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44 1.1 mrg <h1 class="settitle">Installing GCC: Building</h1>
45 1.1 mrg <a name="index-Installing-GCC_003a-Building-1"></a>
46 1.1 mrg Now that GCC is configured, you are ready to build the compiler and
47 1.1 mrg runtime libraries.
48 1.1 mrg
49 1.1 mrg <p>Some commands executed when making the compiler may fail (return a
50 1.1 mrg nonzero status) and be ignored by <samp><span class="command">make</span></samp>. These failures, which
51 1.1 mrg are often due to files that were not found, are expected, and can safely
52 1.1 mrg be ignored.
53 1.1 mrg
54 1.1 mrg <p>It is normal to have compiler warnings when compiling certain files.
55 1.1 mrg Unless you are a GCC developer, you can generally ignore these warnings
56 1.1 mrg unless they cause compilation to fail. Developers should attempt to fix
57 1.1 mrg any warnings encountered, however they can temporarily continue past
58 1.1 mrg warnings-as-errors by specifying the configure flag
59 1.1 mrg <samp><span class="option">--disable-werror</span></samp>.
60 1.1 mrg
61 1.1 mrg <p>On certain old systems, defining certain environment variables such as
62 1.1 mrg <samp><span class="env">CC</span></samp> can interfere with the functioning of <samp><span class="command">make</span></samp>.
63 1.1 mrg
64 1.1 mrg <p>If you encounter seemingly strange errors when trying to build the
65 1.1 mrg compiler in a directory other than the source directory, it could be
66 1.1 mrg because you have previously configured the compiler in the source
67 1.1 mrg directory. Make sure you have done all the necessary preparations.
68 1.1 mrg
69 1.1 mrg <p>If you build GCC on a BSD system using a directory stored in an old System
70 1.1 mrg V file system, problems may occur in running <samp><span class="command">fixincludes</span></samp> if the
71 1.1 mrg System V file system doesn't support symbolic links. These problems
72 1.1 mrg result in a failure to fix the declaration of <code>size_t</code> in
73 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
74 1.1 mrg that type mismatches occur, this could be the cause.
75 1.1 mrg
76 1.1 mrg <p>The solution is not to use such a directory for building GCC.
77 1.1 mrg
78 1.1 mrg <p>Similarly, when building from SVN or snapshots, or if you modify
79 1.1 mrg <samp><span class="file">*.l</span></samp> files, you need the Flex lexical analyzer generator
80 1.1 mrg installed. If you do not modify <samp><span class="file">*.l</span></samp> files, releases contain
81 1.1 mrg the Flex-generated files and you do not need Flex installed to build
82 1.1 mrg them. There is still one Flex-based lexical analyzer (part of the
83 1.1 mrg build machinery, not of GCC itself) that is used even if you only
84 1.1 mrg build the C front end.
85 1.1 mrg
86 1.1 mrg <p>When building from SVN or snapshots, or if you modify Texinfo
87 1.1 mrg documentation, you need version 4.7 or later of Texinfo installed if you
88 1.1 mrg want Info documentation to be regenerated. Releases contain Info
89 1.1 mrg documentation pre-built for the unmodified documentation in the release.
90 1.1 mrg
91 1.1 mrg <h3 class="section"><a name="TOC0"></a>Building a native compiler</h3>
92 1.1 mrg
93 1.1 mrg <p>For a native build, the default configuration is to perform
94 1.1 mrg a 3-stage bootstrap of the compiler when ‘<samp><span class="samp">make</span></samp>’ is invoked.
95 1.1 mrg This will build the entire GCC system and ensure that it compiles
96 1.1 mrg itself correctly. It can be disabled with the <samp><span class="option">--disable-bootstrap</span></samp>
97 1.1 mrg parameter to ‘<samp><span class="samp">configure</span></samp>’, but bootstrapping is suggested because
98 1.1 mrg the compiler will be tested more completely and could also have
99 1.1 mrg better performance.
100 1.1 mrg
101 1.1 mrg <p>The bootstrapping process will complete the following steps:
102 1.1 mrg
103 1.1 mrg <ul>
104 1.1 mrg <li>Build tools necessary to build the compiler.
105 1.1 mrg
106 1.1 mrg <li>Perform a 3-stage bootstrap of the compiler. This includes building
107 1.1 mrg three times the target tools for use by the compiler such as binutils
108 1.1 mrg (bfd, binutils, gas, gprof, ld, and opcodes) if they have been
109 1.1 mrg individually linked or moved into the top level GCC source tree before
110 1.1 mrg configuring.
111 1.1 mrg
112 1.1 mrg <li>Perform a comparison test of the stage2 and stage3 compilers.
113 1.1 mrg
114 1.1 mrg <li>Build runtime libraries using the stage3 compiler from the previous step.
115 1.1 mrg
116 1.1 mrg </ul>
117 1.1 mrg
118 1.1 mrg <p>If you are short on disk space you might consider ‘<samp><span class="samp">make
119 1.1 mrg bootstrap-lean</span></samp>’ instead. The sequence of compilation is the
120 1.1 mrg same described above, but object files from the stage1 and
121 1.1 mrg stage2 of the 3-stage bootstrap of the compiler are deleted as
122 1.1 mrg soon as they are no longer needed.
123 1.1 mrg
124 1.1 mrg <p>If you wish to use non-default GCC flags when compiling the stage2
125 1.1 mrg and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when
126 1.1 mrg doing ‘<samp><span class="samp">make</span></samp>’. For example, if you want to save additional space
127 1.1 mrg during the bootstrap and in the final installation as well, you can
128 1.1 mrg build the compiler binaries without debugging information as in the
129 1.1 mrg following example. This will save roughly 40% of disk space both for
130 1.1 mrg the bootstrap and the final installation. (Libraries will still contain
131 1.1 mrg debugging information.)
132 1.1 mrg
133 1.1 mrg <pre class="smallexample"> make BOOT_CFLAGS='-O' bootstrap
134 1.1 mrg </pre>
135 1.1 mrg <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they
136 1.1 mrg are less well tested here than the default of ‘<samp><span class="samp">-g -O2</span></samp>’, but should
137 1.1 mrg still work. In a few cases, you may find that you need to specify special
138 1.1 mrg flags such as <samp><span class="option">-msoft-float</span></samp> here to complete the bootstrap; or,
139 1.1 mrg if the native compiler miscompiles the stage1 compiler, you may need
140 1.1 mrg to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts
141 1.1 mrg of the stage1 compiler that were miscompiled, or by using ‘<samp><span class="samp">make
142 1.1 mrg bootstrap4</span></samp>’ to increase the number of stages of bootstrap.
143 1.1 mrg
144 1.1 mrg <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries.
145 1.1 mrg Since these are always compiled with the compiler currently being
146 1.1 mrg bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their
147 1.1 mrg compilation flags, as for non-bootstrapped target libraries.
148 1.1 mrg Again, if the native compiler miscompiles the stage1 compiler, you may
149 1.1 mrg need to work around this by avoiding non-working parts of the stage1
150 1.1 mrg compiler. Use <code>STAGE1_TFLAGS</code> to this end.
151 1.1 mrg
152 1.1 mrg <p>If you used the flag <samp><span class="option">--enable-languages=...</span></samp> to restrict
153 1.1 mrg the compilers to be built, only those you've actually enabled will be
154 1.1 mrg built. This will of course only build those runtime libraries, for
155 1.1 mrg which the particular compiler has been built. Please note,
156 1.1 mrg that re-defining <samp><span class="env">LANGUAGES</span></samp> when calling ‘<samp><span class="samp">make</span></samp>’
157 1.1 mrg <strong>does not</strong> work anymore!
158 1.1 mrg
159 1.1 mrg <p>If the comparison of stage2 and stage3 fails, this normally indicates
160 1.1 mrg that the stage2 compiler has compiled GCC incorrectly, and is therefore
161 1.1 mrg a potentially serious bug which you should investigate and report. (On
162 1.1 mrg a few systems, meaningful comparison of object files is impossible; they
163 1.1 mrg always appear “different”. If you encounter this problem, you will
164 1.1 mrg need to disable comparison in the <samp><span class="file">Makefile</span></samp>.)
165 1.1 mrg
166 1.1 mrg <p>If you do not want to bootstrap your compiler, you can configure with
167 1.1 mrg <samp><span class="option">--disable-bootstrap</span></samp>. In particular cases, you may want to
168 1.1 mrg bootstrap your compiler even if the target system is not the same as
169 1.1 mrg the one you are building on: for example, you could build a
170 1.1 mrg <code>powerpc-unknown-linux-gnu</code> toolchain on a
171 1.1 mrg <code>powerpc64-unknown-linux-gnu</code> host. In this case, pass
172 1.1 mrg <samp><span class="option">--enable-bootstrap</span></samp> to the configure script.
173 1.1 mrg
174 1.1 mrg <p><code>BUILD_CONFIG</code> can be used to bring in additional customization
175 1.1 mrg to the build. It can be set to a whitespace-separated list of names.
176 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
177 1.1 mrg be included by the top-level <samp><span class="file">Makefile</span></samp>, bringing in any settings
178 1.1 mrg it contains. The default <code>BUILD_CONFIG</code> can be set using the
179 1.1 mrg configure option <samp><span class="option">--with-build-config=</span><code>NAME</code><span class="option">...</span></samp>. Some
180 1.1 mrg examples of supported build configurations are:
181 1.1 mrg
182 1.1 mrg <dl>
183 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
184 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
185 1.1 mrg ‘<samp><span class="samp">BOOT_CFLAGS='-g -O1'</span></samp>’.
186 1.1 mrg
187 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-O3</span></samp>’<dd>Analogous to <code>bootstrap-O1</code>.
188 1.1 mrg
189 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-debug</span></samp>’<dd>Verifies that the compiler generates the same executable code, whether
190 1.1 mrg or not it is asked to emit debug information. To this end, this
191 1.1 mrg option builds stage2 host programs without debug information, and uses
192 1.1 mrg <samp><span class="file">contrib/compare-debug</span></samp> to compare them with the stripped stage3
193 1.1 mrg object files. If <code>BOOT_CFLAGS</code> is overridden so as to not enable
194 1.1 mrg debug information, stage2 will have it, and stage3 won't. This option
195 1.1 mrg is enabled by default when GCC bootstrapping is enabled, if
196 1.1 mrg <code>strip</code> can turn object files compiled with and without debug
197 1.1 mrg info into identical object files. In addition to better test
198 1.1 mrg coverage, this option makes default bootstraps faster and leaner.
199 1.1 mrg
200 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-debug-big</span></samp>’<dd>Rather than comparing stripped object files, as in
201 1.1 mrg <code>bootstrap-debug</code>, this option saves internal compiler dumps
202 1.1 mrg during stage2 and stage3 and compares them as well, which helps catch
203 1.1 mrg additional potential problems, but at a great cost in terms of disk
204 1.1 mrg space. It can be specified in addition to ‘<samp><span class="samp">bootstrap-debug</span></samp>’.
205 1.1 mrg
206 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>,
207 1.1 mrg but at the expense of some recompilation. Instead of saving the dumps
208 1.1 mrg of stage2 and stage3 until the final compare, it uses
209 1.1 mrg <samp><span class="option">-fcompare-debug</span></samp> to generate, compare and remove the dumps
210 1.1 mrg during stage3, repeating the compilation that already took place in
211 1.1 mrg stage2, whose dumps were not saved.
212 1.1 mrg
213 1.1 mrg <br><dt>‘<samp><span class="samp">bootstrap-debug-lib</span></samp>’<dd>This option tests executable code invariance over debug information
214 1.1 mrg generation on target libraries, just like <code>bootstrap-debug-lean</code>
215 1.1 mrg tests it on host programs. It builds stage3 libraries with
216 1.1 mrg <samp><span class="option">-fcompare-debug</span></samp>, and it can be used along with any of the
217 1.1 mrg <code>bootstrap-debug</code> options above.
218 1.1 mrg
219 1.1 mrg <p>There aren't <code>-lean</code> or <code>-big</code> counterparts to this option
220 1.1 mrg because most libraries are only build in stage3, so bootstrap compares
221 1.1 mrg would not get significant coverage. Moreover, the few libraries built
222 1.1 mrg in stage2 are used in stage3 host programs, so we wouldn't want to
223 1.1 mrg compile stage2 libraries with different options for comparison purposes.
224 1.1 mrg
225 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
226 1.1 mrg stage is run without the option <samp><span class="option">-fcompare-debug</span></samp>. This is
227 1.1 mrg useful to verify the full <samp><span class="option">-fcompare-debug</span></samp> testing coverage. It
228 1.1 mrg must be used along with <code>bootstrap-debug-lean</code> and
229 1.1 mrg <code>bootstrap-debug-lib</code>.
230 1.1 mrg
231 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,
232 1.1 mrg built in any stage, to be logged to <samp><span class="file">time.log</span></samp>, in the top level of
233 1.1 mrg the build tree.
234 1.1 mrg
235 1.1 mrg </dl>
236 1.1 mrg
237 1.1 mrg <h3 class="section"><a name="TOC1"></a>Building a cross compiler</h3>
238 1.1 mrg
239 1.1 mrg <p>When building a cross compiler, it is not generally possible to do a
240 1.1 mrg 3-stage bootstrap of the compiler. This makes for an interesting problem
241 1.1 mrg as parts of GCC can only be built with GCC.
242 1.1 mrg
243 1.1 mrg <p>To build a cross compiler, we recommend first building and installing a
244 1.1 mrg native compiler. You can then use the native GCC compiler to build the
245 1.1 mrg cross compiler. The installed native compiler needs to be GCC version
246 1.1 mrg 2.95 or later.
247 1.1 mrg
248 1.1 mrg <p>If the cross compiler is to be built with support for the Java
249 1.1 mrg programming language and the ability to compile .java source files is
250 1.1 mrg desired, the installed native compiler used to build the cross
251 1.1 mrg compiler needs to be the same GCC version as the cross compiler. In
252 1.1 mrg addition the cross compiler needs to be configured with
253 1.1 mrg <samp><span class="option">--with-ecj-jar=...</span></samp>.
254 1.1 mrg
255 1.1 mrg <p>Assuming you have already installed a native copy of GCC and configured
256 1.1 mrg your cross compiler, issue the command <samp><span class="command">make</span></samp>, which performs the
257 1.1 mrg following steps:
258 1.1 mrg
259 1.1 mrg <ul>
260 1.1 mrg <li>Build host tools necessary to build the compiler.
261 1.1 mrg
262 1.1 mrg <li>Build target tools for use by the compiler such as binutils (bfd,
263 1.1 mrg binutils, gas, gprof, ld, and opcodes)
264 1.1 mrg if they have been individually linked or moved into the top level GCC source
265 1.1 mrg tree before configuring.
266 1.1 mrg
267 1.1 mrg <li>Build the compiler (single stage only).
268 1.1 mrg
269 1.1 mrg <li>Build runtime libraries using the compiler from the previous step.
270 1.1 mrg </ul>
271 1.1 mrg
272 1.1 mrg <p>Note that if an error occurs in any step the make process will exit.
273 1.1 mrg
274 1.1 mrg <p>If you are not building GNU binutils in the same source tree as GCC,
275 1.1 mrg you will need a cross-assembler and cross-linker installed before
276 1.1 mrg configuring GCC. Put them in the directory
277 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
278 1.1 mrg you should put in this directory:
279 1.1 mrg
280 1.1 mrg <dl>
281 1.1 mrg <dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler.
282 1.1 mrg
283 1.1 mrg <br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker.
284 1.1 mrg
285 1.1 mrg <br><dt><samp><span class="file">ar</span></samp><dd>This should be the cross-archiver: a program which can manipulate
286 1.1 mrg archive files (linker libraries) in the target machine's format.
287 1.1 mrg
288 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.
289 1.1 mrg </dl>
290 1.1 mrg
291 1.1 mrg <p>The installation of GCC will find these programs in that directory,
292 1.1 mrg and copy or link them to the proper place to for the cross-compiler to
293 1.1 mrg find them when run later.
294 1.1 mrg
295 1.1 mrg <p>The easiest way to provide these files is to build the Binutils package.
296 1.1 mrg Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></samp>
297 1.1 mrg options that you use for configuring GCC, then build and install
298 1.1 mrg them. They install their executables automatically into the proper
299 1.1 mrg directory. Alas, they do not support all the targets that GCC
300 1.1 mrg supports.
301 1.1 mrg
302 1.1 mrg <p>If you are not building a C library in the same source tree as GCC,
303 1.1 mrg you should also provide the target libraries and headers before
304 1.1 mrg configuring GCC, specifying the directories with
305 1.1 mrg <samp><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and
306 1.1 mrg <samp><span class="option">--with-libs</span></samp>. Many targets also require “start files” such
307 1.1 mrg as <samp><span class="file">crt0.o</span></samp> and
308 1.1 mrg <samp><span class="file">crtn.o</span></samp> which are linked into each executable. There may be several
309 1.1 mrg alternatives for <samp><span class="file">crt0.o</span></samp>, for use with profiling or other
310 1.1 mrg compilation options. Check your target's definition of
311 1.1 mrg <code>STARTFILE_SPEC</code> to find out what start files it uses.
312 1.1 mrg
313 1.1 mrg <h3 class="section"><a name="TOC2"></a>Building in parallel</h3>
314 1.1 mrg
315 1.1 mrg <p>GNU Make 3.80 and above, which is necessary to build GCC, support
316 1.1 mrg building in parallel. To activate this, you can use ‘<samp><span class="samp">make -j 2</span></samp>’
317 1.1 mrg instead of ‘<samp><span class="samp">make</span></samp>’. You can also specify a bigger number, and
318 1.1 mrg in most cases using a value greater than the number of processors in
319 1.1 mrg your machine will result in fewer and shorter I/O latency hits, thus
320 1.1 mrg improving overall throughput; this is especially true for slow drives
321 1.1 mrg and network filesystems.
322 1.1 mrg
323 1.1 mrg <h3 class="section"><a name="TOC3"></a>Building the Ada compiler</h3>
324 1.1 mrg
325 1.1 mrg <p>In order to build GNAT, the Ada compiler, you need a working GNAT
326 1.1 mrg compiler (GCC version 3.4 or later).
327 1.1 mrg This includes GNAT tools such as <samp><span class="command">gnatmake</span></samp> and
328 1.1 mrg <samp><span class="command">gnatlink</span></samp>, since the Ada front end is written in Ada and
329 1.1 mrg uses some GNAT-specific extensions.
330 1.1 mrg
331 1.1 mrg <p>In order to build a cross compiler, it is suggested to install
332 1.1 mrg the new compiler as native first, and then use it to build the cross
333 1.1 mrg compiler.
334 1.1 mrg
335 1.1 mrg <p><samp><span class="command">configure</span></samp> does not test whether the GNAT installation works
336 1.1 mrg and has a sufficiently recent version; if too old a GNAT version is
337 1.1 mrg installed, the build will fail unless <samp><span class="option">--enable-languages</span></samp> is
338 1.1 mrg used to disable building the Ada front end.
339 1.1 mrg
340 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
341 1.1 mrg must not be set when building the Ada compiler, the Ada tools, or the
342 1.1 mrg Ada runtime libraries. You can check that your build environment is clean
343 1.1 mrg by verifying that ‘<samp><span class="samp">gnatls -v</span></samp>’ lists only one explicit path in each
344 1.1 mrg section.
345 1.1 mrg
346 1.1 mrg <h3 class="section"><a name="TOC4"></a>Building with profile feedback</h3>
347 1.1 mrg
348 1.1 mrg <p>It is possible to use profile feedback to optimize the compiler itself. This
349 1.1 mrg should result in a faster compiler binary. Experiments done on x86 using gcc
350 1.1 mrg 3.3 showed approximately 7 percent speedup on compiling C programs. To
351 1.1 mrg bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>.
352 1.1 mrg
353 1.1 mrg <p>When ‘<samp><span class="samp">make profiledbootstrap</span></samp>’ is run, it will first build a <code>stage1</code>
354 1.1 mrg compiler. This compiler is used to build a <code>stageprofile</code> compiler
355 1.1 mrg instrumented to collect execution counts of instruction and branch
356 1.1 mrg probabilities. Then runtime libraries are compiled with profile collected.
357 1.1 mrg Finally a <code>stagefeedback</code> compiler is built using the information collected.
358 1.1 mrg
359 1.1 mrg <p>Unlike standard bootstrap, several additional restrictions apply. The
360 1.1 mrg compiler used to build <code>stage1</code> needs to support a 64-bit integral type.
361 1.1 mrg It is recommended to only use GCC for this. Also parallel make is currently
362 1.1 mrg not supported since collisions in profile collecting may occur.
363 1.1 mrg
364 1.1 mrg <p><hr />
365 1.1 mrg <p><a href="./index.html">Return to the GCC Installation page</a>
366 1.1 mrg
367 1.1 mrg <!-- ***Testing***************************************************************** -->
368 1.1 mrg <!-- ***Final install*********************************************************** -->
369 1.1 mrg <!-- ***Binaries**************************************************************** -->
370 1.1 mrg <!-- ***Specific**************************************************************** -->
371 1.1 mrg <!-- ***Old documentation****************************************************** -->
372 1.1 mrg <!-- ***GFDL******************************************************************** -->
373 1.1 mrg <!-- *************************************************************************** -->
374 1.1 mrg <!-- Part 6 The End of the Document -->
375 1.1 mrg </body></html>
376 1.1 mrg
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