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From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
	"Frank Ch. Eigler" <fche@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	yrl.pp-manager.tt@hitachi.com
Subject: Re: [PATCH -tip v2 3/9] ftrace/x86: Support SAVE_REGS feature on i386
Date: Wed, 06 Jun 2012 23:24:58 +0900	[thread overview]
Message-ID: <4FCF683A.90202@hitachi.com> (raw)
In-Reply-To: <m2ehptjull.fsf@firstfloor.org>

(2012/06/06 6:51), Andi Kleen wrote:
> Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> writes:
>>  
>> +	.macro FTRACE_SAVE_ALL
>> +	/* eflags is saved on cs */
>> +	subl $8, %esp		/* skip ip and orig_ax */
>> +	pushl %gs
>> +	pushl %fs
> 
> For pure in kernel use you don't need to save/restore fs/gs
> This is only needed on kernel/user space boundaries.
> 
> And for this usage probably also not flags

I see, most of the case, user doesn't really need it.
But in some case, it can be easily imagined that pt_regs
is used for dumping all registers. Suppose that this
ftrace-based kprobe optimization is done transparently,
they may see that the results of dumping registers
are different even if the probe moves just one instruction
ahead. I'd like to avoid this kind of differences.

Thank you,

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

  reply	other threads:[~2012-06-06 14:25 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-06-05 10:27 [PATCH -tip v2 0/9]ftrace,kprobes: Ftrace-based kprobe optimization Masami Hiramatsu
2012-06-05 10:27 ` [PATCH -tip v2 1/9] ftrace: Add pt_regs acceptable trace callback Masami Hiramatsu
2012-06-05 10:27 ` [PATCH -tip v2 2/9] ftrace/x86-64: support SAVE_REGS feature on x86-64 Masami Hiramatsu
2012-06-05 10:28 ` [PATCH -tip v2 3/9] ftrace/x86: Support SAVE_REGS feature on i386 Masami Hiramatsu
2012-06-05 20:37   ` Steven Rostedt
2012-06-05 21:24     ` Frank Ch. Eigler
2012-06-05 23:37       ` Steven Rostedt
2012-06-05 23:41         ` Frank Ch. Eigler
2012-06-06 14:37           ` Masami Hiramatsu
2012-06-06 14:46             ` Steven Rostedt
2012-06-05 21:51   ` Andi Kleen
2012-06-06 14:24     ` Masami Hiramatsu [this message]
2012-06-05 10:28 ` [PATCH -tip v2 4/9] ftrace: add ftrace_set_filter_ip() for address based filter Masami Hiramatsu
2012-08-21 15:09   ` [tip:perf/core] " tip-bot for Masami Hiramatsu
2012-06-05 10:28 ` [PATCH -tip v2 5/9] kprobes: Inverse taking of module_mutex with kprobe_mutex Masami Hiramatsu
2012-08-21 15:09   ` [tip:perf/core] " tip-bot for Steven Rostedt
2012-06-05 10:28 ` [PATCH -tip v2 6/9] kprobes: cleanup to separate probe-able check Masami Hiramatsu
2012-08-21 15:10   ` [tip:perf/core] " tip-bot for Masami Hiramatsu
2012-06-05 10:28 ` [PATCH -tip v2 7/9] kprobes: Move locks into appropriate functions Masami Hiramatsu
2012-08-21 15:11   ` [tip:perf/core] " tip-bot for Masami Hiramatsu
2012-06-05 10:28 ` [PATCH -tip v2 8/9] kprobes: introduce ftrace based optimization Masami Hiramatsu
2012-08-21 15:13   ` [tip:perf/core] " tip-bot for Masami Hiramatsu
2012-06-05 10:28 ` [PATCH -tip v2 9/9] kprobes/x86: ftrace based optimization for x86 Masami Hiramatsu
2012-08-21 15:14   ` [tip:perf/core] " tip-bot for Masami Hiramatsu
2012-06-05 11:48 ` [PATCH -tip v2 0/9]ftrace,kprobes: Ftrace-based kprobe optimization Steven Rostedt

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