[Mesa-dev] [PATCH 05/21] glsl: Pass _mesa_glsl_parse_state into matching_signature and such.

[Paul Berry]

On 8 September 2013 19:49, Kenneth Graunke <kenneth at whitecape.org> wrote:

> On 09/08/2013 08:48 AM, Paul Berry wrote:
>
>> On 4 September 2013 15:22, Kenneth Graunke <kenneth at whitecape.org
>> <mailto:kenneth at whitecape.org>**> wrote:
>>
>>     During compilation, we'll use this to determine built-in availability.
>>     All the prototypes will be available, but we can filter out the ones
>>     that aren't actually available.
>>
>>
>> I'm having trouble understanding this sentence because it sounds like
>> you're using the word "available" to mean two different things.  Do you
>> perhaps mean something like "when looking up the name of a built-in
>> function, we'll iterate through a list of all the prototypes that exist
>> in all GLSL versions and extensions, but we'll filter out the ones that
>> aren't actually available in the current GLSL version with the currently
>> enabled extensions"?
>>
>
> Poor wording on my part; your understanding is basically correct.
>
> I've replaced it with this text:
> "The plan is to have a single shader containing every built-in in every
> version of the language, but filter out the ones that aren't actually
> available to the shader being compiled."
>
>
>      At link time, we don't actually need this filtering capability, since
>>     we've already imported the prototypes and flagged them as
>> "is_builtin."
>>
>>
>> This sentence tripped me up a bit since the last patch removed the
>> "is_builtin" flag in favor of a function.  Do you mean to say that we've
>> already imported the prototypes and given them a non-null builtin_info
>> (so is_builtin() will return true)?
>>
>
> By "is_builtin flag" I meant "the value of the is_builtin() method."
>
>
>
>>     The linker won't import additional prototypes, so it won't pull in any
>>     unavailable built-ins.  Conversely, the is_builtin flag will prevent a
>>     shader from defining its own prototype and fooling the linker to
>> import
>>     a built-in's body.
>>
>>
>> Similarly, in this case do you mean "conversely, prototypes defined by
>> the shader will have builtin_info = null, so they will return false for
>> is_builtin() and that will prevent the linker from trying to import a
>> built-in's body for those functions"?
>>
>>       All that to say: we can just pass in NULL.  It'll be
>>     fine.
>>
>
> Yes.  I've replaced this text with:
>
> "At link time, we don't actually need this filtering capability: we've
> already imported prototypes for every built-in that the shader actually
> calls, and they're flagged as is_builtin().  The linker doesn't import
> any additional prototypes, so it won't pull in any unavailable
> built-ins.  When resolving prototypes to function definitions, the
> linker ensures the values of is_builtin() match, which means that a
> shader can't trick the linker into importing the body of an unavailable
> built-in by defining a suspiciously similar prototype.
>
> In other words, during linking, we can just pass in NULL.  It will work
> out fine."
>

Ok, that makes sense.  Thanks for the clarification.
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