[RFC] Infinite backtraces...
Fri Dec 3 18:49:00 GMT 2004
> I've a finish up a patch that checks for this:
> > #6 0x7aee0f08 in __pthread_create_system () from /usr/lib/libpthread.1
> > #7 0x00000000 in ?? ()
> I.e., a zero pc unwound from a normal frame. It is ``tricky'' to test
> though :-(
That's pretty much what I have done as a proof of concept.
I ran it through the testsuite on our HP machine, and we got
3 new passes (from 3 unresolved, due to the expect buffer filling up).
> 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
This is of course a good solution, provided that you can use dwarf2.
On 32bit HP/UX, we're stuck.
> 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)
And then, after building each new frame, we display the information
for that new 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
But could we determine that a symbol is outermost. And couldn't the
same symbol be used in both contexts?
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