--- a/hotspot/src/share/vm/runtime/arguments.cpp	Thu Jun 30 00:19:48 2016 +0000
+++ b/hotspot/src/share/vm/runtime/arguments.cpp	Wed Jun 29 16:11:50 2016 +0200
@@ -584,27 +584,26 @@
 // Parses a size specification string.
 bool Arguments::atojulong(const char *s, julong* result) {
   julong n = 0;
-  int args_read = 0;
-  bool is_hex = false;
-  // Skip leading 0[xX] for hexadecimal
-  if (*s =='0' && (*(s+1) == 'x' || *(s+1) == 'X')) {
-    s += 2;
-    is_hex = true;
-    args_read = sscanf(s, JULONG_FORMAT_X, &n);
-  } else {
-    args_read = sscanf(s, JULONG_FORMAT, &n);
-  }
-  if (args_read != 1) {
+
+  // First char must be a digit. Don't allow negative numbers or leading spaces.
+  if (!isdigit(*s)) {
     return false;
   }
-  while (*s != '\0' && (isdigit(*s) || (is_hex && isxdigit(*s)))) {
-    s++;
-  }
-  // 4705540: illegal if more characters are found after the first non-digit
-  if (strlen(s) > 1) {
+
+  bool is_hex = (s[0] == '0' && (s[1] == 'x' || s[1] == 'X'));
+  char* remainder;
+  errno = 0;
+  n = strtoull(s, &remainder, (is_hex ? 16 : 10));
+  if (errno != 0) {
     return false;
   }
-  switch (*s) {
+
+  // Fail if no number was read at all or if the remainder contains more than a single non-digit character.
+  if (remainder == s || strlen(remainder) > 1) {
+    return false;
+  }
+
+  switch (*remainder) {
     case 'T': case 't':
       *result = n * G * K;
       // Check for overflow.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/test/native/runtime/test_arguments.cpp	Wed Jun 29 16:11:50 2016 +0200
@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2016, 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.
+ *
+ */
+#include "precompiled.hpp"
+#include "runtime/arguments.hpp"
+#include "unittest.hpp"
+#include "utilities/globalDefinitions.hpp"
+
+TEST(arguments, atojulong) {
+  char ullong_max[32];
+  int ret = jio_snprintf(ullong_max, sizeof(ullong_max), JULONG_FORMAT, ULLONG_MAX);
+  ASSERT_NE(-1, ret);
+
+  julong value;
+  const char* invalid_strings[] = {
+    "", "-1", "-100", " 1", "2 ", "3 2", "1.0",
+    "0x4.5", "0x", "0x0x1" "0.001", "4e10", "e"
+    "K", "M", "G", "1MB", "1KM", "AA", "0B",
+    "18446744073709551615K", "17179869184G",
+    "999999999999999999999999999999"
+  };
+  for (uint i = 0; i < ARRAY_SIZE(invalid_strings); i++) {
+    ASSERT_FALSE(Arguments::atojulong(invalid_strings[i], &value))
+        << "Invalid string '" << invalid_strings[i] << "' parsed without error.";
+  }
+
+  struct {
+    const char* str;
+    julong expected_value;
+  } valid_strings[] = {
+      { "0", 0 },
+      { "4711", 4711 },
+      { "1K", 1ULL * K },
+      { "1k", 1ULL * K },
+      { "2M", 2ULL * M },
+      { "2m", 2ULL * M },
+      { "4G", 4ULL * G },
+      { "4g", 4ULL * G },
+      { "0K", 0 },
+      { ullong_max, ULLONG_MAX },
+      { "0xcafebabe", 0xcafebabe },
+      { "0XCAFEBABE", 0xcafebabe },
+      { "0XCAFEbabe", 0xcafebabe },
+      { "0x10K", 0x10 * K }
+  };
+  for (uint i = 0; i < ARRAY_SIZE(valid_strings); i++) {
+    ASSERT_TRUE(Arguments::atojulong(valid_strings[i].str, &value))
+        << "Valid string '" << valid_strings[i].str << "' did not parse.";
+    ASSERT_EQ(valid_strings[i].expected_value, value);
+  }
+}