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

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Message-ID: <55511421.6040709@hitachi.com>
Date:	Tue, 12 May 2015 05:42:09 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Richard Weinberger <richard@....at>, akpm@...ux-foundation.org
CC:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: Re: vsprintf: Add support for userspace strings

On 2015/05/11 19:57, Richard Weinberger wrote:
> 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.

Ah, the message is not good... If you give "-vv" (double -v options),
you'll see below reason.

symsrc__init: build id mismatch for /boot/vmlinux-4.1.0-rc2-3.g3541e77-vanilla

I'll fix that.

Thank you for reporting!

-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@...achi.com
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