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 #define _LGPL_SOURCE
  21 #include <helper.h>
  22 #include <string.h>
  23 #include <lttng/align.h>
  24 #include <lttng/ust-elf.h>
  25 #include <sys/types.h>
  26 #include <sys/stat.h>
  27 #include <fcntl.h>
  28 #include <unistd.h>
  29 #include <stdbool.h>
  30 #include <ust-fd.h>
  31 #include "lttng-tracer-core.h"
  32
  33 #define BUF_LEN 4096
  34
  35 #ifndef NT_GNU_BUILD_ID
  36 # define NT_GNU_BUILD_ID        3
  37 #endif
  38
  39 /*
  40  * Retrieve the nth (where n is the `index` argument) phdr (program
  41  * header) from the given elf instance.
  42  *
  43  * A pointer to the phdr is returned on success, NULL on failure.
  44  */
  45 static
  46 struct lttng_ust_elf_phdr *lttng_ust_elf_get_phdr(struct lttng_ust_elf *elf,
  47                                                 uint16_t index)
  48 {
  49         struct lttng_ust_elf_phdr *phdr = NULL;
  50         off_t offset;
  51
  52         if (!elf) {
  53                 goto error;
  54         }
  55
  56         if (index >= elf->ehdr->e_phnum) {
  57                 goto error;
  58         }
  59
  60         phdr = zmalloc(sizeof(struct lttng_ust_elf_phdr));
  61         if (!phdr) {
  62                 goto error;
  63         }
  64
  65         offset = (off_t) elf->ehdr->e_phoff
  66                         + (off_t) index * elf->ehdr->e_phentsize;
  67         if (lseek(elf->fd, offset, SEEK_SET) < 0) {
  68                 goto error;
  69         }
  70
  71         if (is_elf_32_bit(elf)) {
  72                 Elf32_Phdr elf_phdr;
  73
  74                 if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
  75                                 < sizeof(elf_phdr)) {
  76                         goto error;
  77                 }
  78                 if (!is_elf_native_endian(elf)) {
  79                         bswap_phdr(elf_phdr);
  80                 }
  81                 copy_phdr(elf_phdr, *phdr);
  82         } else {
  83                 Elf64_Phdr elf_phdr;
  84
  85                 if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
  86                                 < sizeof(elf_phdr)) {
  87                         goto error;
  88                 }
  89                 if (!is_elf_native_endian(elf)) {
  90                         bswap_phdr(elf_phdr);
  91                 }
  92                 copy_phdr(elf_phdr, *phdr);
  93         }
  94
  95         return phdr;
  96
  97 error:
  98         free(phdr);
  99         return NULL;
 100 }
 101
 102 /*
 103  * Retrieve the nth (where n is the `index` argument) shdr (section
 104  * header) from the given elf instance.
 105  *
 106  * A pointer to the shdr is returned on success, NULL on failure.
 107  */
 108 static
 109 struct lttng_ust_elf_shdr *lttng_ust_elf_get_shdr(struct lttng_ust_elf *elf,
 110                                                 uint16_t index)
 111 {
 112         struct lttng_ust_elf_shdr *shdr = NULL;
 113         off_t offset;
 114
 115         if (!elf) {
 116                 goto error;
 117         }
 118
 119         if (index >= elf->ehdr->e_shnum) {
 120                 goto error;
 121         }
 122
 123         shdr = zmalloc(sizeof(struct lttng_ust_elf_shdr));
 124         if (!shdr) {
 125                 goto error;
 126         }
 127
 128         offset = (off_t) elf->ehdr->e_shoff
 129                         + (off_t) index * elf->ehdr->e_shentsize;
 130         if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 131                 goto error;
 132         }
 133
 134         if (is_elf_32_bit(elf)) {
 135                 Elf32_Shdr elf_shdr;
 136
 137                 if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
 138                                 < sizeof(elf_shdr)) {
 139                         goto error;
 140                 }
 141                 if (!is_elf_native_endian(elf)) {
 142                         bswap_shdr(elf_shdr);
 143                 }
 144                 copy_shdr(elf_shdr, *shdr);
 145         } else {
 146                 Elf64_Shdr elf_shdr;
 147
 148                 if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
 149                                 < sizeof(elf_shdr)) {
 150                         goto error;
 151                 }
 152                 if (!is_elf_native_endian(elf)) {
 153                         bswap_shdr(elf_shdr);
 154                 }
 155                 copy_shdr(elf_shdr, *shdr);
 156         }
 157
 158         return shdr;
 159
 160 error:
 161         free(shdr);
 162         return NULL;
 163 }
 164
 165 /*
 166  * Lookup a section's name from a given offset (usually from an shdr's
 167  * sh_name value) in bytes relative to the beginning of the section
 168  * names string table.
 169  *
 170  * If no name is found, NULL is returned.
 171  */
 172 static
 173 char *lttng_ust_elf_get_section_name(struct lttng_ust_elf *elf, off_t offset)
 174 {
 175         char *name = NULL;
 176         size_t len = 0, to_read;        /* len does not include \0 */
 177
 178         if (!elf) {
 179                 goto error;
 180         }
 181
 182         if (offset >= elf->section_names_size) {
 183                 goto error;
 184         }
 185
 186         if (lseek(elf->fd, elf->section_names_offset + offset, SEEK_SET) < 0) {
 187                 goto error;
 188         }
 189
 190         to_read = elf->section_names_size - offset;
 191
 192         /* Find first \0 after or at current location, remember len. */
 193         for (;;) {
 194                 char buf[BUF_LEN];
 195                 ssize_t read_len;
 196                 size_t i;
 197
 198                 if (!to_read) {
 199                         goto error;
 200                 }
 201                 read_len = lttng_ust_read(elf->fd, buf,
 202                         min_t(size_t, BUF_LEN, to_read));
 203                 if (read_len <= 0) {
 204                         goto error;
 205                 }
 206                 for (i = 0; i < read_len; i++) {
 207                         if (buf[i] == '\0') {
 208                                 len += i;
 209                                 goto end;
 210                         }
 211                 }
 212                 len += read_len;
 213                 to_read -= read_len;
 214         }
 215 end:
 216         name = zmalloc(sizeof(char) * (len + 1));       /* + 1 for \0 */
 217         if (!name) {
 218                 goto error;
 219         }
 220         if (lseek(elf->fd, elf->section_names_offset + offset,
 221                 SEEK_SET) < 0) {
 222                 goto error;
 223         }
 224         if (lttng_ust_read(elf->fd, name, len + 1) < len + 1) {
 225                 goto error;
 226         }
 227
 228         return name;
 229
 230 error:
 231         free(name);
 232         return NULL;
 233 }
 234
 235 /*
 236  * Create an instance of lttng_ust_elf for the ELF file located at
 237  * `path`.
 238  *
 239  * Return a pointer to the instance on success, NULL on failure.
 240  */
 241 struct lttng_ust_elf *lttng_ust_elf_create(const char *path)
 242 {
 243         uint8_t e_ident[EI_NIDENT];
 244         struct lttng_ust_elf_shdr *section_names_shdr;
 245         struct lttng_ust_elf *elf = NULL;
 246
 247         elf = zmalloc(sizeof(struct lttng_ust_elf));
 248         if (!elf) {
 249                 goto error;
 250         }
 251
 252
 253         elf->path = strdup(path);
 254         if (!elf->path) {
 255                 goto error;
 256         }
 257
 258         lttng_ust_lock_fd_tracker();
 259         elf->fd = open(elf->path, O_RDONLY | O_CLOEXEC);
 260         if (elf->fd < 0) {
 261                 lttng_ust_unlock_fd_tracker();
 262                 goto error;
 263         }
 264         lttng_ust_add_fd_to_tracker(elf->fd);
 265         lttng_ust_unlock_fd_tracker();
 266
 267         if (lttng_ust_read(elf->fd, e_ident, EI_NIDENT) < EI_NIDENT) {
 268                 goto error;
 269         }
 270         elf->bitness = e_ident[EI_CLASS];
 271         elf->endianness = e_ident[EI_DATA];
 272
 273         if (lseek(elf->fd, 0, SEEK_SET) < 0) {
 274                 goto error;
 275         }
 276
 277         elf->ehdr = zmalloc(sizeof(struct lttng_ust_elf_ehdr));
 278         if (!elf->ehdr) {
 279                 goto error;
 280         }
 281
 282         if (is_elf_32_bit(elf)) {
 283                 Elf32_Ehdr elf_ehdr;
 284
 285                 if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
 286                                 < sizeof(elf_ehdr)) {
 287                         goto error;
 288                 }
 289                 if (!is_elf_native_endian(elf)) {
 290                         bswap_ehdr(elf_ehdr);
 291                 }
 292                 copy_ehdr(elf_ehdr, *(elf->ehdr));
 293         } else {
 294                 Elf64_Ehdr elf_ehdr;
 295
 296                 if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
 297                                 < sizeof(elf_ehdr)) {
 298                         goto error;
 299                 }
 300                 if (!is_elf_native_endian(elf)) {
 301                         bswap_ehdr(elf_ehdr);
 302                 }
 303                 copy_ehdr(elf_ehdr, *(elf->ehdr));
 304         }
 305
 306         section_names_shdr = lttng_ust_elf_get_shdr(elf, elf->ehdr->e_shstrndx);
 307         if (!section_names_shdr) {
 308                 goto error;
 309         }
 310
 311         elf->section_names_offset = section_names_shdr->sh_offset;
 312         elf->section_names_size = section_names_shdr->sh_size;
 313
 314         free(section_names_shdr);
 315         return elf;
 316
 317 error:
 318         lttng_ust_elf_destroy(elf);
 319         return NULL;
 320 }
 321
 322 /*
 323  * Test whether the ELF file is position independent code (PIC)
 324  */
 325 uint8_t lttng_ust_elf_is_pic(struct lttng_ust_elf *elf)
 326 {
 327         /*
 328          * PIC has and e_type value of ET_DYN, see ELF specification
 329          * version 1.1 p. 1-3.
 330          */
 331         return elf->ehdr->e_type == ET_DYN;
 332 }
 333
 334 /*
 335  * Destroy the given lttng_ust_elf instance.
 336  */
 337 void lttng_ust_elf_destroy(struct lttng_ust_elf *elf)
 338 {
 339         int ret;
 340
 341         if (!elf) {
 342                 return;
 343         }
 344
 345         if (elf->fd >= 0) {
 346                 lttng_ust_lock_fd_tracker();
 347                 ret = close(elf->fd);
 348                 if (!ret) {
 349                         lttng_ust_delete_fd_from_tracker(elf->fd);
 350                 } else {
 351                         PERROR("close");
 352                         abort();
 353                 }
 354                 lttng_ust_unlock_fd_tracker();
 355         }
 356
 357         free(elf->ehdr);
 358         free(elf->path);
 359         free(elf);
 360 }
 361
 362 /*
 363  * Compute the total in-memory size of the ELF file, in bytes.
 364  *
 365  * Returns 0 if successful, -1 if not. On success, the memory size is
 366  * returned through the out parameter `memsz`.
 367  */
 368 int lttng_ust_elf_get_memsz(struct lttng_ust_elf *elf, uint64_t *memsz)
 369 {
 370         uint16_t i;
 371         uint64_t low_addr = UINT64_MAX, high_addr = 0;
 372
 373         if (!elf || !memsz) {
 374                 goto error;
 375         }
 376
 377         for (i = 0; i < elf->ehdr->e_phnum; ++i) {
 378                 struct lttng_ust_elf_phdr *phdr;
 379
 380                 phdr = lttng_ust_elf_get_phdr(elf, i);
 381                 if (!phdr) {
 382                         goto error;
 383                 }
 384
 385                 /*
 386                  * Only PT_LOAD segments contribute to memsz. Skip
 387                  * other segments.
 388                  */
 389                 if (phdr->p_type != PT_LOAD) {
 390                         goto next_loop;
 391                 }
 392
 393                 low_addr = min_t(uint64_t, low_addr, phdr->p_vaddr);
 394                 high_addr = max_t(uint64_t, high_addr,
 395                                 phdr->p_vaddr + phdr->p_memsz);
 396         next_loop:
 397                 free(phdr);
 398         }
 399
 400         if (high_addr < low_addr) {
 401                 /* No PT_LOAD segments or corrupted data. */
 402                 goto error;
 403         }
 404
 405         *memsz = high_addr - low_addr;
 406         return 0;
 407 error:
 408         return -1;
 409 }
 410
 411 /*
 412  * Internal method used to try and get the build_id from a PT_NOTE
 413  * segment ranging from `offset` to `segment_end`.
 414  *
 415  * If the function returns successfully, the out parameter `found`
 416  * indicates whether the build id information was present in the
 417  * segment or not. If `found` is not 0, the out parameters `build_id`
 418  * and `length` will both have been set with the retrieved
 419  * information.
 420  *
 421  * Returns 0 on success, -1 if an error occurred.
 422  */
 423 static
 424 int lttng_ust_elf_get_build_id_from_segment(
 425         struct lttng_ust_elf *elf, uint8_t **build_id, size_t *length,
 426         off_t offset, off_t segment_end)
 427 {
 428         uint8_t *_build_id = NULL;      /* Silence old gcc warning. */
 429         size_t _length = 0;             /* Silence old gcc warning. */
 430
 431         while (offset < segment_end) {
 432                 struct lttng_ust_elf_nhdr nhdr;
 433                 size_t read_len;
 434
 435                 /* Align start of note entry */
 436                 offset += offset_align(offset, ELF_NOTE_ENTRY_ALIGN);
 437                 if (offset >= segment_end) {
 438                         break;
 439                 }
 440                 /*
 441                  * We seek manually because if the note isn't the
 442                  * build id the data following the header will not
 443                  * have been read.
 444                  */
 445                 if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 446                         goto error;
 447                 }
 448                 if (lttng_ust_read(elf->fd, &nhdr, sizeof(nhdr))
 449                                 < sizeof(nhdr)) {
 450                         goto error;
 451                 }
 452
 453                 if (!is_elf_native_endian(elf)) {
 454                         nhdr.n_namesz = bswap_32(nhdr.n_namesz);
 455                         nhdr.n_descsz = bswap_32(nhdr.n_descsz);
 456                         nhdr.n_type = bswap_32(nhdr.n_type);
 457                 }
 458
 459                 offset += sizeof(nhdr) + nhdr.n_namesz;
 460                 /* Align start of desc entry */
 461                 offset += offset_align(offset, ELF_NOTE_DESC_ALIGN);
 462
 463                 if (nhdr.n_type != NT_GNU_BUILD_ID) {
 464                         /*
 465                          * Ignore non build id notes but still
 466                          * increase the offset.
 467                          */
 468                         offset += nhdr.n_descsz;
 469                         continue;
 470                 }
 471
 472                 _length = nhdr.n_descsz;
 473                 _build_id = zmalloc(sizeof(uint8_t) * _length);
 474                 if (!_build_id) {
 475                         goto error;
 476                 }
 477
 478                 if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 479                         goto error;
 480                 }
 481                 read_len = sizeof(*_build_id) * _length;
 482                 if (lttng_ust_read(elf->fd, _build_id, read_len) < read_len) {
 483                         goto error;
 484                 }
 485
 486                 break;
 487         }
 488
 489         if (_build_id) {
 490                 *build_id = _build_id;
 491                 *length = _length;
 492         }
 493
 494         return 0;
 495 error:
 496         free(_build_id);
 497         return -1;
 498 }
 499
 500 /*
 501  * Retrieve a build ID (an array of bytes) from the corresponding
 502  * section in the ELF file. The length of the build ID can be either
 503  * 16 or 20 bytes depending on the method used to generate it, hence
 504  * the length out parameter.
 505  *
 506  * If the function returns successfully, the out parameter `found`
 507  * indicates whether the build id information was present in the ELF
 508  * file or not. If `found` is not 0, the out parameters `build_id` and
 509  * `length` will both have been set with the retrieved information.
 510  *
 511  * Returns 0 on success, -1 if an error occurred.
 512  */
 513 int lttng_ust_elf_get_build_id(struct lttng_ust_elf *elf, uint8_t **build_id,
 514                         size_t *length, int *found)
 515 {
 516         uint16_t i;
 517         uint8_t *_build_id = NULL;      /* Silence old gcc warning. */
 518         size_t _length = 0;             /* Silence old gcc warning. */
 519
 520         if (!elf || !build_id || !length || !found) {
 521                 goto error;
 522         }
 523
 524         for (i = 0; i < elf->ehdr->e_phnum; ++i) {
 525                 off_t offset, segment_end;
 526                 struct lttng_ust_elf_phdr *phdr;
 527                 int ret = 0;
 528
 529                 phdr = lttng_ust_elf_get_phdr(elf, i);
 530                 if (!phdr) {
 531                         goto error;
 532                 }
 533
 534                 /* Build ID will be contained in a PT_NOTE segment. */
 535                 if (phdr->p_type != PT_NOTE) {
 536                         goto next_loop;
 537                 }
 538
 539                 offset = phdr->p_offset;
 540                 segment_end = offset + phdr->p_filesz;
 541                 ret = lttng_ust_elf_get_build_id_from_segment(
 542                         elf, &_build_id, &_length, offset, segment_end);
 543         next_loop:
 544                 free(phdr);
 545                 if (ret) {
 546                         goto error;
 547                 }
 548                 if (_build_id) {
 549                         break;
 550                 }
 551         }
 552
 553         if (_build_id) {
 554                 *build_id = _build_id;
 555                 *length = _length;
 556                 *found = 1;
 557         } else {
 558                 *found = 0;
 559         }
 560
 561         return 0;
 562 error:
 563         free(_build_id);
 564         return -1;
 565 }
 566
 567 /*
 568  * Try to retrieve filename and CRC from given ELF section `shdr`.
 569  *
 570  * If the function returns successfully, the out parameter `found`
 571  * indicates whether the debug link information was present in the ELF
 572  * section or not. If `found` is not 0, the out parameters `filename` and
 573  * `crc` will both have been set with the retrieved information.
 574  *
 575  * Returns 0 on success, -1 if an error occurred.
 576  */
 577 int lttng_ust_elf_get_debug_link_from_section(struct lttng_ust_elf *elf,
 578                                         char **filename, uint32_t *crc,
 579                                         struct lttng_ust_elf_shdr *shdr)
 580 {
 581         char *_filename = NULL;         /* Silence old gcc warning. */
 582         size_t filename_len;
 583         char *section_name = NULL;
 584         uint32_t _crc = 0;              /* Silence old gcc warning. */
 585
 586         if (!elf || !filename || !crc || !shdr) {
 587                 goto error;
 588         }
 589
 590         /*
 591          * The .gnu_debuglink section is of type SHT_PROGBITS,
 592          * skip the other sections.
 593          */
 594         if (shdr->sh_type != SHT_PROGBITS) {
 595                 goto end;
 596         }
 597
 598         section_name = lttng_ust_elf_get_section_name(elf,
 599                                                 shdr->sh_name);
 600         if (!section_name) {
 601                 goto end;
 602         }
 603         if (strcmp(section_name, ".gnu_debuglink")) {
 604                 goto end;
 605         }
 606
 607         /*
 608          * The length of the filename is the sh_size excluding the CRC
 609          * which comes after it in the section.
 610          */
 611         _filename = zmalloc(sizeof(char) * (shdr->sh_size - ELF_CRC_SIZE));
 612         if (!_filename) {
 613                 goto error;
 614         }
 615         if (lseek(elf->fd, shdr->sh_offset, SEEK_SET) < 0) {
 616                 goto error;
 617         }
 618         filename_len = sizeof(*_filename) * (shdr->sh_size - ELF_CRC_SIZE);
 619         if (lttng_ust_read(elf->fd, _filename, filename_len) < filename_len) {
 620                 goto error;
 621         }
 622         if (lttng_ust_read(elf->fd, &_crc, sizeof(_crc)) < sizeof(_crc)) {
 623                 goto error;
 624         }
 625         if (!is_elf_native_endian(elf)) {
 626                 _crc = bswap_32(_crc);
 627         }
 628
 629 end:
 630         free(section_name);
 631         if (_filename) {
 632                 *filename = _filename;
 633                 *crc = _crc;
 634         }
 635
 636         return 0;
 637
 638 error:
 639         free(_filename);
 640         free(section_name);
 641         return -1;
 642 }
 643
 644 /*
 645  * Retrieve filename and CRC from ELF's .gnu_debuglink section, if any.
 646  *
 647  * If the function returns successfully, the out parameter `found`
 648  * indicates whether the debug link information was present in the ELF
 649  * file or not. If `found` is not 0, the out parameters `filename` and
 650  * `crc` will both have been set with the retrieved information.
 651  *
 652  * Returns 0 on success, -1 if an error occurred.
 653  */
 654 int lttng_ust_elf_get_debug_link(struct lttng_ust_elf *elf, char **filename,
 655                                 uint32_t *crc, int *found)
 656 {
 657         int ret;
 658         uint16_t i;
 659         char *_filename = NULL;         /* Silence old gcc warning. */
 660         uint32_t _crc = 0;              /* Silence old gcc warning. */
 661
 662         if (!elf || !filename || !crc || !found) {
 663                 goto error;
 664         }
 665
 666         for (i = 0; i < elf->ehdr->e_shnum; ++i) {
 667                 struct lttng_ust_elf_shdr *shdr = NULL;
 668
 669                 shdr = lttng_ust_elf_get_shdr(elf, i);
 670                 if (!shdr) {
 671                         goto error;
 672                 }
 673
 674                 ret = lttng_ust_elf_get_debug_link_from_section(
 675                         elf, &_filename, &_crc, shdr);
 676                 free(shdr);
 677
 678                 if (ret) {
 679                         goto error;
 680                 }
 681                 if (_filename) {
 682                         break;
 683                 }
 684         }
 685
 686         if (_filename) {
 687                 *filename = _filename;
 688                 *crc = _crc;
 689                 *found = 1;
 690         } else {
 691                 *found = 0;
 692         }
 693
 694         return 0;
 695
 696 error:
 697         free(_filename);
 698         return -1;
 699 }