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Subject: Re: [PATCH v6 15/27] compiler: Option to default to hidden symbols
To:     Thomas Garnier <thgarnie@chromium.org>,
        kernel-hardening@lists.openwall.com
Cc:     kristen@linux.intel.com, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Luis Chamberlain <mcgrof@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Jason Baron <jbaron@akamai.com>,
        Thomas Garnier <thgarnie@google.com>,
        Jordan Borgner <mail@jordan-borgner.de>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Jan Beulich <JBeulich@suse.com>,
        Song Liu <songliubraving@fb.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-sparse@vger.kernel.org
References: <20190131192533.34130-1-thgarnie@chromium.org>
 <20190131192533.34130-16-thgarnie@chromium.org>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
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Date:   Fri, 1 Feb 2019 10:22:22 +0200
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On 31/01/19 9:24 PM, Thomas Garnier wrote:
> Provide an option to default visibility to hidden except for key
> symbols. This option is disabled by default and will be used by x86_64
> PIE support to remove errors between compilation units.
> 
> The default visibility is also enabled for external symbols that are
> compared as they maybe equals (start/end of sections). In this case,
> older versions of GCC will remove the comparison if the symbols are
> hidden. This issue exists at least on gcc 4.9 and before.

What does this mean, if anything, for what/how symbols appear in /proc/kallsyms?