[RFC PATCH] powerpc/64/signal: balance return predictor stack in signal trampoline

[Alan Modra]

On Fri, Apr 17, 2020 at 07:17:47PM +1000, Nicholas Piggin wrote:
> I don't know much about dwarf, gdb still seems to recognize the signal
> frame and unwind properly if I break inside a signal handler.

Yes, the dwarf unwind info still looks good.  The commented out dwarf
near the end of sigtramp.S should probably go.  At least if you really
can't take an async signal in the trampoline (a kernel question, not
anything to do with gcc support of async signals as the comment
wrongly says).  If you *can* take an async signal at some point past
the trampoline addi, then delete the comment and uncomment the code.
Note that the advance_loc there bitrotted ever since the nop was added
before the trampoline, so you'd need to change that to an advance_loc
that moves from .Lsigrt_start to immediately after the addi, ie. 0x42.

-- 
Alan Modra
Australia Development Lab, IBM