Pre Linking

Description
Pre-Linking is a mechanism for linking programs to shared libraries ahead of time. In general, every time an application is run it must have it's external symbols resolved - looked up in the shared library symbol table, and fixed up in the program binary to refer to the correct offsets in the library. To use prelinking, a special utility is run which does this resolution and fixup once for the program. This saves the cost of linking at runtime.

There is an existing package from RedHat which provides this feature.

A drawback of this is that if the shared library is changed, the fixups are no longer correct, and the program must be fixed-up again. This is much less of an issue in an embedded situation, where the programs and libraries are less likely to change than in a desktop or server Linux system.

Overview of linking
There is an excellent paper with an overview of dynamic linking issues at: |Pre Linking Overview This paper describes not only pre-linking, but lazy linking and more exotic systems, like compile-on-load.

Expected Improvement
[This is not measured yet.]

We expect that with use of prelinking, there will be a slight reduction in boot time for Linux system, in the area of initial application loading.

We need to use this system and measure the effect of prelinking for a determined set of applications.

RedHat prelinking system

 * The prelink package is at: http://people.redhat.com/jakub/prelink/
 * A white paper is at: prelink

Instructions for using prelinking with Gentoo
The following page has information on how to use prelinking with a Debian system:

http://www.gentoo.org/doc/en/prelink-howto.xml

Related Projects
http://mail-index.netbsd.org/tech-userlevel/2002/12/01/0000.html http://www.shiningsilence.com/dbsdlog/archives/000215.html
 * Prebinding (RelCache) - RelCache (aka ELF prebinding) news    http://mail-index.netbsd.org/tech-userlevel/2002/12/04/0017.html
 * RelCache vs. Red Hat prelink
 * Resident - Resident Good (comparisons with prebind)

Specifications
None so far.

Patches
No kernel patches required.

Case 1
[put information about an actual use of this technique here. A case study should include:]

Hardware:: [hardware description here] Kernel Version:: [kernel version here] Configuration:: [information about the configuration used here] Time without change:: [put that here] Time with change:: [put that here]

[Add any additional notes as you see fit.]

Case 3
= Future Work = This item is a work-in-progress, and we are just getting started.