Incomputing, theExecutable and Linkable Format^[3] (ELF, formerly namedExtensible Linking Format) is a common standardfile format forexecutable files,object code,shared libraries,device drivers, andcore dumps. First published in the specification for theapplication binary interface (ABI) of theUnix operating system version namedSystem V Release 4 (SVR4),^[4] and later in the Tool Interface Standard,^[1] it was quickly accepted among different vendors ofUnix systems. In 1999, it was chosen as the standard binary file format for Unix andUnix-like systems onx86 processors by the86open project.

By design, the ELF format is flexible, extensible, andcross-platform. For instance, it supports differentendiannesses and address sizes so it does not exclude any particularCPU orinstruction set architecture. This has allowed it to be adopted by many differentoperating systems on many different hardwareplatforms.

Each ELF file is made up of one ELF header, followed by file data. The data can include:

• Program header table, describing zero or morememory segments
• Section header table, describing zero or more sections
• Data referred to by entries in the program header table or section header table

The segments contain information that is needed forrun time execution of the file, while sections contain important data for linking and relocation. Anybyte in the entire file can be owned by one section at most, and orphan bytes can occur which are unowned by any section.

The ELF header defines whether to use32-bit or64-bit 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.

000000007f454c46020101000000000000000000|.ELF............|0000001002003e0001000000c548400000000000|..>......H@.....|

^[10]

The program header table tells the system how to create a process image. It is found at file offsete_phoff, and consists ofe_phnum entries, each with sizee_phentsize. The layout is slightly different in32-bit ELF vs64-bit ELF, because thep_flags are in a different structure location for alignment reasons. Each entry is structured as:

• readelf is a Unix binary utility that displays information about one or more ELF files. Afree software implementation is provided byGNU Binutils.
• elfutils provides alternative tools toGNU Binutils purely for Linux.^[12]
• elfdump is a command for viewing ELF information in an ELF file, available under Solaris andFreeBSD.
• objdump provides a wide range of information about ELF files and other object formats.objdump uses theBinary File Descriptor library as a back-end to structure the ELF data.
• The Unixfile utility can display some information about ELF files, including theinstruction set architecture for which the code in a relocatable, executable, or shared object file is intended, or on which an ELFcore dump was produced.

This articleis inlist format but may read better asprose. You can help byconverting this article, if appropriate.Editing help is available.(November 2016)

The ELF format has replaced older executable formats in various environments.It has replaceda.out andCOFF formats inUnix-like operating systems:

• Linux
• Solaris /Illumos
• IRIX
• FreeBSD^[13]
• NetBSD
• OpenBSD
• Redox
• DragonFly BSD
• Syllable
• HP-UX (except for 32-bit PA-RISC programs which continue to useSOM)
• QNX Neutrino
• MINIX^[14]

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

• OpenVMS, in itsItanium andamd64 versions^[15]
• BeOS Revision 4 and later forx86 based computers (where it replaced thePortable Executable format; thePowerPC version stayed withPreferred Executable Format)
• Haiku, an open source reimplementation of BeOS
• RISC OS^[16]
• Stratus VOS, in PA-RISC and x86 versions
• SkyOS
• Fuchsia OS
• Z/TPF
• HPE NonStop OS^[17]
• Deos

Microsoft Windows also uses the ELF format, but only for itsWindows Subsystem for Linux compatibility system.^[18]

Some game consoles also use ELF:

• PlayStation Portable,^[19] PlayStation Vita, PlayStation, PlayStation 2, PlayStation 3, PlayStation 4, PlayStation 5
• GP2X
• Dreamcast
• GameCube
• Nintendo 64
• Wii
• Wii U

Other (operating) systems running on PowerPC that use ELF:

• AmigaOS 4, the ELF executable has replaced the priorExtended Hunk Format (EHF) which was used on Amigas equipped with PPC processor expansion cards.
• MorphOS
• AROS
• Café OS (The operating system run by the Wii U)

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

• Symbian OS v9 uses E32Image^[20] format that is based on the ELF file format;
• Sony Ericsson, for example, the W800i, W610, W300, etc.
• Siemens, the SGOLD and SGOLD2 platforms: from Siemens C65 to S75 and BenQ-Siemens E71/EL71;
• Motorola, for example, the E398, SLVR L7, v360, v3i (and all phone LTE2 which has the patch applied).
• Bada, for example, the Samsung Wave S8500.
• Nokia phones or tablets running the Maemo or the Meego OS, for example, the Nokia N900.
• Android uses ELF.so (shared object^[21]) libraries for theJava Native Interface.^{[citation needed]} WithAndroid Runtime (ART), the default since Android 5.0 "Lollipop", all applications are compiled into native ELF binaries on installation.^[22] It's also possible to use native Linux software from package managers like Termux, or compile them from sources via Clang or GCC, that are available in repositories.

Some phones can run ELF files through the use of a patch that adds assembly code to the main firmware, which is a feature known asELFPack in the underground modding culture. The ELF file format is also used with theAtmel AVR (8-bit), AVR32^[23]and with Texas Instruments MSP430 microcontroller architectures. Some implementations of Open Firmware can also load ELF files, most notably Apple's implementation used in almost all PowerPC machines the company produced.

• Solana uses ELF format for its on-chain programs (smart contracts). The platform processes ELF files compiled to BPF (Berkeley Packet Filter) byte-code, which are then deployed as shared objects and executed in Solana's runtime environment. The BPF loader validates and processes these ELF files during program deployment.^[24]

86open was a project to form consensus on a common binary file format for Unix and Unix-like operating systems on the common PC compatible x86 architecture, to encourage software developers to port to the architecture.^[25] 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 ade 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. 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 BeOS, BSDI, FreeBSD,Intel, Linux, NetBSD, SCO and SunSoft.

The project progressed and in mid-1998, SCO began developing lxrun, 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 began officially supporting lxrun for Solaris in early 1999,^[26] 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[d] itself dissolved" on July 25, 1999.^[27]

FatELF is an ELF binary-format extension that addsfat binary capabilities.^[28] It is aimed for Linux and other Unix-like operating systems. Additionally to the CPU architecture abstraction (byte order, word size,CPU instruction set etc.), there is the potential advantage of software-platform abstraction e.g., binaries which support multiple kernel ABI versions. As of 2021^[update], FatELF has not been integrated into the mainline Linux kernel.^[29][30][31]

• Application binary interface
• Comparison of executable file formats
• DWARF – a format for debugging data
• Intel Binary Compatibility Standard
• Portable Executable – format used by Windows
• vDSO – virtual DSO
• Position-independent code

• Executable file formats

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