【十分钟教会你汇编】MIPS编程入门
无意中找到一篇十分好用,而且篇幅也不是很大的入门教程,通篇阅后,再把“栗子”敲一遍,基本可以有一个比较理性的认识,从而方便更好地进一步深入学习。
废话不多说,上干货(英语好的直接跳过本人的渣翻译了哈——!纯本人手打原创,有错请指教,要转载请声明出处,谢~~):
MIPS Architecture and Assembly Language Overview
MIPS架构及其汇编初步
(开始之前稍微再提下,整体分为4个结构:)
1:寄存器种类;
2:算术及寻址指令
3:程序结构
4:系统调用
Data Types and Literals
数据类型
- 所有MIPS指令都是32位长的
- 各单位:1字节=8位,半字长=2个字节,1字长=4个字节
- 一个字符空间=1个字节
- 一个整型=一个字长=4个字节
- 单个字符用单引号,例如:'b'
- 字符串用双引号,例如:"A string"
Registers
寄存器
- MIPS下一共有32个通用寄存器
- 在汇编中,寄存器标志由$符开头
- 寄存器表示可以有两种方式
- 直接使用该寄存器对应的编号,例如:从$0到$31
- 使用对应的寄存器名称,例如:$t1, $sp(详细含义,下文有表格
- 对于乘法和除法分别有对应的两个寄存器$lo, $hi
- 对于以上二者,不存在直接寻址;必须要通过mfhi("move from hi")以及mflo("move from lo")分别来进行访问对应的内容
- 栈的走向是从高地址到低地址
MIPS下各个寄存器编号及描述:
RegisterNumber寄存器编号 |
Alternative Name寄存器名 |
Description寄存器用途 |
---|---|---|
0 |
zero |
the value 0永远返回零 |
1 |
$at |
(assembler temporary) reserved by the assembler汇编保留寄存器(不可做其他用途) |
2-3 |
$v0 - $v1 |
(values) from expression evaluation and function results(Value简写)存储表达式或者是函数的返回值 |
4-7 |
$a0 - $a3 |
(arguments) First four parameters for subroutine.Not preserved across procedure calls(Argument简写)存储子程序的前4个参数,在子程序调用过程中释放 |
8-15 |
$t0 - $t7 |
(temporaries) Caller saved if needed. Subroutines can use w/out saving.Not preserved across procedure calls(Temp简写)临时变量,同上调用时不保存 |
16-23 |
$s0 - $s7 |
(saved values) - Callee saved. A subroutine using one of these must save original and restore it before exiting.Preserved across procedure calls(Saved or Static简写?)静态变量?调用时保存 |
24-25 |
$t8 - $t9 |
(temporaries) Caller saved if needed. Subroutines can use w/out saving.These are in addition to $t0 - $t7 above.Not preserved across procedure calls.(Temp简写)算是前面$0~$7的一个继续,属性同$t0~$t7 |
26-27 |
$k0 - $k1 |
reserved for use by the interrupt/trap handler(breaK off简写?)中断函数返回值,不可做其他用途 |
28 |
$gp |
global pointer. Points to the middle of the 64K block of memory in the static data segment.(Global Pointer简写)指向64k(2^16)大小的静态数据块的中间地址(字面上好像就是这个意思,块的中间) |
29 |
$sp |
stack pointer Points to last location on the stack.(Stack Pointer简写)栈指针,指向的是栈顶 |
30 |
$s8/$fp |
saved value / frame pointerPreserved across procedure calls(Saved/Frame Pointer简写)帧指针 |
31 |
$ra |
return address返回地址,目测也是不可做其他用途 |
Program Structure
程序结构
- 本质其实就只是数据声明+普通文本+程序编码(文件后缀为.s,或者.asm也行)
- 数据声明在代码段之后(其实在其之前也没啥问题,也更符合高级程序设计的习惯)
Data Declarations
数据声明
- 数据段以 .data为开始标志
- 声明变量后,即在主存中分配空间。
Code
代码
- 代码段以 .text为开始标志
- 其实就是各项指令操作
- 程序入口为main:标志(这个都一样啦)
- 程序结束标志(详见下文)
Comments
注释
- 同C系语言
-
- MIPS程序的基本模板如下: # Comment giving name of program and description of function # 说明下程序的目的和作用(其实和高级语言都差不多了) # Template.s #Bare-bones outline of MIPS assembly language program .data # variable declarations follow this line # 数据变量声明 # ... .text # instructions follow this line # 代码段部分 main: # indicates start of code (first instruction to execute) # 主程序 # ... # End of program, leave a blank line afterwards to make SPIM happy # 必须多给你一行,你才欢?
Data Declarations
数据声明
format for declarations: 声明的格式:
name: storage_type value(s)
变量名:(冒号别少了) 数据类型 变量值
Note: labels always followed by colon ( : )
example
var1: .word 3 # create a single integer variable with initial value 3
# 声明一个 word 类型的变量 var1, 同时给其赋值为 3
array1: .byte 'a','b' # create a 2-element character array with elements initialized
# to a and b
# 声明一个存储2个字符的数组 array1,并赋值 'a', 'b'
array2: .space 40 # allocate 40 consecutive bytes, with storage uninitialized
# could be used as a 40-element character array, or a
# 10-element integer array; a comment should indicate which!
# 为变量 array2 分配 40字节(bytes)未使用的连续空间,当然,对于这个变量
# 到底要存放什么类型的值, 最好事先声明注释下!
Load / Store Instructions
加载/保存(也许这里写成读取/写入 可能更易理解一点) 指令集
- 如果要访问内存,不好意思,你只能用 load 或者 store 指令
- 其他的只能都一律是寄存器操作
load:
lw register_destination, RAM_source
#copy word (4 bytes) at source RAM location to destination register. 从内存中 复制 RAM_source 的内容到 对应的寄存器中 (lw中的'w'意为'word',即该数据大小为4个字节)
lb register_destination, RAM_source
#copy byte at source RAM location to low-order byte of destination register, # and sign-e.g.tend to higher-order bytes 同上, lb 意为 load byte
store word:
sw register_source, RAM_destination
#store word in source register into RAM destination #将指定寄存器中的数据 写入 到指定的内存中
sb register_source, RAM_destination
#store byte (low-order) in source register into RAM destination
load immediate:
li register_destination, value
#load immediate value into destination register 顾名思义,这里的 li 意为 load immediate
example:
.data
var1: .word 23 # declare storage for var1; initial value is 23
# 先声明一个 word 型的变量 var1 = 3;
.text
__start:
lw $t0, var1 # load contents of RAM location into register $t0: $t0 = var1
# 令寄存器 $t0 = var1 = 3;
li $t1, 5 # $t1 = 5 ("load immediate")
# 令寄存器 $t1 = 5;
sw $t1, var1 # store contents of register $t1 into RAM: var1 = $t1
# 将var1的值修改为$t1中的值:var1 = $t1 = 5;
done
Indirect and Based Addressing
立即与间接寻址
load address:
直接给地址
la $t0, var1
- copy RAM address of var1 (presumably a label defined in the program) into register $t0
indirect addressing:
地址是寄存器的内容(可以理解为指针)
lw $t2, ($t0)
- load word at RAM address contained in $t0 into $t2
sw $t2, ($t0)
- store word in register $t2 into RAM at address contained in $t0
based or indexed addressing:
+偏移量
lw $t2, 4($t0)
- load word at RAM address ($t0+4) into register $t2
- "4" gives offset from address in register $t0
sw $t2, -12($t0)
- store word in register $t2 into RAM at address ($t0 - 12)
- negative offsets are fine
Note: based addressing is especially useful for:
不必多说,要用到偏移量的寻址,基本上使用最多的场景无非两种:数组,栈。
- arrays; access elements as offset from base address
- stacks; easy to access elements at offset from stack pointer or frame pointer
example:
栗子:
.data
array1: .space 12 # declare 12 bytes of storage to hold array of 3 integers
# 定义一个 12字节 长度的数组 array1, 容纳 3个整型
.text
__start: la $t0, array1 # load base address of array into register $t0
# 让 $t0 = 数组首地址
li $t1, 5 # $t1 = 5 ("load immediate")
sw $t1, ($t0) # first array element set to 5; indirect addressing
# 对于 数组第一个元素赋值 array[0] = $1 = 5
li $t1, 13 # $t1 = 13
sw $t1, 4($t0) # second array element set to 13
# 对于 数组第二个元素赋值 array[1] = $1 = 13
# (该数组中每个元素地址相距长度就是自身数据类型长度,即4字节, 所以对于array+4就是array[1])
li $t1, -7 # $t1 = -7
sw $t1, 8($t0) # third array element set to -7
# 同上, array+8 = (address[array[0])+4)+ 4 = address(array[1]) + 4 = address(array[2])
done
Arithmetic Instructions
算术指令集
- 最多3个操作数
- 再说一遍,在这里,操作数只能是寄存器,绝对不允许出现地址
- 所有指令统一是32位 = 4 * 8 bit = 4bytes = 1 word
add $t0,$t1,$t2 # $t0 = $t1 + $t2; add as signed (2's complement) integers
sub $t2,$t3,$t4 # $t2 = $t3 Ð $t4
addi $t2,$t3, 5 # $t2 = $t3 + 5; "add immediate" (no sub immediate)
addu $t1,$t6,$t7 # $t1 = $t6 + $t7; add as unsigned integers
subu $t1,$t6,$t7 # $t1 = $t6 + $t7; subtract as unsigned integers
mult $t3,$t4 # multiply 32-bit quantities in $t3 and $t4, and store 64-bit
# result in special registers Lo and Hi: (Hi,Lo) = $t3 * $t4
运算结果存储在hi,lo(hi高位数据, lo地位数据)
div $t5,$t6 # Lo = $t5 / $t6 (integer quotient)
# Hi = $t5 mod $t6 (remainder)
商数存放在 lo, 余数存放在 hi
mfhi $t0 # move quantity in special register Hi to $t0: $t0 = Hi
不能直接获取 hi 或 lo中的值, 需要mfhi, mflo指令传值给寄存器
mflo $t1 # move quantity in special register Lo to $t1: $t1 = Lo
# used to get at result of product or quotient
move $t2,$t3 # $t2 = $t3
Control Structures
控制流
Branches
分支(if else系列)
- comparison for conditional branches is built into instruction
b target # unconditional branch to program label target
beq $t0,$t1,target # branch to target if $t0 = $t1
blt $t0,$t1,target # branch to target if $t0 < $t1
ble $t0,$t1,target # branch to target if $t0 <= $t1
bgt $t0,$t1,target # branch to target if $t0 > $t1
bge $t0,$t1,target # branch to target if $t0 >= $t1
bne $t0,$t1,target # branch to target if $t0 <> $t1
Jumps
跳转(while, for, goto系列)
j target # unconditional jump to program label target
看到就跳, 不用考虑任何条件
jr $t3 # jump to address contained in $t3 ("jump register")
类似相对寻址,跳到该寄存器给出的地址处
Subroutine Calls
子程序调用
subroutine call: "jump and link" instruction
jal sub_label # "jump and link"
- copy program counter (return address) to register $ra (return address register)
- 将当前的程序计数器保存到 $ra 中
- jump to program statement at sub_label
subroutine return: "jump register" instruction
jr $ra # "jump register"
- jump to return address in $ra (stored by jal instruction)
- 通过上面保存在 $ra 中的计数器返回调用前
Note: return address stored in register $ra; if subroutine will call other subroutines, or is recursive, return address should be copied from $ra onto stack to preserve it, since jal always places return address in this register and hence will overwrite previous value
如果说调用的子程序中有调用了其他子程序,如此往复, 则返回地址的标记就用 栈(stack) 来存储, 毕竟 $ra 只有一个, (哥哥我分身乏术啊~~)。
System Calls and I/O (SPIM Simulator)
系统调用 与 输入/输出(主要针对SPIM模拟器)
(本人使用的是Mars 4.4,也通用--!)
- 通过系统调用实现终端的输入输出,以及声明程序结束
- 学会使用 syscall
- 参数所使用的寄存器:$v0, $a0, $a1
- 返回值使用:$v0
下表给出了系统调用中对应功能,代码,参数机返回值
Service |
Codein $v0对应功能的调用码 |
Arguments所需参数 |
Results返回值 |
---|---|---|---|
print_int打印一个整型 |
$v0 = 1 |
$a0 = integer to be printed将要打印的整型赋值给 $a0 |
|
print_float打印一个浮点 |
$v0 = 2 |
$f12 = float to be printed将要打印的浮点赋值给 $f12 |
|
print_double打印双精度 |
$v0 = 3 |
$f12 = double to be printed将要打印的双精度赋值给 $f12 |
|
print_string |
$v0 = 4 |
$a0 = address of string in memory将要打印的字符串的地址赋值给 $a0 |
|
read_int |
$v0 = 5 |
integer returned in $v0将读取的整型赋值给 $v0 |
|
read_float读取浮点 |
$v0 = 6 |
float returned in $v0将读取的浮点赋值给 $v0 |
|
read_double读取双精度 |
$v0 = 7 |
double returned in $v0将读取的双精度赋值给 $v0 |
|
read_string读取字符串 |
$v0 = 8 |
$a0 = memory address of string input buffer将读取的字符串地址赋值给 $a0$a1 = length of string buffer (n)将读取的字符串长度赋值给 $a1 |
|
sbrk应该同C中的sbrk()函数动态分配内存 |
$v0 = 9 |
$a0 = amount需要分配的空间大小(单位目测是字节 bytes) |
address in $v0将分配好的空间首地址给 $v0 |
exit退出 |
$v0 =10 |
你懂得 |
e.g. Print out integer value contained in register $t2
栗子:打印一个存储在寄存器 $2 里的整型
li $v0, 1 # load appropriate system call code into register $v0;
声明需要调用的操作代码为 1 (print_int) 并赋值给 $v0
# code for printing integer is 1
move $a0, $t2 # move integer to be printed into $a0: $a0 = $t2
将要打印的整型赋值给 $a0
syscall # call operating system to perform operation
e.g. Read integer value, store in RAM location with label int_value (presumably declared in data section)
栗子:读取一个数,并且存储到内存中的 int_value 变量中
li $v0, 5 # load appropriate system call code into register $v0;
# code for reading integer is 5
声明需要调用的操作代码为 5 (read_int) 并赋值给 $v0
syscall # call operating system to perform operation、
经过读取操作后, $v0 的值已经变成了 输入的 5
sw $v0, int_value # value read from keyboard returned in register $v0;
# store this in desired location
通过写入(store_word)指令 将 $v0的值(5) 存入 内存中
e.g. Print out string (useful for prompts)
栗子:打印一个字符串(这是完整的,其实上面栗子都可以直接替换main: 部分,都能直接运行)
.data
string1 .asciiz "Print this.n" # declaration for string variable,
# .asciiz directive makes string null terminated
.text
main: li $v0, 4 # load appropriate system call code into register $v0;
# code for printing string is 4
打印字符串, 赋值对应的操作代码 $v0 = 4
la $a0, string1 # load address of string to be printed into $a0
将要打印的字符串地址赋值 $a0 = address(string1)
syscall # call operating system to perform print operation
e.g. To indicate end of program, use exit system call; thus last lines of program should be:
执行到这里, 程序结束, 立马走人, 管他后边洪水滔天~~
li $v0, 10 # system call code for exit = 10
syscall # call operating sys
-------------------------------------------------我是那个分呀分呀分割线--------------------------------------------------------------------------
OK, 十分轻松又愉快的MIPS入门之旅到此告一段落, 下面我把用到的一些软件和这篇文章的原文链接贴到下边,有需要的, 各位客官自取哈~~~
1.Mars4.4
2.PCSpim Simulator
3.《MIPS Qucik Tutoria
- 关于dg broker的简单配置(r5笔记第99天)
- 三天速成 TensorFlow课件分享
- 干货 | 机器学习算法线上部署方法
- 用于快速开发 3D 数据处理软件的开源数据处理库 —— Open3D | Github 项目推荐
- 【java网络】IO编程
- 一周 Github Trending 热门项目,最全中华古诗词数据库 | Github 项目推荐
- 【线程池】线程池与工作队列
- 一个快速方便的图形化 Python 调试器 —— birdseye | Github 项目推荐
- 关于分区表的在线重定义(r5笔记第98天)
- 10个实用的但偏执的Java编程技术
- 看似诡异的tablespace online问题(r5笔记第95天)
- python2.7进行爬虫POI代码(划分小网格算法)
- 从 Encoder 到 Decoder 实现 Seq2Seq 模型
- python2.7进行爬虫百度POI代码(划分小网格算法)
- JavaScript 教程
- JavaScript 编辑工具
- JavaScript 与HTML
- JavaScript 与Java
- JavaScript 数据结构
- JavaScript 基本数据类型
- JavaScript 特殊数据类型
- JavaScript 运算符
- JavaScript typeof 运算符
- JavaScript 表达式
- JavaScript 类型转换
- JavaScript 基本语法
- JavaScript 注释
- Javascript 基本处理流程
- Javascript 选择结构
- Javascript if 语句
- Javascript if 语句的嵌套
- Javascript switch 语句
- Javascript 循环结构
- Javascript 循环结构实例
- Javascript 跳转语句
- Javascript 控制语句总结
- Javascript 函数介绍
- Javascript 函数的定义
- Javascript 函数调用
- Javascript 几种特殊的函数
- JavaScript 内置函数简介
- Javascript eval() 函数
- Javascript isFinite() 函数
- Javascript isNaN() 函数
- parseInt() 与 parseFloat()
- escape() 与 unescape()
- Javascript 字符串介绍
- Javascript length属性
- javascript 字符串函数
- Javascript 日期对象简介
- Javascript 日期对象用途
- Date 对象属性和方法
- Javascript 数组是什么
- Javascript 创建数组
- Javascript 数组赋值与取值
- Javascript 数组属性和方法