1 //===-- NullabilityChecker.cpp - Nullability checker ----------------------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // This checker tries to find nullability violations. There are several kinds of
10 // possible violations:
11 // * Null pointer is passed to a pointer which has a _Nonnull type.
12 // * Null pointer is returned from a function which has a _Nonnull return type.
13 // * Nullable pointer is passed to a pointer which has a _Nonnull type.
14 // * Nullable pointer is returned from a function which has a _Nonnull return
16 // * Nullable pointer is dereferenced.
18 // This checker propagates the nullability information of the pointers and looks
19 // for the patterns that are described above. Explicit casts are trusted and are
20 // considered a way to suppress false positives for this checker. The other way
21 // to suppress warnings would be to add asserts or guarding if statements to the
22 // code. In addition to the nullability propagation this checker also uses some
23 // heuristics to suppress potential false positives.
25 //===----------------------------------------------------------------------===//
27 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
29 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
30 #include "clang/StaticAnalyzer/Core/Checker.h"
31 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
32 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.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;
44 /// Returns the most nullable nullability. This is used for message expressions
45 /// like [receiver method], where the nullability of this expression is either
46 /// the nullability of the receiver or the nullability of the return type of the
47 /// method, depending on which is more nullable. Contradicted is considered to
48 /// be the most nullable, to avoid false positive results.
49 Nullability getMostNullable(Nullability Lhs, Nullability Rhs) {
50 return static_cast<Nullability>(
51 std::min(static_cast<char>(Lhs), static_cast<char>(Rhs)));
54 const char *getNullabilityString(Nullability Nullab) {
56 case Nullability::Contradicted:
57 return "contradicted";
58 case Nullability::Nullable:
60 case Nullability::Unspecified:
62 case Nullability::Nonnull:
65 llvm_unreachable("Unexpected enumeration.");
69 // These enums are used as an index to ErrorMessages array.
70 enum class ErrorKind : int {
74 NullableAssignedToNonnull,
75 NullableReturnedToNonnull,
77 NullablePassedToNonnull
80 class NullabilityChecker
81 : public Checker<check::Bind, check::PreCall, check::PreStmt<ReturnStmt>,
82 check::PostCall, check::PostStmt<ExplicitCastExpr>,
83 check::PostObjCMessage, check::DeadSymbols,
84 check::Event<ImplicitNullDerefEvent>> {
85 mutable std::unique_ptr<BugType> BT;
88 // If true, the checker will not diagnose nullabilility issues for calls
89 // to system headers. This option is motivated by the observation that large
90 // projects may have many nullability warnings. These projects may
91 // find warnings about nullability annotations that they have explicitly
92 // added themselves higher priority to fix than warnings on calls to system
94 DefaultBool NoDiagnoseCallsToSystemHeaders;
96 void checkBind(SVal L, SVal V, const Stmt *S, CheckerContext &C) const;
97 void checkPostStmt(const ExplicitCastExpr *CE, CheckerContext &C) const;
98 void checkPreStmt(const ReturnStmt *S, CheckerContext &C) const;
99 void checkPostObjCMessage(const ObjCMethodCall &M, CheckerContext &C) const;
100 void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
101 void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
102 void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const;
103 void checkEvent(ImplicitNullDerefEvent Event) const;
105 void printState(raw_ostream &Out, ProgramStateRef State, const char *NL,
106 const char *Sep) const override;
108 struct NullabilityChecksFilter {
109 DefaultBool CheckNullPassedToNonnull;
110 DefaultBool CheckNullReturnedFromNonnull;
111 DefaultBool CheckNullableDereferenced;
112 DefaultBool CheckNullablePassedToNonnull;
113 DefaultBool CheckNullableReturnedFromNonnull;
115 CheckerNameRef CheckNameNullPassedToNonnull;
116 CheckerNameRef CheckNameNullReturnedFromNonnull;
117 CheckerNameRef CheckNameNullableDereferenced;
118 CheckerNameRef CheckNameNullablePassedToNonnull;
119 CheckerNameRef CheckNameNullableReturnedFromNonnull;
122 NullabilityChecksFilter Filter;
123 // When set to false no nullability information will be tracked in
124 // NullabilityMap. It is possible to catch errors like passing a null pointer
125 // to a callee that expects nonnull argument without the information that is
126 // stroed in the NullabilityMap. This is an optimization.
127 DefaultBool NeedTracking;
130 class NullabilityBugVisitor : public BugReporterVisitor {
132 NullabilityBugVisitor(const MemRegion *M) : Region(M) {}
134 void Profile(llvm::FoldingSetNodeID &ID) const override {
137 ID.AddPointer(Region);
140 PathDiagnosticPieceRef VisitNode(const ExplodedNode *N,
141 BugReporterContext &BRC,
142 PathSensitiveBugReport &BR) override;
145 // The tracked region.
146 const MemRegion *Region;
149 /// When any of the nonnull arguments of the analyzed function is null, do not
150 /// report anything and turn off the check.
152 /// When \p SuppressPath is set to true, no more bugs will be reported on this
153 /// path by this checker.
154 void reportBugIfInvariantHolds(StringRef Msg, ErrorKind Error,
155 ExplodedNode *N, const MemRegion *Region,
157 const Stmt *ValueExpr = nullptr,
158 bool SuppressPath = false) const;
160 void reportBug(StringRef Msg, ErrorKind Error, ExplodedNode *N,
161 const MemRegion *Region, BugReporter &BR,
162 const Stmt *ValueExpr = nullptr) const {
164 BT.reset(new BugType(this, "Nullability", categories::MemoryError));
166 auto R = std::make_unique<PathSensitiveBugReport>(*BT, Msg, N);
168 R->markInteresting(Region);
169 R->addVisitor(std::make_unique<NullabilityBugVisitor>(Region));
172 R->addRange(ValueExpr->getSourceRange());
173 if (Error == ErrorKind::NilAssignedToNonnull ||
174 Error == ErrorKind::NilPassedToNonnull ||
175 Error == ErrorKind::NilReturnedToNonnull)
176 if (const auto *Ex = dyn_cast<Expr>(ValueExpr))
177 bugreporter::trackExpressionValue(N, Ex, *R);
179 BR.emitReport(std::move(R));
182 /// If an SVal wraps a region that should be tracked, it will return a pointer
183 /// to the wrapped region. Otherwise it will return a nullptr.
184 const SymbolicRegion *getTrackRegion(SVal Val,
185 bool CheckSuperRegion = false) const;
187 /// Returns true if the call is diagnosable in the current analyzer
189 bool isDiagnosableCall(const CallEvent &Call) const {
190 if (NoDiagnoseCallsToSystemHeaders && Call.isInSystemHeader())
197 class NullabilityState {
199 NullabilityState(Nullability Nullab, const Stmt *Source = nullptr)
200 : Nullab(Nullab), Source(Source) {}
202 const Stmt *getNullabilitySource() const { return Source; }
204 Nullability getValue() const { return Nullab; }
206 void Profile(llvm::FoldingSetNodeID &ID) const {
207 ID.AddInteger(static_cast<char>(Nullab));
208 ID.AddPointer(Source);
211 void print(raw_ostream &Out) const {
212 Out << getNullabilityString(Nullab) << "\n";
217 // Source is the expression which determined the nullability. For example in a
218 // message like [nullable nonnull_returning] has nullable nullability, because
219 // the receiver is nullable. Here the receiver will be the source of the
220 // nullability. This is useful information when the diagnostics are generated.
224 bool operator==(NullabilityState Lhs, NullabilityState Rhs) {
225 return Lhs.getValue() == Rhs.getValue() &&
226 Lhs.getNullabilitySource() == Rhs.getNullabilitySource();
229 } // end anonymous namespace
231 REGISTER_MAP_WITH_PROGRAMSTATE(NullabilityMap, const MemRegion *,
234 // We say "the nullability type invariant is violated" when a location with a
235 // non-null type contains NULL or a function with a non-null return type returns
236 // NULL. Violations of the nullability type invariant can be detected either
237 // directly (for example, when NULL is passed as an argument to a nonnull
238 // parameter) or indirectly (for example, when, inside a function, the
239 // programmer defensively checks whether a nonnull parameter contains NULL and
240 // finds that it does).
242 // As a matter of policy, the nullability checker typically warns on direct
243 // violations of the nullability invariant (although it uses various
244 // heuristics to suppress warnings in some cases) but will not warn if the
245 // invariant has already been violated along the path (either directly or
246 // indirectly). As a practical matter, this prevents the analyzer from
247 // (1) warning on defensive code paths where a nullability precondition is
248 // determined to have been violated, (2) warning additional times after an
249 // initial direct violation has been discovered, and (3) warning after a direct
250 // violation that has been implicitly or explicitly suppressed (for
251 // example, with a cast of NULL to _Nonnull). In essence, once an invariant
252 // violation is detected on a path, this checker will be essentially turned off
253 // for the rest of the analysis
255 // The analyzer takes this approach (rather than generating a sink node) to
256 // ensure coverage of defensive paths, which may be important for backwards
257 // compatibility in codebases that were developed without nullability in mind.
258 REGISTER_TRAIT_WITH_PROGRAMSTATE(InvariantViolated, bool)
260 enum class NullConstraint { IsNull, IsNotNull, Unknown };
262 static NullConstraint getNullConstraint(DefinedOrUnknownSVal Val,
263 ProgramStateRef State) {
264 ConditionTruthVal Nullness = State->isNull(Val);
265 if (Nullness.isConstrainedFalse())
266 return NullConstraint::IsNotNull;
267 if (Nullness.isConstrainedTrue())
268 return NullConstraint::IsNull;
269 return NullConstraint::Unknown;
272 const SymbolicRegion *
273 NullabilityChecker::getTrackRegion(SVal Val, bool CheckSuperRegion) const {
277 auto RegionSVal = Val.getAs<loc::MemRegionVal>();
281 const MemRegion *Region = RegionSVal->getRegion();
283 if (CheckSuperRegion) {
284 if (auto FieldReg = Region->getAs<FieldRegion>())
285 return dyn_cast<SymbolicRegion>(FieldReg->getSuperRegion());
286 if (auto ElementReg = Region->getAs<ElementRegion>())
287 return dyn_cast<SymbolicRegion>(ElementReg->getSuperRegion());
290 return dyn_cast<SymbolicRegion>(Region);
293 PathDiagnosticPieceRef NullabilityChecker::NullabilityBugVisitor::VisitNode(
294 const ExplodedNode *N, BugReporterContext &BRC,
295 PathSensitiveBugReport &BR) {
296 ProgramStateRef State = N->getState();
297 ProgramStateRef StatePrev = N->getFirstPred()->getState();
299 const NullabilityState *TrackedNullab = State->get<NullabilityMap>(Region);
300 const NullabilityState *TrackedNullabPrev =
301 StatePrev->get<NullabilityMap>(Region);
305 if (TrackedNullabPrev &&
306 TrackedNullabPrev->getValue() == TrackedNullab->getValue())
309 // Retrieve the associated statement.
310 const Stmt *S = TrackedNullab->getNullabilitySource();
311 if (!S || S->getBeginLoc().isInvalid()) {
312 S = N->getStmtForDiagnostics();
318 std::string InfoText =
319 (llvm::Twine("Nullability '") +
320 getNullabilityString(TrackedNullab->getValue()) + "' is inferred")
323 // Generate the extra diagnostic.
324 PathDiagnosticLocation Pos(S, BRC.getSourceManager(),
325 N->getLocationContext());
326 return std::make_shared<PathDiagnosticEventPiece>(Pos, InfoText, true);
329 /// Returns true when the value stored at the given location has been
330 /// constrained to null after being passed through an object of nonnnull type.
331 static bool checkValueAtLValForInvariantViolation(ProgramStateRef State,
332 SVal LV, QualType T) {
333 if (getNullabilityAnnotation(T) != Nullability::Nonnull)
336 auto RegionVal = LV.getAs<loc::MemRegionVal>();
340 // If the value was constrained to null *after* it was passed through that
341 // location, it could not have been a concrete pointer *when* it was passed.
342 // In that case we would have handled the situation when the value was
343 // bound to that location, by emitting (or not emitting) a report.
344 // Therefore we are only interested in symbolic regions that can be either
345 // null or non-null depending on the value of their respective symbol.
346 auto StoredVal = State->getSVal(*RegionVal).getAs<loc::MemRegionVal>();
347 if (!StoredVal || !isa<SymbolicRegion>(StoredVal->getRegion()))
350 if (getNullConstraint(*StoredVal, State) == NullConstraint::IsNull)
357 checkParamsForPreconditionViolation(ArrayRef<ParmVarDecl *> Params,
358 ProgramStateRef State,
359 const LocationContext *LocCtxt) {
360 for (const auto *ParamDecl : Params) {
361 if (ParamDecl->isParameterPack())
364 SVal LV = State->getLValue(ParamDecl, LocCtxt);
365 if (checkValueAtLValForInvariantViolation(State, LV,
366 ParamDecl->getType())) {
374 checkSelfIvarsForInvariantViolation(ProgramStateRef State,
375 const LocationContext *LocCtxt) {
376 auto *MD = dyn_cast<ObjCMethodDecl>(LocCtxt->getDecl());
377 if (!MD || !MD->isInstanceMethod())
380 const ImplicitParamDecl *SelfDecl = LocCtxt->getSelfDecl();
384 SVal SelfVal = State->getSVal(State->getRegion(SelfDecl, LocCtxt));
386 const ObjCObjectPointerType *SelfType =
387 dyn_cast<ObjCObjectPointerType>(SelfDecl->getType());
391 const ObjCInterfaceDecl *ID = SelfType->getInterfaceDecl();
395 for (const auto *IvarDecl : ID->ivars()) {
396 SVal LV = State->getLValue(IvarDecl, SelfVal);
397 if (checkValueAtLValForInvariantViolation(State, LV, IvarDecl->getType())) {
404 static bool checkInvariantViolation(ProgramStateRef State, ExplodedNode *N,
406 if (State->get<InvariantViolated>())
409 const LocationContext *LocCtxt = C.getLocationContext();
410 const Decl *D = LocCtxt->getDecl();
414 ArrayRef<ParmVarDecl*> Params;
415 if (const auto *BD = dyn_cast<BlockDecl>(D))
416 Params = BD->parameters();
417 else if (const auto *FD = dyn_cast<FunctionDecl>(D))
418 Params = FD->parameters();
419 else if (const auto *MD = dyn_cast<ObjCMethodDecl>(D))
420 Params = MD->parameters();
424 if (checkParamsForPreconditionViolation(Params, State, LocCtxt) ||
425 checkSelfIvarsForInvariantViolation(State, LocCtxt)) {
427 C.addTransition(State->set<InvariantViolated>(true), N);
433 void NullabilityChecker::reportBugIfInvariantHolds(StringRef Msg,
434 ErrorKind Error, ExplodedNode *N, const MemRegion *Region,
435 CheckerContext &C, const Stmt *ValueExpr, bool SuppressPath) const {
436 ProgramStateRef OriginalState = N->getState();
438 if (checkInvariantViolation(OriginalState, N, C))
441 OriginalState = OriginalState->set<InvariantViolated>(true);
442 N = C.addTransition(OriginalState, N);
445 reportBug(Msg, Error, N, Region, C.getBugReporter(), ValueExpr);
448 /// Cleaning up the program state.
449 void NullabilityChecker::checkDeadSymbols(SymbolReaper &SR,
450 CheckerContext &C) const {
451 ProgramStateRef State = C.getState();
452 NullabilityMapTy Nullabilities = State->get<NullabilityMap>();
453 for (NullabilityMapTy::iterator I = Nullabilities.begin(),
454 E = Nullabilities.end();
456 const auto *Region = I->first->getAs<SymbolicRegion>();
457 assert(Region && "Non-symbolic region is tracked.");
458 if (SR.isDead(Region->getSymbol())) {
459 State = State->remove<NullabilityMap>(I->first);
462 // When one of the nonnull arguments are constrained to be null, nullability
463 // preconditions are violated. It is not enough to check this only when we
464 // actually report an error, because at that time interesting symbols might be
466 if (checkInvariantViolation(State, C.getPredecessor(), C))
468 C.addTransition(State);
471 /// This callback triggers when a pointer is dereferenced and the analyzer does
472 /// not know anything about the value of that pointer. When that pointer is
473 /// nullable, this code emits a warning.
474 void NullabilityChecker::checkEvent(ImplicitNullDerefEvent Event) const {
475 if (Event.SinkNode->getState()->get<InvariantViolated>())
478 const MemRegion *Region =
479 getTrackRegion(Event.Location, /*CheckSuperRegion=*/true);
483 ProgramStateRef State = Event.SinkNode->getState();
484 const NullabilityState *TrackedNullability =
485 State->get<NullabilityMap>(Region);
487 if (!TrackedNullability)
490 if (Filter.CheckNullableDereferenced &&
491 TrackedNullability->getValue() == Nullability::Nullable) {
492 BugReporter &BR = *Event.BR;
493 // Do not suppress errors on defensive code paths, because dereferencing
494 // a nullable pointer is always an error.
495 if (Event.IsDirectDereference)
496 reportBug("Nullable pointer is dereferenced",
497 ErrorKind::NullableDereferenced, Event.SinkNode, Region, BR);
499 reportBug("Nullable pointer is passed to a callee that requires a "
500 "non-null", ErrorKind::NullablePassedToNonnull,
501 Event.SinkNode, Region, BR);
506 /// Find the outermost subexpression of E that is not an implicit cast.
507 /// This looks through the implicit casts to _Nonnull that ARC adds to
508 /// return expressions of ObjC types when the return type of the function or
509 /// method is non-null but the express is not.
510 static const Expr *lookThroughImplicitCasts(const Expr *E) {
513 while (auto *ICE = dyn_cast<ImplicitCastExpr>(E)) {
514 E = ICE->getSubExpr();
520 /// This method check when nullable pointer or null value is returned from a
521 /// function that has nonnull return type.
522 void NullabilityChecker::checkPreStmt(const ReturnStmt *S,
523 CheckerContext &C) const {
524 auto RetExpr = S->getRetValue();
528 if (!RetExpr->getType()->isAnyPointerType())
531 ProgramStateRef State = C.getState();
532 if (State->get<InvariantViolated>())
535 auto RetSVal = C.getSVal(S).getAs<DefinedOrUnknownSVal>();
539 bool InSuppressedMethodFamily = false;
541 QualType RequiredRetType;
542 AnalysisDeclContext *DeclCtxt =
543 C.getLocationContext()->getAnalysisDeclContext();
544 const Decl *D = DeclCtxt->getDecl();
545 if (auto *MD = dyn_cast<ObjCMethodDecl>(D)) {
546 // HACK: This is a big hammer to avoid warning when there are defensive
547 // nil checks in -init and -copy methods. We should add more sophisticated
548 // logic here to suppress on common defensive idioms but still
549 // warn when there is a likely problem.
550 ObjCMethodFamily Family = MD->getMethodFamily();
551 if (OMF_init == Family || OMF_copy == Family || OMF_mutableCopy == Family)
552 InSuppressedMethodFamily = true;
554 RequiredRetType = MD->getReturnType();
555 } else if (auto *FD = dyn_cast<FunctionDecl>(D)) {
556 RequiredRetType = FD->getReturnType();
561 NullConstraint Nullness = getNullConstraint(*RetSVal, State);
563 Nullability RequiredNullability = getNullabilityAnnotation(RequiredRetType);
565 // If the returned value is null but the type of the expression
566 // generating it is nonnull then we will suppress the diagnostic.
567 // This enables explicit suppression when returning a nil literal in a
568 // function with a _Nonnull return type:
569 // return (NSString * _Nonnull)0;
570 Nullability RetExprTypeLevelNullability =
571 getNullabilityAnnotation(lookThroughImplicitCasts(RetExpr)->getType());
573 bool NullReturnedFromNonNull = (RequiredNullability == Nullability::Nonnull &&
574 Nullness == NullConstraint::IsNull);
575 if (Filter.CheckNullReturnedFromNonnull &&
576 NullReturnedFromNonNull &&
577 RetExprTypeLevelNullability != Nullability::Nonnull &&
578 !InSuppressedMethodFamily &&
579 C.getLocationContext()->inTopFrame()) {
580 static CheckerProgramPointTag Tag(this, "NullReturnedFromNonnull");
581 ExplodedNode *N = C.generateErrorNode(State, &Tag);
585 SmallString<256> SBuf;
586 llvm::raw_svector_ostream OS(SBuf);
587 OS << (RetExpr->getType()->isObjCObjectPointerType() ? "nil" : "Null");
588 OS << " returned from a " << C.getDeclDescription(D) <<
589 " that is expected to return a non-null value";
590 reportBugIfInvariantHolds(OS.str(),
591 ErrorKind::NilReturnedToNonnull, N, nullptr, C,
596 // If null was returned from a non-null function, mark the nullability
597 // invariant as violated even if the diagnostic was suppressed.
598 if (NullReturnedFromNonNull) {
599 State = State->set<InvariantViolated>(true);
600 C.addTransition(State);
604 const MemRegion *Region = getTrackRegion(*RetSVal);
608 const NullabilityState *TrackedNullability =
609 State->get<NullabilityMap>(Region);
610 if (TrackedNullability) {
611 Nullability TrackedNullabValue = TrackedNullability->getValue();
612 if (Filter.CheckNullableReturnedFromNonnull &&
613 Nullness != NullConstraint::IsNotNull &&
614 TrackedNullabValue == Nullability::Nullable &&
615 RequiredNullability == Nullability::Nonnull) {
616 static CheckerProgramPointTag Tag(this, "NullableReturnedFromNonnull");
617 ExplodedNode *N = C.addTransition(State, C.getPredecessor(), &Tag);
619 SmallString<256> SBuf;
620 llvm::raw_svector_ostream OS(SBuf);
621 OS << "Nullable pointer is returned from a " << C.getDeclDescription(D) <<
622 " that is expected to return a non-null value";
624 reportBugIfInvariantHolds(OS.str(),
625 ErrorKind::NullableReturnedToNonnull, N,
630 if (RequiredNullability == Nullability::Nullable) {
631 State = State->set<NullabilityMap>(Region,
632 NullabilityState(RequiredNullability,
634 C.addTransition(State);
638 /// This callback warns when a nullable pointer or a null value is passed to a
639 /// function that expects its argument to be nonnull.
640 void NullabilityChecker::checkPreCall(const CallEvent &Call,
641 CheckerContext &C) const {
645 ProgramStateRef State = C.getState();
646 if (State->get<InvariantViolated>())
649 ProgramStateRef OrigState = State;
652 for (const ParmVarDecl *Param : Call.parameters()) {
653 if (Param->isParameterPack())
656 if (Idx >= Call.getNumArgs())
659 const Expr *ArgExpr = Call.getArgExpr(Idx);
660 auto ArgSVal = Call.getArgSVal(Idx++).getAs<DefinedOrUnknownSVal>();
664 if (!Param->getType()->isAnyPointerType() &&
665 !Param->getType()->isReferenceType())
668 NullConstraint Nullness = getNullConstraint(*ArgSVal, State);
670 Nullability RequiredNullability =
671 getNullabilityAnnotation(Param->getType());
672 Nullability ArgExprTypeLevelNullability =
673 getNullabilityAnnotation(ArgExpr->getType());
675 unsigned ParamIdx = Param->getFunctionScopeIndex() + 1;
677 if (Filter.CheckNullPassedToNonnull && Nullness == NullConstraint::IsNull &&
678 ArgExprTypeLevelNullability != Nullability::Nonnull &&
679 RequiredNullability == Nullability::Nonnull &&
680 isDiagnosableCall(Call)) {
681 ExplodedNode *N = C.generateErrorNode(State);
685 SmallString<256> SBuf;
686 llvm::raw_svector_ostream OS(SBuf);
687 OS << (Param->getType()->isObjCObjectPointerType() ? "nil" : "Null");
688 OS << " passed to a callee that requires a non-null " << ParamIdx
689 << llvm::getOrdinalSuffix(ParamIdx) << " parameter";
690 reportBugIfInvariantHolds(OS.str(), ErrorKind::NilPassedToNonnull, N,
692 ArgExpr, /*SuppressPath=*/false);
696 const MemRegion *Region = getTrackRegion(*ArgSVal);
700 const NullabilityState *TrackedNullability =
701 State->get<NullabilityMap>(Region);
703 if (TrackedNullability) {
704 if (Nullness == NullConstraint::IsNotNull ||
705 TrackedNullability->getValue() != Nullability::Nullable)
708 if (Filter.CheckNullablePassedToNonnull &&
709 RequiredNullability == Nullability::Nonnull &&
710 isDiagnosableCall(Call)) {
711 ExplodedNode *N = C.addTransition(State);
712 SmallString<256> SBuf;
713 llvm::raw_svector_ostream OS(SBuf);
714 OS << "Nullable pointer is passed to a callee that requires a non-null "
715 << ParamIdx << llvm::getOrdinalSuffix(ParamIdx) << " parameter";
716 reportBugIfInvariantHolds(OS.str(),
717 ErrorKind::NullablePassedToNonnull, N,
718 Region, C, ArgExpr, /*SuppressPath=*/true);
721 if (Filter.CheckNullableDereferenced &&
722 Param->getType()->isReferenceType()) {
723 ExplodedNode *N = C.addTransition(State);
724 reportBugIfInvariantHolds("Nullable pointer is dereferenced",
725 ErrorKind::NullableDereferenced, N, Region,
726 C, ArgExpr, /*SuppressPath=*/true);
732 if (State != OrigState)
733 C.addTransition(State);
736 /// Suppress the nullability warnings for some functions.
737 void NullabilityChecker::checkPostCall(const CallEvent &Call,
738 CheckerContext &C) const {
739 auto Decl = Call.getDecl();
742 // ObjC Messages handles in a different callback.
743 if (Call.getKind() == CE_ObjCMessage)
745 const FunctionType *FuncType = Decl->getFunctionType();
748 QualType ReturnType = FuncType->getReturnType();
749 if (!ReturnType->isAnyPointerType())
751 ProgramStateRef State = C.getState();
752 if (State->get<InvariantViolated>())
755 const MemRegion *Region = getTrackRegion(Call.getReturnValue());
759 // CG headers are misannotated. Do not warn for symbols that are the results
761 const SourceManager &SM = C.getSourceManager();
762 StringRef FilePath = SM.getFilename(SM.getSpellingLoc(Decl->getBeginLoc()));
763 if (llvm::sys::path::filename(FilePath).startswith("CG")) {
764 State = State->set<NullabilityMap>(Region, Nullability::Contradicted);
765 C.addTransition(State);
769 const NullabilityState *TrackedNullability =
770 State->get<NullabilityMap>(Region);
772 if (!TrackedNullability &&
773 getNullabilityAnnotation(ReturnType) == Nullability::Nullable) {
774 State = State->set<NullabilityMap>(Region, Nullability::Nullable);
775 C.addTransition(State);
779 static Nullability getReceiverNullability(const ObjCMethodCall &M,
780 ProgramStateRef State) {
781 if (M.isReceiverSelfOrSuper()) {
782 // For super and super class receivers we assume that the receiver is
784 return Nullability::Nonnull;
786 // Otherwise look up nullability in the state.
787 SVal Receiver = M.getReceiverSVal();
788 if (auto DefOrUnknown = Receiver.getAs<DefinedOrUnknownSVal>()) {
789 // If the receiver is constrained to be nonnull, assume that it is nonnull
790 // regardless of its type.
791 NullConstraint Nullness = getNullConstraint(*DefOrUnknown, State);
792 if (Nullness == NullConstraint::IsNotNull)
793 return Nullability::Nonnull;
795 auto ValueRegionSVal = Receiver.getAs<loc::MemRegionVal>();
796 if (ValueRegionSVal) {
797 const MemRegion *SelfRegion = ValueRegionSVal->getRegion();
800 const NullabilityState *TrackedSelfNullability =
801 State->get<NullabilityMap>(SelfRegion);
802 if (TrackedSelfNullability)
803 return TrackedSelfNullability->getValue();
805 return Nullability::Unspecified;
808 /// Calculate the nullability of the result of a message expr based on the
809 /// nullability of the receiver, the nullability of the return value, and the
811 void NullabilityChecker::checkPostObjCMessage(const ObjCMethodCall &M,
812 CheckerContext &C) const {
813 auto Decl = M.getDecl();
816 QualType RetType = Decl->getReturnType();
817 if (!RetType->isAnyPointerType())
820 ProgramStateRef State = C.getState();
821 if (State->get<InvariantViolated>())
824 const MemRegion *ReturnRegion = getTrackRegion(M.getReturnValue());
828 auto Interface = Decl->getClassInterface();
829 auto Name = Interface ? Interface->getName() : "";
830 // In order to reduce the noise in the diagnostics generated by this checker,
831 // some framework and programming style based heuristics are used. These
832 // heuristics are for Cocoa APIs which have NS prefix.
833 if (Name.startswith("NS")) {
834 // Developers rely on dynamic invariants such as an item should be available
835 // in a collection, or a collection is not empty often. Those invariants can
836 // not be inferred by any static analysis tool. To not to bother the users
837 // with too many false positives, every item retrieval function should be
838 // ignored for collections. The instance methods of dictionaries in Cocoa
839 // are either item retrieval related or not interesting nullability wise.
840 // Using this fact, to keep the code easier to read just ignore the return
841 // value of every instance method of dictionaries.
842 if (M.isInstanceMessage() && Name.contains("Dictionary")) {
844 State->set<NullabilityMap>(ReturnRegion, Nullability::Contradicted);
845 C.addTransition(State);
848 // For similar reasons ignore some methods of Cocoa arrays.
849 StringRef FirstSelectorSlot = M.getSelector().getNameForSlot(0);
850 if (Name.contains("Array") &&
851 (FirstSelectorSlot == "firstObject" ||
852 FirstSelectorSlot == "lastObject")) {
854 State->set<NullabilityMap>(ReturnRegion, Nullability::Contradicted);
855 C.addTransition(State);
859 // Encoding related methods of string should not fail when lossless
860 // encodings are used. Using lossless encodings is so frequent that ignoring
861 // this class of methods reduced the emitted diagnostics by about 30% on
862 // some projects (and all of that was false positives).
863 if (Name.contains("String")) {
864 for (auto Param : M.parameters()) {
865 if (Param->getName() == "encoding") {
866 State = State->set<NullabilityMap>(ReturnRegion,
867 Nullability::Contradicted);
868 C.addTransition(State);
875 const ObjCMessageExpr *Message = M.getOriginExpr();
876 Nullability SelfNullability = getReceiverNullability(M, State);
878 const NullabilityState *NullabilityOfReturn =
879 State->get<NullabilityMap>(ReturnRegion);
881 if (NullabilityOfReturn) {
882 // When we have a nullability tracked for the return value, the nullability
883 // of the expression will be the most nullable of the receiver and the
885 Nullability RetValTracked = NullabilityOfReturn->getValue();
886 Nullability ComputedNullab =
887 getMostNullable(RetValTracked, SelfNullability);
888 if (ComputedNullab != RetValTracked &&
889 ComputedNullab != Nullability::Unspecified) {
890 const Stmt *NullabilitySource =
891 ComputedNullab == RetValTracked
892 ? NullabilityOfReturn->getNullabilitySource()
893 : Message->getInstanceReceiver();
894 State = State->set<NullabilityMap>(
895 ReturnRegion, NullabilityState(ComputedNullab, NullabilitySource));
896 C.addTransition(State);
901 // No tracked information. Use static type information for return value.
902 Nullability RetNullability = getNullabilityAnnotation(RetType);
904 // Properties might be computed. For this reason the static analyzer creates a
905 // new symbol each time an unknown property is read. To avoid false pozitives
906 // do not treat unknown properties as nullable, even when they explicitly
908 if (M.getMessageKind() == OCM_PropertyAccess && !C.wasInlined)
909 RetNullability = Nullability::Nonnull;
911 Nullability ComputedNullab = getMostNullable(RetNullability, SelfNullability);
912 if (ComputedNullab == Nullability::Nullable) {
913 const Stmt *NullabilitySource = ComputedNullab == RetNullability
915 : Message->getInstanceReceiver();
916 State = State->set<NullabilityMap>(
917 ReturnRegion, NullabilityState(ComputedNullab, NullabilitySource));
918 C.addTransition(State);
922 /// Explicit casts are trusted. If there is a disagreement in the nullability
923 /// annotations in the destination and the source or '0' is casted to nonnull
924 /// track the value as having contraditory nullability. This will allow users to
925 /// suppress warnings.
926 void NullabilityChecker::checkPostStmt(const ExplicitCastExpr *CE,
927 CheckerContext &C) const {
928 QualType OriginType = CE->getSubExpr()->getType();
929 QualType DestType = CE->getType();
930 if (!OriginType->isAnyPointerType())
932 if (!DestType->isAnyPointerType())
935 ProgramStateRef State = C.getState();
936 if (State->get<InvariantViolated>())
939 Nullability DestNullability = getNullabilityAnnotation(DestType);
941 // No explicit nullability in the destination type, so this cast does not
942 // change the nullability.
943 if (DestNullability == Nullability::Unspecified)
946 auto RegionSVal = C.getSVal(CE).getAs<DefinedOrUnknownSVal>();
947 const MemRegion *Region = getTrackRegion(*RegionSVal);
951 // When 0 is converted to nonnull mark it as contradicted.
952 if (DestNullability == Nullability::Nonnull) {
953 NullConstraint Nullness = getNullConstraint(*RegionSVal, State);
954 if (Nullness == NullConstraint::IsNull) {
955 State = State->set<NullabilityMap>(Region, Nullability::Contradicted);
956 C.addTransition(State);
961 const NullabilityState *TrackedNullability =
962 State->get<NullabilityMap>(Region);
964 if (!TrackedNullability) {
965 if (DestNullability != Nullability::Nullable)
967 State = State->set<NullabilityMap>(Region,
968 NullabilityState(DestNullability, CE));
969 C.addTransition(State);
973 if (TrackedNullability->getValue() != DestNullability &&
974 TrackedNullability->getValue() != Nullability::Contradicted) {
975 State = State->set<NullabilityMap>(Region, Nullability::Contradicted);
976 C.addTransition(State);
980 /// For a given statement performing a bind, attempt to syntactically
981 /// match the expression resulting in the bound value.
982 static const Expr * matchValueExprForBind(const Stmt *S) {
983 // For `x = e` the value expression is the right-hand side.
984 if (auto *BinOp = dyn_cast<BinaryOperator>(S)) {
985 if (BinOp->getOpcode() == BO_Assign)
986 return BinOp->getRHS();
989 // For `int x = e` the value expression is the initializer.
990 if (auto *DS = dyn_cast<DeclStmt>(S)) {
991 if (DS->isSingleDecl()) {
992 auto *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
996 if (const Expr *Init = VD->getInit())
1004 /// Returns true if \param S is a DeclStmt for a local variable that
1005 /// ObjC automated reference counting initialized with zero.
1006 static bool isARCNilInitializedLocal(CheckerContext &C, const Stmt *S) {
1007 // We suppress diagnostics for ARC zero-initialized _Nonnull locals. This
1008 // prevents false positives when a _Nonnull local variable cannot be
1009 // initialized with an initialization expression:
1010 // NSString * _Nonnull s; // no-warning
1011 // @autoreleasepool {
1015 // FIXME: We should treat implicitly zero-initialized _Nonnull locals as
1016 // uninitialized in Sema's UninitializedValues analysis to warn when a use of
1017 // the zero-initialized definition will unexpectedly yield nil.
1019 // Locals are only zero-initialized when automated reference counting
1021 if (!C.getASTContext().getLangOpts().ObjCAutoRefCount)
1024 auto *DS = dyn_cast<DeclStmt>(S);
1025 if (!DS || !DS->isSingleDecl())
1028 auto *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
1032 // Sema only zero-initializes locals with ObjCLifetimes.
1033 if(!VD->getType().getQualifiers().hasObjCLifetime())
1036 const Expr *Init = VD->getInit();
1037 assert(Init && "ObjC local under ARC without initializer");
1039 // Return false if the local is explicitly initialized (e.g., with '= nil').
1040 if (!isa<ImplicitValueInitExpr>(Init))
1046 /// Propagate the nullability information through binds and warn when nullable
1047 /// pointer or null symbol is assigned to a pointer with a nonnull type.
1048 void NullabilityChecker::checkBind(SVal L, SVal V, const Stmt *S,
1049 CheckerContext &C) const {
1050 const TypedValueRegion *TVR =
1051 dyn_cast_or_null<TypedValueRegion>(L.getAsRegion());
1055 QualType LocType = TVR->getValueType();
1056 if (!LocType->isAnyPointerType())
1059 ProgramStateRef State = C.getState();
1060 if (State->get<InvariantViolated>())
1063 auto ValDefOrUnknown = V.getAs<DefinedOrUnknownSVal>();
1064 if (!ValDefOrUnknown)
1067 NullConstraint RhsNullness = getNullConstraint(*ValDefOrUnknown, State);
1069 Nullability ValNullability = Nullability::Unspecified;
1070 if (SymbolRef Sym = ValDefOrUnknown->getAsSymbol())
1071 ValNullability = getNullabilityAnnotation(Sym->getType());
1073 Nullability LocNullability = getNullabilityAnnotation(LocType);
1075 // If the type of the RHS expression is nonnull, don't warn. This
1076 // enables explicit suppression with a cast to nonnull.
1077 Nullability ValueExprTypeLevelNullability = Nullability::Unspecified;
1078 const Expr *ValueExpr = matchValueExprForBind(S);
1080 ValueExprTypeLevelNullability =
1081 getNullabilityAnnotation(lookThroughImplicitCasts(ValueExpr)->getType());
1084 bool NullAssignedToNonNull = (LocNullability == Nullability::Nonnull &&
1085 RhsNullness == NullConstraint::IsNull);
1086 if (Filter.CheckNullPassedToNonnull &&
1087 NullAssignedToNonNull &&
1088 ValNullability != Nullability::Nonnull &&
1089 ValueExprTypeLevelNullability != Nullability::Nonnull &&
1090 !isARCNilInitializedLocal(C, S)) {
1091 static CheckerProgramPointTag Tag(this, "NullPassedToNonnull");
1092 ExplodedNode *N = C.generateErrorNode(State, &Tag);
1097 const Stmt *ValueStmt = S;
1099 ValueStmt = ValueExpr;
1101 SmallString<256> SBuf;
1102 llvm::raw_svector_ostream OS(SBuf);
1103 OS << (LocType->isObjCObjectPointerType() ? "nil" : "Null");
1104 OS << " assigned to a pointer which is expected to have non-null value";
1105 reportBugIfInvariantHolds(OS.str(),
1106 ErrorKind::NilAssignedToNonnull, N, nullptr, C,
1111 // If null was returned from a non-null function, mark the nullability
1112 // invariant as violated even if the diagnostic was suppressed.
1113 if (NullAssignedToNonNull) {
1114 State = State->set<InvariantViolated>(true);
1115 C.addTransition(State);
1119 // Intentionally missing case: '0' is bound to a reference. It is handled by
1120 // the DereferenceChecker.
1122 const MemRegion *ValueRegion = getTrackRegion(*ValDefOrUnknown);
1126 const NullabilityState *TrackedNullability =
1127 State->get<NullabilityMap>(ValueRegion);
1129 if (TrackedNullability) {
1130 if (RhsNullness == NullConstraint::IsNotNull ||
1131 TrackedNullability->getValue() != Nullability::Nullable)
1133 if (Filter.CheckNullablePassedToNonnull &&
1134 LocNullability == Nullability::Nonnull) {
1135 static CheckerProgramPointTag Tag(this, "NullablePassedToNonnull");
1136 ExplodedNode *N = C.addTransition(State, C.getPredecessor(), &Tag);
1137 reportBugIfInvariantHolds("Nullable pointer is assigned to a pointer "
1138 "which is expected to have non-null value",
1139 ErrorKind::NullableAssignedToNonnull, N,
1145 const auto *BinOp = dyn_cast<BinaryOperator>(S);
1147 if (ValNullability == Nullability::Nullable) {
1148 // Trust the static information of the value more than the static
1149 // information on the location.
1150 const Stmt *NullabilitySource = BinOp ? BinOp->getRHS() : S;
1151 State = State->set<NullabilityMap>(
1152 ValueRegion, NullabilityState(ValNullability, NullabilitySource));
1153 C.addTransition(State);
1157 if (LocNullability == Nullability::Nullable) {
1158 const Stmt *NullabilitySource = BinOp ? BinOp->getLHS() : S;
1159 State = State->set<NullabilityMap>(
1160 ValueRegion, NullabilityState(LocNullability, NullabilitySource));
1161 C.addTransition(State);
1165 void NullabilityChecker::printState(raw_ostream &Out, ProgramStateRef State,
1166 const char *NL, const char *Sep) const {
1168 NullabilityMapTy B = State->get<NullabilityMap>();
1170 if (State->get<InvariantViolated>())
1172 << "Nullability invariant was violated, warnings suppressed." << NL;
1177 if (!State->get<InvariantViolated>())
1180 for (NullabilityMapTy::iterator I = B.begin(), E = B.end(); I != E; ++I) {
1181 Out << I->first << " : ";
1182 I->second.print(Out);
1187 void ento::registerNullabilityBase(CheckerManager &mgr) {
1188 mgr.registerChecker<NullabilityChecker>();
1191 bool ento::shouldRegisterNullabilityBase(const LangOptions &LO) {
1195 #define REGISTER_CHECKER(name, trackingRequired) \
1196 void ento::register##name##Checker(CheckerManager &mgr) { \
1197 NullabilityChecker *checker = mgr.getChecker<NullabilityChecker>(); \
1198 checker->Filter.Check##name = true; \
1199 checker->Filter.CheckName##name = mgr.getCurrentCheckerName(); \
1200 checker->NeedTracking = checker->NeedTracking || trackingRequired; \
1201 checker->NoDiagnoseCallsToSystemHeaders = \
1202 checker->NoDiagnoseCallsToSystemHeaders || \
1203 mgr.getAnalyzerOptions().getCheckerBooleanOption( \
1204 checker, "NoDiagnoseCallsToSystemHeaders", true); \
1207 bool ento::shouldRegister##name##Checker(const LangOptions &LO) { \
1211 // The checks are likely to be turned on by default and it is possible to do
1212 // them without tracking any nullability related information. As an optimization
1213 // no nullability information will be tracked when only these two checks are
1215 REGISTER_CHECKER(NullPassedToNonnull, false)
1216 REGISTER_CHECKER(NullReturnedFromNonnull, false)
1218 REGISTER_CHECKER(NullableDereferenced, true)
1219 REGISTER_CHECKER(NullablePassedToNonnull, true)
1220 REGISTER_CHECKER(NullableReturnedFromNonnull, true)