[Mesa-dev] [PATCH 2/4] mesa: fix crash when an ATI_fs pass begins with an alpha inst

[Roland Scheidegger]

Am 27.11.2017 um 21:29 schrieb Ian Romanick:
> On 11/20/2017 06:04 PM, Roland Scheidegger wrote:
>> Am 21.11.2017 um 01:40 schrieb Ian Romanick:
>>> On 11/20/2017 04:07 PM, Miklós Máté wrote:
>>>> This fixes crash when:
>>>> - first pass begins with alpha inst
>>>> - first pass ends with color inst, second pass begins with alpha inst
>>>>
>>>> Also, use the symbolic name instead of a number.
>>>> Piglit: spec/ati_fragment_shader/api-alphafirst
>>>>
>>>> Signed-off-by: Miklós Máté <mtmkls at gmail.com>
>>>> ---
>>>>  src/mesa/main/atifragshader.c | 6 ++++--
>>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/src/mesa/main/atifragshader.c b/src/mesa/main/atifragshader.c
>>>> index 49ddb6e5af..d6fc37ac8f 100644
>>>> --- a/src/mesa/main/atifragshader.c
>>>> +++ b/src/mesa/main/atifragshader.c
>>>> @@ -598,8 +598,10 @@ _mesa_FragmentOpXATI(GLint optype, GLuint arg_count, GLenum op, GLuint dst,
>>>>        curProg->cur_pass=3;
>>>>  
>>>>     /* decide whether this is a new instruction or not ... all color instructions are new,
>>>> -      and alpha instructions might also be new if there was no preceding color inst */
>>>> -   if ((optype == 0) || (curProg->last_optype == optype)) {
>>>> +      and alpha instructions might also be new if there was no preceding color inst,
>>>> +      and this may be the first inst of the pass */
>>>
>>> I know the code previously used this same formatting, but the Mesa style
>>> is for the */ of a multi-line comment to be on its own line.  Each other
>>> line should also start with a *.  And line-wrap around 78 characters.
>>> Like:
>>>
>>>    /* Decide whether this is a new instruction or not.  All color instructions
>>>     * are new, and alpha instructions might also be new if there was no
>>>     * preceding color inst.  This may also be the first inst of the pass.
>>>     */
>>>
>>>> +   if ((optype == ATI_FRAGMENT_SHADER_COLOR_OP) || (curProg->last_optype == optype)
>>>> +         || (curProg->numArithInstr[curProg->cur_pass >> 1] == 0)) {
>>>
>>> I lost the debate about where the || (or &&) should go... it should be
>>> on the previous line.  Most of the parenthesis are unnecessary, and the
>>> second line should line up with the opening (.
>>>
>>> On a side topic... if anyone understands how
>>> ati_fragment_shader::cur_pass works, it would be really great if they
>>> could document it in mtypes.h.
>>
>> This just indicates which pass is currently being specified. Some
>> instructions will trigger a new pass, some instructions are only valid
>> in the first or second pass and so on, and you can have a maximum of 2
>> passes.
> 
> Which is the confusing part.  ATI fragment shaders can have two passes,
> but, as far as I can tell by reading the code,
> ati_fragment_shader::cur_pass can have a maximum value of... 5?  At
> least 4 for sure.
Ah yes I wasn't very accurate there.
unlike NumPasses, cur_pass distinguishes between the texture and
arithmetic phases. Hence cur_pass being 0 means currently texture
instructions are specified for the first pass. cur_pass 1 arithmetic for
the first pass. cur_pass 2/3 correspond to the second pass accordingly.
I can't see though how you could get values larger than 3 (if the value
is 3 and there's some instruction which would increase it, that should
be an error).

Roland


> 
>> I guess it's a bit awkward how this needs to work due to the shader
>> being specified bit-by-bit rather than all at once, but the actual
>> concept is very similar to the multiple phases of d3d9 and r300 (and
>> didn't i915 have something similar too). Of course, if you translate it
>> away (on everything but r200) then only the error checking aspect of it
>> really matters in the end.
>>
>> FWIW the patches all look correct to me, apparently there were quite
>> some errors in there (I think it was mostly verified with doom3 at that
>> time...).
>>