__u32 func_info_len;
 };
 
+struct btf_sec_func_info {
+       __u32   sec_name_off;
+       __u32   num_func_info;
+       /* Followed by num_func_info number of bpf func_info records */
+       __u8    data[0];
+};
+
 /* The minimum bpf_func_info checked by the loader */
 struct bpf_func_info_min {
        __u32   insn_off;
        return err;
 }
 
-static int btf_ext_validate_func_info(const void *finfo, __u32 size,
-                                     btf_print_fn_t err_log)
+static int btf_ext_copy_func_info(struct btf_ext *btf_ext,
+                                 __u8 *data, __u32 data_size,
+                                 btf_print_fn_t err_log)
 {
-       int sec_hdrlen = sizeof(struct btf_sec_func_info);
-       __u32 size_left, num_records, record_size;
+       const struct btf_ext_header *hdr = (struct btf_ext_header *)data;
        const struct btf_sec_func_info *sinfo;
-       __u64 total_record_size;
+       __u32 info_left, record_size;
+       /* The start of the info sec (including the __u32 record_size). */
+       const void *info;
+
+       /* data and data_size do not include btf_ext_header from now on */
+       data = data + hdr->hdr_len;
+       data_size -= hdr->hdr_len;
+
+       if (hdr->func_info_off & 0x03) {
+               elog("BTF.ext func_info section is not aligned to 4 bytes\n");
+               return -EINVAL;
+       }
+
+       if (data_size < hdr->func_info_off ||
+           hdr->func_info_len > data_size - hdr->func_info_off) {
+               elog("func_info section (off:%u len:%u) is beyond the end of the ELF section .BTF.ext\n",
+                    hdr->func_info_off, hdr->func_info_len);
+               return -EINVAL;
+       }
+
+       info = data + hdr->func_info_off;
+       info_left = hdr->func_info_len;
 
        /* At least a func_info record size */
-       if (size < sizeof(__u32)) {
+       if (info_left < sizeof(__u32)) {
                elog("BTF.ext func_info record size not found");
                return -EINVAL;
        }
 
-       /* The record size needs to meet below minimum standard */
-       record_size = *(__u32 *)finfo;
+       /* The record size needs to meet the minimum standard */
+       record_size = *(__u32 *)info;
        if (record_size < sizeof(struct bpf_func_info_min) ||
-           record_size % sizeof(__u32)) {
+           record_size & 0x03) {
                elog("BTF.ext func_info invalid record size");
                return -EINVAL;
        }
 
-       sinfo = finfo + sizeof(__u32);
-       size_left = size - sizeof(__u32);
+       sinfo = info + sizeof(__u32);
+       info_left -= sizeof(__u32);
 
        /* If no func_info records, return failure now so .BTF.ext
         * won't be used.
         */
-       if (!size_left) {
+       if (!info_left) {
                elog("BTF.ext no func info records");
                return -EINVAL;
        }
 
-       while (size_left) {
-               if (size_left < sec_hdrlen) {
+       while (info_left) {
+               unsigned int sec_hdrlen = sizeof(struct btf_sec_func_info);
+               __u64 total_record_size;
+               __u32 num_records;
+
+               if (info_left < sec_hdrlen) {
                        elog("BTF.ext func_info header not found");
                        return -EINVAL;
                }
 
                total_record_size = sec_hdrlen +
                                    (__u64)num_records * record_size;
-               if (size_left < total_record_size) {
+               if (info_left < total_record_size) {
                        elog("incorrect BTF.ext num_func_info");
                        return -EINVAL;
                }
 
-               size_left -= total_record_size;
+               info_left -= total_record_size;
                sinfo = (void *)sinfo + total_record_size;
        }
 
+       btf_ext->func_info_len = hdr->func_info_len - sizeof(__u32);
+       btf_ext->func_info_rec_size = record_size;
+       btf_ext->func_info = malloc(btf_ext->func_info_len);
+       if (!btf_ext->func_info)
+               return -ENOMEM;
+       memcpy(btf_ext->func_info, info + sizeof(__u32),
+              btf_ext->func_info_len);
+
        return 0;
 }
 
                             btf_print_fn_t err_log)
 {
        const struct btf_ext_header *hdr = (struct btf_ext_header *)data;
-       __u32 meta_left, last_func_info_pos;
-       void *finfo;
 
        if (data_size < offsetof(struct btf_ext_header, func_info_off) ||
            data_size < hdr->hdr_len) {
                return -ENOTSUP;
        }
 
-       meta_left = data_size - hdr->hdr_len;
-       if (!meta_left) {
+       if (data_size == hdr->hdr_len) {
                elog("BTF.ext has no data\n");
                return -EINVAL;
        }
 
-       if (meta_left < hdr->func_info_off) {
-               elog("Invalid BTF.ext func_info section offset:%u\n",
-                    hdr->func_info_off);
-               return -EINVAL;
-       }
-
-       if (hdr->func_info_off & 0x03) {
-               elog("BTF.ext func_info section is not aligned to 4 bytes\n");
-               return -EINVAL;
-       }
-
-       last_func_info_pos = hdr->hdr_len + hdr->func_info_off +
-                            hdr->func_info_len;
-       if (last_func_info_pos > data_size) {
-               elog("Invalid BTF.ext func_info section size:%u\n",
-                    hdr->func_info_len);
-               return -EINVAL;
-       }
-
-       finfo = data + hdr->hdr_len + hdr->func_info_off;
-       return btf_ext_validate_func_info(finfo, hdr->func_info_len,
-                                         err_log);
+       return 0;
 }
 
 void btf_ext__free(struct btf_ext *btf_ext)
 
 struct btf_ext *btf_ext__new(__u8 *data, __u32 size, btf_print_fn_t err_log)
 {
-       const struct btf_ext_header *hdr;
        struct btf_ext *btf_ext;
-       void *org_fdata, *fdata;
-       __u32 hdrlen, size_u32;
        int err;
 
        err = btf_ext_parse_hdr(data, size, err_log);
        if (!btf_ext)
                return ERR_PTR(-ENOMEM);
 
-       hdr = (const struct btf_ext_header *)data;
-       hdrlen = hdr->hdr_len;
-       size_u32 = sizeof(__u32);
-       fdata = malloc(hdr->func_info_len - size_u32);
-       if (!fdata) {
-               free(btf_ext);
-               return ERR_PTR(-ENOMEM);
+       err = btf_ext_copy_func_info(btf_ext, data, size, err_log);
+       if (err) {
+               btf_ext__free(btf_ext);
+               return ERR_PTR(err);
        }
 
-       /* remember record size and copy rest of func_info data */
-       org_fdata = data + hdrlen + hdr->func_info_off;
-       btf_ext->func_info_rec_size = *(__u32 *)org_fdata;
-       memcpy(fdata, org_fdata + size_u32, hdr->func_info_len - size_u32);
-       btf_ext->func_info = fdata;
-       btf_ext->func_info_len = hdr->func_info_len - size_u32;
-
        return btf_ext;
 }
 
-int btf_ext__reloc_init(struct btf *btf, struct btf_ext *btf_ext,
-                       const char *sec_name, void **func_info,
-                       __u32 *func_info_rec_size, __u32 *func_info_len)
-{
-       __u32 sec_hdrlen = sizeof(struct btf_sec_func_info);
-       __u32 i, record_size, records_len;
-       struct btf_sec_func_info *sinfo;
-       const char *info_sec_name;
-       __s64 remain_len;
-       void *data;
-
-       record_size = btf_ext->func_info_rec_size;
-       sinfo = btf_ext->func_info;
-       remain_len = btf_ext->func_info_len;
-
-       while (remain_len > 0) {
-               records_len = sinfo->num_func_info * record_size;
-               info_sec_name = btf__name_by_offset(btf, sinfo->sec_name_off);
-               if (strcmp(info_sec_name, sec_name)) {
-                       remain_len -= sec_hdrlen + records_len;
-                       sinfo = (void *)sinfo + sec_hdrlen + records_len;
-                       continue;
-               }
-
-               data = malloc(records_len);
-               if (!data)
-                       return -ENOMEM;
-
-               memcpy(data, sinfo->data, records_len);
-
-               /* adjust the insn_off, the data in .BTF.ext is
-                * the actual byte offset, and the kernel expects
-                * the offset in term of bpf_insn.
-                *
-                * adjust the insn offset only, the rest data will
-                * be passed to kernel.
-                */
-               for (i = 0; i < sinfo->num_func_info; i++) {
-                       struct bpf_func_info_min *record;
-
-                       record = data + i * record_size;
-                       record->insn_off /= sizeof(struct bpf_insn);
-               }
-
-               *func_info = data;
-               *func_info_len = records_len;
-               *func_info_rec_size = record_size;
-               return 0;
-       }
-
-       return -EINVAL;
-}
-
-int btf_ext__reloc(struct btf *btf, struct btf_ext *btf_ext,
-                  const char *sec_name, __u32 insns_cnt,
-                  void **func_info, __u32 *func_info_len)
+int btf_ext__reloc_func_info(struct btf *btf, struct btf_ext *btf_ext,
+                            const char *sec_name, __u32 insns_cnt,
+                            void **func_info, __u32 *cnt)
 {
        __u32 sec_hdrlen = sizeof(struct btf_sec_func_info);
        __u32 i, record_size, existing_flen, records_len;
                        continue;
                }
 
-               existing_flen = *func_info_len;
+               existing_flen = (*cnt) * record_size;
                data = realloc(*func_info, existing_flen + records_len);
                if (!data)
                        return -ENOMEM;
                                insns_cnt;
                }
                *func_info = data;
-               *func_info_len = existing_flen + records_len;
+               *cnt += sinfo->num_func_info;
                return 0;
        }
 
-       return -EINVAL;
+       return -ENOENT;
+}
+
+__u32 btf_ext__func_info_rec_size(const struct btf_ext *btf_ext)
+{
+       return btf_ext->func_info_rec_size;
 }
 
        int btf_fd;
        void *func_info;
        __u32 func_info_rec_size;
-       __u32 func_info_len;
+       __u32 func_info_cnt;
 
        struct bpf_capabilities *caps;
 };
 {
        Elf *elf = obj->efile.elf;
        GElf_Ehdr *ep = &obj->efile.ehdr;
+       Elf_Data *btf_ext_data = NULL;
        Elf_Scn *scn = NULL;
        int idx = 0, err = 0;
 
                                obj->btf = NULL;
                        }
                } else if (strcmp(name, BTF_EXT_ELF_SEC) == 0) {
-                       obj->btf_ext = btf_ext__new(data->d_buf, data->d_size,
-                                                   __pr_debug);
-                       if (IS_ERR(obj->btf_ext)) {
-                               pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
-                                          BTF_EXT_ELF_SEC,
-                                          PTR_ERR(obj->btf_ext));
-                               obj->btf_ext = NULL;
-                       }
+                       btf_ext_data = data;
                } else if (sh.sh_type == SHT_SYMTAB) {
                        if (obj->efile.symbols) {
                                pr_warning("bpf: multiple SYMTAB in %s\n",
                pr_warning("Corrupted ELF file: index of strtab invalid\n");
                return LIBBPF_ERRNO__FORMAT;
        }
+       if (btf_ext_data) {
+               if (!obj->btf) {
+                       pr_debug("Ignore ELF section %s because its depending ELF section %s is not found.\n",
+                                BTF_EXT_ELF_SEC, BTF_ELF_SEC);
+               } else {
+                       obj->btf_ext = btf_ext__new(btf_ext_data->d_buf,
+                                                   btf_ext_data->d_size,
+                                                   __pr_debug);
+                       if (IS_ERR(obj->btf_ext)) {
+                               pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
+                                          BTF_EXT_ELF_SEC,
+                                          PTR_ERR(obj->btf_ext));
+                               obj->btf_ext = NULL;
+                       }
+               }
+       }
        if (obj->efile.maps_shndx >= 0) {
                err = bpf_object__init_maps(obj, flags);
                if (err)
        return 0;
 }
 
+static int
+check_btf_ext_reloc_err(struct bpf_program *prog, int err,
+                       void *btf_prog_info, const char *info_name)
+{
+       if (err != -ENOENT) {
+               pr_warning("Error in loading %s for sec %s.\n",
+                          info_name, prog->section_name);
+               return err;
+       }
+
+       /* err == -ENOENT (i.e. prog->section_name not found in btf_ext) */
+
+       if (btf_prog_info) {
+               /*
+                * Some info has already been found but has problem
+                * in the last btf_ext reloc.  Must have to error
+                * out.
+                */
+               pr_warning("Error in relocating %s for sec %s.\n",
+                          info_name, prog->section_name);
+               return err;
+       }
+
+       /*
+        * Have problem loading the very first info.  Ignore
+        * the rest.
+        */
+       pr_warning("Cannot find %s for main program sec %s. Ignore all %s.\n",
+                  info_name, prog->section_name, info_name);
+       return 0;
+}
+
+static int
+bpf_program_reloc_btf_ext(struct bpf_program *prog, struct bpf_object *obj,
+                         const char *section_name,  __u32 insn_offset)
+{
+       int err;
+
+       if (!insn_offset || prog->func_info) {
+               /*
+                * !insn_offset => main program
+                *
+                * For sub prog, the main program's func_info has to
+                * be loaded first (i.e. prog->func_info != NULL)
+                */
+               err = btf_ext__reloc_func_info(obj->btf, obj->btf_ext,
+                                              section_name, insn_offset,
+                                              &prog->func_info,
+                                              &prog->func_info_cnt);
+               if (err)
+                       return check_btf_ext_reloc_err(prog, err,
+                                                      prog->func_info,
+                                                      "bpf_func_info");
+
+               prog->func_info_rec_size = btf_ext__func_info_rec_size(obj->btf_ext);
+       }
+
+       if (!insn_offset)
+               prog->btf_fd = btf__fd(obj->btf);
+
+       return 0;
+}
+
 static int
 bpf_program__reloc_text(struct bpf_program *prog, struct bpf_object *obj,
                        struct reloc_desc *relo)
                        return -ENOMEM;
                }
 
-               if (obj->btf && obj->btf_ext) {
-                       err = btf_ext__reloc(obj->btf, obj->btf_ext,
-                                            text->section_name,
-                                            prog->insns_cnt,
-                                            &prog->func_info,
-                                            &prog->func_info_len);
-                       if (err) {
-                               pr_warning("error in btf_ext__reloc for sec %s\n",
-                                          text->section_name);
+               if (obj->btf_ext) {
+                       err = bpf_program_reloc_btf_ext(prog, obj,
+                                                       text->section_name,
+                                                       prog->insns_cnt);
+                       if (err)
                                return err;
-                       }
                }
 
                memcpy(new_insn + prog->insns_cnt, text->insns,
        if (!prog)
                return 0;
 
-       if (obj->btf && obj->btf_ext) {
-               err = btf_ext__reloc_init(obj->btf, obj->btf_ext,
-                                         prog->section_name,
-                                         &prog->func_info,
-                                         &prog->func_info_rec_size,
-                                         &prog->func_info_len);
-               if (err) {
-                       pr_warning("err in btf_ext__reloc_init for sec %s\n",
-                                  prog->section_name);
+       if (obj->btf_ext) {
+               err = bpf_program_reloc_btf_ext(prog, obj,
+                                               prog->section_name, 0);
+               if (err)
                        return err;
-               }
-               prog->btf_fd = btf__fd(obj->btf);
        }
 
        if (!prog->reloc_desc)
 
 static int
 load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
-            char *license, __u32 kern_version, int *pfd,
-            __u32 func_info_cnt)
+            char *license, __u32 kern_version, int *pfd)
 {
        struct bpf_load_program_attr load_attr;
        char *cp, errmsg[STRERR_BUFSIZE];
        load_attr.prog_btf_fd = prog->btf_fd >= 0 ? prog->btf_fd : 0;
        load_attr.func_info = prog->func_info;
        load_attr.func_info_rec_size = prog->func_info_rec_size;
-       load_attr.func_info_cnt = func_info_cnt;
-
+       load_attr.func_info_cnt = prog->func_info_cnt;
        if (!load_attr.insns || !load_attr.insns_cnt)
                return -EINVAL;
 
 bpf_program__load(struct bpf_program *prog,
                  char *license, __u32 kern_version)
 {
-       __u32 func_info_cnt;
        int err = 0, fd, i;
 
-       if (prog->func_info_len == 0)
-               func_info_cnt = 0;
-       else
-               func_info_cnt = prog->func_info_len / prog->func_info_rec_size;
-
        if (prog->instances.nr < 0 || !prog->instances.fds) {
                if (prog->preprocessor) {
                        pr_warning("Internal error: can't load program '%s'\n",
                                   prog->section_name, prog->instances.nr);
                }
                err = load_program(prog, prog->insns, prog->insns_cnt,
-                                  license, kern_version, &fd,
-                                  func_info_cnt);
+                                  license, kern_version, &fd);
                if (!err)
                        prog->instances.fds[0] = fd;
                goto out;
 
                err = load_program(prog, result.new_insn_ptr,
                                   result.new_insn_cnt,
-                                  license, kern_version, &fd,
-                                  func_info_cnt);
+                                  license, kern_version, &fd);
 
                if (err) {
                        pr_warning("Loading the %dth instance of program '%s' failed\n",