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From: Milian Wolff <milian.wolff@kdab.com>
To: Travis Downs <travis.downs@gmail.com>
Cc: ak@linux.intel.com, jolsa@redhat.com,
	linux-kernel@vger.kernel.org, jolsa@kernel.org,
	namhyung@kernel.org, linux-perf-users@vger.kernel.org,
	acme@kernel.org
Subject: Re: PEBS level 2/3 breaks dwarf unwinding! [WAS: Re: Broken dwarf unwinding - wrong stack pointer register value?]
Date: Thu, 15 Nov 2018 10:10:13 +0100	[thread overview]
Message-ID: <6310843.N4ooJGWzKY@agathebauer> (raw)
In-Reply-To: <CAOBGo4wPeobp90eqZF1apZxHUn-dnh6L3Rpt_=beR49o3XHY7g@mail.gmail.com>

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On Donnerstag, 15. November 2018 03:05:32 CET Travis Downs wrote:
> On Wed, Nov 14, 2018 at 8:20 AM Milian Wolff <milian.wolff@kdab.com> wrote:
> > 3) I suggest we always keep the first frame and sample IP from the user
> > regs, i.e. the accurate PEBS/IBS IP. Then we add the following frames
> > from unwinding the ustack with the iregs.
> 
> Does this mean that the displayed unwind will sometimes be
> "impossible" to have actually be generated from a consistent execution
> of the user program?

Yes, that is exactly what I'm saying.

> For example, the top frame (from PEBS) and second frame (from iregs)
> may be inconsistent in that the latter function never calls the first.
> At this point it would be good to have an indication at the top frame
> is from a different source than the rest of the frames, lest the user
> pull is hair out trying to determine how function X seems to call
> function Y despite that not being the case in the source.

I agree. I personally like your suggested approach - only add an indication 
when the IP differs so much that it points to a different function. What do 
others say to this?

Cheers

-- 
Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
KDAB (Deutschland) GmbH, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt, C++ and OpenGL Experts

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  reply	other threads:[~2018-11-15  9:10 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-20 22:39 Broken dwarf unwinding - wrong stack pointer register value? Milian Wolff
2018-10-21 20:32 ` Milian Wolff
2018-10-22 10:35 ` Milian Wolff
2018-10-22 11:17   ` Milian Wolff
2018-10-22 13:58     ` Andi Kleen
2018-10-22 19:26       ` Milian Wolff
2018-10-23  4:03         ` Andi Kleen
2018-10-23 10:34           ` Milian Wolff
2018-10-24 14:48             ` Andi Kleen
2018-10-30 22:34               ` Milian Wolff
2018-11-01 22:08                 ` PEBS level 2/3 breaks dwarf unwinding! [WAS: Re: Broken dwarf unwinding - wrong stack pointer register value?] Milian Wolff
2018-11-02 11:26                   ` Jiri Olsa
2018-11-02 17:56                     ` Milian Wolff
2018-11-05 20:51                       ` Jiri Olsa
2018-11-05 22:54                         ` Milian Wolff
2018-11-06  0:10                           ` Andi Kleen
2018-11-06  8:39                             ` Jiri Olsa
2018-11-06 17:26                               ` Andi Kleen
2018-11-06 20:04                               ` Milian Wolff
2018-11-06 20:24                                 ` Andi Kleen
2018-11-07 22:41                                   ` Milian Wolff
2018-11-08 12:41                                     ` Milian Wolff
2018-11-09  0:55                                       ` Andi Kleen
2018-11-09  0:54                                     ` Andi Kleen
2018-11-10 21:42                             ` Travis Downs
2018-11-11  1:07                               ` Andi Kleen
     [not found]                                 ` <CAOBGo4zirLiKX8VcROAE=kAD0+qkF0E-cBv9DtBiQr=_obDv5w@mail.gmail.com>
2018-11-11  2:54                                   ` Travis Downs
2018-11-12  3:26                                   ` Andi Kleen
2018-11-14 13:20                                     ` Milian Wolff
2018-11-15  2:05                                       ` Travis Downs
2018-11-15  9:10                                         ` Milian Wolff [this message]
2018-11-15 19:00                                           ` Andi Kleen
2018-11-15  2:15                                     ` Travis Downs

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