Weak symbols don't work too well _between_ libraries. If libc is linked before libpthread, any unresolved references when libc is searched will use the weak symbols from there, regardless of the fact that a strong symbol exists in libpthread. If libc is linked after libpthread, then you can have libc internal references to things that should been resolved to things in libpthread, but end up using the weak symbols in libc because that is all there is left. 8-(

Not a simple problem to solve. The current tools don't help at all. A second library pass to resolve weak symbols would have been better. It's too late for that now, though, since you can change the semantics on the shared loader.