如何在内联汇编C ++中设置eax寄存器 [英] How to set eax register in, inline assembly C++

问题描述

eax和ebx是32位寄存器。 a []和b []数组有4个字符和32位数据。我可以在每个寄存器中单独设置数组的每个索引，例如mov eax，a [1]。

但是我想将所有4个数组'a'的字符设置为eax寄存器。重要的是序列。我想设置这两个寄存器而不对数组内容序列进行任何更改。例如，第一个数组是[0] ='a'，a [1] ='b'，a [2] ='c'，a [3] ='d'，eax寄存器必须为abcd 。我怎么能这样做？



我尝试过：

eax and ebx are 32 bits registers. a[] and b[] arrays have 4 chars and 32 bits data. i can separately set each index of array in each register for example mov eax,a[1].
but I wanna set all 4 chars of array 'a' to eax register. the important thing is the sequence. I want to set those two registers without any changes in the arrays content sequence. for example first array is a[0]='a',a[1]='b',a[2]='c',a[3]='d' and the eax register must be as "abcd". how can I do that?

What I have tried:

<pre lang="c++">
int _tmain()
{
char b[4],a[4];
b[0]='A',b[1]='T',b[2]='C',b[3]='G';
a[0]='A',a[1]='T',a[2]='C',a[3]='G';
__asm
{
    movzx eax,a[1]  //here i want to load all 4 char of a
    movzx ebx,b[1]  //here i want to load all 4 char of b 
}
getchar();
return 0;
}

推荐答案

编译器知道数组是char类型并生成一个

The compiler knows that the arrays are of type char and generates a

MOV EAX,BYTE PTR [addr]

如果要从字节数组加载32位值，请告诉编译器他必须加载32位字（未经测试但应该这样做）：

If you want to load a 32 bit value from a byte array, tell the compiler that he has to load 32 bit words (untested but should do it):

__asm
{
    mov eax,DWORD PTR [a]
    mov ebx,DWORD PTR [b]
}

或者将 char 数组指针转换为 DWORD 指针：

Or cast the char array pointers to DWORD pointers:

uint32_t* a32 = reinterpret_cast<uint32_t*>(a);
uint32_t* b32 = reinterpret_cast<uint32_t*>(b);
__asm
{
    mov eax,a32[0]
    mov ebx,b32[0]
}

请注意在这两种情况下使用 MOVZX 在源和目的地大小相同时没有任何意义。





同时进行了测试。使用 DWORD PTR 按预期工作，而使用转换指针不起作用（加载寄存器的地址为a32或b32）。

[/ EDIT ]

Note that in both cases using MOVZX makes no sense when source and destination have the same size.


Have tested it meanwhile. Using DWORD PTR works as expected while using a casted pointer does not work (loads register with address of a32 resp. b32).
[/EDIT]

Quote：

eax和ebx是32位寄存器。 a []和b []数组有4个字符和32位数据。我可以在每个寄存器中单独设置数组的每个索引，例如mov eax，a [1]。

eax and ebx are 32 bits registers. a[] and b[] arrays have 4 chars and 32 bits data. i can separately set each index of array in each register for example mov eax,a[1].

首先，你应该尝试更换

first of all, you should try to replace

movzx eax,a[1]  //here i want to load all 4 char of a
movzx ebx,b[1]  //here i want to load all 4 char of b

by

by

movzx eax,a[0]  //here i want to load all 4 char of a
movzx ebx,b[0]  //here i want to load all 4 char of b

因为数组是0的基础C ++。

because arrays are 0 based in C++.

Quote：

如何设置eax寄存器，内联汇编C ++

How to set eax register in, inline assembly C++

否则，你的问题是什么使用此代码？

otherwise, what is your problem with this code ?

这篇关于如何在内联汇编C ++中设置eax寄存器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！