linux-kernel - Re: [PATCH v6 15/27] compiler: Option to default to hidden symbols

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Message-ID: <CAJcbSZEkc2Rc7uemA0Qw2uJhvNciLRxPrMVSQV_-O_N8zozZ_Q@mail.gmail.com>
Date:   Fri, 1 Feb 2019 09:35:00 -0800
From:   Thomas Garnier <thgarnie@...gle.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Thomas Garnier <thgarnie@...omium.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        kristen@...ux.intel.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jason Baron <jbaron@...mai.com>,
        Jordan Borgner <mail@...dan-borgner.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Jan Beulich <JBeulich@...e.com>,
        Song Liu <songliubraving@...com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Sparse Mailing-list <linux-sparse@...r.kernel.org>
Subject: Re: [PATCH v6 15/27] compiler: Option to default to hidden symbols

On Fri, Feb 1, 2019 at 12:24 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> 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?

No, they will still appear in kallsyms. Some symbols are not absolute
anymore or moved sections but still present.

-- 
Thomas