Messages in this thread | | | Date | Mon, 20 Dec 2021 17:44:35 +0000 | From | Wei Liu <> | Subject | Re: [hyperv:hyperv-next 4/5] drivers/hv/vmbus_drv.c:2082:29: warning: shift count >= width of type |
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On Mon, Dec 20, 2021 at 09:53:30AM -0700, Nathan Chancellor wrote: > Hi Wei, > > On Sun, Dec 19, 2021 at 12:29:37PM +0000, Wei Liu wrote: > > On Sat, Dec 18, 2021 at 06:20:43PM +0800, kernel test robot wrote: > > > tree: https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git hyperv-next > > > head: 19fd7ca00201c0525452dcf5a490e4b01674ef4c > > > commit: 6327882f7b4a476ea902de4bee5657f1028d6859 [4/5] scsi: storvsc: Add Isolation VM support for storvsc driver > > > config: x86_64-randconfig-a013-20211216 (https://download.01.org/0day-ci/archive/20211218/202112181827.o3X7GmHz-lkp@intel.com/config) > > > compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project 4c9e31a4814592bbda7153833e46728dc7b21100) > > > 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/hyperv/linux.git/commit/?id=6327882f7b4a476ea902de4bee5657f1028d6859 > > > git remote add hyperv https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git > > > git fetch --no-tags hyperv hyperv-next > > > git checkout 6327882f7b4a476ea902de4bee5657f1028d6859 > > > # save the config file to linux build tree > > > mkdir build_dir > > > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash drivers/hv/ > > > > > > 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 >>): > > > > > > >> drivers/hv/vmbus_drv.c:2082:29: warning: shift count >= width of type [-Wshift-count-overflow] > > > static u64 vmbus_dma_mask = DMA_BIT_MASK(64); > > > ^~~~~~~~~~~~~~~~ > > > include/linux/dma-mapping.h:76:54: note: expanded from macro 'DMA_BIT_MASK' > > > #define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1)) > > > ^ ~~~ > > > > I don't think there is anything wrong with the code. When n is 64 the > > problematic expression is not evaluated. > > Yes, unfortunately, this is an outstanding bug in clang where it does > not properly build a control flow graph for expressions at a global > scope: > > https://github.com/ClangBuiltLinux/linux/issues/92 > > We should absolutely fix that but it has not come up too often so other > fires have been prioritized. Now that -Werror is a thing, that issue's > priority should probably be upgraded, as this warning will break > allmodconfig for clang.
Thanks for the explanation.
> > If you were feeling generous, just changing that to ~0ULL directly would > solve the warning but I get that it is less documentation that way.
I would actually like to keep the code as-is because it gives a clear idea what it is doing.
Wei.
> > Cheers, > Nathan
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