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Re: Invalid program counters and unwinding
On 06/26/2018 12:56 PM, Nathan Sidwell wrote:
On 06/26/2018 05:26 AM, Florian Weimer wrote:
So it looks to me that the caller of _Unwind_Find_FDE needs to ensure
that the PC is a valid element of the call stack. Is this a correct
assumption?
I thought this was an (implicit?) requirement. You're unwinding a stack
to deliver an exception up it. Are there use cases where that is not
the case?
We have something approaching this scenario.
pthread_cancel in glibc unwinds the stack using DWARF information until
encounters a frame without unwind information, when it switches to
longjmp to get past that obstacle.
However, at the point of transition from a valid DWARF frame into the
wilderness (without unwind data), we should still have accurate
information on the caller's PC, so _Unwind_Find_FDE will reliably fail
to find any unwind data for it. It's not a random pointer somewhere
else, so I think even the pthread_cancel case is fully supported.
Thanks,
Florian