Could you please explain the criteria you used to determine where CAMLextern is needed? For example, I agree caml_setup_stack_overflow_detection must be exported because it's used from the systhreads stub code. But I don't see any use of caml_set_action_pending outside of the run-time system. Did you find a use in stub code somewhere in OPAM? Do you anticipate this function to be used in stub code?

I thought all these were either critical (the build fails) or mentioned in the C API. I appear to have made a mistake with caml_set_action_pending and caml_process_pending_actions_with_root. I've removed those two. The others are either clearly referenced outside the runtime or are referred to in the manual as being available (the Windows string functions and caml_process_pending_signals_exn) or were inconsistently declared before (caml_read_directory).