Custom Attribute Validation

[ds5678]

AsmResolver Version

5.0.0

.NET Version

.NET 6

Operating System

Windows

Describe the Bug

Assemblies created with AsmResolver seem to have invalid custom attribute blobs. Several problems were noticed when loading generated assemblies into popular .NET decompilers.

How To Reproduce

The bug was initially noticed in an assembly created by Cpp2IL with the latest NuGet version of AsmResolver. Although I cannot be sure that the 5.0 beta versions were without issue, I only noticed this in the full release.

In ILSpy 8 Preview 3, the assembly attributes are decoded like this:

using System.Diagnostics;
using System.Reflection;
using System.Runtime.CompilerServices;

[assembly: CompilationRelaxations(/*Could not decode attribute arguments.*/)]
[assembly: RuntimeCompatibility]
[assembly: Debuggable(/*Could not decode attribute arguments.*/)]
[assembly: InternalsVisibleTo(/*Could not decode attribute arguments.*/)]
[assembly: InternalsVisibleTo(/*Could not decode attribute arguments.*/)]
[assembly: AssemblyVersion("0.0.0.0")]

Similarly, dnSpyEx decompiles the assembly attributes as:

using System;
using System.Diagnostics;
using System.Reflection;
using System.Runtime.CompilerServices;

[assembly: AssemblyVersion("0.0.0.0")]
[assembly: CompilationRelaxations]
[assembly: RuntimeCompatibility]
[assembly: Debuggable]
[assembly: InternalsVisibleTo]
[assembly: InternalsVisibleTo]

However, not all cases are handled so cleanly. Attempting to view `` in ILSpy throws an exception:

System.BadImageFormatException: Read out of bounds.
   at System.Reflection.Throw.OutOfBounds()
   at System.Reflection.Metadata.Ecma335.CustomAttributeDecoder`1.DecodeNamedArguments(BlobReader& valueReader)
   at System.Reflection.Metadata.Ecma335.CustomAttributeDecoder`1.DecodeValue(EntityHandle constructor, BlobHandle value)
   at ICSharpCode.Decompiler.TypeSystem.MetadataModule.GetInternalsVisibleTo() in /_/ICSharpCode.Decompiler/TypeSystem/MetadataModule.cs:line 176
   at ICSharpCode.Decompiler.TypeSystem.MetadataModule.InternalsVisibleTo(IModule module) in /_/ICSharpCode.Decompiler/TypeSystem/MetadataModule.cs:line 151
   at ICSharpCode.Decompiler.CSharp.Resolver.CSharpResolver.LookInCurrentUsingScope(String identifier, IReadOnlyList`1 typeArguments, Boolean isInUsingDeclaration, Boolean parameterizeResultType) in /_/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs:line 1728
   at ICSharpCode.Decompiler.CSharp.Resolver.CSharpResolver.LookupSimpleNameOrTypeName(String identifier, IReadOnlyList`1 typeArguments, NameLookupMode lookupMode) in /_/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs:line 1609
   at ICSharpCode.Decompiler.CSharp.Syntax.TypeSystemAstBuilder.ConvertTypeHelper(IType genericType, IReadOnlyList`1 typeArguments) in /_/ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs:line 506
   at ICSharpCode.Decompiler.CSharp.Syntax.TypeSystemAstBuilder.ConvertTypeHelper(IType type) in /_/ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs:line 424
   at ICSharpCode.Decompiler.CSharp.Syntax.TypeSystemAstBuilder.ConvertType(IType type) in /_/ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs:line 238
   at ICSharpCode.Decompiler.CSharp.Transforms.IntroduceUsingDeclarations.FullyQualifyAmbiguousTypeNamesVisitor.VisitSimpleType(SimpleType simpleType) in /_/ICSharpCode.Decompiler/CSharp/Transforms/IntroduceUsingDeclarations.cs:line 319
   at ICSharpCode.Decompiler.CSharp.Syntax.DepthFirstAstVisitor.VisitChildren(AstNode node) in /_/ICSharpCode.Decompiler/CSharp/Syntax/DepthFirstAstVisitor.cs:line 43
   at ICSharpCode.Decompiler.CSharp.Syntax.DepthFirstAstVisitor.VisitChildren(AstNode node) in /_/ICSharpCode.Decompiler/CSharp/Syntax/DepthFirstAstVisitor.cs:line 43
   at ICSharpCode.Decompiler.CSharp.Transforms.IntroduceUsingDeclarations.FullyQualifyAmbiguousTypeNamesVisitor.Visit[T](T entityDeclaration, Action`1 baseCall) in /_/ICSharpCode.Decompiler/CSharp/Transforms/IntroduceUsingDeclarations.cs:line 289
   at ICSharpCode.Decompiler.CSharp.Syntax.DepthFirstAstVisitor.VisitChildren(AstNode node) in /_/ICSharpCode.Decompiler/CSharp/Syntax/DepthFirstAstVisitor.cs:line 43
   at ICSharpCode.Decompiler.CSharp.Transforms.IntroduceUsingDeclarations.FullyQualifyAmbiguousTypeNamesVisitor.VisitTypeDeclaration(TypeDeclaration typeDeclaration) in /_/ICSharpCode.Decompiler/CSharp/Transforms/IntroduceUsingDeclarations.cs:line 226
   at ICSharpCode.Decompiler.CSharp.Syntax.DepthFirstAstVisitor.VisitChildren(AstNode node) in /_/ICSharpCode.Decompiler/CSharp/Syntax/DepthFirstAstVisitor.cs:line 43
   at ICSharpCode.Decompiler.CSharp.Transforms.IntroduceUsingDeclarations.Run(AstNode rootNode, TransformContext context) in /_/ICSharpCode.Decompiler/CSharp/Transforms/IntroduceUsingDeclarations.cs:line 73
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.RunTransforms(AstNode rootNode, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in /_/ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs:line 564
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.Decompile(IEnumerable`1 definitions) in /_/ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs:line 1088
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.Decompile(EntityHandle[] definitions) in /_/ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs:line 1004
   at ICSharpCode.ILSpy.CSharpLanguage.DecompileType(ITypeDefinition type, ITextOutput output, DecompilationOptions options)
   at ICSharpCode.ILSpy.TreeNodes.TypeTreeNode.Decompile(Language language, ITextOutput output, DecompilationOptions options)
   at ICSharpCode.ILSpy.TextView.DecompilerTextView.DecompileNodes(DecompilationContext context, ITextOutput textOutput)
   at ICSharpCode.ILSpy.TextView.DecompilerTextView.<>c__DisplayClass52_0.<DecompileAsync>b__0()

dnSpyEx handles any problems silently and prints the following code:

using System;
using UnityEngine;
using UnityEngine.TextCore.LowLevel;

namespace TMPro
{
	[Serializable]
	public class TMP_GlyphPairAdjustmentRecord
	{
		public TMP_GlyphAdjustmentRecord firstAdjustmentRecord
		{
			get
			{
				return default(TMP_GlyphAdjustmentRecord);
			}
			set
			{
			}
		}

		public TMP_GlyphAdjustmentRecord secondAdjustmentRecord
		{
			get
			{
				return default(TMP_GlyphAdjustmentRecord);
			}
			set
			{
			}
		}

		public FontFeatureLookupFlags featureLookupFlags
		{
			get
			{
				return (FontFeatureLookupFlags)0;
			}
			set
			{
			}
		}

		public TMP_GlyphPairAdjustmentRecord(TMP_GlyphAdjustmentRecord firstAdjustmentRecord, TMP_GlyphAdjustmentRecord secondAdjustmentRecord)
		{
		}

		internal TMP_GlyphPairAdjustmentRecord(GlyphPairAdjustmentRecord glyphPairAdjustmentRecord)
		{
		}

		[SerializeField]
		private TMP_GlyphAdjustmentRecord m_FirstAdjustmentRecord;

		[SerializeField]
		private TMP_GlyphAdjustmentRecord m_SecondAdjustmentRecord;

		[SerializeField]
		private FontFeatureLookupFlags m_FeatureLookupFlags;
	}
}

Expected Behavior

The assemblies should be valid enough for decompilers to properly load and analyze them.

Actual Behavior

The decompilers fail to load custom attribute blobs.

Additional Context

No response

[ds5678]

As discussed in discord, this was caused by invalid input to AsmResolver which propagated into its output. Cpp2IL couldn't decode custom attributes on my Unity version, so it has nothing to fill attribute constructor parameters with. Instead of providing a default value for each parameter, Cpp2IL gave it nothing and caused this issue to occur. It would be nice if AsmResolver was able to provide some validation for custom attributes.

[Washi1337]

Implemented in #407 , will be available in 5.1.0