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//==- NonnullGlobalConstantsChecker.cpp ---------------------------*- C++ -*--//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This checker adds an assumption that constant globals of certain types* are
// non-null, as otherwise they generally do not convey any useful information.
// The assumption is useful, as many framework use e. g. global const strings,
// and the analyzer might not be able to infer the global value if the
// definition is in a separate translation unit.
// The following types (and their typedef aliases) are considered to be
// non-null:
// - `char* const`
// - `const CFStringRef` from CoreFoundation
// - `NSString* const` from Foundation
// - `CFBooleanRef` from Foundation
//
//===----------------------------------------------------------------------===//
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
#include <optional>
using namespace clang;
using namespace ento;
namespace {
class NonnullGlobalConstantsChecker : public Checker<check::Location> {
mutable IdentifierInfo *NSStringII = nullptr;
mutable IdentifierInfo *CFStringRefII = nullptr;
mutable IdentifierInfo *CFBooleanRefII = nullptr;
mutable IdentifierInfo *CFNullRefII = nullptr;
public:
NonnullGlobalConstantsChecker() {}
void checkLocation(SVal l, bool isLoad, const Stmt *S,
CheckerContext &C) const;
private:
void initIdentifierInfo(ASTContext &Ctx) const;
bool isGlobalConstString(SVal V) const;
bool isNonnullType(QualType Ty) const;
};
} // namespace
/// Lazily initialize cache for required identifier information.
void NonnullGlobalConstantsChecker::initIdentifierInfo(ASTContext &Ctx) const {
if (NSStringII)
return;
NSStringII = &Ctx.Idents.get("NSString");
CFStringRefII = &Ctx.Idents.get("CFStringRef");
CFBooleanRefII = &Ctx.Idents.get("CFBooleanRef");
CFNullRefII = &Ctx.Idents.get("CFNullRef");
}
/// Add an assumption that const string-like globals are non-null.
void NonnullGlobalConstantsChecker::checkLocation(SVal location, bool isLoad,
const Stmt *S,
CheckerContext &C) const {
initIdentifierInfo(C.getASTContext());
if (!isLoad || !location.isValid())
return;
ProgramStateRef State = C.getState();
if (isGlobalConstString(location)) {
SVal V = State->getSVal(location.castAs<Loc>());
std::optional<DefinedOrUnknownSVal> Constr =
V.getAs<DefinedOrUnknownSVal>();
if (Constr) {
// Assume that the variable is non-null.
ProgramStateRef OutputState = State->assume(*Constr, true);
C.addTransition(OutputState);
}
}
}
/// \param V loaded lvalue.
/// \return whether @c val is a string-like const global.
bool NonnullGlobalConstantsChecker::isGlobalConstString(SVal V) const {
std::optional<loc::MemRegionVal> RegionVal = V.getAs<loc::MemRegionVal>();
if (!RegionVal)
return false;
auto *Region = dyn_cast<VarRegion>(RegionVal->getAsRegion());
if (!Region)
return false;
const VarDecl *Decl = Region->getDecl();
if (!Decl->hasGlobalStorage())
return false;
QualType Ty = Decl->getType();
bool HasConst = Ty.isConstQualified();
if (isNonnullType(Ty) && HasConst)
return true;
// Look through the typedefs.
while (const Type *T = Ty.getTypePtr()) {
if (const auto *AT = dyn_cast<AttributedType>(T)) {
if (AT->getAttrKind() == attr::TypeNonNull)
return true;
Ty = AT->getModifiedType();
} else if (const auto *ET = dyn_cast<ElaboratedType>(T)) {
const auto *TT = dyn_cast<TypedefType>(ET->getNamedType());
if (!TT)
return false;
Ty = TT->getDecl()->getUnderlyingType();
// It is sufficient for any intermediate typedef
// to be classified const.
HasConst = HasConst || Ty.isConstQualified();
if (isNonnullType(Ty) && HasConst)
return true;
} else {
return false;
}
}
return false;
}
/// \return whether @c type is extremely unlikely to be null
bool NonnullGlobalConstantsChecker::isNonnullType(QualType Ty) const {
if (Ty->isPointerType() && Ty->getPointeeType()->isCharType())
return true;
if (auto *T = dyn_cast<ObjCObjectPointerType>(Ty)) {
return T->getInterfaceDecl() &&
T->getInterfaceDecl()->getIdentifier() == NSStringII;
} else if (auto *T = Ty->getAs<TypedefType>()) {
IdentifierInfo* II = T->getDecl()->getIdentifier();
return II == CFStringRefII || II == CFBooleanRefII || II == CFNullRefII;
}
return false;
}
void ento::registerNonnullGlobalConstantsChecker(CheckerManager &Mgr) {
Mgr.registerChecker<NonnullGlobalConstantsChecker>();
}
bool ento::shouldRegisterNonnullGlobalConstantsChecker(const CheckerManager &mgr) {
return true;
}
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