From: "Ulrich Weigand" <uweigand@de.ibm.com>
To: alves.ped@gmail.com (Pedro Alves)
Cc: gdb-patches@sourceware.org, jan.kratochvil@redhat.com,
sergiodj@redhat.com
Subject: Re: [rfc] Options for "info mappings" etc. (Re: [PATCH] Implement new `info core mappings' command)
Date: Thu, 05 Jan 2012 18:03:00 -0000 [thread overview]
Message-ID: <201201051802.q05I2ZCf016120@d06av02.portsmouth.uk.ibm.com> (raw)
In-Reply-To: <4F05C983.8080905@gmail.com> from "Pedro Alves" at Jan 05, 2012 04:02:11 PM
Pedro Alves wrote:
> On 12/20/2011 10:15 PM, Ulrich Weigand wrote:
> > I actually completed an implementation of this (second) method, before
> > I noticed that it fundamentally does not work with the current remote
> > protocol, for one simple reason: I cannot open /proc/PID/... because
> > I do not even know the PID to use. With the remote target, the "PID"
> > used within GDB may have no relationship whatsoever to the actual PID
> > on a Linux remote target; in fact, it usually is the "magic" 42000 ...
>
> In extended-remote (w/ multiprocess extensions on), we do know the PID,
> because the TID's are in the form pPID.TID. With regular remote, we only
> know the PID on "attach", because the user typed it, otherwise we fall back to
> the magic 42000. But why not simply fix this? We can query the remote
> end for the current process's ID, with target remote, and use that pid if
> supported, otherwise fall back to the current magic 42000 use. All the
> options so far require new packets, so this doesn't seem to make it worse.
> The tdep code in question is handling linux specific bits, so it can
> bail out on the magic 42000 safely.
I'm wondering: How can I distinguish the "magic 42000" from
a regular PID 42000 ?
> Another option, perhaps the cleanest,
> is to start allowing the multiprocess thread id extensions with
> plain "target remote". GDB currently only sends "multiprocess+" qSupported
> feature if connecting in extended-remote mode. I can help and try this is
> you'd like.
Yes, this does sound like an interesting approach.
> > While in some cases, the (a) remote PID may be encoded into the GDB
> > TID field,I cannot use this in -tdep code either, because when used
> > with the native target, the TID is never a PID/LWP.
>
> Not sure what example you're referring to. :-(
Well, GDB's "ptid_t" contains three fields: pid, lwp, and tid. From what
I recall, these are used somewhat differently on different targets.
In particular, with Linux native targets, "pid" is what getpid () returns;
"lwp" is the Linux task ID -- which is equal to the pid for single-threaded
processes, and "tid" is the value of "pthread_t" for the thread.
Now, with the remote target, "pid" seems to be the magic 42000; "lwp" is
never used, and "tid" is used for the thread ID used with the remote
protocol -- and when using gdbserver, the latter is actually the LWP ID
/ Linux task ID.
What I was trying to say with the statement above is: if I knew the LWP
ID, I could use this to access /proc, since there is a /proc/... entry
for all LWP IDs as well as for the main PID. And in fact, at least
for multi-threaded processes, I *do* know the LWP ID, since it is in fact
used as the TID field of the ptid_t with remote/gdbserver targets.
The problem is, with the native target, the TID field is used to hold
the "pthread_t" value, *not* the LWP ID. Since -tdep code needs to
work with either target, I cannot really interpret that field in any
way ...
Bye,
Ulrich
--
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE
Ulrich.Weigand@de.ibm.com
next prev parent reply other threads:[~2012-01-05 18:03 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-26 21:08 [PATCH] Implement new `info core mappings' command Sergio Durigan Junior
2011-10-26 21:25 ` Sergio Durigan Junior
2011-10-27 7:30 ` Eli Zaretskii
2011-10-27 18:09 ` Sergio Durigan Junior
2011-10-29 19:48 ` Eli Zaretskii
2011-10-31 0:34 ` Jan Kratochvil
2011-10-31 7:00 ` Sergio Durigan Junior
2011-10-31 8:13 ` Jan Kratochvil
2011-10-31 12:57 ` Pedro Alves
2011-11-01 11:54 ` [patch] `info proc ' completion [Re: [PATCH] Implement new `info core mappings' command] Jan Kratochvil
2011-11-01 16:23 ` Eli Zaretskii
2011-11-03 14:12 ` [patch] `info proc *' help fix [Re: [patch] `info proc ' completion] Jan Kratochvil
2011-11-03 16:57 ` Eli Zaretskii
2011-11-03 17:07 ` Jan Kratochvil
2011-11-03 18:08 ` Eli Zaretskii
2011-11-03 18:25 ` Jan Kratochvil
2011-11-02 18:30 ` [patch] `info proc ' completion [Re: [PATCH] Implement new `info core mappings' command] Pedro Alves
2011-11-02 18:48 ` [commit] " Jan Kratochvil
2011-11-03 20:01 ` [PATCH] Implement new `info core mappings' command Sergio Durigan Junior
2011-11-04 10:38 ` Eli Zaretskii
2011-11-04 16:27 ` Jan Kratochvil
2011-11-08 1:49 ` Sergio Durigan Junior
2011-11-08 21:47 ` Jan Kratochvil
2011-11-09 20:32 ` Jan Kratochvil
2011-11-16 4:10 ` Sergio Durigan Junior
2011-11-21 16:15 ` Sergio Durigan Junior
2011-11-23 16:32 ` [rfc] Options for "info mappings" etc. (Re: [PATCH] Implement new `info core mappings' command) Ulrich Weigand
2011-11-23 23:37 ` Sergio Durigan Junior
2011-12-01 19:51 ` Ulrich Weigand
2011-12-05 12:59 ` Pedro Alves
2011-12-05 15:02 ` Ulrich Weigand
2011-12-06 16:01 ` Pedro Alves
2011-12-06 17:19 ` Ulrich Weigand
2011-12-07 16:29 ` Pedro Alves
2011-12-07 17:24 ` Pedro Alves
2011-12-07 20:14 ` Ulrich Weigand
2011-12-09 13:28 ` Pedro Alves
2011-12-09 14:10 ` Pedro Alves
2011-12-20 23:08 ` Ulrich Weigand
2011-12-21 22:36 ` Jan Kratochvil
2011-12-22 16:15 ` Ulrich Weigand
2012-01-05 16:02 ` Pedro Alves
2012-01-05 18:03 ` Ulrich Weigand [this message]
2012-01-05 18:20 ` Pedro Alves
2012-01-05 19:54 ` Ulrich Weigand
2012-01-06 6:41 ` Joel Brobecker
2012-01-06 12:29 ` Pedro Alves
2012-01-06 12:27 ` Pedro Alves
2012-01-09 15:44 ` Ulrich Weigand
2012-01-11 16:38 ` Pedro Alves
2012-01-11 18:32 ` Ulrich Weigand
2012-01-05 18:37 ` Mark Kettenis
2012-01-05 19:35 ` Ulrich Weigand
-- strict thread matches above, loose matches on Subject: below --
2012-04-06 3:28 [PATCH 0/4 v2] Implement support for SystemTap probes on userspace Sergio Durigan Junior
2012-04-06 3:32 ` [PATCH 1/4 v2] Refactor internal variable mechanism Sergio Durigan Junior
2012-04-06 3:36 ` [PATCH 2/4 v2] Implement new features needed for handling SystemTap probes Sergio Durigan Junior
2012-04-11 19:06 ` Jan Kratochvil
2012-04-11 22:14 ` Sergio Durigan Junior
2012-04-11 23:33 ` Jan Kratochvil
2012-04-06 3:37 ` [PATCH 4/4 v2] Documentation and testsuite changes Sergio Durigan Junior
2012-04-06 9:27 ` Eli Zaretskii
2012-04-09 21:37 ` Sergio Durigan Junior
2012-04-06 4:11 ` [PATCH 3/4 v2] Use longjmp and exception probes when available Sergio Durigan Junior
2011-04-04 3:09 [PATCH 4/6] Implement support for SystemTap probes Sergio Durigan Junior
2011-04-04 19:06 ` Eli Zaretskii
2011-04-06 20:20 ` Tom Tromey
2011-04-06 20:52 ` Sergio Durigan Junior
2011-04-07 2:41 ` Yao Qi
2011-04-07 3:32 ` Sergio Durigan Junior
2011-04-07 17:04 ` Tom Tromey
2011-04-11 3:21 ` Yao Qi
2011-04-08 12:38 ` Sergio Durigan Junior
2011-04-11 3:52 ` Yao Qi
2011-08-12 15:45 ` Jan Kratochvil
2011-08-12 17:22 ` Frank Ch. Eigler
2011-08-12 21:33 ` Sergio Durigan Junior
2011-04-19 16:42 ` Jan Kratochvil
2012-05-07 19:36 ` Jan Kratochvil
2012-05-07 19:54 ` Sergio Durigan Junior
2012-05-07 19:58 ` Jan Kratochvil
2012-05-07 20:26 ` Sergio Durigan Junior
2012-05-07 20:38 ` Jan Kratochvil
2012-05-08 1:36 ` Sergio Durigan Junior
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