linux-kernel - Re: [BUG] perf tools: Demangle kernel and kernel module symbols too

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Date:	Sun, 14 Sep 2014 20:08:22 +0300
From:	Avi Kivity <avi@...udius-systems.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Jan Stancek <jstancek@...hat.com>
Subject: Re: [BUG] perf tools: Demangle kernel and kernel module symbols too


On 09/14/2014 12:41 PM, Peter Zijlstra wrote:
> On Sat, Sep 13, 2014 at 06:34:37AM +0300, Avi Kivity wrote:
>
>> It's not a simple matter of updating the test: the demangler interprets name
>> beginning with __vt as C++ mangles names, which of course they aren't.
> Oh, that'll give cute 'problems' in a mixed C/C++ project that just
> happens to have __vt names in. Now of course I'm aware that C/C++
> 'reserve' the __ prefix, which I suppose that makes it less likely in
> practise.

If you have clashes there, perf demangling is the least of your worries.

>> The only way I see to proceed is to make the demangling optional, default
>> off.
> Seems like a good way out, we could think about adding a language
> heuristic that tries and guess the target language and auto enables when
> it guesses C++, but that needs to have overrides as well.

It should be easy to look for common C++ mangled name
prefixes and use that as a guess, but I expect that users
who profile C++ guest kernels (or kernel modules) are
capable of adding the switch themselves.
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