Re: RFC: Two small remote protocol extensions

[Quality Quorum <qqi at theworld dot com>]

On Thu, 22 Aug 2002, Andrew Cagney wrote:

> Lets get rid of the easy one (...) `Hg':
>
> ``
>
> @item @code{Hg}@var{id} --- set general thread
> @cindex @code{Hc} packet
>
> Select the general thread.  Register and memory read and write
> operations apply to the most recently selected general thread.


????? Memory is shared between threads, isn't it so ????

IMHO, a multi-process debugging is a very different animal from a
multi-thread debugging and lumping them together only creates more
problems.

Thanks,

Aleksey



> @var{id}, a hex encoded cardinal, is the identifier of the selected thread.
>
> After a target stop, the general thread is reset to the thread
> identifier of the stopped thread.
>
> @emph{Implementation note:  The @code{Hg} packet can not be used to
> determine the most recently selected thread (using the @samp{thread
> @var{thread-id} command).  This is because @value{GDBN} can cache
> per-thread data and avoid the need to re-query the target on each
> @samp{thread} command.}
>
> @c Note the word ``can'' is used, not ``does'' :-)
>
> Reply:
> @table @samp
> @item OK
> for success
> @item E00
> unspecified error
> @c ESRCH --- no such proces/thread?
> @item @samp{}
> unsupported
> @end table
>
> ''
>
> Andrew
>
>
> > On Fri, Aug 16, 2002 at 10:42:42AM -0400, Andrew Cagney wrote:
> >
> >> >On Wed, May 01, 2002 at 10:25:43PM -0400, Daniel Jacobowitz wrote:
> >> >
> >
> >> >>In making remote thread debugging work on GNU/Linux, I needed two
> >> >>additions
> >> >>to the remote protocol.  Neither is strictly necessary, but both are
> >> >>useful,
> >> >>IMHO.
> >> >>
> >> >>They are:
> >> >>
> >> >>  - two new replies to the continue/step packets, 'n' and 'x'.  They
> >> >>indicate thread creation and death respectively, and are asynchronous;
> >> >>the target is not stopped when they are sent.
> >
> >> >
> >> >
> >> >This one got shouted down, I'm not going to bring it up again.
> >> >
> >> >
> >
> >> >>  - A new 'Hs' packet, paralleling Hc and Hg.  This sets the "step"
> >> >>  thread.
> >
> >>
> >> How is ``Hs'' different to:
> >>
> >> 	Hc<PID>
> >> 	s
> >
> >
> > Hc<PID> has a definite meaning right now.  It means, step ONLY this
> > thread.  That corresponds to set scheduler-locking (on|step).  Hc0 will
> > be sent if we are not using scheduler locking.
> >
> > I see nothing wrong with the current meaning of Hc.
> >
> > Also, Hs was never meant to INCLUDE the step command.  It sets a thread
> > context, that's all.
> >
> >
> >> >This one, however, needs feedback.  A user just reported a bogus
> >> >SIGTRAP bug to me which is fixed by the above.
> >> >
> >> >To elaborate on the problem: right now we have two ways of specifying a
> >> >thread to the remote agent.  Hg specifies the "general" thread, and Hc
> >> >specifies the "continue" thread.  These correspond to inferior_ptid and
> >> >resume_ptid, roughly.
> >> >
> >> >When we single-step, if we are not using some form of
> >> >scheduler-locking, resume_ptid is 0.  We don't tell the agent at that
> >> >point what inferior_ptid is; it has to step _some_ thread, and it picks
> >> >one, and if it doesn't pick the one GDB expected we get problems.
> >
> >>
> >> Shouldn't it pick the current-thread.
> >
> >
> > As above.
> >
> >
> >> >We need to either:
> >> >  - Communicate inferior_ptid via Hg at this time
> >> >  - Communicate inferior_ptid via a new Hs explicitly
> >> >
> >> >I think the former makes sense.  Here's a patch; what do you think of
> >> >it?  Also included is the patch for gdbserver; I'd send a separate
> >> >patch along afterwards to remove the vestiges of Hs from my testing,
> >> >which escaped in the original threads patch.
> >
> >>
> >> No.  general thread is really ``selected thread'' the thread for which
> >> the [gG][pP] packets apply.  It is not involved in thread scheduling.
> >
> >
> > We need two thread markers to step correctly; I think using this one is
> > more logical.  If you prefer then the code in gdbserver to use Hs is
> > already there.
> >
> >
> >> Separate to this is the user interface issue of, if you select a
> >> different thread, and then do a step, things get real confused (I think
> >> GDB tries to step the current (or stop) thread).
> >
> >
> > No, actually, gdbserver is what gets confused.  You've said this
> > several times, and the last time you said it I went to check.  In all
> > my tests, both local (lin-lwp) and remote (with Hs patch), everything
> > stepped the selected thread gracefully.  This already works.  Even
> > scheduler locking works.
> >
> > -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer
>
>