I'm looking at

(easy-mmode-defmap gud-minor-mode-map
  (append
     `(([menu-bar debug] . ("Gud" . ,gud-menu-map)))
     ;; Get tool bar like functionality from the menu bar on a text only
     ;; terminal.
   (unless window-system
     `(([menu-bar down]
	. (,(propertize "down" 'face 'font-lock-doc-face) . gud-down))
       ([menu-bar up]
	. (,(propertize "up" 'face 'font-lock-doc-face) . gud-up))
       ([menu-bar finish]
	. (,(propertize "finish" 'face 'font-lock-doc-face) . gud-finish))
       ([menu-bar step]
	. (,(propertize "step" 'face 'font-lock-doc-face) . gud-step))
       ([menu-bar next]
	. (,(propertize "next" 'face 'font-lock-doc-face) . gud-next))

and I'm not quite sure how this is supposed to work.

It's only run in non-graphical Emacsen, and does indeed put those texts
into the window: