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Re: [RFC] [PATCH 2.6.37-rc5-tip 13/20] 13: x86: x86 specific probe handling
- From: Peter Zijlstra <peterz at infradead dot org>
- To: Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>
- 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 11:22:13 +0100
- 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> <20110127094041.GR19725@linux.vnet.ibm.com>
On Thu, 2011-01-27 at 15:10 +0530, Srikar Dronamraju wrote:
> * 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.
Right, because of is_setting_trap_flag()..
> 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.
Its not even close to identical, its very careful to deal with user-mode
already doing single step.
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.