lib/FuzzMutate/IRMutator.cpp

   1 //===-- IRMutator.cpp -----------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "llvm/FuzzMutate/IRMutator.h"
  10 #include "llvm/ADT/Optional.h"
  11 #include "llvm/Analysis/TargetLibraryInfo.h"
  12 #include "llvm/FuzzMutate/Operations.h"
  13 #include "llvm/FuzzMutate/Random.h"
  14 #include "llvm/FuzzMutate/RandomIRBuilder.h"
  15 #include "llvm/IR/BasicBlock.h"
  16 #include "llvm/IR/Function.h"
  17 #include "llvm/IR/InstIterator.h"
  18 #include "llvm/IR/Instructions.h"
  19 #include "llvm/IR/Module.h"
  20 #include "llvm/Support/Debug.h"
  21 #include "llvm/Transforms/Scalar/DCE.h"
  22
  23 using namespace llvm;
  24
  25 static void createEmptyFunction(Module &M) {
  26   // TODO: Some arguments and a return value would probably be more interesting.
  27   LLVMContext &Context = M.getContext();
  28   Function *F = Function::Create(FunctionType::get(Type::getVoidTy(Context), {},
  29                                                    /*isVarArg=*/false),
  30                                  GlobalValue::ExternalLinkage, "f", &M);
  31   BasicBlock *BB = BasicBlock::Create(Context, "BB", F);
  32   ReturnInst::Create(Context, BB);
  33 }
  34
  35 void IRMutationStrategy::mutate(Module &M, RandomIRBuilder &IB) {
  36   if (M.empty())
  37     createEmptyFunction(M);
  38
  39   auto RS = makeSampler<Function *>(IB.Rand);
  40   for (Function &F : M)
  41     if (!F.isDeclaration())
  42       RS.sample(&F, /*Weight=*/1);
  43   mutate(*RS.getSelection(), IB);
  44 }
  45
  46 void IRMutationStrategy::mutate(Function &F, RandomIRBuilder &IB) {
  47   mutate(*makeSampler(IB.Rand, make_pointer_range(F)).getSelection(), IB);
  48 }
  49
  50 void IRMutationStrategy::mutate(BasicBlock &BB, RandomIRBuilder &IB) {
  51   mutate(*makeSampler(IB.Rand, make_pointer_range(BB)).getSelection(), IB);
  52 }
  53
  54 void IRMutator::mutateModule(Module &M, int Seed, size_t CurSize,
  55                              size_t MaxSize) {
  56   std::vector<Type *> Types;
  57   for (const auto &Getter : AllowedTypes)
  58     Types.push_back(Getter(M.getContext()));
  59   RandomIRBuilder IB(Seed, Types);
  60
  61   auto RS = makeSampler<IRMutationStrategy *>(IB.Rand);
  62   for (const auto &Strategy : Strategies)
  63     RS.sample(Strategy.get(),
  64               Strategy->getWeight(CurSize, MaxSize, RS.totalWeight()));
  65   auto Strategy = RS.getSelection();
  66
  67   Strategy->mutate(M, IB);
  68 }
  69
  70 static void eliminateDeadCode(Function &F) {
  71   FunctionPassManager FPM;
  72   FPM.addPass(DCEPass());
  73   FunctionAnalysisManager FAM;
  74   FAM.registerPass([&] { return TargetLibraryAnalysis(); });
  75   FAM.registerPass([&] { return PassInstrumentationAnalysis(); });
  76   FPM.run(F, FAM);
  77 }
  78
  79 void InjectorIRStrategy::mutate(Function &F, RandomIRBuilder &IB) {
  80   IRMutationStrategy::mutate(F, IB);
  81   eliminateDeadCode(F);
  82 }
  83
  84 std::vector<fuzzerop::OpDescriptor> InjectorIRStrategy::getDefaultOps() {
  85   std::vector<fuzzerop::OpDescriptor> Ops;
  86   describeFuzzerIntOps(Ops);
  87   describeFuzzerFloatOps(Ops);
  88   describeFuzzerControlFlowOps(Ops);
  89   describeFuzzerPointerOps(Ops);
  90   describeFuzzerAggregateOps(Ops);
  91   describeFuzzerVectorOps(Ops);
  92   return Ops;
  93 }
  94
  95 Optional<fuzzerop::OpDescriptor>
  96 InjectorIRStrategy::chooseOperation(Value *Src, RandomIRBuilder &IB) {
  97   auto OpMatchesPred = [&Src](fuzzerop::OpDescriptor &Op) {
  98     return Op.SourcePreds[0].matches({}, Src);
  99   };
 100   auto RS = makeSampler(IB.Rand, make_filter_range(Operations, OpMatchesPred));
 101   if (RS.isEmpty())
 102     return None;
 103   return *RS;
 104 }
 105
 106 void InjectorIRStrategy::mutate(BasicBlock &BB, RandomIRBuilder &IB) {
 107   SmallVector<Instruction *, 32> Insts;
 108   for (auto I = BB.getFirstInsertionPt(), E = BB.end(); I != E; ++I)
 109     Insts.push_back(&*I);
 110   if (Insts.size() < 1)
 111     return;
 112
 113   // Choose an insertion point for our new instruction.
 114   size_t IP = uniform<size_t>(IB.Rand, 0, Insts.size() - 1);
 115
 116   auto InstsBefore = makeArrayRef(Insts).slice(0, IP);
 117   auto InstsAfter = makeArrayRef(Insts).slice(IP);
 118
 119   // Choose a source, which will be used to constrain the operation selection.
 120   SmallVector<Value *, 2> Srcs;
 121   Srcs.push_back(IB.findOrCreateSource(BB, InstsBefore));
 122
 123   // Choose an operation that's constrained to be valid for the type of the
 124   // source, collect any other sources it needs, and then build it.
 125   auto OpDesc = chooseOperation(Srcs[0], IB);
 126   // Bail if no operation was found
 127   if (!OpDesc)
 128     return;
 129
 130   for (const auto &Pred : makeArrayRef(OpDesc->SourcePreds).slice(1))
 131     Srcs.push_back(IB.findOrCreateSource(BB, InstsBefore, Srcs, Pred));
 132
 133   if (Value *Op = OpDesc->BuilderFunc(Srcs, Insts[IP])) {
 134     // Find a sink and wire up the results of the operation.
 135     IB.connectToSink(BB, InstsAfter, Op);
 136   }
 137 }
 138
 139 uint64_t InstDeleterIRStrategy::getWeight(size_t CurrentSize, size_t MaxSize,
 140                                           uint64_t CurrentWeight) {
 141   // If we have less than 200 bytes, panic and try to always delete.
 142   if (CurrentSize > MaxSize - 200)
 143     return CurrentWeight ? CurrentWeight * 100 : 1;
 144   // Draw a line starting from when we only have 1k left and increasing linearly
 145   // to double the current weight.
 146   int Line = (-2 * CurrentWeight) * (MaxSize - CurrentSize + 1000);
 147   // Clamp negative weights to zero.
 148   if (Line < 0)
 149     return 0;
 150   return Line;
 151 }
 152
 153 void InstDeleterIRStrategy::mutate(Function &F, RandomIRBuilder &IB) {
 154   auto RS = makeSampler<Instruction *>(IB.Rand);
 155   for (Instruction &Inst : instructions(F)) {
 156     // TODO: We can't handle these instructions.
 157     if (Inst.isTerminator() || Inst.isEHPad() ||
 158         Inst.isSwiftError() || isa<PHINode>(Inst))
 159       continue;
 160
 161     RS.sample(&Inst, /*Weight=*/1);
 162   }
 163   if (RS.isEmpty())
 164     return;
 165
 166   // Delete the instruction.
 167   mutate(*RS.getSelection(), IB);
 168   // Clean up any dead code that's left over after removing the instruction.
 169   eliminateDeadCode(F);
 170 }
 171
 172 void InstDeleterIRStrategy::mutate(Instruction &Inst, RandomIRBuilder &IB) {
 173   assert(!Inst.isTerminator() && "Deleting terminators invalidates CFG");
 174
 175   if (Inst.getType()->isVoidTy()) {
 176     // Instructions with void type (ie, store) have no uses to worry about. Just
 177     // erase it and move on.
 178     Inst.eraseFromParent();
 179     return;
 180   }
 181
 182   // Otherwise we need to find some other value with the right type to keep the
 183   // users happy.
 184   auto Pred = fuzzerop::onlyType(Inst.getType());
 185   auto RS = makeSampler<Value *>(IB.Rand);
 186   SmallVector<Instruction *, 32> InstsBefore;
 187   BasicBlock *BB = Inst.getParent();
 188   for (auto I = BB->getFirstInsertionPt(), E = Inst.getIterator(); I != E;
 189        ++I) {
 190     if (Pred.matches({}, &*I))
 191       RS.sample(&*I, /*Weight=*/1);
 192     InstsBefore.push_back(&*I);
 193   }
 194   if (!RS)
 195     RS.sample(IB.newSource(*BB, InstsBefore, {}, Pred), /*Weight=*/1);
 196
 197   Inst.replaceAllUsesWith(RS.getSelection());
 198   Inst.eraseFromParent();
 199 }