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