xref: /llvm-project/clang/lib/StaticAnalyzer/Checkers/UndefinedAssignmentChecker.cpp (revision 0f1c1be1968076d6f96f8a7bcc4a15cf195ecd97)
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   if (const FunctionDecl *EnclosingFunctionDecl =
43       dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
44     if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
45       return;
46 
47   ExplodedNode *N = C.generateErrorNode();
48 
49   if (!N)
50     return;
51 
52   static const char *const DefaultMsg =
53       "Assigned value is garbage or undefined";
54   if (!BT)
55     BT.reset(new BugType(this, DefaultMsg));
56 
57   // Generate a report for this bug.
58   llvm::SmallString<128> Str;
59   llvm::raw_svector_ostream OS(Str);
60 
61   const Expr *ex = nullptr;
62 
63   while (StoreE) {
64     if (const UnaryOperator *U = dyn_cast<UnaryOperator>(StoreE)) {
65       OS << "The expression is an uninitialized value. "
66             "The computed value will also be garbage";
67 
68       ex = U->getSubExpr();
69       break;
70     }
71 
72     if (const BinaryOperator *B = dyn_cast<BinaryOperator>(StoreE)) {
73       if (B->isCompoundAssignmentOp()) {
74         if (C.getSVal(B->getLHS()).isUndef()) {
75           OS << "The left expression of the compound assignment is an "
76                 "uninitialized value. The computed value will also be garbage";
77           ex = B->getLHS();
78           break;
79         }
80       }
81 
82       ex = B->getRHS();
83       break;
84     }
85 
86     if (const DeclStmt *DS = dyn_cast<DeclStmt>(StoreE)) {
87       const VarDecl *VD = cast<VarDecl>(DS->getSingleDecl());
88       ex = VD->getInit();
89     }
90 
91     if (const auto *CD =
92             dyn_cast<CXXConstructorDecl>(C.getStackFrame()->getDecl())) {
93       if (CD->isImplicit()) {
94         for (auto *I : CD->inits()) {
95           if (I->getInit()->IgnoreImpCasts() == StoreE) {
96             OS << "Value assigned to field '" << I->getMember()->getName()
97                << "' in implicit constructor is garbage or undefined";
98             break;
99           }
100         }
101       }
102     }
103 
104     break;
105   }
106 
107   if (OS.str().empty())
108     OS << DefaultMsg;
109 
110   auto R = std::make_unique<PathSensitiveBugReport>(*BT, OS.str(), N);
111   if (ex) {
112     R->addRange(ex->getSourceRange());
113     bugreporter::trackExpressionValue(N, ex, *R);
114   }
115   C.emitReport(std::move(R));
116 }
117 
118 void ento::registerUndefinedAssignmentChecker(CheckerManager &mgr) {
119   mgr.registerChecker<UndefinedAssignmentChecker>();
120 }
121 
122 bool ento::shouldRegisterUndefinedAssignmentChecker(const CheckerManager &mgr) {
123   return true;
124 }
125