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assemblybinutilsobjdump

How to get information from objdump

I encounter a problem when reading information dumped out from an executable file in linux. The information is as follows:

804a0ea:  04 08            add $0x8, %al
     ...
804a0f4:  a6               cmpsb %es:(%edi),%ds:(%esi)

I have two questions:

  1. what does the address 804a0ea and 804a0f4 mean? the virtual address in the process's address space?
  2. what does the ... mean? how can I get instruction at address 804a0f0?

Thanks in advance.

More information around this part of code:

Disassembly of section .got.plt:

    0804a0e8 <_GLOBAL_OFFSET_TABLE_>:
     804a0e8:       14 a0                   adc    $0xa0,%al
     804a0ea:       04 08                   add    $0x8,%al
            ...
     804a0f4:       a6                      cmpsb  %es:(%edi),%ds:(%esi)
     804a0f5:       87 04 08                xchg   %eax,(%eax,%ecx,1)
     804a0f8:       b6 87                   mov    $0x87,%dh
     804a0fa:       04 08                   add    $0x8,%al
     804a0fc:       c6 87 04 08 d6 87 04    movb   $0x4,-0x7829f7fc(%edi)
     804a103:       08 e6                   or     %ah,%dh
     804a105:       87 04 08                xchg   %eax,(%eax,%ecx,1)
     804a108:       f6 87 04 08 06 88 04    testb  $0x4,-0x77f9f7fc(%edi)
     804a10f:       08 16                   or     %dl,(%esi)
     804a111:       88 04 08                mov    %al,(%eax,%ecx,1)
     804a114:       26 88 04 08             mov    %al,%es:(%eax,%ecx,1)
     804a118:       36 88 04 08             mov    %al,%ss:(%eax,%ecx,1)
     804a11c:       46                      inc    %esi

Hope anyone can give me a hand.:-)

Solution

  • The global offset table is not pointing to code, it's pointing to data (hrm... offsets, actually). So trying to disassemble it will not give very meaningful code. (you can actually find which offsets by looking at the code values. 0804a014, ... 080487a6).

    The ... usually mean a bunch of 0's are in the stream.