8274322: Problems with oopDesc construction

Reviewed-by: dholmes, stefank

src/hotspot/share/oops/instanceOop.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2021, 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
@@ -26,6 +26,7 @@
 #define SHARE_OOPS_INSTANCEOOP_HPP
 
 #include "oops/oop.hpp"
+#include <type_traits>
 
 // An instanceOop is an instance of a Java Class
 // Evaluating "new HashTable()" will create an instanceOop.
@@ -44,4 +45,7 @@ class instanceOopDesc : public oopDesc {
   }
 };
 
+// See similar requirement for oopDesc.
+static_assert(std::is_trivially_default_constructible<instanceOopDesc>::value, "required");
+
 #endif // SHARE_OOPS_INSTANCEOOP_HPP

src/hotspot/share/oops/markWord.hpp

@@ -73,10 +73,13 @@ class markWord {
  public:
   explicit markWord(uintptr_t value) : _value(value) {}
 
-  markWord() { /* uninitialized */}
+  markWord() = default;         // Doesn't initialize _value.
 
   // It is critical for performance that this class be trivially
   // destructable, copyable, and assignable.
+  ~markWord() = default;
+  markWord(const markWord&) = default;
+  markWord& operator=(const markWord&) = default;
 
   static markWord from_pointer(void* ptr) {
     return markWord((uintptr_t)ptr);

src/hotspot/share/oops/objArrayOop.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2021, 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
@@ -27,6 +27,7 @@
 
 #include "oops/arrayOop.hpp"
 #include "utilities/align.hpp"
+#include <type_traits>
 
 class Klass;
 
@@ -109,4 +110,7 @@ public:
   void oop_iterate_range(OopClosureType* blk, int start, int end);
 };
 
+// See similar requirement for oopDesc.
+static_assert(std::is_trivially_default_constructible<objArrayOopDesc>::value, "required");
+
 #endif // SHARE_OOPS_OBJARRAYOOP_HPP

src/hotspot/share/oops/oop.hpp

@@ -31,7 +31,9 @@
 #include "oops/markWord.hpp"
 #include "oops/metadata.hpp"
 #include "runtime/atomic.hpp"
+#include "utilities/globalDefinitions.hpp"
 #include "utilities/macros.hpp"
+#include <type_traits>
 
 // oopDesc is the top baseclass for objects classes. The {name}Desc classes describe
 // the format of Java objects so the fields can be accessed from C++.
@@ -57,7 +59,14 @@ class oopDesc {
     narrowKlass _compressed_klass;
   } _metadata;
 
+  // There may be ordering constraints on the initialization of fields that
+  // make use of the C++ copy/assign incorrect.
+  NONCOPYABLE(oopDesc);
+
  public:
+  // Must be trivial; see verifying static assert after the class.
+  oopDesc() = default;
+
   inline markWord  mark()          const;
   inline markWord  mark_acquire()  const;
   inline markWord* mark_addr() const;
@@ -311,4 +320,11 @@ class oopDesc {
   DEBUG_ONLY(bool get_UseG1GC();)
 };
 
+// An oopDesc is not initialized via a constructor.  Space is allocated in
+// the Java heap, and static functions provided here on HeapWord* are used
+// to fill in certain parts of that memory.  The allocated memory is then
+// treated as referring to an oopDesc.  For that to be valid, the oopDesc
+// class must have a trivial default constructor (C++14 3.8/1).
+static_assert(std::is_trivially_default_constructible<oopDesc>::value, "required");
+
 #endif // SHARE_OOPS_OOP_HPP

src/hotspot/share/oops/typeArrayOop.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2021, 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
@@ -27,6 +27,7 @@
 
 #include "oops/arrayOop.hpp"
 #include "oops/typeArrayKlass.hpp"
+#include <type_traits>
 
 // A typeArrayOop is an array containing basic types (non oop elements).
 // It is used for arrays of {characters, singles, doubles, bytes, shorts, integers, longs}
@@ -134,4 +135,7 @@ private:
   inline int object_size(const TypeArrayKlass* tk) const;
 };
 
+// See similar requirement for oopDesc.
+static_assert(std::is_trivially_default_constructible<typeArrayOopDesc>::value, "required");
+
 #endif // SHARE_OOPS_TYPEARRAYOOP_HPP