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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, $hi
- 对于以上二者，不存在直接寻址；必须要通过mfhi("move from hi")以及mflo("move from lo")分别来进行访问对应的内容
- 栈的走向是从高地址到低地址
MIPS下各个寄存器编号及描述：
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Register
Number
寄存器编号
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Alternative
Name
寄存器名
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Description
寄存器用途
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0
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zero
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the value 0
永远返回零
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1
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$at
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(assembler temporary) reserved by the assembler
汇编保留寄存器（不可做其他用途）
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2-3
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$v0 - $v1
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(values) from expression evaluation and function results
（Value简写）存储表达式或者是函数的返回值
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4-7
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$a0 - $a3
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(arguments) First four parameters for subroutine.
Not preserved across procedure calls
（Argument简写）存储子程序的前4个参数，在子程序调用过程中释放
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8-15
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$t0 - $t7
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(temporaries) Caller saved if needed. Subroutines can use w/out saving.
Not preserved across procedure calls
（Temp简写）临时变量，同上调用时不保存
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16-23
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$s0 - $s7
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(saved values) - Callee saved.
A subroutine using one of these must save original and restore it before exiting.
Preserved across procedure calls
（Saved or Static简写？）静态变量？调用时保存
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24-25
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$t8 - $t9
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(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~$t7
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26-27
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$k0 - $k1
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reserved for use by the interrupt/trap handler
（breaK off简写？）中断函数返回值，不可做其他用途
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28
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$gp
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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）
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29
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$sp
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stack pointer
Points to last location on the stack.
(Stack Pointer简写）栈指针，指向的是栈顶
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30
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$s8/$fp
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saved value / frame pointer
Preserved across procedure calls
(Saved/Frame Pointer简写)帧指针
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31
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$ra
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return address
返回地址，目测也是不可做其他用途
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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
- create storage for variable of specified type with given name and specified value
- value(s) usually gives initial value(s); for storage type .space, gives number of spaces to be allocated
- 通常给变量赋一个初始值；对于.space,需要指明需要多少大小空间（bytes)
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 D $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 |
Code
in $v0
对应功能的调用码
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Arguments
所需参数
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Results
返回值
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print_int
打印一个整型
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$v0 = 1
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$a0 = integer to be printed
将要打印的整型赋值给 $a0
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print_float
打印一个浮点
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$v0 = 2
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$f12 = float to be printed
将要打印的浮点赋值给 $f12
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print_double
打印双精度
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$v0 = 3
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$f12 = double to be printed
将要打印的双精度赋值给 $f12
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| print_string |
$v0 = 4
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$a0 = address of string in memory
将要打印的字符串的地址赋值给 $a0
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| read_int |
$v0 = 5
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integer returned in $v0
将读取的整型赋值给 $v0
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read_float
读取浮点
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$v0 = 6
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float returned in $v0
将读取的浮点赋值给 $v0
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read_double
读取双精度
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$v0 = 7
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double returned in $v0
将读取的双精度赋值给 $v0
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read_string
读取字符串
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$v0 = 8
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$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 $a1
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sbrk
应该同C中的sbrk()函数
动态分配内存
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$v0 = 9
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$a0 = amount
需要分配的空间大小（单位目测是字节 bytes）
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address in $v0
将分配好的空间首地址给 $v0
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exit
退出
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$v0 =10
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你懂得 |
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- 大概意思是要打印的字符串应该有一个终止符，估计类似C中的'\0', 在这里我们只要声明字符串为 .asciiz 类型即可。下面给个我用Mars4.4的提示：
 - .ascii 与 .asciiz唯一区别就是 后者会在字符串最后自动加上一个终止符， 仅此而已
- The read_int, read_float and read_double services read an entire line of input up to and including the newline character.
- 对于读取整型， 浮点型，双精度的数据操作， 系统会读取一整行，（也就是说以换行符为标志 '\n'）
- The read_string service has the same semantices as the UNIX library routine fgets.
- It reads up to n-1 characters into a buffer and terminates the string with a null character.
- If fewer than n-1 characters are in the current line, it reads up to and including the newline and terminates the string with a null character.
- 这个不多说了，反正就是输入过长就截取，过短就这样，最后都要加一个终止符。
- The sbrk service returns the address to a block of memory containing n additional bytes. This would be used for dynamic memory allocation.
- 上边的表里已经说得很清楚了。
- The exit service stops a program from running.
- 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 Tutorial》
你都看到这里了， 难道还怕点那么一个赞么~~~~~ 
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