To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        "H. Peter Anvin" <hpa@zytor.com>, fche@redhat.com
Subject: Re: [PATCH 6/9][RFC] kprobes: Allow probe on ftrace reserved text (but move it)
References: <20120502192418.024103772@goodmis.org>
	<20120502193237.321234712@goodmis.org>
From: fche@redhat.com (Frank Ch. Eigler)
Date: Wed, 02 May 2012 16:40:15 -0400
In-Reply-To: <20120502193237.321234712@goodmis.org> (Steven Rostedt's message of "Wed, 02 May 2012 15:24:24 -0400")
Message-ID: <y0mhavyl3kg.fsf@fche.csb>
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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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