...hook a function (in your own application) ?

Thomas Stutz

type

 TSaveRedir = packed record

   Addr: Pointer;

   Bytes: array[0..4] of Byte;

 end;

 PSaveRedir = ^TSaveRedir;

procedure RedirectCall(FromAddr, ToAddr: Pointer; SaveRedir: PSaveRedir);

var

 OldProtect: Cardinal;

 NewCode: packed record

   JMP: Byte;

   Distance: Integer;

 end;

begin

 if not VirtualProtect(FromAddr, 5, PAGE_EXECUTE_READWRITE, OldProtect) then

   RaiseLastWin32Error;

 if Assigned(SaveRedir) then

 begin

   SaveRedir^.Addr := FromAddr;

   Move(FromAddr^, SaveRedir^.Bytes, 5);

 end;

 NewCode.JMP := $E9;

 NewCode.Distance := PChar(ToAddr) - PChar(FromAddr) - 5;

 Move(NewCode, FromAddr^, 5);

 if not VirtualProtect(FromAddr, 5, OldProtect, OldProtect) then

   RaiseLastWin32Error;

end;

procedure UndoRedirectCall(const SaveRedir: TSaveRedir);

var

 OldProtect: Cardinal;

begin

 if not VirtualProtect(SaveRedir.Addr, 5, PAGE_EXECUTE_READWRITE, OldProtect) then

   RaiseLastWin32Error;

 Move(SaveRedir.Bytes, SaveRedir.Addr^, 5);

 if not VirtualProtect(SaveRedir.Addr, 5, OldProtect, OldProtect) then

   RaiseLastWin32Error;

end;

// Example: Replace Application.MessageBox with your own.

function MyNewMessageBox(Self: TApplication; const Text, Caption: PChar;

 Flags: Longint): Integer;

begin

 ShowMessage('New Messagebox');

 //....

end;

procedure TForm1.Button1Click(Sender: TObject);

begin

 Application.MessageBox('You'll never see this Text /

   Diesen Text wirst du nie sehen', '...', MB_OK);

end;

var

 S: TSaveRedir;

initialization

 RedirectCall(@TApplication.MessageBox, @MyNewMessageBox, @S);

finalization

 UndoRedirectCall(S);