8325870: Zap end padding bits for ArrayOops in non-release builds

src/hotspot/share/gc/shared/memAllocator.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2024, 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
@@ -41,6 +41,7 @@
 #include "services/lowMemoryDetector.hpp"
 #include "utilities/align.hpp"
 #include "utilities/copy.hpp"
+#include "utilities/globalDefinitions.hpp"
 
 class MemAllocator::Allocation: StackObj {
   friend class MemAllocator;
@@ -408,11 +409,30 @@ oop ObjArrayAllocator::initialize(HeapWord* mem) const {
   assert(_length >= 0, "length should be non-negative");
   if (_do_zero) {
     mem_clear(mem);
+    mem_zap_end_padding(mem);
   }
   arrayOopDesc::set_length(mem, _length);
   return finish(mem);
 }
 
+#ifndef PRODUCT
+void ObjArrayAllocator::mem_zap_end_padding(HeapWord* mem) const {
+  const size_t length_in_bytes = static_cast<size_t>(_length) << ArrayKlass::cast(_klass)->log2_element_size();
+  const BasicType element_type = ArrayKlass::cast(_klass)->element_type();
+  const size_t base_offset_in_bytes = arrayOopDesc::base_offset_in_bytes(element_type);
+  const size_t size_in_bytes = _word_size * BytesPerWord;
+
+  const address obj_end = reinterpret_cast<address>(mem) + size_in_bytes;
+  const address base = reinterpret_cast<address>(mem) + base_offset_in_bytes;
+  const address elements_end = base + length_in_bytes;
+  assert(elements_end <= obj_end, "payload must fit in object");
+  if (elements_end < obj_end) {
+    const size_t padding_in_bytes = obj_end - elements_end;
+    Copy::fill_to_bytes(elements_end, padding_in_bytes, heapPaddingByteVal);
+  }
+}
+#endif
+
 oop ClassAllocator::initialize(HeapWord* mem) const {
   // Set oop_size field before setting the _klass field because a
   // non-null _klass field indicates that the object is parsable by

src/hotspot/share/gc/shared/memAllocator.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2024, 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
@@ -98,6 +98,8 @@ class ObjArrayAllocator: public MemAllocator {
   const int  _length;
   const bool _do_zero;
 
+  void mem_zap_end_padding(HeapWord* mem) const PRODUCT_RETURN;
+
 public:
   ObjArrayAllocator(Klass* klass, size_t word_size, int length, bool do_zero,
                     Thread* thread = Thread::current())

src/hotspot/share/gc/z/zObjArrayAllocator.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024, 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
@@ -132,6 +132,8 @@ oop ZObjArrayAllocator::initialize(HeapWord* mem) const {
     assert(result, "Array initialization should always succeed the second time");
   }
 
+  mem_zap_end_padding(mem);
+
   ZThreadLocalData::clear_invisible_root(_thread);
 
   // Signal to the ZIterator that this is no longer an invisible root

src/hotspot/share/utilities/globalDefinitions.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2024, 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
@@ -1025,19 +1025,20 @@ enum LockingMode {
 //----------------------------------------------------------------------------------------------------
 // Special constants for debugging
 
-const jint     badInt           = -3;                       // generic "bad int" value
-const intptr_t badAddressVal    = -2;                       // generic "bad address" value
-const intptr_t badOopVal        = -1;                       // generic "bad oop" value
-const intptr_t badHeapOopVal    = (intptr_t) CONST64(0x2BAD4B0BBAADBABE); // value used to zap heap after GC
-const int      badStackSegVal   = 0xCA;                     // value used to zap stack segments
-const int      badHandleValue   = 0xBC;                     // value used to zap vm handle area
-const int      badResourceValue = 0xAB;                     // value used to zap resource area
-const int      freeBlockPad     = 0xBA;                     // value used to pad freed blocks.
-const int      uninitBlockPad   = 0xF1;                     // value used to zap newly malloc'd blocks.
-const juint    uninitMetaWordVal= 0xf7f7f7f7;               // value used to zap newly allocated metachunk
-const juint    badHeapWordVal   = 0xBAADBABE;               // value used to zap heap after GC
-const juint    badMetaWordVal   = 0xBAADFADE;               // value used to zap metadata heap after GC
-const int      badCodeHeapNewVal= 0xCC;                     // value used to zap Code heap at allocation
+const jint     badInt             = -3;                     // generic "bad int" value
+const intptr_t badAddressVal      = -2;                     // generic "bad address" value
+const intptr_t badOopVal          = -1;                     // generic "bad oop" value
+const intptr_t badHeapOopVal      = (intptr_t) CONST64(0x2BAD4B0BBAADBABE); // value used to zap heap after GC
+const int      badStackSegVal     = 0xCA;                   // value used to zap stack segments
+const int      badHandleValue     = 0xBC;                   // value used to zap vm handle area
+const int      badResourceValue   = 0xAB;                   // value used to zap resource area
+const int      freeBlockPad       = 0xBA;                   // value used to pad freed blocks.
+const int      uninitBlockPad     = 0xF1;                   // value used to zap newly malloc'd blocks.
+const juint    uninitMetaWordVal  = 0xf7f7f7f7;             // value used to zap newly allocated metachunk
+const jubyte   heapPaddingByteVal = 0xBD;                   // value used to zap object padding in the heap
+const juint    badHeapWordVal     = 0xBAADBABE;             // value used to zap heap after GC
+const juint    badMetaWordVal     = 0xBAADFADE;             // value used to zap metadata heap after GC
+const int      badCodeHeapNewVal  = 0xCC;                   // value used to zap Code heap at allocation
 const int      badCodeHeapFreeVal = 0xDD;                   // value used to zap Code heap at deallocation
 const intptr_t badDispHeaderDeopt = 0xDE0BD000;             // value to fill unused displaced header during deoptimization
 const intptr_t badDispHeaderOSR   = 0xDEAD05A0;             // value to fill unused displaced header during OSR