Use os::is_readable_range().

Author: TheRealMDoerr

src/hotspot/share/memory/guardedMemory.hpp

@@ -26,6 +26,7 @@
 #define SHARE_MEMORY_GUARDEDMEMORY_HPP
 
 #include "memory/allocation.hpp"
+#include "runtime/os.hpp"
 #include "runtime/safefetch.hpp"
 #include "utilities/globalDefinitions.hpp"
 
@@ -113,14 +114,14 @@ class GuardedMemory : StackObj { // Wrapper on stack
     }
 
     bool verify() const {
+      // We may not be able to dereference directly.
+      if (!os::is_readable_range((const void*) _guard, (const void*) (_guard + GUARD_SIZE))) {
+        return false;
+      }
       u_char* c = (u_char*) _guard;
       u_char* end = c + GUARD_SIZE;
       while (c < end) {
-        // We may not be able to dereference directly so use
-        // SafeFetch. It doesn't matter if the value read happens
-        // to be 0xFF as that is not what we expect anyway.
-        u_char val = (u_char) (SafeFetch32((int*)c, 0xFF) BIG_ENDIAN_ONLY(>> 24));
-        if (val != badResourceValue) {
+        if (*c != badResourceValue) {
           return false;
         }
         c++;