为什么mov指令不能取局部变量的地址？

[swimmer2000]

我在看一本叫《PC Assembly Language》的汇编教程，对其中一段不明白，希望有人给个解释，
原文如下：
"
Consider the case of passing the address of a variable (let’s call it x) to a function
(let’s call it foo). If x is located at EBP − 8 on the stack, one cannot just use:
mov eax, ebp - 8

Why? The value that MOV stores into EAX must be computed by the assembler
(that is, it must in the end be a constant).However, there is an instruction that does the desired calculation.
It is called LEA (for Load Effective Address).

The following would calculate the address of x and store it into EAX:
lea eax, [ebp - 8]
"
作者说“MOV到EAX的数据必须由Assembler（汇编器）计算，MOV指令的第二个操作数必须是一个常量”
这点我不是很清楚。

看到有人说，将它改为:
mov eax, ebp
sub eax, 8
执行结果和lea指令相同，只是效率低，是这样吗？

[zara]

引用

执行结果和lea指令相同，只是效率低，是这样吗？

大致是的，只是 lea 不影响标记位，而你这个会影响到。
其实，这个解释有些简单事儿复杂化了，也就只是 MOV 指令没有运算功能，所以源操作数必须的直接的、确定的。