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42 1.1 mrg <h1 class="settitle">Installing GCC: Building</h1>
43 1.1 mrg <a name="index-Installing-GCC_003a-Building-1"></a>
44 1.1 mrg Now that GCC is configured, you are ready to build the compiler and
45 1.1 mrg runtime libraries.
46 1.1 mrg
47 1.1 mrg <p>Some commands executed when making the compiler may fail (return a
48 1.1 mrg nonzero status) and be ignored by <samp><span class="command">make</span></samp>. These failures, which
49 1.1 mrg are often due to files that were not found, are expected, and can safely
50 1.1 mrg be ignored.
51 1.1 mrg
52 1.1 mrg <p>It is normal to have compiler warnings when compiling certain files.
53 1.1 mrg Unless you are a GCC developer, you can generally ignore these warnings
54 1.1 mrg unless they cause compilation to fail. Developers should attempt to fix
55 1.1 mrg any warnings encountered, however they can temporarily continue past
56 1.1 mrg warnings-as-errors by specifying the configure flag
57 1.1 mrg <samp><span class="option">--disable-werror</span></samp>.
58 1.1 mrg
59 1.1 mrg <p>On certain old systems, defining certain environment variables such as
60 1.1 mrg <samp><span class="env">CC</span></samp> can interfere with the functioning of <samp><span class="command">make</span></samp>.
61 1.1 mrg
62 1.1 mrg <p>If you encounter seemingly strange errors when trying to build the
63 1.1 mrg compiler in a directory other than the source directory, it could be
64 1.1 mrg because you have previously configured the compiler in the source
65 1.1 mrg directory. Make sure you have done all the necessary preparations.
66 1.1 mrg
67 1.1 mrg <p>If you build GCC on a BSD system using a directory stored in an old System
68 1.1 mrg V file system, problems may occur in running <samp><span class="command">fixincludes</span></samp> if the
69 1.1 mrg System V file system doesn't support symbolic links. These problems
70 1.1 mrg result in a failure to fix the declaration of <code>size_t</code> in
71 1.1 mrg <samp><span class="file">sys/types.h</span></samp>. If you find that <code>size_t</code> is a signed type and
72 1.1 mrg that type mismatches occur, this could be the cause.
73 1.1 mrg
74 1.1 mrg <p>The solution is not to use such a directory for building GCC.
75 1.1 mrg
76 1.1 mrg <p>Similarly, when building from SVN or snapshots, or if you modify
77 1.1 mrg <samp><span class="file">*.l</span></samp> files, you need the Flex lexical analyzer generator
78 1.1 mrg installed. If you do not modify <samp><span class="file">*.l</span></samp> files, releases contain
79 1.1 mrg the Flex-generated files and you do not need Flex installed to build
80 1.1 mrg them. There is still one Flex-based lexical analyzer (part of the
81 1.1 mrg build machinery, not of GCC itself) that is used even if you only
82 1.1 mrg build the C front end.
83 1.1 mrg
84 1.1 mrg <p>When building from SVN or snapshots, or if you modify Texinfo
85 1.1 mrg documentation, you need version 4.7 or later of Texinfo installed if you
86 1.1 mrg want Info documentation to be regenerated. Releases contain Info
87 1.1 mrg documentation pre-built for the unmodified documentation in the release.
88 1.1 mrg
89 1.1 mrg <h3 class="section"><a name="TOC0"></a>Building a native compiler</h3>
90 1.1 mrg
91 1.1 mrg <p>For a native build, the default configuration is to perform
92 1.1 mrg a 3-stage bootstrap of the compiler when ‘<samp><span class="samp">make</span></samp>’ is invoked.
93 1.1 mrg This will build the entire GCC system and ensure that it compiles
94 1.1 mrg itself correctly. It can be disabled with the <samp><span class="option">--disable-bootstrap</span></samp>
95 1.1 mrg parameter to ‘<samp><span class="samp">configure</span></samp>’, but bootstrapping is suggested because
96 1.1 mrg the compiler will be tested more completely and could also have
97 1.1 mrg better performance.
98 1.1 mrg
99 1.1 mrg <p>The bootstrapping process will complete the following steps:
100 1.1 mrg
101 1.1 mrg <ul>
102 1.1 mrg <li>Build tools necessary to build the compiler.
103 1.1 mrg
104 1.1 mrg <li>Perform a 3-stage bootstrap of the compiler. This includes building
105 1.1 mrg three times the target tools for use by the compiler such as binutils
106 1.1 mrg (bfd, binutils, gas, gprof, ld, and opcodes) if they have been
107 1.1 mrg individually linked or moved into the top level GCC source tree before
108 1.1 mrg configuring.
109 1.1 mrg
110 1.1 mrg <li>Perform a comparison test of the stage2 and stage3 compilers.
111 1.1 mrg
112 1.1 mrg <li>Build runtime libraries using the stage3 compiler from the previous step.
113 1.1 mrg
114 1.1 mrg </ul>
115 1.1 mrg
116 1.1 mrg <p>If you are short on disk space you might consider ‘<samp><span class="samp">make
117 1.1 mrg bootstrap-lean</span></samp>’ instead. The sequence of compilation is the
118 1.1 mrg same described above, but object files from the stage1 and
119 1.1 mrg stage2 of the 3-stage bootstrap of the compiler are deleted as
120 1.1 mrg soon as they are no longer needed.
121 1.1 mrg
122 1.1 mrg <p>If you wish to use non-default GCC flags when compiling the stage2
123 1.1 mrg and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when
124 1.1 mrg doing ‘<samp><span class="samp">make</span></samp>’. For example, if you want to save additional space
125 1.1 mrg during the bootstrap and in the final installation as well, you can
126 1.1 mrg build the compiler binaries without debugging information as in the
127 1.1 mrg following example. This will save roughly 40% of disk space both for
128 1.1 mrg the bootstrap and the final installation. (Libraries will still contain
129 1.1 mrg debugging information.)
130 1.1 mrg
131 1.3 skrll <pre class="smallexample"> make BOOT_CFLAGS='-O' bootstrap
132 1.1 mrg </pre>
133 1.1 mrg <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they
134 1.1 mrg are less well tested here than the default of ‘<samp><span class="samp">-g -O2</span></samp>’, but should
135 1.1 mrg still work. In a few cases, you may find that you need to specify special
136 1.1 mrg flags such as <samp><span class="option">-msoft-float</span></samp> here to complete the bootstrap; or,
137 1.1 mrg if the native compiler miscompiles the stage1 compiler, you may need
138 1.1 mrg to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts
139 1.1 mrg of the stage1 compiler that were miscompiled, or by using ‘<samp><span class="samp">make
140 1.1 mrg bootstrap4</span></samp>’ to increase the number of stages of bootstrap.
141 1.1 mrg
142 1.1 mrg <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries.
143 1.1 mrg Since these are always compiled with the compiler currently being
144 1.1 mrg bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their
145 1.1 mrg compilation flags, as for non-bootstrapped target libraries.
146 1.1 mrg Again, if the native compiler miscompiles the stage1 compiler, you may
147 1.1 mrg need to work around this by avoiding non-working parts of the stage1
148 1.1 mrg compiler. Use <code>STAGE1_TFLAGS</code> to this end.
149 1.1 mrg
150 1.1 mrg <p>If you used the flag <samp><span class="option">--enable-languages=...</span></samp> to restrict
151 1.1 mrg the compilers to be built, only those you've actually enabled will be
152 1.1 mrg built. This will of course only build those runtime libraries, for
153 1.1 mrg which the particular compiler has been built. Please note,
154 1.1 mrg that re-defining <samp><span class="env">LANGUAGES</span></samp> when calling ‘<samp><span class="samp">make</span></samp>’
155 1.1 mrg <strong>does not</strong> work anymore!
156 1.1 mrg
157 1.1 mrg <p>If the comparison of stage2 and stage3 fails, this normally indicates
158 1.1 mrg that the stage2 compiler has compiled GCC incorrectly, and is therefore
159 1.1 mrg a potentially serious bug which you should investigate and report. (On
160 1.1 mrg a few systems, meaningful comparison of object files is impossible; they
161 1.1 mrg always appear “different”. If you encounter this problem, you will
162 1.1 mrg need to disable comparison in the <samp><span class="file">Makefile</span></samp>.)
163 1.1 mrg
164 1.1 mrg <p>If you do not want to bootstrap your compiler, you can configure with
165 1.1 mrg <samp><span class="option">--disable-bootstrap</span></samp>. In particular cases, you may want to
166 1.1 mrg bootstrap your compiler even if the target system is not the same as
167 1.1 mrg the one you are building on: for example, you could build a
168 1.1 mrg <code>powerpc-unknown-linux-gnu</code> toolchain on a
169 1.1 mrg <code>powerpc64-unknown-linux-gnu</code> host. In this case, pass
170 1.1 mrg <samp><span class="option">--enable-bootstrap</span></samp> to the configure script.
171 1.1 mrg
172 1.1 mrg <p><code>BUILD_CONFIG</code> can be used to bring in additional customization
173 1.1 mrg to the build. It can be set to a whitespace-separated list of names.
174 1.1 mrg For each such <code>NAME</code>, top-level <samp><span class="file">config/</span><code>NAME</code><span class="file">.mk</span></samp> will
175 1.1 mrg be included by the top-level <samp><span class="file">Makefile</span></samp>, bringing in any settings
176 1.1 mrg it contains. The default <code>BUILD_CONFIG</code> can be set using the
177 1.1 mrg configure option <samp><span class="option">--with-build-config=</span><code>NAME</code><span class="option">...</span></samp>. Some
178 1.1 mrg examples of supported build configurations are:
179 1.1 mrg
180 1.1 mrg <dl>
181 1.1 mrg <dt>‘<samp><span class="samp">bootstrap-O1</span></samp>’<dd>Removes any <samp><span class="option">-O</span></samp>-started option from <code>BOOT_CFLAGS</code>, and adds
182 1.1 mrg <samp><span class="option">-O1</span></samp> to it. ‘<samp><span class="samp">BUILD_CONFIG=bootstrap-O1</span></samp>’ is equivalent to
183 1.1 mrg ‘<samp><span class="samp">BOOT_CFLAGS='-g -O1'</span></samp>’.
184 1.1 mrg
185 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-O3</span></samp>’<dd>Analogous to <code>bootstrap-O1</code>.
186 1.1 mrg
187 1.3 skrll <br><dt>‘<samp><span class="samp">bootstrap-lto</span></samp>’<dd>Enables Link-Time Optimization for host tools during bootstrapping.
188 1.3 skrll ‘<samp><span class="samp">BUILD_CONFIG=bootstrap-lto</span></samp>’ is equivalent to adding
189 1.3 skrll <samp><span class="option">-flto</span></samp> to ‘<samp><span class="samp">BOOT_CFLAGS</span></samp>’.
190 1.3 skrll
191 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-debug</span></samp>’<dd>Verifies that the compiler generates the same executable code, whether
192 1.1 mrg or not it is asked to emit debug information. To this end, this
193 1.1 mrg option builds stage2 host programs without debug information, and uses
194 1.1 mrg <samp><span class="file">contrib/compare-debug</span></samp> to compare them with the stripped stage3
195 1.1 mrg object files. If <code>BOOT_CFLAGS</code> is overridden so as to not enable
196 1.1 mrg debug information, stage2 will have it, and stage3 won't. This option
197 1.1 mrg is enabled by default when GCC bootstrapping is enabled, if
198 1.1 mrg <code>strip</code> can turn object files compiled with and without debug
199 1.1 mrg info into identical object files. In addition to better test
200 1.1 mrg coverage, this option makes default bootstraps faster and leaner.
201 1.1 mrg
202 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-debug-big</span></samp>’<dd>Rather than comparing stripped object files, as in
203 1.1 mrg <code>bootstrap-debug</code>, this option saves internal compiler dumps
204 1.1 mrg during stage2 and stage3 and compares them as well, which helps catch
205 1.1 mrg additional potential problems, but at a great cost in terms of disk
206 1.1 mrg space. It can be specified in addition to ‘<samp><span class="samp">bootstrap-debug</span></samp>’.
207 1.1 mrg
208 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-debug-lean</span></samp>’<dd>This option saves disk space compared with <code>bootstrap-debug-big</code>,
209 1.1 mrg but at the expense of some recompilation. Instead of saving the dumps
210 1.1 mrg of stage2 and stage3 until the final compare, it uses
211 1.1 mrg <samp><span class="option">-fcompare-debug</span></samp> to generate, compare and remove the dumps
212 1.1 mrg during stage3, repeating the compilation that already took place in
213 1.1 mrg stage2, whose dumps were not saved.
214 1.1 mrg
215 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-debug-lib</span></samp>’<dd>This option tests executable code invariance over debug information
216 1.1 mrg generation on target libraries, just like <code>bootstrap-debug-lean</code>
217 1.1 mrg tests it on host programs. It builds stage3 libraries with
218 1.1 mrg <samp><span class="option">-fcompare-debug</span></samp>, and it can be used along with any of the
219 1.1 mrg <code>bootstrap-debug</code> options above.
220 1.1 mrg
221 1.1 mrg <p>There aren't <code>-lean</code> or <code>-big</code> counterparts to this option
222 1.1 mrg because most libraries are only build in stage3, so bootstrap compares
223 1.1 mrg would not get significant coverage. Moreover, the few libraries built
224 1.1 mrg in stage2 are used in stage3 host programs, so we wouldn't want to
225 1.1 mrg compile stage2 libraries with different options for comparison purposes.
226 1.1 mrg
227 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-debug-ckovw</span></samp>’<dd>Arranges for error messages to be issued if the compiler built on any
228 1.1 mrg stage is run without the option <samp><span class="option">-fcompare-debug</span></samp>. This is
229 1.1 mrg useful to verify the full <samp><span class="option">-fcompare-debug</span></samp> testing coverage. It
230 1.1 mrg must be used along with <code>bootstrap-debug-lean</code> and
231 1.1 mrg <code>bootstrap-debug-lib</code>.
232 1.1 mrg
233 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-time</span></samp>’<dd>Arranges for the run time of each program started by the GCC driver,
234 1.1 mrg built in any stage, to be logged to <samp><span class="file">time.log</span></samp>, in the top level of
235 1.1 mrg the build tree.
236 1.1 mrg
237 1.1 mrg </dl>
238 1.1 mrg
239 1.1 mrg <h3 class="section"><a name="TOC1"></a>Building a cross compiler</h3>
240 1.1 mrg
241 1.1 mrg <p>When building a cross compiler, it is not generally possible to do a
242 1.1 mrg 3-stage bootstrap of the compiler. This makes for an interesting problem
243 1.1 mrg as parts of GCC can only be built with GCC.
244 1.1 mrg
245 1.1 mrg <p>To build a cross compiler, we recommend first building and installing a
246 1.1 mrg native compiler. You can then use the native GCC compiler to build the
247 1.1 mrg cross compiler. The installed native compiler needs to be GCC version
248 1.1 mrg 2.95 or later.
249 1.1 mrg
250 1.1 mrg <p>If the cross compiler is to be built with support for the Java
251 1.1 mrg programming language and the ability to compile .java source files is
252 1.1 mrg desired, the installed native compiler used to build the cross
253 1.1 mrg compiler needs to be the same GCC version as the cross compiler. In
254 1.1 mrg addition the cross compiler needs to be configured with
255 1.1 mrg <samp><span class="option">--with-ecj-jar=...</span></samp>.
256 1.1 mrg
257 1.1 mrg <p>Assuming you have already installed a native copy of GCC and configured
258 1.1 mrg your cross compiler, issue the command <samp><span class="command">make</span></samp>, which performs the
259 1.1 mrg following steps:
260 1.1 mrg
261 1.1 mrg <ul>
262 1.1 mrg <li>Build host tools necessary to build the compiler.
263 1.1 mrg
264 1.1 mrg <li>Build target tools for use by the compiler such as binutils (bfd,
265 1.1 mrg binutils, gas, gprof, ld, and opcodes)
266 1.1 mrg if they have been individually linked or moved into the top level GCC source
267 1.1 mrg tree before configuring.
268 1.1 mrg
269 1.1 mrg <li>Build the compiler (single stage only).
270 1.1 mrg
271 1.1 mrg <li>Build runtime libraries using the compiler from the previous step.
272 1.1 mrg </ul>
273 1.1 mrg
274 1.1 mrg <p>Note that if an error occurs in any step the make process will exit.
275 1.1 mrg
276 1.1 mrg <p>If you are not building GNU binutils in the same source tree as GCC,
277 1.1 mrg you will need a cross-assembler and cross-linker installed before
278 1.1 mrg configuring GCC. Put them in the directory
279 1.1 mrg <samp><var>prefix</var><span class="file">/</span><var>target</var><span class="file">/bin</span></samp>. Here is a table of the tools
280 1.1 mrg you should put in this directory:
281 1.1 mrg
282 1.1 mrg <dl>
283 1.1 mrg <dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler.
284 1.1 mrg
285 1.1 mrg <br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker.
286 1.1 mrg
287 1.1 mrg <br><dt><samp><span class="file">ar</span></samp><dd>This should be the cross-archiver: a program which can manipulate
288 1.1 mrg archive files (linker libraries) in the target machine's format.
289 1.1 mrg
290 1.1 mrg <br><dt><samp><span class="file">ranlib</span></samp><dd>This should be a program to construct a symbol table in an archive file.
291 1.1 mrg </dl>
292 1.1 mrg
293 1.1 mrg <p>The installation of GCC will find these programs in that directory,
294 1.1 mrg and copy or link them to the proper place to for the cross-compiler to
295 1.1 mrg find them when run later.
296 1.1 mrg
297 1.1 mrg <p>The easiest way to provide these files is to build the Binutils package.
298 1.1 mrg Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></samp>
299 1.1 mrg options that you use for configuring GCC, then build and install
300 1.1 mrg them. They install their executables automatically into the proper
301 1.1 mrg directory. Alas, they do not support all the targets that GCC
302 1.1 mrg supports.
303 1.1 mrg
304 1.1 mrg <p>If you are not building a C library in the same source tree as GCC,
305 1.1 mrg you should also provide the target libraries and headers before
306 1.1 mrg configuring GCC, specifying the directories with
307 1.1 mrg <samp><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and
308 1.1 mrg <samp><span class="option">--with-libs</span></samp>. Many targets also require “start files” such
309 1.1 mrg as <samp><span class="file">crt0.o</span></samp> and
310 1.1 mrg <samp><span class="file">crtn.o</span></samp> which are linked into each executable. There may be several
311 1.1 mrg alternatives for <samp><span class="file">crt0.o</span></samp>, for use with profiling or other
312 1.1 mrg compilation options. Check your target's definition of
313 1.1 mrg <code>STARTFILE_SPEC</code> to find out what start files it uses.
314 1.1 mrg
315 1.1 mrg <h3 class="section"><a name="TOC2"></a>Building in parallel</h3>
316 1.1 mrg
317 1.1 mrg <p>GNU Make 3.80 and above, which is necessary to build GCC, support
318 1.1 mrg building in parallel. To activate this, you can use ‘<samp><span class="samp">make -j 2</span></samp>’
319 1.1 mrg instead of ‘<samp><span class="samp">make</span></samp>’. You can also specify a bigger number, and
320 1.1 mrg in most cases using a value greater than the number of processors in
321 1.1 mrg your machine will result in fewer and shorter I/O latency hits, thus
322 1.1 mrg improving overall throughput; this is especially true for slow drives
323 1.1 mrg and network filesystems.
324 1.1 mrg
325 1.1 mrg <h3 class="section"><a name="TOC3"></a>Building the Ada compiler</h3>
326 1.1 mrg
327 1.1 mrg <p>In order to build GNAT, the Ada compiler, you need a working GNAT
328 1.3 skrll compiler (GCC version 4.0 or later).
329 1.1 mrg This includes GNAT tools such as <samp><span class="command">gnatmake</span></samp> and
330 1.1 mrg <samp><span class="command">gnatlink</span></samp>, since the Ada front end is written in Ada and
331 1.1 mrg uses some GNAT-specific extensions.
332 1.1 mrg
333 1.1 mrg <p>In order to build a cross compiler, it is suggested to install
334 1.1 mrg the new compiler as native first, and then use it to build the cross
335 1.1 mrg compiler.
336 1.1 mrg
337 1.1 mrg <p><samp><span class="command">configure</span></samp> does not test whether the GNAT installation works
338 1.1 mrg and has a sufficiently recent version; if too old a GNAT version is
339 1.1 mrg installed, the build will fail unless <samp><span class="option">--enable-languages</span></samp> is
340 1.1 mrg used to disable building the Ada front end.
341 1.1 mrg
342 1.1 mrg <p><samp><span class="env">ADA_INCLUDE_PATH</span></samp> and <samp><span class="env">ADA_OBJECT_PATH</span></samp> environment variables
343 1.1 mrg must not be set when building the Ada compiler, the Ada tools, or the
344 1.1 mrg Ada runtime libraries. You can check that your build environment is clean
345 1.1 mrg by verifying that ‘<samp><span class="samp">gnatls -v</span></samp>’ lists only one explicit path in each
346 1.1 mrg section.
347 1.1 mrg
348 1.1 mrg <h3 class="section"><a name="TOC4"></a>Building with profile feedback</h3>
349 1.1 mrg
350 1.1 mrg <p>It is possible to use profile feedback to optimize the compiler itself. This
351 1.1 mrg should result in a faster compiler binary. Experiments done on x86 using gcc
352 1.1 mrg 3.3 showed approximately 7 percent speedup on compiling C programs. To
353 1.1 mrg bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>.
354 1.1 mrg
355 1.1 mrg <p>When ‘<samp><span class="samp">make profiledbootstrap</span></samp>’ is run, it will first build a <code>stage1</code>
356 1.1 mrg compiler. This compiler is used to build a <code>stageprofile</code> compiler
357 1.1 mrg instrumented to collect execution counts of instruction and branch
358 1.1 mrg probabilities. Then runtime libraries are compiled with profile collected.
359 1.1 mrg Finally a <code>stagefeedback</code> compiler is built using the information collected.
360 1.1 mrg
361 1.1 mrg <p>Unlike standard bootstrap, several additional restrictions apply. The
362 1.1 mrg compiler used to build <code>stage1</code> needs to support a 64-bit integral type.
363 1.1 mrg It is recommended to only use GCC for this. Also parallel make is currently
364 1.1 mrg not supported since collisions in profile collecting may occur.
365 1.1 mrg
366 1.1 mrg <p><hr />
367 1.1 mrg <p><a href="./index.html">Return to the GCC Installation page</a>
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376 1.1 mrg <!-- Part 6 The End of the Document -->
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