tree: https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git kspp/memcpy/next-20210803/v2-devel head: 4752984fc24104f399e70f99d48afa047d86a381 commit: 0faff4e74f49485683ea9757f2e49fdab41c7f20 [77/86] netlink: Use flex_cpy() to avoid false-positive memcpy() warning config: nios2-defconfig (attached as .config) compiler: nios2-linux-gcc (GCC) 10.3.0 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 # https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?id... git remote add kees https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git git fetch --no-tags kees kspp/memcpy/next-20210803/v2-devel git checkout 0faff4e74f49485683ea9757f2e49fdab41c7f20 # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-10.3.0 make.cross ARCH=nios2 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 include/linux/bitmap.h:10, from include/linux/cpumask.h:12, from include/linux/mm_types_task.h:14, from include/linux/mm_types.h:5, from include/linux/buildid.h:5, from include/linux/module.h:14, from net/netlink/af_netlink.c:21: net/netlink/af_netlink.c: In function 'netlink_ack': 297 | __underlying_memcpy(dst, src, __src_bytes); \ | ^~~~~~~~~~~~~~~~~~~ net/netlink/af_netlink.c:2452:2: note: in expansion of macro 'flex_cpy' 2452 | flex_cpy(&errmsg->msg, errlen, nlh, errlen, nlmsg_content); | ^~~~~~~~ cc1: some warnings being treated as errors vim +297 include/linux/string.h 01f33c336e2d29 Martin Wilck 2017-08-14 274 1e9264c10e1d25 Kees Cook 2021-08-10 275 /** flex_cpy - Copy between two flexible array members. 1e9264c10e1d25 Kees Cook 2021-08-10 276 * 1e9264c10e1d25 Kees Cook 2021-08-10 277 * @dst: Destination pointer 1e9264c10e1d25 Kees Cook 2021-08-10 278 * @dst_count: Number of @member elements to copy at end of @dst struct 1e9264c10e1d25 Kees Cook 2021-08-10 279 * @src: Source pointer 1e9264c10e1d25 Kees Cook 2021-08-10 280 * @src_count: Number of @member elements to copy from end of @src struct 1e9264c10e1d25 Kees Cook 2021-08-10 281 * @member: The flexible array member of both @src and @dst 1e9264c10e1d25 Kees Cook 2021-08-10 282 * 1e9264c10e1d25 Kees Cook 2021-08-10 283 * The full structure of @src will be copied to @dst, as well as 1e9264c10e1d25 Kees Cook 2021-08-10 284 * @src_count @member elements. @src and @dst must reference the same type. 1e9264c10e1d25 Kees Cook 2021-08-10 285 * @dst_count must be >= @src_count. 1e9264c10e1d25 Kees Cook 2021-08-10 286 */ 1e9264c10e1d25 Kees Cook 2021-08-10 287 #define flex_cpy(dst, dst_count, src, src_count, member) ({ \ 1e9264c10e1d25 Kees Cook 2021-08-10 288 size_t __dst_bytes = struct_size(dst, member, dst_count); \ 1e9264c10e1d25 Kees Cook 2021-08-10 289 size_t __src_bytes = struct_size(src, member, src_count); \ 1e9264c10e1d25 Kees Cook 2021-08-10 290 BUILD_BUG_ON(!__same_type(*(dst), *(src))); \ 1e9264c10e1d25 Kees Cook 2021-08-10 291 WARN_ONCE(IS_ENABLED(CONFIG_FORTIFY_SOURCE) && \ 1e9264c10e1d25 Kees Cook 2021-08-10 292 __dst_bytes < __src_bytes, \ 1e9264c10e1d25 Kees Cook 2021-08-10 293 "flex_cpy: detected write overflow (size %zu) of %s (size %zu)\n", \ 1e9264c10e1d25 Kees Cook 2021-08-10 294 __src_bytes, \ 1e9264c10e1d25 Kees Cook 2021-08-10 295 "field \"" #dst "\" at " __FILE__ ":" __stringify(__LINE__), \ 1e9264c10e1d25 Kees Cook 2021-08-10 296 __dst_bytes); \ 1e9264c10e1d25 Kees Cook 2021-08-10 @297 __underlying_memcpy(dst, src, __src_bytes); \ 1e9264c10e1d25 Kees Cook 2021-08-10 298 }) 1e9264c10e1d25 Kees Cook 2021-08-10 299 :::::: The code at line 297 was first introduced by commit :::::: 1e9264c10e1d259549421c6f5adfedb80144a6b3 string: Introduce flexible array memcpy() helpers :::::: TO: Kees Cook <keescook(a)chromium.org&gt; :::::: CC: Kees Cook <keescook(a)chromium.org&gt; --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org