UndefBranchChecker.cpp revision 9c378f705405d37f49795d5e915989de774fe11f 
1//=== UndefBranchChecker.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 UndefBranchChecker, which checks for undefined branch
11// condition.
12//
13//===----------------------------------------------------------------------===//
14
15#include "ClangSACheckers.h"
16#include "clang/StaticAnalyzer/Core/Checker.h"
17#include "clang/StaticAnalyzer/Core/CheckerManager.h"
18#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
20
21using namespace clang;
22using namespace ento;
23
24namespace {
25
26class UndefBranchChecker : public Checker<check::BranchCondition> {
27  mutable llvm::OwningPtr<BuiltinBug> BT;
28
29  struct FindUndefExpr {
30    GRStateManager& VM;
31    const GRState *St;
32
33    FindUndefExpr(GRStateManager& V, const GRState *S) : VM(V), St(S) {}
34
35    const Expr *FindExpr(const Expr *Ex) {
36      if (!MatchesCriteria(Ex))
37        return 0;
38
39      for (Stmt::const_child_iterator I = Ex->child_begin(),
40                                      E = Ex->child_end();I!=E;++I)
41        if (const Expr *ExI = dyn_cast_or_null<Expr>(*I)) {
42          const Expr *E2 = FindExpr(ExI);
43          if (E2) return E2;
44        }
45
46      return Ex;
47    }
48
49    bool MatchesCriteria(const Expr *Ex) { return St->getSVal(Ex).isUndef(); }
50  };
51
52public:
53  void checkBranchCondition(const Stmt *Condition, BranchNodeBuilder &Builder,
54                            ExprEngine &Eng) const;
55};
56
57}
58
59void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
60                                              BranchNodeBuilder &Builder,
61                                              ExprEngine &Eng) const {
62  const GRState *state = Builder.getState();
63  SVal X = state->getSVal(Condition);
64  if (X.isUndef()) {
65    ExplodedNode *N = Builder.generateNode(state, true);
66    if (N) {
67      N->markAsSink();
68      if (!BT)
69        BT.reset(
70               new BuiltinBug("Branch condition evaluates to a garbage value"));
71
72      // What's going on here: we want to highlight the subexpression of the
73      // condition that is the most likely source of the "uninitialized
74      // branch condition."  We do a recursive walk of the condition's
75      // subexpressions and roughly look for the most nested subexpression
76      // that binds to Undefined.  We then highlight that expression's range.
77      BlockEdge B = cast<BlockEdge>(N->getLocation());
78      const Expr *Ex = cast<Expr>(B.getSrc()->getTerminatorCondition());
79      assert (Ex && "Block must have a terminator.");
80
81      // Get the predecessor node and check if is a PostStmt with the Stmt
82      // being the terminator condition.  We want to inspect the state
83      // of that node instead because it will contain main information about
84      // the subexpressions.
85      assert (!N->pred_empty());
86
87      // Note: any predecessor will do.  They should have identical state,
88      // since all the BlockEdge did was act as an error sink since the value
89      // had to already be undefined.
90      ExplodedNode *PrevN = *N->pred_begin();
91      ProgramPoint P = PrevN->getLocation();
92      const GRState *St = N->getState();
93
94      if (PostStmt *PS = dyn_cast<PostStmt>(&P))
95        if (PS->getStmt() == Ex)
96          St = PrevN->getState();
97
98      FindUndefExpr FindIt(Eng.getStateManager(), St);
99      Ex = FindIt.FindExpr(Ex);
100
101      // Emit the bug report.
102      EnhancedBugReport *R = new EnhancedBugReport(*BT, BT->getDescription(),N);
103      R->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, Ex);
104      R->addRange(Ex->getSourceRange());
105
106      Eng.getBugReporter().EmitReport(R);
107    }
108
109    Builder.markInfeasible(true);
110    Builder.markInfeasible(false);
111  }
112}
113
114void ento::registerUndefBranchChecker(CheckerManager &mgr) {
115  mgr.registerChecker<UndefBranchChecker>();
116}
117