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

From: Randy Dunlap <rdunlap@infradead.org>
To: Thomas Garnier <thgarnie@google.com>,
	kernel-hardening@lists.openwall.com
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, Borislav Petkov <bp@alien8.de>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Christopher Li <sparse@chrisli.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Jason Baron <jbaron@akamai.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Lukas Wunner <lukas@wunner.de>, Kees Cook <keescook@chromium.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Petr Mladek <pmladek@suse.com>,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-sparse@vger.kernel.org
Subject: Re: [PATCH v5 15/27] compiler: Option to default to hidden symbols
Date: Mon, 25 Jun 2018 16:25:03 -0700	[thread overview]
Message-ID: <8486eb8b-e233-4e2f-e976-da7b4cefc673@infradead.org> (raw)
In-Reply-To: <20180625224014.134829-16-thgarnie@google.com>

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@google.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