6.20. GCC-7.3.0

6.20.1. Installation of GCC

If building on x86_64, change the default directory name for 64-bit libraries to “lib”:

case $(uname -m) in
  x86_64)
    sed -e '/m64=/s/lib64/lib/' \
        -i.orig gcc/config/i386/t-linux64
  ;;
esac

Remove the symlink created earlier as the final gcc includes will be installed here:

rm -f /usr/lib/gcc

The GCC documentation recommends building GCC in a dedicated build directory:

mkdir -v build
cd       build

Prepare GCC for compilation:

SED=sed                               \
../configure --prefix=/usr            \
             --enable-languages=c,c++ \
             --disable-multilib       \
             --disable-bootstrap      \
             --with-system-zlib

Note that for other languages, there are some prerequisites that are not yet available. See the BLFS Book for instructions on how to build all of GCC's supported languages.

Compile the package:

make

One set of tests in the GCC test suite is known to exhaust the stack, so increase the stack size prior to running the tests:

ulimit -s 32768

Test the results, but do not stop at errors:

make -k check

To receive a summary of the test suite results, run:

../contrib/test_summary

For only the summaries, pipe the output through grep -A7 Summ.

Results can be compared with those located at http://www.linuxfromscratch.org/lfs/build-logs/8.2/ and http://gcc.gnu.org/ml/gcc-testresults/.

A few unexpected failures cannot always be avoided. The GCC developers are usually aware of these issues, but have not resolved them yet. In particular, six tests in the libstdc++ test suite are known to fail when running as the root user as we do here. Unless the test results are vastly different from those at the above URL, it is safe to continue.

Install the package:

make install

Create a symlink required by the FHS for "historical" reasons.

ln -sv ../usr/bin/cpp /lib

Many packages use the name cc to call the C compiler. To satisfy those packages, create a symlink:

ln -sv gcc /usr/bin/cc

Add a compatibility symlink to enable building programs with Link Time Optimization (LTO):

install -v -dm755 /usr/lib/bfd-plugins
ln -sfv ../../libexec/gcc/$(gcc -dumpmachine)/7.3.0/liblto_plugin.so \
        /usr/lib/bfd-plugins/

Now that our final toolchain is in place, it is important to again ensure that compiling and linking will work as expected. We do this by performing the same sanity checks as we did earlier in the chapter:

echo 'int main(){}' > dummy.c
cc dummy.c -v -Wl,--verbose &> dummy.log
readelf -l a.out | grep ': /lib'

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: /lib64/ld-linux-x86-64.so.2]

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

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

The output of the last command should be:

/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib/crt1.o succeeded
/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib/crti.o succeeded
/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../lib/crtn.o succeeded

Depending on your machine architecture, the above may differ slightly, the difference usually being the name of the directory after /usr/lib/gcc. The important thing to look for here is that gcc has found all three crt*.o files under the /usr/lib directory.

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

grep -B4 '^ /usr/include' dummy.log

This command should return the following output:

#include <...> search starts here:
 /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include
 /usr/local/include
 /usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include-fixed
 /usr/include

Again, note that the directory named after your target triplet may be different than the above, depending on your architecture.

Next, verify that the new linker is being used with the correct search paths:

grep 'SEARCH.*/usr/lib' dummy.log |sed 's|; |\n|g'

References to paths that have components with '-linux-gnu' should be ignored, but otherwise the output of the last command should be:

SEARCH_DIR("/usr/x86_64-pc-linux-gnu/lib64")
SEARCH_DIR("/usr/local/lib64")
SEARCH_DIR("/lib64")
SEARCH_DIR("/usr/lib64")
SEARCH_DIR("/usr/x86_64-pc-linux-gnu/lib")
SEARCH_DIR("/usr/local/lib")
SEARCH_DIR("/lib")
SEARCH_DIR("/usr/lib");

A 32-bit system may see a few different directories. For example, here is the output from an i686 machine:

SEARCH_DIR("/usr/i686-pc-linux-gnu/lib32")
SEARCH_DIR("/usr/local/lib32")
SEARCH_DIR("/lib32")
SEARCH_DIR("/usr/lib32")
SEARCH_DIR("/usr/i686-pc-linux-gnu/lib")
SEARCH_DIR("/usr/local/lib")
SEARCH_DIR("/lib")
SEARCH_DIR("/usr/lib");

Next make sure that we're using the correct libc:

grep "/lib.*/libc.so.6 " dummy.log

The output of the last command should be:

attempt to open /lib/libc.so.6 succeeded

Lastly, make sure GCC is using the correct dynamic linker:

grep found dummy.log

The output of the last command should be (allowing for platform-specific differences in dynamic linker name):

found ld-linux-x86-64.so.2 at /lib/ld-linux-x86-64.so.2

If the output does not appear as shown above or is not received at all, then something is seriously wrong. Investigate and retrace the steps to find out where the problem is and correct it. The most likely reason is that something went wrong with the specs file adjustment. Any issues will need to be resolved before continuing with the process.

Once everything is working correctly, clean up the test files:

rm -v dummy.c a.out dummy.log

Finally, move a misplaced file:

mkdir -pv /usr/share/gdb/auto-load/usr/lib
mv -v /usr/lib/*gdb.py /usr/share/gdb/auto-load/usr/lib