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Kitt3n
12-28-2010, 02:03 PM
I just started learning C from a book in Linux and it told me to use objdump to look at the code in assembly. However I run into the problem that the output objdump gives me is not the same as is in the book. That other addresses are used I understand. But why is the program not executed the exact same way even know I use the same processor (x86) as is used in the book.

Sins I have not found out yet how I can copy text from the command line in my virtual box in windows I can only give you the example from the book. What I am reffering to is the 3th and 4th column the left.

Example:


reader:~/booksrc $ objdump -M intel -D a.out | grep -A20 main.:
08048374 <main>:
8048374: 55 push ebp
8048375: 89 e5 mov ebp,esp
8048377: 83 ec 08 sub esp,0x8
804837a: 83 e4 f0 and esp,0xfffffff0
804837d: b8 00 00 00 00 mov eax,0x0
8048382: 29 c4 sub esp,eax
8048384: c7 45 fc 00 00 00 00 mov DWORD PTR [ebp-4],0x0
804838b: 83 7d fc 09 cmp DWORD PTR [ebp-4],0x9
804838f: 7e 02 jle 8048393 <main+0x1f>
8048391: eb 13 jmp 80483a6 <main+0x32>
8048393: c7 04 24 84 84 04 08 mov DWORD PTR [esp],0x8048484
804839a: e8 01 ff ff ff call 80482a0 <printf@plt>
804839f: 8d 45 fc lea eax,[ebp-4]
80483a2: ff 00 inc DWORD PTR [eax]
80483a4: eb e5 jmp 804838b <main+0x17>
80483a6: c9 leave
80483a7: c3 ret
80483a8: 90 nop
80483a9: 90 nop
80483aa: 90 nop
reader:~/booksrc $

Sebastiani
12-28-2010, 02:09 PM
Don't worry about it. Unless you compiled with the *exact* same version of compiler, compilation flags, etc, you should expect some differences...

Kitt3n
12-28-2010, 02:15 PM
Thanks. I was getting worried I overlooked something and that I could trow the book in the trashcan.