ARM汇编程序闪烁灯与其反汇编代码比较

/*
*LED闪烁
*led.s
*/
 #define GPJ0CON 0xE0200240
 #define GPJ0DAT 0xE0200244
 .global _start                //把 _start 链接属性改为外部
_start:
    //第一步 ：把0x1111 1111写入 0xe0200240(gpj0con)
    ldr r0, =0x11111111   //这里ldr 为伪指令 
    ldr r1,    =GPJ0CON
    str r0, [r1]          //寄存器间接寻址 将r0的值给ri所指地址的内存中
    
    
flash:
    //第二部：把 0x0写入0xe0200244（GPJ0DAT） 点亮
    //ldr r0, =0x28//  第一种 缺陷是需要人为计算设定值  可阅读型差    
    
    ldr r0, =(0<<3) |(0<<4)| (0<<5)// 等效于 0b0010_1000 即 0x28
    ldr r1, =GPJ0DAT
    str r0, [r1]            //点亮
    //第三步: 延迟
    bl delay                //使用bl进行调用可以将当前执行地址存入lr
    
    //第四部：灭
    //ldr r0, =0x28//  第一种 缺陷是需要人为计算设定值  可阅读型差    
    
    ldr r0, =(1<<3) |(1<<4)| (1<<5)
    ldr r1, =GPJ0DAT
    str r0, [r1]            //熄灭
    bl delay    
    b flash                   
    
    b .                       //写一个死循环 防止CPU跑飞
    
delay:
    ldr r2, =1000000
    ldr r3, =0
delay_loop:
    sub r2, r2, #1      //r2=r2-1
    cmp r2, r3        //cmp 比较r2 r3 如果相等 Z 为1
    bne delay_loop    //bne 为当Z为1时执行跳转  bne 为 b+后缀
    mov pc, lr          //函数调用返回  mov 为 寄存器间寻址    

 反汇编

led.elf:     file format elf32-littlearm


Disassembly of section .text:

00000000 <_start>:
   0:    e59f0044     ldr    r0, [pc, #68]    ; 4c <delay_loop+0x10>
   4:    e59f1044     ldr    r1, [pc, #68]    ; 50 <delay_loop+0x14>
   8:    e5810000     str    r0, [r1]

0000000c <flash>:
   c:    e3a00000     mov    r0, #0
  10:    e59f103c     ldr    r1, [pc, #60]    ; 54 <delay_loop+0x18>
  14:    e5810000     str    r0, [r1]
  18:    eb000005     bl    34 <delay>
  1c:    e3a00038     mov    r0, #56    ; 0x38
  20:    e59f102c     ldr    r1, [pc, #44]    ; 54 <delay_loop+0x18>
  24:    e5810000     str    r0, [r1]
  28:    eb000001     bl    34 <delay>
  2c:    eafffff6     b    c <flash>
  30:    eafffffe     b    30 <flash+0x24>

00000034 <delay>:
  34:    e59f201c     ldr    r2, [pc, #28]    ; 58 <delay_loop+0x1c>
  38:    e3a03000     mov    r3, #0

0000003c <delay_loop>:
  3c:    e2422001     sub    r2, r2, #1
  40:    e1520003     cmp    r2, r3
  44:    1afffffc     bne    3c <delay_loop>
  48:    e1a0f00e     mov    pc, lr
  4c:    11111111     tstne    r1, r1, lsl r1
  50:    e0200240     eor    r0, r0, r0, asr #4
  54:    e0200244     eor    r0, r0, r4, asr #4
  58:    000f4240     andeq    r4, pc, r0, asr #4

Disassembly of section .ARM.attributes:

00000000 <.ARM.attributes>:
   0:    00001a41     andeq    r1, r0, r1, asr #20
   4:    61656100     cmnvs    r5, r0, lsl #2
   8:    01006962     tsteq    r0, r2, ror #18
   c:    00000010     andeq    r0, r0, r0, lsl r0
  10:    45543505     ldrbmi    r3, [r4, #-1285]    ; 0x505
  14:    08040600     stmdaeq    r4, {r9, sl}
  18:    Address 0x00000018 is out of bounds.