message: Tell the kernel where the app put its stack
  This doesn't have any correctness implications, but it does help with
  debugging when the app memory map is printed during debugging.
diff: @@ -71,6 +71,10 @@ pub unsafe extern "C" fn _start(
  asm!("mov sp, $0" : : "r"(effective_stack_top) : "memory" : "volatile" );
  + syscalls::memop(0, effective_stack_top + HEAP_SIZE);
  + syscalls::memop(11, effective_stack_top + HEAP_SIZE);
  + syscalls::memop(10, effective_stack_top);
  +
  main(0, ptr::null());
  loop {
  