linux-kernel - Re: [PATCH v5 3.1.0-rc4-tip 8/26] x86: analyze instruction and determine fixups.

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Message-ID: <20110920171310.GC27959@stefanha-thinkpad.localdomain>
Date:	Tue, 20 Sep 2011 18:13:10 +0100
From:	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jonathan Corbet <corbet@....net>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 8/26]   x86: analyze instruction and
 determine fixups.

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@...ibm.com>
> Signed-off-by: Srikar Dronamraju <srikar@...ux.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
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