1 //===- BoundsChecking.cpp - Instrumentation for run-time bounds checking --===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements a pass that instruments the code to perform run-time
11 // bounds checking on loads, stores, and other memory intrinsics.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Instrumentation.h"
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/Analysis/MemoryBuiltins.h"
18 #include "llvm/Analysis/TargetFolder.h"
19 #include "llvm/IR/DataLayout.h"
20 #include "llvm/IR/IRBuilder.h"
21 #include "llvm/IR/InstIterator.h"
22 #include "llvm/IR/Intrinsics.h"
23 #include "llvm/Pass.h"
24 #include "llvm/Support/CommandLine.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include "llvm/Target/TargetLibraryInfo.h"
30 #define DEBUG_TYPE "bounds-checking"
32 static cl::opt<bool> SingleTrapBB("bounds-checking-single-trap",
33 cl::desc("Use one trap block per function"));
35 STATISTIC(ChecksAdded, "Bounds checks added");
36 STATISTIC(ChecksSkipped, "Bounds checks skipped");
37 STATISTIC(ChecksUnable, "Bounds checks unable to add");
39 typedef IRBuilder<true, TargetFolder> BuilderTy;
42 struct BoundsChecking : public FunctionPass {
45 BoundsChecking() : FunctionPass(ID) {
46 initializeBoundsCheckingPass(*PassRegistry::getPassRegistry());
49 bool runOnFunction(Function &F) override;
51 void getAnalysisUsage(AnalysisUsage &AU) const override {
52 AU.addRequired<DataLayoutPass>();
53 AU.addRequired<TargetLibraryInfo>();
58 const TargetLibraryInfo *TLI;
59 ObjectSizeOffsetEvaluator *ObjSizeEval;
64 BasicBlock *getTrapBB();
65 void emitBranchToTrap(Value *Cmp = nullptr);
66 bool instrument(Value *Ptr, Value *Val);
70 char BoundsChecking::ID = 0;
71 INITIALIZE_PASS(BoundsChecking, "bounds-checking", "Run-time bounds checking",
75 /// getTrapBB - create a basic block that traps. All overflowing conditions
76 /// branch to this block. There's only one trap block per function.
77 BasicBlock *BoundsChecking::getTrapBB() {
78 if (TrapBB && SingleTrapBB)
81 Function *Fn = Inst->getParent()->getParent();
82 IRBuilder<>::InsertPointGuard Guard(*Builder);
83 TrapBB = BasicBlock::Create(Fn->getContext(), "trap", Fn);
84 Builder->SetInsertPoint(TrapBB);
86 llvm::Value *F = Intrinsic::getDeclaration(Fn->getParent(), Intrinsic::trap);
87 CallInst *TrapCall = Builder->CreateCall(F);
88 TrapCall->setDoesNotReturn();
89 TrapCall->setDoesNotThrow();
90 TrapCall->setDebugLoc(Inst->getDebugLoc());
91 Builder->CreateUnreachable();
97 /// emitBranchToTrap - emit a branch instruction to a trap block.
98 /// If Cmp is non-null, perform a jump only if its value evaluates to true.
99 void BoundsChecking::emitBranchToTrap(Value *Cmp) {
100 // check if the comparison is always false
101 ConstantInt *C = dyn_cast_or_null<ConstantInt>(Cmp);
104 if (!C->getZExtValue())
107 Cmp = nullptr; // unconditional branch
111 Instruction *Inst = Builder->GetInsertPoint();
112 BasicBlock *OldBB = Inst->getParent();
113 BasicBlock *Cont = OldBB->splitBasicBlock(Inst);
114 OldBB->getTerminator()->eraseFromParent();
117 BranchInst::Create(getTrapBB(), Cont, Cmp, OldBB);
119 BranchInst::Create(getTrapBB(), OldBB);
123 /// instrument - adds run-time bounds checks to memory accessing instructions.
124 /// Ptr is the pointer that will be read/written, and InstVal is either the
125 /// result from the load or the value being stored. It is used to determine the
126 /// size of memory block that is touched.
127 /// Returns true if any change was made to the IR, false otherwise.
128 bool BoundsChecking::instrument(Value *Ptr, Value *InstVal) {
129 uint64_t NeededSize = DL->getTypeStoreSize(InstVal->getType());
130 DEBUG(dbgs() << "Instrument " << *Ptr << " for " << Twine(NeededSize)
133 SizeOffsetEvalType SizeOffset = ObjSizeEval->compute(Ptr);
135 if (!ObjSizeEval->bothKnown(SizeOffset)) {
140 Value *Size = SizeOffset.first;
141 Value *Offset = SizeOffset.second;
142 ConstantInt *SizeCI = dyn_cast<ConstantInt>(Size);
144 Type *IntTy = DL->getIntPtrType(Ptr->getType());
145 Value *NeededSizeVal = ConstantInt::get(IntTy, NeededSize);
147 // three checks are required to ensure safety:
148 // . Offset >= 0 (since the offset is given from the base ptr)
149 // . Size >= Offset (unsigned)
150 // . Size - Offset >= NeededSize (unsigned)
152 // optimization: if Size >= 0 (signed), skip 1st check
153 // FIXME: add NSW/NUW here? -- we dont care if the subtraction overflows
154 Value *ObjSize = Builder->CreateSub(Size, Offset);
155 Value *Cmp2 = Builder->CreateICmpULT(Size, Offset);
156 Value *Cmp3 = Builder->CreateICmpULT(ObjSize, NeededSizeVal);
157 Value *Or = Builder->CreateOr(Cmp2, Cmp3);
158 if (!SizeCI || SizeCI->getValue().slt(0)) {
159 Value *Cmp1 = Builder->CreateICmpSLT(Offset, ConstantInt::get(IntTy, 0));
160 Or = Builder->CreateOr(Cmp1, Or);
162 emitBranchToTrap(Or);
167 bool BoundsChecking::runOnFunction(Function &F) {
168 DL = &getAnalysis<DataLayoutPass>().getDataLayout();
169 TLI = &getAnalysis<TargetLibraryInfo>();
172 BuilderTy TheBuilder(F.getContext(), TargetFolder(DL));
173 Builder = &TheBuilder;
174 ObjectSizeOffsetEvaluator TheObjSizeEval(DL, TLI, F.getContext(),
175 /*RoundToAlign=*/true);
176 ObjSizeEval = &TheObjSizeEval;
178 // check HANDLE_MEMORY_INST in include/llvm/Instruction.def for memory
179 // touching instructions
180 std::vector<Instruction*> WorkList;
181 for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) {
182 Instruction *I = &*i;
183 if (isa<LoadInst>(I) || isa<StoreInst>(I) || isa<AtomicCmpXchgInst>(I) ||
184 isa<AtomicRMWInst>(I))
185 WorkList.push_back(I);
188 bool MadeChange = false;
189 for (std::vector<Instruction*>::iterator i = WorkList.begin(),
190 e = WorkList.end(); i != e; ++i) {
193 Builder->SetInsertPoint(Inst);
194 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
195 MadeChange |= instrument(LI->getPointerOperand(), LI);
196 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
197 MadeChange |= instrument(SI->getPointerOperand(), SI->getValueOperand());
198 } else if (AtomicCmpXchgInst *AI = dyn_cast<AtomicCmpXchgInst>(Inst)) {
199 MadeChange |= instrument(AI->getPointerOperand(),AI->getCompareOperand());
200 } else if (AtomicRMWInst *AI = dyn_cast<AtomicRMWInst>(Inst)) {
201 MadeChange |= instrument(AI->getPointerOperand(), AI->getValOperand());
203 llvm_unreachable("unknown Instruction type");
209 FunctionPass *llvm::createBoundsCheckingPass() {
210 return new BoundsChecking();