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I just started learning C from a book 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:

Code:

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 $

Quote:

Originally Posted by Kitt3n (Post 4205747)

I just started learning C from a book and it told me to use objdump to look at the code in assembly.

Yes, you could use objdump(1) or a debugger (which should be capable to disassemble).

Quote:

Originally Posted by Kitt3n (Post 4205747)

However I run into the problem that the output objdump gives me is not the same as is in the book. 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.

That's hard to tell from just the original assembly code. If my internal de-compiler worked correctly ;-), the original C code seems to be a for (i = 0; i<10; i++) while each iteration prints the same string. Though, what do you mean by "not executed the exact same way"? Do you get a different number of iterations? Don't you get ANY output? Does it run forever? Does your program crash?

Quote:

Originally Posted by Kitt3n (Post 4205747)

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.

Your disassembly (and possibly our C-code) would be really helpful ...

Andi