DynamicTypePropagation.cpp

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//== DynamicTypePropagation.cpp -------------------------------- -*- C++ -*--=//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This checker defines the rules for dynamic type gathering and propagation.
//
//===----------------------------------------------------------------------===//

#include "ClangSACheckers.h"
#include "clang/Basic/Builtins.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/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"

using namespace clang;
using namespace ento;

namespace {
class DynamicTypePropagation:
    public Checker< check::PreCall,
                    check::PostCall,
                    check::PostStmt<ImplicitCastExpr>,
                    check::PostStmt<CXXNewExpr> > {
  const ObjCObjectType *getObjectTypeForAllocAndNew(const ObjCMessageExpr *MsgE,
                                                    CheckerContext &C) const;

  /// \brief Return a better dynamic type if one can be derived from the cast.
  const ObjCObjectPointerType *getBetterObjCType(const Expr *CastE,
                                                 CheckerContext &C) const;
public:
  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
  void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
  void checkPostStmt(const ImplicitCastExpr *CastE, CheckerContext &C) const;
  void checkPostStmt(const CXXNewExpr *NewE, CheckerContext &C) const;
};
}

static void recordFixedType(const MemRegion *Region, const CXXMethodDecl *MD,
                            CheckerContext &C) {
  assert(Region);
  assert(MD);

  ASTContext &Ctx = C.getASTContext();
  QualType Ty = Ctx.getPointerType(Ctx.getRecordType(MD->getParent()));

  ProgramStateRef State = C.getState();
  State = State->setDynamicTypeInfo(Region, Ty, /*CanBeSubclass=*/false);
  C.addTransition(State);
  return;
}

void DynamicTypePropagation::checkPreCall(const CallEvent &Call,
                                          CheckerContext &C) const {
  if (const CXXConstructorCall *Ctor = dyn_cast<CXXConstructorCall>(&Call)) {
    // C++11 [class.cdtor]p4: When a virtual function is called directly or
    //   indirectly from a constructor or from a destructor, including during
    //   the construction or destruction of the class's non-static data members,
    //   and the object to which the call applies is the object under
    //   construction or destruction, the function called is the final overrider
    //   in the constructor's or destructor's class and not one overriding it in
    //   a more-derived class.

    switch (Ctor->getOriginExpr()->getConstructionKind()) {
    case CXXConstructExpr::CK_Complete:
    case CXXConstructExpr::CK_Delegating:
      // No additional type info necessary.
      return;
    case CXXConstructExpr::CK_NonVirtualBase:
    case CXXConstructExpr::CK_VirtualBase:
      if (const MemRegion *Target = Ctor->getCXXThisVal().getAsRegion())
        recordFixedType(Target, Ctor->getDecl(), C);
      return;
    }

    return;
  }

  if (const CXXDestructorCall *Dtor = dyn_cast<CXXDestructorCall>(&Call)) {
    // C++11 [class.cdtor]p4 (see above)
    if (!Dtor->isBaseDestructor())
      return;

    const MemRegion *Target = Dtor->getCXXThisVal().getAsRegion();
    if (!Target)
      return;

    const Decl *D = Dtor->getDecl();
    if (!D)
      return;

    recordFixedType(Target, cast<CXXDestructorDecl>(D), C);
    return;
  }
}

void DynamicTypePropagation::checkPostCall(const CallEvent &Call,
                                           CheckerContext &C) const {
  // We can obtain perfect type info for return values from some calls.
  if (const ObjCMethodCall *Msg = dyn_cast<ObjCMethodCall>(&Call)) {

    // Get the returned value if it's a region.
    const MemRegion *RetReg = Call.getReturnValue().getAsRegion();
    if (!RetReg)
      return;

    ProgramStateRef State = C.getState();
    const ObjCMethodDecl *D = Msg->getDecl();
    
    if (D && D->hasRelatedResultType()) {
      switch (Msg->getMethodFamily()) {
      default:
        break;

      // We assume that the type of the object returned by alloc and new are the
      // pointer to the object of the class specified in the receiver of the
      // message.
      case OMF_alloc:
      case OMF_new: {
        // Get the type of object that will get created.
        const ObjCMessageExpr *MsgE = Msg->getOriginExpr();
        const ObjCObjectType *ObjTy = getObjectTypeForAllocAndNew(MsgE, C);
        if (!ObjTy)
          return;
        QualType DynResTy =
                 C.getASTContext().getObjCObjectPointerType(QualType(ObjTy, 0));
        C.addTransition(State->setDynamicTypeInfo(RetReg, DynResTy, false));
        break;
      }
      case OMF_init: {
        // Assume, the result of the init method has the same dynamic type as
        // the receiver and propagate the dynamic type info.
        const MemRegion *RecReg = Msg->getReceiverSVal().getAsRegion();
        if (!RecReg)
          return;
        DynamicTypeInfo RecDynType = State->getDynamicTypeInfo(RecReg);
        C.addTransition(State->setDynamicTypeInfo(RetReg, RecDynType));
        break;
      }
      }
    }
    return;
  }

  if (const CXXConstructorCall *Ctor = dyn_cast<CXXConstructorCall>(&Call)) {
    // We may need to undo the effects of our pre-call check.
    switch (Ctor->getOriginExpr()->getConstructionKind()) {
    case CXXConstructExpr::CK_Complete:
    case CXXConstructExpr::CK_Delegating:
      // No additional work necessary.
      // Note: This will leave behind the actual type of the object for
      // complete constructors, but arguably that's a good thing, since it
      // means the dynamic type info will be correct even for objects
      // constructed with operator new.
      return;
    case CXXConstructExpr::CK_NonVirtualBase:
    case CXXConstructExpr::CK_VirtualBase:
      if (const MemRegion *Target = Ctor->getCXXThisVal().getAsRegion()) {
        // We just finished a base constructor. Now we can use the subclass's
        // type when resolving virtual calls.
        const Decl *D = C.getLocationContext()->getDecl();
        recordFixedType(Target, cast<CXXConstructorDecl>(D), C);
      }
      return;
    }
  }
}

void DynamicTypePropagation::checkPostStmt(const ImplicitCastExpr *CastE,
                                           CheckerContext &C) const {
  // We only track dynamic type info for regions.
  const MemRegion *ToR = C.getSVal(CastE).getAsRegion();
  if (!ToR)
    return;

  switch (CastE->getCastKind()) {
  default:
    break;
  case CK_BitCast:
    // Only handle ObjCObjects for now.
    if (const Type *NewTy = getBetterObjCType(CastE, C))
      C.addTransition(C.getState()->setDynamicTypeInfo(ToR, QualType(NewTy,0)));
    break;
  }
  return;
}

void DynamicTypePropagation::checkPostStmt(const CXXNewExpr *NewE,
                                           CheckerContext &C) const {
  if (NewE->isArray())
    return;

  // We only track dynamic type info for regions.
  const MemRegion *MR = C.getSVal(NewE).getAsRegion();
  if (!MR)
    return;
  
  C.addTransition(C.getState()->setDynamicTypeInfo(MR, NewE->getType(),
                                                   /*CanBeSubclass=*/false));
}

const ObjCObjectType *
DynamicTypePropagation::getObjectTypeForAllocAndNew(const ObjCMessageExpr *MsgE,
                                                    CheckerContext &C) const {
  if (MsgE->getReceiverKind() == ObjCMessageExpr::Class) {
    if (const ObjCObjectType *ObjTy
          = MsgE->getClassReceiver()->getAs<ObjCObjectType>())
    return ObjTy;
  }

  if (MsgE->getReceiverKind() == ObjCMessageExpr::SuperClass) {
    if (const ObjCObjectType *ObjTy
          = MsgE->getSuperType()->getAs<ObjCObjectType>())
      return ObjTy;
  }

  const Expr *RecE = MsgE->getInstanceReceiver();
  if (!RecE)
    return nullptr;

  RecE= RecE->IgnoreParenImpCasts();
  if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(RecE)) {
    const StackFrameContext *SFCtx = C.getStackFrame();
    // Are we calling [self alloc]? If this is self, get the type of the
    // enclosing ObjC class.
    if (DRE->getDecl() == SFCtx->getSelfDecl()) {
      if (const ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(SFCtx->getDecl()))
        if (const ObjCObjectType *ObjTy =
            dyn_cast<ObjCObjectType>(MD->getClassInterface()->getTypeForDecl()))
          return ObjTy;
    }
  }
  return nullptr;
}

// Return a better dynamic type if one can be derived from the cast.
// Compare the current dynamic type of the region and the new type to which we
// are casting. If the new type is lower in the inheritance hierarchy, pick it.
const ObjCObjectPointerType *
DynamicTypePropagation::getBetterObjCType(const Expr *CastE,
                                          CheckerContext &C) const {
  const MemRegion *ToR = C.getSVal(CastE).getAsRegion();
  assert(ToR);

  // Get the old and new types.
  const ObjCObjectPointerType *NewTy =
      CastE->getType()->getAs<ObjCObjectPointerType>();
  if (!NewTy)
    return nullptr;
  QualType OldDTy = C.getState()->getDynamicTypeInfo(ToR).getType();
  if (OldDTy.isNull()) {
    return NewTy;
  }
  const ObjCObjectPointerType *OldTy =
    OldDTy->getAs<ObjCObjectPointerType>();
  if (!OldTy)
    return nullptr;

  // Id the old type is 'id', the new one is more precise.
  if (OldTy->isObjCIdType() && !NewTy->isObjCIdType())
    return NewTy;

  // Return new if it's a subclass of old.
  const ObjCInterfaceDecl *ToI = NewTy->getInterfaceDecl();
  const ObjCInterfaceDecl *FromI = OldTy->getInterfaceDecl();
  if (ToI && FromI && FromI->isSuperClassOf(ToI))
    return NewTy;

  return nullptr;
}

void ento::registerDynamicTypePropagation(CheckerManager &mgr) {
  mgr.registerChecker<DynamicTypePropagation>();
}