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Remove unused local variables

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This commit is contained in:
de4dot 2011-10-20 02:38:44 +02:00
parent c3d6e25ad7
commit c8500b4f33
3 changed files with 126 additions and 1 deletions
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121
blocks/Blocks.cs
View File

@ -81,5 +81,126 @@ namespace de4dot.blocks {
public void getCode(out IList<Instruction> allInstructions, out IList<ExceptionHandler> allExceptionHandlers) {
new CodeGenerator(methodBlocks).getCode(out allInstructions, out allExceptionHandlers);
}
struct LocalVariableInfo {
public Block block;
public int index;
public LocalVariableInfo(Block block, int index) {
this.block = block;
this.index = index;
}
}
public int optimizeLocals() {
if (locals.Count == 0)
return 0;
var allBlocks = new List<Block>(methodBlocks.getAllBlocks());
var usedLocals = new Dictionary<VariableDefinition, List<LocalVariableInfo>>();
foreach (var block in allBlocks) {
for (int i = 0; i < block.Instructions.Count; i++) {
var instr = block.Instructions[i];
VariableDefinition local;
switch (instr.OpCode.Code) {
case Code.Ldloc:
case Code.Ldloc_S:
case Code.Ldloc_0:
case Code.Ldloc_1:
case Code.Ldloc_2:
case Code.Ldloc_3:
case Code.Stloc:
case Code.Stloc_S:
case Code.Stloc_0:
case Code.Stloc_1:
case Code.Stloc_2:
case Code.Stloc_3:
local = Instr.getLocalVar(locals, instr);
break;
case Code.Ldloca_S:
case Code.Ldloca:
local = (VariableDefinition)instr.Operand;
break;
default:
local = null;
break;
}
if (local == null)
continue;
List<LocalVariableInfo> list;
if (!usedLocals.TryGetValue(local, out list))
usedLocals[local] = list = new List<LocalVariableInfo>();
list.Add(new LocalVariableInfo(block, i));
if (usedLocals.Count == locals.Count)
return 0;
}
}
int newIndex = -1;
var newLocals = new List<VariableDefinition>(usedLocals.Count);
foreach (var local in usedLocals.Keys) {
newIndex++;
newLocals.Add(local);
foreach (var info in usedLocals[local])
info.block.Instructions[info.index] = new Instr(optimizeLocalInstr(info.block.Instructions[info.index], local, (uint)newIndex));
}
int numRemoved = locals.Count - newLocals.Count;
locals.Clear();
foreach (var local in newLocals)
locals.Add(local);
return numRemoved;
}
static Instruction optimizeLocalInstr(Instr instr, VariableDefinition local, uint newIndex) {
switch (instr.OpCode.Code) {
case Code.Ldloc:
case Code.Ldloc_S:
case Code.Ldloc_0:
case Code.Ldloc_1:
case Code.Ldloc_2:
case Code.Ldloc_3:
if (newIndex == 0)
return Instruction.Create(OpCodes.Ldloc_0);
if (newIndex == 1)
return Instruction.Create(OpCodes.Ldloc_1);
if (newIndex == 2)
return Instruction.Create(OpCodes.Ldloc_2);
if (newIndex == 3)
return Instruction.Create(OpCodes.Ldloc_3);
if (newIndex <= 0xFF)
return Instruction.Create(OpCodes.Ldloc_S, local);
return Instruction.Create(OpCodes.Ldloc, local);
case Code.Stloc:
case Code.Stloc_S:
case Code.Stloc_0:
case Code.Stloc_1:
case Code.Stloc_2:
case Code.Stloc_3:
if (newIndex == 0)
return Instruction.Create(OpCodes.Stloc_0);
if (newIndex == 1)
return Instruction.Create(OpCodes.Stloc_1);
if (newIndex == 2)
return Instruction.Create(OpCodes.Stloc_2);
if (newIndex == 3)
return Instruction.Create(OpCodes.Stloc_3);
if (newIndex <= 0xFF)
return Instruction.Create(OpCodes.Stloc_S, local);
return Instruction.Create(OpCodes.Stloc, local);
case Code.Ldloca_S:
case Code.Ldloca:
if (newIndex <= 0xFF)
return Instruction.Create(OpCodes.Ldloca_S, local);
return Instruction.Create(OpCodes.Ldloca, local);
default:
throw new ApplicationException("Invalid ld/st local instruction");
}
}
}
}

3
blocks/Instr.cs
View File

@ -42,7 +42,8 @@ namespace de4dot.blocks {
get { return instruction; }
}
// Returns the variable or null if it's not a ldloc/stloc instruction
// Returns the variable or null if it's not a ldloc/stloc instruction. It does not return
// a local variable if it's a ldloca/ldloca.s instruction.
public static VariableDefinition getLocalVar(IList<VariableDefinition> locals, Instr instr) {
switch (instr.OpCode.Code) {
case Code.Ldloc:

3
de4dot.code/ObfuscatedFile.cs
View File

@ -457,6 +457,9 @@ namespace de4dot {
int numDeadBlocks = cflowDeobfuscator.NumberOfRemovedDeadBlocks;
if (numDeadBlocks > 0)
Log.v("Removed {0} dead block(s)", numDeadBlocks);
int numRemovedLocals = blocks.optimizeLocals();
if (numRemovedLocals > 0)
Log.v("Removed {0} unused local(s)", numRemovedLocals);
}
deobfuscateStrings(blocks);
deob.deobfuscateMethodEnd(blocks);