add rust kernel stub

nix/pkgs/bootler.nix

@@ -0,0 +1,49 @@
+{
+  stdenv,
+  nasm,
+  qemu,
+  ...
+}: let
+  bootImg = "boot";
+in
+  stdenv.mkDerivation {
+    pname = "bootler";
+    version = "0.1.0";
+    src = ../../.;
+    buildPhase = ''
+      ${nasm}/bin/nasm asm/boot.asm -o boot.bin
+      ${nasm}/bin/nasm asm/kernel.asm -o dummy.bin
+
+      dd if=/dev/zero of=${bootImg} bs=512 count=2
+      dd if=boot.bin of=${bootImg} conv=notrunc
+      dd if=dummy.bin of=${bootImg} bs=512 seek=1 conv=notrunc
+    '';
+    installPhase = ''
+      mkdir -p $out/bin
+      cp boot.bin $out/bin
+      cp dummy.bin $out/bin
+      cp ${bootImg} $out/bin
+
+      # create emulation binary
+      cat<<EOF>$out/bin/bootler
+      #!/usr/bin/env bash
+
+      # create temp dir
+      mkdir -p ./.bootler
+      cp $(echo $out)/bin/${bootImg} ./.bootler/${bootImg}
+      chmod a+w ./.bootler/${bootImg}
+
+      # run image
+      ${qemu}/bin/qemu-system-x86_64 \
+        -nographic \
+        -drive file=./.bootler/${bootImg},format=raw,index=0,media=disk
+
+      # clean up
+      rm ./.bootler -r
+
+      EOF
+
+      chmod +x $out/bin/${bootImg}
+      chmod +x $out/bin/bootler
+    '';
+  }