[FFmpeg-devel] [PATCH 3/3] avcodec/x86/diracdsp: Fix incorrect src addressing in dequant_subband_32()

Michael Niedermayer michael at niedermayer.cc
Fri Jan 31 00:56:35 EET 2020


On Thu, Jan 30, 2020 at 11:11:27PM +0100, Carl Eugen Hoyos wrote:
> Am Mi., 29. Jan. 2020 um 22:56 Uhr schrieb Michael Niedermayer
> <michael at niedermayer.cc>:
> >
> > Fixes: Segfault (not reproducable with asm, which made this hard to debug)
> 
> without?

wellllll
i had the testcase from ossfuzz but that didnt reproduce any anomaly at all
and the back traces from ossfuzz from the server where it did crash are
just useless when asm is involved.

so with a bit of guessing and guessing wrong (thought first its alignment)
and more guessing and looking at the asm i modified the C 
implementation to behave like the SSE4 that then allowed reproducing the crash
and seperately after that building a valid testfile which triggers this
codepath to allow testing the fix.
And a few more things here and there
And still theres was a bug left in the fix :(


Thanks

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is what and why we do it that matters, not just one of them.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: not available
URL: <https://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20200130/efecd9dd/attachment.sig>


More information about the ffmpeg-devel mailing list