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

[Marius Gräfe]

I can fix the remaining integer div/mod opcodes, no problem. I think a 
consistent error value would be beneficial, would opt for ~0u for 32-bit 
values and ~0ull for 64 bit values to keep it consistent with the only 
existing requirement (that is d3d10). Should I just submit another patch 
based on my original one with the fixed values? I am unsure about the 
correct procedure, still new to this whole mailing list procedure.
As far as src/gallium/docs/source/tgsi.rst is concerned, the docs don't 
seem to mention any error value anyway.

Marius


Am 08.06.2017 um 22:28 schrieb 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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