x86汇编中lock指令的有关问题

x86汇编中lock指令的问题
代码如下：

Assembly code

test_and_set_ptr:    movl         4(%esp),%ecx    movl         8(%esp),%eax    movl        12(%esp),%edx    lock     cmpxchgl    %edx,(%ecx)    mov        $0,%eax    sete        %al    ret    .align    4,0x90    .type    q_atomic_test_and_set_ptr,@function    .size    q_atomic_test_and_set_ptr,.-q_atomic_test_and_set_ptr