Re: Patch to allow make to load plugins that add new functions.

[Paul Smith]

Hi Tim;

Before going too much further note that I've got a semi-implemented
"load" operator in my source already, which fulfills a similar function
except in a less sophisticated way: it just calls a function in the
loaded object after loading and that function can do whatever it wants.

I can send along a patch if you're interested in checking it out.  I
have some regression tests added, documentation, autoconf, etc.

Boris and I discussed this on the alpha list a number of months ago and
his position was that we should not try to restrict things.  His
suggestion was to follow the GCC model and just let people do what they
wanted to.  The downside of this is that we wouldn't be defining a big
stable API: we would reserve the right to change things internally with
every release, which would potentially break loadable objects.

There are some outstanding issues: the first one is that I'd like the
"load" operation to behave like the "include" operation, in that make
would try to rebuild the target of the load and, if it were rebuilt,
re-exec itself to reload it.  That's not implemented yet.

Second, the way in which the objects are found for loading.  Do we just
use the default dlopen() process?  Or do something more (or less!)
sophisticated?

Finally, as you've noted in order for this to be useful generally we
need to start publishing some header files.  What goes into them and how
they get published is something of an open question.  It's possible that
this will require a significant reworking of the current make header
files (which would be OK with me since they're pretty messy currently).
We could choose the public interface through what structures and
functions we put into the publicly-facing header.

The most obvious interface is "define a new function", but others could
also be useful: eval, set variables, etc.