Re: arch/x86/kvm/vmx/hyperv.h:79:30: sparse: sparse: cast truncates bits from constant value (1b009b becomes 9b)

Sean Christopherson
2023-11-30T17:49:50Z

On Thu, Nov 30, 2023, Vitaly Kuznetsov wrote:
> kernel test robot <lkp@intel.com> writes:
>
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head: 3b47bc037bd44f142ac09848e8d3ecccc726be99
> > commit: a789aeba419647c44d7e7320de20fea037c211d0 KVM: VMX: Rename "vmx/evmcs.{ch}" to "vmx/hyperv.{ch}"
> > date: 1 year ago
> > config: x86_64-randconfig-123-20231130 (https://download.01.org/0day-ci/archive/20231130/202311302231.sinLrAig-lkp@intel.com/config)
> > compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231130/202311302231.sinLrAig-lkp@intel.com/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202311302231.sinLrAig-lkp@intel.com/
> >
> > sparse warnings: (new ones prefixed by >>)
> > arch/x86/kvm/vmx/hyperv.h:79:30: sparse: sparse: cast truncates bits from constant value (a000a becomes a)
>
> This is what ROL16() macro does but the thing is: we actually want to
> truncate bits by doing an explicit (u16) cast. We can probably replace
> this with '& 0xffff':
>
> #define ROL16(val, n) ((((u16)(val) << (n)) | ((u16)(val) >> (16 - (n)))) & 0xffff)
>
> but honestly I don't see much point...

Yeah, just ignore 'em, we get the exact same sparse complaints in vmcs12.c and
have had great success ignoring those too :-)