tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master head: d949689e7383cd5271470f2b99dbe2fd3199bffd commit: 37564ed834aca26993b77b9b2a0119ec1ba6e00c [5813/6512] s390/uv: add prot virt guest/host indication files config: s390-randconfig-r002-20210323 (attached as .config) compiler: s390-linux-gcc (GCC) 9.3.0 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/next/linux-next.git/commi... git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git git fetch --no-tags linux-next master git checkout 37564ed834aca26993b77b9b2a0119ec1ba6e00c # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=s390 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All errors (new ones prefixed by >>): arch/s390/kernel/uv.c: In function 'uv_is_prot_virt_host': 423 | return scnprintf(page, PAGE_SIZE, "%d\n", prot_virt_host); | ^~~~~~~~~~~~~~ | prot_virt_guest arch/s390/kernel/uv.c:423:44: note: each undeclared identifier is reported only once for each function it appears in arch/s390/kernel/uv.c:424:1: error: control reaches end of non-void function [-Werror=return-type] 424 | } | ^ cc1: some warnings being treated as errors vim +423 arch/s390/kernel/uv.c 419 420 static ssize_t uv_is_prot_virt_host(struct kobject *kobj, 421 struct kobj_attribute *attr, char *page) 422 { 424 } 425 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org