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// elfcpp_file.h -- file access for elfcpp   -*- C++ -*-

// Copyright 2006, 2007, Free Software Foundation, Inc.

// Written by Ian Lance Taylor <iant@google.com>.

// This file is part of elfcpp.

// This program is free software; you can redistribute it and/or

// modify it under the terms of the GNU Library General Public License

// as published by the Free Software Foundation; either version 2, or

// (at your option) any later version.

// In addition to the permissions in the GNU Library General Public

// License, the Free Software Foundation gives you unlimited

// permission to link the compiled version of this file into

// combinations with other programs, and to distribute those

// combinations without any restriction coming from the use of this

// file.  (The Library Public License restrictions do apply in other

// respects; for example, they cover modification of the file, and

/// distribution when not linked into a combined executable.)

// This program is distributed in the hope that it will be useful, but

// WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

// Library General Public License for more details.

// You should have received a copy of the GNU Library General Public

// License along with this program; if not, write to the Free Software

// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA

// 02110-1301, USA.

// This header file defines the class Elf_file which can be used to

// read useful data from an ELF file.  The functions here are all

// templates which take a file interface object as a parameter.  This

// type must have a subtype View.  This type must support two methods:

//     View view(off_t file_offset, off_t data_size)

// returns a View for the specified part of the file.

//     void error(const char* printf_format, ...)

// prints an error message and does not return.  The subtype View must

// support a method

//     const unsigned char* data()

// which returns a pointer to a buffer containing the requested data.

// This general interface is used to read data from the file.  Objects

// of type View will never survive longer than the elfcpp function.

// Some of these functions must return a reference to part of the

// file.  To use these, the file interface must support a subtype

// Location:

//    Location(off_t file_offset, off_t data_size)

// To use this in conjunction with the accessors types Shdr, etc., the

// file interface should support an overload of view:

//    View view(Location)

// This permits writing

//    elfcpp::Shdr shdr(file, ef.section_header(n));

#ifndef ELFCPP_FILE_H

#define ELFCPP_FILE_H

#include <string>

#include <cstdio>

#include <cstring>

namespace elfcpp

{

// A simple helper class to recognize if a file has an ELF header.

class Elf_recognizer

{

 public:

  // Maximum header size.  The user should try to read this much of

  // the file when using this class.

  static const int max_header_size = Elf_sizes<64>::ehdr_size;

  // Checks if the file contains the ELF magic.  Other header fields

  // are not checked.

  static bool

  is_elf_file(const unsigned char* ehdr_buf, int size);

  // Check if EHDR_BUF/BUFSIZE is a valid header of a 32-bit or

  // 64-bit, little-endian or big-endian ELF file.  Assumes

  // is_elf_file() has been checked to be true.  If the header is not

  // valid, *ERROR contains a human-readable error message.  If is is,

  // *SIZE is set to either 32 or 64, *BIG_ENDIAN is set to indicate

  // whether the file is big-endian.

  static bool

  is_valid_header(const unsigned char* ehdr_buf, off_t bufsize,

                  int* size, bool* big_endian,

                  std::string* error);

};

// This object is used to read an ELF file.

//   SIZE: The size of file, 32 or 64.

//   BIG_ENDIAN: Whether the file is in big-endian format.

//   FILE: A file reading type as described above.

template<int size, bool big_endian, typename File>

class Elf_file

{

 private:

  typedef Elf_file<size, big_endian, File> This;

 public:

  static const int ehdr_size = Elf_sizes<size>::ehdr_size;

  static const int phdr_size = Elf_sizes<size>::phdr_size;

  static const int shdr_size = Elf_sizes<size>::shdr_size;

  static const int sym_size = Elf_sizes<size>::sym_size;

  static const int rel_size = Elf_sizes<size>::rel_size;

  static const int rela_size = Elf_sizes<size>::rela_size;

  typedef Ehdr<size, big_endian> Ef_ehdr;

  typedef Phdr<size, big_endian> Ef_phdr;

  typedef Shdr<size, big_endian> Ef_shdr;

  typedef Sym<size, big_endian> Ef_sym;

  // Construct an Elf_file given an ELF file header.

  Elf_file(File* file, const Ef_ehdr& ehdr)

  { this->construct(file, ehdr); }

  // Construct an ELF file.

  inline

  Elf_file(File* file);

  // Return the file offset to the section headers.

  off_t

  shoff() const

  { return this->shoff_; }

  // Find the first section with an sh_type field equal to TYPE and

  // return its index.  Returns SHN_UNDEF if there is no such section.

  unsigned int

  find_section_by_type(unsigned int type);

  // Return the number of sections.

  unsigned int

  shnum()

  {

    this->initialize_shnum();

    return this->shnum_;

  }

  // Return the section index of the section name string table.

  unsigned int

  shstrndx()

  {

    this->initialize_shnum();

    return this->shstrndx_;

  }

  // Return the value to subtract from section indexes >=

  // SHN_LORESERVE.  See the comment in initialize_shnum.

  int

  large_shndx_offset()

  {

    this->initialize_shnum();

    return this->large_shndx_offset_;

  }

  // Return the location of the header of section SHNDX.

  typename File::Location

  section_header(unsigned int shndx)

  {

    return typename File::Location(this->section_header_offset(shndx),

                                   shdr_size);

  }

  // Return the name of section SHNDX.

  std::string

  section_name(unsigned int shndx);

  // Return the location of the contents of section SHNDX.

  typename File::Location

  section_contents(unsigned int shndx);

  // Return the size of section SHNDX.

  typename Elf_types<size>::Elf_WXword

  section_size(unsigned int shndx);

  // Return the flags of section SHNDX.

  typename Elf_types<size>::Elf_WXword

  section_flags(unsigned int shndx);

  // Return the address of section SHNDX.

  typename Elf_types<size>::Elf_Addr

  section_addr(unsigned int shndx);

  // Return the type of section SHNDX.

  Elf_Word

  section_type(unsigned int shndx);

  // Return the link field of section SHNDX.

  Elf_Word

  section_link(unsigned int shndx);

  // Return the info field of section SHNDX.

  Elf_Word

  section_info(unsigned int shndx);

  // Return the addralign field of section SHNDX.

  typename Elf_types<size>::Elf_WXword

  section_addralign(unsigned int shndx);

 private:

  // Shared constructor code.

  void

  construct(File* file, const Ef_ehdr& ehdr);

  // Initialize shnum_ and shstrndx_.

  void

  initialize_shnum();

  // Return the file offset of the header of section SHNDX.

  off_t

  section_header_offset(unsigned int shndx);

  // The file we are reading.

  File* file_;

  // The file offset to the section headers.

  off_t shoff_;

  // The number of sections.

  unsigned int shnum_;

  // The section index of the section name string table.

  unsigned int shstrndx_;

  // Offset to add to sections larger than SHN_LORESERVE.

  int large_shndx_offset_;

};

// A small wrapper around SHT_STRTAB data mapped to memory. It checks that the

// index is not out of bounds and the string is NULL-terminated.

class Elf_strtab

{

 public:

  // Construct an Elf_strtab for a section with contents *P and size SIZE.

  Elf_strtab(const unsigned char* p, size_t size);

  // Return the file offset to the section headers.

  bool

  get_c_string(size_t offset, const char** cstring) const

  {

    if (offset >= this->usable_size_)

      return false;

    *cstring = this->base_ + offset;

    return true;

  }

 private:

  // Contents of the section mapped to memory.

  const char* base_;

  // One larger that the position of the last NULL character in the section.

  // For valid SHT_STRTAB sections, this is the size of the section.

  size_t usable_size_;

};

// Inline function definitions.

// Check for presence of the ELF magic number.

inline bool

Elf_recognizer::is_elf_file(const unsigned char* ehdr_buf, int size)

{

  if (size < 4)

    return false;

  static unsigned char elfmagic[4] =

    {

      elfcpp::ELFMAG0, elfcpp::ELFMAG1,

      elfcpp::ELFMAG2, elfcpp::ELFMAG3

    };

  return memcmp(ehdr_buf, elfmagic, 4) == 0;

}

namespace

{

// Print a number to a string.

inline std::string

internal_printf_int(const char* format, int arg)

{

  char buf[256];

  snprintf(buf, sizeof(buf), format, arg);

  return std::string(buf);

}

}  // End anonymous namespace.

// Check the validity of the ELF header.

inline bool

Elf_recognizer::is_valid_header(

    const unsigned char* ehdr_buf,

    off_t bufsize,

    int* size,

    bool* big_endian,

    std::string* error)

{

  if (bufsize < elfcpp::EI_NIDENT)

    {

      *error = _("ELF file too short");

      return false;

    }

  int v = ehdr_buf[elfcpp::EI_VERSION];

  if (v != elfcpp::EV_CURRENT)

    {

      if (v == elfcpp::EV_NONE)

        *error = _("invalid ELF version 0");

      else

        *error = internal_printf_int(_("unsupported ELF version %d"), v);

      return false;

    }

  int c = ehdr_buf[elfcpp::EI_CLASS];

  if (c == elfcpp::ELFCLASSNONE)

    {

      *error = _("invalid ELF class 0");

      return false;

    }

  else if (c != elfcpp::ELFCLASS32

           && c != elfcpp::ELFCLASS64)

    {

      *error = internal_printf_int(_("unsupported ELF class %d"), c);

      return false;

    }

  int d = ehdr_buf[elfcpp::EI_DATA];

  if (d == elfcpp::ELFDATANONE)

    {

      *error = _("invalid ELF data encoding");

      return false;

    }

  else if (d != elfcpp::ELFDATA2LSB

           && d != elfcpp::ELFDATA2MSB)

    {

      *error = internal_printf_int(_("unsupported ELF data encoding %d"), d);

      return false;

    }

  *big_endian = (d == elfcpp::ELFDATA2MSB);

  if (c == elfcpp::ELFCLASS32)

    {

      if (bufsize < elfcpp::Elf_sizes<32>::ehdr_size)

        {

          *error = _("ELF file too short");

          return false;

        }

      *size = 32;

    }

  else

    {

      if (bufsize < elfcpp::Elf_sizes<64>::ehdr_size)

        {

          *error = _("ELF file too short");

          return false;

        }

      *size = 64;

    }

  return true;

}

// Template function definitions.

// Construct an Elf_file given an ELF file header.

template<int size, bool big_endian, typename File>

void

Elf_file<size, big_endian, File>::construct(File* file, const Ef_ehdr& ehdr)

{

  this->file_ = file;

  this->shoff_ = ehdr.get_e_shoff();

  this->shnum_ = ehdr.get_e_shnum();

  this->shstrndx_ = ehdr.get_e_shstrndx();

  this->large_shndx_offset_ = 0;

  if (ehdr.get_e_ehsize() != This::ehdr_size)

    file->error(_("bad e_ehsize (%d != %d)"),

                ehdr.get_e_ehsize(), This::ehdr_size);

  if (ehdr.get_e_shentsize() != This::shdr_size)

    file->error(_("bad e_shentsize (%d != %d)"),

                ehdr.get_e_shentsize(), This::shdr_size);

}

// Construct an ELF file.

template<int size, bool big_endian, typename File>

inline

Elf_file<size, big_endian, File>::Elf_file(File* file)

{

  typename File::View v(file->view(file_header_offset, This::ehdr_size));

  this->construct(file, Ef_ehdr(v.data()));

}

// Initialize the shnum_ and shstrndx_ fields, handling overflow.

template<int size, bool big_endian, typename File>

void

Elf_file<size, big_endian, File>::initialize_shnum()

{

  if ((this->shnum_ == 0 || this->shstrndx_ == SHN_XINDEX)

      && this->shoff_ != 0)

    {

      typename File::View v(this->file_->view(this->shoff_, This::shdr_size));

      Ef_shdr shdr(v.data());

      if (this->shnum_ == 0)

        this->shnum_ = shdr.get_sh_size();

      if (this->shstrndx_ == SHN_XINDEX)

        {

          this->shstrndx_ = shdr.get_sh_link();

          // Versions of the GNU binutils between 2.12 and 2.18 did

          // not handle objects with more than SHN_LORESERVE sections

          // correctly.  All large section indexes were offset by

          // 0x100.  Some information can be found here:

          // http://sourceware.org/bugzilla/show_bug.cgi?id=5900 .

          // Fortunately these object files are easy to detect, as the

          // GNU binutils always put the section header string table

          // near the end of the list of sections.  Thus if the

          // section header string table index is larger than the

          // number of sections, then we know we have to subtract

          // 0x100 to get the real section index.

          if (this->shstrndx_ >= this->shnum_)

            {

              if (this->shstrndx_ >= elfcpp::SHN_LORESERVE + 0x100)

                {

                  this->large_shndx_offset_ = - 0x100;

                  this->shstrndx_ -= 0x100;

                }

              if (this->shstrndx_ >= this->shnum_)

                this->file_->error(_("bad shstrndx: %u >= %u"),

                                   this->shstrndx_, this->shnum_);

            }

        }

    }

}

// Find section with sh_type equal to TYPE and return its index.

// Returns SHN_UNDEF if not found.

template<int size, bool big_endian, typename File>

unsigned int

Elf_file<size, big_endian, File>::find_section_by_type(unsigned int type)

{

  unsigned int shnum = this->shnum();

  typename File::View v(this->file_->view(this->shoff_,

                                          This::shdr_size * shnum));

  for (unsigned int i = 0; i < shnum; i++)

    {

      Ef_shdr shdr(v.data() + This::shdr_size * i);

      if (shdr.get_sh_type() == type)

        return i;

    }

  return SHN_UNDEF;

}

// Return the file offset of the section header of section SHNDX.

template<int size, bool big_endian, typename File>

off_t

Elf_file<size, big_endian, File>::section_header_offset(unsigned int shndx)

{

  if (shndx >= this->shnum())

    this->file_->error(_("section_header_offset: bad shndx %u >= %u"),

                       shndx, this->shnum());

  return this->shoff_ + This::shdr_size * shndx;

}

// Return the name of section SHNDX.

template<int size, bool big_endian, typename File>

std::string

Elf_file<size, big_endian, File>::section_name(unsigned int shndx)

{

  File* const file = this->file_;

  // Get the section name offset.

  unsigned int sh_name;

  {

    typename File::View v(file->view(this->section_header_offset(shndx),

                                     This::shdr_size));

    Ef_shdr shdr(v.data());

    sh_name = shdr.get_sh_name();

  }

  // Get the file offset for the section name string table data.

  off_t shstr_off;

  typename Elf_types<size>::Elf_WXword shstr_size;

  {

    const unsigned int shstrndx = this->shstrndx_;

    typename File::View v(file->view(this->section_header_offset(shstrndx),

                                     This::shdr_size));

    Ef_shdr shstr_shdr(v.data());

    shstr_off = shstr_shdr.get_sh_offset();

    shstr_size = shstr_shdr.get_sh_size();

  }

  if (sh_name >= shstr_size)

    file->error(_("bad section name offset for section %u: %u"),

                shndx, sh_name);

  typename File::View v(file->view(shstr_off, shstr_size));

  const unsigned char* datau = v.data();

  const char* data = reinterpret_cast<const char*>(datau);

  const void* p = ::memchr(data + sh_name, '\0', shstr_size - sh_name);

  if (p == NULL)

    file->error(_("missing null terminator for name of section %u"),

                shndx);

  size_t len = static_cast<const char*>(p) - (data + sh_name);

  return std::string(data + sh_name, len);

}

// Return the contents of section SHNDX.

template<int size, bool big_endian, typename File>

typename File::Location

Elf_file<size, big_endian, File>::section_contents(unsigned int shndx)

{

  File* const file = this->file_;

  if (shndx >= this->shnum())

    file->error(_("section_contents: bad shndx %u >= %u"),

                shndx, this->shnum());

  typename File::View v(file->view(this->section_header_offset(shndx),

                                   This::shdr_size));

  Ef_shdr shdr(v.data());

  return typename File::Location(shdr.get_sh_offset(), shdr.get_sh_size());

}

// Get the size of section SHNDX.

template<int size, bool big_endian, typename File>

typename Elf_types<size>::Elf_WXword

Elf_file<size, big_endian, File>::section_size(unsigned int shndx)

{

  File* const file = this->file_;

  if (shndx >= this->shnum())

    file->error(_("section_size: bad shndx %u >= %u"),

                shndx, this->shnum());

  typename File::View v(file->view(this->section_header_offset(shndx),

                                   This::shdr_size));

  Ef_shdr shdr(v.data());

  return shdr.get_sh_size();

}

// Return the section flags of section SHNDX.

template<int size, bool big_endian, typename File>

typename Elf_types<size>::Elf_WXword

Elf_file<size, big_endian, File>::section_flags(unsigned int shndx)

{

  File* const file = this->file_;

  if (shndx >= this->shnum())

    file->error(_("section_flags: bad shndx %u >= %u"),

                shndx, this->shnum());

  typename File::View v(file->view(this->section_header_offset(shndx),

                                   This::shdr_size));

  Ef_shdr shdr(v.data());

  return shdr.get_sh_flags();

}

// Return the address of section SHNDX.

template<int size, bool big_endian, typename File>

typename Elf_types<size>::Elf_Addr

Elf_file<size, big_endian, File>::section_addr(unsigned int shndx)

{

  File* const file = this->file_;

  if (shndx >= this->shnum())

    file->error(_("section_flags: bad shndx %u >= %u"),

                shndx, this->shnum());

  typename File::View v(file->view(this->section_header_offset(shndx),

                                   This::shdr_size));

  Ef_shdr shdr(v.data());

  return shdr.get_sh_addr();

}

// Return the type of section SHNDX.

template<int size, bool big_endian, typename File>

Elf_Word

Elf_file<size, big_endian, File>::section_type(unsigned int shndx)

{

  File* const file = this->file_;

  if (shndx >= this->shnum())

    file->error(_("section_type: bad shndx %u >= %u"),

                shndx, this->shnum());

  typename File::View v(file->view(this->section_header_offset(shndx),

                                   This::shdr_size));

  Ef_shdr shdr(v.data());

  return shdr.get_sh_type();

}

// Return the sh_link field of section SHNDX.

template<int size, bool big_endian, typename File>

Elf_Word

Elf_file<size, big_endian, File>::section_link(unsigned int shndx)

{

  File* const file = this->file_;

  if (shndx >= this->shnum())

    file->error(_("section_link: bad shndx %u >= %u"),

                shndx, this->shnum());

  typename File::View v(file->view(this->section_header_offset(shndx),

                                   This::shdr_size));

  Ef_shdr shdr(v.data());

  return shdr.get_sh_link();

}

// Return the sh_info field of section SHNDX.

template<int size, bool big_endian, typename File>

Elf_Word

Elf_file<size, big_endian, File>::section_info(unsigned int shndx)

{

  File* const file = this->file_;

  if (shndx >= this->shnum())

    file->error(_("section_info: bad shndx %u >= %u"),

                shndx, this->shnum());

  typename File::View v(file->view(this->section_header_offset(shndx),

                                   This::shdr_size));

  Ef_shdr shdr(v.data());

  return shdr.get_sh_info();

}

// Return the sh_addralign field of section SHNDX.

template<int size, bool big_endian, typename File>

typename Elf_types<size>::Elf_WXword

Elf_file<size, big_endian, File>::section_addralign(unsigned int shndx)

{

  File* const file = this->file_;

  if (shndx >= this->shnum())

    file->error(_("section_addralign: bad shndx %u >= %u"),

                shndx, this->shnum());

  typename File::View v(file->view(this->section_header_offset(shndx),

                                   This::shdr_size));

  Ef_shdr shdr(v.data());

  return shdr.get_sh_addralign();