linux-kernel - Re: vsprintf: Add support for userspace strings

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Message-ID: <55508AFC.2010809@nod.at>
Date:	Mon, 11 May 2015 12:57:00 +0200
From:	Richard Weinberger <richard@....at>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	akpm@...ux-foundation.org
CC:	linux-kernel@...r.kernel.org
Subject: Re: vsprintf: Add support for userspace strings

Am 11.05.2015 um 10:59 schrieb Richard Weinberger:
> Am 11.05.2015 um 02:24 schrieb Masami Hiramatsu:
>> On 2015/05/11 4:42, Richard Weinberger wrote:
>>> While debugging issues I often add (trace_)printks to strategic positions.
>>> Dealing with user provided string is complicated as an extra buffer a
>>> copy_from_user() is needed.
>>> This adds a new format string to allow direct printing of such strings.
>>>
>>> My initial plan was to use %pU but 'U' is already taken, therefore
>>> I used the next letter which comes in mind when one thinks of userpace,
>>> 'L'.
>>> The %pL format string works exactly like %s.
>>
>> BTW, if you need to do this for debug, you can also use ftrace's kprobe-tracer
>> (and perf probe) which allows you to dump userspace strings :)
> 
> Sounds promising!
> 
> But I fail to use it:
> $ perf probe -vv -L do_sys_open:0-3 -k /boot/vmlinux-4.1.0-rc2-3.g3541e77-vanilla
> Line range is 0 to 3
> Use vmlinux: /boot/vmlinux-4.1.0-rc2-3.g3541e77-vanilla
> Failed to find path of kernel module.
>   Error: Failed to show lines. Reason: No such file or directory (Code: -2)
> 
> Any idea what's the issue?

Okay, works now as expected. :-)
Had the wrong debuginfo package installed.

Thanks,
//richard
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