Can't delete unused method

[Rick Martin]

I have an assembly with a single module.

I'm iterating over all the methods in this module and wish to delete the ones that aren't used. I'm positive that they aren't used, as they're the result of an obfuscator adding junk code.

To determine whether a method is used, I iterate all call instructions from all methods of all types in the main module and cache the distinct full names. Inefficient but so be it.

var assembly = AssemblyDefinition.ReadAssembly(path);

var module = assembly.MainModule;

var calls = module.Types

    .SelectMany(m => m.Methods)

    .Where(m => m.HasBody)

    .SelectMany(m => m.Body.Instructions)

    .Where(m => m.OpCode == OpCodes.Call)

    .Select(i => i.Operand as MethodReference)

    .Select(i => i.FullName)

    .Distinct().ToArray();

I then iterate the methods of all types and see if the method's full name is in this list. If it's not, it's not referenced anywhere and should be removed.

foreach (var t in module.Types)

{

        var toRemove = new List<MethodDefinition>();

    foreach (var m in t.Methods)

    {

        if (calls.All(c => c != m.FullName))

        {

            toRemove.Add(m);

        }

    }

    foreach (var m in toRemove)

    {

        t.Methods.Remove(m);

    }

}

Seems fine, I see the methods that I would have removed by hand. However, when I then go to write the assembly back, I get a vague error.

System.ArgumentException: 'Member 'System.Void Foo(System.Int32)' is declared in another module and needs to be imported'

Have I missed something in finding all the method usages? Am I wrong in thinking that I don't need to import references since I'm not adding anything new?

Thanks in advance

[Jb Evain]

Hey Rick,

Yes, it seems you missed some usages :)

In the IL, the method call be called using callvirt for instance, or referenced by a ldtoken.

Unfortunately the error is not very explicit, but you're completely right, you don't need to import a reference here. It just means that Cecil is seeing a reference to a stray method that is without a module.

Jb

--
--
--
mono-cecil
---
You received this message because you are subscribed to the Google Groups "mono-cecil" group.
To unsubscribe from this group and stop receiving emails from it, send an email to mono-cecil+...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/mono-cecil/9764e3d5-21a8-4017-84e4-2eb89f18ec5f%40googlegroups.com.

[Rick Martin]

Hiya :)

Thanks for the reply, yes I did some reading and ended up finding that some methods are called with callvirt, or ldftn/ldvirtftn in some cases. I also ran in to a case where a usage was in a nested type, and my original code wasn't searching through the nesting.

Problem solved.

I'm trying to apply the same logic to find fields which are only written to and never read. I'm whitelisting fields by finding all reads, assuming that Ldfld, Ldflda, Ldsfld and Ldsflda are the only Opcodes I should expect for reading.

private static IEnumerable<FieldReference> GetFieldReadsInProperties(IEnumerable<PropertyDefinition> properties)

{

    var getMethods = properties.Select(p => p.GetMethod).Where(m => m != null);

    var setMethods = properties.Select(p => p.SetMethod).Where(m => m != null);

    var allMethods = getMethods.Concat(setMethods).Where(m => m.HasBody);

            

    return allMethods

        .SelectMany(m => m.Body.Instructions)

        .Where(i => ReadOpCodes.Any(o => i.OpCode == o))

        .Select(f => f.Operand as FieldReference)

        .DistinctBy(f => f.FullName);

}

private static IEnumerable<FieldReference> GetFieldReadsInMethods(IEnumerable<MethodDefinition> methods)

{

    return methods.Where(m => m.HasBody)

        .SelectMany(m => m.Body.Instructions)

        .Where(i => ReadOpCodes.Any(o => i.OpCode == o))

        .Select(f => f.Operand as FieldReference)

        .DistinctBy(f => f.FullName);

}

private static OpCode[] ReadOpCodes = new[] { OpCodes.Ldfld, OpCodes.Ldflda, OpCodes.Ldsfld, OpCodes.Ldsflda };

This seems to be ok, but it trips up with enum fields, again with a vague error :D

System.ArgumentException

  HResult=0x80070057

  Message=Value does not fall within the expected range.

  Source=Mono.Cecil

  StackTrace:

   at Mono.Cecil.Mixin.GetEnumUnderlyingType(TypeDefinition self) in <redacted>\cecil-master\Mono.Cecil\TypeDefinition.cs:line 600

   at Mono.Cecil.MetadataBuilder.GetConstantType(TypeReference constant_type, Object constant) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1882

   at Mono.Cecil.MetadataBuilder.AddConstant(IConstantProvider owner, TypeReference type) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1864

   at Mono.Cecil.MetadataBuilder.AddField(FieldDefinition field) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1624

   at Mono.Cecil.MetadataBuilder.AddFields(TypeDefinition type) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1602

   at Mono.Cecil.MetadataBuilder.AddType(TypeDefinition type) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1437

   at Mono.Cecil.MetadataBuilder.AddNestedTypes(TypeDefinition type) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1592

   at Mono.Cecil.MetadataBuilder.AddType(TypeDefinition type) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1455

   at Mono.Cecil.MetadataBuilder.AddTypes() in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1413

   at Mono.Cecil.MetadataBuilder.BuildTypes() in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1266

   at Mono.Cecil.MetadataBuilder.BuildModule() in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1036

   at Mono.Cecil.MetadataBuilder.BuildMetadata() in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 1006

   at Mono.Cecil.ModuleWriter.<>c.<BuildMetadata>b__2_0(MetadataBuilder builder, MetadataReader _) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 144

   at Mono.Cecil.ModuleDefinition.Read[TItem,TRet](TItem item, Func`3 read) in <redacted>\cecil-master\Mono.Cecil\ModuleDefinition.cs:line 950

   at Mono.Cecil.ModuleWriter.BuildMetadata(ModuleDefinition module, MetadataBuilder metadata) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 143

   at Mono.Cecil.ModuleWriter.Write(ModuleDefinition module, Disposable`1 stream, WriterParameters parameters) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 119

   at Mono.Cecil.ModuleWriter.WriteModule(ModuleDefinition module, Disposable`1 stream, WriterParameters parameters) in <redacted>\cecil-master\Mono.Cecil\AssemblyWriter.cs:line 78

   at Mono.Cecil.ModuleDefinition.Write(String fileName, WriterParameters parameters) in <redacted>\cecil-master\Mono.Cecil\ModuleDefinition.cs:line 1139

   at Mono.Cecil.AssemblyDefinition.Write(String fileName, WriterParameters parameters) in <redacted>\cecil-master\Mono.Cecil\AssemblyDefinition.cs:line 161

   at Mono.Cecil.AssemblyDefinition.Write(String fileName) in <redacted>\cecil-master\Mono.Cecil\AssemblyDefinition.cs:line 156

   at <redacted>(String[] args) in <redacted>

Guess I need to do some more reading :D

[Jb Evain]

The error originates from:

https://github.com/jbevain/cecil/blob/0a2f2944638c13987d8a2318bc34bd64fdac55fd/Mono.Cecil/TypeDefinition.cs#L590

Which points at you removing the magic instance field of an enum type that Cecil uses to find out what primitive type the enum is. (Don't remove this field :) )

Jb

--

--
--
mono-cecil
---
You received this message because you are subscribed to the Google Groups "mono-cecil" group.
To unsubscribe from this group and stop receiving emails from it, send an email to mono-cecil+...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/mono-cecil/5a43d2b0-918d-4249-beff-e667bc80026d%40googlegroups.com.