source: chapter08/adjusting.xml@ bf0d4ff

xry111/usr-move
Last change on this file since bf0d4ff was bf0d4ff, checked in by Xi Ruoyao <xry111@…>, 21 months ago

usr-move: update gcc sanity check output

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1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
6]>
7
8<sect1 id="ch-system-adjusting">
9 <?dbhtml filename="adjusting.html"?>
10
11 <title>Adjusting the Toolchain</title>
12
13 <para>Now that the final C libraries have been installed, it is time to adjust
14 the toolchain so that it will link any
15 newly compiled program against these new libraries.</para>
16
17 <para>First, backup the <filename class="directory">/tools</filename> linker,
18 and replace it with the adjusted linker we made in chapter 5. We'll also create
19 a link to its counterpart in
20 <filename class="directory">/tools/$(uname -m)-pc-linux-gnu/bin</filename>:</para>
21
22<screen><userinput>mv -v /tools/bin/{ld,ld-old}
23mv -v /tools/$(uname -m)-pc-linux-gnu/bin/{ld,ld-old}
24mv -v /tools/bin/{ld-new,ld}
25ln -sv /tools/bin/ld /tools/$(uname -m)-pc-linux-gnu/bin/ld</userinput></screen>
26
27 <para>the next command amends the GCC specs file to achieve three goals:
28 first point GCC to the new dynamic linker. Simply deleting all instances of
29 <quote>/tools</quote> should leave us with the correct path to the dynamic
30 linker. Second, let GCC know where to find the Glibc start files. Third,
31 add the /usr/include directory at the end of the default search path, so
32 that header files added in chapter 6 are found.
33 A <command>sed</command> command accomplishes this:</para>
34
35<screen><userinput>gcc -dumpspecs | sed -e 's@/tools@@g' \
36 -e '/\*startfile_prefix_spec:/{n;s@.*@/usr/lib/ @}' \
37 -e '/\*cpp:/{n;s@$@ -idirafter /usr/include@}' &gt; \
38 `dirname $(gcc --print-libgcc-file-name)`/specs</userinput></screen>
39
40 <para>It is a good idea to visually inspect the specs file to verify the
41 intended change was actually made.</para>
42
43 <para>It is imperative at this point to ensure that the basic
44 functions (compiling and linking) of the adjusted toolchain are working
45 as expected. To do this, perform the following sanity checks:</para>
46
47<screen os="a"><userinput>echo 'int main(){}' &gt; dummy.c
48cc dummy.c -v -Wl,--verbose &amp;&gt; dummy.log
49readelf -l a.out | grep ': /lib'</userinput></screen>
50
51 <para os="b">There should be no errors,
52 and the output of the last command will be (allowing for
53 platform-specific differences in the dynamic linker name):</para>
54
55<screen os="c"><computeroutput>[Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]</computeroutput></screen>
56
57 <para>Note that on 64-bit systems <filename class="directory">/lib</filename> is
58 the location of our dynamic linker, but is accessed via a symbolic link
59 in /lib64.</para>
60
61 <note><para>On 32-bit systems the interpreter should be
62 /lib/ld-linux.so.2.</para></note>
63
64 <para os="d">Now make sure that we're setup to use the correct start files:</para>
65
66<screen os="e"><userinput>grep -o '/usr/lib.*/crt[1in].*succeeded' dummy.log</userinput></screen>
67
68 <para os="f">The output of the last command should be:</para>
69
70<screen><computeroutput>/usr/lib/../lib/crt1.o succeeded
71/usr/lib/../lib/crti.o succeeded
72/usr/lib/../lib/crtn.o succeeded</computeroutput></screen>
73
74 <para os="g">Verify that the compiler is searching for the correct header
75 files:</para>
76
77<screen><userinput>grep -B4 '^ /usr/include' dummy.log</userinput></screen>
78
79 <para os="h">This command should return the following output:</para>
80
81<screen><computeroutput>#include &lt;...&gt; search starts here:
82 /tools/lib/gcc/x86_64-pc-linux-gnu/&gcc-version;/include
83 /tools/include
84 /tools/lib/gcc/x86_64-pc-linux-gnu/&gcc-version;/include-fixed
85 /usr/include</computeroutput></screen>
86
87 <note><para>On a 32 bit system, x86_64 is replaced with i686.</para></note>
88
89 <para os="i">Next, verify that the new linker is being used with the correct search paths:</para>
90
91<screen os="j"><userinput>grep 'SEARCH.*/usr/lib' dummy.log |sed 's|; |\n|g'</userinput></screen>
92
93 <para os="k">References to paths that have components with '-linux-gnu' should
94 be ignored, but otherwise the output of the last command should be:</para>
95
96<screen><computeroutput>SEARCH_DIR("/usr/lib")
97SEARCH_DIR("/lib")</computeroutput></screen>
98
99 <para os="l">Next make sure that we're using the correct libc:</para>
100
101<screen os="m"><userinput>grep "/lib.*/libc.so.6 " dummy.log</userinput></screen>
102
103 <para os="n">The output of the last command should be:</para>
104
105<screen os="o"><computeroutput>attempt to open /usr/lib/libc.so.6 succeeded</computeroutput></screen>
106
107 <para os="p">Make sure GCC is using the correct dynamic linker:</para>
108
109<screen os="q"><userinput>grep found dummy.log</userinput></screen>
110
111 <para os="r">The output of the last command should be (allowing for
112 platform-specific differences in dynamic linker name):</para>
113
114<screen os="s"><computeroutput>found ld-linux-x86-64.so.2 at /usr/lib/ld-linux-x86-64.so.2</computeroutput></screen>
115
116 <para os="t">If the output does not appear as shown above or is not received
117 at all, then something is seriously wrong. Investigate and retrace the
118 steps to find out where the problem is and correct it. <!--The most likely
119 reason is that something went wrong with the specs file adjustment.--> Any
120 issues will need to be resolved before continuing with the process.</para>
121
122 <para os="u">Once everything is working correctly, clean up the test files:</para>
123
124<screen os="v"><userinput>rm -v dummy.c a.out dummy.log</userinput></screen>
125
126</sect1>
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