Building libc6 compat

Building libc6-compat

Below version of libc6-compat (musl-libc) is available in respective distributions at the time of creation of these build instructions:

• Ubuntu 22.04 has 1.2.2
• Ubuntu 24.04 has 1.2.4
• Ubuntu 24.10 has 1.2.5

The instructions provided below specify the steps to build libc6-compat version 1.2.5 on Linux on IBM Z for the following distributions:

• RHEL (8.8, 8.10, 9.2. 9.4, 9.5)
• SLES 15 SP6
• Ubuntu (22.04, 24.04)

General Notes:

• When following the steps below please use a standard permission user unless otherwise specified

• A directory /<source_root>/ will be referred to in these instructions, this is a temporary writable directory anywhere you'd like to place it

1. Build using script

If you want to build libc6-compat using manual steps, go to Step 2.

Use the following commands to build libc6-compat using the build script. Please make sure you have wget installed.

wget -q https://raw.githubusercontent.com/linux-on-ibm-z/scripts/master/libc6-compat/1.2.5/build_libc6compat.sh
# Build libc6-compat
bash build_libc6compat.sh

If the build completes successfully, go to STEP 4. In case of error, check logs for more details or go to STEP 2 to follow manual build steps.

2. Install the Dependencies

export SOURCE_ROOT=/<source_root>/

• RHEL (8.8, 8.10, 9.2. 9.4, 9.5)

sudo yum install -y gcc gcc-c++ make wget tar

• SLES 15 SP6

sudo zypper install -y gcc gcc-c++ make wget tar bzip2 zlib-devel gzip

• Ubuntu (22.04, 24.04)

sudo apt-get update
sudo apt-get install -y gcc g++ tar wget make cmake bzip2 zlib1g-dev g++-multilib

3. Build and Install libc6-compat

• Download source code

  cd $SOURCE_ROOT
  wget http://git.musl-libc.org/cgit/musl/snapshot/musl-1.2.5.tar.gz
  tar -xzf musl-1.2.5.tar.gz

• Build and Install libc6-compat

  cd $SOURCE_ROOT/musl-1.2.5
  ./configure
  make
  sudo make install

Note: By default, configure installs to a prefix of "/usr/local/musl". This differs from the behavior of most configure scripts, and is chosen specifically to avoid clashing with libraries already present on the system. DO NOT set the prefix to "/usr", "/usr/local", or "/" unless you're upgrading libc on an existing musl-based system. Doing so will break your existing system when you run "make install" and it may be difficult to recover.

4. Verify libc6-compat (Optional)

• After installing, you should be able to use musl via the musl-gcc wrapper. For example:

cat > hello.c <<EOF
#include <stdio.h>
int main()
{
	printf("hello, world!\n");
	return 0;
}
EOF
/usr/local/musl/bin/musl-gcc hello.c
./a.out

Note: The above program should compile and execute successfully printing the string hello, world.

Notes:

• To configure autoconf-based program to compile and link against musl, set the CC variable to musl-gcc when running configure, as in:

CC=musl-gcc ./configure ...

• You will probably also want to use --prefix when building libraries to ensure that they are installed under the musl prefix and not in the main host system library directories.

References:

• https://pkgs.alpinelinux.org/package/edge/main/s390x/libc6-compat
• http://musl.libc.org/
• http://git.musl-libc.org/cgit/musl/tree/INSTALL#n161