8031686: G1: assert(_hrs.max_length() == _expansion_regions) failed

Summary: Using pointer_delta to avoid overflowing pointer calculation.
Reviewed-by: jwilhelm, ehelin

src/share/vm/gc_implementation/g1/g1BiasedArray.hpp

@@ -75,7 +75,7 @@ protected:
     assert((uintptr_t)end % mapping_granularity_in_bytes == 0,
       err_msg("end mapping area address must be a multiple of mapping granularity %zd, is " PTR_FORMAT,
         mapping_granularity_in_bytes, p2i(end)));
-    size_t num_target_elems = (end - bottom) / (mapping_granularity_in_bytes / HeapWordSize);
+    size_t num_target_elems = pointer_delta(end, bottom, mapping_granularity_in_bytes);
     idx_t bias = (uintptr_t)bottom / mapping_granularity_in_bytes;
     address base = create_new_base_array(num_target_elems, target_elem_size_in_bytes);
     initialize_base(base, num_target_elems, bias, target_elem_size_in_bytes, log2_intptr(mapping_granularity_in_bytes));

test/gc/g1/Test2GbHeap.java

+/*
+ * Copyright (c) 2014, 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 Test2GbHeap
+ * @bug 8031686
+ * @summary Regression test to ensure we can start G1 with 2gb heap.
+ * @key gc
+ * @key regression
+ * @library /testlibrary
+ */
+
+import java.util.ArrayList;
+
+import com.oracle.java.testlibrary.OutputAnalyzer;
+import com.oracle.java.testlibrary.ProcessTools;
+
+public class Test2GbHeap {
+  public static void main(String[] args) throws Exception {
+    ArrayList<String> testArguments = new ArrayList<String>();
+
+    testArguments.add("-XX:+UseG1GC");
+    testArguments.add("-Xmx2g");
+    testArguments.add("-version");
+
+    ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(testArguments.toArray(new String[0]));
+
+    OutputAnalyzer output = new OutputAnalyzer(pb.start());
+
+    // Avoid failing test for setups not supported.
+    if (output.getOutput().contains("Could not reserve enough space for 2097152KB object heap")) {
+      // Will fail on machines with too little memory (and Windows 32-bit VM), ignore such failures.
+      output.shouldHaveExitValue(1);
+    } else if (output.getOutput().contains("G1 GC is disabled in this release")) {
+      // G1 is not supported on embedded, ignore such failures.
+      output.shouldHaveExitValue(1);
+    } else {
+      // Normally everything should be fine.
+      output.shouldHaveExitValue(0);
+    }
+  }
+}