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Date:	Thu, 07 Aug 2014 15:59:29 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	davem@...emloft.net, Russell King <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	peifeiyue@...wei.com, Li Zefan <lizefan@...wei.com>
Subject: Re: Re: [RFC PATCH] kprobes: arm: enable OPTPROBES for arm 32

(2014/08/06 15:24), Wang Nan wrote:
>>> +
>>> +static void
>>> +optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
>>> +{
>>> +	unsigned long flags;
>>> +
>>> +	regs->ARM_pc = (unsigned long)op->kp.addr;
>>> +	regs->ARM_ORIG_r0 = ~0UL;
>>> +
>>> +
>>> +	local_irq_save(flags);
>>> +	/* 
>>> +	 * This is possible if op is under delayed unoptimizing.
>>> +	 * We need simulate the replaced instruction.
>>> +	 */
>>> +	if (kprobe_disabled(&op->kp)) {
>>> +		struct kprobe *p = &op->kp;
>>> +		op->kp.ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
>>> +	} else {
>>> +		kprobe_handler(regs);
>>> +	}
>>
>> You don't need brace "{}" for one statement.
>> By the way, why don't you call opt_pre_handler()?
>>
> 
> I use kprobe_handler because it handles instruction emulation.
> 
> In addition, I'm not very sure whether skipping the complex checks
> in kprobe_handler() is safe or not.

That seems to do same thing on x86. Then you should do something like
the optimized_callback() on x86 as below.

static void
optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        unsigned long flags;

        local_irq_save(flags);
        if (kprobe_running()) {
                kprobes_inc_nmissed_count(&op->kp);
        } else {
                /* Save skipped registers */
                regs->ARM_pc = (unsigned long)op->kp.addr;
                regs->ARM_ORIG_r0 = ~0UL;

                __this_cpu_write(current_kprobe, &op->kp);
                kcb->kprobe_status = KPROBE_HIT_ACTIVE;
                opt_pre_handler(&op->kp, regs);
                __this_cpu_write(current_kprobe, NULL);
		op->kp.ainsn.insn_singlestep(op->kp.opcode, &op->kp.ainsn, regs);
        }
        local_irq_restore(flags);
}

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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