btf__add_func
new_func_id = btf__add_func(btf, tmp_name, linkage, proto_id);
LIBBPF_API int btf__add_func(struct btf *btf, const char *name,
fn_id = btf__add_func(btf, prog->name, linkage, fn_proto_id);
btf__add_func(btf2, "fn", BTF_FUNC_STATIC, 14); /* [27] int fn(int p1); */
btf__add_func(btf, "func", BTF_FUNC_GLOBAL, 13);/* [14] int func(int p1, int *p2); */
btf__add_func(split_btf, "f", BTF_FUNC_STATIC, 5); /* [6] int f(int *p); */
btf__add_func(btf, "f", BTF_FUNC_STATIC, 5); /* [6] int f(int *p); */
id = btf__add_func(btf, "func1", BTF_FUNC_GLOBAL, 15);