[MPlayer-dev-eng] Segfault caused by the "expand" filter

[Reimar Döffinger]

On Sat, Mar 19, 2011 at 10:30:14PM +0800, Zuxy Meng wrote:
> 2011/3/17 Reimar Döffinger <Reimar.Doeffinger at gmx.de>:
> > On Wed, Mar 16, 2011 at 06:19:04PM +0800, Zuxy Meng wrote:
> >> 2011/3/16 Reimar Döffinger <Reimar.Doeffinger at gmx.de>:
> >> > On 15 Mar 2011, at 03:57, Zuxy Meng <zuxy.meng at gmail.com> wrote:
> >> >> Hope here's still atmosphere for technical discussions:
> >> >>
> >> >> I met segfaults triggered by unaligned accesses of SSE instructions.
> >> >> The root cause is within the get_image() function of the "expand"
> >> >> filter, in lines like:
> >> >>
> >> >>    if(mpi->flags&MP_IMGFLAG_PLANAR){
> >> >>        mpi->planes[0]=vf->dmpi->planes[0]+
> >> >>        vf->priv->exp_y*vf->dmpi->stride[0]+vf->priv->exp_x;
> >> >>
> >> >> Here vf->dmpi->planes[0] is 16-byte aligned, but mpi->planes[0] may not be.
> >> >>
> >> >> I'm not sure what's the correct fix here. Would a simple forced align
> >> >> before the assignment work (e.g. ((vf->dmpi->planes[0] + ...)&~15))?
> >> >
> >> > To solve it properly you have to allocate a new image and memcpy instead of using EXPORT image type (or is this the DR path? Disable DR in that case).
> >>
> >> Yes I guess it's the DR path.
> >>
> >> > Alternatively filters requiring the alignment could do the memcpy, but I think that's more effort for little gain.
> >>
> >> The problem happens when expand isn't the last filter, e.g. vf=expand...,pp=ac
> >
> > That doesn't make sense, the line you quoted only causes the filters (and decoder)
> > _before_ to get unaligned pointers.
> 
> I'm puzzled too. But in my case vf=pp=ac,expand=::::1:8/5 works and
> vf=expand=::::1:8/5,pp=ac crashes.

That doesn't say anything at all about where and why the crash happens.
Probably the pp filter allocates a new frame to pass to the decoder whereas
it itself doesn't need the pointers to be aligned