Clarify header format

dotnet · May 1, 2017 · b1ac2aa · b1ac2aa
1 parent ec9b2d4
commit b1ac2aa
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Showing 3 changed files with 12 additions and 8 deletions.
diff --git a/docs/features/refout.md b/docs/features/refout.md
@@ -43,7 +43,6 @@ When the compiler produces documentation, the contents produced will match the A
 
 The compilation from the command-line will either produce both assemblies (implementation and ref) or neither. There is no "partial success" scenario.
 
-
 ### CscTask/CoreCompile
 The `CoreCompile` target will support a new output, called `IntermediateRefAssembly`, which parallels the existing `IntermediateAssembly`.
 The `Csc` task will support a new output, called `OutputRefAssembly`, which parallels the existing `OutputAssembly`.

diff --git a/src/Compilers/Core/MSBuildTask/MvidReader.cs b/src/Compilers/Core/MSBuildTask/MvidReader.cs
@@ -23,17 +23,17 @@ private static Guid ReadAssemblyMvidOrEmpty(BinaryReader reader)
                 return empty;
             }
 
-            // DOS Header: PE (2)
-            if (reader.ReadUInt16() != 0x5a4d)
+            // DOS Header: Magic number (2)
+            if (reader.ReadUInt16() != 0x5a4d) // "MZ"
             {
                 return empty;
             }
 
-            // DOS Header: Start (58)
-            Skip(58, reader);
+            // DOS Header: Address of PE Signature (at 0x3C)
+            MoveTo(0x3C, reader);
+            uint lfanew = reader.ReadUInt32();
 
-            // DOS Header: Address of PE Signature
-            MoveTo(reader.ReadUInt32(), reader);
+            MoveTo(lfanew, reader); // jump over the MS DOS Stub to the PE Signature
 
             // PE Signature ('P' 'E' null null)
             if (reader.ReadUInt32() != 0x00004550)
@@ -65,6 +65,11 @@ private static Guid ReadAssemblyMvidOrEmpty(BinaryReader reader)
 
         private static Guid FindMvidInSections(ushort count, BinaryReader reader)
         {
+            if (count == 0)
+            {
+                return Guid.Empty;
+            }
+
             // .mvid section must be first, if it's there
             // Section: Name (8)
             byte[] name = reader.ReadBytes(8);

diff --git a/src/Compilers/Core/Portable/PEWriter/ExtendedPEBuilder.cs b/src/Compilers/Core/Portable/PEWriter/ExtendedPEBuilder.cs
@@ -24,7 +24,7 @@ internal sealed class ExtendedPEBuilder
         private Blob _mvidSectionFixup = default(Blob);
 
         // Only include the .mvid section in ref assemblies
-        private bool _withMvidSection;
+        private readonly bool _withMvidSection;
 
         public ExtendedPEBuilder(
             PEHeaderBuilder header,