NixOS Rust-for-Linux

Assuming you mean Rust-for-Linux (in-tree kernel modules), the usual workflow is a dev shell for the build plus QEMU for testing, rather than booting the kernel on your NixOS machine.

1. Dev shell (shell.nix, channels-style):

{ pkgs ? import <nixpkgs> {} }:
pkgs.mkShell {
  nativeBuildInputs = with pkgs; [
    gnumake flex bison bc pkg-config ncurses
    llvmPackages.clang llvmPackages.lld llvmPackages.libclang
    rustc cargo rust-bindgen rustfmt clippy rust-analyzer
    openssl elfutils perl qemu busybox
  ];
  RUST_LIB_SRC = "${pkgs.rustPlatform.rustLibSrc}";
  LIBCLANG_PATH = "${pkgs.llvmPackages.libclang.lib}/lib";
  hardeningDisable = [ "all" ];
}

hardeningDisable matters because Nix’s default hardening flags break kernel builds.

2. Toolchain version: each kernel release needs a specific minimum rustc and bindgen version. Check with make LLVM=1 rustavailable. If nixpkgs is too new or too old, pin one with rust-overlay or fenix (you’ll need the rust-src component).

3. Build loop:

make LLVM=1 defconfig
make LLVM=1 menuconfig        # General setup -> Rust support
make LLVM=1 -j$(nproc)
make LLVM=1 rust-analyzer     # generates rust-project.json for your editor
make LLVM=1 rustfmtcheck clippy

For fast iteration, use a minimal config: make LLVM=1 allnoconfig qemu-busybox-min.config rust.config.

4. Test in QEMU: build a busybox initramfs (nixpkgs has a static busybox via pkgsStatic.busybox), then boot arch/x86/boot/bzImage with -nographic -append "console=ttyS0". Use -s -S and gdb vmlinux for debugging. Keep sample modules under samples/rust/ and enable them as =m or =y.

5. Out-of-tree modules: Rust out-of-tree support is still rough. If you try it, the kernel needs to be built with CONFIG_RUST=y and you need kernel.dev headers. On NixOS that means boot.kernelPackages.kernel.dev plus kernel.moduleBuildDependencies, and the kernel itself must be a Rust-enabled build (via structuredExtraConfig = { RUST = lib.kernel.yes; } and adding rustc, rust-bindgen and rustPlatform.rustLibSrc to its build inputs). In-tree plus QEMU is far less painful.

If you meant writing your own hobby kernel in Rust (bare-metal target, bootimage, etc.), that’s a different setup, and I can sketch that one too.