Cheat Engine

[onlyus]

procedure JumpHook(Oldfunc, Newfunc: Pointer);
var
Jmpto, OldProtect: DWORD;
begin
VirtualProtect(Oldfunc, 6, PAGE_EXECUTE_READWRITE, @OldProtect);
Jmpto:= DWORD(Newfunc);
PDWORD(Oldfunc)^:= $25FF;
PDWORD(DWORD(Oldfunc)+2)^:= Jmpto;
VirtualProtect(Oldfunc, 6, OldProtect, @OldProtect);
end;

procedure MSGBOX(hWnd: HWND; l1, l2: PAnsiChar; uType: Cardinal); stdcall;
begin
ShowMessage('called');
end;

.
.

JumpHook(GetProcAddress(GetModuleHandle('user32.dll'), 'MessageBoxA'), @MSGBOX);
MessageBoxA(0, 'asd', 'asd', MB_OK); // error




i try 6-byte jmp hook but doesn't work what's wrong my code?

[dnsi0]

probably because jmpto is in the stack and after that function executes, it gets messed up. You're better off with the 5 byte rel jump OR declaring it as a global.

Rel jump:

pByte(Address)^:=$E9;
pDword(Address+1)^:=Dword(@DestinationFunction)-Address-5;

[Dark Byte]

It's probably because showmessage calls messageboxa which then calls your hook which calls showmessage which calls messageboxa which then calls your hook which calls showmessage which calls messageboxa which then calls your hook which calls showmessage which calls messageboxa which then calls your hook which calls showmessage which calls messageboxa which then calls your hook which calls showmessage which calls messageboxa which then calls your hook which calls showmessage which calls messageboxa which then calls your hook which calls showmessage which calls messageboxa which then calls your hook ...
Until the end of the stack is reached and the program crashes

[dnsi0]