484 lines
14 KiB
C#
484 lines
14 KiB
C#
/*
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Copyright (C) 2011-2015 de4dot@gmail.com
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This file is part of de4dot.
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de4dot is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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de4dot is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with de4dot. If not, see <http://www.gnu.org/licenses/>.
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*/
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using System;
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using System.Collections.Generic;
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using dnlib.DotNet;
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using dnlib.DotNet.Emit;
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namespace de4dot.blocks.cflow {
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class SwitchCflowDeobfuscator : BlockDeobfuscator {
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InstructionEmulator instructionEmulator = new InstructionEmulator();
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protected override bool Deobfuscate(Block switchBlock) {
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if (switchBlock.LastInstr.OpCode.Code != Code.Switch)
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return false;
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if (IsSwitchTopOfStack(switchBlock) && DeobfuscateTOS(switchBlock))
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return true;
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if (IsLdlocBranch(switchBlock, true) && DeobfuscateLdloc(switchBlock))
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return true;
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if (IsStLdlocBranch(switchBlock, true) && DeobfuscateStLdloc(switchBlock))
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return true;
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if (IsSwitchType1(switchBlock) && DeobfuscateType1(switchBlock))
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return true;
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if (IsSwitchType2(switchBlock) && DeobfuscateType2(switchBlock))
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return true;
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if (switchBlock.FirstInstr.IsLdloc() && FixSwitchBranch(switchBlock))
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return true;
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return false;
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}
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static bool IsSwitchTopOfStack(Block switchBlock) {
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return switchBlock.Instructions.Count == 1;
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}
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static bool IsLdlocBranch(Block switchBlock, bool isSwitch) {
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int numInstrs = 1 + (isSwitch ? 1 : 0);
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return switchBlock.Instructions.Count == numInstrs && switchBlock.Instructions[0].IsLdloc();
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}
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static bool IsSwitchType1(Block switchBlock) {
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return switchBlock.FirstInstr.IsLdloc();
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}
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bool IsSwitchType2(Block switchBlock) {
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Local local = null;
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foreach (var instr in switchBlock.Instructions) {
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if (!instr.IsLdloc())
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continue;
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local = Instr.GetLocalVar(blocks.Locals, instr);
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break;
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}
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if (local == null)
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return false;
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foreach (var source in switchBlock.Sources) {
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var instrs = source.Instructions;
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for (int i = 1; i < instrs.Count; i++) {
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var ldci4 = instrs[i - 1];
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if (!ldci4.IsLdcI4())
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continue;
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var stloc = instrs[i];
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if (!stloc.IsStloc())
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continue;
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if (Instr.GetLocalVar(blocks.Locals, stloc) != local)
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continue;
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return true;
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}
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}
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return false;
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}
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bool IsStLdlocBranch(Block switchBlock, bool isSwitch) {
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int numInstrs = 2 + (isSwitch ? 1 : 0);
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return switchBlock.Instructions.Count == numInstrs &&
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switchBlock.Instructions[0].IsStloc() &&
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switchBlock.Instructions[1].IsLdloc() &&
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Instr.GetLocalVar(blocks.Locals, switchBlock.Instructions[0]) == Instr.GetLocalVar(blocks.Locals, switchBlock.Instructions[1]);
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}
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bool DeobfuscateTOS(Block switchBlock) {
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bool modified = false;
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if (switchBlock.Targets == null)
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return modified;
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var targets = new List<Block>(switchBlock.Targets);
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modified |= DeobfuscateTOS(targets, switchBlock.FallThrough, switchBlock);
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return modified;
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}
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bool DeobfuscateLdloc(Block switchBlock) {
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bool modified = false;
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var switchVariable = Instr.GetLocalVar(blocks.Locals, switchBlock.Instructions[0]);
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if (switchVariable == null)
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return modified;
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if (switchBlock.Targets == null)
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return modified;
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var targets = new List<Block>(switchBlock.Targets);
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modified |= DeobfuscateLdloc(targets, switchBlock.FallThrough, switchBlock, switchVariable);
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return modified;
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}
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bool DeobfuscateStLdloc(Block switchBlock) {
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bool modified = false;
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var switchVariable = Instr.GetLocalVar(blocks.Locals, switchBlock.Instructions[0]);
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if (switchVariable == null)
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return modified;
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if (switchBlock.Targets == null)
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return modified;
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var targets = new List<Block>(switchBlock.Targets);
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modified |= DeobfuscateStLdloc(targets, switchBlock.FallThrough, switchBlock);
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return modified;
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}
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// Switch deobfuscation when block uses stloc N, ldloc N to load switch constant
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// blk1:
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// ldc.i4 X
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// br swblk
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// swblk:
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// stloc N
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// ldloc N
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// switch (......)
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bool DeobfuscateStLdloc(IList<Block> switchTargets, Block switchFallThrough, Block block) {
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bool modified = false;
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foreach (var source in new List<Block>(block.Sources)) {
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if (!isBranchBlock(source))
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continue;
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instructionEmulator.Initialize(blocks, allBlocks[0] == source);
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instructionEmulator.Emulate(source.Instructions);
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var target = GetSwitchTarget(switchTargets, switchFallThrough, instructionEmulator.Pop());
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if (target == null)
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continue;
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source.ReplaceLastNonBranchWithBranch(0, target);
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source.Add(new Instr(OpCodes.Pop.ToInstruction()));
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modified = true;
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}
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return modified;
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}
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// Switch deobfuscation when block uses ldloc N to load switch constant
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// blk1:
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// ldc.i4 X
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// stloc N
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// br swblk / bcc swblk
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// swblk:
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// ldloc N
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// switch (......)
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bool DeobfuscateLdloc(IList<Block> switchTargets, Block switchFallThrough, Block block, Local switchVariable) {
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bool modified = false;
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foreach (var source in new List<Block>(block.Sources)) {
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if (isBranchBlock(source)) {
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instructionEmulator.Initialize(blocks, allBlocks[0] == source);
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instructionEmulator.Emulate(source.Instructions);
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var target = GetSwitchTarget(switchTargets, switchFallThrough, instructionEmulator.GetLocal(switchVariable));
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if (target == null)
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continue;
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source.ReplaceLastNonBranchWithBranch(0, target);
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modified = true;
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}
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else if (IsBccBlock(source)) {
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instructionEmulator.Initialize(blocks, allBlocks[0] == source);
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instructionEmulator.Emulate(source.Instructions);
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var target = GetSwitchTarget(switchTargets, switchFallThrough, instructionEmulator.GetLocal(switchVariable));
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if (target == null)
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continue;
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if (source.Targets[0] == block) {
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source.SetNewTarget(0, target);
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modified = true;
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}
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if (source.FallThrough == block) {
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source.SetNewFallThrough(target);
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modified = true;
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}
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}
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}
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return modified;
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}
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// Switch deobfuscation when block has switch contant on TOS:
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// blk1:
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// ldc.i4 X
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// br swblk
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// swblk:
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// switch (......)
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bool DeobfuscateTOS(IList<Block> switchTargets, Block switchFallThrough, Block block) {
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bool modified = false;
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foreach (var source in new List<Block>(block.Sources)) {
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if (!isBranchBlock(source))
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continue;
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instructionEmulator.Initialize(blocks, allBlocks[0] == source);
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instructionEmulator.Emulate(source.Instructions);
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var target = GetSwitchTarget(switchTargets, switchFallThrough, instructionEmulator.Pop());
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if (target == null) {
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modified |= DeobfuscateTos_Ldloc(switchTargets, switchFallThrough, source);
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}
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else {
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source.ReplaceLastNonBranchWithBranch(0, target);
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source.Add(new Instr(OpCodes.Pop.ToInstruction()));
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modified = true;
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}
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}
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return modified;
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}
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// ldloc N
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// br swblk
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// or
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// stloc N
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// ldloc N
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// br swblk
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bool DeobfuscateTos_Ldloc(IList<Block> switchTargets, Block switchFallThrough, Block block) {
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if (IsLdlocBranch(block, false)) {
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var switchVariable = Instr.GetLocalVar(blocks.Locals, block.Instructions[0]);
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if (switchVariable == null)
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return false;
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return DeobfuscateLdloc(switchTargets, switchFallThrough, block, switchVariable);
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}
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else if (IsStLdlocBranch(block, false))
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return DeobfuscateStLdloc(switchTargets, switchFallThrough, block);
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return false;
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}
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static bool isBranchBlock(Block block) {
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if (block.Targets != null)
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return false;
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if (block.FallThrough == null)
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return false;
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switch (block.LastInstr.OpCode.Code) {
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case Code.Switch:
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case Code.Leave:
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case Code.Leave_S:
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return false;
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default:
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return true;
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}
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}
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static bool IsBccBlock(Block block) {
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if (block.Targets == null || block.Targets.Count != 1)
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return false;
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if (block.FallThrough == null)
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return false;
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switch (block.LastInstr.OpCode.Code) {
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case Code.Beq:
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case Code.Beq_S:
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case Code.Bge:
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case Code.Bge_S:
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case Code.Bge_Un:
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case Code.Bge_Un_S:
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case Code.Bgt:
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case Code.Bgt_S:
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case Code.Bgt_Un:
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case Code.Bgt_Un_S:
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case Code.Ble:
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case Code.Ble_S:
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case Code.Ble_Un:
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case Code.Ble_Un_S:
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case Code.Blt:
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case Code.Blt_S:
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case Code.Blt_Un:
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case Code.Blt_Un_S:
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case Code.Bne_Un:
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case Code.Bne_Un_S:
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case Code.Brfalse:
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case Code.Brfalse_S:
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case Code.Brtrue:
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case Code.Brtrue_S:
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return true;
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default:
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return false;
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}
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}
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bool DeobfuscateType1(Block switchBlock) {
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Block target;
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if (!EmulateGetTarget(switchBlock, out target) || target != null)
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return false;
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bool modified = false;
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foreach (var source in new List<Block>(switchBlock.Sources)) {
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if (!source.CanAppend(switchBlock))
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continue;
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if (!WillHaveKnownTarget(switchBlock, source))
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continue;
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source.Append(switchBlock);
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modified = true;
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}
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return modified;
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}
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bool DeobfuscateType2(Block switchBlock) {
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bool modified = false;
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var bccSources = new List<Block>();
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foreach (var source in new List<Block>(switchBlock.Sources)) {
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if (source.LastInstr.IsConditionalBranch()) {
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bccSources.Add(source);
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continue;
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}
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if (!source.CanAppend(switchBlock))
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continue;
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if (!WillHaveKnownTarget(switchBlock, source))
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continue;
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source.Append(switchBlock);
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modified = true;
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}
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foreach (var bccSource in bccSources) {
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if (!WillHaveKnownTarget(switchBlock, bccSource))
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continue;
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var consts = GetBccLocalConstants(bccSource);
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if (consts.Count == 0)
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continue;
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var newFallThrough = CreateBlock(consts, bccSource.FallThrough);
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var newTarget = CreateBlock(consts, bccSource.Targets[0]);
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var oldFallThrough = bccSource.FallThrough;
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var oldTarget = bccSource.Targets[0];
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bccSource.SetNewFallThrough(newFallThrough);
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bccSource.SetNewTarget(0, newTarget);
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newFallThrough.SetNewFallThrough(oldFallThrough);
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newTarget.SetNewFallThrough(oldTarget);
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modified = true;
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}
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return modified;
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}
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static Block CreateBlock(Dictionary<Local, int> consts, Block fallThrough) {
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var block = new Block();
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foreach (var kv in consts) {
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block.Instructions.Add(new Instr(Instruction.CreateLdcI4(kv.Value)));
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block.Instructions.Add(new Instr(OpCodes.Stloc.ToInstruction(kv.Key)));
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}
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fallThrough.Parent.Add(block);
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return block;
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}
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Dictionary<Local, int> GetBccLocalConstants(Block block) {
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var dict = new Dictionary<Local, int>();
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var instrs = block.Instructions;
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for (int i = 0; i < instrs.Count; i++) {
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var instr = instrs[i];
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if (instr.IsStloc()) {
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var local = Instr.GetLocalVar(blocks.Locals, instr);
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if (local == null)
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continue;
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var ldci4 = i == 0 ? null : instrs[i - 1];
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if (ldci4 == null || !ldci4.IsLdcI4())
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dict.Remove(local);
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else
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dict[local] = ldci4.GetLdcI4Value();
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}
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else if (instr.IsLdloc()) {
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var local = Instr.GetLocalVar(blocks.Locals, instr);
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if (local != null)
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dict.Remove(local);
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}
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else if (instr.OpCode.Code == Code.Ldloca || instr.OpCode.Code == Code.Ldloca_S) {
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var local = instr.Operand as Local;
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if (local != null)
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dict.Remove(local);
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}
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}
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return dict;
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}
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bool EmulateGetTarget(Block switchBlock, out Block target) {
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instructionEmulator.Initialize(blocks, allBlocks[0] == switchBlock);
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try {
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instructionEmulator.Emulate(switchBlock.Instructions, 0, switchBlock.Instructions.Count - 1);
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}
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catch (NullReferenceException) {
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// Here if eg. invalid metadata token in a call instruction (operand is null)
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target = null;
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return false;
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}
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target = GetTarget(switchBlock);
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return true;
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}
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bool WillHaveKnownTarget(Block switchBlock, Block source) {
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instructionEmulator.Initialize(blocks, allBlocks[0] == source);
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try {
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instructionEmulator.Emulate(source.Instructions);
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instructionEmulator.Emulate(switchBlock.Instructions, 0, switchBlock.Instructions.Count - 1);
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}
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catch (NullReferenceException) {
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// Here if eg. invalid metadata token in a call instruction (operand is null)
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return false;
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}
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return GetTarget(switchBlock) != null;
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}
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Block GetTarget(Block switchBlock) {
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var val1 = instructionEmulator.Pop();
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if (!val1.IsInt32())
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return null;
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return CflowUtils.GetSwitchTarget(switchBlock.Targets, switchBlock.FallThrough, (Int32Value)val1);
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}
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static Block GetSwitchTarget(IList<Block> targets, Block fallThrough, Value value) {
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if (!value.IsInt32())
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return null;
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return CflowUtils.GetSwitchTarget(targets, fallThrough, (Int32Value)value);
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}
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static bool FixSwitchBranch(Block switchBlock) {
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// Code:
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// blk1:
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// ldc.i4 XXX
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// br common
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// blk2:
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// ldc.i4 YYY
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// br common
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// common:
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// stloc X
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// br swblk
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// swblk:
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// ldloc X
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// switch
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// Inline common into blk1 and blk2.
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bool modified = false;
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foreach (var commonSource in new List<Block>(switchBlock.Sources)) {
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if (commonSource.Instructions.Count != 1)
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continue;
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if (!commonSource.FirstInstr.IsStloc())
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continue;
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foreach (var blk in new List<Block>(commonSource.Sources)) {
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if (blk.CanAppend(commonSource)) {
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blk.Append(commonSource);
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modified = true;
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}
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}
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}
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return modified;
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}
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}
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}
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