nix-linux

This repository contains a framework for configuring and building Linux and U-Boot using Nixpkgs. It also includes utilities for building out-of-tree kernel modules and various types of U-Boot images.

The infrastructure for configuring and building Linux within Nixpkgs is a beast: nixpkgs/pkgs/os-specific/linux/kernel. This project provides an alternative with a focus on minimalism and control.

Tutorial

This tutorial shows how to build Linux for the Raspberry Pi 4 with a modified Kconfig and an out-of-tree module. The full source of this example can be found in ./examples/rpi4.

To get started, include ./overlay.nix in your project. This overlay provides the attribute linuxHelpers.

Express the source of your kernel. This expression can include patches and other hooks used by stdenv:

{
  source = linuxHelpers.linux.prepareSource {
    version = "5.2.15";
    src = fetchgit {
      url = "https://github.com/raspberrypi/linux";
      rev = "bab1c236e844b0a891201c08b3da62dbedc10408";
      sha256 = "0s35hp3bai9sv0h0gkb21304mv79myb7ar50f4wfij7py833g6nc";
    };
    patches = with linuxHelpers.linux.kernelPatches; [
      bridge_stp_helper
    ];
  };
}

Express the Kconfig of your kernel. In this case, our Kconfig will be created from the bcm2711_defconfig make target. Check out ./linux/config/make-allconfig.nix for the definition of makeConfig.

{
  config = linuxHelpers.linux.makeConfig {
    inherit source;
    target = "bcm2711_defconfig";
  };
}

Build your kernel.

{
  kernel = linuxHelpers.linux.buildKernel rec {
    inherit source config;
    dtbs = true;
}

$ nix-build kernel

Modify your Kconfig using menuconfig to disable the ELF binary format (CONFIG_BINFMT_ELF=n). This is done in an environment provided by nix-shell. Check out ./linux/config/env.nix for the details of this environment.

$ nix-shell -A kernel.configEnv
$ mm # alias for make $makeFlags menuconfig
(navigate and set CONFIG_BINFMT_ELF=n)
$ ms # alias for make $makeFlags savedefconfig, creates a minimal ./defconfig

Update the kernel to use your modified Kconfig.

{
  config = makeConfig {
    inherit source;
    target = "alldefconfig";
    allconfig = ./defconfig;
  };
}

$ nix-build kernel

Build an out of tree module. See ./examples/rpi4/module.nix for an example.

Plans

• Include helpers for manipulating device trees.
• Design and include utilities for programatically interacting with Kconfig (similar to those used in NixOS).