Linux From Scratch - Version 12.3-systemd-rc2

Chapter 8. Installing Basic System Software

8.29. GCC-14.2.0

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

Approximate build time: 46 SBU (with tests)
Required disk space: 6.3 GB

8.29.1. 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: 

../configure --prefix=/usr            \
             LD=ld                    \
             --enable-languages=c,c++ \
             --enable-default-pie     \
             --enable-default-ssp     \
             --enable-host-pie        \
             --disable-multilib       \
             --disable-bootstrap      \
             --disable-fixincludes    \
             --with-system-zlib

GCC supports seven different computer languages, but the prerequisites for most of them have not yet been installed. See the BLFS Book GCC page for instructions on how to build all of GCC's supported languages.

The meaning of the new configure parameters:

LD=ld

This parameter makes the configure script use the ld program installed by the Binutils package built earlier in this chapter, rather than the cross-built version which would otherwise be used.

--disable-fixincludes

By default, during the installation of GCC some system headers would be “fixed” to be used with GCC. This is not necessary for a modern Linux system, and potentially harmful if a package is reinstalled after installing GCC. This switch prevents GCC from “fixing” the headers.

--with-system-zlib

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

[Note]

Note

PIE (position-independent executables) are binary programs that can be loaded anywhere in memory. Without PIE, the security feature named ASLR (Address Space Layout Randomization) can be applied for the shared libraries, but not for the executables themselves. Enabling PIE allows ASLR for the executables in addition to the shared libraries, and mitigates some attacks based on fixed addresses of sensitive code or data in the executables.

SSP (Stack Smashing Protection) is a technique to ensure that the parameter stack is not corrupted. Stack corruption can, for example, alter the return address of a subroutine, thus transferring control to some dangerous code (existing in the program or shared libraries, or injected by the attacker somehow).

Compile the package: 

make
[Important]

Important

In this section, the test suite for GCC is considered important, but it takes a long time. First-time builders are encouraged to run the test suite. The time to run the tests can be reduced significantly by adding -jx to the make -k check command below, where x is the number of CPU cores on your system.

GCC may need more stack space compiling some extremely complex code patterns. As a precaution for the host distros with a tight stack limit, explicitly set the stack size hard limit to infinite. On most host distros (and the final LFS system) the hard limit is infinite by default, but there is no harm done by setting it explicitly. It's not necessary to change the stack size soft limit because GCC will automatically set it to an appropriate value, as long as the value does not exceed the hard limit: 

ulimit -s -H unlimited

Now remove/fix several known test failures: 

sed -e '/cpython/d'               -i ../gcc/testsuite/gcc.dg/plugin/plugin.exp
sed -e 's/no-pic /&-no-pie /'     -i ../gcc/testsuite/gcc.target/i386/pr113689-1.c
sed -e 's/300000/(1|300000)/'     -i ../libgomp/testsuite/libgomp.c-c++-common/pr109062.c
sed -e 's/{ target nonpic } //' \
    -e '/GOTPCREL/d'              -i ../gcc/testsuite/gcc.target/i386/fentryname3.c

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

chown -R tester .
su tester -c "PATH=$PATH make -k check"

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

../contrib/test_summary

To filter out only the summaries, pipe the output through grep -A7 Summ.

Results can be compared with those located at https://www.linuxfromscratch.org/lfs/build-logs/12.3-rc2/ and https://gcc.gnu.org/ml/gcc-testresults/.

The tsan tests are known to fail on some host distros.

A few unexpected failures cannot always be avoided. In some cases test failures depend on the specific hardware of the system. Unless the test results are vastly different from those at the above URL, it is safe to continue.

Install the package: 

make install

The GCC build directory is owned by tester now, and the ownership of the installed header directory (and its content) is incorrect. Change the ownership to the root user and group: 

chown -v -R root:root \
    /usr/lib/gcc/$(gcc -dumpmachine)/14.2.0/include{,-fixed}

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

ln -svr /usr/bin/cpp /usr/lib

Many packages use the name cc to call the C compiler. We've already created cc as a symlink in gcc-pass2, create its man page as a symlink as well: 

ln -sv gcc.1 /usr/share/man/man1/cc.1

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

ln -sfv ../../libexec/gcc/$(gcc -dumpmachine)/14.2.0/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 some sanity checks: 

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 the dynamic linker name): 

[Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]

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

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

The output of the last command should be: 

/usr/lib/gcc/x86_64-pc-linux-gnu/14.2.0/../../../../lib/Scrt1.o succeeded
/usr/lib/gcc/x86_64-pc-linux-gnu/14.2.0/../../../../lib/crti.o succeeded
/usr/lib/gcc/x86_64-pc-linux-gnu/14.2.0/../../../../lib/crtn.o succeeded

Depending on your machine architecture, the above may differ slightly. The difference will be 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/14.2.0/include
 /usr/local/include
 /usr/lib/gcc/x86_64-pc-linux-gnu/14.2.0/include-fixed
 /usr/include

Again, the directory named after your target triplet may be different than the above, depending on your system 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 use a few other 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 /usr/lib/libc.so.6 succeeded

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 /usr/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. Any issues should 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

8.29.2. Contents of GCC

Installed programs: c++, cc (link to gcc), cpp, g++, gcc, gcc-ar, gcc-nm, gcc-ranlib, gcov, gcov-dump, gcov-tool, and lto-dump
Installed libraries: libasan.{a,so}, libatomic.{a,so}, libcc1.so, libgcc.a, libgcc_eh.a, libgcc_s.so, libgcov.a, libgomp.{a,so}, libhwasan.{a,so}, libitm.{a,so}, liblsan.{a,so}, liblto_plugin.so, libquadmath.{a,so}, libssp.{a,so}, libssp_nonshared.a, libstdc++.{a,so}, libstdc++exp.a, 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-14.2.0

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 directives 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 greatest effect

gcov-dump

Offline gcda and gcno profile dump tool

gcov-tool

Offline gcda profile processing tool

lto-dump

Tool for dumping object files produced by GCC with LTO enabled

libasan

The Address Sanitizer runtime library

libatomic

GCC atomic built-in runtime library

libcc1

A library that allows GDB to make use of GCC

libgcc

Contains run-time support for gcc

libgcov

This library is linked into 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

libhwasan

The Hardware-assisted Address Sanitizer runtime library

libitm

The GNU transactional memory library

liblsan

The Leak Sanitizer runtime library

liblto_plugin

GCC's LTO plugin allows Binutils to process object files produced by GCC with LTO enabled

libquadmath

GCC Quad Precision Math Library API

libssp

Contains routines supporting GCC's stack-smashing protection functionality. Normally it is not used, because Glibc also provides those routines.

libstdc++

The standard C++ library

libstdc++exp

Experimental C++ Contracts 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