Executable and Linkable Format

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

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

ELF header#edit

The ELF header defines whether to use 32-bit or 64-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.

Example hexdump#edit

00000000  7f 45 4c 46 02 01 01 00  00 00 00 00 00 00 00 00  |.ELF............|
00000010  02 00 3e 00 01 00 00 00  c5 48 40 00 00 00 00 00  |..>......H@.....|

^[10]

Program header#edit

The program header table tells the system how to create a process image. It is found at file offset e_phoff, and consists of e_phnum entries, each with size e_phentsize. The layout is slightly different in 32-bit ELF vs 64-bit ELF, because the p_flags are in a different structure location for alignment reasons. Each entry is structured as:

Section header#edit

• 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.^[12]
• 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.

Unix-like systems#edit

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

Non-Unix adoption#edit

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

• OpenVMS, in its Itanium and amd64 versions^[15]
• BeOS Revision 4 and later for x86 based computers (where it replaced the Portable Executable format; the PowerPC version stayed with Preferred 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 its Windows Subsystem for Linux compatibility system.^[18]

Game consoles#edit

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

PowerPC#edit

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

• AmigaOS 4, 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 run by the Wii U)

Mobile phones#edit

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 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.^[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 as ELFPack in the underground modding culture. The ELF file format is also used with the Atmel 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.

Blockchain platforms#edit

• 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]

The Linux Standard Base (LSB) supplements some of the above specifications for architectures in which it is specified.^[25] For example, that is the case for the System V ABI, AMD64 Supplement.^[26][27]

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.^[28] 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. 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,^[29] 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.^[30]

• 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

1. ^ a b Tool Interface Standard (TIS) Executable and Linking Format (ELF) Specification Version 1.2 (May 1995)
2. ^ ELF Object File Format: Appendix C: Revision History
3. ^ Tool Interface Standard (TIS) Portable Formats Specification Version 1.1 (October 1993)
4. ^ System V Application Binary Interface Edition 4.1 (1997-03-18)
5. ^ "ELF Header". Sco.com. July 2000. Retrieved 2014-02-07.
6. ^ "LXR linux/include/linux/elf.h". linux.no. Retrieved 27 April 2015.
7. ^ "glibc 2.12 announce".
8. ^ "sourceware.org Git - glibc.git/blob - libc-abis".
9. ^ "sourceware.org Git - glibc.git/blob - sysdeps/gnu/ldsodefs.h". Archived from the original on 2021-03-07. Retrieved 2019-10-28.
10. ^ "Available lexers — Pygments". pygments.org. Retrieved 2024-12-19.
11. ^ "Program Header". Sco.com. July 2000. Retrieved 2017-04-05.
12. ^ "elfutils". sourceware.org. Retrieved 30 April 2017.
13. ^ "Binary Formats". Archived from the original on 2019-03-31. Retrieved 2019-03-31.
14. ^ "MinixReleases – Minix Wiki". Wiki.minix3.org. Archived from the original on 2013-03-30. Retrieved 2014-01-19.
15. ^ "State of the Port to x86_64" (PDF). Archived from the original (PDF) on 2020-09-15. Retrieved 2016-10-19.
16. ^ "GCCSDK – RISC OS". Riscos.info. 2012-04-22. Archived from the original on 2014-02-19. Retrieved 2014-01-19.
17. ^ "Guardian Programmer's Guide" (PDF). Hewlett Packard Enterprise. Archived from the original (PDF) on 2018-05-30. Retrieved 2018-05-30. p. 44 archived from the original Archived 2018-05-30 at the Wayback Machine on 2018-5-30
18. ^ Foley, Mary Jo. "Under the hood of Microsoft's Windows Subsystem for Linux". ZDNet. Retrieved 2016-08-19.
19. ^ PlayStation Portable use encrypted & relocated ELF : PSP
20. ^ Symbian OS executable file format
21. ^ Rosen, Kenneth; Host, Douglas; Klee, Rachel; Rosinski, Richard (2007). UNIX: The Complete Reference (2 ed.). McGraw Hill Professional. p. 707. ISBN 9780071706988. Retrieved 2017-06-08. Dynamically linked libraries are also called shared objects (.so).
22. ^ Thomas, Romain. "Android formats". Quarks Lab. Retrieved 17 Jan 2023.
23. ^ "Chapter 4: Object Files", System V Application Binary Interface, 2009-10-26, e_machine
24. ^ "Solana Programs". Solana Foundation. 2024-11-11. Retrieved 2024-11-11. Solana leverages the LLVM compiler infrastructure to compile programs into Executable and Linkable Format (ELF) files.
25. ^ "LSB Referenced Specifications". linuxfoundation.org. Retrieved 27 April 2015.
26. ^ "Executable and Linking Format (ELF)". linuxfoundation.org. Retrieved 27 April 2015.
27. ^ "Introduction". linuxfoundation.org. Retrieved 27 April 2015.
28. ^ Leibovitch, Evan (1997-12-23). "86Open Frequently-Asked Questions". Archived from the original on 2007-03-11. Retrieved 2007-06-06.
29. ^ Record, Ronald (1998-05-21). "Bulletin on status of 86open at SCO". Archived from the original on 2008-12-08. Retrieved 2008-05-06.
30. ^ Leibovitch, Evan (1999-07-25). "The86open Project – Final Update". Archived from the original on 2007-02-27. Retrieved 2007-05-06.
31. ^ "Linkers and Loaders: Sample code".

• Evolution of the ELF object file format, by Fangrui Song.
• Levine, John R. (2000) [October 1999]. Linkers and Loaders. The Morgan Kaufmann Series in Software Engineering and Programming (1 ed.). San Francisco, USA: Morgan Kaufmann. ISBN 1-55860-496-0. OCLC 42413382. Retrieved 2020-01-12. Code:^[31][1] Errata: [2]
• Ulrich Drepper, How To Write Shared Libraries, Version 4.1.2 (2011). Published on the author's web page, https://www.akkadia.org/drepper.
• An unsung hero: The hardworking ELF by Peter Seebach, December 20, 2005, archived from the original on February 24, 2007
• LibElf and GElf – A Library to Manipulate ELf Files at the Wayback Machine (archived February 25, 2004)
• The ELF Object File Format: Introduction, The ELF Object File Format by Dissection by Eric Youngdale (1995-05-01)
• A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux by Brian Raiter
• ELF relocation into non-relocatable objects by Julien Vanegue (2003-08-13)
• Embedded ELF debugging without ptrace by the ELFsh team (2005-08-01)
• Study of ELF loading and relocs by Pat Beirne (1999-08-03)

• ELF Object File Format Specification
• ELF Object File Format on GitHub
• System V Application Binary Interface and Interface Definition
• FreeBSD Handbook: Binary formats (archived version)
• FreeBSD elf(5) manual page
• NetBSD ELF FAQ
• Linux elf(5) manual page
• Oracle Solaris Linker and Libraries Guide
• The ERESI project: reverse engineering on ELF-based operating systems Archived 2021-03-14 at the Wayback Machine
• Linux Today article on 86open Archived 2021-03-08 at the Wayback Machine July 26, 1999
• Announcement of 86open on Debian Announce mailing list 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