On 8 September 2013 19:49, Kenneth Graunke <kenn...@whitecape.org> wrote:
> On 09/08/2013 08:48 AM, Paul Berry wrote: > >> On 4 September 2013 15:22, Kenneth Graunke <kenn...@whitecape.org >> <mailto:kenn...@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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