[Ffmpeg-devel] Stack alignment warning

Michael Niedermayer michaelni
Sat Dec 16 01:24:28 CET 2006


On Fri, Dec 15, 2006 at 04:20:09PM -0700, Loren Merritt wrote:
> On Sat, 16 Dec 2006, Uoti Urpala wrote:
> >>2006/12/15, Ismail Donmez <ismail at pardus.org.tr>:
> >
> >> (support stack aligned local arrays)
> >
> >The warning test in ffmpeg does not use arrays (it's a single int
> >variable), and the alignment does seem to work for arrays too in gcc
> >4.1.
> In particular, gcc 3.4.3 completely ignores __attribute__((aligned(...)))
> for scalar variables and 1-element arrays, but obeys it on multi-element
> arrays (given the aligned-stack abi assumption, which was the original
> problem). Thus it miscompiles ff_check_alignment even though the other 
> instances of alignment are ok.

in dsputil_h264_template_mmx.c there is:
    DECLARE_ALIGNED_8(uint64_t, AA);
    DECLARE_ALIGNED_8(uint64_t, DD);

also there are plenty of const static uint64_t over the code though maybe
they are unaffected as they arent on the stack ...

iam not against changing the uint64_t to somethingelse[X] and doing the
same to ff_check_alignment() if this helps ...


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato

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