方括号在x86汇编中是什么意思? [英] What do square brackets mean in x86 assembly?

问题描述

我刚接触汇编，并且有一些非常基本的问题.

I'm very new to assembly, and have some very basic questions.

这四个命令有什么区别?

What is the difference between these four commands?

mov ebx, eax
mov [ebx], eax
mov ebx, [eax]
mov [ebx], [eax]

他们说方括号的意思是获取地址的值".但是，那第一行实际上是做什么的呢?它不会将eax的价值转移到ebx吗?如果可以，那么括号的意义是什么?

They say that the brackets mean "get the value of the address". But what, then, does that very first line really do? Does it not move the value of eax into ebx? If it does, then what are the point of the brackets?

推荐答案

让我们举一个非常简单的示例，并假设我们有一个只有两个寄存器(EAX和EBX)的CPU.

Let's make a very simple example and imagine we have a CPU with only two registers, EAX and EBX.

mov ebx，eax

mov ebx, eax

只需将eax中的值复制到ebx寄存器

Simply copies the value in eax to the ebx register

 | EAX : 0123456 |   ---->   | EAX : 0123456 |
 | EBX : 0000000 |   ====>   | EBX : 0123456 |

---

现在让我们添加一些内存空间

---

Now let's add some memory space

ADDRESS         VALUE
000000          6543210
000004          5189784
000008          1698791
00000C          9816517
000010          9816875
000014          5498156

mov [ebx]，eax

mov [ebx], eax

将eax中的值移动到ebx中包含的内存地址.

Moves the value in eax to the memory address contained in ebx.

 | EAX : 0123456 |   --no-->   | EAX : 0123456 |
 | EBX : 0000008 | --change--> | EBX : 0000008 |

ADDRESS         VALUE           VALUE
000000          6543210   ----> 6543210   
000004          5189784   ----> 5189784   
000008          1698791   ====> 0123456
00000C          9816517   ----> 9816517   
000010          9816875   ----> 9816875   
000014          5498156   ----> 5498156   

---

mov ebx，[eax]

mov ebx, [eax]

将值从eax中包含的内存地址移动到ebx.

Moves the value from the memory address contained in eax to ebx.

 | EAX : 0000008 |   ---->   | EAX : 0000008 |
 | EBX : 0123456 |   ====>   | EBX : 1698791 |

ADDRESS         VALUE    
000000          6543210    
000004          5189784  
000008          1698791  
00000C          9816517   
000010          9816875    
000014          5498156    

---

mov [ebx]，[eax]

mov [ebx], [eax]

最后，您会认为会将值从eax中包含的内存地址移动到ebx中包含的内存地址.

This, finally, you would think would move the value from the memory address contained in eax to the memory address contained in ebx.

 | EAX : 0000008 |   --no-->   | EAX : 0000008 |
 | EBX : 000000c | --change--> | EBX : 000000c |

ADDRESS         VALUE           VALUE
000000          6543210   ----> 6543210   
000004          5189784   ----> 5189784   
000008          1698791   ----> 1698791   
00000C          9816517   ====> 1698791   
000010          9816875   ----> 9816875   
000014          5498156   ----> 5498156 

但是x86体系结构不允许这种组合. 您不能在内存之间移动.

But this combination is disallowed by the x86 architecture. You cannot move from memory to memory.

因此，括号的使用等效于 取消引用 操作.

The use of brackets is therefore equivalent to a dereferencing operation.

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