path: root/lib/Analysis/NaCl/PNaClABIVerifyFunctions.cpp

//===- PNaClABIVerifyFunctions.cpp - Verify PNaCl ABI rules ---------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Verify function-level PNaCl ABI requirements.
//
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/Twine.h"
#include "llvm/Analysis/NaCl.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Support/raw_ostream.h"

#include "PNaClABITypeChecker.h"
using namespace llvm;

namespace {

// Checks that examine anything in the function body should be in
// FunctionPasses to make them streaming-friendly
class PNaClABIVerifyFunctions : public FunctionPass {
 public:
  static char ID;
  PNaClABIVerifyFunctions() :
      FunctionPass(ID),
      Reporter(new PNaClABIErrorReporter),
      ReporterIsOwned(true) {
    initializePNaClABIVerifyFunctionsPass(*PassRegistry::getPassRegistry());
  }
  explicit PNaClABIVerifyFunctions(PNaClABIErrorReporter *Reporter_) :
      FunctionPass(ID),
      Reporter(Reporter_),
      ReporterIsOwned(false) {
    initializePNaClABIVerifyFunctionsPass(*PassRegistry::getPassRegistry());
  }
  ~PNaClABIVerifyFunctions() {
    if (ReporterIsOwned)
      delete Reporter;
  }
  bool runOnFunction(Function &F);
  virtual void print(raw_ostream &O, const Module *M) const;
 private:
  bool IsWhitelistedMetadata(unsigned MDKind);
  const char *checkInstruction(const Instruction *Inst);
  PNaClABIErrorReporter *Reporter;
  bool ReporterIsOwned;
};

} // and anonymous namespace

// There's no built-in way to get the name of an MDNode, so use a
// string ostream to print it.
static std::string getMDNodeString(unsigned Kind,
                                   const SmallVectorImpl<StringRef> &MDNames) {
  std::string MDName;
  raw_string_ostream N(MDName);
  if (Kind < MDNames.size()) {
    N << "!" << MDNames[Kind];
  } else {
    N << "!<unknown kind #" << Kind << ">";
  }
  return N.str();
}

bool PNaClABIVerifyFunctions::IsWhitelistedMetadata(unsigned MDKind) {
  return MDKind == LLVMContext::MD_dbg && PNaClABIAllowDebugMetadata;
}

// A valid pointer type is either:
//  * a pointer to a valid PNaCl scalar type, or
//  * a function pointer (with valid argument and return types).
static bool isValidPointerType(Type *Ty) {
  if (PointerType *PtrTy = dyn_cast<PointerType>(Ty)) {
    if (PtrTy->getAddressSpace() != 0)
      return false;
    if (PNaClABITypeChecker::isValidScalarType(PtrTy->getElementType()))
      return true;
    if (FunctionType *FTy = dyn_cast<FunctionType>(PtrTy->getElementType()))
      return PNaClABITypeChecker::isValidFunctionType(FTy);
  }
  return false;
}

static bool isIntrinsicFunc(const Value *Val) {
  if (const Function *F = dyn_cast<Function>(Val))
    return F->isIntrinsic();
  return false;
}

// InherentPtrs may be referenced by casts -- PtrToIntInst and
// BitCastInst -- that produce NormalizedPtrs.
//
// InherentPtrs exclude intrinsic functions in order to prevent taking
// the address of an intrinsic function.  InherentPtrs include
// intrinsic calls because some intrinsics return pointer types
// (e.g. nacl.read.tp returns i8*).
static bool isInherentPtr(const Value *Val) {
  return isa<AllocaInst>(Val) ||
         (isa<GlobalValue>(Val) && !isIntrinsicFunc(Val)) ||
         isa<IntrinsicInst>(Val);
}

// NormalizedPtrs may be used where pointer types are required -- for
// loads, stores, etc.  Note that this excludes ConstantExprs,
// ConstantPointerNull and UndefValue.
static bool isNormalizedPtr(const Value *Val) {
  if (!isValidPointerType(Val->getType()))
    return false;
  // The bitcast must also be a bitcast of an InherentPtr, but we
  // check that when visiting the bitcast instruction.
  return isa<IntToPtrInst>(Val) || isa<BitCastInst>(Val) || isInherentPtr(Val);
}

static bool isValidScalarOperand(const Value *Val) {
  // The types of Instructions and Arguments are checked elsewhere
  // (when visiting the Instruction or the Function).  BasicBlocks are
  // included here because branch instructions have BasicBlock
  // operands.
  if (isa<Instruction>(Val) || isa<Argument>(Val) || isa<BasicBlock>(Val))
    return true;

  // Allow some Constants.  Note that this excludes ConstantExprs.
  return PNaClABITypeChecker::isValidScalarType(Val->getType()) &&
         (isa<ConstantInt>(Val) ||
          isa<ConstantFP>(Val) ||
          isa<UndefValue>(Val));
}

static bool isAllowedAlignment(unsigned Alignment, Type *Ty, bool IsAtomic) {
  if (IsAtomic) {
    // For atomic operations, the alignment must match the size of the type.
    if (Ty->isIntegerTy()) {
      unsigned Bits = Ty->getIntegerBitWidth();
      return Bits % 8 == 0 && Alignment == Bits / 8;
    }
    return (Ty->isDoubleTy() && Alignment == 8) ||
           (Ty->isFloatTy() && Alignment == 4);
  }
  // Non-atomic integer operations must always use "align 1", since we
  // do not want the backend to generate code with non-portable
  // undefined behaviour (such as misaligned access faults) if user
  // code specifies "align 4" but uses a misaligned pointer.  As a
  // concession to performance, we allow larger alignment values for
  // floating point types.
  //
  // To reduce the set of alignment values that need to be encoded in
  // pexes, we disallow other alignment values.  We require alignments
  // to be explicit by disallowing Alignment == 0.
  return Alignment == 1 ||
         (Ty->isDoubleTy() && Alignment == 8) ||
         (Ty->isFloatTy() && Alignment == 4);
}

// Check the instruction's opcode and its operands.  The operands may
// require opcode-specific checking.
//
// This returns an error string if the instruction is rejected, or
// NULL if the instruction is allowed.
const char *PNaClABIVerifyFunctions::checkInstruction(const Instruction *Inst) {
  // If the instruction has a single pointer operand, PtrOperandIndex is
  // set to its operand index.
  unsigned PtrOperandIndex = -1;

  switch (Inst->getOpcode()) {
    // Disallowed instructions. Default is to disallow.
    // We expand GetElementPtr out into arithmetic.
    case Instruction::GetElementPtr:
    // VAArg is expanded out by ExpandVarArgs.
    case Instruction::VAArg:
    // Zero-cost C++ exception handling is not supported yet.
    case Instruction::Invoke:
    case Instruction::LandingPad:
    case Instruction::Resume:
    // indirectbr may interfere with streaming
    case Instruction::IndirectBr:
    // No vector instructions yet
    case Instruction::ExtractElement:
    case Instruction::InsertElement:
    case Instruction::ShuffleVector:
    // ExtractValue and InsertValue operate on struct values.
    case Instruction::ExtractValue:
    case Instruction::InsertValue:
      return "bad instruction opcode";
    default:
      return "unknown instruction opcode";

    // Terminator instructions
    case Instruction::Ret:
    case Instruction::Br:
    case Instruction::Unreachable:
    // Binary operations
    case Instruction::Add:
    case Instruction::FAdd:
    case Instruction::Sub:
    case Instruction::FSub:
    case Instruction::Mul:
    case Instruction::FMul:
    case Instruction::UDiv:
    case Instruction::SDiv:
    case Instruction::FDiv:
    case Instruction::URem:
    case Instruction::SRem:
    case Instruction::FRem:
    // Bitwise binary operations
    case Instruction::Shl:
    case Instruction::LShr:
    case Instruction::AShr:
    case Instruction::And:
    case Instruction::Or:
    case Instruction::Xor:
    // Memory instructions
    case Instruction::Fence:
    // Conversion operations
    case Instruction::Trunc:
    case Instruction::ZExt:
    case Instruction::SExt:
    case Instruction::FPTrunc:
    case Instruction::FPExt:
    case Instruction::FPToUI:
    case Instruction::FPToSI:
    case Instruction::UIToFP:
    case Instruction::SIToFP:
    // Other operations
    case Instruction::ICmp:
    case Instruction::FCmp:
    case Instruction::PHI:
    case Instruction::Select:
      break;

    // Memory accesses.
    case Instruction::Load: {
      const LoadInst *Load = cast<LoadInst>(Inst);
      if (!isAllowedAlignment(Load->getAlignment(),
                              Load->getType(),
                              Load->isAtomic()))
        return "bad alignment";
      PtrOperandIndex = 0;
      if (!isNormalizedPtr(Inst->getOperand(PtrOperandIndex)))
        return "bad pointer";
      break;
    }
    case Instruction::Store: {
      const StoreInst *Store = cast<StoreInst>(Inst);
      if (!isAllowedAlignment(Store->getAlignment(),
                              Store->getValueOperand()->getType(),
                              Store->isAtomic()))
        return "bad alignment";
      PtrOperandIndex = 1;
      if (!isNormalizedPtr(Inst->getOperand(PtrOperandIndex)))
        return "bad pointer";
      break;
    }
    case Instruction::AtomicCmpXchg:
    case Instruction::AtomicRMW:
      PtrOperandIndex = 0;
      if (!isNormalizedPtr(Inst->getOperand(PtrOperandIndex)))
        return "bad pointer";
      break;

    // Casts.
    case Instruction::BitCast:
      if (Inst->getType()->isPointerTy()) {
        PtrOperandIndex = 0;
        if (!isInherentPtr(Inst->getOperand(PtrOperandIndex)))
          return "operand not InherentPtr";
      }
      break;
    case Instruction::IntToPtr:
      if (!cast<IntToPtrInst>(Inst)->getSrcTy()->isIntegerTy(32))
        return "non-i32 inttoptr";
      break;
    case Instruction::PtrToInt:
      PtrOperandIndex = 0;
      if (!isInherentPtr(Inst->getOperand(PtrOperandIndex)))
        return "operand not InherentPtr";
      if (!Inst->getType()->isIntegerTy(32))
        return "non-i32 ptrtoint";
      break;

    case Instruction::Alloca: {
      if (!cast<AllocaInst>(Inst)->getAllocatedType()->isIntegerTy(8))
        return "non-i8 alloca";
      break;
    }

    case Instruction::Call: {
      const CallInst *Call = cast<CallInst>(Inst);
      if (Call->isInlineAsm())
        return "inline assembly";
      if (!Call->getAttributes().isEmpty())
        return "bad call attributes";
      if (Call->getCallingConv() != CallingConv::C)
        return "bad calling convention";

      // Intrinsic calls can have multiple pointer arguments and
      // metadata arguments, so handle them specially.
      if (const IntrinsicInst *Call = dyn_cast<IntrinsicInst>(Inst)) {
        for (unsigned ArgNum = 0, E = Call->getNumArgOperands();
             ArgNum < E; ++ArgNum) {
          const Value *Arg = Call->getArgOperand(ArgNum);
          if (!(isValidScalarOperand(Arg) ||
                isNormalizedPtr(Arg) ||
                isa<MDNode>(Arg)))
            return "bad intrinsic operand";
        }
        // Disallow alignments other than 1 on memcpy() etc., for the
        // same reason that we disallow them on integer loads and
        // stores.
        if (const MemIntrinsic *MemOp = dyn_cast<MemIntrinsic>(Call)) {
          // Avoid the getAlignment() method here because it aborts if
          // the alignment argument is not a Constant.
          Value *AlignArg = MemOp->getArgOperand(3);
          if (!isa<ConstantInt>(AlignArg) ||
              cast<ConstantInt>(AlignArg)->getZExtValue() != 1) {
            return "bad alignment";
          }
        }
        // Allow the instruction and skip the later checks.
        return NULL;
      }

      // The callee is the last operand.
      PtrOperandIndex = Inst->getNumOperands() - 1;
      if (!isNormalizedPtr(Inst->getOperand(PtrOperandIndex)))
        return "bad function callee operand";
      break;
    }

    case Instruction::Switch: {
      // SwitchInst represents switch cases using array and vector
      // constants, which we normally reject, so we must check
      // SwitchInst specially here.
      const SwitchInst *Switch = cast<SwitchInst>(Inst);
      if (!isValidScalarOperand(Switch->getCondition()))
        return "bad switch condition";

      // SwitchInst requires the cases to be ConstantInts, but it
      // doesn't require their types to be the same as the condition
      // value, so check all the cases too.
      for (SwitchInst::ConstCaseIt Case = Switch->case_begin(),
             E = Switch->case_end(); Case != E; ++Case) {
        IntegersSubset CaseRanges = Case.getCaseValueEx();
        for (unsigned I = 0, E = CaseRanges.getNumItems(); I < E ; ++I) {
          if (!isValidScalarOperand(
                  CaseRanges.getItem(I).getLow().toConstantInt()) ||
              !isValidScalarOperand(
                  CaseRanges.getItem(I).getHigh().toConstantInt())) {
            return "bad switch case";
          }
        }
      }

      // Allow the instruction and skip the later checks.
      return NULL;
    }
  }

  // Check the instruction's operands.  We have already checked any
  // pointer operands.  Any remaining operands must be scalars.
  for (unsigned OpNum = 0, E = Inst->getNumOperands(); OpNum < E; ++OpNum) {
    if (OpNum != PtrOperandIndex &&
        !isValidScalarOperand(Inst->getOperand(OpNum)))
      return "bad operand";
  }

  // Check arithmetic attributes.
  if (const OverflowingBinaryOperator *Op =
          dyn_cast<OverflowingBinaryOperator>(Inst)) {
    if (Op->hasNoUnsignedWrap())
      return "has \"nuw\" attribute";
    if (Op->hasNoSignedWrap())
      return "has \"nsw\" attribute";
  }
  if (const PossiblyExactOperator *Op =
          dyn_cast<PossiblyExactOperator>(Inst)) {
    if (Op->isExact())
      return "has \"exact\" attribute";
  }

  // Allow the instruction.
  return NULL;
}

bool PNaClABIVerifyFunctions::runOnFunction(Function &F) {
  SmallVector<StringRef, 8> MDNames;
  F.getContext().getMDKindNames(MDNames);

  for (Function::const_iterator FI = F.begin(), FE = F.end();
           FI != FE; ++FI) {
    for (BasicBlock::const_iterator BBI = FI->begin(), BBE = FI->end();
             BBI != BBE; ++BBI) {
      const Instruction *Inst = BBI;
      // Check the instruction opcode first.  This simplifies testing,
      // because some instruction opcodes must be rejected out of hand
      // (regardless of the instruction's result type) and the tests
      // check the reason for rejection.
      const char *Error = checkInstruction(BBI);
      // Check the instruction's result type.
      if (!Error && !(PNaClABITypeChecker::isValidScalarType(Inst->getType()) ||
                      isNormalizedPtr(Inst) ||
                      isa<AllocaInst>(Inst))) {
        Error = "bad result type";
      }
      if (Error) {
        Reporter->addError() << "Function " << F.getName() <<
          " disallowed: " << Error << ": " << *BBI << "\n";
      }

      // Check instruction attachment metadata.
      SmallVector<std::pair<unsigned, MDNode*>, 4> MDForInst;
      BBI->getAllMetadata(MDForInst);

      for (unsigned i = 0, e = MDForInst.size(); i != e; i++) {
        if (!IsWhitelistedMetadata(MDForInst[i].first)) {
          Reporter->addError()
              << "Function " << F.getName()
              << " has disallowed instruction metadata: "
              << getMDNodeString(MDForInst[i].first, MDNames) << "\n";
        }
      }
    }
  }

  Reporter->checkForFatalErrors();
  return false;
}

// This method exists so that the passes can easily be run with opt -analyze.
// In this case the default constructor is used and we want to reset the error
// messages after each print.
void PNaClABIVerifyFunctions::print(llvm::raw_ostream &O, const Module *M)
    const {
  Reporter->printErrors(O);
  Reporter->reset();
}

char PNaClABIVerifyFunctions::ID = 0;
INITIALIZE_PASS(PNaClABIVerifyFunctions, "verify-pnaclabi-functions",
                "Verify functions for PNaCl", false, true)

FunctionPass *llvm::createPNaClABIVerifyFunctionsPass(
    PNaClABIErrorReporter *Reporter) {
  return new PNaClABIVerifyFunctions(Reporter);
}