SEH. Проблемы с установкой собственного обработчика

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;


function AddVectoredExceptionHandler(FirstHandler: CARDINAL; VectoredHandler: POINTER): POINTER; stdcall; external 'Kernel32.dll' name 'AddVectoredExceptionHandler';


type
  TForm1 = class(TForm)
    Memo1: TMemo;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Edit1: TEdit;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;




type
  PEXCEPTION_RECORD = ^EXCEPTION_RECORD;
  EXCEPTION_RECORD = packed record
                     ExceptionCode: CARDINAL;
                     ExceptionFlags: CARDINAL;
                     ExceptionRecord: PEXCEPTION_RECORD;
                     ExceptionAddress: POINTER;
                     NumberParameters: CARDINAL;
                     ExceptionInformation: ULONG_PTR;
                     end;



type
  PEXCEPTION_POINTERS = ^EXCEPTION_POINTERS;
  EXCEPTION_POINTERS = packed record
                       ExceptionRecord: PEXCEPTION_RECORD;
                       ContextRecord: PCONTEXT;
                       end;




const
  CALL_LAST = 0;
  CALL_FIRST = 1;
  EXCEPTION_CONTINUE_SEARCH = $0;
  EXCEPTION_EXECUTE_HANDLER = $1;
  EXCEPTION_CONTINUE_EXECUTION = $FFFFFFFF;




var
  Form1: TForm1;
  SI: SYSTEM_INFO;
  MemAddr: POINTER;
  lpflOldProtect: CARDINAL;





implementation

{$R *.dfm}



  // ОБРАБОТЧИК ИСКЛЮЧЕНИЙ ПОВЕРХ СИСТЕМНОГО
function MyVectoredHandler(ExceptionInfo: PEXCEPTION_POINTERS): INTEGER; stdcall;
begin
   if ExceptionInfo.ExceptionRecord.ExceptionCode = EXCEPTION_ACCESS_VIOLATION then
   begin
      ShowMessage('Произошло исключение. ExceptionCode = EXCEPTION_ACCESS_VIOLATION');
      VirtualProtect(MemAddr, SI.dwPageSize * 10, PAGE_READWRITE, @lpflOldProtect);
      result := EXCEPTION_CONTINUE_EXECUTION;
      end
   else
   result := EXCEPTION_CONTINUE_SEARCH;
end;





procedure TForm1.Button1Click(Sender: TObject);
var
PrevHandler: POINTER;
begin
   PrevHandler := AddVectoredExceptionHandler(CALL_FIRST, Addr(MyVectoredHandler));
end;



procedure TForm1.Button2Click(Sender: TObject);
begin
   VirtualProtect(MemAddr, SI.dwPageSize * 10, PAGE_READONLY, Addr(lpflOldProtect));

end;


  // КНОПКА ВЫЗЫВАЮЩАЯ ИСКЛЮЧЕНИЕ
procedure TForm1.Button3Click(Sender: TObject);
var
A: PAnsiChar;
begin
   A := MemAddr;
   A^ := 'S';

end;



procedure TForm1.FormCreate(Sender: TObject);
begin
   Memo1.Clear;
   GetSystemInfo(SI);
   MemAddr := VirtualAlloc(NIL, SI.dwPageSize * 10, MEM_COMMIT, PAGE_READWRITE);
   Edit1.Text := IntToHex(CARDINAL(MemAddr), 8);
end;



procedure TForm1.FormDestroy(Sender: TObject);
begin
   VirtualFree(MemAddr, SI.dwPageSize * 10, 0);
end;



end.