Add comments to BCFPass

Slattz · Apr 11, 2023 · 46dd82f · 46dd82f
1 parent 6f9731a
commit 46dd82f
Showing 1 changed file with 24 additions and 11 deletions.
diff --git a/source/BCF/BcfPass.cpp b/source/BCF/BcfPass.cpp
@@ -11,42 +11,50 @@ namespace obfusc {
     bool BcfPass::obfuscate(llvm::Module& mod, llvm::Function& func) {
         bool changed = false;
 
-        std::vector<llvm::BasicBlock*> basicBlocks;
+        std::vector<llvm::BasicBlock*> basicBlocks; //make copy of blocks
         for (auto& block : func) {
             basicBlocks.push_back(&block);
         }
 
+        //For every block copied
         for (llvm::BasicBlock* block : basicBlocks) {
             auto instruction = block->begin();
             if (block->getFirstNonPHIOrDbgOrLifetime()) {
-                instruction = static_cast<llvm::BasicBlock::iterator>(block->getFirstNonPHIOrDbgOrLifetime());
+                instruction = static_cast<llvm::BasicBlock::iterator>(block->getFirstNonPHIOrDbgOrLifetime()); //skip past PHI instructions
             }
 
-            llvm::BasicBlock* origBlock = block->splitBasicBlock(instruction);
-            llvm::BasicBlock* changedBlock = MakeBogusBlock(origBlock, func);
+            llvm::BasicBlock* origBlock = block->splitBasicBlock(instruction); //Get original block
+            llvm::BasicBlock* changedBlock = MakeBogusBlock(origBlock, func); //Get Bogus/altered version of same block
 
+            //Erase from parents for each block
             changedBlock->getTerminator()->eraseFromParent();
             block->getTerminator()->eraseFromParent();
 
             llvm::Type* int32Type = llvm::Type::getInt32Ty(mod.getContext());
 
+            //Create global variables for comparison
             llvm::GlobalVariable* x = new llvm::GlobalVariable(mod, int32Type, false, llvm::GlobalValue::LinkageTypes::InternalLinkage, llvm::ConstantInt::get(int32Type, 1));
             llvm::GlobalVariable* y = new llvm::GlobalVariable(mod, int32Type, false, llvm::GlobalValue::LinkageTypes::InternalLinkage, llvm::ConstantInt::get(int32Type, 3));
 
+            //Load values from global vars
             llvm::LoadInst* opX = new llvm::LoadInst(int32Type, x, "", block);
             llvm::LoadInst* opY = new llvm::LoadInst(int32Type, y, "", block);
 
+            //Create compare instruction
             llvm::ICmpInst* cmpInstr = new llvm::ICmpInst(*block, llvm::CmpInst::Predicate::ICMP_ULT, opX, opY);
+
+            //Create branches to each block based on cmp instr
             llvm::BranchInst::Create(origBlock, changedBlock, cmpInstr, block);
             llvm::BranchInst::Create(origBlock, changedBlock);
 
             auto endInstr = origBlock->end();
-            endInstr--;
+            endInstr--; //Get actual last instr
             auto endBlock = origBlock->splitBasicBlock(endInstr);
-            origBlock->getTerminator()->eraseFromParent();
+            origBlock->getTerminator()->eraseFromParent(); //remove from parent block
 
+            //Make cmp instruction
             cmpInstr = new llvm::ICmpInst(*origBlock, llvm::CmpInst::Predicate::ICMP_ULT, opX, opY);
-            llvm::BranchInst::Create(endBlock, changedBlock, cmpInstr, origBlock);
+            llvm::BranchInst::Create(endBlock, changedBlock, cmpInstr, origBlock); //Loop back from bogus block to changed block
 
             changed = true;
         }
@@ -58,17 +66,18 @@ namespace obfusc {
         llvm::ValueToValueMapTy valMap;
         llvm::BasicBlock* retBlock = llvm::CloneBasicBlock(originalBlock, valMap, "", &func);
 
+        //Start remapping information for each instruction
         auto origInstruction = originalBlock->begin();
         for (auto instruction = retBlock->begin(); instruction != retBlock->end(); instruction++) {
             for (auto op = instruction->op_begin(); op != instruction->op_end(); ++op) {
-                llvm::Value* val = llvm::MapValue(*op, valMap);
+                llvm::Value* val = llvm::MapValue(*op, valMap); //Map operations of new instrs
                 if (val) {
                     *op = val;
                 }
             }
 
             llvm::PHINode* phiNode = llvm::dyn_cast<llvm::PHINode>(instruction);
-            if (phiNode) {
+            if (phiNode) { //Remap PHI nodes 
                 for (unsigned int i = 0; i != phiNode->getNumIncomingValues(); ++i) {
                     llvm::Value* val = llvm::MapValue(phiNode->getIncomingBlock(i), valMap);
                     if (val) {
@@ -80,17 +89,21 @@ namespace obfusc {
             llvm::SmallVector<std::pair<unsigned int, llvm::MDNode*>> metadata;
             instruction->getAllMetadata(metadata);
 
+            //Needed for DWARF symbols
             instruction->setDebugLoc(origInstruction->getDebugLoc());
             origInstruction++;
 
-            if (instruction->isBinaryOp()) {
+            /* Start altering blocks!! */
+
+            if (instruction->isBinaryOp()) { //Swap operators for binary instrs
                 llvm::Value* op0 = instruction->getOperand(0);
                 llvm::Value* op1 = instruction->getOperand(1);
 
                 instruction->setOperand(0, op1);
                 instruction->setOperand(1, op0);
             }
 
+            //Make Load instrs into Store instrs
             else if (instruction->getOpcode() == llvm::Instruction::Load) {
                 llvm::Value* op0 = instruction->getOperand(0);
                 llvm::AllocaInst* allocIns = (llvm::AllocaInst*)op0;
@@ -102,6 +115,7 @@ namespace obfusc {
                 instruction = instruction->eraseFromParent();
             }
 
+            //Make Store instrs into Load instrs
             else if (instruction->getOpcode() == llvm::Instruction::Store) {
                 llvm::Value* op0 = instruction->getOperand(0);
                 llvm::Value* op1 = instruction->getOperand(1);
@@ -113,5 +127,4 @@ namespace obfusc {
 
         return retBlock;
     }
-
 }