let
  update_microcode = true;
in
{
  hostPlatform = (import <nixpkgs/lib>).systems.examples.gnu64;

  overlay = (final: prev: {

    platform_name = "kgpe";

    kernel =
      final.lib.makeOverridable (prev.kernel.override {
        config = ./linux.config;
        buildTargets = [ "bzImage" ];
      }).overrideAttrs (a: {
        postInstall = (a.postInstall or "") + ''
          cp arch/x86_64/boot/bzImage $out
        '';
      });

    userspace = prev.userspace.overrideAttrs (a: {
      postInstall = (a.postInstall or "") + ''
        cp ${final.coreboot.src}/mainboard/asus/kgpe-d16/cmos.layout $out/etc/
        cp ${final.coreboot.src}/mainboard/asus/kgpe-d16/cmos.default $out/etc/
      '';
    });

    coreboot = let
      # does include spectre mitigations (performance hit)
      #linux-firmware = final.nixpkgsOnBuildForBuild.linux-firmware;
      #path-within-linux-firmware = "lib/firmware/amd-ucode/microcode_amd_fam15h.bin";

      # does *not* include spectre mitigations (no performance hit)
      linux-firmware = final.nixpkgsOnBuildForBuild.fetchgit {
        # most recent update that does *not* include spectre
        # mitigations; needed for 63xx processors due to an exploitable
        # NMI defect in that sieres (only)
        url = "https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git";
        rev = "5f8ca0c1db6106a2d6d7e85eee778917ff03c3de";
        branchName = "main";
        #sparseCheckout = path-within-linux-firmware;
        hash = "sha256-uwzz0z2+uPke8AVKb80Cy620efdRBSuwjfoIrQhepc8=";
      };
      path-within-linux-firmware = "amd-ucode/microcode_amd_fam15h.bin";
    in
      final.lib.makeOverridable (prev.coreboot.override {
      iasl = final.iasl_20180531;
      payload = "${final.kernel}/bzImage";
      fmap = ./custom.fmap;
      config = ./coreboot.config;
      coreboot-toolchain = with final.coreboot-toolchain; [ x64 i386 ];
      linux-command-line = "console=ttyS1,115200n8";
    }).overrideAttrs (a: {
      postConfigure = if update_microcode then ''
        echo CONFIG_CPU_MICROCODE_MULTIPLE_FILES=y >> .config
      '' else ''
        echo CONFIG_CPU_MICROCODE_CBFS_NONE=y >> .config
      '';
      preBuild = final.lib.optionalString update_microcode ''
        mkdir -p 3rdparty/blobs/cpu/amd/family_15h/
        ln -sfT ${linux-firmware}/${path-within-linux-firmware} \
          3rdparty/blobs/cpu/amd/family_15h/microcode_amd_fam15h.bin
        mkdir -p 3rdparty/blobs/cpu/amd/family_10h-family_14h/
        touch 3rdparty/blobs/cpu/amd/family_10h-family_14h/microcode_amd.bin
      '';
      postInstall = (a.postInstall or "") + ''
        cp src/mainboard/asus/kgpe-d16/cmos.layout $out/
        cp src/mainboard/asus/kgpe-d16/cmos.default $out/
    '';
    });
  });
}