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 CheckName CheckNameNullPassedToNonnull;
116 CheckName CheckNameNullReturnedFromNonnull;
117 CheckName CheckNameNullableDereferenced;
118 CheckName CheckNameNullablePassedToNonnull;
119 CheckName 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 std::shared_ptr<PathDiagnosticPiece> VisitNode(const ExplodedNode *N,
141 BugReporterContext &BRC,
142 BugReport &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 = llvm::make_unique<BugReport>(*BT, Msg, N);
168 R->markInteresting(Region);
169 R->addVisitor(llvm::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 std::shared_ptr<PathDiagnosticPiece>
294 NullabilityChecker::NullabilityBugVisitor::VisitNode(const ExplodedNode *N,
295 BugReporterContext &BRC,
297 ProgramStateRef State = N->getState();
298 ProgramStateRef StatePrev = N->getFirstPred()->getState();
300 const NullabilityState *TrackedNullab = State->get<NullabilityMap>(Region);
301 const NullabilityState *TrackedNullabPrev =
302 StatePrev->get<NullabilityMap>(Region);
306 if (TrackedNullabPrev &&
307 TrackedNullabPrev->getValue() == TrackedNullab->getValue())
310 // Retrieve the associated statement.
311 const Stmt *S = TrackedNullab->getNullabilitySource();
312 if (!S || S->getBeginLoc().isInvalid()) {
313 S = PathDiagnosticLocation::getStmt(N);
319 std::string InfoText =
320 (llvm::Twine("Nullability '") +
321 getNullabilityString(TrackedNullab->getValue()) + "' is inferred")
324 // Generate the extra diagnostic.
325 PathDiagnosticLocation Pos(S, BRC.getSourceManager(),
326 N->getLocationContext());
327 return std::make_shared<PathDiagnosticEventPiece>(Pos, InfoText, true,
331 /// Returns true when the value stored at the given location has been
332 /// constrained to null after being passed through an object of nonnnull type.
333 static bool checkValueAtLValForInvariantViolation(ProgramStateRef State,
334 SVal LV, QualType T) {
335 if (getNullabilityAnnotation(T) != Nullability::Nonnull)
338 auto RegionVal = LV.getAs<loc::MemRegionVal>();
342 // If the value was constrained to null *after* it was passed through that
343 // location, it could not have been a concrete pointer *when* it was passed.
344 // In that case we would have handled the situation when the value was
345 // bound to that location, by emitting (or not emitting) a report.
346 // Therefore we are only interested in symbolic regions that can be either
347 // null or non-null depending on the value of their respective symbol.
348 auto StoredVal = State->getSVal(*RegionVal).getAs<loc::MemRegionVal>();
349 if (!StoredVal || !isa<SymbolicRegion>(StoredVal->getRegion()))
352 if (getNullConstraint(*StoredVal, State) == NullConstraint::IsNull)
359 checkParamsForPreconditionViolation(ArrayRef<ParmVarDecl *> Params,
360 ProgramStateRef State,
361 const LocationContext *LocCtxt) {
362 for (const auto *ParamDecl : Params) {
363 if (ParamDecl->isParameterPack())
366 SVal LV = State->getLValue(ParamDecl, LocCtxt);
367 if (checkValueAtLValForInvariantViolation(State, LV,
368 ParamDecl->getType())) {
376 checkSelfIvarsForInvariantViolation(ProgramStateRef State,
377 const LocationContext *LocCtxt) {
378 auto *MD = dyn_cast<ObjCMethodDecl>(LocCtxt->getDecl());
379 if (!MD || !MD->isInstanceMethod())
382 const ImplicitParamDecl *SelfDecl = LocCtxt->getSelfDecl();
386 SVal SelfVal = State->getSVal(State->getRegion(SelfDecl, LocCtxt));
388 const ObjCObjectPointerType *SelfType =
389 dyn_cast<ObjCObjectPointerType>(SelfDecl->getType());
393 const ObjCInterfaceDecl *ID = SelfType->getInterfaceDecl();
397 for (const auto *IvarDecl : ID->ivars()) {
398 SVal LV = State->getLValue(IvarDecl, SelfVal);
399 if (checkValueAtLValForInvariantViolation(State, LV, IvarDecl->getType())) {
406 static bool checkInvariantViolation(ProgramStateRef State, ExplodedNode *N,
408 if (State->get<InvariantViolated>())
411 const LocationContext *LocCtxt = C.getLocationContext();
412 const Decl *D = LocCtxt->getDecl();
416 ArrayRef<ParmVarDecl*> Params;
417 if (const auto *BD = dyn_cast<BlockDecl>(D))
418 Params = BD->parameters();
419 else if (const auto *FD = dyn_cast<FunctionDecl>(D))
420 Params = FD->parameters();
421 else if (const auto *MD = dyn_cast<ObjCMethodDecl>(D))
422 Params = MD->parameters();
426 if (checkParamsForPreconditionViolation(Params, State, LocCtxt) ||
427 checkSelfIvarsForInvariantViolation(State, LocCtxt)) {
429 C.addTransition(State->set<InvariantViolated>(true), N);
435 void NullabilityChecker::reportBugIfInvariantHolds(StringRef Msg,
436 ErrorKind Error, ExplodedNode *N, const MemRegion *Region,
437 CheckerContext &C, const Stmt *ValueExpr, bool SuppressPath) const {
438 ProgramStateRef OriginalState = N->getState();
440 if (checkInvariantViolation(OriginalState, N, C))
443 OriginalState = OriginalState->set<InvariantViolated>(true);
444 N = C.addTransition(OriginalState, N);
447 reportBug(Msg, Error, N, Region, C.getBugReporter(), ValueExpr);
450 /// Cleaning up the program state.
451 void NullabilityChecker::checkDeadSymbols(SymbolReaper &SR,
452 CheckerContext &C) const {
453 ProgramStateRef State = C.getState();
454 NullabilityMapTy Nullabilities = State->get<NullabilityMap>();
455 for (NullabilityMapTy::iterator I = Nullabilities.begin(),
456 E = Nullabilities.end();
458 const auto *Region = I->first->getAs<SymbolicRegion>();
459 assert(Region && "Non-symbolic region is tracked.");
460 if (SR.isDead(Region->getSymbol())) {
461 State = State->remove<NullabilityMap>(I->first);
464 // When one of the nonnull arguments are constrained to be null, nullability
465 // preconditions are violated. It is not enough to check this only when we
466 // actually report an error, because at that time interesting symbols might be
468 if (checkInvariantViolation(State, C.getPredecessor(), C))
470 C.addTransition(State);
473 /// This callback triggers when a pointer is dereferenced and the analyzer does
474 /// not know anything about the value of that pointer. When that pointer is
475 /// nullable, this code emits a warning.
476 void NullabilityChecker::checkEvent(ImplicitNullDerefEvent Event) const {
477 if (Event.SinkNode->getState()->get<InvariantViolated>())
480 const MemRegion *Region =
481 getTrackRegion(Event.Location, /*CheckSuperRegion=*/true);
485 ProgramStateRef State = Event.SinkNode->getState();
486 const NullabilityState *TrackedNullability =
487 State->get<NullabilityMap>(Region);
489 if (!TrackedNullability)
492 if (Filter.CheckNullableDereferenced &&
493 TrackedNullability->getValue() == Nullability::Nullable) {
494 BugReporter &BR = *Event.BR;
495 // Do not suppress errors on defensive code paths, because dereferencing
496 // a nullable pointer is always an error.
497 if (Event.IsDirectDereference)
498 reportBug("Nullable pointer is dereferenced",
499 ErrorKind::NullableDereferenced, Event.SinkNode, Region, BR);
501 reportBug("Nullable pointer is passed to a callee that requires a "
502 "non-null", ErrorKind::NullablePassedToNonnull,
503 Event.SinkNode, Region, BR);
508 /// Find the outermost subexpression of E that is not an implicit cast.
509 /// This looks through the implicit casts to _Nonnull that ARC adds to
510 /// return expressions of ObjC types when the return type of the function or
511 /// method is non-null but the express is not.
512 static const Expr *lookThroughImplicitCasts(const Expr *E) {
515 while (auto *ICE = dyn_cast<ImplicitCastExpr>(E)) {
516 E = ICE->getSubExpr();
522 /// This method check when nullable pointer or null value is returned from a
523 /// function that has nonnull return type.
524 void NullabilityChecker::checkPreStmt(const ReturnStmt *S,
525 CheckerContext &C) const {
526 auto RetExpr = S->getRetValue();
530 if (!RetExpr->getType()->isAnyPointerType())
533 ProgramStateRef State = C.getState();
534 if (State->get<InvariantViolated>())
537 auto RetSVal = C.getSVal(S).getAs<DefinedOrUnknownSVal>();
541 bool InSuppressedMethodFamily = false;
543 QualType RequiredRetType;
544 AnalysisDeclContext *DeclCtxt =
545 C.getLocationContext()->getAnalysisDeclContext();
546 const Decl *D = DeclCtxt->getDecl();
547 if (auto *MD = dyn_cast<ObjCMethodDecl>(D)) {
548 // HACK: This is a big hammer to avoid warning when there are defensive
549 // nil checks in -init and -copy methods. We should add more sophisticated
550 // logic here to suppress on common defensive idioms but still
551 // warn when there is a likely problem.
552 ObjCMethodFamily Family = MD->getMethodFamily();
553 if (OMF_init == Family || OMF_copy == Family || OMF_mutableCopy == Family)
554 InSuppressedMethodFamily = true;
556 RequiredRetType = MD->getReturnType();
557 } else if (auto *FD = dyn_cast<FunctionDecl>(D)) {
558 RequiredRetType = FD->getReturnType();
563 NullConstraint Nullness = getNullConstraint(*RetSVal, State);
565 Nullability RequiredNullability = getNullabilityAnnotation(RequiredRetType);
567 // If the returned value is null but the type of the expression
568 // generating it is nonnull then we will suppress the diagnostic.
569 // This enables explicit suppression when returning a nil literal in a
570 // function with a _Nonnull return type:
571 // return (NSString * _Nonnull)0;
572 Nullability RetExprTypeLevelNullability =
573 getNullabilityAnnotation(lookThroughImplicitCasts(RetExpr)->getType());
575 bool NullReturnedFromNonNull = (RequiredNullability == Nullability::Nonnull &&
576 Nullness == NullConstraint::IsNull);
577 if (Filter.CheckNullReturnedFromNonnull &&
578 NullReturnedFromNonNull &&
579 RetExprTypeLevelNullability != Nullability::Nonnull &&
580 !InSuppressedMethodFamily &&
581 C.getLocationContext()->inTopFrame()) {
582 static CheckerProgramPointTag Tag(this, "NullReturnedFromNonnull");
583 ExplodedNode *N = C.generateErrorNode(State, &Tag);
587 SmallString<256> SBuf;
588 llvm::raw_svector_ostream OS(SBuf);
589 OS << (RetExpr->getType()->isObjCObjectPointerType() ? "nil" : "Null");
590 OS << " returned from a " << C.getDeclDescription(D) <<
591 " that is expected to return a non-null value";
592 reportBugIfInvariantHolds(OS.str(),
593 ErrorKind::NilReturnedToNonnull, N, nullptr, C,
598 // If null was returned from a non-null function, mark the nullability
599 // invariant as violated even if the diagnostic was suppressed.
600 if (NullReturnedFromNonNull) {
601 State = State->set<InvariantViolated>(true);
602 C.addTransition(State);
606 const MemRegion *Region = getTrackRegion(*RetSVal);
610 const NullabilityState *TrackedNullability =
611 State->get<NullabilityMap>(Region);
612 if (TrackedNullability) {
613 Nullability TrackedNullabValue = TrackedNullability->getValue();
614 if (Filter.CheckNullableReturnedFromNonnull &&
615 Nullness != NullConstraint::IsNotNull &&
616 TrackedNullabValue == Nullability::Nullable &&
617 RequiredNullability == Nullability::Nonnull) {
618 static CheckerProgramPointTag Tag(this, "NullableReturnedFromNonnull");
619 ExplodedNode *N = C.addTransition(State, C.getPredecessor(), &Tag);
621 SmallString<256> SBuf;
622 llvm::raw_svector_ostream OS(SBuf);
623 OS << "Nullable pointer is returned from a " << C.getDeclDescription(D) <<
624 " that is expected to return a non-null value";
626 reportBugIfInvariantHolds(OS.str(),
627 ErrorKind::NullableReturnedToNonnull, N,
632 if (RequiredNullability == Nullability::Nullable) {
633 State = State->set<NullabilityMap>(Region,
634 NullabilityState(RequiredNullability,
636 C.addTransition(State);
640 /// This callback warns when a nullable pointer or a null value is passed to a
641 /// function that expects its argument to be nonnull.
642 void NullabilityChecker::checkPreCall(const CallEvent &Call,
643 CheckerContext &C) const {
647 ProgramStateRef State = C.getState();
648 if (State->get<InvariantViolated>())
651 ProgramStateRef OrigState = State;
654 for (const ParmVarDecl *Param : Call.parameters()) {
655 if (Param->isParameterPack())
658 if (Idx >= Call.getNumArgs())
661 const Expr *ArgExpr = Call.getArgExpr(Idx);
662 auto ArgSVal = Call.getArgSVal(Idx++).getAs<DefinedOrUnknownSVal>();
666 if (!Param->getType()->isAnyPointerType() &&
667 !Param->getType()->isReferenceType())
670 NullConstraint Nullness = getNullConstraint(*ArgSVal, State);
672 Nullability RequiredNullability =
673 getNullabilityAnnotation(Param->getType());
674 Nullability ArgExprTypeLevelNullability =
675 getNullabilityAnnotation(ArgExpr->getType());
677 unsigned ParamIdx = Param->getFunctionScopeIndex() + 1;
679 if (Filter.CheckNullPassedToNonnull && Nullness == NullConstraint::IsNull &&
680 ArgExprTypeLevelNullability != Nullability::Nonnull &&
681 RequiredNullability == Nullability::Nonnull &&
682 isDiagnosableCall(Call)) {
683 ExplodedNode *N = C.generateErrorNode(State);
687 SmallString<256> SBuf;
688 llvm::raw_svector_ostream OS(SBuf);
689 OS << (Param->getType()->isObjCObjectPointerType() ? "nil" : "Null");
690 OS << " passed to a callee that requires a non-null " << ParamIdx
691 << llvm::getOrdinalSuffix(ParamIdx) << " parameter";
692 reportBugIfInvariantHolds(OS.str(), ErrorKind::NilPassedToNonnull, N,
694 ArgExpr, /*SuppressPath=*/false);
698 const MemRegion *Region = getTrackRegion(*ArgSVal);
702 const NullabilityState *TrackedNullability =
703 State->get<NullabilityMap>(Region);
705 if (TrackedNullability) {
706 if (Nullness == NullConstraint::IsNotNull ||
707 TrackedNullability->getValue() != Nullability::Nullable)
710 if (Filter.CheckNullablePassedToNonnull &&
711 RequiredNullability == Nullability::Nonnull &&
712 isDiagnosableCall(Call)) {
713 ExplodedNode *N = C.addTransition(State);
714 SmallString<256> SBuf;
715 llvm::raw_svector_ostream OS(SBuf);
716 OS << "Nullable pointer is passed to a callee that requires a non-null "
717 << ParamIdx << llvm::getOrdinalSuffix(ParamIdx) << " parameter";
718 reportBugIfInvariantHolds(OS.str(),
719 ErrorKind::NullablePassedToNonnull, N,
720 Region, C, ArgExpr, /*SuppressPath=*/true);
723 if (Filter.CheckNullableDereferenced &&
724 Param->getType()->isReferenceType()) {
725 ExplodedNode *N = C.addTransition(State);
726 reportBugIfInvariantHolds("Nullable pointer is dereferenced",
727 ErrorKind::NullableDereferenced, N, Region,
728 C, ArgExpr, /*SuppressPath=*/true);
733 // No tracked nullability yet.
734 if (ArgExprTypeLevelNullability != Nullability::Nullable)
736 State = State->set<NullabilityMap>(
737 Region, NullabilityState(ArgExprTypeLevelNullability, ArgExpr));
739 if (State != OrigState)
740 C.addTransition(State);
743 /// Suppress the nullability warnings for some functions.
744 void NullabilityChecker::checkPostCall(const CallEvent &Call,
745 CheckerContext &C) const {
746 auto Decl = Call.getDecl();
749 // ObjC Messages handles in a different callback.
750 if (Call.getKind() == CE_ObjCMessage)
752 const FunctionType *FuncType = Decl->getFunctionType();
755 QualType ReturnType = FuncType->getReturnType();
756 if (!ReturnType->isAnyPointerType())
758 ProgramStateRef State = C.getState();
759 if (State->get<InvariantViolated>())
762 const MemRegion *Region = getTrackRegion(Call.getReturnValue());
766 // CG headers are misannotated. Do not warn for symbols that are the results
768 const SourceManager &SM = C.getSourceManager();
769 StringRef FilePath = SM.getFilename(SM.getSpellingLoc(Decl->getBeginLoc()));
770 if (llvm::sys::path::filename(FilePath).startswith("CG")) {
771 State = State->set<NullabilityMap>(Region, Nullability::Contradicted);
772 C.addTransition(State);
776 const NullabilityState *TrackedNullability =
777 State->get<NullabilityMap>(Region);
779 if (!TrackedNullability &&
780 getNullabilityAnnotation(ReturnType) == Nullability::Nullable) {
781 State = State->set<NullabilityMap>(Region, Nullability::Nullable);
782 C.addTransition(State);
786 static Nullability getReceiverNullability(const ObjCMethodCall &M,
787 ProgramStateRef State) {
788 if (M.isReceiverSelfOrSuper()) {
789 // For super and super class receivers we assume that the receiver is
791 return Nullability::Nonnull;
793 // Otherwise look up nullability in the state.
794 SVal Receiver = M.getReceiverSVal();
795 if (auto DefOrUnknown = Receiver.getAs<DefinedOrUnknownSVal>()) {
796 // If the receiver is constrained to be nonnull, assume that it is nonnull
797 // regardless of its type.
798 NullConstraint Nullness = getNullConstraint(*DefOrUnknown, State);
799 if (Nullness == NullConstraint::IsNotNull)
800 return Nullability::Nonnull;
802 auto ValueRegionSVal = Receiver.getAs<loc::MemRegionVal>();
803 if (ValueRegionSVal) {
804 const MemRegion *SelfRegion = ValueRegionSVal->getRegion();
807 const NullabilityState *TrackedSelfNullability =
808 State->get<NullabilityMap>(SelfRegion);
809 if (TrackedSelfNullability)
810 return TrackedSelfNullability->getValue();
812 return Nullability::Unspecified;
815 /// Calculate the nullability of the result of a message expr based on the
816 /// nullability of the receiver, the nullability of the return value, and the
818 void NullabilityChecker::checkPostObjCMessage(const ObjCMethodCall &M,
819 CheckerContext &C) const {
820 auto Decl = M.getDecl();
823 QualType RetType = Decl->getReturnType();
824 if (!RetType->isAnyPointerType())
827 ProgramStateRef State = C.getState();
828 if (State->get<InvariantViolated>())
831 const MemRegion *ReturnRegion = getTrackRegion(M.getReturnValue());
835 auto Interface = Decl->getClassInterface();
836 auto Name = Interface ? Interface->getName() : "";
837 // In order to reduce the noise in the diagnostics generated by this checker,
838 // some framework and programming style based heuristics are used. These
839 // heuristics are for Cocoa APIs which have NS prefix.
840 if (Name.startswith("NS")) {
841 // Developers rely on dynamic invariants such as an item should be available
842 // in a collection, or a collection is not empty often. Those invariants can
843 // not be inferred by any static analysis tool. To not to bother the users
844 // with too many false positives, every item retrieval function should be
845 // ignored for collections. The instance methods of dictionaries in Cocoa
846 // are either item retrieval related or not interesting nullability wise.
847 // Using this fact, to keep the code easier to read just ignore the return
848 // value of every instance method of dictionaries.
849 if (M.isInstanceMessage() && Name.contains("Dictionary")) {
851 State->set<NullabilityMap>(ReturnRegion, Nullability::Contradicted);
852 C.addTransition(State);
855 // For similar reasons ignore some methods of Cocoa arrays.
856 StringRef FirstSelectorSlot = M.getSelector().getNameForSlot(0);
857 if (Name.contains("Array") &&
858 (FirstSelectorSlot == "firstObject" ||
859 FirstSelectorSlot == "lastObject")) {
861 State->set<NullabilityMap>(ReturnRegion, Nullability::Contradicted);
862 C.addTransition(State);
866 // Encoding related methods of string should not fail when lossless
867 // encodings are used. Using lossless encodings is so frequent that ignoring
868 // this class of methods reduced the emitted diagnostics by about 30% on
869 // some projects (and all of that was false positives).
870 if (Name.contains("String")) {
871 for (auto Param : M.parameters()) {
872 if (Param->getName() == "encoding") {
873 State = State->set<NullabilityMap>(ReturnRegion,
874 Nullability::Contradicted);
875 C.addTransition(State);
882 const ObjCMessageExpr *Message = M.getOriginExpr();
883 Nullability SelfNullability = getReceiverNullability(M, State);
885 const NullabilityState *NullabilityOfReturn =
886 State->get<NullabilityMap>(ReturnRegion);
888 if (NullabilityOfReturn) {
889 // When we have a nullability tracked for the return value, the nullability
890 // of the expression will be the most nullable of the receiver and the
892 Nullability RetValTracked = NullabilityOfReturn->getValue();
893 Nullability ComputedNullab =
894 getMostNullable(RetValTracked, SelfNullability);
895 if (ComputedNullab != RetValTracked &&
896 ComputedNullab != Nullability::Unspecified) {
897 const Stmt *NullabilitySource =
898 ComputedNullab == RetValTracked
899 ? NullabilityOfReturn->getNullabilitySource()
900 : Message->getInstanceReceiver();
901 State = State->set<NullabilityMap>(
902 ReturnRegion, NullabilityState(ComputedNullab, NullabilitySource));
903 C.addTransition(State);
908 // No tracked information. Use static type information for return value.
909 Nullability RetNullability = getNullabilityAnnotation(RetType);
911 // Properties might be computed. For this reason the static analyzer creates a
912 // new symbol each time an unknown property is read. To avoid false pozitives
913 // do not treat unknown properties as nullable, even when they explicitly
915 if (M.getMessageKind() == OCM_PropertyAccess && !C.wasInlined)
916 RetNullability = Nullability::Nonnull;
918 Nullability ComputedNullab = getMostNullable(RetNullability, SelfNullability);
919 if (ComputedNullab == Nullability::Nullable) {
920 const Stmt *NullabilitySource = ComputedNullab == RetNullability
922 : Message->getInstanceReceiver();
923 State = State->set<NullabilityMap>(
924 ReturnRegion, NullabilityState(ComputedNullab, NullabilitySource));
925 C.addTransition(State);
929 /// Explicit casts are trusted. If there is a disagreement in the nullability
930 /// annotations in the destination and the source or '0' is casted to nonnull
931 /// track the value as having contraditory nullability. This will allow users to
932 /// suppress warnings.
933 void NullabilityChecker::checkPostStmt(const ExplicitCastExpr *CE,
934 CheckerContext &C) const {
935 QualType OriginType = CE->getSubExpr()->getType();
936 QualType DestType = CE->getType();
937 if (!OriginType->isAnyPointerType())
939 if (!DestType->isAnyPointerType())
942 ProgramStateRef State = C.getState();
943 if (State->get<InvariantViolated>())
946 Nullability DestNullability = getNullabilityAnnotation(DestType);
948 // No explicit nullability in the destination type, so this cast does not
949 // change the nullability.
950 if (DestNullability == Nullability::Unspecified)
953 auto RegionSVal = C.getSVal(CE).getAs<DefinedOrUnknownSVal>();
954 const MemRegion *Region = getTrackRegion(*RegionSVal);
958 // When 0 is converted to nonnull mark it as contradicted.
959 if (DestNullability == Nullability::Nonnull) {
960 NullConstraint Nullness = getNullConstraint(*RegionSVal, State);
961 if (Nullness == NullConstraint::IsNull) {
962 State = State->set<NullabilityMap>(Region, Nullability::Contradicted);
963 C.addTransition(State);
968 const NullabilityState *TrackedNullability =
969 State->get<NullabilityMap>(Region);
971 if (!TrackedNullability) {
972 if (DestNullability != Nullability::Nullable)
974 State = State->set<NullabilityMap>(Region,
975 NullabilityState(DestNullability, CE));
976 C.addTransition(State);
980 if (TrackedNullability->getValue() != DestNullability &&
981 TrackedNullability->getValue() != Nullability::Contradicted) {
982 State = State->set<NullabilityMap>(Region, Nullability::Contradicted);
983 C.addTransition(State);
987 /// For a given statement performing a bind, attempt to syntactically
988 /// match the expression resulting in the bound value.
989 static const Expr * matchValueExprForBind(const Stmt *S) {
990 // For `x = e` the value expression is the right-hand side.
991 if (auto *BinOp = dyn_cast<BinaryOperator>(S)) {
992 if (BinOp->getOpcode() == BO_Assign)
993 return BinOp->getRHS();
996 // For `int x = e` the value expression is the initializer.
997 if (auto *DS = dyn_cast<DeclStmt>(S)) {
998 if (DS->isSingleDecl()) {
999 auto *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
1003 if (const Expr *Init = VD->getInit())
1011 /// Returns true if \param S is a DeclStmt for a local variable that
1012 /// ObjC automated reference counting initialized with zero.
1013 static bool isARCNilInitializedLocal(CheckerContext &C, const Stmt *S) {
1014 // We suppress diagnostics for ARC zero-initialized _Nonnull locals. This
1015 // prevents false positives when a _Nonnull local variable cannot be
1016 // initialized with an initialization expression:
1017 // NSString * _Nonnull s; // no-warning
1018 // @autoreleasepool {
1022 // FIXME: We should treat implicitly zero-initialized _Nonnull locals as
1023 // uninitialized in Sema's UninitializedValues analysis to warn when a use of
1024 // the zero-initialized definition will unexpectedly yield nil.
1026 // Locals are only zero-initialized when automated reference counting
1028 if (!C.getASTContext().getLangOpts().ObjCAutoRefCount)
1031 auto *DS = dyn_cast<DeclStmt>(S);
1032 if (!DS || !DS->isSingleDecl())
1035 auto *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
1039 // Sema only zero-initializes locals with ObjCLifetimes.
1040 if(!VD->getType().getQualifiers().hasObjCLifetime())
1043 const Expr *Init = VD->getInit();
1044 assert(Init && "ObjC local under ARC without initializer");
1046 // Return false if the local is explicitly initialized (e.g., with '= nil').
1047 if (!isa<ImplicitValueInitExpr>(Init))
1053 /// Propagate the nullability information through binds and warn when nullable
1054 /// pointer or null symbol is assigned to a pointer with a nonnull type.
1055 void NullabilityChecker::checkBind(SVal L, SVal V, const Stmt *S,
1056 CheckerContext &C) const {
1057 const TypedValueRegion *TVR =
1058 dyn_cast_or_null<TypedValueRegion>(L.getAsRegion());
1062 QualType LocType = TVR->getValueType();
1063 if (!LocType->isAnyPointerType())
1066 ProgramStateRef State = C.getState();
1067 if (State->get<InvariantViolated>())
1070 auto ValDefOrUnknown = V.getAs<DefinedOrUnknownSVal>();
1071 if (!ValDefOrUnknown)
1074 NullConstraint RhsNullness = getNullConstraint(*ValDefOrUnknown, State);
1076 Nullability ValNullability = Nullability::Unspecified;
1077 if (SymbolRef Sym = ValDefOrUnknown->getAsSymbol())
1078 ValNullability = getNullabilityAnnotation(Sym->getType());
1080 Nullability LocNullability = getNullabilityAnnotation(LocType);
1082 // If the type of the RHS expression is nonnull, don't warn. This
1083 // enables explicit suppression with a cast to nonnull.
1084 Nullability ValueExprTypeLevelNullability = Nullability::Unspecified;
1085 const Expr *ValueExpr = matchValueExprForBind(S);
1087 ValueExprTypeLevelNullability =
1088 getNullabilityAnnotation(lookThroughImplicitCasts(ValueExpr)->getType());
1091 bool NullAssignedToNonNull = (LocNullability == Nullability::Nonnull &&
1092 RhsNullness == NullConstraint::IsNull);
1093 if (Filter.CheckNullPassedToNonnull &&
1094 NullAssignedToNonNull &&
1095 ValNullability != Nullability::Nonnull &&
1096 ValueExprTypeLevelNullability != Nullability::Nonnull &&
1097 !isARCNilInitializedLocal(C, S)) {
1098 static CheckerProgramPointTag Tag(this, "NullPassedToNonnull");
1099 ExplodedNode *N = C.generateErrorNode(State, &Tag);
1104 const Stmt *ValueStmt = S;
1106 ValueStmt = ValueExpr;
1108 SmallString<256> SBuf;
1109 llvm::raw_svector_ostream OS(SBuf);
1110 OS << (LocType->isObjCObjectPointerType() ? "nil" : "Null");
1111 OS << " assigned to a pointer which is expected to have non-null value";
1112 reportBugIfInvariantHolds(OS.str(),
1113 ErrorKind::NilAssignedToNonnull, N, nullptr, C,
1118 // If null was returned from a non-null function, mark the nullability
1119 // invariant as violated even if the diagnostic was suppressed.
1120 if (NullAssignedToNonNull) {
1121 State = State->set<InvariantViolated>(true);
1122 C.addTransition(State);
1126 // Intentionally missing case: '0' is bound to a reference. It is handled by
1127 // the DereferenceChecker.
1129 const MemRegion *ValueRegion = getTrackRegion(*ValDefOrUnknown);
1133 const NullabilityState *TrackedNullability =
1134 State->get<NullabilityMap>(ValueRegion);
1136 if (TrackedNullability) {
1137 if (RhsNullness == NullConstraint::IsNotNull ||
1138 TrackedNullability->getValue() != Nullability::Nullable)
1140 if (Filter.CheckNullablePassedToNonnull &&
1141 LocNullability == Nullability::Nonnull) {
1142 static CheckerProgramPointTag Tag(this, "NullablePassedToNonnull");
1143 ExplodedNode *N = C.addTransition(State, C.getPredecessor(), &Tag);
1144 reportBugIfInvariantHolds("Nullable pointer is assigned to a pointer "
1145 "which is expected to have non-null value",
1146 ErrorKind::NullableAssignedToNonnull, N,
1152 const auto *BinOp = dyn_cast<BinaryOperator>(S);
1154 if (ValNullability == Nullability::Nullable) {
1155 // Trust the static information of the value more than the static
1156 // information on the location.
1157 const Stmt *NullabilitySource = BinOp ? BinOp->getRHS() : S;
1158 State = State->set<NullabilityMap>(
1159 ValueRegion, NullabilityState(ValNullability, NullabilitySource));
1160 C.addTransition(State);
1164 if (LocNullability == Nullability::Nullable) {
1165 const Stmt *NullabilitySource = BinOp ? BinOp->getLHS() : S;
1166 State = State->set<NullabilityMap>(
1167 ValueRegion, NullabilityState(LocNullability, NullabilitySource));
1168 C.addTransition(State);
1172 void NullabilityChecker::printState(raw_ostream &Out, ProgramStateRef State,
1173 const char *NL, const char *Sep) const {
1175 NullabilityMapTy B = State->get<NullabilityMap>();
1177 if (State->get<InvariantViolated>())
1179 << "Nullability invariant was violated, warnings suppressed." << NL;
1184 if (!State->get<InvariantViolated>())
1187 for (NullabilityMapTy::iterator I = B.begin(), E = B.end(); I != E; ++I) {
1188 Out << I->first << " : ";
1189 I->second.print(Out);
1194 void ento::registerNullabilityBase(CheckerManager &mgr) {
1195 mgr.registerChecker<NullabilityChecker>();
1198 bool ento::shouldRegisterNullabilityBase(const LangOptions &LO) {
1202 #define REGISTER_CHECKER(name, trackingRequired) \
1203 void ento::register##name##Checker(CheckerManager &mgr) { \
1204 NullabilityChecker *checker = mgr.getChecker<NullabilityChecker>(); \
1205 checker->Filter.Check##name = true; \
1206 checker->Filter.CheckName##name = mgr.getCurrentCheckName(); \
1207 checker->NeedTracking = checker->NeedTracking || trackingRequired; \
1208 checker->NoDiagnoseCallsToSystemHeaders = \
1209 checker->NoDiagnoseCallsToSystemHeaders || \
1210 mgr.getAnalyzerOptions().getCheckerBooleanOption( \
1211 checker, "NoDiagnoseCallsToSystemHeaders", true); \
1214 bool ento::shouldRegister##name##Checker(const LangOptions &LO) { \
1218 // The checks are likely to be turned on by default and it is possible to do
1219 // them without tracking any nullability related information. As an optimization
1220 // no nullability information will be tracked when only these two checks are
1222 REGISTER_CHECKER(NullPassedToNonnull, false)
1223 REGISTER_CHECKER(NullReturnedFromNonnull, false)
1225 REGISTER_CHECKER(NullableDereferenced, true)
1226 REGISTER_CHECKER(NullablePassedToNonnull, true)
1227 REGISTER_CHECKER(NullableReturnedFromNonnull, true)