linux-kernel - Re: Re: [RFC PATCH -tip 0/9]ftrace, kprobes: Ftrace-based kprobe optimization

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Date:	Thu, 31 May 2012 11:15:46 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: Re: [RFC PATCH -tip  0/9]ftrace, kprobes: Ftrace-based kprobe
 optimization

On Fri, 2012-06-01 at 00:01 +0900, Masami Hiramatsu wrote:

> OK, that's same as what I expected. In that case,
> all __kprobes functions are already filtered out
> by kprobes itself. So we don't need to set that anymore.
> 
> Hmm, CFLAGS_REMOVE_kprobes.o can also keep kprobes from
> function tracer. So I'd like to try to use that instead
> of including notrace into __kprobes.
> However, in that case, kprobe users must remove -pg from
> their kernel modules too, and take care that they must
> call only notrace kernel APIs...
> 
> Perhaps, we'd better introduce new kprobe flag which allow
> kprobe to accept new probe on ftrace, so that user can
> explicitly understand what he will do.

Please do not make kprobe functions not allow function tracing! I *want*
to trace these functions! For example, I trace functions in NMIs all the
time, and I know these are prohibited by kprobes.

Why can't we function trace this? If kprobes does not trace functions
marked with kprobes already, then it should not have any issue. Kprobes
will only use the function tracer for what its allowed to use.

Do not remove -pg from anything to satisfy kprobes. It shouldn't need
it.

-- Steve




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