Question

I have this hook function that works fine on x86. Thanks to Bo Persson.

void __fastcall Hook(Class* ThisInECX, int UnknownEDX, OtherClass* P1, void* P2, void* P3)
{
    static void* OriginalFunctionPointer = GetProcAddress(GetModuleHandleA("Some.dll"), "[...]");
    static auto OriginalFunction = ((void(__fastcall*)(Class* ThisInECX, int UnknownEDX, OtherClass* P1, void* P2, void* P3))OriginalFunctionPointer);

    OriginalFunction(ThisInECX, UnknownEDX, P1, P2, P3);
}

Now I’m trying to port it to x64. What I found and understood from a few snippets is that:
I had another variable “int UnknownRDX” at front but without it at atleast called the OriginalFunction correctly.
My real variables (P1 etc) seem to be somehow offsetted (or my problem is something different).
I actually need to know if this declaration is right so I can look for the problem at even worse positions.

void Hook(Class* This, int Unknown0, int Unknown1, OtherClass* P1, void* P2, void* P3)
{
    static void* OriginalFunctionPointer = GetProcAddress(GetModuleHandleA("Some64.dll"), "[...]");
    static auto OriginalFunction = ((void(*)(Class* This, int Unknown0, int Unknown1, OtherClass* P1, void* P2, void* P3))OriginalFunctionPointer);

    // Using P1 here is fine on x86 but not on x64

    OriginalFunction(This, Unknown0, Unknown1, P1, P2, P3)
}

Answer 1

There is only one calling convention on x64, so you can ditch that from the signature. What’s likely going wrong is that you’re trying to load the x86 version of a procedure from an x64 function.

Edit: Oh wait, you posted that question about x86/x64 hooking before, right? I’m pretty confident that’s not the problem here.

What I would say is that previously, your code depended on calling-convention specific hacks, but on x64 there is only one calling convention.

http://msdn.microsoft.com/en-us/library/ms235286.aspx