linux-kernel - Re: [RFC] [PATCH 2.6.37-rc5-tip 13/20] 13: x86: x86 specific probe handling

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Message-ID: <20110128045721.GV19725@linux.vnet.ibm.com>
Date:	Fri, 28 Jan 2011 10:27:21 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 13/20] 13: x86: x86 specific probe
 handling

Hi Roland,

> > But I'll leave this to the x86 people who actually know the intricacies
> > of the single step cruft, I was just wondering why you weren't using (or
> > extending) the existing code.
> 
> The hairy aspects of the step.c code are hairy (and not usable at interrupt
> level) because they do some instruction analysis.  Since uprobes already
> does its own instruction analysis, reusing step.c's separate hacks makes
> less sense to me than integrating knowledge of the single-step vs
> pushf/popf issues into the uprobes instruction analysis.
> 
> That said, there is further nontriviality just to do with the block-step
> support and with not clobbering user-visible usage of TF in eflags, which
> uprobes needs to handle as well.  It makes sense to share that code rather
> than repeating it, even if that entails changes to the step.c code.
> 

Uprobes doesn't request/handle block-step for now. So can we postpone
your suggested changes till uprobes needs to handle block-step?

-- 
Thanks and Regards
Srikar

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