clang  10.0.0git
UndefBranchChecker.cpp
Go to the documentation of this file.
1 //=== UndefBranchChecker.cpp -----------------------------------*- 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 file defines UndefBranchChecker, which checks for undefined branch
10 // condition.
11 //
12 //===----------------------------------------------------------------------===//
13 
19 #include <utility>
20 
21 using namespace clang;
22 using namespace ento;
23 
24 namespace {
25 
26 class UndefBranchChecker : public Checker<check::BranchCondition> {
27  mutable std::unique_ptr<BuiltinBug> BT;
28 
29  struct FindUndefExpr {
30  ProgramStateRef St;
31  const LocationContext *LCtx;
32 
33  FindUndefExpr(ProgramStateRef S, const LocationContext *L)
34  : St(std::move(S)), LCtx(L) {}
35 
36  const Expr *FindExpr(const Expr *Ex) {
37  if (!MatchesCriteria(Ex))
38  return nullptr;
39 
40  for (const Stmt *SubStmt : Ex->children())
41  if (const Expr *ExI = dyn_cast_or_null<Expr>(SubStmt))
42  if (const Expr *E2 = FindExpr(ExI))
43  return E2;
44 
45  return Ex;
46  }
47 
48  bool MatchesCriteria(const Expr *Ex) {
49  return St->getSVal(Ex, LCtx).isUndef();
50  }
51  };
52 
53 public:
54  void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const;
55 };
56 
57 }
58 
59 void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
60  CheckerContext &Ctx) const {
61  SVal X = Ctx.getSVal(Condition);
62  if (X.isUndef()) {
63  // Generate a sink node, which implicitly marks both outgoing branches as
64  // infeasible.
65  ExplodedNode *N = Ctx.generateErrorNode();
66  if (N) {
67  if (!BT)
68  BT.reset(new BuiltinBug(
69  this, "Branch condition evaluates to a garbage value"));
70 
71  // What's going on here: we want to highlight the subexpression of the
72  // condition that is the most likely source of the "uninitialized
73  // branch condition." We do a recursive walk of the condition's
74  // subexpressions and roughly look for the most nested subexpression
75  // that binds to Undefined. We then highlight that expression's range.
76 
77  // Get the predecessor node and check if is a PostStmt with the Stmt
78  // being the terminator condition. We want to inspect the state
79  // of that node instead because it will contain main information about
80  // the subexpressions.
81 
82  // Note: any predecessor will do. They should have identical state,
83  // since all the BlockEdge did was act as an error sink since the value
84  // had to already be undefined.
85  assert (!N->pred_empty());
86  const Expr *Ex = cast<Expr>(Condition);
87  ExplodedNode *PrevN = *N->pred_begin();
88  ProgramPoint P = PrevN->getLocation();
89  ProgramStateRef St = N->getState();
90 
91  if (Optional<PostStmt> PS = P.getAs<PostStmt>())
92  if (PS->getStmt() == Ex)
93  St = PrevN->getState();
94 
95  FindUndefExpr FindIt(St, Ctx.getLocationContext());
96  Ex = FindIt.FindExpr(Ex);
97 
98  // Emit the bug report.
99  auto R = std::make_unique<PathSensitiveBugReport>(
100  *BT, BT->getDescription(), N);
101  bugreporter::trackExpressionValue(N, Ex, *R);
102  R->addRange(Ex->getSourceRange());
103 
104  Ctx.emitReport(std::move(R));
105  }
106  }
107 }
108 
109 void ento::registerUndefBranchChecker(CheckerManager &mgr) {
110  mgr.registerChecker<UndefBranchChecker>();
111 }
112 
113 bool ento::shouldRegisterUndefBranchChecker(const LangOptions &LO) {
114  return true;
115 }
Stmt - This represents one statement.
Definition: Stmt.h:66
IntrusiveRefCntPtr< const ProgramState > ProgramStateRef
StringRef P
Definition: Format.h:2445
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:53
child_range children()
Definition: Stmt.cpp:224
This represents one expression.
Definition: Expr.h:108
Dataflow Directional Tag Classes.
X
Add a minimal nested name specifier fixit hint to allow lookup of a tag name from an outer enclosing ...
Definition: SemaDecl.cpp:14781
Optional< T > getAs() const
Convert to the specified ProgramPoint type, returning None if this ProgramPoint is not of the desired...
Definition: ProgramPoint.h:151