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1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- Copyright (C) 1988-2020 Free Software Foundation, Inc. 4 5Permission is granted to copy, distribute and/or modify this document 6under the terms of the GNU Free Documentation License, Version 1.3 or 7any later version published by the Free Software Foundation; with no 8Invariant Sections, the Front-Cover texts being (a) (see below), and 9with the Back-Cover Texts being (b) (see below). A copy of the 10license is included in the section entitled "GNU 11Free Documentation License". 12 13(a) The FSF's Front-Cover Text is: 14 15A GNU Manual 16 17(b) The FSF's Back-Cover Text is: 18 19You have freedom to copy and modify this GNU Manual, like GNU 20 software. Copies published by the Free Software Foundation raise 21 funds for GNU development. --> 22<!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ --> 23<head> 24<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 25<title>Installing GCC: Building</title> 26 27<meta name="description" content="Installing GCC: Building"> 28<meta name="keywords" content="Installing GCC: Building"> 29<meta name="resource-type" content="document"> 30<meta name="distribution" content="global"> 31<meta name="Generator" content="makeinfo"> 32<style type="text/css"> 33<!-- 34a.summary-letter {text-decoration: none} 35blockquote.indentedblock {margin-right: 0em} 36blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} 37blockquote.smallquotation {font-size: smaller} 38div.display {margin-left: 3.2em} 39div.example {margin-left: 3.2em} 40div.lisp {margin-left: 3.2em} 41div.smalldisplay {margin-left: 3.2em} 42div.smallexample {margin-left: 3.2em} 43div.smalllisp {margin-left: 3.2em} 44kbd {font-style: oblique} 45pre.display {font-family: inherit} 46pre.format {font-family: inherit} 47pre.menu-comment {font-family: serif} 48pre.menu-preformatted {font-family: serif} 49pre.smalldisplay {font-family: inherit; font-size: smaller} 50pre.smallexample {font-size: smaller} 51pre.smallformat {font-family: inherit; font-size: smaller} 52pre.smalllisp {font-size: smaller} 53span.nolinebreak {white-space: nowrap} 54span.roman {font-family: initial; font-weight: normal} 55span.sansserif {font-family: sans-serif; font-weight: normal} 56ul.no-bullet {list-style: none} 57--> 58</style> 59 60 61</head> 62 63<body lang="en"> 64<h1 class="settitle" align="center">Installing GCC: Building</h1> 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85<a name="index-Installing-GCC_003a-Building"></a> 86 87<p>Now that GCC is configured, you are ready to build the compiler and 88runtime libraries. 89</p> 90<p>Some commands executed when making the compiler may fail (return a 91nonzero status) and be ignored by <code>make</code>. These failures, which 92are often due to files that were not found, are expected, and can safely 93be ignored. 94</p> 95<p>It is normal to have compiler warnings when compiling certain files. 96Unless you are a GCC developer, you can generally ignore these warnings 97unless they cause compilation to fail. Developers should attempt to fix 98any warnings encountered, however they can temporarily continue past 99warnings-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 106compiler in a directory other than the source directory, it could be 107because you have previously configured the compiler in the source 108directory. 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 111V file system, problems may occur in running <code>fixincludes</code> if the 112System V file system doesn’t support symbolic links. These problems 113result 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 115that 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 121installed. If you do not modify <samp>*.l</samp> files, releases contain 122the Flex-generated files and you do not need Flex installed to build 123them. There is still one Flex-based lexical analyzer (part of the 124build machinery, not of GCC itself) that is used even if you only 125build the C front end. 126</p> 127<p>When building from the source repository or snapshots, or if you modify Texinfo 128documentation, you need version 4.7 or later of Texinfo installed if you 129want Info documentation to be regenerated. Releases contain Info 130documentation 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 136a 3-stage bootstrap of the compiler when ‘<samp>make</samp>’ is invoked. 137This will build the entire GCC system and ensure that it compiles 138itself correctly. It can be disabled with the <samp>--disable-bootstrap</samp> 139parameter to ‘<samp>configure</samp>’, but bootstrapping is suggested because 140the compiler will be tested more completely and could also have 141better 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 149three times the target tools for use by the compiler such as binutils 150(bfd, binutils, gas, gprof, ld, and opcodes) if they have been 151individually linked or moved into the top level GCC source tree before 152configuring. 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 161bootstrap-lean</samp>’ instead. The sequence of compilation is the 162same described above, but object files from the stage1 and 163stage2 of the 3-stage bootstrap of the compiler are deleted as 164soon as they are no longer needed. 165</p> 166<p>If you wish to use non-default GCC flags when compiling the stage2 167and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when 168doing ‘<samp>make</samp>’. For example, if you want to save additional space 169during the bootstrap and in the final installation as well, you can 170build the compiler binaries without debugging information as in the 171following example. This will save roughly 40% of disk space both for 172the bootstrap and the final installation. (Libraries will still contain 173debugging 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 180are less well tested here than the default of ‘<samp>-g -O2</samp>’, but should 181still work. In a few cases, you may find that you need to specify special 182flags such as <samp>-msoft-float</samp> here to complete the bootstrap; or, 183if the native compiler miscompiles the stage1 compiler, you may need 184to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts 185of the stage1 compiler that were miscompiled, or by using ‘<samp>make 186bootstrap4</samp>’ to increase the number of stages of bootstrap. 187</p> 188<p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries. 189Since these are always compiled with the compiler currently being 190bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their 191compilation flags, as for non-bootstrapped target libraries. 192Again, if the native compiler miscompiles the stage1 compiler, you may 193need to work around this by avoiding non-working parts of the stage1 194compiler. Use <code>STAGE1_TFLAGS</code> to this end. 195</p> 196<p>If you used the flag <samp>--enable-languages=…</samp> to restrict 197the compilers to be built, only those you’ve actually enabled will be 198built. This will of course only build those runtime libraries, for 199which the particular compiler has been built. Please note, 200that 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 204that the stage2 compiler has compiled GCC incorrectly, and is therefore 205a potentially serious bug which you should investigate and report. (On 206a few systems, meaningful comparison of object files is impossible; they 207always appear “different”. If you encounter this problem, you will 208need 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 212bootstrap your compiler even if the target system is not the same as 213the 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 219to the build. It can be set to a whitespace-separated list of names. 220For each such <code>NAME</code>, top-level <samp>config/<code>NAME</code>.mk</samp> will 221be included by the top-level <samp>Makefile</samp>, bringing in any settings 222it contains. The default <code>BUILD_CONFIG</code> can be set using the 223configure option <samp>--with-build-config=<code>NAME</code>...</samp>. Some 224examples 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 242supports the linker plugin (e.g. GNU ld version 2.21 or later or GNU gold 243version 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 248hosts that do not support the linker plugin. Without the linker plugin 249static libraries are not compiled with link-time optimizations. Since 250the GCC middle end and back end are in <samp>libbackend.a</samp> this means 251that 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 256faster build by only using LTO in the final bootstrap stage. 257With ‘<samp>make profiledbootstrap</samp>’ the LTO frontend 258is 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 263or not it is asked to emit debug information. To this end, this 264option builds stage2 host programs without debug information, and uses 265<samp>contrib/compare-debug</samp> to compare them with the stripped stage3 266object files. If <code>BOOT_CFLAGS</code> is overridden so as to not enable 267debug information, stage2 will have it, and stage3 won’t. This option 268is enabled by default when GCC bootstrapping is enabled, if 269<code>strip</code> can turn object files compiled with and without debug 270info into identical object files. In addition to better test 271coverage, 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 277during stage2 and stage3 and compares them as well, which helps catch 278additional potential problems, but at a great cost in terms of disk 279space. 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>, 284but at the expense of some recompilation. Instead of saving the dumps 285of stage2 and stage3 until the final compare, it uses 286<samp>-fcompare-debug</samp> to generate, compare and remove the dumps 287during stage3, repeating the compilation that already took place in 288stage2, 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 293generation on target libraries, just like <code>bootstrap-debug-lean</code> 294tests 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 299because most libraries are only build in stage3, so bootstrap compares 300would not get significant coverage. Moreover, the few libraries built 301in stage2 are used in stage3 host programs, so we wouldn’t want to 302compile 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 307stage is run without the option <samp>-fcompare-debug</samp>. This is 308useful to verify the full <samp>-fcompare-debug</samp> testing coverage. It 309must 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 317assumes that the host supports Intel CET (e.g. GNU assembler version 3182.30 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, 323built in any stage, to be logged to <samp>time.log</samp>, in the top level of 324the 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 329accesses within the GCC code. 330</p> 331</dd> 332</dl> 333 334<a name="Building-a-cross-compiler"></a> 335<h3 class="section">Building a cross compiler</h3> 336 337<p>When building a cross compiler, it is not generally possible to do a 3383-stage bootstrap of the compiler. This makes for an interesting problem 339as parts of GCC can only be built with GCC. 340</p> 341<p>To build a cross compiler, we recommend first building and installing a 342native compiler. You can then use the native GCC compiler to build the 343cross compiler. The installed native compiler needs to be GCC version 3442.95 or later. 345</p> 346<p>Assuming you have already installed a native copy of GCC and configured 347your cross compiler, issue the command <code>make</code>, which performs the 348following steps: 349</p> 350<ul> 351<li> Build host tools necessary to build the compiler. 352 353</li><li> Build target tools for use by the compiler such as binutils (bfd, 354binutils, gas, gprof, ld, and opcodes) 355if they have been individually linked or moved into the top level GCC source 356tree before configuring. 357 358</li><li> Build the compiler (single stage only). 359 360</li><li> Build runtime libraries using the compiler from the previous step. 361</li></ul> 362 363<p>Note that if an error occurs in any step the make process will exit. 364</p> 365<p>If you are not building GNU binutils in the same source tree as GCC, 366you will need a cross-assembler and cross-linker installed before 367configuring GCC. Put them in the directory 368<samp><var>prefix</var>/<var>target</var>/bin</samp>. Here is a table of the tools 369you should put in this directory: 370</p> 371<dl compact="compact"> 372<dt><samp>as</samp></dt> 373<dd><p>This should be the cross-assembler. 374</p> 375</dd> 376<dt><samp>ld</samp></dt> 377<dd><p>This should be the cross-linker. 378</p> 379</dd> 380<dt><samp>ar</samp></dt> 381<dd><p>This should be the cross-archiver: a program which can manipulate 382archive files (linker libraries) in the target machine’s format. 383</p> 384</dd> 385<dt><samp>ranlib</samp></dt> 386<dd><p>This should be a program to construct a symbol table in an archive file. 387</p></dd> 388</dl> 389 390<p>The installation of GCC will find these programs in that directory, 391and copy or link them to the proper place to for the cross-compiler to 392find them when run later. 393</p> 394<p>The easiest way to provide these files is to build the Binutils package. 395Configure it with the same <samp>--host</samp> and <samp>--target</samp> 396options that you use for configuring GCC, then build and install 397them. They install their executables automatically into the proper 398directory. Alas, they do not support all the targets that GCC 399supports. 400</p> 401<p>If you are not building a C library in the same source tree as GCC, 402you should also provide the target libraries and headers before 403configuring GCC, specifying the directories with 404<samp>--with-sysroot</samp> or <samp>--with-headers</samp> and 405<samp>--with-libs</samp>. Many targets also require “start files” such 406as <samp>crt0.o</samp> and 407<samp>crtn.o</samp> which are linked into each executable. There may be several 408alternatives for <samp>crt0.o</samp>, for use with profiling or other 409compilation options. Check your target’s definition of 410<code>STARTFILE_SPEC</code> to find out what start files it uses. 411</p> 412<a name="Building-in-parallel"></a> 413<h3 class="section">Building in parallel</h3> 414 415<p>GNU Make 3.80 and above, which is necessary to build GCC, support 416building in parallel. To activate this, you can use ‘<samp>make -j 2</samp>’ 417instead of ‘<samp>make</samp>’. You can also specify a bigger number, and 418in most cases using a value greater than the number of processors in 419your machine will result in fewer and shorter I/O latency hits, thus 420improving overall throughput; this is especially true for slow drives 421and network filesystems. 422</p> 423<a name="Building-the-Ada-compiler"></a> 424<h3 class="section">Building the Ada compiler</h3> 425 426<p><a href="prerequisites.html#GNAT-prerequisite">GNAT prerequisites</a>. 427</p> 428<a name="Building-with-profile-feedback"></a> 429<h3 class="section">Building with profile feedback</h3> 430 431<p>It is possible to use profile feedback to optimize the compiler itself. This 432should result in a faster compiler binary. Experiments done on x86 using gcc 4333.3 showed approximately 7 percent speedup on compiling C programs. To 434bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>. 435</p> 436<p>When ‘<samp>make profiledbootstrap</samp>’ is run, it will first build a <code>stage1</code> 437compiler. This compiler is used to build a <code>stageprofile</code> compiler 438instrumented to collect execution counts of instruction and branch 439probabilities. Training run is done by building <code>stagetrain</code> 440compiler. Finally a <code>stagefeedback</code> compiler is built 441using the information collected. 442</p> 443<p>Unlike standard bootstrap, several additional restrictions apply. The 444compiler used to build <code>stage1</code> needs to support a 64-bit integral type. 445It is recommended to only use GCC for this. 446</p> 447<p>On Linux/x86_64 hosts with some restrictions (no virtualization) it is 448also possible to do autofdo build with ‘<samp>make 449autoprofiledback</samp>’. This uses Linux perf to sample branches in the 450binary and then rebuild it with feedback derived from the profile. 451Linux perf and the <code>autofdo</code> toolkit needs to be installed for 452this. 453</p> 454<p>Only the profile from the current build is used, so when an error 455occurs it is recommended to clean before restarting. Otherwise 456the code quality may be much worse. 457</p> 458<hr /> 459<p> 460<p><a href="./index.html">Return to the GCC Installation page</a> 461</p> 462 463 464 465 466 467 468 469<hr> 470 471 472 473</body> 474</html> 475