linux-kernel - Re: [PATCH 1/2] kprobes/x86: Use 5-byte NOP when the code might be modified by ftrace

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Message-ID: <20150220102625.GC25076@gmail.com>
Date:	Fri, 20 Feb 2015 11:26:25 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"David S. Miller" <davem@...emloft.net>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Ananth NMavinakayanahalli <ananth@...ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] kprobes/x86: Use 5-byte NOP when the code might be
 modified by ftrace


* Petr Mladek <pmladek@...e.cz> wrote:

> can_probe() checks if the given address points to the 
> beginning of an instruction. It analyzes all the 
> instructions from the beginning of the function until the 
> given address. The code might be modified by another 
> Kprobe. In this case, the current code is read into a 
> buffer, int3 breakpoint is replaced by the saved opcode 
> in the buffer, and can_probe() analyzes the buffer 
> instead.
>
> [...]

Had to drop this patch due to build failures on 32-bit x86:

arch/x86/kernel/kprobes/core.c:258:40: error: ‘MCOUNT_INSN_SIZE’ undeclared (first use in this function)

Thanks,

	Ingo
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