A reflection based disassembler

MethodBaseRocks.cs

//
// MethodBaseRocks.cs
//
// Author:
//   Jb Evain ([email protected])
//
// WARNING: code now lives in http://github.com/jbevain/mono.reflection
//
// (C) 2009 Novell, Inc. (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;

namespace Mono.Reflection {

	public sealed class Instruction {

		int offset;
		OpCode opcode;
		object operand;

		Instruction previous;
		Instruction next;

		public int Offset {
			get { return offset; }
		}

		public OpCode OpCode {
			get { return opcode; }
		}

		public object Operand {
			get { return operand; }
			internal set { operand = value; }
		}

		public Instruction Previous {
			get { return previous; }
			internal set { previous = value; }
		}

		public Instruction Next {
			get { return next; }
			internal set { next = value; }
		}

		internal Instruction (int offset, OpCode opcode)
		{
			this.offset = offset;
			this.opcode = opcode;
		}

		public int GetSize ()
		{
			int size = opcode.Size;

			switch (opcode.OperandType) {
			case OperandType.InlineSwitch:
				size += (1 + ((int []) operand).Length) * 4;
				break;
			case OperandType.InlineI8:
			case OperandType.InlineR:
				size += 8;
				break;
			case OperandType.InlineBrTarget:
			case OperandType.InlineField:
			case OperandType.InlineI:
			case OperandType.InlineMethod:
			case OperandType.InlineString:
			case OperandType.InlineTok:
			case OperandType.InlineType:
			case OperandType.ShortInlineR:
				size += 4;
				break;
			case OperandType.InlineVar:
				size += 2;
				break;
			case OperandType.ShortInlineBrTarget:
			case OperandType.ShortInlineI:
			case OperandType.ShortInlineVar:
				size += 1;
				break;
			}

			return size;
		}

		public override string ToString ()
		{
			return opcode.Name;
		}
	}

	class MethodBodyReader {

		static OpCode [] one_byte_opcodes;
		static OpCode [] two_bytes_opcodes;

		static MethodBodyReader ()
		{
			one_byte_opcodes = new OpCode [0xe1];
			two_bytes_opcodes = new OpCode [0x1f];

			var fields = GetOpCodeFields ();

			for (int i = 0; i < fields.Length; i++) {
				var opcode = (OpCode) fields [i].GetValue (null);
				if (opcode.OpCodeType == OpCodeType.Nternal)
					continue;

				if (opcode.Size == 1)
					one_byte_opcodes [opcode.Value] = opcode;
				else
					two_bytes_opcodes [opcode.Value & 0xff] = opcode;
			}
		}

		static FieldInfo [] GetOpCodeFields ()
		{
			return typeof (OpCodes).GetFields (BindingFlags.Public | BindingFlags.Static);
		}

		class ByteBuffer {

			internal byte [] buffer;
			internal int position;

			public ByteBuffer (byte [] buffer)
			{
				this.buffer = buffer;
			}

			public byte ReadByte ()
			{
				CheckCanRead (1);
				return buffer [position++];
			}

			public byte [] ReadBytes (int length)
			{
				CheckCanRead (length);
				var value = new byte [length];
				Buffer.BlockCopy (buffer, position, value, 0, length);
				position += length;
				return value;
			}

			public short ReadInt16 ()
			{
				CheckCanRead (2);
				short value = (short) (buffer [position]
					| (buffer [position + 1] << 8));
				position += 2;
				return value;
			}

			public int ReadInt32 ()
			{
				CheckCanRead (4);
				int value = buffer [position]
					| (buffer [position + 1] << 8)
					| (buffer [position + 2] << 16)
					| (buffer [position + 3] << 24);
				position += 4;
				return value;
			}

			public long ReadInt64 ()
			{
				CheckCanRead (8);
				uint low = (uint) (buffer [position]
					| (buffer [position + 1] << 8)
					| (buffer [position + 2] << 16)
					| (buffer [position + 3] << 24));

				uint high = (uint) (buffer [position + 4]
					| (buffer [position + 5] << 8)
					| (buffer [position + 6] << 16)
					| (buffer [position + 7] << 24));

				long value = (((long) high) << 32) | low;
				position += 8;
				return value;
			}

			public float ReadSingle ()
			{
				if (!BitConverter.IsLittleEndian) {
					var bytes = ReadBytes (4);
					Array.Reverse (bytes);
					return BitConverter.ToSingle (bytes, 0);
				}

				CheckCanRead (4);
				float value = BitConverter.ToSingle (buffer, position);
				position += 4;
				return value;
			}

			public double ReadDouble ()
			{
				if (!BitConverter.IsLittleEndian) {
					var bytes = ReadBytes (8);
					Array.Reverse (bytes);
					return BitConverter.ToDouble (bytes, 0);
				}

				CheckCanRead (8);
				double value = BitConverter.ToDouble (buffer, position);
				position += 8;
				return value;
			}

			void CheckCanRead (int count)
			{
				if (position + count > buffer.Length)
					throw new ArgumentOutOfRangeException ();
			}
		}

		MethodBase method;
		MethodBody body;
		Module module;
		Type [] type_arguments;
		Type [] method_arguments;
		ByteBuffer il;
		ParameterInfo [] parameters;
		IList<LocalVariableInfo> locals;
		List<Instruction> instructions = new List<Instruction> ();

		MethodBodyReader (MethodBase method)
		{
			this.method = method;

			this.body = method.GetMethodBody ();
			if (this.body == null)
				throw new ArgumentException ();

			var bytes = body.GetILAsByteArray ();
			if (bytes == null)
				throw new ArgumentException ();

			if (!(method is ConstructorInfo))
				method_arguments = method.GetGenericArguments ();

			if (method.DeclaringType != null)
				type_arguments = method.DeclaringType.GetGenericArguments ();

			this.parameters = method.GetParameters ();
			this.locals = body.LocalVariables;
			this.module = method.Module;
			this.il = new ByteBuffer (bytes);
		}

		void ReadInstructions ()
		{
			Instruction previous = null;

			while (il.position < il.buffer.Length) {
				var instruction = new Instruction (il.position, ReadOpCode ());

				ReadOperand (instruction);

				if (previous != null) {
					instruction.Previous = previous;
					previous.Next = instruction;
				}

				instructions.Add (instruction);
				previous = instruction;
			}
		}

		void ReadOperand (Instruction instruction)
		{
			switch (instruction.OpCode.OperandType) {
			case OperandType.InlineNone:
				break;
			case OperandType.InlineSwitch:
				int length = il.ReadInt32 ();
				int [] branches = new int [length];
				int [] offsets = new int [length];
				for (int i = 0; i < length; i++)
					offsets [i] = il.ReadInt32 ();
				for (int i = 0; i < length; i++)
					branches [i] = il.position + offsets [i];

				instruction.Operand = branches;
				break;
			case OperandType.ShortInlineBrTarget:
				instruction.Operand = (sbyte) (il.ReadByte () + il.position);
				break;
			case OperandType.InlineBrTarget:
				instruction.Operand = il.ReadInt32 () + il.position;
				break;
			case OperandType.ShortInlineI:
				if (instruction.OpCode == OpCodes.Ldc_I4_S)
					instruction.Operand = (sbyte) il.ReadByte ();
				else
					instruction.Operand = il.ReadByte ();
				break;
			case OperandType.InlineI:
				instruction.Operand = il.ReadInt32 ();
				break;
			case OperandType.ShortInlineR:
				instruction.Operand = il.ReadSingle ();
				break;
			case OperandType.InlineR:
				instruction.Operand = il.ReadDouble ();
				break;
			case OperandType.InlineI8:
				instruction.Operand = il.ReadInt64 ();
				break;
			case OperandType.InlineSig:
				instruction.Operand = module.ResolveSignature (il.ReadInt32 ());
				break;
			case OperandType.InlineString:
				instruction.Operand = module.ResolveString (il.ReadInt32 ());
				break;
			case OperandType.InlineTok:
				instruction.Operand = module.ResolveMember (il.ReadInt32 (), type_arguments, method_arguments);
				break;
			case OperandType.InlineType:
				instruction.Operand = module.ResolveType (il.ReadInt32 (), type_arguments, method_arguments);
				break;
			case OperandType.InlineMethod:
				instruction.Operand = module.ResolveMethod (il.ReadInt32 (), type_arguments, method_arguments);
				break;
			case OperandType.InlineField:
				instruction.Operand = module.ResolveField (il.ReadInt32 (), type_arguments, method_arguments);
				break;
			case OperandType.ShortInlineVar:
				instruction.Operand = GetVariable (instruction, il.ReadByte ());
				break;
			case OperandType.InlineVar:
				instruction.Operand = GetVariable (instruction, il.ReadInt16 ());
				break;
			default:
				throw new NotSupportedException ();
			}
		}

		object GetVariable (Instruction instruction, int index)
		{
			if (TargetsLocalVariable (instruction.OpCode))
				return GetLocalVariable (index);
			else
				return GetParameter (index);
		}

		static bool TargetsLocalVariable (OpCode opcode)
		{
			return opcode.Name.Contains ("loc");
		}

		LocalVariableInfo GetLocalVariable (int index)
		{
			return locals [index];
		}

		ParameterInfo GetParameter (int index)
		{
			if (!method.IsStatic)
				index--;

			return parameters [index];
		}

		OpCode ReadOpCode ()
		{
			byte op = il.ReadByte ();
			return op != 0xfe
				? one_byte_opcodes [op]
				: two_bytes_opcodes [il.ReadByte ()];
		}

		public static List<Instruction> GetInstructions (MethodBase method)
		{
			var reader = new MethodBodyReader (method);
			reader.ReadInstructions ();
			return reader.instructions;
		}
	}

	public static class MethodBaseRocks {

		public static IList<Instruction> GetInstructions (this MethodBase self)
		{
			return MethodBodyReader.GetInstructions (self).AsReadOnly ();
		}
	}
}

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