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-system-adjusting">
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9 | <?dbhtml filename="adjusting.html"?>
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10 |
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11 | <title>Adjusting the Toolchain</title>
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12 |
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13 | <para>Now that the final C libraries have been installed, it is time to adjust
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14 | the toolchain so that it will link any
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15 | newly compiled program against these new libraries.</para>
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16 |
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17 | <para>First, backup the <filename class="directory">/tools</filename> linker,
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18 | and replace it with the adjusted linker we made in chapter 5. We'll also create
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19 | a link to its counterpart in
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20 | <filename class="directory">/tools/$(uname -m)-pc-linux-gnu/bin</filename>:</para>
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21 |
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22 | <screen><userinput>mv -v /tools/bin/{ld,ld-old}
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23 | mv -v /tools/$(uname -m)-pc-linux-gnu/bin/{ld,ld-old}
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24 | mv -v /tools/bin/{ld-new,ld}
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25 | ln -sv /tools/bin/ld /tools/$(uname -m)-pc-linux-gnu/bin/ld</userinput></screen>
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26 |
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27 | <para>Next, amend the GCC specs file so that it points to the new
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28 | dynamic linker. Simply deleting all instances of <quote>/tools</quote> should
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29 | leave us with the correct path to the dynamic linker. Also adjust the specs file
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30 | so that GCC knows where to find the correct headers and Glibc start files.
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31 | A <command>sed</command> command accomplishes this:</para>
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32 |
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33 | <screen><userinput>gcc -dumpspecs | sed -e 's@/tools@@g' \
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34 | -e '/\*startfile_prefix_spec:/{n;s@.*@/usr/lib/ @}' \
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35 | -e '/\*cpp:/{n;s@$@ -isystem /usr/include@}' > \
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36 | `dirname $(gcc --print-libgcc-file-name)`/specs</userinput></screen>
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37 |
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38 | <para>It is a good idea to visually inspect the specs file to verify the
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39 | intended change was actually made.</para>
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40 |
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41 | <para>It is imperative at this point to ensure that the basic
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42 | functions (compiling and linking) of the adjusted toolchain are working
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43 | as expected. To do this, perform the following sanity checks:</para>
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44 |
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45 | <screen os="a"><userinput>echo 'int main(){}' > dummy.c
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46 | cc dummy.c -v -Wl,--verbose &> dummy.log
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47 | readelf -l a.out | grep ': /lib'</userinput></screen>
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48 |
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49 | <para os="b">There should be no errors,
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50 | and the output of the last command will be (allowing for
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51 | platform-specific differences in dynamic linker name):</para>
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52 |
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53 | <screen os="c"><computeroutput>[Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]</computeroutput></screen>
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54 |
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55 | <para>Note that on 64-bit systems <filename class="directory">/lib</filename> is
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56 | the location of our dynamic linker, but is accessed via a symbolic link
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57 | in /lib64.</para>
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58 |
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59 | <note><para>On 32-bit systems the interpreter should be
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60 | /lib/ld-linux.so.2.</para></note>
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61 |
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62 | <para os="d">Now make sure that we're setup to use the correct start files:</para>
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63 |
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64 | <screen os="e"><userinput>grep -o '/usr/lib.*/crt[1in].*succeeded' dummy.log</userinput></screen>
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65 |
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66 | <para os="f">The output of the last command should be:</para>
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67 |
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68 | <screen><computeroutput>/usr/lib/../lib/crt1.o succeeded
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69 | /usr/lib/../lib/crti.o succeeded
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70 | /usr/lib/../lib/crtn.o succeeded</computeroutput></screen>
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71 |
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72 | <para os="g">Verify that the compiler is searching for the correct header
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73 | files:</para>
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74 |
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75 | <screen><userinput>grep -B1 '^ /usr/include' dummy.log</userinput></screen>
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76 |
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77 | <para os="h">This command should return the following output:</para>
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78 |
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79 | <screen><computeroutput>#include <...> search starts here:
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80 | /usr/include</computeroutput></screen>
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81 |
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82 | <para os="i">Next, verify that the new linker is being used with the correct search paths:</para>
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83 |
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84 | <screen os="j"><userinput>grep 'SEARCH.*/usr/lib' dummy.log |sed 's|; |\n|g'</userinput></screen>
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85 |
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86 | <para os="k">References to paths that have components with '-linux-gnu' should
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87 | be ignored, but otherwise the output of the last command should be:</para>
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88 |
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89 | <screen><computeroutput>SEARCH_DIR("/usr/lib")
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90 | SEARCH_DIR("/lib")</computeroutput></screen>
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91 |
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92 | <para os="l">Next make sure that we're using the correct libc:</para>
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93 |
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94 | <screen os="m"><userinput>grep "/lib.*/libc.so.6 " dummy.log</userinput></screen>
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95 |
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96 | <para os="n">The output of the last command should be:</para>
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97 |
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98 | <screen os="o"><computeroutput>attempt to open /lib/libc.so.6 succeeded</computeroutput></screen>
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99 |
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100 | <para os="p">Lastly, make sure GCC is using the correct dynamic linker:</para>
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101 |
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102 | <screen os="q"><userinput>grep found dummy.log</userinput></screen>
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103 |
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104 | <para os="r">The output of the last command should be (allowing for
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105 | platform-specific differences in dynamic linker name):</para>
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106 |
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107 | <screen os="s"><computeroutput>found ld-linux-x86-64.so.2 at /lib/ld-linux-x86-64.so.2</computeroutput></screen>
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108 |
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109 | <para os="t">If the output does not appear as shown above or is not received
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110 | at all, then something is seriously wrong. Investigate and retrace the
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111 | steps to find out where the problem is and correct it. The most likely
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112 | reason is that something went wrong with the specs file adjustment. Any
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113 | issues will need to be resolved before continuing with the process.</para>
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114 |
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115 | <para os="u">Once everything is working correctly, clean up the test files:</para>
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116 |
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117 | <screen os="v"><userinput>rm -v dummy.c a.out dummy.log</userinput></screen>
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118 |
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119 | </sect1>
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