设置SVC模式

 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