BoundsChecking.cpp revision 263508 
1//===- BoundsChecking.cpp - Instrumentation for run-time bounds checking --===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements a pass that instruments the code to perform run-time
11// bounds checking on loads, stores, and other memory intrinsics.
12//
13//===----------------------------------------------------------------------===//
14
15#define DEBUG_TYPE "bounds-checking"
16#include "llvm/Transforms/Instrumentation.h"
17#include "llvm/ADT/Statistic.h"
18#include "llvm/Analysis/MemoryBuiltins.h"
19#include "llvm/IR/DataLayout.h"
20#include "llvm/IR/IRBuilder.h"
21#include "llvm/IR/Intrinsics.h"
22#include "llvm/Pass.h"
23#include "llvm/Support/CommandLine.h"
24#include "llvm/Support/Debug.h"
25#include "llvm/Support/InstIterator.h"
26#include "llvm/Support/TargetFolder.h"
27#include "llvm/Support/raw_ostream.h"
28#include "llvm/Target/TargetLibraryInfo.h"
29using namespace llvm;
30
31static cl::opt<bool> SingleTrapBB("bounds-checking-single-trap",
32                                  cl::desc("Use one trap block per function"));
33
34STATISTIC(ChecksAdded, "Bounds checks added");
35STATISTIC(ChecksSkipped, "Bounds checks skipped");
36STATISTIC(ChecksUnable, "Bounds checks unable to add");
37
38typedef IRBuilder<true, TargetFolder> BuilderTy;
39
40namespace {
41  struct BoundsChecking : public FunctionPass {
42    static char ID;
43
44    BoundsChecking() : FunctionPass(ID) {
45      initializeBoundsCheckingPass(*PassRegistry::getPassRegistry());
46    }
47
48    virtual bool runOnFunction(Function &F);
49
50    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
51      AU.addRequired<DataLayout>();
52      AU.addRequired<TargetLibraryInfo>();
53    }
54
55  private:
56    const DataLayout *TD;
57    const TargetLibraryInfo *TLI;
58    ObjectSizeOffsetEvaluator *ObjSizeEval;
59    BuilderTy *Builder;
60    Instruction *Inst;
61    BasicBlock *TrapBB;
62
63    BasicBlock *getTrapBB();
64    void emitBranchToTrap(Value *Cmp = 0);
65    bool computeAllocSize(Value *Ptr, APInt &Offset, Value* &OffsetValue,
66                          APInt &Size, Value* &SizeValue);
67    bool instrument(Value *Ptr, Value *Val);
68 };
69}
70
71char BoundsChecking::ID = 0;
72INITIALIZE_PASS(BoundsChecking, "bounds-checking", "Run-time bounds checking",
73                false, false)
74
75
76/// getTrapBB - create a basic block that traps. All overflowing conditions
77/// branch to this block. There's only one trap block per function.
78BasicBlock *BoundsChecking::getTrapBB() {
79  if (TrapBB && SingleTrapBB)
80    return TrapBB;
81
82  Function *Fn = Inst->getParent()->getParent();
83  IRBuilder<>::InsertPointGuard Guard(*Builder);
84  TrapBB = BasicBlock::Create(Fn->getContext(), "trap", Fn);
85  Builder->SetInsertPoint(TrapBB);
86
87  llvm::Value *F = Intrinsic::getDeclaration(Fn->getParent(), Intrinsic::trap);
88  CallInst *TrapCall = Builder->CreateCall(F);
89  TrapCall->setDoesNotReturn();
90  TrapCall->setDoesNotThrow();
91  TrapCall->setDebugLoc(Inst->getDebugLoc());
92  Builder->CreateUnreachable();
93
94  return TrapBB;
95}
96
97
98/// emitBranchToTrap - emit a branch instruction to a trap block.
99/// If Cmp is non-null, perform a jump only if its value evaluates to true.
100void BoundsChecking::emitBranchToTrap(Value *Cmp) {
101  // check if the comparison is always false
102  ConstantInt *C = dyn_cast_or_null<ConstantInt>(Cmp);
103  if (C) {
104    ++ChecksSkipped;
105    if (!C->getZExtValue())
106      return;
107    else
108      Cmp = 0; // unconditional branch
109  }
110  ++ChecksAdded;
111
112  Instruction *Inst = Builder->GetInsertPoint();
113  BasicBlock *OldBB = Inst->getParent();
114  BasicBlock *Cont = OldBB->splitBasicBlock(Inst);
115  OldBB->getTerminator()->eraseFromParent();
116
117  if (Cmp)
118    BranchInst::Create(getTrapBB(), Cont, Cmp, OldBB);
119  else
120    BranchInst::Create(getTrapBB(), OldBB);
121}
122
123
124/// instrument - adds run-time bounds checks to memory accessing instructions.
125/// Ptr is the pointer that will be read/written, and InstVal is either the
126/// result from the load or the value being stored. It is used to determine the
127/// size of memory block that is touched.
128/// Returns true if any change was made to the IR, false otherwise.
129bool BoundsChecking::instrument(Value *Ptr, Value *InstVal) {
130  uint64_t NeededSize = TD->getTypeStoreSize(InstVal->getType());
131  DEBUG(dbgs() << "Instrument " << *Ptr << " for " << Twine(NeededSize)
132              << " bytes\n");
133
134  SizeOffsetEvalType SizeOffset = ObjSizeEval->compute(Ptr);
135
136  if (!ObjSizeEval->bothKnown(SizeOffset)) {
137    ++ChecksUnable;
138    return false;
139  }
140
141  Value *Size   = SizeOffset.first;
142  Value *Offset = SizeOffset.second;
143  ConstantInt *SizeCI = dyn_cast<ConstantInt>(Size);
144
145  Type *IntTy = TD->getIntPtrType(Ptr->getType());
146  Value *NeededSizeVal = ConstantInt::get(IntTy, NeededSize);
147
148  // three checks are required to ensure safety:
149  // . Offset >= 0  (since the offset is given from the base ptr)
150  // . Size >= Offset  (unsigned)
151  // . Size - Offset >= NeededSize  (unsigned)
152  //
153  // optimization: if Size >= 0 (signed), skip 1st check
154  // FIXME: add NSW/NUW here?  -- we dont care if the subtraction overflows
155  Value *ObjSize = Builder->CreateSub(Size, Offset);
156  Value *Cmp2 = Builder->CreateICmpULT(Size, Offset);
157  Value *Cmp3 = Builder->CreateICmpULT(ObjSize, NeededSizeVal);
158  Value *Or = Builder->CreateOr(Cmp2, Cmp3);
159  if (!SizeCI || SizeCI->getValue().slt(0)) {
160    Value *Cmp1 = Builder->CreateICmpSLT(Offset, ConstantInt::get(IntTy, 0));
161    Or = Builder->CreateOr(Cmp1, Or);
162  }
163  emitBranchToTrap(Or);
164
165  return true;
166}
167
168bool BoundsChecking::runOnFunction(Function &F) {
169  TD = &getAnalysis<DataLayout>();
170  TLI = &getAnalysis<TargetLibraryInfo>();
171
172  TrapBB = 0;
173  BuilderTy TheBuilder(F.getContext(), TargetFolder(TD));
174  Builder = &TheBuilder;
175  ObjectSizeOffsetEvaluator TheObjSizeEval(TD, TLI, F.getContext(),
176                                           /*RoundToAlign=*/true);
177  ObjSizeEval = &TheObjSizeEval;
178
179  // check HANDLE_MEMORY_INST in include/llvm/Instruction.def for memory
180  // touching instructions
181  std::vector<Instruction*> WorkList;
182  for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) {
183    Instruction *I = &*i;
184    if (isa<LoadInst>(I) || isa<StoreInst>(I) || isa<AtomicCmpXchgInst>(I) ||
185        isa<AtomicRMWInst>(I))
186        WorkList.push_back(I);
187  }
188
189  bool MadeChange = false;
190  for (std::vector<Instruction*>::iterator i = WorkList.begin(),
191       e = WorkList.end(); i != e; ++i) {
192    Inst = *i;
193
194    Builder->SetInsertPoint(Inst);
195    if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
196      MadeChange |= instrument(LI->getPointerOperand(), LI);
197    } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
198      MadeChange |= instrument(SI->getPointerOperand(), SI->getValueOperand());
199    } else if (AtomicCmpXchgInst *AI = dyn_cast<AtomicCmpXchgInst>(Inst)) {
200      MadeChange |= instrument(AI->getPointerOperand(),AI->getCompareOperand());
201    } else if (AtomicRMWInst *AI = dyn_cast<AtomicRMWInst>(Inst)) {
202      MadeChange |= instrument(AI->getPointerOperand(), AI->getValOperand());
203    } else {
204      llvm_unreachable("unknown Instruction type");
205    }
206  }
207  return MadeChange;
208}
209
210FunctionPass *llvm::createBoundsCheckingPass() {
211  return new BoundsChecking();
212}
213