Get assembly / C code map with objdump
We can use objdump to disassamble a binary executable. Sometimes it
would be handy if we can get a map between the assambly and C source
code, which enables us to quickly locate the assembly of a specific C
block. -S and -l flags of objdump provide some means to archive
that.
-S
–source
Display source code intermixed with disassembly, if possible. Implies -d.
-l
–line-numbers
Label the display (using debugging information) with the filename and source line numbers corresponding to the object code or relocs shown. Only useful with -d, -D, or -r.
As long as the application is compiled with gcc -g, we can use
objdump -S -l to disassemble the application binary and get the map
we want.
$ arm-linux-gcc -g zero_checksum.c -c
$ arm-linux-objdump -Sl zero_checksum.o | head -40
zero_checksum.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <main>:
main():
/home/ender/src/tmp/zero_checksum.c:5
#include <stdio.h>
int
main(int argc, char **argv)
{
0: e1a0c00d mov ip, sp
4: e92dd800 stmdb sp!, {fp, ip, lr, pc}
8: e24cb004 sub fp, ip, #4 ; 0x4
c: e24dd010 sub sp, sp, #16 ; 0x10
10: e50b0010 str r0, [fp, #-16]
14: e50b1014 str r1, [fp, #-20]
/home/ender/src/tmp/zero_checksum.c:7
int i;
unsigned char sum = 0;
18: e3a03000 mov r3, #0 ; 0x0
1c: e54b3019 strb r3, [fp, #-25]
/home/ender/src/tmp/zero_checksum.c:9
signed char ssum;
for (i=1; i<argc; i++) {
20: e3a03001 mov r3, #1 ; 0x1
24: e50b3018 str r3, [fp, #-24]
28: e51b2018 ldr r2, [fp, #-24]
2c: e51b3010 ldr r3, [fp, #-16]
30: e1520003 cmp r2, r3
34: aa000020 bge bc <.text+0xbc>
/home/ender/src/tmp/zero_checksum.c:10
sum += (unsigned char)strtol(argv[i], NULL, 0);
38: e51b3018 ldr r3, [fp, #-24]
3c: e1a02103 mov r2, r3, lsl #2
40: e51b3014 ldr r3, [fp, #-20]
44: e0823003 add r3, r2, r3
48: e5930000 ldr r0, [r3]