linux-kernel - Re: [PATCH v3 3/3] perf probe: Show better error message when failed to find variable

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Message-ID: <555079CF.40701@huawei.com>
Date:	Mon, 11 May 2015 17:43:43 +0800
From:	He Kuang <hekuang@...wei.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	<masami.hiramatsu.pt@...achi.com>, <a.p.zijlstra@...llo.nl>,
	<acme@...nel.org>, <jolsa@...nel.org>, <mingo@...hat.com>,
	<wangnan0@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] perf probe: Show better error message when failed
 to find variable

Hi, Ingo

On 2015/5/11 17:30, Ingo Molnar wrote:
> * He Kuang <hekuang@...wei.com> wrote:
>
>> Indicate to check variable location range in error message when we got
>> failed to find the variable.
>>
>> Before this patch:
>>
>>    $ perf probe --add 'generic_perform_write+118 bytes'
>>    Failed to find the location of bytes at this address.
>>     Perhaps, it has been optimized out.
>>      Error: Failed to add events.
>>
>> After this patch:
>>    $ perf probe --add 'generic_perform_write+118 bytes'
>>    Failed to find the location of bytes at this address.
> What does this sentence mean? I thought 'address' means 'location of
> bytes'. So the address identifies the location and obviously we know
> that. So this message wants to say something else.

'generic_perform_write' is a function name, while 'bytes' is a local
variable in this function. Maybe the variable I chose make you confused.

This maybe clear:
   Failed to find the location of 'bytes' at this address.

>>     Perhaps, it has been optimized out.
>>     Use -V with --range option to show variable location range.
> This suggestion is useful.
>
>>      Error: Failed to add events.
> Thanks,
>
> 	Ingo
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