Re: RFA[threads]: Fork event updates, part the thirteenth

[Daniel Jacobowitz <drow at mvista dot com>]

On Mon, Jan 06, 2003 at 03:53:52PM -0800, Michael Snyder wrote:
> Daniel Jacobowitz wrote:
> > 
> > Now is where it starts to get interesting.  Michael, I mentioned this patch
> > to you at lunch last week.  If you take a short-lived program, run it, and
> > detach it, and run it again, you'll see the exit of the _previous_ copy.
> > Then GDB gets hopelessly confused.  I have a testcase for this which I'll
> > post in a moment.
> > 
> > The reason it's included here is that that's essentially what happens if you
> > are using "set follow-fork-mode child".  We detach from the parent, which
> > exits, confusing GDB.
> > 
> > Is this OK?
> 
> Hi Dan, 
> 
> Please excuse the delay.  This seems OK.  In child_wait, 
> would it be possible to add a check to see if the exiting
> process is in our lwp list?

I _think_ that child_wait will never be called if there is anything in
the LWP list; if we have LWPs, we'll have pushed thread_db onto the
stack, and we'll go to lin_lwp_wait instead if thre are any LWPs.  But
I'm sleepy, so I may be missing something; I'll sit on this and look at
it again tomorrow :)

Thanks.

> > 2002-12-15  Daniel Jacobowitz  <drow@mvista.com>
> > 
> >         * lin-lwp.c (child_wait): Ignore exit statuses for processes other
> >         than inferior_ptid.
> >         (lin_lwp_wait): Ignore exit statuses for unknown LWPs.
> > 
> > Index: lin-lwp.c
> > ===================================================================
> > RCS file: /cvs/src/src/gdb/lin-lwp.c,v
> > retrieving revision 1.39
> > diff -u -p -r1.39 lin-lwp.c
> > --- lin-lwp.c   9 Dec 2002 18:41:42 -0000       1.39
> > +++ lin-lwp.c   15 Dec 2002 21:16:34 -0000
> > @@ -964,6 +964,14 @@ child_wait (ptid_t ptid, struct target_w
> >         pid = waitpid (GET_PID (ptid), &status, __WCLONE);
> >        save_errno = errno;
> > 
> > +      /* Make sure we don't report an event for the exit of the
> > +        original program, if we've detached from it.  */
> > +      if (pid != -1 && ! WIFSTOPPED (status) && pid != GET_PID (inferior_ptid))
> > +       {
> > +         pid = -1;
> > +         save_errno = EINTR;
> > +       }
> > +
> >        clear_sigio_trap ();
> >        clear_sigint_trap ();
> >      }
> > @@ -1091,6 +1099,17 @@ lin_lwp_wait (ptid_t ptid, struct target
> >           gdb_assert (pid == -1 || lwpid == pid);
> > 
> >           lp = find_lwp_pid (pid_to_ptid (lwpid));
> > +
> > +         /* Make sure we don't report an event for the exit of an LWP not in
> > +            our list, i.e.  not part of the current process.  This can happen
> > +            if we detach from a program we original forked and then it
> > +            exits.  */
> > +         if (! WIFSTOPPED (status) && ! lp)
> > +           {
> > +             status = 0;
> > +             continue;
> > +           }
> > +
> >           if (! lp)
> >             {
> >               lp = add_lwp (BUILD_LWP (lwpid, GET_PID (inferior_ptid)));
> 

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer