The attached testcase usually segfaults on i?86-linux and x86_64-linux
(and likely on most other DWARF2_UNWIND_INFO 1 targets, though the testcase
would need to be tweaked for them).
The problem is that instruction pointer saved in the signal frame is after
last successfully executed instruction and before first non-executed
instruction,
while .eh_frame and unwind-dw2.c basically expects context->ra to be after the
first non-executed instruction.
To find FDE, unwind-dw2.c uses context->ra - 1, which is good for normal
unwinding, but if e.g. a signal is sent while $pc is at the very beginning
of some function, context->ra - 1 either corresponds to a previous function
or is not covered by any FDE.
Similarly, execute_cfa_program has a loop:
while (insn_ptr < insn_end && fs->pc < context->ra)
which is good in most cases, but when context->ra is saved IP from sigcontext
in signal frame, this means that the last set of unwind instructions will
not be executed, while it ought to (for signal frame context->ra we'd need
to also execute fs->pc == context->ra instructions).
--
Summary: Serious problem with unwinding through signal frames
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jakub at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26208
