Table of Contents
List of Tables
- ELFIO is a C++ library for reading and generating files in ELF binary - format. This library is independent and does not require any other product. - It is also cross-platform - the library uses standard ANSI C++ constructions - and runs on wide variety of architectures. -
- While the library's implementation does make your work much easier: basic - knowledge of the ELF binary format is required. Information about ELF - format can be found widely on the web. -
- The ELFIO library is a header only library. No preparatory compilation
- steps are required. To make your application be aware about the
- ELFIO classes and types declarations, just include elfio.hpp header file.
- All ELFIO library declarations reside in ELFIO namespace.
- So, this tutorial code starts from the following code:
-
-#include <iostream>
-#include <elfio.hpp>
-
-using namespace ELFIO;
-
-int main( int argc, char** argv )
-{
- if ( argc != 2 ) {
- std::cout << "Usage: tutorial <elf_file>" << std::endl;
- return 1;
- }
-
|
- Include |
| - The ELFIO namespace usage - |
- This chapter will explain how to work with the reader portion
- of the ELFIO library. The first step would be creation of the elfio
- class instance. The elfio constructor does not
- receive any parameters. After creation of a class object, we initialize
- the instance by invoking load function
- passing ELF file name as a parameter.
-
- // Create an elfio reader
- elfio reader;
-
- // Load ELF data
- if ( !reader.load( argv[1] ) ) {
- std::cout << "Can't find or process ELF file " << argv[1] << std::endl;
- return 2;
- }
-
|
- Create |
|
- Initialize the instance by loading ELF file. The function
- |
-
- From here, ELF header properties are accessible. This makes it possible - to request file parameters such as encoding, machine type, - entry point, etc. To get the class and the encoding of the file use: -
- // Print ELF file properties - std::cout << "ELF file class : "; - if ( reader.get_class() == ELFCLASS32 ) - std::cout << "ELF32" << std::endl; - else - std::cout << "ELF64" << std::endl; - - std::cout << "ELF file encoding : "; - if ( reader.get_encoding() == ELFDATA2LSB ) - std::cout << "Little endian" << std::endl; - else - std::cout << "Big endian" << std::endl; -
|
- Member function |
|
- Member function |
-
Note
- Standard ELF types, flags and constants
- are defined in the elf_types.hpp header file.
- This file is included automatically into the project.
- For example: ELFCLASS32,
- ELFCLASS64 constants define a value for 32/64 bit
- architectures. ELFDATA2LSB and
- ELFDATA2MSB constants define value
- for little and big endian encoding.
-
- ELF binary files may consist of several sections. Each section has it's own - responsibility: some contain executable code; others describe program - dependencies; others symbol tables and so on. See ELF binary format - documentation for a full description of each section. -
- The following code demonstrates how to find out the amount of sections - the ELF file contains. The code also presents how to access particular - section properties like names and sizes: -
- // Print ELF file sections info
- Elf_Half sec_num = reader.sections.size();
- std::cout << "Number of sections: " << sec_num << std::endl;
- for ( int i = 0; i < sec_num; ++i ) {
- const section* psec = reader.sections[i];
- std::cout << " [" << i << "] "
- << psec->get_name()
- << "\t"
- << psec->get_size()
- << std::endl;
- // Access to section's data
- // const char* p = reader.sections[i]->get_data()
- }
--
- sections member of reader
- object permits to obtain number of sections the ELF file contains. It
- also serves for getting access to individual section by using
- operator[], which returns a pointer to
- corresponding section's interface.
-
- Similarly, segments of the ELF file can be processed: -
- // Print ELF file segments info
- Elf_Half seg_num = reader.segments.size();
- std::cout << "Number of segments: " << seg_num << std::endl;
- for ( int i = 0; i < seg_num; ++i ) {
- const segment* pseg = reader.segments[i];
- std::cout << " [" << i << "] 0x" << std::hex
- << pseg->get_flags()
- << "\t0x"
- << pseg->get_virtual_address()
- << "\t0x"
- << pseg->get_file_size()
- << "\t0x"
- << pseg->get_memory_size()
- << std::endl;
- // Access to segments's data
- // const char* p = reader.segments[i]->get_data()
- }
-
- In this case, segments' attributes and data are obtained by using
- segments member of the reader.
-
- The full text of this example comes together with ELFIO library - distribution. -
- To simplify creation and interpretation of the ELF sections' data, - the ELFIO library comes with auxiliary classes - accessors. To the moment - of this document writing, the following accessors are available: -
-
string_section_accessor--
symbol_section_accessor--
relocation_section_accessor--
note_section_accessor-
- Definitely, it is possible to extend the library by implementing additional - accessors serving particular purposes. -
- Let's see how the accessors can be used with the previous ELF file reader - example. For this example purposes, we will print out all symbols in a - symbol section. -
- if ( psec->get_type() == SHT_SYMTAB ) {
- const symbol_section_accessor symbols( reader, psec );
- for ( unsigned int j = 0; j < symbols.get_symbols_num(); ++j ) {
- std::string name;
- Elf64_Addr value;
- Elf_Xword size;
- unsigned char bind;
- unsigned char type;
- Elf_Half section_index;
- unsigned char other;
-
- symbols.get_symbol( j, name, value, size, bind,
- type, section_index, other );
- std::cout << j << " " << name << std::endl;
- }
- }
-
- We create symbol_section_accessor instance first.
- Usually, accessors receive the elfio and
- section* parameters for their constructors.
- get_symbol is used to retrieve a particular entry
- in the symbol table.
-
- The source code for the ELF Dumping Utility can be found in - the "examples" directory; there also located more examples on how - to use different ELFIO reader interfaces. -
Table of Contents
- The ELFIO library's main class is elfio. The class
- contains the following two public data members: sections and segments:
-
-
Table 2.1. Class elfio member functions
| Data member | Description |
|---|---|
| - sections - | - The container stores ELFIO library section instances. - Implements operator[] and size(). operator[] permits access to - individual ELF file section according to its index. - |
| - segments - | - The container stores ELFIO library segment instances. - Implements operator[] and size(). operator[] permits access to - individual ELF file segment according to its index. - |
-
-
- Here is the list of elfio public member functions.
- Most of the functions permit to retrieve or set ELF file properties.
-
-
Table 2.2. Class elfio member functions
| Function | Description | ||||||
|---|---|---|---|---|---|---|---|
-
| - The constructor. - | ||||||
-
| - The destructor. - | ||||||
-
unsigned char file_class
- ;unsigned char encoding
- ; |
- Cleans and initializes empty elfio object.
- file_class is either ELFCLASS32 or ELFCLASS64.
- file_class is either ELFDATA2LSB or ELFDATA2MSB.
- | ||||||
-
const std::string& file_name
- ; |
- Initializes elfio object by loading data
- from ELF binary file. File name provided in file_name.
- Returns true if the file was processed successfully.
- | ||||||
-
const std::string& file_name
- ; |
- Creates a file in ELF binary format. File name provided in file_name.
- Returns true if the file was created successfully.
- | ||||||
-
| - Returns ELF file class. Possible values are ELFCLASS32 or ELFCLASS64. - | ||||||
-
| - Returns ELF file format version. - | ||||||
-
| - Returns ELF file format encoding. Possible values are ELFDATA2LSB and - ELFDATA2MSB. - | ||||||
-
| - Identifies the object file version. - | ||||||
-
| - Returns the ELF header's size in bytes. - | ||||||
-
| - Returns a section's entry size in ELF file header section table. - | ||||||
-
| - Returns a segment's entry size in ELF file header program table. - | ||||||
-
| - Returns operating system ABI identification. - | ||||||
-
unsigned char value
- ; | - Sets operating system ABI identification. - | ||||||
-
| - Returns ABI version. - | ||||||
-
unsigned char value
- ; | - Sets ABI version. - | ||||||
-
| - Returns the object file type. - | ||||||
-
Elf_Half value
- ; | - Sets the object file type. - | ||||||
-
| - Returns the object file's architecture. - | ||||||
-
Elf_Half value
- ; | - Sets the object file's architecture. - | ||||||
-
| - Returns processor-specific flags associated with the file. - | ||||||
-
Elf_Word value
- ; | - Sets processor-specific flags associated with the file. - |
-
-
-
Table 2.3. Class elfio member functions (continue)
| Function | Description | |||
|---|---|---|---|---|
-
| - Returns the virtual address to which the system first transfers control. - | |||
-
Elf64_Addr value
- ; | - Sets the virtual address to which the system first transfers control. - | |||
-
| - Returns the section header table's file offset in bytes. - | |||
-
Elf64_Off value
- ; | - Sets the section header table's file offset. Attention! - The value can be overridden by the library, when it creates new ELF - file layout. - | |||
-
| - Returns the program header table's file offset. - | |||
-
Elf64_Off value
- ; | - Sets the program header table's file offset. Attention! - The value can be overridden by the library, when it creates new ELF - file layout. - | |||
-
| - Returns the section header table index of the entry associated with - the section name string table. - | |||
-
Elf_Half value
- ; | - Sets the section header table index of the entry associated with - the section name string table. - | |||
-
|
- Returns endianess convertor reference for the specific
- elfio object instance.
- | |||
-
Elf_Word section_type
- ; | - Returns default entry size for known section types having different values - on 32 and 64 bit architectures. At the moment, only SHT_RELA, SHT_REL, - SHT_SYMTAB and SHT_DYNAMIC are 'known' section types. The function - returns 0 for other section types. - |
-
-
- Class section has no public data members.
-