Re: [PATCH v1 bpf-next 3/4] btf: Descend into structs and arrays during special field search

[kernel test robot <lkp@intel.com>]

Hi Dave,

kernel test robot noticed the following build warnings:

[auto build test WARNING on bpf-next/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Dave-Marchevsky/bpf-Fix-btf_get_field_type-to-fail-for-multiple-bpf_refcount-fields/20231024-060227
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
patch link:    https://lore.kernel.org/r/20231023220030.2556229-4-davemarchevsky%40fb.com
patch subject: [PATCH v1 bpf-next 3/4] btf: Descend into structs and arrays during special field search
config: x86_64-rhel-8.3-rust (https://download.01.org/0day-ci/archive/20231026/202310260952.C9Gb9Avi-lkp@intel.com/config)
compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231026/202310260952.C9Gb9Avi-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202310260952.C9Gb9Avi-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/bpf/btf.c:3634:70: warning: variable 'off' is uninitialized when used here [-Wuninitialized]
           ret = btf_find_struct_field(btf, elem_type, srch, array_field_off + off, rec);
                                                                               ^~~
   kernel/bpf/btf.c:3625:15: note: initialize the variable 'off' to silence this warning
           u32 i, j, off, nelems;
                        ^
                         = 0
   1 warning generated.


vim +/off +3634 kernel/bpf/btf.c

  3616	
  3617	static int btf_flatten_array_field(const struct btf *btf,
  3618					   const struct btf_type *t,
  3619					   struct btf_field_info_search *srch,
  3620					   int array_field_off, int rec)
  3621	{
  3622		int ret, start_idx, elem_field_cnt;
  3623		const struct btf_type *elem_type;
  3624		struct btf_field_info *info;
  3625		u32 i, j, off, nelems;
  3626	
  3627		if (!btf_type_is_array(t))
  3628			return -EINVAL;
  3629		nelems = __multi_dim_elem_type_nelems(btf, t, &elem_type);
  3630		if (!nelems || !__btf_type_is_struct(elem_type))
  3631			return srch->idx;
  3632	
  3633		start_idx = srch->idx;
> 3634		ret = btf_find_struct_field(btf, elem_type, srch, array_field_off + off, rec);
  3635		if (ret < 0)
  3636			return ret;
  3637	
  3638		/* No btf_field_info's added */
  3639		if (srch->idx == start_idx)
  3640			return srch->idx;
  3641	
  3642		elem_field_cnt = srch->idx - start_idx;
  3643		info = __next_field_infos(srch, elem_field_cnt * (nelems - 1));
  3644		if (IS_ERR_OR_NULL(info))
  3645			return PTR_ERR(info);
  3646	
  3647		/* Array elems after the first can copy first elem's btf_field_infos
  3648		 * and adjust offset
  3649		 */
  3650		for (i = 1; i < nelems; i++) {
  3651			memcpy(info, &srch->infos[start_idx],
  3652			       elem_field_cnt * sizeof(struct btf_field_info));
  3653			for (j = 0; j < elem_field_cnt; j++) {
  3654				info->off += (i * elem_type->size);
  3655				info++;
  3656			}
  3657		}
  3658		return srch->idx;
  3659	}
  3660	

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