1 #include <stdio.h>
 2 #include <stdlib.h>
 3
 4 //加子函数防止变量优化没了
 5 void pfunc(int a, int b)
 6 {
 7         int i = 0;
 8         int sum = 0;
 9         for (i = 0; i < b; i++)
10         {
11                 sum += a * i;
12         }
13
14         printf("sum %x\n", sum);
15 }
16
17 int main()
18 {
19         int i = 0x102;
20         int a = (volatile int)i;
21         int b = *(volatile int *)&i;
22
23         pfunc(a, b);
24 } 

 1 000083ec <main>:
 2     83ec:        e92d4800         push        {fp, lr}
 3     83f0:        e28db004         add        fp, sp, #4
 4     83f4:        e24dd010         sub        sp, sp, #16
 5     83f8:        e59f3028         ldr        r3, [pc, #40]        ; 8428 <main+0x3c>
 6     83fc:        e50b3010         str        r3, [fp, #-16]
 7     8400:        e51b3010         ldr        r3, [fp, #-16]
 8     8404:        e50b3008         str        r3, [fp, #-8]
 9     8408:        e51b3010         ldr        r3, [fp, #-16]
10     840c:        e50b300c         str        r3, [fp, #-12]
11     8410:        e51b000c         ldr        r0, [fp, #-12]
12     8414:        e51b1008         ldr        r1, [fp, #-8]
13     8418:        eb000003         bl        842c <pfunc>
14     841c:        e1a00003         mov        r0, r3
15     8420:        e24bd004         sub        sp, fp, #4
16     8424:        e8bd8800         pop        {fp, pc}
17     8428:        00000102         andeq        r0, r0, r2, lsl #2 

 1 00008430 <main>:
 2     8430:        e52de004         push        {lr}                ; (str lr, [sp, #-4]!)
 3     8434:        e24dd00c         sub        sp, sp, #12
 4     8438:        e59f0010         ldr        r0, [pc, #16]        ; 8450 <main+0x20>
 5     843c:        e58d0004         str        r0, [sp, #4]
 6     8440:        e59d1004         ldr        r1, [sp, #4]
 7     8444:        ebffffe8         bl        83ec <pfunc>
 8     8448:        e28dd00c         add        sp, sp, #12
 9     844c:        e49df004         pop        {pc}                ; (ldr pc, [sp], #4)
10     8450:        00000102         andeq        r0, r0, r2, lsl #2