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

// Copyright (C) 2006-2024 Free Software Foundation, Inc.
// Written by Ian Lance Taylor <[email protected]>.

// 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>

#include "elfcpp.h"

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_;
 }

 unsigned int
 shnum() const
 {
   if (this->shnum_ == 0 && this->shoff_ != 0)
     this->file_->error(_("ELF file has not been initialized yet"
                          " (internal error)"));
   return this->shnum_;
 }

 // Return the section index of the section name string table.
 unsigned int
 shstrndx()
 {
   this->initialize_shnum();
   return this->shstrndx_;
 }

 unsigned int
 shstrndx() const
 {
   if (this->shstrndx_ == SHN_XINDEX && this->shoff_ != 0)
     {
       this->file_->error(_("ELF file has not been initialized yet"
                            " (internal error)"));
       return 0;
     }
   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_;
 }

 int
 large_shndx_offset() const
 {
   if (this->shstrndx_ == SHN_XINDEX && this->shoff_ != 0)
     this->file_->error(_("ELF file has not been initialized yet"
                          " (internal error)"));
   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) const;

 // 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) const;

 // 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) const
{
 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) const
{
 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();
}

inline
Elf_strtab::Elf_strtab(const unsigned char* p, size_t size)
{
 // Check if the section is NUL-terminated. If it isn't, we ignore
 // the last part to make sure we don't return non-NUL-terminated
 // strings.
 while (size > 0 && p[size - 1] != 0)
   size--;
 this->base_ = reinterpret_cast<const char*>(p);
 this->usable_size_ = size;
}

} // End namespace elfcpp.

#endif // !defined(ELFCPP_FILE_H)

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