tree: https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git 20211116-sysctl-cleanups-v3 head: 06113f1d9a2d0669964adfa2e0128bd50e56b621 commit: 766042fb8971eaa61f89cdf9b340e602ad6bc7ef [9/20] hpet: use new sysctl subdir helper register_sysctl_subdir() config: x86_64-randconfig-a001-20211116 (attached as .config) compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project 4c2cf3a314d9131b1b288e7c8ab0c75ac1b2be1d) 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/mcgrof/linux-next.git/com... git remote add mcgrof-next https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git git fetch --no-tags mcgrof-next 20211116-sysctl-cleanups-v3 git checkout 766042fb8971eaa61f89cdf9b340e602ad6bc7ef # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=x86_64 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>): drivers/char/hpet.c:1044:18: error: implicit declaration of function 'register_sysctl_subdir' [-Werror,-Wimplicit-function-declaration] sysctl_header = register_sysctl_subdir("dev", "hpet", hpet_table); ^ sysctl_header = register_sysctl_subdir("dev", "hpet", hpet_table); ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1 warning and 1 error generated. vim +1044 drivers/char/hpet.c 1035 1036 static int __init hpet_init(void) 1037 { 1038 int result; 1039 1040 result = misc_register(&hpet_misc); 1041 if (result < 0) 1042 return -ENODEV; 1043 1045 1046 result = acpi_bus_register_driver(&hpet_acpi_driver); 1047 if (result < 0) { 1048 if (sysctl_header) 1049 unregister_sysctl_table(sysctl_header); 1050 misc_deregister(&hpet_misc); 1051 return result; 1052 } 1053 1054 return 0; 1055 } 1056 device_initcall(hpet_init); 1057 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org