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The new _Unwind_GetIPInfo function allows us to determine if a frame's
IP points to the instruction following a call instruction, or to a
faulting instruction itself. In the case where it points to a following
instruction, we need to "roll back" the IP used in line-number lookup so
that the line number is that of the call itself, not the next line.
Previously we would do this roll-back unconditionally, but this meant
that exceptions generated by faults (eg NullPointerException) would
sometimes show the wrong line number on their inner-most frame. Using
_Unwind_GetIpInfo fixes this.
I'm also checking in a test case which verifies that stack trace line
numbers are correct (now that it finally passes!). I'm checking this in
to trunk.
Can you also add a check in configure if _Unwind_GetIPInfo exists?
See PR 26792 for why you need this (there is even a patch against libstdc++
for this configure test).