Hi,
On Fri, 21 Oct 2016, Florian Weimer wrote:
On 10/21/2016 02:58 PM, Michael Matz wrote:
+This function returns the same value as \code{\_Unwind\_GetIP}. In
+addition, the argument \code{ip\_before\_insn} must not be not null, and
+\code{*ip\_before\_insn} is updated with a flag which indicates whether
+the returned pointer is at or after the first not yet fully executed
+instruction.
I think this is rather misleading. On x86_64, the location of the IP
value is the same for calls and asynchronous signals: it always points
to the next instruction to be executed.
No, that's simply wrong. The saved instruction pointer points _at_ the
instruction causing the fault for faults, and _after_ the instruction for
traps. Traps are things like single-stepping, breakpoints or INTO. Most
other interrupts are faults or aborts (the latter being imprecise and
hence can't be restarted anyway).
For calls the saved instruction pointer always points to after the call
and hence can be handled like a trap for unwinding purposes.
Except for those situations where it doesn't, for which this function was
introduced to start with, in order to be able to differ between those
(basically the kernel needs to mark the signal frame as being the result
of a fault or a trap, and GetIPInfo uses this to set the flag).