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From: Andi Kleen <ak@linux.intel.com>
To: Milian Wolff <milian.wolff@kdab.com>
Cc: Jiri Olsa <jolsa@redhat.com>,
	linux-kernel@vger.kernel.org, Jiri Olsa <jolsa@kernel.org>,
	namhyung@kernel.org, linux-perf-users@vger.kernel.org,
	Arnaldo Carvalho <acme@kernel.org>
Subject: Re: PEBS level 2/3 breaks dwarf unwinding! [WAS: Re: Broken dwarf unwinding - wrong stack pointer register value?]
Date: Thu, 8 Nov 2018 16:54:23 -0800	[thread overview]
Message-ID: <20181109005423.GZ6218@tassilo.jf.intel.com> (raw)
In-Reply-To: <1584560.aXQ729uQp3@agathebauer>

> - Independently, when I add a custom printk manually in `arch/x86/events/
> intel/ds.c` at the end of `setup_pebs_sample_data`, then I'm never seeing any 
> differences between SP in iregs/pebs/regs. Shouldn't it also be recorded via 
> PEBS? Or is it just chance that I'm never seeing any difference in 
> setup_pebs_sample_data between iregs->sp and regs->sp?

It will depend on the workload.

> 
> - Generally, how do we want to handle this bug? If `--intr-regs` would 
> actually record a different IP than stored in uregs in the perf.data file, 
> then we could use that as a fallback for unwinding, when it fails the first 
> time. Or should we always unwind from that IP? How do we mark the "actual" 
> frame/IP then, if that differs?

I don't think the regs include IP currently? Would need to add it.
Then could report everything from the original stack in intr-regs,
and this would address that problem.

Yes it might be useful to add some indication to the sample that
there is a potential divergence between the backtrace and the IP.
Would also need to report that in perf report then.

-Andi

  parent reply	other threads:[~2018-11-09  0:54 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 [this message]
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
2018-11-15 19:00                                           ` Andi Kleen
2018-11-15  2:15                                     ` Travis Downs

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