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
21 using namespace clang;
22 using namespace ento;
23
24 namespace {
25
26 class UndefBranchChecker : public Checker<check::BranchCondition> {
27 mutable std::unique_ptr<BuiltinBug> BT;
28
29 struct FindUndefExpr {
30 ProgramStateRef St;
31 const LocationContext *LCtx;
32
FindUndefExpr__anon250752a90111::UndefBranchChecker::FindUndefExpr33 FindUndefExpr(ProgramStateRef S, const LocationContext *L)
34 : St(S), LCtx(L) {}
35
FindExpr__anon250752a90111::UndefBranchChecker::FindUndefExpr36 const Expr *FindExpr(const Expr *Ex) {
37 if (!MatchesCriteria(Ex))
38 return nullptr;
39
40 for (Stmt::const_child_iterator I = Ex->child_begin(),
41 E = Ex->child_end();I!=E;++I)
42 if (const Expr *ExI = dyn_cast_or_null<Expr>(*I)) {
43 const Expr *E2 = FindExpr(ExI);
44 if (E2) return E2;
45 }
46
47 return Ex;
48 }
49
MatchesCriteria__anon250752a90111::UndefBranchChecker::FindUndefExpr50 bool MatchesCriteria(const Expr *Ex) {
51 return St->getSVal(Ex, LCtx).isUndef();
52 }
53 };
54
55 public:
56 void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const;
57 };
58
59 }
60
checkBranchCondition(const Stmt * Condition,CheckerContext & Ctx) const61 void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
62 CheckerContext &Ctx) const {
63 SVal X = Ctx.getState()->getSVal(Condition, Ctx.getLocationContext());
64 if (X.isUndef()) {
65 // Generate a sink node, which implicitly marks both outgoing branches as
66 // infeasible.
67 ExplodedNode *N = Ctx.generateSink();
68 if (N) {
69 if (!BT)
70 BT.reset(new BuiltinBug(
71 this, "Branch condition evaluates to a garbage value"));
72
73 // What's going on here: we want to highlight the subexpression of the
74 // condition that is the most likely source of the "uninitialized
75 // branch condition." We do a recursive walk of the condition's
76 // subexpressions and roughly look for the most nested subexpression
77 // that binds to Undefined. We then highlight that expression's range.
78
79 // Get the predecessor node and check if is a PostStmt with the Stmt
80 // being the terminator condition. We want to inspect the state
81 // of that node instead because it will contain main information about
82 // the subexpressions.
83
84 // Note: any predecessor will do. They should have identical state,
85 // since all the BlockEdge did was act as an error sink since the value
86 // had to already be undefined.
87 assert (!N->pred_empty());
88 const Expr *Ex = cast<Expr>(Condition);
89 ExplodedNode *PrevN = *N->pred_begin();
90 ProgramPoint P = PrevN->getLocation();
91 ProgramStateRef St = N->getState();
92
93 if (Optional<PostStmt> PS = P.getAs<PostStmt>())
94 if (PS->getStmt() == Ex)
95 St = PrevN->getState();
96
97 FindUndefExpr FindIt(St, Ctx.getLocationContext());
98 Ex = FindIt.FindExpr(Ex);
99
100 // Emit the bug report.
101 BugReport *R = new BugReport(*BT, BT->getDescription(), N);
102 bugreporter::trackNullOrUndefValue(N, Ex, *R);
103 R->addRange(Ex->getSourceRange());
104
105 Ctx.emitReport(R);
106 }
107 }
108 }
109
registerUndefBranchChecker(CheckerManager & mgr)110 void ento::registerUndefBranchChecker(CheckerManager &mgr) {
111 mgr.registerChecker<UndefBranchChecker>();
112 }
113