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

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Message-ID: <87d2mex77f.fsf@sejong.aot.lge.com>
Date:	Wed, 06 Nov 2013 17:31:00 +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)

Hi Oleg,

On Tue, 5 Nov 2013 17:28:20 +0100, Oleg Nesterov wrote:
> On 11/05, Namhyung Kim wrote:
>>
>> On Mon, 4 Nov 2013 16:01:12 +0100, Oleg Nesterov wrote:
>> > Or the syntax should be "name=probe @file/addr" or something like this.
>>
>> Okay.  Let's call this kind of thing "cross-fetch" (or a better name can
>> be suggested).
>
> Yes ;) and I am afraid there was some confusion in our discussion.
> I probably confused "probe other binaries" with cross-fetch and vice
> versa sometimes.

Sorry for not being clear enough.

>
>> > So far I think that trace_uprobes.c should not play games with vma. At all.
>>
>> Yes, playing with vma is fragile.  But otherwise how can we get the
>> address from the file+offset in random processes?
>
> Yes, this is not as simple as I thought.
>
> Let me repeat, somehow I completely forgot we need to probe other (libc)
> binaries (not only the executable itself) and dump the data from that
> binary. That is why I wrongly thought that that ->start_data trick can
> work.
>
> OK, I see other emails from you. Perhaps we can rely on instruction_pointer(),
> (I'll write more emails on this), But if not, then we probably need tu->inode
> and vma games in fetch/get_user_vaddr(). I'd still like to avoid this, if
> possible, but I am no longer sure.

Yes, I think it'll be necessary for the cross-fetch anyway.

Thanks,
Namhyung
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