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25 <title>Installing GCC</title>
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64 <h1 class="settitle" align="center">Installing GCC</h1>
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85 <a name="index-Installing-GCC_003a-Building"></a>
86
87 <p>Now that GCC is configured, you are ready to build the compiler and
88 runtime libraries.
89 </p>
90 <p>Some commands executed when making the compiler may fail (return a
91 nonzero status) and be ignored by <code>make</code>. These failures, which
92 are often due to files that were not found, are expected, and can safely
93 be ignored.
94 </p>
95 <p>It is normal to have compiler warnings when compiling certain files.
96 Unless you are a GCC developer, you can generally ignore these warnings
97 unless they cause compilation to fail. Developers should attempt to fix
98 any warnings encountered, however they can temporarily continue past
99 warnings-as-errors by specifying the configure flag
100 <samp>--disable-werror</samp>.
101 </p>
102 <p>On certain old systems, defining certain environment variables such as
103 <code>CC</code> can interfere with the functioning of <code>make</code>.
104 </p>
105 <p>If you encounter seemingly strange errors when trying to build the
106 compiler in a directory other than the source directory, it could be
107 because you have previously configured the compiler in the source
108 directory. Make sure you have done all the necessary preparations.
109 </p>
110 <p>If you build GCC on a BSD system using a directory stored in an old System
111 V file system, problems may occur in running <code>fixincludes</code> if the
112 System V file system doesn’t support symbolic links. These problems
113 result in a failure to fix the declaration of <code>size_t</code> in
114 <samp>sys/types.h</samp>. If you find that <code>size_t</code> is a signed type and
115 that type mismatches occur, this could be the cause.
116 </p>
117 <p>The solution is not to use such a directory for building GCC.
118 </p>
119 <p>Similarly, when building from the source repository or snapshots, or if you modify
120 <samp>*.l</samp> files, you need the Flex lexical analyzer generator
121 installed. If you do not modify <samp>*.l</samp> files, releases contain
122 the Flex-generated files and you do not need Flex installed to build
123 them. There is still one Flex-based lexical analyzer (part of the
124 build machinery, not of GCC itself) that is used even if you only
125 build the C front end.
126 </p>
127 <p>When building from the source repository or snapshots, or if you modify Texinfo
128 documentation, you need version 4.7 or later of Texinfo installed if you
129 want Info documentation to be regenerated. Releases contain Info
130 documentation pre-built for the unmodified documentation in the release.
131 </p>
132 <a name="Building-a-native-compiler"></a>
133 <h3 class="section">Building a native compiler</h3>
134
135 <p>For a native build, the default configuration is to perform
136 a 3-stage bootstrap of the compiler when ‘<samp>make</samp>’ is invoked.
137 This will build the entire GCC system and ensure that it compiles
138 itself correctly. It can be disabled with the <samp>--disable-bootstrap</samp>
139 parameter to ‘<samp>configure</samp>’, but bootstrapping is suggested because
140 the compiler will be tested more completely and could also have
141 better performance.
142 </p>
143 <p>The bootstrapping process will complete the following steps:
144 </p>
145 <ul>
146 <li> Build tools necessary to build the compiler.
147
148 </li><li> Perform a 3-stage bootstrap of the compiler. This includes building
149 three times the target tools for use by the compiler such as binutils
150 (bfd, binutils, gas, gprof, ld, and opcodes) if they have been
151 individually linked or moved into the top level GCC source tree before
152 configuring.
153
154 </li><li> Perform a comparison test of the stage2 and stage3 compilers.
155
156 </li><li> Build runtime libraries using the stage3 compiler from the previous step.
157
158 </li></ul>
159
160 <p>If you are short on disk space you might consider ‘<samp>make
161 bootstrap-lean</samp>’ instead. The sequence of compilation is the
162 same described above, but object files from the stage1 and
163 stage2 of the 3-stage bootstrap of the compiler are deleted as
164 soon as they are no longer needed.
165 </p>
166 <p>If you wish to use non-default GCC flags when compiling the stage2
167 and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when
168 doing ‘<samp>make</samp>’. For example, if you want to save additional space
169 during the bootstrap and in the final installation as well, you can
170 build the compiler binaries without debugging information as in the
171 following example. This will save roughly 40% of disk space both for
172 the bootstrap and the final installation. (Libraries will still contain
173 debugging information.)
174 </p>
175 <div class="smallexample">
176 <pre class="smallexample">make BOOT_CFLAGS='-O' bootstrap
177 </pre></div>
178
179 <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they
180 are less well tested here than the default of ‘<samp>-g -O2</samp>’, but should
181 still work. In a few cases, you may find that you need to specify special
182 flags such as <samp>-msoft-float</samp> here to complete the bootstrap; or,
183 if the native compiler miscompiles the stage1 compiler, you may need
184 to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts
185 of the stage1 compiler that were miscompiled, or by using ‘<samp>make
186 bootstrap4</samp>’ to increase the number of stages of bootstrap.
187 </p>
188 <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries.
189 Since these are always compiled with the compiler currently being
190 bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their
191 compilation flags, as for non-bootstrapped target libraries.
192 Again, if the native compiler miscompiles the stage1 compiler, you may
193 need to work around this by avoiding non-working parts of the stage1
194 compiler. Use <code>STAGE1_TFLAGS</code> to this end.
195 </p>
196 <p>If you used the flag <samp>--enable-languages=…</samp> to restrict
197 the compilers to be built, only those you’ve actually enabled will be
198 built. This will of course only build those runtime libraries, for
199 which the particular compiler has been built. Please note,
200 that re-defining <code>LANGUAGES</code> when calling ‘<samp>make</samp>’
201 <strong>does not</strong> work anymore!
202 </p>
203 <p>If the comparison of stage2 and stage3 fails, this normally indicates
204 that the stage2 compiler has compiled GCC incorrectly, and is therefore
205 a potentially serious bug which you should investigate and report. (On
206 a few systems, meaningful comparison of object files is impossible; they
207 always appear “different”. If you encounter this problem, you will
208 need to disable comparison in the <samp>Makefile</samp>.)
209 </p>
210 <p>If you do not want to bootstrap your compiler, you can configure with
211 <samp>--disable-bootstrap</samp>. In particular cases, you may want to
212 bootstrap your compiler even if the target system is not the same as
213 the one you are building on: for example, you could build a
214 <code>powerpc-unknown-linux-gnu</code> toolchain on a
215 <code>powerpc64-unknown-linux-gnu</code> host. In this case, pass
216 <samp>--enable-bootstrap</samp> to the configure script.
217 </p>
218 <p><code>BUILD_CONFIG</code> can be used to bring in additional customization
219 to the build. It can be set to a whitespace-separated list of names.
220 For each such <code>NAME</code>, top-level <samp>config/<code>NAME</code>.mk</samp> will
221 be included by the top-level <samp>Makefile</samp>, bringing in any settings
222 it contains. The default <code>BUILD_CONFIG</code> can be set using the
223 configure option <samp>--with-build-config=<code>NAME</code>...</samp>. Some
224 examples of supported build configurations are:
225 </p>
226 <dl compact="compact">
227 <dt>‘<samp>bootstrap-O1</samp>’</dt>
228 <dd><p>Removes any <samp>-O</samp>-started option from <code>BOOT_CFLAGS</code>, and adds
229 <samp>-O1</samp> to it. ‘<samp>BUILD_CONFIG=bootstrap-O1</samp>’ is equivalent to
230 ‘<samp>BOOT_CFLAGS='-g -O1'</samp>’.
231 </p>
232 </dd>
233 <dt>‘<samp>bootstrap-O3</samp>’</dt>
234 <dd><p>Analogous to <code>bootstrap-O1</code>.
235 </p>
236 </dd>
237 <dt>‘<samp>bootstrap-lto</samp>’</dt>
238 <dd><p>Enables Link-Time Optimization for host tools during bootstrapping.
239 ‘<samp>BUILD_CONFIG=bootstrap-lto</samp>’ is equivalent to adding
240 <samp>-flto</samp> to ‘<samp>BOOT_CFLAGS</samp>’. This option assumes that the host
241 supports the linker plugin (e.g. GNU ld version 2.21 or later or GNU gold
242 version 2.21 or later).
243 </p>
244 </dd>
245 <dt>‘<samp>bootstrap-lto-noplugin</samp>’</dt>
246 <dd><p>This option is similar to <code>bootstrap-lto</code>, but is intended for
247 hosts that do not support the linker plugin. Without the linker plugin
248 static libraries are not compiled with link-time optimizations. Since
249 the GCC middle end and back end are in <samp>libbackend.a</samp> this means
250 that only the front end is actually LTO optimized.
251 </p>
252 </dd>
253 <dt>‘<samp>bootstrap-lto-lean</samp>’</dt>
254 <dd><p>This option is similar to <code>bootstrap-lto</code>, but is intended for
255 faster build by only using LTO in the final bootstrap stage.
256 With ‘<samp>make profiledbootstrap</samp>’ the LTO frontend
257 is trained only on generator files.
258 </p>
259 </dd>
260 <dt>‘<samp>bootstrap-debug</samp>’</dt>
261 <dd><p>Verifies that the compiler generates the same executable code, whether
262 or not it is asked to emit debug information. To this end, this
263 option builds stage2 host programs without debug information, and uses
264 <samp>contrib/compare-debug</samp> to compare them with the stripped stage3
265 object files. If <code>BOOT_CFLAGS</code> is overridden so as to not enable
266 debug information, stage2 will have it, and stage3 won’t. This option
267 is enabled by default when GCC bootstrapping is enabled, if
268 <code>strip</code> can turn object files compiled with and without debug
269 info into identical object files. In addition to better test
270 coverage, this option makes default bootstraps faster and leaner.
271 </p>
272 </dd>
273 <dt>‘<samp>bootstrap-debug-big</samp>’</dt>
274 <dd><p>Rather than comparing stripped object files, as in
275 <code>bootstrap-debug</code>, this option saves internal compiler dumps
276 during stage2 and stage3 and compares them as well, which helps catch
277 additional potential problems, but at a great cost in terms of disk
278 space. It can be specified in addition to ‘<samp>bootstrap-debug</samp>’.
279 </p>
280 </dd>
281 <dt>‘<samp>bootstrap-debug-lean</samp>’</dt>
282 <dd><p>This option saves disk space compared with <code>bootstrap-debug-big</code>,
283 but at the expense of some recompilation. Instead of saving the dumps
284 of stage2 and stage3 until the final compare, it uses
285 <samp>-fcompare-debug</samp> to generate, compare and remove the dumps
286 during stage3, repeating the compilation that already took place in
287 stage2, whose dumps were not saved.
288 </p>
289 </dd>
290 <dt>‘<samp>bootstrap-debug-lib</samp>’</dt>
291 <dd><p>This option tests executable code invariance over debug information
292 generation on target libraries, just like <code>bootstrap-debug-lean</code>
293 tests it on host programs. It builds stage3 libraries with
294 <samp>-fcompare-debug</samp>, and it can be used along with any of the
295 <code>bootstrap-debug</code> options above.
296 </p>
297 <p>There aren’t <code>-lean</code> or <code>-big</code> counterparts to this option
298 because most libraries are only build in stage3, so bootstrap compares
299 would not get significant coverage. Moreover, the few libraries built
300 in stage2 are used in stage3 host programs, so we wouldn’t want to
301 compile stage2 libraries with different options for comparison purposes.
302 </p>
303 </dd>
304 <dt>‘<samp>bootstrap-debug-ckovw</samp>’</dt>
305 <dd><p>Arranges for error messages to be issued if the compiler built on any
306 stage is run without the option <samp>-fcompare-debug</samp>. This is
307 useful to verify the full <samp>-fcompare-debug</samp> testing coverage. It
308 must be used along with <code>bootstrap-debug-lean</code> and
309 <code>bootstrap-debug-lib</code>.
310 </p>
311 </dd>
312 <dt>‘<samp>bootstrap-cet</samp>’</dt>
313 <dd><p>This option enables Intel CET for host tools during bootstrapping.
314 ‘<samp>BUILD_CONFIG=bootstrap-cet</samp>’ is equivalent to adding
315 <samp>-fcf-protection</samp> to ‘<samp>BOOT_CFLAGS</samp>’. This option
316 assumes that the host supports Intel CET (e.g. GNU assembler version
317 2.30 or later).
318 </p>
319 </dd>
320 <dt>‘<samp>bootstrap-time</samp>’</dt>
321 <dd><p>Arranges for the run time of each program started by the GCC driver,
322 built in any stage, to be logged to <samp>time.log</samp>, in the top level of
323 the build tree.
324 </p>
325 </dd>
326 </dl>
327
328 <a name="Building-a-cross-compiler"></a>
329 <h3 class="section">Building a cross compiler</h3>
330
331 <p>When building a cross compiler, it is not generally possible to do a
332 3-stage bootstrap of the compiler. This makes for an interesting problem
333 as parts of GCC can only be built with GCC.
334 </p>
335 <p>To build a cross compiler, we recommend first building and installing a
336 native compiler. You can then use the native GCC compiler to build the
337 cross compiler. The installed native compiler needs to be GCC version
338 2.95 or later.
339 </p>
340 <p>Assuming you have already installed a native copy of GCC and configured
341 your cross compiler, issue the command <code>make</code>, which performs the
342 following steps:
343 </p>
344 <ul>
345 <li> Build host tools necessary to build the compiler.
346
347 </li><li> Build target tools for use by the compiler such as binutils (bfd,
348 binutils, gas, gprof, ld, and opcodes)
349 if they have been individually linked or moved into the top level GCC source
350 tree before configuring.
351
352 </li><li> Build the compiler (single stage only).
353
354 </li><li> Build runtime libraries using the compiler from the previous step.
355 </li></ul>
356
357 <p>Note that if an error occurs in any step the make process will exit.
358 </p>
359 <p>If you are not building GNU binutils in the same source tree as GCC,
360 you will need a cross-assembler and cross-linker installed before
361 configuring GCC. Put them in the directory
362 <samp><var>prefix</var>/<var>target</var>/bin</samp>. Here is a table of the tools
363 you should put in this directory:
364 </p>
365 <dl compact="compact">
366 <dt><samp>as</samp></dt>
367 <dd><p>This should be the cross-assembler.
368 </p>
369 </dd>
370 <dt><samp>ld</samp></dt>
371 <dd><p>This should be the cross-linker.
372 </p>
373 </dd>
374 <dt><samp>ar</samp></dt>
375 <dd><p>This should be the cross-archiver: a program which can manipulate
376 archive files (linker libraries) in the target machine’s format.
377 </p>
378 </dd>
379 <dt><samp>ranlib</samp></dt>
380 <dd><p>This should be a program to construct a symbol table in an archive file.
381 </p></dd>
382 </dl>
383
384 <p>The installation of GCC will find these programs in that directory,
385 and copy or link them to the proper place to for the cross-compiler to
386 find them when run later.
387 </p>
388 <p>The easiest way to provide these files is to build the Binutils package.
389 Configure it with the same <samp>--host</samp> and <samp>--target</samp>
390 options that you use for configuring GCC, then build and install
391 them. They install their executables automatically into the proper
392 directory. Alas, they do not support all the targets that GCC
393 supports.
394 </p>
395 <p>If you are not building a C library in the same source tree as GCC,
396 you should also provide the target libraries and headers before
397 configuring GCC, specifying the directories with
398 <samp>--with-sysroot</samp> or <samp>--with-headers</samp> and
399 <samp>--with-libs</samp>. Many targets also require “start files” such
400 as <samp>crt0.o</samp> and
401 <samp>crtn.o</samp> which are linked into each executable. There may be several
402 alternatives for <samp>crt0.o</samp>, for use with profiling or other
403 compilation options. Check your target’s definition of
404 <code>STARTFILE_SPEC</code> to find out what start files it uses.
405 </p>
406 <a name="Building-in-parallel"></a>
407 <h3 class="section">Building in parallel</h3>
408
409 <p>GNU Make 3.80 and above, which is necessary to build GCC, support
410 building in parallel. To activate this, you can use ‘<samp>make -j 2</samp>’
411 instead of ‘<samp>make</samp>’. You can also specify a bigger number, and
412 in most cases using a value greater than the number of processors in
413 your machine will result in fewer and shorter I/O latency hits, thus
414 improving overall throughput; this is especially true for slow drives
415 and network filesystems.
416 </p>
417 <a name="Building-the-Ada-compiler"></a>
418 <h3 class="section">Building the Ada compiler</h3>
419
420 <p>In order to build GNAT, the Ada compiler, you need a working GNAT
421 compiler (GCC version 4.0 or later).
422 This includes GNAT tools such as <code>gnatmake</code> and
423 <code>gnatlink</code>, since the Ada front end is written in Ada and
424 uses some GNAT-specific extensions.
425 </p>
426 <p>In order to build a cross compiler, it is suggested to install
427 the new compiler as native first, and then use it to build the cross
428 compiler.
429 </p>
430 <p><code>configure</code> does not test whether the GNAT installation works
431 and has a sufficiently recent version; if too old a GNAT version is
432 installed, the build will fail unless <samp>--enable-languages</samp> is
433 used to disable building the Ada front end.
434 </p>
435 <p><code>ADA_INCLUDE_PATH</code> and <code>ADA_OBJECT_PATH</code> environment variables
436 must not be set when building the Ada compiler, the Ada tools, or the
437 Ada runtime libraries. You can check that your build environment is clean
438 by verifying that ‘<samp>gnatls -v</samp>’ lists only one explicit path in each
439 section.
440 </p>
441 <a name="Building-with-profile-feedback"></a>
442 <h3 class="section">Building with profile feedback</h3>
443
444 <p>It is possible to use profile feedback to optimize the compiler itself. This
445 should result in a faster compiler binary. Experiments done on x86 using gcc
446 3.3 showed approximately 7 percent speedup on compiling C programs. To
447 bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>.
448 </p>
449 <p>When ‘<samp>make profiledbootstrap</samp>’ is run, it will first build a <code>stage1</code>
450 compiler. This compiler is used to build a <code>stageprofile</code> compiler
451 instrumented to collect execution counts of instruction and branch
452 probabilities. Training run is done by building <code>stagetrain</code>
453 compiler. Finally a <code>stagefeedback</code> compiler is built
454 using the information collected.
455 </p>
456 <p>Unlike standard bootstrap, several additional restrictions apply. The
457 compiler used to build <code>stage1</code> needs to support a 64-bit integral type.
458 It is recommended to only use GCC for this.
459 </p>
460 <p>On Linux/x86_64 hosts with some restrictions (no virtualization) it is
461 also possible to do autofdo build with ‘<samp>make
462 autoprofiledback</samp>’. This uses Linux perf to sample branches in the
463 binary and then rebuild it with feedback derived from the profile.
464 Linux perf and the <code>autofdo</code> toolkit needs to be installed for
465 this.
466 </p>
467 <p>Only the profile from the current build is used, so when an error
468 occurs it is recommended to clean before restarting. Otherwise
469 the code quality may be much worse.
470 </p>
471 <hr />
472 <p>
473 <p><a href="./index.html">Return to the GCC Installation page</a>
474 </p>
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