linux-kernel - Re: [PATCH 3/4] uprobes/x86: Cleanup the single-stepping code

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Date:	Fri, 2 Nov 2012 18:21:13 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Anton Arapov <anton@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Rabin Vincent <rabin@....in>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] uprobes/x86: Cleanup the single-stepping code

* Oleg Nesterov <oleg@...hat.com> [2012-10-28 18:39:31]:

> No functional changes.
> 
> Now that default arch_uprobe_enable/disable_step() helpers do nothing,
> x86 has no reason to reimplement them. Change arch_uprobe_*_xol() hooks
> to do the necessary work and remove the x86-specific hooks.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>


Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

> ---
>  arch/x86/kernel/uprobes.c |   54 +++++++++++++++-----------------------------
>  1 files changed, 19 insertions(+), 35 deletions(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index aafa555..c71025b 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -478,6 +478,11 @@ int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  	regs->ip = current->utask->xol_vaddr;
>  	pre_xol_rip_insn(auprobe, regs, autask);
> 
> +	autask->saved_tf = !!(regs->flags & X86_EFLAGS_TF);
> +	regs->flags |= X86_EFLAGS_TF;
> +	if (test_tsk_thread_flag(current, TIF_BLOCKSTEP))
> +		set_task_blockstep(current, false);
> +
>  	return 0;
>  }
> 
> @@ -603,6 +608,16 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  	if (auprobe->fixups & UPROBE_FIX_CALL)
>  		result = adjust_ret_addr(regs->sp, correction);
> 
> +	/*
> +	 * arch_uprobe_pre_xol() doesn't save the state of TIF_BLOCKSTEP
> +	 * so we can get an extra SIGTRAP if we do not clear TF. We need
> +	 * to examine the opcode to make it right.
> +	 */
> +	if (utask->autask.saved_tf)
> +		send_sig(SIGTRAP, current, 0);
> +	else if (!(auprobe->fixups & UPROBE_FIX_SETF))
> +		regs->flags &= ~X86_EFLAGS_TF;
> +
>  	return result;
>  }
> 
> @@ -647,6 +662,10 @@ void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  	current->thread.trap_nr = utask->autask.saved_trap_nr;
>  	handle_riprel_post_xol(auprobe, regs, NULL);
>  	instruction_pointer_set(regs, utask->vaddr);
> +
> +	/* clear TF if it was set by us in arch_uprobe_pre_xol() */
> +	if (!utask->autask.saved_tf)
> +		regs->flags &= ~X86_EFLAGS_TF;
>  }
> 
>  /*
> @@ -676,38 +695,3 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  		send_sig(SIGTRAP, current, 0);
>  	return ret;
>  }
> -
> -void arch_uprobe_enable_step(struct arch_uprobe *auprobe)
> -{
> -	struct task_struct *task = current;
> -	struct arch_uprobe_task	*autask	= &task->utask->autask;
> -	struct pt_regs *regs = task_pt_regs(task);
> -
> -	autask->saved_tf = !!(regs->flags & X86_EFLAGS_TF);
> -
> -	regs->flags |= X86_EFLAGS_TF;
> -	if (test_tsk_thread_flag(task, TIF_BLOCKSTEP))
> -		set_task_blockstep(task, false);
> -}
> -
> -void arch_uprobe_disable_step(struct arch_uprobe *auprobe)
> -{
> -	struct task_struct *task = current;
> -	struct arch_uprobe_task	*autask	= &task->utask->autask;
> -	bool trapped = (task->utask->state == UTASK_SSTEP_TRAPPED);
> -	struct pt_regs *regs = task_pt_regs(task);
> -	/*
> -	 * The state of TIF_BLOCKSTEP was not saved so we can get an extra
> -	 * SIGTRAP if we do not clear TF. We need to examine the opcode to
> -	 * make it right.
> -	 */
> -	if (unlikely(trapped)) {
> -		if (!autask->saved_tf)
> -			regs->flags &= ~X86_EFLAGS_TF;
> -	} else {
> -		if (autask->saved_tf)
> -			send_sig(SIGTRAP, task, 0);
> -		else if (!(auprobe->fixups & UPROBE_FIX_SETF))
> -			regs->flags &= ~X86_EFLAGS_TF;
> -	}
> -}
> -- 
> 1.5.5.1
> 

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