jiffies存放

固然书本上讲明jiffies是jiffies_64的低32位，但是我还是自己测试了下，重点在于链接脚本的写法。

此处只是为了测试，因此简化链接脚本。

 /* link.lds */
 1 ENTRY(_start)                                                                                                      

 2 

 3 jiffies = jiffies_64;

 4 

 5 SECTIONS

 6 {

 7 

 8     . = 0x0;

 9 

10     . = ALIGN(4);

11     .text      :

12     {

13       test.o (.text) 

14       *(.text)

15     }

16 

17     . = ALIGN(4);

18     .rodata : { *(.rodata) }

19 

20     . = ALIGN(4);

21     .data : { *(.data) }

22 

23     . = ALIGN(4);

24     .got : { *(.got) }

25 

26     . = ALIGN(4);

27     __bss_start = .;

28     .bss : { *(.bss) }

29     _end = .;

30 }

 

 

#Makefile
 1 CROPROSS_COMPILER = arm-none-linux-gnueabi-

 2 LD := ${CROPROSS_COMPILER}ld

 3 AS := ${CROPROSS_COMPILER}as

 4 GCC := ${CROPROSS_COMPILER}gcc 

 5 

 6 mytest: test.o main.o

 7     ${LD} -T link.lds $^ -o $@

 8 

 9 test.o: test.S

10     ${AS} $^ -o $@

11 

12 main.o : main.c

13     ${GCC} -c $^ -o $@

14 

15 .PHONY: clean

16 

17 clean:

18     @rm -f -r mytest test.o main.o 

 

 

#test.S
 1 .text

 2 .global _start

 3 _start:

 4     b 1f    

 5 1:

 6     mov r0, r0

 7 2:

 8     mov r0, r0

 9 3:

10     mov r0, r0

11 1:

12     b main  

 

 //main.c
 1 unsigned long long jiffies_64 = -300 * 250;

 2 

 3 extern int jiffies;

 4 

 5 int main(void)

 6 {

 7 

 8     jiffies_64 += 1;

 9     jiffies += 3;

10 

11     return 0;

12 }

 

#反汇编，省略了一部分
 1 00000000 <_start>:                                                                                                 

 2    0:   b    4 <_start+0x4>

 3    4:   nop

 4    8:   nop

 5    c:   nop

 6   10:   b   14 <main>

 7 

 8 00000014 <main>: 

 9 

10   1c:   ldr r3, [pc, #64]   ; 取jiffies_64地址

11 

12   20:   ldm r3, {r1, r2}

13   24:   mov r3, #1  ; 0x1   ; jiffies_64低位加1

14   28:   mov r4, #0  ; 0x0   ; jiffies_64高位加0

15   2c:   adds    r3, r3, r1

16   30:   adc r4, r4, r2

17   34:   ldr r2, [pc, #40]   ; 取jiffies_64地址

18   38:   stm r2, {r3, r4}    ; 将jiffies_64 + 1 存入jiffies_64

19 

20   3c:   ldr r3, [pc, #36]   ; 取jiffies地址

21 

22   40:   ldr r3, [r3]

23   44:   add r2, r3, #3      ; jiffies低位加3

24   48:   ldr r3, [pc, #24]   ; 取jiffies地址

25   4c:   str r2, [r3]        ; 将jiffies + 3 存入jiffies 

26 

27 

28   64:   .word   0x00000070  ; jiffies_64地址

29   68:   .word   0x00000070  ; jiffies地址

30 Disassembly of section .data:

31 

32 00000070 <jiffies>:

33   70:   .word   0xfffedb08

34   74:   .word   0xffffffff