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These failures, which 92 are often due to files that were not found, are expected, and can safely 93 be ignored. 94 </p> 95 <p>It is normal to have compiler warnings when compiling certain files. 96 Unless you are a GCC developer, you can generally ignore these warnings 97 unless they cause compilation to fail. Developers should attempt to fix 98 any warnings encountered, however they can temporarily continue past 99 warnings-as-errors by specifying the configure flag 100 <samp>--disable-werror</samp>. 101 </p> 102 <p>On certain old systems, defining certain environment variables such as 103 <code>CC</code> can interfere with the functioning of <code>make</code>. 104 </p> 105 <p>If you encounter seemingly strange errors when trying to build the 106 compiler in a directory other than the source directory, it could be 107 because you have previously configured the compiler in the source 108 directory. Make sure you have done all the necessary preparations. 109 </p> 110 <p>If you build GCC on a BSD system using a directory stored in an old System 111 V file system, problems may occur in running <code>fixincludes</code> if the 112 System V file system doesn’t support symbolic links. These problems 113 result in a failure to fix the declaration of <code>size_t</code> in 114 <samp>sys/types.h</samp>. If you find that <code>size_t</code> is a signed type and 115 that type mismatches occur, this could be the cause. 116 </p> 117 <p>The solution is not to use such a directory for building GCC. 118 </p> 119 <p>Similarly, when building from the source repository or snapshots, or if you modify 120 <samp>*.l</samp> files, you need the Flex lexical analyzer generator 121 installed. If you do not modify <samp>*.l</samp> files, releases contain 122 the Flex-generated files and you do not need Flex installed to build 123 them. There is still one Flex-based lexical analyzer (part of the 124 build machinery, not of GCC itself) that is used even if you only 125 build the C front end. 126 </p> 127 <p>When building from the source repository or snapshots, or if you modify Texinfo 128 documentation, you need version 4.7 or later of Texinfo installed if you 129 want Info documentation to be regenerated. Releases contain Info 130 documentation pre-built for the unmodified documentation in the release. 131 </p> 132 <a name="Building-a-native-compiler"></a> 133 <h3 class="section">Building a native compiler</h3> 134 135 <p>For a native build, the default configuration is to perform 136 a 3-stage bootstrap of the compiler when ‘<samp>make</samp>’ is invoked. 137 This will build the entire GCC system and ensure that it compiles 138 itself correctly. It can be disabled with the <samp>--disable-bootstrap</samp> 139 parameter to ‘<samp>configure</samp>’, but bootstrapping is suggested because 140 the compiler will be tested more completely and could also have 141 better performance. 142 </p> 143 <p>The bootstrapping process will complete the following steps: 144 </p> 145 <ul> 146 <li> Build tools necessary to build the compiler. 147 148 </li><li> Perform a 3-stage bootstrap of the compiler. This includes building 149 three times the target tools for use by the compiler such as binutils 150 (bfd, binutils, gas, gprof, ld, and opcodes) if they have been 151 individually linked or moved into the top level GCC source tree before 152 configuring. 153 154 </li><li> Perform a comparison test of the stage2 and stage3 compilers. 155 156 </li><li> Build runtime libraries using the stage3 compiler from the previous step. 157 158 </li></ul> 159 160 <p>If you are short on disk space you might consider ‘<samp>make 161 bootstrap-lean</samp>’ instead. The sequence of compilation is the 162 same described above, but object files from the stage1 and 163 stage2 of the 3-stage bootstrap of the compiler are deleted as 164 soon as they are no longer needed. 165 </p> 166 <p>If you wish to use non-default GCC flags when compiling the stage2 167 and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when 168 doing ‘<samp>make</samp>’. For example, if you want to save additional space 169 during the bootstrap and in the final installation as well, you can 170 build the compiler binaries without debugging information as in the 171 following example. This will save roughly 40% of disk space both for 172 the bootstrap and the final installation. (Libraries will still contain 173 debugging information.) 174 </p> 175 <div class="smallexample"> 176 <pre class="smallexample">make BOOT_CFLAGS='-O' bootstrap 177 </pre></div> 178 179 <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they 180 are less well tested here than the default of ‘<samp>-g -O2</samp>’, but should 181 still work. In a few cases, you may find that you need to specify special 182 flags such as <samp>-msoft-float</samp> here to complete the bootstrap; or, 183 if the native compiler miscompiles the stage1 compiler, you may need 184 to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts 185 of the stage1 compiler that were miscompiled, or by using ‘<samp>make 186 bootstrap4</samp>’ to increase the number of stages of bootstrap. 187 </p> 188 <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries. 189 Since these are always compiled with the compiler currently being 190 bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their 191 compilation flags, as for non-bootstrapped target libraries. 192 Again, if the native compiler miscompiles the stage1 compiler, you may 193 need to work around this by avoiding non-working parts of the stage1 194 compiler. Use <code>STAGE1_TFLAGS</code> to this end. 195 </p> 196 <p>If you used the flag <samp>--enable-languages=…</samp> to restrict 197 the compilers to be built, only those you’ve actually enabled will be 198 built. This will of course only build those runtime libraries, for 199 which the particular compiler has been built. Please note, 200 that re-defining <code>LANGUAGES</code> when calling ‘<samp>make</samp>’ 201 <strong>does not</strong> work anymore! 202 </p> 203 <p>If the comparison of stage2 and stage3 fails, this normally indicates 204 that the stage2 compiler has compiled GCC incorrectly, and is therefore 205 a potentially serious bug which you should investigate and report. (On 206 a few systems, meaningful comparison of object files is impossible; they 207 always appear “different”. If you encounter this problem, you will 208 need to disable comparison in the <samp>Makefile</samp>.) 209 </p> 210 <p>If you do not want to bootstrap your compiler, you can configure with 211 <samp>--disable-bootstrap</samp>. In particular cases, you may want to 212 bootstrap your compiler even if the target system is not the same as 213 the one you are building on: for example, you could build a 214 <code>powerpc-unknown-linux-gnu</code> toolchain on a 215 <code>powerpc64-unknown-linux-gnu</code> host. In this case, pass 216 <samp>--enable-bootstrap</samp> to the configure script. 217 </p> 218 <p><code>BUILD_CONFIG</code> can be used to bring in additional customization 219 to the build. It can be set to a whitespace-separated list of names. 220 For each such <code>NAME</code>, top-level <samp>config/<code>NAME</code>.mk</samp> will 221 be included by the top-level <samp>Makefile</samp>, bringing in any settings 222 it contains. The default <code>BUILD_CONFIG</code> can be set using the 223 configure option <samp>--with-build-config=<code>NAME</code>...</samp>. Some 224 examples of supported build configurations are: 225 </p> 226 <dl compact="compact"> 227 <dt>‘<samp>bootstrap-O1</samp>’</dt> 228 <dd><p>Removes any <samp>-O</samp>-started option from <code>BOOT_CFLAGS</code>, and adds 229 <samp>-O1</samp> to it. ‘<samp>BUILD_CONFIG=bootstrap-O1</samp>’ is equivalent to 230 ‘<samp>BOOT_CFLAGS='-g -O1'</samp>’. 231 </p> 232 </dd> 233 <dt>‘<samp>bootstrap-O3</samp>’</dt> 234 <dt>‘<samp>bootstrap-Og</samp>’</dt> 235 <dd><p>Analogous to <code>bootstrap-O1</code>. 236 </p> 237 </dd> 238 <dt>‘<samp>bootstrap-lto</samp>’</dt> 239 <dd><p>Enables Link-Time Optimization for host tools during bootstrapping. 240 ‘<samp>BUILD_CONFIG=bootstrap-lto</samp>’ is equivalent to adding 241 <samp>-flto</samp> to ‘<samp>BOOT_CFLAGS</samp>’. This option assumes that the host 242 supports the linker plugin (e.g. GNU ld version 2.21 or later or GNU gold 243 version 2.21 or later). 244 </p> 245 </dd> 246 <dt>‘<samp>bootstrap-lto-noplugin</samp>’</dt> 247 <dd><p>This option is similar to <code>bootstrap-lto</code>, but is intended for 248 hosts that do not support the linker plugin. Without the linker plugin 249 static libraries are not compiled with link-time optimizations. Since 250 the GCC middle end and back end are in <samp>libbackend.a</samp> this means 251 that only the front end is actually LTO optimized. 252 </p> 253 </dd> 254 <dt>‘<samp>bootstrap-lto-lean</samp>’</dt> 255 <dd><p>This option is similar to <code>bootstrap-lto</code>, but is intended for 256 faster build by only using LTO in the final bootstrap stage. 257 With ‘<samp>make profiledbootstrap</samp>’ the LTO frontend 258 is trained only on generator files. 259 </p> 260 </dd> 261 <dt>‘<samp>bootstrap-debug</samp>’</dt> 262 <dd><p>Verifies that the compiler generates the same executable code, whether 263 or not it is asked to emit debug information. To this end, this 264 option builds stage2 host programs without debug information, and uses 265 <samp>contrib/compare-debug</samp> to compare them with the stripped stage3 266 object files. If <code>BOOT_CFLAGS</code> is overridden so as to not enable 267 debug information, stage2 will have it, and stage3 won’t. This option 268 is enabled by default when GCC bootstrapping is enabled, if 269 <code>strip</code> can turn object files compiled with and without debug 270 info into identical object files. In addition to better test 271 coverage, this option makes default bootstraps faster and leaner. 272 </p> 273 </dd> 274 <dt>‘<samp>bootstrap-debug-big</samp>’</dt> 275 <dd><p>Rather than comparing stripped object files, as in 276 <code>bootstrap-debug</code>, this option saves internal compiler dumps 277 during stage2 and stage3 and compares them as well, which helps catch 278 additional potential problems, but at a great cost in terms of disk 279 space. It can be specified in addition to ‘<samp>bootstrap-debug</samp>’. 280 </p> 281 </dd> 282 <dt>‘<samp>bootstrap-debug-lean</samp>’</dt> 283 <dd><p>This option saves disk space compared with <code>bootstrap-debug-big</code>, 284 but at the expense of some recompilation. Instead of saving the dumps 285 of stage2 and stage3 until the final compare, it uses 286 <samp>-fcompare-debug</samp> to generate, compare and remove the dumps 287 during stage3, repeating the compilation that already took place in 288 stage2, whose dumps were not saved. 289 </p> 290 </dd> 291 <dt>‘<samp>bootstrap-debug-lib</samp>’</dt> 292 <dd><p>This option tests executable code invariance over debug information 293 generation on target libraries, just like <code>bootstrap-debug-lean</code> 294 tests it on host programs. It builds stage3 libraries with 295 <samp>-fcompare-debug</samp>, and it can be used along with any of the 296 <code>bootstrap-debug</code> options above. 297 </p> 298 <p>There aren’t <code>-lean</code> or <code>-big</code> counterparts to this option 299 because most libraries are only build in stage3, so bootstrap compares 300 would not get significant coverage. Moreover, the few libraries built 301 in stage2 are used in stage3 host programs, so we wouldn’t want to 302 compile stage2 libraries with different options for comparison purposes. 303 </p> 304 </dd> 305 <dt>‘<samp>bootstrap-debug-ckovw</samp>’</dt> 306 <dd><p>Arranges for error messages to be issued if the compiler built on any 307 stage is run without the option <samp>-fcompare-debug</samp>. This is 308 useful to verify the full <samp>-fcompare-debug</samp> testing coverage. It 309 must be used along with <code>bootstrap-debug-lean</code> and 310 <code>bootstrap-debug-lib</code>. 311 </p> 312 </dd> 313 <dt>‘<samp>bootstrap-cet</samp>’</dt> 314 <dd><p>This option enables Intel CET for host tools during bootstrapping. 315 ‘<samp>BUILD_CONFIG=bootstrap-cet</samp>’ is equivalent to adding 316 <samp>-fcf-protection</samp> to ‘<samp>BOOT_CFLAGS</samp>’. This option 317 assumes that the host supports Intel CET (e.g. GNU assembler version 318 2.30 or later). 319 </p> 320 </dd> 321 <dt>‘<samp>bootstrap-time</samp>’</dt> 322 <dd><p>Arranges for the run time of each program started by the GCC driver, 323 built in any stage, to be logged to <samp>time.log</samp>, in the top level of 324 the build tree. 325 </p> 326 </dd> 327 <dt>‘<samp>bootstrap-asan</samp>’</dt> 328 <dd><p>Compiles GCC itself using Address Sanitization in order to catch invalid memory 329 accesses within the GCC code. 330 </p> 331 </dd> 332 <dt>‘<samp>bootstrap-hwasan</samp>’</dt> 333 <dd><p>Compiles GCC itself using HWAddress Sanitization in order to catch invalid 334 memory accesses within the GCC code. This option is only available on AArch64 335 systems that are running Linux kernel version 5.4 or later. 336 </p> 337 </dd> 338 </dl> 339 340 <a name="Building-a-cross-compiler"></a> 341 <h3 class="section">Building a cross compiler</h3> 342 343 <p>When building a cross compiler, it is not generally possible to do a 344 3-stage bootstrap of the compiler. This makes for an interesting problem 345 as parts of GCC can only be built with GCC. 346 </p> 347 <p>To build a cross compiler, we recommend first building and installing a 348 native compiler. You can then use the native GCC compiler to build the 349 cross compiler. The installed native compiler needs to be GCC version 350 2.95 or later. 351 </p> 352 <p>Assuming you have already installed a native copy of GCC and configured 353 your cross compiler, issue the command <code>make</code>, which performs the 354 following steps: 355 </p> 356 <ul> 357 <li> Build host tools necessary to build the compiler. 358 359 </li><li> Build target tools for use by the compiler such as binutils (bfd, 360 binutils, gas, gprof, ld, and opcodes) 361 if they have been individually linked or moved into the top level GCC source 362 tree before configuring. 363 364 </li><li> Build the compiler (single stage only). 365 366 </li><li> Build runtime libraries using the compiler from the previous step. 367 </li></ul> 368 369 <p>Note that if an error occurs in any step the make process will exit. 370 </p> 371 <p>If you are not building GNU binutils in the same source tree as GCC, 372 you will need a cross-assembler and cross-linker installed before 373 configuring GCC. Put them in the directory 374 <samp><var>prefix</var>/<var>target</var>/bin</samp>. Here is a table of the tools 375 you should put in this directory: 376 </p> 377 <dl compact="compact"> 378 <dt><samp>as</samp></dt> 379 <dd><p>This should be the cross-assembler. 380 </p> 381 </dd> 382 <dt><samp>ld</samp></dt> 383 <dd><p>This should be the cross-linker. 384 </p> 385 </dd> 386 <dt><samp>ar</samp></dt> 387 <dd><p>This should be the cross-archiver: a program which can manipulate 388 archive files (linker libraries) in the target machine’s format. 389 </p> 390 </dd> 391 <dt><samp>ranlib</samp></dt> 392 <dd><p>This should be a program to construct a symbol table in an archive file. 393 </p></dd> 394 </dl> 395 396 <p>The installation of GCC will find these programs in that directory, 397 and copy or link them to the proper place to for the cross-compiler to 398 find them when run later. 399 </p> 400 <p>The easiest way to provide these files is to build the Binutils package. 401 Configure it with the same <samp>--host</samp> and <samp>--target</samp> 402 options that you use for configuring GCC, then build and install 403 them. They install their executables automatically into the proper 404 directory. Alas, they do not support all the targets that GCC 405 supports. 406 </p> 407 <p>If you are not building a C library in the same source tree as GCC, 408 you should also provide the target libraries and headers before 409 configuring GCC, specifying the directories with 410 <samp>--with-sysroot</samp> or <samp>--with-headers</samp> and 411 <samp>--with-libs</samp>. Many targets also require “start files” such 412 as <samp>crt0.o</samp> and 413 <samp>crtn.o</samp> which are linked into each executable. There may be several 414 alternatives for <samp>crt0.o</samp>, for use with profiling or other 415 compilation options. Check your target’s definition of 416 <code>STARTFILE_SPEC</code> to find out what start files it uses. 417 </p> 418 <a name="Building-in-parallel"></a> 419 <h3 class="section">Building in parallel</h3> 420 421 <p>GNU Make 3.80 and above, which is necessary to build GCC, support 422 building in parallel. To activate this, you can use ‘<samp>make -j 2</samp>’ 423 instead of ‘<samp>make</samp>’. You can also specify a bigger number, and 424 in most cases using a value greater than the number of processors in 425 your machine will result in fewer and shorter I/O latency hits, thus 426 improving overall throughput; this is especially true for slow drives 427 and network filesystems. 428 </p> 429 <a name="Building-the-Ada-compiler"></a> 430 <h3 class="section">Building the Ada compiler</h3> 431 432 <p><a href="prerequisites.html#GNAT-prerequisite">GNAT prerequisites</a>. 433 </p> 434 <a name="Building-the-D-compiler"></a> 435 <h3 class="section">Building the D compiler</h3> 436 437 <p><a href="prerequisites.html#GDC-prerequisite">GDC prerequisites</a>. 438 </p> 439 <a name="Building-with-profile-feedback"></a> 440 <h3 class="section">Building with profile feedback</h3> 441 442 <p>It is possible to use profile feedback to optimize the compiler itself. This 443 should result in a faster compiler binary. Experiments done on x86 using gcc 444 3.3 showed approximately 7 percent speedup on compiling C programs. To 445 bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>. 446 </p> 447 <p>When ‘<samp>make profiledbootstrap</samp>’ is run, it will first build a <code>stage1</code> 448 compiler. This compiler is used to build a <code>stageprofile</code> compiler 449 instrumented to collect execution counts of instruction and branch 450 probabilities. Training run is done by building <code>stagetrain</code> 451 compiler. Finally a <code>stagefeedback</code> compiler is built 452 using the information collected. 453 </p> 454 <p>Unlike standard bootstrap, several additional restrictions apply. The 455 compiler used to build <code>stage1</code> needs to support a 64-bit integral type. 456 It is recommended to only use GCC for this. 457 </p> 458 <p>On Linux/x86_64 hosts with some restrictions (no virtualization) it is 459 also possible to do autofdo build with ‘<samp>make 460 autoprofiledback</samp>’. This uses Linux perf to sample branches in the 461 binary and then rebuild it with feedback derived from the profile. 462 Linux perf and the <code>autofdo</code> toolkit needs to be installed for 463 this. 464 </p> 465 <p>Only the profile from the current build is used, so when an error 466 occurs it is recommended to clean before restarting. Otherwise 467 the code quality may be much worse. 468 </p> 469 <hr /> 470 <p> 471 <p><a href="./index.html">Return to the GCC Installation page</a> 472 </p> 473 474 475 476 477 478 479 <hr> 480 481 482 483 </body> 484 </html> 485