ClangBuiltArduino Toolchain

Build scripts for a slim LLVM-based toolchain targeting AVR and ARM (Arduino).

Build locally

./build.sh llvm          # Build complete LLVM toolchain
./build.sh llvm --head-source  # Build LLVM from a shallow git checkout of HEAD
./build.sh sysroot-avr   # Build AVR sysroot
./build.sh sysroot-avr --head-source  # avr-libc from git HEAD (nightly)
./build.sh --help        # See all options

Project Structure

tc-build/
├── build.sh           # Local build entry point
├── versions.conf      # All versions and URLs for source tarballs
├── common/            # Shared scripts
│   ├── utils.sh       # Common functions
│   ├── build-deps.sh  # Build dependencies
│   └── push-build.sh  # Package and release
├── llvm/              # LLVM build scripts
├── sysroot/           # Sysroot build scripts
├── binutils/          # BFD linker build
└── dockerfiles/       # Docker builds for CI

Toolchain Components

Component	Selection
Compiler	Clang/Clang++
Binary Tools	LLVM Tools
Linker	LLD (default), BFD (AVR only)
Libc Library	avr-libc (AVR), newlib (ARM)
Runtime Library	libgcc

AVR Linker Support

Due to incomplete AVR linker script support in LLD, the toolchain includes the GNU BFD linker as a workaround. Once LLD fully supports AVR linker scripts, BFD will be removed.

Arduino Compatibility

A clang-wrapper is included to improve compatibility with the Arduino build system by handling specific flag adjustments.

Distribution and Packaging

1. LLVM Toolchain - Statically linked Clang/LLVM binaries
2. Sysroot - Target libraries (avr-libc/newlib + libgcc)
3. BFD Linker - Optional GNU linker for AVR

Host coverage

Host	LLVM + gold	BFD	How
x86_64-linux-gnu	musl-static, 2-stage	musl + glibc variants	alpine/debian containers on x86 runners
aarch64-linux-gnu	musl-static, 2-stage	musl + glibc variants	same containers, native on ubuntu-24.04-arm runners
i686-mingw32	single-stage mingw-w64 cross	mingw cross	llvm-windows-i686.Dockerfile
x86_64-apple-darwin12	native, 2-stage	native	llvm-darwin-build.yml on macos-15-intel runners

The sysroot is host-independent (AVR target libraries, one -any archive). Linux archives ship musl/glibc variants side by side; clang-wrapper picks the right one at runtime. Windows/macOS archives are flat.

Portability model per host

• Linux hosts span many libcs/distros, so the toolchain is fully statically linked (musl libc + libc++) and ships musl/glibc variants where relevant.
• Windows (mingw-w64) relies on the stable mingw ABI; binaries are statically linked and self-contained.
• macOS has a stable ABI, so binaries link dynamically against the system libSystem/libc++ and one build covers a range of macOS versions via MACOSX_DEPLOYMENT_TARGET (mirrors llvm-mingw's MACOS_REDIST builds).

Channels

Packages are published as GitHub releases in two flavors:

• Stable — pinned upstream releases from versions.conf, tagged like llvm-<ver>-<date>.
• Nightly — LLVM and avr-libc built from upstream git HEAD (libgcc stays on a pinned GCC release), tagged with a nightly- prefix so the BoardManagerFiles updater can pick them out.

Automation

• Check for Updates opens a PR when upstream versions change.
• The LLVM and sysroot pipelines run on a daily schedule as nightly builds and can also be dispatched manually (nightly input toggles the flavor).
• After a successful publish, the pipelines send a repository_dispatch to BoardManagerFiles (requires the org secret CBA_DISPATCH_TOKEN) so the package index refreshes itself.

License

Apache-2.0 - See LICENSE