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44 <h1 class="settitle">Installing GCC: Building</h1>
45 <a name="index-Installing-GCC_003a-Building-1"></a>
46 Now that GCC is configured, you are ready to build the compiler and
49 <p>Some commands executed when making the compiler may fail (return a
50 nonzero status) and be ignored by <samp><span class="command">make</span></samp>. These failures, which
51 are often due to files that were not found, are expected, and can safely
54 <p>It is normal to have compiler warnings when compiling certain files.
55 Unless you are a GCC developer, you can generally ignore these warnings
56 unless they cause compilation to fail. Developers should attempt to fix
57 any warnings encountered, however they can temporarily continue past
58 warnings-as-errors by specifying the configure flag
59 <samp><span class="option">--disable-werror</span></samp>.
61 <p>On certain old systems, defining certain environment variables such as
62 <samp><span class="env">CC</span></samp> can interfere with the functioning of <samp><span class="command">make</span></samp>.
64 <p>If you encounter seemingly strange errors when trying to build the
65 compiler in a directory other than the source directory, it could be
66 because you have previously configured the compiler in the source
67 directory. Make sure you have done all the necessary preparations.
69 <p>If you build GCC on a BSD system using a directory stored in an old System
70 V file system, problems may occur in running <samp><span class="command">fixincludes</span></samp> if the
71 System V file system doesn't support symbolic links. These problems
72 result in a failure to fix the declaration of <code>size_t</code> in
73 <samp><span class="file">sys/types.h</span></samp>. If you find that <code>size_t</code> is a signed type and
74 that type mismatches occur, this could be the cause.
76 <p>The solution is not to use such a directory for building GCC.
78 <p>Similarly, when building from SVN or snapshots, or if you modify
79 <samp><span class="file">*.l</span></samp> files, you need the Flex lexical analyzer generator
80 installed. If you do not modify <samp><span class="file">*.l</span></samp> files, releases contain
81 the Flex-generated files and you do not need Flex installed to build
82 them. There is still one Flex-based lexical analyzer (part of the
83 build machinery, not of GCC itself) that is used even if you only
84 build the C front end.
86 <p>When building from SVN or snapshots, or if you modify Texinfo
87 documentation, you need version 4.7 or later of Texinfo installed if you
88 want Info documentation to be regenerated. Releases contain Info
89 documentation pre-built for the unmodified documentation in the release.
91 <h3 class="section"><a name="TOC0"></a>Building a native compiler</h3>
93 <p>For a native build, the default configuration is to perform
94 a 3-stage bootstrap of the compiler when ‘<samp><span class="samp">make</span></samp>’ is invoked.
95 This will build the entire GCC system and ensure that it compiles
96 itself correctly. It can be disabled with the <samp><span class="option">--disable-bootstrap</span></samp>
97 parameter to ‘<samp><span class="samp">configure</span></samp>’, but bootstrapping is suggested because
98 the compiler will be tested more completely and could also have
101 <p>The bootstrapping process will complete the following steps:
104 <li>Build tools necessary to build the compiler.
106 <li>Perform a 3-stage bootstrap of the compiler. This includes building
107 three times the target tools for use by the compiler such as binutils
108 (bfd, binutils, gas, gprof, ld, and opcodes) if they have been
109 individually linked or moved into the top level GCC source tree before
112 <li>Perform a comparison test of the stage2 and stage3 compilers.
114 <li>Build runtime libraries using the stage3 compiler from the previous step.
118 <p>If you are short on disk space you might consider ‘<samp><span class="samp">make
119 bootstrap-lean</span></samp>’ instead. The sequence of compilation is the
120 same described above, but object files from the stage1 and
121 stage2 of the 3-stage bootstrap of the compiler are deleted as
122 soon as they are no longer needed.
124 <p>If you wish to use non-default GCC flags when compiling the stage2
125 and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when
126 doing ‘<samp><span class="samp">make</span></samp>’. For example, if you want to save additional space
127 during the bootstrap and in the final installation as well, you can
128 build the compiler binaries without debugging information as in the
129 following example. This will save roughly 40% of disk space both for
130 the bootstrap and the final installation. (Libraries will still contain
131 debugging information.)
133 <pre class="smallexample"> make BOOT_CFLAGS='-O' bootstrap
135 <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they
136 are less well tested here than the default of ‘<samp><span class="samp">-g -O2</span></samp>’, but should
137 still work. In a few cases, you may find that you need to specify special
138 flags such as <samp><span class="option">-msoft-float</span></samp> here to complete the bootstrap; or,
139 if the native compiler miscompiles the stage1 compiler, you may need
140 to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts
141 of the stage1 compiler that were miscompiled, or by using ‘<samp><span class="samp">make
142 bootstrap4</span></samp>’ to increase the number of stages of bootstrap.
144 <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries.
145 Since these are always compiled with the compiler currently being
146 bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their
147 compilation flags, as for non-bootstrapped target libraries.
148 Again, if the native compiler miscompiles the stage1 compiler, you may
149 need to work around this by avoiding non-working parts of the stage1
150 compiler. Use <code>STAGE1_TFLAGS</code> to this end.
152 <p>If you used the flag <samp><span class="option">--enable-languages=...</span></samp> to restrict
153 the compilers to be built, only those you've actually enabled will be
154 built. This will of course only build those runtime libraries, for
155 which the particular compiler has been built. Please note,
156 that re-defining <samp><span class="env">LANGUAGES</span></samp> when calling ‘<samp><span class="samp">make</span></samp>’
157 <strong>does not</strong> work anymore!
159 <p>If the comparison of stage2 and stage3 fails, this normally indicates
160 that the stage2 compiler has compiled GCC incorrectly, and is therefore
161 a potentially serious bug which you should investigate and report. (On
162 a few systems, meaningful comparison of object files is impossible; they
163 always appear “different”. If you encounter this problem, you will
164 need to disable comparison in the <samp><span class="file">Makefile</span></samp>.)
166 <p>If you do not want to bootstrap your compiler, you can configure with
167 <samp><span class="option">--disable-bootstrap</span></samp>. In particular cases, you may want to
168 bootstrap your compiler even if the target system is not the same as
169 the one you are building on: for example, you could build a
170 <code>powerpc-unknown-linux-gnu</code> toolchain on a
171 <code>powerpc64-unknown-linux-gnu</code> host. In this case, pass
172 <samp><span class="option">--enable-bootstrap</span></samp> to the configure script.
174 <p><code>BUILD_CONFIG</code> can be used to bring in additional customization
175 to the build. It can be set to a whitespace-separated list of names.
176 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 be included by the top-level <samp><span class="file">Makefile</span></samp>, bringing in any settings
178 it contains. The default <code>BUILD_CONFIG</code> can be set using the
179 configure option <samp><span class="option">--with-build-config=</span><code>NAME</code><span class="option">...</span></samp>. Some
180 examples of supported build configurations are:
183 <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 <samp><span class="option">-O1</span></samp> to it. ‘<samp><span class="samp">BUILD_CONFIG=bootstrap-O1</span></samp>’ is equivalent to
185 ‘<samp><span class="samp">BOOT_CFLAGS='-g -O1'</span></samp>’.
187 <br><dt>‘<samp><span class="samp">bootstrap-O3</span></samp>’<dd>Analogous to <code>bootstrap-O1</code>.
189 <br><dt>‘<samp><span class="samp">bootstrap-lto</span></samp>’<dd>Enables Link-Time Optimization for host tools during bootstrapping.
190 ‘<samp><span class="samp">BUILD_CONFIG=bootstrap-lto</span></samp>’ is equivalent to adding
191 <samp><span class="option">-flto</span></samp> to ‘<samp><span class="samp">BOOT_CFLAGS</span></samp>’.
193 <br><dt>‘<samp><span class="samp">bootstrap-debug</span></samp>’<dd>Verifies that the compiler generates the same executable code, whether
194 or not it is asked to emit debug information. To this end, this
195 option builds stage2 host programs without debug information, and uses
196 <samp><span class="file">contrib/compare-debug</span></samp> to compare them with the stripped stage3
197 object files. If <code>BOOT_CFLAGS</code> is overridden so as to not enable
198 debug information, stage2 will have it, and stage3 won't. This option
199 is enabled by default when GCC bootstrapping is enabled, if
200 <code>strip</code> can turn object files compiled with and without debug
201 info into identical object files. In addition to better test
202 coverage, this option makes default bootstraps faster and leaner.
204 <br><dt>‘<samp><span class="samp">bootstrap-debug-big</span></samp>’<dd>Rather than comparing stripped object files, as in
205 <code>bootstrap-debug</code>, this option saves internal compiler dumps
206 during stage2 and stage3 and compares them as well, which helps catch
207 additional potential problems, but at a great cost in terms of disk
208 space. It can be specified in addition to ‘<samp><span class="samp">bootstrap-debug</span></samp>’.
210 <br><dt>‘<samp><span class="samp">bootstrap-debug-lean</span></samp>’<dd>This option saves disk space compared with <code>bootstrap-debug-big</code>,
211 but at the expense of some recompilation. Instead of saving the dumps
212 of stage2 and stage3 until the final compare, it uses
213 <samp><span class="option">-fcompare-debug</span></samp> to generate, compare and remove the dumps
214 during stage3, repeating the compilation that already took place in
215 stage2, whose dumps were not saved.
217 <br><dt>‘<samp><span class="samp">bootstrap-debug-lib</span></samp>’<dd>This option tests executable code invariance over debug information
218 generation on target libraries, just like <code>bootstrap-debug-lean</code>
219 tests it on host programs. It builds stage3 libraries with
220 <samp><span class="option">-fcompare-debug</span></samp>, and it can be used along with any of the
221 <code>bootstrap-debug</code> options above.
223 <p>There aren't <code>-lean</code> or <code>-big</code> counterparts to this option
224 because most libraries are only build in stage3, so bootstrap compares
225 would not get significant coverage. Moreover, the few libraries built
226 in stage2 are used in stage3 host programs, so we wouldn't want to
227 compile stage2 libraries with different options for comparison purposes.
229 <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
230 stage is run without the option <samp><span class="option">-fcompare-debug</span></samp>. This is
231 useful to verify the full <samp><span class="option">-fcompare-debug</span></samp> testing coverage. It
232 must be used along with <code>bootstrap-debug-lean</code> and
233 <code>bootstrap-debug-lib</code>.
235 <br><dt>‘<samp><span class="samp">bootstrap-time</span></samp>’<dd>Arranges for the run time of each program started by the GCC driver,
236 built in any stage, to be logged to <samp><span class="file">time.log</span></samp>, in the top level of
241 <h3 class="section"><a name="TOC1"></a>Building a cross compiler</h3>
243 <p>When building a cross compiler, it is not generally possible to do a
244 3-stage bootstrap of the compiler. This makes for an interesting problem
245 as parts of GCC can only be built with GCC.
247 <p>To build a cross compiler, we recommend first building and installing a
248 native compiler. You can then use the native GCC compiler to build the
249 cross compiler. The installed native compiler needs to be GCC version
252 <p>If the cross compiler is to be built with support for the Java
253 programming language and the ability to compile .java source files is
254 desired, the installed native compiler used to build the cross
255 compiler needs to be the same GCC version as the cross compiler. In
256 addition the cross compiler needs to be configured with
257 <samp><span class="option">--with-ecj-jar=...</span></samp>.
259 <p>Assuming you have already installed a native copy of GCC and configured
260 your cross compiler, issue the command <samp><span class="command">make</span></samp>, which performs the
264 <li>Build host tools necessary to build the compiler.
266 <li>Build target tools for use by the compiler such as binutils (bfd,
267 binutils, gas, gprof, ld, and opcodes)
268 if they have been individually linked or moved into the top level GCC source
269 tree before configuring.
271 <li>Build the compiler (single stage only).
273 <li>Build runtime libraries using the compiler from the previous step.
276 <p>Note that if an error occurs in any step the make process will exit.
278 <p>If you are not building GNU binutils in the same source tree as GCC,
279 you will need a cross-assembler and cross-linker installed before
280 configuring GCC. Put them in the directory
281 <samp><var>prefix</var><span class="file">/</span><var>target</var><span class="file">/bin</span></samp>. Here is a table of the tools
282 you should put in this directory:
285 <dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler.
287 <br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker.
289 <br><dt><samp><span class="file">ar</span></samp><dd>This should be the cross-archiver: a program which can manipulate
290 archive files (linker libraries) in the target machine's format.
292 <br><dt><samp><span class="file">ranlib</span></samp><dd>This should be a program to construct a symbol table in an archive file.
295 <p>The installation of GCC will find these programs in that directory,
296 and copy or link them to the proper place to for the cross-compiler to
297 find them when run later.
299 <p>The easiest way to provide these files is to build the Binutils package.
300 Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></samp>
301 options that you use for configuring GCC, then build and install
302 them. They install their executables automatically into the proper
303 directory. Alas, they do not support all the targets that GCC
306 <p>If you are not building a C library in the same source tree as GCC,
307 you should also provide the target libraries and headers before
308 configuring GCC, specifying the directories with
309 <samp><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and
310 <samp><span class="option">--with-libs</span></samp>. Many targets also require “start files” such
311 as <samp><span class="file">crt0.o</span></samp> and
312 <samp><span class="file">crtn.o</span></samp> which are linked into each executable. There may be several
313 alternatives for <samp><span class="file">crt0.o</span></samp>, for use with profiling or other
314 compilation options. Check your target's definition of
315 <code>STARTFILE_SPEC</code> to find out what start files it uses.
317 <h3 class="section"><a name="TOC2"></a>Building in parallel</h3>
319 <p>GNU Make 3.80 and above, which is necessary to build GCC, support
320 building in parallel. To activate this, you can use ‘<samp><span class="samp">make -j 2</span></samp>’
321 instead of ‘<samp><span class="samp">make</span></samp>’. You can also specify a bigger number, and
322 in most cases using a value greater than the number of processors in
323 your machine will result in fewer and shorter I/O latency hits, thus
324 improving overall throughput; this is especially true for slow drives
325 and network filesystems.
327 <h3 class="section"><a name="TOC3"></a>Building the Ada compiler</h3>
329 <p>In order to build GNAT, the Ada compiler, you need a working GNAT
330 compiler (GCC version 4.0 or later).
331 This includes GNAT tools such as <samp><span class="command">gnatmake</span></samp> and
332 <samp><span class="command">gnatlink</span></samp>, since the Ada front end is written in Ada and
333 uses some GNAT-specific extensions.
335 <p>In order to build a cross compiler, it is suggested to install
336 the new compiler as native first, and then use it to build the cross
339 <p><samp><span class="command">configure</span></samp> does not test whether the GNAT installation works
340 and has a sufficiently recent version; if too old a GNAT version is
341 installed, the build will fail unless <samp><span class="option">--enable-languages</span></samp> is
342 used to disable building the Ada front end.
344 <p><samp><span class="env">ADA_INCLUDE_PATH</span></samp> and <samp><span class="env">ADA_OBJECT_PATH</span></samp> environment variables
345 must not be set when building the Ada compiler, the Ada tools, or the
346 Ada runtime libraries. You can check that your build environment is clean
347 by verifying that ‘<samp><span class="samp">gnatls -v</span></samp>’ lists only one explicit path in each
350 <h3 class="section"><a name="TOC4"></a>Building with profile feedback</h3>
352 <p>It is possible to use profile feedback to optimize the compiler itself. This
353 should result in a faster compiler binary. Experiments done on x86 using gcc
354 3.3 showed approximately 7 percent speedup on compiling C programs. To
355 bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>.
357 <p>When ‘<samp><span class="samp">make profiledbootstrap</span></samp>’ is run, it will first build a <code>stage1</code>
358 compiler. This compiler is used to build a <code>stageprofile</code> compiler
359 instrumented to collect execution counts of instruction and branch
360 probabilities. Then runtime libraries are compiled with profile collected.
361 Finally a <code>stagefeedback</code> compiler is built using the information collected.
363 <p>Unlike standard bootstrap, several additional restrictions apply. The
364 compiler used to build <code>stage1</code> needs to support a 64-bit integral type.
365 It is recommended to only use GCC for this. Also parallel make is currently
366 not supported since collisions in profile collecting may occur.
369 <p><a href="./index.html">Return to the GCC Installation page</a>
371 <!-- ***Testing***************************************************************** -->
372 <!-- ***Final install*********************************************************** -->
373 <!-- ***Binaries**************************************************************** -->
374 <!-- ***Specific**************************************************************** -->
375 <!-- ***Old documentation****************************************************** -->
376 <!-- ***GFDL******************************************************************** -->
377 <!-- *************************************************************************** -->
378 <!-- Part 6 The End of the Document -->