1 | <sect1 id="ch05-locking-glibc">
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2 | <title>"Locking in" Glibc</title>
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3 | <?dbhtml filename="lockingglibc.html" dir="chapter05"?>
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4 |
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5 | <para>Now that the temporary C libraries have been installed, we want all
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6 | the tools compiled in the rest of this chapter to be linked against these
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7 | libraries. To accomplish this, we need to adjust the linker and the compiler's
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8 | specs file.</para>
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9 |
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10 | <para>First install the adjusted linker by running the following from within
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11 | the <filename class="directory">binutils-build</filename> directory:</para>
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12 |
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13 | <para><screen><userinput>make -C ld install</userinput></screen></para>
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14 |
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15 | <para>The linker was adjusted a little while back, at the end of the first
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16 | pass of Binutils. From this point onwards everything will link <emphasis>only
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17 | </emphasis> against the libraries in <filename>/tools/lib</filename>.</para>
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18 |
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19 | <para>Now that the adjusted linker is installed, you have to remove the
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20 | Binutils build and source directories.</para>
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21 |
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22 | <para>The next thing to do is to amend our GCC specs file so that it points
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23 | to the new dynamic linker. A simple sed will accomplish this:</para>
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24 |
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25 | <para><screen><userinput>SPECFILE=/tools/lib/gcc-lib/*/*/specs
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26 | sed -e 's@/lib/ld.so.1@/tools/lib/ld.so.1@g' \
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27 | -e 's@/lib/ld-linux.so.2@/tools/lib/ld-linux.so.2@g' \
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28 | $SPECFILE > tempspecfile
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29 | mv tempspecfile $SPECFILE
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30 | unset SPECFILE</userinput></screen></para>
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31 |
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32 | <para>We recommend that you cut-and-paste the above rather than try and type it
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33 | all in. Or you can edit the specs file by hand if you want to: just replace
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34 | "/lib/ld-linux.so.2" with "/tools/lib/ld-linux.so.2" and "/lib/ld.so.1" with
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35 | "/tools/lib/ld.so.1".</para>
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36 |
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37 | <para>Lastly, there is a possibility that some include files from the host
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38 | system have found their way into GCC's private include dir. This can happen
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39 | because of GCC's "fixincludes" process which runs as part of the GCC build.
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40 | We'll explain more about this further on in this chapter. For now, run the
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41 | following commands to eliminate this possibility:</para>
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42 |
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43 | <para><screen><userinput>rm -f /tools/lib/gcc-lib/*/*/include/{pthread.h,bits/sigthread.h}</userinput></screen></para>
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44 |
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45 | <caution><para>It is imperative at this point to stop and ensure that the basic
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46 | functions (compiling and linking) of the new toolchain are working as expected.
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47 | For this we are going to perform a simple sanity check:</para>
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48 |
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49 | <para><screen><userinput>echo 'main(){}' > dummy.c
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50 | gcc dummy.c
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51 | readelf -l a.out | grep ': /tools'</userinput></screen></para>
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52 |
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53 | <para>If everything is working correctly, there should be no errors, and the
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54 | output of the last command will be:</para>
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55 |
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56 | <blockquote><screen>[Requesting program interpreter: /tools/lib/ld-linux.so.2]</screen></blockquote>
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57 |
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58 | <para>If you did not receive the output as shown above, then something is
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59 | seriously wrong. You will need to investigate and retrace your steps to find
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60 | out where the problem is and correct it. There is no point in continuing
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61 | until this is done. Most likely something went wrong with the specs file
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62 | amendment above. Note especially that <filename>/tools/lib</filename> appears
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63 | as the prefix of our dynamic linker. Of course, if you are working on a
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64 | platform where the name of the dynamic linker is something other than
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65 | <filename>ld-linux.so.2</filename>, then the output will be slightly different.
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66 | </para>
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67 |
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68 | <para>Once you are satisfied that all is well, clean up the test files:</para>
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69 |
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70 | <para><screen><userinput>rm dummy.c a.out</userinput></screen></para>
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71 | </caution>
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72 |
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73 | <para>This completes the installation of the self-contained toolchain, and it
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74 | can now be used to build the rest of the temporary tools.</para>
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75 |
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76 | </sect1>
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77 |
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