Re: [RFC]: x86 threaded watchpoint support [2/3]

Daniel Jacobowitz
2004-06-15T12:22:20Z

On Tue, Jun 15, 2004 at 07:19:17AM +0200, Eli Zaretskii wrote:
> > Date: Mon, 14 Jun 2004 17:40:20 -0400
> > From: Jeff Johnston <jjohnstn@redhat.com>
> >
> > The change is needed because with the threading model, you can have multiple
> > events to process. So, if you check your watchpoint values, all of them may
> > have changed but you end up reporting an invalid thread location. For example,
> > I was getting watchpoints changing at the same time of a new thread event (it
> > couldn't discern). The reported location was __nptl_create_event (not very
> > useful).
>
> Does this mean that when a watchpoint breaks, it stops only the thread
> that hit the watchpoint, while other threads continue to run?
>
> If all threads stop, then there could not be multiple events, unless
> we are talking about a machine with more than one CPU.
>
> Or am I missing something?

It's the same problem we already have, just more likely to trigger.
The kernel does not stop threads for us; we do it ourselves after we
see the first thread trap. Even if the kernel did it, there would be a
substantial window for other threads to run.

So any time that we see an event from one thread, there can be an
arbitrary set of events from other threads. In a heavily threaded
application, having extra events at the thread creation breakpoint is
typical.

--
Daniel Jacobowitz