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// elfcpp_file.h -- file access for elfcpp -*- C++ -*-
// Copyright (C) 2006-2020 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>
#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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