On Thu, Jun 23, 2016 at 09:35:29AM -0700, Andy Lutomirski wrote:

quoted

So which is the least-bad option?  To summarize:

  1) task flag(s) for preemption and page faults

  2) turn pt_regs into a stack frame

  3) annotate all calls from entry code in a table

  4) encode rbp on entry

They all have their issues, though I'm partial to #2.

Any more hare-brained ideas? :-)

I'll try to take a closer look at #2 and see just how much I dislike
all the stack frame munging.

Ok.

Also, in principle, it's only the
sleeping calls and the calls that make it into real (non-entry) kernel
code that really want to be unwindable through this mechanism.

Yeah, that's true.  We could modify options 2 or 3 to be less absolute.
Though I think that makes them more prone to future breakage.

FWIW, I don't care that much about preserving gdb's partial ability to
unwind through pt_regs, especially because gdb really ought to be able
to use DWARF, too.

Hm, that's a good point.  I really don't know if there are any other
external tools out there that would care.  Maybe we could try option 4
and then see if anybody complains.

-- 
Josh