Debugging glX apps

[tom fogal]

I'm hitting an issue appropriately establishing a glX context (it
seems), and I'm looking for a good way to debug it.

Quick overview in case someone happens to recognize the issue: I'm
getting a segfault in X functions when trying to initialize GLEW.
XOpenDisplay has succeded, and I'm not sure yet if glXCreateContext
succeeded, but it seems like the library I'm using would have aborted
if it had failed.  Call stack:

    #0 XQueryExtension () from /usr/lib64/libX11.so.6
    #1 XInitExtension () from /usr/lib64/libX11.so.6
    #2 XextAddDisplay () from /usr/lib64/libXext.so.6
    #3 ?? () from /usr/lib64/libGL.so.1
    #4 glXQueryVersion () from /usr/lib64/libGL.so.1
    #5 glxewContextInit () at glew/src/glew.c:6987
    #6 glewInit () at glew/src/glew.c:7186

(addresses removed)

Is there a list of environment variables which affect X / GLX
behavior?  For example, it would be nice if I could set an environment
variable which would force XSynchronize(3) to `on', or cause library
functions to abort() rather than return error codes.

Any other tips for debugging?  My next step[s] are to build private
debug versions of some X libraries and force loading them via
LD_LIBRARY_PATH or similar.

Thanks,

-tom