elfcpp/elfcpp_file.h

   1 // elfcpp_file.h -- file access for elfcpp   -*- C++ -*-
   2
   3 // This header file defines the class Elf_file which can be used to
   4 // read useful data from an ELF file.  The functions here are all
   5 // templates which take a file interface object as a parameter.  This
   6 // type must have a subtype View.  This type must support two methods:
   7 //     View view(off_t file_offset, off_t data_size)
   8 // returns a View for the specified part of the file.
   9 //     void error(const char* printf_format, ...)
  10 // prints an error message and does not return.  The subtype View must
  11 // support a method
  12 //     const unsigned char* data()
  13 // which returns a pointer to a buffer containing the requested data.
  14 // This general interface is used to read data from the file.  Objects
  15 // of type View will never survive longer than the elfcpp function.
  16
  17 // Some of these functions must return a reference to part of the
  18 // file.  To use these, the file interface must support a subtype
  19 // Location:
  20 //    Location(off_t file_offset, off_t data_size)
  21 // To use this in conjunction with the accessors types Shdr, etc., the
  22 // file interface should support an overload of view:
  23 //    View view(Location)
  24 // This permits writing
  25 //    elfcpp::Shdr shdr(file, ef.section_header(n));
  26
  27 #ifndef ELFPCP_FILE_H
  28 #define ELFCPP_FILE_H
  29
  30 #include <string>
  31 #include <cstring>
  32
  33 namespace elfcpp
  34 {
  35
  36 // This object is used to read an ELF file.
  37 //   SIZE: The size of file, 32 or 64.
  38 //   BIG_ENDIAN: Whether the file is in big-endian format.
  39 //   FILE: A file reading type as described above.
  40
  41 template<int size, bool big_endian, typename File>
  42 class Elf_file
  43 {
  44  private:
  45   typedef Elf_file<size, big_endian, File> This;
  46
  47  public:
  48   static const int ehdr_size = Elf_sizes<size>::ehdr_size;
  49   static const int phdr_size = Elf_sizes<size>::phdr_size;
  50   static const int shdr_size = Elf_sizes<size>::shdr_size;
  51   static const int sym_size = Elf_sizes<size>::sym_size;
  52   static const int rel_size = Elf_sizes<size>::rel_size;
  53   static const int rela_size = Elf_sizes<size>::rela_size;
  54
  55   typedef Ehdr<size, big_endian> Ef_ehdr;
  56   typedef Phdr<size, big_endian> Ef_phdr;
  57   typedef Shdr<size, big_endian> Ef_shdr;
  58   typedef Sym<size, big_endian> Ef_sym;
  59
  60   // Construct an Elf_file given an ELF file header.
  61   Elf_file(File* file, const Ef_ehdr& ehdr)
  62   { this->construct(file, ehdr); }
  63
  64   // Construct an ELF file.
  65   inline
  66   Elf_file(File* file);
  67
  68   // Return the file offset to the section headers.
  69   off_t
  70   shoff() const
  71   { return this->shoff_; }
  72
  73   // Return the number of sections.
  74   unsigned int
  75   shnum()
  76   {
  77     this->initialize_shnum();
  78     return this->shnum_;
  79   }
  80
  81   // Return the section index of the section name string table.
  82   unsigned int
  83   shstrndx()
  84   {
  85     this->initialize_shnum();
  86     return this->shstrndx_;
  87   }
  88
  89   // Return the location of the header of section SHNDX.
  90   typename File::Location
  91   section_header(unsigned int shndx)
  92   {
  93     return typename File::Location(this->section_header_offset(shndx),
  94                                    shdr_size);
  95   }
  96
  97   // Return the name of section SHNDX.
  98   std::string
  99   section_name(unsigned int shndx);
 100
 101   // Return the location of the contents of section SHNDX.
 102   typename File::Location
 103   section_contents(unsigned int shndx);
 104
 105   // Return the flags of section SHNDX.
 106   typename Elf_types<size>::Elf_WXword
 107   section_flags(unsigned int shndx);
 108
 109  private:
 110   // Shared constructor code.
 111   void
 112   construct(File* file, const Ef_ehdr& ehdr);
 113
 114   // Initialize shnum_ and shstrndx_.
 115   void
 116   initialize_shnum();
 117
 118   // Return the file offset of the header of section SHNDX.
 119   off_t
 120   section_header_offset(unsigned int shndx);
 121
 122   // The file we are reading.
 123   File* file_;
 124   // The file offset to the section headers.
 125   off_t shoff_;
 126   // The number of sections.
 127   unsigned int shnum_;
 128   // The section index of the section name string table.
 129   unsigned int shstrndx_;
 130 };
 131
 132 // Template function definitions.
 133
 134 // Construct an Elf_file given an ELF file header.
 135
 136 template<int size, bool big_endian, typename File>
 137 void
 138 Elf_file<size, big_endian, File>::construct(File* file, const Ef_ehdr& ehdr)
 139 {
 140   this->file_ = file;
 141   this->shoff_ = ehdr.get_e_shoff();
 142   this->shnum_ = ehdr.get_e_shnum();
 143   this->shstrndx_ = ehdr.get_e_shstrndx();
 144   if (ehdr.get_e_ehsize() != This::ehdr_size)
 145     file->error(_("bad e_ehsize (%d != %d)"),
 146                 ehdr.get_e_ehsize(), This::ehdr_size);
 147   if (ehdr.get_e_shentsize() != This::shdr_size)
 148     file->error(_("bad e_shentsize (%d != %d)"),
 149                 ehdr.get_e_shentsize(), This::shdr_size);
 150 }
 151
 152 // Construct an ELF file.
 153
 154 template<int size, bool big_endian, typename File>
 155 inline
 156 Elf_file<size, big_endian, File>::Elf_file(File* file)
 157 {
 158   typename File::View v(file->view(file_header_offset, This::ehdr_size));
 159   this->construct(file, Ef_ehdr(v.data()));
 160 }
 161
 162 // Initialize the shnum_ and shstrndx_ fields, handling overflow.
 163
 164 template<int size, bool big_endian, typename File>
 165 void
 166 Elf_file<size, big_endian, File>::initialize_shnum()
 167 {
 168   if ((this->shnum_ == 0 || this->shstrndx_ == SHN_XINDEX)
 169       && this->shoff_ != 0)
 170     {
 171       typename File::View v(this->file_->view(this->shoff_, This::shdr_size));
 172       Ef_shdr shdr(v.data());
 173       if (this->shnum_ == 0)
 174         this->shnum_ = shdr.get_sh_size();
 175       if (this->shstrndx_ == SHN_XINDEX)
 176         this->shstrndx_ = shdr.get_sh_link();
 177     }
 178 }
 179
 180 // Return the file offset of the section header of section SHNDX.
 181
 182 template<int size, bool big_endian, typename File>
 183 off_t
 184 Elf_file<size, big_endian, File>::section_header_offset(unsigned int shndx)
 185 {
 186   if (shndx >= this->shnum())
 187     this->file_->error(_("section_header_offset: bad shndx %u >= %u"),
 188                        shndx, this->shnum());
 189   return this->shoff_ + This::shdr_size * shndx;
 190 }
 191
 192 // Return the name of section SHNDX.
 193
 194 template<int size, bool big_endian, typename File>
 195 std::string
 196 Elf_file<size, big_endian, File>::section_name(unsigned int shndx)
 197 {
 198   File* const file = this->file_;
 199
 200   // Get the section name offset.
 201   unsigned int sh_name;
 202   {
 203     typename File::View v(file->view(this->section_header_offset(shndx),
 204                                      This::shdr_size));
 205     Ef_shdr shdr(v.data());
 206     sh_name = shdr.get_sh_name();
 207   }
 208
 209   // Get the file offset for the section name string table data.
 210   off_t shstr_off;
 211   off_t shstr_size;
 212   {
 213     const unsigned int shstrndx = this->shstrndx_;
 214     typename File::View v(file->view(this->section_header_offset(shstrndx),
 215                                      This::shdr_size));
 216     Ef_shdr shstr_shdr(v.data());
 217     shstr_off = shstr_shdr.get_sh_offset();
 218     shstr_size = shstr_shdr.get_sh_size();
 219   }
 220
 221   if (sh_name >= shstr_size)
 222     file->error(_("bad section name offset for section %u: %u"),
 223                 shndx, sh_name);
 224
 225   typename File::View v(file->view(shstr_off, shstr_size));
 226
 227   const unsigned char* datau = v.data();
 228   const char* data = reinterpret_cast<const char*>(datau);
 229   const void* p = ::memchr(data + sh_name, '\0', shstr_size - sh_name);
 230   if (p == NULL)
 231     file->error(_("missing null terminator for name of section %u"),
 232                 shndx);
 233
 234   size_t len = static_cast<const char*>(p) - (data + sh_name);
 235
 236   return std::string(data + sh_name, len);
 237 }
 238
 239 // Return the contents of section SHNDX.
 240
 241 template<int size, bool big_endian, typename File>
 242 typename File::Location
 243 Elf_file<size, big_endian, File>::section_contents(unsigned int shndx)
 244 {
 245   File* const file = this->file_;
 246
 247   if (shndx >= this->shnum())
 248     file->error(_("section_contents: bad shndx %u >= %u"),
 249                 shndx, this->shnum());
 250
 251   typename File::View v(file->view(this->section_header_offset(shndx),
 252                                    This::shdr_size));
 253   Ef_shdr shdr(v.data());
 254   return typename File::Location(shdr.get_sh_offset(), shdr.get_sh_size());
 255 }
 256
 257 // Return the section flags of section SHNDX.
 258
 259 template<int size, bool big_endian, typename File>
 260 typename Elf_types<size>::Elf_WXword
 261 Elf_file<size, big_endian, File>::section_flags(unsigned int shndx)
 262 {
 263   File* const file = this->file_;
 264
 265   if (shndx >= this->shnum())
 266     file->error(_("section_flags: bad shndx %u >= %u"),
 267                 shndx, this->shnum());
 268
 269   typename File::View v(file->view(this->section_header_offset(shndx),
 270                                    This::shdr_size));
 271
 272   Ef_shdr shdr(v.data());
 273   return shdr.get_sh_flags();
 274 }
 275
 276 } // End namespace elfcpp.
 277
 278 #endif // !defined(ELFCPP_FILE_H)