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ELFIO/elfio/elfio.hpp
Serge Lamikhov-Center e07864463c Experimental change of section table alignment to 16
2023-10-16 20:19:00 +03:00

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/*
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 <array>
#include <vector>
#include <deque>
#include <memory>
#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 )
{
create( ELFCLASS32, ELFDATA2LSB );
}
explicit elfio( compression_interface* compression ) noexcept
: sections( this ), segments( this ),
compression( std::shared_ptr<compression_interface>( compression ) )
{
elfio();
}
elfio( elfio&& other ) noexcept
: sections( this ), segments( this ),
current_file_pos( other.current_file_pos )
{
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 );
compression = std::move( other.compression );
other.header = nullptr;
other.sections_.clear();
other.segments_.clear();
other.compression = nullptr;
}
elfio& operator=( elfio&& other ) noexcept
{
if ( this != &other ) {
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 = other.current_file_pos;
compression = std::move( other.compression );
other.current_file_pos = 0;
other.header = nullptr;
other.compression = nullptr;
other.sections_.clear();
other.segments_.clear();
}
return *this;
}
//------------------------------------------------------------------------------
// clang-format off
elfio( const elfio& ) = delete;
elfio& operator=( const elfio& ) = delete;
~elfio() = default;
// clang-format on
//------------------------------------------------------------------------------
void create( unsigned char file_class, unsigned char encoding )
{
sections_.clear();
segments_.clear();
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, bool is_lazy = false )
{
pstream = std::make_unique<std::ifstream>();
pstream->open( file_name.c_str(), std::ios::in | std::ios::binary );
if ( pstream == nullptr || !*pstream ) {
return false;
}
bool ret = load( *pstream, is_lazy );
if ( !is_lazy ) {
pstream.reset();
}
return ret;
}
//------------------------------------------------------------------------------
bool load( std::istream& stream, bool is_lazy = false )
{
sections_.clear();
segments_.clear();
std::array<char, EI_NIDENT> e_ident = { 0 };
// Read ELF file signature
stream.seekg( addr_translator[0] );
stream.read( e_ident.data(), 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;
}
load_sections( stream, is_lazy );
bool is_still_good = load_segments( stream, is_lazy );
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";
}
}
}
// clang-format on
// 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];
const section* sec =
find_prog_section_for_offset( seg->get_offset() );
if ( seg->get_type() == PT_LOAD && seg->get_file_size() > 0 &&
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;
}
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 ( const auto& sec : sections ) {
if ( sec->get_type() == SHT_PROGBITS &&
is_offset_in_section( offset, sec.get() ) ) {
return sec.get();
}
}
return nullptr;
}
//------------------------------------------------------------------------------
std::unique_ptr<elf_header> create_header( unsigned char file_class,
unsigned char encoding )
{
std::unique_ptr<elf_header> new_header;
if ( file_class == ELFCLASS64 ) {
new_header = std::unique_ptr<elf_header>(
new ( std::nothrow ) elf_header_impl<Elf64_Ehdr>(
&convertor, encoding, &addr_translator ) );
}
else if ( file_class == ELFCLASS32 ) {
new_header = std::unique_ptr<elf_header>(
new ( std::nothrow ) elf_header_impl<Elf32_Ehdr>(
&convertor, encoding, &addr_translator ) );
}
else {
return nullptr;
}
return new_header;
}
//------------------------------------------------------------------------------
section* create_section()
{
if ( auto file_class = get_class(); file_class == ELFCLASS64 ) {
sections_.emplace_back(
new ( std::nothrow ) section_impl<Elf64_Shdr>(
&convertor, &addr_translator, compression ) );
}
else if ( file_class == ELFCLASS32 ) {
sections_.emplace_back(
new ( std::nothrow ) section_impl<Elf32_Shdr>(
&convertor, &addr_translator, compression ) );
}
else {
sections_.pop_back();
return nullptr;
}
section* new_section = sections_.back().get();
new_section->set_index( static_cast<Elf_Half>( sections_.size() - 1 ) );
return new_section;
}
//------------------------------------------------------------------------------
segment* create_segment()
{
if ( auto file_class = header->get_class(); file_class == ELFCLASS64 ) {
segments_.emplace_back(
new ( std::nothrow )
segment_impl<Elf64_Phdr>( &convertor, &addr_translator ) );
}
else if ( file_class == ELFCLASS32 ) {
segments_.emplace_back(
new ( std::nothrow )
segment_impl<Elf32_Phdr>( &convertor, &addr_translator ) );
}
else {
segments_.pop_back();
return nullptr;
}
segment* new_segment = segments_.back().get();
new_segment->set_index( static_cast<Elf_Half>( segments_.size() - 1 ) );
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, bool is_lazy )
{
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,
is_lazy );
// To mark that the section is not permitted to reassign address
// during layout calculation
sec->set_address( sec->get_address() );
}
if ( Elf_Half shstrndx = get_section_name_str_index();
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, bool is_lazy )
{
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 ) {
if ( file_class == ELFCLASS64 ) {
segments_.emplace_back(
new ( std::nothrow ) segment_impl<Elf64_Phdr>(
&convertor, &addr_translator ) );
}
else if ( file_class == ELFCLASS32 ) {
segments_.emplace_back(
new ( std::nothrow ) segment_impl<Elf32_Phdr>(
&convertor, &addr_translator ) );
}
else {
segments_.pop_back();
return false;
}
segment* seg = segments_.back().get();
if ( !seg->load( stream,
static_cast<std::streamoff>( offset ) +
static_cast<std::streampos>( i ) * entry_size,
is_lazy ) ||
stream.fail() ) {
segments_.pop_back();
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 ( const 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 );
}
}
}
return true;
}
//------------------------------------------------------------------------------
bool save_header( std::ostream& stream ) const
{
return header->save( stream );
}
//------------------------------------------------------------------------------
bool save_sections( std::ostream& stream ) const
{
for ( const 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 ) const
{
for ( const 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 ( Elf_Half 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( const segment* seg1, const 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() const
{
std::vector<segment*> res;
std::deque<segment*> worklist;
res.reserve( segments.size() );
for ( const auto& seg : segments ) {
worklist.emplace_back( seg.get() );
}
// 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 ) ) {
const auto& sec = sections_[i];
if ( Elf_Xword section_align = sec->get_addr_align();
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() const
{
for ( const auto& seg : segments_ ) {
for ( Elf_Half i = 0; i < seg->get_sections_num(); ++i ) {
const auto& 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
if ( !write_segment_data( seg, section_generated, segment_memory,
segment_filesize, seg_start_pos ) ) {
return false;
}
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 % 16;
current_file_pos += 16 - alignmentError;
header->set_sections_offset( current_file_pos );
return true;
}
//------------------------------------------------------------------------------
bool write_segment_data( const segment* seg,
std::vector<bool>& section_generated,
Elf_Xword& segment_memory,
Elf_Xword& segment_filesize,
const Elf_Xword& seg_start_pos )
{
for ( Elf_Half 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;
}
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].get();
}
return sec;
}
//------------------------------------------------------------------------------
section* operator[]( const std::string_view& name ) const
{
section* sec = nullptr;
for ( const auto& it : parent->sections_ ) {
if ( it->get_name() == name ) {
sec = it.get();
break;
}
}
return sec;
}
//------------------------------------------------------------------------------
section* add( const std::string& name ) const
{
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].get() );
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<std::unique_ptr<section>>::iterator begin()
{
return parent->sections_.begin();
}
//------------------------------------------------------------------------------
std::vector<std::unique_ptr<section>>::iterator end()
{
return parent->sections_.end();
}
//------------------------------------------------------------------------------
std::vector<std::unique_ptr<section>>::const_iterator begin() const
{
return parent->sections_.cbegin();
}
//------------------------------------------------------------------------------
std::vector<std::unique_ptr<section>>::const_iterator end() const
{
return parent->sections_.cend();
}
//------------------------------------------------------------------------------
private:
elfio* parent;
};
Sections 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].get();
}
//------------------------------------------------------------------------------
segment* add() { return parent->create_segment(); }
//------------------------------------------------------------------------------
std::vector<std::unique_ptr<segment>>::iterator begin()
{
return parent->segments_.begin();
}
//------------------------------------------------------------------------------
std::vector<std::unique_ptr<segment>>::iterator end()
{
return parent->segments_.end();
}
//------------------------------------------------------------------------------
std::vector<std::unique_ptr<segment>>::const_iterator begin() const
{
return parent->segments_.cbegin();
}
//------------------------------------------------------------------------------
std::vector<std::unique_ptr<segment>>::const_iterator end() const
{
return parent->segments_.cend();
}
//------------------------------------------------------------------------------
private:
elfio* parent;
};
Segments segments;
//------------------------------------------------------------------------------
private:
std::unique_ptr<std::ifstream> pstream = nullptr;
std::unique_ptr<elf_header> header = nullptr;
std::vector<std::unique_ptr<section>> sections_;
std::vector<std::unique_ptr<segment>> segments_;
endianess_convertor convertor;
address_translator addr_translator;
std::shared_ptr<compression_interface> compression = nullptr;
Elf_Xword current_file_pos = 0;
};
} // 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
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