What is prebinding?

dstranathan

Please define this for me. Thanks.

cubedude

[quote] From man pages:

update_prebinding(1) System General Commands Manual update_prebinding(1)



NAME

update_prebinding - Update prebinding information for newly changed files



SYNOPSIS

update_prebinding -root directory [-debug] [-force]

[-pkgs package-name install-location ...]

[-files filename ...]



DESCRIPTION

update_prebinding tries to synchronize prebinding information for

libraries and executables when new files are added to a system. Prebind-

ing information is pre-calculated address information for libraries used

by a given executable or library. By pre-determining where a function in

another library is destined to be placed, the dynamic linker does not

have to resolve symbols at application startup time, and the application

can launch faster.



Because each recompilation of a library or executable may place functions

at different addresses, a newly installed library or executable's pre-

binding information might not match the libraries already on the disk.

When the dynamic linker determines that prebinding information for a library could be invalid, it defaults to resolving all the names for that

library, and for all libraries referenced by that library, losing any

advantage of having the prebinding information.



update_prebinding ensures that prebinding information is up-to-date after

new prebound applications or new versions of system libraries are

installed. Given a list of the newly installed files in a package,

update_prebinding finds all the libraries and executables that may dynam-

ically load the changed files. If so, the prebinding information must be

updated, and update_prebinding performs redo_prebinding to update that

file. update_prebinding builds a dependency graph to minimize the files

that must be updated, and applies a few other heuristics to only call

redo_prebinding when necessary.



The root argument specifies the directory tree to search for changed

files. This is usually the root directory. update_prebinding will look

for dependent libraries and executables within this directory hierarchy,

but will not go to different file systems. The argument allows you to

update prebinding information for a specific file to match a non-running

version of the operating system on another partition. update_prebinding

uses the root to find the system libraries for that version of the OS.

The root argument is not intended to limit update_prebinding's effect to

a particular set of executables; instead, you must specify the changed files using -files or -pkgs.



The pkgs argument specifies the packages containing the files to be

updated. update_prebinding uses this list to determine the files that

must change, and thus identify the scope of updates necessary. After the

option name, list every package that changed, along with its install root

so that update_prebinding can find the newly installed files.



If no packages are named on the command line, then update_prebinding

scans the entire directory hierarchy from the named root looking for exe-

cutables, then prebinds all executables from least dependent to most.



The files option allows a list of changed files to be provided as subse-

quent arguments instead of a list of packages. Any libraries or executa-

bles in the root directory that depend on these files will also be re-

prebound.



The debug option does not actually change prebinding, but merely goes

through the effort of figuring out what will change, and lists the files

it would update if allowed.



By default, update_prebinding only changes a file if the prebinding is

out of date. The -force option ensures that all files examined are re- prebound, even if the prebinding is otherwise up-to-date. The command

update_prebinding -root / -force will prebind all binaries on the root

volume, even if otherwise correct.



Issues

update_prebinding (and redo_prebinding) only work on applications and

libraries that have been compiled and linked with the prebinding informa-

tion added. Applications that have not been prebound still gain the ben-

efits of prebinding as long as the system libraries used by the applica-

tion have been correctly prebound.



Updating prebinding for a given library or application can fail if any of

its dependent libraries are invalid -- not prebound, expected load

address conflicting with other loaded libraries, or missing architecture

in a fat library. To test if an application is able to use prebinding

information, set the environment variable DYLD_PREBIND_DEBUG. (See

dyld(1) for details on this option.)



update_prebinding does not actually execute /usr/bin/redo_prebinding when

re-prebinding files, but instead contains equivalent code. .Pp



SEE ALSO

dyld(1) redo_prebinding(1)



BSD February 14, 2001 BSD





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All that is from man update_prebinding