In computing, the Executable and Linkable 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.
In 1999 it was chosen as the standard binary file format for Unix and Unix-like systems
on x86 by the 86open project.
ELF is flexible and extensible by design, and it is not bound to any particular processor
or architecture.
This has allowed it to be adopted by many different operating systems on many different
platforms.
File layout
Each ELF file is made up of one ELF header, followed by file data.
The file data can include: Program header table, describing zero or more
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 necessary
for runtime execution of the file, while sections contain important data for linking and relocation.
Any byte in the entire file can be owned by at most one section, and there can be orphan
bytes which are not owned by any section.
File header The ELF header defines whether 32- or 64-bit
addresses are to be used.
The header itself contains three fields that are affected by this setting and offset other
fields that follow them.
The 64-bit header is 64 bytes long.
Tools readelf is a Unix binary utility that displays
information about one or more ELF files.
A free software 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.
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 instruction
set architecture for which the code in a relocatable, executable, or shared object file is intended,
or on which an ELF core dump was produced.
Applications The ELF format has replaced older executable
formats in various environments.
It has replaced a.out and COFF formats in Unix-like operating systems:
Linux Solaris
IRIX FreeBSD
NetBSD OpenBSD
DragonFly BSD Syllable
HP-UX QNX Neutrino
MINIX ELF has also seen some adoption in non-Unix
operating systems, such as: OpenVMS, in its Itanium version
BeOS Revision 4 and later for x86 based computers.
Haiku, the open source reimplementation of BeOS.
RISC OS Some game consoles also use ELF:
PlayStation Portable, PlayStation 2, PlayStation 3, PlayStation 4
GP2X Dreamcast
GameCube, Wii Other operating systems running on PowerPC
using ELF: AmigaOS 4, the ELF executable has replaced
the previous EHF which was used on Amigas equipped with PPC processor expansion cards.
MorphOS AROS
Some operating systems for mobile phones and mobile devices use ELF:
Symbian OS v9 uses E32Image 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
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 libraries for the Java Native Interface.
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 as ELFPack in the underground modding culture.
The ELF file format is also used with the Atmel AVR, AVR32 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.
Specifications
86open 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, so as 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 to enable unmodified binaries to run on the
x86 UNIX-like operating systems.
The project was originally referred to as "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 started email discussions in 1997 and first met in person at the Santa Cruz
Operation offices on 1997-08-22.
The steering committee was Marc Ewing, Dion Johnson, Evan Leibovitch, Bruce Perens, Andrew
Roach, Bryan Sparks and Linus Torvalds.
Other people on the project were Tim Bird, 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, Inc..
The project progressed and in mid-1998, SCO began developing lxrun, an open-source compatibility
layer capable of running 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, and has since
moved to integrated support of the Linux binary format via Solaris Containers for Linux Applications.
With the BSDs having long supported Linux binaries 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.
FatELF: Universal Binaries for Linux FatELF is an ELF binary-format extension which
adds Fat binary capabilities.
It is aimed for Linux and other Unix-like operating systems.
Additionally to the CPU architecture abstraction, there is the potential advantage of software-platform
abstraction e.g. binaries which support multiple kernel ABIs versions.
A proof-of-concept Ubuntu 9.04 image and development tools are available.
As of 2014, support for FatELF is not integrated in the Linux kernel mainline.
See also Comparison of executable file formats
Portable Executable DWARF, a format for debugging data
Application binary interface VDSO - Virtual DSO
References
Further reading
External links