On 28 December 2015 at 01:55, Michael Davidsaver <mdavidsa...@gmail.com> wrote: > On 12/17/2015 10:38 AM, Peter Maydell wrote: >> We could use a comment here (a) explaining what we're doing and (b) >> mentioning that this isn't architecturally correct -- ideally we should >> catch these exception exits on execution of the jump insn, not by >> letting the jump execute and then trapping when we actually try to >> execute at the magic addresses. > > I had an instructive little digression to investigate doing things the > "right way" (in tcg). I can see how it would be done by adding a > conditional every time the PC could be updated. To me the unassigned > handler trick/hack seems simpler (less likely to add a bug) and avoids > emitting more code for every ldm/pop instruction.
Yes, it's faster, which is why we do it this way. It is however not what the hardware does (in a way which is visible to guest code which is specifically looking for the difference), which is why it's worth commenting on. thanks -- PMM
