[Mesa-dev] [PATCH 5/6] glsl/linker: simplify xfb_offset vs xfb_stride overflow check

[Andres Gomez]

On Fri, 2019-02-01 at 13:17 -0500, Ilia Mirkin wrote:
> On Fri, Feb 1, 2019 at 1:08 PM Andres Gomez <agomez at igalia.com> wrote:
> > Current implementation uses a complicated calculation which relies in
> > an implicit conversion to check the integral part of 2 division
> > results.
> > 
> > However, the calculation actually checks that the xfb_offset is
> > smaller or a multiplier of the xfb_stride. For example, while this is
> > expected to fail, it actually succeeds:
> > 
> >   "
> > 
> >     ...
> > 
> >     layout(xfb_buffer = 2, xfb_stride = 12) out block3 {
> >       layout(xfb_offset = 0) vec3 c;
> >       layout(xfb_offset = 12) vec3 d; // ERROR, requires stride of 24
> >     };
> > 
> >     ...
> > 
> >   "
> > 
> > Fixes: 2fab85aaea5 ("glsl: add xfb_stride link time validation")
> > Cc: Timothy Arceri <tarceri at itsqueeze.com>
> > Signed-off-by: Andres Gomez <agomez at igalia.com>
> > ---
> >  src/compiler/glsl/link_varyings.cpp | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
> > index 6cebc5b3c5a..ab66ceb0d00 100644
> > --- a/src/compiler/glsl/link_varyings.cpp
> > +++ b/src/compiler/glsl/link_varyings.cpp
> > @@ -1213,8 +1213,7 @@ tfeedback_decl::store(struct gl_context *ctx, struct gl_shader_program *prog,
> >           return false;
> >        }
> > 
> > -      if ((this->offset / 4) / info->Buffers[buffer].Stride !=
> > -          (xfb_offset - 1) / info->Buffers[buffer].Stride) {
> > +      if (xfb_offset > info->Buffers[buffer].Stride) {
>  >= ?

I believe it is correct as it is.

> >           linker_error(prog, "xfb_offset (%d) overflows xfb_stride (%d) for "
> >                        "buffer (%d)", xfb_offset * 4,
> >                        info->Buffers[buffer].Stride * 4, buffer);
> > --
> > 2.20.1
> > 
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
-- 
Br,

Andres