Fixes qemu issues.

.gitignore

@@ -1 +1,2 @@
 result
+sd-card.img

flake.nix

@@ -25,7 +25,9 @@
 
       vmscript = pkgs.writeScriptBin "vmscript" ''
       #!${pkgs.runtimeShell}
-      img=${self.outputs.packages.${system}.uncompressed}/sd-card.img
+      img=./sd-card.img
+      cp ${self.outputs.packages.${system}.uncompressed}/sd-card.img $img
+      chmod 640 $img
       ${pkgs.qemu}/bin/qemu-system-aarch64 \
         -machine raspi3b \
         -kernel "${crossPkgs.ubootRaspberryPi3_64bit}/u-boot.bin" \

sd-card.nix

@@ -5,7 +5,7 @@ let
     offset = 8;
     id = "0xfeed3425";
     name = "FIRMWARE";
-    size = 512;
+    size = 504; # offset + size = 512. Must be power of two.
   };
   rootfsImage = import ./rootfs.nix { inherit pkgs; };