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From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
To: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	linux-arch@vger.kernel.org,
	Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@linaro.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	x86@kernel.org, lkml <linux-kernel@vger.kernel.org>,
	"Steven Rostedt (Red Hat)" <rostedt@goodmis.org>,
	virtualization@lists.linux-foundation.org,
	Ingo Molnar <mingo@redhat.com>,
	systemtap@sourceware.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Seiji Aguchi <seiji.aguchi@hds.com>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: Re: [PATCH -tip v3 13/23] x86/trap: Use NOKPROBE_SYMBOL macro in trap.c
Date: Wed, 27 Nov 2013 10:38:12 +0900	[thread overview]
Message-ID: <52954D04.8090101@hitachi.com> (raw)
In-Reply-To: <20131122212119.GE19762@tassilo.jf.intel.com>

(2013/11/23 6:21), Andi Kleen wrote:
> On Wed, Nov 20, 2013 at 04:22:21AM +0000, Masami Hiramatsu wrote:
>> Use NOKPROBE_SYMBOL macro to protect functions from kprobes
>> instead of __kprobes annotation in trap.c.
>> This also applies __always_inline annotation for some cases,
>> because NOKPROBE_SYMBOL() will inhibit inlining by referring
>> the symbol address.
> 
> NOKPROBE_SYMBOL seems to add a reference from some variable to the function?
> 
> With LTO we can optimize away unused functions, but not
> when there are references to the symbol. So this would likely
> prevent optimizations with LTO.

After considering this problem deeper, I decide to say NO against
to your opinion. IMHO, the LTO is just an optimization, on the other
hand, NOKPROBE_SYMBOL is more important because it is for avoiding
kernel crash. I mean, the safety and stability should be prior to
the performance. Anyway, such side-effect of NOKPROBE_SYMBOL looks
very limited. Perhaps, less than 1% of functions will be marked.
How much does it affect for the optimization?

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com



  parent reply	other threads:[~2013-11-27  1:38 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-11-20  4:21 [PATCH -tip v3 00/23] kprobes: introduce NOKPROBE_SYMBOL() and general cleaning of kprobe blacklist Masami Hiramatsu
2013-11-20  4:21 ` [PATCH -tip v3 01/23] kprobes: Prohibit probing on .entry.text code Masami Hiramatsu
2013-11-20  4:21 ` [PATCH -tip v3 02/23] kprobes: Introduce NOKPROBE_SYMBOL() macro for blacklist Masami Hiramatsu
2013-11-27 13:32   ` Ingo Molnar
2013-11-28  7:56     ` Masami Hiramatsu
2013-11-20  4:21 ` [PATCH -tip v3 03/23] kprobes: Show blacklist entries via debugfs Masami Hiramatsu
2013-11-20  4:21 ` [PATCH -tip v3 04/23] kprobes: Support blacklist functions in module Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 05/23] kprobes: Use NOKPROBE_SYMBOL() in sample modules Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 06/23] kprobes/x86: Allow probe on some kprobe preparation functions Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 07/23] kprobes/x86: Use NOKPROBE_SYMBOL instead of __kprobes Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 08/23] kprobes: Allow probe on some kprobe functions Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 09/23] kprobes: Use NOKPROBE_SYMBOL macro instead of __kprobes Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 10/23] ftrace/kprobes: Allow probing on some preparation functions Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 11/23] ftrace/kprobes: Use NOKPROBE_SYMBOL macro in ftrace Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 12/23] x86/hw_breakpoint: Use NOKPROBE_SYMBOL macro in hw_breakpoint Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 13/23] x86/trap: Use NOKPROBE_SYMBOL macro in trap.c Masami Hiramatsu
2013-11-22 21:21   ` Andi Kleen
2013-11-23 12:11     ` Masami Hiramatsu
2013-11-27  1:38     ` Masami Hiramatsu [this message]
2013-11-20  4:22 ` [PATCH -tip v3 14/23] x86/fault: Use NOKPROBE_SYMBOL macro in fault.c Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 15/23] x86/alternative: Use NOKPROBE_SYMBOL macro in alternative.c Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 16/23] x86/nmi: Use NOKPROBE_SYMBOL macro for nmi handlers Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 17/23] x86/kvm: Use NOKPROBE_SYMBOL macro in kvm.c Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 18/23] x86/dumpstack: Use NOKPROBE_SYMBOL macro in dumpstack.c Masami Hiramatsu
2013-11-21 11:30   ` Ingo Molnar
2013-11-22  2:08     ` Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 19/23] [BUGFIX] kprobes/x86: Prohibit probing on debug_stack_* Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 20/23] [BUGFIX] kprobes: Prohibit probing on func_ptr_is_kernel_text Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 21/23] notifier: Use NOKPROBE_SYMBOL macro in notifier Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 22/23] sched: Use NOKPROBE_SYMBOL macro in sched Masami Hiramatsu
2013-11-20  4:22 ` [PATCH -tip v3 23/23] kprobes/x86: Use kprobe_blacklist for .kprobes.text and .entry.text Masami Hiramatsu
2013-11-20 14:26 ` [PATCH -tip v3 00/23] kprobes: introduce NOKPROBE_SYMBOL() and general cleaning of kprobe blacklist Frank Ch. Eigler
2013-11-20 15:38   ` Ingo Molnar
2013-11-20 17:36     ` Frank Ch. Eigler
2013-11-20 17:56       ` Steven Rostedt
2013-11-20 18:09         ` Josh Stone
2013-11-21  2:14       ` Masami Hiramatsu
2013-11-21  7:29         ` Ingo Molnar
2013-11-22  2:35           ` Masami Hiramatsu
2013-11-22 11:46             ` Masami Hiramatsu
2013-11-27 13:30               ` Ingo Molnar
2013-11-28 10:43                 ` Masami Hiramatsu
2013-11-30 13:46                   ` Ingo Molnar
2013-12-01  2:16                     ` Masami Hiramatsu

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