UndefinedAssignmentChecker.cpp revision 360784 
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
20using namespace clang;
21using namespace ento;
22
23namespace {
24class UndefinedAssignmentChecker
25  : public Checker<check::Bind> {
26  mutable std::unique_ptr<BugType> BT;
27
28public:
29  void checkBind(SVal location, SVal val, const Stmt *S,
30                 CheckerContext &C) const;
31};
32}
33
34void 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
119void ento::registerUndefinedAssignmentChecker(CheckerManager &mgr) {
120  mgr.registerChecker<UndefinedAssignmentChecker>();
121}
122
123bool ento::shouldRegisterUndefinedAssignmentChecker(const LangOptions &LO) {
124  return true;
125}
126