It's also possible that xchg %ax,%ax is has been decoded from a multi-byte nop (to align memory) before the function call.
Typically, you use xchg %ax,%ax because you can replace it with a jump if you want.
Now if the author can provide some more details, we'll see if the call is aligned on some interesting boundary.
I always wonder how much aligning code helps in real code. They seem waste a lot of bytes in the code segment. Aligning data, yes, that changes a lot, but the return position of a call in code?
Is a good post in regards to code alignment effects.