MIPS汇编语言之常用指令介绍

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时间 2021-11-22 11:15:57

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简介

咱们知道x86架构cpu用于PC端和工作站较多,ARM架构cpu常见于手机和单片机,那么MIPS架构的cpu主要在哪些设备可以找到它们的身影呢?

  • 中国龙芯
  • PS游戏机

学习环境搭建

  • 安装JDK, 主要用于运行mips模拟器mars
  • MARS模拟器:http://courses.missouristate.edu/KenVollmar/mars/download.htm

寄存器

在mips中通用寄存器用$开头表示,一共有32个

| 寄存器编号 | 寄存器名 | 寄存器用途 | | :----------: | :------------------------------------------------------------ :|: -----------------------------------------------------------:| | $0 | $zero | 永远返回0 | | $1 | $at | 保留寄存器 | | $2-$3 | $v0-$v1 | 一般用于存储表达式或者函数的返回值(value的简写) | | $4-$7 | $a0-$a3 | 参数寄存器(Argument简写) | | $8-$15 | $t0-$t7 | 一般用于存储临时变量(temp简写) | | $16-$23 | $s0-$s7 | 存放子函数调用过程需要被保留的数据(saved values) | | $24-$25 | $t8-$t9 | 属性同$t0-$t7 | | $26-$27 | $k0-$k1 | 一般存储中断函数返回值 | | $28 | $gp | GlobalPointer简写 | | $29 | $sp | 栈指针，指向栈顶(Stack Pointer简写) | | $30 | $s8/$fp | (Save / Frame Pointer)帧指针 | | $31 | $ra | 一般用于存储函数返回地址(return address简写) |

寄存器编号和别名一一对应,同一个寄存器可以有两种不同表示方法:$0或者$zero

  • program counter (PC) 无法直接修改，通过跳转指令可以改动
  • HI 和 LO ：这两个寄存器特别用来保存乘法、除法、乘法累加的结果。

MIPS汇编中的分段处理

```assembly .data #数据段

.text #代码段 ```

传送指令

  1. 加载立即数指令 li

li(load immediate) :用于将立即数传送给寄存器

assembly li $t0,1 ;十六进制数据使用0x前缀表示

  1. 加载地址指令 la

la(load address) :用于将地址传送至寄存器中, 多用于通过地址获取数据段中的地址

```assembly .data msg: .ascii "hello world"

.text la $a0,msg # 将字符串数据所在的地址赋值给$a0寄存器

```

  1. 寄存器数据传送指令move

用于将一个寄存器中的数据传送至另一个寄存器当中

assembly move $t0,$t1 # 将寄存器$t1中的数据传送至$t0

系统服务指令 syscall

在C语言中输出文本可以使用printf函数,但是汇编中没有printf这么一说,如果想要输出文本,需要借助syscall指令

如果想要输出一个数字1,那么syscall指令从$a0寄存器中取出需要输出的数据

因此, 你在执行syscall指令之前需要将数据提前放入$a0之中:

assembly li $a0,1 syscall

同时,还需要指定输出的数据类型,数据类型的指定保存在$v0寄存器中

```assembly

$v0=1, syscall--->print_int

$v0=4, syscall--->print_string

```

$v0存入1,表示syscall将$a0中的数据当做数字输出

$v0存入4,表示syscall将$a0中的数据当做数据的地址,然后输出对应的数据

syscall指令读写对照表

| Service | Code in $v0 | Arguments | Result | | ------------------------------------------------------------ | ----------- | ------------------------------------------------------------ | ------------------------------------------------------------ | | print integer | 1 | $a0 = integer to print | | | print float | 2 | $f12 = float to print | | | print double | 3 | $f12 = double to print | | | print string | 4 | $a0 = address of null-terminated string to print | | | read integer | 5 | | $v0 contains integer read | | read float | 6 | | $f0 contains float read | | read double | 7 | | $f0 contains double read | | read string | 8 | $a0 = address of input buffer $a1 = maximum number of characters to read | See note below table | | sbrk (allocate heap memory) | 9 | $a0 = number of bytes to allocate | $v0 contains address of allocated memory | | exit (terminate execution) | 10 | | | | print character | 11 | $a0 = character to print | See note below table | | read character | 12 | | $v0 contains character read | | open file | 13 | $a0 = address of null-terminated string containing filename $a1 = flags $a2 = mode | $v0 contains file descriptor (negative if error). See note below table | | read from file | 14 | $a0 = file descriptor $a1 = address of input buffer $a2 = maximum number of characters to read | $v0 contains number of characters read (0 if end-of-file, negative if error). See note below table | | write to file | 15 | $a0 = file descriptor $a1 = address of output buffer $a2 = number of characters to write | $v0 contains number of characters written (negative if error). See note below table | | close file | 16 | $a0 = file descriptor | | | exit2 (terminate with value) | 17 | $a0 = termination result | See note below table | | Services 1 through 17 are compatible with the SPIM simulator, other than Open File (13) as described in the Notes below the table. Services 30 and higher are exclusive to MARS. | | | | | time (system time) | 30 | | $a0 = low order 32 bits of system time $a1 = high order 32 bits of system time. See note below table | | MIDI out | 31 | $a0 = pitch (0-127) $a1 = duration in milliseconds $a2 = instrument (0-127) $a3 = volume (0-127) | Generate tone and return immediately. See note below table | | sleep | 32 | $a0 = the length of time to sleep in milliseconds. | Causes the MARS Java thread to sleep for (at least) the specified number of milliseconds. This timing will not be precise, as the Java implementation will add some overhead. | | MIDI out synchronous | 33 | $a0 = pitch (0-127) $a1 = duration in milliseconds $a2 = instrument (0-127) $a3 = volume (0-127) | Generate tone and return upon tone completion. See note below table | | print integer in hexadecimal | 34 | $a0 = integer to print | Displayed value is 8 hexadecimal digits, left-padding with zeroes if necessary. | | print integer in binary | 35 | $a0 = integer to print | Displayed value is 32 bits, left-padding with zeroes if necessary. | | print integer as unsigned | 36 | $a0 = integer to print | Displayed as unsigned decimal value. | | (not used) | 37-39 | | | | set seed | 40 | $a0 = i.d. of pseudorandom number generator (any int). $a1 = seed for corresponding pseudorandom number generator. | No values are returned. Sets the seed of the corresponding underlying Java pseudorandom number generator (java.util.Random). See note below table | | random int | 41 | $a0 = i.d. of pseudorandom number generator (any int). | $a0 contains the next pseudorandom, uniformly distributed int value from this random number generator's sequence. See note below table | | random int range | 42 | $a0 = i.d. of pseudorandom number generator (any int). $a1 = upper bound of range of returned values. | $a0 contains pseudorandom, uniformly distributed int value in the range 0 = [int] [upper bound], drawn from this random number generator's sequence. See note below table | | random float | 43 | $a0 = i.d. of pseudorandom number generator (any int). | $f0 contains the next pseudorandom, uniformly distributed float value in the range 0.0 = f 1.0 from this random number generator's sequence. See note below table | | random double | 44 | $a0 = i.d. of pseudorandom number generator (any int). | $f0 contains the next pseudorandom, uniformly distributed double value in the range 0.0 = f 1.0 from this random number generator's sequence. See note below table | | (not used) | 45-49 | | | | ConfirmDialog | 50 | $a0 = address of null-terminated string that is the message to user | $a0 contains value of user-chosen option 0: Yes 1: No 2: Cancel | | InputDialogInt | 51 | $a0 = address of null-terminated string that is the message to user | $a0 contains int read $a1 contains status value 0: OK status -1: input data cannot be correctly parsed -2: Cancel was chosen -3: OK was chosen but no data had been input into field | | InputDialogFloat | 52 | $a0 = address of null-terminated string that is the message to user | $f0 contains float read $a1 contains status value 0: OK status -1: input data cannot be correctly parsed -2: Cancel was chosen -3: OK was chosen but no data had been input into field | | InputDialogDouble | 53 | $a0 = address of null-terminated string that is the message to user | $f0 contains double read $a1 contains status value 0: OK status -1: input data cannot be correctly parsed -2: Cancel was chosen -3: OK was chosen but no data had been input into field | | InputDialogString | 54 | $a0 = address of null-terminated string that is the message to user $a1 = address of input buffer $a2 = maximum number of characters to read | See Service 8 note below table $a1 contains status value 0: OK status. Buffer contains the input string. -2: Cancel was chosen. No change to buffer. -3: OK was chosen but no data had been input into field. No change to buffer. -4: length of the input string exceeded the specified maximum. Buffer contains the maximum allowable input string plus a terminating null. | | MessageDialog | 55 | $a0 = address of null-terminated string that is the message to user $a1 = the type of message to be displayed: 0: error message, indicated by Error icon 1: information message, indicated by Information icon 2: warning message, indicated by Warning icon 3: question message, indicated by Question icon other: plain message (no icon displayed) | N/A | | MessageDialogInt | 56 | $a0 = address of null-terminated string that is an information-type message to user $a1 = int value to display in string form after the first string | N/A | | MessageDialogFloat | 57 | $a0 = address of null-terminated string that is an information-type message to user $f12 = float value to display in string form after the first string | N/A | | MessageDialogDouble | 58 | $a0 = address of null-terminated string that is an information-type message to user $f12 = double value to display in string form after the first string | N/A | | MessageDialogString | 59 | $a0 = address of null-terminated string that is an information-type message to user $a1 = address of null-terminated string to display after the first string | N/A |

使用syscall指令输出helloworld示例:

```assembly .data

msg: .ascii "hello world\0" #类似于C语言中 char* msg="hello world"

.text la $a0,msg li $v0,4 syscall ```

Mips汇编指令汇总表

类别

指令名称

实例

含义

注释

英文注解

算

数

加法

add $s1,  $s2,  $s3

$s1 = $s2 + $s3

三个寄存器操作数

addition 加法

减法

sub $s1,  $s2,  $s3

$s1 = $s2 - $s3

三个寄存器操作数

subtraction 减法

立即数加法

addi $s1, $s2,  20

$s1 = $s2 + 20

用于加常数数据

add immediate 立即加法

数

据

传

输

取字

lw $s1, 20 ($s2)

$s1 = Memory[$s2 + 20]

将一个字从内存中取到寄存器中

load word 加载字

存字

sw $s1, 20 ($s2)

Memory[$s2 + 20] = $s1

将一个字从寄存器中取到内存中

store word 存储字

取半字

lh $s1, 20 ($s2)

$s1 = Memory[$s2 + 20]

将半个字从内存中取到寄存器中

load halfword 加载半字

取无符号半字

lhu $s1, 20 ($s2)

$s1 = Memory[$s2 + 20]

将半个字从内存中取到寄存器中

load halfword unsigned

存半字

sh $s1, 20 ($s2)

Memory[$s2 + 20] = $s1

将半个字从寄存器中取到内存中

stroe halfword 存储半字

取字节

lb $s1, 20 ($s2)

$s1 = Memory[$s2 + 20]

将一字节从内存中取到寄存器中

load byte

取无符号字节

lbu $s1, 20 ($s2)

$s1 = Memory[$s2 + 20]

将一字节从内存中取到寄存器中

load byte unsigned

存字节

sb $s1, 20 ($s2)

Memory[$s2 + 20] = $s1

将一字节从寄存器中取到内存中

store byte

取链接字

ll $s1, 20 ($s2)

$s1 = Memory[$s2 + 20]

取字作为原子交换的前半部

load linked

存条件字

sc $s1, 20 ($s2)

Memory[$s2 + 20] = $s1;

$s1 = 0 or 1

存字作为原子交换的后半部分

store conditional

取立即数的高位

lui $s1, 20

$s1 = 20 * 216

取立即数并放到高16位

load upper immediate

逻

辑

与

and $s1, $s2, $s3

$s1 = $s2 & $s3

三个寄存器操作数按位与

and

或

or $s1, $s2, $s3

$s1 = $s2 | $s3

三个寄存器操作数按位或

or

或非

nor $s1, $s2, $s3

$s1 = ~ ($s2 | $s3)

三个寄存器操作数按位或非

not or

立即数与

andi $s1, $s2, 20

$s1 = $s2 & 20

和常数按位与

and immediate

立即数或

ori $s1, $s2, 20

$s1 = $s2 | 20

和常数按位或

or immediate

逻辑左移

sll $s1, $s2, 10

$s1 = $s2 << 20

根据常数左移相应位

set left logical

逻辑右移

srl $s1, $s2, 10

$s1 = $s2 >> 20

根据常数右移相应位

set right logical

条

件

分

支

相等时跳转

beq $s1, $s2, 25

if ($s1 == $s2) go to 

PC + 4 + 25 * 4

相等检测：

和PC相关的跳转

branch on equal

不相等时跳转

bne $s1, $s2, 25

if ($s1 != $s2) go to 

PC + 4 + 25 * 4

不相等检测：

和PC相关的跳转

branch on not equal

小于时跳转

slt $1, $s2, $3

if ($s2 < $s3) $s1 = 1; 

else $s1 = 0

比较是否小于

set less than

无符号数比较小时置位

sltu $1, $s2, $3

if ($s2 < $s3) $s1 = 1; 

else $s1 = 0

比较是否小于无符号数

set less than unsigned

无符号数小于立即数时置位

slti $1, $s2, 20

if ($s2 < 20) $s1 = 1; 

else $s1 = 0

比较是否小于常数

set less than immediate

无符号数比较小于无符号立即数时置位

sltiu $1, $s2, 20

if ($s2 < 20) $s1 = 1; 

else $s1 = 0

比较是否小于无符号常数

set less than immediate unsigned

无

条

件

跳

转

跳转

j 2500

go to 2500 * 4

跳转到目标地址

jump

跳转至寄存器所指位置

jr $ra

go to $ra

用于switch语句，以及过程调用

jump register

跳转并链接

jal 2500

$ra = PC + 4;

go to 2500 * 4;

用于过程调用(方法)

正常的执行流程执行完A自然要执行B指令，现在要跳转执行C方法，这时就把B地址存入寄存器中，执行完C后跳转到B

jump and link

Mips内存结构图:

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