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Re: [RFC] [PATCH 2.6.37-rc5-tip 13/20] 13: x86: x86 specific probe handling
- From: Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>
- To: Peter Zijlstra <peterz at infradead dot org>
- Cc: Ingo Molnar <mingo at elte dot hu>, Steven Rostedt <rostedt at goodmis dot org>, Arnaldo Carvalho de Melo <acme at infradead dot org>, Linus Torvalds <torvalds at linux-foundation dot org>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, Christoph Hellwig <hch at infradead dot org>, Andi Kleen <andi at firstfloor dot org>, Oleg Nesterov <oleg at redhat dot com>, Andrew Morton <akpm at linux-foundation dot org>, SystemTap <systemtap at sources dot redhat dot com>, Jim Keniston <jkenisto at linux dot vnet dot ibm dot com>, Frederic Weisbecker <fweisbec at gmail dot com>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, LKML <linux-kernel at vger dot kernel dot org>, Roland McGrath <roland at redhat dot com>, "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>
- Date: Thu, 27 Jan 2011 15:10:41 +0530
- Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 13/20] 13: x86: x86 specific probe handling
- References: <20101216095714.23751.52601.sendpatchset@localhost6.localdomain6> <20101216095947.23751.75003.sendpatchset@localhost6.localdomain6> <1295963783.28776.1061.camel@laptop>
- Reply-to: Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>
* Peter Zijlstra <peterz@infradead.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