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/BugReporter/BugType.h"
17#include "clang/StaticAnalyzer/Core/Checker.h"
18#include "clang/StaticAnalyzer/Core/CheckerManager.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
20#include <utility>
21
22using namespace clang;
23using namespace ento;
24
25namespace {
26
27class UndefBranchChecker : public Checker<check::BranchCondition> {
28  mutable std::unique_ptr<BuiltinBug> BT;
29
30  struct FindUndefExpr {
31    ProgramStateRef St;
32    const LocationContext *LCtx;
33
34    FindUndefExpr(ProgramStateRef S, const LocationContext *L)
35        : St(std::move(S)), LCtx(L) {}
36
37    const Expr *FindExpr(const Expr *Ex) {
38      if (!MatchesCriteria(Ex))
39        return nullptr;
40
41      for (const Stmt *SubStmt : Ex->children())
42        if (const Expr *ExI = dyn_cast_or_null<Expr>(SubStmt))
43          if (const Expr *E2 = FindExpr(ExI))
44            return E2;
45
46      return Ex;
47    }
48
49    bool MatchesCriteria(const Expr *Ex) {
50      return St->getSVal(Ex, LCtx).isUndef();
51    }
52  };
53
54public:
55  void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const;
56};
57
58}
59
60void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
61                                              CheckerContext &Ctx) const {
62  SVal X = Ctx.getState()->getSVal(Condition, Ctx.getLocationContext());
63  if (X.isUndef()) {
64    // Generate a sink node, which implicitly marks both outgoing branches as
65    // infeasible.
66    ExplodedNode *N = Ctx.generateErrorNode();
67    if (N) {
68      if (!BT)
69        BT.reset(new BuiltinBug(
70            this, "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
78      // Get the predecessor node and check if is a PostStmt with the Stmt
79      // being the terminator condition.  We want to inspect the state
80      // of that node instead because it will contain main information about
81      // the subexpressions.
82
83      // Note: any predecessor will do.  They should have identical state,
84      // since all the BlockEdge did was act as an error sink since the value
85      // had to already be undefined.
86      assert (!N->pred_empty());
87      const Expr *Ex = cast<Expr>(Condition);
88      ExplodedNode *PrevN = *N->pred_begin();
89      ProgramPoint P = PrevN->getLocation();
90      ProgramStateRef St = N->getState();
91
92      if (Optional<PostStmt> PS = P.getAs<PostStmt>())
93        if (PS->getStmt() == Ex)
94          St = PrevN->getState();
95
96      FindUndefExpr FindIt(St, Ctx.getLocationContext());
97      Ex = FindIt.FindExpr(Ex);
98
99      // Emit the bug report.
100      auto R = llvm::make_unique<BugReport>(*BT, BT->getDescription(), N);
101      bugreporter::trackNullOrUndefValue(N, Ex, *R);
102      R->addRange(Ex->getSourceRange());
103
104      Ctx.emitReport(std::move(R));
105    }
106  }
107}
108
109void ento::registerUndefBranchChecker(CheckerManager &mgr) {
110  mgr.registerChecker<UndefBranchChecker>();
111}
112