Index: toolchain-funcs.eclass
===================================================================
RCS file: /var/cvsroot/gentoo-x86/eclass/toolchain-funcs.eclass,v
retrieving revision 1.131
diff -u -B -r1.131 toolchain-funcs.eclass
--- toolchain-funcs.eclass	1 Nov 2014 05:19:20 -0000	1.131
+++ toolchain-funcs.eclass	20 Jan 2015 17:22:38 -0000
@@ -640,12 +640,29 @@
 	tc-is-static-only && return
 
 	# Eventually we'd like to get rid of this func completely #417451
-	case ${CTARGET:-${CHOST}} in
-	*-darwin*) ;;
-	*linux*|*-freebsd*|*-openbsd*|*-netbsd*)
-		use prefix && return 0 ;;
-	*) return 0 ;;
-	esac
+	if [[ -z ${GENTOO_ENABLE_SPLIT_USR} ]] ; then
+		case ${CTARGET:-${CHOST}} in
+		*-darwin*) GENTOO_ENABLE_SPLIT_USR='yes' ;;
+		*-freebsd*|*-openbsd*|*-netbsd*)
+			use prefix || GENTOO_ENABLE_SPLIT_USR='yes' ;;
+		*Linux*)
+			# Do a sanity check on users to see if they have a split-/usr.
+			# If so, for now, we warn & still do this stuff.
+			# The ROOT hack isn't entirely correct, but we don't really care.
+			# If you're deploying binpkgs, you can sort it out yourself.
+			if [[ ${ROOT} == "/" && $(stat -c %d /) != "$(stat -c %d /usr)" ]]; then
+				ewarn "You have a /usr mount point, but have not set GENTOO_ENABLE_SPLIT_USR=yes"
+				ewarn "in your make.conf.  Please do so now as future builds will stop setting"
+				ewarn "this for you automatically and your system might stop booting."
+				ewarn "See http://bugs.gentoo.org/417451 for more details."
+				GENTOO_ENABLE_SPLIT_USR='yes'
+			fi
+			;;
+		esac
+	fi
+	if [[ ${GENTOO_ENABLE_SPLIT_USR} != "yes" ]] ; then
+		return 0
+	fi
 
 	# Just make sure it exists
 	dodir /usr/${libdir}