--- a/hotspot/src/share/vm/gc_implementation/g1/concurrentMark.cpp	Wed Sep 11 10:14:32 2013 +0200
+++ b/hotspot/src/share/vm/gc_implementation/g1/concurrentMark.cpp	Wed Sep 11 10:19:16 2013 +0200
@@ -481,9 +481,8 @@
 
 ConcurrentMark::ConcurrentMark(G1CollectedHeap* g1h, ReservedSpace heap_rs) :
   _g1h(g1h),
-  _markBitMap1(MinObjAlignment - 1),
-  _markBitMap2(MinObjAlignment - 1),
-
+  _markBitMap1(log2_intptr(MinObjAlignment)),
+  _markBitMap2(log2_intptr(MinObjAlignment)),
   _parallel_marking_threads(0),
   _max_parallel_marking_threads(0),
   _sleep_factor(0.0),

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/test/gc/TestObjectAlignment.java	Wed Sep 11 10:19:16 2013 +0200
@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 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.
+ *
+ * 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 TestObjectAlignment
+ * @key gc
+ * @bug 8021823
+ * @summary G1: Concurrent marking crashes with -XX:ObjectAlignmentInBytes>=32 in 64bit VMs
+ * @library /testlibrary
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:+ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=8
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:+ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=16
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:+ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=32
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:+ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=64
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:+ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=128
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:+ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=256
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:-ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=8
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:-ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=16
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:-ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=32
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:-ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=64
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:-ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=128
+ * @run main/othervm TestObjectAlignment -Xmx20M -XX:-ExplicitGCInvokesConcurrent -XX:+IgnoreUnrecognizedVMOptions -XX:ObjectAlignmentInBytes=256
+ */
+
+import com.oracle.java.testlibrary.ProcessTools;
+import com.oracle.java.testlibrary.OutputAnalyzer;
+
+public class TestObjectAlignment {
+
+  public static byte[] garbage;
+
+  private static boolean runsOn32bit() {
+    return System.getProperty("sun.arch.data.model").equals("32");
+  }
+
+  public static void main(String[] args) throws Exception {
+    if (runsOn32bit()) {
+      // 32 bit VMs do not allow setting ObjectAlignmentInBytes, so there is nothing to test. We still get called.
+      return;
+    }
+    for (int i = 0; i < 10; i++) {
+      garbage = new byte[1000];
+      System.gc();
+    }
+  }
+}