Question

I have some code from a function

subl $24, %esp
movl 8(%ebp), %eax
cmpl 12(%ebp), %eax

Before the code is just the ‘ENTER’ command and afterwards there’s an if statement to return 1 if ebp > eax or 0 if it’s less. I’m assuming cmpl means compare, but I can’t tell what the concrete values are. Can anyone tell me what’s happening?

Answer 1

Yes cmpl means compare (with 4-byte arguments). Suppose the piece of code is followed by a jg <addr>:

movl 8(%ebp), %eax
cmpl 12(%ebp), %eax
jg <addr>

Then the code is similar to

eax = ebp[8];
if (eax > ebp[12])
   goto <addr>;