--- linux-grsec_old/PKGBUILD	2016-07-20 11:12:19.959696356 +0200
+++ linux-grsec/PKGBUILD	2016-07-20 11:13:37.232500588 +0200
@@ -263,6 +263,12 @@
     cp ${i} "${pkgdir}/usr/lib/modules/${_kernver}/build/${i}"
   done
 
+  # add objtool for external module building and enabled VALIDATION_STACK option
+  if [ -f tools/objtool/objtool ]; then
+    mkdir -p "${pkgdir}/usr/lib/modules/${_kernver}/build/tools/objtool"
+    cp -a tools/objtool/objtool ${pkgdir}/usr/lib/modules/${_kernver}/build/tools/objtool/
+  fi
+
   chown -R root.root "${pkgdir}/usr/lib/modules/${_kernver}/build"
   find "${pkgdir}/usr/lib/modules/${_kernver}/build" -type d -exec chmod 755 {} \;