liblttng-ust/lttng-ust-elf.c

   1 /*
   2  * Copyright (C) 2015  Antoine Busque <abusque@efficios.com>
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2.1 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with this library; if not, write to the Free Software
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
  17  */
  18
  19 #define _GNU_SOURCE
  20 #include <helper.h>
  21 #include <string.h>
  22 #include <lttng/align.h>
  23 #include <lttng/ust-elf.h>
  24 #include <sys/types.h>
  25 #include <sys/stat.h>
  26 #include <fcntl.h>
  27 #include <unistd.h>
  28 #include "lttng-tracer-core.h"
  29
  30 #define BUF_LEN 4096
  31
  32 #ifndef NT_GNU_BUILD_ID
  33 # define NT_GNU_BUILD_ID        3
  34 #endif
  35
  36 /*
  37  * Retrieve the nth (where n is the `index` argument) phdr (program
  38  * header) from the given elf instance.
  39  *
  40  * A pointer to the phdr is returned on success, NULL on failure.
  41  */
  42 static
  43 struct lttng_ust_elf_phdr *lttng_ust_elf_get_phdr(struct lttng_ust_elf *elf,
  44                                                 uint16_t index)
  45 {
  46         struct lttng_ust_elf_phdr *phdr = NULL;
  47         off_t offset;
  48
  49         if (!elf) {
  50                 goto error;
  51         }
  52
  53         if (index >= elf->ehdr->e_phnum) {
  54                 goto error;
  55         }
  56
  57         phdr = zmalloc(sizeof(struct lttng_ust_elf_phdr));
  58         if (!phdr) {
  59                 goto error;
  60         }
  61
  62         offset = (off_t) elf->ehdr->e_phoff
  63                         + (off_t) index * elf->ehdr->e_phentsize;
  64         if (lseek(elf->fd, offset, SEEK_SET) < 0) {
  65                 goto error;
  66         }
  67
  68         if (is_elf_32_bit(elf)) {
  69                 Elf32_Phdr elf_phdr;
  70
  71                 if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
  72                                 < sizeof(elf_phdr)) {
  73                         goto error;
  74                 }
  75                 if (!is_elf_native_endian(elf)) {
  76                         bswap_phdr(elf_phdr);
  77                 }
  78                 copy_phdr(elf_phdr, *phdr);
  79         } else {
  80                 Elf64_Phdr elf_phdr;
  81
  82                 if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
  83                                 < sizeof(elf_phdr)) {
  84                         goto error;
  85                 }
  86                 if (!is_elf_native_endian(elf)) {
  87                         bswap_phdr(elf_phdr);
  88                 }
  89                 copy_phdr(elf_phdr, *phdr);
  90         }
  91
  92         return phdr;
  93
  94 error:
  95         free(phdr);
  96         return NULL;
  97 }
  98
  99 /*
 100  * Retrieve the nth (where n is the `index` argument) shdr (section
 101  * header) from the given elf instance.
 102  *
 103  * A pointer to the shdr is returned on success, NULL on failure.
 104  */
 105 static
 106 struct lttng_ust_elf_shdr *lttng_ust_elf_get_shdr(struct lttng_ust_elf *elf,
 107                                                 uint16_t index)
 108 {
 109         struct lttng_ust_elf_shdr *shdr = NULL;
 110         off_t offset;
 111
 112         if (!elf) {
 113                 goto error;
 114         }
 115
 116         if (index >= elf->ehdr->e_shnum) {
 117                 goto error;
 118         }
 119
 120         shdr = zmalloc(sizeof(struct lttng_ust_elf_shdr));
 121         if (!shdr) {
 122                 goto error;
 123         }
 124
 125         offset = (off_t) elf->ehdr->e_shoff
 126                         + (off_t) index * elf->ehdr->e_shentsize;
 127         if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 128                 goto error;
 129         }
 130
 131         if (is_elf_32_bit(elf)) {
 132                 Elf32_Shdr elf_shdr;
 133
 134                 if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
 135                                 < sizeof(elf_shdr)) {
 136                         goto error;
 137                 }
 138                 if (!is_elf_native_endian(elf)) {
 139                         bswap_shdr(elf_shdr);
 140                 }
 141                 copy_shdr(elf_shdr, *shdr);
 142         } else {
 143                 Elf64_Shdr elf_shdr;
 144
 145                 if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
 146                                 < sizeof(elf_shdr)) {
 147                         goto error;
 148                 }
 149                 if (!is_elf_native_endian(elf)) {
 150                         bswap_shdr(elf_shdr);
 151                 }
 152                 copy_shdr(elf_shdr, *shdr);
 153         }
 154
 155         return shdr;
 156
 157 error:
 158         free(shdr);
 159         return NULL;
 160 }
 161
 162 /*
 163  * Lookup a section's name from a given offset (usually from an shdr's
 164  * sh_name value) in bytes relative to the beginning of the section
 165  * names string table.
 166  *
 167  * If no name is found, NULL is returned.
 168  */
 169 static
 170 char *lttng_ust_elf_get_section_name(struct lttng_ust_elf *elf, off_t offset)
 171 {
 172         char *name = NULL;
 173         size_t len = 0, to_read;        /* len does not include \0 */
 174
 175         if (!elf) {
 176                 goto error;
 177         }
 178
 179         if (offset >= elf->section_names_size) {
 180                 goto error;
 181         }
 182
 183         if (lseek(elf->fd, elf->section_names_offset + offset, SEEK_SET) < 0) {
 184                 goto error;
 185         }
 186
 187         to_read = elf->section_names_size - offset;
 188
 189         /* Find first \0 after or at current location, remember len. */
 190         for (;;) {
 191                 char buf[BUF_LEN];
 192                 ssize_t read_len;
 193                 size_t i;
 194
 195                 if (!to_read) {
 196                         goto error;
 197                 }
 198                 read_len = lttng_ust_read(elf->fd, buf,
 199                         min_t(size_t, BUF_LEN, to_read));
 200                 if (read_len <= 0) {
 201                         goto error;
 202                 }
 203                 for (i = 0; i < read_len; i++) {
 204                         if (buf[i] == '\0') {
 205                                 len += i;
 206                                 goto end;
 207                         }
 208                 }
 209                 len += read_len;
 210                 to_read -= read_len;
 211         }
 212 end:
 213         name = zmalloc(sizeof(char) * (len + 1));       /* + 1 for \0 */
 214         if (!name) {
 215                 goto error;
 216         }
 217         if (lseek(elf->fd, elf->section_names_offset + offset,
 218                 SEEK_SET) < 0) {
 219                 goto error;
 220         }
 221         if (lttng_ust_read(elf->fd, name, len + 1) < len + 1) {
 222                 goto error;
 223         }
 224
 225         return name;
 226
 227 error:
 228         free(name);
 229         return NULL;
 230 }
 231
 232 /*
 233  * Create an instance of lttng_ust_elf for the ELF file located at
 234  * `path`.
 235  *
 236  * Return a pointer to the instance on success, NULL on failure.
 237  */
 238 struct lttng_ust_elf *lttng_ust_elf_create(const char *path)
 239 {
 240         uint8_t e_ident[EI_NIDENT];
 241         struct lttng_ust_elf_shdr *section_names_shdr;
 242         struct lttng_ust_elf *elf = NULL;
 243
 244         elf = zmalloc(sizeof(struct lttng_ust_elf));
 245         if (!elf) {
 246                 goto error;
 247         }
 248
 249         elf->path = strdup(path);
 250         if (!elf->path) {
 251                 goto error;
 252         }
 253
 254         elf->fd = open(elf->path, O_RDONLY | O_CLOEXEC);
 255         if (elf->fd < 0) {
 256                 goto error;
 257         }
 258
 259         if (lttng_ust_read(elf->fd, e_ident, EI_NIDENT) < EI_NIDENT) {
 260                 goto error;
 261         }
 262         elf->bitness = e_ident[EI_CLASS];
 263         elf->endianness = e_ident[EI_DATA];
 264
 265         if (lseek(elf->fd, 0, SEEK_SET) < 0) {
 266                 goto error;
 267         }
 268
 269         elf->ehdr = zmalloc(sizeof(struct lttng_ust_elf_ehdr));
 270         if (!elf->ehdr) {
 271                 goto error;
 272         }
 273
 274         if (is_elf_32_bit(elf)) {
 275                 Elf32_Ehdr elf_ehdr;
 276
 277                 if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
 278                                 < sizeof(elf_ehdr)) {
 279                         goto error;
 280                 }
 281                 if (!is_elf_native_endian(elf)) {
 282                         bswap_ehdr(elf_ehdr);
 283                 }
 284                 copy_ehdr(elf_ehdr, *(elf->ehdr));
 285         } else {
 286                 Elf64_Ehdr elf_ehdr;
 287
 288                 if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
 289                                 < sizeof(elf_ehdr)) {
 290                         goto error;
 291                 }
 292                 if (!is_elf_native_endian(elf)) {
 293                         bswap_ehdr(elf_ehdr);
 294                 }
 295                 copy_ehdr(elf_ehdr, *(elf->ehdr));
 296         }
 297
 298         section_names_shdr = lttng_ust_elf_get_shdr(elf, elf->ehdr->e_shstrndx);
 299         if (!section_names_shdr) {
 300                 goto error;
 301         }
 302
 303         elf->section_names_offset = section_names_shdr->sh_offset;
 304         elf->section_names_size = section_names_shdr->sh_size;
 305
 306         free(section_names_shdr);
 307         return elf;
 308
 309 error:
 310         if (elf) {
 311                 free(elf->ehdr);
 312                 if (elf->fd >= 0) {
 313                         if (close(elf->fd)) {
 314                                 abort();
 315                         }
 316                 }
 317                 free(elf->path);
 318                 free(elf);
 319         }
 320         return NULL;
 321 }
 322
 323 /*
 324  * Test whether the ELF file is position independent code (PIC)
 325  */
 326 uint8_t lttng_ust_elf_is_pic(struct lttng_ust_elf *elf)
 327 {
 328         /*
 329          * PIC has and e_type value of ET_DYN, see ELF specification
 330          * version 1.1 p. 1-3.
 331          */
 332         return elf->ehdr->e_type == ET_DYN;
 333 }
 334
 335 /*
 336  * Destroy the given lttng_ust_elf instance.
 337  */
 338 void lttng_ust_elf_destroy(struct lttng_ust_elf *elf)
 339 {
 340         if (!elf) {
 341                 return;
 342         }
 343
 344         free(elf->ehdr);
 345         if (close(elf->fd)) {
 346                 abort();
 347         }
 348         free(elf->path);
 349         free(elf);
 350 }
 351
 352 /*
 353  * Compute the total in-memory size of the ELF file, in bytes.
 354  *
 355  * Returns 0 if successful, -1 if not. On success, the memory size is
 356  * returned through the out parameter `memsz`.
 357  */
 358 int lttng_ust_elf_get_memsz(struct lttng_ust_elf *elf, uint64_t *memsz)
 359 {
 360         uint16_t i;
 361         uint64_t low_addr = UINT64_MAX, high_addr = 0;
 362
 363         if (!elf || !memsz) {
 364                 goto error;
 365         }
 366
 367         for (i = 0; i < elf->ehdr->e_phnum; ++i) {
 368                 struct lttng_ust_elf_phdr *phdr;
 369
 370                 phdr = lttng_ust_elf_get_phdr(elf, i);
 371                 if (!phdr) {
 372                         goto error;
 373                 }
 374
 375                 /*
 376                  * Only PT_LOAD segments contribute to memsz. Skip
 377                  * other segments.
 378                  */
 379                 if (phdr->p_type != PT_LOAD) {
 380                         goto next_loop;
 381                 }
 382
 383                 low_addr = min_t(uint64_t, low_addr, phdr->p_vaddr);
 384                 high_addr = max_t(uint64_t, high_addr,
 385                                 phdr->p_vaddr + phdr->p_memsz);
 386         next_loop:
 387                 free(phdr);
 388         }
 389
 390         if (high_addr < low_addr) {
 391                 /* No PT_LOAD segments or corrupted data. */
 392                 goto error;
 393         }
 394
 395         *memsz = high_addr - low_addr;
 396         return 0;
 397 error:
 398         return -1;
 399 }
 400
 401 /*
 402  * Internal method used to try and get the build_id from a PT_NOTE
 403  * segment ranging from `offset` to `segment_end`.
 404  *
 405  * If the function returns successfully, the out parameter `found`
 406  * indicates whether the build id information was present in the
 407  * segment or not. If `found` is not 0, the out parameters `build_id`
 408  * and `length` will both have been set with the retrieved
 409  * information.
 410  *
 411  * Returns 0 on success, -1 if an error occurred.
 412  */
 413 static
 414 int lttng_ust_elf_get_build_id_from_segment(
 415         struct lttng_ust_elf *elf, uint8_t **build_id, size_t *length,
 416         off_t offset, off_t segment_end)
 417 {
 418         uint8_t *_build_id = NULL;      /* Silence old gcc warning. */
 419         size_t _length = 0;             /* Silence old gcc warning. */
 420
 421         while (offset < segment_end) {
 422                 struct lttng_ust_elf_nhdr nhdr;
 423                 size_t read_len;
 424
 425                 /* Align start of note entry */
 426                 offset += offset_align(offset, ELF_NOTE_ENTRY_ALIGN);
 427                 if (offset >= segment_end) {
 428                         break;
 429                 }
 430                 /*
 431                  * We seek manually because if the note isn't the
 432                  * build id the data following the header will not
 433                  * have been read.
 434                  */
 435                 if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 436                         goto error;
 437                 }
 438                 if (lttng_ust_read(elf->fd, &nhdr, sizeof(nhdr))
 439                                 < sizeof(nhdr)) {
 440                         goto error;
 441                 }
 442
 443                 if (!is_elf_native_endian(elf)) {
 444                         nhdr.n_namesz = bswap_32(nhdr.n_namesz);
 445                         nhdr.n_descsz = bswap_32(nhdr.n_descsz);
 446                         nhdr.n_type = bswap_32(nhdr.n_type);
 447                 }
 448
 449                 offset += sizeof(nhdr) + nhdr.n_namesz;
 450                 /* Align start of desc entry */
 451                 offset += offset_align(offset, ELF_NOTE_DESC_ALIGN);
 452
 453                 if (nhdr.n_type != NT_GNU_BUILD_ID) {
 454                         /*
 455                          * Ignore non build id notes but still
 456                          * increase the offset.
 457                          */
 458                         offset += nhdr.n_descsz;
 459                         continue;
 460                 }
 461
 462                 _length = nhdr.n_descsz;
 463                 _build_id = zmalloc(sizeof(uint8_t) * _length);
 464                 if (!_build_id) {
 465                         goto error;
 466                 }
 467
 468                 if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 469                         goto error;
 470                 }
 471                 read_len = sizeof(*_build_id) * _length;
 472                 if (lttng_ust_read(elf->fd, _build_id, read_len) < read_len) {
 473                         goto error;
 474                 }
 475
 476                 break;
 477         }
 478
 479         if (_build_id) {
 480                 *build_id = _build_id;
 481                 *length = _length;
 482         }
 483
 484         return 0;
 485 error:
 486         free(_build_id);
 487         return -1;
 488 }
 489
 490 /*
 491  * Retrieve a build ID (an array of bytes) from the corresponding
 492  * section in the ELF file. The length of the build ID can be either
 493  * 16 or 20 bytes depending on the method used to generate it, hence
 494  * the length out parameter.
 495  *
 496  * If the function returns successfully, the out parameter `found`
 497  * indicates whether the build id information was present in the ELF
 498  * file or not. If `found` is not 0, the out parameters `build_id` and
 499  * `length` will both have been set with the retrieved information.
 500  *
 501  * Returns 0 on success, -1 if an error occurred.
 502  */
 503 int lttng_ust_elf_get_build_id(struct lttng_ust_elf *elf, uint8_t **build_id,
 504                         size_t *length, int *found)
 505 {
 506         uint16_t i;
 507         uint8_t *_build_id = NULL;      /* Silence old gcc warning. */
 508         size_t _length = 0;             /* Silence old gcc warning. */
 509
 510         if (!elf || !build_id || !length || !found) {
 511                 goto error;
 512         }
 513
 514         for (i = 0; i < elf->ehdr->e_phnum; ++i) {
 515                 off_t offset, segment_end;
 516                 struct lttng_ust_elf_phdr *phdr;
 517                 int ret = 0;
 518
 519                 phdr = lttng_ust_elf_get_phdr(elf, i);
 520                 if (!phdr) {
 521                         goto error;
 522                 }
 523
 524                 /* Build ID will be contained in a PT_NOTE segment. */
 525                 if (phdr->p_type != PT_NOTE) {
 526                         goto next_loop;
 527                 }
 528
 529                 offset = phdr->p_offset;
 530                 segment_end = offset + phdr->p_filesz;
 531                 ret = lttng_ust_elf_get_build_id_from_segment(
 532                         elf, &_build_id, &_length, offset, segment_end);
 533         next_loop:
 534                 free(phdr);
 535                 if (ret) {
 536                         goto error;
 537                 }
 538                 if (_build_id) {
 539                         break;
 540                 }
 541         }
 542
 543         if (_build_id) {
 544                 *build_id = _build_id;
 545                 *length = _length;
 546                 *found = 1;
 547         } else {
 548                 *found = 0;
 549         }
 550
 551         return 0;
 552 error:
 553         free(_build_id);
 554         return -1;
 555 }
 556
 557 /*
 558  * Try to retrieve filename and CRC from given ELF section `shdr`.
 559  *
 560  * If the function returns successfully, the out parameter `found`
 561  * indicates whether the debug link information was present in the ELF
 562  * section or not. If `found` is not 0, the out parameters `filename` and
 563  * `crc` will both have been set with the retrieved information.
 564  *
 565  * Returns 0 on success, -1 if an error occurred.
 566  */
 567 int lttng_ust_elf_get_debug_link_from_section(struct lttng_ust_elf *elf,
 568                                         char **filename, uint32_t *crc,
 569                                         struct lttng_ust_elf_shdr *shdr)
 570 {
 571         char *_filename = NULL;         /* Silence old gcc warning. */
 572         size_t filename_len;
 573         char *section_name = NULL;
 574         uint32_t _crc = 0;              /* Silence old gcc warning. */
 575
 576         if (!elf || !filename || !crc || !shdr) {
 577                 goto error;
 578         }
 579
 580         /*
 581          * The .gnu_debuglink section is of type SHT_PROGBITS,
 582          * skip the other sections.
 583          */
 584         if (shdr->sh_type != SHT_PROGBITS) {
 585                 goto end;
 586         }
 587
 588         section_name = lttng_ust_elf_get_section_name(elf,
 589                                                 shdr->sh_name);
 590         if (!section_name) {
 591                 goto end;
 592         }
 593         if (strcmp(section_name, ".gnu_debuglink")) {
 594                 goto end;
 595         }
 596
 597         /*
 598          * The length of the filename is the sh_size excluding the CRC
 599          * which comes after it in the section.
 600          */
 601         _filename = zmalloc(sizeof(char) * (shdr->sh_size - ELF_CRC_SIZE));
 602         if (!_filename) {
 603                 goto error;
 604         }
 605         if (lseek(elf->fd, shdr->sh_offset, SEEK_SET) < 0) {
 606                 goto error;
 607         }
 608         filename_len = sizeof(*_filename) * (shdr->sh_size - ELF_CRC_SIZE);
 609         if (lttng_ust_read(elf->fd, _filename, filename_len) < filename_len) {
 610                 goto error;
 611         }
 612         if (lttng_ust_read(elf->fd, &_crc, sizeof(_crc)) < sizeof(_crc)) {
 613                 goto error;
 614         }
 615         if (!is_elf_native_endian(elf)) {
 616                 _crc = bswap_32(_crc);
 617         }
 618
 619 end:
 620         free(section_name);
 621         if (_filename) {
 622                 *filename = _filename;
 623                 *crc = _crc;
 624         }
 625
 626         return 0;
 627
 628 error:
 629         free(_filename);
 630         free(section_name);
 631         return -1;
 632 }
 633
 634 /*
 635  * Retrieve filename and CRC from ELF's .gnu_debuglink section, if any.
 636  *
 637  * If the function returns successfully, the out parameter `found`
 638  * indicates whether the debug link information was present in the ELF
 639  * file or not. If `found` is not 0, the out parameters `filename` and
 640  * `crc` will both have been set with the retrieved information.
 641  *
 642  * Returns 0 on success, -1 if an error occurred.
 643  */
 644 int lttng_ust_elf_get_debug_link(struct lttng_ust_elf *elf, char **filename,
 645                                 uint32_t *crc, int *found)
 646 {
 647         int ret;
 648         uint16_t i;
 649         char *_filename = NULL;         /* Silence old gcc warning. */
 650         uint32_t _crc = 0;              /* Silence old gcc warning. */
 651
 652         if (!elf || !filename || !crc || !found) {
 653                 goto error;
 654         }
 655
 656         for (i = 0; i < elf->ehdr->e_shnum; ++i) {
 657                 struct lttng_ust_elf_shdr *shdr = NULL;
 658
 659                 shdr = lttng_ust_elf_get_shdr(elf, i);
 660                 if (!shdr) {
 661                         goto error;
 662                 }
 663
 664                 ret = lttng_ust_elf_get_debug_link_from_section(
 665                         elf, &_filename, &_crc, shdr);
 666                 free(shdr);
 667
 668                 if (ret) {
 669                         goto error;
 670                 }
 671                 if (_filename) {
 672                         break;
 673                 }
 674         }
 675
 676         if (_filename) {
 677                 *filename = _filename;
 678                 *crc = _crc;
 679                 *found = 1;
 680         } else {
 681                 *found = 0;
 682         }
 683
 684         return 0;
 685
 686 error:
 687         free(_filename);
 688         return -1;
 689 }