6.21. GCC-9.2.0

#### Linux From Scratch - Version 9.0-systemd

### Chapter 6. Installing Basic System Software

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# 6.21. GCC-9.2.0

The GCC package contains the GNU compiler collection, which includes the C and C++ compilers.

Approximate build time: 95 SBU (with tests)
Required disk space: 4.2 GB

## 6.21.1. 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

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.

The meaning of the new configure parameters:

`SED=sed`

  Setting this environment variable prevents a hard-coded path to /tools/bin/sed.

`--with-system-zlib`

  This switch tells GCC to link to the system installed copy of the Zlib library, rather than its own internal copy.

Compile the package:

    make

### Important

In this section, the test suite for GCC is considered critical. Do not skip it under any circumstance.

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 as a non-privileged user, but do not stop at errors:

    chown -Rv nobody .
    su nobody -s /bin/bash -c "PATH=$PATH 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/9.0/ and https://gcc.gnu.org/ml/gcc-testresults/.

Six tests related to get_time are known to fail. These are apparently related to the en_HK locale.

Two tests named lookup.cc and reverse.cc in experimental/net are known to fail in LFS chroot environment because they require /etc/hosts and iana-etc.

Two tests named pr57193.c and pr90178.c are known to fail.

A few unexpected failures cannot always be avoided. The GCC developers are usually aware of these issues, but have not resolved them yet. Unless the test results are vastly different from those at the above URL, it is safe to continue.

Install the package and remove an unneeded directory:

    make install
    rm -rf /usr/lib/gcc/$(gcc -dumpmachine)/9.2.0/include-fixed/bits/

The GCC build directory is owned by `nobody` now and the ownership of the installed header directory (and its content) will be incorrect. Change the ownership to `root` user and group:

    chown -v -R root:root \
        /usr/lib/gcc/*linux-gnu/9.2.0/include{,-fixed}

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)/9.2.0/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/9.2.0/../../../../lib/crt1.o succeeded
    /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/../../../../lib/crti.o succeeded
    /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/../../../../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/9.2.0/include
     /usr/local/include
     /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/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

## 6.21.2. Contents of GCC

Installed programs: c++, cc (link to gcc), cpp, g++, gcc, gcc-ar, gcc-nm, gcc-ranlib, gcov, gcov-dump, and gcov-tool
Installed libraries: libasan.{a,so}, libatomic.{a,so}, libcc1.so, libgcc.a, libgcc_eh.a, libgcc_s.so, libgcov.a, libgomp.{a,so}, libitm.{a,so}, liblsan.{a,so}, liblto_plugin.so, libquadmath.{a,so}, libssp.{a,so}, libssp_nonshared.a, libstdc++.{a,so}, libstdc++fs.a, libsupc++.a, libtsan.{a,so}, and libubsan.{a,so}
Installed directories: /usr/include/c++, /usr/lib/gcc, /usr/libexec/gcc, and /usr/share/gcc-9.2.0

### Short Descriptions

c++ | The C++ compiler
cc | The C compiler
cpp | The C preprocessor; it is used by the compiler to expand the #include, #define, and similar statements in the source files
g++ | The C++ compiler
gcc | The C compiler
gcc-ar | A wrapper around ar that adds a plugin to the command line. This program is only used to add "link time optimization" and is not useful with the default build options
gcc-nm | A wrapper around nm that adds a plugin to the command line. This program is only used to add "link time optimization" and is not useful with the default build options
gcc-ranlib | A wrapper around ranlib that adds a plugin to the command line. This program is only used to add "link time optimization" and is not useful with the default build options
gcov | A coverage testing tool; it is used to analyze programs to determine where optimizations will have the most effect
gcov-dump | Offline gcda and gcno profile dump tool
gcov-tool | Offline gcda profile processing tool
`libasan` | The Address Sanitizer runtime library
`libatomic` | GCC atomic built-in runtime library
`libcc1` | The C preprocessing library
`libgcc` | Contains run-time support for gcc
`libgcov` | This library is linked in to a program when GCC is instructed to enable profiling
`libgomp` | GNU implementation of the OpenMP API for multi-platform shared-memory parallel programming in C/C++ and Fortran
`liblsan` | The Leak Sanitizer runtime library
`liblto_plugin` | GCC's Link Time Optimization (LTO) plugin allows GCC to perform optimizations across compilation units
`libquadmath` | GCC Quad Precision Math Library API
`libssp` | Contains routines supporting GCC's stack-smashing protection functionality
`libstdc++` | The standard C++ library
`libstdc++fs` | ISO/IEC TS 18822:2015 Filesystem library
`libsupc++` | Provides supporting routines for the C++ programming language
`libtsan` | The Thread Sanitizer runtime library
`libubsan` | The Undefined Behavior Sanitizer runtime library

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