Re: FYI: Linker & Verifier fixes (really GC mark procedures)

[David Daney <ddaney at avtrex dot com>]

Tom Tromey wrote:
> > > > > > "Hans" == Hans Boehm <Hans.Boehm@hp.com> writes:
>
>
> > > I looked at this today.  We can't scan Class using a bitmap descriptor
> > > yet, because its layout is wrong for this.  The descriptor overflows
> > > and we have to fall back to procedural scanning.
>
>
> Hans> Just to be clear, since I'm not quite sure I understand what
> Hans> you're saying here: I don't think it's the mark procedure per se
> Hans> that's the problem.  The issue is having a mark procedure that
> Hans> walks complicated data structures and traces those instead of
> Hans> just pushing directly referenced objects.
>
> I was interested in removing the mark procedure for Class objects, but
> that isn't possible on 32 bit systems -- our choices are continue to
> mark them procedurally, or mark them conservatively.
>
> But, yeah, part of my patch is to allocate things that are pointed to
> by Class such that they are scanned themselves and don't require
> special treatment in the procedural scanner.  This will remove the
> ugly/fragile/problematic code.

This is slightly off topic, but could you put the bitmap descriptor as 
the last field in the Class object?  Then make a variable length bit 
string with the high (or perhaps low) order bit indicating if there was 
another segment of bit string following?

One word of bit string would mark the first 31 (or 63) fields, then if 
the high bit were set there would be another word for the next 31 (or 
63) fields...


David Daney.