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Executable and Linkable Format

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ELF
Filename extension
none, .o, .so, .elf, .prx
Developed byUnix System Laboratories
Type of formatBinary, executable, object, shared libraries, core dump

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 file format is also used as a generic object and executable format for binary images used with embedded processors like AVR's.

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 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.

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.
  • 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:

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

Some game consoles also use ELF:

Other operating systems running on PowerPC using ELF:

  • AmigaOS 4, the ELF executable has replaced the previous EHF (Extended Hunk Format) which was used on Amigas equipped with PPC processor expansion cards.
  • MorphOS

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

Some 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).

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.[5] 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 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,[6] 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.[7]

FatELF: Universal Binaries for Linux

FatELF is an ELF binary-format extension which adds Fat binary capabilities.[8] It is aimed for Linux and other Unix-like operations 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 ABIs versions. A proof-of-concept Ubuntu 9.04 image (VM image of Ubuntu 9.04 with Fat Binary support) and development tools are available. Up to now the FatELF is not integrated in the kernel mainline.[9][10][11]

See also

References

  1. ^ System V Application Binary Interface Edition 4.1 (1997-03-18)
  2. ^ Tool Interface Standard (TIS) Executable and Linking Format (ELF) Specification Version 1.2 (May 1995)
  3. ^ PlayStation Portable use encrypted & relocated ELF : PSP
  4. ^ Symbian OS executable file format
  5. ^ Leibovitch, Evan (1997-12-23). "86Open Frequently-Asked Questions". Archived from the original on 2007-03-11. Retrieved 2007-06-06. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
  6. ^ Record, Ronald (1998-05-21). "Bulletin on status of 86open at SCO". Retrieved 2008-05-06.
  7. ^ Leibovitch, Evan (1999-07-25). "The86open Project - FINAL UPDATE". Archived from the original on 2007-02-27. Retrieved 2007-05-06.
  8. ^ Gordon, Ryan. "fatelf-specification v1". icculus.org. Retrieved 2010-07-25.
  9. ^ Gordon, Ryan. "FatELF: Turns out I liked the uncertainty better". icculus.org. Retrieved 2010-07-13.
  10. ^ Holwerda, Thom (2009-11-03). "Ryan Gordon Halts FatELF Project". osnews.com. Retrieved 2010-07-05.
  11. ^ Brockmeier, Joe (June 23, 2010). "SELF: Anatomy of an (alleged) failure". Linux Weekly News. Retrieved 2011-02-06.

Further reading

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