bootable aarch64 liminux with qemu

I may have broken the run-liminix-vm command a bit for MIPS due to
necessary changes in how we pass the command line.  If CI isn't green
for this commit and youre trying the worked examples, I suggest
reverting to the commit before this one.

devices/qemu-aarch64/default.nix

@@ -0,0 +1,69 @@
+# This "device" generates images that can be used with the QEMU
+# emulator. The default output is a directory containing separate
+# kernel ("Image" format) and root filesystem (squashfs or jffs2)
+# images
+{
+  system = {
+    crossSystem = {
+      config = "aarch64-unknown-linux-musl";
+    };
+  };
+
+  module = {pkgs, config, ... }: {
+    imports = [ ../../modules/arch/aarch64.nix ];
+    kernel = {
+      src = pkgs.pkgsBuildBuild.fetchurl {
+        name = "linux.tar.gz";
+        url = "https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.15.71.tar.gz";
+        hash = "sha256-yhO2cXIeIgUxkSZf/4aAsF11uxyh+UUZu6D1h92vCD8=";
+      };
+      config = {
+        VIRTUALIZATION = "y";
+        PCI_HOST_GENERIC="y";
+
+        MTD = "y";
+        MTD_BLOCK2MTD = "y";
+        MTD_BLKDEVS = "y";
+        MTD_BLOCK = "y";
+
+        VIRTIO_MENU = "y";
+        PCI = "y";
+        VIRTIO_PCI = "y";
+        BLOCK = "y";
+        VIRTIO_BLK = "y";
+        NETDEVICES = "y";
+        VIRTIO_NET = "y";
+
+        SERIAL_EARLYCON_ARM_SEMIHOST = "y"; # earlycon=smh
+        SERIAL_AMBA_PL011 = "y";
+        SERIAL_AMBA_PL011_CONSOLE = "y";
+      };
+    };
+    hardware =
+      let
+        mac80211 =  pkgs.mac80211.override {
+          drivers = ["mac80211_hwsim"];
+          klibBuild = config.system.outputs.kernel.modulesupport;
+        };
+      in {
+        defaultOutput = "vmroot";
+        loadAddress = "0x0";
+        entryPoint  = "0x0";
+        rootDevice = "/dev/mtdblock0";
+
+        flash.eraseBlockSize = "65536"; # c.f. pkgs/mips-vm/mips-vm.sh
+        networkInterfaces =
+          let inherit (config.system.service.network) link;
+          in {
+            wan = link.build { ifname = "eth0"; };
+            lan = link.build { ifname = "eth1"; };
+
+            wlan_24 = link.build {
+              ifname = "wlan0";
+              dependencies = [ mac80211 ];
+            };
+          };
+      };
+
+  };
+}

devices/qemu/default.nix

@@ -49,6 +49,7 @@
         };
       in {
         defaultOutput = "vmroot";
+        rootDevice = "/dev/mtdblock0";
         flash.eraseBlockSize = "65536"; # c.f. pkgs/run-liminix-vm/run-liminix-vm.sh
         networkInterfaces =
           let inherit (config.system.service.network) link;

modules/arch/aarch64.nix

@@ -0,0 +1,16 @@
+{ lib, pkgs, config, ...}:
+{
+  config = {
+    kernel.config = {
+      CPU_LITTLE_ENDIAN= "y";
+      CPU_BIG_ENDIAN= "n";
+      # CMDLINE_FROM_BOOTLOADER availability is conditional
+      # on CMDLINE being set to something non-empty
+      CMDLINE="\"console=ttyAMA0\"";
+      CMDLINE_FROM_BOOTLOADER = "y";
+    };
+    boot.commandLine = [
+      "console=ttyAMA0,38400"
+    ];
+  };
+}

modules/outputs.nix

@@ -7,6 +7,12 @@
 let
   inherit (lib) mkOption types concatStringsSep;
   inherit (pkgs) liminix callPackage writeText;
+  arch = let s = pkgs.stdenv; in
+         if s.isAarch64
+         then "aarch64"
+         else if s.isMips
+         then "mips"
+         else throw "can't determine arch";
 in
 {
   imports = [
@@ -76,14 +82,27 @@ in
         inherit dtb;
       };
       # could use trivial-builders.linkFarmFromDrvs here?
-      vmroot = pkgs.runCommand "qemu" {} ''
-        mkdir $out
-        cd $out
-        ln -s ${config.system.outputs.rootfs} rootfs
-        ln -s ${kernel} vmlinux
-        ln -s ${manifest} manifest
-        ln -s ${kernel.headers} build
-      '';
+      vmroot =
+        let
+          cmdline = builtins.toJSON (concatStringsSep " " config.boot.commandLine);
+          makeBootableImage = pkgs.runCommandCC "objcopy" {}
+            (if pkgs.stdenv.isAarch64
+             then "${pkgs.stdenv.cc.targetPrefix}objcopy -O binary -S ${kernel} $out"
+             else "cp ${kernel} $out");
+        in pkgs.runCommandCC "vmroot" {} ''
+          mkdir $out
+          cd $out
+          ln -s ${config.system.outputs.rootfs} rootfs
+          ln -s ${kernel} vmlinux
+          ln -s ${manifest} manifest
+          ln -s ${kernel.headers} build
+          echo ${cmdline} > commandline
+          cat > run.sh << EOF
+          #!${pkgs.runtimeShell}
+          CMDLINE=${cmdline} run-liminix-vm --arch ${arch} ${makeBootableImage} ${config.system.outputs.rootfs}
+          EOF
+          chmod +x run.sh
+       '';
 
       manifest = writeText "manifest.json" (builtins.toJSON config.filesystem.contents);
     };

pkgs/run-liminix-vm/run-liminix-vm.sh

@@ -12,6 +12,12 @@ usage(){
     exit 1
 }
 
+arch="mips"
+if test "$1" = "--arch" ; then
+    arch=$2
+    shift;shift
+fi
+
 if test "$1" = "--background" ; then
     statedir=$2
     if test -z "$statedir" || ! test -d $statedir ; then
@@ -39,13 +45,21 @@ if test -n "$3"; then
     initramfs="-initrd $3"
 fi
 
+case "$arch" in
+    mips)
+	QEMU="qemu-system-mips -M malta"
+	;;
+    aarch64)
+	QEMU="qemu-system-aarch64 -M virt -semihosting -cpu cortex-a72"
+	;;
+esac
 
 INIT=${INIT-/bin/init}
-echo $QEMU_OPTIONS
-qemu-system-mips \
-    -M malta -m 256 \
+set -x
+$QEMU \
+    -m 256 \
     -echr 16 \
-    -append "liminix default console=ttyS0,38400n8 panic=10 oops=panic init=$INIT loglevel=8 root=/dev/mtdblock0 block2mtd.block2mtd=/dev/vda,65536" \
+    -append "$CMDLINE liminix root=/dev/mtdblock0 block2mtd.block2mtd=/dev/vda,65536" \
     -drive file=$rootfs,format=raw,readonly=off,if=virtio,index=0 \
     ${initramfs} \
     -netdev socket,id=access,mcast=230.0.0.1:1234,localaddr=127.0.0.1 \