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 doesn't work in QEMU but I think the problem is with the
U-Boot configuration for QEMU. It does work on at least one
hardware device so I'm pushing it anyway

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 +7,8 @@
 let
   inherit (lib) mkOption types concatStringsSep;
   cfg = config.boot.tftp;
+  hw = config.hardware;
+  arch = pkgs.stdenv.hostPlatform.linuxArch;
 in {
   imports = [ ../ramdisk.nix ];
   options.boot.tftp = {
@@ -22,6 +24,10 @@ in {
       type = types.bool;
       default = false;
     };
+    appendDTB = mkOption {
+      type = types.bool;
+      default = false;
+    };
   };
   options.system.outputs = {
     tftpboot = mkOption {
@@ -62,24 +68,46 @@ 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=$(fdtget dtb / '#size-cells')
@@ -93,34 +121,40 @@ in {
             fdtput -p -t s dtb /reserved-memory/$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}
+              mkimage -A ${arch} -O linux -T kernel -C lzma -a $(hex ${toString hw.loadAddress}) -e $(hex ${toString hw.entryPoint}) -n '${lib.toUpper arch} Liminix Linux tftpboot' -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 +44,11 @@ in {
   mipsLz = check  "qemu" {
     boot.tftp.compressRoot = true;
   };
+  # this works on real hardware but I haven't figured out how
+  # to make it work on qemu: it says
+  # "OF: fdt: No chosen node found, continuing without"
+
+  # mipsOldUboot = check  "qemu" {
+  #   boot.tftp.appendDTB = true;
+  # };
 }