Date: Wed, 22 Aug 2012 09:28:22 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Luigi Semenzato <semenzato@chromium.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@elte.hu>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vasiliy Kulikov <segoon@openwall.com>,
        Stephen Wilson <wilsons@start.ca>, Oleg Nesterov <oleg@redhat.com>,
        Tejun Heo <tj@kernel.org>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Andi Kleen <ak@linux.intel.com>,
        Lucas De Marchi <lucas.demarchi@profusion.mobi>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "Rafael J. Wysocki" <rjw@sisk.pl>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        David Ahern <dsahern@gmail.com>, Namhyung Kim <namhyung@gmail.com>,
        Robert Richter <robert.richter@amd.com>, linux-kernel@vger.kernel.org,
        sonnyrao@chromium.org, olofj@chromium.org, eranian@google.com
Subject: Re: [PATCH] perf: do not flush maps on COMM for perf report
Message-ID: <20120822072822.GA11042@gmail.com>
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* Luigi Semenzato <semenzato@chromium.org> wrote:

> This fixes a long-standing bug caused by the lack of separate
> COMM and EXEC record types, which makes "perf report" lose
> track of symbols when a process renames itself.
> 
> With this fix (suggested by Stephane Eranian), a COMM (rename)
> no longer flushes the maps, which is the correct behavior.
> An EXEC also no longer flushes the maps, but this doesn't
> matter because as new mappings are created (for the executable
> and the libraries) the old mappings are automatically removed.
> This is not by accident: the functionality is necessary because
> DLLs can be explicitly loaded at any time with dlopen(),
> possibly on top of existing text, so "perf report" handles
> correctly the clobbering of new mappings on top of old ones.
> 
> An alternative patch (which I proposed earlier) would be to
> introduce a separate PERF_RECORD_EXEC type, but it is a much
> larger change (about 300 lines) and is not necessary.

It would be nice to add that too - we already have FORK/EXIT, 
this seems like a natural extension.

Thanks,

	Ingo
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