[Mesa-dev] [Bug 32285] Check OpenGL and OpenGL ES2.0 renderer info in one process

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=32285

--- Comment #3 from Chia-I Wu <olvaffe at gmail.com> 2010-12-10 00:08:24 PST ---
(In reply to comment #2)
> (In reply to comment #1)
> Thanks for the quick response and detailed explanation.
> 
> > Created an attachment (id=40980)
 View: https://bugs.freedesktop.org/attachment.cgi?id=40980
 Review: https://bugs.freedesktop.org/review?bug=32285&attachment=40980

> > hack to work
> > 
> > It may depend on your setup and the dynamic linker, but this patch to
> > renderer_info.c may "fix" the issue, even with the "failed to remap ..."
> > messages.  Or alternatively, you can try linking to libGL.so directly when
> > compiling and call glGetString directly.
> 
> With this patch, both GL and GLESv2 renderer info can be got successfully now.
> But this seems a little tricky, and in this case the dispatch table of GLESv2
> is also used for OpenGL/GLX context. I am curious why "dlclose(gles2_handle);"
> didn't clean libGLESv2.so out of the address space?
Because it is linked to by st_GLESv2.so, which is not unloaded until the app
exits.
> By the way, because I want to make my application independent of both libGL and
> libGLESv2, I cannot link it directly to libGL.so or libGLESv2.so.
It should also work if you dlopen with RTLD_GLOBAL.  But these are all (very
bad) workarounds.  It is still the best to fix the bug.
> > 
> > The bug here is that there are two copies of glapi: one in libGL.so and the
> > other in libGLESv2.so.  One of the things that glapi does is to manage the
> > dispatch table of the current context.  When the OpenGL ES context is first
> > made current, the dispatch table in libGLESv2.so is updated.  Calling
> > glGetString from libGLESv2.so gives the correct result.
> > 
> > But when the OpenGL context is made current, the dynamic linker decides to
> > update the dispatch table in libGLESv2.so again.  If you call glGetString from
> > libGL.so, it will be no-op since the dispatch table in libGL.so is never
> > updated.
> > 
> > For the same reason, when the OpenGL context is created, the remap table in
> > libGLESv2.so is updated.  Since OpenGL has much more entry points than
> > libGLESv2.so can handle, you will see the "failed to remap ..." messages after
> > the entry points in libGLESv2.so run out.
> 
> Hmm... resonable
> 
> > 
> > 16ee7a55ae26 only fixed core mesa (src/mesa/).  It will only work when an app
> > links to either one of libGL.so or libGLESv2.so, and use eglGetProcAddress to
> > get the addresses of the entry points that are not statically available.
> > 
> > But when both libGL.so and libGLESv2.so are used, the app will be affected by
> > this bug.  A fix to glapi (src/mapi/glapi/) is required.

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