[VB6] - Calling functions by pointer.

ACTUAL VERSION IN 9 POST
Exploring the function VBA6 figured out a way to call functions the pointer.
It's simple. Declare a function prototype (void function), where the first argument will be further transferred to the function address. Next, do a patch, so he tossed to us at the address specified in the first parameter. Thus it is possible to call functions in the standard modules, class modules, forms, API-functions (eg obtained through LoadLibrary and GetProcAddress).* One note, run the project through Ctrl + F5. And working in the IDE and compiled form.
For "patching" the prototype I made a separate module:

Code:

---

Option Explicit

Private Declare Function GetMem4 Lib "msvbvm60" (src As Any, dst As Any) As Long
Private Declare Function VirtualProtect Lib "kernel32" (ByVal lpAddress As Long, ByVal dwSize As Long, ByVal flNewProtect As Long, lpflOldProtect As Long) As Long
Private Declare Sub EbGetExecutingProj Lib "vba6" (hProject As Long)
Private Declare Function TipGetFunctionId Lib "vba6" (ByVal hProj As Long, ByVal bstrName As Long, ByRef bstrId As Long) As Long
Private Declare Function TipGetLpfnOfFunctionId Lib "vba6" (ByVal hProject As Long, ByVal bstrId As Long, ByRef lpAddress As Long) As Long
Private Declare Sub SysFreeString Lib "oleaut32" (ByVal lpbstr As Long)

Private Const PAGE_EXECUTE_READWRITE = &H40

' Вспомогательные функции
Public Sub PatchFunc(FuncName As String, ByVal Addr As Long)
    Dim lpAddr As Long, hProj As Long, sId As Long, InIDE As Boolean

    Debug.Assert MakeTrue(InIDE)

    ' Получаем адрес функции
    If InIDE Then
        EbGetExecutingProj hProj
        TipGetFunctionId hProj, StrPtr(FuncName), sId
        TipGetLpfnOfFunctionId hProj, sId, lpAddr
        SysFreeString sId
    Else
        lpAddr = GetAddr(Addr)
        VirtualProtect lpAddr, 8, PAGE_EXECUTE_READWRITE, 0
    End If

    ' Записываем вставку
    ' Запускать только по Ctrl+F5!!
    ' pop eax
    ' pop ecx
    ' push eax
    ' jmp ecx

    GetMem4 &HFF505958, ByVal lpAddr
    GetMem4 &HE1, ByVal lpAddr + 4
End Sub

Private Function GetAddr(ByVal Addr As Long) As Long
    GetAddr = Addr
End Function
Public Function MakeTrue(ByRef bvar As Boolean) As Boolean
    bvar = True: MakeTrue = True
End Function

---

Example call normal functions in a standard module:

Code:

---

' Пример вызова обычных функции по указателю
Public Sub Main()

    ' Пропатчиваем функции, перед первым вызовом
    PatchFunc "Proto1", AddressOf Proto1
    PatchFunc "Proto2", AddressOf Proto2

    MsgBox Proto1(AddressOf Func1, 1, "Вызов")
    MsgBox Proto1(AddressOf Func2, 2, "По указателю")
    MsgBox Proto1(AddressOf Func3, 3, ";)")

    Call Proto2(AddressOf Sub1)
    Call Proto2(AddressOf Sub2)
End Sub

' Прототип функций
Private Function Proto1(ByVal Addr As Long, ByVal x As Long, y As String) As String
End Function
Private Sub Proto2(ByVal Addr As Long)
End Sub
' Функции
Private Function Func1(ByVal x As Long, y As String) As String
    Func1 = "Func1_" & y
End Function
Private Function Func2(ByVal x As Long, y As String) As String
    Func2 = "Func2_" & y
End Function
Private Function Func3(ByVal x As Long, y As String) As String
    Func3 = "Func3_" & y
End Function
Private Sub Sub1()
    MsgBox "Sub1"
End Sub
Private Sub Sub2()
    MsgBox "Sub2"
End Sub

---

Example API calls at getting through GetProcAddress:

Code:

---

Private Declare Function GetMem4 Lib "msvbvm60" (src As Any, dst As Any) As Long
Private Declare Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" (ByVal lpLibFileName As String) As Long
Private Declare Function GetProcAddress Lib "kernel32" (ByVal hModule As Long, ByVal lpProcName As String) As Long


' Пример вызова WinApi функций по указателю
Public Sub Main()
    Dim hUser As Long, hGDI As Long
    Dim DC As Long

    hUser = LoadLibrary("user32")
    hGDI = LoadLibrary("gdi32")

    PatchFunc "GetDC", AddressOf GetDC
    PatchFunc "ReleaseDC", AddressOf ReleaseDC
    PatchFunc "Ellipse", AddressOf Ellipse

    DC = GetDC(GetProcAddress(hUser, "GetDC"), 0)
    Ellipse GetProcAddress(hGDI, "Ellipse"), DC, 0, 0, 500, 500
    ReleaseDC GetProcAddress(hUser, "ReleaseDC"), 0, DC
End Sub

' Прототип функций
Private Function GetDC(ByVal Addr As Long, ByVal hWnd As Long) As Long
End Function
Private Function ReleaseDC(ByVal Addr As Long, ByVal hWnd As Long, ByVal hdc As Long) As Long
End Function
Private Function Ellipse(ByVal Addr As Long, ByVal hdc As Long, ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long
End Function

---

Example call class methods on the pointer:
.bas module:

Code:

---

Private Declare Function GetMem4 Lib "msvbvm60" (src As Any, dst As Any) As Long

' Пример вызова методов объекта по указателю
Public Sub Main()
    Dim IUnk    As Long
    Dim lpProp  As Long
    Dim lpView  As Long
    Dim Obj1    As clsTest
    Dim Obj2    As clsTest
    Dim ret    As Long

    Set Obj1 = New clsTest
    Set Obj2 = New clsTest
   
    GetMem4 ByVal ObjPtr(Obj1), IUnk
    GetMem4 ByVal IUnk + &H1C, lpProp
    GetMem4 ByVal IUnk + &H20, lpView
   
    PatchFunc "clsTest_PropLet", AddressOf clsTest_PropLet
    PatchFunc "clsTest_View", AddressOf clsTest_View
   
    clsTest_PropLet lpProp, Obj1, 1234
    clsTest_PropLet lpProp, Obj2, 9876
   
    clsTest_View lpView, Obj1, ret
    Debug.Print ret
    clsTest_View lpView, Obj2, ret
    Debug.Print ret
End Sub

' Прототип функций
Private Function clsTest_PropLet(ByVal Addr As Long, ByVal Obj As clsTest, ByVal Value As Long) As Long
End Function
Private Function clsTest_View(ByVal Addr As Long, ByVal Obj As clsTest, ret As Long) As Long
End Function

---

Class module:

Code:

---

Option Explicit

Dim mValue As Long

Public Property Let Prop(ByVal Value As Long)
    mValue = Value
End Property
Public Function View() As Long
    View = MsgBox(mValue, vbYesNoCancel)
End Function

---

Good luck!

Attachment 123741

Another way, rather simple and less limitations, would be the use of the API DispCallFunc.

DispCallFunc much slower. DispCallFunc can be used for other calling conventions (CC_CDECL etc.). DispCallFunc also preferable to use to call methods on a COM object. For example:

Code:

---

Private Function IAccessibleGet_accState(obj As IUnknown, VarID As Variant) As Variant
    Dim types() As Integer, param() As Long
    ReDim types(1): ReDim param(1)
    types(0) = vbVariant: types(1) = vbLong
    param(0) = VarPtr(VarID): param(1) = VarPtr(IAccessibleGet_accState): IAccessibleGet_accState = param(1)
    Call DispCallFunc(obj, 56, CC_STDCALL, vbLong, 2, types(0), param(0), 0)
End Function

---

True, but DispCallFunc can be wrapped in a generic function and that function can be called for both GetProcAddress pointers and COM objects, with variable parameters, and without having to create prototypes or patching VTables. Just another way to skin a cat.

Here too so it is possible. I normally use DispCallFunc when you do not want to add modules (to make all of the code in the class). Such as registration of libraries, etc. The main plus - is to support different calling conventions, but the code can also be slightly modified to support other agreements.

On another note...

All these methods (as the above trick) which depend on vba6.dll -
are not usable within your Applications "in the wild"...

They will work only on machines where the VB6-IDE is installed
(and are therefore useful for IDE-plugins and stuff) - but not much
else, since - IIRC - vba6.dll is not listed in redist.txt...

Edit: Overlooked the InIde-check, so all fine for the above code...

Olaf

Olaf, haven't reviewed his other threads, but in this thread vba6.dll appears to be only called if project is in the IDE.

Quote:

---

Originally Posted by LaVolpe

Olaf, haven't reviewed his other threads, but in this thread vba6.dll appears to be only called if project is in the IDE.

---

Oops - right you are - sorry @ Кривоус.

Olaf

I've modified this module (now it is yet smaller):

Code:

---

Option Explicit

Private Declare Function GetMem4 Lib "msvbvm60" ( _
                        ByRef src As Any, _
                        ByRef dst As Any) As Long
Private Declare Function VirtualProtect Lib "kernel32" ( _
                        ByVal lpAddress As Long, _
                        ByVal dwSize As Long, _
                        ByVal flNewProtect As Long, _
                        ByRef lpflOldProtect As Long) As Long
 
Private Const PAGE_EXECUTE_READWRITE = &H40

' // Helpers functions
Public Sub PatchFunc(ByVal Addr As Long)
    Dim InIDE As Boolean
 
    Debug.Assert MakeTrue(InIDE)
 
    If InIDE Then
        GetMem4 ByVal Addr + &H16, Addr
    Else
        VirtualProtect Addr, 8, PAGE_EXECUTE_READWRITE, 0
    End If

    GetMem4 &HFF505958, ByVal Addr
    GetMem4 &HE1, ByVal Addr + 4
End Sub
 
Public Function MakeTrue(ByRef bvar As Boolean) As Boolean
    bvar = True: MakeTrue = True
End Function

---

Also i've added the new example that show the analog of the c++ function - qsort, where the comparing parameter is the user function:

Code:

---

Option Explicit

Private Type Vector2D
    posX As Single
    posY As Single
End Type

Private Declare Sub memcpy Lib "kernel32" _
                    Alias "RtlMoveMemory" ( _
                    ByRef Destination As Any, _
                    ByRef Source As Any, _
                    ByVal Length As Long)
                   
' // Buffer for exchanging
Dim buffer()    As Byte
Dim isInit      As Boolean

' // Calling of the standard functions using the pointers
Public Sub Main()
    Dim lngArray()  As Long
    Dim index      As Long
   
    ' // We're testing the function that sorts the long-array
    ReDim lngArray(99)
   
    For index = 0 To UBound(lngArray)
        lngArray(index) = Rnd * 100
    Next
   
    ' // Magic of the function pointers
    QuickSort VarPtr(lngArray(0)), UBound(lngArray) + 1, Len(lngArray(0)), AddressOf ComparatorLong
   
    ' // Now we're testing the function that sorts the string-array
    Dim strArray()  As String
   
    ReDim strArray(5)
   
    strArray(0) = "Calling"
    strArray(1) = "of the standard functions"
    strArray(2) = "using the pointers"
    strArray(3) = "on VB6"
    strArray(4) = "by The trick"
    strArray(5) = "2015"
   
    ' // We're calling same function using the magic of pointers
    QuickSort VarPtr(strArray(0)), UBound(strArray) + 1, 4, AddressOf ComparatorString
   
    ' // Now we're testing the function that sorts the UDT-array (2D-vectors)
    ' // For example we'll sorting the array by vector length
    Dim vecArray() As Vector2D
   
    ReDim vecArray(99)
   
    For index = 0 To UBound(vecArray)
        vecArray(index).posX = Rnd * 10
        vecArray(index).posY = Rnd * 10
    Next
   
    ' // We're calling same function for the sorting of the UDT-array
    QuickSort VarPtr(vecArray(0)), UBound(vecArray) + 1, LenB(vecArray(0)), AddressOf ComparatorVector2D
   
    ' // Test length
    For index = 0 To UBound(vecArray)
        Debug.Print Sqr(vecArray(index).posX ^ 2 + vecArray(index).posY ^ 2)
    Next
   
End Sub

' // This callback function which sorts two long values
Public Function ComparatorLong( _
                ByRef lItem1 As Long, _
                ByRef lItem2 As Long) As Long
    ComparatorLong = Sgn(lItem1 - lItem2)
End Function

' // This callback function which sorts two string values
Public Function ComparatorString( _
                ByRef lItem1 As String, _
                ByRef lItem2 As String) As Long
    ComparatorString = StrComp(lItem1, lItem2, vbTextCompare)
End Function

' // This callback function which sorts two 2D-vectors values by length
Public Function ComparatorVector2D( _
                ByRef lItem1 As Vector2D, _
                ByRef lItem2 As Vector2D) As Long
    ' // Optimize sqr
    ComparatorVector2D = Sgn((lItem1.posX * lItem1.posX + lItem1.posY * lItem1.posY) - _
                            (lItem2.posX * lItem2.posX + lItem2.posY * lItem2.posY))
End Function

' // Quick-sort using the callback function for a comparing
' // This function uses callback function (lpfnComparator)
Public Sub QuickSort( _
          ByVal lpFirstPtr As Long, _
          ByVal lNumOfItems As Long, _
          ByVal lSizeElement As Long, _
          ByVal lpfnComparator As Long)
         
    Dim lpI    As Long
    Dim lpJ    As Long
    Dim lpM    As Long
    Dim lpLast  As Long
   
    If Not isInit Then
        ' // Initialize patching and buffer for exchanging
        ReDim buffer(lSizeElement - 1)
        PatchFunc AddressOf MainComparator
        isInit = True
       
    End If
   
    lpLast = lpFirstPtr + (lNumOfItems - 1) * lSizeElement
    lpI = lpFirstPtr
    lpJ = lpLast
    lpM = lpFirstPtr + ((lNumOfItems - 1) \ 2) * lSizeElement

    Do Until lpI > lpJ
       
        ' // Call function that being passed into the lpfnComparator parameter
        Do While MainComparator(lpfnComparator, lpI, lpM) = -1
            lpI = lpI + lSizeElement
        Loop
       
        ' // Call function that being passed into the lpfnComparator parameter
        Do While MainComparator(lpfnComparator, lpJ, lpM) = 1
            lpJ = lpJ - lSizeElement
        Loop
       
        ' // Exchanging
        If (lpI <= lpJ) Then
           
            If lpI = lpM Then
                lpM = lpJ
            ElseIf lpJ = lpM Then
                lpM = lpI
            End If
           
            If lSizeElement > UBound(buffer) + 1 Then
                ReDim buffer(lSizeElement - 1)
            End If
           
            memcpy buffer(0), ByVal lpI, lSizeElement
            memcpy ByVal lpI, ByVal lpJ, lSizeElement
            memcpy ByVal lpJ, buffer(0), lSizeElement
 
            lpI = lpI + lSizeElement
            lpJ = lpJ - lSizeElement
           
        End If
       
    Loop

    If lpFirstPtr < lpJ Then
        QuickSort lpFirstPtr, (lpJ - lpFirstPtr) \ lSizeElement + 1, lSizeElement, lpfnComparator
    End If
   
    If lpI < lpLast Then
        QuickSort lpI, (lpLast - lpI) \ lSizeElement + 1, lSizeElement, lpfnComparator
    End If
   
End Sub

' // Prototype for comparator function
' // If lpItem1 > lpItem2 then function return 1
' // If lpItem1 = lpItem2 then function return 0
' // If lpItem1 < lpItem2 then function return -1
Public Function MainComparator( _
                ByVal lpAddressOfFunction As Long, _
                ByVal lpItem1 As Long, _
                ByVal lpItem2 As Long) As Long
End Function

---

Download.

Insetad of keeping track with isInit can you call PatchFunc in MainComparator like this

Code:

---

Public Function MainComparator( _
                ByVal lpAddressOfFunction As Long, _
                ByVal lpItem1 As Long, _
                ByVal lpItem2 As Long) As Long
    PatchFunc AddressOf MainComparator
    MainComparator = MainComparator(lpAddressOfFunction, lpItem1, lpItem2)
End Function

---

... for some wicked self-modifying code :-))

cheers,
</wqw>

If we have a function in an object, then is it possible to call that function and use the objects variables to hold total or other values from more than one call to function, to this object?

Quote:

---

Originally Posted by georgekar

If we have a function in an object, then is it possible to call that function and use the objects variables to hold total or other values from more than one call to function, to this object?

---

Do you saw the TrickCallPointerClass example? This example shows how can you call the methods of the objects by the pointer. You should pass the object as the second parameter, and the return value (if need) is passed in the last parameters as the pointer (ByRef).

Quote:

---

Originally Posted by wqweto

Insetad of keeping track with isInit can you call PatchFunc in MainComparator like this

Code:

---

Public Function MainComparator( _
                ByVal lpAddressOfFunction As Long, _
                ByVal lpItem1 As Long, _
                ByVal lpItem2 As Long) As Long
    PatchFunc AddressOf MainComparator
    MainComparator = MainComparator(lpAddressOfFunction, lpItem1, lpItem2)
End Function

---

... for some wicked self-modifying code :-))

cheers,
</wqw>

---

Nice advice. It needs to test it on the compiled file.

It seems there is a limitation of `AddressOf` operator -- you cannot use it inside a function to get current function address, i.e. `AddressOf MainComparator` cannot be compiled inside `MainComparator` function.

So you have to use a helper function like this

Code:

---

Public Function MainComparator( _
                ByVal lpAddressOfFunction As Long, _
                ByVal lpItem1 As Long, _
                ByVal lpItem2 As Long) As Long
    PatchFunc pvMainComparatorAddr
    MainComparator = MainComparator(lpAddressOfFunction, lpItem1, lpItem2)
End Function

Private Function pvMainComparatorAddr() As Long
    Call memcpy(pvMainComparatorAddr, AddressOf MainComparator, 4)
End Function

---

The self-modifying part seems to work both in IDE and compiled.

Btw, I would call `MainComparator` something like `DelegateCompare` or similar. Every VB6 developer has a personal implementation of a similar delegator. I'm personally using the exactly same ASM thunk on a lightweight object with number of functions like Call1, Call2, Call3, etc each accepting 1, 2, 3, etc. number of (long) parameters. Popping return address from stack hides the delegator from call-stack too.

This is my delegator initialization function

Code:

---

Private Function pvInitDelegator(This As DelegatorData) As IDelegator
'00401030 59                  pop        ecx
'00401031 58                  pop        eax
'00401032 58                  pop        eax
'00401033 51                  push        ecx
'00401034 FF E0                jmp        eax
'00401036 90                  nop
'00401037 90                  nop
    Dim dwDummy        As Long
    Dim lIdx            As Long

    If m_aDelegatorVtbl(0) = 0 Then
        m_uDelegatorThunk.Code.Thunk(0) = &H51585859
        m_uDelegatorThunk.Code.Thunk(1) = &H9090E0FF
        Call VirtualProtect(m_uDelegatorThunk.Code.Thunk(0), 8, PAGE_EXECUTE_READWRITE, dwDummy)
        m_aDelegatorVtbl(0) = pvAddr(AddressOf pvDelegatorQI)
        m_aDelegatorVtbl(1) = pvAddr(AddressOf pvDelegatorAR)
        m_aDelegatorVtbl(2) = pvAddr(AddressOf pvDelegatorAR)
        For lIdx = 3 To UBound(m_aDelegatorVtbl)
            m_aDelegatorVtbl(lIdx) = VarPtr(m_uDelegatorThunk.Code.Thunk(0))
        Next
    End If
    This.pVTable = VarPtr(m_aDelegatorVtbl(0))
    Call CopyMemory(pvInitDelegator, VarPtr(This), 4)
End Function

---

This allows me to use comctl subclassing with a single redirection function like this

Code:

---

Private Function pvRedirectComCtlProc( _
            ByVal hWnd As Long, _
            ByVal wMsg As Long, _
            ByVal wParam As Long, _
            ByVal lParam As Long, _
            ByVal uIdSubclass As Long, _
            ByVal ThisPtr As Long) As Long
    #If NO_DELEGATOR Then
        m_uComCtlThunk.Code.Thunk(1) = ThisPtr
        m_uComCtlThunk.Code.Thunk(4) = uIdSubclass
        pvRedirectComCtlProc = CallWindowProc(m_uComCtlThunk.pfn, hWnd, wMsg, wParam, lParam)
    #Else
        pvRedirectComCtlProc = m_pDelegator.Call5(uIdSubclass, ThisPtr, hWnd, wMsg, wParam, lParam)
    #End If
End Function

---

Your code looks much better and will allow me to get rid of the custom typelib and simplify the whole delegation story a lot. Kudos!

cheers,
</wqw>

Quote:

---

Originally Posted by wqweto

It seems there is a limitation of `AddressOf` operator -- you cannot use it inside a function to get current function address, i.e. `AddressOf MainComparator` cannot be compiled inside `MainComparator` function.

---

Quote:

---

Originally Posted by Bonnie West

Yep, that's a known bug. The suggested workaround in the KB article PRB: Recursive Use of AddressOf Operator Fails is qualifying the procedure's name with the module's name. It'll work even if the procedure is Private and thus not shown in the IntelliSense list.

---

http://www.vbforums.com/image.php?u=...ine=1374042884

dose it support cdecl dll api?

i'm sorry,it can't support cdecl dll api

may be the same

Code:

---

MakeFunction GetProcAddress(hUser, "ReleaseDC"),addressof MyReleaseDC
 Function MyReleaseDC( ByVal hWnd As Long, ByVal hdc As Long) As Long
msgbox "test"
End Function

Public Sub MakeFunction(DllFunAddr As Long, BackFunAddr As Long)
  Dim code() As Byte, JmpBackAddr As Long
  Dim OldProtect As Long
  Dim ByteLen As Long
  ByteLen = 5
  ReDim code(ByteLen)
  Vblegend.VirtualProtect ByVal DllFunAddr, ByteLen, 64, OldProtect  '更改函数地址所在页面属性
 
  JmpBackAddr = DllFunAddr - BackFunAddr - 5
  code(0) = &HE9
  Vblegend.CopyMemory code(1), JmpBackAddr, 4
  Vblegend.WriteProcessMemory -1, ByVal BackFunAddr, code(0), ByteLen, 0
End Sub



Public Sub PatchFunc(ByVal Addr As Long)
    Dim InIDE As Boolean
 
    Debug.Assert MakeTrue(InIDE)
 
    If InIDE Then
        GetMem4 ByVal Addr + &H16, Addr
    Else
        VirtualProtect Addr, 8, PAGE_EXECUTE_READWRITE, 0
    End If

    GetMem4 &HFF505958, ByVal Addr
    GetMem4 &HE1, ByVal Addr + 4
End Sub
 
Public Function MakeTrue(ByRef bvar As Boolean) As Boolean
    bvar = True:

---

You can read this thread to add the __cdecl support.

VBE x86 can use this module
but VBE x64 i do not know how to change it

Code:

---

'Func Addr: 26D01E5C
'26D01E5C: A1 581ED026  mov eax,26D01E58
'26D01E61: 0B C0        or eax, eax
'26D01E63: 74 13        je 26D01E78
'26D01E65: B8 C7C7386A  mov eax, VBE7.EbMode
'26D01E6A: FF D0        call eax
'26D01E6C: 83 f8 02    cmp, 02
'26D01E6F: 74 07        je 26D01E78
'26D01E71: B8 A22F9621  mov eax, 21962FA2

21962FA2 - 58                    - pop eax
21962FA3 - 59                    - pop ecx
21962FA4 - 50                    - push eax
21962FA5 - FF E1                - jmp ecx
21962FA7 - 00 58 59              - add [eax+59],bl
21962FAA - 4D                    - dec ebp
21962FAB - 6A FF                - push -01 { 255 }
21962FAD - E1 00                - loope 21962FAF
21962FAF - 00 24 05 00000300    - add [eax+00030000],ah  'seems only this line change to 00 00 00 after PatchFunc
21962FB6 - 58                    - pop eax
21962FB7 - 59                    - pop ecx
21962FB8 - 50                    - push eax
21962FB9 - FF E1                - jmp ecx
21962FBB - 00 00                - add [eax],al
21962FBD - 00 4D 6A              - add [ebp+6A],cl
21962FC0 - FF E1                - jmp ecx
21962FC2 - 00 00                - add [eax],al
21962FC4 - 24 05                - and al,05 { 5 }
21962FC6 - 00 00                - add [eax],al
21962FC8 - 04 00                - add al,00 { 0 }
21962FCA - 58                    - pop eax
21962FCB - 59                    - pop ecx
21962FCC - 50                    - push eax
21962FCD - FF E1                - jmp ecx
21962FCF - 00 58 59              - add [eax+59],bl
21962FD2 - 4D                    - dec ebp
21962FD3 - 6A FF                - push -01 { 255 }
21962FD5 - E1 00                - loope 21962FD7
21962FD7 - 00 24 05 00000500    - add [eax+00050000],ah
21962FDE - BA 54CB3B19          - mov edx,193BCB54 { (21962F64) }
21962FE3 - B9 03E24D6A          - mov ecx,VBE7.ProcCallEngine { (139) }
21962FE8 - FF E1                - jmp ecx

---

and x64

Code:

---

Func Addr: 1E408398654
1E408398654 - 48 89 4C 24 08        - mov [rsp+08],rcx
1E408398659 - 48 89 54 24 10        - mov [rsp+10],rdx
1E40839865E - 4C 89 44 24 18        - mov [rsp+18],r8
1E408398663 - 4C 89 4C 24 20        - mov [rsp+20],r9
1E408398668 - 48 B8 50863908E4010000 - mov rax,000001E408398650 { (1) }
1E408398672 - 48 0B C0              - or rax,rax
1E408398675 - 74 32                - je 1E4083986A9
1E408398677 - 48 B8 70D09733FB7F0000 - mov rax,VBE7.EbMode { (-1958193856) }
1E408398681 - FF D0                - call rax
1E408398683 - 48 83 F8 02          - cmp rax,02 { 2 }
1E408398687 - 74 20                - je 1E4083986A9
1E408398689 - 48 B8 8CBA560CE4010000 - mov rax,000001E40C56BA8C { (1846495590) }

1E40C56BA8C - 66 49 0F6E EC        - movq xmm5,r12
1E40C56BA91 - 48 B8 9863C733FB7F0000 - mov rax,VBE7.g_PPExSP { (7FFB33C71868) }
1E40C56BA9B - 48 8B 00              - mov rax,[rax]
1E40C56BA9E - 4C 8B 20              - mov r12,[rax]
1E40C56BAA1 - 49 81 EC 10000000    - sub r12,00000010 { 16 }
1E40C56BAA8 - 49 8B C4              - mov rax,r12
1E40C56BAAB - 49 89 8C 24 00000000  - mov [r12+00000000],rcx
1E40C56BAB3 - 49 89 94 24 08000000  - mov [r12+00000008],rdx
1E40C56BABB - 48 BA 38BA560CE4010000 - mov rdx,000001E40C56BA38 { (0) }
1E40C56BAC5 - 48 B8 1A17C033FB7F0000 - mov rax,VBE7.ProcCallEngine { (72) }
1E40C56BACF - FF E0                - jmp rax
1E40C56BAD1 - AB                    - stosd
1E40C56BAD2 - BE 58BE0000          - mov esi,0000BE58 { 48728 }
1E40C56BAD7 - 00 62 92              - add [rdx-6E],ah
1E40C56BADA - A0 33FB7F0000BB275C  - mov al,[5C27BB00007FFB33] { ("reate") }
1E40C56BAE3 - 68 7D000000          - push 0000007D { 125 }
1E40C56BAE8 - 24 07                - and al,07 { 7 }

---

As far as i know VBA64 calls ProcCallEngine directly (i didn't check exactly) so this trick won't work.

How to change code to support cdecl api?

Public Sub PatchFunc(FuncName As String, ByVal CdeclAddr As Long)

hao to call Sqlite3.dll with cdecl?-VBForums
https://www.vbforums.com/showthread....dll-with-cdecl

Just use VBCdeclFix.

call cdecl api by vb6:

how to simplified code without toBytes(*) like this?

Code:

---


GetMem4 &HFF505958, ByVal lpAddr
GetMem4 &HE1, ByVal lpAddr + 4

---

Because modifying the assembly code during the function process in the IDE may cause VB6.EXE to crash, this method was used, but the stability is unknown.

CopyMemory2 VbFunction, ByVal VbFunction + &H16, 4

Code:

---

sub main()
Dim CdeclApi As Long
CdeclApi = GetProcAddress(LoadLibrary("cdecl.dll"), "ADD")

FixCdecl AddressOf VB_Sum, CdeclApi, 2

Dim A As Long, B As Long, c As Long
A = 11
B = 22
c = VB_Sum(A, B)
end sub

Function VB_Sum(ByVal A As Long, ByVal B As Long, Optional NullArg As Long) As Long

MsgBox 1
MsgBox 2
MsgBox 3
MsgBox 4
MsgBox 5
MsgBox 6
MsgBox 7
MsgBox 8
End Function

---

Code:

---

Public Const PAGE_EXECUTE_READWRITE As Long = &H40
Private Declare Sub CopyMemory2 Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)
Declare Function WriteProcessMemory2 Lib "kernel32" Alias "WriteProcessMemory" (ByVal hProcess As Long, ByVal lpBaseAddress As Any, ByVal lpBuffer As Any, ByVal nSize As Long, lpNumberOfBytesWritten As Long) As Long
Declare Function VirtualProtect2 Lib "kernel32" Alias "VirtualProtect" (ByRef lpAddress As Any, ByVal dwSize As Long, ByVal flNewProtect As Long, lpflOldProtect As Long) As Long  '设置内存可读写

Sub FixCdecl(VbFunction As Long, CdeclApi As Long, Args As Long) 'GOOD
'cdecl绑定vb函数模块 qq 2776478814

'VbFunction,vb模块中的函数地址，用来绑定cdecl函数
'CdeclApi,cdecl的函数地址
'Args=cdecl函数需要几个参数
'
    Dim Asm(4) As String, Stub() As Byte, THUNK_SIZE As Long
    '  0: 58                  pop        eax
    '  1: 89 84 24 XX XX XX XX mov        dword ptr [esp+Xh],eax
    Asm(0) = "58 89 84 24 " & LongToHex(Args * 4) '&H24848958
    Asm(1) = "B8 " & LongToHex(CdeclApi)      'B8 90807000    MOV EAX,708090
    Asm(2) = "FF D0"                          'FFD0          CALL EAX
    Asm(3) = "83 C4 " & Hex(Args * 4) '83 C4 XX      add esp, XX    'cleanup args
    Asm(4) = "C3"
   
    Stub() = toBytes(Join(Asm, " "))
    THUNK_SIZE = UBound(Stub) + 1
   
    Dim bInIDE          As Boolean
    Debug.Assert pvSetTrue(bInIDE)
 
    If bInIDE Then
        CopyMemory2 VbFunction, ByVal VbFunction + &H16, 4
    Else
        VirtualProtect2 VbFunction, THUNK_SIZE, PAGE_EXECUTE_READWRITE, 0    '更改函数地址所在页面属性
    End If
    WriteProcessMemory2 -1, VbFunction, VarPtr(Stub(0)), THUNK_SIZE, 0
End Sub

Function toBytes(x As String) As Byte()
    Dim tmp() As String
    Dim fx() As Byte
    Dim i As Long
    tmp = Split(x, " ")
    ReDim fx(UBound(tmp))
    For i = 0 To UBound(tmp)
        fx(i) = CInt("&h" & tmp(i))
    Next
    toBytes = fx()
End Function

 Function LongToHex(x As Long) As String
    Dim B(1 To 4) As Byte
    CopyMemory2 B(1), x, 4
    LongToHex = Hex(B(1)) & " " & Hex(B(2)) & " " & Hex(B(3)) & " " & Hex(B(4))
End Function
 Function pvSetTrue(bValue As Boolean) As Boolean
    bValue = True
    pvSetTrue = True
End Function

---

It feels like I'm talking to some kind of artificial intelligence.

Quote:

---

Originally Posted by The trick

It feels like I'm talking to some kind of artificial intelligence.

---

use cdecl add-in It's a great method, I want to try another one. Because my CDECL.DLL is in memory, there is no such file on the hard drive. So it is not possible to directly declare API adding CDECL keywords

Quote:

---

Originally Posted by xiaoyao

use cdecl add-in It's a great method, I want to try another one. Because my CDECL.DLL is in memory, there is no such file on the hard drive. So it is not possible to directly declare API adding CDECL keywords

---

Using Add-in you can use any function because it adds the support of CDecl keyword to user functions (no external thunk is needed).

Maybe you can add the keyword CDECL to the function in the VB module, and then jump an API address JMP in the data area of CDECL.DLL in the memory to the process function in VB. This is also a method
However, I still prefer not to use the CDECL add-on ADD-IN to handle it.
The only issue currently encountered is that it is not possible to write assembly code to this VB6 function unless' fully compiled execution 'is executed (After compiling into EXE, it runs completely normally)
If the code in the module is modified or only 2 blank lines are added, it will cause the assembly to fail writing VB functions.
Click the second button,
Execute 'FixCdecl AddressOf VB_Sum, CdeclApi, 2' for the second time before the assembly can write or bind successfully.

Is it possible that the process address in memory may change at any time without complete compilation in the IDE?

Code:

---

        EbGetExecutingProj hProj
        TipGetFunctionId hProj, StrPtr(FuncName), sId
        TipGetLpfnOfFunctionId hProj, sId, lpAddr
        SysFreeString sId
       
       
        'CopyMemory2 lpAddr, ByVal lpAddr + &H16, 4
        VirtualProtect2 VbFunction, THUNK_SIZE, PAGE_EXECUTE_READWRITE, 0

---

how to get real address of VB_Sum ,by TipGetLpfnOfFunctionId ( lpAddr )?
maybe write asmcode err?

Çàïèñûâàåì âñòàâêó
' Çàïóñêàòü òîëüêî ïî Ctrl+F5!!

I didn't understand what the text was. Do I also need to press CTRL+F5 to run normally?
My CDECL also encountered this issue when calling by function address. I ran it directly with F5, but the assembly I wrote did not seem to take effect.

It only takes effect when the button is clicked to run for the second time (press f5)

ctrl+f5 No problem at all, no need to press the button twice

Quote:

---

Originally Posted by The trick

ACTUAL VERSION IN 9 POST
Exploring the function VBA6 figured out a way to call functions the pointer.
It's simple. Declare a function prototype (void function), where the first argument will be further transferred to the function address. Next, do a patch, so he tossed to us at the address specified in the first parameter. Thus it is possible to call functions in the standard modules, class modules, forms, API-functions (eg obtained through LoadLibrary and GetProcAddress).* One note, run the project through Ctrl + F5. And working in the IDE and compiled form.
For "patching" the prototype I made a separate module:
[CODE]
' ?????? ?????? WinApi ??????? ?? ?????????
Public Sub Main()
Dim hUser As Long, hGDI As Long
Dim DC As Long

hUser = LoadLibrary("user32")
hGDI = LoadLibrary("gdi32")

PatchFunc "GetDC", AddressOf GetDC
PatchFunc "ReleaseDC", AddressOf ReleaseDC
PatchFunc "Ellipse", AddressOf Ellipse

---

If two modules have the same function, how to solve the problem of calling under IDE?
model1.bas
model2.bas
"GetDC", AddressOf GetDC

need use
PatchFunc "model2.GetDC", AddressOf model2.

Code:

---

TipGetFunctionId hProj, StrPtr(FuncName), sId
        If sId = 0 Then MsgBox "Can't find function by name?" & FuncName: Exit Sub

---