/*
Copyright (C) 2011-2013 de4dot@gmail.com
This file is part of de4dot.
de4dot is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
de4dot is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with de4dot. If not, see .
*/
using System.Collections.Generic;
using dnlib.DotNet.Emit;
namespace de4dot.blocks.cflow {
// Removes dead code that is the result of one of our optimizations, or created by the
// obfuscator.
class DeadCodeRemover : BlockDeobfuscator {
List allDeadInstructions = new List();
InstructionExpressionFinder instructionExpressionFinder = new InstructionExpressionFinder();
protected override bool deobfuscate(Block block) {
allDeadInstructions.Clear();
bool changed = false;
var instructions = block.Instructions;
for (int i = 0; i < instructions.Count; i++) {
var instr = instructions[i];
switch (instr.OpCode.Code) {
case Code.Nop:
// The NOP is recreated if the block is empty so don't remove it if it's
// the only instruction.
if (instructions.Count > 1)
allDeadInstructions.Add(i);
break;
case Code.Dup:
if (i + 1 >= instructions.Count)
break;
if (instructions[i + 1].OpCode.Code != Code.Pop)
break;
allDeadInstructions.Add(i);
allDeadInstructions.Add(i + 1);
i++;
break;
case Code.Leave:
case Code.Leave_S:
case Code.Endfinally:
case Code.Pop:
instructionExpressionFinder.init(block, false);
if (!instructionExpressionFinder.find(i))
continue;
if (!okInstructions(block, instructionExpressionFinder.DeadInstructions))
continue;
allDeadInstructions.AddRange(instructionExpressionFinder.DeadInstructions);
break;
default:
break;
}
}
if (allDeadInstructions.Count > 0) {
block.remove(allDeadInstructions);
changed = true;
}
return changed;
}
bool okInstructions(Block block, IEnumerable indexes) {
foreach (var index in indexes) {
var instr = block.Instructions[index];
switch (instr.OpCode.Code) {
case Code.Add:
case Code.Add_Ovf:
case Code.Add_Ovf_Un:
case Code.And:
case Code.Arglist:
case Code.Beq:
case Code.Beq_S:
case Code.Bge:
case Code.Bge_S:
case Code.Bge_Un:
case Code.Bge_Un_S:
case Code.Bgt:
case Code.Bgt_S:
case Code.Bgt_Un:
case Code.Bgt_Un_S:
case Code.Ble:
case Code.Ble_S:
case Code.Ble_Un:
case Code.Ble_Un_S:
case Code.Blt:
case Code.Blt_S:
case Code.Blt_Un:
case Code.Blt_Un_S:
case Code.Bne_Un:
case Code.Bne_Un_S:
case Code.Box:
case Code.Br:
case Code.Br_S:
case Code.Break:
case Code.Brfalse:
case Code.Brfalse_S:
case Code.Brtrue:
case Code.Brtrue_S:
case Code.Castclass:
case Code.Ceq:
case Code.Cgt:
case Code.Cgt_Un:
case Code.Ckfinite:
case Code.Clt:
case Code.Clt_Un:
case Code.Constrained:
case Code.Conv_I:
case Code.Conv_I1:
case Code.Conv_I2:
case Code.Conv_I4:
case Code.Conv_I8:
case Code.Conv_Ovf_I:
case Code.Conv_Ovf_I1:
case Code.Conv_Ovf_I1_Un:
case Code.Conv_Ovf_I2:
case Code.Conv_Ovf_I2_Un:
case Code.Conv_Ovf_I4:
case Code.Conv_Ovf_I4_Un:
case Code.Conv_Ovf_I8:
case Code.Conv_Ovf_I8_Un:
case Code.Conv_Ovf_I_Un:
case Code.Conv_Ovf_U:
case Code.Conv_Ovf_U1:
case Code.Conv_Ovf_U1_Un:
case Code.Conv_Ovf_U2:
case Code.Conv_Ovf_U2_Un:
case Code.Conv_Ovf_U4:
case Code.Conv_Ovf_U4_Un:
case Code.Conv_Ovf_U8:
case Code.Conv_Ovf_U8_Un:
case Code.Conv_Ovf_U_Un:
case Code.Conv_R4:
case Code.Conv_R8:
case Code.Conv_R_Un:
case Code.Conv_U:
case Code.Conv_U1:
case Code.Conv_U2:
case Code.Conv_U4:
case Code.Conv_U8:
case Code.Div:
case Code.Div_Un:
case Code.Dup:
case Code.Endfilter:
case Code.Endfinally:
case Code.Isinst:
case Code.Jmp:
case Code.Ldarg:
case Code.Ldarg_0:
case Code.Ldarg_1:
case Code.Ldarg_2:
case Code.Ldarg_3:
case Code.Ldarg_S:
case Code.Ldarga:
case Code.Ldarga_S:
case Code.Ldc_I4:
case Code.Ldc_I4_0:
case Code.Ldc_I4_1:
case Code.Ldc_I4_2:
case Code.Ldc_I4_3:
case Code.Ldc_I4_4:
case Code.Ldc_I4_5:
case Code.Ldc_I4_6:
case Code.Ldc_I4_7:
case Code.Ldc_I4_8:
case Code.Ldc_I4_M1:
case Code.Ldc_I4_S:
case Code.Ldc_I8:
case Code.Ldc_R4:
case Code.Ldc_R8:
case Code.Ldelem:
case Code.Ldelem_I:
case Code.Ldelem_I1:
case Code.Ldelem_I2:
case Code.Ldelem_I4:
case Code.Ldelem_I8:
case Code.Ldelem_R4:
case Code.Ldelem_R8:
case Code.Ldelem_Ref:
case Code.Ldelem_U1:
case Code.Ldelem_U2:
case Code.Ldelem_U4:
case Code.Ldelema:
case Code.Ldfld:
case Code.Ldflda:
case Code.Ldftn:
case Code.Ldind_I:
case Code.Ldind_I1:
case Code.Ldind_I2:
case Code.Ldind_I4:
case Code.Ldind_I8:
case Code.Ldind_R4:
case Code.Ldind_R8:
case Code.Ldind_Ref:
case Code.Ldind_U1:
case Code.Ldind_U2:
case Code.Ldind_U4:
case Code.Ldlen:
case Code.Ldloc:
case Code.Ldloc_0:
case Code.Ldloc_1:
case Code.Ldloc_2:
case Code.Ldloc_3:
case Code.Ldloc_S:
case Code.Ldloca:
case Code.Ldloca_S:
case Code.Ldnull:
case Code.Ldobj:
case Code.Ldsfld:
case Code.Ldsflda:
case Code.Ldstr:
case Code.Ldtoken:
case Code.Ldvirtftn:
case Code.Leave:
case Code.Leave_S:
case Code.Localloc:
case Code.Mkrefany:
case Code.Mul:
case Code.Mul_Ovf:
case Code.Mul_Ovf_Un:
case Code.Neg:
case Code.Newarr:
case Code.Nop:
case Code.Not:
case Code.Or:
case Code.Pop:
case Code.Readonly:
case Code.Refanytype:
case Code.Refanyval:
case Code.Rem:
case Code.Rem_Un:
case Code.Ret:
case Code.Rethrow:
case Code.Shl:
case Code.Shr:
case Code.Shr_Un:
case Code.Sizeof:
case Code.Sub:
case Code.Sub_Ovf:
case Code.Sub_Ovf_Un:
case Code.Switch:
case Code.Tailcall:
case Code.Throw:
case Code.Unaligned:
case Code.Unbox:
case Code.Unbox_Any:
case Code.Volatile:
case Code.Xor:
break;
case Code.Call:
case Code.Calli:
case Code.Callvirt:
case Code.Cpblk:
case Code.Cpobj:
case Code.Initblk:
case Code.Initobj:
case Code.Newobj:
case Code.Starg:
case Code.Starg_S:
case Code.Stelem:
case Code.Stelem_I:
case Code.Stelem_I1:
case Code.Stelem_I2:
case Code.Stelem_I4:
case Code.Stelem_I8:
case Code.Stelem_R4:
case Code.Stelem_R8:
case Code.Stelem_Ref:
case Code.Stfld:
case Code.Stind_I:
case Code.Stind_I1:
case Code.Stind_I2:
case Code.Stind_I4:
case Code.Stind_I8:
case Code.Stind_R4:
case Code.Stind_R8:
case Code.Stind_Ref:
case Code.Stloc:
case Code.Stloc_0:
case Code.Stloc_1:
case Code.Stloc_2:
case Code.Stloc_3:
case Code.Stloc_S:
case Code.Stobj:
case Code.Stsfld:
default:
return false;
}
}
return true;
}
class InstructionExpressionFinder {
List deadInstructions = new List();
Block block;
bool methodHasReturnValue;
public List DeadInstructions {
get { return deadInstructions; }
}
public void init(Block block, bool methodHasReturnValue) {
deadInstructions.Clear();
this.block = block;
this.methodHasReturnValue = methodHasReturnValue;
}
public bool find(int index) {
return find(ref index, true);
}
bool find(ref int index, bool addIt) {
if (index < 0)
return false;
var startInstr = block.Instructions[index];
int startInstrPushes, startInstrPops;
calculateStackUsage(startInstr.Instruction, false, out startInstrPushes, out startInstrPops);
// Don't add it if it clears the stack (eg. leave)
if (addIt && startInstrPops >= 0)
addIndex(index);
if (startInstrPops == 0)
return true;
while (index > 0) {
var instr = block.Instructions[index - 1];
if (startInstrPops == 0 && instr.OpCode.OpCodeType != OpCodeType.Prefix)
break;
int pushes, pops;
calculateStackUsage(instr.Instruction, methodHasReturnValue, out pushes, out pops);
if (pops < 0)
break; // eg. leave
index--;
if (pops > 0) { // if instr uses any args
bool otherExpr = pops > 0 && pushes == 0;
if (!find(ref index, addIt && !otherExpr))
break;
}
else if (pushes != 0 || pops != 0) {
if (addIt)
addIndex(index);
}
if (pushes > 0 && startInstrPops >= 0) {
if (pushes > startInstrPops)
return false;
startInstrPops -= pushes;
}
}
return startInstrPops <= 0;
}
void addIndex(int index) {
deadInstructions.Add(index);
}
}
static void calculateStackUsage(Instruction instr, bool methodHasReturnValue, out int pushes, out int pops) {
instr.CalculateStackUsage(false, out pushes, out pops);
}
}
}