linux-kernel - Re: [PATCH v5 15/27] compiler: Option to default to hidden symbols

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Date:   Mon, 25 Jun 2018 16:25:03 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Thomas Garnier <thgarnie@...gle.com>,
        kernel-hardening@...ts.openwall.com
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christopher Li <sparse@...isli.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jason Baron <jbaron@...mai.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Lukas Wunner <lukas@...ner.de>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-sparse@...r.kernel.org
Subject: Re: [PATCH v5 15/27] compiler: Option to default to hidden symbols

On 06/25/18 15:39, 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.
> 
> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
> ---

> diff --git a/init/Kconfig b/init/Kconfig
> index 24b60536e26b..d4f90cc38ede 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1718,6 +1718,13 @@ config PROFILING
>  config TRACEPOINTS
>  	bool
>  
> +#
> +# Default to hidden visibility for all symbols.
> +# Useful for Position Independent Code to reduce global references.
> +#
> +config DEFAULT_HIDDEN
> +	bool
> +

I certainly would appreciate a better/more descriptive kconfig symbol name
here.

>  source "arch/Kconfig"
>  
>  endmenu		# General setup


thanks,
-- 
~Randy