When debugging sooner or later you will need to disassemble code to get a better understanding of that code.

By disassembling the code, you get the mnemonics translated from the 0s and 1s that constitute the binary code. It is a low level view of the code, but a higher level than seeing just numbers.

 

The commands syntaxes are:

 

u[b] [address]

u[b] [range]

u[b]

 

uf [options] <address>

 

Where options are:

 

/c - Displays only the call instructions in a routine.

/D - Creates linked callee names for navigation of the call graph.

/o - Sorts the display by address instead of by function offset.

/O - Creates linked call lines for accessing call information and creating breakpoints.

/i - Displays the number of instructions in a routine.

 

 

To demonstrate this command, let’s use this simple Visual C++ application that recursively calculates the Fibonacci from a specific number:

 

#include "stdafx.h"

 

using namespace std;

 

// Recursive function.

unsigned FiboRecursive(unsigned n, int nNum = 0)

{       

          if(n <= 1)

          {

                    return n;

          }

                   

          return FiboRecursive(n - 1, 1) + FiboRecursive(n - 2, 2);

}

 

int _tmain(int argc, _TCHAR* argv[])

{

          cout << FiboRecursive(5) << endl;

 

          return 0;

}

 

Let’s break the execution when the line from main() only is being executed, using a breakpoint for that.

 

Now let’s disassemble the eip register.

 

0:000> u @eip

Fibo!wmain+0x1e [c:\development\my tools\fibo\fibo\fibo.cpp @ 21]:

00a7145e 8bf4            mov     esi,esp

00a71460 a19882a700      mov     eax,dword ptr [Fibo!_imp_?endlstdYAAAV?$basic_ostreamDU?$char_traitsDstd (00a78298)]

00a71465 50              push    eax

00a71466 6a00            push    0

00a71468 6a05            push    5

00a7146a e89bfbffff      call    Fibo!ILT+5(?FiboRecursiveYAIIHZ) (00a7100a)

00a7146f 83c408          add     esp,8

00a71472 8bfc            mov     edi,esp

 

Using this approach we see the disassembled code starting from eip.

We can see the disassembled code that comes before eip using this approach:

 

0:000> ub @eip L8

Fibo!wmain+0x3 [c:\development\my tools\fibo\fibo\fibo.cpp @ 20]:

00a71443 81ecc0000000    sub     esp,0C0h

00a71449 53              push    ebx

00a7144a 56              push    esi

00a7144b 57              push    edi

00a7144c 8dbd40ffffff    lea     edi,[ebp-0C0h]

00a71452 b930000000      mov     ecx,30h

00a71457 b8cccccccc      mov     eax,0CCCCCCCCh

00a7145c f3ab            rep stos dword ptr es:[edi]

 

Keep in mind that b is for backward.

 

Let’s suppose you want to disassemble the entire function without having the work of finding the beginning of the function.

To accomplish that you use uf, and it automatically does that for you:

 

0:000> uf @eip

Fibo!wmain [c:\development\my tools\fibo\fibo\fibo.cpp @ 20]:

   20 00a71440 55              push    ebp

   20 00a71441 8bec            mov     ebp,esp

   20 00a71443 81ecc0000000    sub     esp,0C0h

   20 00a71449 53              push    ebx

   20 00a7144a 56              push    esi

   20 00a7144b 57              push    edi

   20 00a7144c 8dbd40ffffff    lea     edi,[ebp-0C0h]

   20 00a71452 b930000000      mov     ecx,30h

   20 00a71457 b8cccccccc      mov     eax,0CCCCCCCCh

   20 00a7145c f3ab            rep stos dword ptr es:[edi]

   21 00a7145e 8bf4            mov     esi,esp

   21 00a71460 a19882a700      mov     eax,dword ptr [Fibo!_imp_?endlstdYAAAV?$basic_ostreamDU?$char_traitsDstd (00a78298)]

   21 00a71465 50              push    eax

   21 00a71466 6a00            push    0

   21 00a71468 6a05            push    5

   21 00a7146a e89bfbffff      call    Fibo!ILT+5(?FiboRecursiveYAIIHZ) (00a7100a)

   21 00a7146f 83c408          add     esp,8

   21 00a71472 8bfc            mov     edi,esp

   21 00a71474 50              push    eax

   21 00a71475 8b0d9082a700    mov     ecx,dword ptr [Fibo!_imp_?coutstd (00a78290)]

   21 00a7147b ff159482a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01IZ (00a78294)]

   21 00a71481 3bfc            cmp     edi,esp

   21 00a71483 e8d1fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   21 00a71488 8bc8            mov     ecx,eax

   21 00a7148a ff159c82a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01P6AAAV01AAV01ZZ (00a7829c)]

   21 00a71490 3bf4            cmp     esi,esp

   21 00a71492 e8c2fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   23 00a71497 33c0            xor     eax,eax

   24 00a71499 5f              pop     edi

   24 00a7149a 5e              pop     esi

   24 00a7149b 5b              pop     ebx

   24 00a7149c 81c4c0000000    add     esp,0C0h

   24 00a714a2 3bec            cmp     ebp,esp

   24 00a714a4 e8b0fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   24 00a714a9 8be5            mov     esp,ebp

   24 00a714ab 5d              pop     ebp

   24 00a714ac c3              ret

 

Let’s see just the calls made by this function:

 

0:000> uf /c @eip

Fibo!wmain (00a71440) [c:\development\my tools\fibo\fibo\fibo.cpp @ 20]

  Fibo!wmain+0x2a (00a7146a) [c:\development\my tools\fibo\fibo\fibo.cpp @ 21]:

    call to Fibo!ILT+5(?FiboRecursiveYAIIHZ) (00a7100a)

  Fibo!wmain+0x3b (00a7147b) [c:\development\my tools\fibo\fibo\fibo.cpp @ 21]:

    call to MSVCP90D!std::basic_ostream<char,std::char_traits<char> >::operator<< (690fa700) [f:\dd\vctools\crt_bld\self_x86\crt\src\ostream @ 289]

  Fibo!wmain+0x43 (00a71483) [c:\development\my tools\fibo\fibo\fibo.cpp @ 21]:

    call to Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

  Fibo!wmain+0x4a (00a7148a) [c:\development\my tools\fibo\fibo\fibo.cpp @ 21]:

    call to MSVCP90D!std::basic_ostream<char,std::char_traits<char> >::operator<< (690f9f60) [f:\dd\vctools\crt_bld\self_x86\crt\src\ostream @ 171]

  Fibo!wmain+0x52 (00a71492) [c:\development\my tools\fibo\fibo\fibo.cpp @ 21]:

    call to Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

  Fibo!wmain+0x64 (00a714a4) [c:\development\my tools\fibo\fibo\fibo.cpp @ 24]:

    call to Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

 

 

Creates linked callee names from the same function:

 

0:000> uf /D @eip

Fibo!wmain [c:\development\my tools\fibo\fibo\fibo.cpp @ 20]:

   20 00a71440 55              push    ebp

   20 00a71441 8bec            mov     ebp,esp

   20 00a71443 81ecc0000000    sub     esp,0C0h

   20 00a71449 53              push    ebx

   20 00a7144a 56              push    esi

   20 00a7144b 57              push    edi

   20 00a7144c 8dbd40ffffff    lea     edi,[ebp-0C0h]

   20 00a71452 b930000000      mov     ecx,30h

   20 00a71457 b8cccccccc      mov     eax,0CCCCCCCCh

   20 00a7145c f3ab            rep stos dword ptr es:[edi]

   21 00a7145e 8bf4            mov     esi,esp

   21 00a71460 a19882a700      mov     eax,dword ptr [Fibo!_imp_?endlstdYAAAV?$basic_ostreamDU?$char_traitsDstd (00a78298)]

   21 00a71465 50              push    eax

   21 00a71466 6a00            push    0

   21 00a71468 6a05            push    5

   21 00a7146a e89bfbffff      call    Fibo!ILT+5(?FiboRecursiveYAIIHZ) (00a7100a)

   21 00a7146f 83c408          add     esp,8

   21 00a71472 8bfc            mov     edi,esp

   21 00a71474 50              push    eax

   21 00a71475 8b0d9082a700    mov     ecx,dword ptr [Fibo!_imp_?coutstd (00a78290)]

   21 00a7147b ff159482a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01IZ (00a78294)]

   21 00a71481 3bfc            cmp     edi,esp

   21 00a71483 e8d1fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   21 00a71488 8bc8            mov     ecx,eax

   21 00a7148a ff159c82a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01P6AAAV01AAV01ZZ (00a7829c)]

   21 00a71490 3bf4            cmp     esi,esp

   21 00a71492 e8c2fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   23 00a71497 33c0            xor     eax,eax

   24 00a71499 5f              pop     edi

   24 00a7149a 5e              pop     esi

   24 00a7149b 5b              pop     ebx

   24 00a7149c 81c4c0000000    add     esp,0C0h

   24 00a714a2 3bec            cmp     ebp,esp

   24 00a714a4 e8b0fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   24 00a714a9 8be5            mov     esp,ebp

   24 00a714ab 5d              pop     ebp

   24 00a714ac c3              ret

 

 

Sorts the output by address:

 

0:000> uf /o @eip

Fibo!wmain [c:\development\my tools\fibo\fibo\fibo.cpp @ 20]:

   20 00a71440 55              push    ebp

   20 00a71441 8bec            mov     ebp,esp

   20 00a71443 81ecc0000000    sub     esp,0C0h

   20 00a71449 53              push    ebx

   20 00a7144a 56              push    esi

   20 00a7144b 57              push    edi

   20 00a7144c 8dbd40ffffff    lea     edi,[ebp-0C0h]

   20 00a71452 b930000000      mov     ecx,30h

   20 00a71457 b8cccccccc      mov     eax,0CCCCCCCCh

   20 00a7145c f3ab            rep stos dword ptr es:[edi]

   21 00a7145e 8bf4            mov     esi,esp

   21 00a71460 a19882a700      mov     eax,dword ptr [Fibo!_imp_?endlstdYAAAV?$basic_ostreamDU?$char_traitsDstd (00a78298)]

   21 00a71465 50              push    eax

   21 00a71466 6a00            push    0

   21 00a71468 6a05            push    5

   21 00a7146a e89bfbffff      call    Fibo!ILT+5(?FiboRecursiveYAIIHZ) (00a7100a)

   21 00a7146f 83c408          add     esp,8

   21 00a71472 8bfc            mov     edi,esp

   21 00a71474 50              push    eax

   21 00a71475 8b0d9082a700    mov     ecx,dword ptr [Fibo!_imp_?coutstd (00a78290)]

   21 00a7147b ff159482a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01IZ (00a78294)]

   21 00a71481 3bfc            cmp     edi,esp

   21 00a71483 e8d1fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   21 00a71488 8bc8            mov     ecx,eax

   21 00a7148a ff159c82a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01P6AAAV01AAV01ZZ (00a7829c)]

   21 00a71490 3bf4            cmp     esi,esp

   21 00a71492 e8c2fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   23 00a71497 33c0            xor     eax,eax

   24 00a71499 5f              pop     edi

   24 00a7149a 5e              pop     esi

   24 00a7149b 5b              pop     ebx

   24 00a7149c 81c4c0000000    add     esp,0C0h

   24 00a714a2 3bec            cmp     ebp,esp

   24 00a714a4 e8b0fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   24 00a714a9 8be5            mov     esp,ebp

   24 00a714ab 5d              pop     ebp

   24 00a714ac c3              ret

 

 

Creates linked call lines for accessing call information and creating breakpoints:

 

0:000> uf /O @eip

Fibo!wmain [c:\development\my tools\fibo\fibo\fibo.cpp @ 20]:

   20 00a71440 55              push    ebp

   20 00a71441 8bec            mov     ebp,esp

   20 00a71443 81ecc0000000    sub     esp,0C0h

   20 00a71449 53              push    ebx

   20 00a7144a 56              push    esi

   20 00a7144b 57              push    edi

   20 00a7144c 8dbd40ffffff    lea     edi,[ebp-0C0h]

   20 00a71452 b930000000      mov     ecx,30h

   20 00a71457 b8cccccccc      mov     eax,0CCCCCCCCh

   20 00a7145c f3ab            rep stos dword ptr es:[edi]

   21 00a7145e 8bf4            mov     esi,esp

   21 00a71460 a19882a700      mov     eax,dword ptr [Fibo!_imp_?endlstdYAAAV?$basic_ostreamDU?$char_traitsDstd (00a78298)]

   21 00a71465 50              push    eax

   21 00a71466 6a00            push    0

   21 00a71468 6a05            push    5

   21 00a7146a e89bfbffff      call    Fibo!ILT+5(?FiboRecursiveYAIIHZ) (00a7100a)

   21 00a7146f 83c408          add     esp,8

   21 00a71472 8bfc            mov     edi,esp

   21 00a71474 50              push    eax

   21 00a71475 8b0d9082a700    mov     ecx,dword ptr [Fibo!_imp_?coutstd (00a78290)]

   21 00a7147b ff159482a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01IZ (00a78294)]

   21 00a71481 3bfc            cmp     edi,esp

   21 00a71483 e8d1fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   21 00a71488 8bc8            mov     ecx,eax

   21 00a7148a ff159c82a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01P6AAAV01AAV01ZZ (00a7829c)]

   21 00a71490 3bf4            cmp     esi,esp

   21 00a71492 e8c2fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   23 00a71497 33c0            xor     eax,eax

   24 00a71499 5f              pop     edi

   24 00a7149a 5e              pop     esi

   24 00a7149b 5b              pop     ebx

   24 00a7149c 81c4c0000000    add     esp,0C0h

   24 00a714a2 3bec            cmp     ebp,esp

   24 00a714a4 e8b0fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   24 00a714a9 8be5            mov     esp,ebp

   24 00a714ab 5d              pop     ebp

   24 00a714ac c3              ret

 

 

Displays the number of instructions in a routine:

 

0:000> uf /i @eip

37 instructions scanned

 

Fibo!wmain [c:\development\my tools\fibo\fibo\fibo.cpp @ 20]:

   20 00a71440 55              push    ebp

   20 00a71441 8bec            mov     ebp,esp

   20 00a71443 81ecc0000000    sub     esp,0C0h

   20 00a71449 53              push    ebx

   20 00a7144a 56              push    esi

   20 00a7144b 57              push    edi

   20 00a7144c 8dbd40ffffff    lea     edi,[ebp-0C0h]

   20 00a71452 b930000000      mov     ecx,30h

   20 00a71457 b8cccccccc      mov     eax,0CCCCCCCCh

   20 00a7145c f3ab            rep stos dword ptr es:[edi]

   21 00a7145e 8bf4            mov     esi,esp

   21 00a71460 a19882a700      mov     eax,dword ptr [Fibo!_imp_?endlstdYAAAV?$basic_ostreamDU?$char_traitsDstd (00a78298)]

   21 00a71465 50              push    eax

   21 00a71466 6a00            push    0

   21 00a71468 6a05            push    5

   21 00a7146a e89bfbffff      call    Fibo!ILT+5(?FiboRecursiveYAIIHZ) (00a7100a)

   21 00a7146f 83c408          add     esp,8

   21 00a71472 8bfc            mov     edi,esp

   21 00a71474 50              push    eax

   21 00a71475 8b0d9082a700    mov     ecx,dword ptr [Fibo!_imp_?coutstd (00a78290)]

   21 00a7147b ff159482a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01IZ (00a78294)]

   21 00a71481 3bfc            cmp     edi,esp

   21 00a71483 e8d1fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   21 00a71488 8bc8            mov     ecx,eax

   21 00a7148a ff159c82a700    call    dword ptr [Fibo!_imp_??6?$basic_ostreamDU?$char_traitsDstdstdQAEAAV01P6AAAV01AAV01ZZ (00a7829c)]

   21 00a71490 3bf4            cmp     esi,esp

   21 00a71492 e8c2fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   23 00a71497 33c0            xor     eax,eax

   24 00a71499 5f              pop     edi

   24 00a7149a 5e              pop     esi

   24 00a7149b 5b              pop     ebx

   24 00a7149c 81c4c0000000    add     esp,0C0h

   24 00a714a2 3bec            cmp     ebp,esp

   24 00a714a4 e8b0fcffff      call    Fibo!ILT+340(__RTC_CheckEsp) (00a71159)

   24 00a714a9 8be5            mov     esp,ebp

   24 00a714ab 5d              pop     ebp

   24 00a714ac c3              ret