Re: [RFA 2/3] Demote to sw watchpoint only in update_watchpoint

Ulrich Weigand
2011-05-05T11:10:32Z

Pedro Alves wrote:
> On Wednesday 04 May 2011 23:20:48, Thiago Jung Bauermann wrote:
> > Pedro's suggestion:
> >
> > 1. The inferior is stopped and software bp_locations (both breakpoints
> > and watchpoints) are removed. Hardware ones stay in place.
> > 2. The user asks for a new watchpoint.
> > 3. GDB evaluates the expression and creates the bp_locations.
> > 4. GDB tries to insert the bp_locations as hw watches. If that fails,
> > then converts to sw and registers the watchpoint for insertion.
> > 5. The user asks the inferior to be continued.
> > 6. GDB inserts sw breakpoints and watchpoints and resumes the inferior.
>
> Either that or try keep hardware breakpoints and watchpoints uninserted,
> and insert them just before 4. This variant is a bit safer in case GDB crashes,
> but is a bit less efficient in case there are many watchpoints. But then
> again we already remove/insert them all at each step, so that is kind of moot.
> I've no real preference on which. This is a minor detail in the grand scheme
> from my perspective.

One thing I'm wondering about is the comment before update_watchpoints:

Even with `set breakpoint always-inserted on' the watchpoints are
removed + inserted on each stop here. Normal breakpoints must
never be removed because they might be missed by a running thread
when debugging in non-stop mode. On the other hand, hardware
watchpoints (is_hardware_watchpoint; processed here) are specific
to each LWP since they are stored in each LWP's hardware debug
registers. Therefore, such LWP must be stopped first in order to
be able to modify its hardware watchpoints.
[etc.]

Is this still valid, and would it affect this current discussion if so?

Bye,
Ulrich

--
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE
Ulrich.Weigand@de.ibm.com