which-function-mode

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

nil

Documentation:
Non-nil if Which-Function mode is enabled.
See the command `which-function-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `which-function-mode'.

You can customize this variable.