[Mesa-stable] [PATCH 3/4] i965: Handle non-zero texture buffer offsets in buffer object range calculation.

[Francisco Jerez]

Hey Nanley,

Nanley Chery <nanleychery at gmail.com> writes:

> On Mon, Mar 19, 2018 at 11:26:58AM -0700, Francisco Jerez wrote:
>> Otherwise the specified surface state will allow the GPU to access
>> memory up to BufferOffset bytes past the end of the buffer.  Found by
>> inspection.
>> 
>> Cc: mesa-stable at lists.freedesktop.org
>> ---
>>  src/mesa/drivers/dri/i965/brw_wm_surface_state.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> 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 ed4def9046e..2ab15af793a 100644
>> --- a/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
>> +++ b/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
>> @@ -654,7 +654,8 @@ buffer_texture_range_size(struct brw_context *brw,
>>      * so that when ISL divides by stride to obtain the number of texels, that
>>      * texel count is clamped to MAX_TEXTURE_BUFFER_SIZE.
>>      */
>> -   return MIN3((unsigned)obj->BufferSize, buffer_size,
>> +   return MIN3((unsigned)obj->BufferSize,
>> +               buffer_size - obj->BufferOffset,
>>                 brw->ctx.Const.MaxTextureBufferSize * texel_size);
>
> I don't understand this change. Previously we took the minimum between:
> 1) The TextureBuffer size specified by glTexBufferRange().
> 2) The size of the buffer object specified by glTexBuffer().
> 3) The maximum allowed texture buffer size.
>
> This patch modifies case 2 to be subtracted by the offset which will
> always be 0 for glTexBuffer().
>

The second argument of the MIN3 function is calculating the size of the
buffer object range accessible to the GPU.  The correct offset interval
that is supposed to be mapped to the GPU is [obj->BufferOffset,
obj->BufferObject->Size[, from where the expression above follows.

>>  }
>>  
>> -- 
>> 2.16.1
>> 
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