设置SVC模式

清0：bic

置1：orr

访问cpsr和spdr要用到mrs和msr指令

mrs是把状态寄存器的值赋给通用寄存器

msr是把通用寄存器的值赋给状态寄存器

 1 .text
 2 .global _start
 3 _start:
 4     b reset
 5     ldr pc, _undefined_instruction
 6     ldr pc, _software_interrupt
 7     ldr pc, _prefetch_abort
 8     ldr pc, _data_abort
 9     ldr pc, _not_used
10     ldr pc, _irq
11     ldr pc, _fiq
12
13 _undefined_instruction: .word undefined_instruction
14 _software_interrupt:.word software_interrupt
15 _prefetch_abort:.word prefetch_abort
16 _data_abort:.word data_abort
17 _not_used:.word not_used
18 _irq:.word irq
19 _fiq:.word fiq
20
21 undefined_instruction:
22     nop
23
24 software_interrupt:
25     nop
26
27 prefetch_abort:
28     nop
29
30 data_abort:
31     nop
32
33 not_used:
34     nop
35
36 irq:
37     nop
38
39 fiq:
40     nop
41
42 reset:
43     bl set_svc
44
45 set_svc:
46     mrs r0, cpsr
47     bic r0, r0, #0x1f
48     orr r0, r0, #0xd3
49     msr cpsr, r0

黄色部分就是设置处理器在svc模式

原文地址：https://www.cnblogs.com/sanshijvshi/p/8335116.html