x86 cmpl和jne [英] x86 cmpl and jne

问题描述

我正在为某个作业跟踪一些x86代码，而我想知道到底是什么"cmpl"?以及如何预测"jne"是否将会满足.

I'm tracing some x86 code for an assignment, and I was wondering what exactly "cmpl" does and how to predict whether or not the "jne" will be met.

80484bf:    83 7d f0 07             cmpl   $0x7,-0x10(%ebp)
80484c3:    75 16                   jne    80484db

推荐答案

cmpl 从$ 0x7减去-0x10(％ebp)并修改标志: AF CF OF PF SF ZF .

1. 如果-0x10(％ebp)处的内存等于立即数0x7，则设置标志 ZF .该值低于EBP，因此，如果这是使用EBP作为帧指针的未优化构建，则它可能是局部变量.
2. jne 80484db 意味着，如果两个比较的数字不同(ZF = 0)，请跳至 80484db

1. If memory at -0x10(%ebp) equals immediate 0x7 then the flag ZF is set. This is below EBP so it's probably a local variable, if this is an un-optimized build using EBP as a frame pointer.
2. jne 80484db means that if the two compared numbers are different (ZF=0), jump to 80484db

总而言之，您的代码等效于:

To summarize, your code is equivalent to :

compare A to 7
jump to 0x80484db if they are different.

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