The Performance Schema user_defined_functions table contains information about the currently installed loadable functions:

SELECT * FROM performance_schema.user_defined_functions;

The mysql.func system table also lists installed loadable functions, but only those installed using CREATE FUNCTION. The user_defined_functions table lists loadable functions installed using CREATE FUNCTION as well as loadable functions installed automatically by components or plugins. This difference makes user_defined_functions preferable to mysql.func for checking which loadable functions are installed. See Section 29.12.22.12, “The user_defined_functions Table”.