Hi Lorenzo, Thank you for the patch! Perhaps something to improve: [auto build test WARNING on bpf-next/master] url: https://github.com/0day-ci/linux/commits/Lorenzo-Bianconi/mvneta-introduc... base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master config: arm-randconfig-r023-20210318 (attached as .config) compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 436c6c9c20cc522c92a923440a5fc509c342a7db) 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 arm cross compiling tool for clang build # apt-get install binutils-arm-linux-gnueabi # https://github.com/0day-ci/linux/commit/9603affe766576f892f3a8e02d58dbe83... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Lorenzo-Bianconi/mvneta-introduce-XDP-multi-buffer-support/20210320-055103 git checkout 9603affe766576f892f3a8e02d58dbe83092c74a # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm 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 >>): for (i = 0; i < xdp_sinfo->nr_frags; i++) { ^~~~~~~~~~~~~~~~~~~~~~~ net/core/filter.c:4593:30: note: uninitialized use occurs here memcpy(dst_buff, src_buff, copy_len); ^~~~~~~~ net/core/filter.c:4579:16: note: remove the condition if it is always true for (i = 0; i < xdp_sinfo->nr_frags; i++) { ^~~~~~~~~~~~~~~~~~~~~~~ net/core/filter.c:4570:25: note: initialize the variable 'copy_len' to silence this warning unsigned long copy_len; ^ = 0 1 warning generated. vim +4579 net/core/filter.c 4551 4552 static unsigned long bpf_xdp_copy(void *dst_buff, const void *ctx, 4553 unsigned long off, unsigned long len) 4554 { 4555 struct xdp_buff *xdp = (struct xdp_buff *)ctx; 4556 struct xdp_shared_info *xdp_sinfo; 4557 unsigned long base_len; 4558 const void *src_buff; 4559 4560 if (likely(!xdp->mb)) { 4561 src_buff = xdp->data; 4562 memcpy(dst_buff, src_buff + off, len); 4563 4564 return 0; 4565 } 4566 4567 base_len = xdp->data_end - xdp->data; 4568 xdp_sinfo = xdp_get_shared_info_from_buff(xdp); 4569 do { 4570 unsigned long copy_len; 4571 4572 if (off < base_len) { 4573 src_buff = xdp->data + off; 4574 copy_len = min(len, base_len - off); 4575 } else { 4576 unsigned long frag_off_total = base_len; 4577 int i; 4578 4580 skb_frag_t *frag = &xdp_sinfo->frags[i]; 4581 unsigned long frag_len = xdp_get_frag_size(frag); 4582 unsigned long frag_off = off - frag_off_total; 4583 4584 if (frag_off < frag_len) { 4585 src_buff = xdp_get_frag_address(frag) + 4586 frag_off; 4587 copy_len = min(len, frag_len - frag_off); 4588 break; 4589 } 4590 frag_off_total += frag_len; 4591 } 4592 } 4593 memcpy(dst_buff, src_buff, copy_len); 4594 off += copy_len; 4595 len -= copy_len; 4596 dst_buff += copy_len; 4597 } while (len); 4598 4599 return 0; 4600 } 4601 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org