[Mesa-dev] [PATCH v2 2/2] i965: Fix invalid pointer read in dead_control_flow_eliminate().

[Kenneth Graunke]

On Monday, April 4, 2016 12:19:57 AM PDT Jason Ekstrand wrote:
> On Sun, Apr 3, 2016 at 10:56 PM, Kenneth Graunke <kenneth at whitecape.org>
> wrote:
> 
> > There may not be a previous block.  In this case, there's no real work
> > to do, so just continue on to the next one.
> >
> > v2: Update for bblock->prev() API change.
> >
> > Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> > ---
> >  src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp
> > b/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp
> > index 2c1abaf..114dc6c 100644
> > --- a/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp
> > @@ -42,6 +42,10 @@ dead_control_flow_eliminate(backend_shader *s)
> >
> >     foreach_block_safe (block, s->cfg) {
> >        bblock_t *prev_block = block->prev();
> > +
> > +      if (!prev_block)
> > +         continue;
> > +
> >        backend_instruction *const inst = block->start();
> >        backend_instruction *const prev_inst = prev_block->end();
> >
> 
> Yeah, that guy right there will be a problem on the first loop iteration
> every time.  I've seen this in valgrind quite a bit lately.  Thanks for
> fixing it!
> 
> Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
> 
> Maybe Cc stable?
> --Jason

I checked 10.2 on the first spin of this series, and I didn't see the
valgrind errors there.
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