[Mesa-dev] [PATCH] gallium: fixed modulo zero crashes in tgsi interpreter

[Roland Scheidegger]

The behavior is probably undefined for most of the opcodes (signed 32bit
div, all 64bit div/mod), the docs don't state anything. But in general,
this is all undefined in all apis (opencl, glsl, spir-v), with the only
exception being d3d10 - which only has udiv and umod, hence these
stating in the gallium docs the required result (~0u).
So, I suppose we could let the docs say it's actually undefined, right
now gallivm will actually return 0 for idiv but all-ones for idiv64 and
so on, it's not really consistent...

Roland


Am 08.06.2017 um 21:51 schrieb Brian Paul:
> Marius,
> 
> As long as you're working on this, would you review
> src/gallium/docs/source/tgsi.rst to check if all the div/mod
> instructions document div/mod by zero behavior?  Thanks.
> 
> -Brian
> 
> 
> On 06/08/2017 11:10 AM, Roland Scheidegger wrote:
>> I don't really know if it makes sense to have different "error values"
>> for signed vs. unsigned modulo 0 - maybe the "all bits set" approach
>> would do too (the gallivm code does this, because it is actually
>> easier). But since it's undefined in any case pretty much everywhere, I
>> suppose any value will do (only the 32bit umod really has a requirement
>> for all bits set due do d3d10 requirements, but d3d has neither signed
>> nor 64bit versions of it).
>> And I don't know why it would only crash in geometry shaders...
>>
>> Reviewed-by: Roland Scheidegger <sroland at vmware.com>
>>
>>
>> Am 08.06.2017 um 18:28 schrieb Marius Gräfe:
>>> softpipe throws integer division by zero exceptions on windows
>>> when using % with integers in a geometry shader.
>>> ---
>>>   src/gallium/auxiliary/tgsi/tgsi_exec.c | 24 ++++++++++++------------
>>>   1 file changed, 12 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/src/gallium/auxiliary/tgsi/tgsi_exec.c
>>> b/src/gallium/auxiliary/tgsi/tgsi_exec.c
>>> index c41954c..abd2d16 100644
>>> --- a/src/gallium/auxiliary/tgsi/tgsi_exec.c
>>> +++ b/src/gallium/auxiliary/tgsi/tgsi_exec.c
>>> @@ -866,20 +866,20 @@ static void
>>>   micro_u64mod(union tgsi_double_channel *dst,
>>>                const union tgsi_double_channel *src)
>>>   {
>>> -   dst->u64[0] = src[0].u64[0] % src[1].u64[0];
>>> -   dst->u64[1] = src[0].u64[1] % src[1].u64[1];
>>> -   dst->u64[2] = src[0].u64[2] % src[1].u64[2];
>>> -   dst->u64[3] = src[0].u64[3] % src[1].u64[3];
>>> +   dst->u64[0] = src[1].u64[0] ? src[0].u64[0] % src[1].u64[0] :
>>> UINT64_MAX;
>>> +   dst->u64[1] = src[1].u64[1] ? src[0].u64[1] % src[1].u64[1] :
>>> UINT64_MAX;
>>> +   dst->u64[2] = src[1].u64[2] ? src[0].u64[2] % src[1].u64[2] :
>>> UINT64_MAX;
>>> +   dst->u64[3] = src[1].u64[3] ? src[0].u64[3] % src[1].u64[3] :
>>> UINT64_MAX;
>>>   }
>>>
>>>   static void
>>>   micro_i64mod(union tgsi_double_channel *dst,
>>>                const union tgsi_double_channel *src)
>>>   {
>>> -   dst->i64[0] = src[0].i64[0] % src[1].i64[0];
>>> -   dst->i64[1] = src[0].i64[1] % src[1].i64[1];
>>> -   dst->i64[2] = src[0].i64[2] % src[1].i64[2];
>>> -   dst->i64[3] = src[0].i64[3] % src[1].i64[3];
>>> +   dst->i64[0] = src[1].i64[0] ? src[0].i64[0] % src[1].i64[0] :
>>> INT64_MAX;
>>> +   dst->i64[1] = src[1].i64[1] ? src[0].i64[1] % src[1].i64[1] :
>>> INT64_MAX;
>>> +   dst->i64[2] = src[1].i64[2] ? src[0].i64[2] % src[1].i64[2] :
>>> INT64_MAX;
>>> +   dst->i64[3] = src[1].i64[3] ? src[0].i64[3] % src[1].i64[3] :
>>> INT64_MAX;
>>>   }
>>>
>>>   static void
>>> @@ -4653,10 +4653,10 @@ micro_mod(union tgsi_exec_channel *dst,
>>>             const union tgsi_exec_channel *src0,
>>>             const union tgsi_exec_channel *src1)
>>>   {
>>> -   dst->i[0] = src0->i[0] % src1->i[0];
>>> -   dst->i[1] = src0->i[1] % src1->i[1];
>>> -   dst->i[2] = src0->i[2] % src1->i[2];
>>> -   dst->i[3] = src0->i[3] % src1->i[3];
>>> +   dst->i[0] = src1->i[0] ? src0->i[0] % src1->i[0] : INT_MAX;
>>> +   dst->i[1] = src1->i[1] ? src0->i[1] % src1->i[1] : INT_MAX;
>>> +   dst->i[2] = src1->i[2] ? src0->i[2] % src1->i[2] : INT_MAX;
>>> +   dst->i[3] = src1->i[3] ? src0->i[3] % src1->i[3] : INT_MAX;
>>>   }
>>>
>>>   static void
>>>
>>
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