linux-kernel - Re: [hyperv:hyperv-next 4/5] drivers/hv/vmbus_drv.c:2082:29: warning: shift count >= width of type

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Date:   Sun, 19 Dec 2021 12:29:37 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     kernel test robot <lkp@...el.com>
Cc:     Tianyu Lan <Tianyu.Lan@...rosoft.com>, llvm@...ts.linux.dev,
        kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Wei Liu <wei.liu@...nel.org>, Long Li <longli@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>
Subject: Re: [hyperv:hyperv-next 4/5] drivers/hv/vmbus_drv.c:2082:29:
 warning: shift count >= width of type

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@...el.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.

Wei.