This Docker script creates environment for building small static Linux musl executables for x86_64 and ARM from Rust with Xargo.

Project configuration

panic=abort and lto=1 is a requirement.

Docker image contains pre-built toolchains for projects of approximately this layout:

Cargo.toml contains

[profile.release]
panic="abort"
lto=true
opt-level="s"
codegen-units=1

Xargo.toml contains

[dependencies]
std = {}

Compilation with those should be faster.

Usage

Supposing you have a Rust project without system dependencies, you add a release profile and Xargo.toml listed above.

Then you run

docker run --rm -it -w /wd -v $PWD:/wd vi0oss/xargo-musl xargo build --release --target=x86_64-unknown-linux-musl

and see something like

   Compiling helloworld v0.1.0 (/wd)
    Finished release [optimized] target(s) in 2.30s

Your unstripped executable is ready at target/x86_64-unknown-linux-gnu/release.

Targets to use:

• x86_64-unknown-linux-musl
• arm-unknown-linux-musleabi
• arm-unknown-linux-musleabihf
• mips-unknown-linux-musl (non-static)
• mipsel-unknown-linux-musl (non-static)

Building the image

Building depends on the following external resources:

• rustlang/rust:nightly base image, which contains rustc 1.35.0-nightly (26b4cb484 2019-03-09) at the moment of writing;
• github.com/rob-ward/rob-ward-toolchains repository and Github allowing to download tar.gz

docker build -t vi0oss/xargo-musl . should work and produce output similar to this sample output.

68K arm
68K armhf
68K mips
68K mipsel
64K x86_64

x86_64: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, BuildID[sha1]=d2392e42038410a4f381d229b23da97198ee0209, stripped
arm:    ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, stripped
armhf:  ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, stripped
mips:   ELF 32-bit MSB shared object, MIPS, MIPS32 rel2 version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-mips.so.1, stripped
mipsel: ELF 32-bit LSB shared object, MIPS, MIPS32 rel2 version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-mipsel.so.1, stripped

Unfortunately mips executables are not static.

Hacks

The following hacks are applied during the build:

• Usage of pre-built downloaded musl toolchains
• Manually specifying -L native= to make it find libc.a
• Creating dummy libunwind.a just to avoid it stopping compilation

See also

• https://github.com/messense/rust-musl-cross
• https://github.com/johnthagen/min-sized-rust