ELF Object File Format

Appendix C: Revision History

First Draft (Published May 14, 1998)

Second Draft (Published May 3, 1999)

  • New values introduced for ELF header e_machine field.

  • Revised language for EI_OSABI and EI_ABIVERSION fields of the ELF header e_ident array.

  • New section flags SHF_MERGE and SHF_STRINGS added.

  • New values added to a symbol table entry’s st_other field to describe a symbol’s visibility.

  • New dynamic section tags DT_RUNPATH and DT_FLAGS added. Deprecated dynamic section tag DT_RPATH.

  • New semantics for shared object path searching, including new “Substitution Sequences”.

Third Draft (Published May 12, 1999)

  • A new symbol type, STT_COMMON, has been added.

  • Added language restricting the types of objects that may contain symbols with the section index SHN_COMMON.

  • Dynamic section entries DT_SYMBOLIC, DT_TEXTREL and DT_BIND_NOW have been deprecated. New DT_FLAGS values DF_SYMBOLIC, DF_TEXTREL and DF_BIND_NOW have been added as replacements.

  • New rules for interpreting dynamic section tag encodings have been added.

  • The OS and processor specific ranges for DT_FLAGS have been removed.

  • The language motivating the use of DF_ORIGIN has been changed.

Fourth Draft (Published July 6, 1999)

  • New language has been added warning about the use of WEAK symbols in application programs.

  • New rules have been defined for composition of consecutive relocation entries that reference the same location.

  • Language has been added clarifying the order of execution for functions specified by initialization and termination arrays.

Fifth Draft (Published July 21, 1999)

  • New section types and section names added for init arrays, fini arrays, and pre-init arrays.

  • An object may now have both DT_INIT and DT_INIT_ARRAY entries (and both DT_FINI and DT_FINI_ARRAY entries). The relative execution order is specified.

  • The language describing the order of execution for termination functions has been revised.

  • A new pre-initialization mechanism has been added.

  • It is now up to the psABI supplement for each processor to specify whether the dynamic linker must invoke the executable file’s init and fini routines.

Sixth Draft (Published September 14, 1999)

  • Changed the numbering of some new section types previously added to account for type numbers already in use in particular vendor implementations.

  • Increased the number of section flag bits available in the OS specific range.

Seventh Draft (Published October 4, 1999)

  • Changed the values used for some new section attribute flags to accommodate platforms already using previously assigned values.

  • Added new section attribute flags SHF_INFO_LINK, SHF_LINK_ORDER, and SHF_OS_NONCONFORMING

  • Added rules for linkers when linking sections with unrecognized types or flags.

Eighth Draft (Published March 30, 2000)

  • Added the concept of section groups.

  • Removed the macros for ELF32_ST_OTHER and ELF64_ST_OTHER.

Ninth Draft (Published March 30, 2000)

  • Added language clarifying the semantics of symbols marked as STV_PROTECTED.

  • Added language clarifying the contents of the initialization and termination arrays.

Tenth Draft (Published 22 June 2000)

  • Added a sentence spelling out the behavior when resolving a symbol to a STV_PROTECTED definition from a shared object.

  • Added support for more than 65,000 sections in the ELF header, and with SHT_SYMTAB_SHNDX sections, and in symbol tables.

Eleventh Draft (Published 24 April 2001)

  • Updated table of EM_* entries.

  • Added GRP_MASKOS and GRP_MASKPROC. Changed section group description in a few ways, clarifying some fuzzy points and rewriting the rules for symbols referencing into section groups.

  • Changed the warning about using weak to be stronger.

  • Reworded the EI_OSABI byte description to make its use clearer.

  • Added the table of now generic EI_OSABI values.

  • Added SHF_TLS, PT_TLS and its contents, DF_STATIC_TLS, STT_TLS, .tbss, and .tdata.

  • Changed the rules for SHT_SYMTAB_SHNDX contents to require 0 when the corresponding st_shndx field is not SHN_XINDEX.

Twelfth Draft (Published 26 March 2007)

  • Updated table of EM_* entries.

Thirteenth Draft (Published 03 November 2009)

  • Updated table of EM_* entries.

  • Added ELFOSABI_FENIXOS to the EI_OSABI values.

  • Added ELFOSABI_GNU to the EI_OSABI values; aliased to ELFOSABI_LINUX.

Fourteenth Draft (Published 10 June 2013)

  • Added SHF_COMPRESSED to the Section Attribute Flags.

  • Updated table of EM_* entries.

Fifteenth Draft (Published 23 July 2015)

  • Clarified the description of SHT_SYMTAB_SHNDX; allow usage with any symbol table section.

  • Added DT_SYMTAB_SHNDX to the Dynamic Array Tags.

Version 4.2 (Published 2025)

  • Converted to ReStructuredText.

  • ELF specification is now separate from the gABI document.

  • Removed empty placeholders for psABI sections.

Version 4.3 (DRAFT)

  • Added extra requirements for SHF_LINKORDER flag.

  • Added relative relocation table (Elf32_Relr and Elf64_Relr).

  • Changed the symbol visibility attribute to use the lower 3 bits of st_other (instead of 2 bits).

  • Added DT_SYMTABSZ entry, and made DT_HASH optional if DT_SYMTABSZ is provided.

  • Changed SHF_COMPRESSED to allow with SHF_ALLOC sections in ET_REL objects.

  • Added ELFCOMPRESS_ZSTD compression algorithm.