tools/lib/bpf/linker.c

   1 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
   2 /*
   3  * BPF static linker
   4  *
   5  * Copyright (c) 2021 Facebook
   6  */
   7 #include <stdbool.h>
   8 #include <stddef.h>
   9 #include <stdio.h>
  10 #include <stdlib.h>
  11 #include <string.h>
  12 #include <unistd.h>
  13 #include <errno.h>
  14 #include <linux/err.h>
  15 #include <linux/btf.h>
  16 #include <elf.h>
  17 #include <libelf.h>
  18 #include <fcntl.h>
  19 #include "libbpf.h"
  20 #include "btf.h"
  21 #include "libbpf_internal.h"
  22 #include "strset.h"
  23
  24 #define BTF_EXTERN_SEC ".extern"
  25
  26 struct src_sec {
  27         const char *sec_name;
  28         /* positional (not necessarily ELF) index in an array of sections */
  29         int id;
  30         /* positional (not necessarily ELF) index of a matching section in a final object file */
  31         int dst_id;
  32         /* section data offset in a matching output section */
  33         int dst_off;
  34         /* whether section is omitted from the final ELF file */
  35         bool skipped;
  36         /* whether section is an ephemeral section, not mapped to an ELF section */
  37         bool ephemeral;
  38
  39         /* ELF info */
  40         size_t sec_idx;
  41         Elf_Scn *scn;
  42         Elf64_Shdr *shdr;
  43         Elf_Data *data;
  44
  45         /* corresponding BTF DATASEC type ID */
  46         int sec_type_id;
  47 };
  48
  49 struct src_obj {
  50         const char *filename;
  51         int fd;
  52         Elf *elf;
  53         /* Section header strings section index */
  54         size_t shstrs_sec_idx;
  55         /* SYMTAB section index */
  56         size_t symtab_sec_idx;
  57
  58         struct btf *btf;
  59         struct btf_ext *btf_ext;
  60
  61         /* List of sections (including ephemeral). Slot zero is unused. */
  62         struct src_sec *secs;
  63         int sec_cnt;
  64
  65         /* mapping of symbol indices from src to dst ELF */
  66         int *sym_map;
  67         /* mapping from the src BTF type IDs to dst ones */
  68         int *btf_type_map;
  69 };
  70
  71 /* single .BTF.ext data section */
  72 struct btf_ext_sec_data {
  73         size_t rec_cnt;
  74         __u32 rec_sz;
  75         void *recs;
  76 };
  77
  78 struct glob_sym {
  79         /* ELF symbol index */
  80         int sym_idx;
  81         /* associated section id for .ksyms, .kconfig, etc, but not .extern */
  82         int sec_id;
  83         /* extern name offset in STRTAB */
  84         int name_off;
  85         /* optional associated BTF type ID */
  86         int btf_id;
  87         /* BTF type ID to which VAR/FUNC type is pointing to; used for
  88          * rewriting types when extern VAR/FUNC is resolved to a concrete
  89          * definition
  90          */
  91         int underlying_btf_id;
  92         /* sec_var index in the corresponding dst_sec, if exists */
  93         int var_idx;
  94
  95         /* extern or resolved/global symbol */
  96         bool is_extern;
  97         /* weak or strong symbol, never goes back from strong to weak */
  98         bool is_weak;
  99 };
 100
 101 struct dst_sec {
 102         char *sec_name;
 103         /* positional (not necessarily ELF) index in an array of sections */
 104         int id;
 105
 106         bool ephemeral;
 107
 108         /* ELF info */
 109         size_t sec_idx;
 110         Elf_Scn *scn;
 111         Elf64_Shdr *shdr;
 112         Elf_Data *data;
 113
 114         /* final output section size */
 115         int sec_sz;
 116         /* final output contents of the section */
 117         void *raw_data;
 118
 119         /* corresponding STT_SECTION symbol index in SYMTAB */
 120         int sec_sym_idx;
 121
 122         /* section's DATASEC variable info, emitted on BTF finalization */
 123         bool has_btf;
 124         int sec_var_cnt;
 125         struct btf_var_secinfo *sec_vars;
 126
 127         /* section's .BTF.ext data */
 128         struct btf_ext_sec_data func_info;
 129         struct btf_ext_sec_data line_info;
 130         struct btf_ext_sec_data core_relo_info;
 131 };
 132
 133 struct bpf_linker {
 134         char *filename;
 135         int fd;
 136         Elf *elf;
 137         Elf64_Ehdr *elf_hdr;
 138
 139         /* Output sections metadata */
 140         struct dst_sec *secs;
 141         int sec_cnt;
 142
 143         struct strset *strtab_strs; /* STRTAB unique strings */
 144         size_t strtab_sec_idx; /* STRTAB section index */
 145         size_t symtab_sec_idx; /* SYMTAB section index */
 146
 147         struct btf *btf;
 148         struct btf_ext *btf_ext;
 149
 150         /* global (including extern) ELF symbols */
 151         int glob_sym_cnt;
 152         struct glob_sym *glob_syms;
 153 };
 154
 155 #define pr_warn_elf(fmt, ...)                                                                   \
 156         libbpf_print(LIBBPF_WARN, "libbpf: " fmt ": %s\n", ##__VA_ARGS__, elf_errmsg(-1))
 157
 158 static int init_output_elf(struct bpf_linker *linker, const char *file);
 159
 160 static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
 161                                 const struct bpf_linker_file_opts *opts,
 162                                 struct src_obj *obj);
 163 static int linker_sanity_check_elf(struct src_obj *obj);
 164 static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec);
 165 static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec);
 166 static int linker_sanity_check_btf(struct src_obj *obj);
 167 static int linker_sanity_check_btf_ext(struct src_obj *obj);
 168 static int linker_fixup_btf(struct src_obj *obj);
 169 static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj);
 170 static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj);
 171 static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
 172                                  Elf64_Sym *sym, const char *sym_name, int src_sym_idx);
 173 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj);
 174 static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj);
 175 static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj);
 176
 177 static int finalize_btf(struct bpf_linker *linker);
 178 static int finalize_btf_ext(struct bpf_linker *linker);
 179
 180 void bpf_linker__free(struct bpf_linker *linker)
 181 {
 182         int i;
 183
 184         if (!linker)
 185                 return;
 186
 187         free(linker->filename);
 188
 189         if (linker->elf)
 190                 elf_end(linker->elf);
 191
 192         if (linker->fd >= 0)
 193                 close(linker->fd);
 194
 195         strset__free(linker->strtab_strs);
 196
 197         btf__free(linker->btf);
 198         btf_ext__free(linker->btf_ext);
 199
 200         for (i = 1; i < linker->sec_cnt; i++) {
 201                 struct dst_sec *sec = &linker->secs[i];
 202
 203                 free(sec->sec_name);
 204                 free(sec->raw_data);
 205                 free(sec->sec_vars);
 206
 207                 free(sec->func_info.recs);
 208                 free(sec->line_info.recs);
 209                 free(sec->core_relo_info.recs);
 210         }
 211         free(linker->secs);
 212
 213         free(linker->glob_syms);
 214         free(linker);
 215 }
 216
 217 struct bpf_linker *bpf_linker__new(const char *filename, struct bpf_linker_opts *opts)
 218 {
 219         struct bpf_linker *linker;
 220         int err;
 221
 222         if (!OPTS_VALID(opts, bpf_linker_opts))
 223                 return errno = EINVAL, NULL;
 224
 225         if (elf_version(EV_CURRENT) == EV_NONE) {
 226                 pr_warn_elf("libelf initialization failed");
 227                 return errno = EINVAL, NULL;
 228         }
 229
 230         linker = calloc(1, sizeof(*linker));
 231         if (!linker)
 232                 return errno = ENOMEM, NULL;
 233
 234         linker->fd = -1;
 235
 236         err = init_output_elf(linker, filename);
 237         if (err)
 238                 goto err_out;
 239
 240         return linker;
 241
 242 err_out:
 243         bpf_linker__free(linker);
 244         return errno = -err, NULL;
 245 }
 246
 247 static struct dst_sec *add_dst_sec(struct bpf_linker *linker, const char *sec_name)
 248 {
 249         struct dst_sec *secs = linker->secs, *sec;
 250         size_t new_cnt = linker->sec_cnt ? linker->sec_cnt + 1 : 2;
 251
 252         secs = libbpf_reallocarray(secs, new_cnt, sizeof(*secs));
 253         if (!secs)
 254                 return NULL;
 255
 256         /* zero out newly allocated memory */
 257         memset(secs + linker->sec_cnt, 0, (new_cnt - linker->sec_cnt) * sizeof(*secs));
 258
 259         linker->secs = secs;
 260         linker->sec_cnt = new_cnt;
 261
 262         sec = &linker->secs[new_cnt - 1];
 263         sec->id = new_cnt - 1;
 264         sec->sec_name = strdup(sec_name);
 265         if (!sec->sec_name)
 266                 return NULL;
 267
 268         return sec;
 269 }
 270
 271 static Elf64_Sym *add_new_sym(struct bpf_linker *linker, size_t *sym_idx)
 272 {
 273         struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
 274         Elf64_Sym *syms, *sym;
 275         size_t sym_cnt = symtab->sec_sz / sizeof(*sym);
 276
 277         syms = libbpf_reallocarray(symtab->raw_data, sym_cnt + 1, sizeof(*sym));
 278         if (!syms)
 279                 return NULL;
 280
 281         sym = &syms[sym_cnt];
 282         memset(sym, 0, sizeof(*sym));
 283
 284         symtab->raw_data = syms;
 285         symtab->sec_sz += sizeof(*sym);
 286         symtab->shdr->sh_size += sizeof(*sym);
 287         symtab->data->d_size += sizeof(*sym);
 288
 289         if (sym_idx)
 290                 *sym_idx = sym_cnt;
 291
 292         return sym;
 293 }
 294
 295 static int init_output_elf(struct bpf_linker *linker, const char *file)
 296 {
 297         int err, str_off;
 298         Elf64_Sym *init_sym;
 299         struct dst_sec *sec;
 300
 301         linker->filename = strdup(file);
 302         if (!linker->filename)
 303                 return -ENOMEM;
 304
 305         linker->fd = open(file, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
 306         if (linker->fd < 0) {
 307                 err = -errno;
 308                 pr_warn("failed to create '%s': %d\n", file, err);
 309                 return err;
 310         }
 311
 312         linker->elf = elf_begin(linker->fd, ELF_C_WRITE, NULL);
 313         if (!linker->elf) {
 314                 pr_warn_elf("failed to create ELF object");
 315                 return -EINVAL;
 316         }
 317
 318         /* ELF header */
 319         linker->elf_hdr = elf64_newehdr(linker->elf);
 320         if (!linker->elf_hdr) {
 321                 pr_warn_elf("failed to create ELF header");
 322                 return -EINVAL;
 323         }
 324
 325         linker->elf_hdr->e_machine = EM_BPF;
 326         linker->elf_hdr->e_type = ET_REL;
 327 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 328         linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2LSB;
 329 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 330         linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2MSB;
 331 #else
 332 #error "Unknown __BYTE_ORDER__"
 333 #endif
 334
 335         /* STRTAB */
 336         /* initialize strset with an empty string to conform to ELF */
 337         linker->strtab_strs = strset__new(INT_MAX, "", sizeof(""));
 338         if (libbpf_get_error(linker->strtab_strs))
 339                 return libbpf_get_error(linker->strtab_strs);
 340
 341         sec = add_dst_sec(linker, ".strtab");
 342         if (!sec)
 343                 return -ENOMEM;
 344
 345         sec->scn = elf_newscn(linker->elf);
 346         if (!sec->scn) {
 347                 pr_warn_elf("failed to create STRTAB section");
 348                 return -EINVAL;
 349         }
 350
 351         sec->shdr = elf64_getshdr(sec->scn);
 352         if (!sec->shdr)
 353                 return -EINVAL;
 354
 355         sec->data = elf_newdata(sec->scn);
 356         if (!sec->data) {
 357                 pr_warn_elf("failed to create STRTAB data");
 358                 return -EINVAL;
 359         }
 360
 361         str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
 362         if (str_off < 0)
 363                 return str_off;
 364
 365         sec->sec_idx = elf_ndxscn(sec->scn);
 366         linker->elf_hdr->e_shstrndx = sec->sec_idx;
 367         linker->strtab_sec_idx = sec->sec_idx;
 368
 369         sec->shdr->sh_name = str_off;
 370         sec->shdr->sh_type = SHT_STRTAB;
 371         sec->shdr->sh_flags = SHF_STRINGS;
 372         sec->shdr->sh_offset = 0;
 373         sec->shdr->sh_link = 0;
 374         sec->shdr->sh_info = 0;
 375         sec->shdr->sh_addralign = 1;
 376         sec->shdr->sh_size = sec->sec_sz = 0;
 377         sec->shdr->sh_entsize = 0;
 378
 379         /* SYMTAB */
 380         sec = add_dst_sec(linker, ".symtab");
 381         if (!sec)
 382                 return -ENOMEM;
 383
 384         sec->scn = elf_newscn(linker->elf);
 385         if (!sec->scn) {
 386                 pr_warn_elf("failed to create SYMTAB section");
 387                 return -EINVAL;
 388         }
 389
 390         sec->shdr = elf64_getshdr(sec->scn);
 391         if (!sec->shdr)
 392                 return -EINVAL;
 393
 394         sec->data = elf_newdata(sec->scn);
 395         if (!sec->data) {
 396                 pr_warn_elf("failed to create SYMTAB data");
 397                 return -EINVAL;
 398         }
 399
 400         str_off = strset__add_str(linker->strtab_strs, sec->sec_name);
 401         if (str_off < 0)
 402                 return str_off;
 403
 404         sec->sec_idx = elf_ndxscn(sec->scn);
 405         linker->symtab_sec_idx = sec->sec_idx;
 406
 407         sec->shdr->sh_name = str_off;
 408         sec->shdr->sh_type = SHT_SYMTAB;
 409         sec->shdr->sh_flags = 0;
 410         sec->shdr->sh_offset = 0;
 411         sec->shdr->sh_link = linker->strtab_sec_idx;
 412         /* sh_info should be one greater than the index of the last local
 413          * symbol (i.e., binding is STB_LOCAL). But why and who cares?
 414          */
 415         sec->shdr->sh_info = 0;
 416         sec->shdr->sh_addralign = 8;
 417         sec->shdr->sh_entsize = sizeof(Elf64_Sym);
 418
 419         /* .BTF */
 420         linker->btf = btf__new_empty();
 421         err = libbpf_get_error(linker->btf);
 422         if (err)
 423                 return err;
 424
 425         /* add the special all-zero symbol */
 426         init_sym = add_new_sym(linker, NULL);
 427         if (!init_sym)
 428                 return -EINVAL;
 429
 430         init_sym->st_name = 0;
 431         init_sym->st_info = 0;
 432         init_sym->st_other = 0;
 433         init_sym->st_shndx = SHN_UNDEF;
 434         init_sym->st_value = 0;
 435         init_sym->st_size = 0;
 436
 437         return 0;
 438 }
 439
 440 int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
 441                          const struct bpf_linker_file_opts *opts)
 442 {
 443         struct src_obj obj = {};
 444         int err = 0;
 445
 446         if (!OPTS_VALID(opts, bpf_linker_file_opts))
 447                 return libbpf_err(-EINVAL);
 448
 449         if (!linker->elf)
 450                 return libbpf_err(-EINVAL);
 451
 452         err = err ?: linker_load_obj_file(linker, filename, opts, &obj);
 453         err = err ?: linker_append_sec_data(linker, &obj);
 454         err = err ?: linker_append_elf_syms(linker, &obj);
 455         err = err ?: linker_append_elf_relos(linker, &obj);
 456         err = err ?: linker_append_btf(linker, &obj);
 457         err = err ?: linker_append_btf_ext(linker, &obj);
 458
 459         /* free up src_obj resources */
 460         free(obj.btf_type_map);
 461         btf__free(obj.btf);
 462         btf_ext__free(obj.btf_ext);
 463         free(obj.secs);
 464         free(obj.sym_map);
 465         if (obj.elf)
 466                 elf_end(obj.elf);
 467         if (obj.fd >= 0)
 468                 close(obj.fd);
 469
 470         return libbpf_err(err);
 471 }
 472
 473 static bool is_dwarf_sec_name(const char *name)
 474 {
 475         /* approximation, but the actual list is too long */
 476         return strncmp(name, ".debug_", sizeof(".debug_") - 1) == 0;
 477 }
 478
 479 static bool is_ignored_sec(struct src_sec *sec)
 480 {
 481         Elf64_Shdr *shdr = sec->shdr;
 482         const char *name = sec->sec_name;
 483
 484         /* no special handling of .strtab */
 485         if (shdr->sh_type == SHT_STRTAB)
 486                 return true;
 487
 488         /* ignore .llvm_addrsig section as well */
 489         if (shdr->sh_type == SHT_LLVM_ADDRSIG)
 490                 return true;
 491
 492         /* no subprograms will lead to an empty .text section, ignore it */
 493         if (shdr->sh_type == SHT_PROGBITS && shdr->sh_size == 0 &&
 494             strcmp(sec->sec_name, ".text") == 0)
 495                 return true;
 496
 497         /* DWARF sections */
 498         if (is_dwarf_sec_name(sec->sec_name))
 499                 return true;
 500
 501         if (strncmp(name, ".rel", sizeof(".rel") - 1) == 0) {
 502                 name += sizeof(".rel") - 1;
 503                 /* DWARF section relocations */
 504                 if (is_dwarf_sec_name(name))
 505                         return true;
 506
 507                 /* .BTF and .BTF.ext don't need relocations */
 508                 if (strcmp(name, BTF_ELF_SEC) == 0 ||
 509                     strcmp(name, BTF_EXT_ELF_SEC) == 0)
 510                         return true;
 511         }
 512
 513         return false;
 514 }
 515
 516 static struct src_sec *add_src_sec(struct src_obj *obj, const char *sec_name)
 517 {
 518         struct src_sec *secs = obj->secs, *sec;
 519         size_t new_cnt = obj->sec_cnt ? obj->sec_cnt + 1 : 2;
 520
 521         secs = libbpf_reallocarray(secs, new_cnt, sizeof(*secs));
 522         if (!secs)
 523                 return NULL;
 524
 525         /* zero out newly allocated memory */
 526         memset(secs + obj->sec_cnt, 0, (new_cnt - obj->sec_cnt) * sizeof(*secs));
 527
 528         obj->secs = secs;
 529         obj->sec_cnt = new_cnt;
 530
 531         sec = &obj->secs[new_cnt - 1];
 532         sec->id = new_cnt - 1;
 533         sec->sec_name = sec_name;
 534
 535         return sec;
 536 }
 537
 538 static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
 539                                 const struct bpf_linker_file_opts *opts,
 540                                 struct src_obj *obj)
 541 {
 542 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 543         const int host_endianness = ELFDATA2LSB;
 544 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 545         const int host_endianness = ELFDATA2MSB;
 546 #else
 547 #error "Unknown __BYTE_ORDER__"
 548 #endif
 549         int err = 0;
 550         Elf_Scn *scn;
 551         Elf_Data *data;
 552         Elf64_Ehdr *ehdr;
 553         Elf64_Shdr *shdr;
 554         struct src_sec *sec;
 555
 556         pr_debug("linker: adding object file '%s'...\n", filename);
 557
 558         obj->filename = filename;
 559
 560         obj->fd = open(filename, O_RDONLY | O_CLOEXEC);
 561         if (obj->fd < 0) {
 562                 err = -errno;
 563                 pr_warn("failed to open file '%s': %d\n", filename, err);
 564                 return err;
 565         }
 566         obj->elf = elf_begin(obj->fd, ELF_C_READ_MMAP, NULL);
 567         if (!obj->elf) {
 568                 err = -errno;
 569                 pr_warn_elf("failed to parse ELF file '%s'", filename);
 570                 return err;
 571         }
 572
 573         /* Sanity check ELF file high-level properties */
 574         ehdr = elf64_getehdr(obj->elf);
 575         if (!ehdr) {
 576                 err = -errno;
 577                 pr_warn_elf("failed to get ELF header for %s", filename);
 578                 return err;
 579         }
 580         if (ehdr->e_ident[EI_DATA] != host_endianness) {
 581                 err = -EOPNOTSUPP;
 582                 pr_warn_elf("unsupported byte order of ELF file %s", filename);
 583                 return err;
 584         }
 585         if (ehdr->e_type != ET_REL
 586             || ehdr->e_machine != EM_BPF
 587             || ehdr->e_ident[EI_CLASS] != ELFCLASS64) {
 588                 err = -EOPNOTSUPP;
 589                 pr_warn_elf("unsupported kind of ELF file %s", filename);
 590                 return err;
 591         }
 592
 593         if (elf_getshdrstrndx(obj->elf, &obj->shstrs_sec_idx)) {
 594                 err = -errno;
 595                 pr_warn_elf("failed to get SHSTRTAB section index for %s", filename);
 596                 return err;
 597         }
 598
 599         scn = NULL;
 600         while ((scn = elf_nextscn(obj->elf, scn)) != NULL) {
 601                 size_t sec_idx = elf_ndxscn(scn);
 602                 const char *sec_name;
 603
 604                 shdr = elf64_getshdr(scn);
 605                 if (!shdr) {
 606                         err = -errno;
 607                         pr_warn_elf("failed to get section #%zu header for %s",
 608                                     sec_idx, filename);
 609                         return err;
 610                 }
 611
 612                 sec_name = elf_strptr(obj->elf, obj->shstrs_sec_idx, shdr->sh_name);
 613                 if (!sec_name) {
 614                         err = -errno;
 615                         pr_warn_elf("failed to get section #%zu name for %s",
 616                                     sec_idx, filename);
 617                         return err;
 618                 }
 619
 620                 data = elf_getdata(scn, 0);
 621                 if (!data) {
 622                         err = -errno;
 623                         pr_warn_elf("failed to get section #%zu (%s) data from %s",
 624                                     sec_idx, sec_name, filename);
 625                         return err;
 626                 }
 627
 628                 sec = add_src_sec(obj, sec_name);
 629                 if (!sec)
 630                         return -ENOMEM;
 631
 632                 sec->scn = scn;
 633                 sec->shdr = shdr;
 634                 sec->data = data;
 635                 sec->sec_idx = elf_ndxscn(scn);
 636
 637                 if (is_ignored_sec(sec)) {
 638                         sec->skipped = true;
 639                         continue;
 640                 }
 641
 642                 switch (shdr->sh_type) {
 643                 case SHT_SYMTAB:
 644                         if (obj->symtab_sec_idx) {
 645                                 err = -EOPNOTSUPP;
 646                                 pr_warn("multiple SYMTAB sections found, not supported\n");
 647                                 return err;
 648                         }
 649                         obj->symtab_sec_idx = sec_idx;
 650                         break;
 651                 case SHT_STRTAB:
 652                         /* we'll construct our own string table */
 653                         break;
 654                 case SHT_PROGBITS:
 655                         if (strcmp(sec_name, BTF_ELF_SEC) == 0) {
 656                                 obj->btf = btf__new(data->d_buf, shdr->sh_size);
 657                                 err = libbpf_get_error(obj->btf);
 658                                 if (err) {
 659                                         pr_warn("failed to parse .BTF from %s: %d\n", filename, err);
 660                                         return err;
 661                                 }
 662                                 sec->skipped = true;
 663                                 continue;
 664                         }
 665                         if (strcmp(sec_name, BTF_EXT_ELF_SEC) == 0) {
 666                                 obj->btf_ext = btf_ext__new(data->d_buf, shdr->sh_size);
 667                                 err = libbpf_get_error(obj->btf_ext);
 668                                 if (err) {
 669                                         pr_warn("failed to parse .BTF.ext from '%s': %d\n", filename, err);
 670                                         return err;
 671                                 }
 672                                 sec->skipped = true;
 673                                 continue;
 674                         }
 675
 676                         /* data & code */
 677                         break;
 678                 case SHT_NOBITS:
 679                         /* BSS */
 680                         break;
 681                 case SHT_REL:
 682                         /* relocations */
 683                         break;
 684                 default:
 685                         pr_warn("unrecognized section #%zu (%s) in %s\n",
 686                                 sec_idx, sec_name, filename);
 687                         err = -EINVAL;
 688                         return err;
 689                 }
 690         }
 691
 692         err = err ?: linker_sanity_check_elf(obj);
 693         err = err ?: linker_sanity_check_btf(obj);
 694         err = err ?: linker_sanity_check_btf_ext(obj);
 695         err = err ?: linker_fixup_btf(obj);
 696
 697         return err;
 698 }
 699
 700 static int linker_sanity_check_elf(struct src_obj *obj)
 701 {
 702         struct src_sec *sec;
 703         int i, err;
 704
 705         if (!obj->symtab_sec_idx) {
 706                 pr_warn("ELF is missing SYMTAB section in %s\n", obj->filename);
 707                 return -EINVAL;
 708         }
 709         if (!obj->shstrs_sec_idx) {
 710                 pr_warn("ELF is missing section headers STRTAB section in %s\n", obj->filename);
 711                 return -EINVAL;
 712         }
 713
 714         for (i = 1; i < obj->sec_cnt; i++) {
 715                 sec = &obj->secs[i];
 716
 717                 if (sec->sec_name[0] == '\0') {
 718                         pr_warn("ELF section #%zu has empty name in %s\n", sec->sec_idx, obj->filename);
 719                         return -EINVAL;
 720                 }
 721
 722                 if (sec->shdr->sh_addralign && !is_pow_of_2(sec->shdr->sh_addralign))
 723                         return -EINVAL;
 724                 if (sec->shdr->sh_addralign != sec->data->d_align)
 725                         return -EINVAL;
 726
 727                 if (sec->shdr->sh_size != sec->data->d_size)
 728                         return -EINVAL;
 729
 730                 switch (sec->shdr->sh_type) {
 731                 case SHT_SYMTAB:
 732                         err = linker_sanity_check_elf_symtab(obj, sec);
 733                         if (err)
 734                                 return err;
 735                         break;
 736                 case SHT_STRTAB:
 737                         break;
 738                 case SHT_PROGBITS:
 739                         if (sec->shdr->sh_flags & SHF_EXECINSTR) {
 740                                 if (sec->shdr->sh_size % sizeof(struct bpf_insn) != 0)
 741                                         return -EINVAL;
 742                         }
 743                         break;
 744                 case SHT_NOBITS:
 745                         break;
 746                 case SHT_REL:
 747                         err = linker_sanity_check_elf_relos(obj, sec);
 748                         if (err)
 749                                 return err;
 750                         break;
 751                 case SHT_LLVM_ADDRSIG:
 752                         break;
 753                 default:
 754                         pr_warn("ELF section #%zu (%s) has unrecognized type %zu in %s\n",
 755                                 sec->sec_idx, sec->sec_name, (size_t)sec->shdr->sh_type, obj->filename);
 756                         return -EINVAL;
 757                 }
 758         }
 759
 760         return 0;
 761 }
 762
 763 static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec)
 764 {
 765         struct src_sec *link_sec;
 766         Elf64_Sym *sym;
 767         int i, n;
 768
 769         if (sec->shdr->sh_entsize != sizeof(Elf64_Sym))
 770                 return -EINVAL;
 771         if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
 772                 return -EINVAL;
 773
 774         if (!sec->shdr->sh_link || sec->shdr->sh_link >= obj->sec_cnt) {
 775                 pr_warn("ELF SYMTAB section #%zu points to missing STRTAB section #%zu in %s\n",
 776                         sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
 777                 return -EINVAL;
 778         }
 779         link_sec = &obj->secs[sec->shdr->sh_link];
 780         if (link_sec->shdr->sh_type != SHT_STRTAB) {
 781                 pr_warn("ELF SYMTAB section #%zu points to invalid STRTAB section #%zu in %s\n",
 782                         sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
 783                 return -EINVAL;
 784         }
 785
 786         n = sec->shdr->sh_size / sec->shdr->sh_entsize;
 787         sym = sec->data->d_buf;
 788         for (i = 0; i < n; i++, sym++) {
 789                 int sym_type = ELF64_ST_TYPE(sym->st_info);
 790                 int sym_bind = ELF64_ST_BIND(sym->st_info);
 791                 int sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
 792
 793                 if (i == 0) {
 794                         if (sym->st_name != 0 || sym->st_info != 0
 795                             || sym->st_other != 0 || sym->st_shndx != 0
 796                             || sym->st_value != 0 || sym->st_size != 0) {
 797                                 pr_warn("ELF sym #0 is invalid in %s\n", obj->filename);
 798                                 return -EINVAL;
 799                         }
 800                         continue;
 801                 }
 802                 if (sym_bind != STB_LOCAL && sym_bind != STB_GLOBAL && sym_bind != STB_WEAK) {
 803                         pr_warn("ELF sym #%d in section #%zu has unsupported symbol binding %d\n",
 804                                 i, sec->sec_idx, sym_bind);
 805                         return -EINVAL;
 806                 }
 807                 if (sym_vis != STV_DEFAULT && sym_vis != STV_HIDDEN) {
 808                         pr_warn("ELF sym #%d in section #%zu has unsupported symbol visibility %d\n",
 809                                 i, sec->sec_idx, sym_vis);
 810                         return -EINVAL;
 811                 }
 812                 if (sym->st_shndx == 0) {
 813                         if (sym_type != STT_NOTYPE || sym_bind == STB_LOCAL
 814                             || sym->st_value != 0 || sym->st_size != 0) {
 815                                 pr_warn("ELF sym #%d is invalid extern symbol in %s\n",
 816                                         i, obj->filename);
 817
 818                                 return -EINVAL;
 819                         }
 820                         continue;
 821                 }
 822                 if (sym->st_shndx < SHN_LORESERVE && sym->st_shndx >= obj->sec_cnt) {
 823                         pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n",
 824                                 i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
 825                         return -EINVAL;
 826                 }
 827                 if (sym_type == STT_SECTION) {
 828                         if (sym->st_value != 0)
 829                                 return -EINVAL;
 830                         continue;
 831                 }
 832         }
 833
 834         return 0;
 835 }
 836
 837 static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec)
 838 {
 839         struct src_sec *link_sec, *sym_sec;
 840         Elf64_Rel *relo;
 841         int i, n;
 842
 843         if (sec->shdr->sh_entsize != sizeof(Elf64_Rel))
 844                 return -EINVAL;
 845         if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0)
 846                 return -EINVAL;
 847
 848         /* SHT_REL's sh_link should point to SYMTAB */
 849         if (sec->shdr->sh_link != obj->symtab_sec_idx) {
 850                 pr_warn("ELF relo section #%zu points to invalid SYMTAB section #%zu in %s\n",
 851                         sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename);
 852                 return -EINVAL;
 853         }
 854
 855         /* SHT_REL's sh_info points to relocated section */
 856         if (!sec->shdr->sh_info || sec->shdr->sh_info >= obj->sec_cnt) {
 857                 pr_warn("ELF relo section #%zu points to missing section #%zu in %s\n",
 858                         sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
 859                 return -EINVAL;
 860         }
 861         link_sec = &obj->secs[sec->shdr->sh_info];
 862
 863         /* .rel<secname> -> <secname> pattern is followed */
 864         if (strncmp(sec->sec_name, ".rel", sizeof(".rel") - 1) != 0
 865             || strcmp(sec->sec_name + sizeof(".rel") - 1, link_sec->sec_name) != 0) {
 866                 pr_warn("ELF relo section #%zu name has invalid name in %s\n",
 867                         sec->sec_idx, obj->filename);
 868                 return -EINVAL;
 869         }
 870
 871         /* don't further validate relocations for ignored sections */
 872         if (link_sec->skipped)
 873                 return 0;
 874
 875         /* relocatable section is data or instructions */
 876         if (link_sec->shdr->sh_type != SHT_PROGBITS && link_sec->shdr->sh_type != SHT_NOBITS) {
 877                 pr_warn("ELF relo section #%zu points to invalid section #%zu in %s\n",
 878                         sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename);
 879                 return -EINVAL;
 880         }
 881
 882         /* check sanity of each relocation */
 883         n = sec->shdr->sh_size / sec->shdr->sh_entsize;
 884         relo = sec->data->d_buf;
 885         sym_sec = &obj->secs[obj->symtab_sec_idx];
 886         for (i = 0; i < n; i++, relo++) {
 887                 size_t sym_idx = ELF64_R_SYM(relo->r_info);
 888                 size_t sym_type = ELF64_R_TYPE(relo->r_info);
 889
 890                 if (sym_type != R_BPF_64_64 && sym_type != R_BPF_64_32 &&
 891                     sym_type != R_BPF_64_ABS64 && sym_type != R_BPF_64_ABS32) {
 892                         pr_warn("ELF relo #%d in section #%zu has unexpected type %zu in %s\n",
 893                                 i, sec->sec_idx, sym_type, obj->filename);
 894                         return -EINVAL;
 895                 }
 896
 897                 if (!sym_idx || sym_idx * sizeof(Elf64_Sym) >= sym_sec->shdr->sh_size) {
 898                         pr_warn("ELF relo #%d in section #%zu points to invalid symbol #%zu in %s\n",
 899                                 i, sec->sec_idx, sym_idx, obj->filename);
 900                         return -EINVAL;
 901                 }
 902
 903                 if (link_sec->shdr->sh_flags & SHF_EXECINSTR) {
 904                         if (relo->r_offset % sizeof(struct bpf_insn) != 0) {
 905                                 pr_warn("ELF relo #%d in section #%zu points to missing symbol #%zu in %s\n",
 906                                         i, sec->sec_idx, sym_idx, obj->filename);
 907                                 return -EINVAL;
 908                         }
 909                 }
 910         }
 911
 912         return 0;
 913 }
 914
 915 static int check_btf_type_id(__u32 *type_id, void *ctx)
 916 {
 917         struct btf *btf = ctx;
 918
 919         if (*type_id >= btf__type_cnt(btf))
 920                 return -EINVAL;
 921
 922         return 0;
 923 }
 924
 925 static int check_btf_str_off(__u32 *str_off, void *ctx)
 926 {
 927         struct btf *btf = ctx;
 928         const char *s;
 929
 930         s = btf__str_by_offset(btf, *str_off);
 931
 932         if (!s)
 933                 return -EINVAL;
 934
 935         return 0;
 936 }
 937
 938 static int linker_sanity_check_btf(struct src_obj *obj)
 939 {
 940         struct btf_type *t;
 941         int i, n, err = 0;
 942
 943         if (!obj->btf)
 944                 return 0;
 945
 946         n = btf__type_cnt(obj->btf);
 947         for (i = 1; i < n; i++) {
 948                 t = btf_type_by_id(obj->btf, i);
 949
 950                 err = err ?: btf_type_visit_type_ids(t, check_btf_type_id, obj->btf);
 951                 err = err ?: btf_type_visit_str_offs(t, check_btf_str_off, obj->btf);
 952                 if (err)
 953                         return err;
 954         }
 955
 956         return 0;
 957 }
 958
 959 static int linker_sanity_check_btf_ext(struct src_obj *obj)
 960 {
 961         int err = 0;
 962
 963         if (!obj->btf_ext)
 964                 return 0;
 965
 966         /* can't use .BTF.ext without .BTF */
 967         if (!obj->btf)
 968                 return -EINVAL;
 969
 970         err = err ?: btf_ext_visit_type_ids(obj->btf_ext, check_btf_type_id, obj->btf);
 971         err = err ?: btf_ext_visit_str_offs(obj->btf_ext, check_btf_str_off, obj->btf);
 972         if (err)
 973                 return err;
 974
 975         return 0;
 976 }
 977
 978 static int init_sec(struct bpf_linker *linker, struct dst_sec *dst_sec, struct src_sec *src_sec)
 979 {
 980         Elf_Scn *scn;
 981         Elf_Data *data;
 982         Elf64_Shdr *shdr;
 983         int name_off;
 984
 985         dst_sec->sec_sz = 0;
 986         dst_sec->sec_idx = 0;
 987         dst_sec->ephemeral = src_sec->ephemeral;
 988
 989         /* ephemeral sections are just thin section shells lacking most parts */
 990         if (src_sec->ephemeral)
 991                 return 0;
 992
 993         scn = elf_newscn(linker->elf);
 994         if (!scn)
 995                 return -ENOMEM;
 996         data = elf_newdata(scn);
 997         if (!data)
 998                 return -ENOMEM;
 999         shdr = elf64_getshdr(scn);
1000         if (!shdr)
1001                 return -ENOMEM;
1002
1003         dst_sec->scn = scn;
1004         dst_sec->shdr = shdr;
1005         dst_sec->data = data;
1006         dst_sec->sec_idx = elf_ndxscn(scn);
1007
1008         name_off = strset__add_str(linker->strtab_strs, src_sec->sec_name);
1009         if (name_off < 0)
1010                 return name_off;
1011
1012         shdr->sh_name = name_off;
1013         shdr->sh_type = src_sec->shdr->sh_type;
1014         shdr->sh_flags = src_sec->shdr->sh_flags;
1015         shdr->sh_size = 0;
1016         /* sh_link and sh_info have different meaning for different types of
1017          * sections, so we leave it up to the caller code to fill them in, if
1018          * necessary
1019          */
1020         shdr->sh_link = 0;
1021         shdr->sh_info = 0;
1022         shdr->sh_addralign = src_sec->shdr->sh_addralign;
1023         shdr->sh_entsize = src_sec->shdr->sh_entsize;
1024
1025         data->d_type = src_sec->data->d_type;
1026         data->d_size = 0;
1027         data->d_buf = NULL;
1028         data->d_align = src_sec->data->d_align;
1029         data->d_off = 0;
1030
1031         return 0;
1032 }
1033
1034 static struct dst_sec *find_dst_sec_by_name(struct bpf_linker *linker, const char *sec_name)
1035 {
1036         struct dst_sec *sec;
1037         int i;
1038
1039         for (i = 1; i < linker->sec_cnt; i++) {
1040                 sec = &linker->secs[i];
1041
1042                 if (strcmp(sec->sec_name, sec_name) == 0)
1043                         return sec;
1044         }
1045
1046         return NULL;
1047 }
1048
1049 static bool secs_match(struct dst_sec *dst, struct src_sec *src)
1050 {
1051         if (dst->ephemeral || src->ephemeral)
1052                 return true;
1053
1054         if (dst->shdr->sh_type != src->shdr->sh_type) {
1055                 pr_warn("sec %s types mismatch\n", dst->sec_name);
1056                 return false;
1057         }
1058         if (dst->shdr->sh_flags != src->shdr->sh_flags) {
1059                 pr_warn("sec %s flags mismatch\n", dst->sec_name);
1060                 return false;
1061         }
1062         if (dst->shdr->sh_entsize != src->shdr->sh_entsize) {
1063                 pr_warn("sec %s entsize mismatch\n", dst->sec_name);
1064                 return false;
1065         }
1066
1067         return true;
1068 }
1069
1070 static bool sec_content_is_same(struct dst_sec *dst_sec, struct src_sec *src_sec)
1071 {
1072         if (dst_sec->sec_sz != src_sec->shdr->sh_size)
1073                 return false;
1074         if (memcmp(dst_sec->raw_data, src_sec->data->d_buf, dst_sec->sec_sz) != 0)
1075                 return false;
1076         return true;
1077 }
1078
1079 static int extend_sec(struct bpf_linker *linker, struct dst_sec *dst, struct src_sec *src)
1080 {
1081         void *tmp;
1082         size_t dst_align, src_align;
1083         size_t dst_align_sz, dst_final_sz;
1084         int err;
1085
1086         /* Ephemeral source section doesn't contribute anything to ELF
1087          * section data.
1088          */
1089         if (src->ephemeral)
1090                 return 0;
1091
1092         /* Some sections (like .maps) can contain both externs (and thus be
1093          * ephemeral) and non-externs (map definitions). So it's possible that
1094          * it has to be "upgraded" from ephemeral to non-ephemeral when the
1095          * first non-ephemeral entity appears. In such case, we add ELF
1096          * section, data, etc.
1097          */
1098         if (dst->ephemeral) {
1099                 err = init_sec(linker, dst, src);
1100                 if (err)
1101                         return err;
1102         }
1103
1104         dst_align = dst->shdr->sh_addralign;
1105         src_align = src->shdr->sh_addralign;
1106         if (dst_align == 0)
1107                 dst_align = 1;
1108         if (dst_align < src_align)
1109                 dst_align = src_align;
1110
1111         dst_align_sz = (dst->sec_sz + dst_align - 1) / dst_align * dst_align;
1112
1113         /* no need to re-align final size */
1114         dst_final_sz = dst_align_sz + src->shdr->sh_size;
1115
1116         if (src->shdr->sh_type != SHT_NOBITS) {
1117                 tmp = realloc(dst->raw_data, dst_final_sz);
1118                 /* If dst_align_sz == 0, realloc() behaves in a special way:
1119                  * 1. When dst->raw_data is NULL it returns:
1120                  *    "either NULL or a pointer suitable to be passed to free()" [1].
1121                  * 2. When dst->raw_data is not-NULL it frees dst->raw_data and returns NULL,
1122                  *    thus invalidating any "pointer suitable to be passed to free()" obtained
1123                  *    at step (1).
1124                  *
1125                  * The dst_align_sz > 0 check avoids error exit after (2), otherwise
1126                  * dst->raw_data would be freed again in bpf_linker__free().
1127                  *
1128                  * [1] man 3 realloc
1129                  */
1130                 if (!tmp && dst_align_sz > 0)
1131                         return -ENOMEM;
1132                 dst->raw_data = tmp;
1133
1134                 /* pad dst section, if it's alignment forced size increase */
1135                 memset(dst->raw_data + dst->sec_sz, 0, dst_align_sz - dst->sec_sz);
1136                 /* now copy src data at a properly aligned offset */
1137                 memcpy(dst->raw_data + dst_align_sz, src->data->d_buf, src->shdr->sh_size);
1138         }
1139
1140         dst->sec_sz = dst_final_sz;
1141         dst->shdr->sh_size = dst_final_sz;
1142         dst->data->d_size = dst_final_sz;
1143
1144         dst->shdr->sh_addralign = dst_align;
1145         dst->data->d_align = dst_align;
1146
1147         src->dst_off = dst_align_sz;
1148
1149         return 0;
1150 }
1151
1152 static bool is_data_sec(struct src_sec *sec)
1153 {
1154         if (!sec || sec->skipped)
1155                 return false;
1156         /* ephemeral sections are data sections, e.g., .kconfig, .ksyms */
1157         if (sec->ephemeral)
1158                 return true;
1159         return sec->shdr->sh_type == SHT_PROGBITS || sec->shdr->sh_type == SHT_NOBITS;
1160 }
1161
1162 static bool is_relo_sec(struct src_sec *sec)
1163 {
1164         if (!sec || sec->skipped || sec->ephemeral)
1165                 return false;
1166         return sec->shdr->sh_type == SHT_REL;
1167 }
1168
1169 static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj)
1170 {
1171         int i, err;
1172
1173         for (i = 1; i < obj->sec_cnt; i++) {
1174                 struct src_sec *src_sec;
1175                 struct dst_sec *dst_sec;
1176
1177                 src_sec = &obj->secs[i];
1178                 if (!is_data_sec(src_sec))
1179                         continue;
1180
1181                 dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
1182                 if (!dst_sec) {
1183                         dst_sec = add_dst_sec(linker, src_sec->sec_name);
1184                         if (!dst_sec)
1185                                 return -ENOMEM;
1186                         err = init_sec(linker, dst_sec, src_sec);
1187                         if (err) {
1188                                 pr_warn("failed to init section '%s'\n", src_sec->sec_name);
1189                                 return err;
1190                         }
1191                 } else {
1192                         if (!secs_match(dst_sec, src_sec)) {
1193                                 pr_warn("ELF sections %s are incompatible\n", src_sec->sec_name);
1194                                 return -1;
1195                         }
1196
1197                         /* "license" and "version" sections are deduped */
1198                         if (strcmp(src_sec->sec_name, "license") == 0
1199                             || strcmp(src_sec->sec_name, "version") == 0) {
1200                                 if (!sec_content_is_same(dst_sec, src_sec)) {
1201                                         pr_warn("non-identical contents of section '%s' are not supported\n", src_sec->sec_name);
1202                                         return -EINVAL;
1203                                 }
1204                                 src_sec->skipped = true;
1205                                 src_sec->dst_id = dst_sec->id;
1206                                 continue;
1207                         }
1208                 }
1209
1210                 /* record mapped section index */
1211                 src_sec->dst_id = dst_sec->id;
1212
1213                 err = extend_sec(linker, dst_sec, src_sec);
1214                 if (err)
1215                         return err;
1216         }
1217
1218         return 0;
1219 }
1220
1221 static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj)
1222 {
1223         struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
1224         Elf64_Sym *sym = symtab->data->d_buf;
1225         int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize, err;
1226         int str_sec_idx = symtab->shdr->sh_link;
1227         const char *sym_name;
1228
1229         obj->sym_map = calloc(n + 1, sizeof(*obj->sym_map));
1230         if (!obj->sym_map)
1231                 return -ENOMEM;
1232
1233         for (i = 0; i < n; i++, sym++) {
1234                 /* We already validated all-zero symbol #0 and we already
1235                  * appended it preventively to the final SYMTAB, so skip it.
1236                  */
1237                 if (i == 0)
1238                         continue;
1239
1240                 sym_name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
1241                 if (!sym_name) {
1242                         pr_warn("can't fetch symbol name for symbol #%d in '%s'\n", i, obj->filename);
1243                         return -EINVAL;
1244                 }
1245
1246                 err = linker_append_elf_sym(linker, obj, sym, sym_name, i);
1247                 if (err)
1248                         return err;
1249         }
1250
1251         return 0;
1252 }
1253
1254 static Elf64_Sym *get_sym_by_idx(struct bpf_linker *linker, size_t sym_idx)
1255 {
1256         struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
1257         Elf64_Sym *syms = symtab->raw_data;
1258
1259         return &syms[sym_idx];
1260 }
1261
1262 static struct glob_sym *find_glob_sym(struct bpf_linker *linker, const char *sym_name)
1263 {
1264         struct glob_sym *glob_sym;
1265         const char *name;
1266         int i;
1267
1268         for (i = 0; i < linker->glob_sym_cnt; i++) {
1269                 glob_sym = &linker->glob_syms[i];
1270                 name = strset__data(linker->strtab_strs) + glob_sym->name_off;
1271
1272                 if (strcmp(name, sym_name) == 0)
1273                         return glob_sym;
1274         }
1275
1276         return NULL;
1277 }
1278
1279 static struct glob_sym *add_glob_sym(struct bpf_linker *linker)
1280 {
1281         struct glob_sym *syms, *sym;
1282
1283         syms = libbpf_reallocarray(linker->glob_syms, linker->glob_sym_cnt + 1,
1284                                    sizeof(*linker->glob_syms));
1285         if (!syms)
1286                 return NULL;
1287
1288         sym = &syms[linker->glob_sym_cnt];
1289         memset(sym, 0, sizeof(*sym));
1290         sym->var_idx = -1;
1291
1292         linker->glob_syms = syms;
1293         linker->glob_sym_cnt++;
1294
1295         return sym;
1296 }
1297
1298 static bool glob_sym_btf_matches(const char *sym_name, bool exact,
1299                                  const struct btf *btf1, __u32 id1,
1300                                  const struct btf *btf2, __u32 id2)
1301 {
1302         const struct btf_type *t1, *t2;
1303         bool is_static1, is_static2;
1304         const char *n1, *n2;
1305         int i, n;
1306
1307 recur:
1308         n1 = n2 = NULL;
1309         t1 = skip_mods_and_typedefs(btf1, id1, &id1);
1310         t2 = skip_mods_and_typedefs(btf2, id2, &id2);
1311
1312         /* check if only one side is FWD, otherwise handle with common logic */
1313         if (!exact && btf_is_fwd(t1) != btf_is_fwd(t2)) {
1314                 n1 = btf__str_by_offset(btf1, t1->name_off);
1315                 n2 = btf__str_by_offset(btf2, t2->name_off);
1316                 if (strcmp(n1, n2) != 0) {
1317                         pr_warn("global '%s': incompatible forward declaration names '%s' and '%s'\n",
1318                                 sym_name, n1, n2);
1319                         return false;
1320                 }
1321                 /* validate if FWD kind matches concrete kind */
1322                 if (btf_is_fwd(t1)) {
1323                         if (btf_kflag(t1) && btf_is_union(t2))
1324                                 return true;
1325                         if (!btf_kflag(t1) && btf_is_struct(t2))
1326                                 return true;
1327                         pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
1328                                 sym_name, btf_kflag(t1) ? "union" : "struct", btf_kind_str(t2));
1329                 } else {
1330                         if (btf_kflag(t2) && btf_is_union(t1))
1331                                 return true;
1332                         if (!btf_kflag(t2) && btf_is_struct(t1))
1333                                 return true;
1334                         pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
1335                                 sym_name, btf_kflag(t2) ? "union" : "struct", btf_kind_str(t1));
1336                 }
1337                 return false;
1338         }
1339
1340         if (btf_kind(t1) != btf_kind(t2)) {
1341                 pr_warn("global '%s': incompatible BTF kinds %s and %s\n",
1342                         sym_name, btf_kind_str(t1), btf_kind_str(t2));
1343                 return false;
1344         }
1345
1346         switch (btf_kind(t1)) {
1347         case BTF_KIND_STRUCT:
1348         case BTF_KIND_UNION:
1349         case BTF_KIND_ENUM:
1350         case BTF_KIND_ENUM64:
1351         case BTF_KIND_FWD:
1352         case BTF_KIND_FUNC:
1353         case BTF_KIND_VAR:
1354                 n1 = btf__str_by_offset(btf1, t1->name_off);
1355                 n2 = btf__str_by_offset(btf2, t2->name_off);
1356                 if (strcmp(n1, n2) != 0) {
1357                         pr_warn("global '%s': incompatible %s names '%s' and '%s'\n",
1358                                 sym_name, btf_kind_str(t1), n1, n2);
1359                         return false;
1360                 }
1361                 break;
1362         default:
1363                 break;
1364         }
1365
1366         switch (btf_kind(t1)) {
1367         case BTF_KIND_UNKN: /* void */
1368         case BTF_KIND_FWD:
1369                 return true;
1370         case BTF_KIND_INT:
1371         case BTF_KIND_FLOAT:
1372         case BTF_KIND_ENUM:
1373         case BTF_KIND_ENUM64:
1374                 /* ignore encoding for int and enum values for enum */
1375                 if (t1->size != t2->size) {
1376                         pr_warn("global '%s': incompatible %s '%s' size %u and %u\n",
1377                                 sym_name, btf_kind_str(t1), n1, t1->size, t2->size);
1378                         return false;
1379                 }
1380                 return true;
1381         case BTF_KIND_PTR:
1382                 /* just validate overall shape of the referenced type, so no
1383                  * contents comparison for struct/union, and allowd fwd vs
1384                  * struct/union
1385                  */
1386                 exact = false;
1387                 id1 = t1->type;
1388                 id2 = t2->type;
1389                 goto recur;
1390         case BTF_KIND_ARRAY:
1391                 /* ignore index type and array size */
1392                 id1 = btf_array(t1)->type;
1393                 id2 = btf_array(t2)->type;
1394                 goto recur;
1395         case BTF_KIND_FUNC:
1396                 /* extern and global linkages are compatible */
1397                 is_static1 = btf_func_linkage(t1) == BTF_FUNC_STATIC;
1398                 is_static2 = btf_func_linkage(t2) == BTF_FUNC_STATIC;
1399                 if (is_static1 != is_static2) {
1400                         pr_warn("global '%s': incompatible func '%s' linkage\n", sym_name, n1);
1401                         return false;
1402                 }
1403
1404                 id1 = t1->type;
1405                 id2 = t2->type;
1406                 goto recur;
1407         case BTF_KIND_VAR:
1408                 /* extern and global linkages are compatible */
1409                 is_static1 = btf_var(t1)->linkage == BTF_VAR_STATIC;
1410                 is_static2 = btf_var(t2)->linkage == BTF_VAR_STATIC;
1411                 if (is_static1 != is_static2) {
1412                         pr_warn("global '%s': incompatible var '%s' linkage\n", sym_name, n1);
1413                         return false;
1414                 }
1415
1416                 id1 = t1->type;
1417                 id2 = t2->type;
1418                 goto recur;
1419         case BTF_KIND_STRUCT:
1420         case BTF_KIND_UNION: {
1421                 const struct btf_member *m1, *m2;
1422
1423                 if (!exact)
1424                         return true;
1425
1426                 if (btf_vlen(t1) != btf_vlen(t2)) {
1427                         pr_warn("global '%s': incompatible number of %s fields %u and %u\n",
1428                                 sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
1429                         return false;
1430                 }
1431
1432                 n = btf_vlen(t1);
1433                 m1 = btf_members(t1);
1434                 m2 = btf_members(t2);
1435                 for (i = 0; i < n; i++, m1++, m2++) {
1436                         n1 = btf__str_by_offset(btf1, m1->name_off);
1437                         n2 = btf__str_by_offset(btf2, m2->name_off);
1438                         if (strcmp(n1, n2) != 0) {
1439                                 pr_warn("global '%s': incompatible field #%d names '%s' and '%s'\n",
1440                                         sym_name, i, n1, n2);
1441                                 return false;
1442                         }
1443                         if (m1->offset != m2->offset) {
1444                                 pr_warn("global '%s': incompatible field #%d ('%s') offsets\n",
1445                                         sym_name, i, n1);
1446                                 return false;
1447                         }
1448                         if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
1449                                 return false;
1450                 }
1451
1452                 return true;
1453         }
1454         case BTF_KIND_FUNC_PROTO: {
1455                 const struct btf_param *m1, *m2;
1456
1457                 if (btf_vlen(t1) != btf_vlen(t2)) {
1458                         pr_warn("global '%s': incompatible number of %s params %u and %u\n",
1459                                 sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
1460                         return false;
1461                 }
1462
1463                 n = btf_vlen(t1);
1464                 m1 = btf_params(t1);
1465                 m2 = btf_params(t2);
1466                 for (i = 0; i < n; i++, m1++, m2++) {
1467                         /* ignore func arg names */
1468                         if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
1469                                 return false;
1470                 }
1471
1472                 /* now check return type as well */
1473                 id1 = t1->type;
1474                 id2 = t2->type;
1475                 goto recur;
1476         }
1477
1478         /* skip_mods_and_typedefs() make this impossible */
1479         case BTF_KIND_TYPEDEF:
1480         case BTF_KIND_VOLATILE:
1481         case BTF_KIND_CONST:
1482         case BTF_KIND_RESTRICT:
1483         /* DATASECs are never compared with each other */
1484         case BTF_KIND_DATASEC:
1485         default:
1486                 pr_warn("global '%s': unsupported BTF kind %s\n",
1487                         sym_name, btf_kind_str(t1));
1488                 return false;
1489         }
1490 }
1491
1492 static bool map_defs_match(const char *sym_name,
1493                            const struct btf *main_btf,
1494                            const struct btf_map_def *main_def,
1495                            const struct btf_map_def *main_inner_def,
1496                            const struct btf *extra_btf,
1497                            const struct btf_map_def *extra_def,
1498                            const struct btf_map_def *extra_inner_def)
1499 {
1500         const char *reason;
1501
1502         if (main_def->map_type != extra_def->map_type) {
1503                 reason = "type";
1504                 goto mismatch;
1505         }
1506
1507         /* check key type/size match */
1508         if (main_def->key_size != extra_def->key_size) {
1509                 reason = "key_size";
1510                 goto mismatch;
1511         }
1512         if (!!main_def->key_type_id != !!extra_def->key_type_id) {
1513                 reason = "key type";
1514                 goto mismatch;
1515         }
1516         if ((main_def->parts & MAP_DEF_KEY_TYPE)
1517              && !glob_sym_btf_matches(sym_name, true /*exact*/,
1518                                       main_btf, main_def->key_type_id,
1519                                       extra_btf, extra_def->key_type_id)) {
1520                 reason = "key type";
1521                 goto mismatch;
1522         }
1523
1524         /* validate value type/size match */
1525         if (main_def->value_size != extra_def->value_size) {
1526                 reason = "value_size";
1527                 goto mismatch;
1528         }
1529         if (!!main_def->value_type_id != !!extra_def->value_type_id) {
1530                 reason = "value type";
1531                 goto mismatch;
1532         }
1533         if ((main_def->parts & MAP_DEF_VALUE_TYPE)
1534              && !glob_sym_btf_matches(sym_name, true /*exact*/,
1535                                       main_btf, main_def->value_type_id,
1536                                       extra_btf, extra_def->value_type_id)) {
1537                 reason = "key type";
1538                 goto mismatch;
1539         }
1540
1541         if (main_def->max_entries != extra_def->max_entries) {
1542                 reason = "max_entries";
1543                 goto mismatch;
1544         }
1545         if (main_def->map_flags != extra_def->map_flags) {
1546                 reason = "map_flags";
1547                 goto mismatch;
1548         }
1549         if (main_def->numa_node != extra_def->numa_node) {
1550                 reason = "numa_node";
1551                 goto mismatch;
1552         }
1553         if (main_def->pinning != extra_def->pinning) {
1554                 reason = "pinning";
1555                 goto mismatch;
1556         }
1557
1558         if ((main_def->parts & MAP_DEF_INNER_MAP) != (extra_def->parts & MAP_DEF_INNER_MAP)) {
1559                 reason = "inner map";
1560                 goto mismatch;
1561         }
1562
1563         if (main_def->parts & MAP_DEF_INNER_MAP) {
1564                 char inner_map_name[128];
1565
1566                 snprintf(inner_map_name, sizeof(inner_map_name), "%s.inner", sym_name);
1567
1568                 return map_defs_match(inner_map_name,
1569                                       main_btf, main_inner_def, NULL,
1570                                       extra_btf, extra_inner_def, NULL);
1571         }
1572
1573         return true;
1574
1575 mismatch:
1576         pr_warn("global '%s': map %s mismatch\n", sym_name, reason);
1577         return false;
1578 }
1579
1580 static bool glob_map_defs_match(const char *sym_name,
1581                                 struct bpf_linker *linker, struct glob_sym *glob_sym,
1582                                 struct src_obj *obj, Elf64_Sym *sym, int btf_id)
1583 {
1584         struct btf_map_def dst_def = {}, dst_inner_def = {};
1585         struct btf_map_def src_def = {}, src_inner_def = {};
1586         const struct btf_type *t;
1587         int err;
1588
1589         t = btf__type_by_id(obj->btf, btf_id);
1590         if (!btf_is_var(t)) {
1591                 pr_warn("global '%s': invalid map definition type [%d]\n", sym_name, btf_id);
1592                 return false;
1593         }
1594         t = skip_mods_and_typedefs(obj->btf, t->type, NULL);
1595
1596         err = parse_btf_map_def(sym_name, obj->btf, t, true /*strict*/, &src_def, &src_inner_def);
1597         if (err) {
1598                 pr_warn("global '%s': invalid map definition\n", sym_name);
1599                 return false;
1600         }
1601
1602         /* re-parse existing map definition */
1603         t = btf__type_by_id(linker->btf, glob_sym->btf_id);
1604         t = skip_mods_and_typedefs(linker->btf, t->type, NULL);
1605         err = parse_btf_map_def(sym_name, linker->btf, t, true /*strict*/, &dst_def, &dst_inner_def);
1606         if (err) {
1607                 /* this should not happen, because we already validated it */
1608                 pr_warn("global '%s': invalid dst map definition\n", sym_name);
1609                 return false;
1610         }
1611
1612         /* Currently extern map definition has to be complete and match
1613          * concrete map definition exactly. This restriction might be lifted
1614          * in the future.
1615          */
1616         return map_defs_match(sym_name, linker->btf, &dst_def, &dst_inner_def,
1617                               obj->btf, &src_def, &src_inner_def);
1618 }
1619
1620 static bool glob_syms_match(const char *sym_name,
1621                             struct bpf_linker *linker, struct glob_sym *glob_sym,
1622                             struct src_obj *obj, Elf64_Sym *sym, size_t sym_idx, int btf_id)
1623 {
1624         const struct btf_type *src_t;
1625
1626         /* if we are dealing with externs, BTF types describing both global
1627          * and extern VARs/FUNCs should be completely present in all files
1628          */
1629         if (!glob_sym->btf_id || !btf_id) {
1630                 pr_warn("BTF info is missing for global symbol '%s'\n", sym_name);
1631                 return false;
1632         }
1633
1634         src_t = btf__type_by_id(obj->btf, btf_id);
1635         if (!btf_is_var(src_t) && !btf_is_func(src_t)) {
1636                 pr_warn("only extern variables and functions are supported, but got '%s' for '%s'\n",
1637                         btf_kind_str(src_t), sym_name);
1638                 return false;
1639         }
1640
1641         /* deal with .maps definitions specially */
1642         if (glob_sym->sec_id && strcmp(linker->secs[glob_sym->sec_id].sec_name, MAPS_ELF_SEC) == 0)
1643                 return glob_map_defs_match(sym_name, linker, glob_sym, obj, sym, btf_id);
1644
1645         if (!glob_sym_btf_matches(sym_name, true /*exact*/,
1646                                   linker->btf, glob_sym->btf_id, obj->btf, btf_id))
1647                 return false;
1648
1649         return true;
1650 }
1651
1652 static bool btf_is_non_static(const struct btf_type *t)
1653 {
1654         return (btf_is_var(t) && btf_var(t)->linkage != BTF_VAR_STATIC)
1655                || (btf_is_func(t) && btf_func_linkage(t) != BTF_FUNC_STATIC);
1656 }
1657
1658 static int find_glob_sym_btf(struct src_obj *obj, Elf64_Sym *sym, const char *sym_name,
1659                              int *out_btf_sec_id, int *out_btf_id)
1660 {
1661         int i, j, n, m, btf_id = 0;
1662         const struct btf_type *t;
1663         const struct btf_var_secinfo *vi;
1664         const char *name;
1665
1666         if (!obj->btf) {
1667                 pr_warn("failed to find BTF info for object '%s'\n", obj->filename);
1668                 return -EINVAL;
1669         }
1670
1671         n = btf__type_cnt(obj->btf);
1672         for (i = 1; i < n; i++) {
1673                 t = btf__type_by_id(obj->btf, i);
1674
1675                 /* some global and extern FUNCs and VARs might not be associated with any
1676                  * DATASEC, so try to detect them in the same pass
1677                  */
1678                 if (btf_is_non_static(t)) {
1679                         name = btf__str_by_offset(obj->btf, t->name_off);
1680                         if (strcmp(name, sym_name) != 0)
1681                                 continue;
1682
1683                         /* remember and still try to find DATASEC */
1684                         btf_id = i;
1685                         continue;
1686                 }
1687
1688                 if (!btf_is_datasec(t))
1689                         continue;
1690
1691                 vi = btf_var_secinfos(t);
1692                 for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
1693                         t = btf__type_by_id(obj->btf, vi->type);
1694                         name = btf__str_by_offset(obj->btf, t->name_off);
1695
1696                         if (strcmp(name, sym_name) != 0)
1697                                 continue;
1698                         if (btf_is_var(t) && btf_var(t)->linkage == BTF_VAR_STATIC)
1699                                 continue;
1700                         if (btf_is_func(t) && btf_func_linkage(t) == BTF_FUNC_STATIC)
1701                                 continue;
1702
1703                         if (btf_id && btf_id != vi->type) {
1704                                 pr_warn("global/extern '%s' BTF is ambiguous: both types #%d and #%u match\n",
1705                                         sym_name, btf_id, vi->type);
1706                                 return -EINVAL;
1707                         }
1708
1709                         *out_btf_sec_id = i;
1710                         *out_btf_id = vi->type;
1711
1712                         return 0;
1713                 }
1714         }
1715
1716         /* free-floating extern or global FUNC */
1717         if (btf_id) {
1718                 *out_btf_sec_id = 0;
1719                 *out_btf_id = btf_id;
1720                 return 0;
1721         }
1722
1723         pr_warn("failed to find BTF info for global/extern symbol '%s'\n", sym_name);
1724         return -ENOENT;
1725 }
1726
1727 static struct src_sec *find_src_sec_by_name(struct src_obj *obj, const char *sec_name)
1728 {
1729         struct src_sec *sec;
1730         int i;
1731
1732         for (i = 1; i < obj->sec_cnt; i++) {
1733                 sec = &obj->secs[i];
1734
1735                 if (strcmp(sec->sec_name, sec_name) == 0)
1736                         return sec;
1737         }
1738
1739         return NULL;
1740 }
1741
1742 static int complete_extern_btf_info(struct btf *dst_btf, int dst_id,
1743                                     struct btf *src_btf, int src_id)
1744 {
1745         struct btf_type *dst_t = btf_type_by_id(dst_btf, dst_id);
1746         struct btf_type *src_t = btf_type_by_id(src_btf, src_id);
1747         struct btf_param *src_p, *dst_p;
1748         const char *s;
1749         int i, n, off;
1750
1751         /* We already made sure that source and destination types (FUNC or
1752          * VAR) match in terms of types and argument names.
1753          */
1754         if (btf_is_var(dst_t)) {
1755                 btf_var(dst_t)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
1756                 return 0;
1757         }
1758
1759         dst_t->info = btf_type_info(BTF_KIND_FUNC, BTF_FUNC_GLOBAL, 0);
1760
1761         /* now onto FUNC_PROTO types */
1762         src_t = btf_type_by_id(src_btf, src_t->type);
1763         dst_t = btf_type_by_id(dst_btf, dst_t->type);
1764
1765         /* Fill in all the argument names, which for extern FUNCs are missing.
1766          * We'll end up with two copies of FUNCs/VARs for externs, but that
1767          * will be taken care of by BTF dedup at the very end.
1768          * It might be that BTF types for extern in one file has less/more BTF
1769          * information (e.g., FWD instead of full STRUCT/UNION information),
1770          * but that should be (in most cases, subject to BTF dedup rules)
1771          * handled and resolved by BTF dedup algorithm as well, so we won't
1772          * worry about it. Our only job is to make sure that argument names
1773          * are populated on both sides, otherwise BTF dedup will pedantically
1774          * consider them different.
1775          */
1776         src_p = btf_params(src_t);
1777         dst_p = btf_params(dst_t);
1778         for (i = 0, n = btf_vlen(dst_t); i < n; i++, src_p++, dst_p++) {
1779                 if (!src_p->name_off)
1780                         continue;
1781
1782                 /* src_btf has more complete info, so add name to dst_btf */
1783                 s = btf__str_by_offset(src_btf, src_p->name_off);
1784                 off = btf__add_str(dst_btf, s);
1785                 if (off < 0)
1786                         return off;
1787                 dst_p->name_off = off;
1788         }
1789         return 0;
1790 }
1791
1792 static void sym_update_bind(Elf64_Sym *sym, int sym_bind)
1793 {
1794         sym->st_info = ELF64_ST_INFO(sym_bind, ELF64_ST_TYPE(sym->st_info));
1795 }
1796
1797 static void sym_update_type(Elf64_Sym *sym, int sym_type)
1798 {
1799         sym->st_info = ELF64_ST_INFO(ELF64_ST_BIND(sym->st_info), sym_type);
1800 }
1801
1802 static void sym_update_visibility(Elf64_Sym *sym, int sym_vis)
1803 {
1804         /* libelf doesn't provide setters for ST_VISIBILITY,
1805          * but it is stored in the lower 2 bits of st_other
1806          */
1807         sym->st_other &= ~0x03;
1808         sym->st_other |= sym_vis;
1809 }
1810
1811 static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
1812                                  Elf64_Sym *sym, const char *sym_name, int src_sym_idx)
1813 {
1814         struct src_sec *src_sec = NULL;
1815         struct dst_sec *dst_sec = NULL;
1816         struct glob_sym *glob_sym = NULL;
1817         int name_off, sym_type, sym_bind, sym_vis, err;
1818         int btf_sec_id = 0, btf_id = 0;
1819         size_t dst_sym_idx;
1820         Elf64_Sym *dst_sym;
1821         bool sym_is_extern;
1822
1823         sym_type = ELF64_ST_TYPE(sym->st_info);
1824         sym_bind = ELF64_ST_BIND(sym->st_info);
1825         sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
1826         sym_is_extern = sym->st_shndx == SHN_UNDEF;
1827
1828         if (sym_is_extern) {
1829                 if (!obj->btf) {
1830                         pr_warn("externs without BTF info are not supported\n");
1831                         return -ENOTSUP;
1832                 }
1833         } else if (sym->st_shndx < SHN_LORESERVE) {
1834                 src_sec = &obj->secs[sym->st_shndx];
1835                 if (src_sec->skipped)
1836                         return 0;
1837                 dst_sec = &linker->secs[src_sec->dst_id];
1838
1839                 /* allow only one STT_SECTION symbol per section */
1840                 if (sym_type == STT_SECTION && dst_sec->sec_sym_idx) {
1841                         obj->sym_map[src_sym_idx] = dst_sec->sec_sym_idx;
1842                         return 0;
1843                 }
1844         }
1845
1846         if (sym_bind == STB_LOCAL)
1847                 goto add_sym;
1848
1849         /* find matching BTF info */
1850         err = find_glob_sym_btf(obj, sym, sym_name, &btf_sec_id, &btf_id);
1851         if (err)
1852                 return err;
1853
1854         if (sym_is_extern && btf_sec_id) {
1855                 const char *sec_name = NULL;
1856                 const struct btf_type *t;
1857
1858                 t = btf__type_by_id(obj->btf, btf_sec_id);
1859                 sec_name = btf__str_by_offset(obj->btf, t->name_off);
1860
1861                 /* Clang puts unannotated extern vars into
1862                  * '.extern' BTF DATASEC. Treat them the same
1863                  * as unannotated extern funcs (which are
1864                  * currently not put into any DATASECs).
1865                  * Those don't have associated src_sec/dst_sec.
1866                  */
1867                 if (strcmp(sec_name, BTF_EXTERN_SEC) != 0) {
1868                         src_sec = find_src_sec_by_name(obj, sec_name);
1869                         if (!src_sec) {
1870                                 pr_warn("failed to find matching ELF sec '%s'\n", sec_name);
1871                                 return -ENOENT;
1872                         }
1873                         dst_sec = &linker->secs[src_sec->dst_id];
1874                 }
1875         }
1876
1877         glob_sym = find_glob_sym(linker, sym_name);
1878         if (glob_sym) {
1879                 /* Preventively resolve to existing symbol. This is
1880                  * needed for further relocation symbol remapping in
1881                  * the next step of linking.
1882                  */
1883                 obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
1884
1885                 /* If both symbols are non-externs, at least one of
1886                  * them has to be STB_WEAK, otherwise they are in
1887                  * a conflict with each other.
1888                  */
1889                 if (!sym_is_extern && !glob_sym->is_extern
1890                     && !glob_sym->is_weak && sym_bind != STB_WEAK) {
1891                         pr_warn("conflicting non-weak symbol #%d (%s) definition in '%s'\n",
1892                                 src_sym_idx, sym_name, obj->filename);
1893                         return -EINVAL;
1894                 }
1895
1896                 if (!glob_syms_match(sym_name, linker, glob_sym, obj, sym, src_sym_idx, btf_id))
1897                         return -EINVAL;
1898
1899                 dst_sym = get_sym_by_idx(linker, glob_sym->sym_idx);
1900
1901                 /* If new symbol is strong, then force dst_sym to be strong as
1902                  * well; this way a mix of weak and non-weak extern
1903                  * definitions will end up being strong.
1904                  */
1905                 if (sym_bind == STB_GLOBAL) {
1906                         /* We still need to preserve type (NOTYPE or
1907                          * OBJECT/FUNC, depending on whether the symbol is
1908                          * extern or not)
1909                          */
1910                         sym_update_bind(dst_sym, STB_GLOBAL);
1911                         glob_sym->is_weak = false;
1912                 }
1913
1914                 /* Non-default visibility is "contaminating", with stricter
1915                  * visibility overwriting more permissive ones, even if more
1916                  * permissive visibility comes from just an extern definition.
1917                  * Currently only STV_DEFAULT and STV_HIDDEN are allowed and
1918                  * ensured by ELF symbol sanity checks above.
1919                  */
1920                 if (sym_vis > ELF64_ST_VISIBILITY(dst_sym->st_other))
1921                         sym_update_visibility(dst_sym, sym_vis);
1922
1923                 /* If the new symbol is extern, then regardless if
1924                  * existing symbol is extern or resolved global, just
1925                  * keep the existing one untouched.
1926                  */
1927                 if (sym_is_extern)
1928                         return 0;
1929
1930                 /* If existing symbol is a strong resolved symbol, bail out,
1931                  * because we lost resolution battle have nothing to
1932                  * contribute. We already checked abover that there is no
1933                  * strong-strong conflict. We also already tightened binding
1934                  * and visibility, so nothing else to contribute at that point.
1935                  */
1936                 if (!glob_sym->is_extern && sym_bind == STB_WEAK)
1937                         return 0;
1938
1939                 /* At this point, new symbol is strong non-extern,
1940                  * so overwrite glob_sym with new symbol information.
1941                  * Preserve binding and visibility.
1942                  */
1943                 sym_update_type(dst_sym, sym_type);
1944                 dst_sym->st_shndx = dst_sec->sec_idx;
1945                 dst_sym->st_value = src_sec->dst_off + sym->st_value;
1946                 dst_sym->st_size = sym->st_size;
1947
1948                 /* see comment below about dst_sec->id vs dst_sec->sec_idx */
1949                 glob_sym->sec_id = dst_sec->id;
1950                 glob_sym->is_extern = false;
1951
1952                 if (complete_extern_btf_info(linker->btf, glob_sym->btf_id,
1953                                              obj->btf, btf_id))
1954                         return -EINVAL;
1955
1956                 /* request updating VAR's/FUNC's underlying BTF type when appending BTF type */
1957                 glob_sym->underlying_btf_id = 0;
1958
1959                 obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
1960                 return 0;
1961         }
1962
1963 add_sym:
1964         name_off = strset__add_str(linker->strtab_strs, sym_name);
1965         if (name_off < 0)
1966                 return name_off;
1967
1968         dst_sym = add_new_sym(linker, &dst_sym_idx);
1969         if (!dst_sym)
1970                 return -ENOMEM;
1971
1972         dst_sym->st_name = name_off;
1973         dst_sym->st_info = sym->st_info;
1974         dst_sym->st_other = sym->st_other;
1975         dst_sym->st_shndx = dst_sec ? dst_sec->sec_idx : sym->st_shndx;
1976         dst_sym->st_value = (src_sec ? src_sec->dst_off : 0) + sym->st_value;
1977         dst_sym->st_size = sym->st_size;
1978
1979         obj->sym_map[src_sym_idx] = dst_sym_idx;
1980
1981         if (sym_type == STT_SECTION && dst_sym) {
1982                 dst_sec->sec_sym_idx = dst_sym_idx;
1983                 dst_sym->st_value = 0;
1984         }
1985
1986         if (sym_bind != STB_LOCAL) {
1987                 glob_sym = add_glob_sym(linker);
1988                 if (!glob_sym)
1989                         return -ENOMEM;
1990
1991                 glob_sym->sym_idx = dst_sym_idx;
1992                 /* we use dst_sec->id (and not dst_sec->sec_idx), because
1993                  * ephemeral sections (.kconfig, .ksyms, etc) don't have
1994                  * sec_idx (as they don't have corresponding ELF section), but
1995                  * still have id. .extern doesn't have even ephemeral section
1996                  * associated with it, so dst_sec->id == dst_sec->sec_idx == 0.
1997                  */
1998                 glob_sym->sec_id = dst_sec ? dst_sec->id : 0;
1999                 glob_sym->name_off = name_off;
2000                 /* we will fill btf_id in during BTF merging step */
2001                 glob_sym->btf_id = 0;
2002                 glob_sym->is_extern = sym_is_extern;
2003                 glob_sym->is_weak = sym_bind == STB_WEAK;
2004         }
2005
2006         return 0;
2007 }
2008
2009 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj)
2010 {
2011         struct src_sec *src_symtab = &obj->secs[obj->symtab_sec_idx];
2012         int i, err;
2013
2014         for (i = 1; i < obj->sec_cnt; i++) {
2015                 struct src_sec *src_sec, *src_linked_sec;
2016                 struct dst_sec *dst_sec, *dst_linked_sec;
2017                 Elf64_Rel *src_rel, *dst_rel;
2018                 int j, n;
2019
2020                 src_sec = &obj->secs[i];
2021                 if (!is_relo_sec(src_sec))
2022                         continue;
2023
2024                 /* shdr->sh_info points to relocatable section */
2025                 src_linked_sec = &obj->secs[src_sec->shdr->sh_info];
2026                 if (src_linked_sec->skipped)
2027                         continue;
2028
2029                 dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
2030                 if (!dst_sec) {
2031                         dst_sec = add_dst_sec(linker, src_sec->sec_name);
2032                         if (!dst_sec)
2033                                 return -ENOMEM;
2034                         err = init_sec(linker, dst_sec, src_sec);
2035                         if (err) {
2036                                 pr_warn("failed to init section '%s'\n", src_sec->sec_name);
2037                                 return err;
2038                         }
2039                 } else if (!secs_match(dst_sec, src_sec)) {
2040                         pr_warn("sections %s are not compatible\n", src_sec->sec_name);
2041                         return -1;
2042                 }
2043
2044                 /* shdr->sh_link points to SYMTAB */
2045                 dst_sec->shdr->sh_link = linker->symtab_sec_idx;
2046
2047                 /* shdr->sh_info points to relocated section */
2048                 dst_linked_sec = &linker->secs[src_linked_sec->dst_id];
2049                 dst_sec->shdr->sh_info = dst_linked_sec->sec_idx;
2050
2051                 src_sec->dst_id = dst_sec->id;
2052                 err = extend_sec(linker, dst_sec, src_sec);
2053                 if (err)
2054                         return err;
2055
2056                 src_rel = src_sec->data->d_buf;
2057                 dst_rel = dst_sec->raw_data + src_sec->dst_off;
2058                 n = src_sec->shdr->sh_size / src_sec->shdr->sh_entsize;
2059                 for (j = 0; j < n; j++, src_rel++, dst_rel++) {
2060                         size_t src_sym_idx, dst_sym_idx, sym_type;
2061                         Elf64_Sym *src_sym;
2062
2063                         src_sym_idx = ELF64_R_SYM(src_rel->r_info);
2064                         src_sym = src_symtab->data->d_buf + sizeof(*src_sym) * src_sym_idx;
2065
2066                         dst_sym_idx = obj->sym_map[src_sym_idx];
2067                         dst_rel->r_offset += src_linked_sec->dst_off;
2068                         sym_type = ELF64_R_TYPE(src_rel->r_info);
2069                         dst_rel->r_info = ELF64_R_INFO(dst_sym_idx, sym_type);
2070
2071                         if (ELF64_ST_TYPE(src_sym->st_info) == STT_SECTION) {
2072                                 struct src_sec *sec = &obj->secs[src_sym->st_shndx];
2073                                 struct bpf_insn *insn;
2074
2075                                 if (src_linked_sec->shdr->sh_flags & SHF_EXECINSTR) {
2076                                         /* calls to the very first static function inside
2077                                          * .text section at offset 0 will
2078                                          * reference section symbol, not the
2079                                          * function symbol. Fix that up,
2080                                          * otherwise it won't be possible to
2081                                          * relocate calls to two different
2082                                          * static functions with the same name
2083                                          * (rom two different object files)
2084                                          */
2085                                         insn = dst_linked_sec->raw_data + dst_rel->r_offset;
2086                                         if (insn->code == (BPF_JMP | BPF_CALL))
2087                                                 insn->imm += sec->dst_off / sizeof(struct bpf_insn);
2088                                         else
2089                                                 insn->imm += sec->dst_off;
2090                                 } else {
2091                                         pr_warn("relocation against STT_SECTION in non-exec section is not supported!\n");
2092                                         return -EINVAL;
2093                                 }
2094                         }
2095
2096                 }
2097         }
2098
2099         return 0;
2100 }
2101
2102 static Elf64_Sym *find_sym_by_name(struct src_obj *obj, size_t sec_idx,
2103                                    int sym_type, const char *sym_name)
2104 {
2105         struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
2106         Elf64_Sym *sym = symtab->data->d_buf;
2107         int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize;
2108         int str_sec_idx = symtab->shdr->sh_link;
2109         const char *name;
2110
2111         for (i = 0; i < n; i++, sym++) {
2112                 if (sym->st_shndx != sec_idx)
2113                         continue;
2114                 if (ELF64_ST_TYPE(sym->st_info) != sym_type)
2115                         continue;
2116
2117                 name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
2118                 if (!name)
2119                         return NULL;
2120
2121                 if (strcmp(sym_name, name) != 0)
2122                         continue;
2123
2124                 return sym;
2125         }
2126
2127         return NULL;
2128 }
2129
2130 static int linker_fixup_btf(struct src_obj *obj)
2131 {
2132         const char *sec_name;
2133         struct src_sec *sec;
2134         int i, j, n, m;
2135
2136         if (!obj->btf)
2137                 return 0;
2138
2139         n = btf__type_cnt(obj->btf);
2140         for (i = 1; i < n; i++) {
2141                 struct btf_var_secinfo *vi;
2142                 struct btf_type *t;
2143
2144                 t = btf_type_by_id(obj->btf, i);
2145                 if (btf_kind(t) != BTF_KIND_DATASEC)
2146                         continue;
2147
2148                 sec_name = btf__str_by_offset(obj->btf, t->name_off);
2149                 sec = find_src_sec_by_name(obj, sec_name);
2150                 if (sec) {
2151                         /* record actual section size, unless ephemeral */
2152                         if (sec->shdr)
2153                                 t->size = sec->shdr->sh_size;
2154                 } else {
2155                         /* BTF can have some sections that are not represented
2156                          * in ELF, e.g., .kconfig, .ksyms, .extern, which are used
2157                          * for special extern variables.
2158                          *
2159                          * For all but one such special (ephemeral)
2160                          * sections, we pre-create "section shells" to be able
2161                          * to keep track of extra per-section metadata later
2162                          * (e.g., those BTF extern variables).
2163                          *
2164                          * .extern is even more special, though, because it
2165                          * contains extern variables that need to be resolved
2166                          * by static linker, not libbpf and kernel. When such
2167                          * externs are resolved, we are going to remove them
2168                          * from .extern BTF section and might end up not
2169                          * needing it at all. Each resolved extern should have
2170                          * matching non-extern VAR/FUNC in other sections.
2171                          *
2172                          * We do support leaving some of the externs
2173                          * unresolved, though, to support cases of building
2174                          * libraries, which will later be linked against final
2175                          * BPF applications. So if at finalization we still
2176                          * see unresolved externs, we'll create .extern
2177                          * section on our own.
2178                          */
2179                         if (strcmp(sec_name, BTF_EXTERN_SEC) == 0)
2180                                 continue;
2181
2182                         sec = add_src_sec(obj, sec_name);
2183                         if (!sec)
2184                                 return -ENOMEM;
2185
2186                         sec->ephemeral = true;
2187                         sec->sec_idx = 0; /* will match UNDEF shndx in ELF */
2188                 }
2189
2190                 /* remember ELF section and its BTF type ID match */
2191                 sec->sec_type_id = i;
2192
2193                 /* fix up variable offsets */
2194                 vi = btf_var_secinfos(t);
2195                 for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
2196                         const struct btf_type *vt = btf__type_by_id(obj->btf, vi->type);
2197                         const char *var_name = btf__str_by_offset(obj->btf, vt->name_off);
2198                         int var_linkage = btf_var(vt)->linkage;
2199                         Elf64_Sym *sym;
2200
2201                         /* no need to patch up static or extern vars */
2202                         if (var_linkage != BTF_VAR_GLOBAL_ALLOCATED)
2203                                 continue;
2204
2205                         sym = find_sym_by_name(obj, sec->sec_idx, STT_OBJECT, var_name);
2206                         if (!sym) {
2207                                 pr_warn("failed to find symbol for variable '%s' in section '%s'\n", var_name, sec_name);
2208                                 return -ENOENT;
2209                         }
2210
2211                         vi->offset = sym->st_value;
2212                 }
2213         }
2214
2215         return 0;
2216 }
2217
2218 static int remap_type_id(__u32 *type_id, void *ctx)
2219 {
2220         int *id_map = ctx;
2221         int new_id = id_map[*type_id];
2222
2223         /* Error out if the type wasn't remapped. Ignore VOID which stays VOID. */
2224         if (new_id == 0 && *type_id != 0) {
2225                 pr_warn("failed to find new ID mapping for original BTF type ID %u\n", *type_id);
2226                 return -EINVAL;
2227         }
2228
2229         *type_id = id_map[*type_id];
2230
2231         return 0;
2232 }
2233
2234 static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
2235 {
2236         const struct btf_type *t;
2237         int i, j, n, start_id, id;
2238         const char *name;
2239
2240         if (!obj->btf)
2241                 return 0;
2242
2243         start_id = btf__type_cnt(linker->btf);
2244         n = btf__type_cnt(obj->btf);
2245
2246         obj->btf_type_map = calloc(n + 1, sizeof(int));
2247         if (!obj->btf_type_map)
2248                 return -ENOMEM;
2249
2250         for (i = 1; i < n; i++) {
2251                 struct glob_sym *glob_sym = NULL;
2252
2253                 t = btf__type_by_id(obj->btf, i);
2254
2255                 /* DATASECs are handled specially below */
2256                 if (btf_kind(t) == BTF_KIND_DATASEC)
2257                         continue;
2258
2259                 if (btf_is_non_static(t)) {
2260                         /* there should be glob_sym already */
2261                         name = btf__str_by_offset(obj->btf, t->name_off);
2262                         glob_sym = find_glob_sym(linker, name);
2263
2264                         /* VARs without corresponding glob_sym are those that
2265                          * belong to skipped/deduplicated sections (i.e.,
2266                          * license and version), so just skip them
2267                          */
2268                         if (!glob_sym)
2269                                 continue;
2270
2271                         /* linker_append_elf_sym() might have requested
2272                          * updating underlying type ID, if extern was resolved
2273                          * to strong symbol or weak got upgraded to non-weak
2274                          */
2275                         if (glob_sym->underlying_btf_id == 0)
2276                                 glob_sym->underlying_btf_id = -t->type;
2277
2278                         /* globals from previous object files that match our
2279                          * VAR/FUNC already have a corresponding associated
2280                          * BTF type, so just make sure to use it
2281                          */
2282                         if (glob_sym->btf_id) {
2283                                 /* reuse existing BTF type for global var/func */
2284                                 obj->btf_type_map[i] = glob_sym->btf_id;
2285                                 continue;
2286                         }
2287                 }
2288
2289                 id = btf__add_type(linker->btf, obj->btf, t);
2290                 if (id < 0) {
2291                         pr_warn("failed to append BTF type #%d from file '%s'\n", i, obj->filename);
2292                         return id;
2293                 }
2294
2295                 obj->btf_type_map[i] = id;
2296
2297                 /* record just appended BTF type for var/func */
2298                 if (glob_sym) {
2299                         glob_sym->btf_id = id;
2300                         glob_sym->underlying_btf_id = -t->type;
2301                 }
2302         }
2303
2304         /* remap all the types except DATASECs */
2305         n = btf__type_cnt(linker->btf);
2306         for (i = start_id; i < n; i++) {
2307                 struct btf_type *dst_t = btf_type_by_id(linker->btf, i);
2308
2309                 if (btf_type_visit_type_ids(dst_t, remap_type_id, obj->btf_type_map))
2310                         return -EINVAL;
2311         }
2312
2313         /* Rewrite VAR/FUNC underlying types (i.e., FUNC's FUNC_PROTO and VAR's
2314          * actual type), if necessary
2315          */
2316         for (i = 0; i < linker->glob_sym_cnt; i++) {
2317                 struct glob_sym *glob_sym = &linker->glob_syms[i];
2318                 struct btf_type *glob_t;
2319
2320                 if (glob_sym->underlying_btf_id >= 0)
2321                         continue;
2322
2323                 glob_sym->underlying_btf_id = obj->btf_type_map[-glob_sym->underlying_btf_id];
2324
2325                 glob_t = btf_type_by_id(linker->btf, glob_sym->btf_id);
2326                 glob_t->type = glob_sym->underlying_btf_id;
2327         }
2328
2329         /* append DATASEC info */
2330         for (i = 1; i < obj->sec_cnt; i++) {
2331                 struct src_sec *src_sec;
2332                 struct dst_sec *dst_sec;
2333                 const struct btf_var_secinfo *src_var;
2334                 struct btf_var_secinfo *dst_var;
2335
2336                 src_sec = &obj->secs[i];
2337                 if (!src_sec->sec_type_id || src_sec->skipped)
2338                         continue;
2339                 dst_sec = &linker->secs[src_sec->dst_id];
2340
2341                 /* Mark section as having BTF regardless of the presence of
2342                  * variables. In some cases compiler might generate empty BTF
2343                  * with no variables information. E.g., when promoting local
2344                  * array/structure variable initial values and BPF object
2345                  * file otherwise has no read-only static variables in
2346                  * .rodata. We need to preserve such empty BTF and just set
2347                  * correct section size.
2348                  */
2349                 dst_sec->has_btf = true;
2350
2351                 t = btf__type_by_id(obj->btf, src_sec->sec_type_id);
2352                 src_var = btf_var_secinfos(t);
2353                 n = btf_vlen(t);
2354                 for (j = 0; j < n; j++, src_var++) {
2355                         void *sec_vars = dst_sec->sec_vars;
2356                         int new_id = obj->btf_type_map[src_var->type];
2357                         struct glob_sym *glob_sym = NULL;
2358
2359                         t = btf_type_by_id(linker->btf, new_id);
2360                         if (btf_is_non_static(t)) {
2361                                 name = btf__str_by_offset(linker->btf, t->name_off);
2362                                 glob_sym = find_glob_sym(linker, name);
2363                                 if (glob_sym->sec_id != dst_sec->id) {
2364                                         pr_warn("global '%s': section mismatch %d vs %d\n",
2365                                                 name, glob_sym->sec_id, dst_sec->id);
2366                                         return -EINVAL;
2367                                 }
2368                         }
2369
2370                         /* If there is already a member (VAR or FUNC) mapped
2371                          * to the same type, don't add a duplicate entry.
2372                          * This will happen when multiple object files define
2373                          * the same extern VARs/FUNCs.
2374                          */
2375                         if (glob_sym && glob_sym->var_idx >= 0) {
2376                                 __s64 sz;
2377
2378                                 dst_var = &dst_sec->sec_vars[glob_sym->var_idx];
2379                                 /* Because underlying BTF type might have
2380                                  * changed, so might its size have changed, so
2381                                  * re-calculate and update it in sec_var.
2382                                  */
2383                                 sz = btf__resolve_size(linker->btf, glob_sym->underlying_btf_id);
2384                                 if (sz < 0) {
2385                                         pr_warn("global '%s': failed to resolve size of underlying type: %d\n",
2386                                                 name, (int)sz);
2387                                         return -EINVAL;
2388                                 }
2389                                 dst_var->size = sz;
2390                                 continue;
2391                         }
2392
2393                         sec_vars = libbpf_reallocarray(sec_vars,
2394                                                        dst_sec->sec_var_cnt + 1,
2395                                                        sizeof(*dst_sec->sec_vars));
2396                         if (!sec_vars)
2397                                 return -ENOMEM;
2398
2399                         dst_sec->sec_vars = sec_vars;
2400                         dst_sec->sec_var_cnt++;
2401
2402                         dst_var = &dst_sec->sec_vars[dst_sec->sec_var_cnt - 1];
2403                         dst_var->type = obj->btf_type_map[src_var->type];
2404                         dst_var->size = src_var->size;
2405                         dst_var->offset = src_sec->dst_off + src_var->offset;
2406
2407                         if (glob_sym)
2408                                 glob_sym->var_idx = dst_sec->sec_var_cnt - 1;
2409                 }
2410         }
2411
2412         return 0;
2413 }
2414
2415 static void *add_btf_ext_rec(struct btf_ext_sec_data *ext_data, const void *src_rec)
2416 {
2417         void *tmp;
2418
2419         tmp = libbpf_reallocarray(ext_data->recs, ext_data->rec_cnt + 1, ext_data->rec_sz);
2420         if (!tmp)
2421                 return NULL;
2422         ext_data->recs = tmp;
2423
2424         tmp += ext_data->rec_cnt * ext_data->rec_sz;
2425         memcpy(tmp, src_rec, ext_data->rec_sz);
2426
2427         ext_data->rec_cnt++;
2428
2429         return tmp;
2430 }
2431
2432 static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj)
2433 {
2434         const struct btf_ext_info_sec *ext_sec;
2435         const char *sec_name, *s;
2436         struct src_sec *src_sec;
2437         struct dst_sec *dst_sec;
2438         int rec_sz, str_off, i;
2439
2440         if (!obj->btf_ext)
2441                 return 0;
2442
2443         rec_sz = obj->btf_ext->func_info.rec_size;
2444         for_each_btf_ext_sec(&obj->btf_ext->func_info, ext_sec) {
2445                 struct bpf_func_info_min *src_rec, *dst_rec;
2446
2447                 sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
2448                 src_sec = find_src_sec_by_name(obj, sec_name);
2449                 if (!src_sec) {
2450                         pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
2451                         return -EINVAL;
2452                 }
2453                 dst_sec = &linker->secs[src_sec->dst_id];
2454
2455                 if (dst_sec->func_info.rec_sz == 0)
2456                         dst_sec->func_info.rec_sz = rec_sz;
2457                 if (dst_sec->func_info.rec_sz != rec_sz) {
2458                         pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
2459                         return -EINVAL;
2460                 }
2461
2462                 for_each_btf_ext_rec(&obj->btf_ext->func_info, ext_sec, i, src_rec) {
2463                         dst_rec = add_btf_ext_rec(&dst_sec->func_info, src_rec);
2464                         if (!dst_rec)
2465                                 return -ENOMEM;
2466
2467                         dst_rec->insn_off += src_sec->dst_off;
2468                         dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
2469                 }
2470         }
2471
2472         rec_sz = obj->btf_ext->line_info.rec_size;
2473         for_each_btf_ext_sec(&obj->btf_ext->line_info, ext_sec) {
2474                 struct bpf_line_info_min *src_rec, *dst_rec;
2475
2476                 sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
2477                 src_sec = find_src_sec_by_name(obj, sec_name);
2478                 if (!src_sec) {
2479                         pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
2480                         return -EINVAL;
2481                 }
2482                 dst_sec = &linker->secs[src_sec->dst_id];
2483
2484                 if (dst_sec->line_info.rec_sz == 0)
2485                         dst_sec->line_info.rec_sz = rec_sz;
2486                 if (dst_sec->line_info.rec_sz != rec_sz) {
2487                         pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
2488                         return -EINVAL;
2489                 }
2490
2491                 for_each_btf_ext_rec(&obj->btf_ext->line_info, ext_sec, i, src_rec) {
2492                         dst_rec = add_btf_ext_rec(&dst_sec->line_info, src_rec);
2493                         if (!dst_rec)
2494                                 return -ENOMEM;
2495
2496                         dst_rec->insn_off += src_sec->dst_off;
2497
2498                         s = btf__str_by_offset(obj->btf, src_rec->file_name_off);
2499                         str_off = btf__add_str(linker->btf, s);
2500                         if (str_off < 0)
2501                                 return -ENOMEM;
2502                         dst_rec->file_name_off = str_off;
2503
2504                         s = btf__str_by_offset(obj->btf, src_rec->line_off);
2505                         str_off = btf__add_str(linker->btf, s);
2506                         if (str_off < 0)
2507                                 return -ENOMEM;
2508                         dst_rec->line_off = str_off;
2509
2510                         /* dst_rec->line_col is fine */
2511                 }
2512         }
2513
2514         rec_sz = obj->btf_ext->core_relo_info.rec_size;
2515         for_each_btf_ext_sec(&obj->btf_ext->core_relo_info, ext_sec) {
2516                 struct bpf_core_relo *src_rec, *dst_rec;
2517
2518                 sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
2519                 src_sec = find_src_sec_by_name(obj, sec_name);
2520                 if (!src_sec) {
2521                         pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
2522                         return -EINVAL;
2523                 }
2524                 dst_sec = &linker->secs[src_sec->dst_id];
2525
2526                 if (dst_sec->core_relo_info.rec_sz == 0)
2527                         dst_sec->core_relo_info.rec_sz = rec_sz;
2528                 if (dst_sec->core_relo_info.rec_sz != rec_sz) {
2529                         pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
2530                         return -EINVAL;
2531                 }
2532
2533                 for_each_btf_ext_rec(&obj->btf_ext->core_relo_info, ext_sec, i, src_rec) {
2534                         dst_rec = add_btf_ext_rec(&dst_sec->core_relo_info, src_rec);
2535                         if (!dst_rec)
2536                                 return -ENOMEM;
2537
2538                         dst_rec->insn_off += src_sec->dst_off;
2539                         dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
2540
2541                         s = btf__str_by_offset(obj->btf, src_rec->access_str_off);
2542                         str_off = btf__add_str(linker->btf, s);
2543                         if (str_off < 0)
2544                                 return -ENOMEM;
2545                         dst_rec->access_str_off = str_off;
2546
2547                         /* dst_rec->kind is fine */
2548                 }
2549         }
2550
2551         return 0;
2552 }
2553
2554 int bpf_linker__finalize(struct bpf_linker *linker)
2555 {
2556         struct dst_sec *sec;
2557         size_t strs_sz;
2558         const void *strs;
2559         int err, i;
2560
2561         if (!linker->elf)
2562                 return libbpf_err(-EINVAL);
2563
2564         err = finalize_btf(linker);
2565         if (err)
2566                 return libbpf_err(err);
2567
2568         /* Finalize strings */
2569         strs_sz = strset__data_size(linker->strtab_strs);
2570         strs = strset__data(linker->strtab_strs);
2571
2572         sec = &linker->secs[linker->strtab_sec_idx];
2573         sec->data->d_align = 1;
2574         sec->data->d_off = 0LL;
2575         sec->data->d_buf = (void *)strs;
2576         sec->data->d_type = ELF_T_BYTE;
2577         sec->data->d_size = strs_sz;
2578         sec->shdr->sh_size = strs_sz;
2579
2580         for (i = 1; i < linker->sec_cnt; i++) {
2581                 sec = &linker->secs[i];
2582
2583                 /* STRTAB is handled specially above */
2584                 if (sec->sec_idx == linker->strtab_sec_idx)
2585                         continue;
2586
2587                 /* special ephemeral sections (.ksyms, .kconfig, etc) */
2588                 if (!sec->scn)
2589                         continue;
2590
2591                 sec->data->d_buf = sec->raw_data;
2592         }
2593
2594         /* Finalize ELF layout */
2595         if (elf_update(linker->elf, ELF_C_NULL) < 0) {
2596                 err = -errno;
2597                 pr_warn_elf("failed to finalize ELF layout");
2598                 return libbpf_err(err);
2599         }
2600
2601         /* Write out final ELF contents */
2602         if (elf_update(linker->elf, ELF_C_WRITE) < 0) {
2603                 err = -errno;
2604                 pr_warn_elf("failed to write ELF contents");
2605                 return libbpf_err(err);
2606         }
2607
2608         elf_end(linker->elf);
2609         close(linker->fd);
2610
2611         linker->elf = NULL;
2612         linker->fd = -1;
2613
2614         return 0;
2615 }
2616
2617 static int emit_elf_data_sec(struct bpf_linker *linker, const char *sec_name,
2618                              size_t align, const void *raw_data, size_t raw_sz)
2619 {
2620         Elf_Scn *scn;
2621         Elf_Data *data;
2622         Elf64_Shdr *shdr;
2623         int name_off;
2624
2625         name_off = strset__add_str(linker->strtab_strs, sec_name);
2626         if (name_off < 0)
2627                 return name_off;
2628
2629         scn = elf_newscn(linker->elf);
2630         if (!scn)
2631                 return -ENOMEM;
2632         data = elf_newdata(scn);
2633         if (!data)
2634                 return -ENOMEM;
2635         shdr = elf64_getshdr(scn);
2636         if (!shdr)
2637                 return -EINVAL;
2638
2639         shdr->sh_name = name_off;
2640         shdr->sh_type = SHT_PROGBITS;
2641         shdr->sh_flags = 0;
2642         shdr->sh_size = raw_sz;
2643         shdr->sh_link = 0;
2644         shdr->sh_info = 0;
2645         shdr->sh_addralign = align;
2646         shdr->sh_entsize = 0;
2647
2648         data->d_type = ELF_T_BYTE;
2649         data->d_size = raw_sz;
2650         data->d_buf = (void *)raw_data;
2651         data->d_align = align;
2652         data->d_off = 0;
2653
2654         return 0;
2655 }
2656
2657 static int finalize_btf(struct bpf_linker *linker)
2658 {
2659         LIBBPF_OPTS(btf_dedup_opts, opts);
2660         struct btf *btf = linker->btf;
2661         const void *raw_data;
2662         int i, j, id, err;
2663         __u32 raw_sz;
2664
2665         /* bail out if no BTF data was produced */
2666         if (btf__type_cnt(linker->btf) == 1)
2667                 return 0;
2668
2669         for (i = 1; i < linker->sec_cnt; i++) {
2670                 struct dst_sec *sec = &linker->secs[i];
2671
2672                 if (!sec->has_btf)
2673                         continue;
2674
2675                 id = btf__add_datasec(btf, sec->sec_name, sec->sec_sz);
2676                 if (id < 0) {
2677                         pr_warn("failed to add consolidated BTF type for datasec '%s': %d\n",
2678                                 sec->sec_name, id);
2679                         return id;
2680                 }
2681
2682                 for (j = 0; j < sec->sec_var_cnt; j++) {
2683                         struct btf_var_secinfo *vi = &sec->sec_vars[j];
2684
2685                         if (btf__add_datasec_var_info(btf, vi->type, vi->offset, vi->size))
2686                                 return -EINVAL;
2687                 }
2688         }
2689
2690         err = finalize_btf_ext(linker);
2691         if (err) {
2692                 pr_warn(".BTF.ext generation failed: %d\n", err);
2693                 return err;
2694         }
2695
2696         opts.btf_ext = linker->btf_ext;
2697         err = btf__dedup(linker->btf, &opts);
2698         if (err) {
2699                 pr_warn("BTF dedup failed: %d\n", err);
2700                 return err;
2701         }
2702
2703         /* Emit .BTF section */
2704         raw_data = btf__raw_data(linker->btf, &raw_sz);
2705         if (!raw_data)
2706                 return -ENOMEM;
2707
2708         err = emit_elf_data_sec(linker, BTF_ELF_SEC, 8, raw_data, raw_sz);
2709         if (err) {
2710                 pr_warn("failed to write out .BTF ELF section: %d\n", err);
2711                 return err;
2712         }
2713
2714         /* Emit .BTF.ext section */
2715         if (linker->btf_ext) {
2716                 raw_data = btf_ext__get_raw_data(linker->btf_ext, &raw_sz);
2717                 if (!raw_data)
2718                         return -ENOMEM;
2719
2720                 err = emit_elf_data_sec(linker, BTF_EXT_ELF_SEC, 8, raw_data, raw_sz);
2721                 if (err) {
2722                         pr_warn("failed to write out .BTF.ext ELF section: %d\n", err);
2723                         return err;
2724                 }
2725         }
2726
2727         return 0;
2728 }
2729
2730 static int emit_btf_ext_data(struct bpf_linker *linker, void *output,
2731                              const char *sec_name, struct btf_ext_sec_data *sec_data)
2732 {
2733         struct btf_ext_info_sec *sec_info;
2734         void *cur = output;
2735         int str_off;
2736         size_t sz;
2737
2738         if (!sec_data->rec_cnt)
2739                 return 0;
2740
2741         str_off = btf__add_str(linker->btf, sec_name);
2742         if (str_off < 0)
2743                 return -ENOMEM;
2744
2745         sec_info = cur;
2746         sec_info->sec_name_off = str_off;
2747         sec_info->num_info = sec_data->rec_cnt;
2748         cur += sizeof(struct btf_ext_info_sec);
2749
2750         sz = sec_data->rec_cnt * sec_data->rec_sz;
2751         memcpy(cur, sec_data->recs, sz);
2752         cur += sz;
2753
2754         return cur - output;
2755 }
2756
2757 static int finalize_btf_ext(struct bpf_linker *linker)
2758 {
2759         size_t funcs_sz = 0, lines_sz = 0, core_relos_sz = 0, total_sz = 0;
2760         size_t func_rec_sz = 0, line_rec_sz = 0, core_relo_rec_sz = 0;
2761         struct btf_ext_header *hdr;
2762         void *data, *cur;
2763         int i, err, sz;
2764
2765         /* validate that all sections have the same .BTF.ext record sizes
2766          * and calculate total data size for each type of data (func info,
2767          * line info, core relos)
2768          */
2769         for (i = 1; i < linker->sec_cnt; i++) {
2770                 struct dst_sec *sec = &linker->secs[i];
2771
2772                 if (sec->func_info.rec_cnt) {
2773                         if (func_rec_sz == 0)
2774                                 func_rec_sz = sec->func_info.rec_sz;
2775                         if (func_rec_sz != sec->func_info.rec_sz) {
2776                                 pr_warn("mismatch in func_info record size %zu != %u\n",
2777                                         func_rec_sz, sec->func_info.rec_sz);
2778                                 return -EINVAL;
2779                         }
2780
2781                         funcs_sz += sizeof(struct btf_ext_info_sec) + func_rec_sz * sec->func_info.rec_cnt;
2782                 }
2783                 if (sec->line_info.rec_cnt) {
2784                         if (line_rec_sz == 0)
2785                                 line_rec_sz = sec->line_info.rec_sz;
2786                         if (line_rec_sz != sec->line_info.rec_sz) {
2787                                 pr_warn("mismatch in line_info record size %zu != %u\n",
2788                                         line_rec_sz, sec->line_info.rec_sz);
2789                                 return -EINVAL;
2790                         }
2791
2792                         lines_sz += sizeof(struct btf_ext_info_sec) + line_rec_sz * sec->line_info.rec_cnt;
2793                 }
2794                 if (sec->core_relo_info.rec_cnt) {
2795                         if (core_relo_rec_sz == 0)
2796                                 core_relo_rec_sz = sec->core_relo_info.rec_sz;
2797                         if (core_relo_rec_sz != sec->core_relo_info.rec_sz) {
2798                                 pr_warn("mismatch in core_relo_info record size %zu != %u\n",
2799                                         core_relo_rec_sz, sec->core_relo_info.rec_sz);
2800                                 return -EINVAL;
2801                         }
2802
2803                         core_relos_sz += sizeof(struct btf_ext_info_sec) + core_relo_rec_sz * sec->core_relo_info.rec_cnt;
2804                 }
2805         }
2806
2807         if (!funcs_sz && !lines_sz && !core_relos_sz)
2808                 return 0;
2809
2810         total_sz += sizeof(struct btf_ext_header);
2811         if (funcs_sz) {
2812                 funcs_sz += sizeof(__u32); /* record size prefix */
2813                 total_sz += funcs_sz;
2814         }
2815         if (lines_sz) {
2816                 lines_sz += sizeof(__u32); /* record size prefix */
2817                 total_sz += lines_sz;
2818         }
2819         if (core_relos_sz) {
2820                 core_relos_sz += sizeof(__u32); /* record size prefix */
2821                 total_sz += core_relos_sz;
2822         }
2823
2824         cur = data = calloc(1, total_sz);
2825         if (!data)
2826                 return -ENOMEM;
2827
2828         hdr = cur;
2829         hdr->magic = BTF_MAGIC;
2830         hdr->version = BTF_VERSION;
2831         hdr->flags = 0;
2832         hdr->hdr_len = sizeof(struct btf_ext_header);
2833         cur += sizeof(struct btf_ext_header);
2834
2835         /* All offsets are in bytes relative to the end of this header */
2836         hdr->func_info_off = 0;
2837         hdr->func_info_len = funcs_sz;
2838         hdr->line_info_off = funcs_sz;
2839         hdr->line_info_len = lines_sz;
2840         hdr->core_relo_off = funcs_sz + lines_sz;
2841         hdr->core_relo_len = core_relos_sz;
2842
2843         if (funcs_sz) {
2844                 *(__u32 *)cur = func_rec_sz;
2845                 cur += sizeof(__u32);
2846
2847                 for (i = 1; i < linker->sec_cnt; i++) {
2848                         struct dst_sec *sec = &linker->secs[i];
2849
2850                         sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->func_info);
2851                         if (sz < 0) {
2852                                 err = sz;
2853                                 goto out;
2854                         }
2855
2856                         cur += sz;
2857                 }
2858         }
2859
2860         if (lines_sz) {
2861                 *(__u32 *)cur = line_rec_sz;
2862                 cur += sizeof(__u32);
2863
2864                 for (i = 1; i < linker->sec_cnt; i++) {
2865                         struct dst_sec *sec = &linker->secs[i];
2866
2867                         sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->line_info);
2868                         if (sz < 0) {
2869                                 err = sz;
2870                                 goto out;
2871                         }
2872
2873                         cur += sz;
2874                 }
2875         }
2876
2877         if (core_relos_sz) {
2878                 *(__u32 *)cur = core_relo_rec_sz;
2879                 cur += sizeof(__u32);
2880
2881                 for (i = 1; i < linker->sec_cnt; i++) {
2882                         struct dst_sec *sec = &linker->secs[i];
2883
2884                         sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->core_relo_info);
2885                         if (sz < 0) {
2886                                 err = sz;
2887                                 goto out;
2888                         }
2889
2890                         cur += sz;
2891                 }
2892         }
2893
2894         linker->btf_ext = btf_ext__new(data, total_sz);
2895         err = libbpf_get_error(linker->btf_ext);
2896         if (err) {
2897                 linker->btf_ext = NULL;
2898                 pr_warn("failed to parse final .BTF.ext data: %d\n", err);
2899                 goto out;
2900         }
2901
2902 out:
2903         free(data);
2904         return err;
2905 }