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jbevain / cecil

Cecil is a library to inspect, modify and create .NET programs and libraries.
MIT License
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Exception when writing assembly with a null call instruction #908

Open Alyxsqrd opened 1 year ago

Alyxsqrd commented 1 year ago

Hello, would just like to report a bug. If you try to call AsssemblyDefinition.Write() while any methods in the module make a OpCodes.Call with a NULL operand, there will be an exception. This should compile properly, as the instruction works fine in the .NET runtime which will just disregard the call.

Unhandled exception. System.ArgumentNullException: Value cannot be null.
   at Mono.Cecil.MetadataBuilder.LookupToken(IMetadataTokenProvider provider)
   at Mono.Cecil.Cil.CodeReader.PatchRawCode(ByteBuffer buffer, Int32 code_size, CodeWriter writer)
   at Mono.Cecil.Cil.CodeReader.PatchRawMethodBody(MethodDefinition method, CodeWriter writer, Int32& code_size, MetadataToken& local_var_token)
   at Mono.Cecil.Cil.CodeWriter.WriteUnresolvedMethodBody(MethodDefinition method)
   at Mono.Cecil.Cil.CodeWriter.WriteMethodBody(MethodDefinition method)
   at Mono.Cecil.MetadataBuilder.AddMethod(MethodDefinition method)
   at Mono.Cecil.MetadataBuilder.AddMethods(TypeDefinition type)
   at Mono.Cecil.MetadataBuilder.AddType(TypeDefinition type)
   at Mono.Cecil.MetadataBuilder.AddTypes()
   at Mono.Cecil.MetadataBuilder.BuildTypes()
   at Mono.Cecil.MetadataBuilder.BuildModule()
   at Mono.Cecil.MetadataBuilder.BuildMetadata()
   at Mono.Cecil.ModuleWriter.<>c.<BuildMetadata>b__2_0(MetadataBuilder builder, MetadataReader _)
   at Mono.Cecil.ModuleDefinition.Read[TItem,TRet](TItem item, Func`3 read)
   at Mono.Cecil.ModuleWriter.BuildMetadata(ModuleDefinition module, MetadataBuilder metadata)
   at Mono.Cecil.ModuleWriter.Write(ModuleDefinition module, Disposable`1 stream, WriterParameters parameters)
   at Mono.Cecil.ModuleWriter.WriteModule(ModuleDefinition module, Disposable`1 stream, WriterParameters parameters)
   at Mono.Cecil.ModuleDefinition.Write(String fileName, WriterParameters parameters)
   at Mono.Cecil.AssemblyDefinition.Write(String fileName, WriterParameters parameters)
   at Mono.Cecil.AssemblyDefinition.Write(String fileName)
   at App.Program.Main(String[] args)
Alyxsqrd commented 1 year ago

Any updates on this? This scenario can be found when loading in some types of obfuscated assemblies.