说明

文档来源

https://flint.cs.yale.edu/cs421/papers/x86-asm/asm.html
使用AT&T语法; 原文档是intel语法翻译过来的;

内容

基于32位, x86的硬件环境;
指令仅仅介绍常用, 即还有很大一部分的指令并没有支持;

编译器(汇编器)

GAS(GNU assembler: 即gnu组织提供; 使用标准AT&T语法;

注意

金介绍少部分指令; 其他指令查官方文档;
使用32位而不是16位; 16比较复杂, 有偏移量之类的;

寄存器

`32`寄存器

eax: Accumulator, 数学计算
ebx:
ecx: Counter, 循环的index
edx:
esp: stack pointer, 栈顶;
ebp: base pointer, 函数第一个局部变量在栈的位置; 上一个是之前的eip地址;
eip: instruction pointer, 指令寄存器;

`16,8`位寄存器

共用寄存器, 也就是一改其他都被改;
eax, ax, ah, al; ax = (ah << 8) + al
好处就是兼容且可以操作更小字节数据;

内存

说明

全局变量或静态变量; 即共享的; bss + dss;

汇编全局变量申请

.data
var:
    .byte 64        /* Declare a byte, referred to as location var, containing the value 64. */

    .byte 10        /* Declare a byte with no label, containing the value 10. Its location is var + 1. */

x:
    .short 42       /* Declare a 2-byte value initialized to 42, referred to as location x. */
y:
    .long 30000     /* Declare a 4-byte value, referred to as location y, initialized to 30000. */

类型, 初始值, 类型决定数据占用字节;

汇编数组申请

s:
    .long 1, 2, 3    /* Declare three 4-byte values, initialized to 1, 2, and 3. The value at location s + 8 will be 3. */

barr:
    .zero 10        /* Declare 10 bytes starting at location barr, initialized to 0. */
str:
    .string "hello" /* Declare 6 bytes starting at the address str initialized to
the ASCII character values for hello followed by a nul (0) byte. */

类型加若干初始值;
.zero加长度
字符串, 加\0

地址格式

地址对应操作

加载地址对应的内存放入寄存器; reg=*addr;
lea: load effective address, 即给地址代表地址, 用地址赋值; reg=addr

三种

一元组: offset(reg)
三元组: offset(reg1, reg2, number), number={2^n|n=[0,3]}即, number={1,2,4,8}; 其他错误;
地址: var(,1), *var
offset, var常数；offset可以为正负数, var同理;

`label`

编译后编程地址; 编程时方便阅读而已;

地址访问几种格式

// eax = *ebx
mov (%ebx), %eax        /* Load 4 bytes from the memory address in EBX into EAX. */

// *var=*ebx
mov %ebx, var(,1)       /* Move the contents of EBX into the 4 bytes at memory address var. (Note, var is a 32-bit constant). */

// eax=*(esi - 4)
mov -4(%esi), %eax      /* Move 4 bytes at memory address ESI + (-4) into EAX. */

// *(esi + eax * 1) = *cl
mov %cl, (%esi,%eax,1)  /* Move the contents of CL into the byte at address ESI+EAX. */

mov (%esi,%ebx,4), %edx /* Move the 4 bytes of data at address ESI+4*EBX into EDX. */