linux-kernel - Re: failed to add c++ probe

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Message-ID: <20160922085406.GY5008@twins.programming.kicks-ass.net>
Date:   Thu, 22 Sep 2016 10:54:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>
Subject: Re: failed to add c++ probe

On Wed, Sep 21, 2016 at 01:43:24PM +0900, Masami Hiramatsu wrote:
> On Wed, 21 Sep 2016 12:37:59 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:

> Hmm, I found there are 3 issues in perf-probe to define event on C++ libs.
> 
> 1) No mangle/demangle symbol support. This needs a) fix option parser to
>    accept C++ method name correctly, b) mangle that method, and c) demangle
>    it when we show the probe point.

I think we should also allow using the mangled name, supporting (de)mangling
is of course nice, but not required per-se. Esp. since there's more than
just C++ mangling. Having the mangling stuff as optional makes it a
convenience but still allows using this on other languages for which we
do not support the mangling.

> 2) @plt symbol should be skipped since the real function will be called(jumped)
>    from plt, when searching probe point.
> 
> 3) Event group name is including some characters which can not be used (e.g. "++").
>    Thus we have to remove it or replace it with '_' or other alphabet.("PP"?)

What is the problem with the '+' character? Why cannot this be used?