nixos-conf/custom/modules/kernel.nix

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

let
  makefile = builtins.readFile "${kernel-src}/Makefile";
  lines = lib.splitString "\n" makefile;
  normalizeKernelPatch = p: p // { patch = p.patch or null; };
  kernelPatches' = map normalizeKernelPatch kernelPatches;

  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
let
  args = {
    inherit
      buildLinux
      features
      randstructSeed
      ;
  };
  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"
  '';
  sccacheSetup = lib.optionalString enforceSccache ''
    mkdir -p ${lib.escapeShellArg sccacheDir} 2>/dev/null || true
    export SCCACHE_CONF=${lib.escapeShellArg sccacheConfig}
    ${lib.optionalString (sccacheServerUds != null) "export SCCACHE_SERVER_UDS=${lib.escapeShellArg sccacheServerUds}"}
  '';

  mkSccacheWrapper =
    name: compiler:
    pkgs.writeShellScriptBin name ''
      set -euo pipefail
      mkdir -p ${lib.escapeShellArg sccacheDir} 2>/dev/null || true
      export SCCACHE_CONF=${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
    mkdir -p ${lib.escapeShellArg sccacheDir} 2>/dev/null || true
    export SCCACHE_CONF=${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
    mkdir -p ${lib.escapeShellArg sccacheDir} 2>/dev/null || true
    export SCCACHE_CONF=${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
  // {
    kernelPatches = kernelPatches';
    inherit 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}"
      ]
      ;

    preConfigure = (args.preConfigure or "") + sccacheSetup;

    preBuild = (args.preBuild or "") + sccacheSetup;

    buildPhase =
      if enforceSccache then
        ''
          runHook preBuild
          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}";
  }
)