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

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Message-Id: <20110128062316.9515018099A@magilla.sf.frob.com>
Date:	Thu, 27 Jan 2011 22:23:16 -0800 (PST)
From:	Roland McGrath <roland@...hat.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>,
	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

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

That's not the issue.  The way the hardware works is that if the bit is set
in the MSR, then the TF eflags bit means block-step instead of single-step.
So if PTRACE_SINGLEBLOCK has been used (i.e. user_enable_block_step), then
this can interfere with your use of single-step.  You need to do the work
in the else branch of step.c:enable_step to ensure that the hardware is not
left in the state where it will do block-step instead of single-step when
uprobes wants a single-step done.


Thanks,
Roland
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