1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
8 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
9 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.2 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU project C and C++ compiler
33 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
42 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
52 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
53 script to report bugs is recommended.
56 See the Info entry for @command{gcc}, or
57 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
58 for contributors to GCC@.
63 @chapter GCC Command Options
64 @cindex GCC command options
65 @cindex command options
66 @cindex options, GCC command
68 @c man begin DESCRIPTION
69 When you invoke GCC, it normally does preprocessing, compilation,
70 assembly and linking. The ``overall options'' allow you to stop this
71 process at an intermediate stage. For example, the @option{-c} option
72 says not to run the linker. Then the output consists of object files
73 output by the assembler.
75 Other options are passed on to one stage of processing. Some options
76 control the preprocessor and others the compiler itself. Yet other
77 options control the assembler and linker; most of these are not
78 documented here, since you rarely need to use any of them.
80 @cindex C compilation options
81 Most of the command line options that you can use with GCC are useful
82 for C programs; when an option is only useful with another language
83 (usually C++), the explanation says so explicitly. If the description
84 for a particular option does not mention a source language, you can use
85 that option with all supported languages.
87 @cindex C++ compilation options
88 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
89 options for compiling C++ programs.
91 @cindex grouping options
92 @cindex options, grouping
93 The @command{gcc} program accepts options and file names as operands. Many
94 options have multi-letter names; therefore multiple single-letter options
95 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
98 @cindex order of options
99 @cindex options, order
100 You can mix options and other arguments. For the most part, the order
101 you use doesn't matter. Order does matter when you use several options
102 of the same kind; for example, if you specify @option{-L} more than once,
103 the directories are searched in the order specified.
105 Many options have long names starting with @samp{-f} or with
106 @samp{-W}---for example, @option{-fforce-mem},
107 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
108 these have both positive and negative forms; the negative form of
109 @option{-ffoo} would be @option{-fno-foo}. This manual documents
110 only one of these two forms, whichever one is not the default.
114 @xref{Option Index}, for an index to GCC's options.
117 * Option Summary:: Brief list of all options, without explanations.
118 * Overall Options:: Controlling the kind of output:
119 an executable, object files, assembler files,
120 or preprocessed source.
121 * Invoking G++:: Compiling C++ programs.
122 * C Dialect Options:: Controlling the variant of C language compiled.
123 * C++ Dialect Options:: Variations on C++.
124 * Objective-C Dialect Options:: Variations on Objective-C.
125 * Language Independent Options:: Controlling how diagnostics should be
127 * Warning Options:: How picky should the compiler be?
128 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
129 * Optimize Options:: How much optimization?
130 * Preprocessor Options:: Controlling header files and macro definitions.
131 Also, getting dependency information for Make.
132 * Assembler Options:: Passing options to the assembler.
133 * Link Options:: Specifying libraries and so on.
134 * Directory Options:: Where to find header files and libraries.
135 Where to find the compiler executable files.
136 * Spec Files:: How to pass switches to sub-processes.
137 * Target Options:: Running a cross-compiler, or an old version of GCC.
138 * Submodel Options:: Specifying minor hardware or convention variations,
139 such as 68010 vs 68020.
140 * Code Gen Options:: Specifying conventions for function calls, data layout
142 * Environment Variables:: Env vars that affect GCC.
143 * Precompiled Headers:: Compiling a header once, and using it many times.
144 * Running Protoize:: Automatically adding or removing function prototypes.
150 @section Option Summary
152 Here is a summary of all the options, grouped by type. Explanations are
153 in the following sections.
156 @item Overall Options
157 @xref{Overall Options,,Options Controlling the Kind of Output}.
158 @gccoptlist{-c -S -E -o @var{file} -pipe -pass-exit-codes @gol
159 -x @var{language} -v -### --help --target-help --version}
161 @item C Language Options
162 @xref{C Dialect Options,,Options Controlling C Dialect}.
163 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
164 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
165 -fhosted -ffreestanding -fms-extensions @gol
166 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
167 -fallow-single-precision -fcond-mismatch @gol
168 -fsigned-bitfields -fsigned-char @gol
169 -funsigned-bitfields -funsigned-char @gol
172 @item C++ Language Options
173 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
174 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
175 -fconserve-space -fno-const-strings @gol
176 -fno-elide-constructors @gol
177 -fno-enforce-eh-specs -fexternal-templates @gol
178 -falt-external-templates @gol
179 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
180 -fno-implicit-templates @gol
181 -fno-implicit-inline-templates @gol
182 -fno-implement-inlines -fms-extensions @gol
183 -fno-nonansi-builtins -fno-operator-names @gol
184 -fno-optional-diags -fpermissive @gol
185 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
186 -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
187 -fno-default-inline -Wabi -Wctor-dtor-privacy @gol
188 -Wnon-virtual-dtor -Wreorder @gol
189 -Weffc++ -Wno-deprecated @gol
190 -Wno-non-template-friend -Wold-style-cast @gol
191 -Woverloaded-virtual -Wno-pmf-conversions @gol
192 -Wsign-promo -Wsynth}
194 @item Objective-C Language Options
195 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
196 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
197 -fgnu-runtime -fnext-runtime -gen-decls @gol
198 -Wno-protocol -Wselector -Wundeclared-selector}
200 @item Language Independent Options
201 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
202 @gccoptlist{-fmessage-length=@var{n} @gol
203 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
205 @item Warning Options
206 @xref{Warning Options,,Options to Request or Suppress Warnings}.
207 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
208 -w -Wextra -Wall -Waggregate-return @gol
209 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
210 -Wconversion -Wno-deprecated-declarations @gol
211 -Wdisabled-optimization -Wno-div-by-zero -Werror @gol
212 -Wfloat-equal -Wformat -Wformat=2 @gol
213 -Wformat-nonliteral -Wformat-security @gol
214 -Wimplicit -Wimplicit-int @gol
215 -Wimplicit-function-declaration @gol
216 -Werror-implicit-function-declaration @gol
217 -Winit-self Wimport -Winline -Winvalid-pch -Wno-endif-labels @gol
218 -Wno-invalid-offsetof @gol
219 -Wlarger-than-@var{len} -Wlong-long @gol
220 -Wmain -Wmissing-braces @gol
221 -Wmissing-format-attribute -Wmissing-noreturn @gol
222 -Wno-multichar -Wno-format-extra-args -Wno-format-y2k @gol
223 -Wno-import -Wnonnull -Wpacked -Wpadded @gol
224 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
225 -Wreturn-type -Wsequence-point -Wshadow @gol
226 -Wsign-compare -Wstrict-aliasing @gol
227 -Wswitch -Wswitch-default -Wswitch-enum @gol
228 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
229 -Wunknown-pragmas -Wunreachable-code @gol
230 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
231 -Wunused-value -Wunused-variable -Wwrite-strings}
233 @item C-only Warning Options
234 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
235 -Wmissing-prototypes -Wnested-externs @gol
236 -Wstrict-prototypes -Wtraditional @gol
237 -Wdeclaration-after-statement}
239 @item Debugging Options
240 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
241 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
242 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
243 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
244 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
245 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
246 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
247 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
248 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
249 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
250 -ftest-coverage -ftime-report @gol
251 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
252 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
253 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
254 -print-multi-directory -print-multi-lib @gol
255 -print-prog-name=@var{program} -print-search-dirs -Q @gol
258 @item Optimization Options
259 @xref{Optimize Options,,Options that Control Optimization}.
260 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
261 -falign-labels=@var{n} -falign-loops=@var{n} @gol
262 -fbranch-probabilities -fprofile-values -fbranch-target-load-optimize @gol
263 -fbranch-target-load-optimize2 -fcaller-saves -fcprop-registers @gol
264 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
265 -fdelayed-branch -fdelete-null-pointer-checks @gol
266 -fexpensive-optimizations -ffast-math -ffloat-store @gol
267 -fforce-addr -fforce-mem -ffunction-sections @gol
268 -fgcse -fgcse-lm -fgcse-sm -floop-optimize -fcrossjumping @gol
269 -fif-conversion -fif-conversion2 @gol
270 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
271 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
272 -fmove-all-movables -fnew-ra -fno-branch-count-reg @gol
273 -fno-default-inline -fno-defer-pop @gol
274 -fno-function-cse -fno-guess-branch-probability @gol
275 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
276 -funsafe-math-optimizations -ffinite-math-only @gol
277 -fno-trapping-math -fno-zero-initialized-in-bss @gol
278 -fomit-frame-pointer -foptimize-register-move @gol
279 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
280 -freduce-all-givs -fregmove -frename-registers @gol
281 -freorder-blocks -freorder-functions @gol
282 -frerun-cse-after-loop -frerun-loop-opt @gol
283 -frounding-math -fschedule-insns -fschedule-insns2 @gol
284 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
285 -fsched-spec-load-dangerous -fsched2-use-superblocks @gol
286 -fsched2-use-traces -fsignaling-nans @gol
287 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
288 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
289 -funroll-all-loops -funroll-loops -fpeel-loops @gol
290 -funswitch-loops -fold-unroll-loops -fold-unroll-all-loops @gol
291 --param @var{name}=@var{value}
292 -O -O0 -O1 -O2 -O3 -Os}
294 @item Preprocessor Options
295 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
296 @gccoptlist{-A@var{question}=@var{answer} @gol
297 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
298 -C -dD -dI -dM -dN @gol
299 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
300 -idirafter @var{dir} @gol
301 -include @var{file} -imacros @var{file} @gol
302 -iprefix @var{file} -iwithprefix @var{dir} @gol
303 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
304 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
305 -P -fworking-directory -remap @gol
306 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
307 -Xpreprocessor @var{option}}
309 @item Assembler Option
310 @xref{Assembler Options,,Passing Options to the Assembler}.
311 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
314 @xref{Link Options,,Options for Linking}.
315 @gccoptlist{@var{object-file-name} -l@var{library} @gol
316 -nostartfiles -nodefaultlibs -nostdlib -pie @gol
317 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
318 -Wl,@var{option} -Xlinker @var{option} @gol
321 @item Directory Options
322 @xref{Directory Options,,Options for Directory Search}.
323 @gccoptlist{-B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
326 @c I wrote this xref this way to avoid overfull hbox. -- rms
327 @xref{Target Options}.
328 @gccoptlist{-V @var{version} -b @var{machine}}
330 @item Machine Dependent Options
331 @xref{Submodel Options,,Hardware Models and Configurations}.
333 @emph{M680x0 Options}
334 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
335 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
336 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
337 -malign-int -mstrict-align}
339 @emph{M68hc1x Options}
340 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
341 -mauto-incdec -minmax -mlong-calls -mshort @gol
342 -msoft-reg-count=@var{count}}
345 @gccoptlist{-mg -mgnu -munix}
348 @gccoptlist{-mcpu=@var{cpu-type} @gol
349 -mtune=@var{cpu-type} @gol
350 -mcmodel=@var{code-model} @gol
352 -mapp-regs -mbroken-saverestore -mcypress @gol
353 -mfaster-structs -mflat @gol
354 -mfpu -mhard-float -mhard-quad-float @gol
355 -mimpure-text -mlittle-endian -mlive-g0 -mno-app-regs @gol
356 -mno-faster-structs -mno-flat -mno-fpu @gol
357 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
358 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
359 -msupersparc -munaligned-doubles -mv8}
362 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
363 -mapcs-26 -mapcs-32 @gol
364 -mapcs-stack-check -mno-apcs-stack-check @gol
365 -mapcs-float -mno-apcs-float @gol
366 -mapcs-reentrant -mno-apcs-reentrant @gol
367 -msched-prolog -mno-sched-prolog @gol
368 -mlittle-endian -mbig-endian -mwords-little-endian @gol
369 -malignment-traps -mno-alignment-traps @gol
370 -msoft-float -mhard-float -mfpe @gol
371 -mthumb-interwork -mno-thumb-interwork @gol
372 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
373 -mstructure-size-boundary=@var{n} @gol
374 -mabort-on-noreturn @gol
375 -mlong-calls -mno-long-calls @gol
376 -msingle-pic-base -mno-single-pic-base @gol
377 -mpic-register=@var{reg} @gol
378 -mnop-fun-dllimport @gol
379 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
380 -mpoke-function-name @gol
382 -mtpcs-frame -mtpcs-leaf-frame @gol
383 -mcaller-super-interworking -mcallee-super-interworking}
385 @emph{MN10200 Options}
388 @emph{MN10300 Options}
389 @gccoptlist{-mmult-bug -mno-mult-bug @gol
390 -mam33 -mno-am33 @gol
391 -mam33-2 -mno-am33-2 @gol
394 @emph{M32R/D Options}
395 @gccoptlist{-m32rx -m32r -mcode-model=@var{model-type} @gol
396 -msdata=@var{sdata-type} -G @var{num}}
399 @gccoptlist{-m88000 -m88100 -m88110 -mbig-pic @gol
400 -mcheck-zero-division -mhandle-large-shift @gol
401 -midentify-revision -mno-check-zero-division @gol
402 -mno-ocs-debug-info -mno-ocs-frame-position @gol
403 -mno-optimize-arg-area -mno-serialize-volatile @gol
404 -mno-underscores -mocs-debug-info @gol
405 -mocs-frame-position -moptimize-arg-area @gol
406 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
407 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
408 -mversion-03.00 -mwarn-passed-structs}
410 @emph{RS/6000 and PowerPC Options}
411 @gccoptlist{-mcpu=@var{cpu-type} @gol
412 -mtune=@var{cpu-type} @gol
413 -mpower -mno-power -mpower2 -mno-power2 @gol
414 -mpowerpc -mpowerpc64 -mno-powerpc @gol
415 -maltivec -mno-altivec @gol
416 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
417 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
418 -mnew-mnemonics -mold-mnemonics @gol
419 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
420 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
421 -malign-power -malign-natural @gol
422 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
423 -mstring -mno-string -mupdate -mno-update @gol
424 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
425 -mstrict-align -mno-strict-align -mrelocatable @gol
426 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
427 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
428 -mdynamic-no-pic @gol
429 -mcall-sysv -mcall-netbsd @gol
430 -maix-struct-return -msvr4-struct-return @gol
431 -mabi=altivec -mabi=no-altivec @gol
432 -mabi=spe -mabi=no-spe @gol
433 -misel=yes -misel=no @gol
434 -mspe=yes -mspe=no @gol
435 -mfloat-gprs=yes -mfloat-gprs=no @gol
436 -mprototype -mno-prototype @gol
437 -msim -mmvme -mads -myellowknife -memb -msdata @gol
438 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
440 @emph{Darwin Options}
441 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
442 -arch_only -bind_at_load -bundle -bundle_loader @gol
443 -client_name -compatibility_version -current_version @gol
444 -dependency-file -dylib_file -dylinker_install_name @gol
445 -dynamic -dynamiclib -exported_symbols_list @gol
446 -filelist -flat_namespace -force_cpusubtype_ALL @gol
447 -force_flat_namespace -headerpad_max_install_names @gol
448 -image_base -init -install_name -keep_private_externs @gol
449 -multi_module -multiply_defined -multiply_defined_unused @gol
450 -noall_load -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
451 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
452 -private_bundle -read_only_relocs -sectalign @gol
453 -sectobjectsymbols -whyload -seg1addr @gol
454 -sectcreate -sectobjectsymbols -sectorder @gol
455 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
456 -segprot -segs_read_only_addr -segs_read_write_addr @gol
457 -single_module -static -sub_library -sub_umbrella @gol
458 -twolevel_namespace -umbrella -undefined @gol
459 -unexported_symbols_list -weak_reference_mismatches @gol
463 @gccoptlist{-mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
464 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
465 -mminimum-fp-blocks -mnohc-struct-return}
468 @gccoptlist{-mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
469 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
470 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
471 -mgas -mgp32 -mgp64 -mhard-float -mint64 -mips1 @gol
472 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
473 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
474 -mmips-as -mmips-tfile -mno-abicalls -mxgot @gol
475 -mno-embedded-data -mno-uninit-const-in-rodata @gol
476 -mno-embedded-pic -mno-long-calls @gol
477 -mno-memcpy -mno-mips-tfile -mno-rnames @gol
478 -mrnames -msoft-float @gol
479 -m4650 -msingle-float -mmad @gol
480 -EL -EB -G @var{num} -nocpp @gol
481 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi -mabi-fake-default @gol
482 -mfix7000 -mfix-sb1 -mno-fix-sb1 @gol
483 -mno-crt0 -mflush-func=@var{func} -mno-flush-func @gol
484 -mbranch-likely -mno-branch-likely}
486 @emph{i386 and x86-64 Options}
487 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
488 -mfpmath=@var{unit} @gol
489 -masm=@var{dialect} -mno-fancy-math-387 @gol
490 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
491 -mno-wide-multiply -mrtd -malign-double @gol
492 -mpreferred-stack-boundary=@var{num} @gol
493 -mmmx -msse -msse2 -mpni -m3dnow @gol
494 -mthreads -mno-align-stringops -minline-all-stringops @gol
495 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
496 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
497 -mno-red-zone -mno-tls-direct-seg-refs @gol
498 -mcmodel=@var{code-model} @gol
502 @gccoptlist{-march=@var{architecture-type} @gol
503 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
504 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
505 -mjump-in-delay -mlinker-opt -mlong-calls @gol
506 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
507 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
508 -mno-jump-in-delay -mno-long-load-store @gol
509 -mno-portable-runtime -mno-soft-float @gol
510 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
511 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
512 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
513 -nolibdld -static -threads}
515 @emph{Intel 960 Options}
516 @gccoptlist{-m@var{cpu-type} -masm-compat -mclean-linkage @gol
517 -mcode-align -mcomplex-addr -mleaf-procedures @gol
518 -mic-compat -mic2.0-compat -mic3.0-compat @gol
519 -mintel-asm -mno-clean-linkage -mno-code-align @gol
520 -mno-complex-addr -mno-leaf-procedures @gol
521 -mno-old-align -mno-strict-align -mno-tail-call @gol
522 -mnumerics -mold-align -msoft-float -mstrict-align @gol
525 @emph{DEC Alpha Options}
526 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
527 -mieee -mieee-with-inexact -mieee-conformant @gol
528 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
529 -mtrap-precision=@var{mode} -mbuild-constants @gol
530 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
531 -mbwx -mmax -mfix -mcix @gol
532 -mfloat-vax -mfloat-ieee @gol
533 -mexplicit-relocs -msmall-data -mlarge-data @gol
534 -msmall-text -mlarge-text @gol
535 -mmemory-latency=@var{time}}
537 @emph{DEC Alpha/VMS Options}
538 @gccoptlist{-mvms-return-codes}
540 @emph{H8/300 Options}
541 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
544 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
545 -m4-nofpu -m4-single-only -m4-single -m4 @gol
546 -m5-64media -m5-64media-nofpu @gol
547 -m5-32media -m5-32media-nofpu @gol
548 -m5-compact -m5-compact-nofpu @gol
549 -mb -ml -mdalign -mrelax @gol
550 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
551 -mieee -misize -mpadstruct -mspace @gol
552 -mprefergot -musermode}
554 @emph{System V Options}
555 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
558 @gccoptlist{-EB -EL @gol
559 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
560 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
562 @emph{TMS320C3x/C4x Options}
563 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
564 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
565 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
566 -mparallel-insns -mparallel-mpy -mpreserve-float}
569 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
570 -mprolog-function -mno-prolog-function -mspace @gol
571 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
572 -mapp-regs -mno-app-regs @gol
573 -mdisable-callt -mno-disable-callt @gol
579 @gccoptlist{-m32032 -m32332 -m32532 -m32081 -m32381 @gol
580 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
581 -mregparam -mnoregparam -msb -mnosb @gol
582 -mbitfield -mnobitfield -mhimem -mnohimem}
585 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
586 -mcall-prologues -mno-tablejump -mtiny-stack}
589 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
590 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
591 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
592 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
593 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
596 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
597 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
598 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
599 -mno-base-addresses -msingle-exit -mno-single-exit}
602 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
603 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
604 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
605 -minline-float-divide-max-throughput @gol
606 -minline-int-divide-min-latency @gol
607 -minline-int-divide-max-throughput -mno-dwarf2-asm @gol
608 -mfixed-range=@var{register-range}}
611 @gccoptlist{-mextmem -mextmemory -monchip -mno-asm-optimize @gol
612 -masm-optimize -mbranch-cost=@var{n} -mcond-exec=@var{n}}
614 @emph{S/390 and zSeries Options}
615 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
616 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
617 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
618 -m64 -m31 -mdebug -mno-debug -mesa -mzarch}
621 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
622 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
623 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
624 -mstack-align -mdata-align -mconst-align @gol
625 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
626 -melf -maout -melinux -mlinux -sim -sim2}
628 @emph{PDP-11 Options}
629 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
630 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
631 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
632 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
633 -mbranch-expensive -mbranch-cheap @gol
634 -msplit -mno-split -munix-asm -mdec-asm}
636 @emph{Xstormy16 Options}
639 @emph{Xtensa Options}
640 @gccoptlist{-mconst16 -mno-const16 @gol
641 -mfused-madd -mno-fused-madd @gol
642 -mtext-section-literals -mno-text-section-literals @gol
643 -mtarget-align -mno-target-align @gol
644 -mlongcalls -mno-longcalls}
647 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
648 -mhard-float -msoft-float @gol
649 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
650 -mdouble -mno-double @gol
651 -mmedia -mno-media -mmuladd -mno-muladd @gol
652 -mlibrary-pic -macc-4 -macc-8 @gol
653 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
654 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
655 -mvliw-branch -mno-vliw-branch @gol
656 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
657 -mno-nested-cond-exec -mtomcat-stats @gol
660 @item Code Generation Options
661 @xref{Code Gen Options,,Options for Code Generation Conventions}.
662 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
663 -ffixed-@var{reg} -fexceptions @gol
664 -fnon-call-exceptions -funwind-tables @gol
665 -fasynchronous-unwind-tables @gol
666 -finhibit-size-directive -finstrument-functions @gol
667 -fno-common -fno-ident -fno-gnu-linker @gol
668 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
669 -freg-struct-return -fshared-data -fshort-enums @gol
670 -fshort-double -fshort-wchar @gol
671 -fverbose-asm -fpack-struct -fstack-check @gol
672 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
673 -fargument-alias -fargument-noalias @gol
674 -fargument-noalias-global -fleading-underscore @gol
675 -ftls-model=@var{model} @gol
676 -ftrapv -fwrapv -fbounds-check}
680 * Overall Options:: Controlling the kind of output:
681 an executable, object files, assembler files,
682 or preprocessed source.
683 * C Dialect Options:: Controlling the variant of C language compiled.
684 * C++ Dialect Options:: Variations on C++.
685 * Objective-C Dialect Options:: Variations on Objective-C.
686 * Language Independent Options:: Controlling how diagnostics should be
688 * Warning Options:: How picky should the compiler be?
689 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
690 * Optimize Options:: How much optimization?
691 * Preprocessor Options:: Controlling header files and macro definitions.
692 Also, getting dependency information for Make.
693 * Assembler Options:: Passing options to the assembler.
694 * Link Options:: Specifying libraries and so on.
695 * Directory Options:: Where to find header files and libraries.
696 Where to find the compiler executable files.
697 * Spec Files:: How to pass switches to sub-processes.
698 * Target Options:: Running a cross-compiler, or an old version of GCC.
701 @node Overall Options
702 @section Options Controlling the Kind of Output
704 Compilation can involve up to four stages: preprocessing, compilation
705 proper, assembly and linking, always in that order. GCC is capable of
706 preprocessing and compiling several files either into several
707 assembler input files, or into one assembler input file; then each
708 assembler input file produces an object file, and linking combines all
709 the object files (those newly compiled, and those specified as input)
710 into an executable file.
712 @cindex file name suffix
713 For any given input file, the file name suffix determines what kind of
718 C source code which must be preprocessed.
721 C source code which should not be preprocessed.
724 C++ source code which should not be preprocessed.
727 Objective-C source code. Note that you must link with the library
728 @file{libobjc.a} to make an Objective-C program work.
731 Objective-C source code which should not be preprocessed.
734 C or C++ header file to be turned into a precompiled header.
738 @itemx @var{file}.cxx
739 @itemx @var{file}.cpp
740 @itemx @var{file}.CPP
741 @itemx @var{file}.c++
743 C++ source code which must be preprocessed. Note that in @samp{.cxx},
744 the last two letters must both be literally @samp{x}. Likewise,
745 @samp{.C} refers to a literal capital C@.
749 C++ header file to be turned into a precompiled header.
752 @itemx @var{file}.for
753 @itemx @var{file}.FOR
754 Fortran source code which should not be preprocessed.
757 @itemx @var{file}.fpp
758 @itemx @var{file}.FPP
759 Fortran source code which must be preprocessed (with the traditional
763 Fortran source code which must be preprocessed with a RATFOR
764 preprocessor (not included with GCC)@.
766 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
767 Using and Porting GNU Fortran}, for more details of the handling of
770 @c FIXME: Descriptions of Java file types.
777 Ada source code file which contains a library unit declaration (a
778 declaration of a package, subprogram, or generic, or a generic
779 instantiation), or a library unit renaming declaration (a package,
780 generic, or subprogram renaming declaration). Such files are also
783 @itemx @var{file}.adb
784 Ada source code file containing a library unit body (a subprogram or
785 package body). Such files are also called @dfn{bodies}.
787 @c GCC also knows about some suffixes for languages not yet included:
796 Assembler code which must be preprocessed.
799 An object file to be fed straight into linking.
800 Any file name with no recognized suffix is treated this way.
804 You can specify the input language explicitly with the @option{-x} option:
807 @item -x @var{language}
808 Specify explicitly the @var{language} for the following input files
809 (rather than letting the compiler choose a default based on the file
810 name suffix). This option applies to all following input files until
811 the next @option{-x} option. Possible values for @var{language} are:
813 c c-header cpp-output
814 c++ c++-header c++-cpp-output
815 objective-c objective-c-header objc-cpp-output
816 assembler assembler-with-cpp
818 f77 f77-cpp-input ratfor
824 Turn off any specification of a language, so that subsequent files are
825 handled according to their file name suffixes (as they are if @option{-x}
826 has not been used at all).
828 @item -pass-exit-codes
829 @opindex pass-exit-codes
830 Normally the @command{gcc} program will exit with the code of 1 if any
831 phase of the compiler returns a non-success return code. If you specify
832 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
833 numerically highest error produced by any phase that returned an error
837 If you only want some of the stages of compilation, you can use
838 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
839 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
840 @command{gcc} is to stop. Note that some combinations (for example,
841 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
846 Compile or assemble the source files, but do not link. The linking
847 stage simply is not done. The ultimate output is in the form of an
848 object file for each source file.
850 By default, the object file name for a source file is made by replacing
851 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
853 Unrecognized input files, not requiring compilation or assembly, are
858 Stop after the stage of compilation proper; do not assemble. The output
859 is in the form of an assembler code file for each non-assembler input
862 By default, the assembler file name for a source file is made by
863 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
865 Input files that don't require compilation are ignored.
869 Stop after the preprocessing stage; do not run the compiler proper. The
870 output is in the form of preprocessed source code, which is sent to the
873 Input files which don't require preprocessing are ignored.
875 @cindex output file option
878 Place output in file @var{file}. This applies regardless to whatever
879 sort of output is being produced, whether it be an executable file,
880 an object file, an assembler file or preprocessed C code.
882 If you specify @option{-o} when compiling more than one input file, or
883 you are producing an executable file as output, all the source files
884 on the command line will be compiled at once.
886 If @option{-o} is not specified, the default is to put an executable file
887 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
888 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
889 all preprocessed C source on standard output.
893 Print (on standard error output) the commands executed to run the stages
894 of compilation. Also print the version number of the compiler driver
895 program and of the preprocessor and the compiler proper.
899 Like @option{-v} except the commands are not executed and all command
900 arguments are quoted. This is useful for shell scripts to capture the
901 driver-generated command lines.
905 Use pipes rather than temporary files for communication between the
906 various stages of compilation. This fails to work on some systems where
907 the assembler is unable to read from a pipe; but the GNU assembler has
912 Print (on the standard output) a description of the command line options
913 understood by @command{gcc}. If the @option{-v} option is also specified
914 then @option{--help} will also be passed on to the various processes
915 invoked by @command{gcc}, so that they can display the command line options
916 they accept. If the @option{-Wextra} option is also specified then command
917 line options which have no documentation associated with them will also
922 Print (on the standard output) a description of target specific command
923 line options for each tool.
927 Display the version number and copyrights of the invoked GCC.
931 @section Compiling C++ Programs
933 @cindex suffixes for C++ source
934 @cindex C++ source file suffixes
935 C++ source files conventionally use one of the suffixes @samp{.C},
936 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
937 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
938 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
939 files with these names and compiles them as C++ programs even if you
940 call the compiler the same way as for compiling C programs (usually
941 with the name @command{gcc}).
945 However, C++ programs often require class libraries as well as a
946 compiler that understands the C++ language---and under some
947 circumstances, you might want to compile programs or header files from
948 standard input, or otherwise without a suffix that flags them as C++
949 programs. You might also like to precompile a C header file with a
950 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
951 program that calls GCC with the default language set to C++, and
952 automatically specifies linking against the C++ library. On many
953 systems, @command{g++} is also installed with the name @command{c++}.
955 @cindex invoking @command{g++}
956 When you compile C++ programs, you may specify many of the same
957 command-line options that you use for compiling programs in any
958 language; or command-line options meaningful for C and related
959 languages; or options that are meaningful only for C++ programs.
960 @xref{C Dialect Options,,Options Controlling C Dialect}, for
961 explanations of options for languages related to C@.
962 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
963 explanations of options that are meaningful only for C++ programs.
965 @node C Dialect Options
966 @section Options Controlling C Dialect
967 @cindex dialect options
968 @cindex language dialect options
969 @cindex options, dialect
971 The following options control the dialect of C (or languages derived
972 from C, such as C++ and Objective-C) that the compiler accepts:
979 In C mode, support all ISO C90 programs. In C++ mode,
980 remove GNU extensions that conflict with ISO C++.
982 This turns off certain features of GCC that are incompatible with ISO
983 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
984 such as the @code{asm} and @code{typeof} keywords, and
985 predefined macros such as @code{unix} and @code{vax} that identify the
986 type of system you are using. It also enables the undesirable and
987 rarely used ISO trigraph feature. For the C compiler,
988 it disables recognition of C++ style @samp{//} comments as well as
989 the @code{inline} keyword.
991 The alternate keywords @code{__asm__}, @code{__extension__},
992 @code{__inline__} and @code{__typeof__} continue to work despite
993 @option{-ansi}. You would not want to use them in an ISO C program, of
994 course, but it is useful to put them in header files that might be included
995 in compilations done with @option{-ansi}. Alternate predefined macros
996 such as @code{__unix__} and @code{__vax__} are also available, with or
997 without @option{-ansi}.
999 The @option{-ansi} option does not cause non-ISO programs to be
1000 rejected gratuitously. For that, @option{-pedantic} is required in
1001 addition to @option{-ansi}. @xref{Warning Options}.
1003 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1004 option is used. Some header files may notice this macro and refrain
1005 from declaring certain functions or defining certain macros that the
1006 ISO standard doesn't call for; this is to avoid interfering with any
1007 programs that might use these names for other things.
1009 Functions which would normally be built in but do not have semantics
1010 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1011 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1012 built-in functions provided by GCC}, for details of the functions
1017 Determine the language standard. This option is currently only
1018 supported when compiling C or C++. A value for this option must be
1019 provided; possible values are
1024 ISO C90 (same as @option{-ansi}).
1026 @item iso9899:199409
1027 ISO C90 as modified in amendment 1.
1033 ISO C99. Note that this standard is not yet fully supported; see
1034 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1035 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1038 Default, ISO C90 plus GNU extensions (including some C99 features).
1042 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1043 this will become the default. The name @samp{gnu9x} is deprecated.
1046 The 1998 ISO C++ standard plus amendments.
1049 The same as @option{-std=c++98} plus GNU extensions. This is the
1050 default for C++ code.
1053 Even when this option is not specified, you can still use some of the
1054 features of newer standards in so far as they do not conflict with
1055 previous C standards. For example, you may use @code{__restrict__} even
1056 when @option{-std=c99} is not specified.
1058 The @option{-std} options specifying some version of ISO C have the same
1059 effects as @option{-ansi}, except that features that were not in ISO C90
1060 but are in the specified version (for example, @samp{//} comments and
1061 the @code{inline} keyword in ISO C99) are not disabled.
1063 @xref{Standards,,Language Standards Supported by GCC}, for details of
1064 these standard versions.
1066 @item -aux-info @var{filename}
1068 Output to the given filename prototyped declarations for all functions
1069 declared and/or defined in a translation unit, including those in header
1070 files. This option is silently ignored in any language other than C@.
1072 Besides declarations, the file indicates, in comments, the origin of
1073 each declaration (source file and line), whether the declaration was
1074 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1075 @samp{O} for old, respectively, in the first character after the line
1076 number and the colon), and whether it came from a declaration or a
1077 definition (@samp{C} or @samp{F}, respectively, in the following
1078 character). In the case of function definitions, a K&R-style list of
1079 arguments followed by their declarations is also provided, inside
1080 comments, after the declaration.
1084 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1085 keyword, so that code can use these words as identifiers. You can use
1086 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1087 instead. @option{-ansi} implies @option{-fno-asm}.
1089 In C++, this switch only affects the @code{typeof} keyword, since
1090 @code{asm} and @code{inline} are standard keywords. You may want to
1091 use the @option{-fno-gnu-keywords} flag instead, which has the same
1092 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1093 switch only affects the @code{asm} and @code{typeof} keywords, since
1094 @code{inline} is a standard keyword in ISO C99.
1097 @itemx -fno-builtin-@var{function}
1098 @opindex fno-builtin
1099 @cindex built-in functions
1100 Don't recognize built-in functions that do not begin with
1101 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1102 functions provided by GCC}, for details of the functions affected,
1103 including those which are not built-in functions when @option{-ansi} or
1104 @option{-std} options for strict ISO C conformance are used because they
1105 do not have an ISO standard meaning.
1107 GCC normally generates special code to handle certain built-in functions
1108 more efficiently; for instance, calls to @code{alloca} may become single
1109 instructions that adjust the stack directly, and calls to @code{memcpy}
1110 may become inline copy loops. The resulting code is often both smaller
1111 and faster, but since the function calls no longer appear as such, you
1112 cannot set a breakpoint on those calls, nor can you change the behavior
1113 of the functions by linking with a different library.
1115 With the @option{-fno-builtin-@var{function}} option
1116 only the built-in function @var{function} is
1117 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1118 function is named this is not built-in in this version of GCC, this
1119 option is ignored. There is no corresponding
1120 @option{-fbuiltin-@var{function}} option; if you wish to enable
1121 built-in functions selectively when using @option{-fno-builtin} or
1122 @option{-ffreestanding}, you may define macros such as:
1125 #define abs(n) __builtin_abs ((n))
1126 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1131 @cindex hosted environment
1133 Assert that compilation takes place in a hosted environment. This implies
1134 @option{-fbuiltin}. A hosted environment is one in which the
1135 entire standard library is available, and in which @code{main} has a return
1136 type of @code{int}. Examples are nearly everything except a kernel.
1137 This is equivalent to @option{-fno-freestanding}.
1139 @item -ffreestanding
1140 @opindex ffreestanding
1141 @cindex hosted environment
1143 Assert that compilation takes place in a freestanding environment. This
1144 implies @option{-fno-builtin}. A freestanding environment
1145 is one in which the standard library may not exist, and program startup may
1146 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1147 This is equivalent to @option{-fno-hosted}.
1149 @xref{Standards,,Language Standards Supported by GCC}, for details of
1150 freestanding and hosted environments.
1152 @item -fms-extensions
1153 @opindex fms-extensions
1154 Accept some non-standard constructs used in Microsoft header files.
1158 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1159 options for strict ISO C conformance) implies @option{-trigraphs}.
1161 @item -no-integrated-cpp
1162 @opindex no-integrated-cpp
1163 Performs a compilation in two passes: preprocessing and compiling. This
1164 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1165 @option{-B} option. The user supplied compilation step can then add in
1166 an additional preprocessing step after normal preprocessing but before
1167 compiling. The default is to use the integrated cpp (internal cpp)
1169 The semantics of this option will change if "cc1", "cc1plus", and
1170 "cc1obj" are merged.
1172 @cindex traditional C language
1173 @cindex C language, traditional
1175 @itemx -traditional-cpp
1176 @opindex traditional-cpp
1177 @opindex traditional
1178 Formerly, these options caused GCC to attempt to emulate a pre-standard
1179 C compiler. They are now only supported with the @option{-E} switch.
1180 The preprocessor continues to support a pre-standard mode. See the GNU
1181 CPP manual for details.
1183 @item -fcond-mismatch
1184 @opindex fcond-mismatch
1185 Allow conditional expressions with mismatched types in the second and
1186 third arguments. The value of such an expression is void. This option
1187 is not supported for C++.
1189 @item -funsigned-char
1190 @opindex funsigned-char
1191 Let the type @code{char} be unsigned, like @code{unsigned char}.
1193 Each kind of machine has a default for what @code{char} should
1194 be. It is either like @code{unsigned char} by default or like
1195 @code{signed char} by default.
1197 Ideally, a portable program should always use @code{signed char} or
1198 @code{unsigned char} when it depends on the signedness of an object.
1199 But many programs have been written to use plain @code{char} and
1200 expect it to be signed, or expect it to be unsigned, depending on the
1201 machines they were written for. This option, and its inverse, let you
1202 make such a program work with the opposite default.
1204 The type @code{char} is always a distinct type from each of
1205 @code{signed char} or @code{unsigned char}, even though its behavior
1206 is always just like one of those two.
1209 @opindex fsigned-char
1210 Let the type @code{char} be signed, like @code{signed char}.
1212 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1213 the negative form of @option{-funsigned-char}. Likewise, the option
1214 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1216 @item -fsigned-bitfields
1217 @itemx -funsigned-bitfields
1218 @itemx -fno-signed-bitfields
1219 @itemx -fno-unsigned-bitfields
1220 @opindex fsigned-bitfields
1221 @opindex funsigned-bitfields
1222 @opindex fno-signed-bitfields
1223 @opindex fno-unsigned-bitfields
1224 These options control whether a bit-field is signed or unsigned, when the
1225 declaration does not use either @code{signed} or @code{unsigned}. By
1226 default, such a bit-field is signed, because this is consistent: the
1227 basic integer types such as @code{int} are signed types.
1229 @item -fwritable-strings
1230 @opindex fwritable-strings
1231 Store string constants in the writable data segment and don't uniquize
1232 them. This is for compatibility with old programs which assume they can
1233 write into string constants.
1235 Writing into string constants is a very bad idea; ``constants'' should
1239 @node C++ Dialect Options
1240 @section Options Controlling C++ Dialect
1242 @cindex compiler options, C++
1243 @cindex C++ options, command line
1244 @cindex options, C++
1245 This section describes the command-line options that are only meaningful
1246 for C++ programs; but you can also use most of the GNU compiler options
1247 regardless of what language your program is in. For example, you
1248 might compile a file @code{firstClass.C} like this:
1251 g++ -g -frepo -O -c firstClass.C
1255 In this example, only @option{-frepo} is an option meant
1256 only for C++ programs; you can use the other options with any
1257 language supported by GCC@.
1259 Here is a list of options that are @emph{only} for compiling C++ programs:
1263 @item -fabi-version=@var{n}
1264 @opindex fabi-version
1265 Use version @var{n} of the C++ ABI. Version 1 is the version of the C++
1266 ABI that first appeared in G++ 3.2. Version 0 will always be the
1267 version that conforms most closely to the C++ ABI specification.
1268 Therefore, the ABI obtained using version 0 will change as ABI bugs are
1271 The default is version 1.
1273 @item -fno-access-control
1274 @opindex fno-access-control
1275 Turn off all access checking. This switch is mainly useful for working
1276 around bugs in the access control code.
1280 Check that the pointer returned by @code{operator new} is non-null
1281 before attempting to modify the storage allocated. This check is
1282 normally unnecessary because the C++ standard specifies that
1283 @code{operator new} will only return @code{0} if it is declared
1284 @samp{throw()}, in which case the compiler will always check the
1285 return value even without this option. In all other cases, when
1286 @code{operator new} has a non-empty exception specification, memory
1287 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1288 @samp{new (nothrow)}.
1290 @item -fconserve-space
1291 @opindex fconserve-space
1292 Put uninitialized or runtime-initialized global variables into the
1293 common segment, as C does. This saves space in the executable at the
1294 cost of not diagnosing duplicate definitions. If you compile with this
1295 flag and your program mysteriously crashes after @code{main()} has
1296 completed, you may have an object that is being destroyed twice because
1297 two definitions were merged.
1299 This option is no longer useful on most targets, now that support has
1300 been added for putting variables into BSS without making them common.
1302 @item -fno-const-strings
1303 @opindex fno-const-strings
1304 Give string constants type @code{char *} instead of type @code{const
1305 char *}. By default, G++ uses type @code{const char *} as required by
1306 the standard. Even if you use @option{-fno-const-strings}, you cannot
1307 actually modify the value of a string constant, unless you also use
1308 @option{-fwritable-strings}.
1310 This option might be removed in a future release of G++. For maximum
1311 portability, you should structure your code so that it works with
1312 string constants that have type @code{const char *}.
1314 @item -fno-elide-constructors
1315 @opindex fno-elide-constructors
1316 The C++ standard allows an implementation to omit creating a temporary
1317 which is only used to initialize another object of the same type.
1318 Specifying this option disables that optimization, and forces G++ to
1319 call the copy constructor in all cases.
1321 @item -fno-enforce-eh-specs
1322 @opindex fno-enforce-eh-specs
1323 Don't check for violation of exception specifications at runtime. This
1324 option violates the C++ standard, but may be useful for reducing code
1325 size in production builds, much like defining @samp{NDEBUG}. The compiler
1326 will still optimize based on the exception specifications.
1328 @item -fexternal-templates
1329 @opindex fexternal-templates
1331 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1332 template instantiation; template instances are emitted or not according
1333 to the location of the template definition. @xref{Template
1334 Instantiation}, for more information.
1336 This option is deprecated.
1338 @item -falt-external-templates
1339 @opindex falt-external-templates
1340 Similar to @option{-fexternal-templates}, but template instances are
1341 emitted or not according to the place where they are first instantiated.
1342 @xref{Template Instantiation}, for more information.
1344 This option is deprecated.
1347 @itemx -fno-for-scope
1349 @opindex fno-for-scope
1350 If @option{-ffor-scope} is specified, the scope of variables declared in
1351 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1352 as specified by the C++ standard.
1353 If @option{-fno-for-scope} is specified, the scope of variables declared in
1354 a @i{for-init-statement} extends to the end of the enclosing scope,
1355 as was the case in old versions of G++, and other (traditional)
1356 implementations of C++.
1358 The default if neither flag is given to follow the standard,
1359 but to allow and give a warning for old-style code that would
1360 otherwise be invalid, or have different behavior.
1362 @item -fno-gnu-keywords
1363 @opindex fno-gnu-keywords
1364 Do not recognize @code{typeof} as a keyword, so that code can use this
1365 word as an identifier. You can use the keyword @code{__typeof__} instead.
1366 @option{-ansi} implies @option{-fno-gnu-keywords}.
1368 @item -fno-implicit-templates
1369 @opindex fno-implicit-templates
1370 Never emit code for non-inline templates which are instantiated
1371 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1372 @xref{Template Instantiation}, for more information.
1374 @item -fno-implicit-inline-templates
1375 @opindex fno-implicit-inline-templates
1376 Don't emit code for implicit instantiations of inline templates, either.
1377 The default is to handle inlines differently so that compiles with and
1378 without optimization will need the same set of explicit instantiations.
1380 @item -fno-implement-inlines
1381 @opindex fno-implement-inlines
1382 To save space, do not emit out-of-line copies of inline functions
1383 controlled by @samp{#pragma implementation}. This will cause linker
1384 errors if these functions are not inlined everywhere they are called.
1386 @item -fms-extensions
1387 @opindex fms-extensions
1388 Disable pedantic warnings about constructs used in MFC, such as implicit
1389 int and getting a pointer to member function via non-standard syntax.
1391 @item -fno-nonansi-builtins
1392 @opindex fno-nonansi-builtins
1393 Disable built-in declarations of functions that are not mandated by
1394 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1395 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1397 @item -fno-operator-names
1398 @opindex fno-operator-names
1399 Do not treat the operator name keywords @code{and}, @code{bitand},
1400 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1401 synonyms as keywords.
1403 @item -fno-optional-diags
1404 @opindex fno-optional-diags
1405 Disable diagnostics that the standard says a compiler does not need to
1406 issue. Currently, the only such diagnostic issued by G++ is the one for
1407 a name having multiple meanings within a class.
1410 @opindex fpermissive
1411 Downgrade some diagnostics about nonconformant code from errors to
1412 warnings. Thus, using @option{-fpermissive} will allow some
1413 nonconforming code to compile.
1417 Enable automatic template instantiation at link time. This option also
1418 implies @option{-fno-implicit-templates}. @xref{Template
1419 Instantiation}, for more information.
1423 Disable generation of information about every class with virtual
1424 functions for use by the C++ runtime type identification features
1425 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1426 of the language, you can save some space by using this flag. Note that
1427 exception handling uses the same information, but it will generate it as
1432 Emit statistics about front-end processing at the end of the compilation.
1433 This information is generally only useful to the G++ development team.
1435 @item -ftemplate-depth-@var{n}
1436 @opindex ftemplate-depth
1437 Set the maximum instantiation depth for template classes to @var{n}.
1438 A limit on the template instantiation depth is needed to detect
1439 endless recursions during template class instantiation. ANSI/ISO C++
1440 conforming programs must not rely on a maximum depth greater than 17.
1442 @item -fuse-cxa-atexit
1443 @opindex fuse-cxa-atexit
1444 Register destructors for objects with static storage duration with the
1445 @code{__cxa_atexit} function rather than the @code{atexit} function.
1446 This option is required for fully standards-compliant handling of static
1447 destructors, but will only work if your C library supports
1448 @code{__cxa_atexit}.
1452 Do not use weak symbol support, even if it is provided by the linker.
1453 By default, G++ will use weak symbols if they are available. This
1454 option exists only for testing, and should not be used by end-users;
1455 it will result in inferior code and has no benefits. This option may
1456 be removed in a future release of G++.
1460 Do not search for header files in the standard directories specific to
1461 C++, but do still search the other standard directories. (This option
1462 is used when building the C++ library.)
1465 In addition, these optimization, warning, and code generation options
1466 have meanings only for C++ programs:
1469 @item -fno-default-inline
1470 @opindex fno-default-inline
1471 Do not assume @samp{inline} for functions defined inside a class scope.
1472 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1473 functions will have linkage like inline functions; they just won't be
1476 @item -Wabi @r{(C++ only)}
1478 Warn when G++ generates code that is probably not compatible with the
1479 vendor-neutral C++ ABI. Although an effort has been made to warn about
1480 all such cases, there are probably some cases that are not warned about,
1481 even though G++ is generating incompatible code. There may also be
1482 cases where warnings are emitted even though the code that is generated
1485 You should rewrite your code to avoid these warnings if you are
1486 concerned about the fact that code generated by G++ may not be binary
1487 compatible with code generated by other compilers.
1489 The known incompatibilities at this point include:
1494 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1495 pack data into the same byte as a base class. For example:
1498 struct A @{ virtual void f(); int f1 : 1; @};
1499 struct B : public A @{ int f2 : 1; @};
1503 In this case, G++ will place @code{B::f2} into the same byte
1504 as@code{A::f1}; other compilers will not. You can avoid this problem
1505 by explicitly padding @code{A} so that its size is a multiple of the
1506 byte size on your platform; that will cause G++ and other compilers to
1507 layout @code{B} identically.
1510 Incorrect handling of tail-padding for virtual bases. G++ does not use
1511 tail padding when laying out virtual bases. For example:
1514 struct A @{ virtual void f(); char c1; @};
1515 struct B @{ B(); char c2; @};
1516 struct C : public A, public virtual B @{@};
1520 In this case, G++ will not place @code{B} into the tail-padding for
1521 @code{A}; other compilers will. You can avoid this problem by
1522 explicitly padding @code{A} so that its size is a multiple of its
1523 alignment (ignoring virtual base classes); that will cause G++ and other
1524 compilers to layout @code{C} identically.
1527 Incorrect handling of bit-fields with declared widths greater than that
1528 of their underlying types, when the bit-fields appear in a union. For
1532 union U @{ int i : 4096; @};
1536 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1537 union too small by the number of bits in an @code{int}.
1540 Empty classes can be placed at incorrect offsets. For example:
1550 struct C : public B, public A @{@};
1554 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1555 it should be placed at offset zero. G++ mistakenly believes that the
1556 @code{A} data member of @code{B} is already at offset zero.
1559 Names of template functions whose types involve @code{typename} or
1560 template template parameters can be mangled incorrectly.
1563 template <typename Q>
1564 void f(typename Q::X) @{@}
1566 template <template <typename> class Q>
1567 void f(typename Q<int>::X) @{@}
1571 Instantiations of these templates may be mangled incorrectly.
1575 @item -Wctor-dtor-privacy @r{(C++ only)}
1576 @opindex Wctor-dtor-privacy
1577 Warn when a class seems unusable because all the constructors or
1578 destructors in that class are private, and it has neither friends nor
1579 public static member functions.
1581 @item -Wnon-virtual-dtor @r{(C++ only)}
1582 @opindex Wnon-virtual-dtor
1583 Warn when a class appears to be polymorphic, thereby requiring a virtual
1584 destructor, yet it declares a non-virtual one.
1585 This warning is enabled by @option{-Wall}.
1587 @item -Wreorder @r{(C++ only)}
1589 @cindex reordering, warning
1590 @cindex warning for reordering of member initializers
1591 Warn when the order of member initializers given in the code does not
1592 match the order in which they must be executed. For instance:
1598 A(): j (0), i (1) @{ @}
1602 The compiler will rearrange the member initializers for @samp{i}
1603 and @samp{j} to match the declaration order of the members, emitting
1604 a warning to that effect. This warning is enabled by @option{-Wall}.
1607 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1610 @item -Weffc++ @r{(C++ only)}
1612 Warn about violations of the following style guidelines from Scott Meyers'
1613 @cite{Effective C++} book:
1617 Item 11: Define a copy constructor and an assignment operator for classes
1618 with dynamically allocated memory.
1621 Item 12: Prefer initialization to assignment in constructors.
1624 Item 14: Make destructors virtual in base classes.
1627 Item 15: Have @code{operator=} return a reference to @code{*this}.
1630 Item 23: Don't try to return a reference when you must return an object.
1634 Also warn about violations of the following style guidelines from
1635 Scott Meyers' @cite{More Effective C++} book:
1639 Item 6: Distinguish between prefix and postfix forms of increment and
1640 decrement operators.
1643 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1647 When selecting this option, be aware that the standard library
1648 headers do not obey all of these guidelines; use @samp{grep -v}
1649 to filter out those warnings.
1651 @item -Wno-deprecated @r{(C++ only)}
1652 @opindex Wno-deprecated
1653 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1655 @item -Wno-non-template-friend @r{(C++ only)}
1656 @opindex Wno-non-template-friend
1657 Disable warnings when non-templatized friend functions are declared
1658 within a template. Since the advent of explicit template specification
1659 support in G++, if the name of the friend is an unqualified-id (i.e.,
1660 @samp{friend foo(int)}), the C++ language specification demands that the
1661 friend declare or define an ordinary, nontemplate function. (Section
1662 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1663 could be interpreted as a particular specialization of a templatized
1664 function. Because this non-conforming behavior is no longer the default
1665 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1666 check existing code for potential trouble spots and is on by default.
1667 This new compiler behavior can be turned off with
1668 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1669 but disables the helpful warning.
1671 @item -Wold-style-cast @r{(C++ only)}
1672 @opindex Wold-style-cast
1673 Warn if an old-style (C-style) cast to a non-void type is used within
1674 a C++ program. The new-style casts (@samp{static_cast},
1675 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1676 unintended effects and much easier to search for.
1678 @item -Woverloaded-virtual @r{(C++ only)}
1679 @opindex Woverloaded-virtual
1680 @cindex overloaded virtual fn, warning
1681 @cindex warning for overloaded virtual fn
1682 Warn when a function declaration hides virtual functions from a
1683 base class. For example, in:
1690 struct B: public A @{
1695 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1703 will fail to compile.
1705 @item -Wno-pmf-conversions @r{(C++ only)}
1706 @opindex Wno-pmf-conversions
1707 Disable the diagnostic for converting a bound pointer to member function
1710 @item -Wsign-promo @r{(C++ only)}
1711 @opindex Wsign-promo
1712 Warn when overload resolution chooses a promotion from unsigned or
1713 enumeral type to a signed type, over a conversion to an unsigned type of
1714 the same size. Previous versions of G++ would try to preserve
1715 unsignedness, but the standard mandates the current behavior.
1717 @item -Wsynth @r{(C++ only)}
1719 @cindex warning for synthesized methods
1720 @cindex synthesized methods, warning
1721 Warn when G++'s synthesis behavior does not match that of cfront. For
1727 A& operator = (int);
1737 In this example, G++ will synthesize a default @samp{A& operator =
1738 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1741 @node Objective-C Dialect Options
1742 @section Options Controlling Objective-C Dialect
1744 @cindex compiler options, Objective-C
1745 @cindex Objective-C options, command line
1746 @cindex options, Objective-C
1747 This section describes the command-line options that are only meaningful
1748 for Objective-C programs, but you can also use most of the GNU compiler
1749 options regardless of what language your program is in. For example,
1750 you might compile a file @code{some_class.m} like this:
1753 gcc -g -fgnu-runtime -O -c some_class.m
1757 In this example, @option{-fgnu-runtime} is an option meant only for
1758 Objective-C programs; you can use the other options with any language
1761 Here is a list of options that are @emph{only} for compiling Objective-C
1765 @item -fconstant-string-class=@var{class-name}
1766 @opindex fconstant-string-class
1767 Use @var{class-name} as the name of the class to instantiate for each
1768 literal string specified with the syntax @code{@@"@dots{}"}. The default
1769 class name is @code{NXConstantString}.
1772 @opindex fgnu-runtime
1773 Generate object code compatible with the standard GNU Objective-C
1774 runtime. This is the default for most types of systems.
1776 @item -fnext-runtime
1777 @opindex fnext-runtime
1778 Generate output compatible with the NeXT runtime. This is the default
1779 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1780 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1785 Dump interface declarations for all classes seen in the source file to a
1786 file named @file{@var{sourcename}.decl}.
1789 @opindex Wno-protocol
1790 If a class is declared to implement a protocol, a warning is issued for
1791 every method in the protocol that is not implemented by the class. The
1792 default behavior is to issue a warning for every method not explicitly
1793 implemented in the class, even if a method implementation is inherited
1794 from the superclass. If you use the @code{-Wno-protocol} option, then
1795 methods inherited from the superclass are considered to be implemented,
1796 and no warning is issued for them.
1800 Warn if multiple methods of different types for the same selector are
1801 found during compilation. The check is performed on the list of methods
1802 in the final stage of compilation. Additionally, a check is performed
1803 for each selector appearing in a @code{@@selector(@dots{})}
1804 expression, and a corresponding method for that selector has been found
1805 during compilation. Because these checks scan the method table only at
1806 the end of compilation, these warnings are not produced if the final
1807 stage of compilation is not reached, for example because an error is
1808 found during compilation, or because the @code{-fsyntax-only} option is
1811 @item -Wundeclared-selector
1812 @opindex Wundeclared-selector
1813 Warn if a @code{@@selector(@dots{})} expression referring to an
1814 undeclared selector is found. A selector is considered undeclared if no
1815 method with that name has been declared before the
1816 @code{@@selector(@dots{})} expression, either explicitly in an
1817 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
1818 an @code{@@implementation} section. This option always performs its
1819 checks as soon as a @code{@@selector(@dots{})} expression is found,
1820 while @code{-Wselector} only performs its checks in the final stage of
1821 compilation. This also enforces the coding style convention
1822 that methods and selectors must be declared before being used.
1824 @c not documented because only avail via -Wp
1825 @c @item -print-objc-runtime-info
1829 @node Language Independent Options
1830 @section Options to Control Diagnostic Messages Formatting
1831 @cindex options to control diagnostics formatting
1832 @cindex diagnostic messages
1833 @cindex message formatting
1835 Traditionally, diagnostic messages have been formatted irrespective of
1836 the output device's aspect (e.g.@: its width, @dots{}). The options described
1837 below can be used to control the diagnostic messages formatting
1838 algorithm, e.g.@: how many characters per line, how often source location
1839 information should be reported. Right now, only the C++ front end can
1840 honor these options. However it is expected, in the near future, that
1841 the remaining front ends would be able to digest them correctly.
1844 @item -fmessage-length=@var{n}
1845 @opindex fmessage-length
1846 Try to format error messages so that they fit on lines of about @var{n}
1847 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1848 the front ends supported by GCC@. If @var{n} is zero, then no
1849 line-wrapping will be done; each error message will appear on a single
1852 @opindex fdiagnostics-show-location
1853 @item -fdiagnostics-show-location=once
1854 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1855 reporter to emit @emph{once} source location information; that is, in
1856 case the message is too long to fit on a single physical line and has to
1857 be wrapped, the source location won't be emitted (as prefix) again,
1858 over and over, in subsequent continuation lines. This is the default
1861 @item -fdiagnostics-show-location=every-line
1862 Only meaningful in line-wrapping mode. Instructs the diagnostic
1863 messages reporter to emit the same source location information (as
1864 prefix) for physical lines that result from the process of breaking
1865 a message which is too long to fit on a single line.
1869 @node Warning Options
1870 @section Options to Request or Suppress Warnings
1871 @cindex options to control warnings
1872 @cindex warning messages
1873 @cindex messages, warning
1874 @cindex suppressing warnings
1876 Warnings are diagnostic messages that report constructions which
1877 are not inherently erroneous but which are risky or suggest there
1878 may have been an error.
1880 You can request many specific warnings with options beginning @samp{-W},
1881 for example @option{-Wimplicit} to request warnings on implicit
1882 declarations. Each of these specific warning options also has a
1883 negative form beginning @samp{-Wno-} to turn off warnings;
1884 for example, @option{-Wno-implicit}. This manual lists only one of the
1885 two forms, whichever is not the default.
1887 The following options control the amount and kinds of warnings produced
1888 by GCC; for further, language-specific options also refer to
1889 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
1892 @cindex syntax checking
1894 @opindex fsyntax-only
1895 Check the code for syntax errors, but don't do anything beyond that.
1899 Issue all the warnings demanded by strict ISO C and ISO C++;
1900 reject all programs that use forbidden extensions, and some other
1901 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1902 version of the ISO C standard specified by any @option{-std} option used.
1904 Valid ISO C and ISO C++ programs should compile properly with or without
1905 this option (though a rare few will require @option{-ansi} or a
1906 @option{-std} option specifying the required version of ISO C)@. However,
1907 without this option, certain GNU extensions and traditional C and C++
1908 features are supported as well. With this option, they are rejected.
1910 @option{-pedantic} does not cause warning messages for use of the
1911 alternate keywords whose names begin and end with @samp{__}. Pedantic
1912 warnings are also disabled in the expression that follows
1913 @code{__extension__}. However, only system header files should use
1914 these escape routes; application programs should avoid them.
1915 @xref{Alternate Keywords}.
1917 Some users try to use @option{-pedantic} to check programs for strict ISO
1918 C conformance. They soon find that it does not do quite what they want:
1919 it finds some non-ISO practices, but not all---only those for which
1920 ISO C @emph{requires} a diagnostic, and some others for which
1921 diagnostics have been added.
1923 A feature to report any failure to conform to ISO C might be useful in
1924 some instances, but would require considerable additional work and would
1925 be quite different from @option{-pedantic}. We don't have plans to
1926 support such a feature in the near future.
1928 Where the standard specified with @option{-std} represents a GNU
1929 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1930 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1931 extended dialect is based. Warnings from @option{-pedantic} are given
1932 where they are required by the base standard. (It would not make sense
1933 for such warnings to be given only for features not in the specified GNU
1934 C dialect, since by definition the GNU dialects of C include all
1935 features the compiler supports with the given option, and there would be
1936 nothing to warn about.)
1938 @item -pedantic-errors
1939 @opindex pedantic-errors
1940 Like @option{-pedantic}, except that errors are produced rather than
1945 Inhibit all warning messages.
1949 Inhibit warning messages about the use of @samp{#import}.
1951 @item -Wchar-subscripts
1952 @opindex Wchar-subscripts
1953 Warn if an array subscript has type @code{char}. This is a common cause
1954 of error, as programmers often forget that this type is signed on some
1959 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1960 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1964 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1965 the arguments supplied have types appropriate to the format string
1966 specified, and that the conversions specified in the format string make
1967 sense. This includes standard functions, and others specified by format
1968 attributes (@pxref{Function Attributes}), in the @code{printf},
1969 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1970 not in the C standard) families.
1972 The formats are checked against the format features supported by GNU
1973 libc version 2.2. These include all ISO C90 and C99 features, as well
1974 as features from the Single Unix Specification and some BSD and GNU
1975 extensions. Other library implementations may not support all these
1976 features; GCC does not support warning about features that go beyond a
1977 particular library's limitations. However, if @option{-pedantic} is used
1978 with @option{-Wformat}, warnings will be given about format features not
1979 in the selected standard version (but not for @code{strfmon} formats,
1980 since those are not in any version of the C standard). @xref{C Dialect
1981 Options,,Options Controlling C Dialect}.
1983 Since @option{-Wformat} also checks for null format arguments for
1984 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
1986 @option{-Wformat} is included in @option{-Wall}. For more control over some
1987 aspects of format checking, the options @option{-Wno-format-y2k},
1988 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
1989 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
1990 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
1992 @item -Wno-format-y2k
1993 @opindex Wno-format-y2k
1994 If @option{-Wformat} is specified, do not warn about @code{strftime}
1995 formats which may yield only a two-digit year.
1997 @item -Wno-format-extra-args
1998 @opindex Wno-format-extra-args
1999 If @option{-Wformat} is specified, do not warn about excess arguments to a
2000 @code{printf} or @code{scanf} format function. The C standard specifies
2001 that such arguments are ignored.
2003 Where the unused arguments lie between used arguments that are
2004 specified with @samp{$} operand number specifications, normally
2005 warnings are still given, since the implementation could not know what
2006 type to pass to @code{va_arg} to skip the unused arguments. However,
2007 in the case of @code{scanf} formats, this option will suppress the
2008 warning if the unused arguments are all pointers, since the Single
2009 Unix Specification says that such unused arguments are allowed.
2011 @item -Wno-format-zero-length
2012 @opindex Wno-format-zero-length
2013 If @option{-Wformat} is specified, do not warn about zero-length formats.
2014 The C standard specifies that zero-length formats are allowed.
2016 @item -Wformat-nonliteral
2017 @opindex Wformat-nonliteral
2018 If @option{-Wformat} is specified, also warn if the format string is not a
2019 string literal and so cannot be checked, unless the format function
2020 takes its format arguments as a @code{va_list}.
2022 @item -Wformat-security
2023 @opindex Wformat-security
2024 If @option{-Wformat} is specified, also warn about uses of format
2025 functions that represent possible security problems. At present, this
2026 warns about calls to @code{printf} and @code{scanf} functions where the
2027 format string is not a string literal and there are no format arguments,
2028 as in @code{printf (foo);}. This may be a security hole if the format
2029 string came from untrusted input and contains @samp{%n}. (This is
2030 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2031 in future warnings may be added to @option{-Wformat-security} that are not
2032 included in @option{-Wformat-nonliteral}.)
2036 Enable @option{-Wformat} plus format checks not included in
2037 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2038 -Wformat-nonliteral -Wformat-security}.
2042 Enable warning about passing a null pointer for arguments marked as
2043 requiring a non-null value by the @code{nonnull} function attribute.
2045 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2046 can be disabled with the @option{-Wno-nonnull} option.
2048 @item -Winit-self @r{(C, C++, and Objective-C only)}
2050 Enable warning about uninitialized variables which are initalized with themselves.
2051 Note this option can only be used with the @option{-Wuninitialized} option and
2052 that only works with @option{-O}.
2054 For an example, the following code will not warn about i being uninitialized
2055 without this option:
2066 @item -Wimplicit-int
2067 @opindex Wimplicit-int
2068 Warn when a declaration does not specify a type.
2070 @item -Wimplicit-function-declaration
2071 @itemx -Werror-implicit-function-declaration
2072 @opindex Wimplicit-function-declaration
2073 @opindex Werror-implicit-function-declaration
2074 Give a warning (or error) whenever a function is used before being
2079 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2083 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2084 function with external linkage, returning int, taking either zero
2085 arguments, two, or three arguments of appropriate types.
2087 @item -Wmissing-braces
2088 @opindex Wmissing-braces
2089 Warn if an aggregate or union initializer is not fully bracketed. In
2090 the following example, the initializer for @samp{a} is not fully
2091 bracketed, but that for @samp{b} is fully bracketed.
2094 int a[2][2] = @{ 0, 1, 2, 3 @};
2095 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2099 @opindex Wparentheses
2100 Warn if parentheses are omitted in certain contexts, such
2101 as when there is an assignment in a context where a truth value
2102 is expected, or when operators are nested whose precedence people
2103 often get confused about.
2105 Also warn about constructions where there may be confusion to which
2106 @code{if} statement an @code{else} branch belongs. Here is an example of
2121 In C, every @code{else} branch belongs to the innermost possible @code{if}
2122 statement, which in this example is @code{if (b)}. This is often not
2123 what the programmer expected, as illustrated in the above example by
2124 indentation the programmer chose. When there is the potential for this
2125 confusion, GCC will issue a warning when this flag is specified.
2126 To eliminate the warning, add explicit braces around the innermost
2127 @code{if} statement so there is no way the @code{else} could belong to
2128 the enclosing @code{if}. The resulting code would look like this:
2144 @item -Wsequence-point
2145 @opindex Wsequence-point
2146 Warn about code that may have undefined semantics because of violations
2147 of sequence point rules in the C standard.
2149 The C standard defines the order in which expressions in a C program are
2150 evaluated in terms of @dfn{sequence points}, which represent a partial
2151 ordering between the execution of parts of the program: those executed
2152 before the sequence point, and those executed after it. These occur
2153 after the evaluation of a full expression (one which is not part of a
2154 larger expression), after the evaluation of the first operand of a
2155 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2156 function is called (but after the evaluation of its arguments and the
2157 expression denoting the called function), and in certain other places.
2158 Other than as expressed by the sequence point rules, the order of
2159 evaluation of subexpressions of an expression is not specified. All
2160 these rules describe only a partial order rather than a total order,
2161 since, for example, if two functions are called within one expression
2162 with no sequence point between them, the order in which the functions
2163 are called is not specified. However, the standards committee have
2164 ruled that function calls do not overlap.
2166 It is not specified when between sequence points modifications to the
2167 values of objects take effect. Programs whose behavior depends on this
2168 have undefined behavior; the C standard specifies that ``Between the
2169 previous and next sequence point an object shall have its stored value
2170 modified at most once by the evaluation of an expression. Furthermore,
2171 the prior value shall be read only to determine the value to be
2172 stored.''. If a program breaks these rules, the results on any
2173 particular implementation are entirely unpredictable.
2175 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2176 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2177 diagnosed by this option, and it may give an occasional false positive
2178 result, but in general it has been found fairly effective at detecting
2179 this sort of problem in programs.
2181 The present implementation of this option only works for C programs. A
2182 future implementation may also work for C++ programs.
2184 The C standard is worded confusingly, therefore there is some debate
2185 over the precise meaning of the sequence point rules in subtle cases.
2186 Links to discussions of the problem, including proposed formal
2187 definitions, may be found on our readings page, at
2188 @w{@uref{http://gcc.gnu.org/readings.html}}.
2191 @opindex Wreturn-type
2192 Warn whenever a function is defined with a return-type that defaults to
2193 @code{int}. Also warn about any @code{return} statement with no
2194 return-value in a function whose return-type is not @code{void}.
2196 For C++, a function without return type always produces a diagnostic
2197 message, even when @option{-Wno-return-type} is specified. The only
2198 exceptions are @samp{main} and functions defined in system headers.
2202 Warn whenever a @code{switch} statement has an index of enumeral type
2203 and lacks a @code{case} for one or more of the named codes of that
2204 enumeration. (The presence of a @code{default} label prevents this
2205 warning.) @code{case} labels outside the enumeration range also
2206 provoke warnings when this option is used.
2208 @item -Wswitch-default
2209 @opindex Wswitch-switch
2210 Warn whenever a @code{switch} statement does not have a @code{default}
2214 @opindex Wswitch-enum
2215 Warn whenever a @code{switch} statement has an index of enumeral type
2216 and lacks a @code{case} for one or more of the named codes of that
2217 enumeration. @code{case} labels outside the enumeration range also
2218 provoke warnings when this option is used.
2222 Warn if any trigraphs are encountered that might change the meaning of
2223 the program (trigraphs within comments are not warned about).
2225 @item -Wunused-function
2226 @opindex Wunused-function
2227 Warn whenever a static function is declared but not defined or a
2228 non\-inline static function is unused.
2230 @item -Wunused-label
2231 @opindex Wunused-label
2232 Warn whenever a label is declared but not used.
2234 To suppress this warning use the @samp{unused} attribute
2235 (@pxref{Variable Attributes}).
2237 @item -Wunused-parameter
2238 @opindex Wunused-parameter
2239 Warn whenever a function parameter is unused aside from its declaration.
2241 To suppress this warning use the @samp{unused} attribute
2242 (@pxref{Variable Attributes}).
2244 @item -Wunused-variable
2245 @opindex Wunused-variable
2246 Warn whenever a local variable or non-constant static variable is unused
2247 aside from its declaration
2249 To suppress this warning use the @samp{unused} attribute
2250 (@pxref{Variable Attributes}).
2252 @item -Wunused-value
2253 @opindex Wunused-value
2254 Warn whenever a statement computes a result that is explicitly not used.
2256 To suppress this warning cast the expression to @samp{void}.
2260 All the above @option{-Wunused} options combined.
2262 In order to get a warning about an unused function parameter, you must
2263 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2264 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2266 @item -Wuninitialized
2267 @opindex Wuninitialized
2268 Warn if an automatic variable is used without first being initialized or
2269 if a variable may be clobbered by a @code{setjmp} call.
2271 These warnings are possible only in optimizing compilation,
2272 because they require data flow information that is computed only
2273 when optimizing. If you don't specify @option{-O}, you simply won't
2276 If you want to warn about code which uses the uninitialized value of the
2277 variable in its own initializer, use the @option{-Winit-self} option.
2279 These warnings occur only for variables that are candidates for
2280 register allocation. Therefore, they do not occur for a variable that
2281 is declared @code{volatile}, or whose address is taken, or whose size
2282 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2283 structures, unions or arrays, even when they are in registers.
2285 Note that there may be no warning about a variable that is used only
2286 to compute a value that itself is never used, because such
2287 computations may be deleted by data flow analysis before the warnings
2290 These warnings are made optional because GCC is not smart
2291 enough to see all the reasons why the code might be correct
2292 despite appearing to have an error. Here is one example of how
2313 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2314 always initialized, but GCC doesn't know this. Here is
2315 another common case:
2320 if (change_y) save_y = y, y = new_y;
2322 if (change_y) y = save_y;
2327 This has no bug because @code{save_y} is used only if it is set.
2329 @cindex @code{longjmp} warnings
2330 This option also warns when a non-volatile automatic variable might be
2331 changed by a call to @code{longjmp}. These warnings as well are possible
2332 only in optimizing compilation.
2334 The compiler sees only the calls to @code{setjmp}. It cannot know
2335 where @code{longjmp} will be called; in fact, a signal handler could
2336 call it at any point in the code. As a result, you may get a warning
2337 even when there is in fact no problem because @code{longjmp} cannot
2338 in fact be called at the place which would cause a problem.
2340 Some spurious warnings can be avoided if you declare all the functions
2341 you use that never return as @code{noreturn}. @xref{Function
2344 @item -Wunknown-pragmas
2345 @opindex Wunknown-pragmas
2346 @cindex warning for unknown pragmas
2347 @cindex unknown pragmas, warning
2348 @cindex pragmas, warning of unknown
2349 Warn when a #pragma directive is encountered which is not understood by
2350 GCC@. If this command line option is used, warnings will even be issued
2351 for unknown pragmas in system header files. This is not the case if
2352 the warnings were only enabled by the @option{-Wall} command line option.
2354 @item -Wstrict-aliasing
2355 @opindex Wstrict-aliasing
2356 This option is only active when @option{-fstrict-aliasing} is active.
2357 It warns about code which might break the strict aliasing rules that the
2358 compiler is using for optimization. The warning does not catch all
2359 cases, but does attempt to catch the more common pitfalls. It is
2360 included in @option{-Wall}.
2364 All of the above @samp{-W} options combined. This enables all the
2365 warnings about constructions that some users consider questionable, and
2366 that are easy to avoid (or modify to prevent the warning), even in
2367 conjunction with macros. This also enables some language-specific
2368 warnings described in @ref{C++ Dialect Options} and
2369 @ref{Objective-C Dialect Options}.
2372 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2373 Some of them warn about constructions that users generally do not
2374 consider questionable, but which occasionally you might wish to check
2375 for; others warn about constructions that are necessary or hard to avoid
2376 in some cases, and there is no simple way to modify the code to suppress
2383 (This option used to be called @option{-W}. The older name is still
2384 supported, but the newer name is more descriptive.) Print extra warning
2385 messages for these events:
2389 A function can return either with or without a value. (Falling
2390 off the end of the function body is considered returning without
2391 a value.) For example, this function would evoke such a
2405 An expression-statement or the left-hand side of a comma expression
2406 contains no side effects.
2407 To suppress the warning, cast the unused expression to void.
2408 For example, an expression such as @samp{x[i,j]} will cause a warning,
2409 but @samp{x[(void)i,j]} will not.
2412 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2415 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2416 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2417 that of ordinary mathematical notation.
2420 Storage-class specifiers like @code{static} are not the first things in
2421 a declaration. According to the C Standard, this usage is obsolescent.
2424 The return type of a function has a type qualifier such as @code{const}.
2425 Such a type qualifier has no effect, since the value returned by a
2426 function is not an lvalue. (But don't warn about the GNU extension of
2427 @code{volatile void} return types. That extension will be warned about
2428 if @option{-pedantic} is specified.)
2431 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2435 A comparison between signed and unsigned values could produce an
2436 incorrect result when the signed value is converted to unsigned.
2437 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2440 An aggregate has an initializer which does not initialize all members.
2441 For example, the following code would cause such a warning, because
2442 @code{x.h} would be implicitly initialized to zero:
2445 struct s @{ int f, g, h; @};
2446 struct s x = @{ 3, 4 @};
2450 A function parameter is declared without a type specifier in K&R-style
2458 An empty body occurs in an @samp{if} or @samp{else} statement.
2461 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2462 @samp{>}, or @samp{>=}.
2465 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2468 Any of several floating-point events that often indicate errors, such as
2469 overflow, underflow, loss of precision, etc.
2471 @item @r{(C++ only)}
2472 An enumerator and a non-enumerator both appear in a conditional expression.
2474 @item @r{(C++ only)}
2475 A non-static reference or non-static @samp{const} member appears in a
2476 class without constructors.
2478 @item @r{(C++ only)}
2479 Ambiguous virtual bases.
2481 @item @r{(C++ only)}
2482 Subscripting an array which has been declared @samp{register}.
2484 @item @r{(C++ only)}
2485 Taking the address of a variable which has been declared @samp{register}.
2487 @item @r{(C++ only)}
2488 A base class is not initialized in a derived class' copy constructor.
2491 @item -Wno-div-by-zero
2492 @opindex Wno-div-by-zero
2493 @opindex Wdiv-by-zero
2494 Do not warn about compile-time integer division by zero. Floating point
2495 division by zero is not warned about, as it can be a legitimate way of
2496 obtaining infinities and NaNs.
2498 @item -Wsystem-headers
2499 @opindex Wsystem-headers
2500 @cindex warnings from system headers
2501 @cindex system headers, warnings from
2502 Print warning messages for constructs found in system header files.
2503 Warnings from system headers are normally suppressed, on the assumption
2504 that they usually do not indicate real problems and would only make the
2505 compiler output harder to read. Using this command line option tells
2506 GCC to emit warnings from system headers as if they occurred in user
2507 code. However, note that using @option{-Wall} in conjunction with this
2508 option will @emph{not} warn about unknown pragmas in system
2509 headers---for that, @option{-Wunknown-pragmas} must also be used.
2512 @opindex Wfloat-equal
2513 Warn if floating point values are used in equality comparisons.
2515 The idea behind this is that sometimes it is convenient (for the
2516 programmer) to consider floating-point values as approximations to
2517 infinitely precise real numbers. If you are doing this, then you need
2518 to compute (by analyzing the code, or in some other way) the maximum or
2519 likely maximum error that the computation introduces, and allow for it
2520 when performing comparisons (and when producing output, but that's a
2521 different problem). In particular, instead of testing for equality, you
2522 would check to see whether the two values have ranges that overlap; and
2523 this is done with the relational operators, so equality comparisons are
2526 @item -Wtraditional @r{(C only)}
2527 @opindex Wtraditional
2528 Warn about certain constructs that behave differently in traditional and
2529 ISO C@. Also warn about ISO C constructs that have no traditional C
2530 equivalent, and/or problematic constructs which should be avoided.
2534 Macro parameters that appear within string literals in the macro body.
2535 In traditional C macro replacement takes place within string literals,
2536 but does not in ISO C@.
2539 In traditional C, some preprocessor directives did not exist.
2540 Traditional preprocessors would only consider a line to be a directive
2541 if the @samp{#} appeared in column 1 on the line. Therefore
2542 @option{-Wtraditional} warns about directives that traditional C
2543 understands but would ignore because the @samp{#} does not appear as the
2544 first character on the line. It also suggests you hide directives like
2545 @samp{#pragma} not understood by traditional C by indenting them. Some
2546 traditional implementations would not recognize @samp{#elif}, so it
2547 suggests avoiding it altogether.
2550 A function-like macro that appears without arguments.
2553 The unary plus operator.
2556 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2557 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2558 constants.) Note, these suffixes appear in macros defined in the system
2559 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2560 Use of these macros in user code might normally lead to spurious
2561 warnings, however gcc's integrated preprocessor has enough context to
2562 avoid warning in these cases.
2565 A function declared external in one block and then used after the end of
2569 A @code{switch} statement has an operand of type @code{long}.
2572 A non-@code{static} function declaration follows a @code{static} one.
2573 This construct is not accepted by some traditional C compilers.
2576 The ISO type of an integer constant has a different width or
2577 signedness from its traditional type. This warning is only issued if
2578 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2579 typically represent bit patterns, are not warned about.
2582 Usage of ISO string concatenation is detected.
2585 Initialization of automatic aggregates.
2588 Identifier conflicts with labels. Traditional C lacks a separate
2589 namespace for labels.
2592 Initialization of unions. If the initializer is zero, the warning is
2593 omitted. This is done under the assumption that the zero initializer in
2594 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2595 initializer warnings and relies on default initialization to zero in the
2599 Conversions by prototypes between fixed/floating point values and vice
2600 versa. The absence of these prototypes when compiling with traditional
2601 C would cause serious problems. This is a subset of the possible
2602 conversion warnings, for the full set use @option{-Wconversion}.
2605 Use of ISO C style function definitions. This warning intentionally is
2606 @emph{not} issued for prototype declarations or variadic functions
2607 because these ISO C features will appear in your code when using
2608 libiberty's traditional C compatibility macros, @code{PARAMS} and
2609 @code{VPARAMS}. This warning is also bypassed for nested functions
2610 because that feature is already a gcc extension and thus not relevant to
2611 traditional C compatibility.
2614 @item -Wdeclaration-after-statement @r{(C only)}
2615 @opindex Wdeclaration-after-statement
2616 Warn when a declaration is found after a statement in a block. This
2617 construct, known from C++, was introduced with ISO C99 and is by default
2618 allowed in GCC@. It is not supported by ISO C90 and was not supported by
2619 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
2623 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2625 @item -Wendif-labels
2626 @opindex Wendif-labels
2627 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2631 Warn whenever a local variable shadows another local variable, parameter or
2632 global variable or whenever a built-in function is shadowed.
2634 @item -Wlarger-than-@var{len}
2635 @opindex Wlarger-than
2636 Warn whenever an object of larger than @var{len} bytes is defined.
2638 @item -Wpointer-arith
2639 @opindex Wpointer-arith
2640 Warn about anything that depends on the ``size of'' a function type or
2641 of @code{void}. GNU C assigns these types a size of 1, for
2642 convenience in calculations with @code{void *} pointers and pointers
2645 @item -Wbad-function-cast @r{(C only)}
2646 @opindex Wbad-function-cast
2647 Warn whenever a function call is cast to a non-matching type.
2648 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2652 Warn whenever a pointer is cast so as to remove a type qualifier from
2653 the target type. For example, warn if a @code{const char *} is cast
2654 to an ordinary @code{char *}.
2657 @opindex Wcast-align
2658 Warn whenever a pointer is cast such that the required alignment of the
2659 target is increased. For example, warn if a @code{char *} is cast to
2660 an @code{int *} on machines where integers can only be accessed at
2661 two- or four-byte boundaries.
2663 @item -Wwrite-strings
2664 @opindex Wwrite-strings
2665 When compiling C, give string constants the type @code{const
2666 char[@var{length}]} so that
2667 copying the address of one into a non-@code{const} @code{char *}
2668 pointer will get a warning; when compiling C++, warn about the
2669 deprecated conversion from string constants to @code{char *}.
2670 These warnings will help you find at
2671 compile time code that can try to write into a string constant, but
2672 only if you have been very careful about using @code{const} in
2673 declarations and prototypes. Otherwise, it will just be a nuisance;
2674 this is why we did not make @option{-Wall} request these warnings.
2677 @opindex Wconversion
2678 Warn if a prototype causes a type conversion that is different from what
2679 would happen to the same argument in the absence of a prototype. This
2680 includes conversions of fixed point to floating and vice versa, and
2681 conversions changing the width or signedness of a fixed point argument
2682 except when the same as the default promotion.
2684 Also, warn if a negative integer constant expression is implicitly
2685 converted to an unsigned type. For example, warn about the assignment
2686 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2687 casts like @code{(unsigned) -1}.
2689 @item -Wsign-compare
2690 @opindex Wsign-compare
2691 @cindex warning for comparison of signed and unsigned values
2692 @cindex comparison of signed and unsigned values, warning
2693 @cindex signed and unsigned values, comparison warning
2694 Warn when a comparison between signed and unsigned values could produce
2695 an incorrect result when the signed value is converted to unsigned.
2696 This warning is also enabled by @option{-Wextra}; to get the other warnings
2697 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2699 @item -Waggregate-return
2700 @opindex Waggregate-return
2701 Warn if any functions that return structures or unions are defined or
2702 called. (In languages where you can return an array, this also elicits
2705 @item -Wstrict-prototypes @r{(C only)}
2706 @opindex Wstrict-prototypes
2707 Warn if a function is declared or defined without specifying the
2708 argument types. (An old-style function definition is permitted without
2709 a warning if preceded by a declaration which specifies the argument
2712 @item -Wmissing-prototypes @r{(C only)}
2713 @opindex Wmissing-prototypes
2714 Warn if a global function is defined without a previous prototype
2715 declaration. This warning is issued even if the definition itself
2716 provides a prototype. The aim is to detect global functions that fail
2717 to be declared in header files.
2719 @item -Wmissing-declarations @r{(C only)}
2720 @opindex Wmissing-declarations
2721 Warn if a global function is defined without a previous declaration.
2722 Do so even if the definition itself provides a prototype.
2723 Use this option to detect global functions that are not declared in
2726 @item -Wmissing-noreturn
2727 @opindex Wmissing-noreturn
2728 Warn about functions which might be candidates for attribute @code{noreturn}.
2729 Note these are only possible candidates, not absolute ones. Care should
2730 be taken to manually verify functions actually do not ever return before
2731 adding the @code{noreturn} attribute, otherwise subtle code generation
2732 bugs could be introduced. You will not get a warning for @code{main} in
2733 hosted C environments.
2735 @item -Wmissing-format-attribute
2736 @opindex Wmissing-format-attribute
2738 If @option{-Wformat} is enabled, also warn about functions which might be
2739 candidates for @code{format} attributes. Note these are only possible
2740 candidates, not absolute ones. GCC will guess that @code{format}
2741 attributes might be appropriate for any function that calls a function
2742 like @code{vprintf} or @code{vscanf}, but this might not always be the
2743 case, and some functions for which @code{format} attributes are
2744 appropriate may not be detected. This option has no effect unless
2745 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2747 @item -Wno-multichar
2748 @opindex Wno-multichar
2750 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2751 Usually they indicate a typo in the user's code, as they have
2752 implementation-defined values, and should not be used in portable code.
2754 @item -Wno-deprecated-declarations
2755 @opindex Wno-deprecated-declarations
2756 Do not warn about uses of functions, variables, and types marked as
2757 deprecated by using the @code{deprecated} attribute.
2758 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2759 @pxref{Type Attributes}.)
2763 Warn if a structure is given the packed attribute, but the packed
2764 attribute has no effect on the layout or size of the structure.
2765 Such structures may be mis-aligned for little benefit. For
2766 instance, in this code, the variable @code{f.x} in @code{struct bar}
2767 will be misaligned even though @code{struct bar} does not itself
2768 have the packed attribute:
2775 @} __attribute__((packed));
2785 Warn if padding is included in a structure, either to align an element
2786 of the structure or to align the whole structure. Sometimes when this
2787 happens it is possible to rearrange the fields of the structure to
2788 reduce the padding and so make the structure smaller.
2790 @item -Wredundant-decls
2791 @opindex Wredundant-decls
2792 Warn if anything is declared more than once in the same scope, even in
2793 cases where multiple declaration is valid and changes nothing.
2795 @item -Wnested-externs @r{(C only)}
2796 @opindex Wnested-externs
2797 Warn if an @code{extern} declaration is encountered within a function.
2799 @item -Wunreachable-code
2800 @opindex Wunreachable-code
2801 Warn if the compiler detects that code will never be executed.
2803 This option is intended to warn when the compiler detects that at
2804 least a whole line of source code will never be executed, because
2805 some condition is never satisfied or because it is after a
2806 procedure that never returns.
2808 It is possible for this option to produce a warning even though there
2809 are circumstances under which part of the affected line can be executed,
2810 so care should be taken when removing apparently-unreachable code.
2812 For instance, when a function is inlined, a warning may mean that the
2813 line is unreachable in only one inlined copy of the function.
2815 This option is not made part of @option{-Wall} because in a debugging
2816 version of a program there is often substantial code which checks
2817 correct functioning of the program and is, hopefully, unreachable
2818 because the program does work. Another common use of unreachable
2819 code is to provide behavior which is selectable at compile-time.
2823 Warn if a function can not be inlined and it was declared as inline.
2824 Even with this option, the compiler will not warn about failures to
2825 inline functions declared in system headers.
2827 The compiler uses a variety of heuristics to determine whether or not
2828 to inline a function. For example, the compiler takes into account
2829 the size of the function being inlined and the the amount of inlining
2830 that has already been done in the current function. Therefore,
2831 seemingly insignificant changes in the source program can cause the
2832 warnings produced by @option{-Winline} to appear or disappear.
2834 @item -Wno-invalid-offsetof @r{(C++ only)}
2835 @opindex Wno-invalid-offsetof
2836 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
2837 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
2838 to a non-POD type is undefined. In existing C++ implementations,
2839 however, @samp{offsetof} typically gives meaningful results even when
2840 applied to certain kinds of non-POD types. (Such as a simple
2841 @samp{struct} that fails to be a POD type only by virtue of having a
2842 constructor.) This flag is for users who are aware that they are
2843 writing nonportable code and who have deliberately chosen to ignore the
2846 The restrictions on @samp{offsetof} may be relaxed in a future version
2847 of the C++ standard.
2850 @opindex Winvalid-pch
2851 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
2852 the search path but can't be used.
2856 @opindex Wno-long-long
2857 Warn if @samp{long long} type is used. This is default. To inhibit
2858 the warning messages, use @option{-Wno-long-long}. Flags
2859 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2860 only when @option{-pedantic} flag is used.
2862 @item -Wdisabled-optimization
2863 @opindex Wdisabled-optimization
2864 Warn if a requested optimization pass is disabled. This warning does
2865 not generally indicate that there is anything wrong with your code; it
2866 merely indicates that GCC's optimizers were unable to handle the code
2867 effectively. Often, the problem is that your code is too big or too
2868 complex; GCC will refuse to optimize programs when the optimization
2869 itself is likely to take inordinate amounts of time.
2873 Make all warnings into errors.
2876 @node Debugging Options
2877 @section Options for Debugging Your Program or GCC
2878 @cindex options, debugging
2879 @cindex debugging information options
2881 GCC has various special options that are used for debugging
2882 either your program or GCC:
2887 Produce debugging information in the operating system's native format
2888 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2891 On most systems that use stabs format, @option{-g} enables use of extra
2892 debugging information that only GDB can use; this extra information
2893 makes debugging work better in GDB but will probably make other debuggers
2895 refuse to read the program. If you want to control for certain whether
2896 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2897 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
2898 or @option{-gvms} (see below).
2900 Unlike most other C compilers, GCC allows you to use @option{-g} with
2901 @option{-O}. The shortcuts taken by optimized code may occasionally
2902 produce surprising results: some variables you declared may not exist
2903 at all; flow of control may briefly move where you did not expect it;
2904 some statements may not be executed because they compute constant
2905 results or their values were already at hand; some statements may
2906 execute in different places because they were moved out of loops.
2908 Nevertheless it proves possible to debug optimized output. This makes
2909 it reasonable to use the optimizer for programs that might have bugs.
2911 The following options are useful when GCC is generated with the
2912 capability for more than one debugging format.
2916 Produce debugging information for use by GDB@. This means to use the
2917 most expressive format available (DWARF 2, stabs, or the native format
2918 if neither of those are supported), including GDB extensions if at all
2923 Produce debugging information in stabs format (if that is supported),
2924 without GDB extensions. This is the format used by DBX on most BSD
2925 systems. On MIPS, Alpha and System V Release 4 systems this option
2926 produces stabs debugging output which is not understood by DBX or SDB@.
2927 On System V Release 4 systems this option requires the GNU assembler.
2929 @item -feliminate-unused-debug-symbols
2930 @opindex feliminate-unused-debug-symbols
2931 Produce debugging information in stabs format (if that is supported),
2932 for only symbols that are actually used.
2936 Produce debugging information in stabs format (if that is supported),
2937 using GNU extensions understood only by the GNU debugger (GDB)@. The
2938 use of these extensions is likely to make other debuggers crash or
2939 refuse to read the program.
2943 Produce debugging information in COFF format (if that is supported).
2944 This is the format used by SDB on most System V systems prior to
2949 Produce debugging information in XCOFF format (if that is supported).
2950 This is the format used by the DBX debugger on IBM RS/6000 systems.
2954 Produce debugging information in XCOFF format (if that is supported),
2955 using GNU extensions understood only by the GNU debugger (GDB)@. The
2956 use of these extensions is likely to make other debuggers crash or
2957 refuse to read the program, and may cause assemblers other than the GNU
2958 assembler (GAS) to fail with an error.
2962 Produce debugging information in DWARF version 1 format (if that is
2963 supported). This is the format used by SDB on most System V Release 4
2966 This option is deprecated.
2970 Produce debugging information in DWARF version 1 format (if that is
2971 supported), using GNU extensions understood only by the GNU debugger
2972 (GDB)@. The use of these extensions is likely to make other debuggers
2973 crash or refuse to read the program.
2975 This option is deprecated.
2979 Produce debugging information in DWARF version 2 format (if that is
2980 supported). This is the format used by DBX on IRIX 6.
2984 Produce debugging information in VMS debug format (if that is
2985 supported). This is the format used by DEBUG on VMS systems.
2988 @itemx -ggdb@var{level}
2989 @itemx -gstabs@var{level}
2990 @itemx -gcoff@var{level}
2991 @itemx -gxcoff@var{level}
2992 @itemx -gvms@var{level}
2993 Request debugging information and also use @var{level} to specify how
2994 much information. The default level is 2.
2996 Level 1 produces minimal information, enough for making backtraces in
2997 parts of the program that you don't plan to debug. This includes
2998 descriptions of functions and external variables, but no information
2999 about local variables and no line numbers.
3001 Level 3 includes extra information, such as all the macro definitions
3002 present in the program. Some debuggers support macro expansion when
3003 you use @option{-g3}.
3005 Note that in order to avoid confusion between DWARF1 debug level 2,
3006 and DWARF2, neither @option{-gdwarf} nor @option{-gdwarf-2} accept
3007 a concatenated debug level. Instead use an additional @option{-g@var{level}}
3008 option to change the debug level for DWARF1 or DWARF2.
3010 @item -feliminate-dwarf2-dups
3011 @opindex feliminate-dwarf2-dups
3012 Compress DWARF2 debugging information by eliminating duplicated
3013 information about each symbol. This option only makes sense when
3014 generating DWARF2 debugging information with @option{-gdwarf-2}.
3016 @cindex @command{prof}
3019 Generate extra code to write profile information suitable for the
3020 analysis program @command{prof}. You must use this option when compiling
3021 the source files you want data about, and you must also use it when
3024 @cindex @command{gprof}
3027 Generate extra code to write profile information suitable for the
3028 analysis program @command{gprof}. You must use this option when compiling
3029 the source files you want data about, and you must also use it when
3034 Makes the compiler print out each function name as it is compiled, and
3035 print some statistics about each pass when it finishes.
3038 @opindex ftime-report
3039 Makes the compiler print some statistics about the time consumed by each
3040 pass when it finishes.
3043 @opindex fmem-report
3044 Makes the compiler print some statistics about permanent memory
3045 allocation when it finishes.
3047 @item -fprofile-arcs
3048 @opindex fprofile-arcs
3049 Add code so that program flow @dfn{arcs} are instrumented. During
3050 execution the program records how many times each branch and call is
3051 executed and how many times it is taken or returns. When the compiled
3052 program exits it saves this data to a file called
3053 @file{@var{auxname}.gcda} for each source file. The data may be used for
3054 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3055 test coverage analysis (@option{-ftest-coverage}). Each object file's
3056 @var{auxname} is generated from the name of the output file, if
3057 explicitly specified and it is not the final executable, otherwise it is
3058 the basename of the source file. In both cases any suffix is removed
3059 (e.g. @file{foo.gcda} for input file @file{dir/foo.c}, or
3060 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3065 Compile the source files with @option{-fprofile-arcs} plus optimization
3066 and code generation options. For test coverage analysis, use the
3067 additional @option{-ftest-coverage} option. You do not need to profile
3068 every source file in a program.
3071 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3072 (the latter implies the former).
3075 Run the program on a representative workload to generate the arc profile
3076 information. This may be repeated any number of times. You can run
3077 concurrent instances of your program, and provided that the file system
3078 supports locking, the data files will be correctly updated. Also
3079 @code{fork} calls are detected and correctly handled (double counting
3083 For profile-directed optimizations, compile the source files again with
3084 the same optimization and code generation options plus
3085 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3086 Control Optimization}).
3089 For test coverage analysis, use @command{gcov} to produce human readable
3090 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3091 @command{gcov} documentation for further information.
3095 With @option{-fprofile-arcs}, for each function of your program GCC
3096 creates a program flow graph, then finds a spanning tree for the graph.
3097 Only arcs that are not on the spanning tree have to be instrumented: the
3098 compiler adds code to count the number of times that these arcs are
3099 executed. When an arc is the only exit or only entrance to a block, the
3100 instrumentation code can be added to the block; otherwise, a new basic
3101 block must be created to hold the instrumentation code.
3104 @item -ftest-coverage
3105 @opindex ftest-coverage
3106 Produce a notes file that the @command{gcov} code-coverage utility
3107 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3108 show program coverage. Each source file's note file is called
3109 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3110 above for a description of @var{auxname} and instructions on how to
3111 generate test coverage data. Coverage data will match the source files
3112 more closely, if you do not optimize.
3114 @item -d@var{letters}
3116 Says to make debugging dumps during compilation at times specified by
3117 @var{letters}. This is used for debugging the compiler. The file names
3118 for most of the dumps are made by appending a pass number and a word to
3119 the @var{dumpname}. @var{dumpname} is generated from the name of the
3120 output file, if explicitly specified and it is not an executable,
3121 otherwise it is the basename of the source file. In both cases any
3122 suffix is removed (e.g. @file{foo.00.rtl} or @file{foo.01.sibling}).
3123 Here are the possible letters for use in @var{letters}, and their
3129 Annotate the assembler output with miscellaneous debugging information.
3132 Dump after computing branch probabilities, to @file{@var{file}.16.bp}.
3135 Dump after block reordering, to @file{@var{file}.32.bbro}.
3138 Dump after instruction combination, to the file @file{@var{file}.22.combine}.
3141 Dump after the first if conversion, to the file @file{@var{file}.17.ce1}.
3142 Also dump after the second if conversion, to the file @file{@var{file}.23.ce2}.
3145 Dump after branch target load optimization, to to @file{@var{file}.34.btl}.
3146 Also dump after delayed branch scheduling, to @file{@var{file}.37.dbr}.
3149 Dump all macro definitions, at the end of preprocessing, in addition to
3153 Dump after SSA optimizations, to @file{@var{file}.05.ssa} and
3154 @file{@var{file}.010.ussa}.
3157 Dump after the second if conversion, to @file{@var{file}.33.ce3}.
3160 Dump after control and data flow analysis, to @file{@var{file}.15.cfg}.
3161 Also dump after life analysis, to @file{@var{file}.21.life}.
3164 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.11.addressof}.
3167 Dump after global register allocation, to @file{@var{file}.27.greg}.
3170 Dump after GCSE, to @file{@var{file}.12.gcse}.
3171 Also dump after jump bypassing and control flow optimizations, to
3172 @file{@var{file}.14.bypass}.
3175 Dump after finalization of EH handling code, to @file{@var{file}.03.eh}.
3178 Dump after sibling call optimizations, to @file{@var{file}.02.sibling}.
3181 Dump after the first jump optimization, to @file{@var{file}.04.jump}.
3184 Dump after conversion from registers to stack, to @file{@var{file}.36.stack}.
3187 Dump after local register allocation, to @file{@var{file}.26.lreg}.
3190 Dump after loop optimization passes, to @file{@var{file}.13.loop} and
3191 @file{@var{file}.19.loop2}.
3194 Dump after performing the machine dependent reorganization pass, to
3195 @file{@var{file}.37.mach}.
3198 Dump after register renumbering, to @file{@var{file}.31.rnreg}.
3201 Dump after the register move pass, to @file{@var{file}.24.regmove}.
3204 Dump after post-reload optimizations, to @file{@var{file}.28.postreload}.
3207 Dump after RTL generation, to @file{@var{file}.01.rtl}.
3210 Dump after the second scheduling pass, to @file{@var{file}.35.sched2}.
3213 Dump after CSE (including the jump optimization that sometimes follows
3214 CSE), to @file{@var{file}.019.cse}.
3217 Dump after the first scheduling pass, to @file{@var{file}.25.sched}.
3220 Dump after the second CSE pass (including the jump optimization that
3221 sometimes follows CSE), to @file{@var{file}.20.cse2}.
3224 Dump after running tracer, to @file{@var{file}.18.tracer}.
3227 Dump after null pointer elimination pass to @file{@var{file}.018.null}.
3230 Dump callgraph and unit-at-a-time optimization @file{@var{file}.00.unit}.
3233 Dump after the second flow pass, to @file{@var{file}.29.flow2}.
3236 Dump after SSA conditional constant propagation, to
3237 @file{@var{file}.06.ssaccp}.
3240 Dump after SSA dead code elimination, to @file{@var{file}.07.ssadce}.
3243 Dump after the peephole pass, to @file{@var{file}.30.peephole2}.
3246 Produce all the dumps listed above.
3249 Produce a core dump whenever an error occurs.
3252 Print statistics on memory usage, at the end of the run, to
3256 Annotate the assembler output with a comment indicating which
3257 pattern and alternative was used. The length of each instruction is
3261 Dump the RTL in the assembler output as a comment before each instruction.
3262 Also turns on @option{-dp} annotation.
3265 For each of the other indicated dump files (except for
3266 @file{@var{file}.01.rtl}), dump a representation of the control flow graph
3267 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3270 Just generate RTL for a function instead of compiling it. Usually used
3274 Dump debugging information during parsing, to standard error.
3277 @item -fdump-unnumbered
3278 @opindex fdump-unnumbered
3279 When doing debugging dumps (see @option{-d} option above), suppress instruction
3280 numbers and line number note output. This makes it more feasible to
3281 use diff on debugging dumps for compiler invocations with different
3282 options, in particular with and without @option{-g}.
3284 @item -fdump-translation-unit @r{(C and C++ only)}
3285 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3286 @opindex fdump-translation-unit
3287 Dump a representation of the tree structure for the entire translation
3288 unit to a file. The file name is made by appending @file{.tu} to the
3289 source file name. If the @samp{-@var{options}} form is used, @var{options}
3290 controls the details of the dump as described for the
3291 @option{-fdump-tree} options.
3293 @item -fdump-class-hierarchy @r{(C++ only)}
3294 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3295 @opindex fdump-class-hierarchy
3296 Dump a representation of each class's hierarchy and virtual function
3297 table layout to a file. The file name is made by appending @file{.class}
3298 to the source file name. If the @samp{-@var{options}} form is used,
3299 @var{options} controls the details of the dump as described for the
3300 @option{-fdump-tree} options.
3302 @item -fdump-tree-@var{switch} @r{(C++ only)}
3303 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3305 Control the dumping at various stages of processing the intermediate
3306 language tree to a file. The file name is generated by appending a switch
3307 specific suffix to the source file name. If the @samp{-@var{options}}
3308 form is used, @var{options} is a list of @samp{-} separated options that
3309 control the details of the dump. Not all options are applicable to all
3310 dumps, those which are not meaningful will be ignored. The following
3311 options are available
3315 Print the address of each node. Usually this is not meaningful as it
3316 changes according to the environment and source file. Its primary use
3317 is for tying up a dump file with a debug environment.
3319 Inhibit dumping of members of a scope or body of a function merely
3320 because that scope has been reached. Only dump such items when they
3321 are directly reachable by some other path.
3323 Turn on all options.
3326 The following tree dumps are possible:
3329 Dump before any tree based optimization, to @file{@var{file}.original}.
3331 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3333 Dump after function inlining, to @file{@var{file}.inlined}.
3336 @item -frandom-seed=@var{string}
3337 @opindex frandom-string
3338 This option provides a seed that GCC uses when it would otherwise use
3339 random numbers. It is used to generate certain symbol names
3340 that have to be different in every compiled file. It is also used to
3341 place unique stamps in coverage data files and the object files that
3342 produce them. You can use the @option{-frandom-seed} option to produce
3343 reproducibly identical object files.
3345 The @var{string} should be different for every file you compile.
3347 @item -fsched-verbose=@var{n}
3348 @opindex fsched-verbose
3349 On targets that use instruction scheduling, this option controls the
3350 amount of debugging output the scheduler prints. This information is
3351 written to standard error, unless @option{-dS} or @option{-dR} is
3352 specified, in which case it is output to the usual dump
3353 listing file, @file{.sched} or @file{.sched2} respectively. However
3354 for @var{n} greater than nine, the output is always printed to standard
3357 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3358 same information as @option{-dRS}. For @var{n} greater than one, it
3359 also output basic block probabilities, detailed ready list information
3360 and unit/insn info. For @var{n} greater than two, it includes RTL
3361 at abort point, control-flow and regions info. And for @var{n} over
3362 four, @option{-fsched-verbose} also includes dependence info.
3366 Store the usual ``temporary'' intermediate files permanently; place them
3367 in the current directory and name them based on the source file. Thus,
3368 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3369 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3370 preprocessed @file{foo.i} output file even though the compiler now
3371 normally uses an integrated preprocessor.
3375 Report the CPU time taken by each subprocess in the compilation
3376 sequence. For C source files, this is the compiler proper and assembler
3377 (plus the linker if linking is done). The output looks like this:
3384 The first number on each line is the ``user time,'' that is time spent
3385 executing the program itself. The second number is ``system time,''
3386 time spent executing operating system routines on behalf of the program.
3387 Both numbers are in seconds.
3389 @item -print-file-name=@var{library}
3390 @opindex print-file-name
3391 Print the full absolute name of the library file @var{library} that
3392 would be used when linking---and don't do anything else. With this
3393 option, GCC does not compile or link anything; it just prints the
3396 @item -print-multi-directory
3397 @opindex print-multi-directory
3398 Print the directory name corresponding to the multilib selected by any
3399 other switches present in the command line. This directory is supposed
3400 to exist in @env{GCC_EXEC_PREFIX}.
3402 @item -print-multi-lib
3403 @opindex print-multi-lib
3404 Print the mapping from multilib directory names to compiler switches
3405 that enable them. The directory name is separated from the switches by
3406 @samp{;}, and each switch starts with an @samp{@@} instead of the
3407 @samp{-}, without spaces between multiple switches. This is supposed to
3408 ease shell-processing.
3410 @item -print-prog-name=@var{program}
3411 @opindex print-prog-name
3412 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3414 @item -print-libgcc-file-name
3415 @opindex print-libgcc-file-name
3416 Same as @option{-print-file-name=libgcc.a}.
3418 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3419 but you do want to link with @file{libgcc.a}. You can do
3422 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3425 @item -print-search-dirs
3426 @opindex print-search-dirs
3427 Print the name of the configured installation directory and a list of
3428 program and library directories gcc will search---and don't do anything else.
3430 This is useful when gcc prints the error message
3431 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3432 To resolve this you either need to put @file{cpp0} and the other compiler
3433 components where gcc expects to find them, or you can set the environment
3434 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3435 Don't forget the trailing '/'.
3436 @xref{Environment Variables}.
3439 @opindex dumpmachine
3440 Print the compiler's target machine (for example,
3441 @samp{i686-pc-linux-gnu})---and don't do anything else.
3444 @opindex dumpversion
3445 Print the compiler version (for example, @samp{3.0})---and don't do
3450 Print the compiler's built-in specs---and don't do anything else. (This
3451 is used when GCC itself is being built.) @xref{Spec Files}.
3453 @item -feliminate-unused-debug-types
3454 @opindex feliminate-unused-debug-types
3455 Normally, when producing DWARF2 output, GCC will emit debugging
3456 information for all types declared in a compilation
3457 unit, regardless of whether or not they are actually used
3458 in that compilation unit. Sometimes this is useful, such as
3459 if, in the debugger, you want to cast a value to a type that is
3460 not actually used in your program (but is declared). More often,
3461 however, this results in a significant amount of wasted space.
3462 With this option, GCC will avoid producing debug symbol output
3463 for types that are nowhere used in the source file being compiled.
3466 @node Optimize Options
3467 @section Options That Control Optimization
3468 @cindex optimize options
3469 @cindex options, optimization
3471 These options control various sorts of optimizations.
3473 Without any optimization option, the compiler's goal is to reduce the
3474 cost of compilation and to make debugging produce the expected
3475 results. Statements are independent: if you stop the program with a
3476 breakpoint between statements, you can then assign a new value to any
3477 variable or change the program counter to any other statement in the
3478 function and get exactly the results you would expect from the source
3481 Turning on optimization flags makes the compiler attempt to improve
3482 the performance and/or code size at the expense of compilation time
3483 and possibly the ability to debug the program.
3485 The compiler performs optimisation based on the knowledge it has of
3486 the program. Using the @option{-funit-at-a-time} flag will allow the
3487 compiler to consider information gained from later functions in the
3488 file when compiling a function. Compiling multiple files at once to a
3489 single output file (and using @option{-funit-at-a-time}) will allow
3490 the compiler to use information gained from all of the files when
3491 compiling each of them.
3493 Not all optimizations are controlled directly by a flag. Only
3494 optimizations that have a flag are listed.
3501 Optimize. Optimizing compilation takes somewhat more time, and a lot
3502 more memory for a large function.
3504 With @option{-O}, the compiler tries to reduce code size and execution
3505 time, without performing any optimizations that take a great deal of
3508 @option{-O} turns on the following optimization flags:
3509 @gccoptlist{-fdefer-pop @gol
3510 -fmerge-constants @gol
3512 -floop-optimize @gol
3514 -fif-conversion @gol
3515 -fif-conversion2 @gol
3516 -fdelayed-branch @gol
3517 -fguess-branch-probability @gol
3520 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
3521 where doing so does not interfere with debugging.
3525 Optimize even more. GCC performs nearly all supported optimizations
3526 that do not involve a space-speed tradeoff. The compiler does not
3527 perform loop unrolling or function inlining when you specify @option{-O2}.
3528 As compared to @option{-O}, this option increases both compilation time
3529 and the performance of the generated code.
3531 @option{-O2} turns on all optimization flags specified by @option{-O}. It
3532 also turns on the following optimization flags:
3533 @gccoptlist{-fforce-mem @gol
3534 -foptimize-sibling-calls @gol
3535 -fstrength-reduce @gol
3536 -fcse-follow-jumps -fcse-skip-blocks @gol
3537 -frerun-cse-after-loop -frerun-loop-opt @gol
3538 -fgcse -fgcse-lm -fgcse-sm @gol
3539 -fdelete-null-pointer-checks @gol
3540 -fexpensive-optimizations @gol
3542 -fschedule-insns -fschedule-insns2 @gol
3543 -fsched-interblock -fsched-spec @gol
3546 -freorder-blocks -freorder-functions @gol
3547 -fstrict-aliasing @gol
3548 -falign-functions -falign-jumps @gol
3549 -falign-loops -falign-labels}
3551 Please note the warning under @option{-fgcse} about
3552 invoking @option{-O2} on programs that use computed gotos.
3556 Optimize yet more. @option{-O3} turns on all optimizations specified by
3557 @option{-O2} and also turns on the @option{-finline-functions},
3558 @option{-funit-at-a-time} and @option{-frename-registers} options.
3562 Do not optimize. This is the default.
3566 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3567 do not typically increase code size. It also performs further
3568 optimizations designed to reduce code size.
3570 @option{-Os} disables the following optimization flags:
3571 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
3572 -falign-labels -freorder-blocks -fprefetch-loop-arrays}
3574 If you use multiple @option{-O} options, with or without level numbers,
3575 the last such option is the one that is effective.
3578 Options of the form @option{-f@var{flag}} specify machine-independent
3579 flags. Most flags have both positive and negative forms; the negative
3580 form of @option{-ffoo} would be @option{-fno-foo}. In the table
3581 below, only one of the forms is listed---the one you typically will
3582 use. You can figure out the other form by either removing @samp{no-}
3585 The following options control specific optimizations. They are either
3586 activated by @option{-O} options or are related to ones that are. You
3587 can use the following flags in the rare cases when ``fine-tuning'' of
3588 optimizations to be performed is desired.
3591 @item -fno-default-inline
3592 @opindex fno-default-inline
3593 Do not make member functions inline by default merely because they are
3594 defined inside the class scope (C++ only). Otherwise, when you specify
3595 @w{@option{-O}}, member functions defined inside class scope are compiled
3596 inline by default; i.e., you don't need to add @samp{inline} in front of
3597 the member function name.
3599 @item -fno-defer-pop
3600 @opindex fno-defer-pop
3601 Always pop the arguments to each function call as soon as that function
3602 returns. For machines which must pop arguments after a function call,
3603 the compiler normally lets arguments accumulate on the stack for several
3604 function calls and pops them all at once.
3606 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3610 Force memory operands to be copied into registers before doing
3611 arithmetic on them. This produces better code by making all memory
3612 references potential common subexpressions. When they are not common
3613 subexpressions, instruction combination should eliminate the separate
3616 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3619 @opindex fforce-addr
3620 Force memory address constants to be copied into registers before
3621 doing arithmetic on them. This may produce better code just as
3622 @option{-fforce-mem} may.
3624 @item -fomit-frame-pointer
3625 @opindex fomit-frame-pointer
3626 Don't keep the frame pointer in a register for functions that
3627 don't need one. This avoids the instructions to save, set up and
3628 restore frame pointers; it also makes an extra register available
3629 in many functions. @strong{It also makes debugging impossible on
3632 On some machines, such as the VAX, this flag has no effect, because
3633 the standard calling sequence automatically handles the frame pointer
3634 and nothing is saved by pretending it doesn't exist. The
3635 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3636 whether a target machine supports this flag. @xref{Registers,,Register
3637 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3639 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3641 @item -foptimize-sibling-calls
3642 @opindex foptimize-sibling-calls
3643 Optimize sibling and tail recursive calls.
3645 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3649 Don't pay attention to the @code{inline} keyword. Normally this option
3650 is used to keep the compiler from expanding any functions inline.
3651 Note that if you are not optimizing, no functions can be expanded inline.
3653 @item -finline-functions
3654 @opindex finline-functions
3655 Integrate all simple functions into their callers. The compiler
3656 heuristically decides which functions are simple enough to be worth
3657 integrating in this way.
3659 If all calls to a given function are integrated, and the function is
3660 declared @code{static}, then the function is normally not output as
3661 assembler code in its own right.
3663 Enabled at level @option{-O3}.
3665 @item -finline-limit=@var{n}
3666 @opindex finline-limit
3667 By default, gcc limits the size of functions that can be inlined. This flag
3668 allows the control of this limit for functions that are explicitly marked as
3669 inline (i.e., marked with the inline keyword or defined within the class
3670 definition in c++). @var{n} is the size of functions that can be inlined in
3671 number of pseudo instructions (not counting parameter handling). The default
3672 value of @var{n} is 600.
3673 Increasing this value can result in more inlined code at
3674 the cost of compilation time and memory consumption. Decreasing usually makes
3675 the compilation faster and less code will be inlined (which presumably
3676 means slower programs). This option is particularly useful for programs that
3677 use inlining heavily such as those based on recursive templates with C++.
3679 Inlining is actually controlled by a number of parameters, which may be
3680 specified individually by using @option{--param @var{name}=@var{value}}.
3681 The @option{-finline-limit=@var{n}} option sets some of these parameters
3685 @item max-inline-insns
3687 @item max-inline-insns-single
3688 is set to @var{n}/2.
3689 @item max-inline-insns-auto
3690 is set to @var{n}/2.
3691 @item min-inline-insns
3692 is set to 130 or @var{n}/4, whichever is smaller.
3693 @item max-inline-insns-rtl
3697 Using @option{-finline-limit=600} thus results in the default settings
3698 for these parameters. See below for a documentation of the individual
3699 parameters controlling inlining.
3701 @emph{Note:} pseudo instruction represents, in this particular context, an
3702 abstract measurement of function's size. In no way, it represents a count
3703 of assembly instructions and as such its exact meaning might change from one
3704 release to an another.
3706 @item -fkeep-inline-functions
3707 @opindex fkeep-inline-functions
3708 Even if all calls to a given function are integrated, and the function
3709 is declared @code{static}, nevertheless output a separate run-time
3710 callable version of the function. This switch does not affect
3711 @code{extern inline} functions.
3713 @item -fkeep-static-consts
3714 @opindex fkeep-static-consts
3715 Emit variables declared @code{static const} when optimization isn't turned
3716 on, even if the variables aren't referenced.
3718 GCC enables this option by default. If you want to force the compiler to
3719 check if the variable was referenced, regardless of whether or not
3720 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3722 @item -fmerge-constants
3723 Attempt to merge identical constants (string constants and floating point
3724 constants) across compilation units.
3726 This option is the default for optimized compilation if the assembler and
3727 linker support it. Use @option{-fno-merge-constants} to inhibit this
3730 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3732 @item -fmerge-all-constants
3733 Attempt to merge identical constants and identical variables.
3735 This option implies @option{-fmerge-constants}. In addition to
3736 @option{-fmerge-constants} this considers e.g. even constant initialized
3737 arrays or initialized constant variables with integral or floating point
3738 types. Languages like C or C++ require each non-automatic variable to
3739 have distinct location, so using this option will result in non-conforming
3744 Use a graph coloring register allocator. Currently this option is meant
3745 for testing, so we are interested to hear about miscompilations with
3748 @item -fno-branch-count-reg
3749 @opindex fno-branch-count-reg
3750 Do not use ``decrement and branch'' instructions on a count register,
3751 but instead generate a sequence of instructions that decrement a
3752 register, compare it against zero, then branch based upon the result.
3753 This option is only meaningful on architectures that support such
3754 instructions, which include x86, PowerPC, IA-64 and S/390.
3756 The default is @option{-fbranch-count-reg}, enabled when
3757 @option{-fstrength-reduce} is enabled.
3759 @item -fno-function-cse
3760 @opindex fno-function-cse
3761 Do not put function addresses in registers; make each instruction that
3762 calls a constant function contain the function's address explicitly.
3764 This option results in less efficient code, but some strange hacks
3765 that alter the assembler output may be confused by the optimizations
3766 performed when this option is not used.
3768 The default is @option{-ffunction-cse}
3770 @item -fno-zero-initialized-in-bss
3771 @opindex fno-zero-initialized-in-bss
3772 If the target supports a BSS section, GCC by default puts variables that
3773 are initialized to zero into BSS@. This can save space in the resulting
3776 This option turns off this behavior because some programs explicitly
3777 rely on variables going to the data section. E.g., so that the
3778 resulting executable can find the beginning of that section and/or make
3779 assumptions based on that.
3781 The default is @option{-fzero-initialized-in-bss}.
3783 @item -fstrength-reduce
3784 @opindex fstrength-reduce
3785 Perform the optimizations of loop strength reduction and
3786 elimination of iteration variables.
3788 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3790 @item -fthread-jumps
3791 @opindex fthread-jumps
3792 Perform optimizations where we check to see if a jump branches to a
3793 location where another comparison subsumed by the first is found. If
3794 so, the first branch is redirected to either the destination of the
3795 second branch or a point immediately following it, depending on whether
3796 the condition is known to be true or false.
3798 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3800 @item -fcse-follow-jumps
3801 @opindex fcse-follow-jumps
3802 In common subexpression elimination, scan through jump instructions
3803 when the target of the jump is not reached by any other path. For
3804 example, when CSE encounters an @code{if} statement with an
3805 @code{else} clause, CSE will follow the jump when the condition
3808 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3810 @item -fcse-skip-blocks
3811 @opindex fcse-skip-blocks
3812 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3813 follow jumps which conditionally skip over blocks. When CSE
3814 encounters a simple @code{if} statement with no else clause,
3815 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3816 body of the @code{if}.
3818 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3820 @item -frerun-cse-after-loop
3821 @opindex frerun-cse-after-loop
3822 Re-run common subexpression elimination after loop optimizations has been
3825 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3827 @item -frerun-loop-opt
3828 @opindex frerun-loop-opt
3829 Run the loop optimizer twice.
3831 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3835 Perform a global common subexpression elimination pass.
3836 This pass also performs global constant and copy propagation.
3838 @emph{Note:} When compiling a program using computed gotos, a GCC
3839 extension, you may get better runtime performance if you disable
3840 the global common subexpression elimination pass by adding
3841 @option{-fno-gcse} to the command line.
3843 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3847 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3848 attempt to move loads which are only killed by stores into themselves. This
3849 allows a loop containing a load/store sequence to be changed to a load outside
3850 the loop, and a copy/store within the loop.
3852 Enabled by default when gcse is enabled.
3856 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3857 subexpression elimination. This pass will attempt to move stores out of loops.
3858 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3859 can be changed to a load before the loop and a store after the loop.
3861 Enabled by default when gcse is enabled.
3863 @item -floop-optimize
3864 @opindex floop-optimize
3865 Perform loop optimizations: move constant expressions out of loops, simplify
3866 exit test conditions and optionally do strength-reduction and loop unrolling as
3869 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3871 @item -fcrossjumping
3872 @opindex crossjumping
3873 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
3874 resulting code may or may not perform better than without cross-jumping.
3876 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3878 @item -fif-conversion
3879 @opindex if-conversion
3880 Attempt to transform conditional jumps into branch-less equivalents. This
3881 include use of conditional moves, min, max, set flags and abs instructions, and
3882 some tricks doable by standard arithmetics. The use of conditional execution
3883 on chips where it is available is controlled by @code{if-conversion2}.
3885 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3887 @item -fif-conversion2
3888 @opindex if-conversion2
3889 Use conditional execution (where available) to transform conditional jumps into
3890 branch-less equivalents.
3892 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3894 @item -fdelete-null-pointer-checks
3895 @opindex fdelete-null-pointer-checks
3896 Use global dataflow analysis to identify and eliminate useless checks
3897 for null pointers. The compiler assumes that dereferencing a null
3898 pointer would have halted the program. If a pointer is checked after
3899 it has already been dereferenced, it cannot be null.
3901 In some environments, this assumption is not true, and programs can
3902 safely dereference null pointers. Use
3903 @option{-fno-delete-null-pointer-checks} to disable this optimization
3904 for programs which depend on that behavior.
3906 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3908 @item -fexpensive-optimizations
3909 @opindex fexpensive-optimizations
3910 Perform a number of minor optimizations that are relatively expensive.
3912 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3914 @item -foptimize-register-move
3916 @opindex foptimize-register-move
3918 Attempt to reassign register numbers in move instructions and as
3919 operands of other simple instructions in order to maximize the amount of
3920 register tying. This is especially helpful on machines with two-operand
3923 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3926 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3928 @item -fdelayed-branch
3929 @opindex fdelayed-branch
3930 If supported for the target machine, attempt to reorder instructions
3931 to exploit instruction slots available after delayed branch
3934 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3936 @item -fschedule-insns
3937 @opindex fschedule-insns
3938 If supported for the target machine, attempt to reorder instructions to
3939 eliminate execution stalls due to required data being unavailable. This
3940 helps machines that have slow floating point or memory load instructions
3941 by allowing other instructions to be issued until the result of the load
3942 or floating point instruction is required.
3944 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3946 @item -fschedule-insns2
3947 @opindex fschedule-insns2
3948 Similar to @option{-fschedule-insns}, but requests an additional pass of
3949 instruction scheduling after register allocation has been done. This is
3950 especially useful on machines with a relatively small number of
3951 registers and where memory load instructions take more than one cycle.
3953 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3955 @item -fno-sched-interblock
3956 @opindex fno-sched-interblock
3957 Don't schedule instructions across basic blocks. This is normally
3958 enabled by default when scheduling before register allocation, i.e.@:
3959 with @option{-fschedule-insns} or at @option{-O2} or higher.
3961 @item -fno-sched-spec
3962 @opindex fno-sched-spec
3963 Don't allow speculative motion of non-load instructions. This is normally
3964 enabled by default when scheduling before register allocation, i.e.@:
3965 with @option{-fschedule-insns} or at @option{-O2} or higher.
3967 @item -fsched-spec-load
3968 @opindex fsched-spec-load
3969 Allow speculative motion of some load instructions. This only makes
3970 sense when scheduling before register allocation, i.e.@: with
3971 @option{-fschedule-insns} or at @option{-O2} or higher.
3973 @item -fsched-spec-load-dangerous
3974 @opindex fsched-spec-load-dangerous
3975 Allow speculative motion of more load instructions. This only makes
3976 sense when scheduling before register allocation, i.e.@: with
3977 @option{-fschedule-insns} or at @option{-O2} or higher.
3979 @item -fsched2-use-superblocks
3980 @opindex fsched2-use-superblocks
3981 When scheduling after register allocation, do use superblock scheduling
3982 algorithm. Superblock scheduling allows motion across basic block boundaries
3983 resulting on faster schedules. This option is experimental, as not all machine
3984 descriptions used by GCC model the CPU closely enough to avoid unreliable
3985 results from the algorithm.
3987 This only makes sense when scheduling after register allocation, i.e.@: with
3988 @option{-fschedule-insns2} or at @option{-O2} or higher.
3990 @item -fsched2-use-traces
3991 @opindex fsched2-use-traces
3992 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
3993 allocation and additionally perform code duplication in order to increase the
3994 size of superblocks using tracer pass. See @option{-ftracer} for details on
3997 This mode should produce faster but significantly longer programs. Also
3998 without @code{-fbranch-probabilities} the traces constructed may not match the
3999 reality and hurt the performance. This only makes
4000 sense when scheduling after register allocation, i.e.@: with
4001 @option{-fschedule-insns2} or at @option{-O2} or higher.
4003 @item -fcaller-saves
4004 @opindex fcaller-saves
4005 Enable values to be allocated in registers that will be clobbered by
4006 function calls, by emitting extra instructions to save and restore the
4007 registers around such calls. Such allocation is done only when it
4008 seems to result in better code than would otherwise be produced.
4010 This option is always enabled by default on certain machines, usually
4011 those which have no call-preserved registers to use instead.
4013 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4015 @item -fmove-all-movables
4016 @opindex fmove-all-movables
4017 Forces all invariant computations in loops to be moved
4020 @item -freduce-all-givs
4021 @opindex freduce-all-givs
4022 Forces all general-induction variables in loops to be
4025 @emph{Note:} When compiling programs written in Fortran,
4026 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
4027 by default when you use the optimizer.
4029 These options may generate better or worse code; results are highly
4030 dependent on the structure of loops within the source code.
4032 These two options are intended to be removed someday, once
4033 they have helped determine the efficacy of various
4034 approaches to improving loop optimizations.
4036 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
4037 know how use of these options affects
4038 the performance of your production code.
4039 We're very interested in code that runs @emph{slower}
4040 when these options are @emph{enabled}.
4043 @itemx -fno-peephole2
4044 @opindex fno-peephole
4045 @opindex fno-peephole2
4046 Disable any machine-specific peephole optimizations. The difference
4047 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4048 are implemented in the compiler; some targets use one, some use the
4049 other, a few use both.
4051 @option{-fpeephole} is enabled by default.
4052 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4054 @item -fno-guess-branch-probability
4055 @opindex fno-guess-branch-probability
4056 Do not guess branch probabilities using a randomized model.
4058 Sometimes gcc will opt to use a randomized model to guess branch
4059 probabilities, when none are available from either profiling feedback
4060 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4061 different runs of the compiler on the same program may produce different
4064 In a hard real-time system, people don't want different runs of the
4065 compiler to produce code that has different behavior; minimizing
4066 non-determinism is of paramount import. This switch allows users to
4067 reduce non-determinism, possibly at the expense of inferior
4070 The default is @option{-fguess-branch-probability} at levels
4071 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4073 @item -freorder-blocks
4074 @opindex freorder-blocks
4075 Reorder basic blocks in the compiled function in order to reduce number of
4076 taken branches and improve code locality.
4078 Enabled at levels @option{-O2}, @option{-O3}.
4080 @item -freorder-functions
4081 @opindex freorder-functions
4082 Reorder basic blocks in the compiled function in order to reduce number of
4083 taken branches and improve code locality. This is implemented by using special
4084 subsections @code{text.hot} for most frequently executed functions and
4085 @code{text.unlikely} for unlikely executed functions. Reordering is done by
4086 the linker so object file format must support named sections and linker must
4087 place them in a reasonable way.
4089 Also profile feedback must be available in to make this option effective. See
4090 @option{-fprofile-arcs} for details.
4092 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4094 @item -fstrict-aliasing
4095 @opindex fstrict-aliasing
4096 Allows the compiler to assume the strictest aliasing rules applicable to
4097 the language being compiled. For C (and C++), this activates
4098 optimizations based on the type of expressions. In particular, an
4099 object of one type is assumed never to reside at the same address as an
4100 object of a different type, unless the types are almost the same. For
4101 example, an @code{unsigned int} can alias an @code{int}, but not a
4102 @code{void*} or a @code{double}. A character type may alias any other
4105 Pay special attention to code like this:
4118 The practice of reading from a different union member than the one most
4119 recently written to (called ``type-punning'') is common. Even with
4120 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4121 is accessed through the union type. So, the code above will work as
4122 expected. However, this code might not:
4133 Every language that wishes to perform language-specific alias analysis
4134 should define a function that computes, given an @code{tree}
4135 node, an alias set for the node. Nodes in different alias sets are not
4136 allowed to alias. For an example, see the C front-end function
4137 @code{c_get_alias_set}.
4139 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4141 @item -falign-functions
4142 @itemx -falign-functions=@var{n}
4143 @opindex falign-functions
4144 Align the start of functions to the next power-of-two greater than
4145 @var{n}, skipping up to @var{n} bytes. For instance,
4146 @option{-falign-functions=32} aligns functions to the next 32-byte
4147 boundary, but @option{-falign-functions=24} would align to the next
4148 32-byte boundary only if this can be done by skipping 23 bytes or less.
4150 @option{-fno-align-functions} and @option{-falign-functions=1} are
4151 equivalent and mean that functions will not be aligned.
4153 Some assemblers only support this flag when @var{n} is a power of two;
4154 in that case, it is rounded up.
4156 If @var{n} is not specified or is zero, use a machine-dependent default.
4158 Enabled at levels @option{-O2}, @option{-O3}.
4160 @item -falign-labels
4161 @itemx -falign-labels=@var{n}
4162 @opindex falign-labels
4163 Align all branch targets to a power-of-two boundary, skipping up to
4164 @var{n} bytes like @option{-falign-functions}. This option can easily
4165 make code slower, because it must insert dummy operations for when the
4166 branch target is reached in the usual flow of the code.
4168 @option{-fno-align-labels} and @option{-falign-labels=1} are
4169 equivalent and mean that labels will not be aligned.
4171 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4172 are greater than this value, then their values are used instead.
4174 If @var{n} is not specified or is zero, use a machine-dependent default
4175 which is very likely to be @samp{1}, meaning no alignment.
4177 Enabled at levels @option{-O2}, @option{-O3}.
4180 @itemx -falign-loops=@var{n}
4181 @opindex falign-loops
4182 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4183 like @option{-falign-functions}. The hope is that the loop will be
4184 executed many times, which will make up for any execution of the dummy
4187 @option{-fno-align-loops} and @option{-falign-loops=1} are
4188 equivalent and mean that loops will not be aligned.
4190 If @var{n} is not specified or is zero, use a machine-dependent default.
4192 Enabled at levels @option{-O2}, @option{-O3}.
4195 @itemx -falign-jumps=@var{n}
4196 @opindex falign-jumps
4197 Align branch targets to a power-of-two boundary, for branch targets
4198 where the targets can only be reached by jumping, skipping up to @var{n}
4199 bytes like @option{-falign-functions}. In this case, no dummy operations
4202 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4203 equivalent and mean that loops will not be aligned.
4205 If @var{n} is not specified or is zero, use a machine-dependent default.
4207 Enabled at levels @option{-O2}, @option{-O3}.
4209 @item -frename-registers
4210 @opindex frename-registers
4211 Attempt to avoid false dependencies in scheduled code by making use
4212 of registers left over after register allocation. This optimization
4213 will most benefit processors with lots of registers. It can, however,
4214 make debugging impossible, since variables will no longer stay in
4215 a ``home register''.
4217 Enabled at levels @option{-O3}.
4219 @item -fno-cprop-registers
4220 @opindex fno-cprop-registers
4221 After register allocation and post-register allocation instruction splitting,
4222 we perform a copy-propagation pass to try to reduce scheduling dependencies
4223 and occasionally eliminate the copy.
4225 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4229 The following options control compiler behavior regarding floating
4230 point arithmetic. These options trade off between speed and
4231 correctness. All must be specifically enabled.
4235 @opindex ffloat-store
4236 Do not store floating point variables in registers, and inhibit other
4237 options that might change whether a floating point value is taken from a
4240 @cindex floating point precision
4241 This option prevents undesirable excess precision on machines such as
4242 the 68000 where the floating registers (of the 68881) keep more
4243 precision than a @code{double} is supposed to have. Similarly for the
4244 x86 architecture. For most programs, the excess precision does only
4245 good, but a few programs rely on the precise definition of IEEE floating
4246 point. Use @option{-ffloat-store} for such programs, after modifying
4247 them to store all pertinent intermediate computations into variables.
4251 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
4252 @option{-fno-trapping-math}, @option{-ffinite-math-only},
4253 @option{-fno-rounding-math} and @option{-fno-signaling-nans}.
4255 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
4257 This option should never be turned on by any @option{-O} option since
4258 it can result in incorrect output for programs which depend on
4259 an exact implementation of IEEE or ISO rules/specifications for
4262 @item -fno-math-errno
4263 @opindex fno-math-errno
4264 Do not set ERRNO after calling math functions that are executed
4265 with a single instruction, e.g., sqrt. A program that relies on
4266 IEEE exceptions for math error handling may want to use this flag
4267 for speed while maintaining IEEE arithmetic compatibility.
4269 This option should never be turned on by any @option{-O} option since
4270 it can result in incorrect output for programs which depend on
4271 an exact implementation of IEEE or ISO rules/specifications for
4274 The default is @option{-fmath-errno}.
4276 @item -funsafe-math-optimizations
4277 @opindex funsafe-math-optimizations
4278 Allow optimizations for floating-point arithmetic that (a) assume
4279 that arguments and results are valid and (b) may violate IEEE or
4280 ANSI standards. When used at link-time, it may include libraries
4281 or startup files that change the default FPU control word or other
4282 similar optimizations.
4284 This option should never be turned on by any @option{-O} option since
4285 it can result in incorrect output for programs which depend on
4286 an exact implementation of IEEE or ISO rules/specifications for
4289 The default is @option{-fno-unsafe-math-optimizations}.
4291 @item -ffinite-math-only
4292 @opindex ffinite-math-only
4293 Allow optimizations for floating-point arithmetic that assume
4294 that arguments and results are not NaNs or +-Infs.
4296 This option should never be turned on by any @option{-O} option since
4297 it can result in incorrect output for programs which depend on
4298 an exact implementation of IEEE or ISO rules/specifications.
4300 The default is @option{-fno-finite-math-only}.
4302 @item -fno-trapping-math
4303 @opindex fno-trapping-math
4304 Compile code assuming that floating-point operations cannot generate
4305 user-visible traps. These traps include division by zero, overflow,
4306 underflow, inexact result and invalid operation. This option implies
4307 @option{-fno-signaling-nans}. Setting this option may allow faster
4308 code if one relies on ``non-stop'' IEEE arithmetic, for example.
4310 This option should never be turned on by any @option{-O} option since
4311 it can result in incorrect output for programs which depend on
4312 an exact implementation of IEEE or ISO rules/specifications for
4315 The default is @option{-ftrapping-math}.
4317 @item -frounding-math
4318 @opindex frounding-math
4319 Disable transformations and optimizations that assume default floating
4320 point rounding behavior. This is round-to-zero for all floating point
4321 to integer conversions, and round-to-nearest for all other arithmetic
4322 truncations. This option should be specified for programs that change
4323 the FP rounding mode dynamically, or that may be executed with a
4324 non-default rounding mode. This option disables constant folding of
4325 floating point expressions at compile-time (which may be affected by
4326 rounding mode) and arithmetic transformations that are unsafe in the
4327 presence of sign-dependent rounding modes.
4329 The default is @option{-fno-rounding-math}.
4331 This option is experimental and does not currently guarantee to
4332 disable all GCC optimizations that are affected by rounding mode.
4333 Future versions of gcc may provide finer control of this setting
4334 using C99's @code{FENV_ACCESS} pragma. This command line option
4335 will be used to specify the default state for @code{FENV_ACCESS}.
4337 @item -fsignaling-nans
4338 @opindex fsignaling-nans
4339 Compile code assuming that IEEE signaling NaNs may generate user-visible
4340 traps during floating-point operations. Setting this option disables
4341 optimizations that may change the number of exceptions visible with
4342 signaling NaNs. This option implies @option{-ftrapping-math}.
4344 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
4347 The default is @option{-fno-signaling-nans}.
4349 This option is experimental and does not currently guarantee to
4350 disable all GCC optimizations that affect signaling NaN behavior.
4352 @item -fsingle-precision-constant
4353 @opindex fsingle-precision-constant
4354 Treat floating point constant as single precision constant instead of
4355 implicitly converting it to double precision constant.
4360 The following options control optimizations that may improve
4361 performance, but are not enabled by any @option{-O} options. This
4362 section includes experimental options that may produce broken code.
4365 @item -fbranch-probabilities
4366 @opindex fbranch-probabilities
4367 After running a program compiled with @option{-fprofile-arcs}
4368 (@pxref{Debugging Options,, Options for Debugging Your Program or
4369 @command{gcc}}), you can compile it a second time using
4370 @option{-fbranch-probabilities}, to improve optimizations based on
4371 the number of times each branch was taken. When the program
4372 compiled with @option{-fprofile-arcs} exits it saves arc execution
4373 counts to a file called @file{@var{sourcename}.gcda} for each source
4374 file The information in this data file is very dependent on the
4375 structure of the generated code, so you must use the same source code
4376 and the same optimization options for both compilations.
4378 With @option{-fbranch-probabilities}, GCC puts a
4379 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
4380 These can be used to improve optimization. Currently, they are only
4381 used in one place: in @file{reorg.c}, instead of guessing which path a
4382 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
4383 exactly determine which path is taken more often.
4385 @item -fprofile-values
4386 @opindex fprofile-values
4387 If combined with @option{-fprofile-arcs}, it adds code so that some
4388 data about values of expressions in the program is gathered.
4390 With @option{-fbranch-probabilities}, it reads back the data gathered
4391 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
4392 notes to instructions for their later usage in optimizations.
4396 Use a graph coloring register allocator. Currently this option is meant
4397 for testing, so we are interested to hear about miscompilations with
4402 Perform tail duplication to enlarge superblock size. This transformation
4403 simplifies the control flow of the function allowing other optimizations to do
4406 @item -funit-at-a-time
4407 @opindex funit-at-a-time
4408 Parse the whole compilation unit before starting to produce code.
4409 This allows some extra optimizations to take place but consumes more
4412 @item -funroll-loops
4413 @opindex funroll-loops
4414 Unroll loops whose number of iterations can be determined at compile time or
4415 upon entry to the loop. @option{-funroll-loops} implies
4416 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
4417 (i.e. complete removal of loops with small constant number of iterations).
4418 This option makes code larger, and may or may not make it run faster.
4420 @item -funroll-all-loops
4421 @opindex funroll-all-loops
4422 Unroll all loops, even if their number of iterations is uncertain when
4423 the loop is entered. This usually makes programs run more slowly.
4424 @option{-funroll-all-loops} implies the same options as
4425 @option{-funroll-loops}.
4428 @opindex fpeel-loops
4429 Peels the loops for that there is enough information that they do not
4430 roll much (from profile feedback). It also turns on complete loop peeling
4431 (i.e. complete removal of loops with small constant number of iterations).
4433 @item -funswitch-loops
4434 @opindex funswitch-loops
4435 Move branches with loop invariant conditions out of the loop, with duplicates
4436 of the loop on both branches (modified according to result of the condition).
4438 @item -fold-unroll-loops
4439 @opindex fold-unroll-loops
4440 Unroll loops whose number of iterations can be determined at compile
4441 time or upon entry to the loop, using the old loop unroller whose loop
4442 recognition is based on notes from frontend. @option{-fold-unroll-loops} implies
4443 both @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4444 option makes code larger, and may or may not make it run faster.
4446 @item -fold-unroll-all-loops
4447 @opindex fold-unroll-all-loops
4448 Unroll all loops, even if their number of iterations is uncertain when
4449 the loop is entered. This is done using the old loop unroller whose loop
4450 recognition is based on notes from frontend. This usually makes programs run more slowly.
4451 @option{-fold-unroll-all-loops} implies the same options as
4452 @option{-fold-unroll-loops}.
4454 @item -funswitch-loops
4455 @opindex funswitch-loops
4456 Move branches with loop invariant conditions out of the loop, with duplicates
4457 of the loop on both branches (modified according to result of the condition).
4459 @item -funswitch-loops
4460 @opindex funswitch-loops
4461 Move branches with loop invariant conditions out of the loop, with duplicates
4462 of the loop on both branches (modified according to result of the condition).
4464 @item -fprefetch-loop-arrays
4465 @opindex fprefetch-loop-arrays
4466 If supported by the target machine, generate instructions to prefetch
4467 memory to improve the performance of loops that access large arrays.
4469 Disabled at level @option{-Os}.
4471 @item -ffunction-sections
4472 @itemx -fdata-sections
4473 @opindex ffunction-sections
4474 @opindex fdata-sections
4475 Place each function or data item into its own section in the output
4476 file if the target supports arbitrary sections. The name of the
4477 function or the name of the data item determines the section's name
4480 Use these options on systems where the linker can perform optimizations
4481 to improve locality of reference in the instruction space. Most systems
4482 using the ELF object format and SPARC processors running Solaris 2 have
4483 linkers with such optimizations. AIX may have these optimizations in
4486 Only use these options when there are significant benefits from doing
4487 so. When you specify these options, the assembler and linker will
4488 create larger object and executable files and will also be slower.
4489 You will not be able to use @code{gprof} on all systems if you
4490 specify this option and you may have problems with debugging if
4491 you specify both this option and @option{-g}.
4495 Perform optimizations in static single assignment form. Each function's
4496 flow graph is translated into SSA form, optimizations are performed, and
4497 the flow graph is translated back from SSA form. Users should not
4498 specify this option, since it is not yet ready for production use.
4502 Perform Sparse Conditional Constant Propagation in SSA form. Requires
4503 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
4507 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
4508 Like @option{-fssa}, this is an experimental feature.
4510 @item -fbranch-target-load-optimize
4511 @opindex fbranch-target-load-optimize
4512 Perform branch target register load optimization before prologue / epilogue
4514 The use of target registers can typically be exposed only during reload,
4515 thus hoisting loads out of loops and doing inter-block scheduling needs
4516 a separate optimization pass.
4518 @item -fbranch-target-load-optimize2
4519 @opindex fbranch-target-load-optimize2
4520 Perform branch target register load optimization after prologue / epilogue
4526 @item --param @var{name}=@var{value}
4528 In some places, GCC uses various constants to control the amount of
4529 optimization that is done. For example, GCC will not inline functions
4530 that contain more that a certain number of instructions. You can
4531 control some of these constants on the command-line using the
4532 @option{--param} option.
4534 In each case, the @var{value} is an integer. The allowable choices for
4535 @var{name} are given in the following table:
4538 @item max-crossjump-edges
4539 The maximum number of incoming edges to consider for crossjumping.
4540 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
4541 the number of edges incoming to each block. Increasing values mean
4542 more aggressive optimization, making the compile time increase with
4543 probably small improvement in executable size.
4545 @item max-delay-slot-insn-search
4546 The maximum number of instructions to consider when looking for an
4547 instruction to fill a delay slot. If more than this arbitrary number of
4548 instructions is searched, the time savings from filling the delay slot
4549 will be minimal so stop searching. Increasing values mean more
4550 aggressive optimization, making the compile time increase with probably
4551 small improvement in executable run time.
4553 @item max-delay-slot-live-search
4554 When trying to fill delay slots, the maximum number of instructions to
4555 consider when searching for a block with valid live register
4556 information. Increasing this arbitrarily chosen value means more
4557 aggressive optimization, increasing the compile time. This parameter
4558 should be removed when the delay slot code is rewritten to maintain the
4561 @item max-gcse-memory
4562 The approximate maximum amount of memory that will be allocated in
4563 order to perform the global common subexpression elimination
4564 optimization. If more memory than specified is required, the
4565 optimization will not be done.
4567 @item max-gcse-passes
4568 The maximum number of passes of GCSE to run.
4570 @item max-pending-list-length
4571 The maximum number of pending dependencies scheduling will allow
4572 before flushing the current state and starting over. Large functions
4573 with few branches or calls can create excessively large lists which
4574 needlessly consume memory and resources.
4576 @item max-inline-insns-single
4577 Several parameters control the tree inliner used in gcc.
4578 This number sets the maximum number of instructions (counted in gcc's
4579 internal representation) in a single function that the tree inliner
4580 will consider for inlining. This only affects functions declared
4581 inline and methods implemented in a class declaration (C++).
4582 The default value is 500.
4584 @item max-inline-insns-auto
4585 When you use @option{-finline-functions} (included in @option{-O3}),
4586 a lot of functions that would otherwise not be considered for inlining
4587 by the compiler will be investigated. To those functions, a different
4588 (more restrictive) limit compared to functions declared inline can
4590 The default value is 150.
4592 @item max-inline-insns
4593 The tree inliner does decrease the allowable size for single functions
4594 to be inlined after we already inlined the number of instructions
4595 given here by repeated inlining. This number should be a factor of
4596 two or more larger than the single function limit.
4597 Higher numbers result in better runtime performance, but incur higher
4598 compile-time resource (CPU time, memory) requirements and result in
4599 larger binaries. Very high values are not advisable, as too large
4600 binaries may adversely affect runtime performance.
4601 The default value is 200.
4603 @item max-inline-slope
4604 After exceeding the maximum number of inlined instructions by repeated
4605 inlining, a linear function is used to decrease the allowable size
4606 for single functions. The slope of that function is the negative
4607 reciprocal of the number specified here.
4608 This parameter is ignored when @option{-funit-at-a-time} is used.
4609 The default value is 32.
4611 @item min-inline-insns
4612 The repeated inlining is throttled more and more by the linear function
4613 after exceeding the limit. To avoid too much throttling, a minimum for
4614 this function is specified here to allow repeated inlining for very small
4615 functions even when a lot of repeated inlining already has been done.
4616 This parameter is ignored when @option{-funit-at-a-time} is used.
4617 The default value is 10.
4619 @item large-function-insns
4620 The limit specifying really large functions. For functions greater than this
4621 limit inlining is constrained by @option{--param large-function-growth}.
4622 This parameter is usefull primarily to avoid extreme compilation time caused by non-linear
4623 algorithms used by the backend.
4624 This parameter is ignored when @option{-funit-at-a-time} is not used.
4625 The default value is 30000.
4627 @item large-function-growth
4628 Specifies maximal growth of large functtion caused by inlining in percents.
4629 This parameter is ignored when @option{-funit-at-a-time} is not used.
4630 The default value is 200.
4632 @item inline-unit-growth
4633 Specifies maximal overall growth of the compilation unit caused by inlining.
4634 This parameter is ignored when @option{-funit-at-a-time} is not used.
4635 The default value is 150.
4637 @item max-inline-insns-rtl
4638 For languages that use the RTL inliner (this happens at a later stage
4639 than tree inlining), you can set the maximum allowable size (counted
4640 in RTL instructions) for the RTL inliner with this parameter.
4641 The default value is 600.
4644 @item max-unrolled-insns
4645 The maximum number of instructions that a loop should have if that loop
4646 is unrolled, and if the loop is unrolled, it determines how many times
4647 the loop code is unrolled.
4649 @item max-average-unrolled-insns
4650 The maximum number of instructions biased by probabilities of their execution
4651 that a loop should have if that loop is unrolled, and if the loop is unrolled,
4652 it determines how many times the loop code is unrolled.
4654 @item max-unroll-times
4655 The maximum number of unrollings of a single loop.
4657 @item max-peeled-insns
4658 The maximum number of instructions that a loop should have if that loop
4659 is peeled, and if the loop is peeled, it determines how many times
4660 the loop code is peeled.
4662 @item max-peel-times
4663 The maximum number of peelings of a single loop.
4665 @item max-completely-peeled-insns
4666 The maximum number of insns of a completely peeled loop.
4668 @item max-completely-peel-times
4669 The maximum number of iterations of a loop to be suitable for complete peeling.
4671 @item max-unswitch-insns
4672 The maximum number of insns of an unswitched loop.
4674 @item max-unswitch-level
4675 The maximum number of branches unswitched in a single loop.
4677 @item hot-bb-count-fraction
4678 Select fraction of the maximal count of repetitions of basic block in program
4679 given basic block needs to have to be considered hot.
4681 @item hot-bb-frequency-fraction
4682 Select fraction of the maximal frequency of executions of basic block in
4683 function given basic block needs to have to be considered hot
4685 @item tracer-dynamic-coverage
4686 @itemx tracer-dynamic-coverage-feedback
4688 This value is used to limit superblock formation once the given percentage of
4689 executed instructions is covered. This limits unnecessary code size
4692 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4693 feedback is available. The real profiles (as opposed to statically estimated
4694 ones) are much less balanced allowing the threshold to be larger value.
4696 @item tracer-max-code-growth
4697 Stop tail duplication once code growth has reached given percentage. This is
4698 rather hokey argument, as most of the duplicates will be eliminated later in
4699 cross jumping, so it may be set to much higher values than is the desired code
4702 @item tracer-min-branch-ratio
4704 Stop reverse growth when the reverse probability of best edge is less than this
4705 threshold (in percent).
4707 @item tracer-min-branch-ratio
4708 @itemx tracer-min-branch-ratio-feedback
4710 Stop forward growth if the best edge do have probability lower than this
4713 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
4714 compilation for profile feedback and one for compilation without. The value
4715 for compilation with profile feedback needs to be more conservative (higher) in
4716 order to make tracer effective.
4718 @item max-cse-path-length
4720 Maximum number of basic blocks on path that cse considers.
4722 @item ggc-min-expand
4724 GCC uses a garbage collector to manage its own memory allocation. This
4725 parameter specifies the minimum percentage by which the garbage
4726 collector's heap should be allowed to expand between collections.
4727 Tuning this may improve compilation speed; it has no effect on code
4730 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
4731 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
4732 the smallest of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If
4733 GCC is not able to calculate RAM on a particular platform, the lower
4734 bound of 30% is used. Setting this parameter and
4735 @option{ggc-min-heapsize} to zero causes a full collection to occur at
4736 every opportunity. This is extremely slow, but can be useful for
4739 @item ggc-min-heapsize
4741 Minimum size of the garbage collector's heap before it begins bothering
4742 to collect garbage. The first collection occurs after the heap expands
4743 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
4744 tuning this may improve compilation speed, and has no effect on code
4747 The default is RAM/8, with a lower bound of 4096 (four megabytes) and an
4748 upper bound of 131072 (128 megabytes). If @code{getrlimit} is
4749 available, the notion of "RAM" is the smallest of actual RAM,
4750 RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If GCC is not able to calculate
4751 RAM on a particular platform, the lower bound is used. Setting this
4752 parameter very large effectively disables garbage collection. Setting
4753 this parameter and @option{ggc-min-expand} to zero causes a full
4754 collection to occur at every opportunity.
4756 @item reorder-blocks-duplicate
4757 @itemx reorder-blocks-duplicate-feedback
4759 Used by basic block reordering pass to decide whether to use unconditional
4760 branch or duplicate the code on its destination. Code is duplicated when its
4761 estimated size is smaller than this value multiplied by the estimated size of
4762 unconditional jump in the hot spots of the program.
4764 The @option{reorder-block-duplicate-feedback} is used only when profile
4765 feedback is available and may be set to higher values than
4766 @option{reorder-block-duplicate} since information about the hot spots is more
4771 @node Preprocessor Options
4772 @section Options Controlling the Preprocessor
4773 @cindex preprocessor options
4774 @cindex options, preprocessor
4776 These options control the C preprocessor, which is run on each C source
4777 file before actual compilation.
4779 If you use the @option{-E} option, nothing is done except preprocessing.
4780 Some of these options make sense only together with @option{-E} because
4781 they cause the preprocessor output to be unsuitable for actual
4786 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4787 and pass @var{option} directly through to the preprocessor. If
4788 @var{option} contains commas, it is split into multiple options at the
4789 commas. However, many options are modified, translated or interpreted
4790 by the compiler driver before being passed to the preprocessor, and
4791 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4792 interface is undocumented and subject to change, so whenever possible
4793 you should avoid using @option{-Wp} and let the driver handle the
4796 @item -Xpreprocessor @var{option}
4797 @opindex preprocessor
4798 Pass @var{option} as an option to the preprocessor. You can use this to
4799 supply system-specific preprocessor options which GCC does not know how to
4802 If you want to pass an option that takes an argument, you must use
4803 @option{-Xpreprocessor} twice, once for the option and once for the argument.
4806 @include cppopts.texi
4808 @node Assembler Options
4809 @section Passing Options to the Assembler
4811 @c prevent bad page break with this line
4812 You can pass options to the assembler.
4815 @item -Wa,@var{option}
4817 Pass @var{option} as an option to the assembler. If @var{option}
4818 contains commas, it is split into multiple options at the commas.
4820 @item -Xassembler @var{option}
4822 Pass @var{option} as an option to the assembler. You can use this to
4823 supply system-specific assembler options which GCC does not know how to
4826 If you want to pass an option that takes an argument, you must use
4827 @option{-Xassembler} twice, once for the option and once for the argument.
4832 @section Options for Linking
4833 @cindex link options
4834 @cindex options, linking
4836 These options come into play when the compiler links object files into
4837 an executable output file. They are meaningless if the compiler is
4838 not doing a link step.
4842 @item @var{object-file-name}
4843 A file name that does not end in a special recognized suffix is
4844 considered to name an object file or library. (Object files are
4845 distinguished from libraries by the linker according to the file
4846 contents.) If linking is done, these object files are used as input
4855 If any of these options is used, then the linker is not run, and
4856 object file names should not be used as arguments. @xref{Overall
4860 @item -l@var{library}
4861 @itemx -l @var{library}
4863 Search the library named @var{library} when linking. (The second
4864 alternative with the library as a separate argument is only for
4865 POSIX compliance and is not recommended.)
4867 It makes a difference where in the command you write this option; the
4868 linker searches and processes libraries and object files in the order they
4869 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4870 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4871 to functions in @samp{z}, those functions may not be loaded.
4873 The linker searches a standard list of directories for the library,
4874 which is actually a file named @file{lib@var{library}.a}. The linker
4875 then uses this file as if it had been specified precisely by name.
4877 The directories searched include several standard system directories
4878 plus any that you specify with @option{-L}.
4880 Normally the files found this way are library files---archive files
4881 whose members are object files. The linker handles an archive file by
4882 scanning through it for members which define symbols that have so far
4883 been referenced but not defined. But if the file that is found is an
4884 ordinary object file, it is linked in the usual fashion. The only
4885 difference between using an @option{-l} option and specifying a file name
4886 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4887 and searches several directories.
4891 You need this special case of the @option{-l} option in order to
4892 link an Objective-C program.
4895 @opindex nostartfiles
4896 Do not use the standard system startup files when linking.
4897 The standard system libraries are used normally, unless @option{-nostdlib}
4898 or @option{-nodefaultlibs} is used.
4900 @item -nodefaultlibs
4901 @opindex nodefaultlibs
4902 Do not use the standard system libraries when linking.
4903 Only the libraries you specify will be passed to the linker.
4904 The standard startup files are used normally, unless @option{-nostartfiles}
4905 is used. The compiler may generate calls to memcmp, memset, and memcpy
4906 for System V (and ISO C) environments or to bcopy and bzero for
4907 BSD environments. These entries are usually resolved by entries in
4908 libc. These entry points should be supplied through some other
4909 mechanism when this option is specified.
4913 Do not use the standard system startup files or libraries when linking.
4914 No startup files and only the libraries you specify will be passed to
4915 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4916 for System V (and ISO C) environments or to bcopy and bzero for
4917 BSD environments. These entries are usually resolved by entries in
4918 libc. These entry points should be supplied through some other
4919 mechanism when this option is specified.
4921 @cindex @option{-lgcc}, use with @option{-nostdlib}
4922 @cindex @option{-nostdlib} and unresolved references
4923 @cindex unresolved references and @option{-nostdlib}
4924 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4925 @cindex @option{-nodefaultlibs} and unresolved references
4926 @cindex unresolved references and @option{-nodefaultlibs}
4927 One of the standard libraries bypassed by @option{-nostdlib} and
4928 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4929 that GCC uses to overcome shortcomings of particular machines, or special
4930 needs for some languages.
4931 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
4932 Collection (GCC) Internals},
4933 for more discussion of @file{libgcc.a}.)
4934 In most cases, you need @file{libgcc.a} even when you want to avoid
4935 other standard libraries. In other words, when you specify @option{-nostdlib}
4936 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4937 This ensures that you have no unresolved references to internal GCC
4938 library subroutines. (For example, @samp{__main}, used to ensure C++
4939 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
4940 GNU Compiler Collection (GCC) Internals}.)
4944 Produce a position independent executable on targets which support it.
4945 For predictable results, you must also specify the same set of options
4946 that were used to generate code (@option{-fpie}, @option{-fPIE},
4947 or model suboptions) when you specify this option.
4951 Remove all symbol table and relocation information from the executable.
4955 On systems that support dynamic linking, this prevents linking with the shared
4956 libraries. On other systems, this option has no effect.
4960 Produce a shared object which can then be linked with other objects to
4961 form an executable. Not all systems support this option. For predictable
4962 results, you must also specify the same set of options that were used to
4963 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4964 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4965 needs to build supplementary stub code for constructors to work. On
4966 multi-libbed systems, @samp{gcc -shared} must select the correct support
4967 libraries to link against. Failing to supply the correct flags may lead
4968 to subtle defects. Supplying them in cases where they are not necessary
4971 @item -shared-libgcc
4972 @itemx -static-libgcc
4973 @opindex shared-libgcc
4974 @opindex static-libgcc
4975 On systems that provide @file{libgcc} as a shared library, these options
4976 force the use of either the shared or static version respectively.
4977 If no shared version of @file{libgcc} was built when the compiler was
4978 configured, these options have no effect.
4980 There are several situations in which an application should use the
4981 shared @file{libgcc} instead of the static version. The most common
4982 of these is when the application wishes to throw and catch exceptions
4983 across different shared libraries. In that case, each of the libraries
4984 as well as the application itself should use the shared @file{libgcc}.
4986 Therefore, the G++ and GCJ drivers automatically add
4987 @option{-shared-libgcc} whenever you build a shared library or a main
4988 executable, because C++ and Java programs typically use exceptions, so
4989 this is the right thing to do.
4991 If, instead, you use the GCC driver to create shared libraries, you may
4992 find that they will not always be linked with the shared @file{libgcc}.
4993 If GCC finds, at its configuration time, that you have a GNU linker that
4994 does not support option @option{--eh-frame-hdr}, it will link the shared
4995 version of @file{libgcc} into shared libraries by default. Otherwise,
4996 it will take advantage of the linker and optimize away the linking with
4997 the shared version of @file{libgcc}, linking with the static version of
4998 libgcc by default. This allows exceptions to propagate through such
4999 shared libraries, without incurring relocation costs at library load
5002 However, if a library or main executable is supposed to throw or catch
5003 exceptions, you must link it using the G++ or GCJ driver, as appropriate
5004 for the languages used in the program, or using the option
5005 @option{-shared-libgcc}, such that it is linked with the shared
5010 Bind references to global symbols when building a shared object. Warn
5011 about any unresolved references (unless overridden by the link editor
5012 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
5015 @item -Xlinker @var{option}
5017 Pass @var{option} as an option to the linker. You can use this to
5018 supply system-specific linker options which GCC does not know how to
5021 If you want to pass an option that takes an argument, you must use
5022 @option{-Xlinker} twice, once for the option and once for the argument.
5023 For example, to pass @option{-assert definitions}, you must write
5024 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
5025 @option{-Xlinker "-assert definitions"}, because this passes the entire
5026 string as a single argument, which is not what the linker expects.
5028 @item -Wl,@var{option}
5030 Pass @var{option} as an option to the linker. If @var{option} contains
5031 commas, it is split into multiple options at the commas.
5033 @item -u @var{symbol}
5035 Pretend the symbol @var{symbol} is undefined, to force linking of
5036 library modules to define it. You can use @option{-u} multiple times with
5037 different symbols to force loading of additional library modules.
5040 @node Directory Options
5041 @section Options for Directory Search
5042 @cindex directory options
5043 @cindex options, directory search
5046 These options specify directories to search for header files, for
5047 libraries and for parts of the compiler:
5052 Add the directory @var{dir} to the head of the list of directories to be
5053 searched for header files. This can be used to override a system header
5054 file, substituting your own version, since these directories are
5055 searched before the system header file directories. However, you should
5056 not use this option to add directories that contain vendor-supplied
5057 system header files (use @option{-isystem} for that). If you use more than
5058 one @option{-I} option, the directories are scanned in left-to-right
5059 order; the standard system directories come after.
5061 If a standard system include directory, or a directory specified with
5062 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5063 option will be ignored. The directory will still be searched but as a
5064 system directory at its normal position in the system include chain.
5065 This is to ensure that GCC's procedure to fix buggy system headers and
5066 the ordering for the include_next directive are not inadvertently changed.
5067 If you really need to change the search order for system directories,
5068 use the @option{-nostdinc} and/or @option{-isystem} options.
5072 Any directories you specify with @option{-I} options before the @option{-I-}
5073 option are searched only for the case of @samp{#include "@var{file}"};
5074 they are not searched for @samp{#include <@var{file}>}.
5076 If additional directories are specified with @option{-I} options after
5077 the @option{-I-}, these directories are searched for all @samp{#include}
5078 directives. (Ordinarily @emph{all} @option{-I} directories are used
5081 In addition, the @option{-I-} option inhibits the use of the current
5082 directory (where the current input file came from) as the first search
5083 directory for @samp{#include "@var{file}"}. There is no way to
5084 override this effect of @option{-I-}. With @option{-I.} you can specify
5085 searching the directory which was current when the compiler was
5086 invoked. That is not exactly the same as what the preprocessor does
5087 by default, but it is often satisfactory.
5089 @option{-I-} does not inhibit the use of the standard system directories
5090 for header files. Thus, @option{-I-} and @option{-nostdinc} are
5095 Add directory @var{dir} to the list of directories to be searched
5098 @item -B@var{prefix}
5100 This option specifies where to find the executables, libraries,
5101 include files, and data files of the compiler itself.
5103 The compiler driver program runs one or more of the subprograms
5104 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5105 @var{prefix} as a prefix for each program it tries to run, both with and
5106 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5108 For each subprogram to be run, the compiler driver first tries the
5109 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5110 was not specified, the driver tries two standard prefixes, which are
5111 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
5112 those results in a file name that is found, the unmodified program
5113 name is searched for using the directories specified in your
5114 @env{PATH} environment variable.
5116 The compiler will check to see if the path provided by the @option{-B}
5117 refers to a directory, and if necessary it will add a directory
5118 separator character at the end of the path.
5120 @option{-B} prefixes that effectively specify directory names also apply
5121 to libraries in the linker, because the compiler translates these
5122 options into @option{-L} options for the linker. They also apply to
5123 includes files in the preprocessor, because the compiler translates these
5124 options into @option{-isystem} options for the preprocessor. In this case,
5125 the compiler appends @samp{include} to the prefix.
5127 The run-time support file @file{libgcc.a} can also be searched for using
5128 the @option{-B} prefix, if needed. If it is not found there, the two
5129 standard prefixes above are tried, and that is all. The file is left
5130 out of the link if it is not found by those means.
5132 Another way to specify a prefix much like the @option{-B} prefix is to use
5133 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5136 As a special kludge, if the path provided by @option{-B} is
5137 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5138 9, then it will be replaced by @file{[dir/]include}. This is to help
5139 with boot-strapping the compiler.
5141 @item -specs=@var{file}
5143 Process @var{file} after the compiler reads in the standard @file{specs}
5144 file, in order to override the defaults that the @file{gcc} driver
5145 program uses when determining what switches to pass to @file{cc1},
5146 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5147 @option{-specs=@var{file}} can be specified on the command line, and they
5148 are processed in order, from left to right.
5154 @section Specifying subprocesses and the switches to pass to them
5157 @command{gcc} is a driver program. It performs its job by invoking a
5158 sequence of other programs to do the work of compiling, assembling and
5159 linking. GCC interprets its command-line parameters and uses these to
5160 deduce which programs it should invoke, and which command-line options
5161 it ought to place on their command lines. This behavior is controlled
5162 by @dfn{spec strings}. In most cases there is one spec string for each
5163 program that GCC can invoke, but a few programs have multiple spec
5164 strings to control their behavior. The spec strings built into GCC can
5165 be overridden by using the @option{-specs=} command-line switch to specify
5168 @dfn{Spec files} are plaintext files that are used to construct spec
5169 strings. They consist of a sequence of directives separated by blank
5170 lines. The type of directive is determined by the first non-whitespace
5171 character on the line and it can be one of the following:
5174 @item %@var{command}
5175 Issues a @var{command} to the spec file processor. The commands that can
5179 @item %include <@var{file}>
5181 Search for @var{file} and insert its text at the current point in the
5184 @item %include_noerr <@var{file}>
5185 @cindex %include_noerr
5186 Just like @samp{%include}, but do not generate an error message if the include
5187 file cannot be found.
5189 @item %rename @var{old_name} @var{new_name}
5191 Rename the spec string @var{old_name} to @var{new_name}.
5195 @item *[@var{spec_name}]:
5196 This tells the compiler to create, override or delete the named spec
5197 string. All lines after this directive up to the next directive or
5198 blank line are considered to be the text for the spec string. If this
5199 results in an empty string then the spec will be deleted. (Or, if the
5200 spec did not exist, then nothing will happened.) Otherwise, if the spec
5201 does not currently exist a new spec will be created. If the spec does
5202 exist then its contents will be overridden by the text of this
5203 directive, unless the first character of that text is the @samp{+}
5204 character, in which case the text will be appended to the spec.
5206 @item [@var{suffix}]:
5207 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
5208 and up to the next directive or blank line are considered to make up the
5209 spec string for the indicated suffix. When the compiler encounters an
5210 input file with the named suffix, it will processes the spec string in
5211 order to work out how to compile that file. For example:
5218 This says that any input file whose name ends in @samp{.ZZ} should be
5219 passed to the program @samp{z-compile}, which should be invoked with the
5220 command-line switch @option{-input} and with the result of performing the
5221 @samp{%i} substitution. (See below.)
5223 As an alternative to providing a spec string, the text that follows a
5224 suffix directive can be one of the following:
5227 @item @@@var{language}
5228 This says that the suffix is an alias for a known @var{language}. This is
5229 similar to using the @option{-x} command-line switch to GCC to specify a
5230 language explicitly. For example:
5237 Says that .ZZ files are, in fact, C++ source files.
5240 This causes an error messages saying:
5243 @var{name} compiler not installed on this system.
5247 GCC already has an extensive list of suffixes built into it.
5248 This directive will add an entry to the end of the list of suffixes, but
5249 since the list is searched from the end backwards, it is effectively
5250 possible to override earlier entries using this technique.
5254 GCC has the following spec strings built into it. Spec files can
5255 override these strings or create their own. Note that individual
5256 targets can also add their own spec strings to this list.
5259 asm Options to pass to the assembler
5260 asm_final Options to pass to the assembler post-processor
5261 cpp Options to pass to the C preprocessor
5262 cc1 Options to pass to the C compiler
5263 cc1plus Options to pass to the C++ compiler
5264 endfile Object files to include at the end of the link
5265 link Options to pass to the linker
5266 lib Libraries to include on the command line to the linker
5267 libgcc Decides which GCC support library to pass to the linker
5268 linker Sets the name of the linker
5269 predefines Defines to be passed to the C preprocessor
5270 signed_char Defines to pass to CPP to say whether @code{char} is signed
5272 startfile Object files to include at the start of the link
5275 Here is a small example of a spec file:
5281 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
5284 This example renames the spec called @samp{lib} to @samp{old_lib} and
5285 then overrides the previous definition of @samp{lib} with a new one.
5286 The new definition adds in some extra command-line options before
5287 including the text of the old definition.
5289 @dfn{Spec strings} are a list of command-line options to be passed to their
5290 corresponding program. In addition, the spec strings can contain
5291 @samp{%}-prefixed sequences to substitute variable text or to
5292 conditionally insert text into the command line. Using these constructs
5293 it is possible to generate quite complex command lines.
5295 Here is a table of all defined @samp{%}-sequences for spec
5296 strings. Note that spaces are not generated automatically around the
5297 results of expanding these sequences. Therefore you can concatenate them
5298 together or combine them with constant text in a single argument.
5302 Substitute one @samp{%} into the program name or argument.
5305 Substitute the name of the input file being processed.
5308 Substitute the basename of the input file being processed.
5309 This is the substring up to (and not including) the last period
5310 and not including the directory.
5313 This is the same as @samp{%b}, but include the file suffix (text after
5317 Marks the argument containing or following the @samp{%d} as a
5318 temporary file name, so that that file will be deleted if GCC exits
5319 successfully. Unlike @samp{%g}, this contributes no text to the
5322 @item %g@var{suffix}
5323 Substitute a file name that has suffix @var{suffix} and is chosen
5324 once per compilation, and mark the argument in the same way as
5325 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
5326 name is now chosen in a way that is hard to predict even when previously
5327 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
5328 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
5329 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
5330 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
5331 was simply substituted with a file name chosen once per compilation,
5332 without regard to any appended suffix (which was therefore treated
5333 just like ordinary text), making such attacks more likely to succeed.
5335 @item %u@var{suffix}
5336 Like @samp{%g}, but generates a new temporary file name even if
5337 @samp{%u@var{suffix}} was already seen.
5339 @item %U@var{suffix}
5340 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
5341 new one if there is no such last file name. In the absence of any
5342 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
5343 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
5344 would involve the generation of two distinct file names, one
5345 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
5346 simply substituted with a file name chosen for the previous @samp{%u},
5347 without regard to any appended suffix.
5349 @item %j@var{suffix}
5350 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
5351 writable, and if save-temps is off; otherwise, substitute the name
5352 of a temporary file, just like @samp{%u}. This temporary file is not
5353 meant for communication between processes, but rather as a junk
5356 @item %|@var{suffix}
5357 @itemx %m@var{suffix}
5358 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
5359 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
5360 all. These are the two most common ways to instruct a program that it
5361 should read from standard input or write to standard output. If you
5362 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
5363 construct: see for example @file{f/lang-specs.h}.
5365 @item %.@var{SUFFIX}
5366 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
5367 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
5368 terminated by the next space or %.
5371 Marks the argument containing or following the @samp{%w} as the
5372 designated output file of this compilation. This puts the argument
5373 into the sequence of arguments that @samp{%o} will substitute later.
5376 Substitutes the names of all the output files, with spaces
5377 automatically placed around them. You should write spaces
5378 around the @samp{%o} as well or the results are undefined.
5379 @samp{%o} is for use in the specs for running the linker.
5380 Input files whose names have no recognized suffix are not compiled
5381 at all, but they are included among the output files, so they will
5385 Substitutes the suffix for object files. Note that this is
5386 handled specially when it immediately follows @samp{%g, %u, or %U},
5387 because of the need for those to form complete file names. The
5388 handling is such that @samp{%O} is treated exactly as if it had already
5389 been substituted, except that @samp{%g, %u, and %U} do not currently
5390 support additional @var{suffix} characters following @samp{%O} as they would
5391 following, for example, @samp{.o}.
5394 Substitutes the standard macro predefinitions for the
5395 current target machine. Use this when running @code{cpp}.
5398 Like @samp{%p}, but puts @samp{__} before and after the name of each
5399 predefined macro, except for macros that start with @samp{__} or with
5400 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
5404 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
5405 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
5406 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
5410 Current argument is the name of a library or startup file of some sort.
5411 Search for that file in a standard list of directories and substitute
5412 the full name found.
5415 Print @var{str} as an error message. @var{str} is terminated by a newline.
5416 Use this when inconsistent options are detected.
5419 Substitute the contents of spec string @var{name} at this point.
5422 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
5424 @item %x@{@var{option}@}
5425 Accumulate an option for @samp{%X}.
5428 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
5432 Output the accumulated assembler options specified by @option{-Wa}.
5435 Output the accumulated preprocessor options specified by @option{-Wp}.
5438 Process the @code{asm} spec. This is used to compute the
5439 switches to be passed to the assembler.
5442 Process the @code{asm_final} spec. This is a spec string for
5443 passing switches to an assembler post-processor, if such a program is
5447 Process the @code{link} spec. This is the spec for computing the
5448 command line passed to the linker. Typically it will make use of the
5449 @samp{%L %G %S %D and %E} sequences.
5452 Dump out a @option{-L} option for each directory that GCC believes might
5453 contain startup files. If the target supports multilibs then the
5454 current multilib directory will be prepended to each of these paths.
5457 Output the multilib directory with directory separators replaced with
5458 @samp{_}. If multilib directories are not set, or the multilib directory is
5459 @file{.} then this option emits nothing.
5462 Process the @code{lib} spec. This is a spec string for deciding which
5463 libraries should be included on the command line to the linker.
5466 Process the @code{libgcc} spec. This is a spec string for deciding
5467 which GCC support library should be included on the command line to the linker.
5470 Process the @code{startfile} spec. This is a spec for deciding which
5471 object files should be the first ones passed to the linker. Typically
5472 this might be a file named @file{crt0.o}.
5475 Process the @code{endfile} spec. This is a spec string that specifies
5476 the last object files that will be passed to the linker.
5479 Process the @code{cpp} spec. This is used to construct the arguments
5480 to be passed to the C preprocessor.
5483 Process the @code{signed_char} spec. This is intended to be used
5484 to tell cpp whether a char is signed. It typically has the definition:
5486 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
5490 Process the @code{cc1} spec. This is used to construct the options to be
5491 passed to the actual C compiler (@samp{cc1}).
5494 Process the @code{cc1plus} spec. This is used to construct the options to be
5495 passed to the actual C++ compiler (@samp{cc1plus}).
5498 Substitute the variable part of a matched option. See below.
5499 Note that each comma in the substituted string is replaced by
5503 Remove all occurrences of @code{-S} from the command line. Note---this
5504 command is position dependent. @samp{%} commands in the spec string
5505 before this one will see @code{-S}, @samp{%} commands in the spec string
5506 after this one will not.
5508 @item %:@var{function}(@var{args})
5509 Call the named function @var{function}, passing it @var{args}.
5510 @var{args} is first processed as a nested spec string, then split
5511 into an argument vector in the usual fashion. The function returns
5512 a string which is processed as if it had appeared literally as part
5513 of the current spec.
5515 The following built-in spec functions are provided:
5518 @item @code{if-exists}
5519 The @code{if-exists} spec function takes one argument, an absolute
5520 pathname to a file. If the file exists, @code{if-exists} returns the
5521 pathname. Here is a small example of its usage:
5525 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
5528 @item @code{if-exists-else}
5529 The @code{if-exists-else} spec function is similar to the @code{if-exists}
5530 spec function, except that it takes two arguments. The first argument is
5531 an absolute pathname to a file. If the file exists, @code{if-exists-else}
5532 returns the pathname. If it does not exist, it returns the second argument.
5533 This way, @code{if-exists-else} can be used to select one file or another,
5534 based on the existence of the first. Here is a small example of its usage:
5538 crt0%O%s %:if-exists(crti%O%s) \
5539 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
5544 Substitutes the @code{-S} switch, if that switch was given to GCC@.
5545 If that switch was not specified, this substitutes nothing. Note that
5546 the leading dash is omitted when specifying this option, and it is
5547 automatically inserted if the substitution is performed. Thus the spec
5548 string @samp{%@{foo@}} would match the command-line option @option{-foo}
5549 and would output the command line option @option{-foo}.
5551 @item %W@{@code{S}@}
5552 Like %@{@code{S}@} but mark last argument supplied within as a file to be
5555 @item %@{@code{S}*@}
5556 Substitutes all the switches specified to GCC whose names start
5557 with @code{-S}, but which also take an argument. This is used for
5558 switches like @option{-o}, @option{-D}, @option{-I}, etc.
5559 GCC considers @option{-o foo} as being
5560 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
5561 text, including the space. Thus two arguments would be generated.
5563 @item %@{@code{S}*&@code{T}*@}
5564 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
5565 (the order of @code{S} and @code{T} in the spec is not significant).
5566 There can be any number of ampersand-separated variables; for each the
5567 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
5569 @item %@{@code{S}:@code{X}@}
5570 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
5572 @item %@{!@code{S}:@code{X}@}
5573 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
5575 @item %@{@code{S}*:@code{X}@}
5576 Substitutes @code{X} if one or more switches whose names start with
5577 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
5578 once, no matter how many such switches appeared. However, if @code{%*}
5579 appears somewhere in @code{X}, then @code{X} will be substituted once
5580 for each matching switch, with the @code{%*} replaced by the part of
5581 that switch that matched the @code{*}.
5583 @item %@{.@code{S}:@code{X}@}
5584 Substitutes @code{X}, if processing a file with suffix @code{S}.
5586 @item %@{!.@code{S}:@code{X}@}
5587 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
5589 @item %@{@code{S}|@code{P}:@code{X}@}
5590 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
5591 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
5592 although they have a stronger binding than the @samp{|}. If @code{%*}
5593 appears in @code{X}, all of the alternatives must be starred, and only
5594 the first matching alternative is substituted.
5596 For example, a spec string like this:
5599 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
5602 will output the following command-line options from the following input
5603 command-line options:
5608 -d fred.c -foo -baz -boggle
5609 -d jim.d -bar -baz -boggle
5612 @item %@{S:X; T:Y; :D@}
5614 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
5615 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
5616 be as many clauses as you need. This may be combined with @code{.},
5617 @code{!}, @code{|}, and @code{*} as needed.
5622 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
5623 construct may contain other nested @samp{%} constructs or spaces, or
5624 even newlines. They are processed as usual, as described above.
5625 Trailing white space in @code{X} is ignored. White space may also
5626 appear anywhere on the left side of the colon in these constructs,
5627 except between @code{.} or @code{*} and the corresponding word.
5629 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
5630 handled specifically in these constructs. If another value of
5631 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
5632 @option{-W} switch is found later in the command line, the earlier
5633 switch value is ignored, except with @{@code{S}*@} where @code{S} is
5634 just one letter, which passes all matching options.
5636 The character @samp{|} at the beginning of the predicate text is used to
5637 indicate that a command should be piped to the following command, but
5638 only if @option{-pipe} is specified.
5640 It is built into GCC which switches take arguments and which do not.
5641 (You might think it would be useful to generalize this to allow each
5642 compiler's spec to say which switches take arguments. But this cannot
5643 be done in a consistent fashion. GCC cannot even decide which input
5644 files have been specified without knowing which switches take arguments,
5645 and it must know which input files to compile in order to tell which
5648 GCC also knows implicitly that arguments starting in @option{-l} are to be
5649 treated as compiler output files, and passed to the linker in their
5650 proper position among the other output files.
5652 @c man begin OPTIONS
5654 @node Target Options
5655 @section Specifying Target Machine and Compiler Version
5656 @cindex target options
5657 @cindex cross compiling
5658 @cindex specifying machine version
5659 @cindex specifying compiler version and target machine
5660 @cindex compiler version, specifying
5661 @cindex target machine, specifying
5663 The usual way to run GCC is to run the executable called @file{gcc}, or
5664 @file{<machine>-gcc} when cross-compiling, or
5665 @file{<machine>-gcc-<version>} to run a version other than the one that
5666 was installed last. Sometimes this is inconvenient, so GCC provides
5667 options that will switch to another cross-compiler or version.
5670 @item -b @var{machine}
5672 The argument @var{machine} specifies the target machine for compilation.
5674 The value to use for @var{machine} is the same as was specified as the
5675 machine type when configuring GCC as a cross-compiler. For
5676 example, if a cross-compiler was configured with @samp{configure
5677 i386v}, meaning to compile for an 80386 running System V, then you
5678 would specify @option{-b i386v} to run that cross compiler.
5680 @item -V @var{version}
5682 The argument @var{version} specifies which version of GCC to run.
5683 This is useful when multiple versions are installed. For example,
5684 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5687 The @option{-V} and @option{-b} options work by running the
5688 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5689 use them if you can just run that directly.
5691 @node Submodel Options
5692 @section Hardware Models and Configurations
5693 @cindex submodel options
5694 @cindex specifying hardware config
5695 @cindex hardware models and configurations, specifying
5696 @cindex machine dependent options
5698 Earlier we discussed the standard option @option{-b} which chooses among
5699 different installed compilers for completely different target
5700 machines, such as VAX vs.@: 68000 vs.@: 80386.
5702 In addition, each of these target machine types can have its own
5703 special options, starting with @samp{-m}, to choose among various
5704 hardware models or configurations---for example, 68010 vs 68020,
5705 floating coprocessor or none. A single installed version of the
5706 compiler can compile for any model or configuration, according to the
5709 Some configurations of the compiler also support additional special
5710 options, usually for compatibility with other compilers on the same
5713 These options are defined by the macro @code{TARGET_SWITCHES} in the
5714 machine description. The default for the options is also defined by
5715 that macro, which enables you to change the defaults.
5727 * RS/6000 and PowerPC Options::
5731 * i386 and x86-64 Options::
5733 * Intel 960 Options::
5734 * DEC Alpha Options::
5735 * DEC Alpha/VMS Options::
5738 * System V Options::
5739 * TMS320C3x/C4x Options::
5747 * S/390 and zSeries Options::
5751 * Xstormy16 Options::
5756 @node M680x0 Options
5757 @subsection M680x0 Options
5758 @cindex M680x0 options
5760 These are the @samp{-m} options defined for the 68000 series. The default
5761 values for these options depends on which style of 68000 was selected when
5762 the compiler was configured; the defaults for the most common choices are
5770 Generate output for a 68000. This is the default
5771 when the compiler is configured for 68000-based systems.
5773 Use this option for microcontrollers with a 68000 or EC000 core,
5774 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5780 Generate output for a 68020. This is the default
5781 when the compiler is configured for 68020-based systems.
5785 Generate output containing 68881 instructions for floating point.
5786 This is the default for most 68020 systems unless @option{--nfp} was
5787 specified when the compiler was configured.
5791 Generate output for a 68030. This is the default when the compiler is
5792 configured for 68030-based systems.
5796 Generate output for a 68040. This is the default when the compiler is
5797 configured for 68040-based systems.
5799 This option inhibits the use of 68881/68882 instructions that have to be
5800 emulated by software on the 68040. Use this option if your 68040 does not
5801 have code to emulate those instructions.
5805 Generate output for a 68060. This is the default when the compiler is
5806 configured for 68060-based systems.
5808 This option inhibits the use of 68020 and 68881/68882 instructions that
5809 have to be emulated by software on the 68060. Use this option if your 68060
5810 does not have code to emulate those instructions.
5814 Generate output for a CPU32. This is the default
5815 when the compiler is configured for CPU32-based systems.
5817 Use this option for microcontrollers with a
5818 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5819 68336, 68340, 68341, 68349 and 68360.
5823 Generate output for a 520X ``coldfire'' family cpu. This is the default
5824 when the compiler is configured for 520X-based systems.
5826 Use this option for microcontroller with a 5200 core, including
5827 the MCF5202, MCF5203, MCF5204 and MCF5202.
5832 Generate output for a 68040, without using any of the new instructions.
5833 This results in code which can run relatively efficiently on either a
5834 68020/68881 or a 68030 or a 68040. The generated code does use the
5835 68881 instructions that are emulated on the 68040.
5839 Generate output for a 68060, without using any of the new instructions.
5840 This results in code which can run relatively efficiently on either a
5841 68020/68881 or a 68030 or a 68040. The generated code does use the
5842 68881 instructions that are emulated on the 68060.
5845 @opindex msoft-float
5846 Generate output containing library calls for floating point.
5847 @strong{Warning:} the requisite libraries are not available for all m68k
5848 targets. Normally the facilities of the machine's usual C compiler are
5849 used, but this can't be done directly in cross-compilation. You must
5850 make your own arrangements to provide suitable library functions for
5851 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5852 @samp{m68k-*-coff} do provide software floating point support.
5856 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5859 @opindex mnobitfield
5860 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5861 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5865 Do use the bit-field instructions. The @option{-m68020} option implies
5866 @option{-mbitfield}. This is the default if you use a configuration
5867 designed for a 68020.
5871 Use a different function-calling convention, in which functions
5872 that take a fixed number of arguments return with the @code{rtd}
5873 instruction, which pops their arguments while returning. This
5874 saves one instruction in the caller since there is no need to pop
5875 the arguments there.
5877 This calling convention is incompatible with the one normally
5878 used on Unix, so you cannot use it if you need to call libraries
5879 compiled with the Unix compiler.
5881 Also, you must provide function prototypes for all functions that
5882 take variable numbers of arguments (including @code{printf});
5883 otherwise incorrect code will be generated for calls to those
5886 In addition, seriously incorrect code will result if you call a
5887 function with too many arguments. (Normally, extra arguments are
5888 harmlessly ignored.)
5890 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5891 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5894 @itemx -mno-align-int
5896 @opindex mno-align-int
5897 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5898 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5899 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5900 Aligning variables on 32-bit boundaries produces code that runs somewhat
5901 faster on processors with 32-bit busses at the expense of more memory.
5903 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5904 align structures containing the above types differently than
5905 most published application binary interface specifications for the m68k.
5909 Use the pc-relative addressing mode of the 68000 directly, instead of
5910 using a global offset table. At present, this option implies @option{-fpic},
5911 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5912 not presently supported with @option{-mpcrel}, though this could be supported for
5913 68020 and higher processors.
5915 @item -mno-strict-align
5916 @itemx -mstrict-align
5917 @opindex mno-strict-align
5918 @opindex mstrict-align
5919 Do not (do) assume that unaligned memory references will be handled by
5924 @node M68hc1x Options
5925 @subsection M68hc1x Options
5926 @cindex M68hc1x options
5928 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5929 microcontrollers. The default values for these options depends on
5930 which style of microcontroller was selected when the compiler was configured;
5931 the defaults for the most common choices are given below.
5938 Generate output for a 68HC11. This is the default
5939 when the compiler is configured for 68HC11-based systems.
5945 Generate output for a 68HC12. This is the default
5946 when the compiler is configured for 68HC12-based systems.
5952 Generate output for a 68HCS12.
5955 @opindex mauto-incdec
5956 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5963 Enable the use of 68HC12 min and max instructions.
5966 @itemx -mno-long-calls
5967 @opindex mlong-calls
5968 @opindex mno-long-calls
5969 Treat all calls as being far away (near). If calls are assumed to be
5970 far away, the compiler will use the @code{call} instruction to
5971 call a function and the @code{rtc} instruction for returning.
5975 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5977 @item -msoft-reg-count=@var{count}
5978 @opindex msoft-reg-count
5979 Specify the number of pseudo-soft registers which are used for the
5980 code generation. The maximum number is 32. Using more pseudo-soft
5981 register may or may not result in better code depending on the program.
5982 The default is 4 for 68HC11 and 2 for 68HC12.
5987 @subsection VAX Options
5990 These @samp{-m} options are defined for the VAX:
5995 Do not output certain jump instructions (@code{aobleq} and so on)
5996 that the Unix assembler for the VAX cannot handle across long
6001 Do output those jump instructions, on the assumption that you
6002 will assemble with the GNU assembler.
6006 Output code for g-format floating point numbers instead of d-format.
6010 @subsection SPARC Options
6011 @cindex SPARC options
6013 These @samp{-m} switches are supported on the SPARC:
6018 @opindex mno-app-regs
6020 Specify @option{-mapp-regs} to generate output using the global registers
6021 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
6024 To be fully SVR4 ABI compliant at the cost of some performance loss,
6025 specify @option{-mno-app-regs}. You should compile libraries and system
6026 software with this option.
6031 @opindex mhard-float
6032 Generate output containing floating point instructions. This is the
6038 @opindex msoft-float
6039 Generate output containing library calls for floating point.
6040 @strong{Warning:} the requisite libraries are not available for all SPARC
6041 targets. Normally the facilities of the machine's usual C compiler are
6042 used, but this cannot be done directly in cross-compilation. You must make
6043 your own arrangements to provide suitable library functions for
6044 cross-compilation. The embedded targets @samp{sparc-*-aout} and
6045 @samp{sparclite-*-*} do provide software floating point support.
6047 @option{-msoft-float} changes the calling convention in the output file;
6048 therefore, it is only useful if you compile @emph{all} of a program with
6049 this option. In particular, you need to compile @file{libgcc.a}, the
6050 library that comes with GCC, with @option{-msoft-float} in order for
6053 @item -mhard-quad-float
6054 @opindex mhard-quad-float
6055 Generate output containing quad-word (long double) floating point
6058 @item -msoft-quad-float
6059 @opindex msoft-quad-float
6060 Generate output containing library calls for quad-word (long double)
6061 floating point instructions. The functions called are those specified
6062 in the SPARC ABI@. This is the default.
6064 As of this writing, there are no sparc implementations that have hardware
6065 support for the quad-word floating point instructions. They all invoke
6066 a trap handler for one of these instructions, and then the trap handler
6067 emulates the effect of the instruction. Because of the trap handler overhead,
6068 this is much slower than calling the ABI library routines. Thus the
6069 @option{-msoft-quad-float} option is the default.
6075 With @option{-mflat}, the compiler does not generate save/restore instructions
6076 and will use a ``flat'' or single register window calling convention.
6077 This model uses %i7 as the frame pointer and is compatible with the normal
6078 register window model. Code from either may be intermixed.
6079 The local registers and the input registers (0--5) are still treated as
6080 ``call saved'' registers and will be saved on the stack as necessary.
6082 With @option{-mno-flat} (the default), the compiler emits save/restore
6083 instructions (except for leaf functions) and is the normal mode of operation.
6085 @item -mno-unaligned-doubles
6086 @itemx -munaligned-doubles
6087 @opindex mno-unaligned-doubles
6088 @opindex munaligned-doubles
6089 Assume that doubles have 8 byte alignment. This is the default.
6091 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
6092 alignment only if they are contained in another type, or if they have an
6093 absolute address. Otherwise, it assumes they have 4 byte alignment.
6094 Specifying this option avoids some rare compatibility problems with code
6095 generated by other compilers. It is not the default because it results
6096 in a performance loss, especially for floating point code.
6098 @item -mno-faster-structs
6099 @itemx -mfaster-structs
6100 @opindex mno-faster-structs
6101 @opindex mfaster-structs
6102 With @option{-mfaster-structs}, the compiler assumes that structures
6103 should have 8 byte alignment. This enables the use of pairs of
6104 @code{ldd} and @code{std} instructions for copies in structure
6105 assignment, in place of twice as many @code{ld} and @code{st} pairs.
6106 However, the use of this changed alignment directly violates the SPARC
6107 ABI@. Thus, it's intended only for use on targets where the developer
6108 acknowledges that their resulting code will not be directly in line with
6109 the rules of the ABI@.
6112 @opindex mimpure-text
6113 @option{-mimpure-text}, used in addition to @option{-shared}, tells
6114 the compiler to not pass @option{-z text} to the linker when linking a
6115 shared object. Using this option, you can link position-dependent
6116 code into a shared object.
6118 @option{-mimpure-text} suppresses the ``relocations remain against
6119 allocatable but non-writable sections'' linker error message.
6120 However, the necessary relocations will trigger copy-on-write, and the
6121 shared object is not actually shared across processes. Instead of
6122 using @option{-mimpure-text}, you should compile all source code with
6123 @option{-fpic} or @option{-fPIC}.
6125 This option is only available on SunOS and Solaris.
6131 These two options select variations on the SPARC architecture.
6133 By default (unless specifically configured for the Fujitsu SPARClite),
6134 GCC generates code for the v7 variant of the SPARC architecture.
6136 @option{-mv8} will give you SPARC v8 code. The only difference from v7
6137 code is that the compiler emits the integer multiply and integer
6138 divide instructions which exist in SPARC v8 but not in SPARC v7.
6140 @option{-msparclite} will give you SPARClite code. This adds the integer
6141 multiply, integer divide step and scan (@code{ffs}) instructions which
6142 exist in SPARClite but not in SPARC v7.
6144 These options are deprecated and will be deleted in a future GCC release.
6145 They have been replaced with @option{-mcpu=xxx}.
6150 @opindex msupersparc
6151 These two options select the processor for which the code is optimized.
6153 With @option{-mcypress} (the default), the compiler optimizes code for the
6154 Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series.
6155 This is also appropriate for the older SPARCStation 1, 2, IPX etc.
6157 With @option{-msupersparc} the compiler optimizes code for the SuperSPARC cpu, as
6158 used in the SPARCStation 10, 1000 and 2000 series. This flag also enables use
6159 of the full SPARC v8 instruction set.
6161 These options are deprecated and will be deleted in a future GCC release.
6162 They have been replaced with @option{-mcpu=xxx}.
6164 @item -mcpu=@var{cpu_type}
6166 Set the instruction set, register set, and instruction scheduling parameters
6167 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
6168 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
6169 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
6170 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
6173 Default instruction scheduling parameters are used for values that select
6174 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
6175 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
6177 Here is a list of each supported architecture and their supported
6182 v8: supersparc, hypersparc
6183 sparclite: f930, f934, sparclite86x
6185 v9: ultrasparc, ultrasparc3
6188 @item -mtune=@var{cpu_type}
6190 Set the instruction scheduling parameters for machine type
6191 @var{cpu_type}, but do not set the instruction set or register set that the
6192 option @option{-mcpu=@var{cpu_type}} would.
6194 The same values for @option{-mcpu=@var{cpu_type}} can be used for
6195 @option{-mtune=@var{cpu_type}}, but the only useful values are those
6196 that select a particular cpu implementation. Those are @samp{cypress},
6197 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
6198 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
6203 These @samp{-m} switches are supported in addition to the above
6204 on the SPARCLET processor.
6207 @item -mlittle-endian
6208 @opindex mlittle-endian
6209 Generate code for a processor running in little-endian mode.
6213 Treat register @code{%g0} as a normal register.
6214 GCC will continue to clobber it as necessary but will not assume
6215 it always reads as 0.
6217 @item -mbroken-saverestore
6218 @opindex mbroken-saverestore
6219 Generate code that does not use non-trivial forms of the @code{save} and
6220 @code{restore} instructions. Early versions of the SPARCLET processor do
6221 not correctly handle @code{save} and @code{restore} instructions used with
6222 arguments. They correctly handle them used without arguments. A @code{save}
6223 instruction used without arguments increments the current window pointer
6224 but does not allocate a new stack frame. It is assumed that the window
6225 overflow trap handler will properly handle this case as will interrupt
6229 These @samp{-m} switches are supported in addition to the above
6230 on SPARC V9 processors in 64-bit environments.
6233 @item -mlittle-endian
6234 @opindex mlittle-endian
6235 Generate code for a processor running in little-endian mode. It is only
6236 available for a few configurations and most notably not on Solaris.
6242 Generate code for a 32-bit or 64-bit environment.
6243 The 32-bit environment sets int, long and pointer to 32 bits.
6244 The 64-bit environment sets int to 32 bits and long and pointer
6247 @item -mcmodel=medlow
6248 @opindex mcmodel=medlow
6249 Generate code for the Medium/Low code model: the program must be linked
6250 in the low 32 bits of the address space. Pointers are 64 bits.
6251 Programs can be statically or dynamically linked.
6253 @item -mcmodel=medmid
6254 @opindex mcmodel=medmid
6255 Generate code for the Medium/Middle code model: the program must be linked
6256 in the low 44 bits of the address space, the text segment must be less than
6257 2G bytes, and data segment must be within 2G of the text segment.
6258 Pointers are 64 bits.
6260 @item -mcmodel=medany
6261 @opindex mcmodel=medany
6262 Generate code for the Medium/Anywhere code model: the program may be linked
6263 anywhere in the address space, the text segment must be less than
6264 2G bytes, and data segment must be within 2G of the text segment.
6265 Pointers are 64 bits.
6267 @item -mcmodel=embmedany
6268 @opindex mcmodel=embmedany
6269 Generate code for the Medium/Anywhere code model for embedded systems:
6270 assume a 32-bit text and a 32-bit data segment, both starting anywhere
6271 (determined at link time). Register %g4 points to the base of the
6272 data segment. Pointers are still 64 bits.
6273 Programs are statically linked, PIC is not supported.
6276 @itemx -mno-stack-bias
6277 @opindex mstack-bias
6278 @opindex mno-stack-bias
6279 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
6280 frame pointer if present, are offset by @minus{}2047 which must be added back
6281 when making stack frame references.
6282 Otherwise, assume no such offset is present.
6286 @subsection ARM Options
6289 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6294 @opindex mapcs-frame
6295 Generate a stack frame that is compliant with the ARM Procedure Call
6296 Standard for all functions, even if this is not strictly necessary for
6297 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6298 with this option will cause the stack frames not to be generated for
6299 leaf functions. The default is @option{-mno-apcs-frame}.
6303 This is a synonym for @option{-mapcs-frame}.
6307 Generate code for a processor running with a 26-bit program counter,
6308 and conforming to the function calling standards for the APCS 26-bit
6309 option. This option replaces the @option{-m2} and @option{-m3} options
6310 of previous releases of the compiler.
6314 Generate code for a processor running with a 32-bit program counter,
6315 and conforming to the function calling standards for the APCS 32-bit
6316 option. This option replaces the @option{-m6} option of previous releases
6320 @c not currently implemented
6321 @item -mapcs-stack-check
6322 @opindex mapcs-stack-check
6323 Generate code to check the amount of stack space available upon entry to
6324 every function (that actually uses some stack space). If there is
6325 insufficient space available then either the function
6326 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6327 called, depending upon the amount of stack space required. The run time
6328 system is required to provide these functions. The default is
6329 @option{-mno-apcs-stack-check}, since this produces smaller code.
6331 @c not currently implemented
6333 @opindex mapcs-float
6334 Pass floating point arguments using the float point registers. This is
6335 one of the variants of the APCS@. This option is recommended if the
6336 target hardware has a floating point unit or if a lot of floating point
6337 arithmetic is going to be performed by the code. The default is
6338 @option{-mno-apcs-float}, since integer only code is slightly increased in
6339 size if @option{-mapcs-float} is used.
6341 @c not currently implemented
6342 @item -mapcs-reentrant
6343 @opindex mapcs-reentrant
6344 Generate reentrant, position independent code. The default is
6345 @option{-mno-apcs-reentrant}.
6348 @item -mthumb-interwork
6349 @opindex mthumb-interwork
6350 Generate code which supports calling between the ARM and Thumb
6351 instruction sets. Without this option the two instruction sets cannot
6352 be reliably used inside one program. The default is
6353 @option{-mno-thumb-interwork}, since slightly larger code is generated
6354 when @option{-mthumb-interwork} is specified.
6356 @item -mno-sched-prolog
6357 @opindex mno-sched-prolog
6358 Prevent the reordering of instructions in the function prolog, or the
6359 merging of those instruction with the instructions in the function's
6360 body. This means that all functions will start with a recognizable set
6361 of instructions (or in fact one of a choice from a small set of
6362 different function prologues), and this information can be used to
6363 locate the start if functions inside an executable piece of code. The
6364 default is @option{-msched-prolog}.
6367 @opindex mhard-float
6368 Generate output containing floating point instructions. This is the
6372 @opindex msoft-float
6373 Generate output containing library calls for floating point.
6374 @strong{Warning:} the requisite libraries are not available for all ARM
6375 targets. Normally the facilities of the machine's usual C compiler are
6376 used, but this cannot be done directly in cross-compilation. You must make
6377 your own arrangements to provide suitable library functions for
6380 @option{-msoft-float} changes the calling convention in the output file;
6381 therefore, it is only useful if you compile @emph{all} of a program with
6382 this option. In particular, you need to compile @file{libgcc.a}, the
6383 library that comes with GCC, with @option{-msoft-float} in order for
6386 @item -mlittle-endian
6387 @opindex mlittle-endian
6388 Generate code for a processor running in little-endian mode. This is
6389 the default for all standard configurations.
6392 @opindex mbig-endian
6393 Generate code for a processor running in big-endian mode; the default is
6394 to compile code for a little-endian processor.
6396 @item -mwords-little-endian
6397 @opindex mwords-little-endian
6398 This option only applies when generating code for big-endian processors.
6399 Generate code for a little-endian word order but a big-endian byte
6400 order. That is, a byte order of the form @samp{32107654}. Note: this
6401 option should only be used if you require compatibility with code for
6402 big-endian ARM processors generated by versions of the compiler prior to
6405 @item -malignment-traps
6406 @opindex malignment-traps
6407 Generate code that will not trap if the MMU has alignment traps enabled.
6408 On ARM architectures prior to ARMv4, there were no instructions to
6409 access half-word objects stored in memory. However, when reading from
6410 memory a feature of the ARM architecture allows a word load to be used,
6411 even if the address is unaligned, and the processor core will rotate the
6412 data as it is being loaded. This option tells the compiler that such
6413 misaligned accesses will cause a MMU trap and that it should instead
6414 synthesize the access as a series of byte accesses. The compiler can
6415 still use word accesses to load half-word data if it knows that the
6416 address is aligned to a word boundary.
6418 This option is ignored when compiling for ARM architecture 4 or later,
6419 since these processors have instructions to directly access half-word
6422 @item -mno-alignment-traps
6423 @opindex mno-alignment-traps
6424 Generate code that assumes that the MMU will not trap unaligned
6425 accesses. This produces better code when the target instruction set
6426 does not have half-word memory operations (i.e.@: implementations prior to
6429 Note that you cannot use this option to access unaligned word objects,
6430 since the processor will only fetch one 32-bit aligned object from
6433 The default setting for most targets is @option{-mno-alignment-traps}, since
6434 this produces better code when there are no half-word memory
6435 instructions available.
6437 @item -mshort-load-bytes
6438 @itemx -mno-short-load-words
6439 @opindex mshort-load-bytes
6440 @opindex mno-short-load-words
6441 These are deprecated aliases for @option{-malignment-traps}.
6443 @item -mno-short-load-bytes
6444 @itemx -mshort-load-words
6445 @opindex mno-short-load-bytes
6446 @opindex mshort-load-words
6447 This are deprecated aliases for @option{-mno-alignment-traps}.
6449 @item -mcpu=@var{name}
6451 This specifies the name of the target ARM processor. GCC uses this name
6452 to determine what kind of instructions it can emit when generating
6453 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6454 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6455 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6456 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6457 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6458 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
6459 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6460 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6461 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
6462 @samp{arm1020t}, @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
6464 @itemx -mtune=@var{name}
6466 This option is very similar to the @option{-mcpu=} option, except that
6467 instead of specifying the actual target processor type, and hence
6468 restricting which instructions can be used, it specifies that GCC should
6469 tune the performance of the code as if the target were of the type
6470 specified in this option, but still choosing the instructions that it
6471 will generate based on the cpu specified by a @option{-mcpu=} option.
6472 For some ARM implementations better performance can be obtained by using
6475 @item -march=@var{name}
6477 This specifies the name of the target ARM architecture. GCC uses this
6478 name to determine what kind of instructions it can emit when generating
6479 assembly code. This option can be used in conjunction with or instead
6480 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6481 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6482 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{iwmmxt}, @samp{ep9312}.
6484 @item -mfpe=@var{number}
6485 @itemx -mfp=@var{number}
6488 This specifies the version of the floating point emulation available on
6489 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6490 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6492 @item -mstructure-size-boundary=@var{n}
6493 @opindex mstructure-size-boundary
6494 The size of all structures and unions will be rounded up to a multiple
6495 of the number of bits set by this option. Permissible values are 8 and
6496 32. The default value varies for different toolchains. For the COFF
6497 targeted toolchain the default value is 8. Specifying the larger number
6498 can produce faster, more efficient code, but can also increase the size
6499 of the program. The two values are potentially incompatible. Code
6500 compiled with one value cannot necessarily expect to work with code or
6501 libraries compiled with the other value, if they exchange information
6502 using structures or unions.
6504 @item -mabort-on-noreturn
6505 @opindex mabort-on-noreturn
6506 Generate a call to the function @code{abort} at the end of a
6507 @code{noreturn} function. It will be executed if the function tries to
6511 @itemx -mno-long-calls
6512 @opindex mlong-calls
6513 @opindex mno-long-calls
6514 Tells the compiler to perform function calls by first loading the
6515 address of the function into a register and then performing a subroutine
6516 call on this register. This switch is needed if the target function
6517 will lie outside of the 64 megabyte addressing range of the offset based
6518 version of subroutine call instruction.
6520 Even if this switch is enabled, not all function calls will be turned
6521 into long calls. The heuristic is that static functions, functions
6522 which have the @samp{short-call} attribute, functions that are inside
6523 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6524 definitions have already been compiled within the current compilation
6525 unit, will not be turned into long calls. The exception to this rule is
6526 that weak function definitions, functions with the @samp{long-call}
6527 attribute or the @samp{section} attribute, and functions that are within
6528 the scope of a @samp{#pragma long_calls} directive, will always be
6529 turned into long calls.
6531 This feature is not enabled by default. Specifying
6532 @option{-mno-long-calls} will restore the default behavior, as will
6533 placing the function calls within the scope of a @samp{#pragma
6534 long_calls_off} directive. Note these switches have no effect on how
6535 the compiler generates code to handle function calls via function
6538 @item -mnop-fun-dllimport
6539 @opindex mnop-fun-dllimport
6540 Disable support for the @code{dllimport} attribute.
6542 @item -msingle-pic-base
6543 @opindex msingle-pic-base
6544 Treat the register used for PIC addressing as read-only, rather than
6545 loading it in the prologue for each function. The run-time system is
6546 responsible for initializing this register with an appropriate value
6547 before execution begins.
6549 @item -mpic-register=@var{reg}
6550 @opindex mpic-register
6551 Specify the register to be used for PIC addressing. The default is R10
6552 unless stack-checking is enabled, when R9 is used.
6554 @item -mcirrus-fix-invalid-insns
6555 @opindex mcirrus-fix-invalid-insns
6556 @opindex mno-cirrus-fix-invalid-insns
6557 Insert NOPs into the instruction stream to in order to work around
6558 problems with invalid Maverick instruction combinations. This option
6559 is only valid if the @option{-mcpu=ep9312} option has been used to
6560 enable generation of instructions for the Cirrus Maverick floating
6561 point co-processor. This option is not enabled by default, since the
6562 problem is only present in older Maverick implementations. The default
6563 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6566 @item -mpoke-function-name
6567 @opindex mpoke-function-name
6568 Write the name of each function into the text section, directly
6569 preceding the function prologue. The generated code is similar to this:
6573 .ascii "arm_poke_function_name", 0
6576 .word 0xff000000 + (t1 - t0)
6577 arm_poke_function_name
6579 stmfd sp!, @{fp, ip, lr, pc@}
6583 When performing a stack backtrace, code can inspect the value of
6584 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6585 location @code{pc - 12} and the top 8 bits are set, then we know that
6586 there is a function name embedded immediately preceding this location
6587 and has length @code{((pc[-3]) & 0xff000000)}.
6591 Generate code for the 16-bit Thumb instruction set. The default is to
6592 use the 32-bit ARM instruction set.
6595 @opindex mtpcs-frame
6596 Generate a stack frame that is compliant with the Thumb Procedure Call
6597 Standard for all non-leaf functions. (A leaf function is one that does
6598 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6600 @item -mtpcs-leaf-frame
6601 @opindex mtpcs-leaf-frame
6602 Generate a stack frame that is compliant with the Thumb Procedure Call
6603 Standard for all leaf functions. (A leaf function is one that does
6604 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6606 @item -mcallee-super-interworking
6607 @opindex mcallee-super-interworking
6608 Gives all externally visible functions in the file being compiled an ARM
6609 instruction set header which switches to Thumb mode before executing the
6610 rest of the function. This allows these functions to be called from
6611 non-interworking code.
6613 @item -mcaller-super-interworking
6614 @opindex mcaller-super-interworking
6615 Allows calls via function pointers (including virtual functions) to
6616 execute correctly regardless of whether the target code has been
6617 compiled for interworking or not. There is a small overhead in the cost
6618 of executing a function pointer if this option is enabled.
6622 @node MN10200 Options
6623 @subsection MN10200 Options
6624 @cindex MN10200 options
6626 These @option{-m} options are defined for Matsushita MN10200 architectures:
6631 Indicate to the linker that it should perform a relaxation optimization pass
6632 to shorten branches, calls and absolute memory addresses. This option only
6633 has an effect when used on the command line for the final link step.
6635 This option makes symbolic debugging impossible.
6638 @node MN10300 Options
6639 @subsection MN10300 Options
6640 @cindex MN10300 options
6642 These @option{-m} options are defined for Matsushita MN10300 architectures:
6647 Generate code to avoid bugs in the multiply instructions for the MN10300
6648 processors. This is the default.
6651 @opindex mno-mult-bug
6652 Do not generate code to avoid bugs in the multiply instructions for the
6657 Generate code which uses features specific to the AM33 processor.
6661 Do not generate code which uses features specific to the AM33 processor. This
6666 Do not link in the C run-time initialization object file.
6670 Indicate to the linker that it should perform a relaxation optimization pass
6671 to shorten branches, calls and absolute memory addresses. This option only
6672 has an effect when used on the command line for the final link step.
6674 This option makes symbolic debugging impossible.
6678 @node M32R/D Options
6679 @subsection M32R/D Options
6680 @cindex M32R/D options
6682 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6687 Generate code for the M32R/X@.
6691 Generate code for the M32R@. This is the default.
6693 @item -mcode-model=small
6694 @opindex mcode-model=small
6695 Assume all objects live in the lower 16MB of memory (so that their addresses
6696 can be loaded with the @code{ld24} instruction), and assume all subroutines
6697 are reachable with the @code{bl} instruction.
6698 This is the default.
6700 The addressability of a particular object can be set with the
6701 @code{model} attribute.
6703 @item -mcode-model=medium
6704 @opindex mcode-model=medium
6705 Assume objects may be anywhere in the 32-bit address space (the compiler
6706 will generate @code{seth/add3} instructions to load their addresses), and
6707 assume all subroutines are reachable with the @code{bl} instruction.
6709 @item -mcode-model=large
6710 @opindex mcode-model=large
6711 Assume objects may be anywhere in the 32-bit address space (the compiler
6712 will generate @code{seth/add3} instructions to load their addresses), and
6713 assume subroutines may not be reachable with the @code{bl} instruction
6714 (the compiler will generate the much slower @code{seth/add3/jl}
6715 instruction sequence).
6718 @opindex msdata=none
6719 Disable use of the small data area. Variables will be put into
6720 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6721 @code{section} attribute has been specified).
6722 This is the default.
6724 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6725 Objects may be explicitly put in the small data area with the
6726 @code{section} attribute using one of these sections.
6729 @opindex msdata=sdata
6730 Put small global and static data in the small data area, but do not
6731 generate special code to reference them.
6735 Put small global and static data in the small data area, and generate
6736 special instructions to reference them.
6740 @cindex smaller data references
6741 Put global and static objects less than or equal to @var{num} bytes
6742 into the small data or bss sections instead of the normal data or bss
6743 sections. The default value of @var{num} is 8.
6744 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6745 for this option to have any effect.
6747 All modules should be compiled with the same @option{-G @var{num}} value.
6748 Compiling with different values of @var{num} may or may not work; if it
6749 doesn't the linker will give an error message---incorrect code will not be
6755 @subsection M88K Options
6756 @cindex M88k options
6758 These @samp{-m} options are defined for Motorola 88k architectures:
6763 Generate code that works well on both the m88100 and the
6768 Generate code that works best for the m88100, but that also
6773 Generate code that works best for the m88110, and may not run
6778 Obsolete option to be removed from the next revision.
6781 @item -midentify-revision
6782 @opindex midentify-revision
6783 @cindex identifying source, compiler (88k)
6784 Include an @code{ident} directive in the assembler output recording the
6785 source file name, compiler name and version, timestamp, and compilation
6788 @item -mno-underscores
6789 @opindex mno-underscores
6790 @cindex underscores, avoiding (88k)
6791 In assembler output, emit symbol names without adding an underscore
6792 character at the beginning of each name. The default is to use an
6793 underscore as prefix on each name.
6795 @item -mocs-debug-info
6796 @itemx -mno-ocs-debug-info
6797 @opindex mocs-debug-info
6798 @opindex mno-ocs-debug-info
6800 @cindex debugging, 88k OCS
6801 Include (or omit) additional debugging information (about registers used
6802 in each stack frame) as specified in the 88open Object Compatibility
6803 Standard, ``OCS''@. This extra information allows debugging of code that
6804 has had the frame pointer eliminated. The default for SVr4 and Delta 88
6805 SVr3.2 is to include this information; other 88k configurations omit this
6806 information by default.
6808 @item -mocs-frame-position
6809 @opindex mocs-frame-position
6810 @cindex register positions in frame (88k)
6811 When emitting COFF debugging information for automatic variables and
6812 parameters stored on the stack, use the offset from the canonical frame
6813 address, which is the stack pointer (register 31) on entry to the
6814 function. The SVr4 and Delta88 SVr3.2, and BCS configurations use
6815 @option{-mocs-frame-position}; other 88k configurations have the default
6816 @option{-mno-ocs-frame-position}.
6818 @item -mno-ocs-frame-position
6819 @opindex mno-ocs-frame-position
6820 @cindex register positions in frame (88k)
6821 When emitting COFF debugging information for automatic variables and
6822 parameters stored on the stack, use the offset from the frame pointer
6823 register (register 30). When this option is in effect, the frame
6824 pointer is not eliminated when debugging information is selected by the
6827 @item -moptimize-arg-area
6828 @opindex moptimize-arg-area
6829 @cindex arguments in frame (88k)
6830 Save space by reorganizing the stack frame. This option generates code
6831 that does not agree with the 88open specifications, but uses less
6834 @itemx -mno-optimize-arg-area
6835 @opindex mno-optimize-arg-area
6836 Do not reorganize the stack frame to save space. This is the default.
6837 The generated conforms to the specification, but uses more memory.
6839 @item -mshort-data-@var{num}
6840 @opindex mshort-data
6841 @cindex smaller data references (88k)
6842 @cindex r0-relative references (88k)
6843 Generate smaller data references by making them relative to @code{r0},
6844 which allows loading a value using a single instruction (rather than the
6845 usual two). You control which data references are affected by
6846 specifying @var{num} with this option. For example, if you specify
6847 @option{-mshort-data-512}, then the data references affected are those
6848 involving displacements of less than 512 bytes.
6849 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6852 @item -mserialize-volatile
6853 @opindex mserialize-volatile
6854 @itemx -mno-serialize-volatile
6855 @opindex mno-serialize-volatile
6856 @cindex sequential consistency on 88k
6857 Do, or don't, generate code to guarantee sequential consistency
6858 of volatile memory references. By default, consistency is
6861 The order of memory references made by the MC88110 processor does
6862 not always match the order of the instructions requesting those
6863 references. In particular, a load instruction may execute before
6864 a preceding store instruction. Such reordering violates
6865 sequential consistency of volatile memory references, when there
6866 are multiple processors. When consistency must be guaranteed,
6867 GCC generates special instructions, as needed, to force
6868 execution in the proper order.
6870 The MC88100 processor does not reorder memory references and so
6871 always provides sequential consistency. However, by default, GCC
6872 generates the special instructions to guarantee consistency
6873 even when you use @option{-m88100}, so that the code may be run on an
6874 MC88110 processor. If you intend to run your code only on the
6875 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6877 The extra code generated to guarantee consistency may affect the
6878 performance of your application. If you know that you can safely
6879 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6885 @cindex assembler syntax, 88k
6887 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6888 related to System V release 4 (SVr4). This controls the following:
6892 Which variant of the assembler syntax to emit.
6894 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6895 that is used on System V release 4.
6897 @option{-msvr4} makes GCC issue additional declaration directives used in
6901 @option{-msvr4} is the default for the m88k-motorola-sysv4 configuration.
6902 @option{-msvr3} is the default for all other m88k configurations.
6904 @item -mversion-03.00
6905 @opindex mversion-03.00
6906 This option is obsolete, and is ignored.
6907 @c ??? which asm syntax better for GAS? option there too?
6909 @item -mno-check-zero-division
6910 @itemx -mcheck-zero-division
6911 @opindex mno-check-zero-division
6912 @opindex mcheck-zero-division
6913 @cindex zero division on 88k
6914 Do, or don't, generate code to guarantee that integer division by
6915 zero will be detected. By default, detection is guaranteed.
6917 Some models of the MC88100 processor fail to trap upon integer
6918 division by zero under certain conditions. By default, when
6919 compiling code that might be run on such a processor, GCC
6920 generates code that explicitly checks for zero-valued divisors
6921 and traps with exception number 503 when one is detected. Use of
6922 @option{-mno-check-zero-division} suppresses such checking for code
6923 generated to run on an MC88100 processor.
6925 GCC assumes that the MC88110 processor correctly detects all instances
6926 of integer division by zero. When @option{-m88110} is specified, no
6927 explicit checks for zero-valued divisors are generated, and both
6928 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
6931 @item -muse-div-instruction
6932 @opindex muse-div-instruction
6933 @cindex divide instruction, 88k
6934 Use the div instruction for signed integer division on the
6935 MC88100 processor. By default, the div instruction is not used.
6937 On the MC88100 processor the signed integer division instruction
6938 div) traps to the operating system on a negative operand. The
6939 operating system transparently completes the operation, but at a
6940 large cost in execution time. By default, when compiling code
6941 that might be run on an MC88100 processor, GCC emulates signed
6942 integer division using the unsigned integer division instruction
6943 divu), thereby avoiding the large penalty of a trap to the
6944 operating system. Such emulation has its own, smaller, execution
6945 cost in both time and space. To the extent that your code's
6946 important signed integer division operations are performed on two
6947 nonnegative operands, it may be desirable to use the div
6948 instruction directly.
6950 On the MC88110 processor the div instruction (also known as the
6951 divs instruction) processes negative operands without trapping to
6952 the operating system. When @option{-m88110} is specified,
6953 @option{-muse-div-instruction} is ignored, and the div instruction is used
6954 for signed integer division.
6956 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6957 particular, the behavior of such a division with and without
6958 @option{-muse-div-instruction} may differ.
6960 @item -mtrap-large-shift
6961 @itemx -mhandle-large-shift
6962 @opindex mtrap-large-shift
6963 @opindex mhandle-large-shift
6964 @cindex bit shift overflow (88k)
6965 @cindex large bit shifts (88k)
6966 Include code to detect bit-shifts of more than 31 bits; respectively,
6967 trap such shifts or emit code to handle them properly. By default GCC
6968 makes no special provision for large bit shifts.
6970 @item -mwarn-passed-structs
6971 @opindex mwarn-passed-structs
6972 @cindex structure passing (88k)
6973 Warn when a function passes a struct as an argument or result.
6974 Structure-passing conventions have changed during the evolution of the C
6975 language, and are often the source of portability problems. By default,
6976 GCC issues no such warning.
6979 @c break page here to avoid unsightly interparagraph stretch.
6983 @node RS/6000 and PowerPC Options
6984 @subsection IBM RS/6000 and PowerPC Options
6985 @cindex RS/6000 and PowerPC Options
6986 @cindex IBM RS/6000 and PowerPC Options
6988 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6996 @itemx -mpowerpc-gpopt
6997 @itemx -mno-powerpc-gpopt
6998 @itemx -mpowerpc-gfxopt
6999 @itemx -mno-powerpc-gfxopt
7001 @itemx -mno-powerpc64
7007 @opindex mno-powerpc
7008 @opindex mpowerpc-gpopt
7009 @opindex mno-powerpc-gpopt
7010 @opindex mpowerpc-gfxopt
7011 @opindex mno-powerpc-gfxopt
7013 @opindex mno-powerpc64
7014 GCC supports two related instruction set architectures for the
7015 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
7016 instructions supported by the @samp{rios} chip set used in the original
7017 RS/6000 systems and the @dfn{PowerPC} instruction set is the
7018 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
7019 the IBM 4xx microprocessors.
7021 Neither architecture is a subset of the other. However there is a
7022 large common subset of instructions supported by both. An MQ
7023 register is included in processors supporting the POWER architecture.
7025 You use these options to specify which instructions are available on the
7026 processor you are using. The default value of these options is
7027 determined when configuring GCC@. Specifying the
7028 @option{-mcpu=@var{cpu_type}} overrides the specification of these
7029 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
7030 rather than the options listed above.
7032 The @option{-mpower} option allows GCC to generate instructions that
7033 are found only in the POWER architecture and to use the MQ register.
7034 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
7035 to generate instructions that are present in the POWER2 architecture but
7036 not the original POWER architecture.
7038 The @option{-mpowerpc} option allows GCC to generate instructions that
7039 are found only in the 32-bit subset of the PowerPC architecture.
7040 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
7041 GCC to use the optional PowerPC architecture instructions in the
7042 General Purpose group, including floating-point square root. Specifying
7043 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
7044 use the optional PowerPC architecture instructions in the Graphics
7045 group, including floating-point select.
7047 The @option{-mpowerpc64} option allows GCC to generate the additional
7048 64-bit instructions that are found in the full PowerPC64 architecture
7049 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
7050 @option{-mno-powerpc64}.
7052 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
7053 will use only the instructions in the common subset of both
7054 architectures plus some special AIX common-mode calls, and will not use
7055 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
7056 permits GCC to use any instruction from either architecture and to
7057 allow use of the MQ register; specify this for the Motorola MPC601.
7059 @item -mnew-mnemonics
7060 @itemx -mold-mnemonics
7061 @opindex mnew-mnemonics
7062 @opindex mold-mnemonics
7063 Select which mnemonics to use in the generated assembler code. With
7064 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
7065 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
7066 assembler mnemonics defined for the POWER architecture. Instructions
7067 defined in only one architecture have only one mnemonic; GCC uses that
7068 mnemonic irrespective of which of these options is specified.
7070 GCC defaults to the mnemonics appropriate for the architecture in
7071 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
7072 value of these option. Unless you are building a cross-compiler, you
7073 should normally not specify either @option{-mnew-mnemonics} or
7074 @option{-mold-mnemonics}, but should instead accept the default.
7076 @item -mcpu=@var{cpu_type}
7078 Set architecture type, register usage, choice of mnemonics, and
7079 instruction scheduling parameters for machine type @var{cpu_type}.
7080 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
7081 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
7082 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
7083 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
7084 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
7085 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
7087 @option{-mcpu=common} selects a completely generic processor. Code
7088 generated under this option will run on any POWER or PowerPC processor.
7089 GCC will use only the instructions in the common subset of both
7090 architectures, and will not use the MQ register. GCC assumes a generic
7091 processor model for scheduling purposes.
7093 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
7094 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
7095 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
7096 types, with an appropriate, generic processor model assumed for
7097 scheduling purposes.
7099 The other options specify a specific processor. Code generated under
7100 those options will run best on that processor, and may not run at all on
7103 The @option{-mcpu} options automatically enable or disable other
7104 @option{-m} options as follows:
7108 @option{-mno-power}, @option{-mno-powerpc}
7115 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
7130 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7133 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7138 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
7141 @item -mtune=@var{cpu_type}
7143 Set the instruction scheduling parameters for machine type
7144 @var{cpu_type}, but do not set the architecture type, register usage, or
7145 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
7146 values for @var{cpu_type} are used for @option{-mtune} as for
7147 @option{-mcpu}. If both are specified, the code generated will use the
7148 architecture, registers, and mnemonics set by @option{-mcpu}, but the
7149 scheduling parameters set by @option{-mtune}.
7154 @opindex mno-altivec
7155 These switches enable or disable the use of built-in functions that
7156 allow access to the AltiVec instruction set. You may also need to set
7157 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
7162 Extend the current ABI with SPE ABI extensions. This does not change
7163 the default ABI, instead it adds the SPE ABI extensions to the current
7167 @opindex mabi=no-spe
7168 Disable Booke SPE ABI extensions for the current ABI.
7170 @item -misel=@var{yes/no}
7173 This switch enables or disables the generation of ISEL instructions.
7175 @item -mspe=@var{yes/no}
7178 This switch enables or disables the generation of SPE simd
7181 @item -mfloat-gprs=@var{yes/no}
7183 @opindex mfloat-gprs
7184 This switch enables or disables the generation of floating point
7185 operations on the general purpose registers for architectures that
7186 support it. This option is currently only available on the MPC8540.
7189 @itemx -mno-fp-in-toc
7190 @itemx -mno-sum-in-toc
7191 @itemx -mminimal-toc
7193 @opindex mno-fp-in-toc
7194 @opindex mno-sum-in-toc
7195 @opindex mminimal-toc
7196 Modify generation of the TOC (Table Of Contents), which is created for
7197 every executable file. The @option{-mfull-toc} option is selected by
7198 default. In that case, GCC will allocate at least one TOC entry for
7199 each unique non-automatic variable reference in your program. GCC
7200 will also place floating-point constants in the TOC@. However, only
7201 16,384 entries are available in the TOC@.
7203 If you receive a linker error message that saying you have overflowed
7204 the available TOC space, you can reduce the amount of TOC space used
7205 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
7206 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
7207 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
7208 generate code to calculate the sum of an address and a constant at
7209 run-time instead of putting that sum into the TOC@. You may specify one
7210 or both of these options. Each causes GCC to produce very slightly
7211 slower and larger code at the expense of conserving TOC space.
7213 If you still run out of space in the TOC even when you specify both of
7214 these options, specify @option{-mminimal-toc} instead. This option causes
7215 GCC to make only one TOC entry for every file. When you specify this
7216 option, GCC will produce code that is slower and larger but which
7217 uses extremely little TOC space. You may wish to use this option
7218 only on files that contain less frequently executed code.
7224 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
7225 @code{long} type, and the infrastructure needed to support them.
7226 Specifying @option{-maix64} implies @option{-mpowerpc64} and
7227 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
7228 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
7233 @opindex mno-xl-call
7234 On AIX, pass floating-point arguments to prototyped functions beyond the
7235 register save area (RSA) on the stack in addition to argument FPRs. The
7236 AIX calling convention was extended but not initially documented to
7237 handle an obscure K&R C case of calling a function that takes the
7238 address of its arguments with fewer arguments than declared. AIX XL
7239 compilers access floating point arguments which do not fit in the
7240 RSA from the stack when a subroutine is compiled without
7241 optimization. Because always storing floating-point arguments on the
7242 stack is inefficient and rarely needed, this option is not enabled by
7243 default and only is necessary when calling subroutines compiled by AIX
7244 XL compilers without optimization.
7248 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
7249 application written to use message passing with special startup code to
7250 enable the application to run. The system must have PE installed in the
7251 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
7252 must be overridden with the @option{-specs=} option to specify the
7253 appropriate directory location. The Parallel Environment does not
7254 support threads, so the @option{-mpe} option and the @option{-pthread}
7255 option are incompatible.
7257 @item -malign-natural
7258 @itemx -malign-power
7259 @opindex malign-natural
7260 @opindex malign-power
7261 On AIX, Darwin, and 64-bit PowerPC Linux, the option
7262 @option{-malign-natural} overrides the ABI-defined alignment of larger
7263 types, such as floating-point doubles, on their natural size-based boundary.
7264 The option @option{-malign-power} instructs GCC to follow the ABI-specified
7265 alignment rules. GCC defaults to the standard alignment defined in the ABI.
7269 @opindex msoft-float
7270 @opindex mhard-float
7271 Generate code that does not use (uses) the floating-point register set.
7272 Software floating point emulation is provided if you use the
7273 @option{-msoft-float} option, and pass the option to GCC when linking.
7276 @itemx -mno-multiple
7278 @opindex mno-multiple
7279 Generate code that uses (does not use) the load multiple word
7280 instructions and the store multiple word instructions. These
7281 instructions are generated by default on POWER systems, and not
7282 generated on PowerPC systems. Do not use @option{-mmultiple} on little
7283 endian PowerPC systems, since those instructions do not work when the
7284 processor is in little endian mode. The exceptions are PPC740 and
7285 PPC750 which permit the instructions usage in little endian mode.
7291 Generate code that uses (does not use) the load string instructions
7292 and the store string word instructions to save multiple registers and
7293 do small block moves. These instructions are generated by default on
7294 POWER systems, and not generated on PowerPC systems. Do not use
7295 @option{-mstring} on little endian PowerPC systems, since those
7296 instructions do not work when the processor is in little endian mode.
7297 The exceptions are PPC740 and PPC750 which permit the instructions
7298 usage in little endian mode.
7304 Generate code that uses (does not use) the load or store instructions
7305 that update the base register to the address of the calculated memory
7306 location. These instructions are generated by default. If you use
7307 @option{-mno-update}, there is a small window between the time that the
7308 stack pointer is updated and the address of the previous frame is
7309 stored, which means code that walks the stack frame across interrupts or
7310 signals may get corrupted data.
7313 @itemx -mno-fused-madd
7314 @opindex mfused-madd
7315 @opindex mno-fused-madd
7316 Generate code that uses (does not use) the floating point multiply and
7317 accumulate instructions. These instructions are generated by default if
7318 hardware floating is used.
7320 @item -mno-bit-align
7322 @opindex mno-bit-align
7324 On System V.4 and embedded PowerPC systems do not (do) force structures
7325 and unions that contain bit-fields to be aligned to the base type of the
7328 For example, by default a structure containing nothing but 8
7329 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
7330 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
7331 the structure would be aligned to a 1 byte boundary and be one byte in
7334 @item -mno-strict-align
7335 @itemx -mstrict-align
7336 @opindex mno-strict-align
7337 @opindex mstrict-align
7338 On System V.4 and embedded PowerPC systems do not (do) assume that
7339 unaligned memory references will be handled by the system.
7342 @itemx -mno-relocatable
7343 @opindex mrelocatable
7344 @opindex mno-relocatable
7345 On embedded PowerPC systems generate code that allows (does not allow)
7346 the program to be relocated to a different address at runtime. If you
7347 use @option{-mrelocatable} on any module, all objects linked together must
7348 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
7350 @item -mrelocatable-lib
7351 @itemx -mno-relocatable-lib
7352 @opindex mrelocatable-lib
7353 @opindex mno-relocatable-lib
7354 On embedded PowerPC systems generate code that allows (does not allow)
7355 the program to be relocated to a different address at runtime. Modules
7356 compiled with @option{-mrelocatable-lib} can be linked with either modules
7357 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
7358 with modules compiled with the @option{-mrelocatable} options.
7364 On System V.4 and embedded PowerPC systems do not (do) assume that
7365 register 2 contains a pointer to a global area pointing to the addresses
7366 used in the program.
7369 @itemx -mlittle-endian
7371 @opindex mlittle-endian
7372 On System V.4 and embedded PowerPC systems compile code for the
7373 processor in little endian mode. The @option{-mlittle-endian} option is
7374 the same as @option{-mlittle}.
7379 @opindex mbig-endian
7380 On System V.4 and embedded PowerPC systems compile code for the
7381 processor in big endian mode. The @option{-mbig-endian} option is
7382 the same as @option{-mbig}.
7384 @item -mdynamic-no-pic
7385 @opindex mdynamic-no-pic
7386 On Darwin and Mac OS X systems, compile code so that it is not
7387 relocatable, but that its external references are relocatable. The
7388 resulting code is suitable for applications, but not shared
7393 On System V.4 and embedded PowerPC systems compile code using calling
7394 conventions that adheres to the March 1995 draft of the System V
7395 Application Binary Interface, PowerPC processor supplement. This is the
7396 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
7398 @item -mcall-sysv-eabi
7399 @opindex mcall-sysv-eabi
7400 Specify both @option{-mcall-sysv} and @option{-meabi} options.
7402 @item -mcall-sysv-noeabi
7403 @opindex mcall-sysv-noeabi
7404 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
7406 @item -mcall-solaris
7407 @opindex mcall-solaris
7408 On System V.4 and embedded PowerPC systems compile code for the Solaris
7412 @opindex mcall-linux
7413 On System V.4 and embedded PowerPC systems compile code for the
7414 Linux-based GNU system.
7418 On System V.4 and embedded PowerPC systems compile code for the
7419 Hurd-based GNU system.
7422 @opindex mcall-netbsd
7423 On System V.4 and embedded PowerPC systems compile code for the
7424 NetBSD operating system.
7426 @item -maix-struct-return
7427 @opindex maix-struct-return
7428 Return all structures in memory (as specified by the AIX ABI)@.
7430 @item -msvr4-struct-return
7431 @opindex msvr4-struct-return
7432 Return structures smaller than 8 bytes in registers (as specified by the
7436 @opindex mabi=altivec
7437 Extend the current ABI with AltiVec ABI extensions. This does not
7438 change the default ABI, instead it adds the AltiVec ABI extensions to
7441 @item -mabi=no-altivec
7442 @opindex mabi=no-altivec
7443 Disable AltiVec ABI extensions for the current ABI.
7446 @itemx -mno-prototype
7448 @opindex mno-prototype
7449 On System V.4 and embedded PowerPC systems assume that all calls to
7450 variable argument functions are properly prototyped. Otherwise, the
7451 compiler must insert an instruction before every non prototyped call to
7452 set or clear bit 6 of the condition code register (@var{CR}) to
7453 indicate whether floating point values were passed in the floating point
7454 registers in case the function takes a variable arguments. With
7455 @option{-mprototype}, only calls to prototyped variable argument functions
7456 will set or clear the bit.
7460 On embedded PowerPC systems, assume that the startup module is called
7461 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
7462 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
7467 On embedded PowerPC systems, assume that the startup module is called
7468 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
7473 On embedded PowerPC systems, assume that the startup module is called
7474 @file{crt0.o} and the standard C libraries are @file{libads.a} and
7478 @opindex myellowknife
7479 On embedded PowerPC systems, assume that the startup module is called
7480 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
7485 On System V.4 and embedded PowerPC systems, specify that you are
7486 compiling for a VxWorks system.
7490 Specify that you are compiling for the WindISS simulation environment.
7494 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
7495 header to indicate that @samp{eabi} extended relocations are used.
7501 On System V.4 and embedded PowerPC systems do (do not) adhere to the
7502 Embedded Applications Binary Interface (eabi) which is a set of
7503 modifications to the System V.4 specifications. Selecting @option{-meabi}
7504 means that the stack is aligned to an 8 byte boundary, a function
7505 @code{__eabi} is called to from @code{main} to set up the eabi
7506 environment, and the @option{-msdata} option can use both @code{r2} and
7507 @code{r13} to point to two separate small data areas. Selecting
7508 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
7509 do not call an initialization function from @code{main}, and the
7510 @option{-msdata} option will only use @code{r13} to point to a single
7511 small data area. The @option{-meabi} option is on by default if you
7512 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
7515 @opindex msdata=eabi
7516 On System V.4 and embedded PowerPC systems, put small initialized
7517 @code{const} global and static data in the @samp{.sdata2} section, which
7518 is pointed to by register @code{r2}. Put small initialized
7519 non-@code{const} global and static data in the @samp{.sdata} section,
7520 which is pointed to by register @code{r13}. Put small uninitialized
7521 global and static data in the @samp{.sbss} section, which is adjacent to
7522 the @samp{.sdata} section. The @option{-msdata=eabi} option is
7523 incompatible with the @option{-mrelocatable} option. The
7524 @option{-msdata=eabi} option also sets the @option{-memb} option.
7527 @opindex msdata=sysv
7528 On System V.4 and embedded PowerPC systems, put small global and static
7529 data in the @samp{.sdata} section, which is pointed to by register
7530 @code{r13}. Put small uninitialized global and static data in the
7531 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7532 The @option{-msdata=sysv} option is incompatible with the
7533 @option{-mrelocatable} option.
7535 @item -msdata=default
7537 @opindex msdata=default
7539 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7540 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7541 same as @option{-msdata=sysv}.
7544 @opindex msdata-data
7545 On System V.4 and embedded PowerPC systems, put small global and static
7546 data in the @samp{.sdata} section. Put small uninitialized global and
7547 static data in the @samp{.sbss} section. Do not use register @code{r13}
7548 to address small data however. This is the default behavior unless
7549 other @option{-msdata} options are used.
7553 @opindex msdata=none
7555 On embedded PowerPC systems, put all initialized global and static data
7556 in the @samp{.data} section, and all uninitialized data in the
7557 @samp{.bss} section.
7561 @cindex smaller data references (PowerPC)
7562 @cindex .sdata/.sdata2 references (PowerPC)
7563 On embedded PowerPC systems, put global and static items less than or
7564 equal to @var{num} bytes into the small data or bss sections instead of
7565 the normal data or bss section. By default, @var{num} is 8. The
7566 @option{-G @var{num}} switch is also passed to the linker.
7567 All modules should be compiled with the same @option{-G @var{num}} value.
7570 @itemx -mno-regnames
7572 @opindex mno-regnames
7573 On System V.4 and embedded PowerPC systems do (do not) emit register
7574 names in the assembly language output using symbolic forms.
7577 @itemx -mno-longcall
7579 @opindex mno-longcall
7580 Default to making all function calls via pointers, so that functions
7581 which reside further than 64 megabytes (67,108,864 bytes) from the
7582 current location can be called. This setting can be overridden by the
7583 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7585 Some linkers are capable of detecting out-of-range calls and generating
7586 glue code on the fly. On these systems, long calls are unnecessary and
7587 generate slower code. As of this writing, the AIX linker can do this,
7588 as can the GNU linker for PowerPC/64. It is planned to add this feature
7589 to the GNU linker for 32-bit PowerPC systems as well.
7591 In the future, we may cause GCC to ignore all longcall specifications
7592 when the linker is known to generate glue.
7596 Adds support for multithreading with the @dfn{pthreads} library.
7597 This option sets flags for both the preprocessor and linker.
7601 @node Darwin Options
7602 @subsection Darwin Options
7603 @cindex Darwin options
7605 These options are defined for all architectures running the Darwin operating
7606 system. They are useful for compatibility with other Mac OS compilers.
7611 Loads all members of static archive libraries.
7612 See man ld(1) for more information.
7614 @item -arch_errors_fatal
7615 @opindex arch_errors_fatal
7616 Cause the errors having to do with files that have the wrong architecture
7620 @opindex bind_at_load
7621 Causes the output file to be marked such that the dynamic linker will
7622 bind all undefined references when the file is loaded or launched.
7626 Produce a Mach-o bundle format file.
7627 See man ld(1) for more information.
7629 @item -bundle_loader @var{executable}
7630 @opindex bundle_loader
7631 This specifies the @var{executable} that will be loading the build
7632 output file being linked. See man ld(1) for more information.
7634 @item -allowable_client @var{client_name}
7638 @item -compatibility_version
7639 @item -current_version
7640 @item -dependency-file
7642 @item -dylinker_install_name
7645 @item -exported_symbols_list
7647 @item -flat_namespace
7648 @item -force_cpusubtype_ALL
7649 @item -force_flat_namespace
7650 @item -headerpad_max_install_names
7654 @item -keep_private_externs
7656 @item -multiply_defined
7657 @item -multiply_defined_unused
7659 @item -nofixprebinding
7662 @item -noseglinkedit
7663 @item -pagezero_size
7665 @item -prebind_all_twolevel_modules
7666 @item -private_bundle
7667 @item -read_only_relocs
7669 @item -sectobjectsymbols
7673 @item -sectobjectsymbols
7675 @item -seg_addr_table
7676 @item -seg_addr_table_filename
7679 @item -segs_read_only_addr
7680 @item -segs_read_write_addr
7681 @item -single_module
7685 @item -twolevel_namespace
7688 @item -unexported_symbols_list
7689 @item -weak_reference_mismatches
7692 @opindex allowable_client
7694 @opindex client_name
7695 @opindex compatibility_version
7696 @opindex current_version
7697 @opindex dependency-file
7699 @opindex dylinker_install_name
7702 @opindex exported_symbols_list
7704 @opindex flat_namespace
7705 @opindex force_cpusubtype_ALL
7706 @opindex force_flat_namespace
7707 @opindex headerpad_max_install_names
7710 @opindex install_name
7711 @opindex keep_private_externs
7712 @opindex multi_module
7713 @opindex multiply_defined
7714 @opindex multiply_defined_unused
7716 @opindex nofixprebinding
7717 @opindex nomultidefs
7719 @opindex noseglinkedit
7720 @opindex pagezero_size
7722 @opindex prebind_all_twolevel_modules
7723 @opindex private_bundle
7724 @opindex read_only_relocs
7726 @opindex sectobjectsymbols
7730 @opindex sectobjectsymbols
7732 @opindex seg_addr_table
7733 @opindex seg_addr_table_filename
7734 @opindex seglinkedit
7736 @opindex segs_read_only_addr
7737 @opindex segs_read_write_addr
7738 @opindex single_module
7740 @opindex sub_library
7741 @opindex sub_umbrella
7742 @opindex twolevel_namespace
7745 @opindex unexported_symbols_list
7746 @opindex weak_reference_mismatches
7747 @opindex whatsloaded
7749 This options are available for Darwin linker. Darwin linker man page
7750 describes them in detail.
7755 @subsection IBM RT Options
7757 @cindex IBM RT options
7759 These @samp{-m} options are defined for the IBM RT PC:
7763 @opindex min-line-mul
7764 Use an in-line code sequence for integer multiplies. This is the
7767 @item -mcall-lib-mul
7768 @opindex mcall-lib-mul
7769 Call @code{lmul$$} for integer multiples.
7771 @item -mfull-fp-blocks
7772 @opindex mfull-fp-blocks
7773 Generate full-size floating point data blocks, including the minimum
7774 amount of scratch space recommended by IBM@. This is the default.
7776 @item -mminimum-fp-blocks
7777 @opindex mminimum-fp-blocks
7778 Do not include extra scratch space in floating point data blocks. This
7779 results in smaller code, but slower execution, since scratch space must
7780 be allocated dynamically.
7782 @cindex @file{stdarg.h} and RT PC
7783 @item -mfp-arg-in-fpregs
7784 @opindex mfp-arg-in-fpregs
7785 Use a calling sequence incompatible with the IBM calling convention in
7786 which floating point arguments are passed in floating point registers.
7787 Note that @code{stdarg.h} will not work with floating point operands
7788 if this option is specified.
7790 @item -mfp-arg-in-gregs
7791 @opindex mfp-arg-in-gregs
7792 Use the normal calling convention for floating point arguments. This is
7795 @item -mhc-struct-return
7796 @opindex mhc-struct-return
7797 Return structures of more than one word in memory, rather than in a
7798 register. This provides compatibility with the MetaWare HighC (hc)
7799 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7800 with the Portable C Compiler (pcc).
7802 @item -mnohc-struct-return
7803 @opindex mnohc-struct-return
7804 Return some structures of more than one word in registers, when
7805 convenient. This is the default. For compatibility with the
7806 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7807 option @option{-mhc-struct-return}.
7811 @subsection MIPS Options
7812 @cindex MIPS options
7814 These @samp{-m} options are defined for the MIPS family of computers:
7818 @item -march=@var{arch}
7820 Generate code that will run on @var{arch}, which can be the name of a
7821 generic MIPS ISA, or the name of a particular processor.
7823 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
7824 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
7825 The processor names are:
7826 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
7828 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
7829 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, @samp{rm7000},
7833 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4300},
7834 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
7835 The special value @samp{from-abi} selects the
7836 most compatible architecture for the selected ABI (that is,
7837 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
7839 In processor names, a final @samp{000} can be abbreviated as @samp{k}
7840 (for example, @samp{-march=r2k}). Prefixes are optional, and
7841 @samp{vr} may be written @samp{r}.
7843 GCC defines two macros based on the value of this option. The first
7844 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
7845 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
7846 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
7847 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
7848 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
7850 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
7851 above. In other words, it will have the full prefix and will not
7852 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
7853 the macro names the resolved architecture (either @samp{"mips1"} or
7854 @samp{"mips3"}). It names the default architecture when no
7855 @option{-march} option is given.
7857 @item -mtune=@var{arch}
7859 Optimize for @var{arch}. Among other things, this option controls
7860 the way instructions are scheduled, and the perceived cost of arithmetic
7861 operations. The list of @var{arch} values is the same as for
7864 When this option is not used, GCC will optimize for the processor
7865 specified by @option{-march}. By using @option{-march} and
7866 @option{-mtune} together, it is possible to generate code that will
7867 run on a family of processors, but optimize the code for one
7868 particular member of that family.
7870 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
7871 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
7872 @samp{-march} ones described above.
7876 Equivalent to @samp{-march=mips1}.
7880 Equivalent to @samp{-march=mips2}.
7884 Equivalent to @samp{-march=mips3}.
7888 Equivalent to @samp{-march=mips4}.
7892 Equivalent to @samp{-march=mips32}.
7896 Equivalent to @samp{-march=mips32r2}.
7900 Equivalent to @samp{-march=mips64}.
7903 @itemx -mno-fused-madd
7904 @opindex mfused-madd
7905 @opindex mno-fused-madd
7906 Generate code that uses (does not use) the floating point multiply and
7907 accumulate instructions, when they are available. These instructions
7908 are generated by default if they are available, but this may be
7909 undesirable if the extra precision causes problems or on certain chips
7910 in the mode where denormals are rounded to zero where denormals
7911 generated by multiply and accumulate instructions cause exceptions
7916 Assume that floating point registers are 32 bits wide.
7920 Assume that floating point registers are 64 bits wide.
7924 Assume that general purpose registers are 32 bits wide.
7928 Assume that general purpose registers are 64 bits wide.
7932 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7933 explanation of the default, and the width of pointers.
7937 Force long types to be 64 bits wide. See @option{-mlong32} for an
7938 explanation of the default, and the width of pointers.
7942 Force long, int, and pointer types to be 32 bits wide.
7944 The default size of ints, longs and pointers depends on the ABI@. All
7945 the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as
7946 does the 64-bit Cygnus EABI; the others use 32-bit longs. Pointers
7947 are the same size as longs, or the same size as integer registers,
7948 whichever is smaller.
7962 Generate code for the given ABI@.
7964 Note that there are two embedded ABIs: @option{-mabi=eabi}
7965 selects the one defined by Cygnus while @option{-meabi=meabi}
7966 selects the one defined by MIPS@. Both these ABIs have
7967 32-bit and 64-bit variants. Normally, GCC will generate
7968 64-bit code when you select a 64-bit architecture, but you
7969 can use @option{-mgp32} to get 32-bit code instead.
7971 @item -mabi-fake-default
7972 @opindex mabi-fake-default
7973 You don't want to know what this option does. No, really. I mean
7974 it. Move on to the next option.
7976 What? You're still here? Oh, well@enddots{} Ok, here's the deal. GCC
7977 wants the default set of options to get the root of the multilib tree,
7978 and the shared library SONAMEs without any multilib-indicating
7979 suffixes. This is not convenience for @samp{mips64-linux-gnu}, since
7980 we want to default to the N32 ABI, while still being binary-compatible
7981 with @samp{mips-linux-gnu} if you stick to the O32 ABI@. Being
7982 binary-compatible means shared libraries should have the same SONAMEs,
7983 and libraries should live in the same location. Having O32 libraries
7984 in a sub-directory named say @file{o32} is not acceptable.
7986 So we trick GCC into believing that O32 is the default ABI, except
7987 that we override the default with some internal command-line
7988 processing magic. Problem is, if we stopped at that, and you then
7989 created a multilib-aware package that used the output of @command{gcc
7990 -print-multi-lib} to decide which multilibs to build, and how, and
7991 you'd find yourself in an awkward situation when you found out that
7992 some of the options listed ended up mapping to the same multilib, and
7993 none of your libraries was actually built for the multilib that
7994 @option{-print-multi-lib} claims to be the default. So we added this
7995 option that disables the default switcher, falling back to GCC's
7996 original notion of the default library. Confused yet?
7998 For short: don't ever use this option, unless you find it in the list
7999 of additional options to be used when building for multilibs, in the
8000 output of @option{gcc -print-multi-lib}.
8004 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
8005 add normal debug information. This is the default for all
8006 platforms except for the OSF/1 reference platform, using the OSF/rose
8007 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
8008 switches are used, the @file{mips-tfile} program will encapsulate the
8009 stabs within MIPS ECOFF@.
8013 Generate code for the GNU assembler. This is the default on the OSF/1
8014 reference platform, using the OSF/rose object format. Also, this is
8015 the default if the configure option @option{--with-gnu-as} is used.
8017 @item -msplit-addresses
8018 @itemx -mno-split-addresses
8019 @opindex msplit-addresses
8020 @opindex mno-split-addresses
8021 Generate code to load the high and low parts of address constants separately.
8022 This allows GCC to optimize away redundant loads of the high order
8023 bits of addresses. This optimization requires GNU as and GNU ld.
8024 This optimization is enabled by default for some embedded targets where
8025 GNU as and GNU ld are standard.
8031 The @option{-mrnames} switch says to output code using the MIPS software
8032 names for the registers, instead of the hardware names (ie, @var{a0}
8033 instead of @var{$4}). The only known assembler that supports this option
8034 is the Algorithmics assembler.
8040 The @option{-mmemcpy} switch makes all block moves call the appropriate
8041 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
8042 generating inline code.
8045 @itemx -mno-mips-tfile
8046 @opindex mmips-tfile
8047 @opindex mno-mips-tfile
8048 The @option{-mno-mips-tfile} switch causes the compiler not
8049 postprocess the object file with the @file{mips-tfile} program,
8050 after the MIPS assembler has generated it to add debug support. If
8051 @file{mips-tfile} is not run, then no local variables will be
8052 available to the debugger. In addition, @file{stage2} and
8053 @file{stage3} objects will have the temporary file names passed to the
8054 assembler embedded in the object file, which means the objects will
8055 not compare the same. The @option{-mno-mips-tfile} switch should only
8056 be used when there are bugs in the @file{mips-tfile} program that
8057 prevents compilation.
8060 @opindex msoft-float
8061 Generate output containing library calls for floating point.
8062 @strong{Warning:} the requisite libraries are not part of GCC@.
8063 Normally the facilities of the machine's usual C compiler are used, but
8064 this can't be done directly in cross-compilation. You must make your
8065 own arrangements to provide suitable library functions for
8069 @opindex mhard-float
8070 Generate output containing floating point instructions. This is the
8071 default if you use the unmodified sources.
8074 @itemx -mno-abicalls
8076 @opindex mno-abicalls
8077 Emit (or do not emit) the pseudo operations @samp{.abicalls},
8078 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
8079 position independent code.
8085 Lift (or do not lift) the usual restrictions on the size of the global
8088 GCC normally uses a single instruction to load values from the GOT.
8089 While this is relatively efficient, it will only work if the GOT
8090 is smaller than about 64k. Anything larger will cause the linker
8091 to report an error such as:
8093 @cindex relocation truncated to fit (MIPS)
8095 relocation truncated to fit: R_MIPS_GOT16 foobar
8098 If this happens, you should recompile your code with @option{-mxgot}.
8099 It should then work with very large GOTs, although it will also be
8100 less efficient, since it will take three instructions to fetch the
8101 value of a global symbol.
8103 Note that some linkers can create multiple GOTs. If you have such a
8104 linker, you should only need to use @option{-mxgot} when a single object
8105 file accesses more than 64k's worth of GOT entries. Very few do.
8107 These options have no effect unless GCC is generating position
8111 @itemx -mno-long-calls
8112 @opindex mlong-calls
8113 @opindex mno-long-calls
8114 Do all calls with the @samp{JALR} instruction, which requires
8115 loading up a function's address into a register before the call.
8116 You need to use this switch, if you call outside of the current
8117 512 megabyte segment to functions that are not through pointers.
8119 @item -membedded-pic
8120 @itemx -mno-embedded-pic
8121 @opindex membedded-pic
8122 @opindex mno-embedded-pic
8123 Generate PIC code suitable for some embedded systems. All calls are
8124 made using PC relative address, and all data is addressed using the $gp
8125 register. No more than 65536 bytes of global data may be used. This
8126 requires GNU as and GNU ld which do most of the work. This currently
8127 only works on targets which use ECOFF; it does not work with ELF@.
8129 @item -membedded-data
8130 @itemx -mno-embedded-data
8131 @opindex membedded-data
8132 @opindex mno-embedded-data
8133 Allocate variables to the read-only data section first if possible, then
8134 next in the small data section if possible, otherwise in data. This gives
8135 slightly slower code than the default, but reduces the amount of RAM required
8136 when executing, and thus may be preferred for some embedded systems.
8138 @item -muninit-const-in-rodata
8139 @itemx -mno-uninit-const-in-rodata
8140 @opindex muninit-const-in-rodata
8141 @opindex mno-uninit-const-in-rodata
8142 When used together with @option{-membedded-data}, it will always store uninitialized
8143 const variables in the read-only data section.
8145 @item -msingle-float
8146 @itemx -mdouble-float
8147 @opindex msingle-float
8148 @opindex mdouble-float
8149 The @option{-msingle-float} switch tells gcc to assume that the floating
8150 point coprocessor only supports single precision operations, as on the
8151 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
8152 double precision operations. This is the default.
8158 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
8159 as on the @samp{r4650} chip.
8163 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
8164 @option{-mcpu=r4650}.
8170 Enable 16-bit instructions.
8174 Use the entry and exit pseudo ops. This option can only be used with
8179 Compile code for the processor in little endian mode.
8180 The requisite libraries are assumed to exist.
8184 Compile code for the processor in big endian mode.
8185 The requisite libraries are assumed to exist.
8189 @cindex smaller data references (MIPS)
8190 @cindex gp-relative references (MIPS)
8191 Put global and static items less than or equal to @var{num} bytes into
8192 the small data or bss sections instead of the normal data or bss
8193 section. This allows the assembler to emit one word memory reference
8194 instructions based on the global pointer (@var{gp} or @var{$28}),
8195 instead of the normal two words used. By default, @var{num} is 8 when
8196 the MIPS assembler is used, and 0 when the GNU assembler is used. The
8197 @option{-G @var{num}} switch is also passed to the assembler and linker.
8198 All modules should be compiled with the same @option{-G @var{num}}
8203 Tell the MIPS assembler to not run its preprocessor over user
8204 assembler files (with a @samp{.s} suffix) when assembling them.
8208 Pass an option to gas which will cause nops to be inserted if
8209 the read of the destination register of an mfhi or mflo instruction
8210 occurs in the following two instructions.
8215 Work around certain SB-1 CPU core errata.
8216 (This flag currently works around the SB-1 revision 2
8217 ``F1'' and ``F2'' floating point errata.)
8221 Do not include the default crt0.
8223 @item -mflush-func=@var{func}
8224 @itemx -mno-flush-func
8225 @opindex mflush-func
8226 Specifies the function to call to flush the I and D caches, or to not
8227 call any such function. If called, the function must take the same
8228 arguments as the common @code{_flush_func()}, that is, the address of the
8229 memory range for which the cache is being flushed, the size of the
8230 memory range, and the number 3 (to flush both caches). The default
8231 depends on the target gcc was configured for, but commonly is either
8232 @samp{_flush_func} or @samp{__cpu_flush}.
8234 @item -mbranch-likely
8235 @itemx -mno-branch-likely
8236 @opindex mbranch-likely
8237 @opindex mno-branch-likely
8238 Enable or disable use of Branch Likely instructions, regardless of the
8239 default for the selected architecture. By default, Branch Likely
8240 instructions may be generated if they are supported by the selected
8241 architecture. An exception is for the MIPS32 and MIPS64 architectures
8242 and processors which implement those architectures; for those, Branch
8243 Likely instructions will not be generated by default because the MIPS32
8244 and MIPS64 architectures specifically deprecate their use.
8247 @node i386 and x86-64 Options
8248 @subsection Intel 386 and AMD x86-64 Options
8249 @cindex i386 Options
8250 @cindex x86-64 Options
8251 @cindex Intel 386 Options
8252 @cindex AMD x86-64 Options
8254 These @samp{-m} options are defined for the i386 and x86-64 family of
8258 @item -mtune=@var{cpu-type}
8260 Tune to @var{cpu-type} everything applicable about the generated code, except
8261 for the ABI and the set of available instructions. The choices for
8262 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
8263 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
8264 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
8265 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp},
8266 @samp{athlon-mp}, @samp{winchip-c6}, @samp{winchip2}, @samp{k8}, @samp{c3}
8269 While picking a specific @var{cpu-type} will schedule things appropriately
8270 for that particular chip, the compiler will not generate any code that
8271 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8272 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
8273 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
8274 AMD chips as opposed to the Intel ones.
8276 @item -march=@var{cpu-type}
8278 Generate instructions for the machine type @var{cpu-type}. The choices
8279 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8280 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8282 @item -mcpu=@var{cpu-type}
8284 A deprecated synonym for @option{-mtune}.
8293 @opindex mpentiumpro
8294 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8295 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8296 These synonyms are deprecated.
8298 @item -mfpmath=@var{unit}
8300 generate floating point arithmetics for selected unit @var{unit}. the choices
8305 Use the standard 387 floating point coprocessor present majority of chips and
8306 emulated otherwise. Code compiled with this option will run almost everywhere.
8307 The temporary results are computed in 80bit precision instead of precision
8308 specified by the type resulting in slightly different results compared to most
8309 of other chips. See @option{-ffloat-store} for more detailed description.
8311 This is the default choice for i386 compiler.
8314 Use scalar floating point instructions present in the SSE instruction set.
8315 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8316 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8317 instruction set supports only single precision arithmetics, thus the double and
8318 extended precision arithmetics is still done using 387. Later version, present
8319 only in Pentium4 and the future AMD x86-64 chips supports double precision
8322 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8323 @option{-msse2} switches to enable SSE extensions and make this option
8324 effective. For x86-64 compiler, these extensions are enabled by default.
8326 The resulting code should be considerably faster in majority of cases and avoid
8327 the numerical instability problems of 387 code, but may break some existing
8328 code that expects temporaries to be 80bit.
8330 This is the default choice for x86-64 compiler.
8333 Use all SSE extensions enabled by @option{-msse2} as well as the new
8334 SSE extensions in Prescott New Instructions. @option{-mpni} also
8335 enables 2 builtin functions, @code{__builtin_ia32_monitor} and
8336 @code{__builtin_ia32_mwait}, for new instructions @code{monitor} and
8340 Attempt to utilize both instruction sets at once. This effectively double the
8341 amount of available registers and on chips with separate execution units for
8342 387 and SSE the execution resources too. Use this option with care, as it is
8343 still experimental, because gcc register allocator does not model separate
8344 functional units well resulting in instable performance.
8347 @item -masm=@var{dialect}
8348 @opindex masm=@var{dialect}
8349 Output asm instructions using selected @var{dialect}. Supported choices are
8350 @samp{intel} or @samp{att} (the default one).
8355 @opindex mno-ieee-fp
8356 Control whether or not the compiler uses IEEE floating point
8357 comparisons. These handle correctly the case where the result of a
8358 comparison is unordered.
8361 @opindex msoft-float
8362 Generate output containing library calls for floating point.
8363 @strong{Warning:} the requisite libraries are not part of GCC@.
8364 Normally the facilities of the machine's usual C compiler are used, but
8365 this can't be done directly in cross-compilation. You must make your
8366 own arrangements to provide suitable library functions for
8369 On machines where a function returns floating point results in the 80387
8370 register stack, some floating point opcodes may be emitted even if
8371 @option{-msoft-float} is used.
8373 @item -mno-fp-ret-in-387
8374 @opindex mno-fp-ret-in-387
8375 Do not use the FPU registers for return values of functions.
8377 The usual calling convention has functions return values of types
8378 @code{float} and @code{double} in an FPU register, even if there
8379 is no FPU@. The idea is that the operating system should emulate
8382 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8383 in ordinary CPU registers instead.
8385 @item -mno-fancy-math-387
8386 @opindex mno-fancy-math-387
8387 Some 387 emulators do not support the @code{sin}, @code{cos} and
8388 @code{sqrt} instructions for the 387. Specify this option to avoid
8389 generating those instructions. This option is the default on FreeBSD,
8390 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8391 indicates that the target cpu will always have an FPU and so the
8392 instruction will not need emulation. As of revision 2.6.1, these
8393 instructions are not generated unless you also use the
8394 @option{-funsafe-math-optimizations} switch.
8396 @item -malign-double
8397 @itemx -mno-align-double
8398 @opindex malign-double
8399 @opindex mno-align-double
8400 Control whether GCC aligns @code{double}, @code{long double}, and
8401 @code{long long} variables on a two word boundary or a one word
8402 boundary. Aligning @code{double} variables on a two word boundary will
8403 produce code that runs somewhat faster on a @samp{Pentium} at the
8404 expense of more memory.
8406 @strong{Warning:} if you use the @option{-malign-double} switch,
8407 structures containing the above types will be aligned differently than
8408 the published application binary interface specifications for the 386
8409 and will not be binary compatible with structures in code compiled
8410 without that switch.
8412 @item -m96bit-long-double
8413 @item -m128bit-long-double
8414 @opindex m96bit-long-double
8415 @opindex m128bit-long-double
8416 These switches control the size of @code{long double} type. The i386
8417 application binary interface specifies the size to be 96 bits,
8418 so @option{-m96bit-long-double} is the default in 32 bit mode.
8420 Modern architectures (Pentium and newer) would prefer @code{long double}
8421 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8422 conforming to the ABI, this would not be possible. So specifying a
8423 @option{-m128bit-long-double} will align @code{long double}
8424 to a 16 byte boundary by padding the @code{long double} with an additional
8427 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8428 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8430 Notice that neither of these options enable any extra precision over the x87
8431 standard of 80 bits for a @code{long double}.
8433 @strong{Warning:} if you override the default value for your target ABI, the
8434 structures and arrays containing @code{long double} will change their size as
8435 well as function calling convention for function taking @code{long double}
8436 will be modified. Hence they will not be binary compatible with arrays or
8437 structures in code compiled without that switch.
8441 @itemx -mno-svr3-shlib
8442 @opindex msvr3-shlib
8443 @opindex mno-svr3-shlib
8444 Control whether GCC places uninitialized local variables into the
8445 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8446 into @code{bss}. These options are meaningful only on System V Release 3.
8450 Use a different function-calling convention, in which functions that
8451 take a fixed number of arguments return with the @code{ret} @var{num}
8452 instruction, which pops their arguments while returning. This saves one
8453 instruction in the caller since there is no need to pop the arguments
8456 You can specify that an individual function is called with this calling
8457 sequence with the function attribute @samp{stdcall}. You can also
8458 override the @option{-mrtd} option by using the function attribute
8459 @samp{cdecl}. @xref{Function Attributes}.
8461 @strong{Warning:} this calling convention is incompatible with the one
8462 normally used on Unix, so you cannot use it if you need to call
8463 libraries compiled with the Unix compiler.
8465 Also, you must provide function prototypes for all functions that
8466 take variable numbers of arguments (including @code{printf});
8467 otherwise incorrect code will be generated for calls to those
8470 In addition, seriously incorrect code will result if you call a
8471 function with too many arguments. (Normally, extra arguments are
8472 harmlessly ignored.)
8474 @item -mregparm=@var{num}
8476 Control how many registers are used to pass integer arguments. By
8477 default, no registers are used to pass arguments, and at most 3
8478 registers can be used. You can control this behavior for a specific
8479 function by using the function attribute @samp{regparm}.
8480 @xref{Function Attributes}.
8482 @strong{Warning:} if you use this switch, and
8483 @var{num} is nonzero, then you must build all modules with the same
8484 value, including any libraries. This includes the system libraries and
8487 @item -mpreferred-stack-boundary=@var{num}
8488 @opindex mpreferred-stack-boundary
8489 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8490 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8491 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8492 size (@option{-Os}), in which case the default is the minimum correct
8493 alignment (4 bytes for x86, and 8 bytes for x86-64).
8495 On Pentium and PentiumPro, @code{double} and @code{long double} values
8496 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8497 suffer significant run time performance penalties. On Pentium III, the
8498 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8499 penalties if it is not 16 byte aligned.
8501 To ensure proper alignment of this values on the stack, the stack boundary
8502 must be as aligned as that required by any value stored on the stack.
8503 Further, every function must be generated such that it keeps the stack
8504 aligned. Thus calling a function compiled with a higher preferred
8505 stack boundary from a function compiled with a lower preferred stack
8506 boundary will most likely misalign the stack. It is recommended that
8507 libraries that use callbacks always use the default setting.
8509 This extra alignment does consume extra stack space, and generally
8510 increases code size. Code that is sensitive to stack space usage, such
8511 as embedded systems and operating system kernels, may want to reduce the
8512 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8530 These switches enable or disable the use of built-in functions that allow
8531 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
8533 @xref{X86 Built-in Functions}, for details of the functions enabled
8534 and disabled by these switches.
8536 To have SSE/SSE2 instructions generated automatically from floating-point
8537 code, see @option{-mfpmath=sse}.
8540 @itemx -mno-push-args
8542 @opindex mno-push-args
8543 Use PUSH operations to store outgoing parameters. This method is shorter
8544 and usually equally fast as method using SUB/MOV operations and is enabled
8545 by default. In some cases disabling it may improve performance because of
8546 improved scheduling and reduced dependencies.
8548 @item -maccumulate-outgoing-args
8549 @opindex maccumulate-outgoing-args
8550 If enabled, the maximum amount of space required for outgoing arguments will be
8551 computed in the function prologue. This is faster on most modern CPUs
8552 because of reduced dependencies, improved scheduling and reduced stack usage
8553 when preferred stack boundary is not equal to 2. The drawback is a notable
8554 increase in code size. This switch implies @option{-mno-push-args}.
8558 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8559 on thread-safe exception handling must compile and link all code with the
8560 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8561 @option{-D_MT}; when linking, it links in a special thread helper library
8562 @option{-lmingwthrd} which cleans up per thread exception handling data.
8564 @item -mno-align-stringops
8565 @opindex mno-align-stringops
8566 Do not align destination of inlined string operations. This switch reduces
8567 code size and improves performance in case the destination is already aligned,
8568 but gcc don't know about it.
8570 @item -minline-all-stringops
8571 @opindex minline-all-stringops
8572 By default GCC inlines string operations only when destination is known to be
8573 aligned at least to 4 byte boundary. This enables more inlining, increase code
8574 size, but may improve performance of code that depends on fast memcpy, strlen
8575 and memset for short lengths.
8577 @item -momit-leaf-frame-pointer
8578 @opindex momit-leaf-frame-pointer
8579 Don't keep the frame pointer in a register for leaf functions. This
8580 avoids the instructions to save, set up and restore frame pointers and
8581 makes an extra register available in leaf functions. The option
8582 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8583 which might make debugging harder.
8585 @item -mtls-direct-seg-refs
8586 @itemx -mno-tls-direct-seg-refs
8587 @opindex mtls-direct-seg-refs
8588 Controls whether TLS variables may be accessed with offsets from the
8589 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8590 or whether the thread base pointer must be added. Whether or not this
8591 is legal depends on the operating system, and whether it maps the
8592 segment to cover the entire TLS area.
8594 For systems that use GNU libc, the default is on.
8597 These @samp{-m} switches are supported in addition to the above
8598 on AMD x86-64 processors in 64-bit environments.
8605 Generate code for a 32-bit or 64-bit environment.
8606 The 32-bit environment sets int, long and pointer to 32 bits and
8607 generates code that runs on any i386 system.
8608 The 64-bit environment sets int to 32 bits and long and pointer
8609 to 64 bits and generates code for AMD's x86-64 architecture.
8612 @opindex no-red-zone
8613 Do not use a so called red zone for x86-64 code. The red zone is mandated
8614 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8615 stack pointer that will not be modified by signal or interrupt handlers
8616 and therefore can be used for temporary data without adjusting the stack
8617 pointer. The flag @option{-mno-red-zone} disables this red zone.
8619 @item -mcmodel=small
8620 @opindex mcmodel=small
8621 Generate code for the small code model: the program and its symbols must
8622 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8623 Programs can be statically or dynamically linked. This is the default
8626 @item -mcmodel=kernel
8627 @opindex mcmodel=kernel
8628 Generate code for the kernel code model. The kernel runs in the
8629 negative 2 GB of the address space.
8630 This model has to be used for Linux kernel code.
8632 @item -mcmodel=medium
8633 @opindex mcmodel=medium
8634 Generate code for the medium model: The program is linked in the lower 2
8635 GB of the address space but symbols can be located anywhere in the
8636 address space. Programs can be statically or dynamically linked, but
8637 building of shared libraries are not supported with the medium model.
8639 @item -mcmodel=large
8640 @opindex mcmodel=large
8641 Generate code for the large model: This model makes no assumptions
8642 about addresses and sizes of sections. Currently GCC does not implement
8647 @subsection HPPA Options
8648 @cindex HPPA Options
8650 These @samp{-m} options are defined for the HPPA family of computers:
8653 @item -march=@var{architecture-type}
8655 Generate code for the specified architecture. The choices for
8656 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8657 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8658 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8659 architecture option for your machine. Code compiled for lower numbered
8660 architectures will run on higher numbered architectures, but not the
8663 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8664 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8668 @itemx -mpa-risc-1-1
8669 @itemx -mpa-risc-2-0
8670 @opindex mpa-risc-1-0
8671 @opindex mpa-risc-1-1
8672 @opindex mpa-risc-2-0
8673 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8676 @opindex mbig-switch
8677 Generate code suitable for big switch tables. Use this option only if
8678 the assembler/linker complain about out of range branches within a switch
8681 @item -mjump-in-delay
8682 @opindex mjump-in-delay
8683 Fill delay slots of function calls with unconditional jump instructions
8684 by modifying the return pointer for the function call to be the target
8685 of the conditional jump.
8687 @item -mdisable-fpregs
8688 @opindex mdisable-fpregs
8689 Prevent floating point registers from being used in any manner. This is
8690 necessary for compiling kernels which perform lazy context switching of
8691 floating point registers. If you use this option and attempt to perform
8692 floating point operations, the compiler will abort.
8694 @item -mdisable-indexing
8695 @opindex mdisable-indexing
8696 Prevent the compiler from using indexing address modes. This avoids some
8697 rather obscure problems when compiling MIG generated code under MACH@.
8699 @item -mno-space-regs
8700 @opindex mno-space-regs
8701 Generate code that assumes the target has no space registers. This allows
8702 GCC to generate faster indirect calls and use unscaled index address modes.
8704 Such code is suitable for level 0 PA systems and kernels.
8706 @item -mfast-indirect-calls
8707 @opindex mfast-indirect-calls
8708 Generate code that assumes calls never cross space boundaries. This
8709 allows GCC to emit code which performs faster indirect calls.
8711 This option will not work in the presence of shared libraries or nested
8714 @item -mlong-load-store
8715 @opindex mlong-load-store
8716 Generate 3-instruction load and store sequences as sometimes required by
8717 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8720 @item -mportable-runtime
8721 @opindex mportable-runtime
8722 Use the portable calling conventions proposed by HP for ELF systems.
8726 Enable the use of assembler directives only GAS understands.
8728 @item -mschedule=@var{cpu-type}
8730 Schedule code according to the constraints for the machine type
8731 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8732 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8733 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8734 proper scheduling option for your machine. The default scheduling is
8738 @opindex mlinker-opt
8739 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8740 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8741 linkers in which they give bogus error messages when linking some programs.
8744 @opindex msoft-float
8745 Generate output containing library calls for floating point.
8746 @strong{Warning:} the requisite libraries are not available for all HPPA
8747 targets. Normally the facilities of the machine's usual C compiler are
8748 used, but this cannot be done directly in cross-compilation. You must make
8749 your own arrangements to provide suitable library functions for
8750 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8751 does provide software floating point support.
8753 @option{-msoft-float} changes the calling convention in the output file;
8754 therefore, it is only useful if you compile @emph{all} of a program with
8755 this option. In particular, you need to compile @file{libgcc.a}, the
8756 library that comes with GCC, with @option{-msoft-float} in order for
8761 Generate the predefine, @code{_SIO}, for server IO. The default is
8762 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8763 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8764 options are available under HP-UX and HI-UX.
8768 Use GNU ld specific options. This passes @option{-shared} to ld when
8769 building a shared library. It is the default when GCC is configured,
8770 explicitly or implicitly, with the GNU linker. This option does not
8771 have any affect on which ld is called, it only changes what parameters
8772 are passed to that ld. The ld that is called is determined by the
8773 @option{--with-ld} configure option, gcc's program search path, and
8774 finally by the user's @env{PATH}. The linker used by GCC can be printed
8775 using @samp{which `gcc -print-prog-name=ld`}.
8779 Use HP ld specific options. This passes @option{-b} to ld when building
8780 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8781 links. It is the default when GCC is configured, explicitly or
8782 implicitly, with the HP linker. This option does not have any affect on
8783 which ld is called, it only changes what parameters are passed to that
8784 ld. The ld that is called is determined by the @option{--with-ld}
8785 configure option, gcc's program search path, and finally by the user's
8786 @env{PATH}. The linker used by GCC can be printed using @samp{which
8787 `gcc -print-prog-name=ld`}.
8790 @opindex mno-long-calls
8791 Generate code that uses long call sequences. This ensures that a call
8792 is always able to reach linker generated stubs. The default is to generate
8793 long calls only when the distance from the call site to the beginning
8794 of the function or translation unit, as the case may be, exceeds a
8795 predefined limit set by the branch type being used. The limits for
8796 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8797 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8800 Distances are measured from the beginning of functions when using the
8801 @option{-ffunction-sections} option, or when using the @option{-mgas}
8802 and @option{-mno-portable-runtime} options together under HP-UX with
8805 It is normally not desirable to use this option as it will degrade
8806 performance. However, it may be useful in large applications,
8807 particularly when partial linking is used to build the application.
8809 The types of long calls used depends on the capabilities of the
8810 assembler and linker, and the type of code being generated. The
8811 impact on systems that support long absolute calls, and long pic
8812 symbol-difference or pc-relative calls should be relatively small.
8813 However, an indirect call is used on 32-bit ELF systems in pic code
8814 and it is quite long.
8818 Suppress the generation of link options to search libdld.sl when the
8819 @option{-static} option is specified on HP-UX 10 and later.
8823 The HP-UX implementation of setlocale in libc has a dependency on
8824 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8825 when the @option{-static} option is specified, special link options
8826 are needed to resolve this dependency.
8828 On HP-UX 10 and later, the GCC driver adds the necessary options to
8829 link with libdld.sl when the @option{-static} option is specified.
8830 This causes the resulting binary to be dynamic. On the 64-bit port,
8831 the linkers generate dynamic binaries by default in any case. The
8832 @option{-nolibdld} option can be used to prevent the GCC driver from
8833 adding these link options.
8837 Add support for multithreading with the @dfn{dce thread} library
8838 under HP-UX. This option sets flags for both the preprocessor and
8842 @node Intel 960 Options
8843 @subsection Intel 960 Options
8845 These @samp{-m} options are defined for the Intel 960 implementations:
8848 @item -m@var{cpu-type}
8856 Assume the defaults for the machine type @var{cpu-type} for some of
8857 the other options, including instruction scheduling, floating point
8858 support, and addressing modes. The choices for @var{cpu-type} are
8859 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8860 @samp{sa}, and @samp{sb}.
8867 @opindex msoft-float
8868 The @option{-mnumerics} option indicates that the processor does support
8869 floating-point instructions. The @option{-msoft-float} option indicates
8870 that floating-point support should not be assumed.
8872 @item -mleaf-procedures
8873 @itemx -mno-leaf-procedures
8874 @opindex mleaf-procedures
8875 @opindex mno-leaf-procedures
8876 Do (or do not) attempt to alter leaf procedures to be callable with the
8877 @code{bal} instruction as well as @code{call}. This will result in more
8878 efficient code for explicit calls when the @code{bal} instruction can be
8879 substituted by the assembler or linker, but less efficient code in other
8880 cases, such as calls via function pointers, or using a linker that doesn't
8881 support this optimization.
8884 @itemx -mno-tail-call
8886 @opindex mno-tail-call
8887 Do (or do not) make additional attempts (beyond those of the
8888 machine-independent portions of the compiler) to optimize tail-recursive
8889 calls into branches. You may not want to do this because the detection of
8890 cases where this is not valid is not totally complete. The default is
8891 @option{-mno-tail-call}.
8893 @item -mcomplex-addr
8894 @itemx -mno-complex-addr
8895 @opindex mcomplex-addr
8896 @opindex mno-complex-addr
8897 Assume (or do not assume) that the use of a complex addressing mode is a
8898 win on this implementation of the i960. Complex addressing modes may not
8899 be worthwhile on the K-series, but they definitely are on the C-series.
8900 The default is currently @option{-mcomplex-addr} for all processors except
8904 @itemx -mno-code-align
8905 @opindex mcode-align
8906 @opindex mno-code-align
8907 Align code to 8-byte boundaries for faster fetching (or don't bother).
8908 Currently turned on by default for C-series implementations only.
8911 @item -mclean-linkage
8912 @itemx -mno-clean-linkage
8913 @opindex mclean-linkage
8914 @opindex mno-clean-linkage
8915 These options are not fully implemented.
8919 @itemx -mic2.0-compat
8920 @itemx -mic3.0-compat
8922 @opindex mic2.0-compat
8923 @opindex mic3.0-compat
8924 Enable compatibility with iC960 v2.0 or v3.0.
8928 @opindex masm-compat
8930 Enable compatibility with the iC960 assembler.
8932 @item -mstrict-align
8933 @itemx -mno-strict-align
8934 @opindex mstrict-align
8935 @opindex mno-strict-align
8936 Do not permit (do permit) unaligned accesses.
8940 Enable structure-alignment compatibility with Intel's gcc release version
8941 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8943 @item -mlong-double-64
8944 @opindex mlong-double-64
8945 Implement type @samp{long double} as 64-bit floating point numbers.
8946 Without the option @samp{long double} is implemented by 80-bit
8947 floating point numbers. The only reason we have it because there is
8948 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8949 is only useful for people using soft-float targets. Otherwise, we
8950 should recommend against use of it.
8954 @node DEC Alpha Options
8955 @subsection DEC Alpha Options
8957 These @samp{-m} options are defined for the DEC Alpha implementations:
8960 @item -mno-soft-float
8962 @opindex mno-soft-float
8963 @opindex msoft-float
8964 Use (do not use) the hardware floating-point instructions for
8965 floating-point operations. When @option{-msoft-float} is specified,
8966 functions in @file{libgcc.a} will be used to perform floating-point
8967 operations. Unless they are replaced by routines that emulate the
8968 floating-point operations, or compiled in such a way as to call such
8969 emulations routines, these routines will issue floating-point
8970 operations. If you are compiling for an Alpha without floating-point
8971 operations, you must ensure that the library is built so as not to call
8974 Note that Alpha implementations without floating-point operations are
8975 required to have floating-point registers.
8980 @opindex mno-fp-regs
8981 Generate code that uses (does not use) the floating-point register set.
8982 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8983 register set is not used, floating point operands are passed in integer
8984 registers as if they were integers and floating-point results are passed
8985 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8986 so any function with a floating-point argument or return value called by code
8987 compiled with @option{-mno-fp-regs} must also be compiled with that
8990 A typical use of this option is building a kernel that does not use,
8991 and hence need not save and restore, any floating-point registers.
8995 The Alpha architecture implements floating-point hardware optimized for
8996 maximum performance. It is mostly compliant with the IEEE floating
8997 point standard. However, for full compliance, software assistance is
8998 required. This option generates code fully IEEE compliant code
8999 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9000 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9001 defined during compilation. The resulting code is less efficient but is
9002 able to correctly support denormalized numbers and exceptional IEEE
9003 values such as not-a-number and plus/minus infinity. Other Alpha
9004 compilers call this option @option{-ieee_with_no_inexact}.
9006 @item -mieee-with-inexact
9007 @opindex mieee-with-inexact
9008 This is like @option{-mieee} except the generated code also maintains
9009 the IEEE @var{inexact-flag}. Turning on this option causes the
9010 generated code to implement fully-compliant IEEE math. In addition to
9011 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9012 macro. On some Alpha implementations the resulting code may execute
9013 significantly slower than the code generated by default. Since there is
9014 very little code that depends on the @var{inexact-flag}, you should
9015 normally not specify this option. Other Alpha compilers call this
9016 option @option{-ieee_with_inexact}.
9018 @item -mfp-trap-mode=@var{trap-mode}
9019 @opindex mfp-trap-mode
9020 This option controls what floating-point related traps are enabled.
9021 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9022 The trap mode can be set to one of four values:
9026 This is the default (normal) setting. The only traps that are enabled
9027 are the ones that cannot be disabled in software (e.g., division by zero
9031 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9035 Like @samp{su}, but the instructions are marked to be safe for software
9036 completion (see Alpha architecture manual for details).
9039 Like @samp{su}, but inexact traps are enabled as well.
9042 @item -mfp-rounding-mode=@var{rounding-mode}
9043 @opindex mfp-rounding-mode
9044 Selects the IEEE rounding mode. Other Alpha compilers call this option
9045 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9050 Normal IEEE rounding mode. Floating point numbers are rounded towards
9051 the nearest machine number or towards the even machine number in case
9055 Round towards minus infinity.
9058 Chopped rounding mode. Floating point numbers are rounded towards zero.
9061 Dynamic rounding mode. A field in the floating point control register
9062 (@var{fpcr}, see Alpha architecture reference manual) controls the
9063 rounding mode in effect. The C library initializes this register for
9064 rounding towards plus infinity. Thus, unless your program modifies the
9065 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9068 @item -mtrap-precision=@var{trap-precision}
9069 @opindex mtrap-precision
9070 In the Alpha architecture, floating point traps are imprecise. This
9071 means without software assistance it is impossible to recover from a
9072 floating trap and program execution normally needs to be terminated.
9073 GCC can generate code that can assist operating system trap handlers
9074 in determining the exact location that caused a floating point trap.
9075 Depending on the requirements of an application, different levels of
9076 precisions can be selected:
9080 Program precision. This option is the default and means a trap handler
9081 can only identify which program caused a floating point exception.
9084 Function precision. The trap handler can determine the function that
9085 caused a floating point exception.
9088 Instruction precision. The trap handler can determine the exact
9089 instruction that caused a floating point exception.
9092 Other Alpha compilers provide the equivalent options called
9093 @option{-scope_safe} and @option{-resumption_safe}.
9095 @item -mieee-conformant
9096 @opindex mieee-conformant
9097 This option marks the generated code as IEEE conformant. You must not
9098 use this option unless you also specify @option{-mtrap-precision=i} and either
9099 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9100 is to emit the line @samp{.eflag 48} in the function prologue of the
9101 generated assembly file. Under DEC Unix, this has the effect that
9102 IEEE-conformant math library routines will be linked in.
9104 @item -mbuild-constants
9105 @opindex mbuild-constants
9106 Normally GCC examines a 32- or 64-bit integer constant to
9107 see if it can construct it from smaller constants in two or three
9108 instructions. If it cannot, it will output the constant as a literal and
9109 generate code to load it from the data segment at runtime.
9111 Use this option to require GCC to construct @emph{all} integer constants
9112 using code, even if it takes more instructions (the maximum is six).
9114 You would typically use this option to build a shared library dynamic
9115 loader. Itself a shared library, it must relocate itself in memory
9116 before it can find the variables and constants in its own data segment.
9122 Select whether to generate code to be assembled by the vendor-supplied
9123 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9141 Indicate whether GCC should generate code to use the optional BWX,
9142 CIX, FIX and MAX instruction sets. The default is to use the instruction
9143 sets supported by the CPU type specified via @option{-mcpu=} option or that
9144 of the CPU on which GCC was built if none was specified.
9149 @opindex mfloat-ieee
9150 Generate code that uses (does not use) VAX F and G floating point
9151 arithmetic instead of IEEE single and double precision.
9153 @item -mexplicit-relocs
9154 @itemx -mno-explicit-relocs
9155 @opindex mexplicit-relocs
9156 @opindex mno-explicit-relocs
9157 Older Alpha assemblers provided no way to generate symbol relocations
9158 except via assembler macros. Use of these macros does not allow
9159 optimal instruction scheduling. GNU binutils as of version 2.12
9160 supports a new syntax that allows the compiler to explicitly mark
9161 which relocations should apply to which instructions. This option
9162 is mostly useful for debugging, as GCC detects the capabilities of
9163 the assembler when it is built and sets the default accordingly.
9167 @opindex msmall-data
9168 @opindex mlarge-data
9169 When @option{-mexplicit-relocs} is in effect, static data is
9170 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9171 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9172 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9173 16-bit relocations off of the @code{$gp} register. This limits the
9174 size of the small data area to 64KB, but allows the variables to be
9175 directly accessed via a single instruction.
9177 The default is @option{-mlarge-data}. With this option the data area
9178 is limited to just below 2GB. Programs that require more than 2GB of
9179 data must use @code{malloc} or @code{mmap} to allocate the data in the
9180 heap instead of in the program's data segment.
9182 When generating code for shared libraries, @option{-fpic} implies
9183 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9187 @opindex msmall-text
9188 @opindex mlarge-text
9189 When @option{-msmall-text} is used, the compiler assumes that the
9190 code of the entire program (or shared library) fits in 4MB, and is
9191 thus reachable with a branch instruction. When @option{-msmall-data}
9192 is used, the compiler can assume that all local symbols share the
9193 same @code{$gp} value, and thus reduce the number of instructions
9194 required for a function call from 4 to 1.
9196 The default is @option{-mlarge-text}.
9198 @item -mcpu=@var{cpu_type}
9200 Set the instruction set and instruction scheduling parameters for
9201 machine type @var{cpu_type}. You can specify either the @samp{EV}
9202 style name or the corresponding chip number. GCC supports scheduling
9203 parameters for the EV4, EV5 and EV6 family of processors and will
9204 choose the default values for the instruction set from the processor
9205 you specify. If you do not specify a processor type, GCC will default
9206 to the processor on which the compiler was built.
9208 Supported values for @var{cpu_type} are
9214 Schedules as an EV4 and has no instruction set extensions.
9218 Schedules as an EV5 and has no instruction set extensions.
9222 Schedules as an EV5 and supports the BWX extension.
9227 Schedules as an EV5 and supports the BWX and MAX extensions.
9231 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9235 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9238 @item -mtune=@var{cpu_type}
9240 Set only the instruction scheduling parameters for machine type
9241 @var{cpu_type}. The instruction set is not changed.
9243 @item -mmemory-latency=@var{time}
9244 @opindex mmemory-latency
9245 Sets the latency the scheduler should assume for typical memory
9246 references as seen by the application. This number is highly
9247 dependent on the memory access patterns used by the application
9248 and the size of the external cache on the machine.
9250 Valid options for @var{time} are
9254 A decimal number representing clock cycles.
9260 The compiler contains estimates of the number of clock cycles for
9261 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9262 (also called Dcache, Scache, and Bcache), as well as to main memory.
9263 Note that L3 is only valid for EV5.
9268 @node DEC Alpha/VMS Options
9269 @subsection DEC Alpha/VMS Options
9271 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9274 @item -mvms-return-codes
9275 @opindex mvms-return-codes
9276 Return VMS condition codes from main. The default is to return POSIX
9277 style condition (e.g.@ error) codes.
9280 @node H8/300 Options
9281 @subsection H8/300 Options
9283 These @samp{-m} options are defined for the H8/300 implementations:
9288 Shorten some address references at link time, when possible; uses the
9289 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9290 ld.info, Using ld}, for a fuller description.
9294 Generate code for the H8/300H@.
9298 Generate code for the H8S@.
9302 Generate code for the H8S and H8/300H in the normal mode. This switch
9303 must be used either with -mh or -ms.
9307 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9311 Make @code{int} data 32 bits by default.
9315 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9316 The default for the H8/300H and H8S is to align longs and floats on 4
9318 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9319 This option has no effect on the H8/300.
9323 @subsection SH Options
9325 These @samp{-m} options are defined for the SH implementations:
9330 Generate code for the SH1.
9334 Generate code for the SH2.
9337 Generate code for the SH2e.
9341 Generate code for the SH3.
9345 Generate code for the SH3e.
9349 Generate code for the SH4 without a floating-point unit.
9351 @item -m4-single-only
9352 @opindex m4-single-only
9353 Generate code for the SH4 with a floating-point unit that only
9354 supports single-precision arithmetic.
9358 Generate code for the SH4 assuming the floating-point unit is in
9359 single-precision mode by default.
9363 Generate code for the SH4.
9367 Compile code for the processor in big endian mode.
9371 Compile code for the processor in little endian mode.
9375 Align doubles at 64-bit boundaries. Note that this changes the calling
9376 conventions, and thus some functions from the standard C library will
9377 not work unless you recompile it first with @option{-mdalign}.
9381 Shorten some address references at link time, when possible; uses the
9382 linker option @option{-relax}.
9386 Use 32-bit offsets in @code{switch} tables. The default is to use
9391 Enable the use of the instruction @code{fmovd}.
9395 Comply with the calling conventions defined by Renesas.
9399 Mark the @code{MAC} register as call-clobbered, even if
9400 @option{-mhitachi} is given.
9404 Increase IEEE-compliance of floating-point code.
9408 Dump instruction size and location in the assembly code.
9412 This option is deprecated. It pads structures to multiple of 4 bytes,
9413 which is incompatible with the SH ABI@.
9417 Optimize for space instead of speed. Implied by @option{-Os}.
9421 When generating position-independent code, emit function calls using
9422 the Global Offset Table instead of the Procedure Linkage Table.
9426 Generate a library function call to invalidate instruction cache
9427 entries, after fixing up a trampoline. This library function call
9428 doesn't assume it can write to the whole memory address space. This
9429 is the default when the target is @code{sh-*-linux*}.
9432 @node System V Options
9433 @subsection Options for System V
9435 These additional options are available on System V Release 4 for
9436 compatibility with other compilers on those systems:
9441 Create a shared object.
9442 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
9446 Identify the versions of each tool used by the compiler, in a
9447 @code{.ident} assembler directive in the output.
9451 Refrain from adding @code{.ident} directives to the output file (this is
9454 @item -YP,@var{dirs}
9456 Search the directories @var{dirs}, and no others, for libraries
9457 specified with @option{-l}.
9461 Look in the directory @var{dir} to find the M4 preprocessor.
9462 The assembler uses this option.
9463 @c This is supposed to go with a -Yd for predefined M4 macro files, but
9464 @c the generic assembler that comes with Solaris takes just -Ym.
9467 @node TMS320C3x/C4x Options
9468 @subsection TMS320C3x/C4x Options
9469 @cindex TMS320C3x/C4x Options
9471 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
9475 @item -mcpu=@var{cpu_type}
9477 Set the instruction set, register set, and instruction scheduling
9478 parameters for machine type @var{cpu_type}. Supported values for
9479 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
9480 @samp{c44}. The default is @samp{c40} to generate code for the
9485 @itemx -msmall-memory
9487 @opindex mbig-memory
9489 @opindex msmall-memory
9491 Generates code for the big or small memory model. The small memory
9492 model assumed that all data fits into one 64K word page. At run-time
9493 the data page (DP) register must be set to point to the 64K page
9494 containing the .bss and .data program sections. The big memory model is
9495 the default and requires reloading of the DP register for every direct
9502 Allow (disallow) allocation of general integer operands into the block
9509 Enable (disable) generation of code using decrement and branch,
9510 DBcond(D), instructions. This is enabled by default for the C4x. To be
9511 on the safe side, this is disabled for the C3x, since the maximum
9512 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
9513 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
9514 that it can utilize the decrement and branch instruction, but will give
9515 up if there is more than one memory reference in the loop. Thus a loop
9516 where the loop counter is decremented can generate slightly more
9517 efficient code, in cases where the RPTB instruction cannot be utilized.
9519 @item -mdp-isr-reload
9521 @opindex mdp-isr-reload
9523 Force the DP register to be saved on entry to an interrupt service
9524 routine (ISR), reloaded to point to the data section, and restored on
9525 exit from the ISR@. This should not be required unless someone has
9526 violated the small memory model by modifying the DP register, say within
9533 For the C3x use the 24-bit MPYI instruction for integer multiplies
9534 instead of a library call to guarantee 32-bit results. Note that if one
9535 of the operands is a constant, then the multiplication will be performed
9536 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
9537 then squaring operations are performed inline instead of a library call.
9540 @itemx -mno-fast-fix
9542 @opindex mno-fast-fix
9543 The C3x/C4x FIX instruction to convert a floating point value to an
9544 integer value chooses the nearest integer less than or equal to the
9545 floating point value rather than to the nearest integer. Thus if the
9546 floating point number is negative, the result will be incorrectly
9547 truncated an additional code is necessary to detect and correct this
9548 case. This option can be used to disable generation of the additional
9549 code required to correct the result.
9555 Enable (disable) generation of repeat block sequences using the RPTB
9556 instruction for zero overhead looping. The RPTB construct is only used
9557 for innermost loops that do not call functions or jump across the loop
9558 boundaries. There is no advantage having nested RPTB loops due to the
9559 overhead required to save and restore the RC, RS, and RE registers.
9560 This is enabled by default with @option{-O2}.
9562 @item -mrpts=@var{count}
9566 Enable (disable) the use of the single instruction repeat instruction
9567 RPTS@. If a repeat block contains a single instruction, and the loop
9568 count can be guaranteed to be less than the value @var{count}, GCC will
9569 emit a RPTS instruction instead of a RPTB@. If no value is specified,
9570 then a RPTS will be emitted even if the loop count cannot be determined
9571 at compile time. Note that the repeated instruction following RPTS does
9572 not have to be reloaded from memory each iteration, thus freeing up the
9573 CPU buses for operands. However, since interrupts are blocked by this
9574 instruction, it is disabled by default.
9576 @item -mloop-unsigned
9577 @itemx -mno-loop-unsigned
9578 @opindex mloop-unsigned
9579 @opindex mno-loop-unsigned
9580 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
9581 is @math{2^{31} + 1} since these instructions test if the iteration count is
9582 negative to terminate the loop. If the iteration count is unsigned
9583 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
9584 exceeded. This switch allows an unsigned iteration count.
9588 Try to emit an assembler syntax that the TI assembler (asm30) is happy
9589 with. This also enforces compatibility with the API employed by the TI
9590 C3x C compiler. For example, long doubles are passed as structures
9591 rather than in floating point registers.
9597 Generate code that uses registers (stack) for passing arguments to functions.
9598 By default, arguments are passed in registers where possible rather
9599 than by pushing arguments on to the stack.
9601 @item -mparallel-insns
9602 @itemx -mno-parallel-insns
9603 @opindex mparallel-insns
9604 @opindex mno-parallel-insns
9605 Allow the generation of parallel instructions. This is enabled by
9606 default with @option{-O2}.
9608 @item -mparallel-mpy
9609 @itemx -mno-parallel-mpy
9610 @opindex mparallel-mpy
9611 @opindex mno-parallel-mpy
9612 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
9613 provided @option{-mparallel-insns} is also specified. These instructions have
9614 tight register constraints which can pessimize the code generation
9620 @subsection V850 Options
9621 @cindex V850 Options
9623 These @samp{-m} options are defined for V850 implementations:
9627 @itemx -mno-long-calls
9628 @opindex mlong-calls
9629 @opindex mno-long-calls
9630 Treat all calls as being far away (near). If calls are assumed to be
9631 far away, the compiler will always load the functions address up into a
9632 register, and call indirect through the pointer.
9638 Do not optimize (do optimize) basic blocks that use the same index
9639 pointer 4 or more times to copy pointer into the @code{ep} register, and
9640 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
9641 option is on by default if you optimize.
9643 @item -mno-prolog-function
9644 @itemx -mprolog-function
9645 @opindex mno-prolog-function
9646 @opindex mprolog-function
9647 Do not use (do use) external functions to save and restore registers
9648 at the prologue and epilogue of a function. The external functions
9649 are slower, but use less code space if more than one function saves
9650 the same number of registers. The @option{-mprolog-function} option
9651 is on by default if you optimize.
9655 Try to make the code as small as possible. At present, this just turns
9656 on the @option{-mep} and @option{-mprolog-function} options.
9660 Put static or global variables whose size is @var{n} bytes or less into
9661 the tiny data area that register @code{ep} points to. The tiny data
9662 area can hold up to 256 bytes in total (128 bytes for byte references).
9666 Put static or global variables whose size is @var{n} bytes or less into
9667 the small data area that register @code{gp} points to. The small data
9668 area can hold up to 64 kilobytes.
9672 Put static or global variables whose size is @var{n} bytes or less into
9673 the first 32 kilobytes of memory.
9677 Specify that the target processor is the V850.
9680 @opindex mbig-switch
9681 Generate code suitable for big switch tables. Use this option only if
9682 the assembler/linker complain about out of range branches within a switch
9687 This option will cause r2 and r5 to be used in the code generated by
9688 the compiler. This setting is the default.
9691 @opindex mno-app-regs
9692 This option will cause r2 and r5 to be treated as fixed registers.
9696 Specify that the target processor is the V850E1. The preprocessor
9697 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
9698 this option is used.
9702 Specify that the target processor is the V850E. The preprocessor
9703 constant @samp{__v850e__} will be defined if this option is used.
9705 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
9706 are defined then a default target processor will be chosen and the
9707 relevant @samp{__v850*__} preprocessor constant will be defined.
9709 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
9710 defined, regardless of which processor variant is the target.
9712 @item -mdisable-callt
9713 @opindex mdisable-callt
9714 This option will suppress generation of the CALLT instruction for the
9715 v850e and v850e1 flavors of the v850 architecture. The default is
9716 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
9721 @subsection ARC Options
9724 These options are defined for ARC implementations:
9729 Compile code for little endian mode. This is the default.
9733 Compile code for big endian mode.
9736 @opindex mmangle-cpu
9737 Prepend the name of the cpu to all public symbol names.
9738 In multiple-processor systems, there are many ARC variants with different
9739 instruction and register set characteristics. This flag prevents code
9740 compiled for one cpu to be linked with code compiled for another.
9741 No facility exists for handling variants that are ``almost identical''.
9742 This is an all or nothing option.
9744 @item -mcpu=@var{cpu}
9746 Compile code for ARC variant @var{cpu}.
9747 Which variants are supported depend on the configuration.
9748 All variants support @option{-mcpu=base}, this is the default.
9750 @item -mtext=@var{text-section}
9751 @itemx -mdata=@var{data-section}
9752 @itemx -mrodata=@var{readonly-data-section}
9756 Put functions, data, and readonly data in @var{text-section},
9757 @var{data-section}, and @var{readonly-data-section} respectively
9758 by default. This can be overridden with the @code{section} attribute.
9759 @xref{Variable Attributes}.
9764 @subsection NS32K Options
9765 @cindex NS32K options
9767 These are the @samp{-m} options defined for the 32000 series. The default
9768 values for these options depends on which style of 32000 was selected when
9769 the compiler was configured; the defaults for the most common choices are
9777 Generate output for a 32032. This is the default
9778 when the compiler is configured for 32032 and 32016 based systems.
9784 Generate output for a 32332. This is the default
9785 when the compiler is configured for 32332-based systems.
9791 Generate output for a 32532. This is the default
9792 when the compiler is configured for 32532-based systems.
9796 Generate output containing 32081 instructions for floating point.
9797 This is the default for all systems.
9801 Generate output containing 32381 instructions for floating point. This
9802 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9803 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9807 Try and generate multiply-add floating point instructions @code{polyF}
9808 and @code{dotF}. This option is only available if the @option{-m32381}
9809 option is in effect. Using these instructions requires changes to
9810 register allocation which generally has a negative impact on
9811 performance. This option should only be enabled when compiling code
9812 particularly likely to make heavy use of multiply-add instructions.
9815 @opindex mnomulti-add
9816 Do not try and generate multiply-add floating point instructions
9817 @code{polyF} and @code{dotF}. This is the default on all platforms.
9820 @opindex msoft-float
9821 Generate output containing library calls for floating point.
9822 @strong{Warning:} the requisite libraries may not be available.
9824 @item -mieee-compare
9825 @itemx -mno-ieee-compare
9826 @opindex mieee-compare
9827 @opindex mno-ieee-compare
9828 Control whether or not the compiler uses IEEE floating point
9829 comparisons. These handle correctly the case where the result of a
9830 comparison is unordered.
9831 @strong{Warning:} the requisite kernel support may not be available.
9834 @opindex mnobitfield
9835 Do not use the bit-field instructions. On some machines it is faster to
9836 use shifting and masking operations. This is the default for the pc532.
9840 Do use the bit-field instructions. This is the default for all platforms
9845 Use a different function-calling convention, in which functions
9846 that take a fixed number of arguments return pop their
9847 arguments on return with the @code{ret} instruction.
9849 This calling convention is incompatible with the one normally
9850 used on Unix, so you cannot use it if you need to call libraries
9851 compiled with the Unix compiler.
9853 Also, you must provide function prototypes for all functions that
9854 take variable numbers of arguments (including @code{printf});
9855 otherwise incorrect code will be generated for calls to those
9858 In addition, seriously incorrect code will result if you call a
9859 function with too many arguments. (Normally, extra arguments are
9860 harmlessly ignored.)
9862 This option takes its name from the 680x0 @code{rtd} instruction.
9867 Use a different function-calling convention where the first two arguments
9868 are passed in registers.
9870 This calling convention is incompatible with the one normally
9871 used on Unix, so you cannot use it if you need to call libraries
9872 compiled with the Unix compiler.
9875 @opindex mnoregparam
9876 Do not pass any arguments in registers. This is the default for all
9881 It is OK to use the sb as an index register which is always loaded with
9882 zero. This is the default for the pc532-netbsd target.
9886 The sb register is not available for use or has not been initialized to
9887 zero by the run time system. This is the default for all targets except
9888 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9889 @option{-fpic} is set.
9893 Many ns32000 series addressing modes use displacements of up to 512MB@.
9894 If an address is above 512MB then displacements from zero can not be used.
9895 This option causes code to be generated which can be loaded above 512MB@.
9896 This may be useful for operating systems or ROM code.
9900 Assume code will be loaded in the first 512MB of virtual address space.
9901 This is the default for all platforms.
9907 @subsection AVR Options
9910 These options are defined for AVR implementations:
9913 @item -mmcu=@var{mcu}
9915 Specify ATMEL AVR instruction set or MCU type.
9917 Instruction set avr1 is for the minimal AVR core, not supported by the C
9918 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9919 attiny11, attiny12, attiny15, attiny28).
9921 Instruction set avr2 (default) is for the classic AVR core with up to
9922 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9923 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9924 at90c8534, at90s8535).
9926 Instruction set avr3 is for the classic AVR core with up to 128K program
9927 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9929 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9930 memory space (MCU types: atmega8, atmega83, atmega85).
9932 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9933 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9934 atmega64, atmega128, at43usb355, at94k).
9938 Output instruction sizes to the asm file.
9940 @item -minit-stack=@var{N}
9941 @opindex minit-stack
9942 Specify the initial stack address, which may be a symbol or numeric value,
9943 @samp{__stack} is the default.
9945 @item -mno-interrupts
9946 @opindex mno-interrupts
9947 Generated code is not compatible with hardware interrupts.
9948 Code size will be smaller.
9950 @item -mcall-prologues
9951 @opindex mcall-prologues
9952 Functions prologues/epilogues expanded as call to appropriate
9953 subroutines. Code size will be smaller.
9955 @item -mno-tablejump
9956 @opindex mno-tablejump
9957 Do not generate tablejump insns which sometimes increase code size.
9960 @opindex mtiny-stack
9961 Change only the low 8 bits of the stack pointer.
9965 @subsection MCore Options
9966 @cindex MCore options
9968 These are the @samp{-m} options defined for the Motorola M*Core
9976 @opindex mno-hardlit
9977 Inline constants into the code stream if it can be done in two
9978 instructions or less.
9984 Use the divide instruction. (Enabled by default).
9986 @item -mrelax-immediate
9987 @itemx -mno-relax-immediate
9988 @opindex mrelax-immediate
9989 @opindex mno-relax-immediate
9990 Allow arbitrary sized immediates in bit operations.
9992 @item -mwide-bitfields
9993 @itemx -mno-wide-bitfields
9994 @opindex mwide-bitfields
9995 @opindex mno-wide-bitfields
9996 Always treat bit-fields as int-sized.
9998 @item -m4byte-functions
9999 @itemx -mno-4byte-functions
10000 @opindex m4byte-functions
10001 @opindex mno-4byte-functions
10002 Force all functions to be aligned to a four byte boundary.
10004 @item -mcallgraph-data
10005 @itemx -mno-callgraph-data
10006 @opindex mcallgraph-data
10007 @opindex mno-callgraph-data
10008 Emit callgraph information.
10011 @itemx -mno-slow-bytes
10012 @opindex mslow-bytes
10013 @opindex mno-slow-bytes
10014 Prefer word access when reading byte quantities.
10016 @item -mlittle-endian
10017 @itemx -mbig-endian
10018 @opindex mlittle-endian
10019 @opindex mbig-endian
10020 Generate code for a little endian target.
10026 Generate code for the 210 processor.
10029 @node IA-64 Options
10030 @subsection IA-64 Options
10031 @cindex IA-64 Options
10033 These are the @samp{-m} options defined for the Intel IA-64 architecture.
10037 @opindex mbig-endian
10038 Generate code for a big endian target. This is the default for HP-UX@.
10040 @item -mlittle-endian
10041 @opindex mlittle-endian
10042 Generate code for a little endian target. This is the default for AIX5
10048 @opindex mno-gnu-as
10049 Generate (or don't) code for the GNU assembler. This is the default.
10050 @c Also, this is the default if the configure option @option{--with-gnu-as}
10056 @opindex mno-gnu-ld
10057 Generate (or don't) code for the GNU linker. This is the default.
10058 @c Also, this is the default if the configure option @option{--with-gnu-ld}
10063 Generate code that does not use a global pointer register. The result
10064 is not position independent code, and violates the IA-64 ABI@.
10066 @item -mvolatile-asm-stop
10067 @itemx -mno-volatile-asm-stop
10068 @opindex mvolatile-asm-stop
10069 @opindex mno-volatile-asm-stop
10070 Generate (or don't) a stop bit immediately before and after volatile asm
10075 Generate code that works around Itanium B step errata.
10077 @item -mregister-names
10078 @itemx -mno-register-names
10079 @opindex mregister-names
10080 @opindex mno-register-names
10081 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
10082 the stacked registers. This may make assembler output more readable.
10088 Disable (or enable) optimizations that use the small data section. This may
10089 be useful for working around optimizer bugs.
10091 @item -mconstant-gp
10092 @opindex mconstant-gp
10093 Generate code that uses a single constant global pointer value. This is
10094 useful when compiling kernel code.
10098 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
10099 This is useful when compiling firmware code.
10101 @item -minline-float-divide-min-latency
10102 @opindex minline-float-divide-min-latency
10103 Generate code for inline divides of floating point values
10104 using the minimum latency algorithm.
10106 @item -minline-float-divide-max-throughput
10107 @opindex minline-float-divide-max-throughput
10108 Generate code for inline divides of floating point values
10109 using the maximum throughput algorithm.
10111 @item -minline-int-divide-min-latency
10112 @opindex minline-int-divide-min-latency
10113 Generate code for inline divides of integer values
10114 using the minimum latency algorithm.
10116 @item -minline-int-divide-max-throughput
10117 @opindex minline-int-divide-max-throughput
10118 Generate code for inline divides of integer values
10119 using the maximum throughput algorithm.
10121 @item -mno-dwarf2-asm
10122 @itemx -mdwarf2-asm
10123 @opindex mno-dwarf2-asm
10124 @opindex mdwarf2-asm
10125 Don't (or do) generate assembler code for the DWARF2 line number debugging
10126 info. This may be useful when not using the GNU assembler.
10128 @item -mfixed-range=@var{register-range}
10129 @opindex mfixed-range
10130 Generate code treating the given register range as fixed registers.
10131 A fixed register is one that the register allocator can not use. This is
10132 useful when compiling kernel code. A register range is specified as
10133 two registers separated by a dash. Multiple register ranges can be
10134 specified separated by a comma.
10136 @item -mearly-stop-bits
10137 @itemx -mno-early-stop-bits
10138 @opindex mearly-stop-bits
10139 @opindex mno-early-stop-bits
10140 Allow stop bits to be placed earlier than immediately preceding the
10141 instruction that triggered the stop bit. This can improve instruction
10142 scheduling, but does not always do so.
10146 @subsection D30V Options
10147 @cindex D30V Options
10149 These @samp{-m} options are defined for D30V implementations:
10154 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
10155 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
10156 memory, which starts at location @code{0x80000000}.
10159 @opindex mextmemory
10160 Same as the @option{-mextmem} switch.
10164 Link the @samp{.text} section into onchip text memory, which starts at
10165 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
10166 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
10167 into onchip data memory, which starts at location @code{0x20000000}.
10169 @item -mno-asm-optimize
10170 @itemx -masm-optimize
10171 @opindex mno-asm-optimize
10172 @opindex masm-optimize
10173 Disable (enable) passing @option{-O} to the assembler when optimizing.
10174 The assembler uses the @option{-O} option to automatically parallelize
10175 adjacent short instructions where possible.
10177 @item -mbranch-cost=@var{n}
10178 @opindex mbranch-cost
10179 Increase the internal costs of branches to @var{n}. Higher costs means
10180 that the compiler will issue more instructions to avoid doing a branch.
10183 @item -mcond-exec=@var{n}
10184 @opindex mcond-exec
10185 Specify the maximum number of conditionally executed instructions that
10186 replace a branch. The default is 4.
10189 @node S/390 and zSeries Options
10190 @subsection S/390 and zSeries Options
10191 @cindex S/390 and zSeries Options
10193 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10197 @itemx -msoft-float
10198 @opindex mhard-float
10199 @opindex msoft-float
10200 Use (do not use) the hardware floating-point instructions and registers
10201 for floating-point operations. When @option{-msoft-float} is specified,
10202 functions in @file{libgcc.a} will be used to perform floating-point
10203 operations. When @option{-mhard-float} is specified, the compiler
10204 generates IEEE floating-point instructions. This is the default.
10207 @itemx -mno-backchain
10208 @opindex mbackchain
10209 @opindex mno-backchain
10210 Generate (or do not generate) code which maintains an explicit
10211 backchain within the stack frame that points to the caller's frame.
10212 This is currently needed to allow debugging. The default is to
10213 generate the backchain.
10216 @itemx -mno-small-exec
10217 @opindex msmall-exec
10218 @opindex mno-small-exec
10219 Generate (or do not generate) code using the @code{bras} instruction
10220 to do subroutine calls.
10221 This only works reliably if the total executable size does not
10222 exceed 64k. The default is to use the @code{basr} instruction instead,
10223 which does not have this limitation.
10229 When @option{-m31} is specified, generate code compliant to the
10230 Linux for S/390 ABI@. When @option{-m64} is specified, generate
10231 code compliant to the Linux for zSeries ABI@. This allows GCC in
10232 particular to generate 64-bit instructions. For the @samp{s390}
10233 targets, the default is @option{-m31}, while the @samp{s390x}
10234 targets default to @option{-m64}.
10240 When @option{-mzarch} is specified, generate code using the
10241 instructions available on z/Architecture.
10242 When @option{-mesa} is specified, generate code using the
10243 instructions available on ESA/390. Note that @option{-mesa} is
10244 not possible with @option{-m64}.
10245 When generating code compliant to the Linux for S/390 ABI,
10246 the default is @option{-mesa}. When generating code compliant
10247 to the Linux for zSeries ABI, the default is @option{-mzarch}.
10253 Generate (or do not generate) code using the @code{mvcle} instruction
10254 to perform block moves. When @option{-mno-mvcle} is specified,
10255 use a @code{mvc} loop instead. This is the default.
10261 Print (or do not print) additional debug information when compiling.
10262 The default is to not print debug information.
10264 @item -march=@var{cpu-type}
10266 Generate code that will run on @var{cpu-type}, which is the name of a system
10267 representing a certain processor type. Possible values for
10268 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10269 When generating code using the instructions available on z/Architecture,
10270 the default is @option{-march=z900}. Otherwise, the default is
10271 @option{-march=g5}.
10273 @item -mtune=@var{cpu-type}
10275 Tune to @var{cpu-type} everything applicable about the generated code,
10276 except for the ABI and the set of available instructions.
10277 The list of @var{cpu-type} values is the same as for @option{-march}.
10278 The default is the value used for @option{-march}.
10283 @subsection CRIS Options
10284 @cindex CRIS Options
10286 These options are defined specifically for the CRIS ports.
10289 @item -march=@var{architecture-type}
10290 @itemx -mcpu=@var{architecture-type}
10293 Generate code for the specified architecture. The choices for
10294 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10295 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
10296 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10299 @item -mtune=@var{architecture-type}
10301 Tune to @var{architecture-type} everything applicable about the generated
10302 code, except for the ABI and the set of available instructions. The
10303 choices for @var{architecture-type} are the same as for
10304 @option{-march=@var{architecture-type}}.
10306 @item -mmax-stack-frame=@var{n}
10307 @opindex mmax-stack-frame
10308 Warn when the stack frame of a function exceeds @var{n} bytes.
10310 @item -melinux-stacksize=@var{n}
10311 @opindex melinux-stacksize
10312 Only available with the @samp{cris-axis-aout} target. Arranges for
10313 indications in the program to the kernel loader that the stack of the
10314 program should be set to @var{n} bytes.
10320 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10321 @option{-march=v3} and @option{-march=v8} respectively.
10325 Enable CRIS-specific verbose debug-related information in the assembly
10326 code. This option also has the effect to turn off the @samp{#NO_APP}
10327 formatted-code indicator to the assembler at the beginning of the
10332 Do not use condition-code results from previous instruction; always emit
10333 compare and test instructions before use of condition codes.
10335 @item -mno-side-effects
10336 @opindex mno-side-effects
10337 Do not emit instructions with side-effects in addressing modes other than
10340 @item -mstack-align
10341 @itemx -mno-stack-align
10342 @itemx -mdata-align
10343 @itemx -mno-data-align
10344 @itemx -mconst-align
10345 @itemx -mno-const-align
10346 @opindex mstack-align
10347 @opindex mno-stack-align
10348 @opindex mdata-align
10349 @opindex mno-data-align
10350 @opindex mconst-align
10351 @opindex mno-const-align
10352 These options (no-options) arranges (eliminate arrangements) for the
10353 stack-frame, individual data and constants to be aligned for the maximum
10354 single data access size for the chosen CPU model. The default is to
10355 arrange for 32-bit alignment. ABI details such as structure layout are
10356 not affected by these options.
10364 Similar to the stack- data- and const-align options above, these options
10365 arrange for stack-frame, writable data and constants to all be 32-bit,
10366 16-bit or 8-bit aligned. The default is 32-bit alignment.
10368 @item -mno-prologue-epilogue
10369 @itemx -mprologue-epilogue
10370 @opindex mno-prologue-epilogue
10371 @opindex mprologue-epilogue
10372 With @option{-mno-prologue-epilogue}, the normal function prologue and
10373 epilogue that sets up the stack-frame are omitted and no return
10374 instructions or return sequences are generated in the code. Use this
10375 option only together with visual inspection of the compiled code: no
10376 warnings or errors are generated when call-saved registers must be saved,
10377 or storage for local variable needs to be allocated.
10381 @opindex mno-gotplt
10383 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10384 instruction sequences that load addresses for functions from the PLT part
10385 of the GOT rather than (traditional on other architectures) calls to the
10386 PLT. The default is @option{-mgotplt}.
10390 Legacy no-op option only recognized with the cris-axis-aout target.
10394 Legacy no-op option only recognized with the cris-axis-elf and
10395 cris-axis-linux-gnu targets.
10399 Only recognized with the cris-axis-aout target, where it selects a
10400 GNU/linux-like multilib, include files and instruction set for
10401 @option{-march=v8}.
10405 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10409 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
10410 to link with input-output functions from a simulator library. Code,
10411 initialized data and zero-initialized data are allocated consecutively.
10415 Like @option{-sim}, but pass linker options to locate initialized data at
10416 0x40000000 and zero-initialized data at 0x80000000.
10420 @subsection MMIX Options
10421 @cindex MMIX Options
10423 These options are defined for the MMIX:
10427 @itemx -mno-libfuncs
10429 @opindex mno-libfuncs
10430 Specify that intrinsic library functions are being compiled, passing all
10431 values in registers, no matter the size.
10434 @itemx -mno-epsilon
10436 @opindex mno-epsilon
10437 Generate floating-point comparison instructions that compare with respect
10438 to the @code{rE} epsilon register.
10440 @item -mabi=mmixware
10442 @opindex mabi-mmixware
10444 Generate code that passes function parameters and return values that (in
10445 the called function) are seen as registers @code{$0} and up, as opposed to
10446 the GNU ABI which uses global registers @code{$231} and up.
10448 @item -mzero-extend
10449 @itemx -mno-zero-extend
10450 @opindex mzero-extend
10451 @opindex mno-zero-extend
10452 When reading data from memory in sizes shorter than 64 bits, use (do not
10453 use) zero-extending load instructions by default, rather than
10454 sign-extending ones.
10457 @itemx -mno-knuthdiv
10459 @opindex mno-knuthdiv
10460 Make the result of a division yielding a remainder have the same sign as
10461 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10462 remainder follows the sign of the dividend. Both methods are
10463 arithmetically valid, the latter being almost exclusively used.
10465 @item -mtoplevel-symbols
10466 @itemx -mno-toplevel-symbols
10467 @opindex mtoplevel-symbols
10468 @opindex mno-toplevel-symbols
10469 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10470 code can be used with the @code{PREFIX} assembly directive.
10474 Generate an executable in the ELF format, rather than the default
10475 @samp{mmo} format used by the @command{mmix} simulator.
10477 @item -mbranch-predict
10478 @itemx -mno-branch-predict
10479 @opindex mbranch-predict
10480 @opindex mno-branch-predict
10481 Use (do not use) the probable-branch instructions, when static branch
10482 prediction indicates a probable branch.
10484 @item -mbase-addresses
10485 @itemx -mno-base-addresses
10486 @opindex mbase-addresses
10487 @opindex mno-base-addresses
10488 Generate (do not generate) code that uses @emph{base addresses}. Using a
10489 base address automatically generates a request (handled by the assembler
10490 and the linker) for a constant to be set up in a global register. The
10491 register is used for one or more base address requests within the range 0
10492 to 255 from the value held in the register. The generally leads to short
10493 and fast code, but the number of different data items that can be
10494 addressed is limited. This means that a program that uses lots of static
10495 data may require @option{-mno-base-addresses}.
10497 @item -msingle-exit
10498 @itemx -mno-single-exit
10499 @opindex msingle-exit
10500 @opindex mno-single-exit
10501 Force (do not force) generated code to have a single exit point in each
10505 @node PDP-11 Options
10506 @subsection PDP-11 Options
10507 @cindex PDP-11 Options
10509 These options are defined for the PDP-11:
10514 Use hardware FPP floating point. This is the default. (FIS floating
10515 point on the PDP-11/40 is not supported.)
10518 @opindex msoft-float
10519 Do not use hardware floating point.
10523 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10527 Return floating-point results in memory. This is the default.
10531 Generate code for a PDP-11/40.
10535 Generate code for a PDP-11/45. This is the default.
10539 Generate code for a PDP-11/10.
10541 @item -mbcopy-builtin
10542 @opindex bcopy-builtin
10543 Use inline @code{movstrhi} patterns for copying memory. This is the
10548 Do not use inline @code{movstrhi} patterns for copying memory.
10554 Use 16-bit @code{int}. This is the default.
10560 Use 32-bit @code{int}.
10563 @itemx -mno-float32
10565 @opindex mno-float32
10566 Use 64-bit @code{float}. This is the default.
10571 @opindex mno-float64
10572 Use 32-bit @code{float}.
10576 Use @code{abshi2} pattern. This is the default.
10580 Do not use @code{abshi2} pattern.
10582 @item -mbranch-expensive
10583 @opindex mbranch-expensive
10584 Pretend that branches are expensive. This is for experimenting with
10585 code generation only.
10587 @item -mbranch-cheap
10588 @opindex mbranch-cheap
10589 Do not pretend that branches are expensive. This is the default.
10593 Generate code for a system with split I&D.
10597 Generate code for a system without split I&D. This is the default.
10601 Use Unix assembler syntax. This is the default when configured for
10602 @samp{pdp11-*-bsd}.
10606 Use DEC assembler syntax. This is the default when configured for any
10607 PDP-11 target other than @samp{pdp11-*-bsd}.
10610 @node Xstormy16 Options
10611 @subsection Xstormy16 Options
10612 @cindex Xstormy16 Options
10614 These options are defined for Xstormy16:
10619 Choose startup files and linker script suitable for the simulator.
10623 @subsection FRV Options
10624 @cindex FRV Options
10630 Only use the first 32 general purpose registers.
10635 Use all 64 general purpose registers.
10640 Use only the first 32 floating point registers.
10645 Use all 64 floating point registers
10648 @opindex mhard-float
10650 Use hardware instructions for floating point operations.
10653 @opindex msoft-float
10655 Use library routines for floating point operations.
10660 Dynamically allocate condition code registers.
10665 Do not try to dynamically allocate condition code registers, only
10666 use @code{icc0} and @code{fcc0}.
10671 Change ABI to use double word insns.
10676 Do not use double word instructions.
10681 Use floating point double instructions.
10684 @opindex mno-double
10686 Do not use floating point double instructions.
10691 Use media instructions.
10696 Do not use media instructions.
10701 Use multiply and add/subtract instructions.
10704 @opindex mno-muladd
10706 Do not use multiply and add/subtract instructions.
10708 @item -mlibrary-pic
10709 @opindex mlibrary-pic
10711 Enable PIC support for building libraries
10716 Use only the first four media accumulator registers.
10721 Use all eight media accumulator registers.
10726 Pack VLIW instructions.
10731 Do not pack VLIW instructions.
10734 @opindex mno-eflags
10736 Do not mark ABI switches in e_flags.
10739 @opindex mcond-move
10741 Enable the use of conditional-move instructions (default).
10743 This switch is mainly for debugging the compiler and will likely be removed
10744 in a future version.
10746 @item -mno-cond-move
10747 @opindex mno-cond-move
10749 Disable the use of conditional-move instructions.
10751 This switch is mainly for debugging the compiler and will likely be removed
10752 in a future version.
10757 Enable the use of conditional set instructions (default).
10759 This switch is mainly for debugging the compiler and will likely be removed
10760 in a future version.
10765 Disable the use of conditional set instructions.
10767 This switch is mainly for debugging the compiler and will likely be removed
10768 in a future version.
10771 @opindex mcond-exec
10773 Enable the use of conditional execution (default).
10775 This switch is mainly for debugging the compiler and will likely be removed
10776 in a future version.
10778 @item -mno-cond-exec
10779 @opindex mno-cond-exec
10781 Disable the use of conditional execution.
10783 This switch is mainly for debugging the compiler and will likely be removed
10784 in a future version.
10786 @item -mvliw-branch
10787 @opindex mvliw-branch
10789 Run a pass to pack branches into VLIW instructions (default).
10791 This switch is mainly for debugging the compiler and will likely be removed
10792 in a future version.
10794 @item -mno-vliw-branch
10795 @opindex mno-vliw-branch
10797 Do not run a pass to pack branches into VLIW instructions.
10799 This switch is mainly for debugging the compiler and will likely be removed
10800 in a future version.
10802 @item -mmulti-cond-exec
10803 @opindex mmulti-cond-exec
10805 Enable optimization of @code{&&} and @code{||} in conditional execution
10808 This switch is mainly for debugging the compiler and will likely be removed
10809 in a future version.
10811 @item -mno-multi-cond-exec
10812 @opindex mno-multi-cond-exec
10814 Disable optimization of @code{&&} and @code{||} in conditional execution.
10816 This switch is mainly for debugging the compiler and will likely be removed
10817 in a future version.
10819 @item -mnested-cond-exec
10820 @opindex mnested-cond-exec
10822 Enable nested conditional execution optimizations (default).
10824 This switch is mainly for debugging the compiler and will likely be removed
10825 in a future version.
10827 @item -mno-nested-cond-exec
10828 @opindex mno-nested-cond-exec
10830 Disable nested conditional execution optimizations.
10832 This switch is mainly for debugging the compiler and will likely be removed
10833 in a future version.
10835 @item -mtomcat-stats
10836 @opindex mtomcat-stats
10838 Cause gas to print out tomcat statistics.
10840 @item -mcpu=@var{cpu}
10843 Select the processor type for which to generate code. Possible values are
10844 @samp{simple}, @samp{tomcat}, @samp{fr500}, @samp{fr400}, @samp{fr300},
10849 @node Xtensa Options
10850 @subsection Xtensa Options
10851 @cindex Xtensa Options
10853 These options are supported for Xtensa targets:
10857 @itemx -mno-const16
10859 @opindex mno-const16
10860 Enable or disable use of @code{CONST16} instructions for loading
10861 constant values. The @code{CONST16} instruction is currently not a
10862 standard option from Tensilica. When enabled, @code{CONST16}
10863 instructions are always used in place of the standard @code{L32R}
10864 instructions. The use of @code{CONST16} is enabled by default only if
10865 the @code{L32R} instruction is not available.
10868 @itemx -mno-fused-madd
10869 @opindex mfused-madd
10870 @opindex mno-fused-madd
10871 Enable or disable use of fused multiply/add and multiply/subtract
10872 instructions in the floating-point option. This has no effect if the
10873 floating-point option is not also enabled. Disabling fused multiply/add
10874 and multiply/subtract instructions forces the compiler to use separate
10875 instructions for the multiply and add/subtract operations. This may be
10876 desirable in some cases where strict IEEE 754-compliant results are
10877 required: the fused multiply add/subtract instructions do not round the
10878 intermediate result, thereby producing results with @emph{more} bits of
10879 precision than specified by the IEEE standard. Disabling fused multiply
10880 add/subtract instructions also ensures that the program output is not
10881 sensitive to the compiler's ability to combine multiply and add/subtract
10884 @item -mtext-section-literals
10885 @itemx -mno-text-section-literals
10886 @opindex mtext-section-literals
10887 @opindex mno-text-section-literals
10888 Control the treatment of literal pools. The default is
10889 @option{-mno-text-section-literals}, which places literals in a separate
10890 section in the output file. This allows the literal pool to be placed
10891 in a data RAM/ROM, and it also allows the linker to combine literal
10892 pools from separate object files to remove redundant literals and
10893 improve code size. With @option{-mtext-section-literals}, the literals
10894 are interspersed in the text section in order to keep them as close as
10895 possible to their references. This may be necessary for large assembly
10898 @item -mtarget-align
10899 @itemx -mno-target-align
10900 @opindex mtarget-align
10901 @opindex mno-target-align
10902 When this option is enabled, GCC instructs the assembler to
10903 automatically align instructions to reduce branch penalties at the
10904 expense of some code density. The assembler attempts to widen density
10905 instructions to align branch targets and the instructions following call
10906 instructions. If there are not enough preceding safe density
10907 instructions to align a target, no widening will be performed. The
10908 default is @option{-mtarget-align}. These options do not affect the
10909 treatment of auto-aligned instructions like @code{LOOP}, which the
10910 assembler will always align, either by widening density instructions or
10911 by inserting no-op instructions.
10914 @itemx -mno-longcalls
10915 @opindex mlongcalls
10916 @opindex mno-longcalls
10917 When this option is enabled, GCC instructs the assembler to translate
10918 direct calls to indirect calls unless it can determine that the target
10919 of a direct call is in the range allowed by the call instruction. This
10920 translation typically occurs for calls to functions in other source
10921 files. Specifically, the assembler translates a direct @code{CALL}
10922 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
10923 The default is @option{-mno-longcalls}. This option should be used in
10924 programs where the call target can potentially be out of range. This
10925 option is implemented in the assembler, not the compiler, so the
10926 assembly code generated by GCC will still show direct call
10927 instructions---look at the disassembled object code to see the actual
10928 instructions. Note that the assembler will use an indirect call for
10929 every cross-file call, not just those that really will be out of range.
10932 @node Code Gen Options
10933 @section Options for Code Generation Conventions
10934 @cindex code generation conventions
10935 @cindex options, code generation
10936 @cindex run-time options
10938 These machine-independent options control the interface conventions
10939 used in code generation.
10941 Most of them have both positive and negative forms; the negative form
10942 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
10943 one of the forms is listed---the one which is not the default. You
10944 can figure out the other form by either removing @samp{no-} or adding
10948 @item -fbounds-check
10949 @opindex fbounds-check
10950 For front-ends that support it, generate additional code to check that
10951 indices used to access arrays are within the declared range. This is
10952 currently only supported by the Java and Fortran 77 front-ends, where
10953 this option defaults to true and false respectively.
10957 This option generates traps for signed overflow on addition, subtraction,
10958 multiplication operations.
10962 This option instructs the compiler to assume that signed arithmetic
10963 overflow of addition, subtraction and multiplication wraps around
10964 using twos-complement representation. This flag enables some optimizations
10965 and disables other. This option is enabled by default for the Java
10966 front-end, as required by the Java language specification.
10969 @opindex fexceptions
10970 Enable exception handling. Generates extra code needed to propagate
10971 exceptions. For some targets, this implies GCC will generate frame
10972 unwind information for all functions, which can produce significant data
10973 size overhead, although it does not affect execution. If you do not
10974 specify this option, GCC will enable it by default for languages like
10975 C++ which normally require exception handling, and disable it for
10976 languages like C that do not normally require it. However, you may need
10977 to enable this option when compiling C code that needs to interoperate
10978 properly with exception handlers written in C++. You may also wish to
10979 disable this option if you are compiling older C++ programs that don't
10980 use exception handling.
10982 @item -fnon-call-exceptions
10983 @opindex fnon-call-exceptions
10984 Generate code that allows trapping instructions to throw exceptions.
10985 Note that this requires platform-specific runtime support that does
10986 not exist everywhere. Moreover, it only allows @emph{trapping}
10987 instructions to throw exceptions, i.e.@: memory references or floating
10988 point instructions. It does not allow exceptions to be thrown from
10989 arbitrary signal handlers such as @code{SIGALRM}.
10991 @item -funwind-tables
10992 @opindex funwind-tables
10993 Similar to @option{-fexceptions}, except that it will just generate any needed
10994 static data, but will not affect the generated code in any other way.
10995 You will normally not enable this option; instead, a language processor
10996 that needs this handling would enable it on your behalf.
10998 @item -fasynchronous-unwind-tables
10999 @opindex funwind-tables
11000 Generate unwind table in dwarf2 format, if supported by target machine. The
11001 table is exact at each instruction boundary, so it can be used for stack
11002 unwinding from asynchronous events (such as debugger or garbage collector).
11004 @item -fpcc-struct-return
11005 @opindex fpcc-struct-return
11006 Return ``short'' @code{struct} and @code{union} values in memory like
11007 longer ones, rather than in registers. This convention is less
11008 efficient, but it has the advantage of allowing intercallability between
11009 GCC-compiled files and files compiled with other compilers, particularly
11010 the Portable C Compiler (pcc).
11012 The precise convention for returning structures in memory depends
11013 on the target configuration macros.
11015 Short structures and unions are those whose size and alignment match
11016 that of some integer type.
11018 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
11019 switch is not binary compatible with code compiled with the
11020 @option{-freg-struct-return} switch.
11021 Use it to conform to a non-default application binary interface.
11023 @item -freg-struct-return
11024 @opindex freg-struct-return
11025 Return @code{struct} and @code{union} values in registers when possible.
11026 This is more efficient for small structures than
11027 @option{-fpcc-struct-return}.
11029 If you specify neither @option{-fpcc-struct-return} nor
11030 @option{-freg-struct-return}, GCC defaults to whichever convention is
11031 standard for the target. If there is no standard convention, GCC
11032 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11033 the principal compiler. In those cases, we can choose the standard, and
11034 we chose the more efficient register return alternative.
11036 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11037 switch is not binary compatible with code compiled with the
11038 @option{-fpcc-struct-return} switch.
11039 Use it to conform to a non-default application binary interface.
11041 @item -fshort-enums
11042 @opindex fshort-enums
11043 Allocate to an @code{enum} type only as many bytes as it needs for the
11044 declared range of possible values. Specifically, the @code{enum} type
11045 will be equivalent to the smallest integer type which has enough room.
11047 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11048 code that is not binary compatible with code generated without that switch.
11049 Use it to conform to a non-default application binary interface.
11051 @item -fshort-double
11052 @opindex fshort-double
11053 Use the same size for @code{double} as for @code{float}.
11055 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11056 code that is not binary compatible with code generated without that switch.
11057 Use it to conform to a non-default application binary interface.
11059 @item -fshort-wchar
11060 @opindex fshort-wchar
11061 Override the underlying type for @samp{wchar_t} to be @samp{short
11062 unsigned int} instead of the default for the target. This option is
11063 useful for building programs to run under WINE@.
11065 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11066 code that is not binary compatible with code generated without that switch.
11067 Use it to conform to a non-default application binary interface.
11069 @item -fshared-data
11070 @opindex fshared-data
11071 Requests that the data and non-@code{const} variables of this
11072 compilation be shared data rather than private data. The distinction
11073 makes sense only on certain operating systems, where shared data is
11074 shared between processes running the same program, while private data
11075 exists in one copy per process.
11078 @opindex fno-common
11079 In C, allocate even uninitialized global variables in the data section of the
11080 object file, rather than generating them as common blocks. This has the
11081 effect that if the same variable is declared (without @code{extern}) in
11082 two different compilations, you will get an error when you link them.
11083 The only reason this might be useful is if you wish to verify that the
11084 program will work on other systems which always work this way.
11088 Ignore the @samp{#ident} directive.
11090 @item -fno-gnu-linker
11091 @opindex fno-gnu-linker
11092 Do not output global initializations (such as C++ constructors and
11093 destructors) in the form used by the GNU linker (on systems where the GNU
11094 linker is the standard method of handling them). Use this option when
11095 you want to use a non-GNU linker, which also requires using the
11096 @command{collect2} program to make sure the system linker includes
11097 constructors and destructors. (@command{collect2} is included in the GCC
11098 distribution.) For systems which @emph{must} use @command{collect2}, the
11099 compiler driver @command{gcc} is configured to do this automatically.
11101 @item -finhibit-size-directive
11102 @opindex finhibit-size-directive
11103 Don't output a @code{.size} assembler directive, or anything else that
11104 would cause trouble if the function is split in the middle, and the
11105 two halves are placed at locations far apart in memory. This option is
11106 used when compiling @file{crtstuff.c}; you should not need to use it
11109 @item -fverbose-asm
11110 @opindex fverbose-asm
11111 Put extra commentary information in the generated assembly code to
11112 make it more readable. This option is generally only of use to those
11113 who actually need to read the generated assembly code (perhaps while
11114 debugging the compiler itself).
11116 @option{-fno-verbose-asm}, the default, causes the
11117 extra information to be omitted and is useful when comparing two assembler
11122 @cindex global offset table
11124 Generate position-independent code (PIC) suitable for use in a shared
11125 library, if supported for the target machine. Such code accesses all
11126 constant addresses through a global offset table (GOT)@. The dynamic
11127 loader resolves the GOT entries when the program starts (the dynamic
11128 loader is not part of GCC; it is part of the operating system). If
11129 the GOT size for the linked executable exceeds a machine-specific
11130 maximum size, you get an error message from the linker indicating that
11131 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11132 instead. (These maximums are 16k on the m88k, 8k on the SPARC, and 32k
11133 on the m68k and RS/6000. The 386 has no such limit.)
11135 Position-independent code requires special support, and therefore works
11136 only on certain machines. For the 386, GCC supports PIC for System V
11137 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11138 position-independent.
11142 If supported for the target machine, emit position-independent code,
11143 suitable for dynamic linking and avoiding any limit on the size of the
11144 global offset table. This option makes a difference on the m68k, m88k,
11147 Position-independent code requires special support, and therefore works
11148 only on certain machines.
11154 These options are similar to @option{-fpic} and @option{-fPIC}, but
11155 generated position independent code can be only linked into executables.
11156 Usually these options are used when @option{-pie} GCC option will be
11157 used during linking.
11159 @item -ffixed-@var{reg}
11161 Treat the register named @var{reg} as a fixed register; generated code
11162 should never refer to it (except perhaps as a stack pointer, frame
11163 pointer or in some other fixed role).
11165 @var{reg} must be the name of a register. The register names accepted
11166 are machine-specific and are defined in the @code{REGISTER_NAMES}
11167 macro in the machine description macro file.
11169 This flag does not have a negative form, because it specifies a
11172 @item -fcall-used-@var{reg}
11173 @opindex fcall-used
11174 Treat the register named @var{reg} as an allocable register that is
11175 clobbered by function calls. It may be allocated for temporaries or
11176 variables that do not live across a call. Functions compiled this way
11177 will not save and restore the register @var{reg}.
11179 It is an error to used this flag with the frame pointer or stack pointer.
11180 Use of this flag for other registers that have fixed pervasive roles in
11181 the machine's execution model will produce disastrous results.
11183 This flag does not have a negative form, because it specifies a
11186 @item -fcall-saved-@var{reg}
11187 @opindex fcall-saved
11188 Treat the register named @var{reg} as an allocable register saved by
11189 functions. It may be allocated even for temporaries or variables that
11190 live across a call. Functions compiled this way will save and restore
11191 the register @var{reg} if they use it.
11193 It is an error to used this flag with the frame pointer or stack pointer.
11194 Use of this flag for other registers that have fixed pervasive roles in
11195 the machine's execution model will produce disastrous results.
11197 A different sort of disaster will result from the use of this flag for
11198 a register in which function values may be returned.
11200 This flag does not have a negative form, because it specifies a
11203 @item -fpack-struct
11204 @opindex fpack-struct
11205 Pack all structure members together without holes.
11207 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
11208 code that is not binary compatible with code generated without that switch.
11209 Additionally, it makes the code suboptimal.
11210 Use it to conform to a non-default application binary interface.
11212 @item -finstrument-functions
11213 @opindex finstrument-functions
11214 Generate instrumentation calls for entry and exit to functions. Just
11215 after function entry and just before function exit, the following
11216 profiling functions will be called with the address of the current
11217 function and its call site. (On some platforms,
11218 @code{__builtin_return_address} does not work beyond the current
11219 function, so the call site information may not be available to the
11220 profiling functions otherwise.)
11223 void __cyg_profile_func_enter (void *this_fn,
11225 void __cyg_profile_func_exit (void *this_fn,
11229 The first argument is the address of the start of the current function,
11230 which may be looked up exactly in the symbol table.
11232 This instrumentation is also done for functions expanded inline in other
11233 functions. The profiling calls will indicate where, conceptually, the
11234 inline function is entered and exited. This means that addressable
11235 versions of such functions must be available. If all your uses of a
11236 function are expanded inline, this may mean an additional expansion of
11237 code size. If you use @samp{extern inline} in your C code, an
11238 addressable version of such functions must be provided. (This is
11239 normally the case anyways, but if you get lucky and the optimizer always
11240 expands the functions inline, you might have gotten away without
11241 providing static copies.)
11243 A function may be given the attribute @code{no_instrument_function}, in
11244 which case this instrumentation will not be done. This can be used, for
11245 example, for the profiling functions listed above, high-priority
11246 interrupt routines, and any functions from which the profiling functions
11247 cannot safely be called (perhaps signal handlers, if the profiling
11248 routines generate output or allocate memory).
11250 @item -fstack-check
11251 @opindex fstack-check
11252 Generate code to verify that you do not go beyond the boundary of the
11253 stack. You should specify this flag if you are running in an
11254 environment with multiple threads, but only rarely need to specify it in
11255 a single-threaded environment since stack overflow is automatically
11256 detected on nearly all systems if there is only one stack.
11258 Note that this switch does not actually cause checking to be done; the
11259 operating system must do that. The switch causes generation of code
11260 to ensure that the operating system sees the stack being extended.
11262 @item -fstack-limit-register=@var{reg}
11263 @itemx -fstack-limit-symbol=@var{sym}
11264 @itemx -fno-stack-limit
11265 @opindex fstack-limit-register
11266 @opindex fstack-limit-symbol
11267 @opindex fno-stack-limit
11268 Generate code to ensure that the stack does not grow beyond a certain value,
11269 either the value of a register or the address of a symbol. If the stack
11270 would grow beyond the value, a signal is raised. For most targets,
11271 the signal is raised before the stack overruns the boundary, so
11272 it is possible to catch the signal without taking special precautions.
11274 For instance, if the stack starts at absolute address @samp{0x80000000}
11275 and grows downwards, you can use the flags
11276 @option{-fstack-limit-symbol=__stack_limit} and
11277 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
11278 of 128KB@. Note that this may only work with the GNU linker.
11280 @cindex aliasing of parameters
11281 @cindex parameters, aliased
11282 @item -fargument-alias
11283 @itemx -fargument-noalias
11284 @itemx -fargument-noalias-global
11285 @opindex fargument-alias
11286 @opindex fargument-noalias
11287 @opindex fargument-noalias-global
11288 Specify the possible relationships among parameters and between
11289 parameters and global data.
11291 @option{-fargument-alias} specifies that arguments (parameters) may
11292 alias each other and may alias global storage.@*
11293 @option{-fargument-noalias} specifies that arguments do not alias
11294 each other, but may alias global storage.@*
11295 @option{-fargument-noalias-global} specifies that arguments do not
11296 alias each other and do not alias global storage.
11298 Each language will automatically use whatever option is required by
11299 the language standard. You should not need to use these options yourself.
11301 @item -fleading-underscore
11302 @opindex fleading-underscore
11303 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
11304 change the way C symbols are represented in the object file. One use
11305 is to help link with legacy assembly code.
11307 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
11308 generate code that is not binary compatible with code generated without that
11309 switch. Use it to conform to a non-default application binary interface.
11310 Not all targets provide complete support for this switch.
11312 @item -ftls-model=@var{model}
11313 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
11314 The @var{model} argument should be one of @code{global-dynamic},
11315 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
11317 The default without @option{-fpic} is @code{initial-exec}; with
11318 @option{-fpic} the default is @code{global-dynamic}.
11323 @node Environment Variables
11324 @section Environment Variables Affecting GCC
11325 @cindex environment variables
11327 @c man begin ENVIRONMENT
11328 This section describes several environment variables that affect how GCC
11329 operates. Some of them work by specifying directories or prefixes to use
11330 when searching for various kinds of files. Some are used to specify other
11331 aspects of the compilation environment.
11333 Note that you can also specify places to search using options such as
11334 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
11335 take precedence over places specified using environment variables, which
11336 in turn take precedence over those specified by the configuration of GCC@.
11337 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
11338 GNU Compiler Collection (GCC) Internals}.
11343 @c @itemx LC_COLLATE
11345 @c @itemx LC_MONETARY
11346 @c @itemx LC_NUMERIC
11351 @c @findex LC_COLLATE
11352 @findex LC_MESSAGES
11353 @c @findex LC_MONETARY
11354 @c @findex LC_NUMERIC
11358 These environment variables control the way that GCC uses
11359 localization information that allow GCC to work with different
11360 national conventions. GCC inspects the locale categories
11361 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
11362 so. These locale categories can be set to any value supported by your
11363 installation. A typical value is @samp{en_UK} for English in the United
11366 The @env{LC_CTYPE} environment variable specifies character
11367 classification. GCC uses it to determine the character boundaries in
11368 a string; this is needed for some multibyte encodings that contain quote
11369 and escape characters that would otherwise be interpreted as a string
11372 The @env{LC_MESSAGES} environment variable specifies the language to
11373 use in diagnostic messages.
11375 If the @env{LC_ALL} environment variable is set, it overrides the value
11376 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
11377 and @env{LC_MESSAGES} default to the value of the @env{LANG}
11378 environment variable. If none of these variables are set, GCC
11379 defaults to traditional C English behavior.
11383 If @env{TMPDIR} is set, it specifies the directory to use for temporary
11384 files. GCC uses temporary files to hold the output of one stage of
11385 compilation which is to be used as input to the next stage: for example,
11386 the output of the preprocessor, which is the input to the compiler
11389 @item GCC_EXEC_PREFIX
11390 @findex GCC_EXEC_PREFIX
11391 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
11392 names of the subprograms executed by the compiler. No slash is added
11393 when this prefix is combined with the name of a subprogram, but you can
11394 specify a prefix that ends with a slash if you wish.
11396 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
11397 an appropriate prefix to use based on the pathname it was invoked with.
11399 If GCC cannot find the subprogram using the specified prefix, it
11400 tries looking in the usual places for the subprogram.
11402 The default value of @env{GCC_EXEC_PREFIX} is
11403 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
11404 of @code{prefix} when you ran the @file{configure} script.
11406 Other prefixes specified with @option{-B} take precedence over this prefix.
11408 This prefix is also used for finding files such as @file{crt0.o} that are
11411 In addition, the prefix is used in an unusual way in finding the
11412 directories to search for header files. For each of the standard
11413 directories whose name normally begins with @samp{/usr/local/lib/gcc}
11414 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
11415 replacing that beginning with the specified prefix to produce an
11416 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
11417 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
11418 These alternate directories are searched first; the standard directories
11421 @item COMPILER_PATH
11422 @findex COMPILER_PATH
11423 The value of @env{COMPILER_PATH} is a colon-separated list of
11424 directories, much like @env{PATH}. GCC tries the directories thus
11425 specified when searching for subprograms, if it can't find the
11426 subprograms using @env{GCC_EXEC_PREFIX}.
11429 @findex LIBRARY_PATH
11430 The value of @env{LIBRARY_PATH} is a colon-separated list of
11431 directories, much like @env{PATH}. When configured as a native compiler,
11432 GCC tries the directories thus specified when searching for special
11433 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
11434 using GCC also uses these directories when searching for ordinary
11435 libraries for the @option{-l} option (but directories specified with
11436 @option{-L} come first).
11440 @cindex locale definition
11441 This variable is used to pass locale information to the compiler. One way in
11442 which this information is used is to determine the character set to be used
11443 when character literals, string literals and comments are parsed in C and C++.
11444 When the compiler is configured to allow multibyte characters,
11445 the following values for @env{LANG} are recognized:
11449 Recognize JIS characters.
11451 Recognize SJIS characters.
11453 Recognize EUCJP characters.
11456 If @env{LANG} is not defined, or if it has some other value, then the
11457 compiler will use mblen and mbtowc as defined by the default locale to
11458 recognize and translate multibyte characters.
11462 Some additional environments variables affect the behavior of the
11465 @include cppenv.texi
11469 @node Precompiled Headers
11470 @section Using Precompiled Headers
11471 @cindex precompiled headers
11472 @cindex speed of compilation
11474 Often large projects have many header files that are included in every
11475 source file. The time the compiler takes to process these header files
11476 over and over again can account for nearly all of the time required to
11477 build the project. To make builds faster, GCC allows users to
11478 `precompile' a header file; then, if builds can use the precompiled
11479 header file they will be much faster.
11481 To create a precompiled header file, simply compile it as you would any
11482 other file, if necessary using the @option{-x} option to make the driver
11483 treat it as a C or C++ header file. You will probably want to use a
11484 tool like @command{make} to keep the precompiled header up-to-date when
11485 the headers it contains change.
11487 A precompiled header file will be searched for when @code{#include} is
11488 seen in the compilation. As it searches for the included file
11489 (@pxref{Search Path,,Search Path,cpp.info,The C Preprocessor}) the
11490 compiler looks for a precompiled header in each directory just before it
11491 looks for the include file in that directory. The name searched for is
11492 the name specified in the @code{#include} with @samp{.gch} appended. If
11493 the precompiled header file can't be used, it is ignored.
11495 For instance, if you have @code{#include "all.h"}, and you have
11496 @file{all.h.gch} in the same directory as @file{all.h}, then the
11497 precompiled header file will be used if possible, and the original
11498 header will be used otherwise.
11500 Alternatively, you might decide to put the precompiled header file in a
11501 directory and use @option{-I} to ensure that directory is searched
11502 before (or instead of) the directory containing the original header.
11503 Then, if you want to check that the precompiled header file is always
11504 used, you can put a file of the same name as the original header in this
11505 directory containing an @code{#error} command.
11507 This also works with @option{-include}. So yet another way to use
11508 precompiled headers, good for projects not designed with precompiled
11509 header files in mind, is to simply take most of the header files used by
11510 a project, include them from another header file, precompile that header
11511 file, and @option{-include} the precompiled header. If the header files
11512 have guards against multiple inclusion, they will be skipped because
11513 they've already been included (in the precompiled header).
11515 If you need to precompile the same header file for different
11516 languages, targets, or compiler options, you can instead make a
11517 @emph{directory} named like @file{all.h.gch}, and put each precompiled
11518 header in the directory. (It doesn't matter what you call the files
11519 in the directory, every precompiled header in the directory will be
11520 considered.) The first precompiled header encountered in the
11521 directory that is valid for this compilation will be used; they're
11522 searched in no particular order.
11524 There are many other possibilities, limited only by your imagination,
11525 good sense, and the constraints of your build system.
11527 A precompiled header file can be used only when these conditions apply:
11531 Only one precompiled header can be used in a particular compilation.
11533 A precompiled header can't be used once the first C token is seen. You
11534 can have preprocessor directives before a precompiled header; you can
11535 even include a precompiled header from inside another header, so long as
11536 there are no C tokens before the @code{#include}.
11538 The precompiled header file must be produced for the same language as
11539 the current compilation. You can't use a C precompiled header for a C++
11542 The precompiled header file must be produced by the same compiler
11543 version and configuration as the current compilation is using.
11544 The easiest way to guarantee this is to use the same compiler binary
11545 for creating and using precompiled headers.
11547 Any macros defined before the precompiled header (including with
11548 @option{-D}) must either be defined in the same way as when the
11549 precompiled header was generated, or must not affect the precompiled
11550 header, which usually means that the they don't appear in the
11551 precompiled header at all.
11553 Certain command-line options must be defined in the same way as when the
11554 precompiled header was generated. At present, it's not clear which
11555 options are safe to change and which are not; the safest choice is to
11556 use exactly the same options when generating and using the precompiled
11560 For all of these but the last, the compiler will automatically ignore
11561 the precompiled header if the conditions aren't met. For the last item,
11562 some option changes will cause the precompiled header to be rejected,
11563 but not all incompatible option combinations have yet been found. If
11564 you find a new incompatible combination, please consider filing a bug
11565 report, see @ref{Bugs}.
11567 @node Running Protoize
11568 @section Running Protoize
11570 The program @code{protoize} is an optional part of GCC@. You can use
11571 it to add prototypes to a program, thus converting the program to ISO
11572 C in one respect. The companion program @code{unprotoize} does the
11573 reverse: it removes argument types from any prototypes that are found.
11575 When you run these programs, you must specify a set of source files as
11576 command line arguments. The conversion programs start out by compiling
11577 these files to see what functions they define. The information gathered
11578 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
11580 After scanning comes actual conversion. The specified files are all
11581 eligible to be converted; any files they include (whether sources or
11582 just headers) are eligible as well.
11584 But not all the eligible files are converted. By default,
11585 @code{protoize} and @code{unprotoize} convert only source and header
11586 files in the current directory. You can specify additional directories
11587 whose files should be converted with the @option{-d @var{directory}}
11588 option. You can also specify particular files to exclude with the
11589 @option{-x @var{file}} option. A file is converted if it is eligible, its
11590 directory name matches one of the specified directory names, and its
11591 name within the directory has not been excluded.
11593 Basic conversion with @code{protoize} consists of rewriting most
11594 function definitions and function declarations to specify the types of
11595 the arguments. The only ones not rewritten are those for varargs
11598 @code{protoize} optionally inserts prototype declarations at the
11599 beginning of the source file, to make them available for any calls that
11600 precede the function's definition. Or it can insert prototype
11601 declarations with block scope in the blocks where undeclared functions
11604 Basic conversion with @code{unprotoize} consists of rewriting most
11605 function declarations to remove any argument types, and rewriting
11606 function definitions to the old-style pre-ISO form.
11608 Both conversion programs print a warning for any function declaration or
11609 definition that they can't convert. You can suppress these warnings
11612 The output from @code{protoize} or @code{unprotoize} replaces the
11613 original source file. The original file is renamed to a name ending
11614 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
11615 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
11616 for DOS) file already exists, then the source file is simply discarded.
11618 @code{protoize} and @code{unprotoize} both depend on GCC itself to
11619 scan the program and collect information about the functions it uses.
11620 So neither of these programs will work until GCC is installed.
11622 Here is a table of the options you can use with @code{protoize} and
11623 @code{unprotoize}. Each option works with both programs unless
11627 @item -B @var{directory}
11628 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
11629 usual directory (normally @file{/usr/local/lib}). This file contains
11630 prototype information about standard system functions. This option
11631 applies only to @code{protoize}.
11633 @item -c @var{compilation-options}
11634 Use @var{compilation-options} as the options when running @command{gcc} to
11635 produce the @samp{.X} files. The special option @option{-aux-info} is
11636 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
11638 Note that the compilation options must be given as a single argument to
11639 @code{protoize} or @code{unprotoize}. If you want to specify several
11640 @command{gcc} options, you must quote the entire set of compilation options
11641 to make them a single word in the shell.
11643 There are certain @command{gcc} arguments that you cannot use, because they
11644 would produce the wrong kind of output. These include @option{-g},
11645 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
11646 the @var{compilation-options}, they are ignored.
11649 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
11650 systems) instead of @samp{.c}. This is convenient if you are converting
11651 a C program to C++. This option applies only to @code{protoize}.
11654 Add explicit global declarations. This means inserting explicit
11655 declarations at the beginning of each source file for each function
11656 that is called in the file and was not declared. These declarations
11657 precede the first function definition that contains a call to an
11658 undeclared function. This option applies only to @code{protoize}.
11660 @item -i @var{string}
11661 Indent old-style parameter declarations with the string @var{string}.
11662 This option applies only to @code{protoize}.
11664 @code{unprotoize} converts prototyped function definitions to old-style
11665 function definitions, where the arguments are declared between the
11666 argument list and the initial @samp{@{}. By default, @code{unprotoize}
11667 uses five spaces as the indentation. If you want to indent with just
11668 one space instead, use @option{-i " "}.
11671 Keep the @samp{.X} files. Normally, they are deleted after conversion
11675 Add explicit local declarations. @code{protoize} with @option{-l} inserts
11676 a prototype declaration for each function in each block which calls the
11677 function without any declaration. This option applies only to
11681 Make no real changes. This mode just prints information about the conversions
11682 that would have been done without @option{-n}.
11685 Make no @samp{.save} files. The original files are simply deleted.
11686 Use this option with caution.
11688 @item -p @var{program}
11689 Use the program @var{program} as the compiler. Normally, the name
11690 @file{gcc} is used.
11693 Work quietly. Most warnings are suppressed.
11696 Print the version number, just like @option{-v} for @command{gcc}.
11699 If you need special compiler options to compile one of your program's
11700 source files, then you should generate that file's @samp{.X} file
11701 specially, by running @command{gcc} on that source file with the
11702 appropriate options and the option @option{-aux-info}. Then run
11703 @code{protoize} on the entire set of files. @code{protoize} will use
11704 the existing @samp{.X} file because it is newer than the source file.
11708 gcc -Dfoo=bar file1.c -aux-info file1.X
11713 You need to include the special files along with the rest in the
11714 @code{protoize} command, even though their @samp{.X} files already
11715 exist, because otherwise they won't get converted.
11717 @xref{Protoize Caveats}, for more information on how to use
11718 @code{protoize} successfully.