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Linux From Scratch - Version 7.0

6.10. Re-adjusting the Toolchain

Now that the final C libraries have been installed, it is time to adjust the toolchain again. The toolchain will be

adjusted so that it will link any newly compiled program against these new libraries. This is a similar process used

in the “Adjusting” phase in the beginning of Chapter 5, but with the adjustments reversed. In Chapter 5, the chain

was guided from the host's /{,usr/}lib directories to the new /tools/lib directory. Now, the chain will be

guided from that same /tools/lib directory to the LFS /{,usr/}lib directories.

First, backup the /tools linker, and replace it with the adjusted linker we made in chapter 5. We'll also create a

link to its counterpart in /tools/$(gcc -dumpmachine)/bin:

mv -v /tools/bin/{ld,ld-old}

mv -v /tools/$(gcc -dumpmachine)/bin/{ld,ld-old}

mv -v /tools/bin/{ld-new,ld}

ln -sv /tools/bin/ld /tools/$(gcc -dumpmachine)/bin/ld

Next, amend the GCC specs file so that it points to the new dynamic linker. Simply deleting all instances of “/tools”

should leave us with the correct path to the dynamic linker. Also adjust the specs file so that GCC knows where to

find the correct headers and Glibc start files. A sed command accomplishes this:

gcc -dumpspecs | sed -e 's@/tools@@g' \

-e '/\*startfile_prefix_spec:/{n;s@.*@/usr/lib/ @}' \

-e '/\*cpp:/{n;s@$@ -isystem /usr/include@}' > \

`dirname $(gcc --print-li/jointfilesconvert/297116/bgcc-file-name)`/specs

It is a good idea to visually inspect the specs file to verify the intended change was actually made.

It is imperative at this point to ensure that the basic functions (compiling and linking) of the adjusted toolchain are

working as expected. To do this, perform the following sanity checks:

echo 'main(){}' > dummy.c

cc dummy.c -v -Wl,--verbose &> dummy.log

readelf -l a.out | grep ': /lib'

If everything is working correctly, there should be no errors, and the output of the last command will be (allowing

for platform-specific differences in dynamic linker name):

[Requesting program interpreter: /lib/ld-linux.so.2]

Note that /lib is now the prefix of our dynamic linker.

Now make sure that we're setup to use the correct startfiles:

grep -o '/usr/lib.*/crt[1in].*succeeded' dummy.log

If everything is working correctly, there should be no errors, and the output of the last command will be:

/usr/lib/crt1.o succeeded

/usr/lib/crti.o succeeded

/usr/lib/crtn.o succeeded

Verify that the compiler is searching for the correct header files:

grep -B1 '^ /usr/include' dummy.log

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MTD 248-645A Manual de usuario Pagina 114