[kees:kspp/memcpy/next-20210803/v2-devel 77/86] include/linux/string.h:297:2: error: implicit declaration of function '__underlying_memcpy'; did you mean '__builtin_memcpy'?

[kees:kspp/memcpy/next-20210803/v2-devel 77/86] include/linux/string.h:297:2: error: implicit declaration of function '__underlying_memcpy'; did you mean '__builtin_memcpy'?

[kernel test robot]

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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=0faff4e74f49485683ea9757f2e49fdab41c7f20
        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@intel.com>

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':
>> include/linux/string.h:297:2: error: implicit declaration of function '__underlying_memcpy'; did you mean '__builtin_memcpy'? [-Werror=implicit-function-declaration]
     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@chromium.org>
:::::: CC: Kees Cook <keescook@chromium.org>

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

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