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//== ObjCAtSyncChecker.cpp - nil mutex checker for @synchronized -*- C++ -*--=//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This defines ObjCAtSyncChecker, a builtin check that checks for null pointers
// used as mutexes for @synchronized.
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/AST/StmtObjC.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"
using namespace clang;
using namespace ento;
namespace {
class ObjCAtSyncChecker
: public Checker< check::PreStmt<ObjCAtSynchronizedStmt> > {
mutable std::unique_ptr<BuiltinBug> BT_null;
mutable std::unique_ptr<BuiltinBug> BT_undef;
void checkPreStmt(const ObjCAtSynchronizedStmt *S, CheckerContext &C) const;
} // end anonymous namespace
void ObjCAtSyncChecker::checkPreStmt(const ObjCAtSynchronizedStmt *S,
CheckerContext &C) const {
const Expr *Ex = S->getSynchExpr();
ProgramStateRef state = C.getState();
SVal V = C.getSVal(Ex);
// Uninitialized value used for the mutex?
if (V.getAs<UndefinedVal>()) {
if (ExplodedNode *N = C.generateErrorNode()) {
if (!BT_undef)
BT_undef.reset(new BuiltinBug(this, "Uninitialized value used as mutex "
"for @synchronized"));
auto report = std::make_unique<PathSensitiveBugReport>(
*BT_undef, BT_undef->getDescription(), N);
bugreporter::trackExpressionValue(N, Ex, *report);
if (V.isUnknown())
// Check for null mutexes.
ProgramStateRef notNullState, nullState;
std::tie(notNullState, nullState) = state->assume(V.castAs<DefinedSVal>());
if (nullState) {
if (!notNullState) {
// Generate an error node. This isn't a sink since
// a null mutex just means no synchronization occurs.
if (ExplodedNode *N = C.generateNonFatalErrorNode(nullState)) {
if (!BT_null)
BT_null.reset(new BuiltinBug(
this, "Nil value used as mutex for @synchronized() "
"(no synchronization will occur)"));
auto report = std::make_unique<PathSensitiveBugReport>(
*BT_null, BT_null->getDescription(), N);
bugreporter::trackExpressionValue(N, Ex, *report);
// Don't add a transition for 'nullState'. If the value is
// under-constrained to be null or non-null, assume it is non-null
// afterwards.
if (notNullState)
void ento::registerObjCAtSyncChecker(CheckerManager &mgr) {
bool ento::shouldRegisterObjCAtSyncChecker(const LangOptions &LO) {
return LO.ObjC;