How do I get postgres to log the stored procedures it is running?
You can see a count of all user-defined functions being called in the system view pg_stat_user_functions.

There is no facility to write all function calls to the log.  That would be quite bulky.

If you're feeling adventurous, you can play with the settings debug_print_parse and debug_print_plan to get more detailed information about what is being called.  Again, this will be bulky.