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Thread: Not able to load a VB application

  1. #1
    yuvarar
    Guest

    Unhappy Not able to load a VB application

    Hi All,
    Whenever I try to load a VB executable in OllyDbg v1.10(OS:Windows XP Professional), I keep getting this error:

    Inexact floating-point result - use Shift+F7/F8/F9 to pass exception to program.
    Is this a Anti-Debugger Trick? I dont think so because I have the plugins like Hide Debugger, IsDebuggerPresent installed.

    Someone please help...

    Thanks in advance!!!
    I promise that I have read the FAQ and tried to use the Search to answer my question.

  2. #2
    Naides is Nobody
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    May be is a trick, may be is just an exception. What happens when you do Shift F9 and pass the exception to the program?

    What happens when you run the app first then attach it to Olly debug?

    Is the app p-code or compilated?

    Common wisdom says that plain old tracing of a VB application with a debugger (Olly) seldom helps. . .

  3. #3
    yuvarar
    Guest
    Thanks for the reply!

    When I press Shift+F9, nothing happens. Then I pressed F9 and I got the message

    INT3 command at ntdll.DbgBreakpoint
    When attached Olly to the running process, it says
    Attached process stopped at ntdll.DbgBreakpoint
    When F9 is pressed, got the same error message as mentioned in my previous post.

    I am not sure if the VB application is Native/P-code compiled..(may be some one help...)

    PS: I tried to run the application with Numega SmartCheck but it crashed.
    But I could successfully decompile the application with VB Decompiler Lite V2.5
    I promise that I have read the FAQ and tried to use the Search to answer my question.

  4. #4
    <script>alert(0)</script> disavowed's Avatar
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    > When F9 is pressed, got the same error message as mentioned in my
    > previous post.

    Keep pressing Shift-F9.

  5. #5
    Super Moderator
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    or if you dont want to keep pressing shift+f9

    add this exception to ignore list

    options -> debuging options -> exceptions -> add last exception
    -> chckmark ignore this check box -> ok

    now you can just shift f9 one time and it will probably run
    withoutproblems or crash if it crashed then its upto
    some mischief and you have work to do to find whats it upto

    else its some incompatibilty between myriad versions of
    os compilers bug of authors and other innumerable aspects

    so whats the solution read around find entry point
    hard break trace trace trace trace till it finds that
    you a stubborn guy/gal and fails in front of you and spitting
    its secrets of why its crashing , generarting exceptions

    oh btw tracing vb applications in olly may be a little pain
    as naides opined but but as he also stated some where else
    in another thread there is nothing to beat tracing
    (including finding out tricks that stop you from tracing)
    if you prefer to name some of the vb jump tables find vbhelper plugin by joe stewert

    or simply find this sequnce

    sub dword ptr ss:[esp+const],const
    jmp const


    there will be several of them

    thats your entry point into the wndproc on almost
    all vb applications

    Code:
    Found sequences
    Address    Disassembly                 Comment
    00401C20   SUB     DWORD PTR SS:[ESP+4], 3B  
    00402258   SUB     DWORD PTR SS:[ESP+4], 43
    00402265   SUB     DWORD PTR SS:[ESP+4], 57
    00402272   SUB     DWORD PTR SS:[ESP+4], 4B
    i found this sequnce on xyz vb application
    -->right click set break point on everycommand
    Code:
    Breakpoints
    Address  Module  Active    Disassembly              Comment
    00401C20   vb  Always    SUB     DWORD PTR SS:[ESP+4], 3B
    00402258   vb  Always    SUB     DWORD PTR SS:[ESP+4], 43
    00402265   vb  Always    SUB     DWORD PTR SS:[ESP+4], 57
    00402272   vb  Always    SUB     DWORD PTR SS:[ESP+4], 4B
    f9nned the application


    and ollydbg broke

    Log data, item 0
    Address=00402258
    Message=Breakpoint at vb.00402258
    the sequnce it broke was

    00402258 SUB DWORD PTR SS:[ESP+4], 43
    00402260 JMP vb.00402CA0




    f7iing two time i land here
    Code:
    00402CA0  PUSH    EBP
    00402CA1  MOV     EBP, ESP
    00402CA3  SUB     ESP, 18
    00402CA6  PUSH  <JMP.&MSVBVM60.__vbaE; SE handler installation
    
    <-----------snip ---------------------->
    00402D05  CALL    NEAR DWORD PTR DS:[<&MSVBVM60.__vbaOnErr>;  MSVBVM60.__vbaOnError
    00402D0B  MOV     DWORD PTR SS:[EBP-4], 3
    00402D12  PUSH    0
    00402D14  PUSH    vb.004024F0      ;  UNICODE "OllyDbg - vb.exe"
    00402D19  LEA     EDX, DWORD PTR SS:[EBP-30]
    00402D1C  PUSH    EDX           ;  MSVBVM60.734242A0
    00402D1D  CALL    NEAR DWORD PTR DS:[<&MSVBVM60.__vbaStrTo>;  MSVBVM60.__vbaStrToAnsi
    
     <------------------- snip ------------------>
    thats it you can beat it now
    Last edited by blabberer; August 24th, 2006 at 12:42.

  6. #6
    To crash or not to crash
    Join Date
    Dec 2001
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    The exception you recieve is no anti-debugger trick. I debugged a lot of (my own) vb programs and you recieve this exception for example when an object is searched in a collection that does not exist. Nothing to worry about and you can indeed add it to the ignore list.

  7. #7
    yuvarar
    Guest
    Thanks everyone for the reply. The problem is solved by adding the exception to the Ignore list.

    Thanks a lot!!!
    I promise that I have read the FAQ and tried to use the Search to answer my question.

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