In Asm-Prozedur eine Exception auslösen

[Kas Ob.]

Zitat von Amateurprofi:

   mov eax,[$00419bc8] // ??? Fragen:
Was wird da in EAX geladen, und wie kann ich das in eigenen Assembler-Routinen realisieren?

In eax a pointer to a type class to create, and Delphi Assembler is very outdated and can't perform many things, in fact it is stuck in 90s, and till this day Embarcadero call it inline-assembler, while it is inline only for 32bit and not inline for 64.

Anyway, i highly recommend to refrain form generating exception from assembly for the same reason above and the share amount of time you will spend on it to work and it most likely will bite you in the butt.

Here a simple code that will work for 32bit

Code:

program AsmException;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

type
  TMyException = class(Exception)
  end;

function GetException(Ex: ExceptClass; const Msg: string): Exception;
begin
  Result := Ex.Create(Msg);
end;

procedure ExceptionPas1;
begin
  raise GetException(Exception, 'Error Message from Exception');
end;

procedure ExceptionPas2;
begin
  raise GetException(TMyException, 'Error Message from MyExeption');
end;

procedure ExceptionAsm32;
const
  pMyExClass: ExceptClass = (TMyException);
  LocalExceptionMsg : string = 'Error from Assembly';
asm
  mov     edx, LocalExceptionMsg
  mov     eax, pMyExClass
  Call    GetException
  Call    system.@RaiseExcept
end;
      {
procedure ExceptionAsm64;  // will not work, may be wrong, may be just need lot of hand tweaking
const
  pMyExClass: ExceptClass = (TMyException);
  LocalExceptionMsg : string = 'Error from Assembly';
asm
  push    rbp
  mov     rbp, rsp
  mov     rdx, LocalExceptionMsg
  mov     rcx, pMyExClass
  Call    GetException
  mov     rcx, rax
  Call    system.@RaiseExcept
  mov     rsp, rbp
  pop     rbp
end; }

begin
  try
    ExceptionPas1;
  except
    on E: Exception do Writeln(E.ClassName, ' class : ', E.Message);
  end;
  try
    ExceptionPas2;
  except
    on E: Exception do Writeln(E.ClassName, ' class : ', E.Message);
  end;
  try
    ExceptionAsm32;
  except
    on E: Exception do Writeln(E.ClassName, ' class : ', E.Message);
  end;
  Readln;
end.

the result on my PC now

Code:

Exception class : Error Message from Exception
TMyException class : Error Message from MyExeption
TMyException class : Error from Assembly

Yet there is som much to this than what meet the eyes, see, when an exception is raised then unwinding process will issued, for 32bit it is way easier because the system and its API where on the stack, on x64 the calling convention is like Delphi mostly with registers so framed stack will be used and these for optimization reason and unnecessity might be omited, here become problems with guessing where to go next, so you have to be sure for your assembly that framing is OK, in my example for 32 bit it is ok unless your assembly started to grow and the compiler added a frame stack to ruin things, same on x64, which is not working in my above code, i left it as example for who want to try to make it work, it is just waste of time.

My suggestion is that for anything with exception use Pascal/Delphi code, only then the compiler might be helpful, put your exception creation and raising in procedure and call it from assembly, easier and might be safer too.

[Kas Ob.]

I just remembered, not long ago there was a thread about disappearing application when an exception raised, tweaking and playing (something like commenting the rbp instructions) with ExceptionAsm64 will produce similar behavior of disappearing application with messages, the OS will just kill it silently and will not look back.