linux-kernel - Re: [PATCH 6/9][RFC] kprobes: Allow probe on ftrace reserved text (but move it)

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Date:	Wed, 02 May 2012 16:40:15 -0400
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"H. Peter Anvin" <hpa@...or.com>, fche@...hat.com
Subject: Re: [PATCH 6/9][RFC] kprobes: Allow probe on ftrace reserved text (but move it)

rostedt wrote:

> [...]  Added KPROBE_FLAG_MOVED (as suggested by Masami) that is set
> when the address is moved to get around an ftrace nop. [...]

Steve, perhaps my earlier comments on this got lost during the mailing
list outage.

The gist is that a KPROBE_FLAG_MOVED being set this way accomplishes
very little since nothing is looking for that flag.  Instead, you
should patch {arch/*}/kernel/kprobe.c kprobe_handler() to subtract
MCOUNT_INSN_SIZE back out from pt_regs->ip if KPROBE_FLAG_MOVED was
set.  That way, kprobes clients need do not perceive the int3 movement.

- FChE
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