Disassembly C Code for fun
.. read other post about addr2line
vim trickline.c
1 #include <stdio.h>
2
3 #define TELLME printf ("This is line %d of file \"%s\" (function <%s>)\n",\
4 __LINE__, __FILE__, __func__)
5
6 #line 1000 "thousand"
7 void whereAmI ()
8 {
9 TELLME;
10 }
11
12 #line 999 "almost_one_thousand"
13 int main ()
14 {
15 TELLME;
16 whereAmI();
17
18 #line 1 "reset_line"
19 whereAmI();
20 TELLME;
21
22 printf("Today is %s %s.\n\n",__DATE__, __TIME__ );
23 return 0;
24 }
After you have created your program, compile it with debugsymbols:
$ gcc -g -o trick.bin trickline.c
iesult of the running trick.bin:
$ ./trick.bin
This is line 1001 of file "almost_one_thousand" (function <main>)
This is line 1002 of file "thousand" (function <whereAmI>)
This is line 1 of file "reset_line" (function <main>
This is line 1002 of file "thousand" (function <whereAmI>)
You can see that the correct number of lines and the file name have been changed by the macro
#line <N> <FILENAME>[1],
watch out for that(I never saw that in kernel source).
Analyze its ASM code:
$ objdump -D trick.bin
...
00000000100006a4 <main>:
100006a4: 02 10 40 3c lis r2,4098
100006a8: 00 7f 42 38 addi r2,r2,32512
100006ac: a6 02 08 7c mflr r0
100006b0: 10 00 01 f8 std r0,16(r1)
100006b4: f8 ff e1 fb std r31,-8(r1)
100006b8: 91 ff 21 f8 stdu r1,-112(r1)
100006bc: 78 0b 3f 7c mr r31,r1
100006c0: fe ff 62 3c addis r3,r2,-2
100006c4: f0 89 63 38 addi r3,r3,-30224
100006c8: e9 03 80 38 li r4,1001
100006cc: fe ff a2 3c addis r5,r2,-2
100006d0: 30 8a a5 38 addi r5,r5,-30160
100006d4: fe ff c2 3c addis r6,r2,-2
100006d8: a0 8a c6 38 addi r6,r6,-30048
100006dc: 65 fd ff 4b bl 10000440
<00000017.plt_call.printf@@GLIBC_2.17>
100006e0: 18 00 41 e8 ld r2,24(r1)
100006e4: 69 ff ff 4b bl 1000064c <whereAmI+0x8>
100006e8: 65 ff ff 4b bl 1000064c <whereAmI+0x8>
100006ec: fe ff 62 3c addis r3,r2,-2
100006f0: f0 89 63 38 addi r3,r3,-30224
100006f4: 02 00 80 38 li r4,2
100006f8: fe ff a2 3c addis r5,r2,-2
100006fc: 48 8a a5 38 addi r5,r5,-30136
10000700: fe ff c2 3c addis r6,r2,-2
10000704: a0 8a c6 38 addi r6,r6,-30048
10000708: 39 fd ff 4b bl 10000440
<00000017.plt_call.printf@@GLIBC_2.17>
1000070c: 18 00 41 e8 ld r2,24(r1)
10000710: fe ff 62 3c addis r3,r2,-2
10000714: 58 8a 63 38 addi r3,r3,-30120
10000718: fe ff 82 3c addis r4,r2,-2
1000071c: 70 8a 84 38 addi r4,r4,-30096
10000720: fe ff a2 3c addis r5,r2,-2
10000724: 80 8a a5 38 addi r5,r5,-30080
10000728: 19 fd ff 4b bl 10000440
<00000017.plt_call.printf@@GLIBC_2.17>
1000072c: 18 00 41 e8 ld r2,24(r1)
...
In this case you know where is which calling for a function, but in doubt you
can clain for a helping, addr2line;
$ addr2line -fip -e trick.bin 1000064c
whereAmI at /home/walbon/coding/thousand:1001
Do you see? The macro #line <N> <FILENAME> has changed the real number of
line and the filename, watch out for that.