From: Milian Wolff <milian.wolff@kdab.com>
To: Milian Wolff <milian.wolff@kdab.com>
Cc: Andi Kleen <ak@linux.intel.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: PEBS level 2/3 breaks dwarf unwinding! [WAS: Re: Broken dwarf unwinding - wrong stack pointer register value?]
Date: Thu, 01 Nov 2018 23:08:18 +0100 [thread overview]
Message-ID: <13521319.OzbRBoFVZM@agathebauer> (raw)
In-Reply-To: <2122395.LD3O1NFKj8@agathebauer>
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On Dienstag, 30. Oktober 2018 23:34:35 CET Milian Wolff wrote:
> On Mittwoch, 24. Oktober 2018 16:48:18 CET Andi Kleen wrote:
> > > Can someone at least confirm whether unwinding from a function prologue
> > > via
> > > .eh_frame (but without .debug_frame) should actually be possible?
> >
> > Yes it should be possible. Asynchronous unwind tables should work
> > from any instruction.
<snip>
> We can find `7f91345bdaf8+1 = 7f91345bdaf9" at offset 16 (search for "f9 da
> 5b 34 91 7f"). Using that address makes unwinding work for this sample.
> What could be the reason for this shift?
I believe I have found the culprit: PEBS seems to be at fault here - i.e. the
RIP/RSP and the ustack dump of the sample simply don't fit together.
Check this out:
```
$ for i in $(seq 10); do perf record -q -e "cycles:" --call-graph dwarf ./cpp-
inlining > /dev/null; perf script | pcre2grep -c -M "hypot_finite.*\n.*\
[unknown\]"; done
0
0
0
0
0
0
0
0
0
0
$ for i in $(seq 10); do perf record -q -e "cycles:p" --call-graph dwarf ./
cpp-inlining > /dev/null; perf script | pcre2grep -c -M "hypot_finite.*\n.*\
[unknown\]"; done
0
0
0
0
0
0
0
0
0
0
$ for i in $(seq 10); do perf record -q -e "cycles:pp" --call-graph dwarf ./
cpp-inlining > /dev/null; perf script | pcre2grep -c -M "hypot_finite.*\n.*\
[unknown\]"; done
37
39
35
28
40
39
29
37
31
26
$ for i in $(seq 10); do perf record -q -e "cycles:ppp" --call-graph dwarf ./
cpp-inlining > /dev/null; perf script | pcre2grep -c -M "hypot_finite.*\n.*\
[unknown\]"; done
79
70
76
77
70
90
64
78
86
74
```
Note how precise levels 0 and 1 do not produce any samples where unwinding
fails. But precise level 2 produces some, and precise level 3 increases the
amount (by ca. ~2x).
I can reproduce this pattern on two separate Intel CPUs and kernel versions
currently:
Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz with 4.18.16-arch1-1-ARCH
Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz with 4.14.78-1-lts
Could someone else try this? What about AMD and IBS - is it also affected?
What about newer/different Intel CPUs?
Better yet, can someone come up with a fix for this on Intel with maximum
precise level?
Thanks
--
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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next prev parent reply other threads:[~2018-11-01 22:08 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 ` Milian Wolff [this message]
2018-11-02 11:26 ` PEBS level 2/3 breaks dwarf unwinding! [WAS: Re: Broken dwarf unwinding - wrong stack pointer register value?] 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
2018-11-15 19:00 ` Andi Kleen
2018-11-15 2:15 ` Travis Downs
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