Add support for null arrays in the blittable array marshaller's pinni…

…ng optimization. (dotnet/runtimelab#1063) * Add support for null arrays in the blittable array marshaller's pinning optimization. * Add comment block about the behavior. * Use pointer casting instead of Unsafe.NullRef since we are already using pointers. Commit migrated from dotnet/runtimelab@c436fda
jkoritzinsky · May 4, 2021 · 1e3f71c · 1e3f71c
1 parent a4e4279
commit 1e3f71c
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Showing 3 changed files with 53 additions and 10 deletions.
diff --git a/...em.Runtime.InteropServices/gen/DllImportGenerator/Marshalling/BlittableArrayMarshaller.cs b/...em.Runtime.InteropServices/gen/DllImportGenerator/Marshalling/BlittableArrayMarshaller.cs
@@ -56,21 +56,58 @@ public override IEnumerable<StatementSyntax> Generate(TypePositionInfo info, Stu
             var (managedIdentifer, nativeIdentifier) = context.GetIdentifiers(info);
             if (!info.IsByRef && !info.IsManagedReturnPosition && context.PinningSupported)
             {
+                string byRefIdentifier = $"__byref_{managedIdentifer}";
+                if (context.CurrentStage == StubCodeContext.Stage.Marshal)
+                {
+                    // [COMPAT] We use explicit byref calculations here instead of just using a fixed statement 
+                    // since a fixed statement converts a zero-length array to a null pointer.
+                    // Many native APIs, such as GDI+, ICU, etc. validate that an array parameter is non-null
+                    // even when the passed in array length is zero. To avoid breaking customers that want to move
+                    // to source-generated interop in subtle ways, we explicitly pass a reference to the 0-th element
+                    // of an array as long as it is non-null, matching the behavior of the built-in interop system
+                    // for single-dimensional zero-based arrays.
+
+                    // ref <elementType> <byRefIdentifier> = <managedIdentifer> == null ? ref *(<elementType*)0 : ref MemoryMarshal.GetArrayDataReference(<managedIdentifer>);
+                    var nullRef =
+                        PrefixUnaryExpression(SyntaxKind.PointerIndirectionExpression,
+                            CastExpression(
+                                PointerType(GetElementTypeSyntax(info)),
+                                LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(0))));
+
+                    var getArrayDataReference =
+                        InvocationExpression(
+                            MemberAccessExpression(
+                                SyntaxKind.SimpleMemberAccessExpression,
+                                ParseTypeName(TypeNames.System_Runtime_InteropServices_MemoryMarshal),
+                                IdentifierName("GetArrayDataReference")),
+                            ArgumentList(SingletonSeparatedList(
+                                Argument(IdentifierName(managedIdentifer)))));
+
+                    yield return LocalDeclarationStatement(
+                        VariableDeclaration(
+                            RefType(GetElementTypeSyntax(info)))
+                        .WithVariables(SingletonSeparatedList(
+                            VariableDeclarator(Identifier(byRefIdentifier))
+                            .WithInitializer(EqualsValueClause(
+                                RefExpression(ParenthesizedExpression(
+                                    ConditionalExpression(
+                                        BinaryExpression(
+                                            SyntaxKind.EqualsExpression,
+                                            IdentifierName(managedIdentifer),
+                                            LiteralExpression(
+                                                SyntaxKind.NullLiteralExpression)),
+                                        RefExpression(nullRef),
+                                        RefExpression(getArrayDataReference)))))))));
+                }
                 if (context.CurrentStage == StubCodeContext.Stage.Pin)
                 {
-                    // fixed (<nativeType> <nativeIdentifier> = &MemoryMarshal.GetArrayDataReference(<managedIdentifer>))
+                    // fixed (<nativeType> <nativeIdentifier> = &<byrefIdentifier>)
                     yield return FixedStatement(
                         VariableDeclaration(AsNativeType(info), SingletonSeparatedList(
                             VariableDeclarator(nativeIdentifier)
                                 .WithInitializer(EqualsValueClause(
                                     PrefixUnaryExpression(SyntaxKind.AddressOfExpression,
-                                        InvocationExpression(
-                                            MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression,
-                                                ParseTypeName(TypeNames.System_Runtime_InteropServices_MemoryMarshal),
-                                                IdentifierName("GetArrayDataReference")),
-                                                ArgumentList(
-                                                    SingletonSeparatedList(Argument(IdentifierName(managedIdentifer)))
-                                                ))))))),
+                                        IdentifierName(byRefIdentifier)))))),
                         EmptyStatement());
                 }
                 yield break;

diff --git a/src/libraries/System.Runtime.InteropServices/gen/DllImportGenerator/TypeNames.cs b/src/libraries/System.Runtime.InteropServices/gen/DllImportGenerator/TypeNames.cs
@@ -44,7 +44,7 @@ public static string MarshalEx(AnalyzerConfigOptions options)
         public const string System_Runtime_InteropServices_OutAttribute = "System.Runtime.InteropServices.OutAttribute";
 
         public const string System_Runtime_InteropServices_InAttribute = "System.Runtime.InteropServices.InAttribute";
-        
+
         public const string System_Runtime_CompilerServices_SkipLocalsInitAttribute = "System.Runtime.CompilerServices.SkipLocalsInitAttribute";
     }
 }
diff --git a/src/libraries/System.Runtime.InteropServices/tests/DllImportGenerator.Tests/ArrayTests.cs b/src/libraries/System.Runtime.InteropServices/tests/DllImportGenerator.Tests/ArrayTests.cs
@@ -67,10 +67,16 @@ public class ArrayTests
         [Fact]
         public void IntArrayMarshalledToNativeAsExpected()
         {
-            var array = new [] { 1, 5, 79, 165, 32, 3 };
+            var array = new[] { 1, 5, 79, 165, 32, 3 };
             Assert.Equal(array.Sum(), NativeExportsNE.Arrays.Sum(array, array.Length));
         }
 
+        [Fact]
+        public void NullIntArrayMarshalledToNativeAsExpected()
+        {
+            Assert.Equal(-1, NativeExportsNE.Arrays.Sum(null, 0));
+        }
+
         [Fact]
         public void ZeroLengthArrayMarshalledAsNonNull()
         {