What is the full form of ELF?

Introduction

Executable and Linkable Format (ELF) are simply executable codes, shared libraries, and core dumps are all stored in binary records, which is utilised by numerous modern operating systems. The Elf arrange was outlined to take the part of prior executable designs like a.out and COFF, which were less adaptable and more difficult to use.

The Elf organise is made up of a header, program headers, segment headers, and real data segments, among other things. The header of an Elf record incorporates general data about the file, such as the sort of Elf record (executable, shared object, or core dump), the design for which it was made, and the program's entry point.

The headers of the program characterise how the distinctive program components, such as the code and information segments, should be stacked into memory. The segment headers include descriptions of the program's several sections, which incorporate the symbol table, relocation data, and debug data.

ELF files can be statically linked or dynamically linked. In a statically linked executable, all of the libraries that the software needs are included in the executable file itself. The code is connected with shared libraries at runtime as a dynamically linked executable, which makes better use of system resources.

The ELF format has established itself as the standard for executables and shared libraries on a wide range of operating systems, including Linux, Unix, macOS, and numerous versions of Windows.

Structure of ELF

An ELF (Executable and Linkable Format) file is divided into different sections, each of which has its own header and data. The primary divisions are −

• ELF header − A file's type (executable, shared object, or core dump), the machine architecture for which it was compiled, and the program's entry point are all listed in the ELF header section.

• Programme header table − In this section, the various parts of the program including the code and data sections are described, along with how they should be loaded into memory. Each programme header in it describes a different section of the programme.

• Section header table − This section lists the various parts of the programme, including the symbol table, relocation data, and debugging data.

• Data sections − These include the program's actual data, including its code, data, and other resources.

The file type, machine architecture, programme entry point, and the position and size of the programme header table and section header table are among the data found in the ELF header. The magic number, which identifies the file as an ELF file, is another field.

A list of programme headers, each of which describes a section of the programme, can be found in the programme header table. The code portion, the data section, and other sections with programme resources are among these segments.

Each section header in the section header table describes a different segment of the programme. The symbol table, string table, relocation information, and debug information are all included in these sections.

The program's actual data, including the code, data, and resources it needs, are contained in the data sections. Using the programme header table as a guide, these parts are loaded into memory.

Advantages of ELF

The advantages of Executable and Linkable Format (ELF) files are as follows −

• Programmes can be created once and run on many platforms because to ELF files' portability across numerous operating systems and architectural frameworks.

• Dynamic linking is possible with ELF files, allowing shared libraries to be loaded at runtime, allowing applications to share resources, and reducing the size of executable files.

• Security − Because ELF files include several security features like read-only segments, position-independent code, and stack protection, they are more resistant to attacks like buffer overflows.

• Debugging − Debugging tools can leverage the debugging information contained in ELF files to assist identify issues with the programme.

• The ELF format is adaptable and extendable, enabling the inclusion of additional sections and headers to enable cutting-edge features and technologies.

• Due to the widespread use of ELF files in contemporary operating systems, they are compatible with a broad variety of tools and development environments.

Comparison of ELF with other executable file formats

The following table contrasts ELF with a few other widely used file formats −

• An older file format called COFF (Common Object File Format) is still in use on several operating systems, including Microsoft Windows. While COFF and ELF have many similarities, they differ in a number of important aspects, including support for position-independent code and dynamic linking.

• The file format used by Apple's macOS and iOS is called Mach-O (Mach Object File Format). Mach-O has a somewhat different structure than ELF and uses a different set of headers, but it also provides dynamic linking and position-independent code.

• Microsoft Windows uses a file format called PE (Portable Executable). Unlike ELF, PE has a distinct structure and set of headers but still provides dynamic linking and position-independent code.

• A.out (Assembler Output) − During the 1980s and 1990s, Unix systems frequently utilised the a.out file format, which is an older one. It has a less complex structure and lacks several of the sophisticated capabilities of ELF, such as dynamic linking and position-independent code.

Conclusion

As a result of providing a consistent way to distribute and operate software applications across numerous platforms, the ELF (Executable and Linkable Format) file format is an essential part of modern operating systems. Due to the format's many advantages, including portability, dynamic linking, security, and flexibility, both users and developers prefer it. Many industries employ the ELF file format, which is also extensively used in Linux and Unix-based systems. Despite the existence of additional file formats, ELF is preferred for executable file formats because of its complex features and compatibility with modern platforms.

FAQs

Q1. Who or what uses ELF?

Ans: ELF is a file format used to store executable code for applications on Unix and Linux-based operating systems. It enables the execution of the programme on a range of various hardware architectures by providing details about the program's code, data, and dependencies.

Q2. ELF differs from other executable file formats in what ways?

Ans: Dynamic linking capabilities, position-independent code, and enhanced security features are just a few of the ways that ELF differs from other file formats. It can also be used with many hardware architectures and operating systems because to its flexible structure.

Q3. Can Windows run ELF files?

Ans: You must utilise third-party software or emulators in order to run ELF files on Windows natively. The Portable Executable is used by Windows.