UndefBranchChecker.cpp revision a19f4af7a94835ce4693bfe12d6270754e79eb56 
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    const ProgramState *St;
31
32    FindUndefExpr(const ProgramState *S) : St(S) {}
33
34    const Expr *FindExpr(const Expr *Ex) {
35      if (!MatchesCriteria(Ex))
36        return 0;
37
38      for (Stmt::const_child_iterator I = Ex->child_begin(),
39                                      E = Ex->child_end();I!=E;++I)
40        if (const Expr *ExI = dyn_cast_or_null<Expr>(*I)) {
41          const Expr *E2 = FindExpr(ExI);
42          if (E2) return E2;
43        }
44
45      return Ex;
46    }
47
48    bool MatchesCriteria(const Expr *Ex) { return St->getSVal(Ex).isUndef(); }
49  };
50
51public:
52  void checkBranchCondition(const Stmt *Condition, BranchNodeBuilder &Builder,
53                            ExprEngine &Eng) const;
54};
55
56}
57
58void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
59                                              BranchNodeBuilder &Builder,
60                                              ExprEngine &Eng) const {
61  const ProgramState *state = Builder.getState();
62  SVal X = state->getSVal(Condition);
63  if (X.isUndef()) {
64    // Generate a sink node.
65    ExplodedNode *N = Builder.generateNode(Condition, state, 0, true);
66    if (N) {
67      if (!BT)
68        BT.reset(
69               new BuiltinBug("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      const ProgramState *St = N->getState();
90
91      if (PostStmt *PS = dyn_cast<PostStmt>(&P))
92        if (PS->getStmt() == Ex)
93          St = PrevN->getState();
94
95      FindUndefExpr FindIt(St);
96      Ex = FindIt.FindExpr(Ex);
97
98      // Emit the bug report.
99      BugReport *R = new BugReport(*BT, BT->getDescription(), N);
100      R->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N, Ex));
101      R->addRange(Ex->getSourceRange());
102
103      Eng.getBugReporter().EmitReport(R);
104    }
105
106    Builder.markInfeasible(true);
107    Builder.markInfeasible(false);
108  }
109}
110
111void ento::registerUndefBranchChecker(CheckerManager &mgr) {
112  mgr.registerChecker<UndefBranchChecker>();
113}
114