clang 10.0.0git

NonnullGlobalConstantsChecker.cpp
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1 //==- NonnullGlobalConstantsChecker.cpp ---------------------------*- C++ -*--//
2 //
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
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This checker adds an assumption that constant globals of certain types* are
10 // non-null, as otherwise they generally do not convey any useful information.
11 // The assumption is useful, as many framework use e. g. global const strings,
12 // and the analyzer might not be able to infer the global value if the
13 // definition is in a separate translation unit.
14 // The following types (and their typedef aliases) are considered to be
15 // non-null:
16 // - `char* const`
17 // - `const CFStringRef` from CoreFoundation
18 // - `NSString* const` from Foundation
19 // - `CFBooleanRef` from Foundation
20 //
21 //===----------------------------------------------------------------------===//
22
23 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
24 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
25 #include "clang/StaticAnalyzer/Core/Checker.h"
26 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
27 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
28 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
29
30 using namespace clang;
31 using namespace ento;
32
33 namespace {
34
35 class NonnullGlobalConstantsChecker : public Checker<check::Location> {
36 mutable IdentifierInfo *NSStringII = nullptr;
37 mutable IdentifierInfo *CFStringRefII = nullptr;
38 mutable IdentifierInfo *CFBooleanRefII = nullptr;
39 mutable IdentifierInfo *CFNullRefII = nullptr;
40
41 public:
42 NonnullGlobalConstantsChecker() {}
43
44 void checkLocation(SVal l, bool isLoad, const Stmt *S,
45 CheckerContext &C) const;
46
47 private:
48 void initIdentifierInfo(ASTContext &Ctx) const;
49
50 bool isGlobalConstString(SVal V) const;
51
52 bool isNonnullType(QualType Ty) const;
53 };
54
55 } // namespace
56
57 /// Lazily initialize cache for required identifier information.
58 void NonnullGlobalConstantsChecker::initIdentifierInfo(ASTContext &Ctx) const {
59 if (NSStringII)
60 return;
61
62 NSStringII = &Ctx.Idents.get("NSString");
63 CFStringRefII = &Ctx.Idents.get("CFStringRef");
64 CFBooleanRefII = &Ctx.Idents.get("CFBooleanRef");
65 CFNullRefII = &Ctx.Idents.get("CFNullRef");
66 }
67
68 /// Add an assumption that const string-like globals are non-null.
69 void NonnullGlobalConstantsChecker::checkLocation(SVal location, bool isLoad,
70 const Stmt *S,
71 CheckerContext &C) const {
72 initIdentifierInfo(C.getASTContext());
73 if (!isLoad || !location.isValid())
74 return;
75
76 ProgramStateRef State = C.getState();
77
78 if (isGlobalConstString(location)) {
79 SVal V = State->getSVal(location.castAs<Loc>());
80 Optional<DefinedOrUnknownSVal> Constr = V.getAs<DefinedOrUnknownSVal>();
81
82 if (Constr) {
83
84 // Assume that the variable is non-null.
85 ProgramStateRef OutputState = State->assume(*Constr, true);
86 C.addTransition(OutputState);
87 }
88 }
89 }
90
91 /// \param V loaded lvalue.
92 /// \return whether {@code val} is a string-like const global.
93 bool NonnullGlobalConstantsChecker::isGlobalConstString(SVal V) const {
94 Optional<loc::MemRegionVal> RegionVal = V.getAs<loc::MemRegionVal>();
95 if (!RegionVal)
96 return false;
97 auto *Region = dyn_cast<VarRegion>(RegionVal->getAsRegion());
98 if (!Region)
99 return false;
100 const VarDecl *Decl = Region->getDecl();
101
102 if (!Decl->hasGlobalStorage())
103 return false;
104
105 QualType Ty = Decl->getType();
106 bool HasConst = Ty.isConstQualified();
107 if (isNonnullType(Ty) && HasConst)
108 return true;
109
110 // Look through the typedefs.
111 while (const Type *T = Ty.getTypePtr()) {
112 if (const auto *TT = dyn_cast<TypedefType>(T)) {
113 Ty = TT->getDecl()->getUnderlyingType();
114 // It is sufficient for any intermediate typedef
115 // to be classified const.
116 HasConst = HasConst || Ty.isConstQualified();
117 if (isNonnullType(Ty) && HasConst)
118 return true;
119 } else if (const auto *AT = dyn_cast<AttributedType>(T)) {
120 if (AT->getAttrKind() == attr::TypeNonNull)
121 return true;
122 Ty = AT->getModifiedType();
123 } else {
124 return false;
125 }
126 }
127 return false;
128 }
129
130 /// \return whether {@code type} is extremely unlikely to be null
131 bool NonnullGlobalConstantsChecker::isNonnullType(QualType Ty) const {
132
133 if (Ty->isPointerType() && Ty->getPointeeType()->isCharType())
134 return true;
135
136 if (auto *T = dyn_cast<ObjCObjectPointerType>(Ty)) {
137 return T->getInterfaceDecl() &&
138 T->getInterfaceDecl()->getIdentifier() == NSStringII;
139 } else if (auto *T = dyn_cast<TypedefType>(Ty)) {
140 IdentifierInfo* II = T->getDecl()->getIdentifier();
141 return II == CFStringRefII || II == CFBooleanRefII || II == CFNullRefII;
142 }
143 return false;
144 }
145
146 void ento::registerNonnullGlobalConstantsChecker(CheckerManager &Mgr) {
147 Mgr.registerChecker<NonnullGlobalConstantsChecker>();
148 }
149
150 bool ento::shouldRegisterNonnullGlobalConstantsChecker(const LangOptions &LO) {
151 return true;
152 }
ento
clang::QualType
A (possibly-)qualified type.
Definition: Type.h:654
clang::Stmt
Stmt - This represents one statement.
Definition: Stmt.h:66
clang::Type::getPointeeType
QualType getPointeeType() const
If this is a pointer, ObjC object pointer, or block pointer, this returns the respective pointee...
Definition: Type.cpp:557
clang::Decl
Decl - This represents one declaration (or definition), e.g.
Definition: DeclBase.h:88
clang::ento::ProgramStateRef
IntrusiveRefCntPtr< const ProgramState > ProgramStateRef
Definition: ProgramState_Fwd.h:37
clang::Type
The base class of the type hierarchy.
Definition: Type.h:1450
BugType.h
clang::VarDecl
Represents a variable declaration or definition.
Definition: Decl.h:820
ExprEngine.h
clang::IdentifierInfo
One of these records is kept for each identifier that is lexed.
Definition: IdentifierTable.h:57
clang::ASTContext
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:168
llvm::Optional
Definition: LLVM.h:37
State
LineState State
Definition: UnwrappedLineFormatter.cpp:932
clang::Type::isCharType
bool isCharType() const
Definition: Type.cpp:1871
Checker.h
CheckerManager.h
clang::LangOptions
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:53
clang::ASTContext::Idents
IdentifierTable & Idents
Definition: ASTContext.h:580
clang::QualType::getTypePtr
const Type * getTypePtr() const
Retrieves a pointer to the underlying (unqualified) type.
Definition: Type.h:6256
V
#define V(N, I)
Definition: ASTContext.h:2941
BuiltinCheckerRegistration.h
clang::QualType::isConstQualified
bool isConstQualified() const
Determine whether this type is const-qualified.
Definition: Type.h:6315
clang::IdentifierTable::get
IdentifierInfo & get(StringRef Name)
Return the identifier token info for the specified named identifier.
Definition: IdentifierTable.h:529
clang::VarDecl::hasGlobalStorage
bool hasGlobalStorage() const
Returns true for all variables that do not have local storage.
Definition: Decl.h:1087
clang
Dataflow Directional Tag Classes.
Definition: CFGReachabilityAnalysis.h:21
clang::Type::isPointerType
bool isPointerType() const
Definition: Type.h:6504
clang::ValueDecl::getType
QualType getType() const
Definition: Decl.h:630
CheckerContext.h