I'm not that familiar with Buddy holly tunes, but I'm pretty sure he's using the chords A , D and E

Because the individual notes of these three chords are all contained in ' A ' major scale you can play A minor pentatonic over the whole song and it will work

A minor pentatonic is : A , C, D , E , G

http://www.bing.com/videos/search?q=Buddy+Holly+youtube&docid=63277891629&mid=E0F0FD5DC1C5E9320083E0F0FD5DC1C5E9320083&FORM=VIRE3#