linux-kernel - Re: lib/atomic64.c:82:5: warning: no previous prototype for 'generic_atomic64_and

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Message-ID: <YaDJWgwqdzNeCFLW@FVFF77S0Q05N>
Date:   Fri, 26 Nov 2021 11:47:38 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: lib/atomic64.c:82:5: warning: no previous prototype for
 'generic_atomic64_and_return'

On Fri, Nov 12, 2021 at 07:08:19AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   debe436e77c72fcee804fb867f275e6d31aa999c
> commit: 1bdadf46eff6804ace5fa46b6856da4799f12b5c locking/atomic: atomic64: support ARCH_ATOMIC
> date:   6 months ago
> config: arc-randconfig-r032-20211109 (attached as .config)
> compiler: arc-elf-gcc (GCC) 11.2.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1bdadf46eff6804ace5fa46b6856da4799f12b5c
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout 1bdadf46eff6804ace5fa46b6856da4799f12b5c
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross ARCH=arc 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> 
> All warnings (new ones prefixed by >>):

> >> lib/atomic64.c:82:5: warning: no previous prototype for 'generic_atomic64_and_return' [-Wmissing-prototypes]

> >> lib/atomic64.c:82:5: warning: no previous prototype for 'generic_atomic64_or_return' [-Wmissing-prototypes]

> >> lib/atomic64.c:82:5: warning: no previous prototype for 'generic_atomic64_xor_return' [-Wmissing-prototypes]

Ah, there are not meant to be return forms of the and/or/xor operations, so
we're pointlessly building code that cannot be used (but this is not otherwise
harmful).

That said, I think this is nothing to do with commit:

  1bdadf46eff6804a ("locking/atomic: atomic64: support ARCH_ATOMIC")

... and is in fact a latent issue introduced by commit:

  28aa2bda2211f432 ("locking/atomic: Implement atomic{,64,_long}_fetch_{add,sub,and,andnot,or,xor}{,_relaxed,_acquire,_release}()")

... where we accidentally left the:

   ATOMIC64_OP_RETURN(op, c_op)

... line for the and/or/xor atomics, even though that wasn't necessary.

This is trivial to avoid, so I'll send a patch shortly.

Thanks,
Mark.