FieldRVA alignment (#817)

* FieldRVA alignment

In support of dotnet/runtime#60948 the linker (an assembly rewriter) will need to be able to preserve the alignment of RVA based fields which are to be used to create the data for `CreateSpan<T>` records

This is implemented by adding a concept that RVA fields detect their required alignment by examining the PackingSize of the type of the field (if the field type is defined locally in the module)

* Update Mono.Cecil.Metadata/Buffers.cs

Co-authored-by: Aaron Robinson <arobins@microsoft.com>

* Enhace logic used to ensure type providing PackingSize is local to the module.

Co-authored-by: Aaron Robinson <arobins@microsoft.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/Test/Mono.Cecil.Tests/FieldTests.cs b/Test/Mono.Cecil.Tests/FieldTests.cs
index 4f575de..93ed350 100644
--- a/Test/Mono.Cecil.Tests/FieldTests.cs
+++ b/Test/Mono.Cecil.Tests/FieldTests.cs
@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 
 using Mono.Cecil.PE;
 
@@ -133,6 +134,49 @@ namespace Mono.Cecil.Tests {
 			});
 		}
 
+		int AlignmentOfInteger(int input)
+		{
+			if (input == 0)
+				return 0x40000000;
+			if (input < 0)
+				Assert.Fail ();
+			int alignment = 1;
+			while ((input & alignment) == 0)
+				alignment *= 2;
+
+			return alignment;
+		}
+
+		[Test]
+		public void FieldRVAAlignment ()
+		{
+			TestIL ("FieldRVAAlignment.il", ilmodule => {
+
+				var path = Path.GetTempFileName ();
+
+				ilmodule.Write (path);
+
+				using (var module = ModuleDefinition.ReadModule (path, new ReaderParameters { ReadWrite = true })) {
+					var priv_impl = GetPrivateImplementationType (module);
+					Assert.IsNotNull (priv_impl);
+
+					Assert.AreEqual (6, priv_impl.Fields.Count);
+
+					foreach (var field in priv_impl.Fields)
+					{
+						Assert.IsNotNull (field);
+
+						Assert.AreNotEqual (0, field.RVA);
+						Assert.IsNotNull (field.InitialValue);
+
+						int rvaAlignment = AlignmentOfInteger (field.RVA);
+						int desiredAlignment = Math.Min(8, AlignmentOfInteger (field.InitialValue.Length));
+						Assert.GreaterOrEqual (rvaAlignment, desiredAlignment);
+					}
+				}
+			});
+		}
+
 		[Test]
 		public void GenericFieldDefinition ()
 		{