Re: [Pnet-developers] Re: [DotGNU] Bug in Pnet

[ktreichel]

Hi Russel,

looks like it's not really the exception height where the problem is but the 
number of nested blocks called through jsr where the catcher is.

So adjusting the frameheight on jsr/ret_jsr sounds reasonable for me because it 
should do the same for other blocks called through jsr too.

Cheers,

Klaus
> -----Ursprüngliche Nachricht-----
> Von: Russell Stuart <address@hidden>
> Gesendet: 30.10.06 10:41:48
> An: address@hidden
> CC: address@hidden
> Betreff: Re: [Pnet-developers] Re: [DotGNU] Bug in Pnet


> On Mon, 2006-10-30 at 18:57 +1000, Russell Stuart wrote:
> > It has taken me this long to figure that out.  The tricky
> > part is fixing it.  The first thing that comes to mind
> > is getting jsr/ret_jsr to adjust the exception frame 
> > height, but that is ugly because it assumes that jsr is 
> > only used for finally.  I think that is true.  Anyone
> > get a better idea?
> 
> Replying to myself ... that does look like a reasonable
> way to fix it.  Unfortunately there is another bug, and
> how to fix it is not so obvious.
> 
> VMCASE(COP_PREFIX_ENTER_TRY) sets thread->exceptHeight.  
> The reason is described in comment above viz: 'It sets 
> the "base height" of the stack so that <i>throw</i> 
> instructions know where to unwind the stack to when an 
> exception is thrown.'
> 
> Fine.  But nowhere is thread->exceptHeight is restored
> when the try{} block exits.  So I expect that something
> like this:
> 
>   try {
>      // thread->exceptHeight = stoptop in COP_PREFIX_ENTER_TRY
>      some code that alters the stack height;
>      try {
>        // thread->exceptHeight = stoptop in COP_PREFIX_ENTER_TRY
>      }
>      catch (Exception e) {}
>      // thread->exceptHeight hasn't been restored at this point
>      throw new Exception();
>   }
>   catch (Exception e) {
>     // e at this point contains an invalid stack.
>   }
> 
> My problem is as far as I can tell, there is no code
> executed when a try{}catch(){} block exits, so its
> not possible to fix the bug without introducing
> another CVM opcode that is executed at the end of
> a try{}catch(){} block.
> 
> I'll just fix the original problem for now.
> 
> 


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