1 //== Nullabilityhecker.cpp - Nullability checker ----------------*- C++ -*--==//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This checker tries to find nullability violations. There are several kinds of
11 // possible violations:
12 // * Null pointer is passed to a pointer which has a _Nonnull type.
13 // * Null pointer is returned from a function which has a _Nonnull return type.
14 // * Nullable pointer is passed to a pointer which has a _Nonnull type.
15 // * Nullable pointer is returned from a function which has a _Nonnull return
17 // * Nullable pointer is dereferenced.
19 // This checker propagates the nullability information of the pointers and looks
20 // for the patterns that are described above. Explicit casts are trusted and are
21 // considered a way to suppress false positives for this checker. The other way
22 // to suppress warnings would be to add asserts or guarding if statements to the
23 // code. In addition to the nullability propagation this checker also uses some
24 // heuristics to suppress potential false positives.
26 //===----------------------------------------------------------------------===//
28 #include "ClangSACheckers.h"
30 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
31 #include "clang/StaticAnalyzer/Core/Checker.h"
32 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
33 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
34 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
36 #include "llvm/ADT/StringExtras.h"
37 #include "llvm/Support/Path.h"
39 using namespace clang;
43 // Do not reorder! The getMostNullable method relies on the order.
44 // Optimization: Most pointers expected to be unspecified. When a symbol has an
45 // unspecified or nonnull type non of the rules would indicate any problem for
46 // that symbol. For this reason only nullable and contradicted nullability are
47 // stored for a symbol. When a symbol is already contradicted, it can not be
48 // casted back to nullable.
49 enum class Nullability : char {
50 Contradicted, // Tracked nullability is contradicted by an explicit cast. Do
51 // not report any nullability related issue for this symbol.
52 // This nullability is propagated agressively to avoid false
53 // positive results. See the comment on getMostNullable method.
59 /// Returns the most nullable nullability. This is used for message expressions
60 /// like [reciever method], where the nullability of this expression is either
61 /// the nullability of the receiver or the nullability of the return type of the
62 /// method, depending on which is more nullable. Contradicted is considered to
63 /// be the most nullable, to avoid false positive results.
64 Nullability getMostNullable(Nullability Lhs, Nullability Rhs) {
65 return static_cast<Nullability>(
66 std::min(static_cast<char>(Lhs), static_cast<char>(Rhs)));
69 const char *getNullabilityString(Nullability Nullab) {
71 case Nullability::Contradicted:
72 return "contradicted";
73 case Nullability::Nullable:
75 case Nullability::Unspecified:
77 case Nullability::Nonnull:
80 llvm_unreachable("Unexpected enumeration.");
84 // These enums are used as an index to ErrorMessages array.
85 enum class ErrorKind : int {
89 NullableAssignedToNonnull,
90 NullableReturnedToNonnull,
92 NullablePassedToNonnull
95 class NullabilityChecker
96 : public Checker<check::Bind, check::PreCall, check::PreStmt<ReturnStmt>,
97 check::PostCall, check::PostStmt<ExplicitCastExpr>,
98 check::PostObjCMessage, check::DeadSymbols,
99 check::Event<ImplicitNullDerefEvent>> {
100 mutable std::unique_ptr<BugType> BT;
103 // If true, the checker will not diagnose nullabilility issues for calls
104 // to system headers. This option is motivated by the observation that large
105 // projects may have many nullability warnings. These projects may
106 // find warnings about nullability annotations that they have explicitly
107 // added themselves higher priority to fix than warnings on calls to system
109 DefaultBool NoDiagnoseCallsToSystemHeaders;
111 void checkBind(SVal L, SVal V, const Stmt *S, CheckerContext &C) const;
112 void checkPostStmt(const ExplicitCastExpr *CE, CheckerContext &C) const;
113 void checkPreStmt(const ReturnStmt *S, CheckerContext &C) const;
114 void checkPostObjCMessage(const ObjCMethodCall &M, CheckerContext &C) const;
115 void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
116 void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
117 void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const;
118 void checkEvent(ImplicitNullDerefEvent Event) const;
120 void printState(raw_ostream &Out, ProgramStateRef State, const char *NL,
121 const char *Sep) const override;
123 struct NullabilityChecksFilter {
124 DefaultBool CheckNullPassedToNonnull;
125 DefaultBool CheckNullReturnedFromNonnull;
126 DefaultBool CheckNullableDereferenced;
127 DefaultBool CheckNullablePassedToNonnull;
128 DefaultBool CheckNullableReturnedFromNonnull;
130 CheckName CheckNameNullPassedToNonnull;
131 CheckName CheckNameNullReturnedFromNonnull;
132 CheckName CheckNameNullableDereferenced;
133 CheckName CheckNameNullablePassedToNonnull;
134 CheckName CheckNameNullableReturnedFromNonnull;
137 NullabilityChecksFilter Filter;
138 // When set to false no nullability information will be tracked in
139 // NullabilityMap. It is possible to catch errors like passing a null pointer
140 // to a callee that expects nonnull argument without the information that is
141 // stroed in the NullabilityMap. This is an optimization.
142 DefaultBool NeedTracking;
145 class NullabilityBugVisitor
146 : public BugReporterVisitorImpl<NullabilityBugVisitor> {
148 NullabilityBugVisitor(const MemRegion *M) : Region(M) {}
150 void Profile(llvm::FoldingSetNodeID &ID) const override {
153 ID.AddPointer(Region);
156 PathDiagnosticPiece *VisitNode(const ExplodedNode *N,
157 const ExplodedNode *PrevN,
158 BugReporterContext &BRC,
159 BugReport &BR) override;
162 // The tracked region.
163 const MemRegion *Region;
166 /// When any of the nonnull arguments of the analyzed function is null, do not
167 /// report anything and turn off the check.
169 /// When \p SuppressPath is set to true, no more bugs will be reported on this
170 /// path by this checker.
171 void reportBugIfInvariantHolds(StringRef Msg, ErrorKind Error,
172 ExplodedNode *N, const MemRegion *Region,
174 const Stmt *ValueExpr = nullptr,
175 bool SuppressPath = false) const;
177 void reportBug(StringRef Msg, ErrorKind Error, ExplodedNode *N,
178 const MemRegion *Region, BugReporter &BR,
179 const Stmt *ValueExpr = nullptr) const {
181 BT.reset(new BugType(this, "Nullability", "Memory error"));
183 auto R = llvm::make_unique<BugReport>(*BT, Msg, N);
185 R->markInteresting(Region);
186 R->addVisitor(llvm::make_unique<NullabilityBugVisitor>(Region));
189 R->addRange(ValueExpr->getSourceRange());
190 if (Error == ErrorKind::NilAssignedToNonnull ||
191 Error == ErrorKind::NilPassedToNonnull ||
192 Error == ErrorKind::NilReturnedToNonnull)
193 bugreporter::trackNullOrUndefValue(N, ValueExpr, *R);
195 BR.emitReport(std::move(R));
198 /// If an SVal wraps a region that should be tracked, it will return a pointer
199 /// to the wrapped region. Otherwise it will return a nullptr.
200 const SymbolicRegion *getTrackRegion(SVal Val,
201 bool CheckSuperRegion = false) const;
203 /// Returns true if the call is diagnosable in the currrent analyzer
205 bool isDiagnosableCall(const CallEvent &Call) const {
206 if (NoDiagnoseCallsToSystemHeaders && Call.isInSystemHeader())
213 class NullabilityState {
215 NullabilityState(Nullability Nullab, const Stmt *Source = nullptr)
216 : Nullab(Nullab), Source(Source) {}
218 const Stmt *getNullabilitySource() const { return Source; }
220 Nullability getValue() const { return Nullab; }
222 void Profile(llvm::FoldingSetNodeID &ID) const {
223 ID.AddInteger(static_cast<char>(Nullab));
224 ID.AddPointer(Source);
227 void print(raw_ostream &Out) const {
228 Out << getNullabilityString(Nullab) << "\n";
233 // Source is the expression which determined the nullability. For example in a
234 // message like [nullable nonnull_returning] has nullable nullability, because
235 // the receiver is nullable. Here the receiver will be the source of the
236 // nullability. This is useful information when the diagnostics are generated.
240 bool operator==(NullabilityState Lhs, NullabilityState Rhs) {
241 return Lhs.getValue() == Rhs.getValue() &&
242 Lhs.getNullabilitySource() == Rhs.getNullabilitySource();
245 } // end anonymous namespace
247 REGISTER_MAP_WITH_PROGRAMSTATE(NullabilityMap, const MemRegion *,
250 // We say "the nullability type invariant is violated" when a location with a
251 // non-null type contains NULL or a function with a non-null return type returns
252 // NULL. Violations of the nullability type invariant can be detected either
253 // directly (for example, when NULL is passed as an argument to a nonnull
254 // parameter) or indirectly (for example, when, inside a function, the
255 // programmer defensively checks whether a nonnull parameter contains NULL and
256 // finds that it does).
258 // As a matter of policy, the nullability checker typically warns on direct
259 // violations of the nullability invariant (although it uses various
260 // heuristics to suppress warnings in some cases) but will not warn if the
261 // invariant has already been violated along the path (either directly or
262 // indirectly). As a practical matter, this prevents the analyzer from
263 // (1) warning on defensive code paths where a nullability precondition is
264 // determined to have been violated, (2) warning additional times after an
265 // initial direct violation has been discovered, and (3) warning after a direct
266 // violation that has been implicitly or explicitly suppressed (for
267 // example, with a cast of NULL to _Nonnull). In essence, once an invariant
268 // violation is detected on a path, this checker will be esentially turned off
269 // for the rest of the analysis
271 // The analyzer takes this approach (rather than generating a sink node) to
272 // ensure coverage of defensive paths, which may be important for backwards
273 // compatibility in codebases that were developed without nullability in mind.
274 REGISTER_TRAIT_WITH_PROGRAMSTATE(InvariantViolated, bool)
276 enum class NullConstraint { IsNull, IsNotNull, Unknown };
278 static NullConstraint getNullConstraint(DefinedOrUnknownSVal Val,
279 ProgramStateRef State) {
280 ConditionTruthVal Nullness = State->isNull(Val);
281 if (Nullness.isConstrainedFalse())
282 return NullConstraint::IsNotNull;
283 if (Nullness.isConstrainedTrue())
284 return NullConstraint::IsNull;
285 return NullConstraint::Unknown;
288 const SymbolicRegion *
289 NullabilityChecker::getTrackRegion(SVal Val, bool CheckSuperRegion) const {
293 auto RegionSVal = Val.getAs<loc::MemRegionVal>();
297 const MemRegion *Region = RegionSVal->getRegion();
299 if (CheckSuperRegion) {
300 if (auto FieldReg = Region->getAs<FieldRegion>())
301 return dyn_cast<SymbolicRegion>(FieldReg->getSuperRegion());
302 if (auto ElementReg = Region->getAs<ElementRegion>())
303 return dyn_cast<SymbolicRegion>(ElementReg->getSuperRegion());
306 return dyn_cast<SymbolicRegion>(Region);
309 PathDiagnosticPiece *NullabilityChecker::NullabilityBugVisitor::VisitNode(
310 const ExplodedNode *N, const ExplodedNode *PrevN, BugReporterContext &BRC,
312 ProgramStateRef State = N->getState();
313 ProgramStateRef StatePrev = PrevN->getState();
315 const NullabilityState *TrackedNullab = State->get<NullabilityMap>(Region);
316 const NullabilityState *TrackedNullabPrev =
317 StatePrev->get<NullabilityMap>(Region);
321 if (TrackedNullabPrev &&
322 TrackedNullabPrev->getValue() == TrackedNullab->getValue())
325 // Retrieve the associated statement.
326 const Stmt *S = TrackedNullab->getNullabilitySource();
328 S = PathDiagnosticLocation::getStmt(N);
334 std::string InfoText =
335 (llvm::Twine("Nullability '") +
336 getNullabilityString(TrackedNullab->getValue()) + "' is inferred")
339 // Generate the extra diagnostic.
340 PathDiagnosticLocation Pos(S, BRC.getSourceManager(),
341 N->getLocationContext());
342 return new PathDiagnosticEventPiece(Pos, InfoText, true, nullptr);
345 static Nullability getNullabilityAnnotation(QualType Type) {
346 const auto *AttrType = Type->getAs<AttributedType>();
348 return Nullability::Unspecified;
349 if (AttrType->getAttrKind() == AttributedType::attr_nullable)
350 return Nullability::Nullable;
351 else if (AttrType->getAttrKind() == AttributedType::attr_nonnull)
352 return Nullability::Nonnull;
353 return Nullability::Unspecified;
356 /// Returns true when the value stored at the given location is null
357 /// and the passed in type is nonnnull.
358 static bool checkValueAtLValForInvariantViolation(ProgramStateRef State,
359 SVal LV, QualType T) {
360 if (getNullabilityAnnotation(T) != Nullability::Nonnull)
363 auto RegionVal = LV.getAs<loc::MemRegionVal>();
368 State->getSVal(RegionVal->getRegion()).getAs<DefinedOrUnknownSVal>();
372 if (getNullConstraint(*StoredVal, State) == NullConstraint::IsNull)
379 checkParamsForPreconditionViolation(ArrayRef<ParmVarDecl *> Params,
380 ProgramStateRef State,
381 const LocationContext *LocCtxt) {
382 for (const auto *ParamDecl : Params) {
383 if (ParamDecl->isParameterPack())
386 SVal LV = State->getLValue(ParamDecl, LocCtxt);
387 if (checkValueAtLValForInvariantViolation(State, LV,
388 ParamDecl->getType())) {
396 checkSelfIvarsForInvariantViolation(ProgramStateRef State,
397 const LocationContext *LocCtxt) {
398 auto *MD = dyn_cast<ObjCMethodDecl>(LocCtxt->getDecl());
399 if (!MD || !MD->isInstanceMethod())
402 const ImplicitParamDecl *SelfDecl = LocCtxt->getSelfDecl();
406 SVal SelfVal = State->getSVal(State->getRegion(SelfDecl, LocCtxt));
408 const ObjCObjectPointerType *SelfType =
409 dyn_cast<ObjCObjectPointerType>(SelfDecl->getType());
413 const ObjCInterfaceDecl *ID = SelfType->getInterfaceDecl();
417 for (const auto *IvarDecl : ID->ivars()) {
418 SVal LV = State->getLValue(IvarDecl, SelfVal);
419 if (checkValueAtLValForInvariantViolation(State, LV, IvarDecl->getType())) {
426 static bool checkInvariantViolation(ProgramStateRef State, ExplodedNode *N,
428 if (State->get<InvariantViolated>())
431 const LocationContext *LocCtxt = C.getLocationContext();
432 const Decl *D = LocCtxt->getDecl();
436 ArrayRef<ParmVarDecl*> Params;
437 if (const auto *BD = dyn_cast<BlockDecl>(D))
438 Params = BD->parameters();
439 else if (const auto *FD = dyn_cast<FunctionDecl>(D))
440 Params = FD->parameters();
441 else if (const auto *MD = dyn_cast<ObjCMethodDecl>(D))
442 Params = MD->parameters();
446 if (checkParamsForPreconditionViolation(Params, State, LocCtxt) ||
447 checkSelfIvarsForInvariantViolation(State, LocCtxt)) {
449 C.addTransition(State->set<InvariantViolated>(true), N);
455 void NullabilityChecker::reportBugIfInvariantHolds(StringRef Msg,
456 ErrorKind Error, ExplodedNode *N, const MemRegion *Region,
457 CheckerContext &C, const Stmt *ValueExpr, bool SuppressPath) const {
458 ProgramStateRef OriginalState = N->getState();
460 if (checkInvariantViolation(OriginalState, N, C))
463 OriginalState = OriginalState->set<InvariantViolated>(true);
464 N = C.addTransition(OriginalState, N);
467 reportBug(Msg, Error, N, Region, C.getBugReporter(), ValueExpr);
470 /// Cleaning up the program state.
471 void NullabilityChecker::checkDeadSymbols(SymbolReaper &SR,
472 CheckerContext &C) const {
473 if (!SR.hasDeadSymbols())
476 ProgramStateRef State = C.getState();
477 NullabilityMapTy Nullabilities = State->get<NullabilityMap>();
478 for (NullabilityMapTy::iterator I = Nullabilities.begin(),
479 E = Nullabilities.end();
481 const auto *Region = I->first->getAs<SymbolicRegion>();
482 assert(Region && "Non-symbolic region is tracked.");
483 if (SR.isDead(Region->getSymbol())) {
484 State = State->remove<NullabilityMap>(I->first);
487 // When one of the nonnull arguments are constrained to be null, nullability
488 // preconditions are violated. It is not enough to check this only when we
489 // actually report an error, because at that time interesting symbols might be
491 if (checkInvariantViolation(State, C.getPredecessor(), C))
493 C.addTransition(State);
496 /// This callback triggers when a pointer is dereferenced and the analyzer does
497 /// not know anything about the value of that pointer. When that pointer is
498 /// nullable, this code emits a warning.
499 void NullabilityChecker::checkEvent(ImplicitNullDerefEvent Event) const {
500 if (Event.SinkNode->getState()->get<InvariantViolated>())
503 const MemRegion *Region =
504 getTrackRegion(Event.Location, /*CheckSuperregion=*/true);
508 ProgramStateRef State = Event.SinkNode->getState();
509 const NullabilityState *TrackedNullability =
510 State->get<NullabilityMap>(Region);
512 if (!TrackedNullability)
515 if (Filter.CheckNullableDereferenced &&
516 TrackedNullability->getValue() == Nullability::Nullable) {
517 BugReporter &BR = *Event.BR;
518 // Do not suppress errors on defensive code paths, because dereferencing
519 // a nullable pointer is always an error.
520 if (Event.IsDirectDereference)
521 reportBug("Nullable pointer is dereferenced",
522 ErrorKind::NullableDereferenced, Event.SinkNode, Region, BR);
524 reportBug("Nullable pointer is passed to a callee that requires a "
525 "non-null", ErrorKind::NullablePassedToNonnull,
526 Event.SinkNode, Region, BR);
531 /// Find the outermost subexpression of E that is not an implicit cast.
532 /// This looks through the implicit casts to _Nonnull that ARC adds to
533 /// return expressions of ObjC types when the return type of the function or
534 /// method is non-null but the express is not.
535 static const Expr *lookThroughImplicitCasts(const Expr *E) {
538 while (auto *ICE = dyn_cast<ImplicitCastExpr>(E)) {
539 E = ICE->getSubExpr();
545 /// This method check when nullable pointer or null value is returned from a
546 /// function that has nonnull return type.
547 void NullabilityChecker::checkPreStmt(const ReturnStmt *S,
548 CheckerContext &C) const {
549 auto RetExpr = S->getRetValue();
553 if (!RetExpr->getType()->isAnyPointerType())
556 ProgramStateRef State = C.getState();
557 if (State->get<InvariantViolated>())
561 State->getSVal(S, C.getLocationContext()).getAs<DefinedOrUnknownSVal>();
565 bool InSuppressedMethodFamily = false;
567 QualType RequiredRetType;
568 AnalysisDeclContext *DeclCtxt =
569 C.getLocationContext()->getAnalysisDeclContext();
570 const Decl *D = DeclCtxt->getDecl();
571 if (auto *MD = dyn_cast<ObjCMethodDecl>(D)) {
572 // HACK: This is a big hammer to avoid warning when there are defensive
573 // nil checks in -init and -copy methods. We should add more sophisticated
574 // logic here to suppress on common defensive idioms but still
575 // warn when there is a likely problem.
576 ObjCMethodFamily Family = MD->getMethodFamily();
577 if (OMF_init == Family || OMF_copy == Family || OMF_mutableCopy == Family)
578 InSuppressedMethodFamily = true;
580 RequiredRetType = MD->getReturnType();
581 } else if (auto *FD = dyn_cast<FunctionDecl>(D)) {
582 RequiredRetType = FD->getReturnType();
587 NullConstraint Nullness = getNullConstraint(*RetSVal, State);
589 Nullability RequiredNullability = getNullabilityAnnotation(RequiredRetType);
591 // If the returned value is null but the type of the expression
592 // generating it is nonnull then we will suppress the diagnostic.
593 // This enables explicit suppression when returning a nil literal in a
594 // function with a _Nonnull return type:
595 // return (NSString * _Nonnull)0;
596 Nullability RetExprTypeLevelNullability =
597 getNullabilityAnnotation(lookThroughImplicitCasts(RetExpr)->getType());
599 bool NullReturnedFromNonNull = (RequiredNullability == Nullability::Nonnull &&
600 Nullness == NullConstraint::IsNull);
601 if (Filter.CheckNullReturnedFromNonnull &&
602 NullReturnedFromNonNull &&
603 RetExprTypeLevelNullability != Nullability::Nonnull &&
604 !InSuppressedMethodFamily &&
605 C.getLocationContext()->inTopFrame()) {
606 static CheckerProgramPointTag Tag(this, "NullReturnedFromNonnull");
607 ExplodedNode *N = C.generateErrorNode(State, &Tag);
611 SmallString<256> SBuf;
612 llvm::raw_svector_ostream OS(SBuf);
613 OS << (RetExpr->getType()->isObjCObjectPointerType() ? "nil" : "Null");
614 OS << " returned from a " << C.getDeclDescription(D) <<
615 " that is expected to return a non-null value";
616 reportBugIfInvariantHolds(OS.str(),
617 ErrorKind::NilReturnedToNonnull, N, nullptr, C,
622 // If null was returned from a non-null function, mark the nullability
623 // invariant as violated even if the diagnostic was suppressed.
624 if (NullReturnedFromNonNull) {
625 State = State->set<InvariantViolated>(true);
626 C.addTransition(State);
630 const MemRegion *Region = getTrackRegion(*RetSVal);
634 const NullabilityState *TrackedNullability =
635 State->get<NullabilityMap>(Region);
636 if (TrackedNullability) {
637 Nullability TrackedNullabValue = TrackedNullability->getValue();
638 if (Filter.CheckNullableReturnedFromNonnull &&
639 Nullness != NullConstraint::IsNotNull &&
640 TrackedNullabValue == Nullability::Nullable &&
641 RequiredNullability == Nullability::Nonnull) {
642 static CheckerProgramPointTag Tag(this, "NullableReturnedFromNonnull");
643 ExplodedNode *N = C.addTransition(State, C.getPredecessor(), &Tag);
645 SmallString<256> SBuf;
646 llvm::raw_svector_ostream OS(SBuf);
647 OS << "Nullable pointer is returned from a " << C.getDeclDescription(D) <<
648 " that is expected to return a non-null value";
650 reportBugIfInvariantHolds(OS.str(),
651 ErrorKind::NullableReturnedToNonnull, N,
656 if (RequiredNullability == Nullability::Nullable) {
657 State = State->set<NullabilityMap>(Region,
658 NullabilityState(RequiredNullability,
660 C.addTransition(State);
664 /// This callback warns when a nullable pointer or a null value is passed to a
665 /// function that expects its argument to be nonnull.
666 void NullabilityChecker::checkPreCall(const CallEvent &Call,
667 CheckerContext &C) const {
671 ProgramStateRef State = C.getState();
672 if (State->get<InvariantViolated>())
675 ProgramStateRef OrigState = State;
678 for (const ParmVarDecl *Param : Call.parameters()) {
679 if (Param->isParameterPack())
682 if (Idx >= Call.getNumArgs())
685 const Expr *ArgExpr = Call.getArgExpr(Idx);
686 auto ArgSVal = Call.getArgSVal(Idx++).getAs<DefinedOrUnknownSVal>();
690 if (!Param->getType()->isAnyPointerType() &&
691 !Param->getType()->isReferenceType())
694 NullConstraint Nullness = getNullConstraint(*ArgSVal, State);
696 Nullability RequiredNullability =
697 getNullabilityAnnotation(Param->getType());
698 Nullability ArgExprTypeLevelNullability =
699 getNullabilityAnnotation(ArgExpr->getType());
701 unsigned ParamIdx = Param->getFunctionScopeIndex() + 1;
703 if (Filter.CheckNullPassedToNonnull && Nullness == NullConstraint::IsNull &&
704 ArgExprTypeLevelNullability != Nullability::Nonnull &&
705 RequiredNullability == Nullability::Nonnull &&
706 isDiagnosableCall(Call)) {
707 ExplodedNode *N = C.generateErrorNode(State);
711 SmallString<256> SBuf;
712 llvm::raw_svector_ostream OS(SBuf);
713 OS << (Param->getType()->isObjCObjectPointerType() ? "nil" : "Null");
714 OS << " passed to a callee that requires a non-null " << ParamIdx
715 << llvm::getOrdinalSuffix(ParamIdx) << " parameter";
716 reportBugIfInvariantHolds(OS.str(), ErrorKind::NilPassedToNonnull, N,
718 ArgExpr, /*SuppressPath=*/false);
722 const MemRegion *Region = getTrackRegion(*ArgSVal);
726 const NullabilityState *TrackedNullability =
727 State->get<NullabilityMap>(Region);
729 if (TrackedNullability) {
730 if (Nullness == NullConstraint::IsNotNull ||
731 TrackedNullability->getValue() != Nullability::Nullable)
734 if (Filter.CheckNullablePassedToNonnull &&
735 RequiredNullability == Nullability::Nonnull &&
736 isDiagnosableCall(Call)) {
737 ExplodedNode *N = C.addTransition(State);
738 SmallString<256> SBuf;
739 llvm::raw_svector_ostream OS(SBuf);
740 OS << "Nullable pointer is passed to a callee that requires a non-null "
741 << ParamIdx << llvm::getOrdinalSuffix(ParamIdx) << " parameter";
742 reportBugIfInvariantHolds(OS.str(),
743 ErrorKind::NullablePassedToNonnull, N,
744 Region, C, ArgExpr, /*SuppressPath=*/true);
747 if (Filter.CheckNullableDereferenced &&
748 Param->getType()->isReferenceType()) {
749 ExplodedNode *N = C.addTransition(State);
750 reportBugIfInvariantHolds("Nullable pointer is dereferenced",
751 ErrorKind::NullableDereferenced, N, Region,
752 C, ArgExpr, /*SuppressPath=*/true);
757 // No tracked nullability yet.
758 if (ArgExprTypeLevelNullability != Nullability::Nullable)
760 State = State->set<NullabilityMap>(
761 Region, NullabilityState(ArgExprTypeLevelNullability, ArgExpr));
763 if (State != OrigState)
764 C.addTransition(State);
767 /// Suppress the nullability warnings for some functions.
768 void NullabilityChecker::checkPostCall(const CallEvent &Call,
769 CheckerContext &C) const {
770 auto Decl = Call.getDecl();
773 // ObjC Messages handles in a different callback.
774 if (Call.getKind() == CE_ObjCMessage)
776 const FunctionType *FuncType = Decl->getFunctionType();
779 QualType ReturnType = FuncType->getReturnType();
780 if (!ReturnType->isAnyPointerType())
782 ProgramStateRef State = C.getState();
783 if (State->get<InvariantViolated>())
786 const MemRegion *Region = getTrackRegion(Call.getReturnValue());
790 // CG headers are misannotated. Do not warn for symbols that are the results
792 const SourceManager &SM = C.getSourceManager();
793 StringRef FilePath = SM.getFilename(SM.getSpellingLoc(Decl->getLocStart()));
794 if (llvm::sys::path::filename(FilePath).startswith("CG")) {
795 State = State->set<NullabilityMap>(Region, Nullability::Contradicted);
796 C.addTransition(State);
800 const NullabilityState *TrackedNullability =
801 State->get<NullabilityMap>(Region);
803 if (!TrackedNullability &&
804 getNullabilityAnnotation(ReturnType) == Nullability::Nullable) {
805 State = State->set<NullabilityMap>(Region, Nullability::Nullable);
806 C.addTransition(State);
810 static Nullability getReceiverNullability(const ObjCMethodCall &M,
811 ProgramStateRef State) {
812 if (M.isReceiverSelfOrSuper()) {
813 // For super and super class receivers we assume that the receiver is
815 return Nullability::Nonnull;
817 // Otherwise look up nullability in the state.
818 SVal Receiver = M.getReceiverSVal();
819 if (auto DefOrUnknown = Receiver.getAs<DefinedOrUnknownSVal>()) {
820 // If the receiver is constrained to be nonnull, assume that it is nonnull
821 // regardless of its type.
822 NullConstraint Nullness = getNullConstraint(*DefOrUnknown, State);
823 if (Nullness == NullConstraint::IsNotNull)
824 return Nullability::Nonnull;
826 auto ValueRegionSVal = Receiver.getAs<loc::MemRegionVal>();
827 if (ValueRegionSVal) {
828 const MemRegion *SelfRegion = ValueRegionSVal->getRegion();
831 const NullabilityState *TrackedSelfNullability =
832 State->get<NullabilityMap>(SelfRegion);
833 if (TrackedSelfNullability)
834 return TrackedSelfNullability->getValue();
836 return Nullability::Unspecified;
839 /// Calculate the nullability of the result of a message expr based on the
840 /// nullability of the receiver, the nullability of the return value, and the
842 void NullabilityChecker::checkPostObjCMessage(const ObjCMethodCall &M,
843 CheckerContext &C) const {
844 auto Decl = M.getDecl();
847 QualType RetType = Decl->getReturnType();
848 if (!RetType->isAnyPointerType())
851 ProgramStateRef State = C.getState();
852 if (State->get<InvariantViolated>())
855 const MemRegion *ReturnRegion = getTrackRegion(M.getReturnValue());
859 auto Interface = Decl->getClassInterface();
860 auto Name = Interface ? Interface->getName() : "";
861 // In order to reduce the noise in the diagnostics generated by this checker,
862 // some framework and programming style based heuristics are used. These
863 // heuristics are for Cocoa APIs which have NS prefix.
864 if (Name.startswith("NS")) {
865 // Developers rely on dynamic invariants such as an item should be available
866 // in a collection, or a collection is not empty often. Those invariants can
867 // not be inferred by any static analysis tool. To not to bother the users
868 // with too many false positives, every item retrieval function should be
869 // ignored for collections. The instance methods of dictionaries in Cocoa
870 // are either item retrieval related or not interesting nullability wise.
871 // Using this fact, to keep the code easier to read just ignore the return
872 // value of every instance method of dictionaries.
873 if (M.isInstanceMessage() && Name.find("Dictionary") != StringRef::npos) {
875 State->set<NullabilityMap>(ReturnRegion, Nullability::Contradicted);
876 C.addTransition(State);
879 // For similar reasons ignore some methods of Cocoa arrays.
880 StringRef FirstSelectorSlot = M.getSelector().getNameForSlot(0);
881 if (Name.find("Array") != StringRef::npos &&
882 (FirstSelectorSlot == "firstObject" ||
883 FirstSelectorSlot == "lastObject")) {
885 State->set<NullabilityMap>(ReturnRegion, Nullability::Contradicted);
886 C.addTransition(State);
890 // Encoding related methods of string should not fail when lossless
891 // encodings are used. Using lossless encodings is so frequent that ignoring
892 // this class of methods reduced the emitted diagnostics by about 30% on
893 // some projects (and all of that was false positives).
894 if (Name.find("String") != StringRef::npos) {
895 for (auto Param : M.parameters()) {
896 if (Param->getName() == "encoding") {
897 State = State->set<NullabilityMap>(ReturnRegion,
898 Nullability::Contradicted);
899 C.addTransition(State);
906 const ObjCMessageExpr *Message = M.getOriginExpr();
907 Nullability SelfNullability = getReceiverNullability(M, State);
909 const NullabilityState *NullabilityOfReturn =
910 State->get<NullabilityMap>(ReturnRegion);
912 if (NullabilityOfReturn) {
913 // When we have a nullability tracked for the return value, the nullability
914 // of the expression will be the most nullable of the receiver and the
916 Nullability RetValTracked = NullabilityOfReturn->getValue();
917 Nullability ComputedNullab =
918 getMostNullable(RetValTracked, SelfNullability);
919 if (ComputedNullab != RetValTracked &&
920 ComputedNullab != Nullability::Unspecified) {
921 const Stmt *NullabilitySource =
922 ComputedNullab == RetValTracked
923 ? NullabilityOfReturn->getNullabilitySource()
924 : Message->getInstanceReceiver();
925 State = State->set<NullabilityMap>(
926 ReturnRegion, NullabilityState(ComputedNullab, NullabilitySource));
927 C.addTransition(State);
932 // No tracked information. Use static type information for return value.
933 Nullability RetNullability = getNullabilityAnnotation(RetType);
935 // Properties might be computed. For this reason the static analyzer creates a
936 // new symbol each time an unknown property is read. To avoid false pozitives
937 // do not treat unknown properties as nullable, even when they explicitly
939 if (M.getMessageKind() == OCM_PropertyAccess && !C.wasInlined)
940 RetNullability = Nullability::Nonnull;
942 Nullability ComputedNullab = getMostNullable(RetNullability, SelfNullability);
943 if (ComputedNullab == Nullability::Nullable) {
944 const Stmt *NullabilitySource = ComputedNullab == RetNullability
946 : Message->getInstanceReceiver();
947 State = State->set<NullabilityMap>(
948 ReturnRegion, NullabilityState(ComputedNullab, NullabilitySource));
949 C.addTransition(State);
953 /// Explicit casts are trusted. If there is a disagreement in the nullability
954 /// annotations in the destination and the source or '0' is casted to nonnull
955 /// track the value as having contraditory nullability. This will allow users to
956 /// suppress warnings.
957 void NullabilityChecker::checkPostStmt(const ExplicitCastExpr *CE,
958 CheckerContext &C) const {
959 QualType OriginType = CE->getSubExpr()->getType();
960 QualType DestType = CE->getType();
961 if (!OriginType->isAnyPointerType())
963 if (!DestType->isAnyPointerType())
966 ProgramStateRef State = C.getState();
967 if (State->get<InvariantViolated>())
970 Nullability DestNullability = getNullabilityAnnotation(DestType);
972 // No explicit nullability in the destination type, so this cast does not
973 // change the nullability.
974 if (DestNullability == Nullability::Unspecified)
978 State->getSVal(CE, C.getLocationContext()).getAs<DefinedOrUnknownSVal>();
979 const MemRegion *Region = getTrackRegion(*RegionSVal);
983 // When 0 is converted to nonnull mark it as contradicted.
984 if (DestNullability == Nullability::Nonnull) {
985 NullConstraint Nullness = getNullConstraint(*RegionSVal, State);
986 if (Nullness == NullConstraint::IsNull) {
987 State = State->set<NullabilityMap>(Region, Nullability::Contradicted);
988 C.addTransition(State);
993 const NullabilityState *TrackedNullability =
994 State->get<NullabilityMap>(Region);
996 if (!TrackedNullability) {
997 if (DestNullability != Nullability::Nullable)
999 State = State->set<NullabilityMap>(Region,
1000 NullabilityState(DestNullability, CE));
1001 C.addTransition(State);
1005 if (TrackedNullability->getValue() != DestNullability &&
1006 TrackedNullability->getValue() != Nullability::Contradicted) {
1007 State = State->set<NullabilityMap>(Region, Nullability::Contradicted);
1008 C.addTransition(State);
1012 /// For a given statement performing a bind, attempt to syntactically
1013 /// match the expression resulting in the bound value.
1014 static const Expr * matchValueExprForBind(const Stmt *S) {
1015 // For `x = e` the value expression is the right-hand side.
1016 if (auto *BinOp = dyn_cast<BinaryOperator>(S)) {
1017 if (BinOp->getOpcode() == BO_Assign)
1018 return BinOp->getRHS();
1021 // For `int x = e` the value expression is the initializer.
1022 if (auto *DS = dyn_cast<DeclStmt>(S)) {
1023 if (DS->isSingleDecl()) {
1024 auto *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
1028 if (const Expr *Init = VD->getInit())
1036 /// Returns true if \param S is a DeclStmt for a local variable that
1037 /// ObjC automated reference counting initialized with zero.
1038 static bool isARCNilInitializedLocal(CheckerContext &C, const Stmt *S) {
1039 // We suppress diagnostics for ARC zero-initialized _Nonnull locals. This
1040 // prevents false positives when a _Nonnull local variable cannot be
1041 // initialized with an initialization expression:
1042 // NSString * _Nonnull s; // no-warning
1043 // @autoreleasepool {
1047 // FIXME: We should treat implicitly zero-initialized _Nonnull locals as
1048 // uninitialized in Sema's UninitializedValues analysis to warn when a use of
1049 // the zero-initialized definition will unexpectedly yield nil.
1051 // Locals are only zero-initialized when automated reference counting
1053 if (!C.getASTContext().getLangOpts().ObjCAutoRefCount)
1056 auto *DS = dyn_cast<DeclStmt>(S);
1057 if (!DS || !DS->isSingleDecl())
1060 auto *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
1064 // Sema only zero-initializes locals with ObjCLifetimes.
1065 if(!VD->getType().getQualifiers().hasObjCLifetime())
1068 const Expr *Init = VD->getInit();
1069 assert(Init && "ObjC local under ARC without initializer");
1071 // Return false if the local is explicitly initialized (e.g., with '= nil').
1072 if (!isa<ImplicitValueInitExpr>(Init))
1078 /// Propagate the nullability information through binds and warn when nullable
1079 /// pointer or null symbol is assigned to a pointer with a nonnull type.
1080 void NullabilityChecker::checkBind(SVal L, SVal V, const Stmt *S,
1081 CheckerContext &C) const {
1082 const TypedValueRegion *TVR =
1083 dyn_cast_or_null<TypedValueRegion>(L.getAsRegion());
1087 QualType LocType = TVR->getValueType();
1088 if (!LocType->isAnyPointerType())
1091 ProgramStateRef State = C.getState();
1092 if (State->get<InvariantViolated>())
1095 auto ValDefOrUnknown = V.getAs<DefinedOrUnknownSVal>();
1096 if (!ValDefOrUnknown)
1099 NullConstraint RhsNullness = getNullConstraint(*ValDefOrUnknown, State);
1101 Nullability ValNullability = Nullability::Unspecified;
1102 if (SymbolRef Sym = ValDefOrUnknown->getAsSymbol())
1103 ValNullability = getNullabilityAnnotation(Sym->getType());
1105 Nullability LocNullability = getNullabilityAnnotation(LocType);
1107 // If the type of the RHS expression is nonnull, don't warn. This
1108 // enables explicit suppression with a cast to nonnull.
1109 Nullability ValueExprTypeLevelNullability = Nullability::Unspecified;
1110 const Expr *ValueExpr = matchValueExprForBind(S);
1112 ValueExprTypeLevelNullability =
1113 getNullabilityAnnotation(lookThroughImplicitCasts(ValueExpr)->getType());
1116 bool NullAssignedToNonNull = (LocNullability == Nullability::Nonnull &&
1117 RhsNullness == NullConstraint::IsNull);
1118 if (Filter.CheckNullPassedToNonnull &&
1119 NullAssignedToNonNull &&
1120 ValNullability != Nullability::Nonnull &&
1121 ValueExprTypeLevelNullability != Nullability::Nonnull &&
1122 !isARCNilInitializedLocal(C, S)) {
1123 static CheckerProgramPointTag Tag(this, "NullPassedToNonnull");
1124 ExplodedNode *N = C.generateErrorNode(State, &Tag);
1129 const Stmt *ValueStmt = S;
1131 ValueStmt = ValueExpr;
1133 SmallString<256> SBuf;
1134 llvm::raw_svector_ostream OS(SBuf);
1135 OS << (LocType->isObjCObjectPointerType() ? "nil" : "Null");
1136 OS << " assigned to a pointer which is expected to have non-null value";
1137 reportBugIfInvariantHolds(OS.str(),
1138 ErrorKind::NilAssignedToNonnull, N, nullptr, C,
1143 // If null was returned from a non-null function, mark the nullability
1144 // invariant as violated even if the diagnostic was suppressed.
1145 if (NullAssignedToNonNull) {
1146 State = State->set<InvariantViolated>(true);
1147 C.addTransition(State);
1151 // Intentionally missing case: '0' is bound to a reference. It is handled by
1152 // the DereferenceChecker.
1154 const MemRegion *ValueRegion = getTrackRegion(*ValDefOrUnknown);
1158 const NullabilityState *TrackedNullability =
1159 State->get<NullabilityMap>(ValueRegion);
1161 if (TrackedNullability) {
1162 if (RhsNullness == NullConstraint::IsNotNull ||
1163 TrackedNullability->getValue() != Nullability::Nullable)
1165 if (Filter.CheckNullablePassedToNonnull &&
1166 LocNullability == Nullability::Nonnull) {
1167 static CheckerProgramPointTag Tag(this, "NullablePassedToNonnull");
1168 ExplodedNode *N = C.addTransition(State, C.getPredecessor(), &Tag);
1169 reportBugIfInvariantHolds("Nullable pointer is assigned to a pointer "
1170 "which is expected to have non-null value",
1171 ErrorKind::NullableAssignedToNonnull, N,
1177 const auto *BinOp = dyn_cast<BinaryOperator>(S);
1179 if (ValNullability == Nullability::Nullable) {
1180 // Trust the static information of the value more than the static
1181 // information on the location.
1182 const Stmt *NullabilitySource = BinOp ? BinOp->getRHS() : S;
1183 State = State->set<NullabilityMap>(
1184 ValueRegion, NullabilityState(ValNullability, NullabilitySource));
1185 C.addTransition(State);
1189 if (LocNullability == Nullability::Nullable) {
1190 const Stmt *NullabilitySource = BinOp ? BinOp->getLHS() : S;
1191 State = State->set<NullabilityMap>(
1192 ValueRegion, NullabilityState(LocNullability, NullabilitySource));
1193 C.addTransition(State);
1197 void NullabilityChecker::printState(raw_ostream &Out, ProgramStateRef State,
1198 const char *NL, const char *Sep) const {
1200 NullabilityMapTy B = State->get<NullabilityMap>();
1207 for (NullabilityMapTy::iterator I = B.begin(), E = B.end(); I != E; ++I) {
1208 Out << I->first << " : ";
1209 I->second.print(Out);
1214 #define REGISTER_CHECKER(name, trackingRequired) \
1215 void ento::register##name##Checker(CheckerManager &mgr) { \
1216 NullabilityChecker *checker = mgr.registerChecker<NullabilityChecker>(); \
1217 checker->Filter.Check##name = true; \
1218 checker->Filter.CheckName##name = mgr.getCurrentCheckName(); \
1219 checker->NeedTracking = checker->NeedTracking || trackingRequired; \
1220 checker->NoDiagnoseCallsToSystemHeaders = \
1221 checker->NoDiagnoseCallsToSystemHeaders || \
1222 mgr.getAnalyzerOptions().getBooleanOption( \
1223 "NoDiagnoseCallsToSystemHeaders", false, checker, true); \
1226 // The checks are likely to be turned on by default and it is possible to do
1227 // them without tracking any nullability related information. As an optimization
1228 // no nullability information will be tracked when only these two checks are
1230 REGISTER_CHECKER(NullPassedToNonnull, false)
1231 REGISTER_CHECKER(NullReturnedFromNonnull, false)
1233 REGISTER_CHECKER(NullableDereferenced, true)
1234 REGISTER_CHECKER(NullablePassedToNonnull, true)
1235 REGISTER_CHECKER(NullableReturnedFromNonnull, true)