elfcpp/elfcpp_file.h

   1 // elfcpp_file.h -- file access for elfcpp   -*- C++ -*-
   2
   3 // Copyright 2006, 2007, Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@google.com>.
   5
   6 // This file is part of elfcpp.
   7
   8 // This program is free software; you can redistribute it and/or
   9 // modify it under the terms of the GNU Library General Public License
  10 // as published by the Free Software Foundation; either version 2, or
  11 // (at your option) any later version.
  12
  13 // In addition to the permissions in the GNU Library General Public
  14 // License, the Free Software Foundation gives you unlimited
  15 // permission to link the compiled version of this file into
  16 // combinations with other programs, and to distribute those
  17 // combinations without any restriction coming from the use of this
  18 // file.  (The Library Public License restrictions do apply in other
  19 // respects; for example, they cover modification of the file, and
  20 /// distribution when not linked into a combined executable.)
  21
  22 // This program is distributed in the hope that it will be useful, but
  23 // WITHOUT ANY WARRANTY; without even the implied warranty of
  24 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  25 // Library General Public License for more details.
  26
  27 // You should have received a copy of the GNU Library General Public
  28 // License along with this program; if not, write to the Free Software
  29 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA
  30 // 02110-1301, USA.
  31
  32 // This header file defines the class Elf_file which can be used to
  33 // read useful data from an ELF file.  The functions here are all
  34 // templates which take a file interface object as a parameter.  This
  35 // type must have a subtype View.  This type must support two methods:
  36 //     View view(off_t file_offset, off_t data_size)
  37 // returns a View for the specified part of the file.
  38 //     void error(const char* printf_format, ...)
  39 // prints an error message and does not return.  The subtype View must
  40 // support a method
  41 //     const unsigned char* data()
  42 // which returns a pointer to a buffer containing the requested data.
  43 // This general interface is used to read data from the file.  Objects
  44 // of type View will never survive longer than the elfcpp function.
  45
  46 // Some of these functions must return a reference to part of the
  47 // file.  To use these, the file interface must support a subtype
  48 // Location:
  49 //    Location(off_t file_offset, off_t data_size)
  50 // To use this in conjunction with the accessors types Shdr, etc., the
  51 // file interface should support an overload of view:
  52 //    View view(Location)
  53 // This permits writing
  54 //    elfcpp::Shdr shdr(file, ef.section_header(n));
  55
  56 #ifndef ELFCPP_FILE_H
  57 #define ELFCPP_FILE_H
  58
  59 #include <string>
  60 #include <cstdio>
  61 #include <cstring>
  62
  63 #include "elfcpp.h"
  64
  65 namespace elfcpp
  66 {
  67
  68 // A simple helper class to recognize if a file has an ELF header.
  69
  70 class Elf_recognizer
  71 {
  72  public:
  73   // Maximum header size.  The user should try to read this much of
  74   // the file when using this class.
  75
  76   static const int max_header_size = Elf_sizes<64>::ehdr_size;
  77
  78   // Checks if the file contains the ELF magic.  Other header fields
  79   // are not checked.
  80
  81   static bool
  82   is_elf_file(const unsigned char* ehdr_buf, int size);
  83
  84   // Check if EHDR_BUF/BUFSIZE is a valid header of a 32-bit or
  85   // 64-bit, little-endian or big-endian ELF file.  Assumes
  86   // is_elf_file() has been checked to be true.  If the header is not
  87   // valid, *ERROR contains a human-readable error message.  If is is,
  88   // *SIZE is set to either 32 or 64, *BIG_ENDIAN is set to indicate
  89   // whether the file is big-endian.
  90
  91   static bool
  92   is_valid_header(const unsigned char* ehdr_buf, off_t bufsize,
  93                   int* size, bool* big_endian,
  94                   std::string* error);
  95 };
  96
  97 // This object is used to read an ELF file.
  98 //   SIZE: The size of file, 32 or 64.
  99 //   BIG_ENDIAN: Whether the file is in big-endian format.
 100 //   FILE: A file reading type as described above.
 101
 102 template<int size, bool big_endian, typename File>
 103 class Elf_file
 104 {
 105  private:
 106   typedef Elf_file<size, big_endian, File> This;
 107
 108  public:
 109   static const int ehdr_size = Elf_sizes<size>::ehdr_size;
 110   static const int phdr_size = Elf_sizes<size>::phdr_size;
 111   static const int shdr_size = Elf_sizes<size>::shdr_size;
 112   static const int sym_size = Elf_sizes<size>::sym_size;
 113   static const int rel_size = Elf_sizes<size>::rel_size;
 114   static const int rela_size = Elf_sizes<size>::rela_size;
 115
 116   typedef Ehdr<size, big_endian> Ef_ehdr;
 117   typedef Phdr<size, big_endian> Ef_phdr;
 118   typedef Shdr<size, big_endian> Ef_shdr;
 119   typedef Sym<size, big_endian> Ef_sym;
 120
 121   // Construct an Elf_file given an ELF file header.
 122   Elf_file(File* file, const Ef_ehdr& ehdr)
 123   { this->construct(file, ehdr); }
 124
 125   // Construct an ELF file.
 126   inline
 127   Elf_file(File* file);
 128
 129   // Return the file offset to the section headers.
 130   off_t
 131   shoff() const
 132   { return this->shoff_; }
 133
 134   // Find the first section with an sh_type field equal to TYPE and
 135   // return its index.  Returns SHN_UNDEF if there is no such section.
 136   unsigned int
 137   find_section_by_type(unsigned int type);
 138
 139   // Return the number of sections.
 140   unsigned int
 141   shnum()
 142   {
 143     this->initialize_shnum();
 144     return this->shnum_;
 145   }
 146
 147   // Return the section index of the section name string table.
 148   unsigned int
 149   shstrndx()
 150   {
 151     this->initialize_shnum();
 152     return this->shstrndx_;
 153   }
 154
 155   // Return the value to subtract from section indexes >=
 156   // SHN_LORESERVE.  See the comment in initialize_shnum.
 157   int
 158   large_shndx_offset()
 159   {
 160     this->initialize_shnum();
 161     return this->large_shndx_offset_;
 162   }
 163
 164   // Return the location of the header of section SHNDX.
 165   typename File::Location
 166   section_header(unsigned int shndx)
 167   {
 168     return typename File::Location(this->section_header_offset(shndx),
 169                                    shdr_size);
 170   }
 171
 172   // Return the name of section SHNDX.
 173   std::string
 174   section_name(unsigned int shndx);
 175
 176   // Return the location of the contents of section SHNDX.
 177   typename File::Location
 178   section_contents(unsigned int shndx);
 179
 180   // Return the size of section SHNDX.
 181   typename Elf_types<size>::Elf_WXword
 182   section_size(unsigned int shndx);
 183
 184   // Return the flags of section SHNDX.
 185   typename Elf_types<size>::Elf_WXword
 186   section_flags(unsigned int shndx);
 187
 188   // Return the address of section SHNDX.
 189   typename Elf_types<size>::Elf_Addr
 190   section_addr(unsigned int shndx);
 191
 192   // Return the type of section SHNDX.
 193   Elf_Word
 194   section_type(unsigned int shndx);
 195
 196   // Return the link field of section SHNDX.
 197   Elf_Word
 198   section_link(unsigned int shndx);
 199
 200   // Return the info field of section SHNDX.
 201   Elf_Word
 202   section_info(unsigned int shndx);
 203
 204   // Return the addralign field of section SHNDX.
 205   typename Elf_types<size>::Elf_WXword
 206   section_addralign(unsigned int shndx);
 207
 208  private:
 209   // Shared constructor code.
 210   void
 211   construct(File* file, const Ef_ehdr& ehdr);
 212
 213   // Initialize shnum_ and shstrndx_.
 214   void
 215   initialize_shnum();
 216
 217   // Return the file offset of the header of section SHNDX.
 218   off_t
 219   section_header_offset(unsigned int shndx);
 220
 221   // The file we are reading.
 222   File* file_;
 223   // The file offset to the section headers.
 224   off_t shoff_;
 225   // The number of sections.
 226   unsigned int shnum_;
 227   // The section index of the section name string table.
 228   unsigned int shstrndx_;
 229   // Offset to add to sections larger than SHN_LORESERVE.
 230   int large_shndx_offset_;
 231 };
 232
 233 // A small wrapper around SHT_STRTAB data mapped to memory. It checks that the
 234 // index is not out of bounds and the string is NULL-terminated.
 235
 236 class Elf_strtab
 237 {
 238  public:
 239   // Construct an Elf_strtab for a section with contents *P and size SIZE.
 240   Elf_strtab(const unsigned char* p, size_t size);
 241
 242   // Return the file offset to the section headers.
 243   bool
 244   get_c_string(size_t offset, const char** cstring) const
 245   {
 246     if (offset >= this->usable_size_)
 247       return false;
 248     *cstring = this->base_ + offset;
 249     return true;
 250   }
 251
 252  private:
 253   // Contents of the section mapped to memory.
 254   const char* base_;
 255   // One larger that the position of the last NULL character in the section.
 256   // For valid SHT_STRTAB sections, this is the size of the section.
 257   size_t usable_size_;
 258 };
 259
 260 // Inline function definitions.
 261
 262 // Check for presence of the ELF magic number.
 263
 264 inline bool
 265 Elf_recognizer::is_elf_file(const unsigned char* ehdr_buf, int size)
 266 {
 267   if (size < 4)
 268     return false;
 269
 270   static unsigned char elfmagic[4] =
 271     {
 272       elfcpp::ELFMAG0, elfcpp::ELFMAG1,
 273       elfcpp::ELFMAG2, elfcpp::ELFMAG3
 274     };
 275   return memcmp(ehdr_buf, elfmagic, 4) == 0;
 276 }
 277
 278 namespace
 279 {
 280
 281 // Print a number to a string.
 282
 283 inline std::string
 284 internal_printf_int(const char* format, int arg)
 285 {
 286   char buf[256];
 287   snprintf(buf, sizeof(buf), format, arg);
 288   return std::string(buf);
 289 }
 290
 291 }  // End anonymous namespace.
 292
 293 // Check the validity of the ELF header.
 294
 295 inline bool
 296 Elf_recognizer::is_valid_header(
 297     const unsigned char* ehdr_buf,
 298     off_t bufsize,
 299     int* size,
 300     bool* big_endian,
 301     std::string* error)
 302 {
 303   if (bufsize < elfcpp::EI_NIDENT)
 304     {
 305       *error = _("ELF file too short");
 306       return false;
 307     }
 308
 309   int v = ehdr_buf[elfcpp::EI_VERSION];
 310   if (v != elfcpp::EV_CURRENT)
 311     {
 312       if (v == elfcpp::EV_NONE)
 313         *error = _("invalid ELF version 0");
 314       else
 315         *error = internal_printf_int(_("unsupported ELF version %d"), v);
 316       return false;
 317     }
 318
 319   int c = ehdr_buf[elfcpp::EI_CLASS];
 320   if (c == elfcpp::ELFCLASSNONE)
 321     {
 322       *error = _("invalid ELF class 0");
 323       return false;
 324     }
 325   else if (c != elfcpp::ELFCLASS32
 326            && c != elfcpp::ELFCLASS64)
 327     {
 328       *error = internal_printf_int(_("unsupported ELF class %d"), c);
 329       return false;
 330     }
 331
 332   int d = ehdr_buf[elfcpp::EI_DATA];
 333   if (d == elfcpp::ELFDATANONE)
 334     {
 335       *error = _("invalid ELF data encoding");
 336       return false;
 337     }
 338   else if (d != elfcpp::ELFDATA2LSB
 339            && d != elfcpp::ELFDATA2MSB)
 340     {
 341       *error = internal_printf_int(_("unsupported ELF data encoding %d"), d);
 342       return false;
 343     }
 344
 345   *big_endian = (d == elfcpp::ELFDATA2MSB);
 346
 347   if (c == elfcpp::ELFCLASS32)
 348     {
 349       if (bufsize < elfcpp::Elf_sizes<32>::ehdr_size)
 350         {
 351           *error = _("ELF file too short");
 352           return false;
 353         }
 354       *size = 32;
 355     }
 356   else
 357     {
 358       if (bufsize < elfcpp::Elf_sizes<64>::ehdr_size)
 359         {
 360           *error = _("ELF file too short");
 361           return false;
 362         }
 363       *size = 64;
 364     }
 365
 366   return true;
 367 }
 368
 369 // Template function definitions.
 370
 371 // Construct an Elf_file given an ELF file header.
 372
 373 template<int size, bool big_endian, typename File>
 374 void
 375 Elf_file<size, big_endian, File>::construct(File* file, const Ef_ehdr& ehdr)
 376 {
 377   this->file_ = file;
 378   this->shoff_ = ehdr.get_e_shoff();
 379   this->shnum_ = ehdr.get_e_shnum();
 380   this->shstrndx_ = ehdr.get_e_shstrndx();
 381   this->large_shndx_offset_ = 0;
 382   if (ehdr.get_e_ehsize() != This::ehdr_size)
 383     file->error(_("bad e_ehsize (%d != %d)"),
 384                 ehdr.get_e_ehsize(), This::ehdr_size);
 385   if (ehdr.get_e_shentsize() != This::shdr_size)
 386     file->error(_("bad e_shentsize (%d != %d)"),
 387                 ehdr.get_e_shentsize(), This::shdr_size);
 388 }
 389
 390 // Construct an ELF file.
 391
 392 template<int size, bool big_endian, typename File>
 393 inline
 394 Elf_file<size, big_endian, File>::Elf_file(File* file)
 395 {
 396   typename File::View v(file->view(file_header_offset, This::ehdr_size));
 397   this->construct(file, Ef_ehdr(v.data()));
 398 }
 399
 400 // Initialize the shnum_ and shstrndx_ fields, handling overflow.
 401
 402 template<int size, bool big_endian, typename File>
 403 void
 404 Elf_file<size, big_endian, File>::initialize_shnum()
 405 {
 406   if ((this->shnum_ == 0 || this->shstrndx_ == SHN_XINDEX)
 407       && this->shoff_ != 0)
 408     {
 409       typename File::View v(this->file_->view(this->shoff_, This::shdr_size));
 410       Ef_shdr shdr(v.data());
 411
 412       if (this->shnum_ == 0)
 413         this->shnum_ = shdr.get_sh_size();
 414
 415       if (this->shstrndx_ == SHN_XINDEX)
 416         {
 417           this->shstrndx_ = shdr.get_sh_link();
 418
 419           // Versions of the GNU binutils between 2.12 and 2.18 did
 420           // not handle objects with more than SHN_LORESERVE sections
 421           // correctly.  All large section indexes were offset by
 422           // 0x100.  Some information can be found here:
 423           // http://sourceware.org/bugzilla/show_bug.cgi?id=5900 .
 424           // Fortunately these object files are easy to detect, as the
 425           // GNU binutils always put the section header string table
 426           // near the end of the list of sections.  Thus if the
 427           // section header string table index is larger than the
 428           // number of sections, then we know we have to subtract
 429           // 0x100 to get the real section index.
 430           if (this->shstrndx_ >= this->shnum_)
 431             {
 432               if (this->shstrndx_ >= elfcpp::SHN_LORESERVE + 0x100)
 433                 {
 434                   this->large_shndx_offset_ = - 0x100;
 435                   this->shstrndx_ -= 0x100;
 436                 }
 437               if (this->shstrndx_ >= this->shnum_)
 438                 this->file_->error(_("bad shstrndx: %u >= %u"),
 439                                    this->shstrndx_, this->shnum_);
 440             }
 441         }
 442     }
 443 }
 444
 445 // Find section with sh_type equal to TYPE and return its index.
 446 // Returns SHN_UNDEF if not found.
 447
 448 template<int size, bool big_endian, typename File>
 449 unsigned int
 450 Elf_file<size, big_endian, File>::find_section_by_type(unsigned int type)
 451 {
 452   unsigned int tshnum = this->shnum();
 453   typename File::View v(this->file_->view(this->shoff_,
 454                                           This::shdr_size * tshnum));
 455   for (unsigned int i = 0; i < tshnum; i++)
 456     {
 457       Ef_shdr shdr(v.data() + This::shdr_size * i);
 458       if (shdr.get_sh_type() == type)
 459         return i;
 460     }
 461   return SHN_UNDEF;
 462 }
 463
 464 // Return the file offset of the section header of section SHNDX.
 465
 466 template<int size, bool big_endian, typename File>
 467 off_t
 468 Elf_file<size, big_endian, File>::section_header_offset(unsigned int shndx)
 469 {
 470   if (shndx >= this->shnum())
 471     this->file_->error(_("section_header_offset: bad shndx %u >= %u"),
 472                        shndx, this->shnum());
 473   return this->shoff_ + This::shdr_size * shndx;
 474 }
 475
 476 // Return the name of section SHNDX.
 477
 478 template<int size, bool big_endian, typename File>
 479 std::string
 480 Elf_file<size, big_endian, File>::section_name(unsigned int shndx)
 481 {
 482   File* const file = this->file_;
 483
 484   // Get the section name offset.
 485   unsigned int sh_name;
 486   {
 487     typename File::View v(file->view(this->section_header_offset(shndx),
 488                                      This::shdr_size));
 489     Ef_shdr shdr(v.data());
 490     sh_name = shdr.get_sh_name();
 491   }
 492
 493   // Get the file offset for the section name string table data.
 494   off_t shstr_off;
 495   typename Elf_types<size>::Elf_WXword shstr_size;
 496   {
 497     const unsigned int fshstrndx = this->shstrndx_;
 498     typename File::View v(file->view(this->section_header_offset(fshstrndx),
 499                                      This::shdr_size));
 500     Ef_shdr shstr_shdr(v.data());
 501     shstr_off = shstr_shdr.get_sh_offset();
 502     shstr_size = shstr_shdr.get_sh_size();
 503   }
 504
 505   if (sh_name >= shstr_size)
 506     file->error(_("bad section name offset for section %u: %u"),
 507                 shndx, sh_name);
 508
 509   typename File::View v(file->view(shstr_off, shstr_size));
 510
 511   const unsigned char* datau = v.data();
 512   const char* data = reinterpret_cast<const char*>(datau);
 513   const void* p = ::memchr(data + sh_name, '\0', shstr_size - sh_name);
 514   if (p == NULL)
 515     file->error(_("missing null terminator for name of section %u"),
 516                 shndx);
 517
 518   size_t len = static_cast<const char*>(p) - (data + sh_name);
 519
 520   return std::string(data + sh_name, len);
 521 }
 522
 523 // Return the contents of section SHNDX.
 524
 525 template<int size, bool big_endian, typename File>
 526 typename File::Location
 527 Elf_file<size, big_endian, File>::section_contents(unsigned int shndx)
 528 {
 529   File* const file = this->file_;
 530
 531   if (shndx >= this->shnum())
 532     file->error(_("section_contents: bad shndx %u >= %u"),
 533                 shndx, this->shnum());
 534
 535   typename File::View v(file->view(this->section_header_offset(shndx),
 536                                    This::shdr_size));
 537   Ef_shdr shdr(v.data());
 538   return typename File::Location(shdr.get_sh_offset(), shdr.get_sh_size());
 539 }
 540
 541 // Get the size of section SHNDX.
 542
 543 template<int size, bool big_endian, typename File>
 544 typename Elf_types<size>::Elf_WXword
 545 Elf_file<size, big_endian, File>::section_size(unsigned int shndx)
 546 {
 547   File* const file = this->file_;
 548
 549   if (shndx >= this->shnum())
 550     file->error(_("section_size: bad shndx %u >= %u"),
 551                 shndx, this->shnum());
 552
 553   typename File::View v(file->view(this->section_header_offset(shndx),
 554                                    This::shdr_size));
 555
 556   Ef_shdr shdr(v.data());
 557   return shdr.get_sh_size();
 558 }
 559
 560 // Return the section flags of section SHNDX.
 561
 562 template<int size, bool big_endian, typename File>
 563 typename Elf_types<size>::Elf_WXword
 564 Elf_file<size, big_endian, File>::section_flags(unsigned int shndx)
 565 {
 566   File* const file = this->file_;
 567
 568   if (shndx >= this->shnum())
 569     file->error(_("section_flags: bad shndx %u >= %u"),
 570                 shndx, this->shnum());
 571
 572   typename File::View v(file->view(this->section_header_offset(shndx),
 573                                    This::shdr_size));
 574
 575   Ef_shdr shdr(v.data());
 576   return shdr.get_sh_flags();
 577 }
 578
 579 // Return the address of section SHNDX.
 580
 581 template<int size, bool big_endian, typename File>
 582 typename Elf_types<size>::Elf_Addr
 583 Elf_file<size, big_endian, File>::section_addr(unsigned int shndx)
 584 {
 585   File* const file = this->file_;
 586
 587   if (shndx >= this->shnum())
 588     file->error(_("section_flags: bad shndx %u >= %u"),
 589                 shndx, this->shnum());
 590
 591   typename File::View v(file->view(this->section_header_offset(shndx),
 592                                    This::shdr_size));
 593
 594   Ef_shdr shdr(v.data());
 595   return shdr.get_sh_addr();
 596 }
 597
 598 // Return the type of section SHNDX.
 599
 600 template<int size, bool big_endian, typename File>
 601 Elf_Word
 602 Elf_file<size, big_endian, File>::section_type(unsigned int shndx)
 603 {
 604   File* const file = this->file_;
 605
 606   if (shndx >= this->shnum())
 607     file->error(_("section_type: bad shndx %u >= %u"),
 608                 shndx, this->shnum());
 609
 610   typename File::View v(file->view(this->section_header_offset(shndx),
 611                                    This::shdr_size));
 612
 613   Ef_shdr shdr(v.data());
 614   return shdr.get_sh_type();
 615 }
 616
 617 // Return the sh_link field of section SHNDX.
 618
 619 template<int size, bool big_endian, typename File>
 620 Elf_Word
 621 Elf_file<size, big_endian, File>::section_link(unsigned int shndx)
 622 {
 623   File* const file = this->file_;
 624
 625   if (shndx >= this->shnum())
 626     file->error(_("section_link: bad shndx %u >= %u"),
 627                 shndx, this->shnum());
 628
 629   typename File::View v(file->view(this->section_header_offset(shndx),
 630                                    This::shdr_size));
 631
 632   Ef_shdr shdr(v.data());
 633   return shdr.get_sh_link();
 634 }
 635
 636 // Return the sh_info field of section SHNDX.
 637
 638 template<int size, bool big_endian, typename File>
 639 Elf_Word
 640 Elf_file<size, big_endian, File>::section_info(unsigned int shndx)
 641 {
 642   File* const file = this->file_;
 643
 644   if (shndx >= this->shnum())
 645     file->error(_("section_info: bad shndx %u >= %u"),
 646                 shndx, this->shnum());
 647
 648   typename File::View v(file->view(this->section_header_offset(shndx),
 649                                    This::shdr_size));
 650
 651   Ef_shdr shdr(v.data());
 652   return shdr.get_sh_info();
 653 }
 654
 655 // Return the sh_addralign field of section SHNDX.
 656
 657 template<int size, bool big_endian, typename File>
 658 typename Elf_types<size>::Elf_WXword
 659 Elf_file<size, big_endian, File>::section_addralign(unsigned int shndx)
 660 {
 661   File* const file = this->file_;
 662
 663   if (shndx >= this->shnum())
 664     file->error(_("section_addralign: bad shndx %u >= %u"),
 665                 shndx, this->shnum());
 666
 667   typename File::View v(file->view(this->section_header_offset(shndx),
 668                                    This::shdr_size));
 669
 670   Ef_shdr shdr(v.data());
 671   return shdr.get_sh_addralign();
 672 }
 673
 674 inline
 675 Elf_strtab::Elf_strtab(const unsigned char* p, size_t size)
 676 {
 677   // Check if the section is NUL-terminated. If it isn't, we ignore
 678   // the last part to make sure we don't return non-NUL-terminated
 679   // strings.
 680   while (size > 0 && p[size - 1] != 0)
 681     size--;
 682   this->base_ = reinterpret_cast<const char*>(p);
 683   this->usable_size_ = size;
 684 }
 685
 686 } // End namespace elfcpp.
 687
 688 #endif // !defined(ELFCPP_FILE_H)