tree: https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git bpf/batch head: b81b17307e02f8e6d4abf87e7ec2d7e5aea1e0b5 commit: 8243d2b414777d88faa88bada9b2ce204d7fcec0 [8/27] ftrace/samples: Add multi direct interface test module config: x86_64-randconfig-r013-20210827 (attached as .config) compiler: gcc-9 (Debian 9.3.0-22) 9.3.0 reproduce (this is a W=1 build): # https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/commit/?id=8243d2b414777d88faa88bada9b2ce204d7fcec0 git remote add jolsa-perf https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git git fetch --no-tags jolsa-perf bpf/batch git checkout 8243d2b414777d88faa88bada9b2ce204d7fcec0 # save the attached .config to linux build tree make W=1 ARCH=x86_64 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot All warnings (new ones prefixed by >>): >> samples/ftrace/ftrace-direct-multi.c:8:6: warning: no previous prototype for 'my_direct_func' [-Wmissing-prototypes] 8 | void my_direct_func(unsigned long ip) | ^~~~~~~~~~~~~~ vim +/my_direct_func +8 samples/ftrace/ftrace-direct-multi.c 7 > 8 void my_direct_func(unsigned long ip) 9 { 10 trace_printk("ip %lx\n", ip); 11 } 12 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org