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

posted on 2013-08-12 09:15  阿加  阅读(346)  评论(0)  编辑  收藏  举报

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