detect arch in kernel and uimage

also move kernel builder to pkgs/

FIXME we need to straighten out the mess in calling
dtb.nix/uimage.nix

modules/outputs.nix

@@ -62,14 +62,14 @@ in
       kernel = liminix.builders.kernel.override {
         inherit (config.kernel) config src extraPatchPhase;
       };
-      dtb =  (callPackage ../kernel/dtb.nix {}) {
+      dtb = liminix.builders.dtb {
         inherit (config.boot) commandLine;
         dts = config.hardware.dts.src;
         includes = config.hardware.dts.includes ++ [
           "${kernel.headers}/include"
         ];
       };
-      uimage = (callPackage ../kernel/uimage.nix {}) {
+      uimage = liminix.builders.uimage {
         commandLine = concatStringsSep " " config.boot.commandLine;
         inherit (config.hardware) loadAddress entryPoint;
         inherit kernel;

pkgs/default.nix

@@ -16,6 +16,8 @@ in {
     networking =  callPackage ./liminix-tools/networking {};
     builders =  {
       squashfs = callPackage ./liminix-tools/builders/squashfs.nix {};
+      dtb = callPackage ./kernel/dtb.nix {};
+      uimage = callPackage ./kernel/uimage.nix {};
       kernel = callPackage ./kernel {};
     };
     callService = path : parameters :

pkgs/kernel/default.nix

@@ -11,6 +11,12 @@
 let
   writeConfig = import ./write-kconfig.nix { inherit lib writeText; };
   kconfigFile = writeConfig "kconfig" config;
+  arch = if stdenv.isMips
+         then "mips"
+         else if stdenv.isAarch64
+         then "arm64"
+         else throw "unknown arch";
+
   inherit lib; in
 stdenv.mkDerivation rec {
   name = "kernel";
@@ -28,7 +34,7 @@ stdenv.mkDerivation rec {
     "-I${openssl.dev}/include -L${openssl.out}/lib -L${ncurses.out}/lib";
   PKG_CONFIG_PATH = "./pkgconfig";
   CROSS_COMPILE = stdenv.cc.bintools.targetPrefix;
-  ARCH = "mips";  # kernel uses "mips" here for both mips and mipsel
+  ARCH = arch;
   KBUILD_BUILD_HOST = "liminix.builder";
 
   dontStrip = true;

pkgs/kernel/uimage.nix

@@ -3,6 +3,7 @@
 , stdenv
 , ubootTools
 , dtc
+, lib
 } :
 let
   objcopy = "${stdenv.cc.bintools.targetPrefix}objcopy";
@@ -37,10 +38,20 @@ stdenv.mkDerivation {
 	  ${objcopy} --update-section .appended_dtb=tmp.dtb vmlinux.elf || ${objcopy} --add-section .appended_dtb=${dtb} vmlinux.elf
   '';
 
-  buildPhase = ''
+  buildPhase =
+    let arch =
+          # per output of "mkimage -A list". I *think* these
+          # are the same as the kernel arch convention, but
+          # maybe that's coincidence
+          if stdenv.isMips
+          then "mips"
+          else if stdenv.isAarch64
+          then "arm64"
+          else throw "unknown arch";
+    in ''
       ${objcopy} -O binary -R .reginfo -R .notes -R .note -R .comment -R .mdebug -R .note.gnu.build-id -S vmlinux.elf vmlinux.bin
       rm -f vmlinux.bin.lzma ; lzma -k -z  vmlinux.bin
-    mkimage -A mips -O linux -T kernel -C lzma -a ${loadAddress} -e ${entryPoint} -n 'MIPS Liminix Linux ${extraName}' -d vmlinux.bin.lzma kernel.uimage
+      mkimage -A ${arch} -O linux -T kernel -C lzma -a ${loadAddress} -e ${entryPoint} -n '${lib.toUpper arch} Liminix Linux ${extraName}' -d vmlinux.bin.lzma kernel.uimage
     '';
   installPhase = ''
     cp kernel.uimage $out