linux-kernel - Re: Re: Re: [PATCH v3 -tip] [BUGFIX] x86/kprobes: Fix to recover instructions on optimized path

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Message-ID: <4F4CA3BC.7050909@hitachi.com>
Date:	Tue, 28 Feb 2012 18:51:56 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, yrl.pp-manager.tt@...achi.com,
	systemtap@...rceware.org, anderson@...hat.com,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: Re: Re: [PATCH v3 -tip] [BUGFIX] x86/kprobes: Fix to recover
 instructions on optimized path

(2012/02/28 17:48), Ingo Molnar wrote:
> 
> * Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
> 
>> (2012/02/27 18:34), Ingo Molnar wrote:
>>>
>>> * Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
>>>
>>>> +
>>>> +#ifdef CONFIG_OPTPROBES
>>>> +static unsigned long __recover_optprobed_insn(struct kprobe *kp,
>>>> +					      kprobe_opcode_t *buf,
>>>> +					      unsigned long addr)
>>>> +{
>>>> +	long offs = addr - (unsigned long)kp->addr - 1;
>>>> +	struct optimized_kprobe *op = container_of(kp, struct optimized_kprobe, kp);
>>>> +
>>>> +	/*
>>>> +	 * If the kprobe can be optimized, original bytes which can be
>>>> +	 * overwritten by jump destination address. In this case, original
>>>> +	 * bytes must be recovered from op->optinsn.copied_insn buffer.
>>>> +	 */
>>>> +	memcpy(buf, (void *)addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
>>>> +	if (addr == (unsigned long)kp->addr) {
>>>> +		buf[0] = kp->opcode;
>>>> +		memcpy(buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
>>>> +	} else
>>>> +		memcpy(buf, op->optinsn.copied_insn + offs, RELATIVE_ADDR_SIZE - offs);
>>>> +
>>>> +	return (unsigned long)buf;
>>>> +}
>>>> +#endif
>>>
>>> Why not stick this into a new kprobes-opt.c file?
>>
>> Would you mean that I should split all optprobe stuffs into 
>> new file?
> 
> Yeah, that would be sensible I think - and it might help avoid 
> similar complications in the future.
> 
> Could (and probably should) be done in a separate patch - to 
> keep the bits that you already fixed and tested intact.

OK, I'll make a separate patch.

>>> This should be a separate, kprobes_recover_opt() method and 
>>> be inside kprobes-opt.c as well.
>>
>> OK, I'll do that. But I think it should be separated work. 
>> Just for the bugfix, I think this should go into this style, 
>> because this should be pushed into stable tree too.
> 
> I don't think we can push such a large and complex looking patch 
> into v3.3 (let alone into -stable) - it's v3.4 material, and 
> that's why I asked for the cleaner split-out as well. This
> optprobes code is really non-obvious at the moment and a 
> split-out might improve that and might make future fixes easier 
> to merge.

Yeah, agreed. it's bigger for stable tree.

Thank you,

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