Re: [PATCH] preventing resuming of threads in gdbserver

[Amit Kale <amitkale at linsyssoft dot com>]

On Wednesday 11 Jan 2006 2:49 am, Michael Snyder wrote:
> Amit Kale wrote:
> > Hi,
> >
> > gdb lets other threads continue execution during single stepping when
> > doing a single step in remote mode. This behavior causes thread switches
> > during step or next commands. Native mode behavior is opposite of it.
> > Attached patch changes it and makes it similar to native mode.
>
> Actually, letting other threads continue during single stepping
> is the norm.  It happens on almost all multi-thread gdb targets.
> Indeed, if you don't allow it to happen, you're risking deadlock,
> and certainly changing the program behavior.

Thanks.
I wasn't aware that this was by design. Native gdb doesn't seem to switch 
threads during a "next", which made me think that it's the other way around.

Digging further, following code in resume() does handle scheduler_mode 
correctly.

      if ((scheduler_mode == schedlock_on)
	  || (scheduler_mode == schedlock_step
	      && (step || singlestep_breakpoints_inserted_p)))
	{
	  /* User-settable 'scheduler' mode requires solo thread resume. */
	  resume_ptid = inferior_ptid;
	}

-Amit

>
> Moreover, a patch that changes the behavior of *all* remote targets
> is going to be challenging to get approved.
>
>
>
> On the other hand, there is a user-setable mode variable
> called "scheduler-locking", which is meant to have the exact
> effect you are looking for.  If you wanted to re-do your patch
> so that it made this change conditionally, under the control of
> that variable, it might be more acceptable.
>
> > ------------------------------------------------------------------------
> >
> > Index: gdb-cvs/gdb/remote.c
> > ===================================================================
> > --- gdb-cvs.orig/gdb/remote.c	2006-01-03 11:24:35.000000000 +0530
> > +++ gdb-cvs/gdb/remote.c	2006-01-10 18:00:05.000000000 +0530
> > @@ -2519,10 +2519,10 @@
> >      {
> >        /* Resume all threads, with preference for INFERIOR_PTID.  */
> >        if (step && siggnal != TARGET_SIGNAL_0)
> > -	outbuf = xstrprintf ("vCont;S%02x:%x;c", siggnal,
> > +	outbuf = xstrprintf ("vCont;S%02x:%x", siggnal,
> >  			     PIDGET (inferior_ptid));
> >        else if (step)
> > -	outbuf = xstrprintf ("vCont;s:%x;c", PIDGET (inferior_ptid));
> > +	outbuf = xstrprintf ("vCont;s:%x", PIDGET (inferior_ptid));
> >        else if (siggnal != TARGET_SIGNAL_0)
> >  	outbuf = xstrprintf ("vCont;C%02x:%x;c", siggnal,
> >  			     PIDGET (inferior_ptid));