1 files changed, 59 insertions, 0 deletions

diff --git a/modules/llvm_kernel.nix b/modules/llvm_kernel.nix
new file mode 100644
index 00000000..71d96320
--- /dev/null
+++ b/modules/llvm_kernel.nix
@@ -0,0 +1,59 @@
+{ config, pkgs, lib, ... }:
+let
+  cfg = config.boot.kernel.llvm;
+in {
+  options = {
+    boot.kernel.llvm = {
+      enable = lib.mkEnableOption "building linux kernel with clang/LLVM" // {
+        default = true;
+      };
+
+      kernel = lib.mkPackageOption pkgs [ "linuxKernel" "kernels" "linux_default" ] {};
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    boot.kernelPackages =
+      with pkgs; # Cut down on repeated `pkgs.` declarations
+      let
+        # Choose whichever LLVM version you please. `llvmPackages` is the
+        # default version, `llvmPackages_latest` is the latest (at the time of
+        # writing, LLVM 17.0.6 and 18.1.8 respectively).
+        llvm = llvmPackages_latest;
+        # Same deal as LLVM; choose whichever kernel version you like.
+        # `linux` is the latest LTS, `linux_latest` is the latest stable.
+        inherit (cfg) kernel;
+      in
+      # Generate kernel modules for our custom kernel.
+      linuxPackagesFor (
+        # Override our chosen kernel version with our custom settings.
+        (kernel.override {
+          # Set our chosen version of LLVM as our standard environment.
+          stdenv = overrideCC llvm.stdenv (
+            # Tell our C compiler (Clang) to use LLVM bintools--normally GNU
+            # binutils are used even with Clang as the compiler.
+            llvm.stdenv.cc.override {
+              bintools = llvm.bintools;
+            }
+          );
+
+          # Tell Linux that we're compiling with Clang and LLVM.
+          extraMakeFlags = [ "LLVM=1" ];
+
+          # If you'd like to edit your kernel configuration, use
+          # `structuredExtraConfig`. For example, some options available to us
+          # when compiling with Clang and linking with LLD:
+          structuredExtraConfig = {
+            CFI_CLANG = lib.kernel.yes;
+            # LTO_CLANG_THIN = lib.kernel.yes;
+          };
+        }
+      ).overrideAttrs
+        # Work around another NixOS specific issue where builds with WERROR=y
+        # are stopped by a benign error. See reference 1 below for details.
+        # Technically, this fix is only necessary with WERROR=y but the issue
+        # still causes a warning on builds where WERROR is unset.
+        { env.NIX_CFLAGS_COMPILE = "-Wno-unused-command-line-argument"; }
+      );
+  };
+}