linux-kernel - Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling taken at 'callq' instruction

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Message-ID: <20151119112850.GM3816@twins.programming.kicks-ass.net>
Date:	Thu, 19 Nov 2015 12:28:50 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	David Ahern <dsahern@...il.com>,
	Milian Wolff <milian.wolff@...b.com>,
	linux-kernel@...r.kernel.org, pi3orama <pi3orama@....com>,
	lizefan 00213767 <lizefan@...wei.com>
Subject: Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling
 taken at 'callq' instruction

On Thu, Nov 19, 2015 at 06:43:14PM +0800, Wangnan (F) wrote:
> Also, why not fixing rsp in kernel if that instruction is a 'callq'?
> For avoiding instruction decoding?

Why would the kernel do that? It doesn't need this.

Have userspace do it when trying to interpret the data.

If PERF_EFLAGS_EXACT is set, you know the IP points to the actual
instruction and you can attempt to undo whatever parts of it you need at
post processing time.


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