-in-data-spec
11196 @opindex msched-br-in-data-spec
11197 @opindex mno-sched-br-in-data-spec
11198 (En/Dis)able speculative scheduling of the instructions that
11199 are dependent on the data speculative loads before reload.
11200 This is effective only with @option{-msched-br-data-spec} enabled.
11201 The default is 'enable'.
11203 @item -msched-ar-in-data-spec
11204 @itemx -mno-sched-ar-in-data-spec
11205 @opindex msched-ar-in-data-spec
11206 @opindex mno-sched-ar-in-data-spec
11207 (En/Dis)able speculative scheduling of the instructions that
11208 are dependent on the data speculative loads after reload.
11209 This is effective only with @option{-msched-ar-data-spec} enabled.
11210 The default is 'enable'.
11212 @item -msched-in-control-spec
11213 @itemx -mno-sched-in-control-spec
11214 @opindex msched-in-control-spec
11215 @opindex mno-sched-in-control-spec
11216 (En/Dis)able speculative scheduling of the instructions that
11217 are dependent on the control speculative loads.
11218 This is effective only with @option{-msched-control-spec} enabled.
11219 The default is 'enable'.
11222 @itemx -mno-sched-ldc
11223 @opindex msched-ldc
11224 @opindex mno-sched-ldc
11225 (En/Dis)able use of simple data speculation checks ld.c .
11226 If disabled, only chk.a instructions will be emitted to check
11227 data speculative loads.
11228 The default is 'enable'.
11230 @item -mno-sched-control-ldc
11231 @itemx -msched-control-ldc
11232 @opindex mno-sched-control-ldc
11233 @opindex msched-control-ldc
11234 (Dis/En)able use of ld.c instructions to check control speculative loads.
11235 If enabled, in case of control speculative load with no speculatively
11236 scheduled dependent instructions this load will be emitted as ld.sa and
11237 ld.c will be used to check it.
11238 The default is 'disable'.
11240 @item -mno-sched-spec-verbose
11241 @itemx -msched-spec-verbose
11242 @opindex mno-sched-spec-verbose
11243 @opindex msched-spec-verbose
11244 (Dis/En)able printing of the information about speculative motions.
11246 @item -mno-sched-prefer-non-data-spec-insns
11247 @itemx -msched-prefer-non-data-spec-insns
11248 @opindex mno-sched-prefer-non-data-spec-insns
11249 @opindex msched-prefer-non-data-spec-insns
11250 If enabled, data speculative instructions will be chosen for schedule
11251 only if there are no other choices at the moment. This will make
11252 the use of the data speculation much more conservative.
11253 The default is 'disable'.
11255 @item -mno-sched-prefer-non-control-spec-insns
11256 @itemx -msched-prefer-non-control-spec-insns
11257 @opindex mno-sched-prefer-non-control-spec-insns
11258 @opindex msched-prefer-non-control-spec-insns
11259 If enabled, control speculative instructions will be chosen for schedule
11260 only if there are no other choices at the moment. This will make
11261 the use of the control speculation much more conservative.
11262 The default is 'disable'.
11264 @item -mno-sched-count-spec-in-critical-path
11265 @itemx -msched-count-spec-in-critical-path
11266 @opindex mno-sched-count-spec-in-critical-path
11267 @opindex msched-count-spec-in-critical-path
11268 If enabled, speculative dependencies will be considered during
11269 computation of the instructions priorities. This will make the use of the
11270 speculation a bit more conservative.
11271 The default is 'disable'.
11276 @subsection M32C Options
11277 @cindex M32C options
11280 @item -mcpu=@var{name}
11282 Select the CPU for which code is generated. @var{name} may be one of
11283 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
11284 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
11285 the M32C/80 series.
11289 Specifies that the program will be run on the simulator. This causes
11290 an alternate runtime library to be linked in which supports, for
11291 example, file I/O@. You must not use this option when generating
11292 programs that will run on real hardware; you must provide your own
11293 runtime library for whatever I/O functions are needed.
11295 @item -memregs=@var{number}
11297 Specifies the number of memory-based pseudo-registers GCC will use
11298 during code generation. These pseudo-registers will be used like real
11299 registers, so there is a tradeoff between GCC's ability to fit the
11300 code into available registers, and the performance penalty of using
11301 memory instead of registers. Note that all modules in a program must
11302 be compiled with the same value for this option. Because of that, you
11303 must not use this option with the default runtime libraries gcc
11308 @node M32R/D Options
11309 @subsection M32R/D Options
11310 @cindex M32R/D options
11312 These @option{-m} options are defined for Renesas M32R/D architectures:
11317 Generate code for the M32R/2@.
11321 Generate code for the M32R/X@.
11325 Generate code for the M32R@. This is the default.
11327 @item -mmodel=small
11328 @opindex mmodel=small
11329 Assume all objects live in the lower 16MB of memory (so that their addresses
11330 can be loaded with the @code{ld24} instruction), and assume all subroutines
11331 are reachable with the @code{bl} instruction.
11332 This is the default.
11334 The addressability of a particular object can be set with the
11335 @code{model} attribute.
11337 @item -mmodel=medium
11338 @opindex mmodel=medium
11339 Assume objects may be anywhere in the 32-bit address space (the compiler
11340 will generate @code{seth/add3} instructions to load their addresses), and
11341 assume all subroutines are reachable with the @code{bl} instruction.
11343 @item -mmodel=large
11344 @opindex mmodel=large
11345 Assume objects may be anywhere in the 32-bit address space (the compiler
11346 will generate @code{seth/add3} instructions to load their addresses), and
11347 assume subroutines may not be reachable with the @code{bl} instruction
11348 (the compiler will generate the much slower @code{seth/add3/jl}
11349 instruction sequence).
11352 @opindex msdata=none
11353 Disable use of the small data area. Variables will be put into
11354 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
11355 @code{section} attribute has been specified).
11356 This is the default.
11358 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
11359 Objects may be explicitly put in the small data area with the
11360 @code{section} attribute using one of these sections.
11362 @item -msdata=sdata
11363 @opindex msdata=sdata
11364 Put small global and static data in the small data area, but do not
11365 generate special code to reference them.
11368 @opindex msdata=use
11369 Put small global and static data in the small data area, and generate
11370 special instructions to reference them.
11374 @cindex smaller data references
11375 Put global and static objects less than or equal to @var{num} bytes
11376 into the small data or bss sections instead of the normal data or bss
11377 sections. The default value of @var{num} is 8.
11378 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
11379 for this option to have any effect.
11381 All modules should be compiled with the same @option{-G @var{num}} value.
11382 Compiling with different values of @var{num} may or may not work; if it
11383 doesn't the linker will give an error message---incorrect code will not be
11388 Makes the M32R specific code in the compiler display some statistics
11389 that might help in debugging programs.
11391 @item -malign-loops
11392 @opindex malign-loops
11393 Align all loops to a 32-byte boundary.
11395 @item -mno-align-loops
11396 @opindex mno-align-loops
11397 Do not enforce a 32-byte alignment for loops. This is the default.
11399 @item -missue-rate=@var{number}
11400 @opindex missue-rate=@var{number}
11401 Issue @var{number} instructions per cycle. @var{number} can only be 1
11404 @item -mbranch-cost=@var{number}
11405 @opindex mbranch-cost=@var{number}
11406 @var{number} can only be 1 or 2. If it is 1 then branches will be
11407 preferred over conditional code, if it is 2, then the opposite will
11410 @item -mflush-trap=@var{number}
11411 @opindex mflush-trap=@var{number}
11412 Specifies the trap number to use to flush the cache. The default is
11413 12. Valid numbers are between 0 and 15 inclusive.
11415 @item -mno-flush-trap
11416 @opindex mno-flush-trap
11417 Specifies that the cache cannot be flushed by using a trap.
11419 @item -mflush-func=@var{name}
11420 @opindex mflush-func=@var{name}
11421 Specifies the name of the operating system function to call to flush
11422 the cache. The default is @emph{_flush_cache}, but a function call
11423 will only be used if a trap is not available.
11425 @item -mno-flush-func
11426 @opindex mno-flush-func
11427 Indicates that there is no OS function for flushing the cache.
11431 @node M680x0 Options
11432 @subsection M680x0 Options
11433 @cindex M680x0 options
11435 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
11436 The default settings depend on which architecture was selected when
11437 the compiler was configured; the defaults for the most common choices
11441 @item -march=@var{arch}
11443 Generate code for a specific M680x0 or ColdFire instruction set
11444 architecture. Permissible values of @var{arch} for M680x0
11445 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
11446 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
11447 architectures are selected according to Freescale's ISA classification
11448 and the permissible values are: @samp{isaa}, @samp{isaaplus},
11449 @samp{isab} and @samp{isac}.
11451 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
11452 code for a ColdFire target. The @var{arch} in this macro is one of the
11453 @option{-march} arguments given above.
11455 When used together, @option{-march} and @option{-mtune} select code
11456 that runs on a family of similar processors but that is optimized
11457 for a particular microarchitecture.
11459 @item -mcpu=@var{cpu}
11461 Generate code for a specific M680x0 or ColdFire processor.
11462 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
11463 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
11464 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
11465 below, which also classifies the CPUs into families:
11467 @multitable @columnfractions 0.20 0.80
11468 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
11469 @item @samp{51qe} @tab @samp{51qe}
11470 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
11471 @item @samp{5206e} @tab @samp{5206e}
11472 @item @samp{5208} @tab @samp{5207} @samp{5208}
11473 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
11474 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
11475 @item @samp{5216} @tab @samp{5214} @samp{5216}
11476 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
11477 @item @samp{5225} @tab @samp{5224} @samp{5225}
11478 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
11479 @item @samp{5249} @tab @samp{5249}
11480 @item @samp{5250} @tab @samp{5250}
11481 @item @samp{5271} @tab @samp{5270} @samp{5271}
11482 @item @samp{5272} @tab @samp{5272}
11483 @item @samp{5275} @tab @samp{5274} @samp{5275}
11484 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
11485 @item @samp{5307} @tab @samp{5307}
11486 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
11487 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
11488 @item @samp{5407} @tab @samp{5407}
11489 @item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485}
11492 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
11493 @var{arch} is compatible with @var{cpu}. Other combinations of
11494 @option{-mcpu} and @option{-march} are rejected.
11496 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
11497 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
11498 where the value of @var{family} is given by the table above.
11500 @item -mtune=@var{tune}
11502 Tune the code for a particular microarchitecture, within the
11503 constraints set by @option{-march} and @option{-mcpu}.
11504 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
11505 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
11506 and @samp{cpu32}. The ColdFire microarchitectures
11507 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
11509 You can also use @option{-mtune=68020-40} for code that needs
11510 to run relatively well on 68020, 68030 and 68040 targets.
11511 @option{-mtune=68020-60} is similar but includes 68060 targets
11512 as well. These two options select the same tuning decisions as
11513 @option{-m68020-40} and @option{-m68020-60} respectively.
11515 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
11516 when tuning for 680x0 architecture @var{arch}. It also defines
11517 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
11518 option is used. If gcc is tuning for a range of architectures,
11519 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
11520 it defines the macros for every architecture in the range.
11522 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
11523 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
11524 of the arguments given above.
11530 Generate output for a 68000. This is the default
11531 when the compiler is configured for 68000-based systems.
11532 It is equivalent to @option{-march=68000}.
11534 Use this option for microcontrollers with a 68000 or EC000 core,
11535 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
11539 Generate output for a 68010. This is the default
11540 when the compiler is configured for 68010-based systems.
11541 It is equivalent to @option{-march=68010}.
11547 Generate output for a 68020. This is the default
11548 when the compiler is configured for 68020-based systems.
11549 It is equivalent to @option{-march=68020}.
11553 Generate output for a 68030. This is the default when the compiler is
11554 configured for 68030-based systems. It is equivalent to
11555 @option{-march=68030}.
11559 Generate output for a 68040. This is the default when the compiler is
11560 configured for 68040-based systems. It is equivalent to
11561 @option{-march=68040}.
11563 This option inhibits the use of 68881/68882 instructions that have to be
11564 emulated by software on the 68040. Use this option if your 68040 does not
11565 have code to emulate those instructions.
11569 Generate output for a 68060. This is the default when the compiler is
11570 configured for 68060-based systems. It is equivalent to
11571 @option{-march=68060}.
11573 This option inhibits the use of 68020 and 68881/68882 instructions that
11574 have to be emulated by software on the 68060. Use this option if your 68060
11575 does not have code to emulate those instructions.
11579 Generate output for a CPU32. This is the default
11580 when the compiler is configured for CPU32-based systems.
11581 It is equivalent to @option{-march=cpu32}.
11583 Use this option for microcontrollers with a
11584 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
11585 68336, 68340, 68341, 68349 and 68360.
11589 Generate output for a 520X ColdFire CPU@. This is the default
11590 when the compiler is configured for 520X-based systems.
11591 It is equivalent to @option{-mcpu=5206}, and is now deprecated
11592 in favor of that option.
11594 Use this option for microcontroller with a 5200 core, including
11595 the MCF5202, MCF5203, MCF5204 and MCF5206.
11599 Generate output for a 5206e ColdFire CPU@. The option is now
11600 deprecated in favor of the equivalent @option{-mcpu=5206e}.
11604 Generate output for a member of the ColdFire 528X family.
11605 The option is now deprecated in favor of the equivalent
11606 @option{-mcpu=528x}.
11610 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
11611 in favor of the equivalent @option{-mcpu=5307}.
11615 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
11616 in favor of the equivalent @option{-mcpu=5407}.
11620 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
11621 This includes use of hardware floating point instructions.
11622 The option is equivalent to @option{-mcpu=547x}, and is now
11623 deprecated in favor of that option.
11627 Generate output for a 68040, without using any of the new instructions.
11628 This results in code which can run relatively efficiently on either a
11629 68020/68881 or a 68030 or a 68040. The generated code does use the
11630 68881 instructions that are emulated on the 68040.
11632 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
11636 Generate output for a 68060, without using any of the new instructions.
11637 This results in code which can run relatively efficiently on either a
11638 68020/68881 or a 68030 or a 68040. The generated code does use the
11639 68881 instructions that are emulated on the 68060.
11641 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
11645 @opindex mhard-float
11647 Generate floating-point instructions. This is the default for 68020
11648 and above, and for ColdFire devices that have an FPU@. It defines the
11649 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
11650 on ColdFire targets.
11653 @opindex msoft-float
11654 Do not generate floating-point instructions; use library calls instead.
11655 This is the default for 68000, 68010, and 68832 targets. It is also
11656 the default for ColdFire devices that have no FPU.
11662 Generate (do not generate) ColdFire hardware divide and remainder
11663 instructions. If @option{-march} is used without @option{-mcpu},
11664 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
11665 architectures. Otherwise, the default is taken from the target CPU
11666 (either the default CPU, or the one specified by @option{-mcpu}). For
11667 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
11668 @option{-mcpu=5206e}.
11670 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
11674 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11675 Additionally, parameters passed on the stack are also aligned to a
11676 16-bit boundary even on targets whose API mandates promotion to 32-bit.
11680 Do not consider type @code{int} to be 16 bits wide. This is the default.
11683 @itemx -mno-bitfield
11684 @opindex mnobitfield
11685 @opindex mno-bitfield
11686 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
11687 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
11691 Do use the bit-field instructions. The @option{-m68020} option implies
11692 @option{-mbitfield}. This is the default if you use a configuration
11693 designed for a 68020.
11697 Use a different function-calling convention, in which functions
11698 that take a fixed number of arguments return with the @code{rtd}
11699 instruction, which pops their arguments while returning. This
11700 saves one instruction in the caller since there is no need to pop
11701 the arguments there.
11703 This calling convention is incompatible with the one normally
11704 used on Unix, so you cannot use it if you need to call libraries
11705 compiled with the Unix compiler.
11707 Also, you must provide function prototypes for all functions that
11708 take variable numbers of arguments (including @code{printf});
11709 otherwise incorrect code will be generated for calls to those
11712 In addition, seriously incorrect code will result if you call a
11713 function with too many arguments. (Normally, extra arguments are
11714 harmlessly ignored.)
11716 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
11717 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
11721 Do not use the calling conventions selected by @option{-mrtd}.
11722 This is the default.
11725 @itemx -mno-align-int
11726 @opindex malign-int
11727 @opindex mno-align-int
11728 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
11729 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
11730 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
11731 Aligning variables on 32-bit boundaries produces code that runs somewhat
11732 faster on processors with 32-bit busses at the expense of more memory.
11734 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
11735 align structures containing the above types differently than
11736 most published application binary interface specifications for the m68k.
11740 Use the pc-relative addressing mode of the 68000 directly, instead of
11741 using a global offset table. At present, this option implies @option{-fpic},
11742 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
11743 not presently supported with @option{-mpcrel}, though this could be supported for
11744 68020 and higher processors.
11746 @item -mno-strict-align
11747 @itemx -mstrict-align
11748 @opindex mno-strict-align
11749 @opindex mstrict-align
11750 Do not (do) assume that unaligned memory references will be handled by
11754 Generate code that allows the data segment to be located in a different
11755 area of memory from the text segment. This allows for execute in place in
11756 an environment without virtual memory management. This option implies
11759 @item -mno-sep-data
11760 Generate code that assumes that the data segment follows the text segment.
11761 This is the default.
11763 @item -mid-shared-library
11764 Generate code that supports shared libraries via the library ID method.
11765 This allows for execute in place and shared libraries in an environment
11766 without virtual memory management. This option implies @option{-fPIC}.
11768 @item -mno-id-shared-library
11769 Generate code that doesn't assume ID based shared libraries are being used.
11770 This is the default.
11772 @item -mshared-library-id=n
11773 Specified the identification number of the ID based shared library being
11774 compiled. Specifying a value of 0 will generate more compact code, specifying
11775 other values will force the allocation of that number to the current
11776 library but is no more space or time efficient than omitting this option.
11782 When generating position-independent code for ColdFire, generate code
11783 that works if the GOT has more than 8192 entries. This code is
11784 larger and slower than code generated without this option. On M680x0
11785 processors, this option is not needed; @option{-fPIC} suffices.
11787 GCC normally uses a single instruction to load values from the GOT@.
11788 While this is relatively efficient, it only works if the GOT
11789 is smaller than about 64k. Anything larger causes the linker
11790 to report an error such as:
11792 @cindex relocation truncated to fit (ColdFire)
11794 relocation truncated to fit: R_68K_GOT16O foobar
11797 If this happens, you should recompile your code with @option{-mxgot}.
11798 It should then work with very large GOTs. However, code generated with
11799 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
11800 the value of a global symbol.
11802 Note that some linkers, including newer versions of the GNU linker,
11803 can create multiple GOTs and sort GOT entries. If you have such a linker,
11804 you should only need to use @option{-mxgot} when compiling a single
11805 object file that accesses more than 8192 GOT entries. Very few do.
11807 These options have no effect unless GCC is generating
11808 position-independent code.
11812 @node M68hc1x Options
11813 @subsection M68hc1x Options
11814 @cindex M68hc1x options
11816 These are the @samp{-m} options defined for the 68hc11 and 68hc12
11817 microcontrollers. The default values for these options depends on
11818 which style of microcontroller was selected when the compiler was configured;
11819 the defaults for the most common choices are given below.
11826 Generate output for a 68HC11. This is the default
11827 when the compiler is configured for 68HC11-based systems.
11833 Generate output for a 68HC12. This is the default
11834 when the compiler is configured for 68HC12-based systems.
11840 Generate output for a 68HCS12.
11842 @item -mauto-incdec
11843 @opindex mauto-incdec
11844 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
11851 Enable the use of 68HC12 min and max instructions.
11854 @itemx -mno-long-calls
11855 @opindex mlong-calls
11856 @opindex mno-long-calls
11857 Treat all calls as being far away (near). If calls are assumed to be
11858 far away, the compiler will use the @code{call} instruction to
11859 call a function and the @code{rtc} instruction for returning.
11863 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11865 @item -msoft-reg-count=@var{count}
11866 @opindex msoft-reg-count
11867 Specify the number of pseudo-soft registers which are used for the
11868 code generation. The maximum number is 32. Using more pseudo-soft
11869 register may or may not result in better code depending on the program.
11870 The default is 4 for 68HC11 and 2 for 68HC12.
11874 @node MCore Options
11875 @subsection MCore Options
11876 @cindex MCore options
11878 These are the @samp{-m} options defined for the Motorola M*Core
11884 @itemx -mno-hardlit
11886 @opindex mno-hardlit
11887 Inline constants into the code stream if it can be done in two
11888 instructions or less.
11894 Use the divide instruction. (Enabled by default).
11896 @item -mrelax-immediate
11897 @itemx -mno-relax-immediate
11898 @opindex mrelax-immediate
11899 @opindex mno-relax-immediate
11900 Allow arbitrary sized immediates in bit operations.
11902 @item -mwide-bitfields
11903 @itemx -mno-wide-bitfields
11904 @opindex mwide-bitfields
11905 @opindex mno-wide-bitfields
11906 Always treat bit-fields as int-sized.
11908 @item -m4byte-functions
11909 @itemx -mno-4byte-functions
11910 @opindex m4byte-functions
11911 @opindex mno-4byte-functions
11912 Force all functions to be aligned to a four byte boundary.
11914 @item -mcallgraph-data
11915 @itemx -mno-callgraph-data
11916 @opindex mcallgraph-data
11917 @opindex mno-callgraph-data
11918 Emit callgraph information.
11921 @itemx -mno-slow-bytes
11922 @opindex mslow-bytes
11923 @opindex mno-slow-bytes
11924 Prefer word access when reading byte quantities.
11926 @item -mlittle-endian
11927 @itemx -mbig-endian
11928 @opindex mlittle-endian
11929 @opindex mbig-endian
11930 Generate code for a little endian target.
11936 Generate code for the 210 processor.
11940 @subsection MIPS Options
11941 @cindex MIPS options
11947 Generate big-endian code.
11951 Generate little-endian code. This is the default for @samp{mips*el-*-*}
11954 @item -march=@var{arch}
11956 Generate code that will run on @var{arch}, which can be the name of a
11957 generic MIPS ISA, or the name of a particular processor.
11959 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
11960 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
11961 The processor names are:
11962 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
11963 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
11964 @samp{5kc}, @samp{5kf},
11966 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
11967 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
11968 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
11969 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
11970 @samp{loongson2e}, @samp{loongson2f},
11973 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
11974 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
11975 @samp{rm7000}, @samp{rm9000},
11978 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
11979 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
11981 The special value @samp{from-abi} selects the
11982 most compatible architecture for the selected ABI (that is,
11983 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
11985 Native Linux/GNU toolchains also support the value @samp{native},
11986 which selects the best architecture option for the host processor.
11987 @option{-march=native} has no effect if GCC does not recognize
11990 In processor names, a final @samp{000} can be abbreviated as @samp{k}
11991 (for example, @samp{-march=r2k}). Prefixes are optional, and
11992 @samp{vr} may be written @samp{r}.
11994 Names of the form @samp{@var{n}f2_1} refer to processors with
11995 FPUs clocked at half the rate of the core, names of the form
11996 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
11997 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
11998 processors with FPUs clocked a ratio of 3:2 with respect to the core.
11999 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
12000 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
12001 accepted as synonyms for @samp{@var{n}f1_1}.
12003 GCC defines two macros based on the value of this option. The first
12004 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
12005 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
12006 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
12007 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
12008 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
12010 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
12011 above. In other words, it will have the full prefix and will not
12012 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
12013 the macro names the resolved architecture (either @samp{"mips1"} or
12014 @samp{"mips3"}). It names the default architecture when no
12015 @option{-march} option is given.
12017 @item -mtune=@var{arch}
12019 Optimize for @var{arch}. Among other things, this option controls
12020 the way instructions are scheduled, and the perceived cost of arithmetic
12021 operations. The list of @var{arch} values is the same as for
12024 When this option is not used, GCC will optimize for the processor
12025 specified by @option{-march}. By using @option{-march} and
12026 @option{-mtune} together, it is possible to generate code that will
12027 run on a family of processors, but optimize the code for one
12028 particular member of that family.
12030 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
12031 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
12032 @samp{-march} ones described above.
12036 Equivalent to @samp{-march=mips1}.
12040 Equivalent to @samp{-march=mips2}.
12044 Equivalent to @samp{-march=mips3}.
12048 Equivalent to @samp{-march=mips4}.
12052 Equivalent to @samp{-march=mips32}.
12056 Equivalent to @samp{-march=mips32r2}.
12060 Equivalent to @samp{-march=mips64}.
12065 @opindex mno-mips16
12066 Generate (do not generate) MIPS16 code. If GCC is targetting a
12067 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
12069 MIPS16 code generation can also be controlled on a per-function basis
12070 by means of @code{mips16} and @code{nomips16} attributes.
12071 @xref{Function Attributes}, for more information.
12073 @item -mflip-mips16
12074 @opindex mflip-mips16
12075 Generate MIPS16 code on alternating functions. This option is provided
12076 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
12077 not intended for ordinary use in compiling user code.
12079 @item -minterlink-mips16
12080 @itemx -mno-interlink-mips16
12081 @opindex minterlink-mips16
12082 @opindex mno-interlink-mips16
12083 Require (do not require) that non-MIPS16 code be link-compatible with
12086 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
12087 it must either use a call or an indirect jump. @option{-minterlink-mips16}
12088 therefore disables direct jumps unless GCC knows that the target of the
12089 jump is not MIPS16.
12101 Generate code for the given ABI@.
12103 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
12104 generates 64-bit code when you select a 64-bit architecture, but you
12105 can use @option{-mgp32} to get 32-bit code instead.
12107 For information about the O64 ABI, see
12108 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
12110 GCC supports a variant of the o32 ABI in which floating-point registers
12111 are 64 rather than 32 bits wide. You can select this combination with
12112 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
12113 and @samp{mfhc1} instructions and is therefore only supported for
12114 MIPS32R2 processors.
12116 The register assignments for arguments and return values remain the
12117 same, but each scalar value is passed in a single 64-bit register
12118 rather than a pair of 32-bit registers. For example, scalar
12119 floating-point values are returned in @samp{$f0} only, not a
12120 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
12121 remains the same, but all 64 bits are saved.
12124 @itemx -mno-abicalls
12126 @opindex mno-abicalls
12127 Generate (do not generate) code that is suitable for SVR4-style
12128 dynamic objects. @option{-mabicalls} is the default for SVR4-based
12133 Generate (do not generate) code that is fully position-independent,
12134 and that can therefore be linked into shared libraries. This option
12135 only affects @option{-mabicalls}.
12137 All @option{-mabicalls} code has traditionally been position-independent,
12138 regardless of options like @option{-fPIC} and @option{-fpic}. However,
12139 as an extension, the GNU toolchain allows executables to use absolute
12140 accesses for locally-binding symbols. It can also use shorter GP
12141 initialization sequences and generate direct calls to locally-defined
12142 functions. This mode is selected by @option{-mno-shared}.
12144 @option{-mno-shared} depends on binutils 2.16 or higher and generates
12145 objects that can only be linked by the GNU linker. However, the option
12146 does not affect the ABI of the final executable; it only affects the ABI
12147 of relocatable objects. Using @option{-mno-shared} will generally make
12148 executables both smaller and quicker.
12150 @option{-mshared} is the default.
12156 Lift (do not lift) the usual restrictions on the size of the global
12159 GCC normally uses a single instruction to load values from the GOT@.
12160 While this is relatively efficient, it will only work if the GOT
12161 is smaller than about 64k. Anything larger will cause the linker
12162 to report an error such as:
12164 @cindex relocation truncated to fit (MIPS)
12166 relocation truncated to fit: R_MIPS_GOT16 foobar
12169 If this happens, you should recompile your code with @option{-mxgot}.
12170 It should then work with very large GOTs, although it will also be
12171 less efficient, since it will take three instructions to fetch the
12172 value of a global symbol.
12174 Note that some linkers can create multiple GOTs. If you have such a
12175 linker, you should only need to use @option{-mxgot} when a single object
12176 file accesses more than 64k's worth of GOT entries. Very few do.
12178 These options have no effect unless GCC is generating position
12183 Assume that general-purpose registers are 32 bits wide.
12187 Assume that general-purpose registers are 64 bits wide.
12191 Assume that floating-point registers are 32 bits wide.
12195 Assume that floating-point registers are 64 bits wide.
12198 @opindex mhard-float
12199 Use floating-point coprocessor instructions.
12202 @opindex msoft-float
12203 Do not use floating-point coprocessor instructions. Implement
12204 floating-point calculations using library calls instead.
12206 @item -msingle-float
12207 @opindex msingle-float
12208 Assume that the floating-point coprocessor only supports single-precision
12211 @item -mdouble-float
12212 @opindex mdouble-float
12213 Assume that the floating-point coprocessor supports double-precision
12214 operations. This is the default.
12220 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
12221 implement atomic memory built-in functions. When neither option is
12222 specified, GCC will use the instructions if the target architecture
12225 @option{-mllsc} is useful if the runtime environment can emulate the
12226 instructions and @option{-mno-llsc} can be useful when compiling for
12227 nonstandard ISAs. You can make either option the default by
12228 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
12229 respectively. @option{--with-llsc} is the default for some
12230 configurations; see the installation documentation for details.
12236 Use (do not use) revision 1 of the MIPS DSP ASE@.
12237 @xref{MIPS DSP Built-in Functions}. This option defines the
12238 preprocessor macro @samp{__mips_dsp}. It also defines
12239 @samp{__mips_dsp_rev} to 1.
12245 Use (do not use) revision 2 of the MIPS DSP ASE@.
12246 @xref{MIPS DSP Built-in Functions}. This option defines the
12247 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
12248 It also defines @samp{__mips_dsp_rev} to 2.
12251 @itemx -mno-smartmips
12252 @opindex msmartmips
12253 @opindex mno-smartmips
12254 Use (do not use) the MIPS SmartMIPS ASE.
12256 @item -mpaired-single
12257 @itemx -mno-paired-single
12258 @opindex mpaired-single
12259 @opindex mno-paired-single
12260 Use (do not use) paired-single floating-point instructions.
12261 @xref{MIPS Paired-Single Support}. This option requires
12262 hardware floating-point support to be enabled.
12268 Use (do not use) MIPS Digital Media Extension instructions.
12269 This option can only be used when generating 64-bit code and requires
12270 hardware floating-point support to be enabled.
12275 @opindex mno-mips3d
12276 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
12277 The option @option{-mips3d} implies @option{-mpaired-single}.
12283 Use (do not use) MT Multithreading instructions.
12287 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
12288 an explanation of the default and the way that the pointer size is
12293 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
12295 The default size of @code{int}s, @code{long}s and pointers depends on
12296 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
12297 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
12298 32-bit @code{long}s. Pointers are the same size as @code{long}s,
12299 or the same size as integer registers, whichever is smaller.
12305 Assume (do not assume) that all symbols have 32-bit values, regardless
12306 of the selected ABI@. This option is useful in combination with
12307 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
12308 to generate shorter and faster references to symbolic addresses.
12312 Put definitions of externally-visible data in a small data section
12313 if that data is no bigger than @var{num} bytes. GCC can then access
12314 the data more efficiently; see @option{-mgpopt} for details.
12316 The default @option{-G} option depends on the configuration.
12318 @item -mlocal-sdata
12319 @itemx -mno-local-sdata
12320 @opindex mlocal-sdata
12321 @opindex mno-local-sdata
12322 Extend (do not extend) the @option{-G} behavior to local data too,
12323 such as to static variables in C@. @option{-mlocal-sdata} is the
12324 default for all configurations.
12326 If the linker complains that an application is using too much small data,
12327 you might want to try rebuilding the less performance-critical parts with
12328 @option{-mno-local-sdata}. You might also want to build large
12329 libraries with @option{-mno-local-sdata}, so that the libraries leave
12330 more room for the main program.
12332 @item -mextern-sdata
12333 @itemx -mno-extern-sdata
12334 @opindex mextern-sdata
12335 @opindex mno-extern-sdata
12336 Assume (do not assume) that externally-defined data will be in
12337 a small data section if that data is within the @option{-G} limit.
12338 @option{-mextern-sdata} is the default for all configurations.
12340 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
12341 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
12342 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
12343 is placed in a small data section. If @var{Var} is defined by another
12344 module, you must either compile that module with a high-enough
12345 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
12346 definition. If @var{Var} is common, you must link the application
12347 with a high-enough @option{-G} setting.
12349 The easiest way of satisfying these restrictions is to compile
12350 and link every module with the same @option{-G} option. However,
12351 you may wish to build a library that supports several different
12352 small data limits. You can do this by compiling the library with
12353 the highest supported @option{-G} setting and additionally using
12354 @option{-mno-extern-sdata} to stop the library from making assumptions
12355 about externally-defined data.
12361 Use (do not use) GP-relative accesses for symbols that are known to be
12362 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
12363 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
12366 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
12367 might not hold the value of @code{_gp}. For example, if the code is
12368 part of a library that might be used in a boot monitor, programs that
12369 call boot monitor routines will pass an unknown value in @code{$gp}.
12370 (In such situations, the boot monitor itself would usually be compiled
12371 with @option{-G0}.)
12373 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
12374 @option{-mno-extern-sdata}.
12376 @item -membedded-data
12377 @itemx -mno-embedded-data
12378 @opindex membedded-data
12379 @opindex mno-embedded-data
12380 Allocate variables to the read-only data section first if possible, then
12381 next in the small data section if possible, otherwise in data. This gives
12382 slightly slower code than the default, but reduces the amount of RAM required
12383 when executing, and thus may be preferred for some embedded systems.
12385 @item -muninit-const-in-rodata
12386 @itemx -mno-uninit-const-in-rodata
12387 @opindex muninit-const-in-rodata
12388 @opindex mno-uninit-const-in-rodata
12389 Put uninitialized @code{const} variables in the read-only data section.
12390 This option is only meaningful in conjunction with @option{-membedded-data}.
12392 @item -mcode-readable=@var{setting}
12393 @opindex mcode-readable
12394 Specify whether GCC may generate code that reads from executable sections.
12395 There are three possible settings:
12398 @item -mcode-readable=yes
12399 Instructions may freely access executable sections. This is the
12402 @item -mcode-readable=pcrel
12403 MIPS16 PC-relative load instructions can access executable sections,
12404 but other instructions must not do so. This option is useful on 4KSc
12405 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
12406 It is also useful on processors that can be configured to have a dual
12407 instruction/data SRAM interface and that, like the M4K, automatically
12408 redirect PC-relative loads to the instruction RAM.
12410 @item -mcode-readable=no
12411 Instructions must not access executable sections. This option can be
12412 useful on targets that are configured to have a dual instruction/data
12413 SRAM interface but that (unlike the M4K) do not automatically redirect
12414 PC-relative loads to the instruction RAM.
12417 @item -msplit-addresses
12418 @itemx -mno-split-addresses
12419 @opindex msplit-addresses
12420 @opindex mno-split-addresses
12421 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
12422 relocation operators. This option has been superseded by
12423 @option{-mexplicit-relocs} but is retained for backwards compatibility.
12425 @item -mexplicit-relocs
12426 @itemx -mno-explicit-relocs
12427 @opindex mexplicit-relocs
12428 @opindex mno-explicit-relocs
12429 Use (do not use) assembler relocation operators when dealing with symbolic
12430 addresses. The alternative, selected by @option{-mno-explicit-relocs},
12431 is to use assembler macros instead.
12433 @option{-mexplicit-relocs} is the default if GCC was configured
12434 to use an assembler that supports relocation operators.
12436 @item -mcheck-zero-division
12437 @itemx -mno-check-zero-division
12438 @opindex mcheck-zero-division
12439 @opindex mno-check-zero-division
12440 Trap (do not trap) on integer division by zero.
12442 The default is @option{-mcheck-zero-division}.
12444 @item -mdivide-traps
12445 @itemx -mdivide-breaks
12446 @opindex mdivide-traps
12447 @opindex mdivide-breaks
12448 MIPS systems check for division by zero by generating either a
12449 conditional trap or a break instruction. Using traps results in
12450 smaller code, but is only supported on MIPS II and later. Also, some
12451 versions of the Linux kernel have a bug that prevents trap from
12452 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
12453 allow conditional traps on architectures that support them and
12454 @option{-mdivide-breaks} to force the use of breaks.
12456 The default is usually @option{-mdivide-traps}, but this can be
12457 overridden at configure time using @option{--with-divide=breaks}.
12458 Divide-by-zero checks can be completely disabled using
12459 @option{-mno-check-zero-division}.
12464 @opindex mno-memcpy
12465 Force (do not force) the use of @code{memcpy()} for non-trivial block
12466 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
12467 most constant-sized copies.
12470 @itemx -mno-long-calls
12471 @opindex mlong-calls
12472 @opindex mno-long-calls
12473 Disable (do not disable) use of the @code{jal} instruction. Calling
12474 functions using @code{jal} is more efficient but requires the caller
12475 and callee to be in the same 256 megabyte segment.
12477 This option has no effect on abicalls code. The default is
12478 @option{-mno-long-calls}.
12484 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
12485 instructions, as provided by the R4650 ISA@.
12488 @itemx -mno-fused-madd
12489 @opindex mfused-madd
12490 @opindex mno-fused-madd
12491 Enable (disable) use of the floating point multiply-accumulate
12492 instructions, when they are available. The default is
12493 @option{-mfused-madd}.
12495 When multiply-accumulate instructions are used, the intermediate
12496 product is calculated to infinite precision and is not subject to
12497 the FCSR Flush to Zero bit. This may be undesirable in some
12502 Tell the MIPS assembler to not run its preprocessor over user
12503 assembler files (with a @samp{.s} suffix) when assembling them.
12506 @itemx -mno-fix-r4000
12507 @opindex mfix-r4000
12508 @opindex mno-fix-r4000
12509 Work around certain R4000 CPU errata:
12512 A double-word or a variable shift may give an incorrect result if executed
12513 immediately after starting an integer division.
12515 A double-word or a variable shift may give an incorrect result if executed
12516 while an integer multiplication is in progress.
12518 An integer division may give an incorrect result if started in a delay slot
12519 of a taken branch or a jump.
12523 @itemx -mno-fix-r4400
12524 @opindex mfix-r4400
12525 @opindex mno-fix-r4400
12526 Work around certain R4400 CPU errata:
12529 A double-word or a variable shift may give an incorrect result if executed
12530 immediately after starting an integer division.
12534 @itemx -mno-fix-vr4120
12535 @opindex mfix-vr4120
12536 Work around certain VR4120 errata:
12539 @code{dmultu} does not always produce the correct result.
12541 @code{div} and @code{ddiv} do not always produce the correct result if one
12542 of the operands is negative.
12544 The workarounds for the division errata rely on special functions in
12545 @file{libgcc.a}. At present, these functions are only provided by
12546 the @code{mips64vr*-elf} configurations.
12548 Other VR4120 errata require a nop to be inserted between certain pairs of
12549 instructions. These errata are handled by the assembler, not by GCC itself.
12552 @opindex mfix-vr4130
12553 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
12554 workarounds are implemented by the assembler rather than by GCC,
12555 although GCC will avoid using @code{mflo} and @code{mfhi} if the
12556 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
12557 instructions are available instead.
12560 @itemx -mno-fix-sb1
12562 Work around certain SB-1 CPU core errata.
12563 (This flag currently works around the SB-1 revision 2
12564 ``F1'' and ``F2'' floating point errata.)
12566 @item -mflush-func=@var{func}
12567 @itemx -mno-flush-func
12568 @opindex mflush-func
12569 Specifies the function to call to flush the I and D caches, or to not
12570 call any such function. If called, the function must take the same
12571 arguments as the common @code{_flush_func()}, that is, the address of the
12572 memory range for which the cache is being flushed, the size of the
12573 memory range, and the number 3 (to flush both caches). The default
12574 depends on the target GCC was configured for, but commonly is either
12575 @samp{_flush_func} or @samp{__cpu_flush}.
12577 @item mbranch-cost=@var{num}
12578 @opindex mbranch-cost
12579 Set the cost of branches to roughly @var{num} ``simple'' instructions.
12580 This cost is only a heuristic and is not guaranteed to produce
12581 consistent results across releases. A zero cost redundantly selects
12582 the default, which is based on the @option{-mtune} setting.
12584 @item -mbranch-likely
12585 @itemx -mno-branch-likely
12586 @opindex mbranch-likely
12587 @opindex mno-branch-likely
12588 Enable or disable use of Branch Likely instructions, regardless of the
12589 default for the selected architecture. By default, Branch Likely
12590 instructions may be generated if they are supported by the selected
12591 architecture. An exception is for the MIPS32 and MIPS64 architectures
12592 and processors which implement those architectures; for those, Branch
12593 Likely instructions will not be generated by default because the MIPS32
12594 and MIPS64 architectures specifically deprecate their use.
12596 @item -mfp-exceptions
12597 @itemx -mno-fp-exceptions
12598 @opindex mfp-exceptions
12599 Specifies whether FP exceptions are enabled. This affects how we schedule
12600 FP instructions for some processors. The default is that FP exceptions are
12603 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
12604 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
12607 @item -mvr4130-align
12608 @itemx -mno-vr4130-align
12609 @opindex mvr4130-align
12610 The VR4130 pipeline is two-way superscalar, but can only issue two
12611 instructions together if the first one is 8-byte aligned. When this
12612 option is enabled, GCC will align pairs of instructions that it
12613 thinks should execute in parallel.
12615 This option only has an effect when optimizing for the VR4130.
12616 It normally makes code faster, but at the expense of making it bigger.
12617 It is enabled by default at optimization level @option{-O3}.
12621 @subsection MMIX Options
12622 @cindex MMIX Options
12624 These options are defined for the MMIX:
12628 @itemx -mno-libfuncs
12630 @opindex mno-libfuncs
12631 Specify that intrinsic library functions are being compiled, passing all
12632 values in registers, no matter the size.
12635 @itemx -mno-epsilon
12637 @opindex mno-epsilon
12638 Generate floating-point comparison instructions that compare with respect
12639 to the @code{rE} epsilon register.
12641 @item -mabi=mmixware
12643 @opindex mabi-mmixware
12645 Generate code that passes function parameters and return values that (in
12646 the called function) are seen as registers @code{$0} and up, as opposed to
12647 the GNU ABI which uses global registers @code{$231} and up.
12649 @item -mzero-extend
12650 @itemx -mno-zero-extend
12651 @opindex mzero-extend
12652 @opindex mno-zero-extend
12653 When reading data from memory in sizes shorter than 64 bits, use (do not
12654 use) zero-extending load instructions by default, rather than
12655 sign-extending ones.
12658 @itemx -mno-knuthdiv
12660 @opindex mno-knuthdiv
12661 Make the result of a division yielding a remainder have the same sign as
12662 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
12663 remainder follows the sign of the dividend. Both methods are
12664 arithmetically valid, the latter being almost exclusively used.
12666 @item -mtoplevel-symbols
12667 @itemx -mno-toplevel-symbols
12668 @opindex mtoplevel-symbols
12669 @opindex mno-toplevel-symbols
12670 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
12671 code can be used with the @code{PREFIX} assembly directive.
12675 Generate an executable in the ELF format, rather than the default
12676 @samp{mmo} format used by the @command{mmix} simulator.
12678 @item -mbranch-predict
12679 @itemx -mno-branch-predict
12680 @opindex mbranch-predict
12681 @opindex mno-branch-predict
12682 Use (do not use) the probable-branch instructions, when static branch
12683 prediction indicates a probable branch.
12685 @item -mbase-addresses
12686 @itemx -mno-base-addresses
12687 @opindex mbase-addresses
12688 @opindex mno-base-addresses
12689 Generate (do not generate) code that uses @emph{base addresses}. Using a
12690 base address automatically generates a request (handled by the assembler
12691 and the linker) for a constant to be set up in a global register. The
12692 register is used for one or more base address requests within the range 0
12693 to 255 from the value held in the register. The generally leads to short
12694 and fast code, but the number of different data items that can be
12695 addressed is limited. This means that a program that uses lots of static
12696 data may require @option{-mno-base-addresses}.
12698 @item -msingle-exit
12699 @itemx -mno-single-exit
12700 @opindex msingle-exit
12701 @opindex mno-single-exit
12702 Force (do not force) generated code to have a single exit point in each
12706 @node MN10300 Options
12707 @subsection MN10300 Options
12708 @cindex MN10300 options
12710 These @option{-m} options are defined for Matsushita MN10300 architectures:
12715 Generate code to avoid bugs in the multiply instructions for the MN10300
12716 processors. This is the default.
12718 @item -mno-mult-bug
12719 @opindex mno-mult-bug
12720 Do not generate code to avoid bugs in the multiply instructions for the
12721 MN10300 processors.
12725 Generate code which uses features specific to the AM33 processor.
12729 Do not generate code which uses features specific to the AM33 processor. This
12732 @item -mreturn-pointer-on-d0
12733 @opindex mreturn-pointer-on-d0
12734 When generating a function which returns a pointer, return the pointer
12735 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
12736 only in a0, and attempts to call such functions without a prototype
12737 would result in errors. Note that this option is on by default; use
12738 @option{-mno-return-pointer-on-d0} to disable it.
12742 Do not link in the C run-time initialization object file.
12746 Indicate to the linker that it should perform a relaxation optimization pass
12747 to shorten branches, calls and absolute memory addresses. This option only
12748 has an effect when used on the command line for the final link step.
12750 This option makes symbolic debugging impossible.
12753 @node PDP-11 Options
12754 @subsection PDP-11 Options
12755 @cindex PDP-11 Options
12757 These options are defined for the PDP-11:
12762 Use hardware FPP floating point. This is the default. (FIS floating
12763 point on the PDP-11/40 is not supported.)
12766 @opindex msoft-float
12767 Do not use hardware floating point.
12771 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
12775 Return floating-point results in memory. This is the default.
12779 Generate code for a PDP-11/40.
12783 Generate code for a PDP-11/45. This is the default.
12787 Generate code for a PDP-11/10.
12789 @item -mbcopy-builtin
12790 @opindex bcopy-builtin
12791 Use inline @code{movmemhi} patterns for copying memory. This is the
12796 Do not use inline @code{movmemhi} patterns for copying memory.
12802 Use 16-bit @code{int}. This is the default.
12808 Use 32-bit @code{int}.
12811 @itemx -mno-float32
12813 @opindex mno-float32
12814 Use 64-bit @code{float}. This is the default.
12817 @itemx -mno-float64
12819 @opindex mno-float64
12820 Use 32-bit @code{float}.
12824 Use @code{abshi2} pattern. This is the default.
12828 Do not use @code{abshi2} pattern.
12830 @item -mbranch-expensive
12831 @opindex mbranch-expensive
12832 Pretend that branches are expensive. This is for experimenting with
12833 code generation only.
12835 @item -mbranch-cheap
12836 @opindex mbranch-cheap
12837 Do not pretend that branches are expensive. This is the default.
12841 Generate code for a system with split I&D@.
12845 Generate code for a system without split I&D@. This is the default.
12849 Use Unix assembler syntax. This is the default when configured for
12850 @samp{pdp11-*-bsd}.
12854 Use DEC assembler syntax. This is the default when configured for any
12855 PDP-11 target other than @samp{pdp11-*-bsd}.
12858 @node PowerPC Options
12859 @subsection PowerPC Options
12860 @cindex PowerPC options
12862 These are listed under @xref{RS/6000 and PowerPC Options}.
12864 @node RS/6000 and PowerPC Options
12865 @subsection IBM RS/6000 and PowerPC Options
12866 @cindex RS/6000 and PowerPC Options
12867 @cindex IBM RS/6000 and PowerPC Options
12869 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
12876 @itemx -mno-powerpc
12877 @itemx -mpowerpc-gpopt
12878 @itemx -mno-powerpc-gpopt
12879 @itemx -mpowerpc-gfxopt
12880 @itemx -mno-powerpc-gfxopt
12882 @itemx -mno-powerpc64
12886 @itemx -mno-popcntb
12894 @itemx -mno-hard-dfp
12898 @opindex mno-power2
12900 @opindex mno-powerpc
12901 @opindex mpowerpc-gpopt
12902 @opindex mno-powerpc-gpopt
12903 @opindex mpowerpc-gfxopt
12904 @opindex mno-powerpc-gfxopt
12905 @opindex mpowerpc64
12906 @opindex mno-powerpc64
12910 @opindex mno-popcntb
12916 @opindex mno-mfpgpr
12918 @opindex mno-hard-dfp
12919 GCC supports two related instruction set architectures for the
12920 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
12921 instructions supported by the @samp{rios} chip set used in the original
12922 RS/6000 systems and the @dfn{PowerPC} instruction set is the
12923 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
12924 the IBM 4xx, 6xx, and follow-on microprocessors.
12926 Neither architecture is a subset of the other. However there is a
12927 large common subset of instructions supported by both. An MQ
12928 register is included in processors supporting the POWER architecture.
12930 You use these options to specify which instructions are available on the
12931 processor you are using. The default value of these options is
12932 determined when configuring GCC@. Specifying the
12933 @option{-mcpu=@var{cpu_type}} overrides the specification of these
12934 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
12935 rather than the options listed above.
12937 The @option{-mpower} option allows GCC to generate instructions that
12938 are found only in the POWER architecture and to use the MQ register.
12939 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
12940 to generate instructions that are present in the POWER2 architecture but
12941 not the original POWER architecture.
12943 The @option{-mpowerpc} option allows GCC to generate instructions that
12944 are found only in the 32-bit subset of the PowerPC architecture.
12945 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
12946 GCC to use the optional PowerPC architecture instructions in the
12947 General Purpose group, including floating-point square root. Specifying
12948 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
12949 use the optional PowerPC architecture instructions in the Graphics
12950 group, including floating-point select.
12952 The @option{-mmfcrf} option allows GCC to generate the move from
12953 condition register field instruction implemented on the POWER4
12954 processor and other processors that support the PowerPC V2.01
12956 The @option{-mpopcntb} option allows GCC to generate the popcount and
12957 double precision FP reciprocal estimate instruction implemented on the
12958 POWER5 processor and other processors that support the PowerPC V2.02
12960 The @option{-mfprnd} option allows GCC to generate the FP round to
12961 integer instructions implemented on the POWER5+ processor and other
12962 processors that support the PowerPC V2.03 architecture.
12963 The @option{-mcmpb} option allows GCC to generate the compare bytes
12964 instruction implemented on the POWER6 processor and other processors
12965 that support the PowerPC V2.05 architecture.
12966 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
12967 general purpose register instructions implemented on the POWER6X
12968 processor and other processors that support the extended PowerPC V2.05
12970 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
12971 point instructions implemented on some POWER processors.
12973 The @option{-mpowerpc64} option allows GCC to generate the additional
12974 64-bit instructions that are found in the full PowerPC64 architecture
12975 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
12976 @option{-mno-powerpc64}.
12978 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
12979 will use only the instructions in the common subset of both
12980 architectures plus some special AIX common-mode calls, and will not use
12981 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
12982 permits GCC to use any instruction from either architecture and to
12983 allow use of the MQ register; specify this for the Motorola MPC601.
12985 @item -mnew-mnemonics
12986 @itemx -mold-mnemonics
12987 @opindex mnew-mnemonics
12988 @opindex mold-mnemonics
12989 Select which mnemonics to use in the generated assembler code. With
12990 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
12991 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
12992 assembler mnemonics defined for the POWER architecture. Instructions
12993 defined in only one architecture have only one mnemonic; GCC uses that
12994 mnemonic irrespective of which of these options is specified.
12996 GCC defaults to the mnemonics appropriate for the architecture in
12997 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
12998 value of these option. Unless you are building a cross-compiler, you
12999 should normally not specify either @option{-mnew-mnemonics} or
13000 @option{-mold-mnemonics}, but should instead accept the default.
13002 @item -mcpu=@var{cpu_type}
13004 Set architecture type, register usage, choice of mnemonics, and
13005 instruction scheduling parameters for machine type @var{cpu_type}.
13006 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
13007 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
13008 @samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
13009 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
13010 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
13011 @samp{860}, @samp{970}, @samp{8540}, @samp{e300c2}, @samp{e300c3},
13012 @samp{e500mc}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
13013 @samp{power}, @samp{power2}, @samp{power3}, @samp{power4},
13014 @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x},
13015 @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
13016 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
13018 @option{-mcpu=common} selects a completely generic processor. Code
13019 generated under this option will run on any POWER or PowerPC processor.
13020 GCC will use only the instructions in the common subset of both
13021 architectures, and will not use the MQ register. GCC assumes a generic
13022 processor model for scheduling purposes.
13024 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
13025 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
13026 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
13027 types, with an appropriate, generic processor model assumed for
13028 scheduling purposes.
13030 The other options specify a specific processor. Code generated under
13031 those options will run best on that processor, and may not run at all on
13034 The @option{-mcpu} options automatically enable or disable the
13037 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
13038 -mnew-mnemonics -mpopcntb -mpower -mpower2 -mpowerpc64 @gol
13039 -mpowerpc-gpopt -mpowerpc-gfxopt -mstring -mmulhw -mdlmzb -mmfpgpr}
13041 The particular options set for any particular CPU will vary between
13042 compiler versions, depending on what setting seems to produce optimal
13043 code for that CPU; it doesn't necessarily reflect the actual hardware's
13044 capabilities. If you wish to set an individual option to a particular
13045 value, you may specify it after the @option{-mcpu} option, like
13046 @samp{-mcpu=970 -mno-altivec}.
13048 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
13049 not enabled or disabled by the @option{-mcpu} option at present because
13050 AIX does not have full support for these options. You may still
13051 enable or disable them individually if you're sure it'll work in your
13054 @item -mtune=@var{cpu_type}
13056 Set the instruction scheduling parameters for machine type
13057 @var{cpu_type}, but do not set the architecture type, register usage, or
13058 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
13059 values for @var{cpu_type} are used for @option{-mtune} as for
13060 @option{-mcpu}. If both are specified, the code generated will use the
13061 architecture, registers, and mnemonics set by @option{-mcpu}, but the
13062 scheduling parameters set by @option{-mtune}.
13068 Generate code to compute division as reciprocal estimate and iterative
13069 refinement, creating opportunities for increased throughput. This
13070 feature requires: optional PowerPC Graphics instruction set for single
13071 precision and FRE instruction for double precision, assuming divides
13072 cannot generate user-visible traps, and the domain values not include
13073 Infinities, denormals or zero denominator.
13076 @itemx -mno-altivec
13078 @opindex mno-altivec
13079 Generate code that uses (does not use) AltiVec instructions, and also
13080 enable the use of built-in functions that allow more direct access to
13081 the AltiVec instruction set. You may also need to set
13082 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
13088 @opindex mno-vrsave
13089 Generate VRSAVE instructions when generating AltiVec code.
13092 @opindex msecure-plt
13093 Generate code that allows ld and ld.so to build executables and shared
13094 libraries with non-exec .plt and .got sections. This is a PowerPC
13095 32-bit SYSV ABI option.
13099 Generate code that uses a BSS .plt section that ld.so fills in, and
13100 requires .plt and .got sections that are both writable and executable.
13101 This is a PowerPC 32-bit SYSV ABI option.
13107 This switch enables or disables the generation of ISEL instructions.
13109 @item -misel=@var{yes/no}
13110 This switch has been deprecated. Use @option{-misel} and
13111 @option{-mno-isel} instead.
13117 This switch enables or disables the generation of SPE simd
13123 @opindex mno-paired
13124 This switch enables or disables the generation of PAIRED simd
13127 @item -mspe=@var{yes/no}
13128 This option has been deprecated. Use @option{-mspe} and
13129 @option{-mno-spe} instead.
13131 @item -mfloat-gprs=@var{yes/single/double/no}
13132 @itemx -mfloat-gprs
13133 @opindex mfloat-gprs
13134 This switch enables or disables the generation of floating point
13135 operations on the general purpose registers for architectures that
13138 The argument @var{yes} or @var{single} enables the use of
13139 single-precision floating point operations.
13141 The argument @var{double} enables the use of single and
13142 double-precision floating point operations.
13144 The argument @var{no} disables floating point operations on the
13145 general purpose registers.
13147 This option is currently only available on the MPC854x.
13153 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
13154 targets (including GNU/Linux). The 32-bit environment sets int, long
13155 and pointer to 32 bits and generates code that runs on any PowerPC
13156 variant. The 64-bit environment sets int to 32 bits and long and
13157 pointer to 64 bits, and generates code for PowerPC64, as for
13158 @option{-mpowerpc64}.
13161 @itemx -mno-fp-in-toc
13162 @itemx -mno-sum-in-toc
13163 @itemx -mminimal-toc
13165 @opindex mno-fp-in-toc
13166 @opindex mno-sum-in-toc
13167 @opindex mminimal-toc
13168 Modify generation of the TOC (Table Of Contents), which is created for
13169 every executable file. The @option{-mfull-toc} option is selected by
13170 default. In that case, GCC will allocate at least one TOC entry for
13171 each unique non-automatic variable reference in your program. GCC
13172 will also place floating-point constants in the TOC@. However, only
13173 16,384 entries are available in the TOC@.
13175 If you receive a linker error message that saying you have overflowed
13176 the available TOC space, you can reduce the amount of TOC space used
13177 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
13178 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
13179 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
13180 generate code to calculate the sum of an address and a constant at
13181 run-time instead of putting that sum into the TOC@. You may specify one
13182 or both of these options. Each causes GCC to produce very slightly
13183 slower and larger code at the expense of conserving TOC space.
13185 If you still run out of space in the TOC even when you specify both of
13186 these options, specify @option{-mminimal-toc} instead. This option causes
13187 GCC to make only one TOC entry for every file. When you specify this
13188 option, GCC will produce code that is slower and larger but which
13189 uses extremely little TOC space. You may wish to use this option
13190 only on files that contain less frequently executed code.
13196 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
13197 @code{long} type, and the infrastructure needed to support them.
13198 Specifying @option{-maix64} implies @option{-mpowerpc64} and
13199 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
13200 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
13203 @itemx -mno-xl-compat
13204 @opindex mxl-compat
13205 @opindex mno-xl-compat
13206 Produce code that conforms more closely to IBM XL compiler semantics
13207 when using AIX-compatible ABI@. Pass floating-point arguments to
13208 prototyped functions beyond the register save area (RSA) on the stack
13209 in addition to argument FPRs. Do not assume that most significant
13210 double in 128-bit long double value is properly rounded when comparing
13211 values and converting to double. Use XL symbol names for long double
13214 The AIX calling convention was extended but not initially documented to
13215 handle an obscure K&R C case of calling a function that takes the
13216 address of its arguments with fewer arguments than declared. IBM XL
13217 compilers access floating point arguments which do not fit in the
13218 RSA from the stack when a subroutine is compiled without
13219 optimization. Because always storing floating-point arguments on the
13220 stack is inefficient and rarely needed, this option is not enabled by
13221 default and only is necessary when calling subroutines compiled by IBM
13222 XL compilers without optimization.
13226 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
13227 application written to use message passing with special startup code to
13228 enable the application to run. The system must have PE installed in the
13229 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
13230 must be overridden with the @option{-specs=} option to specify the
13231 appropriate directory location. The Parallel Environment does not
13232 support threads, so the @option{-mpe} option and the @option{-pthread}
13233 option are incompatible.
13235 @item -malign-natural
13236 @itemx -malign-power
13237 @opindex malign-natural
13238 @opindex malign-power
13239 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
13240 @option{-malign-natural} overrides the ABI-defined alignment of larger
13241 types, such as floating-point doubles, on their natural size-based boundary.
13242 The option @option{-malign-power} instructs GCC to follow the ABI-specified
13243 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
13245 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
13249 @itemx -mhard-float
13250 @opindex msoft-float
13251 @opindex mhard-float
13252 Generate code that does not use (uses) the floating-point register set.
13253 Software floating point emulation is provided if you use the
13254 @option{-msoft-float} option, and pass the option to GCC when linking.
13257 @itemx -mno-multiple
13259 @opindex mno-multiple
13260 Generate code that uses (does not use) the load multiple word
13261 instructions and the store multiple word instructions. These
13262 instructions are generated by default on POWER systems, and not
13263 generated on PowerPC systems. Do not use @option{-mmultiple} on little
13264 endian PowerPC systems, since those instructions do not work when the
13265 processor is in little endian mode. The exceptions are PPC740 and
13266 PPC750 which permit the instructions usage in little endian mode.
13271 @opindex mno-string
13272 Generate code that uses (does not use) the load string instructions
13273 and the store string word instructions to save multiple registers and
13274 do small block moves. These instructions are generated by default on
13275 POWER systems, and not generated on PowerPC systems. Do not use
13276 @option{-mstring} on little endian PowerPC systems, since those
13277 instructions do not work when the processor is in little endian mode.
13278 The exceptions are PPC740 and PPC750 which permit the instructions
13279 usage in little endian mode.
13284 @opindex mno-update
13285 Generate code that uses (does not use) the load or store instructions
13286 that update the base register to the address of the calculated memory
13287 location. These instructions are generated by default. If you use
13288 @option{-mno-update}, there is a small window between the time that the
13289 stack pointer is updated and the address of the previous frame is
13290 stored, which means code that walks the stack frame across interrupts or
13291 signals may get corrupted data.
13294 @itemx -mno-fused-madd
13295 @opindex mfused-madd
13296 @opindex mno-fused-madd
13297 Generate code that uses (does not use) the floating point multiply and
13298 accumulate instructions. These instructions are generated by default if
13299 hardware floating is used.
13305 Generate code that uses (does not use) the half-word multiply and
13306 multiply-accumulate instructions on the IBM 405, 440 and 464 processors.
13307 These instructions are generated by default when targetting those
13314 Generate code that uses (does not use) the string-search @samp{dlmzb}
13315 instruction on the IBM 405, 440 and 464 processors. This instruction is
13316 generated by default when targetting those processors.
13318 @item -mno-bit-align
13320 @opindex mno-bit-align
13321 @opindex mbit-align
13322 On System V.4 and embedded PowerPC systems do not (do) force structures
13323 and unions that contain bit-fields to be aligned to the base type of the
13326 For example, by default a structure containing nothing but 8
13327 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
13328 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
13329 the structure would be aligned to a 1 byte boundary and be one byte in
13332 @item -mno-strict-align
13333 @itemx -mstrict-align
13334 @opindex mno-strict-align
13335 @opindex mstrict-align
13336 On System V.4 and embedded PowerPC systems do not (do) assume that
13337 unaligned memory references will be handled by the system.
13339 @item -mrelocatable
13340 @itemx -mno-relocatable
13341 @opindex mrelocatable
13342 @opindex mno-relocatable
13343 On embedded PowerPC systems generate code that allows (does not allow)
13344 the program to be relocated to a different address at runtime. If you
13345 use @option{-mrelocatable} on any module, all objects linked together must
13346 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
13348 @item -mrelocatable-lib
13349 @itemx -mno-relocatable-lib
13350 @opindex mrelocatable-lib
13351 @opindex mno-relocatable-lib
13352 On embedded PowerPC systems generate code that allows (does not allow)
13353 the program to be relocated to a different address at runtime. Modules
13354 compiled with @option{-mrelocatable-lib} can be linked with either modules
13355 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
13356 with modules compiled with the @option{-mrelocatable} options.
13362 On System V.4 and embedded PowerPC systems do not (do) assume that
13363 register 2 contains a pointer to a global area pointing to the addresses
13364 used in the program.
13367 @itemx -mlittle-endian
13369 @opindex mlittle-endian
13370 On System V.4 and embedded PowerPC systems compile code for the
13371 processor in little endian mode. The @option{-mlittle-endian} option is
13372 the same as @option{-mlittle}.
13375 @itemx -mbig-endian
13377 @opindex mbig-endian
13378 On System V.4 and embedded PowerPC systems compile code for the
13379 processor in big endian mode. The @option{-mbig-endian} option is
13380 the same as @option{-mbig}.
13382 @item -mdynamic-no-pic
13383 @opindex mdynamic-no-pic
13384 On Darwin and Mac OS X systems, compile code so that it is not
13385 relocatable, but that its external references are relocatable. The
13386 resulting code is suitable for applications, but not shared
13389 @item -mprioritize-restricted-insns=@var{priority}
13390 @opindex mprioritize-restricted-insns
13391 This option controls the priority that is assigned to
13392 dispatch-slot restricted instructions during the second scheduling
13393 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
13394 @var{no/highest/second-highest} priority to dispatch slot restricted
13397 @item -msched-costly-dep=@var{dependence_type}
13398 @opindex msched-costly-dep
13399 This option controls which dependences are considered costly
13400 by the target during instruction scheduling. The argument
13401 @var{dependence_type} takes one of the following values:
13402 @var{no}: no dependence is costly,
13403 @var{all}: all dependences are costly,
13404 @var{true_store_to_load}: a true dependence from store to load is costly,
13405 @var{store_to_load}: any dependence from store to load is costly,
13406 @var{number}: any dependence which latency >= @var{number} is costly.
13408 @item -minsert-sched-nops=@var{scheme}
13409 @opindex minsert-sched-nops
13410 This option controls which nop insertion scheme will be used during
13411 the second scheduling pass. The argument @var{scheme} takes one of the
13413 @var{no}: Don't insert nops.
13414 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
13415 according to the scheduler's grouping.
13416 @var{regroup_exact}: Insert nops to force costly dependent insns into
13417 separate groups. Insert exactly as many nops as needed to force an insn
13418 to a new group, according to the estimated processor grouping.
13419 @var{number}: Insert nops to force costly dependent insns into
13420 separate groups. Insert @var{number} nops to force an insn to a new group.
13423 @opindex mcall-sysv
13424 On System V.4 and embedded PowerPC systems compile code using calling
13425 conventions that adheres to the March 1995 draft of the System V
13426 Application Binary Interface, PowerPC processor supplement. This is the
13427 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
13429 @item -mcall-sysv-eabi
13430 @opindex mcall-sysv-eabi
13431 Specify both @option{-mcall-sysv} and @option{-meabi} options.
13433 @item -mcall-sysv-noeabi
13434 @opindex mcall-sysv-noeabi
13435 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
13437 @item -mcall-solaris
13438 @opindex mcall-solaris
13439 On System V.4 and embedded PowerPC systems compile code for the Solaris
13443 @opindex mcall-linux
13444 On System V.4 and embedded PowerPC systems compile code for the
13445 Linux-based GNU system.
13449 On System V.4 and embedded PowerPC systems compile code for the
13450 Hurd-based GNU system.
13452 @item -mcall-netbsd
13453 @opindex mcall-netbsd
13454 On System V.4 and embedded PowerPC systems compile code for the
13455 NetBSD operating system.
13457 @item -maix-struct-return
13458 @opindex maix-struct-return
13459 Return all structures in memory (as specified by the AIX ABI)@.
13461 @item -msvr4-struct-return
13462 @opindex msvr4-struct-return
13463 Return structures smaller than 8 bytes in registers (as specified by the
13466 @item -mabi=@var{abi-type}
13468 Extend the current ABI with a particular extension, or remove such extension.
13469 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
13470 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
13474 Extend the current ABI with SPE ABI extensions. This does not change
13475 the default ABI, instead it adds the SPE ABI extensions to the current
13479 @opindex mabi=no-spe
13480 Disable Booke SPE ABI extensions for the current ABI@.
13482 @item -mabi=ibmlongdouble
13483 @opindex mabi=ibmlongdouble
13484 Change the current ABI to use IBM extended precision long double.
13485 This is a PowerPC 32-bit SYSV ABI option.
13487 @item -mabi=ieeelongdouble
13488 @opindex mabi=ieeelongdouble
13489 Change the current ABI to use IEEE extended precision long double.
13490 This is a PowerPC 32-bit Linux ABI option.
13493 @itemx -mno-prototype
13494 @opindex mprototype
13495 @opindex mno-prototype
13496 On System V.4 and embedded PowerPC systems assume that all calls to
13497 variable argument functions are properly prototyped. Otherwise, the
13498 compiler must insert an instruction before every non prototyped call to
13499 set or clear bit 6 of the condition code register (@var{CR}) to
13500 indicate whether floating point values were passed in the floating point
13501 registers in case the function takes a variable arguments. With
13502 @option{-mprototype}, only calls to prototyped variable argument functions
13503 will set or clear the bit.
13507 On embedded PowerPC systems, assume that the startup module is called
13508 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
13509 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
13514 On embedded PowerPC systems, assume that the startup module is called
13515 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
13520 On embedded PowerPC systems, assume that the startup module is called
13521 @file{crt0.o} and the standard C libraries are @file{libads.a} and
13524 @item -myellowknife
13525 @opindex myellowknife
13526 On embedded PowerPC systems, assume that the startup module is called
13527 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
13532 On System V.4 and embedded PowerPC systems, specify that you are
13533 compiling for a VxWorks system.
13537 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
13538 header to indicate that @samp{eabi} extended relocations are used.
13544 On System V.4 and embedded PowerPC systems do (do not) adhere to the
13545 Embedded Applications Binary Interface (eabi) which is a set of
13546 modifications to the System V.4 specifications. Selecting @option{-meabi}
13547 means that the stack is aligned to an 8 byte boundary, a function
13548 @code{__eabi} is called to from @code{main} to set up the eabi
13549 environment, and the @option{-msdata} option can use both @code{r2} and
13550 @code{r13} to point to two separate small data areas. Selecting
13551 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
13552 do not call an initialization function from @code{main}, and the
13553 @option{-msdata} option will only use @code{r13} to point to a single
13554 small data area. The @option{-meabi} option is on by default if you
13555 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
13558 @opindex msdata=eabi
13559 On System V.4 and embedded PowerPC systems, put small initialized
13560 @code{const} global and static data in the @samp{.sdata2} section, which
13561 is pointed to by register @code{r2}. Put small initialized
13562 non-@code{const} global and static data in the @samp{.sdata} section,
13563 which is pointed to by register @code{r13}. Put small uninitialized
13564 global and static data in the @samp{.sbss} section, which is adjacent to
13565 the @samp{.sdata} section. The @option{-msdata=eabi} option is
13566 incompatible with the @option{-mrelocatable} option. The
13567 @option{-msdata=eabi} option also sets the @option{-memb} option.
13570 @opindex msdata=sysv
13571 On System V.4 and embedded PowerPC systems, put small global and static
13572 data in the @samp{.sdata} section, which is pointed to by register
13573 @code{r13}. Put small uninitialized global and static data in the
13574 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
13575 The @option{-msdata=sysv} option is incompatible with the
13576 @option{-mrelocatable} option.
13578 @item -msdata=default
13580 @opindex msdata=default
13582 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
13583 compile code the same as @option{-msdata=eabi}, otherwise compile code the
13584 same as @option{-msdata=sysv}.
13587 @opindex msdata-data
13588 On System V.4 and embedded PowerPC systems, put small global
13589 data in the @samp{.sdata} section. Put small uninitialized global
13590 data in the @samp{.sbss} section. Do not use register @code{r13}
13591 to address small data however. This is the default behavior unless
13592 other @option{-msdata} options are used.
13596 @opindex msdata=none
13598 On embedded PowerPC systems, put all initialized global and static data
13599 in the @samp{.data} section, and all uninitialized data in the
13600 @samp{.bss} section.
13604 @cindex smaller data references (PowerPC)
13605 @cindex .sdata/.sdata2 references (PowerPC)
13606 On embedded PowerPC systems, put global and static items less than or
13607 equal to @var{num} bytes into the small data or bss sections instead of
13608 the normal data or bss section. By default, @var{num} is 8. The
13609 @option{-G @var{num}} switch is also passed to the linker.
13610 All modules should be compiled with the same @option{-G @var{num}} value.
13613 @itemx -mno-regnames
13615 @opindex mno-regnames
13616 On System V.4 and embedded PowerPC systems do (do not) emit register
13617 names in the assembly language output using symbolic forms.
13620 @itemx -mno-longcall
13622 @opindex mno-longcall
13623 By default assume that all calls are far away so that a longer more
13624 expensive calling sequence is required. This is required for calls
13625 further than 32 megabytes (33,554,432 bytes) from the current location.
13626 A short call will be generated if the compiler knows
13627 the call cannot be that far away. This setting can be overridden by
13628 the @code{shortcall} function attribute, or by @code{#pragma
13631 Some linkers are capable of detecting out-of-range calls and generating
13632 glue code on the fly. On these systems, long calls are unnecessary and
13633 generate slower code. As of this writing, the AIX linker can do this,
13634 as can the GNU linker for PowerPC/64. It is planned to add this feature
13635 to the GNU linker for 32-bit PowerPC systems as well.
13637 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
13638 callee, L42'', plus a ``branch island'' (glue code). The two target
13639 addresses represent the callee and the ``branch island''. The
13640 Darwin/PPC linker will prefer the first address and generate a ``bl
13641 callee'' if the PPC ``bl'' instruction will reach the callee directly;
13642 otherwise, the linker will generate ``bl L42'' to call the ``branch
13643 island''. The ``branch island'' is appended to the body of the
13644 calling function; it computes the full 32-bit address of the callee
13647 On Mach-O (Darwin) systems, this option directs the compiler emit to
13648 the glue for every direct call, and the Darwin linker decides whether
13649 to use or discard it.
13651 In the future, we may cause GCC to ignore all longcall specifications
13652 when the linker is known to generate glue.
13656 Adds support for multithreading with the @dfn{pthreads} library.
13657 This option sets flags for both the preprocessor and linker.
13661 @node S/390 and zSeries Options
13662 @subsection S/390 and zSeries Options
13663 @cindex S/390 and zSeries Options
13665 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
13669 @itemx -msoft-float
13670 @opindex mhard-float
13671 @opindex msoft-float
13672 Use (do not use) the hardware floating-point instructions and registers
13673 for floating-point operations. When @option{-msoft-float} is specified,
13674 functions in @file{libgcc.a} will be used to perform floating-point
13675 operations. When @option{-mhard-float} is specified, the compiler
13676 generates IEEE floating-point instructions. This is the default.
13678 @item -mlong-double-64
13679 @itemx -mlong-double-128
13680 @opindex mlong-double-64
13681 @opindex mlong-double-128
13682 These switches control the size of @code{long double} type. A size
13683 of 64bit makes the @code{long double} type equivalent to the @code{double}
13684 type. This is the default.
13687 @itemx -mno-backchain
13688 @opindex mbackchain
13689 @opindex mno-backchain
13690 Store (do not store) the address of the caller's frame as backchain pointer
13691 into the callee's stack frame.
13692 A backchain may be needed to allow debugging using tools that do not understand
13693 DWARF-2 call frame information.
13694 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
13695 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
13696 the backchain is placed into the topmost word of the 96/160 byte register
13699 In general, code compiled with @option{-mbackchain} is call-compatible with
13700 code compiled with @option{-mmo-backchain}; however, use of the backchain
13701 for debugging purposes usually requires that the whole binary is built with
13702 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
13703 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
13704 to build a linux kernel use @option{-msoft-float}.
13706 The default is to not maintain the backchain.
13708 @item -mpacked-stack
13709 @itemx -mno-packed-stack
13710 @opindex mpacked-stack
13711 @opindex mno-packed-stack
13712 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
13713 specified, the compiler uses the all fields of the 96/160 byte register save
13714 area only for their default purpose; unused fields still take up stack space.
13715 When @option{-mpacked-stack} is specified, register save slots are densely
13716 packed at the top of the register save area; unused space is reused for other
13717 purposes, allowing for more efficient use of the available stack space.
13718 However, when @option{-mbackchain} is also in effect, the topmost word of
13719 the save area is always used to store the backchain, and the return address
13720 register is always saved two words below the backchain.
13722 As long as the stack frame backchain is not used, code generated with
13723 @option{-mpacked-stack} is call-compatible with code generated with
13724 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
13725 S/390 or zSeries generated code that uses the stack frame backchain at run
13726 time, not just for debugging purposes. Such code is not call-compatible
13727 with code compiled with @option{-mpacked-stack}. Also, note that the
13728 combination of @option{-mbackchain},
13729 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
13730 to build a linux kernel use @option{-msoft-float}.
13732 The default is to not use the packed stack layout.
13735 @itemx -mno-small-exec
13736 @opindex msmall-exec
13737 @opindex mno-small-exec
13738 Generate (or do not generate) code using the @code{bras} instruction
13739 to do subroutine calls.
13740 This only works reliably if the total executable size does not
13741 exceed 64k. The default is to use the @code{basr} instruction instead,
13742 which does not have this limitation.
13748 When @option{-m31} is specified, generate code compliant to the
13749 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
13750 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
13751 particular to generate 64-bit instructions. For the @samp{s390}
13752 targets, the default is @option{-m31}, while the @samp{s390x}
13753 targets default to @option{-m64}.
13759 When @option{-mzarch} is specified, generate code using the
13760 instructions available on z/Architecture.
13761 When @option{-mesa} is specified, generate code using the
13762 instructions available on ESA/390. Note that @option{-mesa} is
13763 not possible with @option{-m64}.
13764 When generating code compliant to the GNU/Linux for S/390 ABI,
13765 the default is @option{-mesa}. When generating code compliant
13766 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
13772 Generate (or do not generate) code using the @code{mvcle} instruction
13773 to perform block moves. When @option{-mno-mvcle} is specified,
13774 use a @code{mvc} loop instead. This is the default unless optimizing for
13781 Print (or do not print) additional debug information when compiling.
13782 The default is to not print debug information.
13784 @item -march=@var{cpu-type}
13786 Generate code that will run on @var{cpu-type}, which is the name of a system
13787 representing a certain processor type. Possible values for
13788 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
13789 When generating code using the instructions available on z/Architecture,
13790 the default is @option{-march=z900}. Otherwise, the default is
13791 @option{-march=g5}.
13793 @item -mtune=@var{cpu-type}
13795 Tune to @var{cpu-type} everything applicable about the generated code,
13796 except for the ABI and the set of available instructions.
13797 The list of @var{cpu-type} values is the same as for @option{-march}.
13798 The default is the value used for @option{-march}.
13801 @itemx -mno-tpf-trace
13802 @opindex mtpf-trace
13803 @opindex mno-tpf-trace
13804 Generate code that adds (does not add) in TPF OS specific branches to trace
13805 routines in the operating system. This option is off by default, even
13806 when compiling for the TPF OS@.
13809 @itemx -mno-fused-madd
13810 @opindex mfused-madd
13811 @opindex mno-fused-madd
13812 Generate code that uses (does not use) the floating point multiply and
13813 accumulate instructions. These instructions are generated by default if
13814 hardware floating point is used.
13816 @item -mwarn-framesize=@var{framesize}
13817 @opindex mwarn-framesize
13818 Emit a warning if the current function exceeds the given frame size. Because
13819 this is a compile time check it doesn't need to be a real problem when the program
13820 runs. It is intended to identify functions which most probably cause
13821 a stack overflow. It is useful to be used in an environment with limited stack
13822 size e.g.@: the linux kernel.
13824 @item -mwarn-dynamicstack
13825 @opindex mwarn-dynamicstack
13826 Emit a warning if the function calls alloca or uses dynamically
13827 sized arrays. This is generally a bad idea with a limited stack size.
13829 @item -mstack-guard=@var{stack-guard}
13830 @itemx -mstack-size=@var{stack-size}
13831 @opindex mstack-guard
13832 @opindex mstack-size
13833 If these options are provided the s390 back end emits additional instructions in
13834 the function prologue which trigger a trap if the stack size is @var{stack-guard}
13835 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
13836 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
13837 the frame size of the compiled function is chosen.
13838 These options are intended to be used to help debugging stack overflow problems.
13839 The additionally emitted code causes only little overhead and hence can also be
13840 used in production like systems without greater performance degradation. The given
13841 values have to be exact powers of 2 and @var{stack-size} has to be greater than
13842 @var{stack-guard} without exceeding 64k.
13843 In order to be efficient the extra code makes the assumption that the stack starts
13844 at an address aligned to the value given by @var{stack-size}.
13845 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
13848 @node Score Options
13849 @subsection Score Options
13850 @cindex Score Options
13852 These options are defined for Score implementations:
13857 Compile code for big endian mode. This is the default.
13861 Compile code for little endian mode.
13865 Disable generate bcnz instruction.
13869 Enable generate unaligned load and store instruction.
13873 Enable the use of multiply-accumulate instructions. Disabled by default.
13877 Specify the SCORE5 as the target architecture.
13881 Specify the SCORE5U of the target architecture.
13885 Specify the SCORE7 as the target architecture. This is the default.
13889 Specify the SCORE7D as the target architecture.
13893 @subsection SH Options
13895 These @samp{-m} options are defined for the SH implementations:
13900 Generate code for the SH1.
13904 Generate code for the SH2.
13907 Generate code for the SH2e.
13911 Generate code for the SH3.
13915 Generate code for the SH3e.
13919 Generate code for the SH4 without a floating-point unit.
13921 @item -m4-single-only
13922 @opindex m4-single-only
13923 Generate code for the SH4 with a floating-point unit that only
13924 supports single-precision arithmetic.
13928 Generate code for the SH4 assuming the floating-point unit is in
13929 single-precision mode by default.
13933 Generate code for the SH4.
13937 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
13938 floating-point unit is not used.
13940 @item -m4a-single-only
13941 @opindex m4a-single-only
13942 Generate code for the SH4a, in such a way that no double-precision
13943 floating point operations are used.
13946 @opindex m4a-single
13947 Generate code for the SH4a assuming the floating-point unit is in
13948 single-precision mode by default.
13952 Generate code for the SH4a.
13956 Same as @option{-m4a-nofpu}, except that it implicitly passes
13957 @option{-dsp} to the assembler. GCC doesn't generate any DSP
13958 instructions at the moment.
13962 Compile code for the processor in big endian mode.
13966 Compile code for the processor in little endian mode.
13970 Align doubles at 64-bit boundaries. Note that this changes the calling
13971 conventions, and thus some functions from the standard C library will
13972 not work unless you recompile it first with @option{-mdalign}.
13976 Shorten some address references at link time, when possible; uses the
13977 linker option @option{-relax}.
13981 Use 32-bit offsets in @code{switch} tables. The default is to use
13986 Enable the use of bit manipulation instructions on SH2A.
13990 Enable the use of the instruction @code{fmovd}.
13994 Comply with the calling conventions defined by Renesas.
13998 Comply with the calling conventions defined by Renesas.
14002 Comply with the calling conventions defined for GCC before the Renesas
14003 conventions were available. This option is the default for all
14004 targets of the SH toolchain except for @samp{sh-symbianelf}.
14007 @opindex mnomacsave
14008 Mark the @code{MAC} register as call-clobbered, even if
14009 @option{-mhitachi} is given.
14013 Increase IEEE-compliance of floating-point code.
14014 At the moment, this is equivalent to @option{-fno-finite-math-only}.
14015 When generating 16 bit SH opcodes, getting IEEE-conforming results for
14016 comparisons of NANs / infinities incurs extra overhead in every
14017 floating point comparison, therefore the default is set to
14018 @option{-ffinite-math-only}.
14020 @item -minline-ic_invalidate
14021 @opindex minline-ic_invalidate
14022 Inline code to invalidate instruction cache entries after setting up
14023 nested function trampolines.
14024 This option has no effect if -musermode is in effect and the selected
14025 code generation option (e.g. -m4) does not allow the use of the icbi
14027 If the selected code generation option does not allow the use of the icbi
14028 instruction, and -musermode is not in effect, the inlined code will
14029 manipulate the instruction cache address array directly with an associative
14030 write. This not only requires privileged mode, but it will also
14031 fail if the cache line had been mapped via the TLB and has become unmapped.
14035 Dump instruction size and location in the assembly code.
14038 @opindex mpadstruct
14039 This option is deprecated. It pads structures to multiple of 4 bytes,
14040 which is incompatible with the SH ABI@.
14044 Optimize for space instead of speed. Implied by @option{-Os}.
14047 @opindex mprefergot
14048 When generating position-independent code, emit function calls using
14049 the Global Offset Table instead of the Procedure Linkage Table.
14053 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
14054 if the inlined code would not work in user mode.
14055 This is the default when the target is @code{sh-*-linux*}.
14057 @item -multcost=@var{number}
14058 @opindex multcost=@var{number}
14059 Set the cost to assume for a multiply insn.
14061 @item -mdiv=@var{strategy}
14062 @opindex mdiv=@var{strategy}
14063 Set the division strategy to use for SHmedia code. @var{strategy} must be
14064 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
14065 inv:call2, inv:fp .
14066 "fp" performs the operation in floating point. This has a very high latency,
14067 but needs only a few instructions, so it might be a good choice if
14068 your code has enough easily exploitable ILP to allow the compiler to
14069 schedule the floating point instructions together with other instructions.
14070 Division by zero causes a floating point exception.
14071 "inv" uses integer operations to calculate the inverse of the divisor,
14072 and then multiplies the dividend with the inverse. This strategy allows
14073 cse and hoisting of the inverse calculation. Division by zero calculates
14074 an unspecified result, but does not trap.
14075 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
14076 have been found, or if the entire operation has been hoisted to the same
14077 place, the last stages of the inverse calculation are intertwined with the
14078 final multiply to reduce the overall latency, at the expense of using a few
14079 more instructions, and thus offering fewer scheduling opportunities with
14081 "call" calls a library function that usually implements the inv:minlat
14083 This gives high code density for m5-*media-nofpu compilations.
14084 "call2" uses a different entry point of the same library function, where it
14085 assumes that a pointer to a lookup table has already been set up, which
14086 exposes the pointer load to cse / code hoisting optimizations.
14087 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
14088 code generation, but if the code stays unoptimized, revert to the "call",
14089 "call2", or "fp" strategies, respectively. Note that the
14090 potentially-trapping side effect of division by zero is carried by a
14091 separate instruction, so it is possible that all the integer instructions
14092 are hoisted out, but the marker for the side effect stays where it is.
14093 A recombination to fp operations or a call is not possible in that case.
14094 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
14095 that the inverse calculation was nor separated from the multiply, they speed
14096 up division where the dividend fits into 20 bits (plus sign where applicable),
14097 by inserting a test to skip a number of operations in this case; this test
14098 slows down the case of larger dividends. inv20u assumes the case of a such
14099 a small dividend to be unlikely, and inv20l assumes it to be likely.
14101 @item -mdivsi3_libfunc=@var{name}
14102 @opindex mdivsi3_libfunc=@var{name}
14103 Set the name of the library function used for 32 bit signed division to
14104 @var{name}. This only affect the name used in the call and inv:call
14105 division strategies, and the compiler will still expect the same
14106 sets of input/output/clobbered registers as if this option was not present.
14108 @item -mfixed-range=@var{register-range}
14109 @opindex mfixed-range
14110 Generate code treating the given register range as fixed registers.
14111 A fixed register is one that the register allocator can not use. This is
14112 useful when compiling kernel code. A register range is specified as
14113 two registers separated by a dash. Multiple register ranges can be
14114 specified separated by a comma.
14116 @item -madjust-unroll
14117 @opindex madjust-unroll
14118 Throttle unrolling to avoid thrashing target registers.
14119 This option only has an effect if the gcc code base supports the
14120 TARGET_ADJUST_UNROLL_MAX target hook.
14122 @item -mindexed-addressing
14123 @opindex mindexed-addressing
14124 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
14125 This is only safe if the hardware and/or OS implement 32 bit wrap-around
14126 semantics for the indexed addressing mode. The architecture allows the
14127 implementation of processors with 64 bit MMU, which the OS could use to
14128 get 32 bit addressing, but since no current hardware implementation supports
14129 this or any other way to make the indexed addressing mode safe to use in
14130 the 32 bit ABI, the default is -mno-indexed-addressing.
14132 @item -mgettrcost=@var{number}
14133 @opindex mgettrcost=@var{number}
14134 Set the cost assumed for the gettr instruction to @var{number}.
14135 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
14139 Assume pt* instructions won't trap. This will generally generate better
14140 scheduled code, but is unsafe on current hardware. The current architecture
14141 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
14142 This has the unintentional effect of making it unsafe to schedule ptabs /
14143 ptrel before a branch, or hoist it out of a loop. For example,
14144 __do_global_ctors, a part of libgcc that runs constructors at program
14145 startup, calls functions in a list which is delimited by @minus{}1. With the
14146 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
14147 That means that all the constructors will be run a bit quicker, but when
14148 the loop comes to the end of the list, the program crashes because ptabs
14149 loads @minus{}1 into a target register. Since this option is unsafe for any
14150 hardware implementing the current architecture specification, the default
14151 is -mno-pt-fixed. Unless the user specifies a specific cost with
14152 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
14153 this deters register allocation using target registers for storing
14156 @item -minvalid-symbols
14157 @opindex minvalid-symbols
14158 Assume symbols might be invalid. Ordinary function symbols generated by
14159 the compiler will always be valid to load with movi/shori/ptabs or
14160 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
14161 to generate symbols that will cause ptabs / ptrel to trap.
14162 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
14163 It will then prevent cross-basic-block cse, hoisting and most scheduling
14164 of symbol loads. The default is @option{-mno-invalid-symbols}.
14167 @node SPARC Options
14168 @subsection SPARC Options
14169 @cindex SPARC options
14171 These @samp{-m} options are supported on the SPARC:
14174 @item -mno-app-regs
14176 @opindex mno-app-regs
14178 Specify @option{-mapp-regs} to generate output using the global registers
14179 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
14182 To be fully SVR4 ABI compliant at the cost of some performance loss,
14183 specify @option{-mno-app-regs}. You should compile libraries and system
14184 software with this option.
14187 @itemx -mhard-float
14189 @opindex mhard-float
14190 Generate output containing floating point instructions. This is the
14194 @itemx -msoft-float
14196 @opindex msoft-float
14197 Generate output containing library calls for floating point.
14198 @strong{Warning:} the requisite libraries are not available for all SPARC
14199 targets. Normally the facilities of the machine's usual C compiler are
14200 used, but this cannot be done directly in cross-compilation. You must make
14201 your own arrangements to provide suitable library functions for
14202 cross-compilation. The embedded targets @samp{sparc-*-aout} and
14203 @samp{sparclite-*-*} do provide software floating point support.
14205 @option{-msoft-float} changes the calling convention in the output file;
14206 therefore, it is only useful if you compile @emph{all} of a program with
14207 this option. In particular, you need to compile @file{libgcc.a}, the
14208 library that comes with GCC, with @option{-msoft-float} in order for
14211 @item -mhard-quad-float
14212 @opindex mhard-quad-float
14213 Generate output containing quad-word (long double) floating point
14216 @item -msoft-quad-float
14217 @opindex msoft-quad-float
14218 Generate output containing library calls for quad-word (long double)
14219 floating point instructions. The functions called are those specified
14220 in the SPARC ABI@. This is the default.
14222 As of this writing, there are no SPARC implementations that have hardware
14223 support for the quad-word floating point instructions. They all invoke
14224 a trap handler for one of these instructions, and then the trap handler
14225 emulates the effect of the instruction. Because of the trap handler overhead,
14226 this is much slower than calling the ABI library routines. Thus the
14227 @option{-msoft-quad-float} option is the default.
14229 @item -mno-unaligned-doubles
14230 @itemx -munaligned-doubles
14231 @opindex mno-unaligned-doubles
14232 @opindex munaligned-doubles
14233 Assume that doubles have 8 byte alignment. This is the default.
14235 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
14236 alignment only if they are contained in another type, or if they have an
14237 absolute address. Otherwise, it assumes they have 4 byte alignment.
14238 Specifying this option avoids some rare compatibility problems with code
14239 generated by other compilers. It is not the default because it results
14240 in a performance loss, especially for floating point code.
14242 @item -mno-faster-structs
14243 @itemx -mfaster-structs
14244 @opindex mno-faster-structs
14245 @opindex mfaster-structs
14246 With @option{-mfaster-structs}, the compiler assumes that structures
14247 should have 8 byte alignment. This enables the use of pairs of
14248 @code{ldd} and @code{std} instructions for copies in structure
14249 assignment, in place of twice as many @code{ld} and @code{st} pairs.
14250 However, the use of this changed alignment directly violates the SPARC
14251 ABI@. Thus, it's intended only for use on targets where the developer
14252 acknowledges that their resulting code will not be directly in line with
14253 the rules of the ABI@.
14255 @item -mimpure-text
14256 @opindex mimpure-text
14257 @option{-mimpure-text}, used in addition to @option{-shared}, tells
14258 the compiler to not pass @option{-z text} to the linker when linking a
14259 shared object. Using this option, you can link position-dependent
14260 code into a shared object.
14262 @option{-mimpure-text} suppresses the ``relocations remain against
14263 allocatable but non-writable sections'' linker error message.
14264 However, the necessary relocations will trigger copy-on-write, and the
14265 shared object is not actually shared across processes. Instead of
14266 using @option{-mimpure-text}, you should compile all source code with
14267 @option{-fpic} or @option{-fPIC}.
14269 This option is only available on SunOS and Solaris.
14271 @item -mcpu=@var{cpu_type}
14273 Set the instruction set, register set, and instruction scheduling parameters
14274 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
14275 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
14276 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
14277 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
14278 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
14280 Default instruction scheduling parameters are used for values that select
14281 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
14282 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
14284 Here is a list of each supported architecture and their supported
14289 v8: supersparc, hypersparc
14290 sparclite: f930, f934, sparclite86x
14292 v9: ultrasparc, ultrasparc3, niagara, niagara2
14295 By default (unless configured otherwise), GCC generates code for the V7
14296 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
14297 additionally optimizes it for the Cypress CY7C602 chip, as used in the
14298 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
14299 SPARCStation 1, 2, IPX etc.
14301 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
14302 architecture. The only difference from V7 code is that the compiler emits
14303 the integer multiply and integer divide instructions which exist in SPARC-V8
14304 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
14305 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
14308 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
14309 the SPARC architecture. This adds the integer multiply, integer divide step
14310 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
14311 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
14312 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
14313 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
14314 MB86934 chip, which is the more recent SPARClite with FPU@.
14316 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
14317 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
14318 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
14319 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
14320 optimizes it for the TEMIC SPARClet chip.
14322 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
14323 architecture. This adds 64-bit integer and floating-point move instructions,
14324 3 additional floating-point condition code registers and conditional move
14325 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
14326 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
14327 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
14328 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
14329 @option{-mcpu=niagara}, the compiler additionally optimizes it for
14330 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
14331 additionally optimizes it for Sun UltraSPARC T2 chips.
14333 @item -mtune=@var{cpu_type}
14335 Set the instruction scheduling parameters for machine type
14336 @var{cpu_type}, but do not set the instruction set or register set that the
14337 option @option{-mcpu=@var{cpu_type}} would.
14339 The same values for @option{-mcpu=@var{cpu_type}} can be used for
14340 @option{-mtune=@var{cpu_type}}, but the only useful values are those
14341 that select a particular cpu implementation. Those are @samp{cypress},
14342 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
14343 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
14344 @samp{ultrasparc3}, @samp{niagara}, and @samp{niagara2}.
14349 @opindex mno-v8plus
14350 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
14351 difference from the V8 ABI is that the global and out registers are
14352 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
14353 mode for all SPARC-V9 processors.
14359 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
14360 Visual Instruction Set extensions. The default is @option{-mno-vis}.
14363 These @samp{-m} options are supported in addition to the above
14364 on SPARC-V9 processors in 64-bit environments:
14367 @item -mlittle-endian
14368 @opindex mlittle-endian
14369 Generate code for a processor running in little-endian mode. It is only
14370 available for a few configurations and most notably not on Solaris and Linux.
14376 Generate code for a 32-bit or 64-bit environment.
14377 The 32-bit environment sets int, long and pointer to 32 bits.
14378 The 64-bit environment sets int to 32 bits and long and pointer
14381 @item -mcmodel=medlow
14382 @opindex mcmodel=medlow
14383 Generate code for the Medium/Low code model: 64-bit addresses, programs
14384 must be linked in the low 32 bits of memory. Programs can be statically
14385 or dynamically linked.
14387 @item -mcmodel=medmid
14388 @opindex mcmodel=medmid
14389 Generate code for the Medium/Middle code model: 64-bit addresses, programs
14390 must be linked in the low 44 bits of memory, the text and data segments must
14391 be less than 2GB in size and the data segment must be located within 2GB of
14394 @item -mcmodel=medany
14395 @opindex mcmodel=medany
14396 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
14397 may be linked anywhere in memory, the text and data segments must be less
14398 than 2GB in size and the data segment must be located within 2GB of the
14401 @item -mcmodel=embmedany
14402 @opindex mcmodel=embmedany
14403 Generate code for the Medium/Anywhere code model for embedded systems:
14404 64-bit addresses, the text and data segments must be less than 2GB in
14405 size, both starting anywhere in memory (determined at link time). The
14406 global register %g4 points to the base of the data segment. Programs
14407 are statically linked and PIC is not supported.
14410 @itemx -mno-stack-bias
14411 @opindex mstack-bias
14412 @opindex mno-stack-bias
14413 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
14414 frame pointer if present, are offset by @minus{}2047 which must be added back
14415 when making stack frame references. This is the default in 64-bit mode.
14416 Otherwise, assume no such offset is present.
14419 These switches are supported in addition to the above on Solaris:
14424 Add support for multithreading using the Solaris threads library. This
14425 option sets flags for both the preprocessor and linker. This option does
14426 not affect the thread safety of object code produced by the compiler or
14427 that of libraries supplied with it.
14431 Add support for multithreading using the POSIX threads library. This
14432 option sets flags for both the preprocessor and linker. This option does
14433 not affect the thread safety of object code produced by the compiler or
14434 that of libraries supplied with it.
14438 This is a synonym for @option{-pthreads}.
14442 @subsection SPU Options
14443 @cindex SPU options
14445 These @samp{-m} options are supported on the SPU:
14449 @itemx -merror-reloc
14450 @opindex mwarn-reloc
14451 @opindex merror-reloc
14453 The loader for SPU does not handle dynamic relocations. By default, GCC
14454 will give an error when it generates code that requires a dynamic
14455 relocation. @option{-mno-error-reloc} disables the error,
14456 @option{-mwarn-reloc} will generate a warning instead.
14459 @itemx -munsafe-dma
14461 @opindex munsafe-dma
14463 Instructions which initiate or test completion of DMA must not be
14464 reordered with respect to loads and stores of the memory which is being
14465 accessed. Users typically address this problem using the volatile
14466 keyword, but that can lead to inefficient code in places where the
14467 memory is known to not change. Rather than mark the memory as volatile
14468 we treat the DMA instructions as potentially effecting all memory. With
14469 @option{-munsafe-dma} users must use the volatile keyword to protect
14472 @item -mbranch-hints
14473 @opindex mbranch-hints
14475 By default, GCC will generate a branch hint instruction to avoid
14476 pipeline stalls for always taken or probably taken branches. A hint
14477 will not be generated closer than 8 instructions away from its branch.
14478 There is little reason to disable them, except for debugging purposes,
14479 or to make an object a little bit smaller.
14483 @opindex msmall-mem
14484 @opindex mlarge-mem
14486 By default, GCC generates code assuming that addresses are never larger
14487 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
14488 a full 32 bit address.
14493 By default, GCC links against startup code that assumes the SPU-style
14494 main function interface (which has an unconventional parameter list).
14495 With @option{-mstdmain}, GCC will link your program against startup
14496 code that assumes a C99-style interface to @code{main}, including a
14497 local copy of @code{argv} strings.
14499 @item -mfixed-range=@var{register-range}
14500 @opindex mfixed-range
14501 Generate code treating the given register range as fixed registers.
14502 A fixed register is one that the register allocator can not use. This is
14503 useful when compiling kernel code. A register range is specified as
14504 two registers separated by a dash. Multiple register ranges can be
14505 specified separated by a comma.
14509 @node System V Options
14510 @subsection Options for System V
14512 These additional options are available on System V Release 4 for
14513 compatibility with other compilers on those systems:
14518 Create a shared object.
14519 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
14523 Identify the versions of each tool used by the compiler, in a
14524 @code{.ident} assembler directive in the output.
14528 Refrain from adding @code{.ident} directives to the output file (this is
14531 @item -YP,@var{dirs}
14533 Search the directories @var{dirs}, and no others, for libraries
14534 specified with @option{-l}.
14536 @item -Ym,@var{dir}
14538 Look in the directory @var{dir} to find the M4 preprocessor.
14539 The assembler uses this option.
14540 @c This is supposed to go with a -Yd for predefined M4 macro files, but
14541 @c the generic assembler that comes with Solaris takes just -Ym.
14545 @subsection V850 Options
14546 @cindex V850 Options
14548 These @samp{-m} options are defined for V850 implementations:
14552 @itemx -mno-long-calls
14553 @opindex mlong-calls
14554 @opindex mno-long-calls
14555 Treat all calls as being far away (near). If calls are assumed to be
14556 far away, the compiler will always load the functions address up into a
14557 register, and call indirect through the pointer.
14563 Do not optimize (do optimize) basic blocks that use the same index
14564 pointer 4 or more times to copy pointer into the @code{ep} register, and
14565 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
14566 option is on by default if you optimize.
14568 @item -mno-prolog-function
14569 @itemx -mprolog-function
14570 @opindex mno-prolog-function
14571 @opindex mprolog-function
14572 Do not use (do use) external functions to save and restore registers
14573 at the prologue and epilogue of a function. The external functions
14574 are slower, but use less code space if more than one function saves
14575 the same number of registers. The @option{-mprolog-function} option
14576 is on by default if you optimize.
14580 Try to make the code as small as possible. At present, this just turns
14581 on the @option{-mep} and @option{-mprolog-function} options.
14583 @item -mtda=@var{n}
14585 Put static or global variables whose size is @var{n} bytes or less into
14586 the tiny data area that register @code{ep} points to. The tiny data
14587 area can hold up to 256 bytes in total (128 bytes for byte references).
14589 @item -msda=@var{n}
14591 Put static or global variables whose size is @var{n} bytes or less into
14592 the small data area that register @code{gp} points to. The small data
14593 area can hold up to 64 kilobytes.
14595 @item -mzda=@var{n}
14597 Put static or global variables whose size is @var{n} bytes or less into
14598 the first 32 kilobytes of memory.
14602 Specify that the target processor is the V850.
14605 @opindex mbig-switch
14606 Generate code suitable for big switch tables. Use this option only if
14607 the assembler/linker complain about out of range branches within a switch
14612 This option will cause r2 and r5 to be used in the code generated by
14613 the compiler. This setting is the default.
14615 @item -mno-app-regs
14616 @opindex mno-app-regs
14617 This option will cause r2 and r5 to be treated as fixed registers.
14621 Specify that the target processor is the V850E1. The preprocessor
14622 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
14623 this option is used.
14627 Specify that the target processor is the V850E@. The preprocessor
14628 constant @samp{__v850e__} will be defined if this option is used.
14630 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
14631 are defined then a default target processor will be chosen and the
14632 relevant @samp{__v850*__} preprocessor constant will be defined.
14634 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
14635 defined, regardless of which processor variant is the target.
14637 @item -mdisable-callt
14638 @opindex mdisable-callt
14639 This option will suppress generation of the CALLT instruction for the
14640 v850e and v850e1 flavors of the v850 architecture. The default is
14641 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
14646 @subsection VAX Options
14647 @cindex VAX options
14649 These @samp{-m} options are defined for the VAX:
14654 Do not output certain jump instructions (@code{aobleq} and so on)
14655 that the Unix assembler for the VAX cannot handle across long
14660 Do output those jump instructions, on the assumption that you
14661 will assemble with the GNU assembler.
14665 Output code for g-format floating point numbers instead of d-format.
14668 @node VxWorks Options
14669 @subsection VxWorks Options
14670 @cindex VxWorks Options
14672 The options in this section are defined for all VxWorks targets.
14673 Options specific to the target hardware are listed with the other
14674 options for that target.
14679 GCC can generate code for both VxWorks kernels and real time processes
14680 (RTPs). This option switches from the former to the latter. It also
14681 defines the preprocessor macro @code{__RTP__}.
14684 @opindex non-static
14685 Link an RTP executable against shared libraries rather than static
14686 libraries. The options @option{-static} and @option{-shared} can
14687 also be used for RTPs (@pxref{Link Options}); @option{-static}
14694 These options are passed down to the linker. They are defined for
14695 compatibility with Diab.
14698 @opindex Xbind-lazy
14699 Enable lazy binding of function calls. This option is equivalent to
14700 @option{-Wl,-z,now} and is defined for compatibility with Diab.
14704 Disable lazy binding of function calls. This option is the default and
14705 is defined for compatibility with Diab.
14708 @node x86-64 Options
14709 @subsection x86-64 Options
14710 @cindex x86-64 options
14712 These are listed under @xref{i386 and x86-64 Options}.
14714 @node Xstormy16 Options
14715 @subsection Xstormy16 Options
14716 @cindex Xstormy16 Options
14718 These options are defined for Xstormy16:
14723 Choose startup files and linker script suitable for the simulator.
14726 @node Xtensa Options
14727 @subsection Xtensa Options
14728 @cindex Xtensa Options
14730 These options are supported for Xtensa targets:
14734 @itemx -mno-const16
14736 @opindex mno-const16
14737 Enable or disable use of @code{CONST16} instructions for loading
14738 constant values. The @code{CONST16} instruction is currently not a
14739 standard option from Tensilica. When enabled, @code{CONST16}
14740 instructions are always used in place of the standard @code{L32R}
14741 instructions. The use of @code{CONST16} is enabled by default only if
14742 the @code{L32R} instruction is not available.
14745 @itemx -mno-fused-madd
14746 @opindex mfused-madd
14747 @opindex mno-fused-madd
14748 Enable or disable use of fused multiply/add and multiply/subtract
14749 instructions in the floating-point option. This has no effect if the
14750 floating-point option is not also enabled. Disabling fused multiply/add
14751 and multiply/subtract instructions forces the compiler to use separate
14752 instructions for the multiply and add/subtract operations. This may be
14753 desirable in some cases where strict IEEE 754-compliant results are
14754 required: the fused multiply add/subtract instructions do not round the
14755 intermediate result, thereby producing results with @emph{more} bits of
14756 precision than specified by the IEEE standard. Disabling fused multiply
14757 add/subtract instructions also ensures that the program output is not
14758 sensitive to the compiler's ability to combine multiply and add/subtract
14761 @item -mserialize-volatile
14762 @itemx -mno-serialize-volatile
14763 @opindex mserialize-volatile
14764 @opindex mno-serialize-volatile
14765 When this option is enabled, GCC inserts @code{MEMW} instructions before
14766 @code{volatile} memory references to guarantee sequential consistency.
14767 The default is @option{-mserialize-volatile}. Use
14768 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
14770 @item -mtext-section-literals
14771 @itemx -mno-text-section-literals
14772 @opindex mtext-section-literals
14773 @opindex mno-text-section-literals
14774 Control the treatment of literal pools. The default is
14775 @option{-mno-text-section-literals}, which places literals in a separate
14776 section in the output file. This allows the literal pool to be placed
14777 in a data RAM/ROM, and it also allows the linker to combine literal
14778 pools from separate object files to remove redundant literals and
14779 improve code size. With @option{-mtext-section-literals}, the literals
14780 are interspersed in the text section in order to keep them as close as
14781 possible to their references. This may be necessary for large assembly
14784 @item -mtarget-align
14785 @itemx -mno-target-align
14786 @opindex mtarget-align
14787 @opindex mno-target-align
14788 When this option is enabled, GCC instructs the assembler to
14789 automatically align instructions to reduce branch penalties at the
14790 expense of some code density. The assembler attempts to widen density
14791 instructions to align branch targets and the instructions following call
14792 instructions. If there are not enough preceding safe density
14793 instructions to align a target, no widening will be performed. The
14794 default is @option{-mtarget-align}. These options do not affect the
14795 treatment of auto-aligned instructions like @code{LOOP}, which the
14796 assembler will always align, either by widening density instructions or
14797 by inserting no-op instructions.
14800 @itemx -mno-longcalls
14801 @opindex mlongcalls
14802 @opindex mno-longcalls
14803 When this option is enabled, GCC instructs the assembler to translate
14804 direct calls to indirect calls unless it can determine that the target
14805 of a direct call is in the range allowed by the call instruction. This
14806 translation typically occurs for calls to functions in other source
14807 files. Specifically, the assembler translates a direct @code{CALL}
14808 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
14809 The default is @option{-mno-longcalls}. This option should be used in
14810 programs where the call target can potentially be out of range. This
14811 option is implemented in the assembler, not the compiler, so the
14812 assembly code generated by GCC will still show direct call
14813 instructions---look at the disassembled object code to see the actual
14814 instructions. Note that the assembler will use an indirect call for
14815 every cross-file call, not just those that really will be out of range.
14818 @node zSeries Options
14819 @subsection zSeries Options
14820 @cindex zSeries options
14822 These are listed under @xref{S/390 and zSeries Options}.
14824 @node Code Gen Options
14825 @section Options for Code Generation Conventions
14826 @cindex code generation conventions
14827 @cindex options, code generation
14828 @cindex run-time options
14830 These machine-independent options control the interface conventions
14831 used in code generation.
14833 Most of them have both positive and negative forms; the negative form
14834 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
14835 one of the forms is listed---the one which is not the default. You
14836 can figure out the other form by either removing @samp{no-} or adding
14840 @item -fbounds-check
14841 @opindex fbounds-check
14842 For front-ends that support it, generate additional code to check that
14843 indices used to access arrays are within the declared range. This is
14844 currently only supported by the Java and Fortran front-ends, where
14845 this option defaults to true and false respectively.
14849 This option generates traps for signed overflow on addition, subtraction,
14850 multiplication operations.
14854 This option instructs the compiler to assume that signed arithmetic
14855 overflow of addition, subtraction and multiplication wraps around
14856 using twos-complement representation. This flag enables some optimizations
14857 and disables others. This option is enabled by default for the Java
14858 front-end, as required by the Java language specification.
14861 @opindex fexceptions
14862 Enable exception handling. Generates extra code needed to propagate
14863 exceptions. For some targets, this implies GCC will generate frame
14864 unwind information for all functions, which can produce significant data
14865 size overhead, although it does not affect execution. If you do not
14866 specify this option, GCC will enable it by default for languages like
14867 C++ which normally require exception handling, and disable it for
14868 languages like C that do not normally require it. However, you may need
14869 to enable this option when compiling C code that needs to interoperate
14870 properly with exception handlers written in C++. You may also wish to
14871 disable this option if you are compiling older C++ programs that don't
14872 use exception handling.
14874 @item -fnon-call-exceptions
14875 @opindex fnon-call-exceptions
14876 Generate code that allows trapping instructions to throw exceptions.
14877 Note that this requires platform-specific runtime support that does
14878 not exist everywhere. Moreover, it only allows @emph{trapping}
14879 instructions to throw exceptions, i.e.@: memory references or floating
14880 point instructions. It does not allow exceptions to be thrown from
14881 arbitrary signal handlers such as @code{SIGALRM}.
14883 @item -funwind-tables
14884 @opindex funwind-tables
14885 Similar to @option{-fexceptions}, except that it will just generate any needed
14886 static data, but will not affect the generated code in any other way.
14887 You will normally not enable this option; instead, a language processor
14888 that needs this handling would enable it on your behalf.
14890 @item -fasynchronous-unwind-tables
14891 @opindex fasynchronous-unwind-tables
14892 Generate unwind table in dwarf2 format, if supported by target machine. The
14893 table is exact at each instruction boundary, so it can be used for stack
14894 unwinding from asynchronous events (such as debugger or garbage collector).
14896 @item -fpcc-struct-return
14897 @opindex fpcc-struct-return
14898 Return ``short'' @code{struct} and @code{union} values in memory like
14899 longer ones, rather than in registers. This convention is less
14900 efficient, but it has the advantage of allowing intercallability between
14901 GCC-compiled files and files compiled with other compilers, particularly
14902 the Portable C Compiler (pcc).
14904 The precise convention for returning structures in memory depends
14905 on the target configuration macros.
14907 Short structures and unions are those whose size and alignment match
14908 that of some integer type.
14910 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
14911 switch is not binary compatible with code compiled with the
14912 @option{-freg-struct-return} switch.
14913 Use it to conform to a non-default application binary interface.
14915 @item -freg-struct-return
14916 @opindex freg-struct-return
14917 Return @code{struct} and @code{union} values in registers when possible.
14918 This is more efficient for small structures than
14919 @option{-fpcc-struct-return}.
14921 If you specify neither @option{-fpcc-struct-return} nor
14922 @option{-freg-struct-return}, GCC defaults to whichever convention is
14923 standard for the target. If there is no standard convention, GCC
14924 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
14925 the principal compiler. In those cases, we can choose the standard, and
14926 we chose the more efficient register return alternative.
14928 @strong{Warning:} code compiled with the @option{-freg-struct-return}
14929 switch is not binary compatible with code compiled with the
14930 @option{-fpcc-struct-return} switch.
14931 Use it to conform to a non-default application binary interface.
14933 @item -fshort-enums
14934 @opindex fshort-enums
14935 Allocate to an @code{enum} type only as many bytes as it needs for the
14936 declared range of possible values. Specifically, the @code{enum} type
14937 will be equivalent to the smallest integer type which has enough room.
14939 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
14940 code that is not binary compatible with code generated without that switch.
14941 Use it to conform to a non-default application binary interface.
14943 @item -fshort-double
14944 @opindex fshort-double
14945 Use the same size for @code{double} as for @code{float}.
14947 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
14948 code that is not binary compatible with code generated without that switch.
14949 Use it to conform to a non-default application binary interface.
14951 @item -fshort-wchar
14952 @opindex fshort-wchar
14953 Override the underlying type for @samp{wchar_t} to be @samp{short
14954 unsigned int} instead of the default for the target. This option is
14955 useful for building programs to run under WINE@.
14957 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
14958 code that is not binary compatible with code generated without that switch.
14959 Use it to conform to a non-default application binary interface.
14962 @opindex fno-common
14963 In C, allocate even uninitialized global variables in the data section of the
14964 object file, rather than generating them as common blocks. This has the
14965 effect that if the same variable is declared (without @code{extern}) in
14966 two different compilations, you will get an error when you link them.
14967 The only reason this might be useful is if you wish to verify that the
14968 program will work on other systems which always work this way.
14972 Ignore the @samp{#ident} directive.
14974 @item -finhibit-size-directive
14975 @opindex finhibit-size-directive
14976 Don't output a @code{.size} assembler directive, or anything else that
14977 would cause trouble if the function is split in the middle, and the
14978 two halves are placed at locations far apart in memory. This option is
14979 used when compiling @file{crtstuff.c}; you should not need to use it
14982 @item -fverbose-asm
14983 @opindex fverbose-asm
14984 Put extra commentary information in the generated assembly code to
14985 make it more readable. This option is generally only of use to those
14986 who actually need to read the generated assembly code (perhaps while
14987 debugging the compiler itself).
14989 @option{-fno-verbose-asm}, the default, causes the
14990 extra information to be omitted and is useful when comparing two assembler
14993 @item -frecord-gcc-switches
14994 @opindex frecord-gcc-switches
14995 This switch causes the command line that was used to invoke the
14996 compiler to be recorded into the object file that is being created.
14997 This switch is only implemented on some targets and the exact format
14998 of the recording is target and binary file format dependent, but it
14999 usually takes the form of a section containing ASCII text. This
15000 switch is related to the @option{-fverbose-asm} switch, but that
15001 switch only records information in the assembler output file as
15002 comments, so it never reaches the object file.
15006 @cindex global offset table
15008 Generate position-independent code (PIC) suitable for use in a shared
15009 library, if supported for the target machine. Such code accesses all
15010 constant addresses through a global offset table (GOT)@. The dynamic
15011 loader resolves the GOT entries when the program starts (the dynamic
15012 loader is not part of GCC; it is part of the operating system). If
15013 the GOT size for the linked executable exceeds a machine-specific
15014 maximum size, you get an error message from the linker indicating that
15015 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
15016 instead. (These maximums are 8k on the SPARC and 32k
15017 on the m68k and RS/6000. The 386 has no such limit.)
15019 Position-independent code requires special support, and therefore works
15020 only on certain machines. For the 386, GCC supports PIC for System V
15021 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
15022 position-independent.
15024 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15029 If supported for the target machine, emit position-independent code,
15030 suitable for dynamic linking and avoiding any limit on the size of the
15031 global offset table. This option makes a difference on the m68k,
15032 PowerPC and SPARC@.
15034 Position-independent code requires special support, and therefore works
15035 only on certain machines.
15037 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15044 These options are similar to @option{-fpic} and @option{-fPIC}, but
15045 generated position independent code can be only linked into executables.
15046 Usually these options are used when @option{-pie} GCC option will be
15047 used during linking.
15049 @option{-fpie} and @option{-fPIE} both define the macros
15050 @code{__pie__} and @code{__PIE__}. The macros have the value 1
15051 for @option{-fpie} and 2 for @option{-fPIE}.
15053 @item -fno-jump-tables
15054 @opindex fno-jump-tables
15055 Do not use jump tables for switch statements even where it would be
15056 more efficient than other code generation strategies. This option is
15057 of use in conjunction with @option{-fpic} or @option{-fPIC} for
15058 building code which forms part of a dynamic linker and cannot
15059 reference the address of a jump table. On some targets, jump tables
15060 do not require a GOT and this option is not needed.
15062 @item -ffixed-@var{reg}
15064 Treat the register named @var{reg} as a fixed register; generated code
15065 should never refer to it (except perhaps as a stack pointer, frame
15066 pointer or in some other fixed role).
15068 @var{reg} must be the name of a register. The register names accepted
15069 are machine-specific and are defined in the @code{REGISTER_NAMES}
15070 macro in the machine description macro file.
15072 This flag does not have a negative form, because it specifies a
15075 @item -fcall-used-@var{reg}
15076 @opindex fcall-used
15077 Treat the register named @var{reg} as an allocable register that is
15078 clobbered by function calls. It may be allocated for temporaries or
15079 variables that do not live across a call. Functions compiled this way
15080 will not save and restore the register @var{reg}.
15082 It is an error to used this flag with the frame pointer or stack pointer.
15083 Use of this flag for other registers that have fixed pervasive roles in
15084 the machine's execution model will produce disastrous results.
15086 This flag does not have a negative form, because it specifies a
15089 @item -fcall-saved-@var{reg}
15090 @opindex fcall-saved
15091 Treat the register named @var{reg} as an allocable register saved by
15092 functions. It may be allocated even for temporaries or variables that
15093 live across a call. Functions compiled this way will save and restore
15094 the register @var{reg} if they use it.
15096 It is an error to used this flag with the frame pointer or stack pointer.
15097 Use of this flag for other registers that have fixed pervasive roles in
15098 the machine's execution model will produce disastrous results.
15100 A different sort of disaster will result from the use of this flag for
15101 a register in which function values may be returned.
15103 This flag does not have a negative form, because it specifies a
15106 @item -fpack-struct[=@var{n}]
15107 @opindex fpack-struct
15108 Without a value specified, pack all structure members together without
15109 holes. When a value is specified (which must be a small power of two), pack
15110 structure members according to this value, representing the maximum
15111 alignment (that is, objects with default alignment requirements larger than
15112 this will be output potentially unaligned at the next fitting location.
15114 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
15115 code that is not binary compatible with code generated without that switch.
15116 Additionally, it makes the code suboptimal.
15117 Use it to conform to a non-default application binary interface.
15119 @item -finstrument-functions
15120 @opindex finstrument-functions
15121 Generate instrumentation calls for entry and exit to functions. Just
15122 after function entry and just before function exit, the following
15123 profiling functions will be called with the address of the current
15124 function and its call site. (On some platforms,
15125 @code{__builtin_return_address} does not work beyond the current
15126 function, so the call site information may not be available to the
15127 profiling functions otherwise.)
15130 void __cyg_profile_func_enter (void *this_fn,
15132 void __cyg_profile_func_exit (void *this_fn,
15136 The first argument is the address of the start of the current function,
15137 which may be looked up exactly in the symbol table.
15139 This instrumentation is also done for functions expanded inline in other
15140 functions. The profiling calls will indicate where, conceptually, the
15141 inline function is entered and exited. This means that addressable
15142 versions of such functions must be available. If all your uses of a
15143 function are expanded inline, this may mean an additional expansion of
15144 code size. If you use @samp{extern inline} in your C code, an
15145 addressable version of such functions must be provided. (This is
15146 normally the case anyways, but if you get lucky and the optimizer always
15147 expands the functions inline, you might have gotten away without
15148 providing static copies.)
15150 A function may be given the attribute @code{no_instrument_function}, in
15151 which case this instrumentation will not be done. This can be used, for
15152 example, for the profiling functions listed above, high-priority
15153 interrupt routines, and any functions from which the profiling functions
15154 cannot safely be called (perhaps signal handlers, if the profiling
15155 routines generate output or allocate memory).
15157 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
15158 @opindex finstrument-functions-exclude-file-list
15160 Set the list of functions that are excluded from instrumentation (see
15161 the description of @code{-finstrument-functions}). If the file that
15162 contains a function definition matches with one of @var{file}, then
15163 that function is not instrumented. The match is done on substrings:
15164 if the @var{file} parameter is a substring of the file name, it is
15165 considered to be a match.
15168 @code{-finstrument-functions-exclude-file-list=/bits/stl,include/sys}
15169 will exclude any inline function defined in files whose pathnames
15170 contain @code{/bits/stl} or @code{include/sys}.
15172 If, for some reason, you want to include letter @code{','} in one of
15173 @var{sym}, write @code{'\,'}. For example,
15174 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
15175 (note the single quote surrounding the option).
15177 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
15178 @opindex finstrument-functions-exclude-function-list
15180 This is similar to @code{-finstrument-functions-exclude-file-list},
15181 but this option sets the list of function names to be excluded from
15182 instrumentation. The function name to be matched is its user-visible
15183 name, such as @code{vector<int> blah(const vector<int> &)}, not the
15184 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
15185 match is done on substrings: if the @var{sym} parameter is a substring
15186 of the function name, it is considered to be a match.
15188 @item -fstack-check
15189 @opindex fstack-check
15190 Generate code to verify that you do not go beyond the boundary of the
15191 stack. You should specify this flag if you are running in an
15192 environment with multiple threads, but only rarely need to specify it in
15193 a single-threaded environment since stack overflow is automatically
15194 detected on nearly all systems if there is only one stack.
15196 Note that this switch does not actually cause checking to be done; the
15197 operating system must do that. The switch causes generation of code
15198 to ensure that the operating system sees the stack being extended.
15200 @item -fstack-limit-register=@var{reg}
15201 @itemx -fstack-limit-symbol=@var{sym}
15202 @itemx -fno-stack-limit
15203 @opindex fstack-limit-register
15204 @opindex fstack-limit-symbol
15205 @opindex fno-stack-limit
15206 Generate code to ensure that the stack does not grow beyond a certain value,
15207 either the value of a register or the address of a symbol. If the stack
15208 would grow beyond the value, a signal is raised. For most targets,
15209 the signal is raised before the stack overruns the boundary, so
15210 it is possible to catch the signal without taking special precautions.
15212 For instance, if the stack starts at absolute address @samp{0x80000000}
15213 and grows downwards, you can use the flags
15214 @option{-fstack-limit-symbol=__stack_limit} and
15215 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
15216 of 128KB@. Note that this may only work with the GNU linker.
15218 @cindex aliasing of parameters
15219 @cindex parameters, aliased
15220 @item -fargument-alias
15221 @itemx -fargument-noalias
15222 @itemx -fargument-noalias-global
15223 @itemx -fargument-noalias-anything
15224 @opindex fargument-alias
15225 @opindex fargument-noalias
15226 @opindex fargument-noalias-global
15227 @opindex fargument-noalias-anything
15228 Specify the possible relationships among parameters and between
15229 parameters and global data.
15231 @option{-fargument-alias} specifies that arguments (parameters) may
15232 alias each other and may alias global storage.@*
15233 @option{-fargument-noalias} specifies that arguments do not alias
15234 each other, but may alias global storage.@*
15235 @option{-fargument-noalias-global} specifies that arguments do not
15236 alias each other and do not alias global storage.
15237 @option{-fargument-noalias-anything} specifies that arguments do not
15238 alias any other storage.
15240 Each language will automatically use whatever option is required by
15241 the language standard. You should not need to use these options yourself.
15243 @item -fleading-underscore
15244 @opindex fleading-underscore
15245 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
15246 change the way C symbols are represented in the object file. One use
15247 is to help link with legacy assembly code.
15249 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
15250 generate code that is not binary compatible with code generated without that
15251 switch. Use it to conform to a non-default application binary interface.
15252 Not all targets provide complete support for this switch.
15254 @item -ftls-model=@var{model}
15255 @opindex ftls-model
15256 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
15257 The @var{model} argument should be one of @code{global-dynamic},
15258 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
15260 The default without @option{-fpic} is @code{initial-exec}; with
15261 @option{-fpic} the default is @code{global-dynamic}.
15263 @item -fvisibility=@var{default|internal|hidden|protected}
15264 @opindex fvisibility
15265 Set the default ELF image symbol visibility to the specified option---all
15266 symbols will be marked with this unless overridden within the code.
15267 Using this feature can very substantially improve linking and
15268 load times of shared object libraries, produce more optimized
15269 code, provide near-perfect API export and prevent symbol clashes.
15270 It is @strong{strongly} recommended that you use this in any shared objects
15273 Despite the nomenclature, @code{default} always means public ie;
15274 available to be linked against from outside the shared object.
15275 @code{protected} and @code{internal} are pretty useless in real-world
15276 usage so the only other commonly used option will be @code{hidden}.
15277 The default if @option{-fvisibility} isn't specified is
15278 @code{default}, i.e., make every
15279 symbol public---this causes the same behavior as previous versions of
15282 A good explanation of the benefits offered by ensuring ELF
15283 symbols have the correct visibility is given by ``How To Write
15284 Shared Libraries'' by Ulrich Drepper (which can be found at
15285 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
15286 solution made possible by this option to marking things hidden when
15287 the default is public is to make the default hidden and mark things
15288 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
15289 and @code{__attribute__ ((visibility("default")))} instead of
15290 @code{__declspec(dllexport)} you get almost identical semantics with
15291 identical syntax. This is a great boon to those working with
15292 cross-platform projects.
15294 For those adding visibility support to existing code, you may find
15295 @samp{#pragma GCC visibility} of use. This works by you enclosing
15296 the declarations you wish to set visibility for with (for example)
15297 @samp{#pragma GCC visibility push(hidden)} and
15298 @samp{#pragma GCC visibility pop}.
15299 Bear in mind that symbol visibility should be viewed @strong{as
15300 part of the API interface contract} and thus all new code should
15301 always specify visibility when it is not the default ie; declarations
15302 only for use within the local DSO should @strong{always} be marked explicitly
15303 as hidden as so to avoid PLT indirection overheads---making this
15304 abundantly clear also aids readability and self-documentation of the code.
15305 Note that due to ISO C++ specification requirements, operator new and
15306 operator delete must always be of default visibility.
15308 Be aware that headers from outside your project, in particular system
15309 headers and headers from any other library you use, may not be
15310 expecting to be compiled with visibility other than the default. You
15311 may need to explicitly say @samp{#pragma GCC visibility push(default)}
15312 before including any such headers.
15314 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
15315 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
15316 no modifications. However, this means that calls to @samp{extern}
15317 functions with no explicit visibility will use the PLT, so it is more
15318 effective to use @samp{__attribute ((visibility))} and/or
15319 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
15320 declarations should be treated as hidden.
15322 Note that @samp{-fvisibility} does affect C++ vague linkage
15323 entities. This means that, for instance, an exception class that will
15324 be thrown between DSOs must be explicitly marked with default
15325 visibility so that the @samp{type_info} nodes will be unified between
15328 An overview of these techniques, their benefits and how to use them
15329 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
15335 @node Environment Variables
15336 @section Environment Variables Affecting GCC
15337 @cindex environment variables
15339 @c man begin ENVIRONMENT
15340 This section describes several environment variables that affect how GCC
15341 operates. Some of them work by specifying directories or prefixes to use
15342 when searching for various kinds of files. Some are used to specify other
15343 aspects of the compilation environment.
15345 Note that you can also specify places to search using options such as
15346 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
15347 take precedence over places specified using environment variables, which
15348 in turn take precedence over those specified by the configuration of GCC@.
15349 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
15350 GNU Compiler Collection (GCC) Internals}.
15355 @c @itemx LC_COLLATE
15357 @c @itemx LC_MONETARY
15358 @c @itemx LC_NUMERIC
15363 @c @findex LC_COLLATE
15364 @findex LC_MESSAGES
15365 @c @findex LC_MONETARY
15366 @c @findex LC_NUMERIC
15370 These environment variables control the way that GCC uses
15371 localization information that allow GCC to work with different
15372 national conventions. GCC inspects the locale categories
15373 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
15374 so. These locale categories can be set to any value supported by your
15375 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
15376 Kingdom encoded in UTF-8.
15378 The @env{LC_CTYPE} environment variable specifies character
15379 classification. GCC uses it to determine the character boundaries in
15380 a string; this is needed for some multibyte encodings that contain quote
15381 and escape characters that would otherwise be interpreted as a string
15384 The @env{LC_MESSAGES} environment variable specifies the language to
15385 use in diagnostic messages.
15387 If the @env{LC_ALL} environment variable is set, it overrides the value
15388 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
15389 and @env{LC_MESSAGES} default to the value of the @env{LANG}
15390 environment variable. If none of these variables are set, GCC
15391 defaults to traditional C English behavior.
15395 If @env{TMPDIR} is set, it specifies the directory to use for temporary
15396 files. GCC uses temporary files to hold the output of one stage of
15397 compilation which is to be used as input to the next stage: for example,
15398 the output of the preprocessor, which is the input to the compiler
15401 @item GCC_EXEC_PREFIX
15402 @findex GCC_EXEC_PREFIX
15403 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
15404 names of the subprograms executed by the compiler. No slash is added
15405 when this prefix is combined with the name of a subprogram, but you can
15406 specify a prefix that ends with a slash if you wish.
15408 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
15409 an appropriate prefix to use based on the pathname it was invoked with.
15411 If GCC cannot find the subprogram using the specified prefix, it
15412 tries looking in the usual places for the subprogram.
15414 The default value of @env{GCC_EXEC_PREFIX} is
15415 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
15416 the installed compiler. In many cases @var{prefix} is the value
15417 of @code{prefix} when you ran the @file{configure} script.
15419 Other prefixes specified with @option{-B} take precedence over this prefix.
15421 This prefix is also used for finding files such as @file{crt0.o} that are
15424 In addition, the prefix is used in an unusual way in finding the
15425 directories to search for header files. For each of the standard
15426 directories whose name normally begins with @samp{/usr/local/lib/gcc}
15427 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
15428 replacing that beginning with the specified prefix to produce an
15429 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
15430 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
15431 These alternate directories are searched first; the standard directories
15432 come next. If a standard directory begins with the configured
15433 @var{prefix} then the value of @var{prefix} is replaced by
15434 @env{GCC_EXEC_PREFIX} when looking for header files.
15436 @item COMPILER_PATH
15437 @findex COMPILER_PATH
15438 The value of @env{COMPILER_PATH} is a colon-separated list of
15439 directories, much like @env{PATH}. GCC tries the directories thus
15440 specified when searching for subprograms, if it can't find the
15441 subprograms using @env{GCC_EXEC_PREFIX}.
15444 @findex LIBRARY_PATH
15445 The value of @env{LIBRARY_PATH} is a colon-separated list of
15446 directories, much like @env{PATH}. When configured as a native compiler,
15447 GCC tries the directories thus specified when searching for special
15448 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
15449 using GCC also uses these directories when searching for ordinary
15450 libraries for the @option{-l} option (but directories specified with
15451 @option{-L} come first).
15455 @cindex locale definition
15456 This variable is used to pass locale information to the compiler. One way in
15457 which this information is used is to determine the character set to be used
15458 when character literals, string literals and comments are parsed in C and C++.
15459 When the compiler is configured to allow multibyte characters,
15460 the following values for @env{LANG} are recognized:
15464 Recognize JIS characters.
15466 Recognize SJIS characters.
15468 Recognize EUCJP characters.
15471 If @env{LANG} is not defined, or if it has some other value, then the
15472 compiler will use mblen and mbtowc as defined by the default locale to
15473 recognize and translate multibyte characters.
15477 Some additional environments variables affect the behavior of the
15480 @include cppenv.texi
15484 @node Precompiled Headers
15485 @section Using Precompiled Headers
15486 @cindex precompiled headers
15487 @cindex speed of compilation
15489 Often large projects have many header files that are included in every
15490 source file. The time the compiler takes to process these header files
15491 over and over again can account for nearly all of the time required to
15492 build the project. To make builds faster, GCC allows users to
15493 `precompile' a header file; then, if builds can use the precompiled
15494 header file they will be much faster.
15496 To create a precompiled header file, simply compile it as you would any
15497 other file, if necessary using the @option{-x} option to make the driver
15498 treat it as a C or C++ header file. You will probably want to use a
15499 tool like @command{make} to keep the precompiled header up-to-date when
15500 the headers it contains change.
15502 A precompiled header file will be searched for when @code{#include} is
15503 seen in the compilation. As it searches for the included file
15504 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
15505 compiler looks for a precompiled header in each directory just before it
15506 looks for the include file in that directory. The name searched for is
15507 the name specified in the @code{#include} with @samp{.gch} appended. If
15508 the precompiled header file can't be used, it is ignored.
15510 For instance, if you have @code{#include "all.h"}, and you have
15511 @file{all.h.gch} in the same directory as @file{all.h}, then the
15512 precompiled header file will be used if possible, and the original
15513 header will be used otherwise.
15515 Alternatively, you might decide to put the precompiled header file in a
15516 directory and use @option{-I} to ensure that directory is searched
15517 before (or instead of) the directory containing the original header.
15518 Then, if you want to check that the precompiled header file is always
15519 used, you can put a file of the same name as the original header in this
15520 directory containing an @code{#error} command.
15522 This also works with @option{-include}. So yet another way to use
15523 precompiled headers, good for projects not designed with precompiled
15524 header files in mind, is to simply take most of the header files used by
15525 a project, include them from another header file, precompile that header
15526 file, and @option{-include} the precompiled header. If the header files
15527 have guards against multiple inclusion, they will be skipped because
15528 they've already been included (in the precompiled header).
15530 If you need to precompile the same header file for different
15531 languages, targets, or compiler options, you can instead make a
15532 @emph{directory} named like @file{all.h.gch}, and put each precompiled
15533 header in the directory, perhaps using @option{-o}. It doesn't matter
15534 what you call the files in the directory, every precompiled header in
15535 the directory will be considered. The first precompiled header
15536 encountered in the directory that is valid for this compilation will
15537 be used; they're searched in no particular order.
15539 There are many other possibilities, limited only by your imagination,
15540 good sense, and the constraints of your build system.
15542 A precompiled header file can be used only when these conditions apply:
15546 Only one precompiled header can be used in a particular compilation.
15549 A precompiled header can't be used once the first C token is seen. You
15550 can have preprocessor directives before a precompiled header; you can
15551 even include a precompiled header from inside another header, so long as
15552 there are no C tokens before the @code{#include}.
15555 The precompiled header file must be produced for the same language as
15556 the current compilation. You can't use a C precompiled header for a C++
15560 The precompiled header file must have been produced by the same compiler
15561 binary as the current compilation is using.
15564 Any macros defined before the precompiled header is included must
15565 either be defined in the same way as when the precompiled header was
15566 generated, or must not affect the precompiled header, which usually
15567 means that they don't appear in the precompiled header at all.
15569 The @option{-D} option is one way to define a macro before a
15570 precompiled header is included; using a @code{#define} can also do it.
15571 There are also some options that define macros implicitly, like
15572 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
15575 @item If debugging information is output when using the precompiled
15576 header, using @option{-g} or similar, the same kind of debugging information
15577 must have been output when building the precompiled header. However,
15578 a precompiled header built using @option{-g} can be used in a compilation
15579 when no debugging information is being output.
15581 @item The same @option{-m} options must generally be used when building
15582 and using the precompiled header. @xref{Submodel Options},
15583 for any cases where this rule is relaxed.
15585 @item Each of the following options must be the same when building and using
15586 the precompiled header:
15588 @gccoptlist{-fexceptions}
15591 Some other command-line options starting with @option{-f},
15592 @option{-p}, or @option{-O} must be defined in the same way as when
15593 the precompiled header was generated. At present, it's not clear
15594 which options are safe to change and which are not; the safest choice
15595 is to use exactly the same options when generating and using the
15596 precompiled header. The following are known to be safe:
15598 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
15599 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
15600 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
15605 For all of these except the last, the compiler will automatically
15606 ignore the precompiled header if the conditions aren't met. If you
15607 find an option combination that doesn't work and doesn't cause the
15608 precompiled header to be ignored, please consider filing a bug report,
15611 If you do use differing options when generating and using the
15612 precompiled header, the actual behavior will be a mixture of the
15613 behavior for the options. For instance, if you use @option{-g} to
15614 generate the precompiled header but not when using it, you may or may
15615 not get debugging information for routines in the precompiled header.
15617 @node Running Protoize
15618 @section Running Protoize
15620 The program @code{protoize} is an optional part of GCC@. You can use
15621 it to add prototypes to a program, thus converting the program to ISO
15622 C in one respect. The companion program @code{unprotoize} does the
15623 reverse: it removes argument types from any prototypes that are found.
15625 When you run these programs, you must specify a set of source files as
15626 command line arguments. The conversion programs start out by compiling
15627 these files to see what functions they define. The information gathered
15628 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
15630 After scanning comes actual conversion. The specified files are all
15631 eligible to be converted; any files they include (whether sources or
15632 just headers) are eligible as well.
15634 But not all the eligible files are converted. By default,
15635 @code{protoize} and @code{unprotoize} convert only source and header
15636 files in the current directory. You can specify additional directories
15637 whose files should be converted with the @option{-d @var{directory}}
15638 option. You can also specify particular files to exclude with the
15639 @option{-x @var{file}} option. A file is converted if it is eligible, its
15640 directory name matches one of the specified directory names, and its
15641 name within the directory has not been excluded.
15643 Basic conversion with @code{protoize} consists of rewriting most
15644 function definitions and function declarations to specify the types of
15645 the arguments. The only ones not rewritten are those for varargs
15648 @code{protoize} optionally inserts prototype declarations at the
15649 beginning of the source file, to make them available for any calls that
15650 precede the function's definition. Or it can insert prototype
15651 declarations with block scope in the blocks where undeclared functions
15654 Basic conversion with @code{unprotoize} consists of rewriting most
15655 function declarations to remove any argument types, and rewriting
15656 function definitions to the old-style pre-ISO form.
15658 Both conversion programs print a warning for any function declaration or
15659 definition that they can't convert. You can suppress these warnings
15662 The output from @code{protoize} or @code{unprotoize} replaces the
15663 original source file. The original file is renamed to a name ending
15664 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
15665 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
15666 for DOS) file already exists, then the source file is simply discarded.
15668 @code{protoize} and @code{unprotoize} both depend on GCC itself to
15669 scan the program and collect information about the functions it uses.
15670 So neither of these programs will work until GCC is installed.
15672 Here is a table of the options you can use with @code{protoize} and
15673 @code{unprotoize}. Each option works with both programs unless
15677 @item -B @var{directory}
15678 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
15679 usual directory (normally @file{/usr/local/lib}). This file contains
15680 prototype information about standard system functions. This option
15681 applies only to @code{protoize}.
15683 @item -c @var{compilation-options}
15684 Use @var{compilation-options} as the options when running @command{gcc} to
15685 produce the @samp{.X} files. The special option @option{-aux-info} is
15686 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
15688 Note that the compilation options must be given as a single argument to
15689 @code{protoize} or @code{unprotoize}. If you want to specify several
15690 @command{gcc} options, you must quote the entire set of compilation options
15691 to make them a single word in the shell.
15693 There are certain @command{gcc} arguments that you cannot use, because they
15694 would produce the wrong kind of output. These include @option{-g},
15695 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
15696 the @var{compilation-options}, they are ignored.
15699 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
15700 systems) instead of @samp{.c}. This is convenient if you are converting
15701 a C program to C++. This option applies only to @code{protoize}.
15704 Add explicit global declarations. This means inserting explicit
15705 declarations at the beginning of each source file for each function
15706 that is called in the file and was not declared. These declarations
15707 precede the first function definition that contains a call to an
15708 undeclared function. This option applies only to @code{protoize}.
15710 @item -i @var{string}
15711 Indent old-style parameter declarations with the string @var{string}.
15712 This option applies only to @code{protoize}.
15714 @code{unprotoize} converts prototyped function definitions to old-style
15715 function definitions, where the arguments are declared between the
15716 argument list and the initial @samp{@{}. By default, @code{unprotoize}
15717 uses five spaces as the indentation. If you want to indent with just
15718 one space instead, use @option{-i " "}.
15721 Keep the @samp{.X} files. Normally, they are deleted after conversion
15725 Add explicit local declarations. @code{protoize} with @option{-l} inserts
15726 a prototype declaration for each function in each block which calls the
15727 function without any declaration. This option applies only to
15731 Make no real changes. This mode just prints information about the conversions
15732 that would have been done without @option{-n}.
15735 Make no @samp{.save} files. The original files are simply deleted.
15736 Use this option with caution.
15738 @item -p @var{program}
15739 Use the program @var{program} as the compiler. Normally, the name
15740 @file{gcc} is used.
15743 Work quietly. Most warnings are suppressed.
15746 Print the version number, just like @option{-v} for @command{gcc}.
15749 If you need special compiler options to compile one of your program's
15750 source files, then you should generate that file's @samp{.X} file
15751 specially, by running @command{gcc} on that source file with the
15752 appropriate options and the option @option{-aux-info}. Then run
15753 @code{protoize} on the entire set of files. @code{protoize} will use
15754 the existing @samp{.X} file because it is newer than the source file.
15758 gcc -Dfoo=bar file1.c -aux-info file1.X
15763 You need to include the special files along with the rest in the
15764 @code{protoize} command, even though their @samp{.X} files already
15765 exist, because otherwise they won't get converted.
15767 @xref{Protoize Caveats}, for more information on how to use
15768 @code{protoize} successfully.