UNDER CONSTRUCTION

glibc

glibc is an implementation of the user-space side of standard C/POSIX functions with Linux extensions.

Build system

Cross compilation

To cross compile for aarch64:

../../configure --prefix=/tmp/glibc/aarch64 --host=aarch64-linux-gnu

To cross compile for i686:

../../configure --prefix=/tmp/glibc/i686 --host=i686-linux-gnu CC='gcc -m32' CXX='g++ -m32' && make -j 50 && make -j 50 install && cp -f /usr/lib/i386-linux-gnu/{libgcc_s.so.1,libstdc++.so.6} /tmp/glibc/i686/

For cross compiling, run-built-tests is yes only if test-wrapper is set.

If you don't have a C++ compiler, specify CXX=false.

A very unfortunate fact: glibc can only be built with -O2, not -O0 or -O1. If you want to have an un-optimized debug build, deleting an object file and recompiling it with -g usually works. Another workaround is #pragma GCC optimize ("O0").

The -O2 issue is probably related to (1) expected inlining and (2) avoiding dynamic relocations.

To build a directory:

make -r -C ~/Dev/glibc/stdlib objdir=$PWD subdir=stdlib subdir_lib

The run a program with the built dynamic loader:

$build/testrun.sh $program

# Debug a test. --direct can avoid spawning a new process.
cgdb -ex 'set exec-wrapper env LD_LIBRARY_PATH=.:./math:./elf:./dlfcn:./nss:./nis:./rt:./resolv:./mathvec:./support:./crypt:./nptl' elf/tst-nodelete --direct

To test one directory (say, libio), delete libio/*.out files and run

make -r -C ~/Dev/glibc/libio objdir=$PWD check -j 20

../../configure --prefix=/tmp/glibc/lld && make -j 50 && make -j 50 install && 'cp' -f /usr/lib/x86_64-linux-gnu/libgcc_s.so.1 /tmp/glibc/lld/lib/

)

Delete failed tests so that the next make check invocation will re-run them:

rg -lg '*.test-result' '^FAIL' | while read i; do rm -f ${i/.test-result/.out} $i; done

In a llvm-project build directory, build clang, lld, and clang_rt.crtbegin*.o

ninja -C /tmp/out/custom1 clang crt lld

git checkout origin/google/grte/v5-2.27/master
mkdir -p out/grte && cd out/grte
../../configure --prefix=/tmp/grte/play --disable-werror --disable-float128 --with-clang --with-lld --enable-static-pie CC=/tmp/out/custom1/bin/clang CXX=/tmp/out/custom1/bin/clang++
make -j 30
make -j 30 install

build-many-glibcs.py

Run the following commands to populate /tmp/glibc-many with toolchains. Caution: please make sure the target file system has tens of gigabytes.

Preparation:

scripts/build-many-glibcs.py /tmp/glibc-many checkout --shallow
scripts/build-many-glibcs.py /tmp/glibc-many host-libraries

# Build a bootstrap GCC (static-only, C-only, --with-newlib).
# /tmp/glibc-many/src/gcc/gcc/configure --srcdir=/tmp/glibc-many/src/gcc/gcc --prefix=/tmp/glibc-many/install/compilers/aarch64-linux-gnu --with-sysroot=/tmp/glibc-many/install/compilers/aarch64-linux-gnu/sysroot --with-gmp=/tmp/glibc-many/install/host-libraries --with-mpfr=/tmp/glibc-many/install/host-libraries --with-mpc=/tmp/glibc-many/install/host-libraries --enable-shared --enable-threads --enable-languages=c,c++,lto ... --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu --target=aarch64-glibc-linux-gnu ...
scripts/build-many-glibcs.py /tmp/glibc-many compilers aarch64-linux-gnu
scripts/build-many-glibcs.py /tmp/glibc-many compilers powerpc64le-linux-gnu
scripts/build-many-glibcs.py /tmp/glibc-many compilers sparc64-linux-gnu

• --shallow passes --depth 1 to the git clone command.
• --keep all keeps intermediary build directories intact. You may want this option to investigate build issues.

The glibcs command will delete the glibc build directory, build glibc, and run make check.

# Build glibc using bootstrap GCC in <path>/install/compilers/aarch64-linux-gnu/bin/aarch64-linux-gcc
# Then build GCC using the built glibc.
# /tmp/glibc-many/src/glibc/configure --prefix=/usr --enable-profile --build=x86_64-pc-linux-gnu --host=aarch64-glibc-linux-gnu CC=aarch64-glibc-linux-gnu-gcc CXX=aarch64-glibc-linux-gnu-g++ AR=aarch64-glibc-linux-gnu-ar AS=aarch64-glibc-linux-gnu-as LD=aarch64-glibc-linux-gnu-ld NM=aarch64-glibc-linux-gnu-nm OBJCOPY=aarch64-glibc-linux-gnu-objcopy OBJDUMP=aarch64-glibc-linux-gnu-objdump RANLIB=aarch64-glibc-linux-gnu-ranlib READELF=aarch64-glibc-linux-gnu-readelf STRIP=aarch64-glibc-linux-gnu-strip
# Find built glibc in <path>/install/glibcs/aarch64-linux-gnu
scripts/build-many-glibcs.py /tmp/glibc-many glibcs aarch64-linux-gnu
# Find the logs and test results under /tmp/glibc-many/logs/glibcs/aarch64-linux-gnu/

scripts/build-many-glibcs.py /tmp/glibc-many glibcs powerpc64le-linux-gnu

scripts/build-many-glibcs.py /tmp/glibc-many glibcs sparc64-linux-gnu

For the glibcs command, add --full-gcc to build C++.

many=/tmp/glibc-many
$many/install/compilers/aarch64-linux-gnu/bin/aarch64-glibc-linux-gnu-g++ -Wl,--dynamic-linker=$many/install/glibcs/aarch64-linux-gnu/lib/ld-linux-aarch64.so.1 -Wl,-rpath=$many/install/compilers/aarch64-linux-gnu/sysroot/lib64:$many/install/compilers/aarch64-linux-gnu/aarch64-glibc-linux-gnu/lib64 a.cc
./a.out

$many/install/compilers/x86_64-linux-gnu/bin/x86_64-glibc-linux-gnu-gcc -Wl,--dynamic-linker=$many/install/glibcs/x86_64-linux-gnu/lib64/ld-linux-x86-64.so.2 -Wl,-rpath=$many/install/compilers/x86_64-linux-gnu/sysroot/lib64:$many/install/compilers/x86_64-linux-gnu/x86_64-glibc-linux-gnu/lib64 a.c
./a.out

"On build-many-glibcs.py and most stage1 compiler bootstrap, gcc is build statically against newlib. the static linked gcc (with a lot of disabled features) is then used to build glibc and then the stage2 gcc (which will then have all the features that rely on libc enabled) so the stage1 gcc might not have the require started files"

During development, some interesting targets:

make -C out/debug check-abi

Building with Clang is not an option.

• Clang does not support GCC nested functions BZ #27220
• x86 PRESERVE_BND_REGS_PREFIX: integrated assembler does not support the bnd prefix.
• sysdeps/powerpc/powerpc64/Makefile: Clang does not support -ffixed-vrsave -ffixed-vscr

To regenerate configure from configure.ac: https://sourceware.org/glibc/wiki/Regeneration. Consider installing an autoconf somewhere with the required version.

In elf/, .o objects use -fpie -DPIC -DMODULE_NAME=libc, while .os objects use -fPIC -DPIC -DMODULE_NAME=rtld.