linux-kernel - Re: [tip:perf/urgent] perf symbols: Handle /proc/sys/kernel/kptr

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Message-ID: <20110526212805.GB30593@ghostprotocols.net>
Date:	Thu, 26 May 2011 18:28:05 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org, hpa@...or.com,
	mingo@...hat.com, eranian@...gle.com, tzanussi@...il.com,
	penberg@...helsinki.fi, torvalds@...ux-foundation.org,
	efault@....de, peterz@...radead.org, davej@...hat.com,
	davem@...emloft.net, fweisbec@...il.com, kees.cook@...onical.com,
	tglx@...utronix.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf symbols: Handle
	/proc/sys/kernel/kptr_restrict

Em Thu, May 26, 2011 at 09:39:46PM +0200, Ingo Molnar escreveu:
> Secondly, even though i have the proper 'vmlinux' in cwd, i get half 
> a page long warnings on perf record warning me about the vmlinux:
> 
>   WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted, check /proc/sys/kernel/kptr_restrict.
> 
>   Samples in kernel functions may not be resolved if a suitable 
>   vmlinux file is not found in the buildid cache or in the vmlinux 
>   path.
> 
>   ...
> 
> But a vmlinux file *is* in the cwd.

Well, there was no assumption that 'perf report' would run on the same
directory as 'perf record', the user may have moved to a different
directory or transferred the perf.data file to a different machine.

Also it would have to check that the vmlinux on the path is suitable
(that build-id matches), currently it does that just at 'perf report'
time, that is when it will need to use it. At record time we just
collect the build-ids.

With that in mind, how do you think it should be phrased?

- Arnaldo
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