Add RequiresAlign8 to MethodTable

Author: am11

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/CastHelpers.cs

@@ -557,8 +557,13 @@ internal static object BoxImpl(MethodTable* typeMT, ref byte unboxedData)
             Debug.Assert(typeMT != null);
             Debug.Assert(typeMT->IsValueType);
 
+#if FEATURE_64BIT_ALIGNMENT
+            object boxed = typeMT->RequiresAlign8 ? (RuntimeTypeHandle.GetThreadLocalAllocInternal(typeMT) ??
+                RuntimeTypeHandle.InternalAllocNoChecks(typeMT)) : RuntimeTypeHandle.InternalAllocNoChecks(typeMT);
+#else
             object boxed = RuntimeTypeHandle.GetThreadLocalAllocInternal(typeMT) ??
                 RuntimeTypeHandle.InternalAllocNoChecks(typeMT);
+#endif
 
             if (typeMT->ContainsGCPointers)
             {

src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.CoreCLR.cs

@@ -755,6 +755,9 @@ internal unsafe struct MethodTable
         private const uint enum_flag_HasTypeEquivalence = 0x02000000;
 #endif // FEATURE_TYPEEQUIVALENCE
         private const uint enum_flag_HasFinalizer = 0x00100000;
+#if FEATURE_64BIT_ALIGNMENT
+        private const uint enum_flag_RequiresAlign8 = 0x00800000; // Type requires 8-byte alignment (only set on platforms that require this and don't get it implicitly)
+#endif
         private const uint enum_flag_Category_Mask = 0x000F0000;
         private const uint enum_flag_Category_ValueType = 0x00040000;
         private const uint enum_flag_Category_Nullable = 0x00050000;
@@ -815,6 +818,10 @@ internal unsafe struct MethodTable
 
         public bool HasFinalizer => (Flags & enum_flag_HasFinalizer) != 0;
 
+#if FEATURE_64BIT_ALIGNMENT
+        public bool RequiresAlign8 => (Flags & enum_flag_RequiresAlign8) != 0;
+#endif
+
         internal static bool AreSameType(MethodTable* mt1, MethodTable* mt2) => mt1 == mt2;
 
         public bool HasDefaultConstructor => (Flags & (enum_flag_HasComponentSize | enum_flag_HasDefaultCtor)) == enum_flag_HasDefaultCtor;

src/coreclr/clr.featuredefines.props

@@ -26,6 +26,10 @@
         <FeatureEHFunclets>true</FeatureEHFunclets>
     </PropertyGroup>
 
+    <PropertyGroup Condition="'$(TargetArchitecture)' == 'arm' OR '$(TargetArchitecture)' == 'armel' OR '$(TargetArchitecture)' == 'wasm'">
+        <Feature64BitAlignmentRequired>true</Feature64BitAlignmentRequired>
+    </PropertyGroup>
+
     <PropertyGroup>
         <DefineConstants Condition="'$(FeatureComWrappers)' == 'true'">$(DefineConstants);FEATURE_COMWRAPPERS</DefineConstants>
         <DefineConstants Condition="'$(FeatureCominterop)' == 'true'">$(DefineConstants);FEATURE_COMINTEROP</DefineConstants>
@@ -36,6 +40,7 @@
         <DefineConstants Condition="'$(FeatureXplatEventSource)' == 'true'">$(DefineConstants);FEATURE_EVENTSOURCE_XPLAT</DefineConstants>
         <DefineConstants Condition="'$(FeatureTypeEquivalence)' == 'true'">$(DefineConstants);FEATURE_TYPEEQUIVALENCE</DefineConstants>
         <DefineConstants Condition="'$(FeatureEHFunclets)' == 'true'">$(DefineConstants);FEATURE_EH_FUNCLETS</DefineConstants>
+        <DefineConstants Condition="'$(Feature64BitAlignmentRequired)' == 'true'">$(DefineConstants);FEATURE_64BIT_ALIGNMENT</DefineConstants>
 
         <DefineConstants Condition="'$(ProfilingSupportedBuild)' == 'true'">$(DefineConstants);PROFILING_SUPPORTED</DefineConstants>
     </PropertyGroup>