+ /* For newer versions of qemu, you must run with -device
+ * isa-debug-exit, which exits on any write to an IO port (by
+ * default 0x501). Qemu's exit code is double the value plus one,
+ * so there is no way to exit cleanly. We use 0x31 which should
+ * result in a qemu exit code of 0x63. */
+ outb (0x501, 0x31);
+