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#include <optional>
30
31using namespace clang;
32using namespace ento;
33
34namespace {
35
36class NonnullGlobalConstantsChecker : public Checker<check::Location> {
37 mutable IdentifierInfo *NSStringII = nullptr;
38 mutable IdentifierInfo *CFStringRefII = nullptr;
39 mutable IdentifierInfo *CFBooleanRefII = nullptr;
40 mutable IdentifierInfo *CFNullRefII = nullptr;
41
42public:
43 NonnullGlobalConstantsChecker() {}
44
45 void checkLocation(SVal l, bool isLoad, const Stmt *S,
46 CheckerContext &C) const;
47
48private:
49 void initIdentifierInfo(ASTContext &Ctx) const;
50
51 bool isGlobalConstString(SVal V) const;
52
53 bool isNonnullType(QualType Ty) const;
54};
55
56} // namespace
57
58/// Lazily initialize cache for required identifier information.
59void NonnullGlobalConstantsChecker::initIdentifierInfo(ASTContext &Ctx) const {
60 if (NSStringII)
61 return;
62
63 NSStringII = &Ctx.Idents.get(Name: "NSString");
64 CFStringRefII = &Ctx.Idents.get(Name: "CFStringRef");
65 CFBooleanRefII = &Ctx.Idents.get(Name: "CFBooleanRef");
66 CFNullRefII = &Ctx.Idents.get(Name: "CFNullRef");
67}
68
69/// Add an assumption that const string-like globals are non-null.
70void NonnullGlobalConstantsChecker::checkLocation(SVal location, bool isLoad,
71 const Stmt *S,
72 CheckerContext &C) const {
73 initIdentifierInfo(Ctx&: C.getASTContext());
74 if (!isLoad || !location.isValid())
75 return;
76
77 ProgramStateRef State = C.getState();
78
79 if (isGlobalConstString(V: location)) {
80 SVal V = State->getSVal(LV: location.castAs<Loc>());
81 std::optional<DefinedOrUnknownSVal> Constr =
82 V.getAs<DefinedOrUnknownSVal>();
83
84 if (Constr) {
85
86 // Assume that the variable is non-null.
87 ProgramStateRef OutputState = State->assume(Cond: *Constr, Assumption: true);
88 C.addTransition(State: OutputState);
89 }
90 }
91}
92
93/// \param V loaded lvalue.
94/// \return whether @c val is a string-like const global.
95bool NonnullGlobalConstantsChecker::isGlobalConstString(SVal V) const {
96 std::optional<loc::MemRegionVal> RegionVal = V.getAs<loc::MemRegionVal>();
97 if (!RegionVal)
98 return false;
99 auto *Region = dyn_cast<VarRegion>(Val: RegionVal->getAsRegion());
100 if (!Region)
101 return false;
102 const VarDecl *Decl = Region->getDecl();
103
104 if (!Decl->hasGlobalStorage())
105 return false;
106
107 QualType Ty = Decl->getType();
108 bool HasConst = Ty.isConstQualified();
109 if (isNonnullType(Ty) && HasConst)
110 return true;
111
112 // Look through the typedefs.
113 while (const Type *T = Ty.getTypePtr()) {
114 if (const auto *AT = dyn_cast<AttributedType>(Val: T)) {
115 if (AT->getAttrKind() == attr::TypeNonNull)
116 return true;
117 Ty = AT->getModifiedType();
118 } else if (const auto *ET = dyn_cast<ElaboratedType>(Val: T)) {
119 const auto *TT = dyn_cast<TypedefType>(Val: ET->getNamedType());
120 if (!TT)
121 return false;
122 Ty = TT->getDecl()->getUnderlyingType();
123 // It is sufficient for any intermediate typedef
124 // to be classified const.
125 HasConst = HasConst || Ty.isConstQualified();
126 if (isNonnullType(Ty) && HasConst)
127 return true;
128 } else {
129 return false;
130 }
131 }
132 return false;
133}
134
135/// \return whether @c type is extremely unlikely to be null
136bool NonnullGlobalConstantsChecker::isNonnullType(QualType Ty) const {
137
138 if (Ty->isPointerType() && Ty->getPointeeType()->isCharType())
139 return true;
140
141 if (auto *T = dyn_cast<ObjCObjectPointerType>(Val&: Ty)) {
142 return T->getInterfaceDecl() &&
143 T->getInterfaceDecl()->getIdentifier() == NSStringII;
144 } else if (auto *T = Ty->getAs<TypedefType>()) {
145 IdentifierInfo* II = T->getDecl()->getIdentifier();
146 return II == CFStringRefII || II == CFBooleanRefII || II == CFNullRefII;
147 }
148 return false;
149}
150
151void ento::registerNonnullGlobalConstantsChecker(CheckerManager &Mgr) {
152 Mgr.registerChecker<NonnullGlobalConstantsChecker>();
153}
154
155bool ento::shouldRegisterNonnullGlobalConstantsChecker(const CheckerManager &mgr) {
156 return true;
157}
158