Is there a way to load debug symbols at runtime without any files

[Serg046]

This is what I am trying to do:

class Program
{
	static void Main(string[] args)
	{
		var asmDef = AssemblyDefinition.ReadAssembly(typeof(Test).Module.FullyQualifiedName,
			new ReaderParameters{ReadSymbols = true});
		asmDef.Name.Name += "Fake";
		var typeDef = asmDef.MainModule.GetType(typeof(Test).FullName, runtimeName: true).Resolve();
		var methodDef = typeDef.Methods.Single(m => m.Name == nameof(Test.Print));
		var consoleMethod = typeof(Console)
			.GetMethods()
			.Single(m => m.Name == nameof(Console.WriteLine) && m.GetParameters().Length == 1
			                                                 && m.GetParameters().Single().ParameterType ==
			                                                 typeof(string));
		methodDef.Body.Instructions.Insert(methodDef.Body.Instructions.Count - 1,
			Instruction.Create(OpCodes.Ldstr, "Injected"));
		methodDef.Body.Instructions.Insert(methodDef.Body.Instructions.Count - 1,
			Instruction.Create(OpCodes.Call, asmDef.MainModule.ImportReference(consoleMethod)));
		
		//This one works fine based on the pdb file
		var asm = WriteFileAssembly(asmDef);

		// But this one fails
		//var asm = WriteMemoryAssembly(asmDef);
		
		var type = asm.GetType(typeof(Test).FullName);
		type.InvokeMember(nameof(Test.Print), BindingFlags.InvokeMethod, null,
			Activator.CreateInstance(type), new object[0]);
	}

	private static Assembly WriteFileAssembly(AssemblyDefinition asmDef)
	{
		using var stream = File.Open("test.dll", FileMode.OpenOrCreate);
		asmDef.Write(stream, new WriterParameters {WriteSymbols = true});
		stream.Position = 0;
		// To avoid implicit load by the name
		File.Delete("renamed.pdb");
		File.Move("test.pdb", "renamed.pdb");
		// -----------------------------------
		var pdb = File.OpenRead("renamed.pdb");
		return AssemblyLoadContext.Default.LoadFromStream(stream, pdb);
	}

	private static Assembly WriteMemoryAssembly(AssemblyDefinition asmDef)
	{
		using var stream = new MemoryStream();
		using var symbolsStream = new MemoryStream();
		asmDef.Write(stream, new WriterParameters
		{
			SymbolStream = symbolsStream,
			SymbolWriterProvider = new SymbolsWriterProvider()
		});
		stream.Position = symbolsStream.Position = 0;
		return AssemblyLoadContext.Default.LoadFromStream(stream, symbolsStream);

		// This one doesn't work too with the same error
		// var pdb = File.OpenRead("renamed.pdb");
		// return AssemblyLoadContext.Default.LoadFromStream(stream, pdb);
	}

	private class SymbolsWriterProvider : ISymbolWriterProvider
	{
		public ISymbolWriter GetSymbolWriter(ModuleDefinition module, string fileName)
			=> throw new NotSupportedException();

		public ISymbolWriter GetSymbolWriter(ModuleDefinition module, Stream symbolStream)
			=> module.SymbolReader.GetWriterProvider().GetSymbolWriter(module, symbolStream);
	}
}

class Test
{
	public void Print()
	{
		Console.WriteLine("Test");
	}
}

It works fine when I generate a file but It doesn't when I try to load it in memory.
It fails with the following message: Module was built without symbols;
What is the right way to do it?

[jbevain]

Hey! That's a great question. I'm not really sure to be honest. Maybe when writing to a symbol stream instead of a file Cecil doesn't write the expected information in the debug header (after all, there's no path to write), and then the loader is confused.

[jbevain]

Maybe try to hardcode a file name in there:

https://github.com/jbevain/cecil/blob/master/Mono.Cecil.Cil/PortablePdb.cs#L304

Instead of writer.BaseStream.GetFileName (), as this will return an empty string on a non file based stream.

And see if then the symbols are loaded?

[jbevain]

@Serg046 Did you find something that worked in the end?

[Serg046]

I postponed the task where I need this behaviour that's why I didn't answer anything that time. But actually your idea works fine, thank you! What do you think about this #735?

[jbevain]

This is issue is related to #734 has well. Cecil needs to do a better job at handling filenames for non FileStream scenarios. But I like your fix in the meantime. Thanks!