[RFC] frame_id_inner check and -fsplit-stack
Tue Dec 29 19:07:00 GMT 2009
Ian Taylor just reported on the GDB IRC that the frame_id_inner
check in get_prev_frame_1 is making debugging difficult when
the program has been built with -fsplit-stack. This option
<<permits discontiguous stack segments. The stack segments are
just allocated using mmap, so there is no particular ordering>>.
As a result, if two frames are on different stack segments,
the ordering of the segments might be such that two valid frames
might be failing the frame_id_inner check.
Discussing with Ian, he indicated that it should be easy to produce
a section with magic name. This would allow us to determine that
the program uses split-stack and that the frame_id_inner may not
I can see the following options:
1. do nothing (ahem);
2. remove the check entirely; we currently apply it I think
when the two frames are normal frames. We already skip it
when either frame is not normal.
3. provide a user setting that allows the user to tell GDB
that the program uses split stacks;
4. skip the test when split stacks is detected.
I don't think we should really consider option (3) if we can indeed
easily detect split-stack. (1) seems a bit harsh. I am Ok with either
(2) or (4). It sounds like Ian is willing to make it easy for us to
detect split-stack, so I'd vote for (4). Given that nearly all the code
we debug does not use split-stack, we can keep the frame_id_inner check
a while longer...
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