Re: Prelinking of shared libraries

[Waldo Bastian <bastian at kde dot org>]

On Friday 04 May 2001 00:29, Andreas Jaeger wrote:
> Is there a way to avoid the symbol lookup or to prelink to some
> symbols?

There are two issues of concern:  time and memory. In order to get better 
page sharing you basically must get rid of all relocations. To do that you 
need to take into account all of your dependencies as well. That's not 
impossible I think.

The idea would be to do the prelinking as if you were linking an actual 
application and then store the result for later reuse. When you are about to 
link an actual application you would first try to see if you can use the 
result of prelinking. If that isn't possible (e.g. one of the depending 
libraries changed) you would need to do regular linking and any other library 
that depends on this library wouldn't be able to use a prelinked library 
either.

This approach is basically outlined in the Nelson paper.
(http://www.usenix.org/publications/library/proceedings/cinci93/full_papers/nelson.txt)

Although it talks about Spring it also states:
"However  the  basic  caching techniques  we have described do not require a 
user-level server. A UNIX system might implement an equivalent dynamic 
library cache as  an  operating  system service that is used by the exec 
system call."

The prelinking could then be done just like ldconfig currently updates the 
ld.so.cache and the prelink results could be stored either seperately in the 
file system, or maybe as an additional ELF section in the library. Since 
linking mostly concerns the .data and .got sections maybe one could add an 
additional .data.prelinked and .got.prelinked then. 

Cheers,
Waldo
-- 
bastian@kde.org | SuSE Labs KDE Developer | bastian@suse.com