1 2 .globl _xinc 3 _xinc: 4 movl 4(%esp), %eax 5 lock incl 0(%eax) 6 ret 7 8 .globl _xdec 9 _xdec: 10 movl 4(%esp), %eax 11 lock decl 0(%eax) 12 jz iszero 13 movl %eax, 1 14 ret 15 iszero: 16 movl %eax, 0 17 ret 18