--- a/src/hotspot/share/runtime/os.cpp	Wed Jan 30 18:21:06 2019 +0000
+++ b/src/hotspot/share/runtime/os.cpp	Wed Jan 30 19:45:10 2019 +0100
@@ -885,11 +885,15 @@
   address p = start;
   st->print(PTR_FORMAT ":   ", p2i(start));
   while (p < end) {
-    switch (unitsize) {
-      case 1: st->print("%02x", *(u1*)p); break;
-      case 2: st->print("%04x", *(u2*)p); break;
-      case 4: st->print("%08x", *(u4*)p); break;
-      case 8: st->print("%016" FORMAT64_MODIFIER "x", *(u8*)p); break;
+    if (is_readable_pointer(p)) {
+      switch (unitsize) {
+        case 1: st->print("%02x", *(u1*)p); break;
+        case 2: st->print("%04x", *(u2*)p); break;
+        case 4: st->print("%08x", *(u4*)p); break;
+        case 8: st->print("%016" FORMAT64_MODIFIER "x", *(u8*)p); break;
+      }
+    } else {
+      st->print("%*.*s", 2*unitsize, 2*unitsize, "????????????????");
     }
     p += unitsize;
     cols++;