1//== ObjCAtSyncChecker.cpp - nil mutex checker for @synchronized -*- 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 defines ObjCAtSyncChecker, a builtin check that checks for null pointers
10// used as mutexes for @synchronized.
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15#include "clang/AST/StmtObjC.h"
16#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
17#include "clang/StaticAnalyzer/Core/Checker.h"
18#include "clang/StaticAnalyzer/Core/CheckerManager.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
21
22using namespace clang;
23using namespace ento;
24
25namespace {
26class ObjCAtSyncChecker
27    : public Checker< check::PreStmt<ObjCAtSynchronizedStmt> > {
28  const BugType BT_null{this, "Nil value used as mutex for @synchronized() "
29                              "(no synchronization will occur)"};
30  const BugType BT_undef{this, "Uninitialized value used as mutex "
31                               "for @synchronized"};
32
33public:
34  void checkPreStmt(const ObjCAtSynchronizedStmt *S, CheckerContext &C) const;
35};
36} // end anonymous namespace
37
38void ObjCAtSyncChecker::checkPreStmt(const ObjCAtSynchronizedStmt *S,
39                                     CheckerContext &C) const {
40
41  const Expr *Ex = S->getSynchExpr();
42  ProgramStateRef state = C.getState();
43  SVal V = C.getSVal(Ex);
44
45  // Uninitialized value used for the mutex?
46  if (isa<UndefinedVal>(V)) {
47    if (ExplodedNode *N = C.generateErrorNode()) {
48      auto report = std::make_unique<PathSensitiveBugReport>(
49          BT_undef, BT_undef.getDescription(), N);
50      bugreporter::trackExpressionValue(N, Ex, *report);
51      C.emitReport(std::move(report));
52    }
53    return;
54  }
55
56  if (V.isUnknown())
57    return;
58
59  // Check for null mutexes.
60  ProgramStateRef notNullState, nullState;
61  std::tie(notNullState, nullState) = state->assume(V.castAs<DefinedSVal>());
62
63  if (nullState) {
64    if (!notNullState) {
65      // Generate an error node.  This isn't a sink since
66      // a null mutex just means no synchronization occurs.
67      if (ExplodedNode *N = C.generateNonFatalErrorNode(nullState)) {
68        auto report = std::make_unique<PathSensitiveBugReport>(
69            BT_null, BT_null.getDescription(), N);
70        bugreporter::trackExpressionValue(N, Ex, *report);
71
72        C.emitReport(std::move(report));
73        return;
74      }
75    }
76    // Don't add a transition for 'nullState'.  If the value is
77    // under-constrained to be null or non-null, assume it is non-null
78    // afterwards.
79  }
80
81  if (notNullState)
82    C.addTransition(notNullState);
83}
84
85void ento::registerObjCAtSyncChecker(CheckerManager &mgr) {
86  mgr.registerChecker<ObjCAtSyncChecker>();
87}
88
89bool ento::shouldRegisterObjCAtSyncChecker(const CheckerManager &mgr) {
90  const LangOptions &LO = mgr.getLangOpts();
91  return LO.ObjC;
92}
93