Trying to diagram participle/complement-y thing??

Okay so the sentence I'm looking at is from Madame Bovary: "His hair was cut square on his forhead like a village choir boy; he looked reliable, but very ill at ease" (Flaubert 2).

So I'm just looking at the first clause right now excluding the prepositional phrases:

"His hair was cut square"

I'm tempted to consider "was cut" a linking verb and "square" the predicate adjective, but I don't think that'd be right. "Cut" is the past participle, so I should diagram it as such, right? And what about "square"? Where do I put that?

Thanks