1 //===--- UndefinedAssignmentChecker.h ---------------------------*- 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 defines UndefinedAssignmentChecker, a builtin check in ExprEngine that
10 // checks for assigning undefined values.
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 
20 using namespace clang;
21 using namespace ento;
22 
23 namespace {
24 class UndefinedAssignmentChecker
25   : public Checker<check::Bind> {
26   mutable std::unique_ptr<BugType> BT;
27 
28 public:
29   void checkBind(SVal location, SVal val, const Stmt *S,
30                  CheckerContext &C) const;
31 };
32 }
33 
34 void UndefinedAssignmentChecker::checkBind(SVal location, SVal val,
35                                            const Stmt *StoreE,
36                                            CheckerContext &C) const {
37   if (!val.isUndef())
38     return;
39 
40   // Do not report assignments of uninitialized values inside swap functions.
41   // This should allow to swap partially uninitialized structs
42   // (radar://14129997)
43   if (const FunctionDecl *EnclosingFunctionDecl =
44       dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
45     if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
46       return;
47 
48   ExplodedNode *N = C.generateErrorNode();
49 
50   if (!N)
51     return;
52 
53   static const char *const DefaultMsg =
54       "Assigned value is garbage or undefined";
55   if (!BT)
56     BT.reset(new BuiltinBug(this, DefaultMsg));
57 
58   // Generate a report for this bug.
59   llvm::SmallString<128> Str;
60   llvm::raw_svector_ostream OS(Str);
61 
62   const Expr *ex = nullptr;
63 
64   while (StoreE) {
65     if (const UnaryOperator *U = dyn_cast<UnaryOperator>(StoreE)) {
66       OS << "The expression is an uninitialized value. "
67             "The computed value will also be garbage";
68 
69       ex = U->getSubExpr();
70       break;
71     }
72 
73     if (const BinaryOperator *B = dyn_cast<BinaryOperator>(StoreE)) {
74       if (B->isCompoundAssignmentOp()) {
75         if (C.getSVal(B->getLHS()).isUndef()) {
76           OS << "The left expression of the compound assignment is an "
77                 "uninitialized value. The computed value will also be garbage";
78           ex = B->getLHS();
79           break;
80         }
81       }
82 
83       ex = B->getRHS();
84       break;
85     }
86 
87     if (const DeclStmt *DS = dyn_cast<DeclStmt>(StoreE)) {
88       const VarDecl *VD = cast<VarDecl>(DS->getSingleDecl());
89       ex = VD->getInit();
90     }
91 
92     if (const auto *CD =
93             dyn_cast<CXXConstructorDecl>(C.getStackFrame()->getDecl())) {
94       if (CD->isImplicit()) {
95         for (auto I : CD->inits()) {
96           if (I->getInit()->IgnoreImpCasts() == StoreE) {
97             OS << "Value assigned to field '" << I->getMember()->getName()
98                << "' in implicit constructor is garbage or undefined";
99             break;
100           }
101         }
102       }
103     }
104 
105     break;
106   }
107 
108   if (OS.str().empty())
109     OS << DefaultMsg;
110 
111   auto R = std::make_unique<PathSensitiveBugReport>(*BT, OS.str(), N);
112   if (ex) {
113     R->addRange(ex->getSourceRange());
114     bugreporter::trackExpressionValue(N, ex, *R);
115   }
116   C.emitReport(std::move(R));
117 }
118 
119 void ento::registerUndefinedAssignmentChecker(CheckerManager &mgr) {
120   mgr.registerChecker<UndefinedAssignmentChecker>();
121 }
122 
123 bool ento::shouldRegisterUndefinedAssignmentChecker(const CheckerManager &mgr) {
124   return true;
125 }
126