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From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "Stephane Eranian" <eranian@google.com>,
	"Ingo Molnar" <mingo@redhat.com>, "Jiri Olsa" <jolsa@redhat.com>,
	root <chenggang.qin@gmail.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"秦承刚(承刚)" <chenggang.qcg@taobao.com>,
	"Wu Fengguang" <fengguang.wu@intel.com>,
	"Mike Galbraith" <efault@gmx.de>,
	"Namhyung Kim" <namhyung@gmail.com>,
	"Arjan van de Ven" <arjan@linux.intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	"David Ahern" <dsahern@gmail.com>,
	"Paul Mackerras" <paulus@samba.org>,
	"秦承刚(承刚)" <chenggang.qcg@alibaba-inc.com>,
	"Yanmin Zhang" <yanmin.zhang@intel.com>
Subject: Re: [PATCH 1/2] perf: Move task_pt_regs sampling into arch code
Date: Mon, 5 Jan 2015 17:44:47 +0100	[thread overview]
Message-ID: <20150105164447.GG29390@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CALCETrW6cv_s60uzi_scy5JBdr4+wrz1O5we-3okc-SZKRVofA@mail.gmail.com>

On Mon, Jan 05, 2015 at 08:13:49AM -0800, Andy Lutomirski wrote:
> > Just wondering how bad it would be to fill out the actual pt_regs that
> > was previously partially initialized?
> 
> Bad, for at least two reasons.
> 
> One is that we don't actually know which regs are initialized.  bx,
> bp, r12 etc are particularly bad in this regard, due to the FORK_LIKE
> mechanism and similar optimizations.

Right, but you need to deal with that anyhow.

> The other is that the uninitialized part of task_pt_regs can be used
> for something else entirely.  If we have a syscall instruction
> immediately followed by a regular interrupt, then the interrupt's
> hardware frame will overlap task_pt_regs.  (I'm not going to claim
> that this design is sensible, but it is what it is.  IIRC Denys
> Vlasenko had some patches to partially clean this up.)

Ah, urgh. Yes painful that.

> It would be possible to rework the code to avoid an extra pt_regs
> copy, but I don't see an obvious way to do it cleanly.

Yeah, we'll see how this works, I was just curious on the exact need for
the copy, but if as you say, the original structure might not even exist
properly (even though we have a pointer to it) that's bad (TM).

  reply	other threads:[~2015-01-05 16:45 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-23  6:22 [PATCH] perf core: Use KSTK_ESP() instead of pt_regs->sp while output user regs root
2014-12-23  8:30 ` Andy Lutomirski
     [not found] ` <c027bde0-5f4f-441f-8d45-3e7f6f702231@alibaba-inc.com>
2014-12-25 15:48   ` 答复：[PATCH] " Andy Lutomirski
2014-12-25 16:21     ` Andy Lutomirski
2014-12-30 19:03     ` Peter Zijlstra
2014-12-30 23:29       ` Andy Lutomirski
2014-12-31  2:00         ` Andy Lutomirski
2015-01-02 16:11           ` Jan Beulich
2015-01-02 18:03             ` Andy Lutomirski
2015-01-05  8:47               ` Jan Beulich
2015-01-04 16:10       ` Jiri Olsa
2015-01-04 17:18         ` Andy Lutomirski
2015-01-04 17:41           ` Jiri Olsa
2015-01-04 18:36             ` [PATCH 0/2] perf: Improve user regs sampling Andy Lutomirski
2015-01-04 18:36               ` [PATCH 1/2] perf: Move task_pt_regs sampling into arch code Andy Lutomirski
2015-01-05 14:07                 ` Peter Zijlstra
2015-01-05 16:13                   ` Andy Lutomirski
2015-01-05 16:44                     ` Peter Zijlstra [this message]
2015-01-05 18:28                       ` Andy Lutomirski
2015-01-09 12:32                 ` [tip:perf/urgent] " tip-bot for Andy Lutomirski
2015-01-04 18:36               ` [PATCH 2/2] x86_64, perf: Improve user regs sampling Andy Lutomirski
2015-01-09 12:32                 ` [tip:perf/urgent] perf/x86_64: " tip-bot for Andy Lutomirski
2015-01-05 10:46               ` [PATCH 0/2] perf: " Jiri Olsa

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