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 <stdbool.h>
  29 #include "lttng-tracer-core.h"
  30
  31 #define BUF_LEN 4096
  32
  33 /*
  34  * Retrieve the nth (where n is the `index` argument) phdr (program
  35  * header) from the given elf instance.
  36  *
  37  * A pointer to the phdr is returned on success, NULL on failure.
  38  */
  39 static
  40 struct lttng_ust_elf_phdr *lttng_ust_elf_get_phdr(struct lttng_ust_elf *elf,
  41                                                 uint16_t index)
  42 {
  43         struct lttng_ust_elf_phdr *phdr = NULL;
  44         off_t offset;
  45
  46         if (!elf) {
  47                 goto error;
  48         }
  49
  50         if (index >= elf->ehdr->e_phnum) {
  51                 goto error;
  52         }
  53
  54         phdr = zmalloc(sizeof(struct lttng_ust_elf_phdr));
  55         if (!phdr) {
  56                 goto error;
  57         }
  58
  59         offset = (off_t) elf->ehdr->e_phoff
  60                         + (off_t) index * elf->ehdr->e_phentsize;
  61         if (lseek(elf->fd, offset, SEEK_SET) < 0) {
  62                 goto error;
  63         }
  64
  65         if (is_elf_32_bit(elf)) {
  66                 Elf32_Phdr elf_phdr;
  67
  68                 if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
  69                                 < sizeof(elf_phdr)) {
  70                         goto error;
  71                 }
  72                 if (!is_elf_native_endian(elf)) {
  73                         bswap_phdr(elf_phdr);
  74                 }
  75                 copy_phdr(elf_phdr, *phdr);
  76         } else {
  77                 Elf64_Phdr elf_phdr;
  78
  79                 if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
  80                                 < sizeof(elf_phdr)) {
  81                         goto error;
  82                 }
  83                 if (!is_elf_native_endian(elf)) {
  84                         bswap_phdr(elf_phdr);
  85                 }
  86                 copy_phdr(elf_phdr, *phdr);
  87         }
  88
  89         return phdr;
  90
  91 error:
  92         free(phdr);
  93         return NULL;
  94 }
  95
  96 /*
  97  * Retrieve the nth (where n is the `index` argument) shdr (section
  98  * header) from the given elf instance.
  99  *
 100  * A pointer to the shdr is returned on success, NULL on failure.
 101  */
 102 static
 103 struct lttng_ust_elf_shdr *lttng_ust_elf_get_shdr(struct lttng_ust_elf *elf,
 104                                                 uint16_t index)
 105 {
 106         struct lttng_ust_elf_shdr *shdr = NULL;
 107         off_t offset;
 108
 109         if (!elf) {
 110                 goto error;
 111         }
 112
 113         if (index >= elf->ehdr->e_shnum) {
 114                 goto error;
 115         }
 116
 117         shdr = zmalloc(sizeof(struct lttng_ust_elf_shdr));
 118         if (!shdr) {
 119                 goto error;
 120         }
 121
 122         offset = (off_t) elf->ehdr->e_shoff
 123                         + (off_t) index * elf->ehdr->e_shentsize;
 124         if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 125                 goto error;
 126         }
 127
 128         if (is_elf_32_bit(elf)) {
 129                 Elf32_Shdr elf_shdr;
 130
 131                 if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
 132                                 < sizeof(elf_shdr)) {
 133                         goto error;
 134                 }
 135                 if (!is_elf_native_endian(elf)) {
 136                         bswap_shdr(elf_shdr);
 137                 }
 138                 copy_shdr(elf_shdr, *shdr);
 139         } else {
 140                 Elf64_Shdr elf_shdr;
 141
 142                 if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
 143                                 < sizeof(elf_shdr)) {
 144                         goto error;
 145                 }
 146                 if (!is_elf_native_endian(elf)) {
 147                         bswap_shdr(elf_shdr);
 148                 }
 149                 copy_shdr(elf_shdr, *shdr);
 150         }
 151
 152         return shdr;
 153
 154 error:
 155         free(shdr);
 156         return NULL;
 157 }
 158
 159 /*
 160  * Lookup a section's name from a given offset (usually from an shdr's
 161  * sh_name value) in bytes relative to the beginning of the section
 162  * names string table.
 163  *
 164  * If no name is found, NULL is returned.
 165  */
 166 static
 167 char *lttng_ust_elf_get_section_name(struct lttng_ust_elf *elf, off_t offset)
 168 {
 169         char *name = NULL;
 170         size_t len = 0, to_read;        /* len does not include \0 */
 171
 172         if (!elf) {
 173                 goto error;
 174         }
 175
 176         if (offset >= elf->section_names_size) {
 177                 goto error;
 178         }
 179
 180         if (lseek(elf->fd, elf->section_names_offset + offset, SEEK_SET) < 0) {
 181                 goto error;
 182         }
 183
 184         to_read = elf->section_names_size - offset;
 185
 186         /* Find first \0 after or at current location, remember len. */
 187         for (;;) {
 188                 char buf[BUF_LEN];
 189                 ssize_t read_len;
 190                 size_t i;
 191
 192                 if (!to_read) {
 193                         goto error;
 194                 }
 195                 read_len = lttng_ust_read(elf->fd, buf,
 196                         min_t(size_t, BUF_LEN, to_read));
 197                 if (read_len <= 0) {
 198                         goto error;
 199                 }
 200                 for (i = 0; i < read_len; i++) {
 201                         if (buf[i] == '\0') {
 202                                 len += i;
 203                                 goto end;
 204                         }
 205                 }
 206                 len += read_len;
 207                 to_read -= read_len;
 208         }
 209 end:
 210         name = zmalloc(sizeof(char) * (len + 1));       /* + 1 for \0 */
 211         if (!name) {
 212                 goto error;
 213         }
 214         if (lseek(elf->fd, elf->section_names_offset + offset,
 215                 SEEK_SET) < 0) {
 216                 goto error;
 217         }
 218         if (lttng_ust_read(elf->fd, name, len + 1) < len + 1) {
 219                 goto error;
 220         }
 221
 222         return name;
 223
 224 error:
 225         free(name);
 226         return NULL;
 227 }
 228
 229 /*
 230  * Create an instance of lttng_ust_elf for the ELF file located at
 231  * `path`.
 232  *
 233  * Return a pointer to the instance on success, NULL on failure.
 234  */
 235 struct lttng_ust_elf *lttng_ust_elf_create(const char *path)
 236 {
 237         uint8_t e_ident[EI_NIDENT];
 238         struct lttng_ust_elf_shdr *section_names_shdr;
 239         struct lttng_ust_elf *elf = NULL;
 240
 241         elf = zmalloc(sizeof(struct lttng_ust_elf));
 242         if (!elf) {
 243                 goto error;
 244         }
 245
 246         elf->path = strdup(path);
 247         if (!elf->path) {
 248                 goto error;
 249         }
 250
 251         elf->fd = open(elf->path, O_RDONLY | O_CLOEXEC);
 252         if (elf->fd < 0) {
 253                 goto error;
 254         }
 255
 256         if (lttng_ust_read(elf->fd, e_ident, EI_NIDENT) < EI_NIDENT) {
 257                 goto error;
 258         }
 259         elf->bitness = e_ident[EI_CLASS];
 260         elf->endianness = e_ident[EI_DATA];
 261
 262         if (lseek(elf->fd, 0, SEEK_SET) < 0) {
 263                 goto error;
 264         }
 265
 266         elf->ehdr = zmalloc(sizeof(struct lttng_ust_elf_ehdr));
 267         if (!elf->ehdr) {
 268                 goto error;
 269         }
 270
 271         if (is_elf_32_bit(elf)) {
 272                 Elf32_Ehdr elf_ehdr;
 273
 274                 if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
 275                                 < sizeof(elf_ehdr)) {
 276                         goto error;
 277                 }
 278                 if (!is_elf_native_endian(elf)) {
 279                         bswap_ehdr(elf_ehdr);
 280                 }
 281                 copy_ehdr(elf_ehdr, *(elf->ehdr));
 282         } else {
 283                 Elf64_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         }
 294
 295         section_names_shdr = lttng_ust_elf_get_shdr(elf, elf->ehdr->e_shstrndx);
 296         if (!section_names_shdr) {
 297                 goto error;
 298         }
 299
 300         elf->section_names_offset = section_names_shdr->sh_offset;
 301         elf->section_names_size = section_names_shdr->sh_size;
 302
 303         free(section_names_shdr);
 304         return elf;
 305
 306 error:
 307         if (elf) {
 308                 free(elf->ehdr);
 309                 if (elf->fd >= 0) {
 310                         if (close(elf->fd)) {
 311                                 abort();
 312                         }
 313                 }
 314                 free(elf->path);
 315                 free(elf);
 316         }
 317         return NULL;
 318 }
 319
 320 /*
 321  * Test whether the ELF file is position independent code (PIC)
 322  */
 323 uint8_t lttng_ust_elf_is_pic(struct lttng_ust_elf *elf)
 324 {
 325         /*
 326          * PIC has and e_type value of ET_DYN, see ELF specification
 327          * version 1.1 p. 1-3.
 328          */
 329         return elf->ehdr->e_type == ET_DYN;
 330 }
 331
 332 /*
 333  * Destroy the given lttng_ust_elf instance.
 334  */
 335 void lttng_ust_elf_destroy(struct lttng_ust_elf *elf)
 336 {
 337         if (!elf) {
 338                 return;
 339         }
 340
 341         free(elf->ehdr);
 342         if (close(elf->fd)) {
 343                 abort();
 344         }
 345         free(elf->path);
 346         free(elf);
 347 }
 348
 349 /*
 350  * Compute the total in-memory size of the ELF file, in bytes.
 351  *
 352  * Returns 0 if successful, -1 if not. On success, the memory size is
 353  * returned through the out parameter `memsz`.
 354  */
 355 int lttng_ust_elf_get_memsz(struct lttng_ust_elf *elf, uint64_t *memsz)
 356 {
 357         uint16_t i;
 358         uint64_t low_addr = UINT64_MAX, high_addr = 0;
 359
 360         if (!elf || !memsz) {
 361                 goto error;
 362         }
 363
 364         for (i = 0; i < elf->ehdr->e_phnum; ++i) {
 365                 struct lttng_ust_elf_phdr *phdr;
 366
 367                 phdr = lttng_ust_elf_get_phdr(elf, i);
 368                 if (!phdr) {
 369                         goto error;
 370                 }
 371
 372                 /*
 373                  * Only PT_LOAD segments contribute to memsz. Skip
 374                  * other segments.
 375                  */
 376                 if (phdr->p_type != PT_LOAD) {
 377                         goto next_loop;
 378                 }
 379
 380                 low_addr = min_t(uint64_t, low_addr, phdr->p_vaddr);
 381                 high_addr = max_t(uint64_t, high_addr,
 382                                 phdr->p_vaddr + phdr->p_memsz);
 383         next_loop:
 384                 free(phdr);
 385         }
 386
 387         if (high_addr < low_addr) {
 388                 /* No PT_LOAD segments or corrupted data. */
 389                 goto error;
 390         }
 391
 392         *memsz = high_addr - low_addr;
 393         return 0;
 394 error:
 395         return -1;
 396 }
 397
 398 /*
 399  * Internal method used to try and get the build_id from a PT_NOTE
 400  * segment ranging from `offset` to `segment_end`.
 401  *
 402  * If the function returns successfully, the out parameter `found`
 403  * indicates whether the build id information was present in the
 404  * segment or not. If `found` is not 0, the out parameters `build_id`
 405  * and `length` will both have been set with the retrieved
 406  * information.
 407  *
 408  * Returns 0 on success, -1 if an error occurred.
 409  */
 410 static
 411 int lttng_ust_elf_get_build_id_from_segment(
 412         struct lttng_ust_elf *elf, uint8_t **build_id, size_t *length,
 413         off_t offset, off_t segment_end)
 414 {
 415         uint8_t *_build_id = NULL;      /* Silence old gcc warning. */
 416         size_t _length = 0;             /* Silence old gcc warning. */
 417
 418         while (offset < segment_end) {
 419                 struct lttng_ust_elf_nhdr nhdr;
 420                 size_t read_len;
 421
 422                 /* Align start of note entry */
 423                 offset += offset_align(offset, ELF_NOTE_ENTRY_ALIGN);
 424                 if (offset >= segment_end) {
 425                         break;
 426                 }
 427                 /*
 428                  * We seek manually because if the note isn't the
 429                  * build id the data following the header will not
 430                  * have been read.
 431                  */
 432                 if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 433                         goto error;
 434                 }
 435                 if (lttng_ust_read(elf->fd, &nhdr, sizeof(nhdr))
 436                                 < sizeof(nhdr)) {
 437                         goto error;
 438                 }
 439
 440                 if (!is_elf_native_endian(elf)) {
 441                         nhdr.n_namesz = bswap_32(nhdr.n_namesz);
 442                         nhdr.n_descsz = bswap_32(nhdr.n_descsz);
 443                         nhdr.n_type = bswap_32(nhdr.n_type);
 444                 }
 445
 446                 offset += sizeof(nhdr) + nhdr.n_namesz;
 447                 /* Align start of desc entry */
 448                 offset += offset_align(offset, ELF_NOTE_DESC_ALIGN);
 449
 450                 if (nhdr.n_type != NT_GNU_BUILD_ID) {
 451                         /*
 452                          * Ignore non build id notes but still
 453                          * increase the offset.
 454                          */
 455                         offset += nhdr.n_descsz;
 456                         continue;
 457                 }
 458
 459                 _length = nhdr.n_descsz;
 460                 _build_id = zmalloc(sizeof(uint8_t) * _length);
 461                 if (!_build_id) {
 462                         goto error;
 463                 }
 464
 465                 if (lseek(elf->fd, offset, SEEK_SET) < 0) {
 466                         goto error;
 467                 }
 468                 read_len = sizeof(*_build_id) * _length;
 469                 if (lttng_ust_read(elf->fd, _build_id, read_len) < read_len) {
 470                         goto error;
 471                 }
 472
 473                 break;
 474         }
 475
 476         if (_build_id) {
 477                 *build_id = _build_id;
 478                 *length = _length;
 479         }
 480
 481         return 0;
 482 error:
 483         free(_build_id);
 484         return -1;
 485 }
 486
 487 /*
 488  * Retrieve a build ID (an array of bytes) from the corresponding
 489  * section in the ELF file. The length of the build ID can be either
 490  * 16 or 20 bytes depending on the method used to generate it, hence
 491  * the length out parameter.
 492  *
 493  * If the function returns successfully, the out parameter `found`
 494  * indicates whether the build id information was present in the ELF
 495  * file or not. If `found` is not 0, the out parameters `build_id` and
 496  * `length` will both have been set with the retrieved information.
 497  *
 498  * Returns 0 on success, -1 if an error occurred.
 499  */
 500 int lttng_ust_elf_get_build_id(struct lttng_ust_elf *elf, uint8_t **build_id,
 501                         size_t *length, int *found)
 502 {
 503         uint16_t i;
 504         uint8_t *_build_id = NULL;      /* Silence old gcc warning. */
 505         size_t _length = 0;             /* Silence old gcc warning. */
 506
 507         if (!elf || !build_id || !length || !found) {
 508                 goto error;
 509         }
 510
 511         for (i = 0; i < elf->ehdr->e_phnum; ++i) {
 512                 off_t offset, segment_end;
 513                 struct lttng_ust_elf_phdr *phdr;
 514                 int ret = 0;
 515
 516                 phdr = lttng_ust_elf_get_phdr(elf, i);
 517                 if (!phdr) {
 518                         goto error;
 519                 }
 520
 521                 /* Build ID will be contained in a PT_NOTE segment. */
 522                 if (phdr->p_type != PT_NOTE) {
 523                         goto next_loop;
 524                 }
 525
 526                 offset = phdr->p_offset;
 527                 segment_end = offset + phdr->p_filesz;
 528                 ret = lttng_ust_elf_get_build_id_from_segment(
 529                         elf, &_build_id, &_length, offset, segment_end);
 530         next_loop:
 531                 free(phdr);
 532                 if (ret) {
 533                         goto error;
 534                 }
 535                 if (_build_id) {
 536                         break;
 537                 }
 538         }
 539
 540         if (_build_id) {
 541                 *build_id = _build_id;
 542                 *length = _length;
 543                 *found = 1;
 544         } else {
 545                 *found = 0;
 546         }
 547
 548         return 0;
 549 error:
 550         free(_build_id);
 551         return -1;
 552 }
 553
 554 /*
 555  * Try to retrieve filename and CRC from given ELF section `shdr`.
 556  *
 557  * If the function returns successfully, the out parameter `found`
 558  * indicates whether the debug link information was present in the ELF
 559  * section or not. If `found` is not 0, the out parameters `filename` and
 560  * `crc` will both have been set with the retrieved information.
 561  *
 562  * Returns 0 on success, -1 if an error occurred.
 563  */
 564 int lttng_ust_elf_get_debug_link_from_section(struct lttng_ust_elf *elf,
 565                                         char **filename, uint32_t *crc,
 566                                         struct lttng_ust_elf_shdr *shdr)
 567 {
 568         char *_filename = NULL;         /* Silence old gcc warning. */
 569         size_t filename_len;
 570         char *section_name = NULL;
 571         uint32_t _crc = 0;              /* Silence old gcc warning. */
 572
 573         if (!elf || !filename || !crc || !shdr) {
 574                 goto error;
 575         }
 576
 577         /*
 578          * The .gnu_debuglink section is of type SHT_PROGBITS,
 579          * skip the other sections.
 580          */
 581         if (shdr->sh_type != SHT_PROGBITS) {
 582                 goto end;
 583         }
 584
 585         section_name = lttng_ust_elf_get_section_name(elf,
 586                                                 shdr->sh_name);
 587         if (!section_name) {
 588                 goto end;
 589         }
 590         if (strcmp(section_name, ".gnu_debuglink")) {
 591                 goto end;
 592         }
 593
 594         /*
 595          * The length of the filename is the sh_size excluding the CRC
 596          * which comes after it in the section.
 597          */
 598         _filename = zmalloc(sizeof(char) * (shdr->sh_size - ELF_CRC_SIZE));
 599         if (!_filename) {
 600                 goto error;
 601         }
 602         if (lseek(elf->fd, shdr->sh_offset, SEEK_SET) < 0) {
 603                 goto error;
 604         }
 605         filename_len = sizeof(*_filename) * (shdr->sh_size - ELF_CRC_SIZE);
 606         if (lttng_ust_read(elf->fd, _filename, filename_len) < filename_len) {
 607                 goto error;
 608         }
 609         if (lttng_ust_read(elf->fd, &_crc, sizeof(_crc)) < sizeof(_crc)) {
 610                 goto error;
 611         }
 612         if (!is_elf_native_endian(elf)) {
 613                 _crc = bswap_32(_crc);
 614         }
 615
 616 end:
 617         free(section_name);
 618         if (_filename) {
 619                 *filename = _filename;
 620                 *crc = _crc;
 621         }
 622
 623         return 0;
 624
 625 error:
 626         free(_filename);
 627         free(section_name);
 628         return -1;
 629 }
 630
 631 /*
 632  * Retrieve filename and CRC from ELF's .gnu_debuglink section, if any.
 633  *
 634  * If the function returns successfully, the out parameter `found`
 635  * indicates whether the debug link information was present in the ELF
 636  * file or not. If `found` is not 0, the out parameters `filename` and
 637  * `crc` will both have been set with the retrieved information.
 638  *
 639  * Returns 0 on success, -1 if an error occurred.
 640  */
 641 int lttng_ust_elf_get_debug_link(struct lttng_ust_elf *elf, char **filename,
 642                                 uint32_t *crc, int *found)
 643 {
 644         int ret;
 645         uint16_t i;
 646         char *_filename = NULL;         /* Silence old gcc warning. */
 647         uint32_t _crc = 0;              /* Silence old gcc warning. */
 648
 649         if (!elf || !filename || !crc || !found) {
 650                 goto error;
 651         }
 652
 653         for (i = 0; i < elf->ehdr->e_shnum; ++i) {
 654                 struct lttng_ust_elf_shdr *shdr = NULL;
 655
 656                 shdr = lttng_ust_elf_get_shdr(elf, i);
 657                 if (!shdr) {
 658                         goto error;
 659                 }
 660
 661                 ret = lttng_ust_elf_get_debug_link_from_section(
 662                         elf, &_filename, &_crc, shdr);
 663                 free(shdr);
 664
 665                 if (ret) {
 666                         goto error;
 667                 }
 668                 if (_filename) {
 669                         break;
 670                 }
 671         }
 672
 673         if (_filename) {
 674                 *filename = _filename;
 675                 *crc = _crc;
 676                 *found = 1;
 677         } else {
 678                 *found = 0;
 679         }
 680
 681         return 0;
 682
 683 error:
 684         free(_filename);
 685         return -1;
 686 }