which-func-modes

which-func-modes is a variable defined in `which-func.el'.
Its value is

t

Documentation:
List of major modes for which Which Function mode should be used.
For other modes it is disabled. If this is equal to t,
then Which Function mode is enabled in any major mode that supports it.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.3 of Emacs.