Re: [xine-devel] MMX Motion compensation segfault

[Andrew M. <an...@an...>]

James Courtier-Dutton wrote:
> 
> Most segfaults in the Motion compensation code are due to bad mpeg streams.
> Does it segfault on all mpeg streams, or just the particular one you are
> using.

Oh its undoubtedly a bad stream, but the point was it happened to
segfault where I could just send in a stack trace in half a dozen
keystrokes. I was already looking at something else in the same area
with gdb. Nothing meant by it, other than the folks that know this stuff
backwards might be able to just go "Oh right ... that means that ABCD"
and jump straight to a fix. One more potential weekness (however small
and understandable) zapped, for when this stuff hits the prime time.

I've just discovered a set of extras on the MIB DVD that I didn't know
existed. Normal streams work just fine on my current build .... oss is
out quite badly and alsa09 spends most of its time adjusting its clock,
but ... I actually wonder if this has far more to do with alsa than
xine. Nothing else I use drives the sound system as hard and is so time
crytical.

I had a thought the other day, whether temporarily instrumenting these
areas would help things. How about something like:

o Grab the lower and upper bounds of the data,
  heap and stack areas and check these
  potentially dangerous pointers.

o If they are out of bounds, do something sensible
  to get past the problem.

o Send out a fairly rich exception that might help to
  form a pattern for those that have more knowledge in
  the specific areas.

If the exception was structured in a standardised way, folks could grep
them out of the playback of problem streams and give a better picture of
the stuff that is causing problems.

While I and the others here fully appreciate the fact that some data
sources are not what they could be and it isn't really a player issue; a
segfault might be a little severe for the more general "1.0 audience". A
blip in the colour or sound where they are used to pristine clarity,
will naturally focus their attention on the real source of the problem
.. the media.

Does this sound sensible?

Outer code issues like the build system, snapshots and the above, are
areas I would be very happy to help with. Delving in the depths of the
video_out stuff is something that demands a far greater knowledge of the
code than I have right now. On many of the projects I have run in the
commercial sector, intrumenting (in one form or another) really helps
the little stuff get fixed. Due to the slowdown in the training market,
I have just had the last of my outstanding work cancelled for the
forseeable, so I have the time to spend until things pick up a bit ...
if it would be useful.

Cheers

Andy M