[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 #2 from Jammy Zhou <jammy.zhou at linaro.org> 2010-12-09 23:44:34 PST ---
(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?

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.

> 
> 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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