linux-kernel - Re: 答复：[PATCH] perf core: Use KSTK_ESP() instead of pt

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Date:	Mon, 05 Jan 2015 08:47:17 +0000
From:	"Jan Beulich" <jbeulich@...e.com>
To:	<luto@...capital.net>
Cc:	<chenggang.qcg@...baba-inc.com>, <chenggang.qin@...il.com>,
	<dsahern@...il.com>, <namhyung@...il.com>, <efault@....de>,
	<eranian@...gle.com>, <peterz@...radead.org>,
	<fengguang.wu@...el.com>, <yanmin.zhang@...el.com>,
	<akpm@...ux-foundation.org>, <arjan@...ux.intel.com>,
	<jolsa@...hat.com>, <mingo@...hat.com>, <paulus@...ba.org>,
	<chenggang.qcg@...bao.com>, <linux-kernel@...r.kernel.org>
Subject: Re: 答复：[PATCH] perf core: Use KSTK_ESP() instead of pt_regs->sp while output user regs

>>> Andy Lutomirski <luto@...capital.net> 01/02/15 7:03 PM >>>
>On Jan 2, 2015 8:11 AM, "Jan Beulich" <jbeulich@...e.com> wrote:
>> Trying to guess what you mean by "this": A stack switch gets expressed by
>> CFI annotations just like any other frame pointer adjustments. See for example
>> the CFI_DEF_CFA_REGISTER use in the SAVE_ARGS_IRQ macro.
>>
>> If that wasn't your question, please be more precise.
>
>Sorry, my question was vague.
>
>Is there any way to consume these annotations at runtime in the
>kernel?  The goal would be for perf's NMI handler to consume the CFI
>data to figure out the userspace registers.  I'm guessing that the
>answer might be no, because we seem to be compiling with
>-fno-asynchronous-unwind-tables and we don't seem to be putting any
>.eh_frame stuff into the final kernel image.
>
>I had thought that someone implemented runtime DWARF unwinding, though.

Yes, we do have such code in our kernels, but Linus continues to veto it going
into his tree.

Jan

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