[Mesa-dev] [PATCH v1] i915: fixing driver crashes if too few vertices are submitted

[Predut, Marius]

> -----Original Message-----
> From: Eirik Byrkjeflot Anonsen [mailto:eirik at eirikba.org]
> Sent: Wednesday, September 09, 2015 9:18 PM
> To: Predut, Marius; mesa-dev at lists.freedesktop.org
> Subject: Re: [Mesa-dev] [PATCH v1] i915: fixing driver crashes if too few
> vertices are submitted
> 
> Marius Predut <marius.predut at intel.com> writes:
> 
> > Comparison with a signed expression and unsigned value is converted to
> > unsigned value, reason for minus value is interpreted as a big
> > unsigned value. For this case the "for" loop is going into unexpected
> > behavior.
> >
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38109
> > Signed-off-by: Marius Predut <marius.predut at intel.com>
> > ---
> >  src/mesa/tnl_dd/t_dd_dmatmp.h | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/src/mesa/tnl_dd/t_dd_dmatmp.h
> > b/src/mesa/tnl_dd/t_dd_dmatmp.h index 7be3954..88ecc78 100644
> > --- a/src/mesa/tnl_dd/t_dd_dmatmp.h
> > +++ b/src/mesa/tnl_dd/t_dd_dmatmp.h
> > @@ -627,6 +627,8 @@ static void TAG(render_quads_verts)( struct gl_context
> *ctx,
> >        LOCAL_VARS;
> >        GLuint j;
> >
> > +      if(count%4 != 0) return;
> > +
> 
> Seems to me that does a bit more than just fixing the crash. I would think
> 
>         if (count < 4)
> 
> would fix the crash only. (And then quite possibly you won't need the next
> hunk?) But I have no idea whether the side effect is desired.
> 
> (Actually, what if count is 0? Or is that impossible?)

No count can't be 0 because is check filtered before in validate_render

> 
> eirik
> 
> >        INIT(GL_TRIANGLES);
> >
> >        for (j = start; j < count-3; j += 4) { @@ -1248,7 +1250,7 @@
> > static GLboolean TAG(validate_render)( struct gl_context *ctx,
> >  	    ok = (GLint) count < GET_SUBSEQUENT_VB_MAX_ELTS();
> >  	 }
> >  	 else {
> > -	    ok = HAVE_TRIANGLES; /* flatshading is ok. */
> > +	    ok = HAVE_TRIANGLES && (count%4 == 0); /* flatshading is ok. */
> >  	 }
> >  	 break;
> >        default:
> > --
> > 1.9.1
> >
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