computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...

, the Executable and Linkable FormatTool Interface Standard (TIS)
Portable Formats Specification
Version 1.1'' (October 1993) (ELF, formerly named Extensible Linking Format), is a common standard

file format A file format is a Computer standard, standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary format, pr ...

for

executable In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instructions", as opposed to a data fil ...

files, object code,

shared libraries In computer science, a library is a collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and su ...

, and

core dump In computing, a core dump, memory dump, crash dump, storage dump, system dump, or ABEND dump consists of the recorded state of the working Computer storage, memory of a computer program at a specific time, generally when the program has crash (comp ...

s. First published in the specification for the

application binary interface In computer software, an application binary interface (ABI) is an interface between two binary program modules. Often, one of these modules is a library or operating system facility, and the other is a program that is being run by a user. An ...

(ABI) of the

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

operating system version named System V Release 4 (SVR4), and later in the Tool Interface Standard,Tool Interface Standard (TIS)
Executable and Linking Format (ELF) Specification
Version 1.2'' (May 1995) it was quickly accepted among different vendors of

systems. In 1999, it was chosen as the standard binary file format for Unix and

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

systems on x86 processors by the 86open project. By design, the ELF format is flexible, extensible, and

cross-platform In computing, cross-platform software (also called multi-platform software, platform-agnostic software, or platform-independent software) is computer software that is designed to work in several computing platforms. Some cross-platform software ...

. For instance, it supports different

endiannesses In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most sig ...

and address sizes so it does not exclude any particular

central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...

(CPU) or

instruction set architecture In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...

. This has allowed it to be adopted by many different

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

s on many different hardware platforms.

File layout

Each ELF file is made up of one ELF header, followed by file data. The data can include: * Program header table, describing zero or more memory segments * Section header table, describing zero or more sections * Data referred to by entries in the program header table or section header table ELF Executable and Linkable Format diagram by Ange Albertini

ELF Executable and Linkable Format diagram by Ange Albertini

The segments contain information that is needed for run time execution of the file, while sections contain important data for linking and relocation. Any

byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...

in the entire file can be owned by one section at most, and orphan bytes can occur which are unowned by any section.

File header

The ELF header defines whether to use

32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32- bit units. Compared to smaller bit widths, 32-bit computers can perform large calcula ...

64-bit In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs are those that are based on processor registers, address buses, or data buses of that size. A comp ...

addresses. The header contains three fields that are affected by this setting and offset other fields that follow them. The ELF header is 52 or 64 bytes long for 32-bit and 64-bit binaries respectively.

Program header

The program header table tells the system how to create a process image. It is found at file offset , and consists of entries, each with size . The layout is slightly different in

ELF vs

ELF, because the are in a different structure location for alignment reasons. Each entry is structured as:

Section header

Tools

* readelf is a Unix binary utility that displays information about one or more ELF files. A

free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, ...

implementation is provided by GNU Binutils. * elfutils provides alternative tools to GNU Binutils purely for Linux. * elfdump is a command for viewing ELF information in an ELF file, available under Solaris and

FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

. * objdump provides a wide range of information about ELF files and other object formats. objdump uses the Binary File Descriptor library as a back-end to structure the ELF data. * The Unix file utility can display some information about ELF files, including the

for which the code in a relocatable, executable, or shared object file is intended, or on which an ELF

was produced.

Applications

Unix-like systems

The ELF format has replaced older executable formats in various environments. It has replaced

a.out a.out is a file format used in older versions of Unix-like computer operating systems for executables, object code, and, in later systems, shared libraries. This is an abbreviated form of "assembler output", the filename of the output of Ken Th ...

and COFF formats in

operating systems: *

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which i ...

* Solaris / Illumos *

IRIX IRIX ( ) is a discontinued operating system developed by Silicon Graphics (SGI) to run on the company's proprietary MIPS workstations and servers. It is based on UNIX System V with BSD extensions. In IRIX, SGI originated the XFS file system ...

NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is a ...

OpenBSD OpenBSD is a security-focused operating system, security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by fork (software development), forking N ...

Redox Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction ...

DragonFly BSD DragonFly BSD is a free and open-source Unix-like operating system forked from FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and FreeBSD developer between 1994 and 2003, began working on DragonFly BSD in ...

* Syllable *

HP-UX HP-UX (from "Hewlett Packard Unix") is Hewlett Packard Enterprise's proprietary implementation of the Unix operating system, based on Unix System V (initially System III) and first released in 1984. Current versions support HPE Integrit ...

(except for 32-bit PA-RISC programs which continue to use SOM) * QNX Neutrino * MINIX

Non-Unix adoption

ELF has also seen some adoption in non-Unix operating systems, such as: *

OpenVMS OpenVMS, often referred to as just VMS, is a multi-user, multiprocessing and virtual memory-based operating system. It is designed to support time-sharing, batch processing, transaction processing and workstation applications. Customers using Ope ...

, in its

Itanium Itanium ( ) is a discontinued family of 64-bit Intel microprocessors that implement the Intel Itanium architecture (formerly called IA-64). Launched in June 2001, Intel marketed the processors for enterprise servers and high-performance comp ...

and amd64 versions *

BeOS BeOS is an operating system for personal computers first developed by Be Inc. in 1990. It was first written to run on BeBox hardware. BeOS was positioned as a multimedia platform that could be used by a substantial population of desktop users a ...

Revision 4 and later for x86 based computers (where it replaced the

Portable Executable The Portable Executable (PE) format is a file format for executables, object code, DLLs and others used in 32-bit and 64-bit versions of Windows operating systems. The PE format is a data structure that encapsulates the information necessary f ...

format; the

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple– IBM ...

version stayed with Preferred Executable Format) *

Haiku is a type of short form poetry originally from Japan. Traditional Japanese haiku consist of three phrases that contain a ''kireji'', or "cutting word", 17 ''On (Japanese prosody), on'' (phonetic units similar to syllables) in a 5, 7, 5 pattern, ...

, an open source reimplementation of BeOS *

RISC OS RISC OS is a computer operating system originally designed by Acorn Computers Ltd in Cambridge, England. First released in 1987, it was designed to run on the ARM chipset, which Acorn had designed concurrently for use in its new line of Archi ...

* Stratus VOS, in PA-RISC and x86 versions * SkyOS * Fuchsia OS *

Z/TPF Transaction Processing Facility (TPF) is an IBM real-time operating system for mainframe computers descended from the IBM System/360 family, including zSeries and System z9. TPF delivers fast, high-volume, high-throughput transaction processing ...

* HPE NonStop OS * Deos Microsoft Windows also uses the ELF format, but only for its Windows Subsystem for Linux compatibility system.

Game consoles

Some game consoles also use ELF: *

PlayStation Portable The PlayStation Portable (PSP) is a handheld game console developed and marketed by Sony Computer Entertainment. It was first released in Japan on December 12, 2004, in North America on March 24, 2005, and in PAL regions on September 1, 200 ...

PlayStation Vita The PlayStation Vita (PS Vita, or Vita) is a handheld video game console developed and marketed by Sony Interactive Entertainment. It was first released in Japan on December 17, 2011, and in North America, Europe, and other international terri ...

PlayStation (console) The (abbreviated as PS, commonly known as the PS1/PS one or its codename PSX) is a home video game console developed and marketed by Sony Computer Entertainment. It was released in Japan on 3 December 1994, in North America on 9 September 1995 ...

, PlayStation 2,

PlayStation 3 The PlayStation 3 (PS3) is a home video game console developed by Sony Interactive Entertainment, Sony Computer Entertainment. The successor to the PlayStation 2, it is part of the PlayStation brand of consoles. It was first released on Novemb ...

PlayStation 4 The PlayStation 4 (PS4) is a home video game console developed by Sony Interactive Entertainment. Announced as the successor to the PlayStation 3 in February 2013, it was launched on November 15, 2013, in North America, November 29, 2013 in ...

PlayStation 5 The PlayStation 5 (PS5) is a home video game console developed by Sony Interactive Entertainment. Announced as the successor to the PlayStation 4 in April 2019, it was launched on November 12, 2020, in Australia, Japan, New Zealand, North A ...

* GP2X * Dreamcast *

GameCube The is a home video game console developed and released by Nintendo in Japan on September 14, 2001, in North America on November 18, 2001, and in PAL territories in 2002. It is the successor to the Nintendo 64 (1996), and predecessor of the W ...

Nintendo 64 The (N64) is a home video game console developed by Nintendo. The successor to the Super Nintendo Entertainment System, it was released on June 23, 1996, in Japan, on September 29, 1996, in North America, and on March 1, 1997, in Europe and ...

* Wii *

Wii U The Wii U ( ) is a home video game console developed by Nintendo as the successor to the Wii. Released in late 2012, it is the first eighth-generation video game console and competed with Microsoft's Xbox One and Sony's PlayStation 4. Th ...

PowerPC

Other (operating) systems running on

that use ELF: *

AmigaOS 4 AmigaOS 4 (abbreviated as OS4 or AOS4) is a line of Amiga operating systems which runs on PowerPC microprocessors. It is mainly based on AmigaOS 3.1 source code developed by Commodore International, Commodore, and partially on version 3.9 develop ...

, the ELF executable has replaced the prior Extended Hunk Format (EHF) which was used on Amigas equipped with PPC processor expansion cards. * MorphOS * AROS * Café OS (The operating system ran on Wii U)

Mobile phones

Some operating systems for mobile phones and mobile devices use ELF: *

Symbian Symbian is a discontinued mobile operating system (OS) and computing platform designed for smartphones. It was originally developed as a proprietary software OS for personal digital assistants in 1998 by the Symbian Ltd. consortium. Symbian ...

OS v9 uses E32Image format that is based on the ELF file format; *

Sony Ericsson Sony Mobile Communications Inc. ( ja, ソニーモバイルコミュニケーションズ株式会社) was a multinational telecommunications company founded on October 1, 2001, as a joint venture between Sony Group Corporation and Ericsson. I ...

, for example, the W800i, W610, W300, etc. * Siemens, the SGOLD and SGOLD2 platforms: from Siemens C65 to S75 and BenQ-Siemens E71/ EL71; *

Motorola Motorola, Inc. () was an American multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent public companies, Motorola ...

, for example, the E398, SLVR L7, v360, v3i (and all phone LTE2 which has the patch applied). *

Bada Bada (stylized as bada; Korean: ) is a discontinued mobile operating system developed by Samsung Electronics for devices such as mid- to high-end smartphones and tablet computers. The name is derived from " (bada)", meaning "ocean" or "sea" in ...

, for example, the

Samsung Wave S8500 The Samsung Wave (or Samsung Wave GT-S8500) is a smartphone developed and produced by Samsung Electronics. It is the first smartphone to run the Bada operating system developed by Samsung Electronics, which was commercially released on May 24, 201 ...

. *

Nokia Nokia Corporation (natively Nokia Oyj, referred to as Nokia) is a Finnish multinational telecommunications, information technology, and consumer electronics corporation, established in 1865. Nokia's main headquarters are in Espoo, Finlan ...

phones or tablets running the Maemo or the Meego OS, for example, the Nokia N900. *

Android Android may refer to: Science and technology * Android (robot), a humanoid robot or synthetic organism designed to imitate a human * Android (operating system), Google's mobile operating system ** Bugdroid, a Google mascot sometimes referred to ...

uses ELF (shared object) libraries for the Java Native Interface. With Android Runtime (ART), the default since Android 5.0 "Lollipop", all applications are compiled into native ELF binaries on installation. Some phones can run ELF files through the use of a patch that adds assembly code to the main

firmware In computing, firmware is a specific class of computer software that provides the low-level control for a device's specific hardware. Firmware, such as the BIOS of a personal computer, may contain basic functions of a device, and may provide ...

, which is a feature known as ''ELFPack'' in the underground modding culture. The ELF file format is also used with the

Atmel AVR AVR is a family of microcontrollers developed since 1996 by Atmel, acquired by Microchip Technology in 2016. These are modified Harvard architecture 8-bit RISC single-chip microcontrollers. AVR was one of the first microcontroller families ...

(8-bit), AVR32 and with

Texas Instruments Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globa ...

MSP430 microcontroller architectures. Some implementations of Open Firmware can also load ELF files, most notably

Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ances ...

's implementation used in almost all

machines the company produced.

Specifications

* Generic: **
System V Application Binary Interface
' Edition 4.1 (1997-03-18) **

' (October 2009) * AMD64: **
System V ABI, AMD64 Supplement
' * Arm: **
ELF for the ARM Architecture
' * IA-32: **
System V ABI, Intel386 Architecture Processor Supplement
' *

IA-64 IA-64 (Intel Itanium architecture) is the instruction set architecture (ISA) of the Itanium family of 64-bit Intel microprocessors. The basic ISA specification originated at Hewlett-Packard (HP), and was subsequently implemented by Intel in col ...

: **
Itanium Software Conventions and Runtime Guide
' (September 2000) * M32R: **
M32R ELF ABI Supplement
' Version 1.2 (2004-08-26) * MIPS: **
System V ABI, MIPS RISC Processor Supplement
' **

' (2003-06-11) *

Motorola 6800 The 6800 ("''sixty-eight hundred''") is an 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System (latter dubbed ''68xx'') that also included serial and paral ...

: **
Motorola 8- and 16- bit Embedded ABI
' *

PA-RISC PA-RISC is an instruction set architecture (ISA) developed by Hewlett-Packard. As the name implies, it is a reduced instruction set computer (RISC) architecture, where the PA stands for Precision Architecture. The design is also referred to a ...

: **
ELF Supplement for PA-RISC
' Version 1.43 (October 6, 1997) *

: **
System V ABI, PPC Supplement
' **
PowerPC Embedded Application Binary Interface
32-Bit Implementation'' (1995-10-01) **

' Version 1.9 (2004) *

RISC-V RISC-V (pronounced "risk-five" where five refers to the number of generations of RISC architecture that were developed at the University of California, Berkeley since 1981) is an open standard instruction set architecture (ISA) based on establi ...

: **
RISC-V ELF Specification
' *

SPARC SPARC (Scalable Processor Architecture) is a reduced instruction set computer (RISC) instruction set architecture originally developed by Sun Microsystems. Its design was strongly influenced by the experimental Berkeley RISC system developed ...

: **
System V ABI, SPARC Supplement
' * S/390: **
S/390 32bit ELF ABI Supplement
' * zSeries: **
zSeries 64bit ELF ABI Supplement
' *

OS 9: **
E32Image file format on Symbian OS 9
' The Linux Standard Base (LSB) supplements some of the above specifications for architectures in which it is specified. For example, that is the case for the System V ABI, AMD64 Supplement.

86open

86open was a project to form consensus on a common

binary file A binary file is a computer file that is not a text file. The term "binary file" is often used as a term meaning "non-text file". Many binary file formats contain parts that can be interpreted as text; for example, some computer document fi ...

format for

and

s on the common PC compatible x86 architecture, to encourage software developers to port to the architecture. The initial idea was to standardize on a small subset of Spec 1170, a predecessor of the Single UNIX Specification, and the GNU C Library (glibc) to enable unmodified binaries to run on the x86 Unix-like operating systems. The project was originally designated "Spec 150". The format eventually chosen was ELF, specifically the Linux implementation of ELF, after it had turned out to be a ''de facto'' standard supported by all involved vendors and operating systems. The group began email discussions in 1997 and first met together at the Santa Cruz Operation offices on August 22, 1997. The steering committee was Marc Ewing, Dion Johnson, Evan Leibovitch, Bruce Perens, Andrew Roach, Bryan Wayne Sparks and

Linus Torvalds Linus Benedict Torvalds ( , ; born 28 December 1969) is a Finnish software engineer who is the creator and, historically, the lead developer of the Linux kernel, used by Linux distributions and other operating systems such as Android. He also ...

. Other people on the project were Keith Bostic, Chuck Cranor, Michael Davidson, Chris G. Demetriou, Ulrich Drepper, Don Dugger, Steve Ginzburg, Jon "maddog" Hall, Ron Holt, Jordan Hubbard, Dave Jensen, Kean Johnston, Andrew Josey, Robert Lipe, Bela Lubkin, Tim Marsland, Greg Page, Ronald Joe Record, Tim Ruckle, Joel Silverstein, Chia-pi Tien, and Erik Troan. Operating systems and companies represented were

, BSDI,

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the devel ...

, SCO and

SunSoft , stylized as SUNSOFT, is a Japanese video game developer and publisher. Sunsoft is the video games division of Japanese electronics manufacturer Sun Corporation. Its U.S. subsidiary operated under the name Sun Corporation of America, though, ...

. The project progressed and in mid-1998, SCO began developing

lxrun In Unix computing, lxrun is a compatibility layer to allow Linux binaries to run on UnixWare, SCO OpenServer and Solaris without recompilation. It was created by Mike Davidson. It has been an open source software project since 1997, and is ava ...

, an open-source compatibility layer able to run Linux binaries on OpenServer, UnixWare, and Solaris. SCO announced official support of lxrun at LinuxWorld in March 1999.

Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, ...

began officially supporting lxrun for Solaris in early 1999, and later moved to integrated support of the Linux binary format via Solaris Containers for Linux Applications. With the BSDs having long supported Linux binaries (through a compatibility layer) and the main x86 Unix vendors having added support for the format, the project decided that Linux ELF was the format chosen by the industry and "declare itself dissolved" on July 25, 1999.

FatELF: universal binaries for Linux

FatELF is an ELF binary-format extension that adds fat binary capabilities. It is aimed for

and other

operating systems. Additionally to the CPU architecture abstraction ( byte order, word size,

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

instruction set In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called a ...

etc.), there is the potential advantage of software-platform abstraction e.g., binaries which support multiple kernel ABI versions. , FatELF has not been integrated into the mainline Linux kernel.

References

External links

(archived version)
FreeBSD manual page

Oracle Solaris Linker and Libraries Guide

The ERESI project : reverse engineering on ELF-based operating systems

Linux Today article on 86open
July 26, 1999

October 10, 1997, Bruce Perens
Declaration of Ulrich Drepper (PDF)
in The SCO Group vs IBM, September 19, 2006
86open and ELF discussion
on Groklaw, August 13, 2006 {{Executables Executable file formats