RFR(XS): 8232921: assert(is_object_aligned(result)) failed: address not aligned

[Lindenmaier, Goetz]

Hi Coleen, 

> > java_lang_Boolean::get_TRUE is not working during the initialization
> > because the offsets are not yet set: java_lang_Boolean::_static_TRUE_offset
> > is zero.
> 
> I don't understand this sentence.  The patch 02 looks like it
> initializes it at the right place.  It doesn't work?
Yes, patch 02 works. I just wanted to reason why I'm not using 
get_TRUE()... just ignore ...

Another possibility, much more local, and using Boolean::TRUE, is this:
http://cr.openjdk.java.net/~goetz/wr19/8232921-fix_hidden_frames/03/
It uses _method as a fallback during initialization. Actually, this should never 
happen with the current VM. It does not throw exceptions with hidden frames
during initialization. I only ran into this during testing when I forced all 
exceptions to call get_TRUE.
I still think 01 is the most simple :).

> On second thought, I think I agree with you.  01 looks better, and if
> you can add the comment in BacktraceBuilder, it would be fine.
01 with the comment added:
http://cr.openjdk.java.net/~goetz/wr19/8232921-fix_hidden_frames/01a/

Best regards,
  Goetz.


> 
> thanks,
> Coleen
> 
> >
> > webrev 01 passed our testing tonight.
> >
> > Best regards,
> >    Goetz.
> >
> >> I don't think there's any downside to
> >> putting the methods array there, but it's really mind blowing.
> >>
> >> Sorry I didn't notice this in the review.  I should have looked more
> >> closely when I saw the PauseNoSafepointVerifier.
> >>
> >>     // GC unsafe class for assigning backtrace elements.  Allocation is
> >> only allowed
> >>     // in expand().
> >>     NoSafepointVerifier _nsv;
> >>
> >> You could add a comment like this.
> >>
> >> Coleen
> >>
> >> On 10/29/19 10:32 AM, Lindenmaier, Goetz wrote:
> >>> Hi,
> >>>
> >>> Originally, I wanted to model indicating that frames
> >>> have been dropped nicely in Java using
> >>> a meaningful java object. Exceptions in hidden frames
> >>> should be rare, so allocating only in that case should have
> >>> been cheap. Unfortunately, I can not allocate here.
> >>> Also, Boolean::TRUE is not necessarily initialized properly.
> >>>
> >>> Actually, putting the modeling aside, I only need any legal
> >>> oop for this field. It is only tested for null later on.
> >>> So the most simple (and cheap) fix is just reusing
> >>> one of the oops in the array at hand.
> >>>
> >>> So please review this fix.
> >>> http://cr.openjdk.java.net/~goetz/wr19/8232921-fix_hidden_frames/01/
> >>>
> >>> I'll run it through our testing tonight.
> >>>
> >>> Best regards,
> >>>     Goetz.