[Mesa-dev] [PATCH] i965: Clamp texture buffer size to GL_MAX_TEXTURE_BUFFER_SIZE.

[Anuj Phogat]

On Fri, Mar 3, 2017 at 11:32 AM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> The OpenGL 4.5 specification's description of TexBuffer says:
>
> "The number of texels in the texture image is then clamped to an
>  implementation-dependent limit, the value of MAX_TEXTURE_BUFFER_SIZE."
>
> We set GL_MAX_TEXTURE_BUFFER_SIZE to 2^27.  For buffers with a byte
> element size, this is the maximum possible size we can encode in
> SURFACE_STATE.  If you bind a buffer object larger than this as a
> texture buffer object, we'll exceed that limit and hit an isl assert:
>
>    assert(num_elements <= (1ull << 27));
>
> To fix this, clamp the size in bytes to MaxTextureSize / texel_size.
>
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>  src/mesa/drivers/dri/i965/brw_wm_surface_state.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_wm_surface_state.c b/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
> index 8ffbc0a5fd5..e48b1e1d2d1 100644
> --- a/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
> +++ b/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
> @@ -695,6 +695,24 @@ brw_update_buffer_texture_surface(struct gl_context *ctx,
>        bo = intel_bufferobj_buffer(brw, intel_obj, tObj->BufferOffset, size);
>     }
>
> +   /* The ARB_texture_buffer_specification says:
> +    *
> +    *    "The number of texels in the buffer texture's texel array is given by
> +    *
> +    *       floor(<buffer_size> / (<components> * sizeof(<base_type>)),
> +    *
> +    *     where <buffer_size> is the size of the buffer object, in basic
> +    *     machine units and <components> and <base_type> are the element count
> +    *     and base data type for elements, as specified in Table X.1.  The
> +    *     number of texels in the texel array is then clamped to the
> +    *     implementation-dependent limit MAX_TEXTURE_BUFFER_SIZE_ARB."
> +    *
> +    * We need to clamp the size in bytes to MAX_TEXTURE_BUFFER_SIZE * stride,
> +    * so that when ISL divides by stride to obtain the number of texels, that
> +    * texel count is clamped to MAX_TEXTURE_BUFFER_SIZE.
> +    */
> +   size = MIN2(size, ctx->Const.MaxTextureBufferSize * (unsigned) texel_size);
> +
>     if (brw_format == 0 && format != MESA_FORMAT_RGBA_FLOAT32) {
>        _mesa_problem(NULL, "bad format %s for texture buffer\n",
>                     _mesa_get_format_name(format));
> --
> 2.11.1
>
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LGTM.
Reviewed-by: Anuj Phogat <anuj.phogat at gmail.com>