hook a function (in your own application)

...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);