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

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Date:	Thu, 27 Jan 2011 15:10:41 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	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>,
	Roland McGrath <roland@...hat.com>,
	"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

* Peter Zijlstra <peterz@...radead.org> [2011-01-25 14:56:22]:

> On Thu, 2010-12-16 at 15:29 +0530, Srikar Dronamraju wrote:
> > 
> > +void arch_uprobe_enable_sstep(struct pt_regs *regs)
> > +{
> > +       /*
> > +        * Enable single-stepping by
> > +        * - Set TF on stack
> > +        * - Set TIF_SINGLESTEP: Guarantees that TF is set when
> > +        *      returning to user mode.
> > +        *  - Indicate that TF is set by us.
> > +        */
> > +       regs->flags |= X86_EFLAGS_TF;
> > +       set_thread_flag(TIF_SINGLESTEP);
> > +       set_thread_flag(TIF_FORCED_TF);
> > +}
> > +
> > +void arch_uprobe_disable_sstep(struct pt_regs *regs)
> > +{
> > +       /* Disable single-stepping by clearing what we set */
> > +       clear_thread_flag(TIF_SINGLESTEP);
> > +       clear_thread_flag(TIF_FORCED_TF);
> > +       regs->flags &= ~X86_EFLAGS_TF;
> > +} 
> 
> Why not use the code from arch/x86/kernel/step.c?

user_enable_single_step and user_disable_single_step that are
defined in arch/x86/kernel/step.c cant be called in interrupt context.

Initially we were looking at enabling/disabling singlestep in
interrupt context. Even now we disable singlestep in post notifier in
interrupt context.

Though  arch/x86/kernel/step.c has a static function
enable_single_step which is identical to arch_uprobe_enable_sstep;
there is no equivalent function for arch_uprobe_disable_sstep.

-- 
Thanks and Regards
Srikar
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