linux-kernel - Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch methods (v6)

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Message-ID: <874n7qx6xd.fsf@sejong.aot.lge.com>
Date:	Wed, 06 Nov 2013 17:37:02 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei\(Jovi\)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch methods (v6)

On Tue, 5 Nov 2013 17:41:02 +0100, Oleg Nesterov wrote:
> On 11/05, Namhyung Kim wrote:
>>
>> On Mon, 4 Nov 2013 19:57:54 +0100, Oleg Nesterov wrote:
>> >>
>> >> 	static void __user *get_user_vaddr(struct pt_regs *regs, unsigned long addr)
>> >> 	{
>> >> 		return (void __force __user *)addr + instruction_pointer(regs);
>> >> 	}
>> >>
>> >> ?
>> >>
>> >> This should solve the problems with relocations/randomization/bss.
>> >>
>> >> The obvious disadvantage is that it is not easy to calculate the
>> >> offset we need to pass as an argument, it depends on the probed
>> >> function.
>> >
>> > forgot to mention... and instruction_pointer() can't work in ret-probe,
>> > we need to pass the "unsigned long func" arg somehow...
>>
>> Hmm.. what's the value of tu->offset in this case?  Does it have the
>> offset of the return address or the start of the function?
>
> It is the offest of function. IOW, it is the same regardless of
> is_ret_probe().

Ah, okay.  Thanks for the info.  Then yes, it'd probably better to pass
the func rather than regs since it's the only info we need, right?

Thanks,
Namhyung
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