Optimized RPM packaging for the LLVM project

This repository provides an optimized build of LLVM and Clang. It is self-bootstrapping for the target system and does not depend on a pre-built version of LLVM.

Target system:

• RHEL/CentOS 7.x - x86_64 and aarch64 architectures.

Why this is needed: New and optimized versions of the LLVM toolchain are not directly managed by maintainers of the older target LTS distributions, and not always to the best of ways. Original LLVM builds target Debian-based systems.

Notes:

• Clang is built as an LTO executable that links only to LLVM shared library, so it is fully optimized.
• Aims to backport and preserve original Fedora package work for LLVM packages.
• Target version 13.0.0, bootstrapped by building Clang 11.1.0;
• LLVM sub-projects compiler-rt and lld are also bootstrapped in this build process.

Instructions

Notes:

• Expect the build of this repository to take a few hours.
• Network access is needed for build. The network dependencies are:
  • Access to github.com.
  • Access to Fedora's source package servers.
  • Access to docker.com for base CentOS 7.x image.
  • Access to mirror.centos.org for SCLo repositories.
• A privileged docker instance is needed due to usage of mock inside the container.

Clone

git clone --depth 1 --recursive https://github.com/kernelim/llvm-rpm

Build:

cd llvm-rpm
./run under-container build-all

Expected output is under repo sub directory:

$ ls -l repo/
total 40
drwxr-xr-x. 2 root root 4096 Mar 31 09:33 repodata
drwxrwxr-x. 3 root root 4096 Mar 30 23:07 results_clang
drwxrwxr-x. 3 root root 4096 Mar 30 22:29 results_cmake
drwxrwxr-x. 3 root root 4096 Mar 30 23:22 results_compiler-rt
drwxrwxr-x. 3 root root 4096 Mar 31 09:31 results_libcxx
drwxrwxr-x. 3 root root 4096 Mar 30 23:24 results_libcxxabi
drwxrwxr-x. 3 root root 4096 Mar 31 09:32 results_lld
drwxrwxr-x. 3 root root 4096 Mar 30 22:55 results_llvm
drwxrwxr-x. 3 root root 4096 Mar 30 22:49 results_llvm-11.1.0
drwxrwxr-x. 3 root root 4096 Mar 30 23:22 results_python-lit

Notes:

• Not all outputs are needed for successful usage of the built compiler.
• Specifically, bootstrapping compiler results_llvm-11.1.0 can be removed.
• There is a run-time dependency over libcxx and libcxxabi by the built compiler.
• For repeated executions, some parameters can be provided to under-container to save setup time, e.g. ./run under-container -r -s

Building outside docker

It is also possible to build without depending on docker, directly on a CentOS 7.x system, provided that it has EPEL prerequisites such as fedpkg and mock.

The root-setup stage installs a mock configuration under /etc/mock, and prepares an RPM a repo under /opt/repo, where the outputs will reside.

./run root-setup
./run build-all