linux-kernel - Re: [PATCH] perf tools: Fix not finding kcore in buildid cache

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Date:	Wed, 27 Nov 2013 12:32:48 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf tools: Fix not finding kcore in buildid cache


* Adrian Hunter <adrian.hunter@...el.com> wrote:

> On 26/11/13 18:15, Ingo Molnar wrote:
> > 
> > * Adrian Hunter <adrian.hunter@...el.com> wrote:
> > 
> >> The logic was not looking in the buildid cache for kcore
> >> if the host kernel buildid did not match the recorded
> >> kernel buildid.
> > 
> > It would be nice to also include the specific failure mode in the 
> > changelog: exactly how can users run into this. That will be more 
> > useful to most people reading these changelogs than a more abstract 
> > bug description.
> 
> The preconditions for the problem are that kcore is in the buildid
> cache and that the running kernel has a different buildid e.g.
> 
> $ perf buildid-list | grep kernel.kallsyms
> b18fbe769dea12513028a4287dae02efc1582c29 [kernel.kallsyms]
> 
> $ perf record -o /tmp/junk true >/dev/null 2>&1 ; perf buildid-list -i /tmp/junk | grep kernel.kallsyms
> 504f9fd9328c40714995ce76fe1354c6e90136ce [kernel.kallsyms]
> 
> 
> 
> Before the patch:
> 
> 
> $ perf script -v >out.txt
> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> <SNIP>
> Using /home/ahunter/.debug/[kernel.kallsyms]/b18fbe769dea12513028a4287dae02efc1582c29 for symbols
> 
> perf script stopped
> 
> 
> After the patch:
> 
> 
> $ perf script -v >out.txt
> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> <SNIP>
> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kcore for kernel object code
> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kallsyms for symbols
> 
> perf script stopped

So the result of the patch is that kernel symbols get 
resolved/annotated correctly, as expected from the live kcore feature, 
right?

Thanks,

	Ingo
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