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SubjectRe: kernel/time/clocksource-wdtest.c:47:22: warning: signed shift result (0x27BC86B00) requires 35 bits to represent, but 'long' only has 32 bits
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@intel.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?

> vim +/long +47 kernel/time/clocksource-wdtest.c
>
> 39
> 40 static struct clocksource clocksource_wdtest_jiffies = {
> 41 .name = "wdtest-jiffies",
> 42 .rating = 1, /* lowest valid rating*/
> 43 .uncertainty_margin = TICK_NSEC,
> 44 .read = wdtest_jiffies_read,
> 45 .mask = CLOCKSOURCE_MASK(32),
> 46 .flags = CLOCK_SOURCE_MUST_VERIFY,
> > 47 .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
> 48 .shift = JIFFIES_SHIFT,
> 49 .max_cycles = 10,
> 50 };
> 51

------------------------------------------------------------------------

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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