elf_reader.cpp

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/*******************************************************************\
 
Module: Read ELF
 
Author:
 
\*******************************************************************/
 
 
#include "elf_reader.h"
 
#include <util/exception_utils.h>
 
#include <cstdint>
#include <istream>
 
static void u16_to_native_endian_inplace(bool le_input, uint16_t &input)
{
  const uint8_t *input_as_bytes = reinterpret_cast<uint8_t *>(&input);
  input = (((uint16_t)input_as_bytes[0]) << (le_input ? 0 : 8)) |
          (((uint16_t)input_as_bytes[1]) << (le_input ? 8 : 0));
}
 
static void u32_to_native_endian_inplace(bool le_input, uint32_t &input)
{
  const uint8_t *input_as_bytes = reinterpret_cast<uint8_t *>(&input);
  input = (((uint32_t)input_as_bytes[0]) << (le_input ? 0 : 24)) |
          (((uint32_t)input_as_bytes[1]) << (le_input ? 8 : 16)) |
          (((uint32_t)input_as_bytes[2]) << (le_input ? 16 : 8)) |
          (((uint32_t)input_as_bytes[3]) << (le_input ? 24 : 0));
}
 
static void
u64_to_native_endian_inplace(bool le_input, unsigned long long &input)
{
  static_assert(
    sizeof(unsigned long long) == 8,
    "unsigned long long expected to be 8 bytes");
  const uint8_t *input_as_bytes = reinterpret_cast<uint8_t *>(&input);
  input = (((unsigned long long)input_as_bytes[0]) << (le_input ? 0 : 56)) |
          (((unsigned long long)input_as_bytes[1]) << (le_input ? 8 : 48)) |
          (((unsigned long long)input_as_bytes[2]) << (le_input ? 16 : 40)) |
          (((unsigned long long)input_as_bytes[3]) << (le_input ? 24 : 32)) |
          (((unsigned long long)input_as_bytes[4]) << (le_input ? 32 : 24)) |
          (((unsigned long long)input_as_bytes[5]) << (le_input ? 40 : 16)) |
          (((unsigned long long)input_as_bytes[6]) << (le_input ? 48 : 8)) |
          (((unsigned long long)input_as_bytes[7]) << (le_input ? 56 : 0));
}
 
elf_readert::elf_readert(std::istream &_in):in(_in)
{
  // read 32-bit header
  in.read(
    reinterpret_cast<char*>(&elf32_header),
    sizeof(elf32_header));
 
  if(!in)
    throw deserialization_exceptiont("failed to read ELF header");
 
  if(elf32_header.e_ident[0]!=0x7f ||
     elf32_header.e_ident[1]!='E' ||
     elf32_header.e_ident[2]!='L' ||
     elf32_header.e_ident[3]!='F')
    throw deserialization_exceptiont("ELF header malformed (magic)");
 
  elf_class=(elf_classt)elf32_header.e_ident[4];
 
  if(elf_class==ELF32)
  {
    const auto ei_data = elf32_header.e_ident[5];
 
    if(ei_data==1)
      little_endian=true;
    else if(ei_data==2)
      little_endian=false;
    else
      throw deserialization_exceptiont("ELF32 header malformed (EI_DATA)");
 
    u16_to_native_endian_inplace(little_endian, elf32_header.e_type);
    u16_to_native_endian_inplace(little_endian, elf32_header.e_machine);
    u32_to_native_endian_inplace(little_endian, elf32_header.e_version);
    u32_to_native_endian_inplace(little_endian, elf32_header.e_entry);
    u32_to_native_endian_inplace(little_endian, elf32_header.e_phoff);
    u32_to_native_endian_inplace(little_endian, elf32_header.e_shoff);
    u32_to_native_endian_inplace(little_endian, elf32_header.e_flags);
    u16_to_native_endian_inplace(little_endian, elf32_header.e_ehsize);
    u16_to_native_endian_inplace(little_endian, elf32_header.e_phentsize);
    u16_to_native_endian_inplace(little_endian, elf32_header.e_phnum);
    u16_to_native_endian_inplace(little_endian, elf32_header.e_shentsize);
    u16_to_native_endian_inplace(little_endian, elf32_header.e_shnum);
    u16_to_native_endian_inplace(little_endian, elf32_header.e_shstrndx);
 
    if(elf32_header.e_version!=1)
      throw deserialization_exceptiont("unknown ELF32 version");
 
    // get offset for section header
    if(elf32_header.e_shoff==0 ||
       elf32_header.e_shnum==0)
      throw deserialization_exceptiont("ELF32 without section header");
 
    elf32_section_header_table.resize(elf32_header.e_shnum);
    number_of_sections=elf32_header.e_shnum;
 
    // iterate over these
    for(std::size_t i=0; i<elf32_section_header_table.size(); i++)
    {
      // go to right place
      in.seekg(elf32_header.e_shoff+i*elf32_header.e_shentsize);
 
      // read section header
      in.read(
        reinterpret_cast<char*>(&elf32_section_header_table[i]),
        sizeof(Elf32_Shdr));
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_name);
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_type);
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_flags);
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_addr);
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_offset);
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_size);
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_link);
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_info);
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_addralign);
      u32_to_native_endian_inplace(
        little_endian, elf32_section_header_table[i].sh_entsize);
    }
 
    // string table
    unsigned string_table_nr=elf32_header.e_shstrndx;
    if(string_table_nr>=elf32_section_header_table.size())
      throw deserialization_exceptiont("ELF32 without string table");
 
    string_table_offset=section_offset(string_table_nr);
  }
  else if(elf_class==ELF64)
  {
    // read 64-bit header
    in.seekg(0);
    in.read(
      reinterpret_cast<char*>(&elf64_header),
      sizeof(elf64_header));
 
    const auto ei_data = elf64_header.e_ident[5];
 
    if(ei_data==1)
      little_endian=true;
    else if(ei_data==2)
      little_endian=false;
    else
      throw deserialization_exceptiont("ELF64 header malformed (EI_DATA)");
    u16_to_native_endian_inplace(little_endian, elf64_header.e_type);
    u16_to_native_endian_inplace(little_endian, elf64_header.e_machine);
    u32_to_native_endian_inplace(little_endian, elf64_header.e_version);
    u64_to_native_endian_inplace(little_endian, elf64_header.e_entry);
    u64_to_native_endian_inplace(little_endian, elf64_header.e_phoff);
    u64_to_native_endian_inplace(little_endian, elf64_header.e_shoff);
    u32_to_native_endian_inplace(little_endian, elf64_header.e_flags);
    u16_to_native_endian_inplace(little_endian, elf64_header.e_ehsize);
    u16_to_native_endian_inplace(little_endian, elf64_header.e_phentsize);
    u16_to_native_endian_inplace(little_endian, elf64_header.e_phnum);
    u16_to_native_endian_inplace(little_endian, elf64_header.e_shentsize);
    u16_to_native_endian_inplace(little_endian, elf64_header.e_shnum);
    u16_to_native_endian_inplace(little_endian, elf64_header.e_shstrndx);
 
    if(elf64_header.e_version!=1)
      throw deserialization_exceptiont("unknown ELF64 version");
 
    // get offset for section header
    if(elf64_header.e_shoff==0 ||
       elf64_header.e_shnum==0)
      throw deserialization_exceptiont("ELF64 without section header");
 
    elf64_section_header_table.resize(elf64_header.e_shnum);
    number_of_sections=elf64_header.e_shnum;
 
    // iterate over these
    for(std::size_t i=0; i<elf64_section_header_table.size(); i++)
    {
      // go to right place
      in.seekg(elf64_header.e_shoff+i*elf64_header.e_shentsize);
 
      // read section header
      in.read(
        reinterpret_cast<char*>(&elf64_section_header_table[i]),
        sizeof(Elf64_Shdr));
      u32_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_name);
      u32_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_type);
      u64_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_flags);
      u64_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_addr);
      u64_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_offset);
      u64_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_size);
      u32_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_link);
      u32_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_info);
      u64_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_addralign);
      u64_to_native_endian_inplace(
        little_endian, elf64_section_header_table[i].sh_entsize);
    }
 
    // string table
    unsigned string_table_nr=elf64_header.e_shstrndx;
    if(string_table_nr>=elf64_section_header_table.size())
      throw deserialization_exceptiont("ELF64 without string table");
 
    string_table_offset=section_offset(string_table_nr);
  }
}
 
std::string elf_readert::get_string(std::streampos index) const
{
  in.seekg(string_table_offset+index);
 
  std::string result;
 
  while(in)
  {
    char ch;
    in.read(&ch, 1);
    if(ch==0)
      break;
    result+=ch;
  }
 
  return result;
}
 
bool elf_readert::has_section(const std::string &name) const
{
  for(std::size_t i=0; i<number_of_sections; i++)
    if(section_name(i)==name)
      return true;
 
  return false;
}