linux-kernel - Re: PEBS level 2/3 breaks dwarf unwinding! [WAS: Re: Broken dwarf unwinding

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Message-ID: <2102566.fCj8pZGm78@agathebauer>
Date:   Tue, 06 Nov 2018 21:04:08 +0100
From:   Milian Wolff <milian.wolff@...b.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        Jiri Olsa <jolsa@...nel.org>, namhyung@...nel.org,
        linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho <acme@...nel.org>
Subject: Re: PEBS level 2/3 breaks dwarf unwinding! [WAS: Re: Broken dwarf
 unwinding - wrong stack pointer register value?]

On Dienstag, 6. November 2018 09:39:57 CET Jiri Olsa wrote:
> On Mon, Nov 05, 2018 at 04:10:37PM -0800, Andi Kleen wrote:
> > > > > - PMU triggers interrupt and PEBS stores RIP etc.
> > > > > - code continous to execute, possibly changing the stack
> > > > 
> > > > I dont think the code continues to execute.. the stack is ok
> > > 
> > > Are you sure about this? I mean, isn't that the whole reason why we need
> > > PEBS? Generally, if you are sure about this, can you point me to some
> > > documentation on this to allow me to understand it better?
> > 
> > Milian is right.
> > 
> > There is a execution window from PEBS capturing registers to actually
> > triggering the PMU, and if there is stack manipulation in that window
> > the PEBS state might be out of sync with the real stack.
> 
> hum, is this about having 'large pebs' or there's this window
> if there's also only single pebs record allowed? which should
> be case for dwarf unwind
> 
> > The right RIP/RSP to use for the stack unwinding is always the data
> > in the PMI's exception frame on the stack.
> > 
> > Probably would need to modify perf to report those too in addition
> > to the PEBS registers.
> 
> ok, should not be that hard

Where would I look for the source to change here? So far, I only concentrated 
on the userspace side of perf in tools/perf.

Thanks

-- 
Milian Wolff | milian.wolff@...b.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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