#### Linux From Scratch - Version 7.10

### Chapter 6. Installing Basic System Software

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# 6.17. GCC-6.2.0

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

Approximate build time: 79 SBU (with tests)
Required disk space: 3.3 GB

## 6.17.1. Installation of 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.

The meaning of the new configure option:

`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, 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/7.10/ 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, two 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.

### Note

On some systems, numerous test failures (over 1100 unexpected failures out of over 200,000 tests) have been reported. These failures in `gcc.target/i386/mpx/` are related to the Intel MPX (Memory Protection Extensions) tests and failures are due to the kernel configuration or the specific CPU architecture. These test failures are harmless and can be ignored.

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)/6.2.0/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: /lib/ld-linux.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/i686-pc-linux-gnu/6.2.0/../../../crt1.o succeeded
    /usr/lib/gcc/i686-pc-linux-gnu/6.2.0/../../../crti.o succeeded
    /usr/lib/gcc/i686-pc-linux-gnu/6.2.0/../../../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`. If your machine is a 64-bit system, you may also see a directory named `lib64` towards the end of the string. 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/i686-pc-linux-gnu/6.2.0/include
     /usr/local/include
     /usr/lib/gcc/i686-pc-linux-gnu/6.2.0/include-fixed
     /usr/include

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

### Note

As of version 4.3.0, GCC now unconditionally installs the `limits.h` file into the private `include-fixed` directory, and that directory is required to be in place.

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/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");

A 64-bit system may see a few different directories. For example, here is the output from an x86_64 machine:

    SEARCH_DIR("/usr/x86_64-unknown-linux-gnu/lib64")
    SEARCH_DIR("/usr/local/lib64")
    SEARCH_DIR("/lib64")
    SEARCH_DIR("/usr/lib64")
    SEARCH_DIR("/usr/x86_64-unknown-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 (allowing for a lib64 directory on 64-bit hosts) 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 and a lib64 directory on 64-bit hosts):

    found ld-linux.so.2 at /lib/ld-linux.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 on 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

## 6.17.2. Contents of GCC

Installed programs: c++, cc (link to gcc), cpp, g++, gcc, gcc-ar, gcc-nm, gcc-ranlib, and gcov
Installed libraries: libasan.{a,so}, libatomic.{a,so}, libgcc.a, libgcc_eh.a, libgcc_s.so, libgcov.a, libgomp.{a,so}, libiberty.a, libitm.{a,so}, liblto_plugin.so, libquadmath.{a,so}, libssp.{a,so}, libssp_nonshared.a, libstdc++.{a,so}, libsupc++.a, and libtsan.{a,so}
Installed directories: /usr/include/c++, /usr/lib/gcc, /usr/libexec/gcc, and /usr/share/gcc-6.2.0

### 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
libasan | The Address Sanitizer runtime 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
`libiberty` | Contains routines used by various GNU programs, including getopt, obstack, strerror, strtol, and strtoul
`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
`libsupc++` | Provides supporting routines for the C++ programming language
`libtsan` | The Thread Sanitizer runtime library

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