using get_theme_mod on child theme to get parent theme

I was studying child themes and i am modifying a function and have declared an override in functions.php

the parent theme makes use of get_theme_mod( ‘x_footer_content_display’) to get settings but i did some research and this function only fetches settings of the CURRENT theme, which in this case is the child theme. since the child theme does not have this and only the parent does, then i cannot utilize it. any idea how i can fetch the theme mod from the parent?

http://codex.ww.wp.xz.cn/Function_Reference/get_theme_mod