> When you actually type "make" and build object files, you have to do
> so in a context which contains some information about where the object
> files are going to be.  Currently, you type "make" in the source tree
> and each source directory has "obj" symlinks pointing to where the
> objects are; but if some piece of state in the source tree knows where
> the build directory is, there can really only be one build tree, which
> is very limiting.

One trick that I have occasionally found useful is to make symlinks
like this:

    {top of source tree}/obj             --> {top of obj tree}
    {top of source tree}/usr.bin/obj     --> ../obj/usr.bin
    {top of source tree}/usr.bin/foo/obj --> ../obj/foo

instead of like this:

    {top of source tree}/obj             --> {top of obj tree}
    {top of source tree}/usr.bin/obj     --> {top of obj tree}/usr.bin
    {top of source tree}/usr.bin/foo/obj --> {top of obj tree}/usr.bin/foo

That way, all the symlinks except the very top one are relative
instead of absolute.  This doesn't solve the whole problem, but it might
help a little.

--apb (Alan Barrett)