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

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Date:   Mon, 6 Dec 2021 10:24:07 +0800
From:   Rong Chen <rong.a.chen@...el.com>
To:     Mark Rutland <mark.rutland@....com>,
        kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [kbuild-all] Re: lib/atomic64.c:82:5: warning: no previous
 prototype for 'generic_atomic64_and_return'



On 11/26/21 19:47, Mark Rutland wrote:
> 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.

Hi Mark,

Thanks for the fix, the bot can't always find the first introduced 
commit with the bisection method.

Best Regards,
Rong Chen