Hi Thomas, FYI, the error/warning still remains. tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master head: 625d3449788f85569096780592549d0340e9c0c7 commit: c823f416097879515a02f3d97aecc1204ffc0773 MIPS: SGI-IP27: move registering of smp ops into IP27 specific code date: 8 months ago config: mips-randconfig-r021-20200622 (attached as .config) compiler: mips64-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 git checkout c823f416097879515a02f3d97aecc1204ffc0773 # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=mips 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/mips/sgi-ip27/ip27-init.c:118:13: warning: no previous prototype for 'plat_mem_setup' [-Wmissing-prototypes] 118 | void __init plat_mem_setup(void) | ^~~~~~~~~~~~~~ arch/mips/sgi-ip27/ip27-init.c: In function 'plat_mem_setup': 123 | register_smp_ops(&ip27_smp_ops); | ^~~~~~~~~~~~~~~~ cc1: some warnings being treated as errors vim +/register_smp_ops +123 arch/mips/sgi-ip27/ip27-init.c 117 118 void __init plat_mem_setup(void) 119 { 120 u64 p, e, n_mode; 121 nasid_t nid; 122 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org