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