LibElf [FreeBSD WIKI]

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====== Project Moved ======

**Note**: Ongoing development of ''%%libelf%%'' has moved to the [[http://elftoolchain.sourceforge.net/|Elftoolchain project]] on %%SourceForge%%.Net.

====== LibElf ======

LibElf is project implementing a BSD-licensed implementation of the SVR4 [[http://www.freebsd.org/cgi/man.cgi?query=elf&apropos=0&sektion=0&manpath=SunOS+5.10&format=html|ELF(3)]]
API.  The scope of the project includes:
  * An [[http://www.freebsd.org/cgi/cvsweb.cgi/src/lib/libelf/|implementation of the ELF(3) API]],
  * A [[http://perforce.freebsd.org/depotTreeBrowser.cgi?FSPC=//depot/user/jkoshy/projects/libbsdelf/ts|TET based test-suite]] for the API,
  * [[http://www.freebsd.org/cgi/man.cgi?query=elf&apropos=0&sektion=3&manpath=FreeBSD+8-current&format=html|Manual pages]] for section 3 of the %%FreeBSD%% manual set,
  * A [[http://people.freebsd.org/~jkoshy/download/libelf/article.html|tutorial documentation]] (currently a work-in-progress) suitable for inclusion in the %%FreeBSD%% Developer's Handbook.

JosephKoshy is the developer working on this project.

===== Rationale =====

In the absence of a common API to read and manipulate ELF objects,
many of %%FreeBSD%%'s tools implement ad-hoc ELF parsers inside themselves.

%%FreeBSD%% tools which implement ad-hoc parsers include:
  * ''%%btxld(8)%%'': reads and parses the ELF header when loading files.
  * ''%%elfdump(1)%%'': displays information about ELF files.
  * ''%%gprof(1)%%'': reporting tool for ''%%cc -pg%%'' profiling.
  * ''%%kgzip(8)%%'': compresses a kernel.
  * ''%%pmcstat(8)%%'': performance monitoring controller for PMC based profiling.

The downside of implementing ad-hoc ELF parsers is:
  * the extra effort in developing & maintaining the parser code,
  * parsing bugs that weaken the quality of the overall system,
  * the added difficulty in making such tools //cross-platform//.

The use of a common ELF API alleviates these problems to
some degree.

===== ELF Handling Alternatives =====

The GNU binutils toolset implements one such common API;
the [[http://sources.redhat.com/binutils/|Binary File Descriptor]]
library (''%%-lbfd%%'').  The BFD library supports a very large range
of cross-targets. However, its implementation is distributed
under a restrictive license (GPL, not even LGPL), which makes it
unsuitable for use in developing BSD-licensed tools.

The SVR4 ELF(3) API implements architecture-independent parsing
of ELF files.  While its scope is narrower than that of BFD, it
fits %%FreeBSD%%'s needs reasonably well.  Apart from (Open)Solaris
code, a small number of 3rd-party open-source applications use
this API.

The ERTOS project's [[http://www.ertos.nicta.com.au/software/kenge/libelf/devel/|ELF library]]
can also handle ELF files, but offers an API different from ELF(3).

===== The ELF(3) API =====

The ''%%ELF(3)%%'' API seems to have first appeared in %%SysV%% Unix (namely, SVR4),
As the API evolved, it developed 32 and 64 bit variants.
The [[http://www.freebsd.org/cgi/man.cgi?query=gelf&apropos=0&sektion=0&manpath=SunOS+5.10&format=html|GELF(3)]]
sub-API was added to provide an ELF class-independent way of manipulating ELF files.

ELF(3) is currently in use in Solaris and other SVR4 derived
systems.  An LGPL-ed implementation of this API is present in
some GNU operating systems.

===== Development =====

LibElf is being developed in %%FreeBSD%%'s CVS repository.

CVS: [[http://www.freebsd.org/cgi/cvsweb.cgi/src/lib/libelf/|http://www.freebsd.org/cgi/cvsweb.cgi/src/lib/libelf/]]

Design notes are on a seperate page: [[LibElf/ImplementationNotes|LibElf/ImplementationNotes]].
A 'status' page is at: [[LibElf/ImplementationStatus|LibElf/ImplementationStatus]].

==== LibElf based Tool Development ====

Native toolchain work is being tracked at ElfToolChain.

=== External Projects ===
The following people/projects are using %%FreeBSD%%'s LibElf:
  * [[http://code.google.com/p/aski-m/wiki/ElfUtils|ElfUtils]], an proposed replacement for GNU binutils by Sam Arun Raj.
  * [[http://freemanu1.free.fr/elf_examples/index.html|Emmanuel Azencot]] offers more examples of libelf based tools.

===== References =====
  * [[http://www.caldera.com/developers/gabi/|ELF gABI]] from SCO.
  * [[http://docs.sun.com/app/docs/doc/817-1984|Linker and Libraries Guide]] from Sun Microsystems.
  * [[http://developers.sun.com/solaris/articles/elf.html|LibELF tutorial]] from Sun Microsystems.
  * [[http://devresource.hp.com/drc/STK/docs/refs/elf-64-hp.pdf|ELF-64 Object File Format]] including HP and HP-UX extensions, from Hewlett-Packard.
  * [[http://www.mr511.de/software/english.html|LGPL'ed libelf(3) implementation]] by Michael Riepe.
  * An [[http://www.ertos.nicta.com.au/software/kenge/libelf/devel/|ELF library]] from the ERTOS project (doesn't implement the ''%%elf(3)%%'' API).
  * [[http://www-128.ibm.com/developerworks/power/library/pa-spec12/?ca=dgr-lnxw41ELFHero|Standards and specs: An unsung hero: The hardworking ELF]].  IBM Developerworks article by Peter Seebach.
  * [[http://tetworks.opengroup.org/tet/|Test Execution Toolkit]] from the Open Group.

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