--- /dev/null	2018-08-14 18:25:04.628316445 -0700
+++ new/test/hotspot/jtreg/runtime/SharedArchiveFile/serviceability/ReplaceCriticalClasses.java	2018-10-21 22:34:23.709124227 -0700
@@ -0,0 +1,221 @@
+/*
+ * Copyright (c) 2018, 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.
+ *
+ * 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.
+ *
+ */
+
+/*
+ * @test
+ * @summary Tests how CDS works when critical library classes are replaced with JVMTI ClassFileLoadHook
+ * @library /test/lib
+ * @requires vm.cds
+ * @build sun.hotspot.WhiteBox
+ * @run driver ClassFileInstaller -jar whitebox.jar sun.hotspot.WhiteBox
+ * @run main/othervm/native ReplaceCriticalClasses
+ */
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import jdk.test.lib.cds.CDSTestUtils;
+import jdk.test.lib.cds.CDSOptions;
+import jdk.test.lib.process.OutputAnalyzer;
+import sun.hotspot.WhiteBox;
+
+public class ReplaceCriticalClasses {
+    public static void main(String args[]) throws Throwable {
+        if (args.length == 0) {
+            launchChildProcesses();
+        } else if (args.length == 3 && args[0].equals("child")) {
+            Class klass = Class.forName(args[2].replace("/", "."));
+            if (args[1].equals("-shared")) {
+                testInChild(true, klass);
+            } else if (args[1].equals("-notshared")) {
+                testInChild(false, klass);
+            } else {
+                throw new RuntimeException("Unknown child exec option " + args[1]);
+            }
+            return;
+        } else {
+            throw new RuntimeException("Usage: @run main/othervm/native ReplaceCriticalClasses");
+        }
+    }
+
+    static void launchChildProcesses() throws Throwable {
+        String tests[] = {
+            // CDS should be disabled -- these critical classes will be replaced
+            // because JvmtiExport::early_class_hook_env() is true.
+            "-early -notshared java/lang/Object",
+            "-early -notshared java/lang/String",
+            "-early -notshared java/lang/Cloneable",
+            "-early -notshared java/io/Serializable",
+
+            // CDS should not be disabled -- these critical classes cannot be replaced because JvmtiExport::early_class_hook_env() is false.
+            "java/lang/Object",
+            "java/lang/String",
+            "java/lang/Cloneable",
+            "java/io/Serializable",
+
+            // Try to replace classes that are used by the archived subgraph graphs.
+            "-subgraph java/util/ArrayList",
+            "-subgraph java/lang/module/ResolvedModule",
+
+            // Replace classes that are loaded after JVMTI_PHASE_PRIMORDIAL. It's OK to replace such
+            // classes even when CDS is enabled. Nothing bad should happen.
+            "-notshared jdk/internal/vm/PostVMInitHook",
+            "-notshared java/util/Locale",
+            "-notshared sun/util/locale/BaseLocale",
+            "-notshared java/lang/Readable",
+        };
+
+        int n = 0;
+        for (String s : tests) {
+            System.out.println("Test case[" + (n++) + "] = \"" + s + "\"");
+            String args[] = s.split("\\s+"); // split by space character
+            launchChild(args);
+        }
+    }
+
+    static void launchChild(String args[]) throws Throwable {
+        if (args.length < 1) {
+            throw new RuntimeException("Invalid test case. Should be <-early> <-subgraph> <-notshared> klassName");
+        }
+        String klassName = null;
+        String early = "";
+        boolean subgraph = false;
+        String shared = "-shared";
+
+        for (int i=0; i<args.length-1; i++) {
+            String opt = args[i];
+            if (opt.equals("-early")) {
+                early = "-early,";
+            } else if (opt.equals("-subgraph")) {
+                subgraph = true;
+            } else if (opt.equals("-notshared")) {
+                shared = opt;
+            } else {
+                throw new RuntimeException("Unknown option: " + opt);
+            }
+        }
+        klassName = args[args.length-1];
+        Class.forName(klassName.replace("/", ".")); // make sure it's a valid class
+
+        // We will pass an option like "-agentlib:SimpleClassFileLoadHook=java/util/Locale,XXX,XXX".
+        // The SimpleClassFileLoadHook agent would attempt to hook the java/util/Locale class
+        // but leave the class file bytes unchanged (it replaces all bytes "XXX" with "XXX", i.e.,
+        // a no-op). JVMTI doesn't check the class file bytes returned by the agent, so as long
+        // as the agent returns a buffer, it will not load the class from CDS, and will instead
+        // load the class by parsing the buffer.
+        //
+        // Note that for safety we don't change the contents of the class file bytes. If in the
+        // future JVMTI starts checking the contents of the class file bytes, this test would need
+        // to be updated. (You'd see the test case with java/util/Locale staring to fail).
+        String agent = "-agentlib:SimpleClassFileLoadHook=" + early + klassName + ",XXX,XXX";
+
+        CDSOptions opts = new CDSOptions();
+        opts.setXShareMode("auto")
+            .addSuffix("-showversion")
+            .addSuffix("-Xlog:cds")
+            .addSuffix("-XX:+UnlockDiagnosticVMOptions")
+            .addSuffix(agent)
+            .addSuffix("-XX:+WhiteBoxAPI")
+            .addSuffix("-Xbootclasspath/a:" + ClassFileInstaller.getJarPath("whitebox.jar"));
+
+        if (subgraph) {
+            opts.addSuffix("-Xlog:cds+heap");
+            opts.addSuffix("-Xlog:class+load");
+        }
+
+        opts.addSuffix("ReplaceCriticalClasses")
+            .addSuffix("child")
+            .addSuffix(shared)
+            .addSuffix(klassName)
+            .setUseSystemArchive(true)
+            .setUseVersion(false);
+
+        final boolean expectDisable = !early.equals("");
+        final boolean checkSubgraph = subgraph;
+        CDSTestUtils.run(opts).assertNormalExit(out -> {
+                if (expectDisable) {
+                    out.shouldContain("UseSharedSpaces: CDS is disabled because early JVMTI ClassFileLoadHook is in use.");
+                    System.out.println("CDS disabled as expected");
+                }
+                if (checkSubgraph && false) {
+                    // As of 2018/10/21 the classes in the archived subgraphs won't be
+                    // replaced because all archived subgraphs were loaded in JVMTI_PHASE_PRIMORDIAL.
+                    //
+                    // This is the first class to be loaded after JVMTI has exited JVMTI_PHASE_PRIMORDIAL.
+                    // Make sure no subgraphs are loaded afterwards.
+                    //
+                    // Can't use out.shouldNotMatch() because that doesn't match across multiple lines.
+                    String firstNonPrimordialClass = "jdk.jfr.internal.EventWriter";
+                    String regexp = firstNonPrimordialClass + ".*initialize_from_archived_subgraph";
+                    Pattern regex = Pattern.compile(regexp, Pattern.DOTALL);
+                    Matcher matcher = regex.matcher(out.getStdout());
+                    if (matcher.find()) {
+                        out.reportDiagnosticSummary();
+                        throw new RuntimeException("'" + regexp
+                                                   + "' found in stdout: '" + matcher.group() + "' \n");
+                    }
+                }
+            });
+    }
+
+    static void testInChild(boolean shouldBeShared, Class klass) {
+        WhiteBox wb = WhiteBox.getWhiteBox();
+
+        if (shouldBeShared && !wb.isSharedClass(klass)) {
+            throw new RuntimeException(klass + " should be shared but but actually is not.");
+        }
+        if (!shouldBeShared && wb.isSharedClass(klass)) {
+            throw new RuntimeException(klass + " should not be shared but actually is.");
+        }
+        System.out.println("wb.isSharedClass(klass): " + wb.isSharedClass(klass) + " == " + shouldBeShared);
+
+        String strings[] = {
+            // interned strings from j.l.Object
+            "@",
+            "nanosecond timeout value out of range",
+            "timeoutMillis value is negative",
+
+            // interned strings from j.l.Integer
+            "0",
+            "0X",
+            "0x",
+            "int"
+        };
+
+        // Make sure the interned string table is same
+        for (String s : strings) {
+            String i = s.intern();
+            if (s != i) {
+                throw new RuntimeException("Interned string mismatch: \"" + s + "\" @ " + System.identityHashCode(s) +
+                                           " vs \"" + i + "\" @ " + System.identityHashCode(i));
+            }
+        }
+        // We have tried to use ClassFileLoadHook to replace critical library classes (which may
+        // may not have succeeded, depending on whether the agent has requested
+        // can_generate_all_class_hook_events/can_generate_early_class_hook_events capabilities).
+        //
+        // In any case, the JVM should have started properly (perhaps with CDS disabled) and
+        // the above operations should succeed.
+        System.out.println("If I can come to here without crashing, things should be OK");
+    }
+}