1<html lang="en"> 2<head> 3<title>Installing GCC: Building</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="Installing GCC: Building"> 6<meta name="generator" content="makeinfo 4.12"> 7<link title="Top" rel="top" href="#Top"> 8<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 9<!-- 10Copyright (C) 1988-2015 Free Software Foundation, Inc. 11 12 Permission is granted to copy, distribute and/or modify this document 13under the terms of the GNU Free Documentation License, Version 1.3 or 14any later version published by the Free Software Foundation; with no 15Invariant Sections, the Front-Cover texts being (a) (see below), and 16with the Back-Cover Texts being (b) (see below). 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These failures, which 49are often due to files that were not found, are expected, and can safely 50be ignored. 51 52 <p>It is normal to have compiler warnings when compiling certain files. 53Unless you are a GCC developer, you can generally ignore these warnings 54unless they cause compilation to fail. Developers should attempt to fix 55any warnings encountered, however they can temporarily continue past 56warnings-as-errors by specifying the configure flag 57<samp><span class="option">--disable-werror</span></samp>. 58 59 <p>On certain old systems, defining certain environment variables such as 60<samp><span class="env">CC</span></samp> can interfere with the functioning of <samp><span class="command">make</span></samp>. 61 62 <p>If you encounter seemingly strange errors when trying to build the 63compiler in a directory other than the source directory, it could be 64because you have previously configured the compiler in the source 65directory. Make sure you have done all the necessary preparations. 66 67 <p>If you build GCC on a BSD system using a directory stored in an old System 68V file system, problems may occur in running <samp><span class="command">fixincludes</span></samp> if the 69System V file system doesn't support symbolic links. These problems 70result in a failure to fix the declaration of <code>size_t</code> in 71<samp><span class="file">sys/types.h</span></samp>. If you find that <code>size_t</code> is a signed type and 72that type mismatches occur, this could be the cause. 73 74 <p>The solution is not to use such a directory for building GCC. 75 76 <p>Similarly, when building from SVN or snapshots, or if you modify 77<samp><span class="file">*.l</span></samp> files, you need the Flex lexical analyzer generator 78installed. If you do not modify <samp><span class="file">*.l</span></samp> files, releases contain 79the Flex-generated files and you do not need Flex installed to build 80them. There is still one Flex-based lexical analyzer (part of the 81build machinery, not of GCC itself) that is used even if you only 82build the C front end. 83 84 <p>When building from SVN or snapshots, or if you modify Texinfo 85documentation, you need version 4.7 or later of Texinfo installed if you 86want Info documentation to be regenerated. Releases contain Info 87documentation pre-built for the unmodified documentation in the release. 88 89<h3 class="section"><a name="TOC0"></a>Building a native compiler</h3> 90 91<p>For a native build, the default configuration is to perform 92a 3-stage bootstrap of the compiler when ‘<samp><span class="samp">make</span></samp>’ is invoked. 93This will build the entire GCC system and ensure that it compiles 94itself correctly. It can be disabled with the <samp><span class="option">--disable-bootstrap</span></samp> 95parameter to ‘<samp><span class="samp">configure</span></samp>’, but bootstrapping is suggested because 96the compiler will be tested more completely and could also have 97better performance. 98 99 <p>The bootstrapping process will complete the following steps: 100 101 <ul> 102<li>Build tools necessary to build the compiler. 103 104 <li>Perform a 3-stage bootstrap of the compiler. This includes building 105three times the target tools for use by the compiler such as binutils 106(bfd, binutils, gas, gprof, ld, and opcodes) if they have been 107individually linked or moved into the top level GCC source tree before 108configuring. 109 110 <li>Perform a comparison test of the stage2 and stage3 compilers. 111 112 <li>Build runtime libraries using the stage3 compiler from the previous step. 113 114 </ul> 115 116 <p>If you are short on disk space you might consider ‘<samp><span class="samp">make 117bootstrap-lean</span></samp>’ instead. The sequence of compilation is the 118same described above, but object files from the stage1 and 119stage2 of the 3-stage bootstrap of the compiler are deleted as 120soon as they are no longer needed. 121 122 <p>If you wish to use non-default GCC flags when compiling the stage2 123and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when 124doing ‘<samp><span class="samp">make</span></samp>’. For example, if you want to save additional space 125during the bootstrap and in the final installation as well, you can 126build the compiler binaries without debugging information as in the 127following example. This will save roughly 40% of disk space both for 128the bootstrap and the final installation. (Libraries will still contain 129debugging information.) 130 131<pre class="smallexample"> make BOOT_CFLAGS='-O' bootstrap 132</pre> 133 <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they 134are less well tested here than the default of ‘<samp><span class="samp">-g -O2</span></samp>’, but should 135still work. In a few cases, you may find that you need to specify special 136flags such as <samp><span class="option">-msoft-float</span></samp> here to complete the bootstrap; or, 137if the native compiler miscompiles the stage1 compiler, you may need 138to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts 139of the stage1 compiler that were miscompiled, or by using ‘<samp><span class="samp">make 140bootstrap4</span></samp>’ to increase the number of stages of bootstrap. 141 142 <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries. 143Since these are always compiled with the compiler currently being 144bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their 145compilation flags, as for non-bootstrapped target libraries. 146Again, if the native compiler miscompiles the stage1 compiler, you may 147need to work around this by avoiding non-working parts of the stage1 148compiler. Use <code>STAGE1_TFLAGS</code> to this end. 149 150 <p>If you used the flag <samp><span class="option">--enable-languages=...</span></samp> to restrict 151the compilers to be built, only those you've actually enabled will be 152built. This will of course only build those runtime libraries, for 153which the particular compiler has been built. Please note, 154that re-defining <samp><span class="env">LANGUAGES</span></samp> when calling ‘<samp><span class="samp">make</span></samp>’ 155<strong>does not</strong> work anymore! 156 157 <p>If the comparison of stage2 and stage3 fails, this normally indicates 158that the stage2 compiler has compiled GCC incorrectly, and is therefore 159a potentially serious bug which you should investigate and report. (On 160a few systems, meaningful comparison of object files is impossible; they 161always appear “different”. If you encounter this problem, you will 162need to disable comparison in the <samp><span class="file">Makefile</span></samp>.) 163 164 <p>If you do not want to bootstrap your compiler, you can configure with 165<samp><span class="option">--disable-bootstrap</span></samp>. In particular cases, you may want to 166bootstrap your compiler even if the target system is not the same as 167the one you are building on: for example, you could build a 168<code>powerpc-unknown-linux-gnu</code> toolchain on a 169<code>powerpc64-unknown-linux-gnu</code> host. In this case, pass 170<samp><span class="option">--enable-bootstrap</span></samp> to the configure script. 171 172 <p><code>BUILD_CONFIG</code> can be used to bring in additional customization 173to the build. It can be set to a whitespace-separated list of names. 174For each such <code>NAME</code>, top-level <samp><span class="file">config/</span><code>NAME</code><span class="file">.mk</span></samp> will 175be included by the top-level <samp><span class="file">Makefile</span></samp>, bringing in any settings 176it contains. The default <code>BUILD_CONFIG</code> can be set using the 177configure option <samp><span class="option">--with-build-config=</span><code>NAME</code><span class="option">...</span></samp>. Some 178examples of supported build configurations are: 179 180 <dl> 181<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<samp><span class="option">-O1</span></samp> to it. ‘<samp><span class="samp">BUILD_CONFIG=bootstrap-O1</span></samp>’ is equivalent to 183‘<samp><span class="samp">BOOT_CFLAGS='-g -O1'</span></samp>’. 184 185 <br><dt>‘<samp><span class="samp">bootstrap-O3</span></samp>’<dd>Analogous to <code>bootstrap-O1</code>. 186 187 <br><dt>‘<samp><span class="samp">bootstrap-lto</span></samp>’<dd>Enables Link-Time Optimization for host tools during bootstrapping. 188‘<samp><span class="samp">BUILD_CONFIG=bootstrap-lto</span></samp>’ is equivalent to adding 189<samp><span class="option">-flto</span></samp> to ‘<samp><span class="samp">BOOT_CFLAGS</span></samp>’. This option assumes that the host 190supports the linker plugin (e.g. GNU ld version 2.21 or later or GNU gold 191version 2.21 or later). 192 193 <br><dt>‘<samp><span class="samp">bootstrap-lto-noplugin</span></samp>’<dd>This option is similar to <code>bootstrap-lto</code>, but is intended for 194hosts that do not support the linker plugin. Without the linker plugin 195static libraries are not compiled with link-time optimizations. Since 196the GCC middle end and back end are in <samp><span class="file">libbackend.a</span></samp> this means 197that only the front end is actually LTO optimized. 198 199 <br><dt>‘<samp><span class="samp">bootstrap-debug</span></samp>’<dd>Verifies that the compiler generates the same executable code, whether 200or not it is asked to emit debug information. To this end, this 201option builds stage2 host programs without debug information, and uses 202<samp><span class="file">contrib/compare-debug</span></samp> to compare them with the stripped stage3 203object files. If <code>BOOT_CFLAGS</code> is overridden so as to not enable 204debug information, stage2 will have it, and stage3 won't. This option 205is enabled by default when GCC bootstrapping is enabled, if 206<code>strip</code> can turn object files compiled with and without debug 207info into identical object files. In addition to better test 208coverage, this option makes default bootstraps faster and leaner. 209 210 <br><dt>‘<samp><span class="samp">bootstrap-debug-big</span></samp>’<dd>Rather than comparing stripped object files, as in 211<code>bootstrap-debug</code>, this option saves internal compiler dumps 212during stage2 and stage3 and compares them as well, which helps catch 213additional potential problems, but at a great cost in terms of disk 214space. It can be specified in addition to ‘<samp><span class="samp">bootstrap-debug</span></samp>’. 215 216 <br><dt>‘<samp><span class="samp">bootstrap-debug-lean</span></samp>’<dd>This option saves disk space compared with <code>bootstrap-debug-big</code>, 217but at the expense of some recompilation. Instead of saving the dumps 218of stage2 and stage3 until the final compare, it uses 219<samp><span class="option">-fcompare-debug</span></samp> to generate, compare and remove the dumps 220during stage3, repeating the compilation that already took place in 221stage2, whose dumps were not saved. 222 223 <br><dt>‘<samp><span class="samp">bootstrap-debug-lib</span></samp>’<dd>This option tests executable code invariance over debug information 224generation on target libraries, just like <code>bootstrap-debug-lean</code> 225tests it on host programs. It builds stage3 libraries with 226<samp><span class="option">-fcompare-debug</span></samp>, and it can be used along with any of the 227<code>bootstrap-debug</code> options above. 228 229 <p>There aren't <code>-lean</code> or <code>-big</code> counterparts to this option 230because most libraries are only build in stage3, so bootstrap compares 231would not get significant coverage. Moreover, the few libraries built 232in stage2 are used in stage3 host programs, so we wouldn't want to 233compile stage2 libraries with different options for comparison purposes. 234 235 <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 236stage is run without the option <samp><span class="option">-fcompare-debug</span></samp>. This is 237useful to verify the full <samp><span class="option">-fcompare-debug</span></samp> testing coverage. It 238must be used along with <code>bootstrap-debug-lean</code> and 239<code>bootstrap-debug-lib</code>. 240 241 <br><dt>‘<samp><span class="samp">bootstrap-time</span></samp>’<dd>Arranges for the run time of each program started by the GCC driver, 242built in any stage, to be logged to <samp><span class="file">time.log</span></samp>, in the top level of 243the build tree. 244 245 </dl> 246 247<h3 class="section"><a name="TOC1"></a>Building a cross compiler</h3> 248 249<p>When building a cross compiler, it is not generally possible to do a 2503-stage bootstrap of the compiler. This makes for an interesting problem 251as parts of GCC can only be built with GCC. 252 253 <p>To build a cross compiler, we recommend first building and installing a 254native compiler. You can then use the native GCC compiler to build the 255cross compiler. The installed native compiler needs to be GCC version 2562.95 or later. 257 258 <p>If the cross compiler is to be built with support for the Java 259programming language and the ability to compile .java source files is 260desired, the installed native compiler used to build the cross 261compiler needs to be the same GCC version as the cross compiler. In 262addition the cross compiler needs to be configured with 263<samp><span class="option">--with-ecj-jar=...</span></samp>. 264 265 <p>Assuming you have already installed a native copy of GCC and configured 266your cross compiler, issue the command <samp><span class="command">make</span></samp>, which performs the 267following steps: 268 269 <ul> 270<li>Build host tools necessary to build the compiler. 271 272 <li>Build target tools for use by the compiler such as binutils (bfd, 273binutils, gas, gprof, ld, and opcodes) 274if they have been individually linked or moved into the top level GCC source 275tree before configuring. 276 277 <li>Build the compiler (single stage only). 278 279 <li>Build runtime libraries using the compiler from the previous step. 280</ul> 281 282 <p>Note that if an error occurs in any step the make process will exit. 283 284 <p>If you are not building GNU binutils in the same source tree as GCC, 285you will need a cross-assembler and cross-linker installed before 286configuring GCC. Put them in the directory 287<samp><var>prefix</var><span class="file">/</span><var>target</var><span class="file">/bin</span></samp>. Here is a table of the tools 288you should put in this directory: 289 290 <dl> 291<dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler. 292 293 <br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker. 294 295 <br><dt><samp><span class="file">ar</span></samp><dd>This should be the cross-archiver: a program which can manipulate 296archive files (linker libraries) in the target machine's format. 297 298 <br><dt><samp><span class="file">ranlib</span></samp><dd>This should be a program to construct a symbol table in an archive file. 299</dl> 300 301 <p>The installation of GCC will find these programs in that directory, 302and copy or link them to the proper place to for the cross-compiler to 303find them when run later. 304 305 <p>The easiest way to provide these files is to build the Binutils package. 306Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></samp> 307options that you use for configuring GCC, then build and install 308them. They install their executables automatically into the proper 309directory. Alas, they do not support all the targets that GCC 310supports. 311 312 <p>If you are not building a C library in the same source tree as GCC, 313you should also provide the target libraries and headers before 314configuring GCC, specifying the directories with 315<samp><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and 316<samp><span class="option">--with-libs</span></samp>. Many targets also require “start files” such 317as <samp><span class="file">crt0.o</span></samp> and 318<samp><span class="file">crtn.o</span></samp> which are linked into each executable. There may be several 319alternatives for <samp><span class="file">crt0.o</span></samp>, for use with profiling or other 320compilation options. Check your target's definition of 321<code>STARTFILE_SPEC</code> to find out what start files it uses. 322 323<h3 class="section"><a name="TOC2"></a>Building in parallel</h3> 324 325<p>GNU Make 3.80 and above, which is necessary to build GCC, support 326building in parallel. To activate this, you can use ‘<samp><span class="samp">make -j 2</span></samp>’ 327instead of ‘<samp><span class="samp">make</span></samp>’. You can also specify a bigger number, and 328in most cases using a value greater than the number of processors in 329your machine will result in fewer and shorter I/O latency hits, thus 330improving overall throughput; this is especially true for slow drives 331and network filesystems. 332 333<h3 class="section"><a name="TOC3"></a>Building the Ada compiler</h3> 334 335<p>In order to build GNAT, the Ada compiler, you need a working GNAT 336compiler (GCC version 4.0 or later). 337This includes GNAT tools such as <samp><span class="command">gnatmake</span></samp> and 338<samp><span class="command">gnatlink</span></samp>, since the Ada front end is written in Ada and 339uses some GNAT-specific extensions. 340 341 <p>In order to build a cross compiler, it is suggested to install 342the new compiler as native first, and then use it to build the cross 343compiler. 344 345 <p><samp><span class="command">configure</span></samp> does not test whether the GNAT installation works 346and has a sufficiently recent version; if too old a GNAT version is 347installed, the build will fail unless <samp><span class="option">--enable-languages</span></samp> is 348used to disable building the Ada front end. 349 350 <p><samp><span class="env">ADA_INCLUDE_PATH</span></samp> and <samp><span class="env">ADA_OBJECT_PATH</span></samp> environment variables 351must not be set when building the Ada compiler, the Ada tools, or the 352Ada runtime libraries. You can check that your build environment is clean 353by verifying that ‘<samp><span class="samp">gnatls -v</span></samp>’ lists only one explicit path in each 354section. 355 356<h3 class="section"><a name="TOC4"></a>Building with profile feedback</h3> 357 358<p>It is possible to use profile feedback to optimize the compiler itself. This 359should result in a faster compiler binary. Experiments done on x86 using gcc 3603.3 showed approximately 7 percent speedup on compiling C programs. To 361bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>. 362 363 <p>When ‘<samp><span class="samp">make profiledbootstrap</span></samp>’ is run, it will first build a <code>stage1</code> 364compiler. This compiler is used to build a <code>stageprofile</code> compiler 365instrumented to collect execution counts of instruction and branch 366probabilities. Then runtime libraries are compiled with profile collected. 367Finally a <code>stagefeedback</code> compiler is built using the information collected. 368 369 <p>Unlike standard bootstrap, several additional restrictions apply. The 370compiler used to build <code>stage1</code> needs to support a 64-bit integral type. 371It is recommended to only use GCC for this. 372 373 <p><hr /> 374<p><a href="./index.html">Return to the GCC Installation page</a> 375 376<!-- ***Testing***************************************************************** --> 377<!-- ***Final install*********************************************************** --> 378<!-- ***Binaries**************************************************************** --> 379<!-- ***Specific**************************************************************** --> 380<!-- ***Old documentation****************************************************** --> 381<!-- ***GFDL******************************************************************** --> 382<!-- *************************************************************************** --> 383<!-- Part 6 The End of the Document --> 384</body></html> 385 386