On Sun, 30 Nov 2003, Nicolas Boos wrote:
> Hey, mine is 2.2.5 (Debian Woody) !
Oops. I misremembered it then - but the symptom/bug looks
to be the same one.
> For the moment, I'm using "#undef HAVE_POSIX_MEMALIGN" instead of
> "#define HAVE_POSIX_MEMALIGN 1" in configure as workaround.
I still believe the problem is alignment related. The compatibility
function posix_memalign() has to rely on the underlying malloc()
to perform alignment. Systems which use a power-of-two allocation
scheme (basically all the BSD systems) can force alignment to a
specified boundary by adjusting the allocation size. However,
if the malloc() function does not perform alignment (and I am beginning
to suspect that glibc's does not - at least prior to 2.3.x)) then
the buffers will not be aligned on a 16 byte boundary. SSE
instructions apparently fault if their operands are not correctly
aligned in memory.
As a temporary measure you can try editing the compat function
posix_memalign to return an aligned address. NOTE: this will result
in a pointer that can NOT be passed to 'free()' - which makes this an
unacceptable solution in the long term (but as an experiment it would
be worth trying).
> Yes, It's probably SSE related (mpeg2enc runs fine on my old Celeron),
> but don't know exactly for the glibc case.
Ah, ok - I am becoming convinced that the issue is buffer alignment.
Finding the correct place to disable use of SSE and forcing that
capability off would be one experiment to try, the other way would
be to adjust the return value of posix_memalign(). The long term
fix is to upgrade glibc of course ;)
Cheers,
Steven Schultz
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