Comment by sylware

Then, if I got it right for TLS-ized variables, dlsym should do the trick. Namely, dlsym will return the address of a variable for the calling thread. Then this pointer can be cached the way the thread wants. On x86_64, it can "optimize" the dlsym calls by reusing the same address for all threads, namely 1 call is enough.

Now the real pain is this static libstdc++ not libdl-ing anything, or worse expecting internal glibc symbols (c++ ...)