nixos-conf/custom/modules/kernel.nix

{
  pkgs,
  lib,
  kernel-src,
  structuredExtraConfig ? { },
  kernelPatches ? [ ],
  extraConfig ? "",
  sccacheDir ? "/var/cache/sccache/nix-builds/kernel",
  sccacheServerUds ? null,
  enforceSccache ? true,
}:

let
  makefile = builtins.readFile "${kernel-src}/Makefile";
  lines = lib.splitString "\n" makefile;

  get =
    name:
    let
      line = lib.findFirst (
        l: lib.hasPrefix "${name} =" (lib.strings.trim l)
      ) (throw "Makefile missing ${name}") lines;
    in
    lib.strings.trim (lib.removePrefix "${name} =" (lib.strings.trim line));

  V = get "VERSION";
  P = get "PATCHLEVEL";
  S = get "SUBLEVEL";
  E = get "EXTRAVERSION";

  kver = "${V}.${P}.${S}${E}";
in
pkgs.callPackage (
  { buildLinux, ... }@args:
  let
    llvm = pkgs.llvmPackages_latest;
    rust = pkgs.rustc-unwrapped;

    buildPkgs = args.buildPackages or pkgs.buildPackages;
    buildLlvm = buildPkgs.llvmPackages_latest;
    llvmBuildPackages = buildPkgs // {
      stdenv = buildLlvm.stdenv;
    };

    realClang = lib.getExe llvm.clang-unwrapped;
    realLd = lib.getExe' llvm.lld "ld.lld";
    realAr = lib.getExe' llvm.llvm "llvm-ar";
    realNm = lib.getExe' llvm.llvm "llvm-nm";
    realStrip = lib.getExe' llvm.llvm "llvm-strip";
    realObjcopy = lib.getExe' llvm.llvm "llvm-objcopy";
    realObjdump = lib.getExe' llvm.llvm "llvm-objdump";
    realReadelf = lib.getExe' llvm.llvm "llvm-readelf";

    realHostCC = lib.getExe' buildLlvm.stdenv.cc "${buildLlvm.stdenv.cc.targetPrefix}cc";
    realHostCXX = lib.getExe' buildLlvm.stdenv.cc "${buildLlvm.stdenv.cc.targetPrefix}c++";
    realHostAr = lib.getExe' buildLlvm.llvm "llvm-ar";
    realHostLd = lib.getExe' buildLlvm.lld "ld.lld";
    realRustc = lib.getExe' rust "rustc";
    realHostRustc = realRustc;
    sccacheConfig = pkgs.writeText "kernel-sccache.conf" ''
      [cache.disk]
      dir = "${sccacheDir}"
      size = "100G"
    '';

    mkSccacheWrapper =
      name: compiler:
      pkgs.writeShellScriptBin name ''
        set -euo pipefail
        export SCCACHE_CONF=${lib.escapeShellArg sccacheConfig}
        ${lib.optionalString (sccacheServerUds != null) "export SCCACHE_SERVER_UDS=${lib.escapeShellArg sccacheServerUds}"}
        if [ -n "''${SCCACHE_ENFORCE_MARKER-}" ]; then
          : > "''${SCCACHE_ENFORCE_MARKER}"
        fi
        exec ${pkgs.sccache}/bin/sccache ${compiler} "$@"
      '';

    clangSccache = mkSccacheWrapper "clang" realClang;
    hostccSccache = mkSccacheWrapper "cc" realHostCC;
    hostcxxSccache = mkSccacheWrapper "c++" realHostCXX;
    rustcSccache = pkgs.writeShellScriptBin "rustc" ''
      set -euo pipefail
      export SCCACHE_CONF=${lib.escapeShellArg sccacheConfig}
      ${lib.optionalString (sccacheServerUds != null) "export SCCACHE_SERVER_UDS=${lib.escapeShellArg sccacheServerUds}"}
      if [ -n "''${SCCACHE_ENFORCE_MARKER-}" ]; then
        : > "''${SCCACHE_ENFORCE_MARKER}"
      fi
      exec ${pkgs.sccache}/bin/sccache ${realRustc} "$@"
    '';

    hostrustcSccache = pkgs.writeShellScriptBin "rustc" ''
      set -euo pipefail
      export SCCACHE_CONF=${lib.escapeShellArg sccacheConfig}
      ${lib.optionalString (sccacheServerUds != null) "export SCCACHE_SERVER_UDS=${lib.escapeShellArg sccacheServerUds}"}
      if [ -n "''${SCCACHE_ENFORCE_MARKER-}" ]; then
        : > "''${SCCACHE_ENFORCE_MARKER}"
      fi
      exec ${pkgs.sccache}/bin/sccache ${realHostRustc} "$@"
    '';

    structuredExtraConfig' =
      (with lib.kernel; {
        LTO_CLANG_THIN = yes;
        # LTO_CLANG_FULL = no;
        # LTO_NONE = no;
      })
      // structuredExtraConfig;
  in
  buildLinux (
    args
    // {
      inherit kernelPatches extraConfig;

      version = kver;
      modDirVersion = kver;
      src = kernel-src;

      stdenv = llvm.stdenv;
      buildPackages = llvmBuildPackages;

      extraMakeFlags =
        (args.extraMakeFlags or [ ])
        ++ [
          "LLVM=1"
          "LLVM_IAS=1"
          "CC=${if enforceSccache then lib.getExe clangSccache else realClang}"
          "LD=${realLd}"
          "AR=${realAr}"
          "NM=${realNm}"
          "STRIP=${realStrip}"
          "OBJCOPY=${realObjcopy}"
          "OBJDUMP=${realObjdump}"
          "READELF=${realReadelf}"
          "HOSTCC=${if enforceSccache then lib.getExe hostccSccache else realHostCC}"
          "HOSTCXX=${if enforceSccache then lib.getExe hostcxxSccache else realHostCXX}"
          "HOSTAR=${realHostAr}"
          "HOSTLD=${realHostLd}"
          "RUSTC=${if enforceSccache then lib.getExe rustcSccache else realRustc}"
          "HOSTRUSTC=${if enforceSccache then lib.getExe hostrustcSccache else realHostRustc}"
        ]
        ;

      preBuild =
        (args.preBuild or "")
        + lib.optionalString enforceSccache ''
          mkdir -p ${lib.escapeShellArg sccacheDir}
          chmod 0777 ${lib.escapeShellArg sccacheDir} || true
          export SCCACHE_CONF=${lib.escapeShellArg sccacheConfig}
          ${lib.optionalString (sccacheServerUds != null) "export SCCACHE_SERVER_UDS=${lib.escapeShellArg sccacheServerUds}"}
        '';

      buildPhase =
        if enforceSccache then
          ''
            runHook preBuild
            mkdir -p ${lib.escapeShellArg sccacheDir}
            chmod 0777 ${lib.escapeShellArg sccacheDir} || true
            export SCCACHE_CONF=${lib.escapeShellArg sccacheConfig}
            ${lib.optionalString (sccacheServerUds != null) "export SCCACHE_SERVER_UDS=${lib.escapeShellArg sccacheServerUds}"}
            export SCCACHE_ENFORCE_MARKER="$NIX_BUILD_TOP/.sccache-used"
            rm -f "$SCCACHE_ENFORCE_MARKER"
            make "''${makeFlags[@]}" "''${buildFlags[@]}"
            if [ ! -e "$SCCACHE_ENFORCE_MARKER" ]; then
              echo "FATAL: sccache enforcement failed during buildPhase: compiler wrappers were not invoked."
              echo "This means the build stage did not use your CC/HOSTCC/HOSTCXX/RUSTC/HOSTRUSTC overrides."
              exit 1
            fi
            ${pkgs.sccache}/bin/sccache --show-stats --stats-format text || true
            runHook postBuild
          ''
        else
          (args.buildPhase or ''
            runHook preBuild
            make "''${makeFlags[@]}" "''${buildFlags[@]}"
            runHook postBuild
          '');

      postBuild = args.postBuild or "";

      structuredExtraConfig = structuredExtraConfig';

      ignoreConfigErrors = true;

      extraMeta.branch = "${V}.${P}";
    }
  )
) { }