linux-kernel - Re: [RFC] perf tools: Filter out hidden symbols from labels

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Date:   Tue, 15 Jan 2019 16:13:16 +0000
From:   Nick Clifton <nickc@...hat.com>
To:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Michael Petlan <mpetlan@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [RFC] perf tools: Filter out hidden symbols from labels

Hi Jiri,

> When perf is built with annobin plugin (RHEL8 build) extra symbols
> are added to its binary:

  A bit of background for those wondering why annobin is creating
  these symbols:  Annobin is a plugin for gcc that records data 
  about how object file were built.  It is specifically designed 
  to be able to cope with files that are built using multiple
  different sets of optimization options.  (Eg because of #pragma
  directives or function specific optimization attributes).  It
  generates notes to cover each compiled region of code, and it
  needs the symbols in order to be able to determine exactly which
  areas in a linked binary were compiled with which options.

  In the course of developing this plugin I encountered various
  problems with tools not expecting to find extra symbols in a
  binary.  Hence I made the symbols local, hidden and with no type.
  It was the best I could do to say "ignore these symbols - they
  are not meant to be seen by anyone but annobin".

> +		elf_sym__visibility(sym) != STV_HIDDEN;

  Just to be awkward, if you are going to ignore STV_HIDDEN 
  symbols then you should probably also ignore STV_INTERNAL ones
  as well...  Annobin does not generate them, but you never know,
  one day some other tool might create some.

Cheers
  Nick