[Mesa-dev] [PATCH] i965/fs: Clamp image array indices to the array bounds on IVB.

[Francisco Jerez]

Timothy Arceri <t_arceri at yahoo.com.au> writes:

> On Mon, 2015-07-27 at 16:01 +0300, Francisco Jerez wrote:
>> This fixes the spec at arb_shader_image_load_store@invalid index bounds
>> piglit tests on IVB, which were causing a GPU hang and then a crash
>> due to the invalid binding table index result of the array index
>> calculation.  Other generations seem to behave sensibly when an
>> invalid surface is provided so it doesn't look like we need to care.
>> ---
>>  src/mesa/drivers/dri/i965/brw_fs_nir.cpp | 25 +++++++++++++++++++++----
>>  1 file changed, 21 insertions(+), 4 deletions(-)
>> 
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp 
>> b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
>> index 1671595..b69e96b 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
>> @@ -1216,14 +1216,31 @@ fs_visitor::get_nir_image_deref(const nir_deref_var 
>> *deref)
>>           nir_deref_as_array(deref->deref.child);
>>        assert(deref->deref.child->deref_type == nir_deref_type_array &&
>>               deref_array->deref.child == NULL);
>> +      const unsigned size = glsl_get_length(deref->var->type);
>> +      const unsigned base = MIN2(deref_array->base_offset, size - 1);
>>  
>> -      image = offset(image, bld,
>> -                     deref_array->base_offset * BRW_IMAGE_PARAM_SIZE);
>> +      image = offset(image, bld, base * BRW_IMAGE_PARAM_SIZE);
>>  
>>        if (deref_array->deref_array_type == nir_deref_array_type_indirect) {
>>           fs_reg *tmp = new(mem_ctx) fs_reg(vgrf(glsl_type::int_type));
>> -         bld.MUL(*tmp, get_nir_src(deref_array->indirect),
>> -                 fs_reg(BRW_IMAGE_PARAM_SIZE));
>> +
>> +         if (devinfo->gen == 7 && !devinfo->is_haswell) {
>> +            /* IVB hangs when trying to access an invalid surface index 
>> with
>> +             * the dataport.  According to the spec "if the index used to
>> +             * select an individual element is negative or greater than or
>> +             * equal to the size of the array, the results of the operation
>> +             * are undefined but may not lead to termination" -- which is 
>> one
>> +             * of the possible outcomes of the hang.  Clamp the index to
>> +             * prevent access outside of the array bounds.
>> +             */
>> +            bld.emit_minmax(*tmp, retype(get_nir_src(deref_array
>> ->indirect),
>> +                                         BRW_REGISTER_TYPE_UD),
>> +                            fs_reg(size - base - 1), BRW_CONDITIONAL_L);
>
> I know this was just pushed but I'm working on AoA support for this, and notic
> ed something. Isn't base always going to be 0 in the above line? As it will
> only be set to another value for direct indexing.
>
Currently it may be, but AFAIK the offset of an indirectly-addressed
array in NIR is supposed to be given by base_offset plus the indirect
offset, and none of the surrounding back-end code seemed to make the
assumption that base_offset would be zero in the indirect case, so it
didn't seem reasonable to me to do it here.

>
>> +         } else {
>> +            bld.MOV(*tmp, get_nir_src(deref_array->indirect));
>> +         }
>> +
>> +         bld.MUL(*tmp, *tmp, fs_reg(BRW_IMAGE_PARAM_SIZE));
>>           image.reladdr = tmp;
>>        }
>>     }
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 212 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/mesa-dev/attachments/20150812/49a9fc89/attachment.sig>