fpc/rtl/inc/except.inc

{
    This file is part of the Free Pascal run time library.
    Copyright (c) 1999-2000 by Michael Van Canneyt
    member of the Free Pascal development team

    See the file COPYING.FPC, included in this distribution,
    for details about the copyright.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 **********************************************************************}

{****************************************************************************
                                Exception support
****************************************************************************}


Const
  { Type of exception. Currently only one. }
  FPC_EXCEPTION   = 1;

  { types of frames for the exception address stack }
  cExceptionFrame = 1;
  cFinalizeFrame  = 2;

Type
  PExceptAddr = ^TExceptAddr;
  TExceptAddr = record
    buf       : pjmp_buf;
    next      : PExceptAddr;
{$ifdef CPU16}
    frametype : Smallint;
{$else CPU16}
    frametype : Longint;
{$endif CPU16}
  end;

Const
  CatchAllExceptions = PtrInt(-1);

{$ifdef FPC_HAS_FEATURE_THREADING}
ThreadVar
{$else FPC_HAS_FEATURE_THREADING}
Var
{$endif FPC_HAS_FEATURE_THREADING}
  ExceptAddrStack   : PExceptAddr;
  ExceptObjectStack : PExceptObject;
  ExceptTryLevel    : ObjpasInt;

Function RaiseList : PExceptObject;
begin
  RaiseList:=ExceptObjectStack;
end;


function AcquireExceptionObject: Pointer;
var
  _ExceptObjectStack : PExceptObject;
begin
  _ExceptObjectStack:=ExceptObjectStack;
  If _ExceptObjectStack<>nil then
    begin
      Inc(_ExceptObjectStack^.refcount);
      AcquireExceptionObject := _ExceptObjectStack^.FObject;
    end
  else
    RunError(231);
end;


procedure ReleaseExceptionObject;
var
  _ExceptObjectStack : PExceptObject;
begin
  _ExceptObjectStack:=ExceptObjectStack;
  If _ExceptObjectStack <> nil then
    begin
      if _ExceptObjectStack^.refcount > 0 then
        Dec(_ExceptObjectStack^.refcount);
    end
  else
    RunError(231);
end;


Function fpc_PushExceptAddr (Ft: {$ifdef CPU16}SmallInt{$else}Longint{$endif};_buf,_newaddr : pointer): PJmp_buf ;
  [Public, Alias : 'FPC_PUSHEXCEPTADDR'];compilerproc;
var
  _ExceptAddrstack : ^PExceptAddr;
begin
{$ifdef excdebug}
  writeln ('In PushExceptAddr');
{$endif}
  _ExceptAddrstack:=@ExceptAddrstack;
  PExceptAddr(_newaddr)^.Next:=_ExceptAddrstack^;
  _ExceptAddrStack^:=PExceptAddr(_newaddr);
  PExceptAddr(_newaddr)^.Buf:=PJmp_Buf(_buf);
  PExceptAddr(_newaddr)^.FrameType:=ft;
  result:=PJmp_Buf(_buf);
end;


{ This routine is called only from fpc_raiseexception, which uses ExceptTryLevel
  flag to guard against repeated exceptions which can occur due to corrupted stack
  or heap. }
Procedure PushExceptObject(Obj : TObject; AnAddr : CodePointer; AFrame : Pointer);
var
  Newobj : PExceptObject;
  _ExceptObjectStack : ^PExceptObject;
  framebufsize,
  framecount  : longint;
  frames      : PCodePointer;
  prev_frame,
  curr_frame  : Pointer;
  curr_addr   : CodePointer;
begin
{$ifdef excdebug}
  writeln ('In PushExceptObject');
{$endif}
  _ExceptObjectStack:=@ExceptObjectStack;
  New(NewObj);
  NewObj^.Next:=_ExceptObjectStack^;
  _ExceptObjectStack^:=NewObj;

  NewObj^.FObject:=Obj;
  NewObj^.Addr:=AnAddr;
  NewObj^.refcount:=0;

  { Backtrace }
  curr_frame:=AFrame;
  curr_addr:=AnAddr;
  frames:=nil;
  framebufsize:=0;
  framecount:=0;
  { The frame pointer of this procedure is used as initial stack bottom value. }
  prev_frame:=get_frame;
  while (framecount<RaiseMaxFrameCount) and (curr_frame > prev_frame) and
        (curr_frame<StackTop) do
    Begin
      prev_frame:=curr_frame;
      get_caller_stackinfo(curr_frame,curr_addr);
      if (curr_addr=nil) or
         (curr_frame=nil) then
        break;
      if (framecount>=framebufsize) then
        begin
          inc(framebufsize,16);
          reallocmem(frames,framebufsize*sizeof(codepointer));
        end;
      frames[framecount]:=curr_addr;
      inc(framecount);
    End;
  NewObj^.framecount:=framecount;
  NewObj^.frames:=frames;
end;

Procedure DoUnHandledException;
var
  _ExceptObjectStack : PExceptObject;
begin
  _ExceptObjectStack:=ExceptObjectStack;
  If (ExceptProc<>Nil) and (_ExceptObjectStack<>Nil) then
    with _ExceptObjectStack^ do
      begin
        TExceptProc(ExceptProc)(FObject,Addr,FrameCount,Frames);
        halt(217)
      end;
  if erroraddr = nil then
    RunError(217)
  else
    Halt(errorcode);
end;

{$ifndef FPC_SYSTEM_HAS_RAISEEXCEPTION}
procedure fpc_RaiseException (Obj : TObject; AnAddr : CodePointer; AFrame : Pointer);[Public, Alias : 'FPC_RAISEEXCEPTION']; compilerproc;
var
  _ExceptObjectStack : PExceptObject;
  _ExceptAddrstack : PExceptAddr;
begin
{$ifdef excdebug}
  writeln ('In RaiseException');
{$endif}
  if ExceptTryLevel<>0 then
    Halt(217);
  ExceptTryLevel:=1;
  PushExceptObject(Obj,AnAddr,AFrame);
  { if PushExceptObject causes another exception, the following won't be executed,
    causing halt upon entering this routine recursively. }
  ExceptTryLevel:=0;
  _ExceptAddrstack:=ExceptAddrStack;
  If _ExceptAddrStack=Nil then
    DoUnhandledException;
  _ExceptObjectStack:=ExceptObjectStack;
  if (RaiseProc <> nil) and (_ExceptObjectStack <> nil) then
    with _ExceptObjectStack^ do
      RaiseProc(FObject,Addr,FrameCount,Frames);
  longjmp(_ExceptAddrStack^.Buf^,FPC_Exception);
end;
{$endif FPC_SYSTEM_HAS_RAISEEXCEPTION}


Procedure fpc_PopAddrStack;[Public, Alias : 'FPC_POPADDRSTACK']; compilerproc;
var
  hp : ^PExceptAddr;
begin
{$ifdef excdebug}
  writeln ('In Popaddrstack');
{$endif}
  hp:=@ExceptAddrStack;
  If hp^=nil then
    begin
{$ifdef excdebug}
      writeln ('At end of ExceptionAddresStack');
{$endif}
      halt (255);
    end
  else
    begin
      hp^:=hp^^.Next;
    end;
end;


function fpc_PopObjectStack : TObject;[Public, Alias : 'FPC_POPOBJECTSTACK']; compilerproc;
var
  hp : PExceptObject;
begin
{$ifdef excdebug}
  writeln ('In PopObjectstack');
{$endif}
  hp:=ExceptObjectStack;
  if hp=nil then
    begin
{$ifdef excdebug}
      writeln ('At end of ExceptionObjectStack');
{$endif}
      halt (1);
    end
  else
    begin
       { we need to return the exception object to dispose it }
       if hp^.refcount = 0 then
         fpc_PopObjectStack:=hp^.FObject
       else
         fpc_PopObjectStack:=nil;
       ExceptObjectStack:=hp^.next;
       if assigned(hp^.frames) then
         freemem(hp^.frames);
       dispose(hp);
       erroraddr:=nil;
    end;
end;


{ this is for popping exception objects when a second exception is risen }
{ in an except/on                                                        }
function fpc_PopSecondObjectStack : TObject;[Public, Alias : 'FPC_POPSECONDOBJECTSTACK']; compilerproc;
var
  hp,_ExceptObjectStack : PExceptObject;
begin
{$ifdef excdebug}
  writeln ('In PopObjectstack');
{$endif}
  _ExceptObjectStack:=ExceptObjectStack;
  If not(assigned(_ExceptObjectStack)) or
     not(assigned(_ExceptObjectStack^.next)) then
    begin
{$ifdef excdebug}
      writeln ('At end of ExceptionObjectStack');
{$endif}
      halt (1);
    end
  else
    begin
      if _ExceptObjectStack^.next^.refcount=0 then
        { we need to return the exception object to dispose it if refcount=0 }
        fpc_PopSecondObjectStack:=_ExceptObjectStack^.next^.FObject
      else
        fpc_PopSecondObjectStack:=nil;
      hp:=_ExceptObjectStack^.next;
      _ExceptObjectStack^.next:=hp^.next;
      if assigned(hp^.frames) then
        freemem(hp^.frames);
      dispose(hp);
    end;
end;

{$ifndef FPC_SYSTEM_HAS_RERAISE}
Procedure fpc_ReRaise;[Public, Alias : 'FPC_RERAISE']; compilerproc;
var
  _ExceptAddrStack : PExceptAddr;
begin
{$ifdef excdebug}
  writeln ('In reraise');
{$endif}
  _ExceptAddrStack:=ExceptAddrStack;
  If _ExceptAddrStack=Nil then
    DoUnHandledException;
  ExceptObjectStack^.refcount := 0;
  longjmp(_ExceptAddrStack^.Buf^,FPC_Exception);
end;
{$endif FPC_SYSTEM_HAS_RERAISE}

function Internal_PopSecondObjectStack : TObject; external name 'FPC_POPSECONDOBJECTSTACK';
function Internal_PopObjectStack: TObject; external name 'FPC_POPOBJECTSTACK';
procedure Internal_Reraise; external name 'FPC_RERAISE';

Function fpc_Catches(Objtype : TClass) : TObject;[Public, Alias : 'FPC_CATCHES']; compilerproc;
var
  _ExceptObjectStack : PExceptObject;
begin
  _ExceptObjectStack:=ExceptObjectStack;
  If _ExceptObjectStack=Nil then
   begin
{$ifdef excdebug}
     Writeln ('Internal error.');
{$endif}
     halt (255);
   end;
  if Not ((Objtype = TClass(CatchAllExceptions)) or
         (_ExceptObjectStack^.FObject is ObjType)) then
    fpc_Catches:=Nil
  else
    begin
      // catch !
      fpc_Catches:=_ExceptObjectStack^.FObject;
      { this can't be done, because there could be a reraise (PFV)
       PopObjectStack;

       Also the PopAddrStack shouldn't be done, we do it now
       immediatly in the exception handler (FK)
      PopAddrStack; }
    end;
end;

{$ifdef VER2_6}
Procedure fpc_DestroyException(o : TObject);[Public, Alias : 'FPC_DESTROYEXCEPTION']; compilerproc;
begin
  { with free we're on the really safe side }
  o.Free;
end;

{ TODO: no longer used, clean up }
function fpc_GetExceptionAddr : CodePointer;[Public, Alias : 'FPC_GETEXCEPTIONADDR']; compilerproc;
var
  _ExceptObjectStack : PExceptObject;
begin
  _ExceptObjectStack:=ExceptObjectStack;
  if _ExceptObjectStack=nil then
    fpc_GetExceptionAddr:=nil
  else
    fpc_GetExceptionAddr:=_ExceptObjectStack^.Addr;
end;
{$endif VER2_6}

Procedure SysInitExceptions;
{
  Initialize exceptionsupport
}
begin
  ExceptObjectstack:=Nil;
  ExceptAddrStack:=Nil;
end;


{$ifndef FPC_SYSTEM_HAS_DONEEXCEPTION}
procedure fpc_doneexception;[public,alias:'FPC_DONEEXCEPTION'] compilerproc;
begin
  Internal_PopObjectStack.Free;
end;
{$endif FPC_SYSTEM_HAS_DONEEXCEPTION}

procedure fpc_raise_nested;[public,alias:'FPC_RAISE_NESTED']compilerproc;
begin
  Internal_PopSecondObjectStack.Free;
  Internal_Reraise;
end;

{$ifndef FPC_SYSTEM_HAS_SAFECALLHANDLER}
function fpc_safecallhandler(obj: TObject): HResult; [public,alias:'FPC_SAFECALLHANDLER']; compilerproc;
var
  raiselist: PExceptObject;
  adr: CodePointer;
  exc: TObject;
begin
  raiselist:=ExceptObjectStack;
  if Assigned(raiseList) then
    adr:=raiseList^.Addr
  else
    adr:=nil;
  exc:=Internal_PopObjectStack;
  if Assigned(obj) and Assigned(exc) then
    result:=obj.SafeCallException(exc,adr)
  else
    result:=E_UNEXPECTED;
  exc.Free;
end;
{$endif FPC_SYSTEM_HAS_SAFECALLHANDLER}