musl_toolchain provides a cc_toolchain implementation for Bazel.
This toolchain allows cross-compiling binaries for Linux from various platforms. It can be used to produce binaries which don't dynamically link libc, by statically linking musl's libc implementation.
The supported target and execution platforms are:
Due to limitations of Linux arm64 runners available for GitHub Actions, the toolchain requires glibc >= 2.35 to run on Linux arm64 executors.
Setup instructions are available with each release.
--incompatible_enable_cc_toolchain_resolution is required with Bazel 6.
The toolchain automatically enables the fully_static_link feature to produce statically linked binaries that run anywhere.
cc_binary targets with dynamic library dependencies (e.g. dynamic_deps or cc_imports), linkstatic = False or --dynamic_mode=fully will be linked dynamically. Such binaries require the musl dynamic linker to be present at /lib/ld-musl-<arch>.so.1 on the target system.
Since the path to the dynamic linker is hardcoded into the binary as an absolute path, there is no way to supply it hermetically.
Dynamically linked cc_tests are automatically executed with a hermetic musl dynamic linker (requires Bazel 7 or higher).
cc_toolchain implementationsgcc-toolchain supports building against a known glibc version, rather than building static binaries linking the musl libc implementation.
It also isn't set up for cross-compiling from macOS.
If you're aiming to only compile from Linux, and don't need statically linked binaries, the gcc-toolchain is worth considering.
llvm-toolchain supports cross-compiling, but requires bringing along a sysroot containing a libc to link against.
In contrast, the musl toolchain is designed for building static binaries linking the musl libc implementation.
The musl toolchain's C/C++ compiler is gcc-based rather than llvm-based.
If you don't need to produce statically linked binaries, this toolchain is worth considering.
These toolchains have similar aims.
From having tried out the Zig toolchain, the authors of this toolchain have run into stability/reliability issues due to the relatively early stage of development that Zig is currently at. We look forward to the Zig toolchain maturing beyond these issues in the future!