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Date: Tue, 20 Sep 2011 18:13:10 +0100
From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        Steven Rostedt <rostedt@goodmis.org>, Linux-mm <linux-mm@kvack.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Hugh Dickins <hughd@google.com>, Christoph Hellwig <hch@infradead.org>,
        Andi Kleen <andi@firstfloor.org>, Thomas Gleixner <tglx@linutronix.de>,
        Jonathan Corbet <corbet@lwn.net>, Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Roland McGrath <roland@hack.frob.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 8/26]   x86: analyze instruction and
 determine fixups.
Message-ID: <20110920171310.GC27959@stefanha-thinkpad.localdomain>
References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com>
 <20110920120127.25326.71509.sendpatchset@srdronam.in.ibm.com>
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On Tue, Sep 20, 2011 at 05:31:27PM +0530, Srikar Dronamraju wrote:
> 
> The instruction analysis is based on x86 instruction decoder and
> determines if an instruction can be probed and determines the necessary
> fixups after singlestep.  Instruction analysis is done at probe
> insertion time so that we avoid having to repeat the same analysis every
> time a probe is hit.
> 
> Signed-off-by: Jim Keniston <jkenisto@us.ibm.com>
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
>  arch/x86/Kconfig               |    3 
>  arch/x86/include/asm/uprobes.h |   42 ++++
>  arch/x86/kernel/Makefile       |    1 
>  arch/x86/kernel/uprobes.c      |  385 ++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 431 insertions(+), 0 deletions(-)
>  create mode 100644 arch/x86/include/asm/uprobes.h
>  create mode 100644 arch/x86/kernel/uprobes.c

You've probably thought of this but it would be nice to skip XOL for
nops.  This would be a common case with static probes (e.g. sdt.h) where
the probe template includes a nop where we can easily plant int $0x3.

Perhaps a check can be added to the analysis so that after calling the
filter/handler we can immediately continue the process instead of
executing the (useless) nop out-of-line.

Stefan