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

[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.

> 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...).
> 
> Roland
> 
>>>        if (curProg->numArithInstr[curProg->cur_pass >> 1] > 7) {
>>>  	 _mesa_error(ctx, GL_INVALID_OPERATION, "C/AFragmentOpATI(instrCount)");
>>>  	 return;
>>>
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