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654dce6c52
The kernel's 64-bit signal delivery (signal_64.c) uses:
newsp = frame - __SIGNAL_FRAMESIZE
while the 32-bit path (signal_32.c) uses:
newsp = frame - (__SIGNAL_FRAMESIZE + 16)
The extra 16 bytes in the 32-bit case is to place siginfo and ucontext
at the same offsets as older kernels (see the comment in signal_32.c).
The 64-bit rt_sigframe starts with ucontext directly and does not need
this adjustment.
QEMU's setup_rt_frame() unconditionally used (SIGNAL_FRAMESIZE + 16)
for both 32-bit and 64-bit, placing the handler's SP 16 bytes too low
on ppc64. Signal delivery and return still worked because do_rt_sigreturn
had the matching wrong offset, but the vDSO DWARF unwind info encodes
the correct kernel offset. This caused any DWARF unwinder (libunwind,
libgcc, etc.) to compute a CFA that is 16 bytes off, reading garbage
register values from the signal frame.
Define RT_SIGFRAME_ADJUST (0 on ppc64, 16 on ppc32) and use it in both
setup_rt_frame and do_rt_sigreturn to match the kernel.
This was verified by A/B testing with libunwind's test suite:
ppc64le: Gtest-bt, Ltest-bt, Gtest-concurrent, Ltest-concurrent,
and Ltest-sig-context all change from FAIL to PASS.
ppc64be: Gtest-bt, Ltest-bt, and Ltest-sig-context all change
from FAIL to PASS.
Signed-off-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: qemu-stable@nongnu.org