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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Message-ID: <20210705152107.GV4397@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 5 Jul 2021 08:21:07 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Rong Chen <rong.a.chen@...el.com>
Cc:     kernel test robot <lkp@...el.com>,
        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 Mon, Jul 05, 2021 at 03:47:09PM +0800, Rong Chen wrote:
> 
> 
> 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.

Very good, and thank you!  May I add your Tested-by?

							Thanx, Paul

> 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
> > _______________________________________________
> > kbuild-all mailing list -- kbuild-all@...ts.01.org
> > To unsubscribe send an email to kbuild-all-leave@...ts.01.org
>