toolchain/gcc/INSTALL/build.html

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  42 <h1 class="settitle">Installing GCC: Building</h1>
  43 <a name="index-Installing-GCC_003a-Building-1"></a>
  44 Now that GCC is configured, you are ready to build the compiler and
  45 runtime libraries.
  46
  47    <p>Some commands executed when making the compiler may fail (return a
  48 nonzero status) and be ignored by <span class="command">make</span>.  These failures, which
  49 are often due to files that were not found, are expected, and can safely
  50 be ignored.
  51
  52    <p>It is normal to have compiler warnings when compiling certain files.
  53 Unless you are a GCC developer, you can generally ignore these warnings
  54 unless they cause compilation to fail.  Developers should attempt to fix
  55 any warnings encountered, however they can temporarily continue past
  56 warnings-as-errors by specifying the configure flag
  57 <span class="option">--disable-werror</span>.
  58
  59    <p>On certain old systems, defining certain environment variables such as
  60 <span class="env">CC</span> can interfere with the functioning of <span class="command">make</span>.
  61
  62    <p>If you encounter seemingly strange errors when trying to build the
  63 compiler in a directory other than the source directory, it could be
  64 because you have previously configured the compiler in the source
  65 directory.  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
  68 V file system, problems may occur in running <span class="command">fixincludes</span> if the
  69 System V file system doesn't support symbolic links.  These problems
  70 result in a failure to fix the declaration of <code>size_t</code> in
  71 <span class="file">sys/types.h</span>.  If you find that <code>size_t</code> is a signed type and
  72 that 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>When building from CVS or snapshots, or if you modify parser sources,
  77 you need the Bison parser generator installed.  Any version 1.25 or
  78 later should work; older versions may also work.  If you do not modify
  79 parser sources, releases contain the Bison-generated files and you do
  80 not need Bison installed to build them.
  81
  82    <p>When building from CVS or snapshots, or if you modify Texinfo
  83 documentation, you need version 4.2 or later of Texinfo installed if you
  84 want Info documentation to be regenerated.  Releases contain Info
  85 documentation pre-built for the unmodified documentation in the release.
  86
  87 <h3 class="section"><a name="TOC0"></a>0.1 Building a native compiler</h3>
  88
  89 <p>For a native build issue the command <span class="samp">make bootstrap</span>.  This
  90 will build the entire GCC system, which includes the following steps:
  91
  92      <ul>
  93 <li>Build host tools necessary to build the compiler such as texinfo, bison,
  94 gperf.
  95
  96      <li>Build target tools for use by the compiler such as binutils (bfd,
  97 binutils, gas, gprof, ld, and opcodes)
  98 if they have been individually linked
  99 or moved into the top level GCC source tree before configuring.
 100
 101      <li>Perform a 3-stage bootstrap of the compiler.
 102
 103      <li>Perform a comparison test of the stage2 and stage3 compilers.
 104
 105      <li>Build runtime libraries using the stage3 compiler from the previous step.
 106
 107    </ul>
 108
 109    <p>If you are short on disk space you might consider <span class="samp">make
 110 bootstrap-lean</span> instead.  This is identical to <span class="samp">make
 111 bootstrap</span> except that object files from the stage1 and
 112 stage2 of the 3-stage bootstrap of the compiler are deleted as
 113 soon as they are no longer needed.
 114
 115    <p>If you want to save additional space during the bootstrap and in
 116 the final installation as well, you can build the compiler binaries
 117 without debugging information as in the following example.  This will save
 118 roughly 40% of disk space both for the bootstrap and the final installation.
 119 (Libraries will still contain debugging information.)
 120
 121 <pre class="smallexample">          make CFLAGS='-O' LIBCFLAGS='-g -O2' \
 122             LIBCXXFLAGS='-g -O2 -fno-implicit-templates' bootstrap
 123 </pre>
 124    <p>If you wish to use non-default GCC flags when compiling the stage2 and
 125 stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when doing
 126 <span class="samp">make bootstrap</span>.  Non-default optimization flags are less well
 127 tested here than the default of <span class="samp">-g -O2</span>, but should still work.
 128 In a few cases, you may find that you need to specify special flags such
 129 as <span class="option">-msoft-float</span> here to complete the bootstrap; or, if the
 130 native compiler miscompiles the stage1 compiler, you may need to work
 131 around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts of the
 132 stage1 compiler that were miscompiled, or by using <span class="samp">make
 133 bootstrap4</span> to increase the number of stages of bootstrap.
 134
 135    <p>If you used the flag <span class="option">--enable-languages=...</span> to restrict
 136 the compilers to be built, only those you've actually enabled will be
 137 built.  This will of course only build those runtime libraries, for
 138 which the particular compiler has been built.  Please note,
 139 that re-defining <span class="env">LANGUAGES</span> when calling <span class="samp">make bootstrap</span>
 140 <strong>does not</strong> work anymore!
 141
 142    <p>If the comparison of stage2 and stage3 fails, this normally indicates
 143 that the stage2 compiler has compiled GCC incorrectly, and is therefore
 144 a potentially serious bug which you should investigate and report.  (On
 145 a few systems, meaningful comparison of object files is impossible; they
 146 always appear &ldquo;different&rdquo;.  If you encounter this problem, you will
 147 need to disable comparison in the <span class="file">Makefile</span>.)
 148
 149 <h3 class="section"><a name="TOC1"></a>0.2 Building a cross compiler</h3>
 150
 151 <p>We recommend reading the
 152 <a href="http://www.objsw.com/CrossGCC/">crossgcc FAQ</a>
 153 for information about building cross compilers.
 154
 155    <p>When building a cross compiler, it is not generally possible to do a
 156 3-stage bootstrap of the compiler.  This makes for an interesting problem
 157 as parts of GCC can only be built with GCC.
 158
 159    <p>To build a cross compiler, we first recommend building and installing a
 160 native compiler.  You can then use the native GCC compiler to build the
 161 cross compiler.  The installed native compiler needs to be GCC version
 162 2.95 or later.
 163
 164    <p>Assuming you have already installed a native copy of GCC and configured
 165 your cross compiler, issue the command <span class="command">make</span>, which performs the
 166 following steps:
 167
 168      <ul>
 169 <li>Build host tools necessary to build the compiler such as texinfo, bison,
 170 gperf.
 171
 172      <li>Build target tools for use by the compiler such as binutils (bfd,
 173 binutils, gas, gprof, ld, and opcodes)
 174 if they have been individually linked or moved into the top level GCC source
 175 tree before configuring.
 176
 177      <li>Build the compiler (single stage only).
 178
 179      <li>Build runtime libraries using the compiler from the previous step.
 180 </ul>
 181
 182    <p>Note that if an error occurs in any step the make process will exit.
 183
 184    <p>If you are not building GNU binutils in the same source tree as GCC,
 185 you will need a cross-assembler and cross-linker installed before
 186 configuring GCC.  Put them in the directory
 187 <var>prefix</var><span class="file">/</span><var>target</var><span class="file">/bin</span>.  Here is a table of the tools
 188 you should put in this directory:
 189
 190      <dl>
 191 <dt><span class="file">as</span><dd>This should be the cross-assembler.
 192
 193      <br><dt><span class="file">ld</span><dd>This should be the cross-linker.
 194
 195      <br><dt><span class="file">ar</span><dd>This should be the cross-archiver: a program which can manipulate
 196 archive files (linker libraries) in the target machine's format.
 197
 198      <br><dt><span class="file">ranlib</span><dd>This should be a program to construct a symbol table in an archive file.
 199 </dl>
 200
 201    <p>The installation of GCC will find these programs in that directory,
 202 and copy or link them to the proper place to for the cross-compiler to
 203 find them when run later.
 204
 205    <p>The easiest way to provide these files is to build the Binutils package.
 206 Configure it with the same <span class="option">--host</span> and <span class="option">--target</span>
 207 options that you use for configuring GCC, then build and install
 208 them.  They install their executables automatically into the proper
 209 directory.  Alas, they do not support all the targets that GCC
 210 supports.
 211
 212    <p>If you are not building a C library in the same source tree as GCC,
 213 you should also provide the target libraries and headers before
 214 configuring GCC, specifying the directories with
 215 <span class="option">--with-sysroot</span> or <span class="option">--with-headers</span> and
 216 <span class="option">--with-libs</span>.  Many targets also require &ldquo;start files&rdquo; such
 217 as <span class="file">crt0.o</span> and
 218 <span class="file">crtn.o</span> which are linked into each executable.  There may be several
 219 alternatives for <span class="file">crt0.o</span>, for use with profiling or other
 220 compilation options.  Check your target's definition of
 221 <code>STARTFILE_SPEC</code> to find out what start files it uses.
 222
 223 <h3 class="section"><a name="TOC2"></a>0.3 Building in parallel</h3>
 224
 225 <p>You can use <span class="samp">make bootstrap MAKE="make -j 2" -j 2</span>, or just
 226 <span class="samp">make -j 2 bootstrap</span> for GNU Make 3.79 and above, instead of
 227 <span class="samp">make bootstrap</span> to build GCC in parallel.
 228 You can also specify a bigger number, and in most cases using a value
 229 greater than the number of processors in your machine will result in
 230 fewer and shorter I/O latency hits, thus improving overall throughput;
 231 this is especially true for slow drives and network filesystems.
 232
 233 <h3 class="section"><a name="TOC3"></a>0.4 Building the Ada compiler</h3>
 234
 235 <p>In order to build GNAT, the Ada compiler, you need a working GNAT
 236 compiler (GNAT version 3.14 or later, or GCC version 3.1 or later),
 237 including GNAT tools such as <span class="command">gnatmake</span> and <span class="command">gnatlink</span>,
 238 since the Ada front end is written in Ada (with some
 239 GNAT-specific extensions), and GNU make.
 240
 241    <p><span class="command">configure</span> does not test whether the GNAT installation works
 242 and has a sufficiently recent version; if too old a GNAT version is
 243 installed, the build will fail unless <span class="option">--enable-languages</span> is
 244 used to disable building the Ada front end.
 245
 246    <p>At the moment, the GNAT library and several tools for GNAT are not built
 247 by <span class="samp">make bootstrap</span>.  For a native build, you have to invoke
 248 <span class="samp">make gnatlib_and_tools</span> in the <var>objdir</var><span class="file">/gcc</span>
 249 subdirectory before proceeding with the next steps.
 250 For a cross build, you need to invoke
 251 <span class="samp">make gnatlib cross-gnattools ada.all.cross</span>.  For a canadian
 252 cross you only need to invoke <span class="samp">make cross-gnattools</span>; the GNAT
 253 library would be the same as the one built for the cross compiler.
 254
 255    <p>For example, you can build a native Ada compiler by issuing the
 256 following commands (assuming <span class="command">make</span> is GNU make):
 257
 258 <pre class="smallexample">         cd <var>objdir</var>
 259          <var>srcdir</var>/configure --enable-languages=c,ada
 260          cd <var>objdir</var>
 261          make bootstrap
 262          cd gcc
 263          make gnatlib_and_tools
 264          cd ..
 265 </pre>
 266    <p>Currently, when compiling the Ada front end, you cannot use the parallel
 267 build feature described in the previous section.
 268
 269 <h3 class="section"><a name="TOC4"></a>0.5 Building with profile feedback</h3>
 270
 271 <p>It is possible to use profile feedback to optimize the compiler itself.  This
 272 should result in a faster compiler binary.  Experiments done on x86 using gcc
 273 3.3 showed approximately 7 percent speedup on compiling C programs.  To
 274 bootstrap compiler with profile feedback, use <code>make profiledbootstrap</code>.
 275
 276    <p>When <span class="samp">make profiledbootstrap</span> is run, it will first build a <code>stage1</code>
 277 compiler.  This compiler is used to build a <code>stageprofile</code> compiler
 278 instrumented to collect execution counts of instruction and branch
 279 probabilities.  Then runtime libraries are compiled with profile collected.
 280 Finally a <code>stagefeedback</code> compiler is built using the information collected.
 281
 282    <p>Unlike <span class="samp">make bootstrap</span> several additional restrictions apply.  The
 283 compiler used to build <code>stage1</code> needs to support a 64-bit integral type.
 284 It is recommended to only use GCC for this.  Also parallel make is currently
 285 not supported since collisions in profile collecting may occur.
 286
 287    <p><hr />
 288 <p><a href="./index.html">Return to the GCC Installation page</a>
 289
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