linux-kernel - Re: [kbuild-all] Re: kernel/time/clocksource-wdtest.c:47:22: warning: signed shift result (0x27BC86B00) requires 35 bits to represent, but 'long' only has 32 bits

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Date:   Mon, 5 Jul 2021 15:47:09 +0800
From:   Rong Chen <rong.a.chen@...el.com>
To:     paulmck@...nel.org, kernel test robot <lkp@...el.com>
Cc:     clang-built-linux@...glegroups.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [kbuild-all] Re: kernel/time/clocksource-wdtest.c:47:22: warning:
 signed shift result (0x27BC86B00) requires 35 bits to represent, but 'long'
 only has 32 bits



On 7/5/21 1:43 AM, Paul E. McKenney wrote:
> On Sun, Jul 04, 2021 at 05:42:36AM +0800, kernel test robot wrote:
>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>> head:   303392fd5c160822bf778270b28ec5ea50cab2b4
>> commit: 1253b9b87e42ab6a3d5c2cb27af2bdd67d7e50ff clocksource: Provide kernel module to test clocksource watchdog
>> date:   11 days ago
>> config: mips-randconfig-r015-20210702 (attached as .config)
>> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 9eb613b2de3163686b1a4bd1160f15ac56a4b083)
>> 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
>>          # install mips cross compiling tool for clang build
>>          # apt-get install binutils-mips-linux-gnu
>>          # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1253b9b87e42ab6a3d5c2cb27af2bdd67d7e50ff
>>          git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>>          git fetch --no-tags linus master
>>          git checkout 1253b9b87e42ab6a3d5c2cb27af2bdd67d7e50ff
>>          # save the attached .config to linux build tree
>>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=mips
>>
>> 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 >>):
>>
>>>> kernel/time/clocksource-wdtest.c:47:22: warning: signed shift result (0x27BC86B00) requires 35 bits to represent, but 'long' only has 32 bits [-Wshift-overflow]
>>             .mult                   = TICK_NSEC << JIFFIES_SHIFT, /* details above */
>>                                       ~~~~~~~~~ ^  ~~~~~~~~~~~~~
>>     1 warning generated.
> You have CONFIG_HZ_24=y and this test module assumes HZ > 100, as noted
> just above the excerpt below:
>
> /* Assume HZ > 100. */
> #define JIFFIES_SHIFT   8
>
> So this is expected behavior.
>
> Would it help if I gave that comment some teeth, for example, as
> shown at the end of this email?

Hi Paul,

I have confirmed that the below change can avoid the warning.

Best Regards,
Rong Chen

>
> ------------------------------------------------------------------------
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index e1856030fa66..8f0ad6e4183c 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -2573,6 +2573,7 @@ config TEST_FPU
>   config TEST_CLOCKSOURCE_WATCHDOG
>   	tristate "Test clocksource watchdog in kernel space"
>   	depends on CLOCKSOURCE_WATCHDOG
> +	depends on HZ >= 100
>   	help
>   	  Enable this option to create a kernel module that will trigger
>   	  a test of the clocksource watchdog.  This module may be loaded
> _______________________________________________
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