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. > > In fact I just added a ud1 after your RDI save, and got a blank call > trace. > > Also the RIP printout isn't very helpful, I guess kallsyms doesn't know > about the trampoline? Um, right. I should fix that.
