[Bug runtime/14107] Bad user unwinding from kernel fatal signal handler for some x86_64 kernels

[mjw at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=14107

--- Comment #1 from Mark Wielaard <mjw at redhat dot com> 2012-05-14 15:47:52 UTC ---
The issue is that on x86_64 (it doesn't happen on i686) stap tries to recover
the user space registers by unwinding the kernel stack. This succeeds on the
f16 kernel and then the unwinder takes those recovered registers to do the user
space unwind. But it fails on the rhel6 kernel. See -DDEBUG_UNWIND=99 output:

_stp_get_uregs:194: unwind levels: 15, ret: -5, pc=0xffffffff814ef8f5
_stp_get_uregs:209: failed to recover user reg state

And the for user space the unwinder has to do with partial register values and
fails...

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