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 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
 /*
  * BPF static linker
  *
  * Copyright (c) 2021 Facebook
  */
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <errno.h>
 #include <linux/err.h>
 #include <linux/btf.h>
 #include <elf.h>
 #include <libelf.h>
 #include <fcntl.h>
 #include "libbpf.h"
 #include "btf.h"
 #include "libbpf_internal.h"
 #include "strset.h"
 
 #define BTF_EXTERN_SEC ".extern"
 
 struct src_sec {
     const char *sec_name;
     /* positional (not necessarily ELF) index in an array of sections */
     int id;
     /* positional (not necessarily ELF) index of a matching section in a final object file */
     int dst_id;
     /* section data offset in a matching output section */
     int dst_off;
     /* whether section is omitted from the final ELF file */
     bool skipped;
     /* whether section is an ephemeral section, not mapped to an ELF section */
     bool ephemeral;
 
     /* ELF info */
     size_t sec_idx;
     Elf_Scn *scn;
     Elf64_Shdr *shdr;
     Elf_Data *data;
 
     /* corresponding BTF DATASEC type ID */
     int sec_type_id;
 };
 
 struct src_obj {
     const char *filename;
     int fd;
     Elf *elf;
     /* Section header strings section index */
     size_t shstrs_sec_idx;
     /* SYMTAB section index */
     size_t symtab_sec_idx;
 
     struct btf *btf;
     struct btf_ext *btf_ext;
 
     /* List of sections (including ephemeral). Slot zero is unused. */
     struct src_sec *secs;
     int sec_cnt;
 
     /* mapping of symbol indices from src to dst ELF */
     int *sym_map;
     /* mapping from the src BTF type IDs to dst ones */
     int *btf_type_map;
 };
 
 /* single .BTF.ext data section */
 struct btf_ext_sec_data {
     size_t rec_cnt;
     __u32 rec_sz;
     void *recs;
 };
 
 struct glob_sym {
     /* ELF symbol index */
     int sym_idx;
     /* associated section id for .ksyms, .kconfig, etc, but not .extern */
     int sec_id;
     /* extern name offset in STRTAB */
     int name_off;
     /* optional associated BTF type ID */
     int btf_id;
     /* BTF type ID to which VAR/FUNC type is pointing to; used for
      * rewriting types when extern VAR/FUNC is resolved to a concrete
      * definition
      */
     int underlying_btf_id;
     /* sec_var index in the corresponding dst_sec, if exists */
     int var_idx;
 
     /* extern or resolved/global symbol */
     bool is_extern;
     /* weak or strong symbol, never goes back from strong to weak */
     bool is_weak;
 };
 
 struct dst_sec {
     char *sec_name;
     /* positional (not necessarily ELF) index in an array of sections */
     int id;
 
     bool ephemeral;
 
     /* ELF info */
     size_t sec_idx;
     Elf_Scn *scn;
     Elf64_Shdr *shdr;
     Elf_Data *data;
 
     /* final output section size */
     int sec_sz;
     /* final output contents of the section */
     void *raw_data;
 
     /* corresponding STT_SECTION symbol index in SYMTAB */
     int sec_sym_idx;
 
     /* section's DATASEC variable info, emitted on BTF finalization */
     bool has_btf;
     int sec_var_cnt;
     struct btf_var_secinfo *sec_vars;
 
     /* section's .BTF.ext data */
     struct btf_ext_sec_data func_info;
     struct btf_ext_sec_data line_info;
     struct btf_ext_sec_data core_relo_info;
 };
 
 struct bpf_linker {
     char *filename;
     int fd;
     Elf *elf;
     Elf64_Ehdr *elf_hdr;
 
     /* Output sections metadata */
     struct dst_sec *secs;
     int sec_cnt;
 
     struct strset *strtab_strs; /* STRTAB unique strings */
     size_t strtab_sec_idx; /* STRTAB section index */
     size_t symtab_sec_idx; /* SYMTAB section index */
 
     struct btf *btf;
     struct btf_ext *btf_ext;
 
     /* global (including extern) ELF symbols */
     int glob_sym_cnt;
     struct glob_sym *glob_syms;
 };
 
 #define pr_warn_elf(fmt, ...)                                   \
     libbpf_print(LIBBPF_WARN, "libbpf: " fmt ": %s\n", ##__VA_ARGS__, elf_errmsg(-1))
 
 static int init_output_elf(struct bpf_linker *linker, const char *file);
 
 static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
                 const struct bpf_linker_file_opts *opts,
                 struct src_obj *obj);
 static int linker_sanity_check_elf(struct src_obj *obj);
 static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec);
 static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec);
 static int linker_sanity_check_btf(struct src_obj *obj);
 static int linker_sanity_check_btf_ext(struct src_obj *obj);
 static int linker_fixup_btf(struct src_obj *obj);
 static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj);
 static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj);
 static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
                  Elf64_Sym *sym, const char *sym_name, int src_sym_idx);
 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj);
 static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj);
 static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj);
 
 static int finalize_btf(struct bpf_linker *linker);
 static int finalize_btf_ext(struct bpf_linker *linker);
 
 void bpf_linker__free(struct bpf_linker *linker)
 {
     int i;
 
     if (!linker)
         return;
 
     free(linker->filename);
 
     if (linker->elf)
         elf_end(linker->elf);
 
     if (linker->fd >= 0)
         close(linker->fd);
 
     strset__free(linker->strtab_strs);
 
     btf__free(linker->btf);
     btf_ext__free(linker->btf_ext);
 
     for (i = 1; i < linker->sec_cnt; i++) {
         struct dst_sec *sec = &linker->secs[i];
 
         free(sec->sec_name);
         free(sec->raw_data);
         free(sec->sec_vars);
 
         free(sec->func_info.recs);
         free(sec->line_info.recs);
         free(sec->core_relo_info.recs);
     }
     free(linker->secs);
 
     free(linker->glob_syms);
     free(linker);
 }
 
 struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts *opts)
 {
     struct bpf_linker *linker;
     int err;
 
     if (!OPTS_VALID(opts, bpf_linker_opts))
         return errno = EINVAL, NULL;
 
     if (elf_version(EV_CURRENT) == EV_NONE) {
         pr_warn_elf("libelf initialization failed");
         return errno = EINVAL, NULL;
     }
 
     linker = calloc(1, sizeof(*linker));
     if (!linker)
         return errno = ENOMEM, NULL;
 
     linker->fd = -1;
 
     err = init_output_elf(linker, filename);
     if (err)
         goto err_out;
 
     return linker;
 
 err_out:
     bpf_linker__free(linker);
     return errno = -err, NULL;
 }
 
 static struct dst_sec *add_dst_sec(struct bpf_linker *linker, const char *sec_name)
 {
     struct dst_sec *secs = linker->secs, *sec;
     size_t new_cnt = linker->sec_cnt ? linker->sec_cnt + 1 : 2;
 
     secs = libbpf_reallocarray(secs, new_cnt, sizeof(*secs));
     if (!secs)
         return NULL;
 
     /* zero out newly allocated memory */
     memset(secs + linker->sec_cnt, 0, (new_cnt - linker->sec_cnt) * sizeof(*secs));
 
     linker->secs = secs;
     linker->sec_cnt = new_cnt;
 
     sec = &linker->secs[new_cnt - 1];
     sec->id = new_cnt - 1;
     sec->sec_name = strdup(sec_name);
     if (!sec->sec_name)
         return NULL;
 
     return sec;
 }
 
 static Elf64_Sym *add_new_sym(struct bpf_linker *linker, size_t *sym_idx)
 {
     struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
     Elf64_Sym *syms, *sym;
     size_t sym_cnt = symtab->sec_sz / sizeof(*sym);
 
     syms = libbpf_reallocarray(symtab->raw_data, sym_cnt + 1, sizeof(*sym));
     if (!syms)
         return NULL;
 
     sym = &syms[sym_cnt];
     memset(sym, 0, sizeof(*sym));
 
     symtab->raw_data = syms;
     symtab->sec_sz += sizeof(*sym);
     symtab->shdr->sh_size += sizeof(*sym);
     symtab->data->d_size += sizeof(*sym);
 
     if (sym_idx)
         *sym_idx = sym_cnt;
 
     return sym;
 }
 
 static int init_output_elf(struct bpf_linker *linker, const char *file)
 {
     int err, str_off;
     Elf64_Sym *init_sym;
     struct dst_sec *sec;
 
     linker->filename = strdup(file);
     if (!linker->filename)
         return -ENOMEM;
 
     linker->fd = open(file, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
     if (linker->fd < 0) {
         err = -errno;
         pr_warn("failed to create '%s': %d\n", file, err);
         return err;
     }
 
     linker->elf = elf_begin(linker->fd, ELF_C_WRITE, NULL);
     if (!linker->elf) {
         pr_warn_elf("failed to create ELF object");
         return -EINVAL;
     }
 
     /* ELF header */
     linker->elf_hdr = elf64_newehdr(linker->elf);
     if (!linker->elf_hdr) {
         pr_warn_elf("failed to create ELF header");
         return -EINVAL;
     }
 
     linker->elf_hdr->e_machine = EM_BPF;
     linker->elf_hdr->e_type = ET_REL;
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2LSB;
 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
     linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2MSB;
 #else
 #error "Unknown __BYTE_ORDER__"
 #endif
 
     /* STRTAB */
     /* initialize strset with an empty string to conform to ELF */
     linker->strtab_strs = strset__new(INT_MAX, "", sizeof(""));
     if (libbpf_get_error(linker->strtab_strs))
         return libbpf_get_error(linker->strtab_strs);
 
     sec = add_dst_sec(linker, ".strtab");
     if (!sec)
         return -ENOMEM;
 
     sec->scn = elf_newscn(linker->elf);
     if (!sec->scn) {
         pr_warn_elf("failed to create STRTAB section");
         return -EINVAL;
     }
 
     sec->shdr = elf64_getshdr(sec->scn);
     if (!sec->shdr)
         return -EINVAL;
 
     sec->data = elf_newdata(sec->scn);
     if (!sec->data) {
         pr_warn_elf("failed to create STRTAB data");
         return -EINVAL;
     }
 
     str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
     if (str_off < 0)
         return str_off;
 
     sec->sec_idx = elf_ndxscn(sec->scn);
     linker->elf_hdr->e_shstrndx = sec->sec_idx;
     linker->strtab_sec_idx = sec->sec_idx;
 
     sec->shdr->sh_name = str_off;
     sec->shdr->sh_type = SHT_STRTAB;
     sec->shdr->sh_flags = SHF_STRINGS;
     sec->shdr->sh_offset = 0;
     sec->shdr->sh_link = 0;
     sec->shdr->sh_info = 0;
     sec->shdr->sh_addralign = 1;
     sec->shdr->sh_size = sec->sec_sz = 0;
     sec->shdr->sh_entsize = 0;
 
     /* SYMTAB */
     sec = add_dst_sec(linker, ".symtab");
     if (!sec)
         return -ENOMEM;
 
     sec->scn = elf_newscn(linker->elf);
     if (!sec->scn) {
         pr_warn_elf("failed to create SYMTAB section");
         return -EINVAL;
     }
 
     sec->shdr = elf64_getshdr(sec->scn);
     if (!sec->shdr)
         return -EINVAL;
 
     sec->data = elf_newdata(sec->scn);
     if (!sec->data) {
         pr_warn_elf("failed to create SYMTAB data");
         return -EINVAL;
     }
 
     str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
     if (str_off < 0)
         return str_off;
 
     sec->sec_idx = elf_ndxscn(sec->scn);
     linker->symtab_sec_idx = sec->sec_idx;
 
     sec->shdr->sh_name = str_off;
     sec->shdr->sh_type = SHT_SYMTAB;
     sec->shdr->sh_flags = 0;
     sec->shdr->sh_offset = 0;
     sec->shdr->sh_link = linker->strtab_sec_idx;
     /* sh_info should be one greater than the index of the last local
      * symbol (i.e., binding is STB_LOCAL). But why and who cares?
      */
     sec->shdr->sh_info = 0;
     sec->shdr->sh_addralign = 8;
     sec->shdr->sh_entsize = sizeof(Elf64_Sym);
 
     /* .BTF */
     linker->btf = btf__new_empty();
     err = libbpf_get_error(linker->btf);
     if (err)
         return err;
 
     /* add the special all-zero symbol */
     init_sym = add_new_sym(linker, NULL);
     if (!init_sym)
         return -EINVAL;
 
     init_sym->st_name = 0;
     init_sym->st_info = 0;
     init_sym->st_other = 0;
     init_sym->st_shndx = SHN_UNDEF;
     init_sym->st_value = 0;
     init_sym->st_size = 0;
 
     return 0;
 }
 
 int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
              const struct bpf_linker_file_opts *opts)
 {
     struct src_obj obj = {};
     int err = 0;
 
     if (!OPTS_VALID(opts, bpf_linker_file_opts))
         return libbpf_err(-EINVAL);
 
     if (!linker->elf)
         return libbpf_err(-EINVAL);
 
     err = err ?: linker_load_obj_file(linker, filename, opts, &obj);
     err = err ?: linker_append_sec_data(linker, &obj);
     err = err ?: linker_append_elf_syms(linker, &obj);
     err = err ?: linker_append_elf_relos(linker, &obj);
     err = err ?: linker_append_btf(linker, &obj);
     err = err ?: linker_append_btf_ext(linker, &obj);
 
     /* free up src_obj resources */
     free(obj.btf_type_map);
     btf__free(obj.btf);
     btf_ext__free(obj.btf_ext);
     free(obj.secs);
     free(obj.sym_map);
     if (obj.elf)
         elf_end(obj.elf);
     if (obj.fd >= 0)
         close(obj.fd);
 
     return libbpf_err(err);
 }
 
 static bool is_dwarf_sec_name(const char *name)
 {
     /* approximation, but the actual list is too long */
     return strncmp(name, ".debug_", sizeof(".debug_") - 1) == 0;
 }
 
 static bool is_ignored_sec(struct src_sec *sec)
 {
     Elf64_Shdr *shdr = sec->shdr;
     const char *name = sec->sec_name;
 
     /* no special handling of .strtab */
     if (shdr->sh_type == SHT_STRTAB)
         return true;
 
     /* ignore .llvm_addrsig section as well */
     if (shdr->sh_type == SHT_LLVM_ADDRSIG)
         return true;
 
     /* no subprograms will lead to an empty .text section, ignore it */
     if (shdr->sh_type == SHT_PROGBITS && shdr->sh_size == 0 &&
         strcmp(sec->sec_name, ".text") == 0)
         return true;
 
     /* DWARF sections */
     if (is_dwarf_sec_name(sec->sec_name))
         return true;
 
     if (strncmp(name, ".rel", sizeof(".rel") - 1) == 0) {
         name += sizeof(".rel") - 1;
         /* DWARF section relocations */
         if (is_dwarf_sec_name(name))
             return true;
 
         /* .BTF and .BTF.ext don't need relocations */
         if (strcmp(name, BTF_ELF_SEC) == 0 ||
             strcmp(name, BTF_EXT_ELF_SEC) == 0)
             return true;
     }
 
     return false;
 }
 
 static struct src_sec *add_src_sec(struct src_obj *obj, const char *sec_name)
 {
     struct src_sec *secs = obj->secs, *sec;
     size_t new_cnt = obj->sec_cnt ? obj->sec_cnt + 1 : 2;
 
     secs = libbpf_reallocarray(secs, new_cnt, sizeof(*secs));
     if (!secs)
         return NULL;
 
     /* zero out newly allocated memory */
     memset(secs + obj->sec_cnt, 0, (new_cnt - obj->sec_cnt) * sizeof(*secs));
 
     obj->secs = secs;
     obj->sec_cnt = new_cnt;
 
     sec = &obj->secs[new_cnt - 1];
     sec->id = new_cnt - 1;
     sec->sec_name = sec_name;
 
     return sec;
 }
 
 static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
                 const struct bpf_linker_file_opts *opts,
                 struct src_obj *obj)
 {
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     const int host_endianness = ELFDATA2LSB;
 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
     const int host_endianness = ELFDATA2MSB;
 #else
 #error "Unknown __BYTE_ORDER__"
 #endif
     int err = 0;
     Elf_Scn *scn;
     Elf_Data *data;
     Elf64_Ehdr *ehdr;
     Elf64_Shdr *shdr;
     struct src_sec *sec;
 
     pr_debug("linker: adding object file '%s'...\n", filename);
 
     obj->filename = filename;
 
     obj->fd = open(filename, O_RDONLY | O_CLOEXEC);
     if (obj->fd < 0) {
         err = -errno;
         pr_warn("failed to open file '%s': %d\n", filename, err);
         return err;
     }
     obj->elf = elf_begin(obj->fd, ELF_C_READ_MMAP, NULL);
     if (!obj->elf) {
         err = -errno;
         pr_warn_elf("failed to parse ELF file '%s'", filename);
         return err;
     }
 
     /* Sanity check ELF file high-level properties */
     ehdr = elf64_getehdr(obj->elf);
     if (!ehdr) {
         err = -errno;
         pr_warn_elf("failed to get ELF header for %s", filename);
         return err;
     }
     if (ehdr->e_ident[EI_DATA] != host_endianness) {
         err = -EOPNOTSUPP;
         pr_warn_elf("unsupported byte order of ELF file %s", filename);
         return err;
     }
     if (ehdr->e_type != ET_REL
         || ehdr->e_machine != EM_BPF
         || ehdr->e_ident[EI_CLASS] != ELFCLASS64) {
         err = -EOPNOTSUPP;
         pr_warn_elf("unsupported kind of ELF file %s", filename);
         return err;
     }
 
     if (elf_getshdrstrndx(obj->elf, &obj->shstrs_sec_idx)) {
         err = -errno;
         pr_warn_elf("failed to get SHSTRTAB section index for %s", filename);
         return err;
     }
 
     scn = NULL;
     while ((scn = elf_nextscn(obj->elf, scn)) != NULL) {
         size_t sec_idx = elf_ndxscn(scn);
         const char *sec_name;
 
         shdr = elf64_getshdr(scn);
         if (!shdr) {
             err = -errno;
             pr_warn_elf("failed to get section #%zu header for %s",
                     sec_idx, filename);
             return err;
         }
 
         sec_name = elf_strptr(obj->elf, obj->shstrs_sec_idx, shdr->sh_name);
         if (!sec_name) {
             err = -errno;
             pr_warn_elf("failed to get section #%zu name for %s",
                     sec_idx, filename);
             return err;
         }
 
         data = elf_getdata(scn, 0);
         if (!data) {
             err = -errno;
             pr_warn_elf("failed to get section #%zu (%s) data from %s",
                     sec_idx, sec_name, filename);
             return err;
         }
 
         sec = add_src_sec(obj, sec_name);
         if (!sec)
             return -ENOMEM;
 
         sec->scn = scn;
         sec->shdr = shdr;
         sec->data = data;
         sec->sec_idx = elf_ndxscn(scn);
 
         if (is_ignored_sec(sec)) {
             sec->skipped = true;
             continue;
         }
 
         switch (shdr->sh_type) {
         case SHT_SYMTAB:
             if (obj->symtab_sec_idx) {
                 err = -EOPNOTSUPP;
                 pr_warn("multiple SYMTAB sections found, not supported\n");
                 return err;
             }
             obj->symtab_sec_idx = sec_idx;
             break;
         case SHT_STRTAB:
             /* we'll construct our own string table */
             break;
         case SHT_PROGBITS:
             if (strcmp(sec_name, BTF_ELF_SEC) == 0) {
                 obj->btf = btf__new(data->d_buf, shdr->sh_size);
                 err = libbpf_get_error(obj->btf);
                 if (err) {
                     pr_warn("failed to parse .BTF from %s: %d\n", filename, err);
                     return err;
                 }
                 sec->skipped = true;
                 continue;
             }
             if (strcmp(sec_name, BTF_EXT_ELF_SEC) == 0) {
                 obj->btf_ext = btf_ext__new(data->d_buf, shdr->sh_size);
                 err = libbpf_get_error(obj->btf_ext);
                 if (err) {
                     pr_warn("failed to parse .BTF.ext from '%s': %d\n", filename, err);
                     return err;
                 }
                 sec->skipped = true;
                 continue;
             }
 
             /* data & code */
             break;
         case SHT_NOBITS:
             /* BSS */
             break;
         case SHT_REL:
             /* relocations */
             break;
         default:
             pr_warn("unrecognized section #%zu (%s) in %s\n",
                 sec_idx, sec_name, filename);
             err = -EINVAL;
             return err;
         }
     }
 
     err = err ?: linker_sanity_check_elf(obj);
     err = err ?: linker_sanity_check_btf(obj);
     err = err ?: linker_sanity_check_btf_ext(obj);
     err = err ?: linker_fixup_btf(obj);
 
     return err;
 }
 
 static int linker_sanity_check_elf(struct src_obj *obj)
 {
     struct src_sec *sec;
     int i, err;
 
     if (!obj->symtab_sec_idx) {
         pr_warn("ELF is missing SYMTAB section in %s\n", obj->filename);
         return -EINVAL;
     }
     if (!obj->shstrs_sec_idx) {
         pr_warn("ELF is missing section headers STRTAB section in %s\n", obj->filename);
         return -EINVAL;
     }
 
     for (i = 1; i < obj->sec_cnt; i++) {
         sec = &obj->secs[i];
 
         if (sec->sec_name[0] == '\0') {
             pr_warn("ELF section #%zu has empty name in %s\n", sec->sec_idx, obj->filename);
             return -EINVAL;
         }
 
         if (sec->shdr->sh_addralign && !is_pow_of_2(sec->shdr->sh_addralign))
             return -EINVAL;
         if (sec->shdr->sh_addralign != sec->data->d_align)
             return -EINVAL;
 
         if (sec->shdr->sh_size != sec->data->d_size)
             return -EINVAL;
 
         switch (sec->shdr->sh_type) {
         case SHT_SYMTAB:
             err = linker_sanity_check_elf_symtab(obj, sec);
             if (err)
                 return err;
             break;
         case SHT_STRTAB:
             break;
         case SHT_PROGBITS:
             if (sec->shdr->sh_flags & SHF_EXECINSTR) {
                 if (sec->shdr->sh_size % sizeof(struct bpf_insn) != 0)
                     return -EINVAL;
             }
             break;
         case SHT_NOBITS:
             break;
         case SHT_REL:
             err = linker_sanity_check_elf_relos(obj, sec);
             if (err)
                 return err;
             break;
         case SHT_LLVM_ADDRSIG:
             break;
         default:
             pr_warn("ELF section #%zu (%s) has unrecognized type %zu in %s\n",
                 sec->sec_idx, sec->sec_name, (size_t)sec->shdr->sh_type, obj->filename);
             return -EINVAL;
         }
     }
 
     return 0;
 }
 
 static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec)
 {
     struct src_sec *link_sec;
     Elf64_Sym *sym;
     int i, n;
 
     if (sec->shdr->sh_entsize != sizeof(Elf64_Sym))
         return -EINVAL;
     if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
         return -EINVAL;
 
     if (!sec->shdr->sh_link || sec->shdr->sh_link >= obj->sec_cnt) {
         pr_warn("ELF SYMTAB section #%zu points to missing STRTAB section #%zu in %s\n",
             sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
         return -EINVAL;
     }
     link_sec = &obj->secs[sec->shdr->sh_link];
     if (link_sec->shdr->sh_type != SHT_STRTAB) {
         pr_warn("ELF SYMTAB section #%zu points to invalid STRTAB section #%zu in %s\n",
             sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
         return -EINVAL;
     }
 
     n = sec->shdr->sh_size / sec->shdr->sh_entsize;
     sym = sec->data->d_buf;
     for (i = 0; i < n; i++, sym++) {
         int sym_type = ELF64_ST_TYPE(sym->st_info);
         int sym_bind = ELF64_ST_BIND(sym->st_info);
         int sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
 
         if (i == 0) {
             if (sym->st_name != 0 || sym->st_info != 0
                 || sym->st_other != 0 || sym->st_shndx != 0
                 || sym->st_value != 0 || sym->st_size != 0) {
                 pr_warn("ELF sym #0 is invalid in %s\n", obj->filename);
                 return -EINVAL;
             }
             continue;
         }
         if (sym_bind != STB_LOCAL && sym_bind != STB_GLOBAL && sym_bind != STB_WEAK) {
             pr_warn("ELF sym #%d in section #%zu has unsupported symbol binding %d\n",
                 i, sec->sec_idx, sym_bind);
             return -EINVAL;
         }
         if (sym_vis != STV_DEFAULT && sym_vis != STV_HIDDEN) {
             pr_warn("ELF sym #%d in section #%zu has unsupported symbol visibility %d\n",
                 i, sec->sec_idx, sym_vis);
             return -EINVAL;
         }
         if (sym->st_shndx == 0) {
             if (sym_type != STT_NOTYPE || sym_bind == STB_LOCAL
                 || sym->st_value != 0 || sym->st_size != 0) {
                 pr_warn("ELF sym #%d is invalid extern symbol in %s\n",
                     i, obj->filename);
 
                 return -EINVAL;
             }
             continue;
         }
         if (sym->st_shndx < SHN_LORESERVE && sym->st_shndx >= obj->sec_cnt) {
             pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n",
                 i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
             return -EINVAL;
         }
         if (sym_type == STT_SECTION) {
             if (sym->st_value != 0)
                 return -EINVAL;
             continue;
         }
     }
 
     return 0;
 }
 
 static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec)
 {
     struct src_sec *link_sec, *sym_sec;
     Elf64_Rel *relo;
     int i, n;
 
     if (sec->shdr->sh_entsize != sizeof(Elf64_Rel))
         return -EINVAL;
     if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
         return -EINVAL;
 
     /* SHT_REL's sh_link should point to SYMTAB */
     if (sec->shdr->sh_link != obj->symtab_sec_idx) {
         pr_warn("ELF relo section #%zu points to invalid SYMTAB section #%zu in %s\n",
             sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
         return -EINVAL;
     }
 
     /* SHT_REL's sh_info points to relocated section */
     if (!sec->shdr->sh_info || sec->shdr->sh_info >= obj->sec_cnt) {
         pr_warn("ELF relo section #%zu points to missing section #%zu in %s\n",
             sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
         return -EINVAL;
     }
     link_sec = &obj->secs[sec->shdr->sh_info];
 
     /* .rel<secname> -> <secname> pattern is followed */
     if (strncmp(sec->sec_name, ".rel", sizeof(".rel") - 1) != 0
         || strcmp(sec->sec_name + sizeof(".rel") - 1, link_sec->sec_name) != 0) {
         pr_warn("ELF relo section #%zu name has invalid name in %s\n",
             sec->sec_idx, obj->filename);
         return -EINVAL;
     }
 
     /* don't further validate relocations for ignored sections */
     if (link_sec->skipped)
         return 0;
 
     /* relocatable section is data or instructions */
     if (link_sec->shdr->sh_type != SHT_PROGBITS && link_sec->shdr->sh_type != SHT_NOBITS) {
         pr_warn("ELF relo section #%zu points to invalid section #%zu in %s\n",
             sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
         return -EINVAL;
     }
 
     /* check sanity of each relocation */
     n = sec->shdr->sh_size / sec->shdr->sh_entsize;
     relo = sec->data->d_buf;
     sym_sec = &obj->secs[obj->symtab_sec_idx];
     for (i = 0; i < n; i++, relo++) {
         size_t sym_idx = ELF64_R_SYM(relo->r_info);
         size_t sym_type = ELF64_R_TYPE(relo->r_info);
 
         if (sym_type != R_BPF_64_64 && sym_type != R_BPF_64_32 &&
             sym_type != R_BPF_64_ABS64 && sym_type != R_BPF_64_ABS32) {
             pr_warn("ELF relo #%d in section #%zu has unexpected type %zu in %s\n",
                 i, sec->sec_idx, sym_type, obj->filename);
             return -EINVAL;
         }
 
         if (!sym_idx || sym_idx * sizeof(Elf64_Sym) >= sym_sec->shdr->sh_size) {
             pr_warn("ELF relo #%d in section #%zu points to invalid symbol #%zu in %s\n",
                 i, sec->sec_idx, sym_idx, obj->filename);
             return -EINVAL;
         }
 
         if (link_sec->shdr->sh_flags & SHF_EXECINSTR) {
             if (relo->r_offset % sizeof(struct bpf_insn) != 0) {
                 pr_warn("ELF relo #%d in section #%zu points to missing symbol #%zu in %s\n",
                     i, sec->sec_idx, sym_idx, obj->filename);
                 return -EINVAL;
             }
         }
     }
 
     return 0;
 }
 
 static int check_btf_type_id(__u32 *type_id, void *ctx)
 {
     struct btf *btf = ctx;
 
     if (*type_id >= btf__type_cnt(btf))
         return -EINVAL;
 
     return 0;
 }
 
 static int check_btf_str_off(__u32 *str_off, void *ctx)
 {
     struct btf *btf = ctx;
     const char *s;
 
     s = btf__str_by_offset(btf, *str_off);
 
     if (!s)
         return -EINVAL;
 
     return 0;
 }
 
 static int linker_sanity_check_btf(struct src_obj *obj)
 {
     struct btf_type *t;
     int i, n, err = 0;
 
     if (!obj->btf)
         return 0;
 
     n = btf__type_cnt(obj->btf);
     for (i = 1; i < n; i++) {
         t = btf_type_by_id(obj->btf, i);
 
         err = err ?: btf_type_visit_type_ids(t, check_btf_type_id, obj->btf);
         err = err ?: btf_type_visit_str_offs(t, check_btf_str_off, obj->btf);
         if (err)
             return err;
     }
 
     return 0;
 }
 
 static int linker_sanity_check_btf_ext(struct src_obj *obj)
 {
     int err = 0;
 
     if (!obj->btf_ext)
         return 0;
 
     /* can't use .BTF.ext without .BTF */
     if (!obj->btf)
         return -EINVAL;
 
     err = err ?: btf_ext_visit_type_ids(obj->btf_ext, check_btf_type_id, obj->btf);
     err = err ?: btf_ext_visit_str_offs(obj->btf_ext, check_btf_str_off, obj->btf);
     if (err)
         return err;
 
     return 0;
 }
 
 static int init_sec(struct bpf_linker *linker, struct dst_sec *dst_sec, struct src_sec *src_sec)
 {
     Elf_Scn *scn;
     Elf_Data *data;
     Elf64_Shdr *shdr;
     int name_off;
 
     dst_sec->sec_sz = 0;
     dst_sec->sec_idx = 0;
     dst_sec->ephemeral = src_sec->ephemeral;
 
     /* ephemeral sections are just thin section shells lacking most parts */
     if (src_sec->ephemeral)
         return 0;
 
     scn = elf_newscn(linker->elf);
     if (!scn)
         return -ENOMEM;
     data = elf_newdata(scn);
     if (!data)
         return -ENOMEM;
     shdr = elf64_getshdr(scn);
     if (!shdr)
         return -ENOMEM;
 
     dst_sec->scn = scn;
     dst_sec->shdr = shdr;
     dst_sec->data = data;
     dst_sec->sec_idx = elf_ndxscn(scn);
 
     name_off = strset__add_str(linker->strtab_strs, src_sec->sec_name);
     if (name_off < 0)
         return name_off;
 
     shdr->sh_name = name_off;
     shdr->sh_type = src_sec->shdr->sh_type;
     shdr->sh_flags = src_sec->shdr->sh_flags;
     shdr->sh_size = 0;
     /* sh_link and sh_info have different meaning for different types of
      * sections, so we leave it up to the caller code to fill them in, if
      * necessary
      */
     shdr->sh_link = 0;
     shdr->sh_info = 0;
     shdr->sh_addralign = src_sec->shdr->sh_addralign;
     shdr->sh_entsize = src_sec->shdr->sh_entsize;
 
     data->d_type = src_sec->data->d_type;
     data->d_size = 0;
     data->d_buf = NULL;
     data->d_align = src_sec->data->d_align;
     data->d_off = 0;
 
     return 0;
 }
 
 static struct dst_sec *find_dst_sec_by_name(struct bpf_linker *linker, const char *sec_name)
 {
     struct dst_sec *sec;
     int i;
 
     for (i = 1; i < linker->sec_cnt; i++) {
         sec = &linker->secs[i];
 
         if (strcmp(sec->sec_name, sec_name) == 0)
             return sec;
     }
 
     return NULL;
 }
 
 static bool secs_match(struct dst_sec *dst, struct src_sec *src)
 {
     if (dst->ephemeral || src->ephemeral)
         return true;
 
     if (dst->shdr->sh_type != src->shdr->sh_type) {
         pr_warn("sec %s types mismatch\n", dst->sec_name);
         return false;
     }
     if (dst->shdr->sh_flags != src->shdr->sh_flags) {
         pr_warn("sec %s flags mismatch\n", dst->sec_name);
         return false;
     }
     if (dst->shdr->sh_entsize != src->shdr->sh_entsize) {
         pr_warn("sec %s entsize mismatch\n", dst->sec_name);
         return false;
     }
 
     return true;
 }
 
 static bool sec_content_is_same(struct dst_sec *dst_sec, struct src_sec *src_sec)
 {
     if (dst_sec->sec_sz != src_sec->shdr->sh_size)
         return false;
     if (memcmp(dst_sec->raw_data, src_sec->data->d_buf, dst_sec->sec_sz) != 0)
         return false;
     return true;
 }
 
 static int extend_sec(struct bpf_linker *linker, struct dst_sec *dst, struct src_sec *src)
 {
     void *tmp;
     size_t dst_align, src_align;
     size_t dst_align_sz, dst_final_sz;
     int err;
 
     /* Ephemeral source section doesn't contribute anything to ELF
      * section data.
      */
     if (src->ephemeral)
         return 0;
 
     /* Some sections (like .maps) can contain both externs (and thus be
      * ephemeral) and non-externs (map definitions). So it's possible that
      * it has to be "upgraded" from ephemeral to non-ephemeral when the
      * first non-ephemeral entity appears. In such case, we add ELF
      * section, data, etc.
      */
     if (dst->ephemeral) {
         err = init_sec(linker, dst, src);
         if (err)
             return err;
     }
 
     dst_align = dst->shdr->sh_addralign;
     src_align = src->shdr->sh_addralign;
     if (dst_align == 0)
         dst_align = 1;
     if (dst_align < src_align)
         dst_align = src_align;
 
     dst_align_sz = (dst->sec_sz + dst_align - 1) / dst_align * dst_align;
 
     /* no need to re-align final size */
     dst_final_sz = dst_align_sz + src->shdr->sh_size;
 
     if (src->shdr->sh_type != SHT_NOBITS) {
         tmp = realloc(dst->raw_data, dst_final_sz);
         if (!tmp)
             return -ENOMEM;
         dst->raw_data = tmp;
 
         /* pad dst section, if it's alignment forced size increase */
         memset(dst->raw_data + dst->sec_sz, 0, dst_align_sz - dst->sec_sz);
         /* now copy src data at a properly aligned offset */
         memcpy(dst->raw_data + dst_align_sz, src->data->d_buf, src->shdr->sh_size);
     }
 
     dst->sec_sz = dst_final_sz;
     dst->shdr->sh_size = dst_final_sz;
     dst->data->d_size = dst_final_sz;
 
     dst->shdr->sh_addralign = dst_align;
     dst->data->d_align = dst_align;
 
     src->dst_off = dst_align_sz;
 
     return 0;
 }
 
 static bool is_data_sec(struct src_sec *sec)
 {
     if (!sec || sec->skipped)
         return false;
     /* ephemeral sections are data sections, e.g., .kconfig, .ksyms */
     if (sec->ephemeral)
         return true;
     return sec->shdr->sh_type == SHT_PROGBITS || sec->shdr->sh_type == SHT_NOBITS;
 }
 
 static bool is_relo_sec(struct src_sec *sec)
 {
     if (!sec || sec->skipped || sec->ephemeral)
         return false;
     return sec->shdr->sh_type == SHT_REL;
 }
 
 static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj)
 {
     int i, err;
 
     for (i = 1; i < obj->sec_cnt; i++) {
         struct src_sec *src_sec;
         struct dst_sec *dst_sec;
 
         src_sec = &obj->secs[i];
         if (!is_data_sec(src_sec))
             continue;
 
         dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
         if (!dst_sec) {
             dst_sec = add_dst_sec(linker, src_sec->sec_name);
             if (!dst_sec)
                 return -ENOMEM;
             err = init_sec(linker, dst_sec, src_sec);
             if (err) {
                 pr_warn("failed to init section '%s'\n", src_sec->sec_name);
                 return err;
             }
         } else {
             if (!secs_match(dst_sec, src_sec)) {
                 pr_warn("ELF sections %s are incompatible\n", src_sec->sec_name);
                 return -1;
             }
 
             /* "license" and "version" sections are deduped */
             if (strcmp(src_sec->sec_name, "license") == 0
                 || strcmp(src_sec->sec_name, "version") == 0) {
                 if (!sec_content_is_same(dst_sec, src_sec)) {
                     pr_warn("non-identical contents of section '%s' are not supported\n", src_sec->sec_name);
                     return -EINVAL;
                 }
                 src_sec->skipped = true;
                 src_sec->dst_id = dst_sec->id;
                 continue;
             }
         }
 
         /* record mapped section index */
         src_sec->dst_id = dst_sec->id;
 
         err = extend_sec(linker, dst_sec, src_sec);
         if (err)
             return err;
     }
 
     return 0;
 }
 
 static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj)
 {
     struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
     Elf64_Sym *sym = symtab->data->d_buf;
     int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize, err;
     int str_sec_idx = symtab->shdr->sh_link;
     const char *sym_name;
 
     obj->sym_map = calloc(n + 1, sizeof(*obj->sym_map));
     if (!obj->sym_map)
         return -ENOMEM;
 
     for (i = 0; i < n; i++, sym++) {
         /* We already validated all-zero symbol #0 and we already
          * appended it preventively to the final SYMTAB, so skip it.
          */
         if (i == 0)
             continue;
 
         sym_name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
         if (!sym_name) {
             pr_warn("can't fetch symbol name for symbol #%d in '%s'\n", i, obj->filename);
             return -EINVAL;
         }
 
         err = linker_append_elf_sym(linker, obj, sym, sym_name, i);
         if (err)
             return err;
     }
 
     return 0;
 }
 
 static Elf64_Sym *get_sym_by_idx(struct bpf_linker *linker, size_t sym_idx)
 {
     struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
     Elf64_Sym *syms = symtab->raw_data;
 
     return &syms[sym_idx];
 }
 
 static struct glob_sym *find_glob_sym(struct bpf_linker *linker, const char *sym_name)
 {
     struct glob_sym *glob_sym;
     const char *name;
     int i;
 
     for (i = 0; i < linker->glob_sym_cnt; i++) {
         glob_sym = &linker->glob_syms[i];
         name = strset__data(linker->strtab_strs) + glob_sym->name_off;
 
         if (strcmp(name, sym_name) == 0)
             return glob_sym;
     }
 
     return NULL;
 }
 
 static struct glob_sym *add_glob_sym(struct bpf_linker *linker)
 {
     struct glob_sym *syms, *sym;
 
     syms = libbpf_reallocarray(linker->glob_syms, linker->glob_sym_cnt + 1,
                    sizeof(*linker->glob_syms));
     if (!syms)
         return NULL;
 
     sym = &syms[linker->glob_sym_cnt];
     memset(sym, 0, sizeof(*sym));
     sym->var_idx = -1;
 
     linker->glob_syms = syms;
     linker->glob_sym_cnt++;
 
     return sym;
 }
 
 static bool glob_sym_btf_matches(const char *sym_name, bool exact,
                  const struct btf *btf1, __u32 id1,
                  const struct btf *btf2, __u32 id2)
 {
     const struct btf_type *t1, *t2;
     bool is_static1, is_static2;
     const char *n1, *n2;
     int i, n;
 
 recur:
     n1 = n2 = NULL;
     t1 = skip_mods_and_typedefs(btf1, id1, &id1);
     t2 = skip_mods_and_typedefs(btf2, id2, &id2);
 
     /* check if only one side is FWD, otherwise handle with common logic */
     if (!exact && btf_is_fwd(t1) != btf_is_fwd(t2)) {
         n1 = btf__str_by_offset(btf1, t1->name_off);
         n2 = btf__str_by_offset(btf2, t2->name_off);
         if (strcmp(n1, n2) != 0) {
             pr_warn("global '%s': incompatible forward declaration names '%s' and '%s'\n",
                 sym_name, n1, n2);
             return false;
         }
         /* validate if FWD kind matches concrete kind */
         if (btf_is_fwd(t1)) {
             if (btf_kflag(t1) && btf_is_union(t2))
                 return true;
             if (!btf_kflag(t1) && btf_is_struct(t2))
                 return true;
             pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
                 sym_name, btf_kflag(t1) ? "union" : "struct", btf_kind_str(t2));
         } else {
             if (btf_kflag(t2) && btf_is_union(t1))
                 return true;
             if (!btf_kflag(t2) && btf_is_struct(t1))
                 return true;
             pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
                 sym_name, btf_kflag(t2) ? "union" : "struct", btf_kind_str(t1));
         }
         return false;
     }
 
     if (btf_kind(t1) != btf_kind(t2)) {
         pr_warn("global '%s': incompatible BTF kinds %s and %s\n",
             sym_name, btf_kind_str(t1), btf_kind_str(t2));
         return false;
     }
 
     switch (btf_kind(t1)) {
     case BTF_KIND_STRUCT:
     case BTF_KIND_UNION:
     case BTF_KIND_ENUM:
     case BTF_KIND_ENUM64:
     case BTF_KIND_FWD:
     case BTF_KIND_FUNC:
     case BTF_KIND_VAR:
         n1 = btf__str_by_offset(btf1, t1->name_off);
         n2 = btf__str_by_offset(btf2, t2->name_off);
         if (strcmp(n1, n2) != 0) {
             pr_warn("global '%s': incompatible %s names '%s' and '%s'\n",
                 sym_name, btf_kind_str(t1), n1, n2);
             return false;
         }
         break;
     default:
         break;
     }
 
     switch (btf_kind(t1)) {
     case BTF_KIND_UNKN: /* void */
     case BTF_KIND_FWD:
         return true;
     case BTF_KIND_INT:
     case BTF_KIND_FLOAT:
     case BTF_KIND_ENUM:
     case BTF_KIND_ENUM64:
         /* ignore encoding for int and enum values for enum */
         if (t1->size != t2->size) {
             pr_warn("global '%s': incompatible %s '%s' size %u and %u\n",
                 sym_name, btf_kind_str(t1), n1, t1->size, t2->size);
             return false;
         }
         return true;
     case BTF_KIND_PTR:
         /* just validate overall shape of the referenced type, so no
          * contents comparison for struct/union, and allowd fwd vs
          * struct/union
          */
         exact = false;
         id1 = t1->type;
         id2 = t2->type;
         goto recur;
     case BTF_KIND_ARRAY:
         /* ignore index type and array size */
         id1 = btf_array(t1)->type;
         id2 = btf_array(t2)->type;
         goto recur;
     case BTF_KIND_FUNC:
         /* extern and global linkages are compatible */
         is_static1 = btf_func_linkage(t1) == BTF_FUNC_STATIC;
         is_static2 = btf_func_linkage(t2) == BTF_FUNC_STATIC;
         if (is_static1 != is_static2) {
             pr_warn("global '%s': incompatible func '%s' linkage\n", sym_name, n1);
             return false;
         }
 
         id1 = t1->type;
         id2 = t2->type;
         goto recur;
     case BTF_KIND_VAR:
         /* extern and global linkages are compatible */
         is_static1 = btf_var(t1)->linkage == BTF_VAR_STATIC;
         is_static2 = btf_var(t2)->linkage == BTF_VAR_STATIC;
         if (is_static1 != is_static2) {
             pr_warn("global '%s': incompatible var '%s' linkage\n", sym_name, n1);
             return false;
         }
 
         id1 = t1->type;
         id2 = t2->type;
         goto recur;
     case BTF_KIND_STRUCT:
     case BTF_KIND_UNION: {
         const struct btf_member *m1, *m2;
 
         if (!exact)
             return true;
 
         if (btf_vlen(t1) != btf_vlen(t2)) {
             pr_warn("global '%s': incompatible number of %s fields %u and %u\n",
                 sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
             return false;
         }
 
         n = btf_vlen(t1);
         m1 = btf_members(t1);
         m2 = btf_members(t2);
         for (i = 0; i < n; i++, m1++, m2++) {
             n1 = btf__str_by_offset(btf1, m1->name_off);
             n2 = btf__str_by_offset(btf2, m2->name_off);
             if (strcmp(n1, n2) != 0) {
                 pr_warn("global '%s': incompatible field #%d names '%s' and '%s'\n",
                     sym_name, i, n1, n2);
                 return false;
             }
             if (m1->offset != m2->offset) {
                 pr_warn("global '%s': incompatible field #%d ('%s') offsets\n",
                     sym_name, i, n1);
                 return false;
             }
             if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
                 return false;
         }
 
         return true;
     }
     case BTF_KIND_FUNC_PROTO: {
         const struct btf_param *m1, *m2;
 
         if (btf_vlen(t1) != btf_vlen(t2)) {
             pr_warn("global '%s': incompatible number of %s params %u and %u\n",
                 sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
             return false;
         }
 
         n = btf_vlen(t1);
         m1 = btf_params(t1);
         m2 = btf_params(t2);
         for (i = 0; i < n; i++, m1++, m2++) {
             /* ignore func arg names */
             if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
                 return false;
         }
 
         /* now check return type as well */
         id1 = t1->type;
         id2 = t2->type;
         goto recur;
     }
 
     /* skip_mods_and_typedefs() make this impossible */
     case BTF_KIND_TYPEDEF:
     case BTF_KIND_VOLATILE:
     case BTF_KIND_CONST:
     case BTF_KIND_RESTRICT:
     /* DATASECs are never compared with each other */
     case BTF_KIND_DATASEC:
     default:
         pr_warn("global '%s': unsupported BTF kind %s\n",
             sym_name, btf_kind_str(t1));
         return false;
     }
 }
 
 static bool map_defs_match(const char *sym_name,
                const struct btf *main_btf,
                const struct btf_map_def *main_def,
                const struct btf_map_def *main_inner_def,
                const struct btf *extra_btf,
                const struct btf_map_def *extra_def,
                const struct btf_map_def *extra_inner_def)
 {
     const char *reason;
 
     if (main_def->map_type != extra_def->map_type) {
         reason = "type";
         goto mismatch;
     }
 
     /* check key type/size match */
     if (main_def->key_size != extra_def->key_size) {
         reason = "key_size";
         goto mismatch;
     }
     if (!!main_def->key_type_id != !!extra_def->key_type_id) {
         reason = "key type";
         goto mismatch;
     }
     if ((main_def->parts & MAP_DEF_KEY_TYPE)
          && !glob_sym_btf_matches(sym_name, true /*exact*/,
                       main_btf, main_def->key_type_id,
                       extra_btf, extra_def->key_type_id)) {
         reason = "key type";
         goto mismatch;
     }
 
     /* validate value type/size match */
     if (main_def->value_size != extra_def->value_size) {
         reason = "value_size";
         goto mismatch;
     }
     if (!!main_def->value_type_id != !!extra_def->value_type_id) {
         reason = "value type";
         goto mismatch;
     }
     if ((main_def->parts & MAP_DEF_VALUE_TYPE)
          && !glob_sym_btf_matches(sym_name, true /*exact*/,
                       main_btf, main_def->value_type_id,
                       extra_btf, extra_def->value_type_id)) {
         reason = "key type";
         goto mismatch;
     }
 
     if (main_def->max_entries != extra_def->max_entries) {
         reason = "max_entries";
         goto mismatch;
     }
     if (main_def->map_flags != extra_def->map_flags) {
         reason = "map_flags";
         goto mismatch;
     }
     if (main_def->numa_node != extra_def->numa_node) {
         reason = "numa_node";
         goto mismatch;
     }
     if (main_def->pinning != extra_def->pinning) {
         reason = "pinning";
         goto mismatch;
     }
 
     if ((main_def->parts & MAP_DEF_INNER_MAP) != (extra_def->parts & MAP_DEF_INNER_MAP)) {
         reason = "inner map";
         goto mismatch;
     }
 
     if (main_def->parts & MAP_DEF_INNER_MAP) {
         char inner_map_name[128];
 
         snprintf(inner_map_name, sizeof(inner_map_name), "%s.inner", sym_name);
 
         return map_defs_match(inner_map_name,
                       main_btf, main_inner_def, NULL,
                       extra_btf, extra_inner_def, NULL);
     }
 
     return true;
 
 mismatch:
     pr_warn("global '%s': map %s mismatch\n", sym_name, reason);
     return false;
 }
 
 static bool glob_map_defs_match(const char *sym_name,
                 struct bpf_linker *linker, struct glob_sym *glob_sym,
                 struct src_obj *obj, Elf64_Sym *sym, int btf_id)
 {
     struct btf_map_def dst_def = {}, dst_inner_def = {};
     struct btf_map_def src_def = {}, src_inner_def = {};
     const struct btf_type *t;
     int err;
 
     t = btf__type_by_id(obj->btf, btf_id);
     if (!btf_is_var(t)) {
         pr_warn("global '%s': invalid map definition type [%d]\n", sym_name, btf_id);
         return false;
     }
     t = skip_mods_and_typedefs(obj->btf, t->type, NULL);
 
     err = parse_btf_map_def(sym_name, obj->btf, t, true /*strict*/, &src_def, &src_inner_def);
     if (err) {
         pr_warn("global '%s': invalid map definition\n", sym_name);
         return false;
     }
 
     /* re-parse existing map definition */
     t = btf__type_by_id(linker->btf, glob_sym->btf_id);
     t = skip_mods_and_typedefs(linker->btf, t->type, NULL);
     err = parse_btf_map_def(sym_name, linker->btf, t, true /*strict*/, &dst_def, &dst_inner_def);
     if (err) {
         /* this should not happen, because we already validated it */
         pr_warn("global '%s': invalid dst map definition\n", sym_name);
         return false;
     }
 
     /* Currently extern map definition has to be complete and match
      * concrete map definition exactly. This restriction might be lifted
      * in the future.
      */
     return map_defs_match(sym_name, linker->btf, &dst_def, &dst_inner_def,
                   obj->btf, &src_def, &src_inner_def);
 }
 
 static bool glob_syms_match(const char *sym_name,
                 struct bpf_linker *linker, struct glob_sym *glob_sym,
                 struct src_obj *obj, Elf64_Sym *sym, size_t sym_idx, int btf_id)
 {
     const struct btf_type *src_t;
 
     /* if we are dealing with externs, BTF types describing both global
      * and extern VARs/FUNCs should be completely present in all files
      */
     if (!glob_sym->btf_id || !btf_id) {
         pr_warn("BTF info is missing for global symbol '%s'\n", sym_name);
         return false;
     }
 
     src_t = btf__type_by_id(obj->btf, btf_id);
     if (!btf_is_var(src_t) && !btf_is_func(src_t)) {
         pr_warn("only extern variables and functions are supported, but got '%s' for '%s'\n",
             btf_kind_str(src_t), sym_name);
         return false;
     }
 
     /* deal with .maps definitions specially */
     if (glob_sym->sec_id && strcmp(linker->secs[glob_sym->sec_id].sec_name, MAPS_ELF_SEC) == 0)
         return glob_map_defs_match(sym_name, linker, glob_sym, obj, sym, btf_id);
 
     if (!glob_sym_btf_matches(sym_name, true /*exact*/,
                   linker->btf, glob_sym->btf_id, obj->btf, btf_id))
         return false;
 
     return true;
 }
 
 static bool btf_is_non_static(const struct btf_type *t)
 {
     return (btf_is_var(t) && btf_var(t)->linkage != BTF_VAR_STATIC)
            || (btf_is_func(t) && btf_func_linkage(t) != BTF_FUNC_STATIC);
 }
 
 static int find_glob_sym_btf(struct src_obj *obj, Elf64_Sym *sym, const char *sym_name,
                  int *out_btf_sec_id, int *out_btf_id)
 {
     int i, j, n, m, btf_id = 0;
     const struct btf_type *t;
     const struct btf_var_secinfo *vi;
     const char *name;
 
     if (!obj->btf) {
         pr_warn("failed to find BTF info for object '%s'\n", obj->filename);
         return -EINVAL;
     }
 
     n = btf__type_cnt(obj->btf);
     for (i = 1; i < n; i++) {
         t = btf__type_by_id(obj->btf, i);
 
         /* some global and extern FUNCs and VARs might not be associated with any
          * DATASEC, so try to detect them in the same pass
          */
         if (btf_is_non_static(t)) {
             name = btf__str_by_offset(obj->btf, t->name_off);
             if (strcmp(name, sym_name) != 0)
                 continue;
 
             /* remember and still try to find DATASEC */
             btf_id = i;
             continue;
         }
 
         if (!btf_is_datasec(t))
             continue;
 
         vi = btf_var_secinfos(t);
         for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
             t = btf__type_by_id(obj->btf, vi->type);
             name = btf__str_by_offset(obj->btf, t->name_off);
 
             if (strcmp(name, sym_name) != 0)
                 continue;
             if (btf_is_var(t) && btf_var(t)->linkage == BTF_VAR_STATIC)
                 continue;
             if (btf_is_func(t) && btf_func_linkage(t) == BTF_FUNC_STATIC)
                 continue;
 
             if (btf_id && btf_id != vi->type) {
                 pr_warn("global/extern '%s' BTF is ambiguous: both types #%d and #%u match\n",
                     sym_name, btf_id, vi->type);
                 return -EINVAL;
             }
 
             *out_btf_sec_id = i;
             *out_btf_id = vi->type;
 
             return 0;
         }
     }
 
     /* free-floating extern or global FUNC */
     if (btf_id) {
         *out_btf_sec_id = 0;
         *out_btf_id = btf_id;
         return 0;
     }
 
     pr_warn("failed to find BTF info for global/extern symbol '%s'\n", sym_name);
     return -ENOENT;
 }
 
 static struct src_sec *find_src_sec_by_name(struct src_obj *obj, const char *sec_name)
 {
     struct src_sec *sec;
     int i;
 
     for (i = 1; i < obj->sec_cnt; i++) {
         sec = &obj->secs[i];
 
         if (strcmp(sec->sec_name, sec_name) == 0)
             return sec;
     }
 
     return NULL;
 }
 
 static int complete_extern_btf_info(struct btf *dst_btf, int dst_id,
                     struct btf *src_btf, int src_id)
 {
     struct btf_type *dst_t = btf_type_by_id(dst_btf, dst_id);
     struct btf_type *src_t = btf_type_by_id(src_btf, src_id);
     struct btf_param *src_p, *dst_p;
     const char *s;
     int i, n, off;
 
     /* We already made sure that source and destination types (FUNC or
      * VAR) match in terms of types and argument names.
      */
     if (btf_is_var(dst_t)) {
         btf_var(dst_t)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
         return 0;
     }
 
     dst_t->info = btf_type_info(BTF_KIND_FUNC, BTF_FUNC_GLOBAL, 0);
 
     /* now onto FUNC_PROTO types */
     src_t = btf_type_by_id(src_btf, src_t->type);
     dst_t = btf_type_by_id(dst_btf, dst_t->type);
 
     /* Fill in all the argument names, which for extern FUNCs are missing.
      * We'll end up with two copies of FUNCs/VARs for externs, but that
      * will be taken care of by BTF dedup at the very end.
      * It might be that BTF types for extern in one file has less/more BTF
      * information (e.g., FWD instead of full STRUCT/UNION information),
      * but that should be (in most cases, subject to BTF dedup rules)
      * handled and resolved by BTF dedup algorithm as well, so we won't
      * worry about it. Our only job is to make sure that argument names
      * are populated on both sides, otherwise BTF dedup will pedantically
      * consider them different.
      */
     src_p = btf_params(src_t);
     dst_p = btf_params(dst_t);
     for (i = 0, n = btf_vlen(dst_t); i < n; i++, src_p++, dst_p++) {
         if (!src_p->name_off)
             continue;
 
         /* src_btf has more complete info, so add name to dst_btf */
         s = btf__str_by_offset(src_btf, src_p->name_off);
         off = btf__add_str(dst_btf, s);
         if (off < 0)
             return off;
         dst_p->name_off = off;
     }
     return 0;
 }
 
 static void sym_update_bind(Elf64_Sym *sym, int sym_bind)
 {
     sym->st_info = ELF64_ST_INFO(sym_bind, ELF64_ST_TYPE(sym->st_info));
 }
 
 static void sym_update_type(Elf64_Sym *sym, int sym_type)
 {
     sym->st_info = ELF64_ST_INFO(ELF64_ST_BIND(sym->st_info), sym_type);
 }
 
 static void sym_update_visibility(Elf64_Sym *sym, int sym_vis)
 {
     /* libelf doesn't provide setters for ST_VISIBILITY,
      * but it is stored in the lower 2 bits of st_other
      */
     sym->st_other &= ~0x03;
     sym->st_other |= sym_vis;
 }
 
 static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
                  Elf64_Sym *sym, const char *sym_name, int src_sym_idx)
 {
     struct src_sec *src_sec = NULL;
     struct dst_sec *dst_sec = NULL;
     struct glob_sym *glob_sym = NULL;
     int name_off, sym_type, sym_bind, sym_vis, err;
     int btf_sec_id = 0, btf_id = 0;
     size_t dst_sym_idx;
     Elf64_Sym *dst_sym;
     bool sym_is_extern;
 
     sym_type = ELF64_ST_TYPE(sym->st_info);
     sym_bind = ELF64_ST_BIND(sym->st_info);
     sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
     sym_is_extern = sym->st_shndx == SHN_UNDEF;
 
     if (sym_is_extern) {
         if (!obj->btf) {
             pr_warn("externs without BTF info are not supported\n");
             return -ENOTSUP;
         }
     } else if (sym->st_shndx < SHN_LORESERVE) {
         src_sec = &obj->secs[sym->st_shndx];
         if (src_sec->skipped)
             return 0;
         dst_sec = &linker->secs[src_sec->dst_id];
 
         /* allow only one STT_SECTION symbol per section */
         if (sym_type == STT_SECTION && dst_sec->sec_sym_idx) {
             obj->sym_map[src_sym_idx] = dst_sec->sec_sym_idx;
             return 0;
         }
     }
 
     if (sym_bind == STB_LOCAL)
         goto add_sym;
 
     /* find matching BTF info */
     err = find_glob_sym_btf(obj, sym, sym_name, &btf_sec_id, &btf_id);
     if (err)
         return err;
 
     if (sym_is_extern && btf_sec_id) {
         const char *sec_name = NULL;
         const struct btf_type *t;
 
         t = btf__type_by_id(obj->btf, btf_sec_id);
         sec_name = btf__str_by_offset(obj->btf, t->name_off);
 
         /* Clang puts unannotated extern vars into
          * '.extern' BTF DATASEC. Treat them the same
          * as unannotated extern funcs (which are
          * currently not put into any DATASECs).
          * Those don't have associated src_sec/dst_sec.
          */
         if (strcmp(sec_name, BTF_EXTERN_SEC) != 0) {
             src_sec = find_src_sec_by_name(obj, sec_name);
             if (!src_sec) {
                 pr_warn("failed to find matching ELF sec '%s'\n", sec_name);
                 return -ENOENT;
             }
             dst_sec = &linker->secs[src_sec->dst_id];
         }
     }
 
     glob_sym = find_glob_sym(linker, sym_name);
     if (glob_sym) {
         /* Preventively resolve to existing symbol. This is
          * needed for further relocation symbol remapping in
          * the next step of linking.
          */
         obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
 
         /* If both symbols are non-externs, at least one of
          * them has to be STB_WEAK, otherwise they are in
          * a conflict with each other.
          */
         if (!sym_is_extern && !glob_sym->is_extern
             && !glob_sym->is_weak && sym_bind != STB_WEAK) {
             pr_warn("conflicting non-weak symbol #%d (%s) definition in '%s'\n",
                 src_sym_idx, sym_name, obj->filename);
             return -EINVAL;
         }
 
         if (!glob_syms_match(sym_name, linker, glob_sym, obj, sym, src_sym_idx, btf_id))
             return -EINVAL;
 
         dst_sym = get_sym_by_idx(linker, glob_sym->sym_idx);
 
         /* If new symbol is strong, then force dst_sym to be strong as
          * well; this way a mix of weak and non-weak extern
          * definitions will end up being strong.
          */
         if (sym_bind == STB_GLOBAL) {
             /* We still need to preserve type (NOTYPE or
              * OBJECT/FUNC, depending on whether the symbol is
              * extern or not)
              */
             sym_update_bind(dst_sym, STB_GLOBAL);
             glob_sym->is_weak = false;
         }
 
         /* Non-default visibility is "contaminating", with stricter
          * visibility overwriting more permissive ones, even if more
          * permissive visibility comes from just an extern definition.
          * Currently only STV_DEFAULT and STV_HIDDEN are allowed and
          * ensured by ELF symbol sanity checks above.
          */
         if (sym_vis > ELF64_ST_VISIBILITY(dst_sym->st_other))
             sym_update_visibility(dst_sym, sym_vis);
 
         /* If the new symbol is extern, then regardless if
          * existing symbol is extern or resolved global, just
          * keep the existing one untouched.
          */
         if (sym_is_extern)
             return 0;
 
         /* If existing symbol is a strong resolved symbol, bail out,
          * because we lost resolution battle have nothing to
          * contribute. We already checked abover that there is no
          * strong-strong conflict. We also already tightened binding
          * and visibility, so nothing else to contribute at that point.
          */
         if (!glob_sym->is_extern && sym_bind == STB_WEAK)
             return 0;
 
         /* At this point, new symbol is strong non-extern,
          * so overwrite glob_sym with new symbol information.
          * Preserve binding and visibility.
          */
         sym_update_type(dst_sym, sym_type);
         dst_sym->st_shndx = dst_sec->sec_idx;
         dst_sym->st_value = src_sec->dst_off + sym->st_value;
         dst_sym->st_size = sym->st_size;
 
         /* see comment below about dst_sec->id vs dst_sec->sec_idx */
         glob_sym->sec_id = dst_sec->id;
         glob_sym->is_extern = false;
 
         if (complete_extern_btf_info(linker->btf, glob_sym->btf_id,
                          obj->btf, btf_id))
             return -EINVAL;
 
         /* request updating VAR's/FUNC's underlying BTF type when appending BTF type */
         glob_sym->underlying_btf_id = 0;
 
         obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
         return 0;
     }
 
 add_sym:
     name_off = strset__add_str(linker->strtab_strs, sym_name);
     if (name_off < 0)
         return name_off;
 
     dst_sym = add_new_sym(linker, &dst_sym_idx);
     if (!dst_sym)
         return -ENOMEM;
 
     dst_sym->st_name = name_off;
     dst_sym->st_info = sym->st_info;
     dst_sym->st_other = sym->st_other;
     dst_sym->st_shndx = dst_sec ? dst_sec->sec_idx : sym->st_shndx;
     dst_sym->st_value = (src_sec ? src_sec->dst_off : 0) + sym->st_value;
     dst_sym->st_size = sym->st_size;
 
     obj->sym_map[src_sym_idx] = dst_sym_idx;
 
     if (sym_type == STT_SECTION && dst_sym) {
         dst_sec->sec_sym_idx = dst_sym_idx;
         dst_sym->st_value = 0;
     }
 
     if (sym_bind != STB_LOCAL) {
         glob_sym = add_glob_sym(linker);
         if (!glob_sym)
             return -ENOMEM;
 
         glob_sym->sym_idx = dst_sym_idx;
         /* we use dst_sec->id (and not dst_sec->sec_idx), because
          * ephemeral sections (.kconfig, .ksyms, etc) don't have
          * sec_idx (as they don't have corresponding ELF section), but
          * still have id. .extern doesn't have even ephemeral section
          * associated with it, so dst_sec->id == dst_sec->sec_idx == 0.
          */
         glob_sym->sec_id = dst_sec ? dst_sec->id : 0;
         glob_sym->name_off = name_off;
         /* we will fill btf_id in during BTF merging step */
         glob_sym->btf_id = 0;
         glob_sym->is_extern = sym_is_extern;
         glob_sym->is_weak = sym_bind == STB_WEAK;
     }
 
     return 0;
 }
 
 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj)
 {
     struct src_sec *src_symtab = &obj->secs[obj->symtab_sec_idx];
     struct dst_sec *dst_symtab;
     int i, err;
 
     for (i = 1; i < obj->sec_cnt; i++) {
         struct src_sec *src_sec, *src_linked_sec;
         struct dst_sec *dst_sec, *dst_linked_sec;
         Elf64_Rel *src_rel, *dst_rel;
         int j, n;
 
         src_sec = &obj->secs[i];
         if (!is_relo_sec(src_sec))
             continue;
 
         /* shdr->sh_info points to relocatable section */
         src_linked_sec = &obj->secs[src_sec->shdr->sh_info];
         if (src_linked_sec->skipped)
             continue;
 
         dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
         if (!dst_sec) {
             dst_sec = add_dst_sec(linker, src_sec->sec_name);
             if (!dst_sec)
                 return -ENOMEM;
             err = init_sec(linker, dst_sec, src_sec);
             if (err) {
                 pr_warn("failed to init section '%s'\n", src_sec->sec_name);
                 return err;
             }
         } else if (!secs_match(dst_sec, src_sec)) {
             pr_warn("sections %s are not compatible\n", src_sec->sec_name);
             return -1;
         }
 
         /* add_dst_sec() above could have invalidated linker->secs */
         dst_symtab = &linker->secs[linker->symtab_sec_idx];
 
         /* shdr->sh_link points to SYMTAB */
         dst_sec->shdr->sh_link = linker->symtab_sec_idx;
 
         /* shdr->sh_info points to relocated section */
         dst_linked_sec = &linker->secs[src_linked_sec->dst_id];
         dst_sec->shdr->sh_info = dst_linked_sec->sec_idx;
 
         src_sec->dst_id = dst_sec->id;
         err = extend_sec(linker, dst_sec, src_sec);
         if (err)
             return err;
 
         src_rel = src_sec->data->d_buf;
         dst_rel = dst_sec->raw_data + src_sec->dst_off;
         n = src_sec->shdr->sh_size / src_sec->shdr->sh_entsize;
         for (j = 0; j < n; j++, src_rel++, dst_rel++) {
             size_t src_sym_idx = ELF64_R_SYM(src_rel->r_info);
             size_t sym_type = ELF64_R_TYPE(src_rel->r_info);
             Elf64_Sym *src_sym, *dst_sym;
             size_t dst_sym_idx;
 
             src_sym_idx = ELF64_R_SYM(src_rel->r_info);
             src_sym = src_symtab->data->d_buf + sizeof(*src_sym) * src_sym_idx;
 
             dst_sym_idx = obj->sym_map[src_sym_idx];
             dst_sym = dst_symtab->raw_data + sizeof(*dst_sym) * dst_sym_idx;
             dst_rel->r_offset += src_linked_sec->dst_off;
             sym_type = ELF64_R_TYPE(src_rel->r_info);
             dst_rel->r_info = ELF64_R_INFO(dst_sym_idx, sym_type);
 
             if (ELF64_ST_TYPE(src_sym->st_info) == STT_SECTION) {
                 struct src_sec *sec = &obj->secs[src_sym->st_shndx];
                 struct bpf_insn *insn;
 
                 if (src_linked_sec->shdr->sh_flags & SHF_EXECINSTR) {
                     /* calls to the very first static function inside
                      * .text section at offset 0 will
                      * reference section symbol, not the
                      * function symbol. Fix that up,
                      * otherwise it won't be possible to
                      * relocate calls to two different
                      * static functions with the same name
                      * (rom two different object files)
                      */
                     insn = dst_linked_sec->raw_data + dst_rel->r_offset;
                     if (insn->code == (BPF_JMP | BPF_CALL))
                         insn->imm += sec->dst_off / sizeof(struct bpf_insn);
                     else
                         insn->imm += sec->dst_off;
                 } else {
                     pr_warn("relocation against STT_SECTION in non-exec section is not supported!\n");
                     return -EINVAL;
                 }
             }
 
         }
     }
 
     return 0;
 }
 
 static Elf64_Sym *find_sym_by_name(struct src_obj *obj, size_t sec_idx,
                    int sym_type, const char *sym_name)
 {
     struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
     Elf64_Sym *sym = symtab->data->d_buf;
     int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize;
     int str_sec_idx = symtab->shdr->sh_link;
     const char *name;
 
     for (i = 0; i < n; i++, sym++) {
         if (sym->st_shndx != sec_idx)
             continue;
         if (ELF64_ST_TYPE(sym->st_info) != sym_type)
             continue;
 
         name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
         if (!name)
             return NULL;
 
         if (strcmp(sym_name, name) != 0)
             continue;
 
         return sym;
     }
 
     return NULL;
 }
 
 static int linker_fixup_btf(struct src_obj *obj)
 {
     const char *sec_name;
     struct src_sec *sec;
     int i, j, n, m;
 
     if (!obj->btf)
         return 0;
 
     n = btf__type_cnt(obj->btf);
     for (i = 1; i < n; i++) {
         struct btf_var_secinfo *vi;
         struct btf_type *t;
 
         t = btf_type_by_id(obj->btf, i);
         if (btf_kind(t) != BTF_KIND_DATASEC)
             continue;
 
         sec_name = btf__str_by_offset(obj->btf, t->name_off);
         sec = find_src_sec_by_name(obj, sec_name);
         if (sec) {
             /* record actual section size, unless ephemeral */
             if (sec->shdr)
                 t->size = sec->shdr->sh_size;
         } else {
             /* BTF can have some sections that are not represented
              * in ELF, e.g., .kconfig, .ksyms, .extern, which are used
              * for special extern variables.
              *
              * For all but one such special (ephemeral)
              * sections, we pre-create "section shells" to be able
              * to keep track of extra per-section metadata later
              * (e.g., those BTF extern variables).
              *
              * .extern is even more special, though, because it
              * contains extern variables that need to be resolved
              * by static linker, not libbpf and kernel. When such
              * externs are resolved, we are going to remove them
              * from .extern BTF section and might end up not
              * needing it at all. Each resolved extern should have
              * matching non-extern VAR/FUNC in other sections.
              *
              * We do support leaving some of the externs
              * unresolved, though, to support cases of building
              * libraries, which will later be linked against final
              * BPF applications. So if at finalization we still
              * see unresolved externs, we'll create .extern
              * section on our own.
              */
             if (strcmp(sec_name, BTF_EXTERN_SEC) == 0)
                 continue;
 
             sec = add_src_sec(obj, sec_name);
             if (!sec)
                 return -ENOMEM;
 
             sec->ephemeral = true;
             sec->sec_idx = 0; /* will match UNDEF shndx in ELF */
         }
 
         /* remember ELF section and its BTF type ID match */
         sec->sec_type_id = i;
 
         /* fix up variable offsets */
         vi = btf_var_secinfos(t);
         for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
             const struct btf_type *vt = btf__type_by_id(obj->btf, vi->type);
             const char *var_name = btf__str_by_offset(obj->btf, vt->name_off);
             int var_linkage = btf_var(vt)->linkage;
             Elf64_Sym *sym;
 
             /* no need to patch up static or extern vars */
             if (var_linkage != BTF_VAR_GLOBAL_ALLOCATED)
                 continue;
 
             sym = find_sym_by_name(obj, sec->sec_idx, STT_OBJECT, var_name);
             if (!sym) {
                 pr_warn("failed to find symbol for variable '%s' in section '%s'\n", var_name, sec_name);
                 return -ENOENT;
             }
 
             vi->offset = sym->st_value;
         }
     }
 
     return 0;
 }
 
 static int remap_type_id(__u32 *type_id, void *ctx)
 {
     int *id_map = ctx;
     int new_id = id_map[*type_id];
 
     /* Error out if the type wasn't remapped. Ignore VOID which stays VOID. */
     if (new_id == 0 && *type_id != 0) {
         pr_warn("failed to find new ID mapping for original BTF type ID %u\n", *type_id);
         return -EINVAL;
     }
 
     *type_id = id_map[*type_id];
 
     return 0;
 }
 
 static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
 {
     const struct btf_type *t;
     int i, j, n, start_id, id;
     const char *name;
 
     if (!obj->btf)
         return 0;
 
     start_id = btf__type_cnt(linker->btf);
     n = btf__type_cnt(obj->btf);
 
     obj->btf_type_map = calloc(n + 1, sizeof(int));
     if (!obj->btf_type_map)
         return -ENOMEM;
 
     for (i = 1; i < n; i++) {
         struct glob_sym *glob_sym = NULL;
 
         t = btf__type_by_id(obj->btf, i);
 
         /* DATASECs are handled specially below */
         if (btf_kind(t) == BTF_KIND_DATASEC)
             continue;
 
         if (btf_is_non_static(t)) {
             /* there should be glob_sym already */
             name = btf__str_by_offset(obj->btf, t->name_off);
             glob_sym = find_glob_sym(linker, name);
 
             /* VARs without corresponding glob_sym are those that
              * belong to skipped/deduplicated sections (i.e.,
              * license and version), so just skip them
              */
             if (!glob_sym)
                 continue;
 
             /* linker_append_elf_sym() might have requested
              * updating underlying type ID, if extern was resolved
              * to strong symbol or weak got upgraded to non-weak
              */
             if (glob_sym->underlying_btf_id == 0)
                 glob_sym->underlying_btf_id = -t->type;
 
             /* globals from previous object files that match our
              * VAR/FUNC already have a corresponding associated
              * BTF type, so just make sure to use it
              */
             if (glob_sym->btf_id) {
                 /* reuse existing BTF type for global var/func */
                 obj->btf_type_map[i] = glob_sym->btf_id;
                 continue;
             }
         }
 
         id = btf__add_type(linker->btf, obj->btf, t);
         if (id < 0) {
             pr_warn("failed to append BTF type #%d from file '%s'\n", i, obj->filename);
             return id;
         }
 
         obj->btf_type_map[i] = id;
 
         /* record just appended BTF type for var/func */
         if (glob_sym) {
             glob_sym->btf_id = id;
             glob_sym->underlying_btf_id = -t->type;
         }
     }
 
     /* remap all the types except DATASECs */
     n = btf__type_cnt(linker->btf);
     for (i = start_id; i < n; i++) {
         struct btf_type *dst_t = btf_type_by_id(linker->btf, i);
 
         if (btf_type_visit_type_ids(dst_t, remap_type_id, obj->btf_type_map))
             return -EINVAL;
     }
 
     /* Rewrite VAR/FUNC underlying types (i.e., FUNC's FUNC_PROTO and VAR's
      * actual type), if necessary
      */
     for (i = 0; i < linker->glob_sym_cnt; i++) {
         struct glob_sym *glob_sym = &linker->glob_syms[i];
         struct btf_type *glob_t;
 
         if (glob_sym->underlying_btf_id >= 0)
             continue;
 
         glob_sym->underlying_btf_id = obj->btf_type_map[-glob_sym->underlying_btf_id];
 
         glob_t = btf_type_by_id(linker->btf, glob_sym->btf_id);
         glob_t->type = glob_sym->underlying_btf_id;
     }
 
     /* append DATASEC info */
     for (i = 1; i < obj->sec_cnt; i++) {
         struct src_sec *src_sec;
         struct dst_sec *dst_sec;
         const struct btf_var_secinfo *src_var;
         struct btf_var_secinfo *dst_var;
 
         src_sec = &obj->secs[i];
         if (!src_sec->sec_type_id || src_sec->skipped)
             continue;
         dst_sec = &linker->secs[src_sec->dst_id];
 
         /* Mark section as having BTF regardless of the presence of
          * variables. In some cases compiler might generate empty BTF
          * with no variables information. E.g., when promoting local
          * array/structure variable initial values and BPF object
          * file otherwise has no read-only static variables in
          * .rodata. We need to preserve such empty BTF and just set
          * correct section size.
          */
         dst_sec->has_btf = true;
 
         t = btf__type_by_id(obj->btf, src_sec->sec_type_id);
         src_var = btf_var_secinfos(t);
         n = btf_vlen(t);
         for (j = 0; j < n; j++, src_var++) {
             void *sec_vars = dst_sec->sec_vars;
             int new_id = obj->btf_type_map[src_var->type];
             struct glob_sym *glob_sym = NULL;
 
             t = btf_type_by_id(linker->btf, new_id);
             if (btf_is_non_static(t)) {
                 name = btf__str_by_offset(linker->btf, t->name_off);
                 glob_sym = find_glob_sym(linker, name);
                 if (glob_sym->sec_id != dst_sec->id) {
                     pr_warn("global '%s': section mismatch %d vs %d\n",
                         name, glob_sym->sec_id, dst_sec->id);
                     return -EINVAL;
                 }
             }
 
             /* If there is already a member (VAR or FUNC) mapped
              * to the same type, don't add a duplicate entry.
              * This will happen when multiple object files define
              * the same extern VARs/FUNCs.
              */
             if (glob_sym && glob_sym->var_idx >= 0) {
                 __s64 sz;
 
                 dst_var = &dst_sec->sec_vars[glob_sym->var_idx];
                 /* Because underlying BTF type might have
                  * changed, so might its size have changed, so
                  * re-calculate and update it in sec_var.
                  */
                 sz = btf__resolve_size(linker->btf, glob_sym->underlying_btf_id);
                 if (sz < 0) {
                     pr_warn("global '%s': failed to resolve size of underlying type: %d\n",
                         name, (int)sz);
                     return -EINVAL;
                 }
                 dst_var->size = sz;
                 continue;
             }
 
             sec_vars = libbpf_reallocarray(sec_vars,
                                dst_sec->sec_var_cnt + 1,
                                sizeof(*dst_sec->sec_vars));
             if (!sec_vars)
                 return -ENOMEM;
 
             dst_sec->sec_vars = sec_vars;
             dst_sec->sec_var_cnt++;
 
             dst_var = &dst_sec->sec_vars[dst_sec->sec_var_cnt - 1];
             dst_var->type = obj->btf_type_map[src_var->type];
             dst_var->size = src_var->size;
             dst_var->offset = src_sec->dst_off + src_var->offset;
 
             if (glob_sym)
                 glob_sym->var_idx = dst_sec->sec_var_cnt - 1;
         }
     }
 
     return 0;
 }
 
 static void *add_btf_ext_rec(struct btf_ext_sec_data *ext_data, const void *src_rec)
 {
     void *tmp;
 
     tmp = libbpf_reallocarray(ext_data->recs, ext_data->rec_cnt + 1, ext_data->rec_sz);
     if (!tmp)
         return NULL;
     ext_data->recs = tmp;
 
     tmp += ext_data->rec_cnt * ext_data->rec_sz;
     memcpy(tmp, src_rec, ext_data->rec_sz);
 
     ext_data->rec_cnt++;
 
     return tmp;
 }
 
 static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj)
 {
     const struct btf_ext_info_sec *ext_sec;
     const char *sec_name, *s;
     struct src_sec *src_sec;
     struct dst_sec *dst_sec;
     int rec_sz, str_off, i;
 
     if (!obj->btf_ext)
         return 0;
 
     rec_sz = obj->btf_ext->func_info.rec_size;
     for_each_btf_ext_sec(&obj->btf_ext->func_info, ext_sec) {
         struct bpf_func_info_min *src_rec, *dst_rec;
 
         sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
         src_sec = find_src_sec_by_name(obj, sec_name);
         if (!src_sec) {
             pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
             return -EINVAL;
         }
         dst_sec = &linker->secs[src_sec->dst_id];
 
         if (dst_sec->func_info.rec_sz == 0)
             dst_sec->func_info.rec_sz = rec_sz;
         if (dst_sec->func_info.rec_sz != rec_sz) {
             pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
             return -EINVAL;
         }
 
         for_each_btf_ext_rec(&obj->btf_ext->func_info, ext_sec, i, src_rec) {
             dst_rec = add_btf_ext_rec(&dst_sec->func_info, src_rec);
             if (!dst_rec)
                 return -ENOMEM;
 
             dst_rec->insn_off += src_sec->dst_off;
             dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
         }
     }
 
     rec_sz = obj->btf_ext->line_info.rec_size;
     for_each_btf_ext_sec(&obj->btf_ext->line_info, ext_sec) {
         struct bpf_line_info_min *src_rec, *dst_rec;
 
         sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
         src_sec = find_src_sec_by_name(obj, sec_name);
         if (!src_sec) {
             pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
             return -EINVAL;
         }
         dst_sec = &linker->secs[src_sec->dst_id];
 
         if (dst_sec->line_info.rec_sz == 0)
             dst_sec->line_info.rec_sz = rec_sz;
         if (dst_sec->line_info.rec_sz != rec_sz) {
             pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
             return -EINVAL;
         }
 
         for_each_btf_ext_rec(&obj->btf_ext->line_info, ext_sec, i, src_rec) {
             dst_rec = add_btf_ext_rec(&dst_sec->line_info, src_rec);
             if (!dst_rec)
                 return -ENOMEM;
 
             dst_rec->insn_off += src_sec->dst_off;
 
             s = btf__str_by_offset(obj->btf, src_rec->file_name_off);
             str_off = btf__add_str(linker->btf, s);
             if (str_off < 0)
                 return -ENOMEM;
             dst_rec->file_name_off = str_off;
 
             s = btf__str_by_offset(obj->btf, src_rec->line_off);
             str_off = btf__add_str(linker->btf, s);
             if (str_off < 0)
                 return -ENOMEM;
             dst_rec->line_off = str_off;
 
             /* dst_rec->line_col is fine */
         }
     }
 
     rec_sz = obj->btf_ext->core_relo_info.rec_size;
     for_each_btf_ext_sec(&obj->btf_ext->core_relo_info, ext_sec) {
         struct bpf_core_relo *src_rec, *dst_rec;
 
         sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
         src_sec = find_src_sec_by_name(obj, sec_name);
         if (!src_sec) {
             pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
             return -EINVAL;
         }
         dst_sec = &linker->secs[src_sec->dst_id];
 
         if (dst_sec->core_relo_info.rec_sz == 0)
             dst_sec->core_relo_info.rec_sz = rec_sz;
         if (dst_sec->core_relo_info.rec_sz != rec_sz) {
             pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
             return -EINVAL;
         }
 
         for_each_btf_ext_rec(&obj->btf_ext->core_relo_info, ext_sec, i, src_rec) {
             dst_rec = add_btf_ext_rec(&dst_sec->core_relo_info, src_rec);
             if (!dst_rec)
                 return -ENOMEM;
 
             dst_rec->insn_off += src_sec->dst_off;
             dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
 
             s = btf__str_by_offset(obj->btf, src_rec->access_str_off);
             str_off = btf__add_str(linker->btf, s);
             if (str_off < 0)
                 return -ENOMEM;
             dst_rec->access_str_off = str_off;
 
             /* dst_rec->kind is fine */
         }
     }
 
     return 0;
 }
 
 int bpf_linker__finalize(struct bpf_linker *linker)
 {
     struct dst_sec *sec;
     size_t strs_sz;
     const void *strs;
     int err, i;
 
     if (!linker->elf)
         return libbpf_err(-EINVAL);
 
     err = finalize_btf(linker);
     if (err)
         return libbpf_err(err);
 
     /* Finalize strings */
     strs_sz = strset__data_size(linker->strtab_strs);
     strs = strset__data(linker->strtab_strs);
 
     sec = &linker->secs[linker->strtab_sec_idx];
     sec->data->d_align = 1;
     sec->data->d_off = 0LL;
     sec->data->d_buf = (void *)strs;
     sec->data->d_type = ELF_T_BYTE;
     sec->data->d_size = strs_sz;
     sec->shdr->sh_size = strs_sz;
 
     for (i = 1; i < linker->sec_cnt; i++) {
         sec = &linker->secs[i];
 
         /* STRTAB is handled specially above */
         if (sec->sec_idx == linker->strtab_sec_idx)
             continue;
 
         /* special ephemeral sections (.ksyms, .kconfig, etc) */
         if (!sec->scn)
             continue;
 
         sec->data->d_buf = sec->raw_data;
     }
 
     /* Finalize ELF layout */
     if (elf_update(linker->elf, ELF_C_NULL) < 0) {
         err = -errno;
         pr_warn_elf("failed to finalize ELF layout");
         return libbpf_err(err);
     }
 
     /* Write out final ELF contents */
     if (elf_update(linker->elf, ELF_C_WRITE) < 0) {
         err = -errno;
         pr_warn_elf("failed to write ELF contents");
         return libbpf_err(err);
     }
 
     elf_end(linker->elf);
     close(linker->fd);
 
     linker->elf = NULL;
     linker->fd = -1;
 
     return 0;
 }
 
 static int emit_elf_data_sec(struct bpf_linker *linker, const char *sec_name,
                  size_t align, const void *raw_data, size_t raw_sz)
 {
     Elf_Scn *scn;
     Elf_Data *data;
     Elf64_Shdr *shdr;
     int name_off;
 
     name_off = strset__add_str(linker->strtab_strs, sec_name);
     if (name_off < 0)
         return name_off;
 
     scn = elf_newscn(linker->elf);
     if (!scn)
         return -ENOMEM;
     data = elf_newdata(scn);
     if (!data)
         return -ENOMEM;
     shdr = elf64_getshdr(scn);
     if (!shdr)
         return -EINVAL;
 
     shdr->sh_name = name_off;
     shdr->sh_type = SHT_PROGBITS;
     shdr->sh_flags = 0;
     shdr->sh_size = raw_sz;
     shdr->sh_link = 0;
     shdr->sh_info = 0;
     shdr->sh_addralign = align;
     shdr->sh_entsize = 0;
 
     data->d_type = ELF_T_BYTE;
     data->d_size = raw_sz;
     data->d_buf = (void *)raw_data;
     data->d_align = align;
     data->d_off = 0;
 
     return 0;
 }
 
 static int finalize_btf(struct bpf_linker *linker)
 {
     LIBBPF_OPTS(btf_dedup_opts, opts);
     struct btf *btf = linker->btf;
     const void *raw_data;
     int i, j, id, err;
     __u32 raw_sz;
 
     /* bail out if no BTF data was produced */
     if (btf__type_cnt(linker->btf) == 1)
         return 0;
 
     for (i = 1; i < linker->sec_cnt; i++) {
         struct dst_sec *sec = &linker->secs[i];
 
         if (!sec->has_btf)
             continue;
 
         id = btf__add_datasec(btf, sec->sec_name, sec->sec_sz);
         if (id < 0) {
             pr_warn("failed to add consolidated BTF type for datasec '%s': %d\n",
                 sec->sec_name, id);
             return id;
         }
 
         for (j = 0; j < sec->sec_var_cnt; j++) {
             struct btf_var_secinfo *vi = &sec->sec_vars[j];
 
             if (btf__add_datasec_var_info(btf, vi->type, vi->offset, vi->size))
                 return -EINVAL;
         }
     }
 
     err = finalize_btf_ext(linker);
     if (err) {
         pr_warn(".BTF.ext generation failed: %d\n", err);
         return err;
     }
 
     opts.btf_ext = linker->btf_ext;
     err = btf__dedup(linker->btf, &opts);
     if (err) {
         pr_warn("BTF dedup failed: %d\n", err);
         return err;
     }
 
     /* Emit .BTF section */
     raw_data = btf__raw_data(linker->btf, &raw_sz);
     if (!raw_data)
         return -ENOMEM;
 
     err = emit_elf_data_sec(linker, BTF_ELF_SEC, 8, raw_data, raw_sz);
     if (err) {
         pr_warn("failed to write out .BTF ELF section: %d\n", err);
         return err;
     }
 
     /* Emit .BTF.ext section */
     if (linker->btf_ext) {
         raw_data = btf_ext__get_raw_data(linker->btf_ext, &raw_sz);
         if (!raw_data)
             return -ENOMEM;
 
         err = emit_elf_data_sec(linker, BTF_EXT_ELF_SEC, 8, raw_data, raw_sz);
         if (err) {
             pr_warn("failed to write out .BTF.ext ELF section: %d\n", err);
             return err;
         }
     }
 
     return 0;
 }
 
 static int emit_btf_ext_data(struct bpf_linker *linker, void *output,
                  const char *sec_name, struct btf_ext_sec_data *sec_data)
 {
     struct btf_ext_info_sec *sec_info;
     void *cur = output;
     int str_off;
     size_t sz;
 
     if (!sec_data->rec_cnt)
         return 0;
 
     str_off = btf__add_str(linker->btf, sec_name);
     if (str_off < 0)
         return -ENOMEM;
 
     sec_info = cur;
     sec_info->sec_name_off = str_off;
     sec_info->num_info = sec_data->rec_cnt;
     cur += sizeof(struct btf_ext_info_sec);
 
     sz = sec_data->rec_cnt * sec_data->rec_sz;
     memcpy(cur, sec_data->recs, sz);
     cur += sz;
 
     return cur - output;
 }
 
 static int finalize_btf_ext(struct bpf_linker *linker)
 {
     size_t funcs_sz = 0, lines_sz = 0, core_relos_sz = 0, total_sz = 0;
     size_t func_rec_sz = 0, line_rec_sz = 0, core_relo_rec_sz = 0;
     struct btf_ext_header *hdr;
     void *data, *cur;
     int i, err, sz;
 
     /* validate that all sections have the same .BTF.ext record sizes
      * and calculate total data size for each type of data (func info,
      * line info, core relos)
      */
     for (i = 1; i < linker->sec_cnt; i++) {
         struct dst_sec *sec = &linker->secs[i];
 
         if (sec->func_info.rec_cnt) {
             if (func_rec_sz == 0)
                 func_rec_sz = sec->func_info.rec_sz;
             if (func_rec_sz != sec->func_info.rec_sz) {
                 pr_warn("mismatch in func_info record size %zu != %u\n",
                     func_rec_sz, sec->func_info.rec_sz);
                 return -EINVAL;
             }
 
             funcs_sz += sizeof(struct btf_ext_info_sec) + func_rec_sz * sec->func_info.rec_cnt;
         }
         if (sec->line_info.rec_cnt) {
             if (line_rec_sz == 0)
                 line_rec_sz = sec->line_info.rec_sz;
             if (line_rec_sz != sec->line_info.rec_sz) {
                 pr_warn("mismatch in line_info record size %zu != %u\n",
                     line_rec_sz, sec->line_info.rec_sz);
                 return -EINVAL;
             }
 
             lines_sz += sizeof(struct btf_ext_info_sec) + line_rec_sz * sec->line_info.rec_cnt;
         }
         if (sec->core_relo_info.rec_cnt) {
             if (core_relo_rec_sz == 0)
                 core_relo_rec_sz = sec->core_relo_info.rec_sz;
             if (core_relo_rec_sz != sec->core_relo_info.rec_sz) {
                 pr_warn("mismatch in core_relo_info record size %zu != %u\n",
                     core_relo_rec_sz, sec->core_relo_info.rec_sz);
                 return -EINVAL;
             }
 
             core_relos_sz += sizeof(struct btf_ext_info_sec) + core_relo_rec_sz * sec->core_relo_info.rec_cnt;
         }
     }
 
     if (!funcs_sz && !lines_sz && !core_relos_sz)
         return 0;
 
     total_sz += sizeof(struct btf_ext_header);
     if (funcs_sz) {
         funcs_sz += sizeof(__u32); /* record size prefix */
         total_sz += funcs_sz;
     }
     if (lines_sz) {
         lines_sz += sizeof(__u32); /* record size prefix */
         total_sz += lines_sz;
     }
     if (core_relos_sz) {
         core_relos_sz += sizeof(__u32); /* record size prefix */
         total_sz += core_relos_sz;
     }
 
     cur = data = calloc(1, total_sz);
     if (!data)
         return -ENOMEM;
 
     hdr = cur;
     hdr->magic = BTF_MAGIC;
     hdr->version = BTF_VERSION;
     hdr->flags = 0;
     hdr->hdr_len = sizeof(struct btf_ext_header);
     cur += sizeof(struct btf_ext_header);
 
     /* All offsets are in bytes relative to the end of this header */
     hdr->func_info_off = 0;
     hdr->func_info_len = funcs_sz;
     hdr->line_info_off = funcs_sz;
     hdr->line_info_len = lines_sz;
     hdr->core_relo_off = funcs_sz + lines_sz;
     hdr->core_relo_len = core_relos_sz;
 
     if (funcs_sz) {
         *(__u32 *)cur = func_rec_sz;
         cur += sizeof(__u32);
 
         for (i = 1; i < linker->sec_cnt; i++) {
             struct dst_sec *sec = &linker->secs[i];
 
             sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->func_info);
             if (sz < 0) {
                 err = sz;
                 goto out;
             }
 
             cur += sz;
         }
     }
 
     if (lines_sz) {
         *(__u32 *)cur = line_rec_sz;
         cur += sizeof(__u32);
 
         for (i = 1; i < linker->sec_cnt; i++) {
             struct dst_sec *sec = &linker->secs[i];
 
             sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->line_info);
             if (sz < 0) {
                 err = sz;
                 goto out;
             }
 
             cur += sz;
         }
     }
 
     if (core_relos_sz) {
         *(__u32 *)cur = core_relo_rec_sz;
         cur += sizeof(__u32);
 
         for (i = 1; i < linker->sec_cnt; i++) {
             struct dst_sec *sec = &linker->secs[i];
 
             sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->core_relo_info);
             if (sz < 0) {
                 err = sz;
                 goto out;
             }
 
             cur += sz;
         }
     }
 
     linker->btf_ext = btf_ext__new(data, total_sz);
     err = libbpf_get_error(linker->btf_ext);
     if (err) {
         linker->btf_ext = NULL;
         pr_warn("failed to parse final .BTF.ext data: %d\n", err);
         goto out;
     }
 
 out:
     free(data);
     return err;
 }