Figure out how to handle dlsym with RTLD_NEXT

[mplegendre]

The RTLD_NEXT parameter to dlsym has at least two issues with gotcha:

• When the symbol being passed to dlsym isn't wrapped: the behavior of dlsym with RTLD_NEXT changes based on the caller library. Wrapping dlsym will break this. We need to simulate the bottom level call as if coming from the top level caller.

• Calling dlsym with RTLD_NEXT can return a different "bottom-level symbol" than without. If the symbol is wrapped, should we return the same wrapper function with and without RTLD_NEXT? Should we support different stacks of wrappers?

[DavidPoliakoff]

This comment is to expand on the problem, for my own notes, as this issue is really thorny

An example of this problem is that somebody calls dlsym(RTLD_NEXT, "foo"), where "foo" has been wrapped by Gotcha. Gotcha can rather easily faithfully simulate RTLD_NEXT using the builtin_return_address call we make here. However, it doesn't yet return a wrapped version of that call.

Correct behavior should be returning a function stack with correct wrappers, whose bottom-most ("real") function is the correct RTLD_NEXT-function