8297534: Specify the size of MEMFLAGS

Reviewed-by: stuefe, tschatzl

src/hotspot/share/memory/allocation.hpp

@@ -26,6 +26,7 @@
 #define SHARE_MEMORY_ALLOCATION_HPP
 
 #include "memory/allStatic.hpp"
+#include "utilities/debug.hpp"
 #include "utilities/globalDefinitions.hpp"
 #include "utilities/macros.hpp"
 
@@ -138,11 +139,13 @@ typedef AllocFailStrategy::AllocFailEnum AllocFailType;
 /*
  * Memory types
  */
-enum class MEMFLAGS {
+enum class MEMFLAGS : uint8_t  {
   MEMORY_TYPES_DO(MEMORY_TYPE_DECLARE_ENUM)
   mt_number_of_types   // number of memory types (mtDontTrack
                        // is not included as validate type)
 };
+// Extra insurance that MEMFLAGS truly has the same size as uint8_t.
+STATIC_ASSERT(sizeof(MEMFLAGS) == sizeof(uint8_t));
 
 #define MEMORY_TYPE_SHORTNAME(type, human_readable) \
   constexpr MEMFLAGS type = MEMFLAGS::type;

src/hotspot/share/services/mallocHeader.hpp

@@ -92,7 +92,7 @@ class MallocHeader {
   NOT_LP64(uint32_t _alt_canary);
   const size_t _size;
   const uint32_t _mst_marker;
-  const uint8_t _flags;
+  const MEMFLAGS _flags;
   const uint8_t _unused;
   uint16_t _canary;
 
@@ -119,7 +119,7 @@ class MallocHeader {
   inline MallocHeader(size_t size, MEMFLAGS flags, uint32_t mst_marker);
 
   inline size_t   size()  const { return _size; }
-  inline MEMFLAGS flags() const { return (MEMFLAGS)_flags; }
+  inline MEMFLAGS flags() const { return _flags; }
   inline uint32_t mst_marker() const { return _mst_marker; }
   bool get_stack(NativeCallStack& stack) const;
 

src/hotspot/share/services/mallocHeader.inline.hpp

@@ -35,7 +35,7 @@
 #include "utilities/nativeCallStack.hpp"
 
 inline MallocHeader::MallocHeader(size_t size, MEMFLAGS flags, uint32_t mst_marker)
-  : _size(size), _mst_marker(mst_marker), _flags(NMTUtil::flag_to_index(flags)),
+  : _size(size), _mst_marker(mst_marker), _flags(flags),
     _unused(0), _canary(_header_canary_life_mark)
 {
   assert(size < max_reasonable_malloc_size, "Too large allocation size?");