汇编je，jns，jle使用哪个寄存器? [英] Assembly je, jns, jle which register does it use?

问题描述

情况1:

cmp dword ptr[ebp + 18],00
mov eax, [ebp + 14]
je Game.exe+417442

情况2:

test eax,eax
jns Game.exe+47137

是否总是查看寄存器eax?如果没有，我们如何知道它要查找哪个寄存器来确定跳转?

Does it ALWAYS look at register eax? If not, how do we know what register it looks at to determine the jump?

推荐答案

x86 Jcc(其中cc是条件代码)使用

The x86 Jcc (where cc is a condition code) uses the (R|E)FLAGS register to determine whether the condition is met or not. The flags can be updated by various previous instructions. In traditional x86 assembly you will normally use a cmp or test instruction to set the flags before a jump instruction.

如果您在此说明参考书中查看cmp的文档，并且对于 test ，您将看到它们允许将任何通用寄存器用作操作数

If you look at the documentation for cmp at this instruction reference, and for test, you will see that they permit any of the general purpose registers as operands.

我注意到cmp和test并不是影响标志的 only 操作，只是，当您编写自己的汇编代码时，它们通常是您将用来执行的操作确定是否满足跳转条件.

I note that cmp and test are not the only operations that affect the flags, just, when you are writing your own assembly code, they are normally the operations you will use to determine if a jump condition is met.

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