%esp call ___main movl $1234, 28(%esp) movl 12(%ebp), %eax addl $4, %eax movl (%eax), %eax movl %eax, (%esp) call _atoi movl %eax, 28(%esp) movl 28(%esp), %eax movl %eax, 4(%esp) For our purposes argv[1] = "67" _atoi grabs the char array at the address stored in (%esp), converts the ASCII string to an int, and returns the int in %eax 12(%ebp) argv 8(%ebp) argc 4(%ebp) return addr (%ebp) old %ebp 28(%esp) $1234 24(%esp) 20(%esp) 16(%esp) 12(%esp) 8(%esp) 4(%esp) (%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax argv[1]