What is easiest way to build a BSD 8 binary on a BSD 7 box?

[Peter Steele]

>The easiest way would probably be the following.
>
># SOMEDIR=/path/to/fbsd8buildenv
># mkdir -p ${SOMEDIR}
># cd /path/to/FreeBSD-8.0/src
># make buildworld
># make installworld DESTDIR=${SOMEDIR}
>
>Then adding --sysroot=${SOMEDIR} to all invocations of gcc/ld and/or liberal use of -I and -L gcc options should do the trick.
>
>For example:
># export CFLAGS="-I${SOMEDIR}/usr/include -L${SOMEDIR}/lib -L${SOMEDIR}/usr/lib # make

I've done this and it's clearly working, at least in the sense I can tell the libraries are coming from my BSD 8 repository. My makefile is generating gcc commands that look like this:

gcc -m64 -DHAVE_INT64_T --sysroot=/usr/local/buildrepo/bsd/v8/obj -L/usr/local/buildrepo/bsd/v8/obj/usr/lib ...

I know it's working because if I rename the directory pointed to by sysroot the link fails. My tool is still failing though in exactly the same way in a call to kvm_read. The same call works fine when the tool is built on a BSD 8 box. Is there anything else I need to do to make sure the BSD 7 built binary is a fully complaint BSD 8 binary?