In computing, the Executable and Linkable Format (ELF, formerly called Extensible Linking Format) is a common standard file format for executables, object code, shared libraries, and core dumps. First published in the System V Application Binary Interface specification, and later in the Tool Interface Standard, it was quickly accepted among different vendors of Unix systems.

Today the ELF format has replaced executable formats such as a.out and COFF in the Linux, Solaris, IRIX, and BSD operating systems, with the exception of Mac OS X, which uses Mach-O. Because other formats are proprietary, platform-specific, or less extensible than ELF, some users hold that ELF outperforms other formats, whereas others may consider it a competitor to the other formats. ELF is also used in the Itanium version of OpenVMS, a non-UNIX based operating system, as well as replacing the Preferred Executable Format on BeOS Revision 4 and later for x86 based computers (PPC computers stayed with PEF), which are also not UNIX-based.

ELF file layout

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Each ELF file is made up of one ELF header, followed by zero or more segments and zero or more sections. The segments contain information that is necessary for runtime execution of the file, while sections contain important data for linking and relocation. Each byte in the entire file is taken by no more than one section at a time, but there can be orphan bytes, which are not covered by a section. In the normal case of a UNIX executable one or more sections are enclosed in one segment. The segments and sections of the file are listed in a program header table and section header table respectively.

On many UNIX systems the command

man elf

may provide some more details.

Tools

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• readelf is a UNIX binary utility that displays information about one or more ELF files. A GPL implementation is provided by GNU Binutils.
• elfdump is a Solaris command for viewing ELF information in an elf file.

See also

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• Portable Executable (PE)
• DWARF
• Mach-O

External links

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• Tool Interface Standard (TIS) Executable and Linking Format (ELF) Specification Version 1.2
• Description of the ELF binary format
• Article "LibElf and GElf - A Library to Manipulate ELF Files" by Neelakanth Nadgir
• free ELF object file access library
• manual page
• Elf library routines
• ELFIO: a C++ library for reading and generating files in the ELF binary format.
• "A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux"
• An unsung hero: The hardworking ELF
• NetBSD ELF FAQ
• The ELF Object File Format by Dissection

Executable file formats

Executable and Linking Format | Executable and Linkable Format | Executable and Linking Format | Executable and linkable format | Executable and Linkable Format | ELF