UndefBranchChecker.cpp revision 360784 
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
14#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15#include "clang/StaticAnalyzer/Core/BugReporter/BugType.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 <utility>
20
21using namespace clang;
22using namespace ento;
23
24namespace {
25
26class 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
53public:
54  void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const;
55};
56
57}
58
59void 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
109void ento::registerUndefBranchChecker(CheckerManager &mgr) {
110  mgr.registerChecker<UndefBranchChecker>();
111}
112
113bool ento::shouldRegisterUndefBranchChecker(const LangOptions &LO) {
114  return true;
115}
116