On 06/26/2018 01:15 PM, Nathan Sidwell wrote:
On 06/26/2018 07:01 AM, Florian Weimer wrote:
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.
This is a long jump to the originating pthread function at the end of
the stack, right? We not only get past the obstacle, but any and all
DWARF frames on top of it. (just for my understanding)
Essentially yes. It can also be an intermediate jump buffer, used to to
support compilation in -fno-exceptions mode. In that case, unwinding
tries to proceed from there, again with a valid PC.
That sounds right. It's a PC that you could return to if you weren't trying to unwind the stack.
GCC doesn't do this AFAIK, but it's theoretically possible not to
preserve the return address for a noreturn function. But that would be
very bad for exception handling, so let's hope compilers don't do this.
Florian
