On Mon, Nov 20, 2017 at 01:30:12PM -0800, Andy Lutomirski wrote: > On Mon, Nov 20, 2017 at 1:27 PM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > > On Mon, Nov 20, 2017 at 01:07:16PM -0800, Andy Lutomirski wrote: > >> >> but, more importantly, the OOPS unwinder will just bail without this > >> >> patch. With the patch, we get a valid unwind, except that everything > >> >> has a ? in front. > >> > > >> > Hm. I can't even fathom how that's possible. Are you talking about the > >> > "unwind from NMI to SYSENTER stack" path? Or any unwind to a syscall? > >> > Either way I'm baffled... If the unwinder only encounters the SYSENTER > >> > stack at the end, how could that cause everything beforehand to have a > >> > question mark? > >> > >> I mean that, if I put a ud2 or other bug in the code that runs on the > >> SYSENTER stack, without this patch, I get a totally blank call trace. > > > > I would expect a blank call trace either way... > > Try making sync_regs use a few kB of stack space or, better yet, call > a non-inlined function that uses too much stack.
You mean overflow the exception stack? I still don't see how that would do it. If you could show a specific example, with splats from before/after, that would be helpful. Because I still have no idea how this patch could possibly help. -- Josh
