linux-kernel - Re: [PATCH 3/3] perf tools: adjust symbol address

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Date:	Thu, 31 Dec 2009 19:30:04 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] perf tools: adjust symbol address



Arnaldo Carvalho de Melo wrote:
> Em Thu, Dec 31, 2009 at 06:49:01PM +0800, Xiao Guangrong escreveu:
>>
>> Arnaldo Carvalho de Melo wrote:
>>
>>>> vmlinux* not know it's relocation or not, and we just handle the _specific_
>>>> kernel at the time which match the current system. 
>>> 'perf record' in one machine + 'perf report' in another should be
>>> possible.
>>>  
>> Yeah, but current code not support this since it not record kernel build-id in
>> perf.data while 'perf record' works, maybe you can fix it.
> 
> Huh? Checking...
> 
> [root@ana tmp]# perf record -a -f sleep 1s
> [ perf record: Woken up 3 times to write data ]
> [ perf record: Captured and wrote 0.330 MB perf.data (~14404 samples) ]
> [root@ana tmp]# perf buildid-list | grep kallsyms
> a3301c8755357466e39d71b46e8f69aecf83c0e8 [kernel.kallsyms]
> a3301c8755357466e39d71b46e8f69aecf83c0e8 [kernel.kallsyms]
> [root@ana tmp]#
> 
> In fact there is a bug, but the bug is either in 'perf buildid-list'
> showing it twice or it being recorded twice in 'perf record'.
> 

Ah, it seems some perf tools like 'perf kmem/sched' not use the build-id which it's
recorded in perf.data and it use the current kernel's build-id:

perf kmem/sched -> perf_session__new() -> perf_session__create_kernel_maps() ->
map_groups__create_kernel_maps() -> dsos__create_kernel():

sysfs__read_build_id("/sys/kernel/notes", kernel->build_id,
				 sizeof(kernel->build_id)

Hope i not misunderstand it. :-)

Xiao
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