Message-ID: <1338478160.13348.355.camel@gandalf.stny.rr.com>
Subject: Re: Re: [PATCH 1/5] ftrace: Synchronize variable setting with
 breakpoints
From: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Dave Jones <davej@redhat.com>,
        Andi Kleen <ak@linux.intel.com>
Date: Thu, 31 May 2012 11:29:20 -0400
In-Reply-To: <4FC78B45.9060806@hitachi.com>
References: <20120531012829.160060586@goodmis.org>
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On Fri, 2012-06-01 at 00:16 +0900, Masami Hiramatsu wrote:


> Perhaps, kprobes-*jump*-optimization may be better to handle it
> because the target probe is simultaneously working while
> optimizing (modifying code). This means that if someone hits
> breakpoint of such kprobe, it must be handled by kprobes, not
> only just tweaking IP address.

Yeah, ftrace is easier on what the breakpoint does. For kprobes, it's a
bit more invasive. Ftrace only deals with a nop, or a "trace-me" call.
As the modifications are being done, we always treat it as a nop until
the modification is complete.

With kprobes, the text_poke() is a bit more difficult, because it can't
treat the location as a nop, as what is changing actually performs some
task for the kernel. It requires that the breakpoint know what to do
with the text (out-of-line execution, and such). ftrace has the benefit
of just "skip this instruction" and return.

-- Steve


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