Fix RVA field alignment (#55)

This ensures that section starts are aligned by adjusting the
previous Range's length to ensure the computed start of a new
Range meets the alignment requirements. It was done this way
rather than just computing an aligned start for the new Range,
because the TextMap assumes that the Ranges are contiguous - see
for example GetNextRVA.

Author: sbomer

Mono.Cecil.PE/TextMap.cs

@@ -9,6 +9,7 @@
 //
 
 using System;
+using System.Diagnostics;
 
 using RVA = System.UInt32;
 
@@ -47,11 +48,31 @@ public void AddMap (TextSegment segment, int length)
 			map [(int) segment] = new Range (GetStart (segment), (uint) length);
 		}
 
-		public void AddMap (TextSegment segment, int length, int align)
+		uint AlignUp (uint value, uint align)
 		{
 			align--;
+			return (value + align) & ~align;
+		}
 
-			AddMap (segment, (length + align) & ~align);
+		public void AddMap (TextSegment segment, int length, int align)
+		{
+			var index = (int) segment;
+			uint start;
+			if (index != 0) {
+				// Align up the previous segment's length so that the new
+				// segment's start will be aligned.
+				index--;
+				Range previous = map [index];
+				start = AlignUp (previous.Start + previous.Length, (uint) align);
+				map [index].Length = start - previous.Start;
+			} else {
+				start = ImageWriter.text_rva;
+				// Should already be aligned.
+				Debug.Assert (start == AlignUp (start, (uint) align));
+			}
+			Debug.Assert (start == GetStart (segment));
+
+			map [(int) segment] = new Range (start, (uint) length);
 		}
 
 		public void AddMap (TextSegment segment, Range range)

Test/Mono.Cecil.Tests/FieldTests.cs

@@ -160,7 +160,7 @@ public void FieldRVAAlignment ()
 					var priv_impl = GetPrivateImplementationType (module);
 					Assert.IsNotNull (priv_impl);
 
-					Assert.AreEqual (6, priv_impl.Fields.Count);
+					Assert.AreEqual (8, priv_impl.Fields.Count);
 
 					foreach (var field in priv_impl.Fields)
 					{
@@ -170,7 +170,8 @@ public void FieldRVAAlignment ()
 						Assert.IsNotNull (field.InitialValue);
 
 						int rvaAlignment = AlignmentOfInteger (field.RVA);
-						int desiredAlignment = Math.Min(8, AlignmentOfInteger (field.InitialValue.Length));
+						var fieldType = field.FieldType.Resolve ();
+						int desiredAlignment = fieldType.PackingSize;
 						Assert.GreaterOrEqual (rvaAlignment, desiredAlignment);
 					}
 				}

Test/Resources/il/FieldRVAAlignment.il

@@ -46,12 +46,22 @@
     .size 6
   } // end of class '__StaticArrayInitTypeSize=6'
 
+  .class explicit ansi sealed nested private '__StaticArrayInitTypeSize=4Align=32'
+        extends [mscorlib]System.ValueType
+  {
+    .pack 32
+    .size 4
+  }
+
   .field static assembly valuetype '<PrivateImplementationDetails>{9B33BB20-87EF-4094-9948-34882DB2F001}'/'__StaticArrayInitTypeSize=3' '$$method0x6000001-1' at I_000020F0
   .field static assembly valuetype '<PrivateImplementationDetails>{9B33BB20-87EF-4094-9948-34882DB2F001}'/'__StaticArrayInitTypeSize=20' '$$method0x6000001-2' at I_000020F8
   .field static assembly valuetype '<PrivateImplementationDetails>{9B33BB20-87EF-4094-9948-34882DB2F001}'/'__StaticArrayInitTypeSize=5' '$$method0x6000001-3' at I_00002108
   .field static assembly valuetype '<PrivateImplementationDetails>{9B33BB20-87EF-4094-9948-34882DB2F001}'/'__StaticArrayInitTypeSize=20' '$$method0x6000001-4' at I_00002110
   .field static assembly valuetype '<PrivateImplementationDetails>{9B33BB20-87EF-4094-9948-34882DB2F001}'/'__StaticArrayInitTypeSize=6' '$$method0x6000001-5' at I_00002120
   .field static assembly valuetype '<PrivateImplementationDetails>{9B33BB20-87EF-4094-9948-34882DB2F001}'/'__StaticArrayInitTypeSize=16' '$$method0x6000001-6' at I_00002130
+  .field static assembly valuetype '<PrivateImplementationDetails>{9B33BB20-87EF-4094-9948-34882DB2F001}'/'__StaticArrayInitTypeSize=3' 'separator' at I_00002140
+  .field static assembly valuetype '<PrivateImplementationDetails>{9B33BB20-87EF-4094-9948-34882DB2F001}'/'__StaticArrayInitTypeSize=4Align=32' '32_align' at I_00002150
+
 } // end of class '<PrivateImplementationDetails>{9B33BB20-87EF-4094-9948-34882DB2F001}'
 
 
@@ -69,3 +79,7 @@
                  08 00 0C 00 0D 00) 
 .data cil I_00002130 = bytearray (
                  01 00 00 00 02 00 00 00 03 00 00 00 05 00 00 00) 
+.data cil I_00002140 = bytearray (
+                 01 02 03)
+.data cil I_00002150 = bytearray (
+                 01 02 03 04)