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2 <head>
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3 <title>Installing GCC: Building</title>
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10 Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
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11 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007,
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12 2008 Free Software Foundation, Inc.
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13
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14 Permission is granted to copy, distribute and/or modify this document
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15 under the terms of the GNU Free Documentation License, Version 1.2 or
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16 any later version published by the Free Software Foundation; with no
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17 Invariant Sections, the Front-Cover texts being (a) (see below), and
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18 with the Back-Cover Texts being (b) (see below). A copy of the
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21 (a) The FSF's Front-Cover Text is:
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22
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23 A GNU Manual
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25 (b) The FSF's Back-Cover Text is:
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41 --></style>
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42 </head>
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43 <body>
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44 <h1 class="settitle">Installing GCC: Building</h1>
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45 <a name="index-Installing-GCC_003a-Building-1"></a>
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46 Now that GCC is configured, you are ready to build the compiler and
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47 runtime libraries.
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48
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49 <p>Some commands executed when making the compiler may fail (return a
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50 nonzero status) and be ignored by <samp><span class="command">make</span></samp>. These failures, which
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51 are often due to files that were not found, are expected, and can safely
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52 be ignored.
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53
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54 <p>It is normal to have compiler warnings when compiling certain files.
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55 Unless you are a GCC developer, you can generally ignore these warnings
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56 unless they cause compilation to fail. Developers should attempt to fix
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57 any warnings encountered, however they can temporarily continue past
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58 warnings-as-errors by specifying the configure flag
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59 <samp><span class="option">--disable-werror</span></samp>.
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60
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61 <p>On certain old systems, defining certain environment variables such as
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62 <samp><span class="env">CC</span></samp> can interfere with the functioning of <samp><span class="command">make</span></samp>.
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63
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64 <p>If you encounter seemingly strange errors when trying to build the
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65 compiler in a directory other than the source directory, it could be
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66 because you have previously configured the compiler in the source
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67 directory. Make sure you have done all the necessary preparations.
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68
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69 <p>If you build GCC on a BSD system using a directory stored in an old System
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70 V file system, problems may occur in running <samp><span class="command">fixincludes</span></samp> if the
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71 System V file system doesn't support symbolic links. These problems
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72 result in a failure to fix the declaration of <code>size_t</code> in
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73 <samp><span class="file">sys/types.h</span></samp>. If you find that <code>size_t</code> is a signed type and
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74 that type mismatches occur, this could be the cause.
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75
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76 <p>The solution is not to use such a directory for building GCC.
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77
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78 <p>Similarly, when building from SVN or snapshots, or if you modify
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79 <samp><span class="file">*.l</span></samp> files, you need the Flex lexical analyzer generator
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80 installed. If you do not modify <samp><span class="file">*.l</span></samp> files, releases contain
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81 the Flex-generated files and you do not need Flex installed to build
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82 them. There is still one Flex-based lexical analyzer (part of the
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83 build machinery, not of GCC itself) that is used even if you only
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84 build the C front end.
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85
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86 <p>When building from SVN or snapshots, or if you modify Texinfo
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87 documentation, you need version 4.7 or later of Texinfo installed if you
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88 want Info documentation to be regenerated. Releases contain Info
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89 documentation pre-built for the unmodified documentation in the release.
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90
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91 <h3 class="section"><a name="TOC0"></a>Building a native compiler</h3>
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92
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93 <p>For a native build, the default configuration is to perform
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94 a 3-stage bootstrap of the compiler when ‘<samp><span class="samp">make</span></samp>’ is invoked.
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95 This will build the entire GCC system and ensure that it compiles
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96 itself correctly. It can be disabled with the <samp><span class="option">--disable-bootstrap</span></samp>
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97 parameter to ‘<samp><span class="samp">configure</span></samp>’, but bootstrapping is suggested because
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98 the compiler will be tested more completely and could also have
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99 better performance.
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100
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101 <p>The bootstrapping process will complete the following steps:
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102
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103 <ul>
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104 <li>Build tools necessary to build the compiler.
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105
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106 <li>Perform a 3-stage bootstrap of the compiler. This includes building
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107 three times the target tools for use by the compiler such as binutils
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108 (bfd, binutils, gas, gprof, ld, and opcodes) if they have been
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109 individually linked or moved into the top level GCC source tree before
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110 configuring.
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111
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112 <li>Perform a comparison test of the stage2 and stage3 compilers.
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113
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114 <li>Build runtime libraries using the stage3 compiler from the previous step.
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115
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116 </ul>
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117
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118 <p>If you are short on disk space you might consider ‘<samp><span class="samp">make
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119 bootstrap-lean</span></samp>’ instead. The sequence of compilation is the
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120 same described above, but object files from the stage1 and
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121 stage2 of the 3-stage bootstrap of the compiler are deleted as
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122 soon as they are no longer needed.
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123
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124 <p>If you wish to use non-default GCC flags when compiling the stage2
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125 and stage3 compilers, set <code>BOOT_CFLAGS</code> on the command line when
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126 doing ‘<samp><span class="samp">make</span></samp>’. For example, if you want to save additional space
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127 during the bootstrap and in the final installation as well, you can
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128 build the compiler binaries without debugging information as in the
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129 following example. This will save roughly 40% of disk space both for
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130 the bootstrap and the final installation. (Libraries will still contain
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131 debugging information.)
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132
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133 <pre class="smallexample"> make BOOT_CFLAGS='-O' bootstrap
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134 </pre>
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135 <p>You can place non-default optimization flags into <code>BOOT_CFLAGS</code>; they
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136 are less well tested here than the default of ‘<samp><span class="samp">-g -O2</span></samp>’, but should
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137 still work. In a few cases, you may find that you need to specify special
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138 flags such as <samp><span class="option">-msoft-float</span></samp> here to complete the bootstrap; or,
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139 if the native compiler miscompiles the stage1 compiler, you may need
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140 to work around this, by choosing <code>BOOT_CFLAGS</code> to avoid the parts
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141 of the stage1 compiler that were miscompiled, or by using ‘<samp><span class="samp">make
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142 bootstrap4</span></samp>’ to increase the number of stages of bootstrap.
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143
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144 <p><code>BOOT_CFLAGS</code> does not apply to bootstrapped target libraries.
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145 Since these are always compiled with the compiler currently being
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146 bootstrapped, you can use <code>CFLAGS_FOR_TARGET</code> to modify their
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147 compilation flags, as for non-bootstrapped target libraries.
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148 Again, if the native compiler miscompiles the stage1 compiler, you may
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149 need to work around this by avoiding non-working parts of the stage1
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150 compiler. Use <code>STAGE1_LIBCFLAGS</code> to this end.
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151
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152 <p>If you used the flag <samp><span class="option">--enable-languages=...</span></samp> to restrict
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153 the compilers to be built, only those you've actually enabled will be
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154 built. This will of course only build those runtime libraries, for
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155 which the particular compiler has been built. Please note,
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156 that re-defining <samp><span class="env">LANGUAGES</span></samp> when calling ‘<samp><span class="samp">make</span></samp>’
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157 <strong>does not</strong> work anymore!
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158
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159 <p>If the comparison of stage2 and stage3 fails, this normally indicates
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160 that the stage2 compiler has compiled GCC incorrectly, and is therefore
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161 a potentially serious bug which you should investigate and report. (On
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162 a few systems, meaningful comparison of object files is impossible; they
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163 always appear “different”. If you encounter this problem, you will
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164 need to disable comparison in the <samp><span class="file">Makefile</span></samp>.)
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165
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166 <p>If you do not want to bootstrap your compiler, you can configure with
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167 <samp><span class="option">--disable-bootstrap</span></samp>. In particular cases, you may want to
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168 bootstrap your compiler even if the target system is not the same as
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169 the one you are building on: for example, you could build a
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170 <code>powerpc-unknown-linux-gnu</code> toolchain on a
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171 <code>powerpc64-unknown-linux-gnu</code> host. In this case, pass
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172 <samp><span class="option">--enable-bootstrap</span></samp> to the configure script.
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173
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174 <h3 class="section"><a name="TOC1"></a>Building a cross compiler</h3>
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175
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176 <p>When building a cross compiler, it is not generally possible to do a
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177 3-stage bootstrap of the compiler. This makes for an interesting problem
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178 as parts of GCC can only be built with GCC.
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179
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180 <p>To build a cross compiler, we first recommend building and installing a
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181 native compiler. You can then use the native GCC compiler to build the
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182 cross compiler. The installed native compiler needs to be GCC version
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183 2.95 or later.
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184
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185 <p>If the cross compiler is to be built with support for the Java
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186 programming language and the ability to compile .java source files is
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187 desired, the installed native compiler used to build the cross
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188 compiler needs to be the same GCC version as the cross compiler. In
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189 addition the cross compiler needs to be configured with
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190 <samp><span class="option">--with-ecj-jar=...</span></samp>.
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191
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192 <p>Assuming you have already installed a native copy of GCC and configured
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193 your cross compiler, issue the command <samp><span class="command">make</span></samp>, which performs the
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194 following steps:
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195
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196 <ul>
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197 <li>Build host tools necessary to build the compiler.
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198
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199 <li>Build target tools for use by the compiler such as binutils (bfd,
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200 binutils, gas, gprof, ld, and opcodes)
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201 if they have been individually linked or moved into the top level GCC source
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202 tree before configuring.
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203
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204 <li>Build the compiler (single stage only).
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205
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206 <li>Build runtime libraries using the compiler from the previous step.
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207 </ul>
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208
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209 <p>Note that if an error occurs in any step the make process will exit.
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210
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211 <p>If you are not building GNU binutils in the same source tree as GCC,
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212 you will need a cross-assembler and cross-linker installed before
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213 configuring GCC. Put them in the directory
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214 <samp><var>prefix</var><span class="file">/</span><var>target</var><span class="file">/bin</span></samp>. Here is a table of the tools
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215 you should put in this directory:
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216
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217 <dl>
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218 <dt><samp><span class="file">as</span></samp><dd>This should be the cross-assembler.
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219
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220 <br><dt><samp><span class="file">ld</span></samp><dd>This should be the cross-linker.
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221
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222 <br><dt><samp><span class="file">ar</span></samp><dd>This should be the cross-archiver: a program which can manipulate
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223 archive files (linker libraries) in the target machine's format.
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224
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225 <br><dt><samp><span class="file">ranlib</span></samp><dd>This should be a program to construct a symbol table in an archive file.
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226 </dl>
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227
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228 <p>The installation of GCC will find these programs in that directory,
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229 and copy or link them to the proper place to for the cross-compiler to
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230 find them when run later.
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231
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232 <p>The easiest way to provide these files is to build the Binutils package.
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233 Configure it with the same <samp><span class="option">--host</span></samp> and <samp><span class="option">--target</span></samp>
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234 options that you use for configuring GCC, then build and install
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235 them. They install their executables automatically into the proper
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236 directory. Alas, they do not support all the targets that GCC
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237 supports.
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238
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239 <p>If you are not building a C library in the same source tree as GCC,
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240 you should also provide the target libraries and headers before
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241 configuring GCC, specifying the directories with
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242 <samp><span class="option">--with-sysroot</span></samp> or <samp><span class="option">--with-headers</span></samp> and
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243 <samp><span class="option">--with-libs</span></samp>. Many targets also require “start files” such
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244 as <samp><span class="file">crt0.o</span></samp> and
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245 <samp><span class="file">crtn.o</span></samp> which are linked into each executable. There may be several
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246 alternatives for <samp><span class="file">crt0.o</span></samp>, for use with profiling or other
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247 compilation options. Check your target's definition of
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248 <code>STARTFILE_SPEC</code> to find out what start files it uses.
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249
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250 <h3 class="section"><a name="TOC2"></a>Building in parallel</h3>
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251
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252 <p>GNU Make 3.79 and above, which is necessary to build GCC, support
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253 building in parallel. To activate this, you can use ‘<samp><span class="samp">make -j 2</span></samp>’
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254 instead of ‘<samp><span class="samp">make</span></samp>’. You can also specify a bigger number, and
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255 in most cases using a value greater than the number of processors in
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256 your machine will result in fewer and shorter I/O latency hits, thus
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257 improving overall throughput; this is especially true for slow drives
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258 and network filesystems.
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259
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260 <h3 class="section"><a name="TOC3"></a>Building the Ada compiler</h3>
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261
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262 <p>In order to build GNAT, the Ada compiler, you need a working GNAT
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263 compiler (GCC version 3.4 or later).
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264 This includes GNAT tools such as <samp><span class="command">gnatmake</span></samp> and
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265 <samp><span class="command">gnatlink</span></samp>, since the Ada front end is written in Ada and
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266 uses some GNAT-specific extensions.
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267
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268 <p>In order to build a cross compiler, it is suggested to install
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269 the new compiler as native first, and then use it to build the cross
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270 compiler.
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271
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272 <p><samp><span class="command">configure</span></samp> does not test whether the GNAT installation works
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273 and has a sufficiently recent version; if too old a GNAT version is
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274 installed, the build will fail unless <samp><span class="option">--enable-languages</span></samp> is
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275 used to disable building the Ada front end.
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276
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277 <p><samp><span class="env">ADA_INCLUDE_PATH</span></samp> and <samp><span class="env">ADA_OBJECT_PATH</span></samp> environment variables
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278 must not be set when building the Ada compiler, the Ada tools, or the
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279 Ada runtime libraries. You can check that your build environment is clean
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280 by verifying that ‘<samp><span class="samp">gnatls -v</span></samp>’ lists only one explicit path in each
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281 section.
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282
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283 <h3 class="section"><a name="TOC4"></a>Building with profile feedback</h3>
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284
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285 <p>It is possible to use profile feedback to optimize the compiler itself. This
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286 should result in a faster compiler binary. Experiments done on x86 using gcc
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287 3.3 showed approximately 7 percent speedup on compiling C programs. To
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288 bootstrap the compiler with profile feedback, use <code>make profiledbootstrap</code>.
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289
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290 <p>When ‘<samp><span class="samp">make profiledbootstrap</span></samp>’ is run, it will first build a <code>stage1</code>
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291 compiler. This compiler is used to build a <code>stageprofile</code> compiler
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292 instrumented to collect execution counts of instruction and branch
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293 probabilities. Then runtime libraries are compiled with profile collected.
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294 Finally a <code>stagefeedback</code> compiler is built using the information collected.
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295
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296 <p>Unlike standard bootstrap, several additional restrictions apply. The
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297 compiler used to build <code>stage1</code> needs to support a 64-bit integral type.
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298 It is recommended to only use GCC for this. Also parallel make is currently
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299 not supported since collisions in profile collecting may occur.
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300
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301 <p><hr />
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302 <p><a href="./index.html">Return to the GCC Installation page</a>
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303
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304 <!-- ***Testing***************************************************************** -->
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305 <!-- ***Final install*********************************************************** -->
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306 <!-- ***Binaries**************************************************************** -->
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307 <!-- ***Specific**************************************************************** -->
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308 <!-- ***Old documentation****************************************************** -->
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309 <!-- ***GFDL******************************************************************** -->
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310 <!-- *************************************************************************** -->
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311 <!-- Part 6 The End of the Document -->
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312 </body></html>
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313
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