1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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5 | %general-entities;
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6 | ]>
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7 |
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8 | <sect1 id="ch-tools-gcc-pass2" role="wrap">
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9 | <?dbhtml filename="gcc-pass2.html"?>
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10 |
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11 | <sect1info condition="script">
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12 | <productname>gcc</productname>
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13 | <productnumber>&gcc-version;</productnumber>
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14 | <address>&gcc-url;</address>
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15 | </sect1info>
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16 |
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17 | <title>GCC-&gcc-version; - Pass 2</title>
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18 |
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19 | <indexterm zone="ch-tools-gcc-pass2">
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20 | <primary sortas="a-GCC">GCC</primary>
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21 | <secondary>tools, pass 2</secondary>
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22 | </indexterm>
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23 |
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24 | <sect2 role="package">
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25 | <title/>
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26 |
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27 | <xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
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28 | href="../chapter06/gcc.xml"
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29 | xpointer="xpointer(/sect1/sect2[1]/para[1])"/>
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30 |
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31 | <segmentedlist>
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32 | <segtitle>&buildtime;</segtitle>
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33 | <segtitle>&diskspace;</segtitle>
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34 |
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35 | <seglistitem>
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36 | <seg>&gcc-ch5p2-sbu;</seg>
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37 | <seg>&gcc-ch5p2-du;</seg>
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38 | </seglistitem>
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39 | </segmentedlist>
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40 |
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41 | </sect2>
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42 |
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43 | <sect2 role="installation">
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44 | <title>Installation of GCC</title>
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45 |
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46 | <para>Versions of GCC later than 4.3 will treat this build as if
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47 | it were a relocated compiler and disallow searching for startfiles in
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48 | the location specified by <parameter>--prefix</parameter>. Since this
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49 | will not be a relocated compiler, and the startfiles in
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50 | <filename class="directory">/tools</filename> are crucial to building
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51 | a working compiler linked to the libs in <filename class="directory">/tools</filename>,
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52 | apply the following patch which partially reverts GCC to its old behavior:</para>
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53 |
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54 | <screen><userinput remap="pre">patch -Np1 -i ../&gcc-startfiles-patch;</userinput></screen>
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55 |
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56 | <para>Under normal circumstances the GCC <command>fixincludes</command> script
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57 | is run in order to fix potentially broken header files. As GCC-&gcc-version;
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58 | and Glibc-&glibc-version; have already been installed at this point, and
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59 | their respective header files are known to not require fixing, the
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60 | <command>fixincludes</command> script is not required. In fact, running
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61 | this script may actually pollute the build environment by
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62 | installing fixed headers from the host system into GCC's private include
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63 | directory. The running of the <command>fixincludes</command> script can
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64 | be suppressed by issuing the following commands:</para>
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65 |
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66 | <screen><userinput remap="pre">cp -v gcc/Makefile.in{,.orig}
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67 | sed 's@\./fixinc\.sh@-c true@' gcc/Makefile.in.orig > gcc/Makefile.in</userinput></screen>
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68 |
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69 | <para>For x86 machines, a bootstrap build of GCC uses the
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70 | <option>-fomit-frame-pointer</option> compiler flag. Non-bootstrap builds
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71 | omit this flag by default, and the goal should be to produce a compiler
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72 | that is exactly the same as if it were bootstrapped. Apply the following
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73 | <command>sed</command> command to force the build to use the flag:</para>
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74 |
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75 | <screen><userinput remap="pre">cp -v gcc/Makefile.in{,.tmp}
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76 | sed 's/^T_CFLAGS =$/& -fomit-frame-pointer/' gcc/Makefile.in.tmp \
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77 | > gcc/Makefile.in</userinput></screen>
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78 |
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79 | <para>The following command will change the location of GCC's default
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80 | dynamic linker to use the one installed in
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81 | <filename class="directory">/tools</filename>. It also removes <filename
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82 | class="directory">/usr/include</filename> from GCC's include search path.
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83 | Doing this now rather than adjusting the specs file after installation
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84 | ensures that the new dynamic linker is used during the actual build of
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85 | GCC. That is, all of the binaries created during the build will link
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86 | against the new Glibc. Issue:</para>
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87 |
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88 | <screen><userinput remap="pre">for file in \
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89 | $(find gcc/config -name linux64.h -o -name linux.h -o -name sysv4.h)
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90 | do
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91 | cp -uv $file{,.orig}
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92 | sed -e 's@/lib\(64\)\?\(32\)\?/ld@/tools&@g' \
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93 | -e 's@/usr@/tools@g' $file.orig > $file
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94 | echo '
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95 | #undef STANDARD_INCLUDE_DIR
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96 | #define STANDARD_INCLUDE_DIR 0
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97 | #define STANDARD_STARTFILE_PREFIX_1 ""
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98 | #define STANDARD_STARTFILE_PREFIX_2 ""' >> $file
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99 | touch $file.orig
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100 | done</userinput></screen>
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101 |
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102 | <para>In case the above seems hard to follow, let's break it down a bit.
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103 | First we find all the files under the
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104 | <filename class="directory">gcc/config</filename> directory that are named
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105 | either <filename>linux.h</filename>, <filename>linux64.h</filename> or
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106 | <filename>sysv4.h</filename>.
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107 | For each file found, we copy it to a file of the same name but with an added
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108 | suffix of <quote>.orig</quote>. Then the first sed expression prepends
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109 | <quote>/tools</quote> to every instance of <quote>/lib/ld</quote>,
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110 | <quote>/lib64/ld</quote> or <quote>/lib32/ld</quote>, while the second one
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111 | replaces hard-coded instances of <quote>/usr</quote>. Then we add our define
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112 | statements which alter the include search path and the default startfile prefix
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113 | to the end of the file.
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114 | Finally, we use <command>touch</command> to update the timestamp on the copied files.
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115 | When used in conjunction with <command>cp -u</command>, this prevents unexpected
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116 | changes to the original files in case the commands are inadvertently run twice.
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117 | </para>
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118 |
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119 | <para>On x86_64, unsetting the multilib spec for GCC ensures that it
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120 | won't attempt to link against libraries on the host:</para>
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121 |
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122 | <screen><userinput remap="pre">case $(uname -m) in
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123 | x86_64)
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124 | for file in $(find gcc/config -name t-linux64) ; do \
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125 | cp -v $file{,.orig}
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126 | sed '/MULTILIB_OSDIRNAMES/d' $file.orig > $file
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127 | done
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128 | ;;
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129 | esac</userinput></screen>
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130 |
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131 | <para>As in the first build of GCC it requires the GMP, MPFR and MPC
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132 | packages. Unpack the tarballs and move them into the required directory
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133 | names:</para>
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134 |
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135 | <screen><userinput remap="pre">tar -jxf ../mpfr-&mpfr-version;.tar.bz2
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136 | mv -v mpfr-&mpfr-version; mpfr
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137 | tar -Jxf ../gmp-&gmp-version;.tar.xz
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138 | mv -v gmp-&gmp-version; gmp
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139 | tar -zxf ../mpc-&mpc-version;.tar.gz
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140 | mv -v mpc-&mpc-version; mpc</userinput></screen>
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141 |
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142 | <para>Create a separate build directory again:</para>
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143 |
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144 | <screen><userinput remap="pre">mkdir -v ../gcc-build
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145 | cd ../gcc-build</userinput></screen>
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146 |
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147 | <para>Before starting to build GCC, remember to unset any environment
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148 | variables that override the default optimization flags.</para>
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149 |
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150 | <para>Now prepare GCC for compilation:</para>
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151 |
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152 | <screen><userinput remap="configure">CC="$LFS_TGT-gcc -B/tools/lib/" \
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153 | AR=$LFS_TGT-ar RANLIB=$LFS_TGT-ranlib \
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154 | ../gcc-&gcc-version;/configure --prefix=/tools \
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155 | --with-local-prefix=/tools --enable-clocale=gnu \
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156 | --enable-shared --enable-threads=posix \
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157 | --enable-__cxa_atexit --enable-languages=c,c++ \
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158 | --disable-libstdcxx-pch --disable-multilib \
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159 | --disable-bootstrap --disable-libgomp \
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160 | --without-ppl --without-cloog \
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161 | --with-mpfr-include=$(pwd)/../gcc-&gcc-version;/mpfr/src \
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162 | --with-mpfr-lib=$(pwd)/mpfr/src/.libs</userinput></screen>
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163 |
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164 | <variablelist>
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165 | <title>The meaning of the new configure options:</title>
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166 |
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167 | <varlistentry>
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168 | <term><parameter>--enable-clocale=gnu</parameter></term>
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169 | <listitem>
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170 | <para>This option ensures the correct locale model is selected
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171 | for the C++ libraries under all circumstances. If the configure
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172 | script finds the <emphasis>de_DE</emphasis> locale installed,
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173 | it will select the correct gnu locale model. However, if the
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174 | <emphasis>de_DE</emphasis> locale is not installed, there is the
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175 | risk of building Application Binary Interface (ABI)-incompatible
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176 | C++ libraries because the incorrect generic locale model may be
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177 | selected.</para>
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178 | </listitem>
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179 | </varlistentry>
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180 |
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181 | <varlistentry>
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182 | <term><parameter>--enable-threads=posix</parameter></term>
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183 | <listitem>
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184 | <para>This enables C++ exception handling for multi-threaded code.</para>
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185 | </listitem>
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186 | </varlistentry>
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187 |
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188 | <varlistentry>
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189 | <term><parameter>--enable-__cxa_atexit</parameter></term>
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190 | <listitem>
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191 | <para>This option allows use of <function>__cxa_atexit</function>,
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192 | rather than <function>atexit</function>, to register C++ destructors
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193 | for local statics and global objects. This option is essential for
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194 | fully standards-compliant handling of destructors. It also affects
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195 | the C++ ABI, and therefore results in C++ shared libraries and C++
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196 | programs that are interoperable with other Linux distributions.</para>
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197 | </listitem>
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198 | </varlistentry>
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199 |
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200 | <varlistentry>
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201 | <term><parameter>--enable-languages=c,c++</parameter></term>
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202 | <listitem>
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203 | <para>This option ensures that both the C and C++ compilers are
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204 | built.</para>
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205 | </listitem>
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206 | </varlistentry>
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207 |
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208 | <varlistentry>
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209 | <term><parameter>--disable-libstdcxx-pch</parameter></term>
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210 | <listitem>
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211 | <para>Do not build the pre-compiled header (PCH) for
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212 | <filename class="libraryfile">libstdc++</filename>. It takes up a
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213 | lot of space, and we have no use for it.</para>
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214 | </listitem>
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215 | </varlistentry>
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216 |
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217 | <varlistentry>
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218 | <term><parameter>--disable-bootstrap</parameter></term>
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219 | <listitem>
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220 | <para>For native builds of GCC, the default is to do a "bootstrap"
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221 | build. This does not just compile GCC, but compiles it several times.
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222 | It uses the programs compiled in a first round to compile itself a
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223 | second time, and then again a third time. The second and third
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224 | iterations are compared to make sure it can reproduce itself
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225 | flawlessly. This also implies that it was compiled correctly.
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226 | However, the LFS build method should provide a solid compiler
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227 | without the need to bootstrap each time.</para>
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228 | </listitem>
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229 | </varlistentry>
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230 |
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231 | </variablelist>
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232 |
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233 | <para>Compile the package:</para>
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234 |
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235 | <screen><userinput remap="make">make</userinput></screen>
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236 |
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237 | <para>Install the package:</para>
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238 |
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239 | <screen><userinput remap="install">make install</userinput></screen>
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240 |
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241 | <para>As a finishing touch, create a symlink. Many programs and scripts
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242 | run <command>cc</command> instead of <command>gcc</command>, which is
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243 | used to keep programs generic and therefore usable on all kinds of UNIX
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244 | systems where the GNU C compiler is not always installed. Running
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245 | <command>cc</command> leaves the system administrator free to decide
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246 | which C compiler to install:</para>
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247 |
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248 | <screen><userinput remap="install">ln -vs gcc /tools/bin/cc</userinput></screen>
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249 |
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250 | <caution>
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251 | <para>At this point, it is imperative to stop and ensure that the basic
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252 | functions (compiling and linking) of the new toolchain are working as
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253 | expected. To perform a sanity check, run the following commands:</para>
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254 |
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255 | <screen><userinput>echo 'main(){}' > dummy.c
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256 | cc dummy.c
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257 | readelf -l a.out | grep ': /tools'</userinput></screen>
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258 |
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259 | <para>If everything is working correctly, there should be no errors,
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260 | and the output of the last command will be of the form:</para>
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261 |
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262 | <screen><computeroutput>[Requesting program interpreter: /tools/lib/ld-linux.so.2]</computeroutput></screen>
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263 |
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264 | <para>Note that <filename class="directory">/tools/lib</filename>, or
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265 | <filename class="directory">/tools/lib64</filename> for 64-bit machines
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266 | appears as the prefix of the dynamic linker.</para>
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267 |
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268 | <para>If the output is not shown as above or there was no output at all,
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269 | then something is wrong. Investigate and retrace the steps to find out
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270 | where the problem is and correct it. This issue must be resolved before
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271 | continuing on. First, perform the sanity check again, using
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272 | <command>gcc</command> instead of <command>cc</command>. If this works,
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273 | then the <filename class="symlink">/tools/bin/cc</filename> symlink is
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274 | missing. Install the symlink as per above.
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275 | Next, ensure that the <envar>PATH</envar> is correct. This
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276 | can be checked by running <command>echo $PATH</command> and verifying that
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277 | <filename class="directory">/tools/bin</filename> is at the head of the
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278 | list. If the <envar>PATH</envar> is wrong it could mean that you are not
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279 | logged in as user <systemitem class="username">lfs</systemitem> or that
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280 | something went wrong back in <xref linkend="ch-tools-settingenviron"
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281 | role="."/></para>
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282 |
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283 | <para>Once all is well, clean up the test files:</para>
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284 |
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285 | <screen><userinput>rm -v dummy.c a.out</userinput></screen>
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286 |
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287 | </caution>
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288 |
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289 | </sect2>
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290 |
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291 | <sect2 role="content">
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292 | <title/>
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293 |
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294 | <para>Details on this package are located in
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295 | <xref linkend="contents-gcc" role="."/></para>
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296 |
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297 | </sect2>
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298 |
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299 | </sect1>
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