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Spying on COM Objects


July 1999/Spying on COM Objects/Figure 1

Figure 1: Excerpt from return.cpp

/*----------------------------------------------------------------

   FUNCTION: ReturnMgr::NakedReturnPoint

   PURPOSE:  Interceptor of function returns
----------------------------------------------------------------*/
__declspec(naked) void ReturnMgr::NakedReturnPoint(void)
{
    DWORD  l_dwSavedLastError;
    PDWORD l_pReturnAddress;
    PDWORD l_pReturnValue;

    //It would be much easier to write this function entirely on
    //assembly. The code would be shorter and faster but more
    //difficult to read and compile.
    //Therefore, I limited myself to only few assembly operation,
    //writing the rest on C.
    __asm 
    {
        SUB    ESP,4; Reserve space for return address
        PUSHAD      ; Push EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI
        PUSHFD      ; Store flags
        MOV    EBP, ESP   ; allow access to local variables
        SUB    ESP, __LOCAL_SIZE ;reserve space for local variables
    
        mov l_pReturnAddress, EBP
    }
    l_pReturnAddress += 8+1;
    //adjust for 8 registers pushed by PUSHAD and flags

    l_pReturnValue =l_pReturnAddress-1;//EAX was the first register
                                        //pushed by PUSHAD.
    l_dwSavedLastError = GetLastError();
    
    if(g_Data.m_pRetMgr)
       g_Data.m_pRetMgr->CommonReturnPoint
        (l_pReturnAddress, l_pReturnValue);

    SetLastError(l_dwSavedLastError);

    __asm
    {
        ADD    ESP, __LOCAL_SIZE ;remove local variables from stack
        POPFD                          ;restore flags
        POPAD                          ;restore registers
        ; now ESP should be 4 bytes smaller than on entry to 
        ; this function. that additional space should be already 
        ; filled by an original return address. Now we will return
        ; to this address:
        RET
    }
}//__declspec(naked) ReturnMgr::NakedReturnPoint(void)


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