Re: [rvm-research] Add metadata to each field of an object?

Steve Blackburn wrote:

On 26/06/2009, at 11:33 AM, Eliot Moss wrote:

> An alternative approach -- still not easy though -- would be to use  
> a tool
> like valgrind. You'd have to notify it of object creations, etc., so  
> it
> could keep shadow information. Again, probably a lot of work. Perhaps
> others can comment on the viability of that approach.

I have done this kind of thing before.   It is not particularly  
difficult, though of course it requires you to become familiar with  
valgrind (you could use PIN or any other such tool).

Another alternative is to use a shadow heap within Jikes RVM (rather  
than within another tool such as valgrind).   This avoids the  
unpleasantness of transmitting semantic information from the VM down  
to the VMM (Valgrind).   We already have something a little like this  
in MMTk: the sanity checker (although the metadata there is at the  
object granularity).

Both approaches are what I call "shadow heaps" and they have the  
distinct advantage of not relying on changing the object model etc.    
They are more or less transparent to the system that uses them, which  
can be a huge advantage.

My recommendation would be that you take a peek at the source code for  
MMTk's sanity checker and the build something similar that operates at  
the field granularity.   You'd probably build it in the main rvm code  
base, not MMTk.   The sanity checker is very robust and is a really  
useful tool.  I think you could build a very robust system by  
following the same pattern.

Cheers,

--Steve