Re: [Valgrind-users] New skin available: Annelid, a pointer-misu echecker

[Erik C. <er...@ar...>]

On Wed, Oct 01, 2003 at 06:54:20PM +0100, Nicholas Nethercote wrote:
> On Wed, 1 Oct 2003, Jeremy Fitzhardinge wrote:
> 
> > > * If you generate a new pointer/integer by math between two operands
> > >   with different malloc-area sets then the new integer gets the union
> > >   of the sets.
> >
> > Yep, this is what I suggested.
> 
> But the sets become huge (eg. 1000s of entries), which slows things down
> horrifically.

If a pointer is dereferenced then you can reduce that set to one
single segment, namely the segment it points at when it is
dereferenced.

> Besides, when you do the pointer subtraction, that
> "connection" between them is really a property of the ptrdiff, not a
> property of the segments, so putting the two segments into the same set
> isn't a true reflection of what's happening.
> 
> These two reasons are why I think having a dedicated ptrdiff type is a
> better solution.

For the record, that is what I was suggesting in the "simple"
suggestion snipped above.  It's the new integer (ptrdiff) that
is assigned the union of the sets, not all pointers into the
sets.

> Although I haven't implemented it yet, so I'm yet to see
> how it works in practice.

The idea you explained the other day is a more complex (accurate)
version of the "just taking the union" idea above.  The question
is whether it gives too many false alarms.

-- 
Erik Corry er...@ar...
A: Because it messes up the order in which people normally read text.
Q: Why is top-replying such a bad thing?
A: Top-replying.
Q: What is the most annoying thing in email?