lib/systems: move kernel configuration out of the platform structure

Currently, you need to override `stdenv.hostPlatform` to request a
compressed kernel on AArch64, and the kernel configuration is split
between the central structured configuration and string snippets in
platform definitions. This has consequently made the latter bitrot
terribly. Since the platform‐specific logic is now very limited after
cleaning up the detritus, we can move it into the kernel derivation
and expose the relevant configuration there for anyone who wants to
customize it further or needs to read it out.

Co-authored-by: zowoq <59103226+zowoq@users.noreply.github.com>

doc/release-notes/rl-2611.section.md

@@ -19,6 +19,13 @@
 
 - `uhttpmock` providing 0.0 ABI was removed. `uhttpmock_1_0` providing 1.0 ABI was renamed to `uhttpmock` and `uhttpmock_1_0` was kept as an alias.
 
+- Linux kernel configuration has been moved out of the `linux-kernel` field of the platform structure into the kernel builders:
+  - `linux-kernel.name` has been removed.
+  - `linux-kernel.target` is available as the `target` parameter and passthru attribute on the kernel builders.
+  - `linux-kernel.installTarget` has been removed, as it should not be necessary to customize.
+  - `linux-kernel.DTB` is available as the `buildDTBs` parameter and passthru attribute on the kernel builders.
+  - `linux-kernel.{autoModules,preferBuiltin,extraConfig}` were already available as kernel builder parameters.
+
 - The ARMv5 Linux kernel build now uses a standard configuration and generates a standard compressed image instead of the deprecated legacy U‐Boot image format.
   `lib.systems.{examples,platforms}.{sheevaplug,pogoplug4}` have been unified into `lib.systems.examples.armv5tel-multiplatform`.
   Note that there is no official support for ARMv5 and it is not possible to build even a simple NixOS configuration out of the box.

lib/systems/default.nix

@@ -299,12 +299,10 @@ let
         inherit
           (
             {
-              linux-kernel = args.linux-kernel or { };
               gcc = args.gcc or { };
             }
             // platforms.select final
           )
-          linux-kernel
           gcc
           ;
 
@@ -692,6 +690,11 @@ let
         };
       };
     in
+    # TODO: Remove in 27.05.
+    assert
+      args ? linux-kernel
+      -> throw "lib.systems.elaborate: linux-kernel has been removed; see the 26.11 release notes";
+
     assert final.useAndroidPrebuilt -> final.isAndroid;
     assert foldl' (pass: { assertion, message }: if assertion final then pass else throw message) true (
       final.parsed.abi.assertions or [ ]

lib/systems/platforms.nix

@@ -3,74 +3,21 @@
 # targetPlatform, etc) containing at least the minimal set of attrs
 # required (see types.parsedPlatform in lib/systems/parse.nix).  This
 # file takes an already-valid platform and further elaborates it with
-# optional fields; currently these are: linux-kernel, gcc, and rustc.
+# optional fields; currently these are: gcc, and rustc.
 
 { lib }:
 rec {
-  pc = {
-    linux-kernel = {
-      name = "pc";
-
-      baseConfig = "defconfig";
-      # Build whatever possible as a module, if not stated in the extra config.
-      autoModules = true;
-      target = "bzImage";
-    };
-  };
-
-  ##
-  ## POWER
-  ##
-
-  powernv = {
-    linux-kernel = {
-      name = "PowerNV";
-
-      baseConfig = "powernv_defconfig";
-      target = "vmlinux";
-      autoModules = true;
-    };
-  };
-
-  ppc64 = {
-    linux-kernel = {
-      name = "powerpc64";
-
-      baseConfig = "ppc64_defconfig";
-      target = "vmlinux";
-      autoModules = true;
-    };
-  };
-
   ##
   ## ARM
   ##
 
   armv5tel-multiplatform = {
-    linux-kernel = {
-      name = "armv5tel-multiplatform";
-
-      baseConfig = "multi_v5_defconfig";
-      DTB = true;
-      autoModules = true;
-      preferBuiltin = true;
-      target = "zImage";
-    };
     gcc = {
       arch = "armv5te";
     };
   };
 
   raspberrypi = {
-    linux-kernel = {
-      name = "raspberrypi";
-
-      baseConfig = "bcm2835_defconfig";
-      DTB = true;
-      autoModules = true;
-      preferBuiltin = true;
-      target = "zImage";
-    };
     gcc = {
       # https://en.wikipedia.org/wiki/Raspberry_Pi#Specifications
       arch = "armv6kz";
@@ -105,7 +52,6 @@ rec {
 
   # https://developer.android.com/ndk/guides/abis#v7a
   armv7a-android = {
-    linux-kernel.name = "armeabi-v7a";
     gcc = {
       arch = "armv7-a";
       float-abi = "softfp";
@@ -114,14 +60,6 @@ rec {
   };
 
   armv7l-hf-multiplatform = {
-    linux-kernel = {
-      name = "armv7l-hf-multiplatform";
-      baseConfig = "defconfig";
-      DTB = true;
-      autoModules = true;
-      preferBuiltin = true;
-      target = "zImage";
-    };
     gcc = {
       # Some table about fpu flags:
       # http://community.arm.com/servlet/JiveServlet/showImage/38-1981-3827/blogentry-103749-004812900+1365712953_thumb.png
@@ -146,14 +84,6 @@ rec {
   };
 
   aarch64-multiplatform = {
-    linux-kernel = {
-      name = "aarch64-multiplatform";
-      baseConfig = "defconfig";
-      DTB = true;
-      autoModules = true;
-      preferBuiltin = true;
-      target = "Image";
-    };
     gcc = {
       arch = "armv8-a";
     };
@@ -171,9 +101,6 @@ rec {
   ##
 
   ben_nanonote = {
-    linux-kernel = {
-      name = "ben_nanonote";
-    };
     gcc = {
       arch = "mips32";
       float = "soft";
@@ -230,17 +157,6 @@ rec {
   ## Other
   ##
 
-  riscv-multiplatform = {
-    linux-kernel = {
-      name = "riscv-multiplatform";
-      target = "Image";
-      autoModules = true;
-      preferBuiltin = true;
-      baseConfig = "defconfig";
-      DTB = true;
-    };
-  };
-
   loongarch64-multiplatform = {
     gcc = {
       # https://github.com/loongson/la-softdev-convention/blob/master/la-softdev-convention.adoc#10-operating-system-package-build-requirements
@@ -252,14 +168,6 @@ rec {
       # https://github.com/llvm/llvm-project/pull/132173
       cmodel = "medium";
     };
-    linux-kernel = {
-      name = "loongarch-multiplatform";
-      target = "vmlinuz.efi";
-      autoModules = true;
-      preferBuiltin = true;
-      baseConfig = "defconfig";
-      DTB = true;
-    };
   };
 
   # This function takes a minimally-valid "platform" and returns an
@@ -267,17 +175,13 @@ rec {
   # included in the platform in order to further elaborate it.
   select =
     platform:
-    # x86
-    if platform.isx86 then
-      pc
-
     # ARM
-    else if platform.isAarch32 then
+    if platform.isAarch32 then
       let
         version = platform.parsed.cpu.version or null;
       in
       if version == null then
-        pc
+        { }
       else if lib.versionOlder version "6" then
         armv5tel-multiplatform
       else if lib.versionOlder version "7" then
@@ -291,24 +195,9 @@ rec {
     else if platform.isLoongArch64 then
       loongarch64-multiplatform
 
-    else if platform.isRiscV then
-      riscv-multiplatform
-
     else if platform.parsed.cpu == lib.systems.parse.cpuTypes.mipsel then
       (import ./examples.nix { inherit lib; }).mipsel-linux-gnu
 
-    else if platform.isPower64 then
-      if platform.isLittleEndian then powernv else ppc64
-
-    else if platform.isSh4 then
-      {
-        linux-kernel = {
-          target = "vmlinux";
-          # SH arch doesn't have a 'make install' target.
-          installTarget = "vmlinux";
-        };
-      }
-
     else
       { };
 }

nixos/modules/hardware/device-tree.nix

@@ -123,7 +123,8 @@ in
   options = {
     hardware.deviceTree = {
       enable = lib.mkOption {
-        default = pkgs.stdenv.hostPlatform.linux-kernel.DTB or false;
+        default = config.boot.kernelPackages.kernel.buildDTBs;
+        defaultText = lib.literalExpression "config.boot.kernelPackages.kernel.buildDTBs";
         type = lib.types.bool;
         description = ''
           Build device tree files. These are used to describe the

nixos/modules/installer/netboot/netboot.nix

@@ -111,7 +111,7 @@ with lib;
       #!ipxe
       # Use the cmdline variable to allow the user to specify custom kernel params
       # when chainloading this script from other iPXE scripts like netboot.xyz
-      kernel ${pkgs.stdenv.hostPlatform.linux-kernel.target} init=${config.system.build.toplevel}/init initrd=initrd ${toString config.boot.kernelParams} ''${cmdline}
+      kernel ${config.boot.kernelPackages.kernel.target} init=${config.system.build.toplevel}/init initrd=initrd ${toString config.boot.kernelParams} ''${cmdline}
       initrd initrd
       boot
     '';

nixos/modules/system/activation/top-level.nix

@@ -139,8 +139,8 @@ in
 
     system.boot.loader.kernelFile = mkOption {
       internal = true;
-      default = pkgs.stdenv.hostPlatform.linux-kernel.target;
+      default = config.boot.kernelPackages.kernel.target;
-      defaultText = literalExpression "pkgs.stdenv.hostPlatform.linux-kernel.target";
+      defaultText = literalExpression "config.boot.kernelPackages.kernel.target";
       type = types.str;
       description = ''
         Name of the kernel file to be passed to the bootloader.

nixos/modules/system/boot/loader/generations-dir/generations-dir.nix

@@ -66,7 +66,6 @@ in
 
     system.build.installBootLoader = generationsDirBuilder;
     system.boot.loader.id = "generationsDir";
-    system.boot.loader.kernelFile = pkgs.stdenv.hostPlatform.linux-kernel.target;
 
   };
 }

nixos/release.nix

@@ -152,7 +152,7 @@ let
     tarball
     // {
       meta = {
-        description = "NixOS system tarball for ${system} - ${stdenv.hostPlatform.linux-kernel.name}";
+        description = "NixOS system tarball for ${system}";
         maintainers = map (x: lib.maintainers.${x}) maintainers;
       };
       inherit config;
@@ -188,7 +188,7 @@ let
         modules = makeModules module { };
       };
       build = configEvaled.config.system.build;
-      kernelTarget = configEvaled.pkgs.stdenv.hostPlatform.linux-kernel.target;
+      kernelTarget = build.kernel.target;
     in
     configEvaled.pkgs.symlinkJoin {
       name = "netboot";

pkgs/build-support/vm/default.nix

@@ -27,11 +27,10 @@
 
   # ----------------------------
   # The following  arguments form the "interface" of `pkgs.vmTools`.
-  # Note that `img` is a real package, but is set to this default in `all-packages.nix`.
   # ----------------------------
   customQemu ? null,
   kernel ? linux,
-  img ? stdenv.hostPlatform.linux-kernel.target,
+  img ? kernel.target,
   storeDir ? builtins.storeDir,
   rootModules ? [
     "virtio_pci"

pkgs/os-specific/linux/kernel/build.nix

@@ -63,6 +63,19 @@ lib.makeOverridable (
     kernelPatches ? [ ],
     # The kernel .config file
     configfile,
+    target ?
+      if stdenv.hostPlatform.isx86 then
+        "bzImage"
+      else if stdenv.hostPlatform.isAarch32 then
+        "zImage"
+      else if stdenv.hostPlatform.isAarch64 || stdenv.hostPlatform.isRiscV then
+        "Image"
+      else if stdenv.hostPlatform.isLoongArch64 then
+        "vmlinuz.efi"
+      else
+        "vmlinux",
+    buildDTBs ?
+      stdenv.hostPlatform.isAarch || stdenv.hostPlatform.isRiscV || stdenv.hostPlatform.isLoongArch64,
     # Manually specified nixexpr representing the config
     # If unspecified, this will be autodetected from the .config
     config ? lib.optionalAttrs (builtins.isPath configfile || allowImportFromDerivation) (
@@ -139,9 +152,7 @@ lib.makeOverridable (
     isModular = config.isYes "MODULES";
     withRust = config.isYes "RUST";
 
-    target = stdenv.hostPlatform.linux-kernel.target or "vmlinux";
+    inherit buildDTBs target;
-
-    buildDTBs = stdenv.hostPlatform.linux-kernel.DTB or false;
 
     # Dependencies that are required to build kernel modules
     moduleBuildDependencies = [
@@ -204,7 +215,7 @@ lib.makeOverridable (
 
     buildFlags = [
       "KBUILD_BUILD_VERSION=1-NixOS"
-      stdenv.hostPlatform.linux-kernel.target
+      target
       "vmlinux" # for "perf" and things like that
       "scripts_gdb"
     ]
@@ -496,6 +507,8 @@ lib.makeOverridable (
         config
         kernelPatches
         configfile
+        target
+        buildDTBs
         moduleBuildDependencies
         stdenv
         commonMakeFlags
@@ -511,7 +524,7 @@ lib.makeOverridable (
 
     # Some image types need special install targets
     installTargets = [
-      (stdenv.hostPlatform.linux-kernel.installTarget or (
+      (
         if
           (target == "zImage" || target == "Image.gz" || target == "vmlinuz.efi")
           && builtins.elem stdenv.hostPlatform.linuxArch [
@@ -525,7 +538,6 @@ lib.makeOverridable (
         else
           "install"
       )
-      )
     ];
 
     karch = stdenv.hostPlatform.linuxArch;

pkgs/os-specific/linux/kernel/common-config.nix

@@ -1130,7 +1130,7 @@ let
         useZstd = stdenv.buildPlatform.is64bit;
       in
       {
-        # stdenv.hostPlatform.linux-kernel.target assumes uncompressed on RISC-V.
+        # The default target assumes uncompressed on RISC-V.
         KERNEL_UNCOMPRESSED = lib.mkIf stdenv.hostPlatform.isRiscV yes;
 
         KERNEL_XZ = lib.mkIf (

pkgs/os-specific/linux/kernel/common-flags.nix

@@ -36,5 +36,4 @@
     "CFLAGS_KERNEL=-I${clangLib}/lib/clang/${majorVer}/include"
   ]
 )
-++ (stdenv.hostPlatform.linux-kernel.makeFlags or [ ])
 ++ extraMakeFlags

pkgs/os-specific/linux/kernel/generic.nix

@@ -32,7 +32,16 @@ lib.makeOverridable (
     version,
 
     # Allows overriding the default defconfig
-    defconfig ? null,
+    # TODO: Reconsider some of these defaults?
+    defconfig ?
+      if stdenv.hostPlatform.isAarch32 && stdenv.hostPlatform.parsed.cpu.version or null == "5" then
+        "multi_v5_defconfig"
+      else if stdenv.hostPlatform.isAarch32 && stdenv.hostPlatform.parsed.cpu.version or null == "6" then
+        "bcm2835_defconfig"
+      else if stdenv.hostPlatform.isPower64 then
+        if stdenv.hostPlatform.isLittleEndian then "powernv_defconfig" else "ppc64_defconfig"
+      else
+        "defconfig",
 
     # Legacy overrides to the intermediate kernel config, as string
     extraConfig ? "",
@@ -66,20 +75,17 @@ lib.makeOverridable (
     # symbolic name and `patch' is the actual patch.  The patch may
     # optionally be compressed with gzip or bzip2.
     kernelPatches ? [ ],
-    ignoreConfigErrors ?
+    ignoreConfigErrors ? !(stdenv.hostPlatform.isx86 || stdenv.hostPlatform.isAarch64),
-      !lib.elem stdenv.hostPlatform.linux-kernel.name or "" [
-        "aarch64-multiplatform"
-        "pc"
-      ],
     extraMeta ? { },
     extraPassthru ? { },
 
     isLTS ? false,
     isZen ? false,
 
-    # easy overrides to stdenv.hostPlatform.linux-kernel members
+    autoModules ? true,
-    autoModules ? stdenv.hostPlatform.linux-kernel.autoModules or true,
+    # TODO: Remove this default?
-    preferBuiltin ? stdenv.hostPlatform.linux-kernel.preferBuiltin or false,
+    preferBuiltin ?
+      stdenv.hostPlatform.isAarch || stdenv.hostPlatform.isRiscV || stdenv.hostPlatform.isLoongArch64,
     kernelArch ? stdenv.hostPlatform.linuxArch,
     kernelTests ? { },
 
@@ -116,9 +122,7 @@ lib.makeOverridable (
     intermediateNixConfig =
       configfile.moduleStructuredConfig.intermediateNixConfig
       # extra config in legacy string format
-      + extraConfig
+      + extraConfig;
-      # need the 'or ""' at the end in case enableCommonConfig = true and extraConfig is not present
-      + lib.optionalString enableCommonConfig stdenv.hostPlatform.linux-kernel.extraConfig or "";
 
     structuredConfigFromPatches = map (
       {
@@ -205,8 +209,7 @@ lib.makeOverridable (
       buildPhase =
         let
           # e.g. "defconfig"
-          kernelBaseConfig =
+          kernelBaseConfig = defconfig;
-            if defconfig != null then defconfig else stdenv.hostPlatform.linux-kernel.baseConfig or "defconfig";
           kernelIntermediateConfig = writeText "kernel-intermediate-config" (
             kernelConfigFun intermediateNixConfig
           );

pkgs/top-level/all-packages.nix

@@ -909,9 +909,7 @@ with pkgs;
     inherit (darwin) signingUtils;
   };
 
-  vmTools = callPackage ../build-support/vm {
+  vmTools = callPackage ../build-support/vm { };
-    img = stdenv.hostPlatform.linux-kernel.target;
-  };
 
   releaseTools = callPackage ../build-support/release { };