linux-kernel - Re: [PATCH] powerpc: Remove the static variable initialisations to 0

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Message-ID: <87fsipdg7b.fsf@mpe.ellerman.id.au>
Date:   Mon, 25 Jul 2022 13:27:52 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Segher Boessenkool <segher@...nel.crashing.org>,
        Michal Suchánek 
        <msuchanek@...e.de>
Cc:     lkp@...el.com, linux-kernel@...r.kernel.org, npiggin@...il.com,
        Julia.Lawall@...ia.fr, paulus@...ba.org,
        Jason Wang <wangborong@...rlc.com>,
        linuxppc-dev@...ts.ozlabs.org, hbathini@...ux.ibm.com,
        joel@....id.au
Subject: Re: [PATCH] powerpc: Remove the static variable initialisations to 0

Segher Boessenkool <segher@...nel.crashing.org> writes:
> On Sat, Jul 23, 2022 at 03:34:05PM +0200, Michal Suchánek wrote:
>> Hello,
>> 
>> 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.
>> 
>> Isn't this change also unnecessary?
>> 
>> 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