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 ELFPCP_FILE_H
  57 #define ELFCPP_FILE_H
  58
  59 #include <string>
  60 #include <cstring>
  61
  62 namespace elfcpp
  63 {
  64
  65 // This object is used to read an ELF file.
  66 //   SIZE: The size of file, 32 or 64.
  67 //   BIG_ENDIAN: Whether the file is in big-endian format.
  68 //   FILE: A file reading type as described above.
  69
  70 template<int size, bool big_endian, typename File>
  71 class Elf_file
  72 {
  73  private:
  74   typedef Elf_file<size, big_endian, File> This;
  75
  76  public:
  77   static const int ehdr_size = Elf_sizes<size>::ehdr_size;
  78   static const int phdr_size = Elf_sizes<size>::phdr_size;
  79   static const int shdr_size = Elf_sizes<size>::shdr_size;
  80   static const int sym_size = Elf_sizes<size>::sym_size;
  81   static const int rel_size = Elf_sizes<size>::rel_size;
  82   static const int rela_size = Elf_sizes<size>::rela_size;
  83
  84   typedef Ehdr<size, big_endian> Ef_ehdr;
  85   typedef Phdr<size, big_endian> Ef_phdr;
  86   typedef Shdr<size, big_endian> Ef_shdr;
  87   typedef Sym<size, big_endian> Ef_sym;
  88
  89   // Construct an Elf_file given an ELF file header.
  90   Elf_file(File* file, const Ef_ehdr& ehdr)
  91   { this->construct(file, ehdr); }
  92
  93   // Construct an ELF file.
  94   inline
  95   Elf_file(File* file);
  96
  97   // Return the file offset to the section headers.
  98   off_t
  99   shoff() const
 100   { return this->shoff_; }
 101
 102   // Return the number of sections.
 103   unsigned int
 104   shnum()
 105   {
 106     this->initialize_shnum();
 107     return this->shnum_;
 108   }
 109
 110   // Return the section index of the section name string table.
 111   unsigned int
 112   shstrndx()
 113   {
 114     this->initialize_shnum();
 115     return this->shstrndx_;
 116   }
 117
 118   // Return the location of the header of section SHNDX.
 119   typename File::Location
 120   section_header(unsigned int shndx)
 121   {
 122     return typename File::Location(this->section_header_offset(shndx),
 123                                    shdr_size);
 124   }
 125
 126   // Return the name of section SHNDX.
 127   std::string
 128   section_name(unsigned int shndx);
 129
 130   // Return the location of the contents of section SHNDX.
 131   typename File::Location
 132   section_contents(unsigned int shndx);
 133
 134   // Return the flags of section SHNDX.
 135   typename Elf_types<size>::Elf_WXword
 136   section_flags(unsigned int shndx);
 137
 138   // Return the type of section SHNDX.
 139   Elf_Word
 140   section_type(unsigned int shndx);
 141
 142   // Return the link field of section SHNDX.
 143   Elf_Word
 144   section_link(unsigned int shndx);
 145
 146  private:
 147   // Shared constructor code.
 148   void
 149   construct(File* file, const Ef_ehdr& ehdr);
 150
 151   // Initialize shnum_ and shstrndx_.
 152   void
 153   initialize_shnum();
 154
 155   // Return the file offset of the header of section SHNDX.
 156   off_t
 157   section_header_offset(unsigned int shndx);
 158
 159   // The file we are reading.
 160   File* file_;
 161   // The file offset to the section headers.
 162   off_t shoff_;
 163   // The number of sections.
 164   unsigned int shnum_;
 165   // The section index of the section name string table.
 166   unsigned int shstrndx_;
 167 };
 168
 169 // Template function definitions.
 170
 171 // Construct an Elf_file given an ELF file header.
 172
 173 template<int size, bool big_endian, typename File>
 174 void
 175 Elf_file<size, big_endian, File>::construct(File* file, const Ef_ehdr& ehdr)
 176 {
 177   this->file_ = file;
 178   this->shoff_ = ehdr.get_e_shoff();
 179   this->shnum_ = ehdr.get_e_shnum();
 180   this->shstrndx_ = ehdr.get_e_shstrndx();
 181   if (ehdr.get_e_ehsize() != This::ehdr_size)
 182     file->error(_("bad e_ehsize (%d != %d)"),
 183                 ehdr.get_e_ehsize(), This::ehdr_size);
 184   if (ehdr.get_e_shentsize() != This::shdr_size)
 185     file->error(_("bad e_shentsize (%d != %d)"),
 186                 ehdr.get_e_shentsize(), This::shdr_size);
 187 }
 188
 189 // Construct an ELF file.
 190
 191 template<int size, bool big_endian, typename File>
 192 inline
 193 Elf_file<size, big_endian, File>::Elf_file(File* file)
 194 {
 195   typename File::View v(file->view(file_header_offset, This::ehdr_size));
 196   this->construct(file, Ef_ehdr(v.data()));
 197 }
 198
 199 // Initialize the shnum_ and shstrndx_ fields, handling overflow.
 200
 201 template<int size, bool big_endian, typename File>
 202 void
 203 Elf_file<size, big_endian, File>::initialize_shnum()
 204 {
 205   if ((this->shnum_ == 0 || this->shstrndx_ == SHN_XINDEX)
 206       && this->shoff_ != 0)
 207     {
 208       typename File::View v(this->file_->view(this->shoff_, This::shdr_size));
 209       Ef_shdr shdr(v.data());
 210       if (this->shnum_ == 0)
 211         this->shnum_ = shdr.get_sh_size();
 212       if (this->shstrndx_ == SHN_XINDEX)
 213         this->shstrndx_ = shdr.get_sh_link();
 214     }
 215 }
 216
 217 // Return the file offset of the section header of section SHNDX.
 218
 219 template<int size, bool big_endian, typename File>
 220 off_t
 221 Elf_file<size, big_endian, File>::section_header_offset(unsigned int shndx)
 222 {
 223   if (shndx >= this->shnum())
 224     this->file_->error(_("section_header_offset: bad shndx %u >= %u"),
 225                        shndx, this->shnum());
 226   return this->shoff_ + This::shdr_size * shndx;
 227 }
 228
 229 // Return the name of section SHNDX.
 230
 231 template<int size, bool big_endian, typename File>
 232 std::string
 233 Elf_file<size, big_endian, File>::section_name(unsigned int shndx)
 234 {
 235   File* const file = this->file_;
 236
 237   // Get the section name offset.
 238   unsigned int sh_name;
 239   {
 240     typename File::View v(file->view(this->section_header_offset(shndx),
 241                                      This::shdr_size));
 242     Ef_shdr shdr(v.data());
 243     sh_name = shdr.get_sh_name();
 244   }
 245
 246   // Get the file offset for the section name string table data.
 247   off_t shstr_off;
 248   off_t shstr_size;
 249   {
 250     const unsigned int shstrndx = this->shstrndx_;
 251     typename File::View v(file->view(this->section_header_offset(shstrndx),
 252                                      This::shdr_size));
 253     Ef_shdr shstr_shdr(v.data());
 254     shstr_off = shstr_shdr.get_sh_offset();
 255     shstr_size = shstr_shdr.get_sh_size();
 256   }
 257
 258   if (sh_name >= shstr_size)
 259     file->error(_("bad section name offset for section %u: %u"),
 260                 shndx, sh_name);
 261
 262   typename File::View v(file->view(shstr_off, shstr_size));
 263
 264   const unsigned char* datau = v.data();
 265   const char* data = reinterpret_cast<const char*>(datau);
 266   const void* p = ::memchr(data + sh_name, '\0', shstr_size - sh_name);
 267   if (p == NULL)
 268     file->error(_("missing null terminator for name of section %u"),
 269                 shndx);
 270
 271   size_t len = static_cast<const char*>(p) - (data + sh_name);
 272
 273   return std::string(data + sh_name, len);
 274 }
 275
 276 // Return the contents of section SHNDX.
 277
 278 template<int size, bool big_endian, typename File>
 279 typename File::Location
 280 Elf_file<size, big_endian, File>::section_contents(unsigned int shndx)
 281 {
 282   File* const file = this->file_;
 283
 284   if (shndx >= this->shnum())
 285     file->error(_("section_contents: bad shndx %u >= %u"),
 286                 shndx, this->shnum());
 287
 288   typename File::View v(file->view(this->section_header_offset(shndx),
 289                                    This::shdr_size));
 290   Ef_shdr shdr(v.data());
 291   return typename File::Location(shdr.get_sh_offset(), shdr.get_sh_size());
 292 }
 293
 294 // Return the section flags of section SHNDX.
 295
 296 template<int size, bool big_endian, typename File>
 297 typename Elf_types<size>::Elf_WXword
 298 Elf_file<size, big_endian, File>::section_flags(unsigned int shndx)
 299 {
 300   File* const file = this->file_;
 301
 302   if (shndx >= this->shnum())
 303     file->error(_("section_flags: bad shndx %u >= %u"),
 304                 shndx, this->shnum());
 305
 306   typename File::View v(file->view(this->section_header_offset(shndx),
 307                                    This::shdr_size));
 308
 309   Ef_shdr shdr(v.data());
 310   return shdr.get_sh_flags();
 311 }
 312
 313 // Return the type of section SHNDX.
 314
 315 template<int size, bool big_endian, typename File>
 316 Elf_Word
 317 Elf_file<size, big_endian, File>::section_type(unsigned int shndx)
 318 {
 319   File* const file = this->file_;
 320
 321   if (shndx >= this->shnum())
 322     file->error(_("section_type: bad shndx %u >= %u"),
 323                 shndx, this->shnum());
 324
 325   typename File::View v(file->view(this->section_header_offset(shndx),
 326                                    This::shdr_size));
 327
 328   Ef_shdr shdr(v.data());
 329   return shdr.get_sh_type();
 330 }
 331
 332 // Return the sh_link field of section SHNDX.
 333
 334 template<int size, bool big_endian, typename File>
 335 Elf_Word
 336 Elf_file<size, big_endian, File>::section_link(unsigned int shndx)
 337 {
 338   File* const file = this->file_;
 339
 340   if (shndx >= this->shnum())
 341     file->error(_("section_link: bad shndx %u >= %u"),
 342                 shndx, this->shnum());
 343
 344   typename File::View v(file->view(this->section_header_offset(shndx),
 345                                    This::shdr_size));
 346
 347   Ef_shdr shdr(v.data());
 348   return shdr.get_sh_link();
 349 }
 350
 351 } // End namespace elfcpp.
 352
 353 #endif // !defined(ELFCPP_FILE_H)