Linux From Scratch - Version 7.10-rc1

Chapter 5. Constructing a Temporary System

5.5. GCC-6.2.0 - Pass 1

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

Approximate build time: 7.0 SBU
Required disk space: 2.8 GB

5.5.1. Installation of Cross GCC

GCC now requires the GMP, MPFR and MPC packages. As these packages may not be included in your host distribution, they will be built with GCC. Unpack each package into the GCC source directory and rename the resulting directories so the GCC build procedures will automatically use them:

[Note]

Note

There are frequent misunderstandings about this chapter. The procedures are the same as every other chapter as explained earlier (Package build instructions). First extract the gcc tarball from the sources directory and then change to the directory created. Only then should you proceed with the instructions below. 

tar -xf ../mpfr-3.1.4.tar.xz
mv -v mpfr-3.1.4 mpfr
tar -xf ../gmp-6.1.1.tar.xz
mv -v gmp-6.1.1 gmp
tar -xf ../mpc-1.0.3.tar.gz
mv -v mpc-1.0.3 mpc

The following command will change the location of GCC's default dynamic linker to use the one installed in /tools. It also removes /usr/include from GCC's include search path. Issue: 

for file in \
 $(find gcc/config -name linux64.h -o -name linux.h -o -name sysv4.h)
do
  cp -uv $file{,.orig}
  sed -e 's@/lib\(64\)\?\(32\)\?/ld@/tools&@g' \
      -e 's@/usr@/tools@g' $file.orig > $file
  echo '
#undef STANDARD_STARTFILE_PREFIX_1
#undef STANDARD_STARTFILE_PREFIX_2
#define STANDARD_STARTFILE_PREFIX_1 "/tools/lib/"
#define STANDARD_STARTFILE_PREFIX_2 ""' >> $file
  touch $file.orig
done

In case the above seems hard to follow, let's break it down a bit. First we find all the files under the gcc/config directory that are named either linux.h, linux64.h or sysv4.h. For each file found, we copy it to a file of the same name but with an added suffix of “.orig”. Then the first sed expression prepends “/tools” to every instance of “/lib/ld”, “/lib64/ld” or “/lib32/ld”, while the second one replaces hard-coded instances of “/usr”. Next, we add our define statements which alter the default startfile prefix to the end of the file. Note that the trailing “/” in “/tools/lib/” is required. Finally, we use touch to update the timestamp on the copied files. When used in conjunction with cp -u, this prevents unexpected changes to the original files in case the commands are inadvertently run twice.

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

mkdir -v build
cd       build

Prepare GCC for compilation: 

../configure                                       \
    --target=$LFS_TGT                              \
    --prefix=/tools                                \
    --with-glibc-version=2.11                      \
    --with-sysroot=$LFS                            \
    --with-newlib                                  \
    --without-headers                              \
    --with-local-prefix=/tools                     \
    --with-native-system-header-dir=/tools/include \
    --disable-nls                                  \
    --disable-shared                               \
    --disable-multilib                             \
    --disable-decimal-float                        \
    --disable-threads                              \
    --disable-libatomic                            \
    --disable-libgomp                              \
    --disable-libmpx                               \
    --disable-libquadmath                          \
    --disable-libssp                               \
    --disable-libvtv                               \
    --disable-libstdcxx                            \
    --enable-languages=c,c++

The meaning of the configure options:

--with-newlib

Since a working C library is not yet available, this ensures that the inhibit_libc constant is defined when building libgcc. This prevents the compiling of any code that requires libc support.

--without-headers

When creating a complete cross-compiler, GCC requires standard headers compatible with the target system. For our purposes these headers will not be needed. This switch prevents GCC from looking for them.

--with-local-prefix=/tools

The local prefix is the location in the system that GCC will search for locally installed include files. The default is /usr/local. Setting this to /tools helps keep the host location of /usr/local out of this GCC's search path.

--with-native-system-header-dir=/tools/include

By default GCC searches /usr/include for system headers. In conjunction with the sysroot switch, this would translate normally to $LFS/usr/include. However the headers that will be installed in the next two sections will go to $LFS/tools/include. This switch ensures that gcc will find them correctly. In the second pass of GCC, this same switch will ensure that no headers from the host system are found.

--disable-shared

This switch forces GCC to link its internal libraries statically. We do this to avoid possible issues with the host system.

--disable-decimal-float, --disable-threads, --disable-libatomic, --disable-libgomp, --disable-libmpx, --disable-libquadmath, --disable-libssp, --disable-libvtv, --disable-libstdcxx

These switches disable support for the decimal floating point extension, threading, libatomic, libgomp, libmpx, libquadmath, libssp, libvtv, and the C++ standard library respectively. These features will fail to compile when building a cross-compiler and are not necessary for the task of cross-compiling the temporary libc.

--disable-multilib

On x86_64, LFS does not yet support a multilib configuration. This switch is harmless for x86.

--enable-languages=c,c++

This option ensures that only the C and C++ compilers are built. These are the only languages needed now.

Compile GCC by running: 

make

Compilation is now complete. At this point, the test suite would normally be run, but, as mentioned before, the test suite framework is not in place yet. The benefits of running the tests at this point are minimal since the programs from this first pass will soon be replaced.

Install the package: 

make install

Details on this package are located in Section 6.17.2, “Contents of GCC.”