linux-kernel - Re: perf report: fix off-by-one for non-activation frames

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Message-ID: <8eb7e7d2-6fd6-4f3f-a3ca-265639adc61c@linux.ibm.com>
Date: Thu, 14 Nov 2024 16:27:13 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: Milian Wolff <milian.wolff@...b.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jan Kratochvil <jan.kratochvil@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        "linux-kernel@...r.kernel.org" <Linux-kernel@...r.kernel.org>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        David Ahern <dsahern@...il.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Yao Jin <yao.jin@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>,
        Thomas Richter <tmricht@...ux.ibm.com>
Subject: Re: perf report: fix off-by-one for non-activation frames

On 04.07.2017 09:59, Milian Wolff wrote:
> On Monday, June 19, 2017 8:59:39 PM CEST Arnaldo Carvalho de Melo wrote:
>> Em Sat, Jun 17, 2017 at 01:13:11PM +0200, Milian Wolff escreveu:
>>> On Samstag, 17. Juni 2017 10:04:02 CEST Jan Kratochvil wrote:
>>>> On Sat, 17 Jun 2017 09:56:57 +0200, Namhyung Kim wrote:
>>>>> Not sure whether it needs be fixed or not.  If we fix it, srcline and
>>>>> address would not match so it can give its own confusion to users.
>>>>> Ideally it should display an addressof the instruction before the
>>>>> address IMHO.
>>>>
>>>> One can figure million ways how it can behave and each one has its pros
>>>> and
>>>> cons.  I was just describing the current behavior of GDB and LLDB which
>>>> people are used to already.
>>>
>>> Personally, I agree with Jan that we should mimick existing tool's
>>> behavior. I just fear that it's not trivial to do it with the current
>>> code base...
>> But we agree it is a worthwhile change (have backtraces in perf match
>> what gdb, etc show), right?
>>
>> If you can, please try to do this, your attempt will help us understand
>> more the extent of the changes needed and perhaps someonw can come up
>> with simplifications...
> 
> Sorry for the (long) delay, but I'm sadly busy on other things right now. I
> have this on my radar and will try to find time to look into it. But it
> probably won't happen before end of July. If this is urgent, maybe someone
> else needs to look into it before me.

I ran into the odd "decremented by one" IPs (and function offsets) on
s390, which requires instructions to be aligned on 2 byte boundary, and
ended up debugging the code to learn that this is actually on purpose
and why.

If it cannot easily be "fixed" in the output, could it at least be
documented?

Thanks and regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303) and z/VSE Support
+49-7031-16-1128 Office
jremus@...ibm.com

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