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 std::unique_ptr<BuiltinBug> BT_Undef;
29  mutable std::unique_ptr<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      return;
60
61    // Not all blocks have explicitly-specified return types; if the return type
62    // is not available, but the return value expression has 'void' type, assume
63    // Sema already checked it.
64    if (RT.isNull() && isa<BlockDecl>(SFC->getDecl()) &&
65        RetE->getType()->isVoidType())
66      return;
67
68    emitUndef(C, RetE);
69    return;
70  }
71
72  if (RT.isNull())
73    return;
74
75  if (RT->isReferenceType()) {
76    checkReference(C, RetE, RetVal.castAs<DefinedOrUnknownSVal>());
77    return;
78  }
79}
80
81static void emitBug(CheckerContext &C, BuiltinBug &BT, const Expr *RetE,
82                    const Expr *TrackingE = nullptr) {
83  ExplodedNode *N = C.generateSink();
84  if (!N)
85    return;
86
87  BugReport *Report = new BugReport(BT, BT.getDescription(), N);
88
89  Report->addRange(RetE->getSourceRange());
90  bugreporter::trackNullOrUndefValue(N, TrackingE ? TrackingE : RetE, *Report);
91
92  C.emitReport(Report);
93}
94
95void ReturnUndefChecker::emitUndef(CheckerContext &C, const Expr *RetE) const {
96  if (!BT_Undef)
97    BT_Undef.reset(
98        new BuiltinBug(this, "Garbage return value",
99                       "Undefined or garbage value returned to caller"));
100  emitBug(C, *BT_Undef, RetE);
101}
102
103void ReturnUndefChecker::checkReference(CheckerContext &C, const Expr *RetE,
104                                        DefinedOrUnknownSVal RetVal) const {
105  ProgramStateRef StNonNull, StNull;
106  std::tie(StNonNull, StNull) = C.getState()->assume(RetVal);
107
108  if (StNonNull) {
109    // Going forward, assume the location is non-null.
110    C.addTransition(StNonNull);
111    return;
112  }
113
114  // The return value is known to be null. Emit a bug report.
115  if (!BT_NullReference)
116    BT_NullReference.reset(new BuiltinBug(this, "Returning null reference"));
117
118  emitBug(C, *BT_NullReference, RetE, bugreporter::getDerefExpr(RetE));
119}
120
121void ento::registerReturnUndefChecker(CheckerManager &mgr) {
122  mgr.registerChecker<ReturnUndefChecker>();
123}
124