/*
Copyright (C) 2001-present by Serge Lamikhov-Center

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

#ifndef ELFIO_HPP
#define ELFIO_HPP

#include <string>
#include <iostream>
#include <fstream>
#include <functional>
#include <algorithm>
#include <vector>
#include <deque>

#include <elfio/elf_types.hpp>
#include <elfio/elfio_version.hpp>
#include <elfio/elfio_utils.hpp>
#include <elfio/elfio_header.hpp>
#include <elfio/elfio_section.hpp>
#include <elfio/elfio_segment.hpp>
#include <elfio/elfio_strings.hpp>

#define ELFIO_HEADER_ACCESS_GET( TYPE, FNAME ) \
    TYPE get_##FNAME() const { return header ? ( header->get_##FNAME() ) : 0; }

#define ELFIO_HEADER_ACCESS_GET_SET( TYPE, FNAME )     \
    TYPE get_##FNAME() const                           \
    {                                                  \
        return header ? ( header->get_##FNAME() ) : 0; \
    }                                                  \
    void set_##FNAME( TYPE val )                       \
    {                                                  \
        if ( header ) {                                \
            header->set_##FNAME( val );                \
        }                                              \
    }

namespace ELFIO {

//------------------------------------------------------------------------------
class elfio
{
  public:
    //------------------------------------------------------------------------------
    elfio() noexcept : sections( this ), segments( this )
    {
        header           = nullptr;
        current_file_pos = 0;
        create( ELFCLASS32, ELFDATA2LSB );
    }

    elfio( elfio&& other ) noexcept : sections( this ), segments( this )
    {
        header           = std::move( other.header );
        sections_        = std::move( other.sections_ );
        segments_        = std::move( other.segments_ );
        convertor        = std::move( other.convertor );
        addr_translator  = std::move( other.addr_translator );
        current_file_pos = std::move( other.current_file_pos );

        other.header = nullptr;
        other.sections_.clear();
        other.segments_.clear();
    }

    elfio& operator=( elfio&& other ) noexcept
    {
        if ( this != &other ) {
            clean();

            header           = std::move( other.header );
            sections_        = std::move( other.sections_ );
            segments_        = std::move( other.segments_ );
            convertor        = std::move( other.convertor );
            addr_translator  = std::move( other.addr_translator );
            current_file_pos = std::move( other.current_file_pos );

            other.header = nullptr;
            other.sections_.clear();
            other.segments_.clear();
        }
        return *this;
    }

    //------------------------------------------------------------------------------
    // clang-format off
    elfio( const elfio& )            = delete;
    elfio& operator=( const elfio& ) = delete;
    // clang-format on

    //------------------------------------------------------------------------------
    ~elfio() { clean(); }

    //------------------------------------------------------------------------------
    void create( unsigned char file_class, unsigned char encoding )
    {
        clean();
        convertor.setup( encoding );
        header = create_header( file_class, encoding );
        create_mandatory_sections();
    }

    void set_address_translation( std::vector<address_translation>& addr_trans )
    {
        addr_translator.set_address_translation( addr_trans );
    }

    //------------------------------------------------------------------------------
    bool load( const std::string& file_name )
    {
        std::ifstream stream;
        stream.open( file_name.c_str(), std::ios::in | std::ios::binary );
        if ( !stream ) {
            return false;
        }

        return load( stream );
    }

    //------------------------------------------------------------------------------
    bool load( std::istream& stream )
    {
        clean();

        unsigned char e_ident[EI_NIDENT] = { 0 };
        // Read ELF file signature
        stream.seekg( addr_translator[0] );
        stream.read( reinterpret_cast<char*>( &e_ident ), sizeof( e_ident ) );

        // Is it ELF file?
        if ( stream.gcount() != sizeof( e_ident ) ||
             e_ident[EI_MAG0] != ELFMAG0 || e_ident[EI_MAG1] != ELFMAG1 ||
             e_ident[EI_MAG2] != ELFMAG2 || e_ident[EI_MAG3] != ELFMAG3 ) {
            return false;
        }

        if ( ( e_ident[EI_CLASS] != ELFCLASS64 ) &&
             ( e_ident[EI_CLASS] != ELFCLASS32 ) ) {
            return false;
        }

        if ( ( e_ident[EI_DATA] != ELFDATA2LSB ) &&
             ( e_ident[EI_DATA] != ELFDATA2MSB ) ) {
            return false;
        }

        convertor.setup( e_ident[EI_DATA] );
        header = create_header( e_ident[EI_CLASS], e_ident[EI_DATA] );
        if ( nullptr == header ) {
            return false;
        }
        if ( !header->load( stream ) ) {
            return false;
        }

        bool is_still_good = load_sections( stream );
        is_still_good      = is_still_good && load_segments( stream );
        return is_still_good;
    }

    //------------------------------------------------------------------------------
    bool save( const std::string& file_name )
    {
        std::ofstream stream;
        stream.open( file_name.c_str(), std::ios::out | std::ios::binary );
        if ( !stream ) {
            return false;
        }

        return save( stream );
    }

    //------------------------------------------------------------------------------
    bool save( std::ostream& stream )
    {
        if ( !stream || header == nullptr ) {
            return false;
        }

        // Define layout specific header fields
        // The position of the segment table is fixed after the header.
        // The position of the section table is variable and needs to be fixed
        // before saving.
        header->set_segments_num( segments.size() );
        header->set_segments_offset(
            segments.size() > 0 ? header->get_header_size() : 0 );
        header->set_sections_num( sections.size() );
        header->set_sections_offset( 0 );

        // Layout the first section right after the segment table
        current_file_pos =
            header->get_header_size() +
            header->get_segment_entry_size() *
                static_cast<Elf_Xword>( header->get_segments_num() );

        calc_segment_alignment();

        bool is_still_good = layout_segments_and_their_sections();
        is_still_good = is_still_good && layout_sections_without_segments();
        is_still_good = is_still_good && layout_section_table();

        is_still_good = is_still_good && save_header( stream );
        is_still_good = is_still_good && save_sections( stream );
        is_still_good = is_still_good && save_segments( stream );

        return is_still_good;
    }

    //------------------------------------------------------------------------------
    // ELF header access functions
    ELFIO_HEADER_ACCESS_GET( unsigned char, class );
    ELFIO_HEADER_ACCESS_GET( unsigned char, elf_version );
    ELFIO_HEADER_ACCESS_GET( unsigned char, encoding );
    ELFIO_HEADER_ACCESS_GET( Elf_Word, version );
    ELFIO_HEADER_ACCESS_GET( Elf_Half, header_size );
    ELFIO_HEADER_ACCESS_GET( Elf_Half, section_entry_size );
    ELFIO_HEADER_ACCESS_GET( Elf_Half, segment_entry_size );

    ELFIO_HEADER_ACCESS_GET_SET( unsigned char, os_abi );
    ELFIO_HEADER_ACCESS_GET_SET( unsigned char, abi_version );
    ELFIO_HEADER_ACCESS_GET_SET( Elf_Half, type );
    ELFIO_HEADER_ACCESS_GET_SET( Elf_Half, machine );
    ELFIO_HEADER_ACCESS_GET_SET( Elf_Word, flags );
    ELFIO_HEADER_ACCESS_GET_SET( Elf64_Addr, entry );
    ELFIO_HEADER_ACCESS_GET_SET( Elf64_Off, sections_offset );
    ELFIO_HEADER_ACCESS_GET_SET( Elf64_Off, segments_offset );
    ELFIO_HEADER_ACCESS_GET_SET( Elf_Half, section_name_str_index );

    //------------------------------------------------------------------------------
    const endianess_convertor& get_convertor() const { return convertor; }

    //------------------------------------------------------------------------------
    Elf_Xword get_default_entry_size( Elf_Word section_type ) const
    {
        switch ( section_type ) {
        case SHT_RELA:
            if ( header->get_class() == ELFCLASS64 ) {
                return sizeof( Elf64_Rela );
            }
            else {
                return sizeof( Elf32_Rela );
            }
        case SHT_REL:
            if ( header->get_class() == ELFCLASS64 ) {
                return sizeof( Elf64_Rel );
            }
            else {
                return sizeof( Elf32_Rel );
            }
        case SHT_SYMTAB:
            if ( header->get_class() == ELFCLASS64 ) {
                return sizeof( Elf64_Sym );
            }
            else {
                return sizeof( Elf32_Sym );
            }
        case SHT_DYNAMIC:
            if ( header->get_class() == ELFCLASS64 ) {
                return sizeof( Elf64_Dyn );
            }
            else {
                return sizeof( Elf32_Dyn );
            }
        default:
            return 0;
        }
    }

    //------------------------------------------------------------------------------
    //! returns an empty string if no problems are detected,
    //! or a string containing an error message if problems are found,
    //! with one error per line.
    std::string validate() const
    {
        // clang-format off

        std::string errors;
        // Check for overlapping sections in the file
        // This is explicitly forbidden by ELF specification
        for ( int i = 0; i < sections.size(); ++i) {
            for ( int j = i+1; j < sections.size(); ++j ) {
                const section* a = sections[i];
                const section* b = sections[j];
                if (   ( ( a->get_type() & SHT_NOBITS) == 0 )
                    && ( ( b->get_type() & SHT_NOBITS) == 0 )
                    && ( a->get_size() > 0 )
                    && ( b->get_size() > 0 )
                    && ( a->get_offset() > 0 )
                    && ( b->get_offset() > 0 )
                    && ( is_offset_in_section( a->get_offset(), b )
                      || is_offset_in_section( a->get_offset()+a->get_size()-1, b )
                      || is_offset_in_section( b->get_offset(), a )
                      || is_offset_in_section( b->get_offset()+b->get_size()-1, a ) ) ) {
                        errors += "Sections " + a->get_name() + " and " + b->get_name() + " overlap in file\n";
                }
            }
        }

        // Check for conflicting section / program header tables, where
        // the same offset has different vaddresses in section table and
        // program header table.
        // This doesn't seem to be  explicitly forbidden by ELF specification,
        // but:
        // - it doesn't make any sense
        // - ELFIO relies on this being consistent when writing ELF files,
        //   since offsets are re-calculated from vaddress
        for ( int h = 0; h < segments.size(); ++h ) {
            const segment* seg = segments[h];
            if ( seg->get_type() == PT_LOAD && seg->get_file_size() > 0 ) {
                const section* sec = find_prog_section_for_offset( seg->get_offset() );
                if ( sec != nullptr ) {
                    Elf64_Addr sec_addr = get_virtual_addr( seg->get_offset(), sec );
                    if ( sec_addr != seg->get_virtual_address() ) {
                        errors += "Virtual address of segment " + std::to_string( h ) + " (" + to_hex_string( seg->get_virtual_address() ) + ")"
                               +  " conflicts with address of section " + sec->get_name() + " (" + to_hex_string( sec_addr ) + ")"
                               +  " at offset " + to_hex_string( seg->get_offset() ) + "\n";
                    }
                }
            }
        }

        // more checks to be added here...

        return errors;
        // clang-format on
    }

  private:
    //------------------------------------------------------------------------------
    static bool is_offset_in_section( Elf64_Off offset, const section* sec )
    {
        return ( offset >= sec->get_offset() ) &&
               ( offset < ( sec->get_offset() + sec->get_size() ) );
    }

    //------------------------------------------------------------------------------
    static Elf64_Addr get_virtual_addr( Elf64_Off offset, const section* sec )
    {
        return sec->get_address() + offset - sec->get_offset();
    }

    //------------------------------------------------------------------------------
    const section* find_prog_section_for_offset( Elf64_Off offset ) const
    {
        for ( auto* sec : sections ) {
            if ( sec->get_type() == SHT_PROGBITS &&
                 is_offset_in_section( offset, sec ) ) {
                return sec;
            }
        }
        return nullptr;
    }

    //------------------------------------------------------------------------------
    void clean()
    {
        delete header;
        header = nullptr;

        for ( auto* it : sections_ ) {
            delete it;
        }
        sections_.clear();

        for ( auto* it : segments_ ) {
            delete it;
        }
        segments_.clear();
    }

    //------------------------------------------------------------------------------
    elf_header* create_header( unsigned char file_class,
                               unsigned char encoding )
    {
        elf_header* new_header = nullptr;

        if ( file_class == ELFCLASS64 ) {
            new_header = new elf_header_impl<Elf64_Ehdr>( &convertor, encoding,
                                                          &addr_translator );
        }
        else if ( file_class == ELFCLASS32 ) {
            new_header = new elf_header_impl<Elf32_Ehdr>( &convertor, encoding,
                                                          &addr_translator );
        }
        else {
            return nullptr;
        }

        return new_header;
    }

    //------------------------------------------------------------------------------
    section* create_section()
    {
        section*      new_section = nullptr;
        unsigned char file_class  = get_class();

        if ( file_class == ELFCLASS64 ) {
            new_section =
                new section_impl<Elf64_Shdr>( &convertor, &addr_translator );
        }
        else if ( file_class == ELFCLASS32 ) {
            new_section =
                new section_impl<Elf32_Shdr>( &convertor, &addr_translator );
        }
        else {
            return nullptr;
        }

        new_section->set_index( static_cast<Elf_Half>( sections_.size() ) );
        sections_.emplace_back( new_section );

        return new_section;
    }

    //------------------------------------------------------------------------------
    segment* create_segment()
    {
        segment*      new_segment = nullptr;
        unsigned char file_class  = header->get_class();

        if ( file_class == ELFCLASS64 ) {
            new_segment =
                new segment_impl<Elf64_Phdr>( &convertor, &addr_translator );
        }
        else if ( file_class == ELFCLASS32 ) {
            new_segment =
                new segment_impl<Elf32_Phdr>( &convertor, &addr_translator );
        }
        else {
            return nullptr;
        }

        new_segment->set_index( static_cast<Elf_Half>( segments_.size() ) );
        segments_.emplace_back( new_segment );

        return new_segment;
    }

    //------------------------------------------------------------------------------
    void create_mandatory_sections()
    {
        // Create null section without calling to 'add_section' as no string
        // section containing section names exists yet
        section* sec0 = create_section();
        sec0->set_index( 0 );
        sec0->set_name( "" );
        sec0->set_name_string_offset( 0 );

        set_section_name_str_index( 1 );
        section* shstrtab = sections.add( ".shstrtab" );
        shstrtab->set_type( SHT_STRTAB );
        shstrtab->set_addr_align( 1 );
    }

    //------------------------------------------------------------------------------
    bool load_sections( std::istream& stream )
    {
        unsigned char file_class = header->get_class();
        Elf_Half      entry_size = header->get_section_entry_size();
        Elf_Half      num        = header->get_sections_num();
        Elf64_Off     offset     = header->get_sections_offset();

        if ( ( num != 0 && file_class == ELFCLASS64 &&
               entry_size < sizeof( Elf64_Shdr ) ) ||
             ( num != 0 && file_class == ELFCLASS32 &&
               entry_size < sizeof( Elf32_Shdr ) ) ) {
            return false;
        }

        for ( Elf_Half i = 0; i < num; ++i ) {
            section* sec = create_section();
            sec->load( stream,
                       static_cast<std::streamoff>( offset ) +
                           static_cast<std::streampos>( i ) * entry_size );
            sec->set_index( i );
            // To mark that the section is not permitted to reassign address
            // during layout calculation
            sec->set_address( sec->get_address() );
        }

        Elf_Half shstrndx = get_section_name_str_index();

        if ( SHN_UNDEF != shstrndx ) {
            string_section_accessor str_reader( sections[shstrndx] );
            for ( Elf_Half i = 0; i < num; ++i ) {
                Elf_Word section_offset = sections[i]->get_name_string_offset();
                const char* p = str_reader.get_string( section_offset );
                if ( p != nullptr ) {
                    sections[i]->set_name( p );
                }
            }
        }

        return true;
    }

    //------------------------------------------------------------------------------
    //! Checks whether the addresses of the section entirely fall within the given segment.
    //! It doesn't matter if the addresses are memory addresses, or file offsets,
    //!  they just need to be in the same address space
    static bool is_sect_in_seg( Elf64_Off sect_begin,
                                Elf_Xword sect_size,
                                Elf64_Off seg_begin,
                                Elf64_Off seg_end )
    {
        return ( seg_begin <= sect_begin ) &&
               ( sect_begin + sect_size <= seg_end ) &&
               ( sect_begin <
                 seg_end ); // this is important criteria when sect_size == 0
        // Example:  seg_begin=10, seg_end=12 (-> covering the bytes 10 and 11)
        //           sect_begin=12, sect_size=0  -> shall return false!
    }

    //------------------------------------------------------------------------------
    bool load_segments( std::istream& stream )
    {
        unsigned char file_class = header->get_class();
        Elf_Half      entry_size = header->get_segment_entry_size();
        Elf_Half      num        = header->get_segments_num();
        Elf64_Off     offset     = header->get_segments_offset();

        if ( ( num != 0 && file_class == ELFCLASS64 &&
               entry_size < sizeof( Elf64_Phdr ) ) ||
             ( num != 0 && file_class == ELFCLASS32 &&
               entry_size < sizeof( Elf32_Phdr ) ) ) {
            return false;
        }

        for ( Elf_Half i = 0; i < num; ++i ) {
            segment*      seg        = nullptr;
            unsigned char file_class = header->get_class();

            if ( file_class == ELFCLASS64 ) {
                seg = new segment_impl<Elf64_Phdr>( &convertor,
                                                    &addr_translator );
            }
            else if ( file_class == ELFCLASS32 ) {
                seg = new segment_impl<Elf32_Phdr>( &convertor,
                                                    &addr_translator );
            }
            else {
                return false;
            }

            if ( !seg->load( stream, static_cast<std::streamoff>( offset ) +
                                         static_cast<std::streampos>( i ) *
                                             entry_size ) ||
                 stream.fail() ) {
                delete seg;
                seg = nullptr;
                return false;
            }

            seg->set_index( i );

            // Add sections to the segments (similar to readelfs algorithm)
            Elf64_Off segBaseOffset = seg->get_offset();
            Elf64_Off segEndOffset  = segBaseOffset + seg->get_file_size();
            Elf64_Off segVBaseAddr  = seg->get_virtual_address();
            Elf64_Off segVEndAddr   = segVBaseAddr + seg->get_memory_size();
            for ( auto* psec : sections ) {
                // SHF_ALLOC sections are matched based on the virtual address
                // otherwise the file offset is matched
                if ( ( ( psec->get_flags() & SHF_ALLOC ) == SHF_ALLOC )
                         ? is_sect_in_seg( psec->get_address(),
                                           psec->get_size(), segVBaseAddr,
                                           segVEndAddr )
                         : is_sect_in_seg( psec->get_offset(), psec->get_size(),
                                           segBaseOffset, segEndOffset ) ) {
                    // Alignment of segment shall not be updated, to preserve original value
                    // It will be re-calculated on saving.
                    seg->add_section_index( psec->get_index(), 0 );
                }
            }

            // Add section into the segments' container
            segments_.emplace_back( seg );
        }

        return true;
    }

    //------------------------------------------------------------------------------
    bool save_header( std::ostream& stream ) { return header->save( stream ); }

    //------------------------------------------------------------------------------
    bool save_sections( std::ostream& stream )
    {
        for ( auto* sec : sections_ ) {
            std::streampos headerPosition =
                static_cast<std::streamoff>( header->get_sections_offset() ) +
                static_cast<std::streampos>(
                    header->get_section_entry_size() ) *
                    sec->get_index();

            sec->save( stream, headerPosition, sec->get_offset() );
        }
        return true;
    }

    //------------------------------------------------------------------------------
    bool save_segments( std::ostream& stream )
    {
        for ( auto* seg : segments_ ) {
            std::streampos headerPosition =
                static_cast<std::streamoff>( header->get_segments_offset() ) +
                static_cast<std::streampos>(
                    header->get_segment_entry_size() ) *
                    seg->get_index();

            seg->save( stream, headerPosition, seg->get_offset() );
        }
        return true;
    }

    //------------------------------------------------------------------------------
    bool is_section_without_segment( unsigned int section_index ) const
    {
        bool found = false;

        for ( unsigned int j = 0; !found && ( j < segments.size() ); ++j ) {
            for ( unsigned int k = 0;
                  !found && ( k < segments[j]->get_sections_num() ); ++k ) {
                found = segments[j]->get_section_index_at( k ) == section_index;
            }
        }

        return !found;
    }

    //------------------------------------------------------------------------------
    static bool is_subsequence_of( segment* seg1, segment* seg2 )
    {
        // Return 'true' if sections of seg1 are a subset of sections in seg2
        const std::vector<Elf_Half>& sections1 = seg1->get_sections();
        const std::vector<Elf_Half>& sections2 = seg2->get_sections();

        bool found = false;
        if ( sections1.size() < sections2.size() ) {
            found = std::includes( sections2.begin(), sections2.end(),
                                   sections1.begin(), sections1.end() );
        }

        return found;
    }

    //------------------------------------------------------------------------------
    std::vector<segment*> get_ordered_segments()
    {
        std::vector<segment*> res;
        std::deque<segment*>  worklist;

        res.reserve( segments.size() );
        std::copy( segments_.begin(), segments_.end(),
                   std::back_inserter( worklist ) );

        // Bring the segments which start at address 0 to the front
        size_t nextSlot = 0;
        for ( size_t i = 0; i < worklist.size(); ++i ) {
            if ( i != nextSlot && worklist[i]->is_offset_initialized() &&
                 worklist[i]->get_offset() == 0 ) {
                if ( worklist[nextSlot]->get_offset() == 0 ) {
                    ++nextSlot;
                }
                std::swap( worklist[i], worklist[nextSlot] );
                ++nextSlot;
            }
        }

        while ( !worklist.empty() ) {
            segment* seg = worklist.front();
            worklist.pop_front();

            size_t i = 0;
            for ( ; i < worklist.size(); ++i ) {
                if ( is_subsequence_of( seg, worklist[i] ) ) {
                    break;
                }
            }

            if ( i < worklist.size() ) {
                worklist.emplace_back( seg );
            }
            else {
                res.emplace_back( seg );
            }
        }

        return res;
    }

    //------------------------------------------------------------------------------
    bool layout_sections_without_segments()
    {
        for ( unsigned int i = 0; i < sections_.size(); ++i ) {
            if ( is_section_without_segment( i ) ) {
                section* sec = sections_[i];

                Elf_Xword section_align = sec->get_addr_align();
                if ( section_align > 1 &&
                     current_file_pos % section_align != 0 ) {
                    current_file_pos +=
                        section_align - current_file_pos % section_align;
                }

                if ( 0 != sec->get_index() ) {
                    sec->set_offset( current_file_pos );
                }

                if ( SHT_NOBITS != sec->get_type() &&
                     SHT_NULL != sec->get_type() ) {
                    current_file_pos += sec->get_size();
                }
            }
        }

        return true;
    }

    //------------------------------------------------------------------------------
    void calc_segment_alignment()
    {
        for ( auto* seg : segments_ ) {
            for ( int i = 0; i < seg->get_sections_num(); ++i ) {
                section* sect = sections_[seg->get_section_index_at( i )];
                if ( sect->get_addr_align() > seg->get_align() ) {
                    seg->set_align( sect->get_addr_align() );
                }
            }
        }
    }

    //------------------------------------------------------------------------------
    bool layout_segments_and_their_sections()
    {
        std::vector<segment*> worklist;
        std::vector<bool>     section_generated( sections.size(), false );

        // Get segments in a order in where segments which contain a
        // sub sequence of other segments are located at the end
        worklist = get_ordered_segments();

        for ( auto* seg : worklist ) {
            Elf_Xword segment_memory   = 0;
            Elf_Xword segment_filesize = 0;
            Elf_Xword seg_start_pos    = current_file_pos;
            // Special case: PHDR segment
            // This segment contains the program headers but no sections
            if ( seg->get_type() == PT_PHDR && seg->get_sections_num() == 0 ) {
                seg_start_pos  = header->get_segments_offset();
                segment_memory = segment_filesize =
                    header->get_segment_entry_size() *
                    static_cast<Elf_Xword>( header->get_segments_num() );
            }
            // Special case:
            else if ( seg->is_offset_initialized() && seg->get_offset() == 0 ) {
                seg_start_pos = 0;
                if ( seg->get_sections_num() > 0 ) {
                    segment_memory = segment_filesize = current_file_pos;
                }
            }
            // New segments with not generated sections
            // have to be aligned
            else if ( seg->get_sections_num() > 0 &&
                      !section_generated[seg->get_section_index_at( 0 )] ) {
                Elf_Xword align = seg->get_align() > 0 ? seg->get_align() : 1;
                Elf64_Off cur_page_alignment = current_file_pos % align;
                Elf64_Off req_page_alignment =
                    seg->get_virtual_address() % align;
                Elf64_Off error = req_page_alignment - cur_page_alignment;

                current_file_pos += ( seg->get_align() + error ) % align;
                seg_start_pos = current_file_pos;
            }
            else if ( seg->get_sections_num() > 0 ) {
                seg_start_pos =
                    sections[seg->get_section_index_at( 0 )]->get_offset();
            }

            // Write segment's data
            for ( auto j = 0; j < seg->get_sections_num(); ++j ) {
                Elf_Half index = seg->get_section_index_at( j );

                section* sec = sections[index];

                // The NULL section is always generated
                if ( SHT_NULL == sec->get_type() ) {
                    section_generated[index] = true;
                    continue;
                }

                Elf_Xword section_align = 0;
                // Fix up the alignment
                if ( !section_generated[index] &&
                     sec->is_address_initialized() &&
                     SHT_NOBITS != sec->get_type() &&
                     SHT_NULL != sec->get_type() && 0 != sec->get_size() ) {
                    // Align the sections based on the virtual addresses
                    // when possible (this is what matters for execution)
                    Elf64_Off req_offset =
                        sec->get_address() - seg->get_virtual_address();
                    Elf64_Off cur_offset = current_file_pos - seg_start_pos;
                    if ( req_offset < cur_offset ) {
                        // something has gone awfully wrong, abort!
                        // section_align would turn out negative, seeking backwards and overwriting previous data
                        return false;
                    }
                    section_align = req_offset - cur_offset;
                }
                else if ( !section_generated[index] &&
                          !sec->is_address_initialized() ) {
                    // If no address has been specified then only the section
                    // alignment constraint has to be matched
                    Elf_Xword align = sec->get_addr_align();
                    if ( align == 0 ) {
                        align = 1;
                    }
                    Elf64_Off error = current_file_pos % align;
                    section_align   = ( align - error ) % align;
                }
                else if ( section_generated[index] ) {
                    // Alignment for already generated sections
                    section_align =
                        sec->get_offset() - seg_start_pos - segment_filesize;
                }

                // Determine the segment file and memory sizes
                // Special case .tbss section (NOBITS) in non TLS segment
                if ( ( ( sec->get_flags() & SHF_ALLOC ) == SHF_ALLOC ) &&
                     !( ( ( sec->get_flags() & SHF_TLS ) == SHF_TLS ) &&
                        ( seg->get_type() != PT_TLS ) &&
                        ( SHT_NOBITS == sec->get_type() ) ) ) {
                    segment_memory += sec->get_size() + section_align;
                }

                if ( SHT_NOBITS != sec->get_type() ) {
                    segment_filesize += sec->get_size() + section_align;
                }

                // Nothing to be done when generating nested segments
                if ( section_generated[index] ) {
                    continue;
                }

                current_file_pos += section_align;

                // Set the section addresses when missing
                if ( !sec->is_address_initialized() ) {
                    sec->set_address( seg->get_virtual_address() +
                                      current_file_pos - seg_start_pos );
                }

                if ( 0 != sec->get_index() ) {
                    sec->set_offset( current_file_pos );
                }

                if ( SHT_NOBITS != sec->get_type() ) {
                    current_file_pos += sec->get_size();
                }

                section_generated[index] = true;
            }

            seg->set_file_size( segment_filesize );

            // If we already have a memory size from loading an elf file (value > 0),
            // it must not shrink!
            // Memory size may be bigger than file size and it is the loader's job to do something
            // with the surplus bytes in memory, like initializing them with a defined value.
            if ( seg->get_memory_size() < segment_memory ) {
                seg->set_memory_size( segment_memory );
            }

            seg->set_offset( seg_start_pos );
        }

        return true;
    }

    //------------------------------------------------------------------------------
    bool layout_section_table()
    {
        // Simply place the section table at the end for now
        Elf64_Off alignmentError = current_file_pos % 4;
        current_file_pos += ( 4 - alignmentError ) % 4;
        header->set_sections_offset( current_file_pos );
        return true;
    }

    //------------------------------------------------------------------------------
  public:
    friend class Sections;
    class Sections
    {
      public:
        //------------------------------------------------------------------------------
        explicit Sections( elfio* parent ) : parent( parent ) {}

        //------------------------------------------------------------------------------
        Elf_Half size() const
        {
            return static_cast<Elf_Half>( parent->sections_.size() );
        }

        //------------------------------------------------------------------------------
        section* operator[]( unsigned int index ) const
        {
            section* sec = nullptr;

            if ( index < parent->sections_.size() ) {
                sec = parent->sections_[index];
            }

            return sec;
        }

        //------------------------------------------------------------------------------
        section* operator[]( const std::string& name ) const
        {
            section* sec = nullptr;

            for ( auto* it : parent->sections_ ) {
                if ( it->get_name() == name ) {
                    sec = it;
                    break;
                }
            }

            return sec;
        }

        //------------------------------------------------------------------------------
        section* add( const std::string& name )
        {
            section* new_section = parent->create_section();
            new_section->set_name( name );

            Elf_Half str_index = parent->get_section_name_str_index();
            section* string_table( parent->sections_[str_index] );
            string_section_accessor str_writer( string_table );
            Elf_Word                pos = str_writer.add_string( name );
            new_section->set_name_string_offset( pos );

            return new_section;
        }

        //------------------------------------------------------------------------------
        std::vector<section*>::iterator begin()
        {
            return parent->sections_.begin();
        }

        //------------------------------------------------------------------------------
        std::vector<section*>::iterator end()
        {
            return parent->sections_.end();
        }

        //------------------------------------------------------------------------------
        std::vector<section*>::const_iterator begin() const
        {
            return parent->sections_.cbegin();
        }

        //------------------------------------------------------------------------------
        std::vector<section*>::const_iterator end() const
        {
            return parent->sections_.cend();
        }

        //------------------------------------------------------------------------------
      private:
        elfio* parent;
    } sections;

    //------------------------------------------------------------------------------
    friend class Segments;
    class Segments
    {
      public:
        //------------------------------------------------------------------------------
        explicit Segments( elfio* parent ) : parent( parent ) {}

        //------------------------------------------------------------------------------
        Elf_Half size() const
        {
            return static_cast<Elf_Half>( parent->segments_.size() );
        }

        //------------------------------------------------------------------------------
        segment* operator[]( unsigned int index ) const
        {
            return parent->segments_[index];
        }

        //------------------------------------------------------------------------------
        segment* add() { return parent->create_segment(); }

        //------------------------------------------------------------------------------
        std::vector<segment*>::iterator begin()
        {
            return parent->segments_.begin();
        }

        //------------------------------------------------------------------------------
        std::vector<segment*>::iterator end()
        {
            return parent->segments_.end();
        }

        //------------------------------------------------------------------------------
        std::vector<segment*>::const_iterator begin() const
        {
            return parent->segments_.cbegin();
        }

        //------------------------------------------------------------------------------
        std::vector<segment*>::const_iterator end() const
        {
            return parent->segments_.cend();
        }

        //------------------------------------------------------------------------------
      private:
        elfio* parent;
    } segments;

    //------------------------------------------------------------------------------
  private:
    elf_header*           header;
    std::vector<section*> sections_;
    std::vector<segment*> segments_;
    endianess_convertor   convertor;
    address_translator    addr_translator;

    Elf_Xword current_file_pos;
};

} // namespace ELFIO

#include <elfio/elfio_symbols.hpp>
#include <elfio/elfio_note.hpp>
#include <elfio/elfio_relocation.hpp>
#include <elfio/elfio_dynamic.hpp>
#include <elfio/elfio_array.hpp>
#include <elfio/elfio_modinfo.hpp>
#include <elfio/elfio_versym.hpp>

#endif // ELFIO_HPP