Date: Thu, 19 Nov 2015 07:37:10 +0100
From: Ingo Molnar <mingo@kernel.org>
To: "Wangnan (F)" <wangnan0@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Arnaldo Carvalho de Melo <acme@kernel.org>,
        David Ahern <dsahern@gmail.com>, Peter Zijlstra <peterz@infradead.org>,
        Milian Wolff <milian.wolff@kdab.com>, linux-kernel@vger.kernel.org,
        pi3orama <pi3orama@163.com>, lizefan 00213767 <lizefan@huawei.com>
Subject: Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling
 taken at 'callq' instruction
Message-ID: <20151119063709.GA14852@gmail.com>
References: <564C26C4.2040603@huawei.com>
 <564C3011.8090002@huawei.com>
 <20151118082033.GA24726@gmail.com>
 <564C3A0E.3030502@huawei.com>
 <564C3BAA.4040806@huawei.com>
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* Wangnan (F) <wangnan0@huawei.com> wrote:

> >perf cmdline is
> >
> ># ./pref record  -g -F 9 --call-graph dwarf ./test_dwarf_unwind
> >
> >Use default events, precise_ip == 2 so uses PEBS.
> >
> 
> Testetd 'cycles', 'cycles:p' and 'cycles:pp'. Only 'cycles:pp' captures
> sample at callq. So maybe a PEBS problem?

Well, that's how our PEBS sampling works: we roll back the instruction pointer to 
point at the instruction generating the sample. The state itself is 
post-instruction.

So dwarf unwind has to take this into account. Should the kernel pass in the 
original (uncorrected) RIP as well, perhaps?

Thanks,

	Ingo
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