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  mutable std::unique_ptr<BuiltinBug> BT_null;
29  mutable std::unique_ptr<BuiltinBug> BT_undef;
30
31public:
32  void checkPreStmt(const ObjCAtSynchronizedStmt *S, CheckerContext &C) const;
33};
34} // end anonymous namespace
35
36void ObjCAtSyncChecker::checkPreStmt(const ObjCAtSynchronizedStmt *S,
37                                     CheckerContext &C) const {
38
39  const Expr *Ex = S->getSynchExpr();
40  ProgramStateRef state = C.getState();
41  SVal V = C.getSVal(Ex);
42
43  // Uninitialized value used for the mutex?
44  if (V.getAs<UndefinedVal>()) {
45    if (ExplodedNode *N = C.generateErrorNode()) {
46      if (!BT_undef)
47        BT_undef.reset(new BuiltinBug(this, "Uninitialized value used as mutex "
48                                            "for @synchronized"));
49      auto report = std::make_unique<PathSensitiveBugReport>(
50          *BT_undef, BT_undef->getDescription(), N);
51      bugreporter::trackExpressionValue(N, Ex, *report);
52      C.emitReport(std::move(report));
53    }
54    return;
55  }
56
57  if (V.isUnknown())
58    return;
59
60  // Check for null mutexes.
61  ProgramStateRef notNullState, nullState;
62  std::tie(notNullState, nullState) = state->assume(V.castAs<DefinedSVal>());
63
64  if (nullState) {
65    if (!notNullState) {
66      // Generate an error node.  This isn't a sink since
67      // a null mutex just means no synchronization occurs.
68      if (ExplodedNode *N = C.generateNonFatalErrorNode(nullState)) {
69        if (!BT_null)
70          BT_null.reset(new BuiltinBug(
71              this, "Nil value used as mutex for @synchronized() "
72                    "(no synchronization will occur)"));
73        auto report = std::make_unique<PathSensitiveBugReport>(
74            *BT_null, BT_null->getDescription(), N);
75        bugreporter::trackExpressionValue(N, Ex, *report);
76
77        C.emitReport(std::move(report));
78        return;
79      }
80    }
81    // Don't add a transition for 'nullState'.  If the value is
82    // under-constrained to be null or non-null, assume it is non-null
83    // afterwards.
84  }
85
86  if (notNullState)
87    C.addTransition(notNullState);
88}
89
90void ento::registerObjCAtSyncChecker(CheckerManager &mgr) {
91  mgr.registerChecker<ObjCAtSyncChecker>();
92}
93
94bool ento::shouldRegisterObjCAtSyncChecker(const LangOptions &LO) {
95  return LO.ObjC;
96}
97