message: more documentation of unintuitive packed struct solution
diff: @@ -28,6 +28,7 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  /// Returns true as long as there are more things to do.
  pub fn step(&mut self) -> EvalResult<'tcx, bool> {
  + // see docs on the `Memory::packed` field for why we do this
  self.memory.clear_packed();
  self.inc_step_counter_and_check_limit(1)?;
  if self.stack.is_empty() {
  