lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp - platform/external/clang - Git at Google

 //===--- CallAndMessageChecker.cpp ------------------------------*- C++ -*--==//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This defines CallAndMessageChecker, a builtin checker that checks for various
 // errors of call and objc message expressions.
 //
 //===----------------------------------------------------------------------===//

 #include "ClangSACheckers.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/ObjCMessage.h"
 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
 #include "clang/AST/ParentMap.h"
 #include "clang/Basic/TargetInfo.h"

 using namespace clang;
 using namespace ento;

 namespace {
 class CallAndMessageChecker
   : public Checker< check::PreStmt<CallExpr>, check::PreObjCMessage > {
   mutable llvm::OwningPtr<BugType> BT_call_null;
   mutable llvm::OwningPtr<BugType> BT_call_undef;
   mutable llvm::OwningPtr<BugType> BT_call_arg;
   mutable llvm::OwningPtr<BugType> BT_msg_undef;
   mutable llvm::OwningPtr<BugType> BT_msg_arg;
   mutable llvm::OwningPtr<BugType> BT_msg_ret;
 public:

   void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
   void checkPreObjCMessage(ObjCMessage msg, CheckerContext &C) const;

 private:
   static void PreVisitProcessArgs(CheckerContext &C,CallOrObjCMessage callOrMsg,
                              const char *BT_desc, llvm::OwningPtr<BugType> &BT);
   static bool PreVisitProcessArg(CheckerContext &C, SVal V,SourceRange argRange,
           const Expr *argEx, const char *BT_desc, llvm::OwningPtr<BugType> &BT);

   static void EmitBadCall(BugType *BT, CheckerContext &C, const CallExpr *CE);
   void emitNilReceiverBug(CheckerContext &C, const ObjCMessage &msg,
                           ExplodedNode *N) const;

   void HandleNilReceiver(CheckerContext &C,
                          const ProgramState *state,
                          ObjCMessage msg) const;

   static void LazyInit_BT(const char *desc, llvm::OwningPtr<BugType> &BT) {
     if (!BT)
       BT.reset(new BuiltinBug(desc));
   }
 };
 } // end anonymous namespace

 void CallAndMessageChecker::EmitBadCall(BugType *BT, CheckerContext &C,
                                         const CallExpr *CE) {
   ExplodedNode *N = C.generateSink();
   if (!N)
     return;

   BugReport *R = new BugReport(*BT, BT->getName(), N);
   R->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
                                bugreporter::GetCalleeExpr(N)));
   C.EmitReport(R);
 }

 void CallAndMessageChecker::PreVisitProcessArgs(CheckerContext &C,
                                                 CallOrObjCMessage callOrMsg,
                                                 const char *BT_desc,
                                                 llvm::OwningPtr<BugType> &BT) {
   for (unsigned i = 0, e = callOrMsg.getNumArgs(); i != e; ++i)
     if (PreVisitProcessArg(C, callOrMsg.getArgSVal(i),
                            callOrMsg.getArgSourceRange(i), callOrMsg.getArg(i),
                            BT_desc, BT))
       return;
 }

 bool CallAndMessageChecker::PreVisitProcessArg(CheckerContext &C,
                                                SVal V, SourceRange argRange,
                                                const Expr *argEx,
                                                const char *BT_desc,
                                                llvm::OwningPtr<BugType> &BT) {

   if (V.isUndef()) {
     if (ExplodedNode *N = C.generateSink()) {
       LazyInit_BT(BT_desc, BT);

       // Generate a report for this bug.
       BugReport *R = new BugReport(*BT, BT->getName(), N);
       R->addRange(argRange);
       if (argEx)
         R->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N, argEx));
       C.EmitReport(R);
     }
     return true;
   }

   if (const nonloc::LazyCompoundVal *LV =
         dyn_cast<nonloc::LazyCompoundVal>(&V)) {

     class FindUninitializedField {
     public:
       SmallVector<const FieldDecl *, 10> FieldChain;
     private:
       ASTContext &C;
       StoreManager &StoreMgr;
       MemRegionManager &MrMgr;
       Store store;
     public:
       FindUninitializedField(ASTContext &c, StoreManager &storeMgr,
                              MemRegionManager &mrMgr, Store s)
       : C(c), StoreMgr(storeMgr), MrMgr(mrMgr), store(s) {}

       bool Find(const TypedValueRegion *R) {
         QualType T = R->getValueType();
         if (const RecordType *RT = T->getAsStructureType()) {
           const RecordDecl *RD = RT->getDecl()->getDefinition();
           assert(RD && "Referred record has no definition");
           for (RecordDecl::field_iterator I =
                RD->field_begin(), E = RD->field_end(); I!=E; ++I) {
             const FieldRegion *FR = MrMgr.getFieldRegion(*I, R);
             FieldChain.push_back(*I);
             T = (*I)->getType();
             if (T->getAsStructureType()) {
               if (Find(FR))
                 return true;
             }
             else {
               const SVal &V = StoreMgr.getBinding(store, loc::MemRegionVal(FR));
               if (V.isUndef())
                 return true;
             }
             FieldChain.pop_back();
           }
         }

         return false;
       }
     };

     const LazyCompoundValData *D = LV->getCVData();
     FindUninitializedField F(C.getASTContext(),
                              C.getState()->getStateManager().getStoreManager(),
                              C.getSValBuilder().getRegionManager(),
                              D->getStore());

     if (F.Find(D->getRegion())) {
       if (ExplodedNode *N = C.generateSink()) {
         LazyInit_BT(BT_desc, BT);
         llvm::SmallString<512> Str;
         llvm::raw_svector_ostream os(Str);
         os << "Passed-by-value struct argument contains uninitialized data";

         if (F.FieldChain.size() == 1)
           os << " (e.g., field: '" << *F.FieldChain[0] << "')";
         else {
           os << " (e.g., via the field chain: '";
           bool first = true;
           for (SmallVectorImpl<const FieldDecl *>::iterator
                DI = F.FieldChain.begin(), DE = F.FieldChain.end(); DI!=DE;++DI){
             if (first)
               first = false;
             else
               os << '.';
             os << **DI;
           }
           os << "')";
         }

         // Generate a report for this bug.
         BugReport *R = new BugReport(*BT, os.str(), N);
         R->addRange(argRange);

         // FIXME: enhance track back for uninitialized value for arbitrary
         // memregions
         C.EmitReport(R);
       }
       return true;
     }
   }

   return false;
 }

 void CallAndMessageChecker::checkPreStmt(const CallExpr *CE,
                                          CheckerContext &C) const{

   const Expr *Callee = CE->getCallee()->IgnoreParens();
   const LocationContext *LCtx = C.getLocationContext();
   SVal L = C.getState()->getSVal(Callee, LCtx);

   if (L.isUndef()) {
     if (!BT_call_undef)
       BT_call_undef.reset(new BuiltinBug("Called function pointer is an "
                                          "uninitalized pointer value"));
     EmitBadCall(BT_call_undef.get(), C, CE);
     return;
   }

   if (isa<loc::ConcreteInt>(L)) {
     if (!BT_call_null)
       BT_call_null.reset(
         new BuiltinBug("Called function pointer is null (null dereference)"));
     EmitBadCall(BT_call_null.get(), C, CE);
   }

   PreVisitProcessArgs(C, CallOrObjCMessage(CE, C.getState(), LCtx),
                       "Function call argument is an uninitialized value",
                       BT_call_arg);
 }

 void CallAndMessageChecker::checkPreObjCMessage(ObjCMessage msg,
                                                 CheckerContext &C) const {

   const ProgramState *state = C.getState();
   const LocationContext *LCtx = C.getLocationContext();

   // FIXME: Handle 'super'?
   if (const Expr *receiver = msg.getInstanceReceiver()) {
     SVal recVal = state->getSVal(receiver, LCtx);
     if (recVal.isUndef()) {
       if (ExplodedNode *N = C.generateSink()) {
         if (!BT_msg_undef)
           BT_msg_undef.reset(new BuiltinBug("Receiver in message expression is "
                                             "an uninitialized value"));
         BugReport *R =
           new BugReport(*BT_msg_undef, BT_msg_undef->getName(), N);
         R->addRange(receiver->getSourceRange());
         R->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
                                                                    receiver));
         C.EmitReport(R);
       }
       return;
     } else {
       // Bifurcate the state into nil and non-nil ones.
       DefinedOrUnknownSVal receiverVal = cast<DefinedOrUnknownSVal>(recVal);

       const ProgramState *notNilState, *nilState;
       llvm::tie(notNilState, nilState) = state->assume(receiverVal);

       // Handle receiver must be nil.
       if (nilState && !notNilState) {
         HandleNilReceiver(C, state, msg);
         return;
       }
     }
   }

   const char *bugDesc = msg.isPropertySetter() ?
                      "Argument for property setter is an uninitialized value"
                    : "Argument in message expression is an uninitialized value";
   // Check for any arguments that are uninitialized/undefined.
   PreVisitProcessArgs(C, CallOrObjCMessage(msg, state, LCtx),
                       bugDesc, BT_msg_arg);
 }

 void CallAndMessageChecker::emitNilReceiverBug(CheckerContext &C,
                                                const ObjCMessage &msg,
                                                ExplodedNode *N) const {

   if (!BT_msg_ret)
     BT_msg_ret.reset(
       new BuiltinBug("Receiver in message expression is "
                      "'nil' and returns a garbage value"));

   llvm::SmallString<200> buf;
   llvm::raw_svector_ostream os(buf);
   os << "The receiver of message '" << msg.getSelector().getAsString()
      << "' is nil and returns a value of type '"
      << msg.getType(C.getASTContext()).getAsString() << "' that will be garbage";

   BugReport *report = new BugReport(*BT_msg_ret, os.str(), N);
   if (const Expr *receiver = msg.getInstanceReceiver()) {
     report->addRange(receiver->getSourceRange());
     report->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
                                                                     receiver));
   }
   C.EmitReport(report);
 }

 static bool supportsNilWithFloatRet(const llvm::Triple &triple) {
   return triple.getVendor() == llvm::Triple::Apple &&
          (!triple.isMacOSXVersionLT(10,5) ||
           triple.getArch() == llvm::Triple::arm ||
           triple.getArch() == llvm::Triple::thumb);
 }

 void CallAndMessageChecker::HandleNilReceiver(CheckerContext &C,
                                               const ProgramState *state,
                                               ObjCMessage msg) const {
   ASTContext &Ctx = C.getASTContext();

   // Check the return type of the message expression.  A message to nil will
   // return different values depending on the return type and the architecture.
   QualType RetTy = msg.getType(Ctx);
   CanQualType CanRetTy = Ctx.getCanonicalType(RetTy);
   const LocationContext *LCtx = C.getLocationContext();

   if (CanRetTy->isStructureOrClassType()) {
     // Structure returns are safe since the compiler zeroes them out.
     SVal V = C.getSValBuilder().makeZeroVal(msg.getType(Ctx));
     C.addTransition(state->BindExpr(msg.getOriginExpr(), LCtx, V));
     return;
   }

   // Other cases: check if sizeof(return type) > sizeof(void*)
   if (CanRetTy != Ctx.VoidTy && C.getLocationContext()->getParentMap()
                                   .isConsumedExpr(msg.getOriginExpr())) {
     // Compute: sizeof(void *) and sizeof(return type)
     const uint64_t voidPtrSize = Ctx.getTypeSize(Ctx.VoidPtrTy);
     const uint64_t returnTypeSize = Ctx.getTypeSize(CanRetTy);

     if (voidPtrSize < returnTypeSize &&
         !(supportsNilWithFloatRet(Ctx.getTargetInfo().getTriple()) &&
           (Ctx.FloatTy == CanRetTy ||
            Ctx.DoubleTy == CanRetTy ||
            Ctx.LongDoubleTy == CanRetTy ||
            Ctx.LongLongTy == CanRetTy ||
            Ctx.UnsignedLongLongTy == CanRetTy))) {
       if (ExplodedNode *N = C.generateSink(state))
         emitNilReceiverBug(C, msg, N);
       return;
     }

     // Handle the safe cases where the return value is 0 if the
     // receiver is nil.
     //
     // FIXME: For now take the conservative approach that we only
     // return null values if we *know* that the receiver is nil.
     // This is because we can have surprises like:
     //
     //   ... = [[NSScreens screens] objectAtIndex:0];
     //
     // What can happen is that [... screens] could return nil, but
     // it most likely isn't nil.  We should assume the semantics
     // of this case unless we have *a lot* more knowledge.
     //
     SVal V = C.getSValBuilder().makeZeroVal(msg.getType(Ctx));
     C.addTransition(state->BindExpr(msg.getOriginExpr(), LCtx, V));
     return;
   }

   C.addTransition(state);
 }

 void ento::registerCallAndMessageChecker(CheckerManager &mgr) {
   mgr.registerChecker<CallAndMessageChecker>();
 }
	//===--- CallAndMessageChecker.cpp ------------------------------- C++ ---==//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This defines CallAndMessageChecker, a builtin checker that checks for various
	// errors of call and objc message expressions.
	//
	//===----------------------------------------------------------------------===//

	#include "ClangSACheckers.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/ObjCMessage.h"
	#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
	#include "clang/AST/ParentMap.h"
	#include "clang/Basic/TargetInfo.h"

	using namespace clang;
	using namespace ento;

	namespace {
	class CallAndMessageChecker
	: public Checker< check::PreStmt<CallExpr>, check::PreObjCMessage > {
	mutable llvm::OwningPtr<BugType> BT_call_null;
	mutable llvm::OwningPtr<BugType> BT_call_undef;
	mutable llvm::OwningPtr<BugType> BT_call_arg;
	mutable llvm::OwningPtr<BugType> BT_msg_undef;
	mutable llvm::OwningPtr<BugType> BT_msg_arg;
	mutable llvm::OwningPtr<BugType> BT_msg_ret;
	public:

	void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
	void checkPreObjCMessage(ObjCMessage msg, CheckerContext &C) const;

	private:
	static void PreVisitProcessArgs(CheckerContext &C,CallOrObjCMessage callOrMsg,
	const char *BT_desc, llvm::OwningPtr<BugType> &BT);
	static bool PreVisitProcessArg(CheckerContext &C, SVal V,SourceRange argRange,
	const Expr argEx, const char BT_desc, llvm::OwningPtr<BugType> &BT);

	static void EmitBadCall(BugType BT, CheckerContext &C, const CallExpr CE);
	void emitNilReceiverBug(CheckerContext &C, const ObjCMessage &msg,
	ExplodedNode *N) const;

	void HandleNilReceiver(CheckerContext &C,
	const ProgramState *state,
	ObjCMessage msg) const;

	static void LazyInit_BT(const char *desc, llvm::OwningPtr<BugType> &BT) {
	if (!BT)
	BT.reset(new BuiltinBug(desc));
	}
	};
	} // end anonymous namespace

	void CallAndMessageChecker::EmitBadCall(BugType *BT, CheckerContext &C,
	const CallExpr *CE) {
	ExplodedNode *N = C.generateSink();
	if (!N)
	return;

	BugReport R = new BugReport(BT, BT->getName(), N);
	R->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
	bugreporter::GetCalleeExpr(N)));
	C.EmitReport(R);
	}

	void CallAndMessageChecker::PreVisitProcessArgs(CheckerContext &C,
	CallOrObjCMessage callOrMsg,
	const char *BT_desc,
	llvm::OwningPtr<BugType> &BT) {
	for (unsigned i = 0, e = callOrMsg.getNumArgs(); i != e; ++i)
	if (PreVisitProcessArg(C, callOrMsg.getArgSVal(i),
	callOrMsg.getArgSourceRange(i), callOrMsg.getArg(i),
	BT_desc, BT))
	return;
	}

	bool CallAndMessageChecker::PreVisitProcessArg(CheckerContext &C,
	SVal V, SourceRange argRange,
	const Expr *argEx,
	const char *BT_desc,
	llvm::OwningPtr<BugType> &BT) {

	if (V.isUndef()) {
	if (ExplodedNode *N = C.generateSink()) {
	LazyInit_BT(BT_desc, BT);

	// Generate a report for this bug.
	BugReport R = new BugReport(BT, BT->getName(), N);
	R->addRange(argRange);
	if (argEx)
	R->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N, argEx));
	C.EmitReport(R);
	}
	return true;
	}

	if (const nonloc::LazyCompoundVal *LV =
	dyn_cast<nonloc::LazyCompoundVal>(&V)) {

	class FindUninitializedField {
	public:
	SmallVector<const FieldDecl *, 10> FieldChain;
	private:
	ASTContext &C;
	StoreManager &StoreMgr;
	MemRegionManager &MrMgr;
	Store store;
	public:
	FindUninitializedField(ASTContext &c, StoreManager &storeMgr,
	MemRegionManager &mrMgr, Store s)
	: C(c), StoreMgr(storeMgr), MrMgr(mrMgr), store(s) {}

	bool Find(const TypedValueRegion *R) {
	QualType T = R->getValueType();
	if (const RecordType *RT = T->getAsStructureType()) {
	const RecordDecl *RD = RT->getDecl()->getDefinition();
	assert(RD && "Referred record has no definition");
	for (RecordDecl::field_iterator I =
	RD->field_begin(), E = RD->field_end(); I!=E; ++I) {
	const FieldRegion FR = MrMgr.getFieldRegion(I, R);
	FieldChain.push_back(*I);
	T = (*I)->getType();
	if (T->getAsStructureType()) {
	if (Find(FR))
	return true;
	}
	else {
	const SVal &V = StoreMgr.getBinding(store, loc::MemRegionVal(FR));
	if (V.isUndef())
	return true;
	}
	FieldChain.pop_back();
	}
	}

	return false;
	}
	};

	const LazyCompoundValData *D = LV->getCVData();
	FindUninitializedField F(C.getASTContext(),
	C.getState()->getStateManager().getStoreManager(),
	C.getSValBuilder().getRegionManager(),
	D->getStore());

	if (F.Find(D->getRegion())) {
	if (ExplodedNode *N = C.generateSink()) {
	LazyInit_BT(BT_desc, BT);
	llvm::SmallString<512> Str;
	llvm::raw_svector_ostream os(Str);
	os << "Passed-by-value struct argument contains uninitialized data";

	if (F.FieldChain.size() == 1)
	os << " (e.g., field: '" << *F.FieldChain[0] << "')";
	else {
	os << " (e.g., via the field chain: '";
	bool first = true;
	for (SmallVectorImpl<const FieldDecl *>::iterator
	DI = F.FieldChain.begin(), DE = F.FieldChain.end(); DI!=DE;++DI){
	if (first)
	first = false;
	else
	os << '.';
	os << **DI;
	}
	os << "')";
	}

	// Generate a report for this bug.
	BugReport R = new BugReport(BT, os.str(), N);
	R->addRange(argRange);

	// FIXME: enhance track back for uninitialized value for arbitrary
	// memregions
	C.EmitReport(R);
	}
	return true;
	}
	}

	return false;
	}

	void CallAndMessageChecker::checkPreStmt(const CallExpr *CE,
	CheckerContext &C) const{

	const Expr *Callee = CE->getCallee()->IgnoreParens();
	const LocationContext *LCtx = C.getLocationContext();
	SVal L = C.getState()->getSVal(Callee, LCtx);

	if (L.isUndef()) {
	if (!BT_call_undef)
	BT_call_undef.reset(new BuiltinBug("Called function pointer is an "
	"uninitalized pointer value"));
	EmitBadCall(BT_call_undef.get(), C, CE);
	return;
	}

	if (isa<loc::ConcreteInt>(L)) {
	if (!BT_call_null)
	BT_call_null.reset(
	new BuiltinBug("Called function pointer is null (null dereference)"));
	EmitBadCall(BT_call_null.get(), C, CE);
	}

	PreVisitProcessArgs(C, CallOrObjCMessage(CE, C.getState(), LCtx),
	"Function call argument is an uninitialized value",
	BT_call_arg);
	}

	void CallAndMessageChecker::checkPreObjCMessage(ObjCMessage msg,
	CheckerContext &C) const {

	const ProgramState *state = C.getState();
	const LocationContext *LCtx = C.getLocationContext();

	// FIXME: Handle 'super'?
	if (const Expr *receiver = msg.getInstanceReceiver()) {
	SVal recVal = state->getSVal(receiver, LCtx);
	if (recVal.isUndef()) {
	if (ExplodedNode *N = C.generateSink()) {
	if (!BT_msg_undef)
	BT_msg_undef.reset(new BuiltinBug("Receiver in message expression is "
	"an uninitialized value"));
	BugReport *R =
	new BugReport(*BT_msg_undef, BT_msg_undef->getName(), N);
	R->addRange(receiver->getSourceRange());
	R->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
	receiver));
	C.EmitReport(R);
	}
	return;
	} else {
	// Bifurcate the state into nil and non-nil ones.
	DefinedOrUnknownSVal receiverVal = cast<DefinedOrUnknownSVal>(recVal);

	const ProgramState notNilState, nilState;
	llvm::tie(notNilState, nilState) = state->assume(receiverVal);

	// Handle receiver must be nil.
	if (nilState && !notNilState) {
	HandleNilReceiver(C, state, msg);
	return;
	}
	}
	}

	const char *bugDesc = msg.isPropertySetter() ?
	"Argument for property setter is an uninitialized value"
	: "Argument in message expression is an uninitialized value";
	// Check for any arguments that are uninitialized/undefined.
	PreVisitProcessArgs(C, CallOrObjCMessage(msg, state, LCtx),
	bugDesc, BT_msg_arg);
	}

	void CallAndMessageChecker::emitNilReceiverBug(CheckerContext &C,
	const ObjCMessage &msg,
	ExplodedNode *N) const {

	if (!BT_msg_ret)
	BT_msg_ret.reset(
	new BuiltinBug("Receiver in message expression is "
	"'nil' and returns a garbage value"));

	llvm::SmallString<200> buf;
	llvm::raw_svector_ostream os(buf);
	os << "The receiver of message '" << msg.getSelector().getAsString()
	<< "' is nil and returns a value of type '"
	<< msg.getType(C.getASTContext()).getAsString() << "' that will be garbage";

	BugReport report = new BugReport(BT_msg_ret, os.str(), N);
	if (const Expr *receiver = msg.getInstanceReceiver()) {
	report->addRange(receiver->getSourceRange());
	report->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
	receiver));
	}
	C.EmitReport(report);
	}

	static bool supportsNilWithFloatRet(const llvm::Triple &triple) {
	return triple.getVendor() == llvm::Triple::Apple &&
	(!triple.isMacOSXVersionLT(10,5) \|\|
	triple.getArch() == llvm::Triple::arm \|\|
	triple.getArch() == llvm::Triple::thumb);
	}

	void CallAndMessageChecker::HandleNilReceiver(CheckerContext &C,
	const ProgramState *state,
	ObjCMessage msg) const {
	ASTContext &Ctx = C.getASTContext();

	// Check the return type of the message expression. A message to nil will
	// return different values depending on the return type and the architecture.
	QualType RetTy = msg.getType(Ctx);
	CanQualType CanRetTy = Ctx.getCanonicalType(RetTy);
	const LocationContext *LCtx = C.getLocationContext();

	if (CanRetTy->isStructureOrClassType()) {
	// Structure returns are safe since the compiler zeroes them out.
	SVal V = C.getSValBuilder().makeZeroVal(msg.getType(Ctx));
	C.addTransition(state->BindExpr(msg.getOriginExpr(), LCtx, V));
	return;
	}

	// Other cases: check if sizeof(return type) > sizeof(void*)
	if (CanRetTy != Ctx.VoidTy && C.getLocationContext()->getParentMap()
	.isConsumedExpr(msg.getOriginExpr())) {
	// Compute: sizeof(void *) and sizeof(return type)
	const uint64_t voidPtrSize = Ctx.getTypeSize(Ctx.VoidPtrTy);
	const uint64_t returnTypeSize = Ctx.getTypeSize(CanRetTy);

	if (voidPtrSize < returnTypeSize &&
	!(supportsNilWithFloatRet(Ctx.getTargetInfo().getTriple()) &&
	(Ctx.FloatTy == CanRetTy \|\|
	Ctx.DoubleTy == CanRetTy \|\|
	Ctx.LongDoubleTy == CanRetTy \|\|
	Ctx.LongLongTy == CanRetTy \|\|
	Ctx.UnsignedLongLongTy == CanRetTy))) {
	if (ExplodedNode *N = C.generateSink(state))
	emitNilReceiverBug(C, msg, N);
	return;
	}

	// Handle the safe cases where the return value is 0 if the
	// receiver is nil.
	//
	// FIXME: For now take the conservative approach that we only
	// return null values if we know that the receiver is nil.
	// This is because we can have surprises like:
	//
	// ... = [[NSScreens screens] objectAtIndex:0];
	//
	// What can happen is that [... screens] could return nil, but
	// it most likely isn't nil. We should assume the semantics
	// of this case unless we have a lot more knowledge.
	//
	SVal V = C.getSValBuilder().makeZeroVal(msg.getType(Ctx));
	C.addTransition(state->BindExpr(msg.getOriginExpr(), LCtx, V));
	return;
	}

	C.addTransition(state);
	}

	void ento::registerCallAndMessageChecker(CheckerManager &mgr) {
	mgr.registerChecker<CallAndMessageChecker>();
	}