HookHop von PostMessage geht nicht

[WorstNightmare]

Delphi-Quellcode:

procedure TForm1.FormCreate(Sender: TObject);
begin
  u32 := LoadLibrary(user32);
  PostMessageReal := DWORD(GetProcAddress(u32, 'PostMessageA')) + 5;
end;

function _PostMessage(hWnd: HWND; uMsg: UINT; wParam: WPARAM; lParam: LPARAM): BOOL; stdcall;
asm
  jmp  dword ptr ds:[PostMessageReal]
  mov  eax, 0
end;

procedure TForm1.ToolButton1Click(Sender: TObject);
var
  wnd: hwnd;
begin
  wnd := FindWindowEx(hauptwnd, 0, 'Edit', '');
  _PostMessage(Wnd, WM_CHAR, Ord('A'), 0);
end;

Thanks, this works now.
I add 5 bytes, because I want to avoid calling a hook that might have been installed.
E.g. the first 5 bytes of PostMessageA could look like this:

Code:

mov edi, edi
push ebp
mov ebp, esp

These can be overwritten with a jmp which calls the redirection, which I want to avoid.

But I don't get why I can leave away the other assembler commands in Delphi.