Issue with .net core and portable format

As you may know OpenCover uses Mono.Cecil to leverage the reading of PDB files and I was hoping that the latest release would resolve the issue identified with handling .net core (https://github.com/OpenCover/opencover/issues/610)

I upgraded to 0.9.6.3 through nuget (as it appeared work on portable format had been done between the the 0.9.6.1 and 0.9.6.3 releases) but the library is throwing an OutOfMemoryException(“Array dimensions exceeded supported range.”).

   at Microsoft.Cci.Pdb.MsfDirectory..ctor(PdbReader reader, PdbFileHeader head, BitAccess bits)
   at Microsoft.Cci.Pdb.PdbFile.LoadFunctions(Stream read, Dictionary`2& tokenToSourceMapping, String& sourceServerData, Int32& age, Guid& guid)
   at Mono.Cecil.Pdb.PdbReader.PopulateFunctions()
   at Mono.Cecil.Pdb.PdbReader.ProcessDebugHeader(ImageDebugDirectory directory, Byte[] header)
   at Mono.Cecil.ModuleDefinition.ProcessDebugHeader()
   at Mono.Cecil.ModuleReader.ReadSymbols(ModuleDefinition module, ReaderParameters parameters)
   at Mono.Cecil.ModuleReader.CreateModuleFrom(Image image, ReaderParameters parameters)
   at Mono.Cecil.ModuleDefinition.ReadModule(String fileName, ReaderParameters parameters)
   at Mono.Cecil.AssemblyDefinition.ReadAssembly(String fileName, ReaderParameters parameters)
   at OpenCover.Framework.Symbols.CecilSymbolManager.LoadSourceAssembly() in C:\Projects\opencover.git\working\main\OpenCover.Framework\Symbols\CecilSymbolManager.cs:line 126

I tried to investigate myself but the mainline has moved on and broken backward compatibility (SequencePoint related) and I can’t tell from your git history nor your releases which commit aligns with the nuget package 0.9.6.3.

Can you help by either

1. resolution of the issue
2. identify which commit was used to build the 0.9.6.3 release so that I can investigate the issue myself.

[jbevain]

@sawilde hey Shaun,

As you mentioned, in .NET Core, the pdb format changed. There’s nothing in 0.9.6 to handle the portable pdb files. What’s happening is that Cecil is trying to read a portable pdb file with the native pdb reader, and the native pdb reader crashes while misinterpreting the file. This particular exception has been fixed in master through #279.

To answer your question, the 0.9.6 nuget is maintained through the 0.9.6-nuget branch. 0.9.6.3 has been built off 0f397dbf7059eb1efdeeffe70bdaf13f99c2b447.

Now, to really fix the .NET Core scenario, you’re going to need support for portable pdbs which are in master and aimed at being released through 0.10 based on the master, which is now fairly stable.

There are breaking changes in 0.10 however. To help you update, please find bellow the current breaking change log:

Custom Attributes on interface implementation for winmd files

We used to have:

class TypeDefinition {
   public Collection<TypeReference> Interfaces { get; }
}

We now have:

class TypeDefinition {
   public Collection<InterfaceImplementation> Interfaces { get; }
}

class InterfaceImplementation {
  public TypeReference InterfaceTypes { get; }
  public Collection<CustomAttribute> CustomAttributes { get; }
}

That’s an easy change.

Lower Memory Usage

I’ve merged this branch, meaning that by default a ModuleDefinition keeps an open handle on its file and needs to be disposed. The default behavior for a DefaultAssemblyResolver, which is caching, is to dispose all cached assemblies when the resolver is disposed.

You may override that by setting the InMemory = true of the ReaderParameters, but that will lead to more memory fragmentation.

Because of this, if you were previously reading and writing an assembly on the same file, you need to change how you read and write your assembly to:

// ReaderParameters { ReadWrite = true } is necessary to later write the file
using (var module = ModuleDefinition.ReadModule(file, new ReaderParameters { ReadWrite = true })) 
{
    // Modify the assembly

    module.Write (); // Write to the same file that was used to open the file
}

Portable Pdb Support

This is a large change that introduces support for the new portable pdb information. The nice thing is that when users transition to the new format, all features are supported, and you can debug a rewritten assembly without loss of debug information.

It also simplifies quite a bit the debug symbol reader / writer. For 0.11, I’ll look into improving the native pdb story.

Things that went away:

Instruction.SequencePoint VariableReference.Name

The information moved to MethodDefinition.DebugInformation. You can use instead:

MethodDebugInformation.GetSequencePoint(Instruction) MethodDebugInformation.TryGetName(VariableDefinition, out string)

[jbevain]

@facedbook there’s nothing builtin. The Portable Pdb support uses the Cecil object model to represent debug symbol.

You need to work with the method.DebugInformation.