--- freebsd-sources-9.0.ebuild.orig	2012-01-17 01:37:08.000000000 +0900
+++ freebsd-sources-9.0.ebuild	2012-03-13 20:48:11.349558552 +0900
@@ -64,6 +64,11 @@
 	# as undefined references to ld's commandline to get them.
 	# Without this kernel modules will not load.
 	#epatch "${FILESDIR}/${PN}-7.1-binutils_link.patch"
+
+	# workaround a kernel panic for amd64-fbsd, bug #408019
+	if use amd64-fbsd ; then
+		sed -e "s:-O2:-O:g" -i "${S}/conf/kern.pre.mk" || die
+	fi
 }
 
 src_compile() {