[Mesa-dev] [PATCH] i965: Do not dereference NULL brw_shader pointer when debugging

[Chris Wilson]

On Fri, Oct 09, 2015 at 08:09:20AM +0200, Iago Toral Quiroga wrote:
> For the VS and FS stages that use ARB_vertex_program or
> ARB_fragment_program we don't have a shader program, however,
> when debuging is enabled, we call brw_dump_ir like this:
> 
> brw_dump_ir("vertex", prog, &vs->base, &vp->program.Base);
> 
> which unconditionally dereferences vs, producing a NULL pointer
> dereference in the situation explained above, as observed in this
> gdb session for glxgears right before we call brw_dump_ir:
> 
> prog=0x0, vp=0x960f50, key=0x7fffffffc940) at brw_vs.c:174
> 
> (gdb) p vs
> $7 = (struct brw_shader *) 0x0
> (gdb) p vp
> $8 = (struct brw_vertex_program *) 0x960f50
> ---
>  src/mesa/drivers/dri/i965/brw_vs.c | 2 +-
>  src/mesa/drivers/dri/i965/brw_wm.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_vs.c b/src/mesa/drivers/dri/i965/brw_vs.c
> index 38de98f..60fb5fa 100644
> --- a/src/mesa/drivers/dri/i965/brw_vs.c
> +++ b/src/mesa/drivers/dri/i965/brw_vs.c
> @@ -171,7 +171,7 @@ brw_codegen_vs_prog(struct brw_context *brw,
>     }
>  
>     if (unlikely(INTEL_DEBUG & DEBUG_VS))
> -      brw_dump_ir("vertex", prog, &vs->base, &vp->program.Base);
> +      brw_dump_ir("vertex", prog, vs ? &vs->base : NULL, &vp->program.Base);

The key question is NULL + 0 a nullptr? There's no actual dereference
here but calculation of a relative address.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre