Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Segher Boessenkool <segher@kernel.crashing.org>,
        Michal =?utf-8?Q?Such?= =?utf-8?Q?=C3=A1nek?= 
        <msuchanek@suse.de>
Cc:     lkp@intel.com, linux-kernel@vger.kernel.org, npiggin@gmail.com,
        Julia.Lawall@inria.fr, paulus@samba.org,
        Jason Wang <wangborong@cdjrlc.com>,
        linuxppc-dev@lists.ozlabs.org, hbathini@linux.ibm.com,
        joel@jms.id.au
Subject: Re: [PATCH] powerpc: Remove the static variable initialisations to 0
In-Reply-To: <20220723192211.GP25951@gate.crashing.org>
References: <20220723092436.7149-1-wangborong@cdjrlc.com>
 <20220723133405.GF17705@kitsune.suse.cz>
 <20220723192211.GP25951@gate.crashing.org>
Date:   Mon, 25 Jul 2022 13:27:52 +1000
Message-ID: <87fsipdg7b.fsf@mpe.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Segher Boessenkool <segher@kernel.crashing.org> writes:
> On Sat, Jul 23, 2022 at 03:34:05PM +0200, Michal Such=C3=A1nek wrote:
>> Hello,
>>=20
>> On Sat, Jul 23, 2022 at 05:24:36PM +0800, Jason Wang wrote:
>> > Initialise global and static variable to 0 is always unnecessary.
>> > Remove the unnecessary initialisations.
>>=20
>> Isn't this change also unnecessary?
>>=20
>> Initializing to 0 does not affect correctness, or even any kind of
>> semantics in any way.
>
> It did make a difference when the kernel was still compiled with
> -fcommon (which used to be the GCC default on most configurations, it is
> traditional on Unix).  No explicit initialiser puts an object in .bss if
> you use -fcommon.  This matters a bit for data layout.

The kernel has built with -fno-common since ~2002.

I think the belief is that an explicit initialiser of 0 forces the
variable into .data, but AFAICS that is not true with any compiler we
support.

cheers