Date: Fri, 20 Feb 2015 13:52:23 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Petr Mladek <pmladek@suse.cz>, "David S. Miller" <davem@davemloft.net>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        Ananth NMavinakayanahalli <ananth@in.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>, Jiri Kosina <jkosina@suse.cz>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] kprobes/x86: Use 5-byte NOP when the code might be
 modified by ftrace
Message-ID: <20150220125223.GA28882@gmail.com>
References: <20150218212205.GA26334@gmail.com>
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 <1424427402-11795-2-git-send-email-pmladek@suse.cz>
 <20150220102625.GC25076@gmail.com>
 <54E72ABA.8050804@hitachi.com>
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* Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:

> (2015/02/20 19:26), Ingo Molnar wrote:
> > 
> > * Petr Mladek <pmladek@suse.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)
> 
> Oops, MCOUNT_INSN_SIZE actually depends on 
> CONFIG_FUNCTION_TRACER... I think we can use 5 instead of 
> that since we are copying NOP_ATOMIC5.

Or just make the define more widely available? It's not 
like the size changes from disabling the function tracer.

Thanks,

	Ingo
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