Re: [patch/rfa/hppa] Use frame pointer for unwinding

[Andrew Cagney <cagney@gnu.org>]

>+    if (frame_pc_unwind (next_frame) >= prologue_end
>+        && u->Save_SP && fp != 0)

fp will effectively always be non-zero here, so the ``fp != 0'' is a 
just-in-case?  Suggest adding that, and the GCC bug-number, as additions 
to the comments.


ok. there is no gcc bug yet, but i will file one.

the fp != 0 is there probably because i don't understand correctly how
the unwinder is working. if you have three frames:
frame 3 - unwind from here
frame 2 - doesn't save fp; fp should be constant in this function
frame 1 - saves fp
frame 3 gets frame 2 as next_frame, will it be able to get the value of
fp (from what is saved in frame 1)? it seems to work in my tests, but 
i haven't yet figured out how it works in the code. if frame 2 doesn't
(I'm assuming that the above stack backtrace is in reverse order to what 
GDB would display)

save a register in its cache, is there some code that by default 
propagates the values from the next frame?
yes, if frame-2 didn't save fp, then the trad-frame code will assume 
that frame-3's fp value is frame-2's fp value, and there for ask frame-1 
to unwind it (a recursive call).

Andrew