add support for OpenWrt device trees

kernel/uimage.nix

@@ -2,41 +2,47 @@
   lzma
 , stdenv
 , ubootTools
+, dtc
 } :
 let
   objcopy = "${stdenv.cc.bintools.targetPrefix}objcopy";
 in {
   vmlinux
-# , commandLine
-# , fdt ? null
+, commandLine
 , entryPoint
-# , extraName ? ""                # e.g. socFamily
+, extraName ? ""                # e.g. socFamily
 , loadAddress
+, dtb ? null
 } :
-  # patchDtbCommand = if (fdt != null) then ''
-  #   ( cat vmlinux.stripped ${fdt} > vmlinux.tmp ) && mv vmlinux.tmp vmlinux.stripped
-  # '' else ''
-  #   echo patch-cmdline vmlinux.stripped '${commandLine}'
-  #   patch-cmdline vmlinux.stripped '${commandLine}'
-  #   echo
-  # '';
 stdenv.mkDerivation {
   name = "kernel.image";
-  phases = [ "buildPhase" "installPhase" ];
+  phases = [
+    "preparePhase"
+    (if dtb != null then "dtbPhase" else ":")
+    "buildPhase"
+    "installPhase" ];
   nativeBuildInputs = [
-    # patchImage
     lzma
+    dtc
     stdenv.cc
     ubootTools
   ];
+  preparePhase = ''
+    cp ${vmlinux} vmlinux.elf; chmod +w vmlinux.elf
+  '';
+  dtbPhase = ''
+    dtc -I dtb -O dts -o tmp.dts ${dtb}
+    echo '/{ chosen { bootargs = ${builtins.toJSON commandLine}; }; };'  >> tmp.dts
+    dtc -I dts -O dtb -o tmp.dtb tmp.dts
+	  ${objcopy} --update-section .appended_dtb=tmp.dtb vmlinux.elf || ${objcopy} --add-section .appended_dtb=${dtb} vmlinux.elf
+  '';
+
   buildPhase = ''
-    ${objcopy} -O binary -R .reginfo -R .notes -R .note -R .comment -R .mdebug -R .note.gnu.build-id -S ${vmlinux} vmlinux.stripped
-    # {patchDtbCommand}
-    rm -f vmlinux.stripped.lzma
-    lzma -k -z  vmlinux.stripped
-    mkimage -A mips -O linux -T kernel -C lzma -a ${loadAddress} -e ${entryPoint} -n 'MIPS Liminix Linux ' -d vmlinux.stripped.lzma kernel.image
+    ${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
   '';
   installPhase = ''
-    cp kernel.image $out
+    cp kernel.uimage $out
   '';
 }