From Wikipedia, the free encyclopedia
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,[1] and
later in the Tool Interface Standard,[2] 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.
Unlike many proprietary executable file formats, ELF is very
flexible and extensible, 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.
The ELF format has replaced older executable formats such as a.out and COFF in many Unix-like operating systems such as Linux, Solaris, IRIX, FreeBSD, NetBSD, OpenBSD, DragonFly BSD, Syllable, and HP-UX (except for 32-bit PA-RISC
programs which continue to use SOM). ELF has also
seen some adoption in non-Unix operating systems, such as the
Itanium version of OpenVMS,
BeOS Revision 4 and later for x86 based computers (where it replaced the
Portable
Executable format; the PowerPC version stayed with Preferred Executable
Format), and Haiku. The PlayStation Portable, PlayStation 2, PlayStation 3, Wii, Nintendo DS and GP2X consoles also use ELF. AmigaOS 4 and MorphOS also running on PowerPC machines, use
ELF. On the Amiga platform the ELF executable has replaced the
previous EHF (Extended
Hunk Format) which was used on Amigas equipped with PPC processor
expansion cards. The Symbian OS v9 uses E32Image[3] format
that is based on ELF file format.
Most Sony
Ericsson (for example, the W800i, W610,
W300, etc.), some Siemens (SGOLD and SGOLD2 platforms: from
Siemens C65 to S75
and BenQ-Siemens E71/EL71) and Motorola (for example, the E398, SLVR L7,
v360, v3i and all phone LTE2 which has the patch
applied) phones can run ELF files through the use of a patch that
adds assembly code to the main firmware (known as the
ELFPack, in the underground modding culture).
The ELF file format is also used as a generic object and
executable format for binary images used with embedded
processors.
ELF file
layout
An ELF file has two views: The program header shows the
segments used at run-time, whereas the section header
lists the set of
sections of the binary.
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 the
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. 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.
Tools
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 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.file is a Unix binary utility that displays
information about the architecture of ELF files.
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.[4]
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.
History
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 assisting in
the development of 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,[5] 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 (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.[6]
See also
References
Further
reading
External
links
86open
links
Wikis
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