From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 18860 invoked by alias); 23 Aug 2002 15:57:38 -0000 Mailing-List: contact gdb-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sources.redhat.com Received: (qmail 18853 invoked from network); 23 Aug 2002 15:57:36 -0000 Received: from unknown (HELO localhost.redhat.com) (216.138.202.10) by sources.redhat.com with SMTP; 23 Aug 2002 15:57:36 -0000 Received: from ges.redhat.com (localhost [127.0.0.1]) by localhost.redhat.com (Postfix) with ESMTP id 949B33ED5; Fri, 23 Aug 2002 11:57:31 -0400 (EDT) Message-ID: <3D665B6B.4010201@ges.redhat.com> Date: Fri, 23 Aug 2002 08:57:00 -0000 From: Andrew Cagney User-Agent: Mozilla/5.0 (X11; U; NetBSD macppc; en-US; rv:1.0.0) Gecko/20020810 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Quality Quorum Cc: Daniel Jacobowitz , gdb@sources.redhat.com Subject: Re: RFC: Two small remote protocol extensions References: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-SW-Source: 2002-08/txt/msg00290.txt.bz2 > 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 ???? The above reflects GDB's current behavour (logical or not). When reading or writing memory, gdb specifies a thread. If it turns out that the thread disappeared, GDB picks a thread, any thread (the assumption being that all address spaces are pretty much similar). Mind you, I've seen thread implementations that implemented per-thread local data using VM. enjoy, Andrew > 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 >> >> s > >> > >> > >> > Hc 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 > >> >>