On Tuesday 18 November 2008, Tom Hughes wrote:
> Nicholas Nethercote wrote:
> > On Mon, 17 Nov 2008, Michael Rosellini wrote:
> >> Both of the previous two problems I wrote about (valgrind crash while
> >> delivering a fatal signal and reports that things that were on the heap
> >> were on the stack) are eliminated when my program no longer switches
> >> stacks during startup.  I've confirmed that I'm calling
> >> VALGRIND_STACK_REGISTER correctly.  Has anyone else experienced a
> >> similar problem?
> >
> > I think the stack registration stuff is a bit buggy, but I don't recall
> > the details right now.  I think people must not use it very much.
>
> It's rubbish, and needs a complete ground up rework rather than band aid
> patches. IIRC there are at least two different ideas internally of what
> the current stack is and only one of those pays attention to the user
> stack registration stuff.

I agree.  I never really understood it, and from what I remember from 
looking at it in the distant past, it's conceptually like swiss cheese
-- full of holes.

The relationship to stack unwinding should also be considered. 
At the moment the unwinder can segfault if a corrupted stack takes
it into a non-mapped area.  This ought to be fixed, although perhaps
that's more a question of integration with the address space manager:
what the unwinder really needs is a very fast way to ask whether a 
page is mapped or not; and simply stop if the page isn't mapped.

J

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