//=== BuiltinFunctionChecker.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 checker evaluates clang builtin functions.

//

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

#include "clang/Basic/Builtins.h"

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

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

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

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

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

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

using namespace clang;

using namespace ento;

namespace {

class BuiltinFunctionChecker : public Checker<eval::Call> {

public:

  bool evalCall(const CallEvent &Call, CheckerContext &C) const;

};

}

bool BuiltinFunctionChecker::evalCall(const CallEvent &Call,

                                      CheckerContext &C) const {

  ProgramStateRef state = C.getState();

  const auto *FD = dyn_cast_or_null<FunctionDecl>(Call.getDecl());

  if (!FD)

    return false;

  const LocationContext *LCtx = C.getLocationContext();

  const Expr *CE = Call.getOriginExpr();

  switch (FD->getBuiltinID()) {

  default:

    return false;

  case Builtin::BI__builtin_assume: {

    assert (Call.getNumArgs() > 0);

    SVal Arg = Call.getArgSVal(0);

    if (Arg.isUndef())

      return true; // Return true to model purity.

    state = state->assume(Arg.castAs<DefinedOrUnknownSVal>(), true);

    // FIXME: do we want to warn here? Not right now. The most reports might

    // come from infeasible paths, thus being false positives.

    if (!state) {

      C.generateSink(C.getState(), C.getPredecessor());

      return true;

    }

    C.addTransition(state);

    return true;

  }

  case Builtin::BI__builtin_unpredictable:

  case Builtin::BI__builtin_expect:

  case Builtin::BI__builtin_expect_with_probability:

  case Builtin::BI__builtin_assume_aligned:

  case Builtin::BI__builtin_addressof:

  case Builtin::BI__builtin_function_start: {

    // For __builtin_unpredictable, __builtin_expect,

    // __builtin_expect_with_probability and __builtin_assume_aligned,

    // just return the value of the subexpression.

    // __builtin_addressof is going from a reference to a pointer, but those

    // are represented the same way in the analyzer.

    assert (Call.getNumArgs() > 0);

    SVal Arg = Call.getArgSVal(0);

    C.addTransition(state->BindExpr(CE, LCtx, Arg));

    return true;

  }

  case Builtin::BI__builtin_alloca_with_align:

  case Builtin::BI__builtin_alloca: {

    // FIXME: Refactor into StoreManager itself?

    MemRegionManager& RM = C.getStoreManager().getRegionManager();

    const AllocaRegion* R =

      RM.getAllocaRegion(CE, C.blockCount(), C.getLocationContext());

    // Set the extent of the region in bytes. This enables us to use the

    // SVal of the argument directly. If we save the extent in bits, we

    // cannot represent values like symbol*8.

    auto Size = Call.getArgSVal(0);

    if (Size.isUndef())

      return true; // Return true to model purity.

    state = setDynamicExtent(state, R, Size.castAs<DefinedOrUnknownSVal>(),

                             C.getSValBuilder());

    C.addTransition(state->BindExpr(CE, LCtx, loc::MemRegionVal(R)));

    return true;

  }

  case Builtin::BI__builtin_dynamic_object_size:

  case Builtin::BI__builtin_object_size:

  case Builtin::BI__builtin_constant_p: {

    // This must be resolvable at compile time, so we defer to the constant

    // evaluator for a value.

    SValBuilder &SVB = C.getSValBuilder();

    SVal V = UnknownVal();

    Expr::EvalResult EVResult;

    if (CE->EvaluateAsInt(EVResult, C.getASTContext(), Expr::SE_NoSideEffects)) {

      // Make sure the result has the correct type.

      llvm::APSInt Result = EVResult.Val.getInt();

      BasicValueFactory &BVF = SVB.getBasicValueFactory();

      BVF.getAPSIntType(CE->getType()).apply(Result);

      V = SVB.makeIntVal(Result);

    }

    if (FD->getBuiltinID() == Builtin::BI__builtin_constant_p) {

      // If we didn't manage to figure out if the value is constant or not,

      // it is safe to assume that it's not constant and unsafe to assume

      // that it's constant.

      if (V.isUnknown())

        V = SVB.makeIntVal(0, CE->getType());

    }

    C.addTransition(state->BindExpr(CE, LCtx, V));

    return true;

  }

  }

}

void ento::registerBuiltinFunctionChecker(CheckerManager &mgr) {

  mgr.registerChecker<BuiltinFunctionChecker>();

}

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

  return true;

}