This is the mail archive of the
mailing list for the GDB project.
Re: Checking if addess is on stack?
> Date: Thu, 20 Apr 2006 14:41:53 -0400
> From: Daniel Jacobowitz <firstname.lastname@example.org>
> > > print &ptr->i
> > > watch *$31
> > > (Where $31 is the right number.
> > But "watch ptr->i" already does that for you. Except that it _also_
> > watches &ptr, and that latter address is what goes out of scope when
> > we leave func2.
> These two are not at all the same. Suppose ptr is being walked along a
> linked list. The user might be interested in the expression "ptr->i",
> but in my experience that's almost never what I want if ptr is moving;
> instead, I am interested in (for example) something scribbling over
> this particular element of the linked list. I don't care when ptr goes
> out of scope, or when ptr is changed. I'm interested in the memory.
That's one possible situation, sure. But there are others: someone
could be scribbling over ptr->i by inadvertently changing ptr itself.
If you think this latter situation is unlikely or uninteresting, you
in effect say that our whole concept of watching expression values is
> > So perhaps we need to modify the watchpoint machinery so that when
> > func2 returns, we stop watching the parts of the expression that are
> > popped from the stack, but continue watching those which are still
> > valid and in scope. Would that make sense?
> I don't understand. How could we continue watching anything, if we can
> no longer evaluate the expression? None of the expression is still in
But this particular expression's result is just an address, and that
address can be watched without recomputing the expression.
> > I think it can be achieved with setting 2 watchpoints: one on
> > "ptr->i", the other on the address it points to.
> That will catch when ptr goes out of scope, but we don't care about
> that. In my example, ptr goes out of scope in one function, but the
> thing it points to doesn't go "out of scope" until much later.
In your example, you (the user) knew what you were after. I was
arguing that doing this always in a front end, like what Vladimir was
suggesting, might not be what users expect in each particular case.