On Mon, May 25, 2020 at 10:48:08AM +0800, kbuild test robot wrote:
> Hi Peter,
>
> Thank you for the patch! Perhaps something to improve:
>
> [auto build test WARNING on vhost/linux-next]
> [also build test WARNING on linus/master v5.7-rc7]
> [cannot apply to kvm/linux-next tip/auto-latest linux/master next-20200522]
> [if your patch is applied to the wrong git tree, please drop us a note to help
> improve the system. BTW, we also suggest to use '--base' option to specify the
> base tree in git format-patch, please see
> https://stackoverflow.com/a/37406982]
>
> url:
> https://github.com/0day-ci/linux/commits/Peter-Xu/KVM-Dirty-ring-interface/20200524-070926
> base: https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git
> linux-next
> config: s390-randconfig-s002-20200524 (attached as .config)
> compiler: s390-linux-gcc (GCC) 9.3.0
> reproduce:
> # apt-get install sparse
> # sparse version: v0.6.1-240-gf0fe1cd9-dirty
> # save the attached .config to linux build tree
> make W=1 C=1 ARCH=s390 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kbuild test robot <l...@intel.com>
>
> All warnings (new ones prefixed by >>, old ones prefixed by <<):
>
> arch/s390/kvm/../../../virt/kvm/kvm_main.c: In function
> 'kvm_page_in_dirty_ring':
> >> arch/s390/kvm/../../../virt/kvm/kvm_main.c:2932:16: warning: comparison of
> >> unsigned expression >= 0 is always true [-Wtype-limits]
> 2932 | return (pgoff >= KVM_DIRTY_LOG_PAGE_OFFSET) &&
> | ^~
Should be a false positive, since when KVM_DIRTY_LOG_PAGE_OFFSET==0 (true for
s390) then the code won't reach here at all due to the previous check [1].
I thought gcc should be able to directly remove the below code when it sees "if
(1) return false;", but it seems not...
I wanted to avoid using "#if" macros because I think it always makes the code
harder to read (especially when nested). Maybe it's still ok to use one more
time here.
Thanks,
>
> vim +2932 arch/s390/kvm/../../../virt/kvm/kvm_main.c
>
> 2926
> 2927 static bool kvm_page_in_dirty_ring(struct kvm *kvm, unsigned
> long pgoff)
> 2928 {
> 2929 if (!KVM_DIRTY_LOG_PAGE_OFFSET)
> 2930 return false;
[1]
> 2931
> > 2932 return (pgoff >= KVM_DIRTY_LOG_PAGE_OFFSET) &&
> 2933 (pgoff < KVM_DIRTY_LOG_PAGE_OFFSET +
> 2934 kvm->dirty_ring_size / PAGE_SIZE);
> 2935 }
> 2936
--
Peter Xu
