Clang Cross-Compilation Toolchain Builder

Build tooling that produces a complete Clang + compiler-rt + libc++ + LLDB toolchain for Linux targeting:

Target	Triple
x86_64 glibc	x86_64-linux-gnu
x86_64 musl	x86_64-linux-musl
x86 (i686) glibc	i686-linux-gnu
x86 (i686) musl	i686-linux-musl
armv7 glibc	armv7-linux-gnueabihf
armv7 musl	armv7-linux-musleabihf
aarch64 glibc	aarch64-linux-gnu
aarch64 musl	aarch64-linux-musl
riscv64 glibc	riscv64-linux-gnu
riscv64 musl	riscv64-linux-musl

The host toolchain (clang, lld, lldb, llvm-*) is fully statically linked against musl libc and requires no runtime dependencies on the build machine.

Looking for prebuilt toolchains? This repository is the builder only. Download ready-to-use toolchains, and read usage and remote-debugging docs, at clang-releases.

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Project Structure

The build tooling is split into three .NET 10 projects under the solution file ClangBuilder.slnx:

Project	Binary	Description
ToolchainBuilder/	clang-builder	Builds and packages the LLVM toolchain
SysrootBuilder/	sysroot-builder	Builds glibc (Debian) and musl (Alpine) sysroots
Common/	(library)	Shared utilities used by both tools

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Building

Prerequisites

sudo apt-get install -y cmake ninja-build git python3 curl xz-utils patchelf \
  qemu-user qemu-user-static

QEMU is used to run cross-compiled test binaries on the build machine.

Run the toolchain build

A pre-built clang-builder binary is included at prebuilts/clang-builder.

./prebuilts/clang-builder build \
  --llvm-version 22.1.2 \
  --all \
  --prebuilts-dir ./prebuilts \
  --work-dir      /tmp/toolchain-work \
  --output-dir    . \
  --jobs          $(nproc) \
  --run-tests \
  --package

All prebuilts (bootstrap compiler and cross sysroots) are read from --prebuilts-dir and stored in Git LFS.

Build options

Option	Description
--llvm-version <ver>	LLVM version to build
--all	Build all targets
--x64, --armv7, --aarch64, --riscv64, --x32	Build individual targets
--prebuilts-dir <dir>	Directory containing prebuilt archives
--work-dir <dir>	Working directory for build artifacts
--output-dir <dir>	Where to write the final package
--jobs <N>	Parallel build jobs
--run-tests	Run toolchain tests before packaging
--package	Package the toolchain after a successful build
--keep-work-dir	Do not delete the work directory after the build
--force-reconfigure	Re-run CMake configure even if already configured

Build sysroots

A pre-built sysroot-builder binary is included at prebuilts/sysroot-builder.

# Build an Alpine musl host sysroot
./prebuilts/sysroot-builder make-sysroot \
  --host \
  --output-dir ./prebuilts \
  --work-dir   /tmp/sysroot-work

# Build Debian glibc cross sysroots for all architectures
./prebuilts/sysroot-builder make-sysroot \
  --glibc --all \
  --output-dir ./prebuilts \
  --work-dir   /tmp/sysroot-work

A --package-list <file> option overrides the default package set. The file contains one package per line (# comments and blank lines are ignored) and may include release: and repo-url: directives:

# my custom sysroot
release: bookworm
repo-url: http://my-mirror.internal/debian

libc6-dev
linux-libc-dev
zlib1g-dev

Use --packages alongside --package-list to add or remove individual packages (+pkg or plain pkg to add, -pkg to remove).

Building from source

Install the .NET 10 SDK, then:

# Build clang-builder
dotnet publish -c Release -r linux-x64 -o ./out/clang-builder \
  ToolchainBuilder/ToolchainBuilder.csproj

# Build sysroot-builder
dotnet publish -c Release -r linux-x64 -o ./out/sysroot-builder \
  SysrootBuilder/SysrootBuilder.csproj