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