ReturnUndefChecker.cpp revision c236b7327f989c1e7fe6b08a188bfef86727513d 
1//== ReturnUndefChecker.cpp -------------------------------------*- C++ -*--==//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines ReturnUndefChecker, which is a path-sensitive
11// check which looks for undefined or garbage values being returned to the
12// caller.
13//
14//===----------------------------------------------------------------------===//
15
16#include "ClangSACheckers.h"
17#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
18#include "clang/StaticAnalyzer/Core/Checker.h"
19#include "clang/StaticAnalyzer/Core/CheckerManager.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
21#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
22
23using namespace clang;
24using namespace ento;
25
26namespace {
27class ReturnUndefChecker : public Checker< check::PreStmt<ReturnStmt> > {
28  mutable OwningPtr<BuiltinBug> BT_Undef;
29  mutable OwningPtr<BuiltinBug> BT_NullReference;
30
31  void emitUndef(CheckerContext &C, const Expr *RetE) const;
32  void checkReference(CheckerContext &C, const Expr *RetE,
33                      DefinedOrUnknownSVal RetVal) const;
34public:
35  void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
36};
37}
38
39void ReturnUndefChecker::checkPreStmt(const ReturnStmt *RS,
40                                      CheckerContext &C) const {
41  const Expr *RetE = RS->getRetValue();
42  if (!RetE)
43    return;
44  SVal RetVal = C.getSVal(RetE);
45
46  const StackFrameContext *SFC = C.getStackFrame();
47  QualType RT = CallEvent::getDeclaredResultType(SFC->getDecl());
48
49  if (RetVal.isUndef()) {
50    // "return;" is modeled to evaluate to an UndefinedVal. Allow UndefinedVal
51    // to be returned in functions returning void to support this pattern:
52    //   void foo() {
53    //     return;
54    //   }
55    //   void test() {
56    //     return foo();
57    //   }
58    if (RT.isNull() || !RT->isVoidType())
59      emitUndef(C, RetE);
60    return;
61  }
62
63  if (RT.isNull())
64    return;
65
66  if (RT->isReferenceType()) {
67    checkReference(C, RetE, RetVal.castAs<DefinedOrUnknownSVal>());
68    return;
69  }
70}
71
72static void emitBug(CheckerContext &C, BuiltinBug &BT, const Expr *RetE,
73                    const Expr *TrackingE = 0) {
74  ExplodedNode *N = C.generateSink();
75  if (!N)
76    return;
77
78  BugReport *Report = new BugReport(BT, BT.getDescription(), N);
79
80  Report->addRange(RetE->getSourceRange());
81  bugreporter::trackNullOrUndefValue(N, TrackingE ? TrackingE : RetE, *Report);
82
83  C.emitReport(Report);
84}
85
86void ReturnUndefChecker::emitUndef(CheckerContext &C, const Expr *RetE) const {
87  if (!BT_Undef)
88    BT_Undef.reset(new BuiltinBug("Garbage return value",
89                                  "Undefined or garbage value "
90                                    "returned to caller"));
91  emitBug(C, *BT_Undef, RetE);
92}
93
94void ReturnUndefChecker::checkReference(CheckerContext &C, const Expr *RetE,
95                                        DefinedOrUnknownSVal RetVal) const {
96  ProgramStateRef StNonNull, StNull;
97  llvm::tie(StNonNull, StNull) = C.getState()->assume(RetVal);
98
99  if (StNonNull) {
100    // Going forward, assume the location is non-null.
101    C.addTransition(StNonNull);
102    return;
103  }
104
105  // The return value is known to be null. Emit a bug report.
106  if (!BT_NullReference)
107    BT_NullReference.reset(new BuiltinBug("Returning null reference"));
108
109  emitBug(C, *BT_NullReference, RetE, bugreporter::getDerefExpr(RetE));
110}
111
112void ento::registerReturnUndefChecker(CheckerManager &mgr) {
113  mgr.registerChecker<ReturnUndefChecker>();
114}
115