nix-cross-rust

Nix flake to cross-compile Rust projects. Uses Fenix for toolchains and Naersk for incremental builds.

Usage

Start your own flake using this one as a template:

nix flake init -t github:pbar1/nix-cross-rust
nix flake lock

Flake Outputs

♪ nix flake show
git+file:///Users/pierce/code/nix-cross-rust?ref=refs/heads/main&rev=4028098b657ec2680e2c2e81145e1dfc5205aacf
└───packages
    ├───aarch64-darwin
    │   ├───cross-aarch64-darwin: package 'nix-cross-rust-0.1.0'
    │   ├───cross-aarch64-linux: package 'nix-cross-rust-0.1.0'
    │   ├───cross-x86_64-darwin: package 'nix-cross-rust-0.1.0'
    │   ├───cross-x86_64-linux: package 'nix-cross-rust-0.1.0'
    │   └───default: package 'nix-cross-rust-0.1.0'
    ├───aarch64-linux
    │   ├───cross-aarch64-darwin omitted (use '--all-systems' to show)
    │   ├───cross-aarch64-linux omitted (use '--all-systems' to show)
    │   ├───cross-x86_64-darwin omitted (use '--all-systems' to show)
    │   ├───cross-x86_64-linux omitted (use '--all-systems' to show)
    │   └───default omitted (use '--all-systems' to show)
    ├───x86_64-darwin
    │   ├───cross-aarch64-darwin omitted (use '--all-systems' to show)
    │   ├───cross-aarch64-linux omitted (use '--all-systems' to show)
    │   ├───cross-x86_64-darwin omitted (use '--all-systems' to show)
    │   ├───cross-x86_64-linux omitted (use '--all-systems' to show)
    │   └───default omitted (use '--all-systems' to show)
    └───x86_64-linux
        ├───cross-aarch64-darwin omitted (use '--all-systems' to show)
        ├───cross-aarch64-linux omitted (use '--all-systems' to show)
        ├───cross-x86_64-darwin omitted (use '--all-systems' to show)
        ├───cross-x86_64-linux omitted (use '--all-systems' to show)
        └───default omitted (use '--all-systems' to show)

Timings

System Info

♪ sysctl -a | grep -e machdep\.cpu -e memsize
hw.memsize: 17179869184
hw.memsize_usable: 16585523200
machdep.cpu.cores_per_package: 8
machdep.cpu.core_count: 8
machdep.cpu.logical_per_package: 8
machdep.cpu.thread_count: 8
machdep.cpu.brand_string: Apple M2

Initial Toolchain Build

Initial cross-compile builds are very slow because almost nothing is cached in public Nix caches. Once the first per target platform succeeded though, subsequent builds will be fast.

• aarch64-darwin (native): omitted
• aarch64-darwin -> aarch64-linux-musl: 44m
• aarch64-darwin -> x86_64-linux-musl: 44m

Real Project Clean Build

To test build speed in a real world scenario, I copy-pasted this flake into pbar1/astu and then build it from scratch.

• aarch64-darwin (native): 2m44s
• aarch64-darwin -> aarch64-linux-musl: 2m53s
• aarch64-darwin -> x86_64-linux-musl: 5m20s

Not quite sure why x86_64-linux-musl was slower than the other two. I did run it first, so maybe the extra time was spent downloading Rust crate sources that were then able to be used in the other two builds?

Resources

• Statically Cross-Compiling Rust Projects Using Nix
  • Flake
  • Really, go read that post. This flake is almost exactly that, subbing out the Windows bits for Darwin, and with less emphasis on static.
• Naersk cross-windows
• Nix.dev cross compilation
• Target names
  • Nix
  • Rust