UndefBranchChecker.cpp revision 4e82d3cf6fd4c907265e3fa3aac0a835c35dc759 
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, NodeBuilder &Builder,
53                            ExplodedNode *Pred, ExprEngine &Eng) const;
54};
55
56}
57
58void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
59                                              NodeBuilder &Builder,
60                                              ExplodedNode *Pred,
61                                              ExprEngine &Eng) const {
62  const ProgramState *state = Pred->getState();
63  SVal X = state->getSVal(Condition);
64  if (X.isUndef()) {
65    // TODO: The PP will be generated with the correct tag by the CheckerManager
66    // after we migrate the callback to CheckerContext.
67    const ProgramPointTag *Tag = 0;
68    ProgramPoint PP = PostCondition(Condition, Pred->getLocationContext(), Tag);
69    // Generate a sink node, which implicitly marks both outgoing branches as
70    // infeasible.
71    ExplodedNode *N = Builder.generateNode(PP, state,
72                                           Pred, true);
73    if (N) {
74      if (!BT)
75        BT.reset(
76               new BuiltinBug("Branch condition evaluates to a garbage value"));
77
78      // What's going on here: we want to highlight the subexpression of the
79      // condition that is the most likely source of the "uninitialized
80      // branch condition."  We do a recursive walk of the condition's
81      // subexpressions and roughly look for the most nested subexpression
82      // that binds to Undefined.  We then highlight that expression's range.
83
84      // Get the predecessor node and check if is a PostStmt with the Stmt
85      // being the terminator condition.  We want to inspect the state
86      // of that node instead because it will contain main information about
87      // the subexpressions.
88
89      // Note: any predecessor will do.  They should have identical state,
90      // since all the BlockEdge did was act as an error sink since the value
91      // had to already be undefined.
92      assert (!N->pred_empty());
93      const Expr *Ex = cast<Expr>(Condition);
94      ExplodedNode *PrevN = *N->pred_begin();
95      ProgramPoint P = PrevN->getLocation();
96      const ProgramState *St = N->getState();
97
98      if (PostStmt *PS = dyn_cast<PostStmt>(&P))
99        if (PS->getStmt() == Ex)
100          St = PrevN->getState();
101
102      FindUndefExpr FindIt(St);
103      Ex = FindIt.FindExpr(Ex);
104
105      // Emit the bug report.
106      BugReport *R = new BugReport(*BT, BT->getDescription(), N);
107      R->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N, Ex));
108      R->addRange(Ex->getSourceRange());
109
110      Eng.getBugReporter().EmitReport(R);
111    }
112  }
113}
114
115void ento::registerUndefBranchChecker(CheckerManager &mgr) {
116  mgr.registerChecker<UndefBranchChecker>();
117}
118