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A reflection based disassembler

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MethodBaseRocks.cs
C#
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//
// MethodBaseRocks.cs
//
// Author:
// Jb Evain (jbevain@novell.com)
//
// 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 ();
}
}
}

I'm getting this error message: "Value does not fall within the expected range." from this bit of code:

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

and I'm wondering how there could be bodyless methods (or what else could be going on). any thoughts?

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