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<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
47
runtime libraries.
48
 
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
52
be ignored.
53
 
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>.
60
 
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>.
63
 
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.
68
 
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.
75
 
76
   <p>The solution is not to use such a directory for building GCC.
77
 
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.
85
 
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.
90
 
91
<h3 class="section"><a name="TOC0"></a>Building a native compiler</h3>
92
 
93
<p>For a native build, the default configuration is to perform
94
a 3-stage bootstrap of the compiler when &lsquo;<samp><span class="samp">make</span></samp>&rsquo; 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 &lsquo;<samp><span class="samp">configure</span></samp>&rsquo;, but bootstrapping is suggested because
98
the compiler will be tested more completely and could also have
99
better performance.
100
 
101
   <p>The bootstrapping process will complete the following steps:
102
 
103
     <ul>
104
<li>Build tools necessary to build the compiler.
105
 
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
110
configuring.
111
 
112
     <li>Perform a comparison test of the stage2 and stage3 compilers.
113
 
114
     <li>Build runtime libraries using the stage3 compiler from the previous step.
115
 
116
   </ul>
117
 
118
   <p>If you are short on disk space you might consider &lsquo;<samp><span class="samp">make
119
bootstrap-lean</span></samp>&rsquo; 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.
123
 
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 &lsquo;<samp><span class="samp">make</span></samp>&rsquo;.  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.)
132
 
133
<pre class="smallexample">          make BOOT_CFLAGS='-O' bootstrap
134
</pre>
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 &lsquo;<samp><span class="samp">-g -O2</span></samp>&rsquo;, 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 &lsquo;<samp><span class="samp">make
142
bootstrap4</span></samp>&rsquo; to increase the number of stages of bootstrap.
143
 
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.
151
 
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 &lsquo;<samp><span class="samp">make</span></samp>&rsquo;
157
<strong>does not</strong> work anymore!
158
 
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 &ldquo;different&rdquo;.  If you encounter this problem, you will
164
need to disable comparison in the <samp><span class="file">Makefile</span></samp>.)
165
 
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.
173
 
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:
181
 
182
     <dl>
183
<dt>&lsquo;<samp><span class="samp">bootstrap-O1</span></samp>&rsquo;<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.  &lsquo;<samp><span class="samp">BUILD_CONFIG=bootstrap-O1</span></samp>&rsquo; is equivalent to
185
&lsquo;<samp><span class="samp">BOOT_CFLAGS='-g -O1'</span></samp>&rsquo;.
186
 
187
     <br><dt>&lsquo;<samp><span class="samp">bootstrap-O3</span></samp>&rsquo;<dd>Analogous to <code>bootstrap-O1</code>.
188
 
189
     <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug</span></samp>&rsquo;<dd>Verifies that the compiler generates the same executable code, whether
190
or not it is asked to emit debug information.  To this end, this
191
option builds stage2 host programs without debug information, and uses
192
<samp><span class="file">contrib/compare-debug</span></samp> to compare them with the stripped stage3
193
object files.  If <code>BOOT_CFLAGS</code> is overridden so as to not enable
194
debug information, stage2 will have it, and stage3 won't.  This option
195
is enabled by default when GCC bootstrapping is enabled, if
196
<code>strip</code> can turn object files compiled with and without debug
197
info into identical object files.  In addition to better test
198
coverage, this option makes default bootstraps faster and leaner.
199
 
200
     <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-big</span></samp>&rsquo;<dd>Rather than comparing stripped object files, as in
201
<code>bootstrap-debug</code>, this option saves internal compiler dumps
202
during stage2 and stage3 and compares them as well, which helps catch
203
additional potential problems, but at a great cost in terms of disk
204
space.  It can be specified in addition to &lsquo;<samp><span class="samp">bootstrap-debug</span></samp>&rsquo;.
205
 
206
     <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-lean</span></samp>&rsquo;<dd>This option saves disk space compared with <code>bootstrap-debug-big</code>,
207
but at the expense of some recompilation.  Instead of saving the dumps
208
of stage2 and stage3 until the final compare, it uses
209
<samp><span class="option">-fcompare-debug</span></samp> to generate, compare and remove the dumps
210
during stage3, repeating the compilation that already took place in
211
stage2, whose dumps were not saved.
212
 
213
     <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-lib</span></samp>&rsquo;<dd>This option tests executable code invariance over debug information
214
generation on target libraries, just like <code>bootstrap-debug-lean</code>
215
tests it on host programs.  It builds stage3 libraries with
216
<samp><span class="option">-fcompare-debug</span></samp>, and it can be used along with any of the
217
<code>bootstrap-debug</code> options above.
218
 
219
     <p>There aren't <code>-lean</code> or <code>-big</code> counterparts to this option
220
because most libraries are only build in stage3, so bootstrap compares
221
would not get significant coverage.  Moreover, the few libraries built
222
in stage2 are used in stage3 host programs, so we wouldn't want to
223
compile stage2 libraries with different options for comparison purposes.
224
 
225
     <br><dt>&lsquo;<samp><span class="samp">bootstrap-debug-ckovw</span></samp>&rsquo;<dd>Arranges for error messages to be issued if the compiler built on any
226
stage is run without the option <samp><span class="option">-fcompare-debug</span></samp>.  This is
227
useful to verify the full <samp><span class="option">-fcompare-debug</span></samp> testing coverage.  It
228
must be used along with <code>bootstrap-debug-lean</code> and
229
<code>bootstrap-debug-lib</code>.
230
 
231
     <br><dt>&lsquo;<samp><span class="samp">bootstrap-time</span></samp>&rsquo;<dd>Arranges for the run time of each program started by the GCC driver,
232
built in any stage, to be logged to <samp><span class="file">time.log</span></samp>, in the top level of
233
the build tree.
234
 
235
   </dl>
236
 
237
<h3 class="section"><a name="TOC1"></a>Building a cross compiler</h3>
238
 
239
<p>When building a cross compiler, it is not generally possible to do a
240
3-stage bootstrap of the compiler.  This makes for an interesting problem
241
as parts of GCC can only be built with GCC.
242
 
243
   <p>To build a cross compiler, we recommend first building and installing a
244
native compiler.  You can then use the native GCC compiler to build the
245
cross compiler.  The installed native compiler needs to be GCC version
246
2.95 or later.
247
 
248
   <p>If the cross compiler is to be built with support for the Java
249
programming language and the ability to compile .java source files is
250
desired, the installed native compiler used to build the cross
251
compiler needs to be the same GCC version as the cross compiler.  In
252
addition the cross compiler needs to be configured with
253
<samp><span class="option">--with-ecj-jar=...</span></samp>.
254
 
255
   <p>Assuming you have already installed a native copy of GCC and configured
256
your cross compiler, issue the command <samp><span class="command">make</span></samp>, which performs the
257
following steps:
258
 
259
     <ul>
260
<li>Build host tools necessary to build the compiler.
261
 
262
     <li>Build target tools for use by the compiler such as binutils (bfd,
263
binutils, gas, gprof, ld, and opcodes)
264
if they have been individually linked or moved into the top level GCC source
265
tree before configuring.
266
 
267
     <li>Build the compiler (single stage only).
268
 
269
     <li>Build runtime libraries using the compiler from the previous step.
270
</ul>
271
 
272
   <p>Note that if an error occurs in any step the make process will exit.
273
 
274
   <p>If you are not building GNU binutils in the same source tree as GCC,
275
you will need a cross-assembler and cross-linker installed before
276
configuring GCC.  Put them in the directory
277
<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
you should put in this directory:
279
 
280
     <dl>
281
<dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler.
282
 
283
     <br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker.
284
 
285
     <br><dt><samp><span class="file">ar</span></samp><dd>This should be the cross-archiver: a program which can manipulate
286
archive files (linker libraries) in the target machine's format.
287
 
288
     <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
</dl>
290
 
291
   <p>The installation of GCC will find these programs in that directory,
292
and copy or link them to the proper place to for the cross-compiler to
293
find them when run later.
294
 
295
   <p>The easiest way to provide these files is to build the Binutils package.
296
Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></samp>
297
options that you use for configuring GCC, then build and install
298
them.  They install their executables automatically into the proper
299
directory.  Alas, they do not support all the targets that GCC
300
supports.
301
 
302
   <p>If you are not building a C library in the same source tree as GCC,
303
you should also provide the target libraries and headers before
304
configuring GCC, specifying the directories with
305
<samp><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and
306
<samp><span class="option">--with-libs</span></samp>.  Many targets also require &ldquo;start files&rdquo; such
307
as <samp><span class="file">crt0.o</span></samp> and
308
<samp><span class="file">crtn.o</span></samp> which are linked into each executable.  There may be several
309
alternatives for <samp><span class="file">crt0.o</span></samp>, for use with profiling or other
310
compilation options.  Check your target's definition of
311
<code>STARTFILE_SPEC</code> to find out what start files it uses.
312
 
313
<h3 class="section"><a name="TOC2"></a>Building in parallel</h3>
314
 
315
<p>GNU Make 3.80 and above, which is necessary to build GCC, support
316
building in parallel.  To activate this, you can use &lsquo;<samp><span class="samp">make -j 2</span></samp>&rsquo;
317
instead of &lsquo;<samp><span class="samp">make</span></samp>&rsquo;.  You can also specify a bigger number, and
318
in most cases using a value greater than the number of processors in
319
your machine will result in fewer and shorter I/O latency hits, thus
320
improving overall throughput; this is especially true for slow drives
321
and network filesystems.
322
 
323
<h3 class="section"><a name="TOC3"></a>Building the Ada compiler</h3>
324
 
325
<p>In order to build GNAT, the Ada compiler, you need a working GNAT
326
compiler (GCC version 3.4 or later).
327
This includes GNAT tools such as <samp><span class="command">gnatmake</span></samp> and
328
<samp><span class="command">gnatlink</span></samp>, since the Ada front end is written in Ada and
329
uses some GNAT-specific extensions.
330
 
331
   <p>In order to build a cross compiler, it is suggested to install
332
the new compiler as native first, and then use it to build the cross
333
compiler.
334
 
335
   <p><samp><span class="command">configure</span></samp> does not test whether the GNAT installation works
336
and has a sufficiently recent version; if too old a GNAT version is
337
installed, the build will fail unless <samp><span class="option">--enable-languages</span></samp> is
338
used to disable building the Ada front end.
339
 
340
   <p><samp><span class="env">ADA_INCLUDE_PATH</span></samp> and <samp><span class="env">ADA_OBJECT_PATH</span></samp> environment variables
341
must not be set when building the Ada compiler, the Ada tools, or the
342
Ada runtime libraries. You can check that your build environment is clean
343
by verifying that &lsquo;<samp><span class="samp">gnatls -v</span></samp>&rsquo; lists only one explicit path in each
344
section.
345
 
346
<h3 class="section"><a name="TOC4"></a>Building with profile feedback</h3>
347
 
348
<p>It is possible to use profile feedback to optimize the compiler itself.  This
349
should result in a faster compiler binary.  Experiments done on x86 using gcc
350
3.3 showed approximately 7 percent speedup on compiling C programs.  To
351
bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>.
352
 
353
   <p>When &lsquo;<samp><span class="samp">make profiledbootstrap</span></samp>&rsquo; is run, it will first build a <code>stage1</code>
354
compiler.  This compiler is used to build a <code>stageprofile</code> compiler
355
instrumented to collect execution counts of instruction and branch
356
probabilities.  Then runtime libraries are compiled with profile collected.
357
Finally a <code>stagefeedback</code> compiler is built using the information collected.
358
 
359
   <p>Unlike standard bootstrap, several additional restrictions apply.  The
360
compiler used to build <code>stage1</code> needs to support a 64-bit integral type.
361
It is recommended to only use GCC for this.  Also parallel make is currently
362
not supported since collisions in profile collecting may occur.
363
 
364
   <p><hr />
365
<p><a href="./index.html">Return to the GCC Installation page</a>
366
 
367
<!-- ***Testing***************************************************************** -->
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<!-- ***Final install*********************************************************** -->
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<!-- ***Binaries**************************************************************** -->
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<!-- ***Specific**************************************************************** -->
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<!-- ***Old documentation****************************************************** -->
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<!-- ***GFDL******************************************************************** -->
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<!-- *************************************************************************** -->
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<!-- Part 6 The End of the Document -->
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</body></html>
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