Hi lucaswei, FYI, the error/warning still remains. tree: https://android.googlesource.com/kernel/common android-4.19-stable head: 7609301471f741be6305ea2d04f34e53b5c40546 commit: 3d88b138f0cbafac10e4eaec4c5377827fe7bd8b [9703/9999] ANDROID: extcon: Export symbol of `extcon_get_edev_name` config: x86_64-defconfig (attached as .config) compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project 1d4c87335d5236ea1f35937e1014980ba961ae34) 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 # install x86_64 cross compiling tool for clang build # apt-get install binutils-x86-64-linux-gnu git checkout 3d88b138f0cbafac10e4eaec4c5377827fe7bd8b # 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: kernel test robot <lkp(a)intel.com&gt; All errors (new ones prefixed by >>): In file included from drivers/usb/common/common.c:15: In file included from include/linux/usb/of.h:12: In file included from include/linux/usb/otg.h:14: In file included from include/linux/usb/phy.h:13: include/linux/extcon.h:316:1: warning: declaration specifier missing, defaulting to 'int' EXPORT_SYMBOL_GPU(extcon_get_edev_name); ^ int EXPORT_SYMBOL_GPU(extcon_get_edev_name); ^ 1 warning and 1 error generated. vim +316 include/linux/extcon.h 311 312 static inline const char *extcon_get_edev_name(struct extcon_dev *edev) 313 { 314 return NULL; 315 } 317 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org