which environment variables to use in KBUILD

Hi, I have been looking through KBUILD and trying to determine some things but my makefile skills are not completely up to par. I am wondering if there is a specific variable for adding cflags to object files that are incorporated into the vmlinux kernel image. I see there are three variables KBUILD_VMLINUX_INIT/MAIN/LIBS that specify which files are linked in and it should be relatively easy to modify the link phase but I don't see how to add or modify the cflags. Thanks, Carter.