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Re: [RFC] Infinite backtraces...
The other thing that would help here is for glibc's CFI to identify the
return-address (and CFA) column as unknown (assuming I've got my CFI
term correct) on the outer most frame. It would then be easy for
dwarf2-unwind to identify this. It's been discussed, agreed, but not
implemented.
This is of course a good solution, provided that you can use dwarf2.
On 32bit HP/UX, we're stuck.
Doh!
Right, but it shouldn't need an additional method. The per-architecture
unwinder, when it detects a frame that the ABI specifies as final,
should return a null frame ID. For instance, the PPC ABI explicitly
specifies that it's stack be terminated with a zero SP.
I am not sure this is doable. Is it? Let me check that again. Perhaps
it's ok to create the frame object, but then later compute a null frame
ID for it? As far as I remember, the sequence of events is like this
when trying to build the frame chain:
. get_prev_frame (this_frame):
. get_frame_id (this_frame)
. frame_id (next_frame, this_cache)
. check this frame ID
. build previous frame
(frame ID unset)
Yes, gdb already creates the frame object and then later constructs the
frame ID. The build has been reduced to:
prev_frame = malloc ();
prev_frame->next = this_frame;
return prev_frame;
Also note that, unlike the past, the frame ID is separate to the ``frame
base'' the former can be NULL while the later is still valid.
And then, after building each new frame, we display the information
for that new frame.
It is what lets us "up" on to an apparently corrupt frame.
Finally, a more long term suggestion is that we add a mechanism for
creating or adding attributes to symbols (for instance for signal
trampolines). An atribute of such a symbol could be that it is
outermost.
But could we determine that a symbol is outermost. And couldn't the
same symbol be used in both contexts?
Determining that a symbol is outer-most is somewhat osabi dependant -
the arch dependant code would need to register or mark it up as such.
Yes, the symbol can be used in both contexts vis:
main (argc) { if (argc > 0) main (argc - 1); }
but I suspect it is illegal.
Andrew