Sun . 19 May 2019

Executable and Linkable Format

executable and linkable format, executable and linkable format specification
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 Release 4 SVR4 Application Binary Interface ABI specification,2 and later in the Tool Interface Standard,1 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

Contents

  • 1 File layout
    • 11 File header
    • 12 Program header
    • 13 Section header
  • 2 Tools
  • 3 Applications
    • 31 Unix-like systems
    • 32 Non-Unix adoption
    • 33 Game consoles
    • 34 PowerPC
    • 35 Mobile phones
  • 4 Specifications
  • 5 86open
  • 6 FatELF: universal binaries for Linux
  • 7 See also
  • 8 References
  • 9 Further reading
  • 10 External links

File layoutedit

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

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@|

Example hexdump of ELF file header3

File headeredit

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

ELF header4
Offset Size Bytes Field Purpose
32-bit 64-bit 32-bit 64-bit
0x00 4 e_identEI_MAG0 through e_identEI_MAG3 0x7F followed by ELF45 4c 46 in ASCII; these four bytes constitute the magic number
0x04 1 e_identEI_CLASS This byte is set to either 1 or 2 to signify 32- or 64-bit format, respectively
0x05 1 e_identEI_DATA This byte is set to either 1 or 2 to signify little or big endianness, respectively This affects interpretation of multi-byte fields starting with offset 0x10
0x06 1 e_identEI_VERSION Set to 1 for the original version of ELF
0x07 1 e_identEI_OSABI Identifies the target operating system ABI
Value ABI
0x00 System V
0x01 HP-UX
0x02 NetBSD
0x03 Linux
0x06 Solaris
0x07 AIX
0x08 IRIX
0x09 FreeBSD
0x0C OpenBSD
0x0D OpenVMS
0x0E NonStop Kernel
0x0F AROS
0x10 Fenix OS
0x11 CloudABI
0x53 Sortix

It is often set to 0 regardless of the target platform

0x08 1 e_identEI_ABIVERSION Further specifies the ABI version Its interpretation depends on the target ABI Linux kernel after at least 26 has no definition of it5 In that case, offset and size of EI_PAD are 8
0x09 7 e_identEI_PAD currently unused
0x10 2 e_type 1, 2, 3, 4 specify whether the object is relocatable, executable, shared, or core, respectively
0x12 2 e_machine Specifies target instruction set architecture Some examples are:
Value ISA
0x00 No specific instruction set
0x02 SPARC
0x03 x86
0x08 MIPS
0x14 PowerPC
0x28 ARM
0x2A SuperH
0x32 IA-64
0x3E x86-64
0xB7 AArch64
0x14 4 e_version Set to 1 for the original version of ELF
0x18 4 8 e_entry This is the memory address of the entry point from where the process starts executing This field is either 32 or 64 bits long depending on the format defined earlier
0x1C 0x20 4 8 e_phoff Points to the start of the program header table It usually follows the file header immediately, making the offset 0x34 or 0x40 for 32- and 64-bit ELF executables, respectively
0x20 0x28 4 8 e_shoff Points to the start of the section header table
0x24 0x30 4 e_flags Interpretation of this field depends on the target architecture
0x28 0x34 2 e_ehsize Contains the size of this header, normally 64 Bytes for 64-bit and 52 Bytes for 32-bit format
0x2A 0x36 2 e_phentsize Contains the size of a program header table entry
0x2C 0x38 2 e_phnum Contains the number of entries in the program header table
0x2E 0x3A 2 e_shentsize Contains the size of a section header table entry
0x30 0x3C 2 e_shnum Contains the number of entries in the section header table
0x32 0x3E 2 e_shstrndx Contains index of the section header table entry that contains the section names

Program headeredit

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 For 32-bit ELF, each entry is structured as:

Program header 32-bit6
Offset Size Bytes Field Purpose
0x00 4 p_type Identifies the type of the segment
Value Name
0x00000000 PT_NULL
0x00000001 PT_LOAD
0x00000002 PT_DYNAMIC
0x00000003 PT_INTERP
0x00000004 PT_NOTE
0x00000005 PT_SHLIB
0x00000006 PT_PHDR
0x60000000 PT_LOOS
0x6FFFFFFF PT_HIOS
0x70000000 PT_LOPROC
0x7FFFFFFF PT_HIPROC

PT_LOOS to PT_HIOS PT_LOPROC to PT_HIPROC is an inclusive reserved ranges for operating system processor specific semantics

0x04 4 p_offset Offset of the segment in the file image
0x08 4 p_vaddr Virtual address of the segment in memory
0x0C 4 p_paddr On systems where physical address is relevant, reserved for segment's physical address
0x10 4 p_filesz Size in bytes of the segment in the file image May be 0
0x14 4 p_memsz Size in bytes of the segment in memory May be 0
0x18 4 p_flags Segment-dependent flags
0x1C 4 p_align 0 and 1 specify no alignment Otherwise should be a positive, integral power of 2, with p_vaddr equating p_offset modulus p_align

Section headeredit

Offset Size Bytes Field Purpose
32-bit 64-bit 32-bit 64-bit
0x00 4 sh_name An offset to a string in the shstrtab section that represents the name of this section
0x04 4 sh_type Identifies the type of this header
Value Name Meaning
0x0 SHT_NULL Section header table entry unused
0x1 SHT_PROGBITS Program data
0x2 SHT_SYMTAB Symbol table
0x3 SHT_STRTAB String table
0x4 SHT_RELA Relocation entries with addends
0x5 SHT_HASH Symbol hash table
0x6 SHT_DYNAMIC Dynamic linking information
0x7 SHT_NOTE Notes
0x8 SHT_NOBITS Program space with no data bss
0x9 SHT_REL Relocation entries, no addends
0x0A SHT_SHLIB Reserved
0x0B SHT_DYNSYM Dynamic linker symbol table
0x0E SHT_INIT_ARRAY Array of constructors
0x0F SHT_FINI_ARRAY Array of destructors
0x10 SHT_PREINIT_ARRAY Array of pre-constructors
0x11 SHT_GROUP Section group
0x12 SHT_SYMTAB_SHNDX Extended section indeces
0x13 SHT_NUM Number of defined types
0x60000000 SHT_LOOS Start OS-specific
0x08 4 8 sh_flags Identifies the attributes of the section
Value Name Meaning
0x1 SHF_WRITE Writable
0x2 SHF_ALLOC Occupies memory during execution
0x4 SHF_EXECINSTR Executable
0x10 SHF_MERGE Might be merged
0x20 SHF_STRINGS Contains nul-terminated strings
0x40 SHF_INFO_LINK 'sh_info' contains SHT index
0x80 SHF_LINK_ORDER Preserve order after combining
0x100 SHF_OS_NONCONFORMING Non-standard OS specific handling required
0x200 SHF_GROUP Section is member of a group
0x400 SHF_TLS Section hold thread-local data
0x0ff00000 SHF_MASKOS OS-specific
0xf0000000 SHF_MASKPROC Processor-specific
0x4000000 SHF_ORDERED Special ordering requirement Solaris
0x8000000 SHF_EXCLUDE Section is excluded unless referenced or allocated Solaris
0x0C 0x10 4 8 sh_addr Virtual address of the section in memory, for sections that are loaded
0x10 0x18 4 8 sh_offset Offset of the section in the file image
0x14 0x20 4 8 sh_size Size in bytes of the section in the file image May be 0
0x18 0x28 4 sh_link Contains the section index of an associated section This field is used for several purposes, depending on the type of section
0x1C 0x2C 4 sh_info Contains extra information about the section This field is used for several purposes, depending on the type of section
0x20 0x30 4 8 sh_addralign Contains the required alignment of the section This field must be a power of two
0x24 0x38 4 8 sh_entsize Contains the size, in bytes, of each entry, for sections that contain fixed-size entries Otherwise, this field contains zero
0x28 0x40 End of Section Header size

Toolsedit

  • 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 Linux7
  • 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

Applicationsedit

Unix-like systemsedit

The ELF format has replaced older executable formats in various environments It has replaced aout and COFF formats in Unix-like operating systems:

  • Linux
  • Solaris
  • IRIX
  • FreeBSD
  • NetBSD
  • OpenBSD
  • DragonFly BSD
  • Syllable
  • HP-UX except for 32-bit PA-RISC programs which continue to use SOM
  • QNX Neutrino
  • MINIX8

Non-Unix adoptionedit

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

  • OpenVMS, in its Itanium & X86-64 versions9
  • 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, the open source reimplementation of BeOS
  • RISC OS10
  • Stratus VOS, in PA-RISC and x86 versions
  • Windows 10 Anniversary Update using the Windows Subsystem for Linux1112

Game consolesedit

Some game consoles also use ELF:

  • PlayStation Portable,13 PlayStation Vita, PlayStation 2, PlayStation 3, PlayStation 4
  • GP2X
  • Dreamcast
  • Nintendo DS, GameCube, Wii, Wii U

PowerPCedit

Other operating systems running on PowerPC that use 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
  • AROS

Mobile phonesedit

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

  • Symbian OS v9 uses E32Image14 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 libraries for the Java Native Interface With Android Runtime ART, the default since Android 50 "Lollipop", all applications are compiled into native ELF binaries upon installation

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, AVR3215 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

Specificationsedit

  • Generic:
    • System V Application Binary Interface Edition 41 1997-03-18
    • System V ABI Update October 2009
  • AMD64:
    • System V ABI, AMD64 Supplement
  • ARM:
    • ELF for the ARM Architecture
  • IA-32:
    • System V ABI, Intel386 Architecture Processor Supplement
  • IA-64:
    • Itanium Software Conventions and Runtime Guide September 2000
  • M32R:
    • M32R ELF ABI Supplement Version 12 2004-08-26
  • MIPS:
    • System V ABI, MIPS RISC Processor Supplement
    • MIPS EABI documentation 2003-06-11
  • Motorola 6800:
    • Motorola 8 and 16 bit Embedded ABI
  • PA-RISC:
    • ELF Supplement for PA-RISC Version 143 October 6, 1997
  • PowerPC:
    • System V ABI, PPC Supplement
    • PowerPC Embedded Application Binary Interface 32-Bit Implementation 1995-10-01
    • 64-bit PowerPC ELF Application Binary Interface Supplement Version 19 2004
  • SPARC:
    • System V ABI, SPARC Supplement
  • S/390:
    • S/390 32bit ELF ABI Supplement
  • zSeries:
    • zSeries 64bit ELF ABI Supplement
  • Symbian OS 9:
    • E32Image file format on Symbian OS 9

The Linux Standard Base LSB supplements some of the above specifications for architectures in which it is specified16 For example, that is the case for the System V ABI, AMD64 Supplement1718

86openedit

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, in order to encourage software developers to port to the architecture19 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 started 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 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, 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 1999,20 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 "declared itself dissolved" on July 25, 199921

FatELF: universal binaries for Linuxedit

FatELF is an ELF binary-format extension that adds fat binary capabilities22 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 eg binaries which support multiple kernel ABI versions As of 2014, support for FatELF is not integrated in the Linux kernel mainline232425

See alsoedit

  • Computer programming portal
  • Computing portal
  • Application binary interface
  • Comparison of executable file formats
  • DWARF – a format for debugging data
  • Intel Binary Compatibility Standard
  • Portable Executable
  • vDSO – virtual DSO

Referencesedit

  1. ^ a b Tool Interface Standard TIS Executable and Linking Format ELF Specification Version 12 May 1995
  2. ^ System V Application Binary Interface Edition 41 1997-03-18
  3. ^ http://pygmentsorg/docs/lexers/#lexers-for-hexadecimal-dumps
  4. ^ "ELF Header" Scocom July 2000 Retrieved 2014-02-07 
  5. ^ "LXR linux/include/linux/elfh" linuxno Retrieved 27 April 2015 
  6. ^ "Program Header" Scocom July 2000 Retrieved 2016-01-13 
  7. ^ "elfutils" fedorahostedorg Retrieved 27 April 2015 
  8. ^ "MinixReleases - Minix Wiki" Wikiminix3org Retrieved 2014-01-19 
  9. ^ https://vmssoftwarecom/pdfs/State_of_Port_20160906pdf
  10. ^ "GCCSDK - RISC OS" Riscosinfo 2012-04-22 Retrieved 2014-01-19 
  11. ^ "Announcing Windows 10 Insider Preview Build 14316" Windows Experience Blog Retrieved 2016-04-10 
  12. ^ Foley, Mary Jo "Under the hood of Microsoft's Windows Subsystem for Linux | ZDNet" ZDNet Retrieved 2016-08-19 
  13. ^ PlayStation Portable use encrypted & relocated ELF : PSP
  14. ^ Symbian OS executable file format
  15. ^ "Chapter 4: Object Files", System V Application Binary Interface, 2009-10-26, e_machine 
  16. ^ "LSB Referenced Specifications" linuxfoundationorg Retrieved 27 April 2015 
  17. ^ "Executable and Linking Format ELF" linuxfoundationorg Retrieved 27 April 2015 
  18. ^ "Introduction" linuxfoundationorg Retrieved 27 April 2015 
  19. ^ Leibovitch, Evan 1997-12-23 "86Open Frequently-Asked Questions" Archived from the original on 2007-03-11 Retrieved 2007-06-06 
  20. ^ Record, Ronald 1998-05-21 "Bulletin on status of 86open at SCO" Retrieved 2008-05-06 
  21. ^ Leibovitch, Evan 1999-07-25 "The86open Project - FINAL UPDATE" Archived from the original on 2007-02-27 Retrieved 2007-05-06 
  22. ^ Gordon, Ryan "fatelf-specification v1" icculusorg Retrieved 2010-07-25 
  23. ^ Gordon, Ryan "FatELF: Turns out I liked the uncertainty better" icculusorg Retrieved 2010-07-13 
  24. ^ Holwerda, Thom 2009-11-03 "Ryan Gordon Halts FatELF Project" osnewscom Retrieved 2010-07-05 
  25. ^ Brockmeier, Joe June 23, 2010 "SELF: Anatomy of an alleged failure" Linux Weekly News Retrieved 2011-02-06 

Further readingedit

  • Levine, John R October 1999 Linkers and Loaders Morgan-Kauffman ISBN 1-55860-496-0 
  • Drepper, Ulrich 2006-08-20 "How To Write Shared Libraries" PDF 40 Retrieved 2007-06-20 
  • 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 by Neelakanth Nadgir August 2001
  • 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

External linksedit

  • FreeBSD Handbook: Binary formats archived version
  • FreeBSD elf5 manual page
  • NetBSD ELF FAQ
  • Oracle Solaris Linker and Libraries Guide
  • The ERESI project : reverse engineering on ELF-based operating systems
  • Linux Today article on 86open 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

executable and linkable format, executable and linkable format specification


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Executable and Linkable Format


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