revng-revng/variablemanager.cpp

/// \file variablemanager.cpp
/// \brief This file handles the creation and management of global variables,
///        i.e. mainly parts of the CPU state

//
// This file is distributed under the MIT License. See LICENSE.md for details.
//

// Standard includes
#include <cstdint>
#include <stack>
#include <sstream>
#include <set>
#include <string>

// LLVM includes
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/Support/Casting.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/ValueMapper.h"

// Local includes
#include "debug.h"
#include "ir-helpers.h"
#include "variablemanager.h"
#include "revamb.h"
#include "ptcdump.h"
#include "ptcinterface.h"

using namespace llvm;

class OffsetValueStack {

private:
  using OffsetValuePair = std::pair<int64_t, Value *>;

public:
  void pushIfNew(int64_t Offset, Value *V) {
    OffsetValuePair Element = { Offset, V };
    if (!Seen.count(Element)) {
      Seen.insert(Element);
      Stack.push_back(Element);
    }
  }

  void push(int64_t Offset, Value *V) {
    OffsetValuePair Element = { Offset, V };
    Stack.push_back(Element);
  }

  bool empty() { return Stack.empty(); }

  std::pair<int64_t, Value *> pop() {
    auto Result = Stack.back();
    Stack.pop_back();
    return Result;
  }

  // TODO: this is on O(n)
  void cloneSisters(Value *Old, Value *New) {
    for (auto &OVP : Stack)
      if (OVP.second == Old)
        push(OVP.first, New);
  }

private:
  std::set<OffsetValuePair> Seen;
  std::vector<OffsetValuePair> Stack;
};

static std::pair<IntegerType *, unsigned>
getTypeAtOffset(const DataLayout *TheLayout, Type *VarType, intptr_t Offset) {
  unsigned Depth = 0;
  while (1) {
    switch (VarType->getTypeID()) {
      case llvm::Type::TypeID::PointerTyID:
        // BEWARE: here we return { nullptr, 0 } as an intended workaround for
        // a specific situation.
        //
        // We can't use assertions on pointers, as we do for all the other
        // unhandled types, because they will be inevitably triggered during the
        // execution. Indeed, all the other types are not present in QEMU
        // CPUState and we can safely assert it. This is not true for pointers
        // that are used in different places in QEMU CPUState.
        //
        // Given that we have ruled out assertions, we need to handle the
        // pointer case so that it keeps working. This function is expected to
        // return { nullptr, 0 } when the offset points to a memory location
        // associated to padding space. In principle, pointers are not padding
        // space, but the result of returning { nullptr, 0 } here is that load
        // and store operations treat pointers like padding. This means that
        // pointers cannot be read or written, and memcpy simply skips over them
        // leaving them alone.
        //
        // This behavior is intended, because a pointer into the CPUState could
        // be used to modify CPU registers indirectly, which is against all the
        // assumption of the analysis necessary for the translation, and also
        // against what really happens in a CPU, where CPU state cannot be
        // addressed.
        return { nullptr, 0 };

      case llvm::Type::TypeID::IntegerTyID:
        return { cast<IntegerType>(VarType), Offset };

      case llvm::Type::TypeID::ArrayTyID:
        VarType = VarType->getArrayElementType();
        Offset %= TheLayout->getTypeAllocSize(VarType);
        DBG("type-at-offset", dbg << std::string(Depth++ * 2, ' ')
            << " Is an Array. Offset in Element: " << Offset << '\n');
        break;

      case llvm::Type::TypeID::StructTyID:
        {
          StructType *TheStruct = cast<StructType>(VarType);
          const StructLayout *Layout = TheLayout->getStructLayout(TheStruct);
          unsigned FieldIndex = Layout->getElementContainingOffset(Offset);
          uint64_t FieldOffset = Layout->getElementOffset(FieldIndex);
          VarType = TheStruct->getTypeAtIndex(FieldIndex);
          intptr_t FieldEnd = FieldOffset
                              + TheLayout->getTypeAllocSize(VarType);

          DBG("type-at-offset", dbg
              << std::string(Depth++ * 2, ' ')
              << " Offset: " << Offset
              << " Struct Name: " << TheStruct->getName().str()
              << " Field Index: " << FieldIndex
              << " Field offset: " << FieldOffset
              << " Field end: " << FieldEnd
              << "\n");

          if (Offset >= FieldEnd)
            return { nullptr, 0 }; // It's padding

          Offset -= FieldOffset;
        }
        break;

      default:
        assert(false and "unexpected TypeID");
    }
  }
}

VariableManager::VariableManager(Module& TheModule,
                                 Module& HelpersModule,
                                 Architecture& TargetArchitecture) :
  TheModule(TheModule),
  Builder(TheModule.getContext()),
  CPUStateType(nullptr),
  ModuleLayout(&HelpersModule.getDataLayout()),
  EnvOffset(0),
  Env(nullptr),
  AliasScopeMDKindID(TheModule.getMDKindID("alias.scope")),
  NoAliasMDKindID(TheModule.getMDKindID("noalias")),
  TargetArchitecture(TargetArchitecture) {

  LLVMContext &Context = TheModule.getContext();
  auto *CPUStateAliasDomain = MDNode::getDistinct(Context,
                                                  ArrayRef<Metadata *>());

  auto *Temporary = MDNode::get(Context, ArrayRef<Metadata *>());
  ArrayRef<Metadata *> Arguments({ Temporary, CPUStateAliasDomain });
  auto *CPUStateScope = MDNode::getDistinct(Context, Arguments);
  CPUStateScope->replaceOperandWith(0, CPUStateScope);

  CPUStateScopeSet = MDNode::get(Context,
                                 ArrayRef<Metadata *>({ CPUStateScope }));

  assert(ptc.initialized_env != nullptr);

  using ElectionMap = std::map<StructType *, unsigned>;
  using ElectionMapElement = std::pair<StructType * const, unsigned>;
  ElectionMap EnvElection;
  const std::string HelperPrefix = "helper_";
  std::set<StructType *> Structs;
  for (Function& HelperFunction : HelpersModule) {
    FunctionType *HelperType = HelperFunction.getFunctionType();
    Type *ReturnType = HelperType->getReturnType();
    if (ReturnType->isPointerTy())
      Structs.insert(dyn_cast<StructType>(ReturnType->getPointerElementType()));

    for (Type *Param : HelperType->params())
      if (Param->isPointerTy())
        Structs.insert(dyn_cast<StructType>(Param->getPointerElementType()));

    if (startsWith(HelperFunction.getName(), HelperPrefix)
        && HelperFunction.getFunctionType()->getNumParams() > 1) {

      for (Type *Candidate : HelperType->params()) {
        Structs.insert(dyn_cast<StructType>(Candidate));
        if (Candidate->isPointerTy()) {
          auto *PointeeType = Candidate->getPointerElementType();
          auto *EnvType = dyn_cast<StructType>(PointeeType);
          // Ensure it is a struct and not a union
          if (EnvType != nullptr && EnvType->getNumElements() > 1) {

            auto It = EnvElection.find(EnvType);
            if (It != EnvElection.end())
              EnvElection[EnvType]++;
            else
              EnvElection[EnvType] = 1;
          }
        }
      }
    }
  }

  Structs.erase(nullptr);

  assert(EnvElection.size() > 0);

  auto Compare = [] (ElectionMapElement& It1,
                     ElectionMapElement& It2) {
    return It1.second < It2.second;
  };
  auto Max = std::max_element(EnvElection.begin(), EnvElection.end(), Compare);
  CPUStateType = Max->first;

  // Look for structures containing CPUStateType as a member and promove them
  // to CPUStateType. Basically this is a flexible way to keep track of the *CPU
  // struct too (e.g. MIPSCPU).
  std::set<StructType *> Visited;
  bool Changed = true;
  Visited.insert(CPUStateType);
  while (Changed) {
    Changed = false;
    for (StructType *TheStruct : Structs) {
      if (Visited.find(TheStruct) != Visited.end())
        continue;

      auto Begin = TheStruct->element_begin();
      auto End = TheStruct->element_end();
      auto Found = std::find(Begin, End, CPUStateType);
      if (Found != End) {
        unsigned Index = Found - Begin;
        const StructLayout *Layout = nullptr;
        Layout = ModuleLayout->getStructLayout(TheStruct);
        EnvOffset += Layout->getElementOffset(Index);
        CPUStateType = TheStruct;
        Visited.insert(CPUStateType);
        Changed = true;
        break;
      }
    }
  }
}

bool VariableManager::storeToCPUStateOffset(IRBuilder<> &Builder,
                                            unsigned StoreSize,
                                            unsigned Offset,
                                            Value *ToStore) {
  Value *Target;
  unsigned Remaining;
  std::tie(Target, Remaining) = getByCPUStateOffsetInternal(Offset);

  if (Target == nullptr)
    return false;

  unsigned ShiftAmount = 0;
  if (TargetArchitecture.isLittleEndian())
    ShiftAmount = Remaining;
  else {
    // >> (Size1 - Size2) - Remaining;
    Type *PointeeTy = Target->getType()->getPointerElementType();
    unsigned GlobalSize = cast<IntegerType>(PointeeTy)->getBitWidth() / 8;
    assert(GlobalSize != 0);
    ShiftAmount = (GlobalSize - StoreSize) - Remaining;
  }
  ShiftAmount *= 8;

  // Build blanking mask
  uint64_t BitMask = (StoreSize == 8 ?
                      (uint64_t) -1
                      : ((uint64_t) 1 << StoreSize * 8) - 1);
  assert(ShiftAmount != 64);
  BitMask <<= ShiftAmount;
  BitMask = ~BitMask;

  auto *InputStoreTy = cast<IntegerType>(Builder.getIntNTy(StoreSize * 8));
  auto *FieldTy = cast<IntegerType>(Target->getType()->getPointerElementType());
  unsigned FieldSize = FieldTy->getBitWidth() / 8;

  // Are we trying to store more than it fits?
  if (StoreSize > FieldSize) {
    // If we're storing more than it fits and the following memory is not
    // padding the store is not valid.
    if (getByCPUStateOffsetInternal(Offset + FieldSize).first != nullptr)
      return false;
  }

  // Truncate value to store
  auto *Truncated = Builder.CreateTrunc(ToStore, InputStoreTy);
  if (StoreSize > FieldSize)
    Truncated = Builder.CreateTrunc(Truncated, FieldTy);

  // Re-extend
  ToStore = Builder.CreateZExt(Truncated, FieldTy);

  if (BitMask != 0) {
    // Load the value
    auto *LoadEnvField = Builder.CreateLoad(Target);
    setAliasScope(LoadEnvField);

    auto *Blanked = Builder.CreateAnd(LoadEnvField, BitMask);

    // Shift value to store
    ToStore = Builder.CreateShl(ToStore, ShiftAmount);

    // Combine them
    ToStore = Builder.CreateOr(ToStore, Blanked);
  }

  // Type *TargetPointer = Target->getType()->getPointerElementType();
  // Value *ToStore = Builder.CreateZExt(InArguments[0], TargetPointer);
  auto *Store = Builder.CreateStore(ToStore, Target);
  setAliasScope(Store);

  return true;
}

Value *VariableManager::loadFromCPUStateOffset(IRBuilder<> &Builder,
                                               unsigned LoadSize,
                                               unsigned Offset) {
  Value *Target;
  unsigned Remaining;
  std::tie(Target, Remaining) = getByCPUStateOffsetInternal(Offset);

  if (Target == nullptr)
    return nullptr;

  // Load the whole field
  auto *LoadEnvField = Builder.CreateLoad(Target);
  setAliasScope(LoadEnvField);

  // Extract the desired part
  // Shift right of the desired amount
  unsigned ShiftAmount = 0;
  if (TargetArchitecture.isLittleEndian()) {
    ShiftAmount = Remaining;
  } else {
    // >> (Size1 - Size2) - Remaining;
    auto *LoadedTy = cast<IntegerType>(LoadEnvField->getType());
    unsigned GlobalSize = LoadedTy->getBitWidth() / 8;
    assert(GlobalSize != 0);
    ShiftAmount = (GlobalSize - LoadSize) - Remaining;
  }
  ShiftAmount *= 8;
  Value *Result = LoadEnvField;

  if (ShiftAmount != 0)
    Result = Builder.CreateLShr(Result, ShiftAmount);

  Type *LoadTy = Builder.getIntNTy(LoadSize * 8);

  // Are we trying to load more than its available in the field?
  if (auto FieldTy = dyn_cast<IntegerType>(Result->getType())) {
    unsigned FieldSize = FieldTy->getBitWidth() / 8;
    if (FieldSize < LoadSize) {
      // If after what we are loading ther is something that is not padding we
      // cannot load safely
      if (getByCPUStateOffsetInternal(Offset + FieldSize).first != nullptr)
        return nullptr;
      Result = Builder.CreateZExt(Result, LoadTy);
    }
  }

  // Truncate of the desired amount
  return Builder.CreateTrunc(Result, LoadTy);
}


bool VariableManager::memcpyAtEnvOffset(llvm::IRBuilder<> &Builder,
                                        llvm::CallInst *CallMemcpy,
                                        unsigned InitialEnvOffset,
                                        bool EnvIsSrc) {
  Function *Callee = getCallee(CallMemcpy);
  // We only support memcpys where the last parameter is constant
  assert(Callee != nullptr
         and (Callee->getIntrinsicID() == Intrinsic::memcpy
              and isa<ConstantInt>(CallMemcpy->getArgOperand(2))));

  Value *OtherOp = CallMemcpy->getArgOperand(EnvIsSrc ? 0 : 1);
  auto *MemcpySize = cast<Constant>(CallMemcpy->getArgOperand(2));
  Value *OtherBasePtr = Builder.CreatePtrToInt(OtherOp, Builder.getInt64Ty());

  uint64_t TotalSize = getZExtValue(MemcpySize, *ModuleLayout);
  uint64_t Offset = 0;

  bool OnlyPointersAndPadding = true;
  while (Offset < TotalSize) {
    GlobalVariable *EnvVar = getByEnvOffset(InitialEnvOffset + Offset).first;

    // Consider the case when there's simply nothing there (alignment space).
    if (EnvVar == nullptr) {
      // TODO: remove "false and", but after adding type based stuff
      if (false and EnvIsSrc) {
        ConstantInt *ZeroByte = Builder.getInt8(0);
        ConstantInt *OffsetInt = Builder.getInt64(Offset);
        Value *NewAddress = Builder.CreateAdd(OffsetInt, OtherBasePtr);
        Type *Int8PtrTy = Builder.getInt8Ty()->getPointerTo();
        Value *OtherPtr = Builder.CreateIntToPtr(NewAddress, Int8PtrTy);
        Builder.CreateStore(ZeroByte, OtherPtr);
        OnlyPointersAndPadding = false;
      }
      Offset++;
      continue;
    }
    OnlyPointersAndPadding = false;

    ConstantInt *OffsetInt = Builder.getInt64(Offset);
    Value *NewAddress = Builder.CreateAdd(OffsetInt, OtherBasePtr);
    Value *OtherPtr = Builder.CreateIntToPtr(NewAddress, EnvVar->getType());

    Value *Dst = EnvIsSrc ? OtherPtr : EnvVar;
    Value *Src = EnvIsSrc ? EnvVar : OtherPtr;
    Builder.CreateStore(Builder.CreateLoad(Src), Dst);

    Type *PointeeTy = EnvVar->getType()->getPointerElementType();
    Offset += ModuleLayout->getTypeAllocSize(PointeeTy);
  }

  if (OnlyPointersAndPadding)
    cast<Instruction>(OtherBasePtr)->eraseFromParent();

  return Offset == TotalSize;
}

// TODO: `newFunction` reflects the tcg terminology but in this context is
//       highly misleading
void VariableManager::newFunction(Instruction *Delimiter,
                                  PTCInstructionList *Instructions) {
  LocalTemporaries.clear();
  newBasicBlock(Delimiter, Instructions);
}

/// Informs the VariableManager that a new basic block has begun, so it can
/// discard basic block-level variables.
///
/// \param Delimiter the new point where to insert allocations for local
///                  variables.
/// \param Instructions the new PTCInstructionList to use from now on.
void VariableManager::newBasicBlock(Instruction *Delimiter,
                                    PTCInstructionList *Instructions) {
  Temporaries.clear();
  if (Instructions != nullptr)
    this->Instructions = Instructions;

  if (Delimiter != nullptr)
    Builder.SetInsertPoint(Delimiter);
}

void VariableManager::newBasicBlock(BasicBlock *Delimiter,
                                    PTCInstructionList *Instructions) {
  Temporaries.clear();
  if (Instructions != nullptr)
    this->Instructions = Instructions;

  if (Delimiter != nullptr)
    Builder.SetInsertPoint(Delimiter);
}

bool VariableManager::isEnv(Value *TheValue) {
  auto *Load = dyn_cast<LoadInst>(TheValue);
  if (Load != nullptr)
    return Load->getPointerOperand() == Env;

  return TheValue == Env;
}

static ConstantInt *fromBytes(IntegerType *Type, void *Data) {
  switch (Type->getBitWidth()) {
  case 8:
    return ConstantInt::get(Type, *(static_cast<uint8_t *>(Data)));
  case 16:
    return ConstantInt::get(Type, *(static_cast<uint16_t *>(Data)));
  case 32:
    return ConstantInt::get(Type, *(static_cast<uint32_t *>(Data)));
  case 64:
    return ConstantInt::get(Type, *(static_cast<uint64_t *>(Data)));
  }

  llvm_unreachable("Unexpected type");
}

// TODO: document that it can return nullptr
GlobalVariable* VariableManager::getByCPUStateOffset(intptr_t Offset,
                                                     std::string Name) {
  GlobalVariable *Result = nullptr;
  unsigned Remaining;
  std::tie(Result, Remaining) = getByCPUStateOffsetInternal(Offset, Name);
  assert(Remaining == 0);
  return Result;
}

std::pair<GlobalVariable*, unsigned>
VariableManager::getByCPUStateOffsetInternal(intptr_t Offset,
                                             std::string Name) {
  GlobalsMap::iterator it = CPUStateGlobals.find(Offset);
  static const char * UnknownCSVPref = "state_0x";
  if (it == CPUStateGlobals.end() ||
      (Name.size() != 0 && it->second->getName().startswith(UnknownCSVPref))) {
    Type *VariableType;
    unsigned Remaining;
    std::tie(VariableType, Remaining) = getTypeAtOffset(ModuleLayout,
                                                        CPUStateType,
                                                        Offset);

    // Unsupported type, let the caller handle the situation
    if (VariableType == nullptr)
      return { nullptr, 0 };

    // Check we're not trying to go inside an existing variable
    if (Remaining != 0) {
      GlobalsMap::iterator it = CPUStateGlobals.find(Offset - Remaining);
      if (it != CPUStateGlobals.end())
        return { it->second, Remaining };
    }

    if (Name.size() == 0) {
      std::stringstream NameStream;
      NameStream << UnknownCSVPref << std::hex << Offset;
      Name = NameStream.str();
    }

    // TODO: offset could be negative, we could segfault here
    auto *InitialValue = fromBytes(cast<IntegerType>(VariableType),
                                   ptc.initialized_env - EnvOffset + Offset);

    auto *NewVariable = new GlobalVariable(TheModule,
                                           VariableType,
                                           false,
                                           GlobalValue::ExternalLinkage,
                                           InitialValue,
                                           Name);
    assert(NewVariable != nullptr);

    if (it != CPUStateGlobals.end()) {
      it->second->replaceAllUsesWith(NewVariable);
      it->second->eraseFromParent();
    }

    CPUStateGlobals[Offset] = NewVariable;

    return { NewVariable, Remaining };
  } else {
    return { it->second, 0 };
  }
}

Value *VariableManager::getOrCreate(unsigned TemporaryId, bool Reading) {
  assert(Instructions != nullptr);

  PTCTemp *Temporary = ptc_temp_get(Instructions, TemporaryId);
  Type *VariableType = Temporary->type == PTC_TYPE_I32 ?
    Builder.getInt32Ty() : Builder.getInt64Ty();

  if (ptc_temp_is_global(Instructions, TemporaryId)) {
    // Basically we use fixed_reg to detect "env"
    if (Temporary->fixed_reg == 0) {
      Value *Result = getByCPUStateOffset(EnvOffset + Temporary->mem_offset,
                                          StringRef(Temporary->name));
      assert(Result != nullptr);
      return Result;
    } else {
      GlobalsMap::iterator it = OtherGlobals.find(TemporaryId);
      if (it != OtherGlobals.end()) {
        return it->second;
      } else {
        // TODO: what do we have here, apart from env?
        auto InitialValue = ConstantInt::get(VariableType, 0);
        GlobalVariable *Result = new GlobalVariable(TheModule,
                                                    VariableType,
                                                    false,
                                                    GlobalValue::CommonLinkage,
                                                    InitialValue,
                                                    StringRef(Temporary->name));

        if (Result->getName() == "env")
          Env = Result;

        OtherGlobals[TemporaryId] = Result;
        return Result;
      }
    }
  } else if (Temporary->temp_local) {
    auto it = LocalTemporaries.find(TemporaryId);
    if (it != LocalTemporaries.end()) {
      return it->second;
    } else {
      AllocaInst *NewTemporary = Builder.CreateAlloca(VariableType);
      LocalTemporaries[TemporaryId] = NewTemporary;
      return NewTemporary;
    }
  } else {
    auto it = Temporaries.find(TemporaryId);
    if (it != Temporaries.end()) {
      return it->second;
    } else {
      // Can't read a temporary if it has never been written, we're probably
      // translating rubbish
      if (Reading)
        return nullptr;

      AllocaInst *NewTemporary = Builder.CreateAlloca(VariableType);
      Temporaries[TemporaryId] = NewTemporary;
      return NewTemporary;
    }
  }
}

template LoadInst *VariableManager::setAliasScope(LoadInst *);
template StoreInst *VariableManager::setAliasScope(StoreInst *);

template<typename T>
T *VariableManager::setAliasScope(T *Instruction) {
  auto *Pointer = Instruction->getPointerOperand();
  if (isa<AllocaInst>(Pointer))
    return Instruction;

  Instruction->setMetadata(AliasScopeMDKindID, CPUStateScopeSet);
  return Instruction;
}

template LoadInst *VariableManager::setNoAlias(LoadInst *);
template StoreInst *VariableManager::setNoAlias(StoreInst *);

template<typename T>
T *VariableManager::setNoAlias(T *Instruction) {
  Instruction->setMetadata(NoAliasMDKindID, CPUStateScopeSet);
  return Instruction;
}

Value *VariableManager::computeEnvAddress(Type *TargetType,
                                          Instruction *InsertBefore,
                                          unsigned Offset) {
  auto *LoadEnv = new LoadInst(Env, "", InsertBefore);
  Type *EnvType = Env->getType()->getPointerElementType();
  Value *Integer = LoadEnv;
  if (Offset != 0)
    Integer =  BinaryOperator::Create(Instruction::Add,
                                      LoadEnv,
                                      ConstantInt::get(EnvType, Offset),
                                      "",
                                      InsertBefore);
  return new IntToPtrInst(Integer, TargetType, "", InsertBefore);
}