--- a/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Modules.java	Wed Apr 19 11:36:44 2017 +0200
+++ b/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Modules.java	Wed Apr 19 13:38:36 2017 +0200
@@ -194,7 +194,13 @@
 
         lintOptions = options.isUnset(Option.XLINT_CUSTOM, "-" + LintCategory.OPTIONS.option);
 
-        legacyModuleOverride = options.get(Option.XMODULE);
+        Collection<String> xmodules = options.keySet()
+                                             .stream()
+                                             .filter(opt -> opt.startsWith(XMODULES_PREFIX))
+                                             .map(opt -> opt.substring(XMODULES_PREFIX.length()))
+                                             .collect(Collectors.toList());
+
+        legacyModuleOverride = xmodules.size() == 1 ? xmodules.iterator().next() : null;
 
         multiModuleMode = fileManager.hasLocation(StandardLocation.MODULE_SOURCE_PATH);
         ClassWriter classWriter = ClassWriter.instance(context);
@@ -211,6 +217,8 @@
         limitModsOpt = options.get(Option.LIMIT_MODULES);
         moduleVersionOpt = options.get(Option.MODULE_VERSION);
     }
+    //where
+        private static final String XMODULES_PREFIX = "-Xmodule:";
 
     int depth = -1;
     private void dprintln(String msg) {

--- a/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/main/Option.java	Wed Apr 19 11:36:44 2017 +0200
+++ b/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/main/Option.java	Wed Apr 19 13:38:36 2017 +0200
@@ -603,17 +603,6 @@
         }
     },
 
-    XMODULE("-Xmodule:", "opt.arg.module", "opt.module", HIDDEN, BASIC) {
-        @Override
-        public void process(OptionHelper helper, String option, String arg) throws InvalidValueException {
-            String prev = helper.get(XMODULE);
-            if (prev != null) {
-                throw helper.newInvalidValueException("err.option.too.many", XMODULE.primaryName);
-            }
-            helper.put(XMODULE.primaryName, arg);
-        }
-    },
-
     MODULE("--module -m", "opt.arg.m", "opt.m", STANDARD, BASIC),
 
     ADD_MODULES("--add-modules", "opt.arg.addmods", "opt.addmods", STANDARD, BASIC) {

--- a/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/resources/javac.properties	Wed Apr 19 11:36:44 2017 +0200
+++ b/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/resources/javac.properties	Wed Apr 19 13:38:36 2017 +0200
@@ -312,10 +312,6 @@
     in JAR files or directories
 javac.opt.arg.patch=\
     <module>=<file>(:<file>)*
-javac.opt.module=\
-    Specify a module to which the classes being compiled belong.
-javac.opt.arg.module=\
-    <module>
 javac.opt.addmods=\
     Root modules to resolve in addition to the initial modules, or all modules\n\
     on the module path if <module> is ALL-MODULE-PATH.

--- a/langtools/test/TEST.ROOT	Wed Apr 19 11:36:44 2017 +0200
+++ b/langtools/test/TEST.ROOT	Wed Apr 19 13:38:36 2017 +0200
@@ -19,3 +19,6 @@
 
 # Use new module options
 useNewOptions=true
+
+# Use --patch-module instead of -Xmodule:
+useNewPatchModule=true

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/test/tools/javac/modules/LegacyXModuleTest.java	Wed Apr 19 13:38:36 2017 +0200
@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2017, 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
+ * @bug 8178012
+ * @summary tests for multi-module mode compilation
+ * @library /tools/lib
+ * @modules
+ *      jdk.compiler/com.sun.tools.javac.api
+ *      jdk.compiler/com.sun.tools.javac.main
+ * @build toolbox.ToolBox toolbox.JavacTask toolbox.ModuleBuilder ModuleTestBase
+ * @run main LegacyXModuleTest
+ */
+
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+
+import toolbox.JavacTask;
+import toolbox.Task;
+
+public class LegacyXModuleTest extends ModuleTestBase {
+
+    public static void main(String... args) throws Exception {
+        new LegacyXModuleTest().runTests();
+    }
+
+    @Test
+    public void testLegacyXModule(Path base) throws Exception {
+        //note: avoiding use of java.base, as that gets special handling on some places:
+        Path src = base.resolve("src");
+        tb.writeJavaFiles(src, "package com.sun.tools.javac.comp; public class Extra { Modules modules; }");
+        Path classes = base.resolve("classes");
+        tb.createDirectories(classes);
+
+        new JavacTask(tb)
+            .options("-XD-Xmodule:jdk.compiler")
+            .outdir(classes)
+            .files(findJavaFiles(src))
+            .run()
+            .writeAll()
+            .getOutput(Task.OutputKind.DIRECT);
+
+        List<String> log = new JavacTask(tb)
+                .options("-XD-Xmodule:java.compiler",
+                         "-XD-Xmodule:jdk.compiler",
+                         "-XDrawDiagnostics")
+                .outdir(classes)
+                .files(findJavaFiles(src))
+                .run(Task.Expect.FAIL)
+                .writeAll()
+                .getOutputLines(Task.OutputKind.DIRECT);
+
+        List<String> actual =
+                Arrays.asList("Extra.java:1:56: compiler.err.cant.resolve.location: kindname.class, Modules, , , " +
+                                                "(compiler.misc.location: kindname.class, com.sun.tools.javac.comp.Extra, null)",
+                              "1 error");
+
+        if (!Objects.equals(actual, log))
+            throw new Exception("expected output not found: " + log);
+    }
+
+}