From: "Metzger, Markus T" <markus.t.metzger@intel.com>
To: Pedro Alves <palves@redhat.com>
Cc: "jan.kratochvil@redhat.com" <jan.kratochvil@redhat.com>,
"gdb-patches@sourceware.org" <gdb-patches@sourceware.org>
Subject: RE: [patch v8 23/24] record-btrace: show trace from enable location
Date: Tue, 17 Dec 2013 13:20:00 -0000 [thread overview]
Message-ID: <A78C989F6D9628469189715575E55B230AA3974D@IRSMSX104.ger.corp.intel.com> (raw)
In-Reply-To: <52AF5763.9050800@redhat.com>
> -----Original Message-----
> From: Pedro Alves [mailto:palves@redhat.com]
> Sent: Monday, December 16, 2013 8:41 PM
> >>> After adding incremental updates, we can now add a dummy record for
> the
> >> current
> >>> PC when we enable tracing so we show the trace from the location
> where
> >> branch
> >>> tracing has been enabled.
> >>
> >> Ah, awesome, I was just wondering about that. :-)
> >>
> >> I suppose one can we still access the registers when
> >> inspecting this dummy location, or are the btrace unwinders
> >> preventing that?
> >
> > You can not access registers when you are in the execution history.
> >
> > When we add this dummy record when we enable tracing, you're still
> > outside the execution history, so you can access registers. Also the last
> > instruction will be skipped for all record operations - it corresponds to
> > the current PC and the instruction has not been executed yet.
> >
> > But it allows us to stitch the first trace chunk to this dummy record and
> > thus show the full trace from the enable location.
> >
> > Internally, you're at the same PC if you are replaying and the replay
> > position is at the last instruction or if you are not replaying.
> > The different is that you will be able to access registers and memory
> > only if you are not replaying.
>
> OK, the question was then, would it be wrong to allow
> accessing registers and memory of the live program, if replaying, and
> at that position? Just OOC and for my education, I'm not saying
> it'd be a requirement.
It would be conceptually wrong.
And it would not be necessary, either, since we will never be in
this position when the user gets the prompt. We will only pass
through it internally. When the user gets the prompt, we are
either replaying and we're somewhere in the execution history.
Or we're not replaying and we're at the current location.
> Sorry if the question sounds dumb. I can't actually try out this
> stuff due to broken btrace on my machine, if you'll recall.
That's sad, indeed. For one, this is a really nice feature. And also
it prevents you from finding (and reporting) bugs that I don't find.
Regards,
Markus.
Intel GmbH
Dornacher Strasse 1
85622 Feldkirchen/Muenchen, Deutschland
Sitz der Gesellschaft: Feldkirchen bei Muenchen
Geschaeftsfuehrer: Christian Lamprechter, Hannes Schwaderer, Douglas Lusk
Registergericht: Muenchen HRB 47456
Ust.-IdNr./VAT Registration No.: DE129385895
Citibank Frankfurt a.M. (BLZ 502 109 00) 600119052
next prev parent reply other threads:[~2013-12-17 13:20 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-12 9:15 [patch v8 00/24] record-btrace: reverse Markus Metzger
2013-12-12 9:15 ` [patch v8 14/24] record-btrace: supply register target methods Markus Metzger
2013-12-12 9:15 ` [patch v8 03/24] gdbarch: add instruction predicate methods Markus Metzger
2013-12-12 9:15 ` [patch v8 01/24] btrace, linux: fix memory leak when reading branch trace Markus Metzger
2013-12-12 9:15 ` [patch v8 16/24] record-btrace, frame: supply target-specific unwinder Markus Metzger
2013-12-12 9:16 ` [patch v8 13/24] target: add ops parameter to to_prepare_to_store method Markus Metzger
2013-12-12 9:16 ` [patch v8 15/24] frame, backtrace: allow targets to supply a frame unwinder Markus Metzger
2013-12-13 18:27 ` Pedro Alves
2013-12-16 9:18 ` Metzger, Markus T
2013-12-16 19:02 ` Pedro Alves
2013-12-17 8:26 ` Metzger, Markus T
2013-12-17 9:48 ` Pedro Alves
2013-12-12 9:16 ` [patch v8 24/24] record-btrace: add (reverse-)stepping support Markus Metzger
2013-12-12 16:36 ` Eli Zaretskii
2013-12-13 19:22 ` Pedro Alves
2013-12-16 15:56 ` Metzger, Markus T
2013-12-16 20:30 ` Pedro Alves
2013-12-17 14:14 ` Metzger, Markus T
2013-12-17 15:07 ` Metzger, Markus T
2013-12-17 15:48 ` Metzger, Markus T
2013-12-17 20:41 ` Pedro Alves
2013-12-17 20:34 ` Pedro Alves
2013-12-17 20:07 ` Pedro Alves
2013-12-18 9:44 ` Metzger, Markus T
2013-12-12 9:16 ` [patch v8 21/24] record-btrace: extend unwinder Markus Metzger
2013-12-13 19:45 ` Pedro Alves
2013-12-16 12:42 ` Metzger, Markus T
2013-12-16 19:22 ` Pedro Alves
2013-12-17 12:56 ` Metzger, Markus T
2013-12-12 9:16 ` [patch v8 20/24] record-btrace: add record goto target methods Markus Metzger
2013-12-12 9:16 ` [patch v8 12/24] btrace: add replay position to btrace thread info Markus Metzger
2013-12-12 9:16 ` [patch v8 06/24] btrace: change branch trace data structure Markus Metzger
2013-12-12 9:16 ` [patch v8 18/24] record-btrace: add to_wait and to_resume target methods Markus Metzger
2013-12-12 9:16 ` [patch v8 09/24] btrace: increase buffer size Markus Metzger
2013-12-12 9:16 ` [patch v8 02/24] btrace: uppercase btrace_read_type Markus Metzger
2013-12-12 9:16 ` [patch v8 10/24] record-btrace: optionally indent function call history Markus Metzger
2013-12-12 9:16 ` [patch v8 08/24] record-btrace: start counting at one Markus Metzger
2013-12-12 9:16 ` [patch v8 05/24] frame: artificial frame id's Markus Metzger
2013-12-12 19:39 ` Pedro Alves
2013-12-12 19:55 ` Jan Kratochvil
2013-12-13 8:04 ` Metzger, Markus T
2013-12-13 11:27 ` Jan Kratochvil
2013-12-13 11:42 ` Metzger, Markus T
2013-12-13 12:09 ` Pedro Alves
2013-12-13 13:01 ` Metzger, Markus T
2013-12-13 15:44 ` Pedro Alves
2013-12-13 17:51 ` Pedro Alves
2013-12-18 13:30 ` Metzger, Markus T
2013-12-12 9:16 ` [patch v8 04/24] frame: add frame_is_tailcall function Markus Metzger
2013-12-12 9:16 ` [patch v8 11/24] record-btrace: make ranges include begin and end Markus Metzger
2013-12-13 17:56 ` Pedro Alves
2013-12-12 9:16 ` [patch v8 07/24] record-btrace: fix insn range in function call history Markus Metzger
2013-12-12 9:16 ` [patch v8 23/24] record-btrace: show trace from enable location Markus Metzger
2013-12-13 19:50 ` Pedro Alves
2013-12-16 12:57 ` Metzger, Markus T
2013-12-16 19:41 ` Pedro Alves
2013-12-17 13:20 ` Metzger, Markus T [this message]
2013-12-17 16:59 ` Pedro Alves
2013-12-12 9:16 ` [patch v8 22/24] btrace, gdbserver: read branch trace incrementally Markus Metzger
2013-12-13 19:46 ` Pedro Alves
2013-12-16 12:47 ` Metzger, Markus T
2013-12-16 19:23 ` Pedro Alves
2013-12-12 9:16 ` [patch v8 19/24] record-btrace: provide target_find_new_threads method Markus Metzger
2013-12-12 9:16 ` [patch v8 17/24] record-btrace: provide xfer_partial target method Markus Metzger
2013-12-13 18:43 ` Pedro Alves
2013-12-16 10:53 ` Metzger, Markus T
2013-12-16 19:16 ` Pedro Alves
2013-12-17 11:58 ` Metzger, Markus T
2013-12-17 16:56 ` Pedro Alves
2013-12-18 9:26 ` Metzger, Markus T
2013-12-18 10:39 ` Pedro Alves
2013-12-12 14:07 ` [patch v8 00/24] record-btrace: reverse Jan Kratochvil
2013-12-12 14:19 ` Metzger, Markus T
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