reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?id=4e6f3b85892327c973fb5e7bf4633dce9ea63ec5
        git remote add kvm https://git.kernel.org/pub/scm/virt/kvm/kvm.git
        git fetch --no-tags kvm kvm-mbec
        git checkout 4e6f3b85892327c973fb5e7bf4633dce9ea63ec5
        # apt-get install sparse
        # sparse: v0.6.5-rc1

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=x86_64 olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/kvm/