dotnet · jkoritzinsky · Apr 6, 2024 · Apr 2, 2024 · Apr 3, 2024 · Apr 3, 2024
diff --git a/...eclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.CoreCLR.cs b/...eclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.CoreCLR.cs
@@ -416,6 +416,48 @@ private static unsafe void DispatchTailCalls(
                 }
             }
         }
+
+        /// <summary>
+        /// Create a boxed object of the specified type from the data located at the target reference.
+        /// </summary>
+        /// <param name="target">The target data</param>
+        /// <param name="type">The type of box to create.</param>
+        /// <returns>A boxed object containing the specified data.</returns>
+        /// <exception cref="ArgumentNullException">The specified type handle is <c>null</c>.</exception>
+        /// <exception cref="ArgumentException">The specified type cannot have a boxed instance of itself created.</exception>
+        /// <exception cref="NotSupportedException">The passed in type is a by-ref-like type.</exception>
+        public static unsafe object? Box(ref byte target, RuntimeTypeHandle type)
+        {
+            if (type.IsNullHandle())
+                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.type);
+
+            TypeHandle handle = type.GetNativeTypeHandle();
+
+            if (handle.IsTypeDesc)
+                throw new ArgumentException(SR.Arg_TypeNotSupported);
+
+            MethodTable* pMT = handle.AsMethodTable();
+
+            if (pMT->ContainsGenericVariables)
+                throw new ArgumentException(SR.Arg_TypeNotSupported);
+
+            if (pMT->IsValueType)
+            {
+                if (pMT->IsByRefLike)
+                    throw new NotSupportedException(SR.NotSupported_ByRefLike);
+
+                if (MethodTable.AreSameType(pMT, (MethodTable*)RuntimeTypeHandle.ToIntPtr(typeof(void).TypeHandle)))
+                    throw new ArgumentException(SR.Arg_TypeNotSupported);
+
+                object? result = Box(pMT, ref target);
+                GC.KeepAlive(type);
+                return result;
+            }
+            else
+            {
+                return Unsafe.As<byte, object?>(ref target);
+            }
+        }
     }
     // Helper class to assist with unsafe pinning of arbitrary objects.
     // It's used by VM code.
@@ -523,6 +565,7 @@ internal unsafe struct MethodTable
 
         // WFLAGS_HIGH_ENUM
         private const uint enum_flag_ContainsPointers = 0x01000000;
+        private const uint enum_flag_ContainsGenericVariables = 0x20000000;
         private const uint enum_flag_HasComponentSize = 0x80000000;
         private const uint enum_flag_HasTypeEquivalence = 0x02000000;
         private const uint enum_flag_Category_Mask = 0x000F0000;
@@ -630,6 +673,8 @@ public bool IsConstructedGenericType
             }
         }
 
+        public bool ContainsGenericVariables => (Flags & enum_flag_ContainsGenericVariables) != 0;
+
         /// <summary>
         /// Gets a <see cref="TypeHandle"/> for the element type of the current type.
         /// </summary>

diff --git a/src/coreclr/System.Private.CoreLib/src/System/RuntimeHandles.cs b/src/coreclr/System.Private.CoreLib/src/System/RuntimeHandles.cs
@@ -87,6 +87,11 @@ internal bool IsNullHandle()
             return m_type == null;
         }
 
+        internal TypeHandle GetNativeTypeHandle()
+        {
+            return m_type.GetNativeTypeHandle();
+        }
+
         internal static bool IsTypeDefinition(RuntimeType type)
         {
             CorElementType corElemType = GetCorElementType(type);

@@ -120,6 +120,16 @@ public static T ReadUnaligned<T>(void* source)
             throw new PlatformNotSupportedException();
         }
 
+        /// <summary>
+        /// Reads a value of type <typeparamref name="T"/> from the given location.
+        /// </summary>
+        [Intrinsic]
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static T ReadUnaligned<T>(ref readonly byte source)
+        {
+            throw new PlatformNotSupportedException();
+        }
+
         /// <summary>
         /// Copies bytes from the source address to the destination address.
         /// </summary>

@@ -75,6 +75,9 @@ public static unsafe object RhNewArray(MethodTable* pEEType, int length)
         [RuntimeExport("RhBox")]
         public static unsafe object RhBox(MethodTable* pEEType, ref byte data)
         {
+            // A null can be passed for boxing of a null ref.
+            _ = Unsafe.ReadUnaligned<byte>(ref data);
+
             ref byte dataAdjustedForNullable = ref data;
 
             // Can box non-ByRefLike value types only (which also implies no finalizers).

@@ -361,6 +361,44 @@ public static unsafe object GetUninitializedObject(
 
             return RuntimeImports.RhNewObject(mt);
         }
+
+        /// <summary>
+        /// Create a boxed object of the specified type from the data located at the target reference.
+        /// </summary>
+        /// <param name="target">The target data</param>
+        /// <param name="type">The type of box to create.</param>
+        /// <returns>A boxed object containing the specified data.</returns>
+        /// <exception cref="ArgumentNullException">The specified type handle is <c>null</c>.</exception>
+        /// <exception cref="ArgumentException">The specified type cannot have a boxed instance of itself created.</exception>
+        /// <exception cref="NotSupportedException">The passed in type is a by-ref-like type.</exception>
+        public static unsafe object? Box(ref byte target, RuntimeTypeHandle type)
+        {
+            if (type.IsNull)
+                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.type);
+
+            MethodTable* mt = type.ToMethodTable();
+
+            if (mt->ElementType == EETypeElementType.Void || mt->IsGenericTypeDefinition || mt->IsByRef || mt->IsPointer || mt->IsFunctionPointer)
+                throw new ArgumentException(SR.Arg_TypeNotSupported);
+
+            if (mt->NumVtableSlots == 0)
+            {
+                // This is a type without a vtable or GCDesc. We must not allow creating an instance of it
+                throw ReflectionCoreExecution.ExecutionEnvironment.CreateMissingMetadataException(Type.GetTypeFromHandle(type));
+            }
+            // Paranoid check: not-meant-for-GC-heap types should be reliably identifiable by empty vtable.
+            Debug.Assert(!mt->ContainsGCPointers || RuntimeImports.RhGetGCDescSize(mt) != 0);
+
+            if (!mt->IsValueType)
+            {
+                return Unsafe.As<byte, object>(ref target);
+            }
+
+            if (mt->IsByRefLike)
+                throw new NotSupportedException(SR.NotSupported_ByRefLike);
+
+            return RuntimeImports.RhBox(mt, ref target);
+        }
     }
 
     // CLR arrays are laid out in memory as follows (multidimensional array bounds are optional):

@@ -50,23 +50,18 @@ internal static RuntimeTypeHandle RawTargetTypeToken(TypedReference value)
 
         public static unsafe object ToObject(TypedReference value)
         {
-            RuntimeTypeHandle typeHandle = value._typeHandle;
-            if (typeHandle.IsNull)
+            RuntimeTypeHandle handle = RawTargetTypeToken(value);
+
+            if (handle.IsNull)
                 ThrowHelper.ThrowArgumentException_ArgumentNull_TypedRefType();
 
-            MethodTable* eeType = typeHandle.ToMethodTable();
-            if (eeType->IsValueType)
-            {
-                return RuntimeImports.RhBox(eeType, ref value.Value);
-            }
-            else if (eeType->IsPointer || eeType->IsFunctionPointer)
+            MethodTable* mt = handle.ToMethodTable();
+            if (mt->IsPointer || mt->IsFunctionPointer)
             {
-                return RuntimeImports.RhBox(MethodTable.Of<UIntPtr>(), ref value.Value);
-            }
-            else
-            {
-                return Unsafe.As<byte, object>(ref value.Value);
+                handle = typeof(UIntPtr).TypeHandle;
             }
+
+            return RuntimeHelpers.Box(ref value.Value, handle);
         }
 
         public static void SetTypedReference(TypedReference target, object? value) { throw new NotSupportedException(); }

diff --git a/src/libraries/System.Runtime/ref/System.Runtime.cs b/src/libraries/System.Runtime/ref/System.Runtime.cs
@@ -13149,6 +13149,7 @@ public static partial class RuntimeHelpers
         [System.ObsoleteAttribute("OffsetToStringData has been deprecated. Use string.GetPinnableReference() instead.")]
         public static int OffsetToStringData { get { throw null; } }
         public static System.IntPtr AllocateTypeAssociatedMemory(System.Type type, int size) { throw null; }
+        public static object? Box(ref byte target, System.RuntimeTypeHandle type) { throw null; }
         public static System.ReadOnlySpan<T> CreateSpan<T>(System.RuntimeFieldHandle fldHandle) { throw null; }
         public static void EnsureSufficientExecutionStack() { }
         public static new bool Equals(object? o1, object? o2) { throw null; }

diff --git a/...Runtime/tests/System.Runtime.Tests/System/Runtime/CompilerServices/RuntimeHelpersTests.cs b/...Runtime/tests/System.Runtime.Tests/System/Runtime/CompilerServices/RuntimeHelpersTests.cs
@@ -437,6 +437,173 @@ public static void FixedAddressValueTypeTest()
 
             Assert.Equal(fixedPtr1, fixedPtr2);
         }
+
+        [Fact]
+        public static void BoxPrimitive()
+        {
+            int value = 4;
+            object result = RuntimeHelpers.Box(ref Unsafe.As<int, byte>(ref value), typeof(int).TypeHandle);
+            Assert.Equal(value, Assert.IsType<int>(result));
+        }
+
+        [Fact]
+        public static void BoxPointer()
+        {
+            Assert.Throws<ArgumentException>(() =>
+            {
+                nint value = 3;
+                object result = RuntimeHelpers.Box(ref Unsafe.As<nint, byte>(ref value), typeof(void*).TypeHandle);
+            });
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private ref struct ByRefLikeType
+        {
+            public int i;
+        }
+
+        [Fact]
+        public static void BoxByRefLike()
+        {
+            Assert.Throws<NotSupportedException>(() =>
+            {
+                int value = 3;
+                object result = RuntimeHelpers.Box(ref Unsafe.As<int, byte>(ref value), typeof(ByRefLikeType).TypeHandle);
+            });
+        }
+
+        [Fact]
+        public static void BoxStruct()
+        {
+            Span<int> buffer = [0, 42, int.MaxValue];
+            StructWithoutReferences expected = new()
+            {
+                a = buffer[0],
+                b = buffer[1],
+                c = buffer[2]
+            };
+            object result = RuntimeHelpers.Box(ref MemoryMarshal.AsBytes(buffer)[0], typeof(StructWithoutReferences).TypeHandle);
+
+            Assert.Equal(expected, Assert.IsType<StructWithoutReferences>(result));
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct GenericStruct<T>
+        {
+            public T data;
+        }
+
+        [Fact]
+        public static void BoxUnmanagedGenericStruct()
+        {
+            int value = 3;
+            object result = RuntimeHelpers.Box(ref Unsafe.As<int, byte>(ref value), typeof(GenericStruct<int>).TypeHandle);
+
+            Assert.Equal(value, Assert.IsType<GenericStruct<int>>(result).data);
+        }
+
+        [Fact]
+        public static void BoxManagedGenericStruct()
+        {
+            object value = new();
+            object result = RuntimeHelpers.Box(ref Unsafe.As<object, byte>(ref value), typeof(GenericStruct<object>).TypeHandle);
+
+            Assert.Same(value, Assert.IsType<GenericStruct<object>>(result).data);
+        }
+
+        [Fact]
+        public static void BoxNullable()
+        {
+            float? value = 3.14f;
+            object result = RuntimeHelpers.Box(ref Unsafe.As<float?, byte>(ref value), typeof(float?).TypeHandle);
+            Assert.Equal(value, Assert.IsType<float>(result));
+        }
+
+        [Fact]
+        public static void BoxNullNullable()
+        {
+            float? value = null;
+            object? result = RuntimeHelpers.Box(ref Unsafe.As<float?, byte>(ref value), typeof(float?).TypeHandle);
+            Assert.Null(result);
+        }
+
+        [Fact]
+        public static void NullBox()
+        {
+            Assert.Throws<NullReferenceException>(() => RuntimeHelpers.Box(ref Unsafe.NullRef<byte>(), typeof(byte).TypeHandle));
+        }
+
+        [Fact]
+        public static void BoxNullTypeHandle()
+        {
+            Assert.Throws<ArgumentNullException>(() =>
+            {
+                byte value = 3;
+                RuntimeHelpers.Box(ref value, default(RuntimeTypeHandle));
+            });
+        }
+
+        [Fact]
+        public static void BoxReferenceType()
+        {
+            string str = "ABC";
+            Assert.Same(str, RuntimeHelpers.Box(ref Unsafe.As<string, byte>(ref str), typeof(string).TypeHandle));
+        }
+
+        [Fact]
+        public static void BoxArrayType()
+        {
+            string[] arr = ["a", "b", "c"];
+            Assert.Same(arr, RuntimeHelpers.Box(ref Unsafe.As<string[], byte>(ref arr), typeof(string[]).TypeHandle));
+        }
+
+        // We can't even get a RuntimeTypeHandle for a generic parameter type on NativeAOT,
+        // so we don't even get to the method we're testing.
+        // So, let's not even waste time running this test on NativeAOT
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotNativeAot))]
+        public static void BoxGenericParameterType()
+        {
+            Type t = typeof(List<>).GetGenericArguments()[0];
+            Assert.Throws<ArgumentException>(() =>
+            {
+                byte value = 3;
+                RuntimeHelpers.Box(ref value, t.TypeHandle);
+            });
+        }
+
+        // We can't even get a RuntimeTypeHandle for a partially instantiated generic type on NativeAOT,
+        // so we don't even get to the method we're testing.
+        // So, let's not even waste time running this test on NativeAOT
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotNativeAot))]
+        public static void BoxPartiallyOpenGeneric()
+        {
+            Type t = typeof(Dictionary<,>).MakeGenericType(typeof(object), typeof(Dictionary<,>).GetGenericArguments()[1]);
+            Assert.Throws<ArgumentException>(() =>
+            {
+                byte value = 3;
+                RuntimeHelpers.Box(ref value, t.TypeHandle);
+            });
+        }
+
+        [Fact]
+        public static void BoxGenericTypeDefinition()
+        {
+            Assert.Throws<ArgumentException>(() =>
+            {
+                byte value = 3;
+                RuntimeHelpers.Box(ref value, typeof(List<>).TypeHandle);
+            });
+        }
+
+        [Fact]
+        public static void BoxVoid()
+        {
+            Assert.Throws<ArgumentException>(() =>
+            {
+                byte value = 3;
+                RuntimeHelpers.Box(ref value, typeof(void).TypeHandle);
+            });
+        }
     }
 
     public struct Age