指令是32位
byte 8位，halfword 2个字节，word 4个字节
字面量
数字，如4
字符，如'b'
字符串，如"A string"
32个通用寄存器。
寄存器在汇编语言指令中用$开头，如$0
寄存器可以使用名字$0-$31，或别名，如$sp
特殊寄存器 Lo Hi 用来存储乘和除的运算结果，不能直接访问，使用特殊的指令mfhi和mflo拷贝到其它寄存器。
栈从高内存到低内存生长
寄存器
| Register Number | Alternative Name | Description |
|---|---|---|
0 | zero | the value 0 |
1 | $at | (assembler temporary) reserved by the assembler |
2-3 | $v0 - $v1 | (values) from expression evaluation and function results |
4-7 | $a0 - $a3 | (arguments) First four parameters for subroutine. Not preserved across procedure calls |
8-15 | $t0 - $t7 | (temporaries) Caller saved if needed. Subroutines can use w/out saving. Not preserved across procedure calls |
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 |
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. |
26-27 | $k0 - $k1 | reserved for use by the interrupt/trap handler |
28 | $gp | global pointer. Points to the middle of the 64K block of memory in the static data segment. |
29 | $sp | stack pointer Points to last location on the stack. |
30 | $s8/$fp | saved value / frame pointer Preserved across procedure calls |
31 | $ra | return address |
数据段
.data
代码段
.text
注释
# 之后的内容
# commemt start
.data # data segment
main:
格式
name : storage type value(s)
如果类型是.space，则value表示多个字节
var1: .word 3
array1: .byte 'a', 'b'
array2: .space 40
内存访问只能通过 load /store指令
所有其它的指令只能操作寄存器
load:
lw register_destination, RAM_source #拷贝4字节
lb register_destination, RAM_source #拷贝1个字节
store:
sw
sb
拷贝立即数（硬编码在指令里）
li register_destination, value
example:
.data
var1: .word 23 # declare storage for var1; initial value is 23
.text
__start:
lw $t0, var1 # load contents of RAM location into register $t0: $t0 = var1
li $t1, 5 # $t1 = 5 ("load immediate")
sw $t1, var1 # store contents of register $t1 into RAM: var1 = $t1
doneload address:
la $t0, var1
加载label var1的地址到$t0寄存器
indirect addressing
lw $t2 ($t0)
加载$t0寄存器表示的地址处的内容到寄存器$t2
sw $t2, ($t0)
based or indexed address
lw $t2, 4($t0)
sw $t2, -12($t0)
example
.data
array1: .space 12 # declare 12 bytes of storage to hold array of 3 integers
.text
__start: la $t0, array1 # load base address of array into register $t0
li $t1, 5 # $t1 = 5 ("load immediate")
sw $t1, ($t0) # first array element set to 5; indirect addressing
li $t1, 13 # $t1 = 13
sw $t1, 4($t0) # second array element set to 13
li $t1, -7 # $t1 = -7
sw $t1, 8($t0) # third array element set to -7
done大多数使用3个指令
所有的操作数是寄存器
大小是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 div $t5,$t6 # Lo = $t5 / $t6 (integer quotient) # Hi = $t5 mod $t6 (remainder) mfhi $t0 # move quantity in special register Hi to $t0: $t0 = Hi 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
branches 跳转
16位表示地址，跳转范围64K
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
26位表示地址，跳转范围更大
j target # unconditional jump to program label target
jr $t3 # jump to address contained in $t3 ("jump register")Subroutine Calls
jal sub_label # "jump and link"
拷贝program counter (return address) 到 $ra （return address register)
跳转到sub_label处执行
subroutine return
jr $ra # "jump register"
如有函数嵌套调用，要把$ra保存到栈中。
System Calls
syscall指令，参数存储到通用寄存器
参考
MIPS Instruction Reference. http://www.mrc.uidaho.edu/mrc/people/jff/digital/MIPSir.html
MIPS32® Instruction Set Quick Reference. https://www2.cs.duke.edu/courses/fall13/compsci250/MIPS32_QRC.pdf
MIPS Architecture and Assembly Language Overview. http://logos.cs.uic.edu/366/notes/mips%20quick%20tutorial.htm
https://en.wikipedia.org/wiki/MIPS_architecture
https://learnxinyminutes.com/docs/mips/