//=== UndefResultChecker.cpp ------------------------------------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This defines UndefResultChecker, a builtin check in ExprEngine that

// performs checks for undefined results of non-assignment binary operators.

//

//===----------------------------------------------------------------------===//

#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"

#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"

#include "clang/StaticAnalyzer/Core/Checker.h"

#include "clang/StaticAnalyzer/Core/CheckerManager.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicSize.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"

#include "llvm/ADT/SmallString.h"

#include "llvm/Support/raw_ostream.h"

using namespace clang;

using namespace ento;

namespace {

class UndefResultChecker

  : public Checker< check::PostStmt<BinaryOperator> > {

  mutable std::unique_ptr<BugType> BT;

public:

  void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const;

};

} // end anonymous namespace

static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) {

  ProgramStateRef state = C.getState();

  if (!isa<ArraySubscriptExpr>(Ex))

    return false;

  SVal Loc = C.getSVal(Ex);

  if (!Loc.isValid())

    return false;

  const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion();

  const ElementRegion *ER = dyn_cast<ElementRegion>(MR);

  if (!ER)

    return false;

  DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();

  DefinedOrUnknownSVal ElementCount = getDynamicElementCount(

      state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());

  ProgramStateRef StInBound = state->assumeInBound(Idx, ElementCount, true);

  ProgramStateRef StOutBound = state->assumeInBound(Idx, ElementCount, false);

  return StOutBound && 
!StInBound4
;

}

static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C) {

  return C.isGreaterOrEqual(

      B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType()));

}

static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B,

                                             CheckerContext &C) {

  SValBuilder &SB = C.getSValBuilder();

  ProgramStateRef State = C.getState();

  const llvm::APSInt *LHS = SB.getKnownValue(State, C.getSVal(B->getLHS()));

  const llvm::APSInt *RHS = SB.getKnownValue(State, C.getSVal(B->getRHS()));

  assert(LHS && RHS && "Values unknown, inconsistent state");

  return (unsigned)RHS->getZExtValue() > LHS->countLeadingZeros();

}

void UndefResultChecker::checkPostStmt(const BinaryOperator *B,

                                       CheckerContext &C) const {

  if (C.getSVal(B).isUndef()) {

    // Do not report assignments of uninitialized values inside swap functions.

    // This should allow to swap partially uninitialized structs

    // (radar://14129997)

    if (const FunctionDecl *EnclosingFunctionDecl =

        dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))

      if (C.getCalleeName(EnclosingFunctionDecl) == "swap")

        return;

    // Generate an error node.

    ExplodedNode *N = C.generateErrorNode();

    if (!N)

      return;

    if (!BT)

      BT.reset(

          new BuiltinBug(this, "Result of operation is garbage or undefined"));

    SmallString<256> sbuf;

    llvm::raw_svector_ostream OS(sbuf);

    const Expr *Ex = nullptr;

    bool isLeft = true;

    if (C.getSVal(B->getLHS()).isUndef()) {

      Ex = B->getLHS()->IgnoreParenCasts();

      isLeft = true;

    }

    else if (C.getSVal(B->getRHS()).isUndef()) {

      Ex = B->getRHS()->IgnoreParenCasts();

      isLeft = false;

    }

    if (Ex) {

      OS << "The " << (isLeft ? "left" : 
"right"7
) << " operand of '"

         << BinaryOperator::getOpcodeStr(B->getOpcode())

         << "' is a garbage value";

      if (isArrayIndexOutOfBounds(C, Ex))

        OS << " due to array index out of bounds";

    } else {

      // Neither operand was undefined, but the result is undefined.

      if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||

           B->getOpcode() == BinaryOperatorKind::BO_Shr) &&

          C.isNegative(B->getRHS())) {

        OS << "The result of the "

           << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"

                                                              : "right")

           << " shift is undefined because the right operand is negative";

        Ex = B->getRHS();

      } else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||

                  B->getOpcode() == BinaryOperatorKind::BO_Shr) &&

                 isShiftOverflow(B, C)) {

        OS << "The result of the "

           << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"

                                                              : "right")

           << " shift is undefined due to shifting by ";

        Ex = B->getRHS();

        SValBuilder &SB = C.getSValBuilder();

        const llvm::APSInt *I =

            SB.getKnownValue(C.getState(), C.getSVal(B->getRHS()));

        if (!I)

          OS << "a value that is";

        else if (I->isUnsigned())

          OS << '\'' << I->getZExtValue() << "\', which is";

        else

          OS << '\'' << I->getSExtValue() << "\', which is";

        OS << " greater or equal to the width of type '"

           << B->getLHS()->getType().getAsString() << "'.";

      } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&

                 C.isNegative(B->getLHS())) {

        OS << "The result of the left shift is undefined because the left "

              "operand is negative";

        Ex = B->getLHS();

      } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&

                 isLeftShiftResultUnrepresentable(B, C)) {

        ProgramStateRef State = C.getState();

        SValBuilder &SB = C.getSValBuilder();

        const llvm::APSInt *LHS =

            SB.getKnownValue(State, C.getSVal(B->getLHS()));

        const llvm::APSInt *RHS =

            SB.getKnownValue(State, C.getSVal(B->getRHS()));

        OS << "The result of the left shift is undefined due to shifting \'"

           << LHS->getSExtValue() << "\' by \'" << RHS->getZExtValue()

           << "\', which is unrepresentable in the unsigned version of "

           << "the return type \'" << B->getLHS()->getType().getAsString()

           << "\'";

        Ex = B->getLHS();

      } else {

        OS << "The result of the '"

           << BinaryOperator::getOpcodeStr(B->getOpcode())

           << "' expression is undefined";

      }

    }

    auto report = std::make_unique<PathSensitiveBugReport>(*BT, OS.str(), N);

    if (Ex) {

      report->addRange(Ex->getSourceRange());

      bugreporter::trackExpressionValue(N, Ex, *report);

    }

    else

      bugreporter::trackExpressionValue(N, B, *report);

    C.emitReport(std::move(report));

  }

}

void ento::registerUndefResultChecker(CheckerManager &mgr) {

  mgr.registerChecker<UndefResultChecker>();

}

bool ento::shouldRegisterUndefResultChecker(const CheckerManager &mgr) {

  return true;

}