make tftpboot work on devices with old u-boot

Some devices have a U-boot variant that does not accept a third
parameter on the "bootm" command, meaning we can't override the dtb
in the bootloader so have to smush it back into the kernel image

This is WIP because
- still hardcodes MIPS
- doesn't work in QEMU

Based on
https://gti.telent.net/raboof/liminix/src/branch/tftp-old-uboot

Co-authored-by:  Arnout Engelen <arnout@bzzt.net>

modules/outputs/tftpboot.nix

@@ -7,6 +7,7 @@
 let
   inherit (lib) mkOption types concatStringsSep;
   cfg = config.boot.tftp;
+  hw = config.hardware;
 in {
   imports = [ ../ramdisk.nix ];
   options.boot.tftp = {
@@ -22,6 +23,10 @@ in {
       type = types.bool;
       default = false;
     };
+    appendDTB = mkOption {
+      type = types.bool;
+      default = false;
+    };
   };
   options.system.outputs = {
     tftpboot = mkOption {
@@ -62,24 +67,46 @@ in {
             uimage = "bootm";
             zimage = "bootz";
           }; in choices.${cfg.kernelFormat};
+
           cmdline = concatStringsSep " " config.boot.commandLine;
+          objcopy = "${pkgs.stdenv.cc.bintools.targetPrefix}objcopy";
+          stripAndZip = ''
+            ${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
+          '';
         in
-          pkgs.runCommand "tftpboot" { nativeBuildInputs = with pkgs.pkgsBuildBuild; [ lzma dtc ];  } ''
+          pkgs.runCommand "tftpboot" { nativeBuildInputs = with pkgs.pkgsBuildBuild; [ lzma dtc pkgs.stdenv.cc ubootTools ];  } ''
             mkdir $out
             cd $out
             binsize() { local s=$(stat -L -c %s $1); echo $(($s + 0x1000 &(~0xfff))); }
             binsize64k() { local s=$(stat -L -c %s $1); echo $(($s + 0x10000 &(~0xffff))); }
             hex() { printf "0x%x" $1; }
+
             rootfsStart=${toString cfg.loadAddress}
             rootfsSize=$(binsize64k ${o.rootfs} )
             rootfsSize=$(($rootfsSize + ${toString cfg.freeSpaceBytes} ))
-            dtbStart=$(($rootfsStart + $rootfsSize))
-            imageSize=$(binsize ${image})
 
             ln -s ${o.manifest} manifest
-            ln -s ${image} image
             ln -s ${o.kernel} vmlinux  # handy for gdb
 
+            # if we are transferring kernel and dtb separately, the
+            # dtb has to precede the kernel in ram, because zimage
+            # decompression code will assume that any memory after the
+            # end of the kernel is free
+
+            dtbStart=$(($rootfsStart + $rootfsSize))
+            ${if cfg.compressRoot
+              then ''
+                lzma -z9cv ${o.rootfs} > rootfs.lz
+                rootfsLzStart=$dtbStart
+                rootfsLzSize=$(binsize rootfs.lz)
+                dtbStart=$(($dtbStart + $rootfsLzSize))
+              ''
+              else ''
+                ln -s ${o.rootfs} rootfs
+              ''
+             }
+
             cat ${o.dtb} > dtb
             address_cells=$(fdtget dtb / '#address-cells')
             size_cells=$(fdtget dtb / '#size-cells')
@@ -93,34 +120,41 @@ in {
             fdtput -p -t s dtb /reserved-memory/$node compatible phram
             fdtput -p -t lx dtb /reserved-memory/$node reg $ac_prefix $(hex $rootfsStart) $sz_prefix $(hex $rootfsSize)
 
-            dtbSize=$(binsize ./dtb )
-            imageStart=$(($dtbStart + $dtbSize))
-            ${if cfg.compressRoot
-              then ''
-                lzma -z9cv ${o.rootfs} > rootfs.lz
-                rootfsLzStart=$(($imageStart + $imageSize))
-                rootfsLzSize=$(binsize rootfs.lz)
-              ''
-              else "ln -s ${o.rootfs} rootfs"
-             }
-
             cmd="liminix ${cmdline} mtdparts=phram0:''${rootfsSize}(rootfs) phram.phram=phram0,''${rootfsStart},''${rootfsSize},${toString config.hardware.flash.eraseBlockSize} root=/dev/mtdblock0";
             fdtput -t s dtb /chosen bootargs "$cmd"
 
-            # dtc -I dtb -O dts -o /dev/stdout dtb | grep -A10 chosen ; exit 1
+            dtbSize=$(binsize ./dtb )
+
+            ${if cfg.appendDTB then ''
+              imageStart=$dtbStart
+              # re-package image with updated dtb
+              cat ${o.kernel} > vmlinux.elf
+              ${objcopy} --update-section .appended_dtb=dtb vmlinux.elf
+              ${stripAndZip}
+              # TODO don't hardcode mips, entryPoint, loadAddress, name
+              mkimage -A mips -O linux -T kernel -C lzma -a $(hex ${toString hw.loadAddress}) -e $(hex ${toString hw.entryPoint}) -n 'MIPS Liminix Linux' -d vmlinux.bin.lzma image
+              # dtc -I dtb -O dts -o /dev/stdout dtb | grep -A10 chosen ; exit 1
+              tftpcmd="tftpboot $(hex $imageStart) result/image "
+              bootcmd="bootm $(hex $imageStart)"
+            '' else ''
+              imageStart=$(($dtbStart + $dtbSize))
+              tftpcmd="tftpboot $(hex $imageStart) result/image; tftpboot $(hex $dtbStart) result/dtb "
+              ln -s ${image} image
+              bootcmd="${bootCommand} $(hex $imageStart) - $(hex $dtbStart)"
+            ''}
 
             cat > boot.scr << EOF
             setenv serverip ${cfg.serverip}
             setenv ipaddr ${cfg.ipaddr}
-            tftpboot $(hex $imageStart) result/image ; ${
+            ${
               if cfg.compressRoot
               then "tftpboot $(hex $rootfsLzStart) result/rootfs.lz"
               else "tftpboot $(hex $rootfsStart) result/rootfs"
-            }; tftpboot $(hex $dtbStart) result/dtb
+            }; $tftpcmd
             ${if cfg.compressRoot
               then "lzmadec $(hex $rootfsLzStart)  $(hex $rootfsStart); "
               else ""
-             } ${bootCommand} $(hex $imageStart) - $(hex $dtbStart)
+             } $bootcmd
             EOF
          '';
 

tests/tftpboot/test.nix

@@ -12,7 +12,7 @@ let derivation = (import liminix {
     img = derivation.outputs.tftpboot;
     uboot = derivation.outputs.u-boot;
     pkgsBuild = derivation.pkgs.pkgsBuildBuild;
-in pkgsBuild.runCommand "check" {
+in pkgsBuild.runCommand "check-${deviceName}" {
   nativeBuildInputs = with pkgsBuild; [
     expect
     socat
@@ -44,4 +44,7 @@ in {
   mipsLz = check  "qemu" {
     boot.tftp.compressRoot = true;
   };
+  mipsOldUboot = check  "qemu" {
+    boot.tftp.appendDTB = true;
+  };
 }