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 (!tmp)
1119                         return -ENOMEM;
1120                 dst->raw_data = tmp;
1121
1122                 /* pad dst section, if it's alignment forced size increase */
1123                 memset(dst->raw_data + dst->sec_sz, 0, dst_align_sz - dst->sec_sz);
1124                 /* now copy src data at a properly aligned offset */
1125                 memcpy(dst->raw_data + dst_align_sz, src->data->d_buf, src->shdr->sh_size);
1126         }
1127
1128         dst->sec_sz = dst_final_sz;
1129         dst->shdr->sh_size = dst_final_sz;
1130         dst->data->d_size = dst_final_sz;
1131
1132         dst->shdr->sh_addralign = dst_align;
1133         dst->data->d_align = dst_align;
1134
1135         src->dst_off = dst_align_sz;
1136
1137         return 0;
1138 }
1139
1140 static bool is_data_sec(struct src_sec *sec)
1141 {
1142         if (!sec || sec->skipped)
1143                 return false;
1144         /* ephemeral sections are data sections, e.g., .kconfig, .ksyms */
1145         if (sec->ephemeral)
1146                 return true;
1147         return sec->shdr->sh_type == SHT_PROGBITS || sec->shdr->sh_type == SHT_NOBITS;
1148 }
1149
1150 static bool is_relo_sec(struct src_sec *sec)
1151 {
1152         if (!sec || sec->skipped || sec->ephemeral)
1153                 return false;
1154         return sec->shdr->sh_type == SHT_REL;
1155 }
1156
1157 static int linker_append_sec_data(struct bpf_linker *linker, struct src_obj *obj)
1158 {
1159         int i, err;
1160
1161         for (i = 1; i < obj->sec_cnt; i++) {
1162                 struct src_sec *src_sec;
1163                 struct dst_sec *dst_sec;
1164
1165                 src_sec = &obj->secs[i];
1166                 if (!is_data_sec(src_sec))
1167                         continue;
1168
1169                 dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
1170                 if (!dst_sec) {
1171                         dst_sec = add_dst_sec(linker, src_sec->sec_name);
1172                         if (!dst_sec)
1173                                 return -ENOMEM;
1174                         err = init_sec(linker, dst_sec, src_sec);
1175                         if (err) {
1176                                 pr_warn("failed to init section '%s'\n", src_sec->sec_name);
1177                                 return err;
1178                         }
1179                 } else {
1180                         if (!secs_match(dst_sec, src_sec)) {
1181                                 pr_warn("ELF sections %s are incompatible\n", src_sec->sec_name);
1182                                 return -1;
1183                         }
1184
1185                         /* "license" and "version" sections are deduped */
1186                         if (strcmp(src_sec->sec_name, "license") == 0
1187                             || strcmp(src_sec->sec_name, "version") == 0) {
1188                                 if (!sec_content_is_same(dst_sec, src_sec)) {
1189                                         pr_warn("non-identical contents of section '%s' are not supported\n", src_sec->sec_name);
1190                                         return -EINVAL;
1191                                 }
1192                                 src_sec->skipped = true;
1193                                 src_sec->dst_id = dst_sec->id;
1194                                 continue;
1195                         }
1196                 }
1197
1198                 /* record mapped section index */
1199                 src_sec->dst_id = dst_sec->id;
1200
1201                 err = extend_sec(linker, dst_sec, src_sec);
1202                 if (err)
1203                         return err;
1204         }
1205
1206         return 0;
1207 }
1208
1209 static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj)
1210 {
1211         struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
1212         Elf64_Sym *sym = symtab->data->d_buf;
1213         int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize, err;
1214         int str_sec_idx = symtab->shdr->sh_link;
1215         const char *sym_name;
1216
1217         obj->sym_map = calloc(n + 1, sizeof(*obj->sym_map));
1218         if (!obj->sym_map)
1219                 return -ENOMEM;
1220
1221         for (i = 0; i < n; i++, sym++) {
1222                 /* We already validated all-zero symbol #0 and we already
1223                  * appended it preventively to the final SYMTAB, so skip it.
1224                  */
1225                 if (i == 0)
1226                         continue;
1227
1228                 sym_name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
1229                 if (!sym_name) {
1230                         pr_warn("can't fetch symbol name for symbol #%d in '%s'\n", i, obj->filename);
1231                         return -EINVAL;
1232                 }
1233
1234                 err = linker_append_elf_sym(linker, obj, sym, sym_name, i);
1235                 if (err)
1236                         return err;
1237         }
1238
1239         return 0;
1240 }
1241
1242 static Elf64_Sym *get_sym_by_idx(struct bpf_linker *linker, size_t sym_idx)
1243 {
1244         struct dst_sec *symtab = &linker->secs[linker->symtab_sec_idx];
1245         Elf64_Sym *syms = symtab->raw_data;
1246
1247         return &syms[sym_idx];
1248 }
1249
1250 static struct glob_sym *find_glob_sym(struct bpf_linker *linker, const char *sym_name)
1251 {
1252         struct glob_sym *glob_sym;
1253         const char *name;
1254         int i;
1255
1256         for (i = 0; i < linker->glob_sym_cnt; i++) {
1257                 glob_sym = &linker->glob_syms[i];
1258                 name = strset__data(linker->strtab_strs) + glob_sym->name_off;
1259
1260                 if (strcmp(name, sym_name) == 0)
1261                         return glob_sym;
1262         }
1263
1264         return NULL;
1265 }
1266
1267 static struct glob_sym *add_glob_sym(struct bpf_linker *linker)
1268 {
1269         struct glob_sym *syms, *sym;
1270
1271         syms = libbpf_reallocarray(linker->glob_syms, linker->glob_sym_cnt + 1,
1272                                    sizeof(*linker->glob_syms));
1273         if (!syms)
1274                 return NULL;
1275
1276         sym = &syms[linker->glob_sym_cnt];
1277         memset(sym, 0, sizeof(*sym));
1278         sym->var_idx = -1;
1279
1280         linker->glob_syms = syms;
1281         linker->glob_sym_cnt++;
1282
1283         return sym;
1284 }
1285
1286 static bool glob_sym_btf_matches(const char *sym_name, bool exact,
1287                                  const struct btf *btf1, __u32 id1,
1288                                  const struct btf *btf2, __u32 id2)
1289 {
1290         const struct btf_type *t1, *t2;
1291         bool is_static1, is_static2;
1292         const char *n1, *n2;
1293         int i, n;
1294
1295 recur:
1296         n1 = n2 = NULL;
1297         t1 = skip_mods_and_typedefs(btf1, id1, &id1);
1298         t2 = skip_mods_and_typedefs(btf2, id2, &id2);
1299
1300         /* check if only one side is FWD, otherwise handle with common logic */
1301         if (!exact && btf_is_fwd(t1) != btf_is_fwd(t2)) {
1302                 n1 = btf__str_by_offset(btf1, t1->name_off);
1303                 n2 = btf__str_by_offset(btf2, t2->name_off);
1304                 if (strcmp(n1, n2) != 0) {
1305                         pr_warn("global '%s': incompatible forward declaration names '%s' and '%s'\n",
1306                                 sym_name, n1, n2);
1307                         return false;
1308                 }
1309                 /* validate if FWD kind matches concrete kind */
1310                 if (btf_is_fwd(t1)) {
1311                         if (btf_kflag(t1) && btf_is_union(t2))
1312                                 return true;
1313                         if (!btf_kflag(t1) && btf_is_struct(t2))
1314                                 return true;
1315                         pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
1316                                 sym_name, btf_kflag(t1) ? "union" : "struct", btf_kind_str(t2));
1317                 } else {
1318                         if (btf_kflag(t2) && btf_is_union(t1))
1319                                 return true;
1320                         if (!btf_kflag(t2) && btf_is_struct(t1))
1321                                 return true;
1322                         pr_warn("global '%s': incompatible %s forward declaration and concrete kind %s\n",
1323                                 sym_name, btf_kflag(t2) ? "union" : "struct", btf_kind_str(t1));
1324                 }
1325                 return false;
1326         }
1327
1328         if (btf_kind(t1) != btf_kind(t2)) {
1329                 pr_warn("global '%s': incompatible BTF kinds %s and %s\n",
1330                         sym_name, btf_kind_str(t1), btf_kind_str(t2));
1331                 return false;
1332         }
1333
1334         switch (btf_kind(t1)) {
1335         case BTF_KIND_STRUCT:
1336         case BTF_KIND_UNION:
1337         case BTF_KIND_ENUM:
1338         case BTF_KIND_ENUM64:
1339         case BTF_KIND_FWD:
1340         case BTF_KIND_FUNC:
1341         case BTF_KIND_VAR:
1342                 n1 = btf__str_by_offset(btf1, t1->name_off);
1343                 n2 = btf__str_by_offset(btf2, t2->name_off);
1344                 if (strcmp(n1, n2) != 0) {
1345                         pr_warn("global '%s': incompatible %s names '%s' and '%s'\n",
1346                                 sym_name, btf_kind_str(t1), n1, n2);
1347                         return false;
1348                 }
1349                 break;
1350         default:
1351                 break;
1352         }
1353
1354         switch (btf_kind(t1)) {
1355         case BTF_KIND_UNKN: /* void */
1356         case BTF_KIND_FWD:
1357                 return true;
1358         case BTF_KIND_INT:
1359         case BTF_KIND_FLOAT:
1360         case BTF_KIND_ENUM:
1361         case BTF_KIND_ENUM64:
1362                 /* ignore encoding for int and enum values for enum */
1363                 if (t1->size != t2->size) {
1364                         pr_warn("global '%s': incompatible %s '%s' size %u and %u\n",
1365                                 sym_name, btf_kind_str(t1), n1, t1->size, t2->size);
1366                         return false;
1367                 }
1368                 return true;
1369         case BTF_KIND_PTR:
1370                 /* just validate overall shape of the referenced type, so no
1371                  * contents comparison for struct/union, and allowd fwd vs
1372                  * struct/union
1373                  */
1374                 exact = false;
1375                 id1 = t1->type;
1376                 id2 = t2->type;
1377                 goto recur;
1378         case BTF_KIND_ARRAY:
1379                 /* ignore index type and array size */
1380                 id1 = btf_array(t1)->type;
1381                 id2 = btf_array(t2)->type;
1382                 goto recur;
1383         case BTF_KIND_FUNC:
1384                 /* extern and global linkages are compatible */
1385                 is_static1 = btf_func_linkage(t1) == BTF_FUNC_STATIC;
1386                 is_static2 = btf_func_linkage(t2) == BTF_FUNC_STATIC;
1387                 if (is_static1 != is_static2) {
1388                         pr_warn("global '%s': incompatible func '%s' linkage\n", sym_name, n1);
1389                         return false;
1390                 }
1391
1392                 id1 = t1->type;
1393                 id2 = t2->type;
1394                 goto recur;
1395         case BTF_KIND_VAR:
1396                 /* extern and global linkages are compatible */
1397                 is_static1 = btf_var(t1)->linkage == BTF_VAR_STATIC;
1398                 is_static2 = btf_var(t2)->linkage == BTF_VAR_STATIC;
1399                 if (is_static1 != is_static2) {
1400                         pr_warn("global '%s': incompatible var '%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_STRUCT:
1408         case BTF_KIND_UNION: {
1409                 const struct btf_member *m1, *m2;
1410
1411                 if (!exact)
1412                         return true;
1413
1414                 if (btf_vlen(t1) != btf_vlen(t2)) {
1415                         pr_warn("global '%s': incompatible number of %s fields %u and %u\n",
1416                                 sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
1417                         return false;
1418                 }
1419
1420                 n = btf_vlen(t1);
1421                 m1 = btf_members(t1);
1422                 m2 = btf_members(t2);
1423                 for (i = 0; i < n; i++, m1++, m2++) {
1424                         n1 = btf__str_by_offset(btf1, m1->name_off);
1425                         n2 = btf__str_by_offset(btf2, m2->name_off);
1426                         if (strcmp(n1, n2) != 0) {
1427                                 pr_warn("global '%s': incompatible field #%d names '%s' and '%s'\n",
1428                                         sym_name, i, n1, n2);
1429                                 return false;
1430                         }
1431                         if (m1->offset != m2->offset) {
1432                                 pr_warn("global '%s': incompatible field #%d ('%s') offsets\n",
1433                                         sym_name, i, n1);
1434                                 return false;
1435                         }
1436                         if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
1437                                 return false;
1438                 }
1439
1440                 return true;
1441         }
1442         case BTF_KIND_FUNC_PROTO: {
1443                 const struct btf_param *m1, *m2;
1444
1445                 if (btf_vlen(t1) != btf_vlen(t2)) {
1446                         pr_warn("global '%s': incompatible number of %s params %u and %u\n",
1447                                 sym_name, btf_kind_str(t1), btf_vlen(t1), btf_vlen(t2));
1448                         return false;
1449                 }
1450
1451                 n = btf_vlen(t1);
1452                 m1 = btf_params(t1);
1453                 m2 = btf_params(t2);
1454                 for (i = 0; i < n; i++, m1++, m2++) {
1455                         /* ignore func arg names */
1456                         if (!glob_sym_btf_matches(sym_name, exact, btf1, m1->type, btf2, m2->type))
1457                                 return false;
1458                 }
1459
1460                 /* now check return type as well */
1461                 id1 = t1->type;
1462                 id2 = t2->type;
1463                 goto recur;
1464         }
1465
1466         /* skip_mods_and_typedefs() make this impossible */
1467         case BTF_KIND_TYPEDEF:
1468         case BTF_KIND_VOLATILE:
1469         case BTF_KIND_CONST:
1470         case BTF_KIND_RESTRICT:
1471         /* DATASECs are never compared with each other */
1472         case BTF_KIND_DATASEC:
1473         default:
1474                 pr_warn("global '%s': unsupported BTF kind %s\n",
1475                         sym_name, btf_kind_str(t1));
1476                 return false;
1477         }
1478 }
1479
1480 static bool map_defs_match(const char *sym_name,
1481                            const struct btf *main_btf,
1482                            const struct btf_map_def *main_def,
1483                            const struct btf_map_def *main_inner_def,
1484                            const struct btf *extra_btf,
1485                            const struct btf_map_def *extra_def,
1486                            const struct btf_map_def *extra_inner_def)
1487 {
1488         const char *reason;
1489
1490         if (main_def->map_type != extra_def->map_type) {
1491                 reason = "type";
1492                 goto mismatch;
1493         }
1494
1495         /* check key type/size match */
1496         if (main_def->key_size != extra_def->key_size) {
1497                 reason = "key_size";
1498                 goto mismatch;
1499         }
1500         if (!!main_def->key_type_id != !!extra_def->key_type_id) {
1501                 reason = "key type";
1502                 goto mismatch;
1503         }
1504         if ((main_def->parts & MAP_DEF_KEY_TYPE)
1505              && !glob_sym_btf_matches(sym_name, true /*exact*/,
1506                                       main_btf, main_def->key_type_id,
1507                                       extra_btf, extra_def->key_type_id)) {
1508                 reason = "key type";
1509                 goto mismatch;
1510         }
1511
1512         /* validate value type/size match */
1513         if (main_def->value_size != extra_def->value_size) {
1514                 reason = "value_size";
1515                 goto mismatch;
1516         }
1517         if (!!main_def->value_type_id != !!extra_def->value_type_id) {
1518                 reason = "value type";
1519                 goto mismatch;
1520         }
1521         if ((main_def->parts & MAP_DEF_VALUE_TYPE)
1522              && !glob_sym_btf_matches(sym_name, true /*exact*/,
1523                                       main_btf, main_def->value_type_id,
1524                                       extra_btf, extra_def->value_type_id)) {
1525                 reason = "key type";
1526                 goto mismatch;
1527         }
1528
1529         if (main_def->max_entries != extra_def->max_entries) {
1530                 reason = "max_entries";
1531                 goto mismatch;
1532         }
1533         if (main_def->map_flags != extra_def->map_flags) {
1534                 reason = "map_flags";
1535                 goto mismatch;
1536         }
1537         if (main_def->numa_node != extra_def->numa_node) {
1538                 reason = "numa_node";
1539                 goto mismatch;
1540         }
1541         if (main_def->pinning != extra_def->pinning) {
1542                 reason = "pinning";
1543                 goto mismatch;
1544         }
1545
1546         if ((main_def->parts & MAP_DEF_INNER_MAP) != (extra_def->parts & MAP_DEF_INNER_MAP)) {
1547                 reason = "inner map";
1548                 goto mismatch;
1549         }
1550
1551         if (main_def->parts & MAP_DEF_INNER_MAP) {
1552                 char inner_map_name[128];
1553
1554                 snprintf(inner_map_name, sizeof(inner_map_name), "%s.inner", sym_name);
1555
1556                 return map_defs_match(inner_map_name,
1557                                       main_btf, main_inner_def, NULL,
1558                                       extra_btf, extra_inner_def, NULL);
1559         }
1560
1561         return true;
1562
1563 mismatch:
1564         pr_warn("global '%s': map %s mismatch\n", sym_name, reason);
1565         return false;
1566 }
1567
1568 static bool glob_map_defs_match(const char *sym_name,
1569                                 struct bpf_linker *linker, struct glob_sym *glob_sym,
1570                                 struct src_obj *obj, Elf64_Sym *sym, int btf_id)
1571 {
1572         struct btf_map_def dst_def = {}, dst_inner_def = {};
1573         struct btf_map_def src_def = {}, src_inner_def = {};
1574         const struct btf_type *t;
1575         int err;
1576
1577         t = btf__type_by_id(obj->btf, btf_id);
1578         if (!btf_is_var(t)) {
1579                 pr_warn("global '%s': invalid map definition type [%d]\n", sym_name, btf_id);
1580                 return false;
1581         }
1582         t = skip_mods_and_typedefs(obj->btf, t->type, NULL);
1583
1584         err = parse_btf_map_def(sym_name, obj->btf, t, true /*strict*/, &src_def, &src_inner_def);
1585         if (err) {
1586                 pr_warn("global '%s': invalid map definition\n", sym_name);
1587                 return false;
1588         }
1589
1590         /* re-parse existing map definition */
1591         t = btf__type_by_id(linker->btf, glob_sym->btf_id);
1592         t = skip_mods_and_typedefs(linker->btf, t->type, NULL);
1593         err = parse_btf_map_def(sym_name, linker->btf, t, true /*strict*/, &dst_def, &dst_inner_def);
1594         if (err) {
1595                 /* this should not happen, because we already validated it */
1596                 pr_warn("global '%s': invalid dst map definition\n", sym_name);
1597                 return false;
1598         }
1599
1600         /* Currently extern map definition has to be complete and match
1601          * concrete map definition exactly. This restriction might be lifted
1602          * in the future.
1603          */
1604         return map_defs_match(sym_name, linker->btf, &dst_def, &dst_inner_def,
1605                               obj->btf, &src_def, &src_inner_def);
1606 }
1607
1608 static bool glob_syms_match(const char *sym_name,
1609                             struct bpf_linker *linker, struct glob_sym *glob_sym,
1610                             struct src_obj *obj, Elf64_Sym *sym, size_t sym_idx, int btf_id)
1611 {
1612         const struct btf_type *src_t;
1613
1614         /* if we are dealing with externs, BTF types describing both global
1615          * and extern VARs/FUNCs should be completely present in all files
1616          */
1617         if (!glob_sym->btf_id || !btf_id) {
1618                 pr_warn("BTF info is missing for global symbol '%s'\n", sym_name);
1619                 return false;
1620         }
1621
1622         src_t = btf__type_by_id(obj->btf, btf_id);
1623         if (!btf_is_var(src_t) && !btf_is_func(src_t)) {
1624                 pr_warn("only extern variables and functions are supported, but got '%s' for '%s'\n",
1625                         btf_kind_str(src_t), sym_name);
1626                 return false;
1627         }
1628
1629         /* deal with .maps definitions specially */
1630         if (glob_sym->sec_id && strcmp(linker->secs[glob_sym->sec_id].sec_name, MAPS_ELF_SEC) == 0)
1631                 return glob_map_defs_match(sym_name, linker, glob_sym, obj, sym, btf_id);
1632
1633         if (!glob_sym_btf_matches(sym_name, true /*exact*/,
1634                                   linker->btf, glob_sym->btf_id, obj->btf, btf_id))
1635                 return false;
1636
1637         return true;
1638 }
1639
1640 static bool btf_is_non_static(const struct btf_type *t)
1641 {
1642         return (btf_is_var(t) && btf_var(t)->linkage != BTF_VAR_STATIC)
1643                || (btf_is_func(t) && btf_func_linkage(t) != BTF_FUNC_STATIC);
1644 }
1645
1646 static int find_glob_sym_btf(struct src_obj *obj, Elf64_Sym *sym, const char *sym_name,
1647                              int *out_btf_sec_id, int *out_btf_id)
1648 {
1649         int i, j, n, m, btf_id = 0;
1650         const struct btf_type *t;
1651         const struct btf_var_secinfo *vi;
1652         const char *name;
1653
1654         if (!obj->btf) {
1655                 pr_warn("failed to find BTF info for object '%s'\n", obj->filename);
1656                 return -EINVAL;
1657         }
1658
1659         n = btf__type_cnt(obj->btf);
1660         for (i = 1; i < n; i++) {
1661                 t = btf__type_by_id(obj->btf, i);
1662
1663                 /* some global and extern FUNCs and VARs might not be associated with any
1664                  * DATASEC, so try to detect them in the same pass
1665                  */
1666                 if (btf_is_non_static(t)) {
1667                         name = btf__str_by_offset(obj->btf, t->name_off);
1668                         if (strcmp(name, sym_name) != 0)
1669                                 continue;
1670
1671                         /* remember and still try to find DATASEC */
1672                         btf_id = i;
1673                         continue;
1674                 }
1675
1676                 if (!btf_is_datasec(t))
1677                         continue;
1678
1679                 vi = btf_var_secinfos(t);
1680                 for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
1681                         t = btf__type_by_id(obj->btf, vi->type);
1682                         name = btf__str_by_offset(obj->btf, t->name_off);
1683
1684                         if (strcmp(name, sym_name) != 0)
1685                                 continue;
1686                         if (btf_is_var(t) && btf_var(t)->linkage == BTF_VAR_STATIC)
1687                                 continue;
1688                         if (btf_is_func(t) && btf_func_linkage(t) == BTF_FUNC_STATIC)
1689                                 continue;
1690
1691                         if (btf_id && btf_id != vi->type) {
1692                                 pr_warn("global/extern '%s' BTF is ambiguous: both types #%d and #%u match\n",
1693                                         sym_name, btf_id, vi->type);
1694                                 return -EINVAL;
1695                         }
1696
1697                         *out_btf_sec_id = i;
1698                         *out_btf_id = vi->type;
1699
1700                         return 0;
1701                 }
1702         }
1703
1704         /* free-floating extern or global FUNC */
1705         if (btf_id) {
1706                 *out_btf_sec_id = 0;
1707                 *out_btf_id = btf_id;
1708                 return 0;
1709         }
1710
1711         pr_warn("failed to find BTF info for global/extern symbol '%s'\n", sym_name);
1712         return -ENOENT;
1713 }
1714
1715 static struct src_sec *find_src_sec_by_name(struct src_obj *obj, const char *sec_name)
1716 {
1717         struct src_sec *sec;
1718         int i;
1719
1720         for (i = 1; i < obj->sec_cnt; i++) {
1721                 sec = &obj->secs[i];
1722
1723                 if (strcmp(sec->sec_name, sec_name) == 0)
1724                         return sec;
1725         }
1726
1727         return NULL;
1728 }
1729
1730 static int complete_extern_btf_info(struct btf *dst_btf, int dst_id,
1731                                     struct btf *src_btf, int src_id)
1732 {
1733         struct btf_type *dst_t = btf_type_by_id(dst_btf, dst_id);
1734         struct btf_type *src_t = btf_type_by_id(src_btf, src_id);
1735         struct btf_param *src_p, *dst_p;
1736         const char *s;
1737         int i, n, off;
1738
1739         /* We already made sure that source and destination types (FUNC or
1740          * VAR) match in terms of types and argument names.
1741          */
1742         if (btf_is_var(dst_t)) {
1743                 btf_var(dst_t)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
1744                 return 0;
1745         }
1746
1747         dst_t->info = btf_type_info(BTF_KIND_FUNC, BTF_FUNC_GLOBAL, 0);
1748
1749         /* now onto FUNC_PROTO types */
1750         src_t = btf_type_by_id(src_btf, src_t->type);
1751         dst_t = btf_type_by_id(dst_btf, dst_t->type);
1752
1753         /* Fill in all the argument names, which for extern FUNCs are missing.
1754          * We'll end up with two copies of FUNCs/VARs for externs, but that
1755          * will be taken care of by BTF dedup at the very end.
1756          * It might be that BTF types for extern in one file has less/more BTF
1757          * information (e.g., FWD instead of full STRUCT/UNION information),
1758          * but that should be (in most cases, subject to BTF dedup rules)
1759          * handled and resolved by BTF dedup algorithm as well, so we won't
1760          * worry about it. Our only job is to make sure that argument names
1761          * are populated on both sides, otherwise BTF dedup will pedantically
1762          * consider them different.
1763          */
1764         src_p = btf_params(src_t);
1765         dst_p = btf_params(dst_t);
1766         for (i = 0, n = btf_vlen(dst_t); i < n; i++, src_p++, dst_p++) {
1767                 if (!src_p->name_off)
1768                         continue;
1769
1770                 /* src_btf has more complete info, so add name to dst_btf */
1771                 s = btf__str_by_offset(src_btf, src_p->name_off);
1772                 off = btf__add_str(dst_btf, s);
1773                 if (off < 0)
1774                         return off;
1775                 dst_p->name_off = off;
1776         }
1777         return 0;
1778 }
1779
1780 static void sym_update_bind(Elf64_Sym *sym, int sym_bind)
1781 {
1782         sym->st_info = ELF64_ST_INFO(sym_bind, ELF64_ST_TYPE(sym->st_info));
1783 }
1784
1785 static void sym_update_type(Elf64_Sym *sym, int sym_type)
1786 {
1787         sym->st_info = ELF64_ST_INFO(ELF64_ST_BIND(sym->st_info), sym_type);
1788 }
1789
1790 static void sym_update_visibility(Elf64_Sym *sym, int sym_vis)
1791 {
1792         /* libelf doesn't provide setters for ST_VISIBILITY,
1793          * but it is stored in the lower 2 bits of st_other
1794          */
1795         sym->st_other &= ~0x03;
1796         sym->st_other |= sym_vis;
1797 }
1798
1799 static int linker_append_elf_sym(struct bpf_linker *linker, struct src_obj *obj,
1800                                  Elf64_Sym *sym, const char *sym_name, int src_sym_idx)
1801 {
1802         struct src_sec *src_sec = NULL;
1803         struct dst_sec *dst_sec = NULL;
1804         struct glob_sym *glob_sym = NULL;
1805         int name_off, sym_type, sym_bind, sym_vis, err;
1806         int btf_sec_id = 0, btf_id = 0;
1807         size_t dst_sym_idx;
1808         Elf64_Sym *dst_sym;
1809         bool sym_is_extern;
1810
1811         sym_type = ELF64_ST_TYPE(sym->st_info);
1812         sym_bind = ELF64_ST_BIND(sym->st_info);
1813         sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
1814         sym_is_extern = sym->st_shndx == SHN_UNDEF;
1815
1816         if (sym_is_extern) {
1817                 if (!obj->btf) {
1818                         pr_warn("externs without BTF info are not supported\n");
1819                         return -ENOTSUP;
1820                 }
1821         } else if (sym->st_shndx < SHN_LORESERVE) {
1822                 src_sec = &obj->secs[sym->st_shndx];
1823                 if (src_sec->skipped)
1824                         return 0;
1825                 dst_sec = &linker->secs[src_sec->dst_id];
1826
1827                 /* allow only one STT_SECTION symbol per section */
1828                 if (sym_type == STT_SECTION && dst_sec->sec_sym_idx) {
1829                         obj->sym_map[src_sym_idx] = dst_sec->sec_sym_idx;
1830                         return 0;
1831                 }
1832         }
1833
1834         if (sym_bind == STB_LOCAL)
1835                 goto add_sym;
1836
1837         /* find matching BTF info */
1838         err = find_glob_sym_btf(obj, sym, sym_name, &btf_sec_id, &btf_id);
1839         if (err)
1840                 return err;
1841
1842         if (sym_is_extern && btf_sec_id) {
1843                 const char *sec_name = NULL;
1844                 const struct btf_type *t;
1845
1846                 t = btf__type_by_id(obj->btf, btf_sec_id);
1847                 sec_name = btf__str_by_offset(obj->btf, t->name_off);
1848
1849                 /* Clang puts unannotated extern vars into
1850                  * '.extern' BTF DATASEC. Treat them the same
1851                  * as unannotated extern funcs (which are
1852                  * currently not put into any DATASECs).
1853                  * Those don't have associated src_sec/dst_sec.
1854                  */
1855                 if (strcmp(sec_name, BTF_EXTERN_SEC) != 0) {
1856                         src_sec = find_src_sec_by_name(obj, sec_name);
1857                         if (!src_sec) {
1858                                 pr_warn("failed to find matching ELF sec '%s'\n", sec_name);
1859                                 return -ENOENT;
1860                         }
1861                         dst_sec = &linker->secs[src_sec->dst_id];
1862                 }
1863         }
1864
1865         glob_sym = find_glob_sym(linker, sym_name);
1866         if (glob_sym) {
1867                 /* Preventively resolve to existing symbol. This is
1868                  * needed for further relocation symbol remapping in
1869                  * the next step of linking.
1870                  */
1871                 obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
1872
1873                 /* If both symbols are non-externs, at least one of
1874                  * them has to be STB_WEAK, otherwise they are in
1875                  * a conflict with each other.
1876                  */
1877                 if (!sym_is_extern && !glob_sym->is_extern
1878                     && !glob_sym->is_weak && sym_bind != STB_WEAK) {
1879                         pr_warn("conflicting non-weak symbol #%d (%s) definition in '%s'\n",
1880                                 src_sym_idx, sym_name, obj->filename);
1881                         return -EINVAL;
1882                 }
1883
1884                 if (!glob_syms_match(sym_name, linker, glob_sym, obj, sym, src_sym_idx, btf_id))
1885                         return -EINVAL;
1886
1887                 dst_sym = get_sym_by_idx(linker, glob_sym->sym_idx);
1888
1889                 /* If new symbol is strong, then force dst_sym to be strong as
1890                  * well; this way a mix of weak and non-weak extern
1891                  * definitions will end up being strong.
1892                  */
1893                 if (sym_bind == STB_GLOBAL) {
1894                         /* We still need to preserve type (NOTYPE or
1895                          * OBJECT/FUNC, depending on whether the symbol is
1896                          * extern or not)
1897                          */
1898                         sym_update_bind(dst_sym, STB_GLOBAL);
1899                         glob_sym->is_weak = false;
1900                 }
1901
1902                 /* Non-default visibility is "contaminating", with stricter
1903                  * visibility overwriting more permissive ones, even if more
1904                  * permissive visibility comes from just an extern definition.
1905                  * Currently only STV_DEFAULT and STV_HIDDEN are allowed and
1906                  * ensured by ELF symbol sanity checks above.
1907                  */
1908                 if (sym_vis > ELF64_ST_VISIBILITY(dst_sym->st_other))
1909                         sym_update_visibility(dst_sym, sym_vis);
1910
1911                 /* If the new symbol is extern, then regardless if
1912                  * existing symbol is extern or resolved global, just
1913                  * keep the existing one untouched.
1914                  */
1915                 if (sym_is_extern)
1916                         return 0;
1917
1918                 /* If existing symbol is a strong resolved symbol, bail out,
1919                  * because we lost resolution battle have nothing to
1920                  * contribute. We already checked abover that there is no
1921                  * strong-strong conflict. We also already tightened binding
1922                  * and visibility, so nothing else to contribute at that point.
1923                  */
1924                 if (!glob_sym->is_extern && sym_bind == STB_WEAK)
1925                         return 0;
1926
1927                 /* At this point, new symbol is strong non-extern,
1928                  * so overwrite glob_sym with new symbol information.
1929                  * Preserve binding and visibility.
1930                  */
1931                 sym_update_type(dst_sym, sym_type);
1932                 dst_sym->st_shndx = dst_sec->sec_idx;
1933                 dst_sym->st_value = src_sec->dst_off + sym->st_value;
1934                 dst_sym->st_size = sym->st_size;
1935
1936                 /* see comment below about dst_sec->id vs dst_sec->sec_idx */
1937                 glob_sym->sec_id = dst_sec->id;
1938                 glob_sym->is_extern = false;
1939
1940                 if (complete_extern_btf_info(linker->btf, glob_sym->btf_id,
1941                                              obj->btf, btf_id))
1942                         return -EINVAL;
1943
1944                 /* request updating VAR's/FUNC's underlying BTF type when appending BTF type */
1945                 glob_sym->underlying_btf_id = 0;
1946
1947                 obj->sym_map[src_sym_idx] = glob_sym->sym_idx;
1948                 return 0;
1949         }
1950
1951 add_sym:
1952         name_off = strset__add_str(linker->strtab_strs, sym_name);
1953         if (name_off < 0)
1954                 return name_off;
1955
1956         dst_sym = add_new_sym(linker, &dst_sym_idx);
1957         if (!dst_sym)
1958                 return -ENOMEM;
1959
1960         dst_sym->st_name = name_off;
1961         dst_sym->st_info = sym->st_info;
1962         dst_sym->st_other = sym->st_other;
1963         dst_sym->st_shndx = dst_sec ? dst_sec->sec_idx : sym->st_shndx;
1964         dst_sym->st_value = (src_sec ? src_sec->dst_off : 0) + sym->st_value;
1965         dst_sym->st_size = sym->st_size;
1966
1967         obj->sym_map[src_sym_idx] = dst_sym_idx;
1968
1969         if (sym_type == STT_SECTION && dst_sym) {
1970                 dst_sec->sec_sym_idx = dst_sym_idx;
1971                 dst_sym->st_value = 0;
1972         }
1973
1974         if (sym_bind != STB_LOCAL) {
1975                 glob_sym = add_glob_sym(linker);
1976                 if (!glob_sym)
1977                         return -ENOMEM;
1978
1979                 glob_sym->sym_idx = dst_sym_idx;
1980                 /* we use dst_sec->id (and not dst_sec->sec_idx), because
1981                  * ephemeral sections (.kconfig, .ksyms, etc) don't have
1982                  * sec_idx (as they don't have corresponding ELF section), but
1983                  * still have id. .extern doesn't have even ephemeral section
1984                  * associated with it, so dst_sec->id == dst_sec->sec_idx == 0.
1985                  */
1986                 glob_sym->sec_id = dst_sec ? dst_sec->id : 0;
1987                 glob_sym->name_off = name_off;
1988                 /* we will fill btf_id in during BTF merging step */
1989                 glob_sym->btf_id = 0;
1990                 glob_sym->is_extern = sym_is_extern;
1991                 glob_sym->is_weak = sym_bind == STB_WEAK;
1992         }
1993
1994         return 0;
1995 }
1996
1997 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj)
1998 {
1999         struct src_sec *src_symtab = &obj->secs[obj->symtab_sec_idx];
2000         struct dst_sec *dst_symtab;
2001         int i, err;
2002
2003         for (i = 1; i < obj->sec_cnt; i++) {
2004                 struct src_sec *src_sec, *src_linked_sec;
2005                 struct dst_sec *dst_sec, *dst_linked_sec;
2006                 Elf64_Rel *src_rel, *dst_rel;
2007                 int j, n;
2008
2009                 src_sec = &obj->secs[i];
2010                 if (!is_relo_sec(src_sec))
2011                         continue;
2012
2013                 /* shdr->sh_info points to relocatable section */
2014                 src_linked_sec = &obj->secs[src_sec->shdr->sh_info];
2015                 if (src_linked_sec->skipped)
2016                         continue;
2017
2018                 dst_sec = find_dst_sec_by_name(linker, src_sec->sec_name);
2019                 if (!dst_sec) {
2020                         dst_sec = add_dst_sec(linker, src_sec->sec_name);
2021                         if (!dst_sec)
2022                                 return -ENOMEM;
2023                         err = init_sec(linker, dst_sec, src_sec);
2024                         if (err) {
2025                                 pr_warn("failed to init section '%s'\n", src_sec->sec_name);
2026                                 return err;
2027                         }
2028                 } else if (!secs_match(dst_sec, src_sec)) {
2029                         pr_warn("sections %s are not compatible\n", src_sec->sec_name);
2030                         return -1;
2031                 }
2032
2033                 /* add_dst_sec() above could have invalidated linker->secs */
2034                 dst_symtab = &linker->secs[linker->symtab_sec_idx];
2035
2036                 /* shdr->sh_link points to SYMTAB */
2037                 dst_sec->shdr->sh_link = linker->symtab_sec_idx;
2038
2039                 /* shdr->sh_info points to relocated section */
2040                 dst_linked_sec = &linker->secs[src_linked_sec->dst_id];
2041                 dst_sec->shdr->sh_info = dst_linked_sec->sec_idx;
2042
2043                 src_sec->dst_id = dst_sec->id;
2044                 err = extend_sec(linker, dst_sec, src_sec);
2045                 if (err)
2046                         return err;
2047
2048                 src_rel = src_sec->data->d_buf;
2049                 dst_rel = dst_sec->raw_data + src_sec->dst_off;
2050                 n = src_sec->shdr->sh_size / src_sec->shdr->sh_entsize;
2051                 for (j = 0; j < n; j++, src_rel++, dst_rel++) {
2052                         size_t src_sym_idx = ELF64_R_SYM(src_rel->r_info);
2053                         size_t sym_type = ELF64_R_TYPE(src_rel->r_info);
2054                         Elf64_Sym *src_sym, *dst_sym;
2055                         size_t dst_sym_idx;
2056
2057                         src_sym_idx = ELF64_R_SYM(src_rel->r_info);
2058                         src_sym = src_symtab->data->d_buf + sizeof(*src_sym) * src_sym_idx;
2059
2060                         dst_sym_idx = obj->sym_map[src_sym_idx];
2061                         dst_sym = dst_symtab->raw_data + sizeof(*dst_sym) * dst_sym_idx;
2062                         dst_rel->r_offset += src_linked_sec->dst_off;
2063                         sym_type = ELF64_R_TYPE(src_rel->r_info);
2064                         dst_rel->r_info = ELF64_R_INFO(dst_sym_idx, sym_type);
2065
2066                         if (ELF64_ST_TYPE(src_sym->st_info) == STT_SECTION) {
2067                                 struct src_sec *sec = &obj->secs[src_sym->st_shndx];
2068                                 struct bpf_insn *insn;
2069
2070                                 if (src_linked_sec->shdr->sh_flags & SHF_EXECINSTR) {
2071                                         /* calls to the very first static function inside
2072                                          * .text section at offset 0 will
2073                                          * reference section symbol, not the
2074                                          * function symbol. Fix that up,
2075                                          * otherwise it won't be possible to
2076                                          * relocate calls to two different
2077                                          * static functions with the same name
2078                                          * (rom two different object files)
2079                                          */
2080                                         insn = dst_linked_sec->raw_data + dst_rel->r_offset;
2081                                         if (insn->code == (BPF_JMP | BPF_CALL))
2082                                                 insn->imm += sec->dst_off / sizeof(struct bpf_insn);
2083                                         else
2084                                                 insn->imm += sec->dst_off;
2085                                 } else {
2086                                         pr_warn("relocation against STT_SECTION in non-exec section is not supported!\n");
2087                                         return -EINVAL;
2088                                 }
2089                         }
2090
2091                 }
2092         }
2093
2094         return 0;
2095 }
2096
2097 static Elf64_Sym *find_sym_by_name(struct src_obj *obj, size_t sec_idx,
2098                                    int sym_type, const char *sym_name)
2099 {
2100         struct src_sec *symtab = &obj->secs[obj->symtab_sec_idx];
2101         Elf64_Sym *sym = symtab->data->d_buf;
2102         int i, n = symtab->shdr->sh_size / symtab->shdr->sh_entsize;
2103         int str_sec_idx = symtab->shdr->sh_link;
2104         const char *name;
2105
2106         for (i = 0; i < n; i++, sym++) {
2107                 if (sym->st_shndx != sec_idx)
2108                         continue;
2109                 if (ELF64_ST_TYPE(sym->st_info) != sym_type)
2110                         continue;
2111
2112                 name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
2113                 if (!name)
2114                         return NULL;
2115
2116                 if (strcmp(sym_name, name) != 0)
2117                         continue;
2118
2119                 return sym;
2120         }
2121
2122         return NULL;
2123 }
2124
2125 static int linker_fixup_btf(struct src_obj *obj)
2126 {
2127         const char *sec_name;
2128         struct src_sec *sec;
2129         int i, j, n, m;
2130
2131         if (!obj->btf)
2132                 return 0;
2133
2134         n = btf__type_cnt(obj->btf);
2135         for (i = 1; i < n; i++) {
2136                 struct btf_var_secinfo *vi;
2137                 struct btf_type *t;
2138
2139                 t = btf_type_by_id(obj->btf, i);
2140                 if (btf_kind(t) != BTF_KIND_DATASEC)
2141                         continue;
2142
2143                 sec_name = btf__str_by_offset(obj->btf, t->name_off);
2144                 sec = find_src_sec_by_name(obj, sec_name);
2145                 if (sec) {
2146                         /* record actual section size, unless ephemeral */
2147                         if (sec->shdr)
2148                                 t->size = sec->shdr->sh_size;
2149                 } else {
2150                         /* BTF can have some sections that are not represented
2151                          * in ELF, e.g., .kconfig, .ksyms, .extern, which are used
2152                          * for special extern variables.
2153                          *
2154                          * For all but one such special (ephemeral)
2155                          * sections, we pre-create "section shells" to be able
2156                          * to keep track of extra per-section metadata later
2157                          * (e.g., those BTF extern variables).
2158                          *
2159                          * .extern is even more special, though, because it
2160                          * contains extern variables that need to be resolved
2161                          * by static linker, not libbpf and kernel. When such
2162                          * externs are resolved, we are going to remove them
2163                          * from .extern BTF section and might end up not
2164                          * needing it at all. Each resolved extern should have
2165                          * matching non-extern VAR/FUNC in other sections.
2166                          *
2167                          * We do support leaving some of the externs
2168                          * unresolved, though, to support cases of building
2169                          * libraries, which will later be linked against final
2170                          * BPF applications. So if at finalization we still
2171                          * see unresolved externs, we'll create .extern
2172                          * section on our own.
2173                          */
2174                         if (strcmp(sec_name, BTF_EXTERN_SEC) == 0)
2175                                 continue;
2176
2177                         sec = add_src_sec(obj, sec_name);
2178                         if (!sec)
2179                                 return -ENOMEM;
2180
2181                         sec->ephemeral = true;
2182                         sec->sec_idx = 0; /* will match UNDEF shndx in ELF */
2183                 }
2184
2185                 /* remember ELF section and its BTF type ID match */
2186                 sec->sec_type_id = i;
2187
2188                 /* fix up variable offsets */
2189                 vi = btf_var_secinfos(t);
2190                 for (j = 0, m = btf_vlen(t); j < m; j++, vi++) {
2191                         const struct btf_type *vt = btf__type_by_id(obj->btf, vi->type);
2192                         const char *var_name = btf__str_by_offset(obj->btf, vt->name_off);
2193                         int var_linkage = btf_var(vt)->linkage;
2194                         Elf64_Sym *sym;
2195
2196                         /* no need to patch up static or extern vars */
2197                         if (var_linkage != BTF_VAR_GLOBAL_ALLOCATED)
2198                                 continue;
2199
2200                         sym = find_sym_by_name(obj, sec->sec_idx, STT_OBJECT, var_name);
2201                         if (!sym) {
2202                                 pr_warn("failed to find symbol for variable '%s' in section '%s'\n", var_name, sec_name);
2203                                 return -ENOENT;
2204                         }
2205
2206                         vi->offset = sym->st_value;
2207                 }
2208         }
2209
2210         return 0;
2211 }
2212
2213 static int remap_type_id(__u32 *type_id, void *ctx)
2214 {
2215         int *id_map = ctx;
2216         int new_id = id_map[*type_id];
2217
2218         /* Error out if the type wasn't remapped. Ignore VOID which stays VOID. */
2219         if (new_id == 0 && *type_id != 0) {
2220                 pr_warn("failed to find new ID mapping for original BTF type ID %u\n", *type_id);
2221                 return -EINVAL;
2222         }
2223
2224         *type_id = id_map[*type_id];
2225
2226         return 0;
2227 }
2228
2229 static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
2230 {
2231         const struct btf_type *t;
2232         int i, j, n, start_id, id;
2233         const char *name;
2234
2235         if (!obj->btf)
2236                 return 0;
2237
2238         start_id = btf__type_cnt(linker->btf);
2239         n = btf__type_cnt(obj->btf);
2240
2241         obj->btf_type_map = calloc(n + 1, sizeof(int));
2242         if (!obj->btf_type_map)
2243                 return -ENOMEM;
2244
2245         for (i = 1; i < n; i++) {
2246                 struct glob_sym *glob_sym = NULL;
2247
2248                 t = btf__type_by_id(obj->btf, i);
2249
2250                 /* DATASECs are handled specially below */
2251                 if (btf_kind(t) == BTF_KIND_DATASEC)
2252                         continue;
2253
2254                 if (btf_is_non_static(t)) {
2255                         /* there should be glob_sym already */
2256                         name = btf__str_by_offset(obj->btf, t->name_off);
2257                         glob_sym = find_glob_sym(linker, name);
2258
2259                         /* VARs without corresponding glob_sym are those that
2260                          * belong to skipped/deduplicated sections (i.e.,
2261                          * license and version), so just skip them
2262                          */
2263                         if (!glob_sym)
2264                                 continue;
2265
2266                         /* linker_append_elf_sym() might have requested
2267                          * updating underlying type ID, if extern was resolved
2268                          * to strong symbol or weak got upgraded to non-weak
2269                          */
2270                         if (glob_sym->underlying_btf_id == 0)
2271                                 glob_sym->underlying_btf_id = -t->type;
2272
2273                         /* globals from previous object files that match our
2274                          * VAR/FUNC already have a corresponding associated
2275                          * BTF type, so just make sure to use it
2276                          */
2277                         if (glob_sym->btf_id) {
2278                                 /* reuse existing BTF type for global var/func */
2279                                 obj->btf_type_map[i] = glob_sym->btf_id;
2280                                 continue;
2281                         }
2282                 }
2283
2284                 id = btf__add_type(linker->btf, obj->btf, t);
2285                 if (id < 0) {
2286                         pr_warn("failed to append BTF type #%d from file '%s'\n", i, obj->filename);
2287                         return id;
2288                 }
2289
2290                 obj->btf_type_map[i] = id;
2291
2292                 /* record just appended BTF type for var/func */
2293                 if (glob_sym) {
2294                         glob_sym->btf_id = id;
2295                         glob_sym->underlying_btf_id = -t->type;
2296                 }
2297         }
2298
2299         /* remap all the types except DATASECs */
2300         n = btf__type_cnt(linker->btf);
2301         for (i = start_id; i < n; i++) {
2302                 struct btf_type *dst_t = btf_type_by_id(linker->btf, i);
2303
2304                 if (btf_type_visit_type_ids(dst_t, remap_type_id, obj->btf_type_map))
2305                         return -EINVAL;
2306         }
2307
2308         /* Rewrite VAR/FUNC underlying types (i.e., FUNC's FUNC_PROTO and VAR's
2309          * actual type), if necessary
2310          */
2311         for (i = 0; i < linker->glob_sym_cnt; i++) {
2312                 struct glob_sym *glob_sym = &linker->glob_syms[i];
2313                 struct btf_type *glob_t;
2314
2315                 if (glob_sym->underlying_btf_id >= 0)
2316                         continue;
2317
2318                 glob_sym->underlying_btf_id = obj->btf_type_map[-glob_sym->underlying_btf_id];
2319
2320                 glob_t = btf_type_by_id(linker->btf, glob_sym->btf_id);
2321                 glob_t->type = glob_sym->underlying_btf_id;
2322         }
2323
2324         /* append DATASEC info */
2325         for (i = 1; i < obj->sec_cnt; i++) {
2326                 struct src_sec *src_sec;
2327                 struct dst_sec *dst_sec;
2328                 const struct btf_var_secinfo *src_var;
2329                 struct btf_var_secinfo *dst_var;
2330
2331                 src_sec = &obj->secs[i];
2332                 if (!src_sec->sec_type_id || src_sec->skipped)
2333                         continue;
2334                 dst_sec = &linker->secs[src_sec->dst_id];
2335
2336                 /* Mark section as having BTF regardless of the presence of
2337                  * variables. In some cases compiler might generate empty BTF
2338                  * with no variables information. E.g., when promoting local
2339                  * array/structure variable initial values and BPF object
2340                  * file otherwise has no read-only static variables in
2341                  * .rodata. We need to preserve such empty BTF and just set
2342                  * correct section size.
2343                  */
2344                 dst_sec->has_btf = true;
2345
2346                 t = btf__type_by_id(obj->btf, src_sec->sec_type_id);
2347                 src_var = btf_var_secinfos(t);
2348                 n = btf_vlen(t);
2349                 for (j = 0; j < n; j++, src_var++) {
2350                         void *sec_vars = dst_sec->sec_vars;
2351                         int new_id = obj->btf_type_map[src_var->type];
2352                         struct glob_sym *glob_sym = NULL;
2353
2354                         t = btf_type_by_id(linker->btf, new_id);
2355                         if (btf_is_non_static(t)) {
2356                                 name = btf__str_by_offset(linker->btf, t->name_off);
2357                                 glob_sym = find_glob_sym(linker, name);
2358                                 if (glob_sym->sec_id != dst_sec->id) {
2359                                         pr_warn("global '%s': section mismatch %d vs %d\n",
2360                                                 name, glob_sym->sec_id, dst_sec->id);
2361                                         return -EINVAL;
2362                                 }
2363                         }
2364
2365                         /* If there is already a member (VAR or FUNC) mapped
2366                          * to the same type, don't add a duplicate entry.
2367                          * This will happen when multiple object files define
2368                          * the same extern VARs/FUNCs.
2369                          */
2370                         if (glob_sym && glob_sym->var_idx >= 0) {
2371                                 __s64 sz;
2372
2373                                 dst_var = &dst_sec->sec_vars[glob_sym->var_idx];
2374                                 /* Because underlying BTF type might have
2375                                  * changed, so might its size have changed, so
2376                                  * re-calculate and update it in sec_var.
2377                                  */
2378                                 sz = btf__resolve_size(linker->btf, glob_sym->underlying_btf_id);
2379                                 if (sz < 0) {
2380                                         pr_warn("global '%s': failed to resolve size of underlying type: %d\n",
2381                                                 name, (int)sz);
2382                                         return -EINVAL;
2383                                 }
2384                                 dst_var->size = sz;
2385                                 continue;
2386                         }
2387
2388                         sec_vars = libbpf_reallocarray(sec_vars,
2389                                                        dst_sec->sec_var_cnt + 1,
2390                                                        sizeof(*dst_sec->sec_vars));
2391                         if (!sec_vars)
2392                                 return -ENOMEM;
2393
2394                         dst_sec->sec_vars = sec_vars;
2395                         dst_sec->sec_var_cnt++;
2396
2397                         dst_var = &dst_sec->sec_vars[dst_sec->sec_var_cnt - 1];
2398                         dst_var->type = obj->btf_type_map[src_var->type];
2399                         dst_var->size = src_var->size;
2400                         dst_var->offset = src_sec->dst_off + src_var->offset;
2401
2402                         if (glob_sym)
2403                                 glob_sym->var_idx = dst_sec->sec_var_cnt - 1;
2404                 }
2405         }
2406
2407         return 0;
2408 }
2409
2410 static void *add_btf_ext_rec(struct btf_ext_sec_data *ext_data, const void *src_rec)
2411 {
2412         void *tmp;
2413
2414         tmp = libbpf_reallocarray(ext_data->recs, ext_data->rec_cnt + 1, ext_data->rec_sz);
2415         if (!tmp)
2416                 return NULL;
2417         ext_data->recs = tmp;
2418
2419         tmp += ext_data->rec_cnt * ext_data->rec_sz;
2420         memcpy(tmp, src_rec, ext_data->rec_sz);
2421
2422         ext_data->rec_cnt++;
2423
2424         return tmp;
2425 }
2426
2427 static int linker_append_btf_ext(struct bpf_linker *linker, struct src_obj *obj)
2428 {
2429         const struct btf_ext_info_sec *ext_sec;
2430         const char *sec_name, *s;
2431         struct src_sec *src_sec;
2432         struct dst_sec *dst_sec;
2433         int rec_sz, str_off, i;
2434
2435         if (!obj->btf_ext)
2436                 return 0;
2437
2438         rec_sz = obj->btf_ext->func_info.rec_size;
2439         for_each_btf_ext_sec(&obj->btf_ext->func_info, ext_sec) {
2440                 struct bpf_func_info_min *src_rec, *dst_rec;
2441
2442                 sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
2443                 src_sec = find_src_sec_by_name(obj, sec_name);
2444                 if (!src_sec) {
2445                         pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
2446                         return -EINVAL;
2447                 }
2448                 dst_sec = &linker->secs[src_sec->dst_id];
2449
2450                 if (dst_sec->func_info.rec_sz == 0)
2451                         dst_sec->func_info.rec_sz = rec_sz;
2452                 if (dst_sec->func_info.rec_sz != rec_sz) {
2453                         pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
2454                         return -EINVAL;
2455                 }
2456
2457                 for_each_btf_ext_rec(&obj->btf_ext->func_info, ext_sec, i, src_rec) {
2458                         dst_rec = add_btf_ext_rec(&dst_sec->func_info, src_rec);
2459                         if (!dst_rec)
2460                                 return -ENOMEM;
2461
2462                         dst_rec->insn_off += src_sec->dst_off;
2463                         dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
2464                 }
2465         }
2466
2467         rec_sz = obj->btf_ext->line_info.rec_size;
2468         for_each_btf_ext_sec(&obj->btf_ext->line_info, ext_sec) {
2469                 struct bpf_line_info_min *src_rec, *dst_rec;
2470
2471                 sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
2472                 src_sec = find_src_sec_by_name(obj, sec_name);
2473                 if (!src_sec) {
2474                         pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
2475                         return -EINVAL;
2476                 }
2477                 dst_sec = &linker->secs[src_sec->dst_id];
2478
2479                 if (dst_sec->line_info.rec_sz == 0)
2480                         dst_sec->line_info.rec_sz = rec_sz;
2481                 if (dst_sec->line_info.rec_sz != rec_sz) {
2482                         pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
2483                         return -EINVAL;
2484                 }
2485
2486                 for_each_btf_ext_rec(&obj->btf_ext->line_info, ext_sec, i, src_rec) {
2487                         dst_rec = add_btf_ext_rec(&dst_sec->line_info, src_rec);
2488                         if (!dst_rec)
2489                                 return -ENOMEM;
2490
2491                         dst_rec->insn_off += src_sec->dst_off;
2492
2493                         s = btf__str_by_offset(obj->btf, src_rec->file_name_off);
2494                         str_off = btf__add_str(linker->btf, s);
2495                         if (str_off < 0)
2496                                 return -ENOMEM;
2497                         dst_rec->file_name_off = str_off;
2498
2499                         s = btf__str_by_offset(obj->btf, src_rec->line_off);
2500                         str_off = btf__add_str(linker->btf, s);
2501                         if (str_off < 0)
2502                                 return -ENOMEM;
2503                         dst_rec->line_off = str_off;
2504
2505                         /* dst_rec->line_col is fine */
2506                 }
2507         }
2508
2509         rec_sz = obj->btf_ext->core_relo_info.rec_size;
2510         for_each_btf_ext_sec(&obj->btf_ext->core_relo_info, ext_sec) {
2511                 struct bpf_core_relo *src_rec, *dst_rec;
2512
2513                 sec_name = btf__name_by_offset(obj->btf, ext_sec->sec_name_off);
2514                 src_sec = find_src_sec_by_name(obj, sec_name);
2515                 if (!src_sec) {
2516                         pr_warn("can't find section '%s' referenced from .BTF.ext\n", sec_name);
2517                         return -EINVAL;
2518                 }
2519                 dst_sec = &linker->secs[src_sec->dst_id];
2520
2521                 if (dst_sec->core_relo_info.rec_sz == 0)
2522                         dst_sec->core_relo_info.rec_sz = rec_sz;
2523                 if (dst_sec->core_relo_info.rec_sz != rec_sz) {
2524                         pr_warn("incompatible .BTF.ext record sizes for section '%s'\n", sec_name);
2525                         return -EINVAL;
2526                 }
2527
2528                 for_each_btf_ext_rec(&obj->btf_ext->core_relo_info, ext_sec, i, src_rec) {
2529                         dst_rec = add_btf_ext_rec(&dst_sec->core_relo_info, src_rec);
2530                         if (!dst_rec)
2531                                 return -ENOMEM;
2532
2533                         dst_rec->insn_off += src_sec->dst_off;
2534                         dst_rec->type_id = obj->btf_type_map[dst_rec->type_id];
2535
2536                         s = btf__str_by_offset(obj->btf, src_rec->access_str_off);
2537                         str_off = btf__add_str(linker->btf, s);
2538                         if (str_off < 0)
2539                                 return -ENOMEM;
2540                         dst_rec->access_str_off = str_off;
2541
2542                         /* dst_rec->kind is fine */
2543                 }
2544         }
2545
2546         return 0;
2547 }
2548
2549 int bpf_linker__finalize(struct bpf_linker *linker)
2550 {
2551         struct dst_sec *sec;
2552         size_t strs_sz;
2553         const void *strs;
2554         int err, i;
2555
2556         if (!linker->elf)
2557                 return libbpf_err(-EINVAL);
2558
2559         err = finalize_btf(linker);
2560         if (err)
2561                 return libbpf_err(err);
2562
2563         /* Finalize strings */
2564         strs_sz = strset__data_size(linker->strtab_strs);
2565         strs = strset__data(linker->strtab_strs);
2566
2567         sec = &linker->secs[linker->strtab_sec_idx];
2568         sec->data->d_align = 1;
2569         sec->data->d_off = 0LL;
2570         sec->data->d_buf = (void *)strs;
2571         sec->data->d_type = ELF_T_BYTE;
2572         sec->data->d_size = strs_sz;
2573         sec->shdr->sh_size = strs_sz;
2574
2575         for (i = 1; i < linker->sec_cnt; i++) {
2576                 sec = &linker->secs[i];
2577
2578                 /* STRTAB is handled specially above */
2579                 if (sec->sec_idx == linker->strtab_sec_idx)
2580                         continue;
2581
2582                 /* special ephemeral sections (.ksyms, .kconfig, etc) */
2583                 if (!sec->scn)
2584                         continue;
2585
2586                 sec->data->d_buf = sec->raw_data;
2587         }
2588
2589         /* Finalize ELF layout */
2590         if (elf_update(linker->elf, ELF_C_NULL) < 0) {
2591                 err = -errno;
2592                 pr_warn_elf("failed to finalize ELF layout");
2593                 return libbpf_err(err);
2594         }
2595
2596         /* Write out final ELF contents */
2597         if (elf_update(linker->elf, ELF_C_WRITE) < 0) {
2598                 err = -errno;
2599                 pr_warn_elf("failed to write ELF contents");
2600                 return libbpf_err(err);
2601         }
2602
2603         elf_end(linker->elf);
2604         close(linker->fd);
2605
2606         linker->elf = NULL;
2607         linker->fd = -1;
2608
2609         return 0;
2610 }
2611
2612 static int emit_elf_data_sec(struct bpf_linker *linker, const char *sec_name,
2613                              size_t align, const void *raw_data, size_t raw_sz)
2614 {
2615         Elf_Scn *scn;
2616         Elf_Data *data;
2617         Elf64_Shdr *shdr;
2618         int name_off;
2619
2620         name_off = strset__add_str(linker->strtab_strs, sec_name);
2621         if (name_off < 0)
2622                 return name_off;
2623
2624         scn = elf_newscn(linker->elf);
2625         if (!scn)
2626                 return -ENOMEM;
2627         data = elf_newdata(scn);
2628         if (!data)
2629                 return -ENOMEM;
2630         shdr = elf64_getshdr(scn);
2631         if (!shdr)
2632                 return -EINVAL;
2633
2634         shdr->sh_name = name_off;
2635         shdr->sh_type = SHT_PROGBITS;
2636         shdr->sh_flags = 0;
2637         shdr->sh_size = raw_sz;
2638         shdr->sh_link = 0;
2639         shdr->sh_info = 0;
2640         shdr->sh_addralign = align;
2641         shdr->sh_entsize = 0;
2642
2643         data->d_type = ELF_T_BYTE;
2644         data->d_size = raw_sz;
2645         data->d_buf = (void *)raw_data;
2646         data->d_align = align;
2647         data->d_off = 0;
2648
2649         return 0;
2650 }
2651
2652 static int finalize_btf(struct bpf_linker *linker)
2653 {
2654         LIBBPF_OPTS(btf_dedup_opts, opts);
2655         struct btf *btf = linker->btf;
2656         const void *raw_data;
2657         int i, j, id, err;
2658         __u32 raw_sz;
2659
2660         /* bail out if no BTF data was produced */
2661         if (btf__type_cnt(linker->btf) == 1)
2662                 return 0;
2663
2664         for (i = 1; i < linker->sec_cnt; i++) {
2665                 struct dst_sec *sec = &linker->secs[i];
2666
2667                 if (!sec->has_btf)
2668                         continue;
2669
2670                 id = btf__add_datasec(btf, sec->sec_name, sec->sec_sz);
2671                 if (id < 0) {
2672                         pr_warn("failed to add consolidated BTF type for datasec '%s': %d\n",
2673                                 sec->sec_name, id);
2674                         return id;
2675                 }
2676
2677                 for (j = 0; j < sec->sec_var_cnt; j++) {
2678                         struct btf_var_secinfo *vi = &sec->sec_vars[j];
2679
2680                         if (btf__add_datasec_var_info(btf, vi->type, vi->offset, vi->size))
2681                                 return -EINVAL;
2682                 }
2683         }
2684
2685         err = finalize_btf_ext(linker);
2686         if (err) {
2687                 pr_warn(".BTF.ext generation failed: %d\n", err);
2688                 return err;
2689         }
2690
2691         opts.btf_ext = linker->btf_ext;
2692         err = btf__dedup(linker->btf, &opts);
2693         if (err) {
2694                 pr_warn("BTF dedup failed: %d\n", err);
2695                 return err;
2696         }
2697
2698         /* Emit .BTF section */
2699         raw_data = btf__raw_data(linker->btf, &raw_sz);
2700         if (!raw_data)
2701                 return -ENOMEM;
2702
2703         err = emit_elf_data_sec(linker, BTF_ELF_SEC, 8, raw_data, raw_sz);
2704         if (err) {
2705                 pr_warn("failed to write out .BTF ELF section: %d\n", err);
2706                 return err;
2707         }
2708
2709         /* Emit .BTF.ext section */
2710         if (linker->btf_ext) {
2711                 raw_data = btf_ext__get_raw_data(linker->btf_ext, &raw_sz);
2712                 if (!raw_data)
2713                         return -ENOMEM;
2714
2715                 err = emit_elf_data_sec(linker, BTF_EXT_ELF_SEC, 8, raw_data, raw_sz);
2716                 if (err) {
2717                         pr_warn("failed to write out .BTF.ext ELF section: %d\n", err);
2718                         return err;
2719                 }
2720         }
2721
2722         return 0;
2723 }
2724
2725 static int emit_btf_ext_data(struct bpf_linker *linker, void *output,
2726                              const char *sec_name, struct btf_ext_sec_data *sec_data)
2727 {
2728         struct btf_ext_info_sec *sec_info;
2729         void *cur = output;
2730         int str_off;
2731         size_t sz;
2732
2733         if (!sec_data->rec_cnt)
2734                 return 0;
2735
2736         str_off = btf__add_str(linker->btf, sec_name);
2737         if (str_off < 0)
2738                 return -ENOMEM;
2739
2740         sec_info = cur;
2741         sec_info->sec_name_off = str_off;
2742         sec_info->num_info = sec_data->rec_cnt;
2743         cur += sizeof(struct btf_ext_info_sec);
2744
2745         sz = sec_data->rec_cnt * sec_data->rec_sz;
2746         memcpy(cur, sec_data->recs, sz);
2747         cur += sz;
2748
2749         return cur - output;
2750 }
2751
2752 static int finalize_btf_ext(struct bpf_linker *linker)
2753 {
2754         size_t funcs_sz = 0, lines_sz = 0, core_relos_sz = 0, total_sz = 0;
2755         size_t func_rec_sz = 0, line_rec_sz = 0, core_relo_rec_sz = 0;
2756         struct btf_ext_header *hdr;
2757         void *data, *cur;
2758         int i, err, sz;
2759
2760         /* validate that all sections have the same .BTF.ext record sizes
2761          * and calculate total data size for each type of data (func info,
2762          * line info, core relos)
2763          */
2764         for (i = 1; i < linker->sec_cnt; i++) {
2765                 struct dst_sec *sec = &linker->secs[i];
2766
2767                 if (sec->func_info.rec_cnt) {
2768                         if (func_rec_sz == 0)
2769                                 func_rec_sz = sec->func_info.rec_sz;
2770                         if (func_rec_sz != sec->func_info.rec_sz) {
2771                                 pr_warn("mismatch in func_info record size %zu != %u\n",
2772                                         func_rec_sz, sec->func_info.rec_sz);
2773                                 return -EINVAL;
2774                         }
2775
2776                         funcs_sz += sizeof(struct btf_ext_info_sec) + func_rec_sz * sec->func_info.rec_cnt;
2777                 }
2778                 if (sec->line_info.rec_cnt) {
2779                         if (line_rec_sz == 0)
2780                                 line_rec_sz = sec->line_info.rec_sz;
2781                         if (line_rec_sz != sec->line_info.rec_sz) {
2782                                 pr_warn("mismatch in line_info record size %zu != %u\n",
2783                                         line_rec_sz, sec->line_info.rec_sz);
2784                                 return -EINVAL;
2785                         }
2786
2787                         lines_sz += sizeof(struct btf_ext_info_sec) + line_rec_sz * sec->line_info.rec_cnt;
2788                 }
2789                 if (sec->core_relo_info.rec_cnt) {
2790                         if (core_relo_rec_sz == 0)
2791                                 core_relo_rec_sz = sec->core_relo_info.rec_sz;
2792                         if (core_relo_rec_sz != sec->core_relo_info.rec_sz) {
2793                                 pr_warn("mismatch in core_relo_info record size %zu != %u\n",
2794                                         core_relo_rec_sz, sec->core_relo_info.rec_sz);
2795                                 return -EINVAL;
2796                         }
2797
2798                         core_relos_sz += sizeof(struct btf_ext_info_sec) + core_relo_rec_sz * sec->core_relo_info.rec_cnt;
2799                 }
2800         }
2801
2802         if (!funcs_sz && !lines_sz && !core_relos_sz)
2803                 return 0;
2804
2805         total_sz += sizeof(struct btf_ext_header);
2806         if (funcs_sz) {
2807                 funcs_sz += sizeof(__u32); /* record size prefix */
2808                 total_sz += funcs_sz;
2809         }
2810         if (lines_sz) {
2811                 lines_sz += sizeof(__u32); /* record size prefix */
2812                 total_sz += lines_sz;
2813         }
2814         if (core_relos_sz) {
2815                 core_relos_sz += sizeof(__u32); /* record size prefix */
2816                 total_sz += core_relos_sz;
2817         }
2818
2819         cur = data = calloc(1, total_sz);
2820         if (!data)
2821                 return -ENOMEM;
2822
2823         hdr = cur;
2824         hdr->magic = BTF_MAGIC;
2825         hdr->version = BTF_VERSION;
2826         hdr->flags = 0;
2827         hdr->hdr_len = sizeof(struct btf_ext_header);
2828         cur += sizeof(struct btf_ext_header);
2829
2830         /* All offsets are in bytes relative to the end of this header */
2831         hdr->func_info_off = 0;
2832         hdr->func_info_len = funcs_sz;
2833         hdr->line_info_off = funcs_sz;
2834         hdr->line_info_len = lines_sz;
2835         hdr->core_relo_off = funcs_sz + lines_sz;
2836         hdr->core_relo_len = core_relos_sz;
2837
2838         if (funcs_sz) {
2839                 *(__u32 *)cur = func_rec_sz;
2840                 cur += sizeof(__u32);
2841
2842                 for (i = 1; i < linker->sec_cnt; i++) {
2843                         struct dst_sec *sec = &linker->secs[i];
2844
2845                         sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->func_info);
2846                         if (sz < 0) {
2847                                 err = sz;
2848                                 goto out;
2849                         }
2850
2851                         cur += sz;
2852                 }
2853         }
2854
2855         if (lines_sz) {
2856                 *(__u32 *)cur = line_rec_sz;
2857                 cur += sizeof(__u32);
2858
2859                 for (i = 1; i < linker->sec_cnt; i++) {
2860                         struct dst_sec *sec = &linker->secs[i];
2861
2862                         sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->line_info);
2863                         if (sz < 0) {
2864                                 err = sz;
2865                                 goto out;
2866                         }
2867
2868                         cur += sz;
2869                 }
2870         }
2871
2872         if (core_relos_sz) {
2873                 *(__u32 *)cur = core_relo_rec_sz;
2874                 cur += sizeof(__u32);
2875
2876                 for (i = 1; i < linker->sec_cnt; i++) {
2877                         struct dst_sec *sec = &linker->secs[i];
2878
2879                         sz = emit_btf_ext_data(linker, cur, sec->sec_name, &sec->core_relo_info);
2880                         if (sz < 0) {
2881                                 err = sz;
2882                                 goto out;
2883                         }
2884
2885                         cur += sz;
2886                 }
2887         }
2888
2889         linker->btf_ext = btf_ext__new(data, total_sz);
2890         err = libbpf_get_error(linker->btf_ext);
2891         if (err) {
2892                 linker->btf_ext = NULL;
2893                 pr_warn("failed to parse final .BTF.ext data: %d\n", err);
2894                 goto out;
2895         }
2896
2897 out:
2898         free(data);
2899         return err;
2900 }