tree: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/mm head: bd1de2a7aace4d1d312fb1be264b8fafdb706208 commit: 1f6f655e01adebf5bd5e6c3da2e843c104ded051 [1/23] x86/mm: Add a x86_has_pat_wp() helper config: x86_64-randconfig-r012-20200519 (attached as .config) compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project 135b877874fae96b4372c8a3fbfaa8ff44ff86e3) reproduce: wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # install x86_64 cross compiling tool for clang build # apt-get install binutils-x86-64-linux-gnu git checkout 1f6f655e01adebf5bd5e6c3da2e843c104ded051 # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 If you fix the issue, kindly add following tag as appropriate Reported-by: kbuild test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>, old ones prefixed by <<): bool x86_has_pat_wp(void) ^ arch/x86/mm/init.c:75:1: note: declare 'static' if the function is not intended to be used outside of this translation unit bool x86_has_pat_wp(void) ^ static arch/x86/mm/init.c:866:13: warning: no previous prototype for function 'mem_encrypt_free_decrypted_mem' [-Wmissing-prototypes] void __weak mem_encrypt_free_decrypted_mem(void) { } ^ arch/x86/mm/init.c:866:1: note: declare 'static' if the function is not intended to be used outside of this translation unit void __weak mem_encrypt_free_decrypted_mem(void) { } ^ static 2 warnings generated. vim +/x86_has_pat_wp +75 arch/x86/mm/init.c 73 74 /* Check that the write-protect PAT entry is set for write-protect */ 76 { 77 return __pte2cachemode_tbl[_PAGE_CACHE_MODE_WP] == _PAGE_CACHE_MODE_WP; 78 } 79 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org