Hi Alexandre, [FYI, it's a private test report for your RFC patch.] [auto build test WARNING on tip/x86/mm] [also build test WARNING on v5.10-rc3 next-20201113] [cannot apply to tip/x86/core tip/x86/asm] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/0day-ci/linux/commits/Alexandre-Chartre/x86-pti-Defer-... base: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 1fcd009102ee02e217f2e7635ab65517d785da8e config: x86_64-allyesconfig (attached as .config) compiler: gcc-9 (Debian 9.3.0-15) 9.3.0 reproduce (this is a W=1 build): # https://github.com/0day-ci/linux/commit/63533707f1058d9d8eccb278eb735d9f8... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Alexandre-Chartre/x86-pti-Defer-CR3-switch-to-C-code/20201109-225007 git checkout 63533707f1058d9d8eccb278eb735d9f88fdd222 # 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 <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>): 38 | __visible noinstr void return_from_fork(struct pt_regs *regs, | ^~~~~~~~~~~~~~~~ arch/x86/entry/common.c:223:24: warning: no previous prototype for 'do_SYSENTER_32' [-Wmissing-prototypes] 223 | __visible noinstr long do_SYSENTER_32(struct pt_regs *regs) | ^~~~~~~~~~~~~~ arch/x86/entry/common.c:320:24: warning: no previous prototype for 'xen_pv_evtchn_do_upcall' [-Wmissing-prototypes] 320 | __visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs) | ^~~~~~~~~~~~~~~~~~~~~~~ vim +/return_from_fork +38 arch/x86/entry/common.c 37 39 struct task_struct *prev, 40 void (*kfunc)(void *), void *kargs) 41 { 42 schedule_tail(prev); 43 if (kfunc) { 44 /* kernel thread */ 45 kfunc(kargs); 46 /* 47 * A kernel thread is allowed to return here after 48 * successfully calling kernel_execve(). Exit to 49 * userspace to complete the execve() syscall. 50 */ 51 regs->ax = 0; 52 } 53 syscall_exit_to_user_mode(regs); 54 } 55 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org