Re: [PATCH v5 1/2] lib/test_bitops: Add benchmark test for fns()

[Kuan-Wei Chiu <visitorckw@gmail.com>]

On Fri, May 03, 2024 at 08:49:00AM +0800, kernel test robot wrote:
> Hi Kuan-Wei,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on linus/master]
> [also build test ERROR on v6.9-rc6 next-20240502]
> [cannot apply to akpm-mm/mm-everything akpm-mm/mm-nonmm-unstable]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Kuan-Wei-Chiu/lib-test_bitops-Add-benchmark-test-for-fns/20240502-172638
> base:   linus/master
> patch link:    https://lore.kernel.org/r/20240502092443.6845-2-visitorckw%40gmail.com
> patch subject: [PATCH v5 1/2] lib/test_bitops: Add benchmark test for fns()
> config: x86_64-allyesconfig (https://download.01.org/0day-ci/archive/20240503/202405030808.UsoMKFNP-lkp@intel.com/config)
> compiler: clang version 18.1.4 (https://github.com/llvm/llvm-project e6c3289804a67ea0bb6a86fadbe454dd93b8d855)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240503/202405030808.UsoMKFNP-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202405030808.UsoMKFNP-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
> >> lib/test_bitops.c:56:39: error: variable 'tmp' set but not used [-Werror,-Wunused-but-set-variable]
>       56 |         static volatile __used unsigned long tmp __initdata;
>          |                                              ^
>    1 error generated.
> 
> 
> vim +/tmp +56 lib/test_bitops.c
> 
>     52	
>     53	static int __init test_fns(void)
>     54	{
>     55		static unsigned long buf[10000] __initdata;
>   > 56		static volatile __used unsigned long tmp __initdata;

I apologize for causing the compilation failure with clang. I'm not
very familiar with clang and I'm not sure why something marked as
__used would result in the warning mentioned above. Perhaps clang does
not support attribute((used))? Is there a way to work around this
issue?

Regards,
Kuan-Wei

>     57		unsigned int i, n;
>     58		ktime_t time;
>     59	
>     60		get_random_bytes(buf, sizeof(buf));
>     61		time = ktime_get();
>     62	
>     63		for (n = 0; n < BITS_PER_LONG; n++)
>     64			for (i = 0; i < 10000; i++)
>     65				tmp = fns(buf[i], n);
>     66	
>     67		time = ktime_get() - time;
>     68		pr_err("fns:  %18llu ns\n", time);
>     69	
>     70		return 0;
>     71	}
>     72	
> 
> -- 
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