Bug#550441: advi: statically links to camlimages

[Florian Weimer <fw@deneb.enyo.de>]

* Michael S. Gilbert:

> thanks for the update on the situation.  based on the link, upstream's
> response is not entirely hostile.  see:
>
>   Feature 3- (dynamic code loading) is already available in bytecode
>   through the Dynlink API.  I understand there's a demand for having it
>   in native-code as well, and that might be possible without too much
>   fuss, at least on selected operating systems.
>
> so, perhaps if the work is done for them, they would be willing to
> accept the changes.

Note that dynamic linking in itself doesn't solve our problem.  We
also need a stable ABI across recompilations: we want to be able to
recompile camlimages, and use that from an unchanged advi binary
compiled to a different camlimages version.  (Even without that,
dynamic linking will reduce in disk and memory space savings, so it is
not completely pointless.)

This is not a Caml-specific problem, it is shared by practically all
programming languages which support separate compilation, with the
exception of C (due to its simple linking model) and Java (due to
precise guidelines about binary compatibility).  For example, for both
C++ and Ada, you have to be very careful when you try to make
ABI-preserving changes.  With templatized C++ code, this is often
impossible (and you've got a physical dependency on the template code
anyway).