linux-kernel - Re: [PATCH v3 2.6.39-rc1-tip 14/26] 14: x86: x86 specific probe handling

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Message-ID: <1303145876.32491.892.camel@twins>
Date:	Mon, 18 Apr 2011 18:57:56 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jonathan Corbet <corbet@....net>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	SystemTap <systemtap@...rces.redhat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2.6.39-rc1-tip 14/26] 14: x86: x86 specific probe
 handling

On Fri, 2011-04-01 at 20:05 +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;
> +} 

Don't you loose the single step flag if userspace was already
single-stepping when it hit your breakpoint? Also, you don't seem to
touch the blockstep settings.
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