clang/lib/StaticAnalyzer/Checkers/ReturnUndefChecker.cpp

   1 //== ReturnUndefChecker.cpp -------------------------------------*- 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 file defines ReturnUndefChecker, which is a path-sensitive
  10 // check which looks for undefined or garbage values being returned to the
  11 // caller.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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/CallEvent.h"
  20 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
  21
  22 using namespace clang;
  23 using namespace ento;
  24
  25 namespace {
  26 class ReturnUndefChecker : public Checker< check::PreStmt<ReturnStmt> > {
  27   mutable std::unique_ptr<BugType> BT_Undef;
  28   mutable std::unique_ptr<BugType> BT_NullReference;
  29
  30   void emitUndef(CheckerContext &C, const Expr *RetE) const;
  31   void checkReference(CheckerContext &C, const Expr *RetE,
  32                       DefinedOrUnknownSVal RetVal) const;
  33 public:
  34   void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
  35 };
  36 }
  37
  38 void ReturnUndefChecker::checkPreStmt(const ReturnStmt *RS,
  39                                       CheckerContext &C) const {
  40   const Expr *RetE = RS->getRetValue();
  41   if (!RetE)
  42     return;
  43   SVal RetVal = C.getSVal(RetE);
  44
  45   const StackFrameContext *SFC = C.getStackFrame();
  46   QualType RT = CallEvent::getDeclaredResultType(SFC->getDecl());
  47
  48   if (RetVal.isUndef()) {
  49     // "return;" is modeled to evaluate to an UndefinedVal. Allow UndefinedVal
  50     // to be returned in functions returning void to support this pattern:
  51     //   void foo() {
  52     //     return;
  53     //   }
  54     //   void test() {
  55     //     return foo();
  56     //   }
  57     if (!RT.isNull() && RT->isVoidType())
  58       return;
  59
  60     // Not all blocks have explicitly-specified return types; if the return type
  61     // is not available, but the return value expression has 'void' type, assume
  62     // Sema already checked it.
  63     if (RT.isNull() && isa<BlockDecl>(SFC->getDecl()) &&
  64         RetE->getType()->isVoidType())
  65       return;
  66
  67     emitUndef(C, RetE);
  68     return;
  69   }
  70
  71   if (RT.isNull())
  72     return;
  73
  74   if (RT->isReferenceType()) {
  75     checkReference(C, RetE, RetVal.castAs<DefinedOrUnknownSVal>());
  76     return;
  77   }
  78 }
  79
  80 static void emitBug(CheckerContext &C, BugType &BT, StringRef Msg,
  81                     const Expr *RetE, const Expr *TrackingE = nullptr) {
  82   ExplodedNode *N = C.generateErrorNode();
  83   if (!N)
  84     return;
  85
  86   auto Report = std::make_unique<PathSensitiveBugReport>(BT, Msg, N);
  87
  88   Report->addRange(RetE->getSourceRange());
  89   bugreporter::trackExpressionValue(N, TrackingE ? TrackingE : RetE, *Report);
  90
  91   C.emitReport(std::move(Report));
  92 }
  93
  94 void ReturnUndefChecker::emitUndef(CheckerContext &C, const Expr *RetE) const {
  95   if (!BT_Undef)
  96     BT_Undef.reset(new BugType(this, "Garbage return value"));
  97   emitBug(C, *BT_Undef, "Undefined or garbage value returned to caller", RetE);
  98 }
  99
 100 void ReturnUndefChecker::checkReference(CheckerContext &C, const Expr *RetE,
 101                                         DefinedOrUnknownSVal RetVal) const {
 102   ProgramStateRef StNonNull, StNull;
 103   std::tie(StNonNull, StNull) = C.getState()->assume(RetVal);
 104
 105   if (StNonNull) {
 106     // Going forward, assume the location is non-null.
 107     C.addTransition(StNonNull);
 108     return;
 109   }
 110
 111   // The return value is known to be null. Emit a bug report.
 112   if (!BT_NullReference)
 113     BT_NullReference.reset(new BugType(this, "Returning null reference"));
 114
 115   emitBug(C, *BT_NullReference, BT_NullReference->getDescription(), RetE,
 116           bugreporter::getDerefExpr(RetE));
 117 }
 118
 119 void ento::registerReturnUndefChecker(CheckerManager &mgr) {
 120   mgr.registerChecker<ReturnUndefChecker>();
 121 }
 122
 123 bool ento::shouldRegisterReturnUndefChecker(const CheckerManager &mgr) {
 124   return true;
 125 }