--- a/etc/profile
+++ b/etc/profile
@@ -4,6 +4,46 @@
 # environment for login shells.
 #
 
+#
+# for prefix-chaining, the very first thing to do is to load
+# the profiles for all chained instances above.
+#
+# TODO: is it safe in any case to shell source make.conf?
+# don't do any recursive expansion here. if the parent can
+# use READONLY_EPREFIX's, it has to have the same profile as
+# we have here, and thus it will source parents before
+# evaluating anything from itself.
+#
+if [[ -r /etc/portage/make.conf ]]; then
+	_ro_root=$(. /etc/portage/make.conf && echo $READONLY_EPREFIX)
+elif [[ -r /etc/make.conf ]]; then
+	_ro_root=$(. /etc/make.conf && echo $READONLY_EPREFIX)
+else
+	echo "Failed to read" /etc/portage/make.conf >&2
+fi
+_ro_deps=${_ro_root#*:}
+_ro_root=${_ro_root%:*}
+if [ -n "${_ro_root}" -a -f "${_ro_root}/"etc/profile ]; then
+	. "${_ro_root}/"etc/profile
+fi
+
+#
+# With prefix-chaining we want another set of variables that
+# should be retained for all prefixes. for example it is ok
+# to retain PKG_CONFIG_PATH if the parent of the chain can
+# be used to resolve RDEPEND...
+#
+if [[ -n "${_ro_root}" ]]; then
+	_ro_chained_path_vars="PATH MANPATH"
+
+	[[ ${_ro_deps} == *RDEPEND* ]] &&
+		_ro_chained_path_vars="${_ro_chained_path_vars} PKG_CONFIG_PATH"
+
+	for var in ${_ro_chained_path_vars}; do
+		eval "_ro_backupenv_paths_${var}=\${${var}}"
+	done
+fi
+
 # Load environment settings from profile.env, which is created by
 # env-update from the files in /etc/env.d
 if [ -e /etc/profile.env ] ; then
@@ -61,3 +101,17 @@
 	[ -r "$sh" ] && . "$sh"
 done
 unset sh
+
+#
+# finally chain the save variables for previous prefixes in the chain.
+#
+if [[ -n "${_ro_chained_path_vars}" ]]; then
+	for var in ${_ro_chained_path_vars}; do
+		eval "export ${var}=\${${var}}:\${_ro_backupenv_paths_${var}}"
+		eval "unset _ro_backupenv_paths_${var}"
+	done
+fi
+
+unset _ro_root
+unset _ro_deps
+unset _ro_chained_path_vars