[Bug runtime/13714] panic when sampling backtrace() in timer.profile

[mjw at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=13714

Mark Wielaard <mjw at redhat dot com> changed:

           What    |Removed                     |Added
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             Status|NEW                         |ASSIGNED
         AssignedTo|systemtap at sourceware dot |mjw at redhat dot com
                   |org                         |

--- Comment #2 from Mark Wielaard <mjw at redhat dot com> 2012-02-20 22:08:21 UTC ---
Found the root cause of this issue. It happens when a DW_CFA operation that
defines the CFA as dwarf expression is followed by a DW_CFA operation that
(re)defined the CFA as register+offset. In that case we forgot the reset the
REG_STATE.cfa_is_expr flag which made compute_expr() interpret the reg/offset
as expr pointer (because they share their values in a union).

While adding more sanity checks to make sure we catch such issues I found what
looks like bad CFI in the x86_64 kernel in common_interrupt
(arch/x86/kernel/entry_64.S) which defines CFI "by hand" and has a
CFI_DEF_CFA_REGISTER following a def_cfa_expression, which is invalid.

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