Multilib Linux From Scratch - Version #605e

Chapter 5. Compiling a Cross-Toolchain

5.3. GCC-15.2.0 - Pass 1

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

Approximate build time: 3.8 SBU
Required disk space: 5.4 GB

5.3.1. Installation of Cross GCC

GCC 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-15.2.0 tarball from the sources directory, and then change to the directory created. Only then should you proceed with the instructions below. 

tar -xf ../mpfr-4.2.2.tar.xz
mv -v mpfr-4.2.2 mpfr
tar -xf ../gmp-6.3.0.tar.xz
mv -v gmp-6.3.0 gmp
tar -xf ../mpc-1.3.1.tar.gz
mv -v mpc-1.3.1 mpc

Change the default directory name for libraries: 

sed -e '/m64=/s/lib64/lib/' \
    -e '/m32=/s/m32=.*/m32=..\/lib32$(call if_multiarch,:i386-linux-gnu)/' \
    -i.orig gcc/config/i386/t-linux64
[Note]

Note

This example demonstrates the use of the -i.orig switch. It makes the sed copy the t-linux64 file to t-linux64.orig, and then edit the original t-linux64 file inplace. So you may run diff -u gcc/config/i386/t-linux64{.orig,} to visualize the change done by the sed command afterwards. We'll simply use -i (which just edits the original file inplace without copying it) for all other packages in the book, but you can change it to -i.orig in any case you want to keep a copy of the original file.

Make -mstackrealign a default for 32-bit objects: 

sed '/STACK_REALIGN_DEFAULT/s/0/(!TARGET_64BIT \&\& TARGET_SSE)/' \
      -i gcc/config/i386/i386.h
[Note]

Note

The -mstackrealign has a special purpose for 32-bit. All applications have a stack frame alignment. Typically in old applications (and also some applications in today's age) that are built for 32-bit, typically for Windows, have a stack frame alignment of 4 bytes. The x86 System V ABI Processor Supplement demands that both 32-bit and 64-bit applications have a stack frame alignment of 16 bytes.

The stack frame alignment is necessary for the x86 assembly movaps and movdqa instructions to work, which are used as faster alternatives to movups. When the stack frame alignment is not correct, those assembly instructions will trigger a General Protection Error, leading to a SIGSEGV kill signal.

In order to prevent this, -mstackrealign offers different potential stack frame alignments if necessary. In order to ensure that every piece of software has a good stack frame alignment, every package is compiled with -mstackrealign, which the above makes it the default for targeting 32-bit. Glibc is the main one that needs it.

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

mkdir -v build
cd       build

Prepare GCC for compilation: 

../configure                     \
    --target=$LFS_TGT            \
    --prefix=$LFS/tools          \
    --with-glibc-version=2.43    \
    --with-sysroot=$LFS          \
    --with-newlib                \
    --without-headers            \
    --enable-default-pie         \
    --enable-default-ssp         \
    --enable-initfini-array      \
    --disable-nls                \
    --disable-shared             \
    --enable-multilib            \
    --with-multilib-list=m64,m32 \
    --disable-decimal-float      \
    --disable-threads            \
    --disable-libatomic          \
    --disable-libgomp            \
    --disable-libquadmath        \
    --disable-libssp             \
    --disable-libvtv             \
    --disable-libstdcxx          \
    --enable-languages=c,c++

The meaning of the configure options:

--with-glibc-version=2.43

This option specifies the version of Glibc which will be used on the target. It is not relevant to the libc of the host distro because everything compiled by pass1 GCC will run in the chroot environment, which is isolated from libc of the host distro.

--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.

--enable-default-pie and --enable-default-ssp

Those switches allow GCC to compile programs with some hardening security features (more information on those in the note on PIE and SSP in chapter 8) by default. They are not strictly needed at this stage, since the compiler will only produce temporary executables. But it is cleaner to have the temporary packages be as close as possible to the final ones.

--disable-shared

This switch forces GCC to link its internal libraries statically. We need this because the shared libraries require Glibc, which is not yet installed on the target system.

--enable-multilib --with-multilib-list=...

These parameters both enable multilib and which architectures to support.

--disable-threads, --disable-libatomic, --disable-libgomp, --disable-libquadmath, --disable-libssp, --disable-libvtv, --disable-libstdcxx

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

--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

Install the package: 

make install

This build of GCC has installed a couple of internal system headers. Normally one of them, limits.h, would in turn include the corresponding system limits.h header, in this case, $LFS/usr/include/limits.h. However, at the time of this build of GCC $LFS/usr/include/limits.h does not exist, so the internal header that has just been installed is a partial, self-contained file and does not include the extended features of the system header. This is adequate for building Glibc, but the full internal header will be needed later. Create a full version of the internal header using a command that is identical to what the GCC build system does in normal circumstances:

[Note]

Note

The command below shows an example of nested command substitution using two methods: backquotes and a $() construct. It could be rewritten using the same method for both substitutions, but is shown this way to demonstrate how they can be mixed. Generally the $() method is preferred. 

cd ..
cat gcc/limitx.h gcc/glimits.h gcc/limity.h > \
  `dirname $($LFS_TGT-gcc -print-libgcc-file-name)`/include/limits.h

Details on this package are located in Section 8.31.2, “Contents of GCC.”