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Re: STOPPED_BY_WATCHPOINT peculiarity
Daniel Jacobowitz wrote:
>
> On Tue, Apr 02, 2002 at 05:01:45PM -0500, Daniel Jacobowitz wrote:
> > On Tue, Apr 02, 2002 at 01:54:47PM -0800, Doug Evans wrote:
> > > Something is not right, or at least confusing, in watchpoint-land.
> > >
> > > This code in infrun.c is odd:
> > >
> > > /* It may be possible to simply continue after a watchpoint. */
> > > if (HAVE_CONTINUABLE_WATCHPOINT)
> > > STOPPED_BY_WATCHPOINT (ecs->ws);
> > >
> > > STOPPED_BY_WATCHPOINT is a predicate.
> > > Therefore at first glance this code is pointless.
> > >
> > > Things are slightly less confusing by recognizing that in the
> > > process of computing STOPPED_BY_WATCHPOINT some debugging printf's
> > > may get printed. e.g. grep for maint_show_dr in
> > > i386-nat.c:i386_stopped_data_address.
> > >
> > > nm-i386.h:
> > > #define STOPPED_BY_WATCHPOINT(W) (i386_stopped_data_address () != 0)
> > >
> > > Is that all there is to it?
> > >
> > > If so, a comment should be added, maybe something like
> > >
> > > - /* It may be possible to simply continue after a watchpoint. */
> > > + /* It may be possible to simply continue after a watchpoint.
> > > + While at first glance this code is pointless, STOPPED_BY_WATCHPOINT
> > > + is called in case there are any maintenance debugging printf's. */
> > > if (HAVE_CONTINUABLE_WATCHPOINT)
> > > STOPPED_BY_WATCHPOINT (ecs->ws);
> >
> > What astonishing timing... I believe there is more going on here, and I
> > was in the middle of looking at this code just a moment ago. See the
> > test failure on i386-linux in gdb.c++/annota2.exp (watch a.x). We have
> > a problem actually correctly detecting that we are stopped by a
> > watchpoint.
>
> Actually, I take that back. STOPPED_BY_WATCHPOINT has nothing to do
> with the problem I'm working on. This line came in far enough back
> that the public tree's CVS history appears to be useless; it's been
> through some reformats but that's it. Might want to ask a Cygnus
> person to dig around.
Yo! ;-)
1) History: the line was added in 1995 by Jim Kingdon.
I can't find any explanation in the changelogs or comments.
2) Yes, it is possible for a predicate to have side effects,
and indeed several implementations of this one (eg. sparc)
cause a register to be read, and one (ia64) causes a register
to be modified. Based on that, I don't think it is safe to
remove the line, without much more deliberation.