Hi Martin,

I love your patch! Yet something to improve:

[auto build test ERROR on bpf-next/master]
[cannot apply to bpf/master net/master v5.5-rc3 next-20191219]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Martin-KaFai-Lau/Introduce-BPF-STRUCT_OPS/20191224-085617
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: arm64-defconfig (attached as .config)
compiler: aarch64-linux-gcc (GCC) 7.5.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.5.0 make.cross ARCH=arm64 

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

All errors (new ones prefixed by >>):

   kernel/bpf/bpf_struct_ops.c: In function 'bpf_struct_ops_init':
>> kernel/bpf/bpf_struct_ops.c:86:8: error: implicit declaration of function 'btf_distill_func_proto'; did you mean 'btf_type_is_func_proto'? [-Werror=implicit-function-declaration]
           btf_distill_func_proto(&log, _btf_vmlinux,
           ^~~~~~~~~~~~~~~~~~~~~~
           btf_type_is_func_proto
   cc1: some warnings being treated as errors

vim +86 kernel/bpf/bpf_struct_ops.c

    37	
    38	void bpf_struct_ops_init(struct btf *_btf_vmlinux)
    39	{
    40		const struct btf_member *member;
    41		struct bpf_struct_ops *st_ops;
    42		struct bpf_verifier_log log = {};
    43		const struct btf_type *t;
    44		const char *mname;
    45		s32 type_id;
    46		u32 i, j;
    47	
    48		for (i = 0; i < ARRAY_SIZE(bpf_struct_ops); i++) {
    49			st_ops = bpf_struct_ops[i];
    50	
    51			type_id = btf_find_by_name_kind(_btf_vmlinux, st_ops->name,
    52							BTF_KIND_STRUCT);
    53			if (type_id < 0) {
    54				pr_warn("Cannot find struct %s in btf_vmlinux\n",
    55					st_ops->name);
    56				continue;
    57			}
    58			t = btf_type_by_id(_btf_vmlinux, type_id);
    59			if (btf_type_vlen(t) > BPF_STRUCT_OPS_MAX_NR_MEMBERS) {
    60				pr_warn("Cannot support #%u members in struct %s\n",
    61					btf_type_vlen(t), st_ops->name);
    62				continue;
    63			}
    64	
    65			for_each_member(j, t, member) {
    66				const struct btf_type *func_proto;
    67	
    68				mname = btf_name_by_offset(_btf_vmlinux,
    69							   member->name_off);
    70				if (!*mname) {
    71					pr_warn("anon member in struct %s is not supported\n",
    72						st_ops->name);
    73					break;
    74				}
    75	
    76				if (btf_member_bitfield_size(t, member)) {
    77					pr_warn("bit field member %s in struct %s is not supported\n",
    78						mname, st_ops->name);
    79					break;
    80				}
    81	
    82				func_proto = btf_type_resolve_func_ptr(_btf_vmlinux,
    83								       member->type,
    84								       NULL);
    85				if (func_proto &&
  > 86				    btf_distill_func_proto(&log, _btf_vmlinux,
    87							   func_proto, mname,
    88							   &st_ops->func_models[j])) {
    89					pr_warn("Error in parsing func ptr %s in struct %s\n",
    90						mname, st_ops->name);
    91					break;
    92				}
    93			}
    94	
    95			if (j == btf_type_vlen(t)) {
    96				if (st_ops->init(_btf_vmlinux)) {
    97					pr_warn("Error in init bpf_struct_ops %s\n",
    98						st_ops->name);
    99				} else {
   100					st_ops->type_id = type_id;
   101					st_ops->type = t;
   102				}
   103			}
   104		}
   105	}
   106	

---
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