linux-kernel - Re: Re: [PATCH 1/2] perf probe: Improve error message when function not found

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Date:	Tue, 03 Dec 2013 14:12:04 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	David Ahern <dsahern@...il.com>
Cc:	acme@...stprotocols.net, linux-kernel@...r.kernel.org,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>
Subject: Re: Re: [PATCH 1/2] perf probe: Improve error message when function
 not found

(2013/12/02 23:52), David Ahern wrote:
> On 12/1/13, 10:59 PM, Masami Hiramatsu wrote:
>> (2013/12/02 9:07), David Ahern wrote:
>>> When requesting a function from a userspace library the error message to
>>> the user is less than helpful. e.g.,
>>>
>>>      perf probe -x /lib64/libpthread-2.14.90.so -a 'lock_full=__pthread_mutex_lock_full'
>>>      no symbols found in /lib64/libpthread-2.14.90.so, maybe install a debug package?
>>>      Failed to load map.
>>>         Error: Failed to add events. (-22)
>>>
>>> In this cae the symbol really does exist but is a local symbol which is
>>> filtered:
>>>
>>>      nm /lib64/libpthread-2.14.90.so | grep __pthread_mutex_lock_full
>>>      0000000000005700 t __pthread_mutex_lock_full
>>>
>>> With this patch:
>>>      perf probe -x /lib64/libpthread-2.14.90.so -a 'lock_full=__pthread_mutex_lock_full'
>>>
>>>      no symbols found in /lib64/libpthread-2.14.90.so, maybe install a debug package?
>>>      Failed to find function in /lib64/libpthread-2.14.90.so. Perhaps it is a local variable?
>>
>> Hmm, indeed current message is too less information, but your message looks
>> wired. I think just showing "Failed to find requested symbol in %s" is enough. :)
> 
> I disagree. perf-probe filters non-global variables:
> 
>     if (sym->binding == STB_GLOBAL &&
>         strfilter__compare(available_func_filter, sym->name))
>         return 0;
> 
> That needs to be explicitly stated in the error message -- only global
> symbols may be given.

Ah, I see. In that case, I think the "variable" is not a correct word,
the "symbol" is better, because perf probe can take tracing variable
arguments after the trace point definition. :)

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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