Unit to properly SwitchToFiber() in Delphi without breaking exception handling

DelphiSwitchToFiber.pas

{
  The idea of DelphiSwitchToFiber() function is to backup on a local variable in stack the
  state of the Exception stack right before calling SwitchToFiber() and then restoring its state
  right atfer returns from call to SwitchToFiber().

  If SwitchToFiber() is used directly from within an Except or Finally block, and if there's an exception
  raised after switching to another fiber, upon coming back the results will be unpredictable because
  the exception stack will be completely unwinded and all raise exceptions destroyed.
  In order to prevent this issue we must backup the Exception stack before the call to SwitchToFiber()
  and restore it right after the call.

  Details of 64 bits exception stack persistance in unit uWin64ExceptionStack.pas

  It's important to notice that when getting back from SwitchToFiber() we can't even assume that
  the call was done within the context of Thread where the call was initiated. That's why on
  64 bits implementation of this function, we need to obtain TLS pointer to ThreadVar storage
  area right after the call to SwitchToThread().
  Notice also that 32 bits implementation is dramatically simpler. On 32 bits versions of Delphi
  when compiling under Windows, the system unit simply kept a linked list of stacked exceptions
  so backing up our Exception stack was as simple as storing a pointer to this list on a local
  variable and then restoring this pointer with the provided system API calls.
  Win64 is an entirely different story, system unit hides completely all of the exception management
  details, so we have to essently do a hack by accessing the area of the TLS where threadvars are stored
  to persist the three key elements that participate on Exception management stack. These are:

  RaiseFrames : TRaiseFrames;
  ExceptionObjectCount : Integer;
  RaiseListPtr : PRaiseFrame;

  Notice that when calculating offset into TLS area to backup and restore RaiseListPtr we consider
  ExceptionObjectCount size as NativeUInt (64 bits) rather than a regular integer (32 bits). This is
  because Delphi compiler aligns to 64 bits the elements stored in the ThreadVar storage area.
}

{$IFDEF WIN64}

// Details to implement this function pulled from System.pas unit
procedure DelphiSwitchToFiber(AFiber : Pointer);
var
  Win64ExceptionStack : TWin64ExceptionStack;
begin
  Win64ExceptionStack.LoadFromThreadExceptionStack;
  SwitchToFiber(AFiber);
  Win64ExceptionStack.SaveToThreadExceptionStack;
end;

{$ELSE}

{$IFDEF VER130}
// SetRaiseList is totally broken in Delphi 5. Needs to be replaced by this function
function SetRaiseList(NewPtr: Pointer): Pointer;
asm
  PUSH    EAX
  CALL    SysInit.@GetTLS
  MOV     EDX, [EAX].$0 // Offset of threadvar RaiseListPtr in TLS memory block
  POP     ECX
  MOV     [EAX], ECX
  MOV     EAX, EDX
end;
{$ENDIF}

procedure DelphiSwitchToFiber(AFiber : Pointer);
var
  SavedRaiseList : Pointer;
begin
  SavedRaiseList := RaiseList;
  SwitchToFiber(AFiber);
  SetRaiseList(SavedRaiseList);
end;

{$ENDIF}