While Clint Eastwood's character, Harry Callahan, isn't a drill sergeant in the traditional sense, he does exhibit some drill sergeant-like qualities. He's tough, demanding, and uses harsh language to instill discipline in those around him.
However, there's no movie specifically about Clint Eastwood playing a drill sergeant.
Are you thinking of a specific scene or moment in the film "Dirty Harry"? If you could give me some more information, I might be able to help you pin down what you're looking for.