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

[Pohjolainen, Topi]

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(-)

Thanks for the quick fix, and spotting the problem in the first place!

Reviewed-by: Topi Pohjolainen <topi.pohjolainen at intel.com>

> 
> 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);
>  
>     int st_index = -1;
>     if (INTEL_DEBUG & DEBUG_SHADER_TIME)
> diff --git a/src/mesa/drivers/dri/i965/brw_wm.c b/src/mesa/drivers/dri/i965/brw_wm.c
> index 4d5e7f6..65de543 100644
> --- a/src/mesa/drivers/dri/i965/brw_wm.c
> +++ b/src/mesa/drivers/dri/i965/brw_wm.c
> @@ -222,7 +222,7 @@ brw_codegen_wm_prog(struct brw_context *brw,
>     }
>  
>     if (unlikely(INTEL_DEBUG & DEBUG_WM))
> -      brw_dump_ir("fragment", prog, &fs->base, &fp->program.Base);
> +      brw_dump_ir("fragment", prog, fs ? &fs->base : NULL, &fp->program.Base);
>  
>     int st_index8 = -1, st_index16 = -1;
>     if (INTEL_DEBUG & DEBUG_SHADER_TIME) {
> -- 
> 1.9.1
> 
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