Re: TODO

[Bob Friesenhahn]

On Mon, 15 Nov 2004, Joe Orton wrote:
> > >
> > Yes.  When you're making a distribution, Libtool's behaviour of directly
> > linking indirect-dependencies is insane.  For a SONAME change to a
> > library deep in the stack, that only affects the library immediately
> > above it, you suddenly need to rebuild your entire desktop environment.
>
> How does libtool know that the SONAME change only affects the library
> above it?  What if there is a structure exposed through multiple levels
> of libraries or something like that?  I can think of several cases where
> doing this by default in libtool would be unsafe.

This is an important issue that needs to be carefully considered. 
Libtool itself has no way to know this.  Distribution maintainers have 
to somehow know enough about how the software works that they don't 
accidentally break something.  Or maybe they just wait until the users 
tell them the software doesn't work anymore.

A somewhat related issue is if a library offers extra/different APIs 
if one of the libraries it optionally depends on is available.  This 
is a case where a shared library is not completely compatible even 
though it uses the same name.  If a library supporting fewer/different 
APIs is inserted in the place of a library supporting more APIs, then 
some dependent applications may fail.  There should not usually be 
problem if applications stick to baseline APIs which do not care about 
the extra library.  Do library maintainers test all dependent 
applications to ensure that none of them have broken due to replacing 
an existing library?

Yet another issue is if two libraries depend on the same library, but 
of different versions.  In this case there is a "deadly embrace" and 
problems unless there is some sort of symbol versioning (and maybe 
even if there *is* symbol versioning).

Bob
======================================
Bob Friesenhahn
address@hidden
http://www.simplesystems.org/users/bfriesen