Unfortunate dynamic linking for everything
das at FreeBSD.ORG
Tue Nov 18 21:11:22 PST 2003
On Tue, Nov 18, 2003, Robert Watson wrote:
> On systems like Mac OS X, use of a "shared
> region" permits not only use of prebinding, but assumptions of common load
> addresses for common libraries. In addition, the "shared region" approach
> allows the reuse of page table and VM meta-data across many processes.
> Leaving aside special-purpose optimizations like that, using some simple
> heuristics, we could probably easily reduce the number of load addressed
> dramatically, making prebinding a far more feasible approach, and
> something we should explore thoroughly.
IIRC, Dyson proposed something like that a while ago. It's a neat
idea, particularly if it gets us away from PIC on register-starved
architectures such as the i386.
> John Dyson's suggestion of "mixed mode" linking, in which we statically
> link known required parts of binaries, but permit dynamic linking of
> "plug-in" functionality is another quite reasonable solution, as long as
> we take care of the potential issue of "plug-ins" relying on symbols from
> a library that is statically linked to the application, but not in the set
> of symbols depended on by the application.
Wouldn't the first shared object you loaded instantly pull in
libc.so as a dependency, giving you pieces of both a static and a
dynamic libc? It seems that that would break something...
> For big applications like KDE, Open Office, et al, prebinding probably is
> the right approach, and hopefully we have plenty of time before 5.3 to
> refine Matthew's work and see if we can't get things up to speed.
For these applications, the fork/exec overhead is so far into the
noise and there are so many shared libraries that dynamic linking
wins outright, prebinding or not. Maybe for servers that fork a
lot this would be more contentious.
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