[PATCH 0/8] Attempt to fix GLX for OSX

[Adam Jackson]

On Tue, 2013-12-03 at 17:18 -0800, Jeremy Huddleston Sequoia wrote:

> == 2 ==
> I didn't check line by line, but the pattern looks reasonable if one
> assumes that __glGetProcAddress won't return NULL in any of these
> cases.  Can we make such a guarantee (ie, will a GLX extension not be
> advertised unless the corresponding dependent OpenGL extension is
> available)?  What is to prevent someone from intentionally crashing
> the server by triggering a call to a GLX function which doesn't have
> the backing OpenGL functionality available in libGL?

I should probably have linked to the changes to the codegen code:

http://cgit.freedesktop.org/~ajax/mesa/log/?h=glapi

The GetProcAddress thing is a valid point.  glXGetProcAddress never
returns NULL.  [ew]glGetProcAddress apparently can, so we have to
consider it possible.  And there's nothing to prevent a client from
constructing protocol that calls an entrypoint that the renderer doesn't
support.  In fact all it needs to do is create an indirect context and
call the function, libGL doesn't check this on the client side.

Probably it makes sense to check for this in __glGetProcAddress and
simply return a stub function there, rather than force each DDX to
handle it.

> I'd prefer that we cache these results instead of essentially calling
> into dlsym (or relying on dlsym's cache), but I am satisfied by
> abstracting that away and saying that the caching is the
> responsibility of the GPA routine.  In fact, now that I've thought
> about it, I think I agree that NOT caching the results in dix is the
> right approach.

I'm of two minds about it, I could be convinced either way.  We could
cache them at the DIX level by just changing the function pointers to be
static instead of auto.  I didn't do that because wglGPA function
pointers are per-context and I was assuming that's what the xwin ddx
would use directly.  But as Jon pointed out we have to jump through stub
functions to translate calling conventions.  So if _those_ stubs call
wglGPA afresh every time, the dix level code could safely cache.

- ajax