Re: reliable reproducer, was Re: core dump analysis

Finn Thain
2023-04-24T23:41:50Z

On Mon, 24 Apr 2023, Michael Schmitz wrote:

> > I don't understand these results. If usp was really overwritten, the
> > program would have crashed early, no?
>
> I think we're still at the point where rec() is called recursively,
> before any returns.

Right. I wasn't thinking.

I'll try to confirm that each "overwrote usp" error from movemlrt.c
corresponds to visible corruption at the given address in the core dump.

> >> Exception right before crash was an interrupt in this case (only seen
> >> that once in this context, though I've seen lots of those in the
> >> course of the test runs). Frame start calculated from siginfo pointer
> >> value in this case.
> >
> > I didn't realize that you could get a crash from a signal delivered
> > following an interrupt. I'll try to modify the kernel such that
> > signals are not delivered after page faults.
>
> Yes, that was news to me, too.
>

That seems to be a mistake (?) I didn't see any failures when I patched
the kernel to skip signal delivery after a page fault.