tree:   https://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git for-next
head:   514e9eea526920608dcd6383e79b369f8ce55174
commit: 7b9dbbb41e1e6579d21fbec1d85ed04a392f73e9 [24/26] riscv: add VMAP_STACK overflow detection
config: riscv-randconfig-r015-20210615 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 64720f57bea6a6bf033feef4a5751ab9c0c3b401)
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 riscv cross compiling tool for clang build
        # apt-get install binutils-riscv64-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git/commit/?id=7b9dbbb41e1e6579d21fbec1d85ed04a392f73e9
        git remote add riscv https://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git
        git fetch --no-tags riscv for-next
        git checkout 7b9dbbb41e1e6579d21fbec1d85ed04a392f73e9
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=riscv 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> arch/riscv/kernel/traps.c:210:26: warning: no previous prototype for function 'get_overflow_stack' [-Wmissing-prototypes]
   asmlinkage unsigned long get_overflow_stack(void)
                            ^
   arch/riscv/kernel/traps.c:210:12: note: declare 'static' if the function is not intended to be used outside of this translation unit
   asmlinkage unsigned long get_overflow_stack(void)
              ^
              static 
>> arch/riscv/kernel/traps.c:216:17: warning: no previous prototype for function 'handle_bad_stack' [-Wmissing-prototypes]
   asmlinkage void handle_bad_stack(struct pt_regs *regs)
                   ^
   arch/riscv/kernel/traps.c:216:12: note: declare 'static' if the function is not intended to be used outside of this translation unit
   asmlinkage void handle_bad_stack(struct pt_regs *regs)
              ^
              static 
   2 warnings generated.


vim +/get_overflow_stack +210 arch/riscv/kernel/traps.c

   201	
   202	#ifdef CONFIG_VMAP_STACK
   203	DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack)
   204			__aligned(16);
   205	/*
   206	 * shadow stack, handled_ kernel_ stack_ overflow(in kernel/entry.S) is used
   207	 * to get per-cpu overflow stack(get_overflow_stack).
   208	 */
   209	long shadow_stack[SHADOW_OVERFLOW_STACK_SIZE/sizeof(long)];
 > 210	asmlinkage unsigned long get_overflow_stack(void)
   211	{
   212		return (unsigned long)this_cpu_ptr(overflow_stack) +
   213			OVERFLOW_STACK_SIZE;
   214	}
   215	
 > 216	asmlinkage void handle_bad_stack(struct pt_regs *regs)

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org