diff -r 62406a5c8345 -r d38d876f1654 nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/runtime/linker/NashornBeansLinker.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/nashorn/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/runtime/linker/NashornBeansLinker.java	Sun Aug 17 15:56:32 2014 +0100
@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package jdk.nashorn.internal.runtime.linker;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import jdk.internal.dynalink.beans.BeansLinker;
+import jdk.internal.dynalink.linker.ConversionComparator.Comparison;
+import jdk.internal.dynalink.linker.GuardedInvocation;
+import jdk.internal.dynalink.linker.GuardingDynamicLinker;
+import jdk.internal.dynalink.linker.LinkRequest;
+import jdk.internal.dynalink.linker.LinkerServices;
+import jdk.internal.dynalink.support.Lookup;
+import jdk.nashorn.internal.runtime.ConsString;
+
+/**
+ * This linker delegates to a {@code BeansLinker} but passes it a special linker services object that has a modified
+ * {@code asType} method that will ensure that we never pass internal engine objects that should not be externally
+ * observable (currently only ConsString) to Java APIs, but rather that we flatten it into a String. We can't just add
+ * this functionality as custom converters via {@code GuaardingTypeConverterFactory}, since they are not consulted when
+ * the target method handle parameter signature is {@code Object}.
+ */
+public class NashornBeansLinker implements GuardingDynamicLinker {
+    private static final MethodHandle EXPORT_ARGUMENT = new Lookup(MethodHandles.lookup()).findOwnStatic("exportArgument", Object.class, Object.class);
+
+    private final BeansLinker beansLinker = new BeansLinker();
+
+    @Override
+    public GuardedInvocation getGuardedInvocation(final LinkRequest linkRequest, final LinkerServices linkerServices) throws Exception {
+        return getGuardedInvocation(beansLinker, linkRequest, linkerServices);
+    }
+
+    /**
+     * Delegates to the specified linker but injects its linker services wrapper so that it will apply all special
+     * conversions that this class does.
+     * @param delegateLinker the linker to which the actual work is delegated to.
+     * @param linkRequest the delegated link request
+     * @param linkerServices the original link services that will be augmented with special conversions
+     * @return the guarded invocation from the delegate, possibly augmented with special conversions
+     * @throws Exception if the delegate throws an exception
+     */
+    public static GuardedInvocation getGuardedInvocation(final GuardingDynamicLinker delegateLinker, final LinkRequest linkRequest, final LinkerServices linkerServices) throws Exception {
+        return delegateLinker.getGuardedInvocation(linkRequest, new NashornBeansLinkerServices(linkerServices));
+    }
+
+    static Object exportArgument(final Object arg) {
+        return arg instanceof ConsString ? arg.toString() : arg;
+    }
+
+    private static class NashornBeansLinkerServices implements LinkerServices {
+        private final LinkerServices linkerServices;
+
+        NashornBeansLinkerServices(final LinkerServices linkerServices) {
+            this.linkerServices = linkerServices;
+        }
+
+        @Override
+        public MethodHandle asType(final MethodHandle handle, final MethodType fromType) {
+            final MethodHandle typed = linkerServices.asType(handle, fromType);
+
+            final MethodType handleType = handle.type();
+            final int paramCount = handleType.parameterCount();
+            assert fromType.parameterCount() == handleType.parameterCount();
+
+            MethodHandle[] filters = null;
+            for(int i = 0; i < paramCount; ++i) {
+                if(shouldConvert(handleType.parameterType(i), fromType.parameterType(i))) {
+                    if(filters == null) {
+                        filters = new MethodHandle[paramCount];
+                    }
+                    filters[i] = EXPORT_ARGUMENT;
+                }
+            }
+
+            return filters != null ? MethodHandles.filterArguments(typed, 0, filters) : typed;
+        }
+
+        @Override
+        public MethodHandle asTypeLosslessReturn(final MethodHandle handle, final MethodType fromType) {
+            return Implementation.asTypeLosslessReturn(this, handle, fromType);
+        }
+
+        private static boolean shouldConvert(final Class<?> handleType, final Class<?> fromType) {
+            return handleType == Object.class && fromType == Object.class;
+        }
+
+        @Override
+        public MethodHandle getTypeConverter(final Class<?> sourceType, final Class<?> targetType) {
+            return linkerServices.getTypeConverter(sourceType, targetType);
+        }
+
+        @Override
+        public boolean canConvert(final Class<?> from, final Class<?> to) {
+            return linkerServices.canConvert(from, to);
+        }
+
+        @Override
+        public GuardedInvocation getGuardedInvocation(final LinkRequest linkRequest) throws Exception {
+            return linkerServices.getGuardedInvocation(linkRequest);
+        }
+
+        @Override
+        public Comparison compareConversion(final Class<?> sourceType, final Class<?> targetType1, final Class<?> targetType2) {
+            return linkerServices.compareConversion(sourceType, targetType1, targetType2);
+        }
+    }
+}