[Bug 38402] New: glDebugMessageCallback is broken

[wine-bugs at winehq.org]

https://bugs.winehq.org/show_bug.cgi?id=38402

            Bug ID: 38402
           Summary: glDebugMessageCallback is broken
           Product: Wine
           Version: unspecified
          Hardware: x86
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: opengl
          Assignee: wine-bugs at winehq.org
          Reporter: chris.kcat at gmail.com
      Distribution: ---

According to the KHR_debug extension spec, the function glDebugMessageCallback
takes a function pointer callback with the type:

typedef void (APIENTRY *GLDEBUGPROC)(GLenum source,
                                     GLenum type,
                                     GLuint id,
                                     GLenum severity,
                                     GLsizei length,
                                     const GLchar* message,
                                     const void* userParam);

https://www.opengl.org/registry/specs/KHR/debug.txt

In particular, it notes that the function callback uses the same calling
convention as the other GL functions. The problem is that on Windows, GL uses
the stdcall calling convention, while on Linux it uses cdecl. Wine's
glDebugMessageCallback thunk passes the callback through as-is, so the system's
libGL tries to call an stdcall function as though it was cdecl, causing it to
crash upon returning.

Another problem is that the spec says:

"When DEBUG_OUTPUT_SYNCHRONOUS is disabled, the driver is optionally allowed to
concurrently call the debug callback routine from potentially multiple threads,
including threads that the context that generated the message is not currently
bound to."

meaning the callback can be called on threads other than the one OpenGL is
being used on. This is a problem because it may be called on one or more
internal driver threads that were not created using the Windows API, and if the
callback function tries to do anything that relies on Windows-related thread
information, it won't be there.

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