Author: Dave
Date: 09.13.16 - 5:19am

So normally when calling cdecl exports from VB i do a generated asm thunk technique with CallWindowProc to launch it.( Example at bottom or download here)

Looking through the vbforums today I found a couple more. Archiving them here so I can find them again!

A TLB based one from The Trick (local copy) - Note compiled exe only

and one from Ben321 below.

Private Declare Function DispCallFunc Lib "oleaut32.dll" ( _
     ByVal pvInstance As Long, _
     ByVal oVft As Long, _
     ByVal cc As Long, _
     ByVal vtReturn As Integer, _
     ByVal cActuals As Long, _
     ByRef prgvt As Integer, _
     ByRef prgpvarg As Long, _
     ByRef pvargResult As Variant _
) As Long

Private Function CallCDECL(ByVal FuncAddr As Long, ByRef Params() As Variant, ByVal ReturnType As VbVarType) As Variant Dim ParamCount As Long Dim ParamTypes() As Integer Dim ParamPtrs() As Long Dim n As Long ParamCount = UBound(Params) + 1 If ParamCount > 0 Then ReDim ParamTypes(ParamCount - 1) ReDim ParamPtrs(ParamCount - 1) For n = 0 To ParamCount - 1 ParamTypes(n) = VarType(Params(n)) ParamPtrs(n) = VarPtr(Params(n)) Next n DispCallFunc 0, FuncAddr, 1, ReturnType, ParamCount, ParamTypes(0), ParamPtrs(0), CallCDECL Else DispCallFunc 0, FuncAddr, 1, ReturnType, ParamCount, ByVal 0, ByVal 0&, CallCDECL End If End Function

My example:
Private Declare Function CallAsmAddr Lib "user32" Alias "CallWindowProcA" (
    ByVal lpCode As Long, ByVal hwnd As Long,
    ByVal msg As Long, ByVal wParam As Long,
    ByVal lParam As Long
) As Long

Private Declare Function VirtualAlloc Lib "kernel32" (
    ByVal lpAddress As Long, ByVal dwSize As Long, 
    ByVal flAllocationType As Long, ByVal flProtect As Long
) As Long

Private Declare Function VirtualFree Lib "kernel32" (
    ByVal lpAddress As Long, ByVal dwSize As Long, 
    ByVal dwFreeType As Long
) As Long

Private Declare Sub RtlMoveMemory Lib "kernel32" (
    ByVal Destination As Long,
    ByVal Source As Long, ByVal Length As Long

'should be dep safe..
Function CallCdecl(lpfn As Long, ParamArray args()) As Long

    Dim asm() As String
    Dim stub() As Byte
    Dim i As Long
    Dim argSize As Byte
    Dim ret As Long
    Const PAGE_RWX      As Long = &H40
    Const MEM_COMMIT    As Long = &H1000
    Dim asmAddr As Long
    Dim sz As Long
    Const depSafe = True
    If lpfn = 0 Then Exit Function
    'push asm(), "CC"  'enable this to debug asm
    'we step through args backwards to preserve intutive ordering
    For i = UBound(args) To 0 Step -1
        If Not IsNumeric(args(i)) Then
            MsgBox "CallCdecl Invalid Parameter #" & i & " TypeName=" & TypeName(args(i))
            Exit Function
        End If
        push asm(), "68 " & lng2Hex(CLng(args(i)))  '68 90807000    PUSH 708090
        argSize = argSize + 4

    push asm(), "B8 " & lng2Hex(lpfn)        'B8 90807000    MOV EAX,708090
    push asm(), "FF D0"                      'FFD0           CALL EAX
    push asm(), "83 C4 " & Hex(argSize)      '83 C4 XX       add esp, XX     'cleanup args
    push asm(), "C2 10 00"                   'C2 10 00       retn 10h        'cleanup our callwindowproc args
    stub() = toBytes(Join(asm, " "))
    If Not depSafe Then
        CallCdecl = CallAsm(stub(0), 0, 0, 0, 0)
        Exit Function
    End If
    sz = UBound(stub) + 1
    asmAddr = VirtualAlloc(ByVal 0&, sz, MEM_COMMIT, PAGE_RWX)
    If asmAddr = 0 Then
        MsgBox "Failed to allocate RWE memory size: " & sz, vbInformation
        Exit Function
    End If
    RtlMoveMemory asmAddr, VarPtr(stub(0)), sz
    CallCdecl = CallAsmAddr(asmAddr, 0, 0, 0, 0)
    VirtualFree asmAddr, sz, 0
End Function

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