121 lines · 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-exception6//7//===----------------------------------------------------------------------===//8//9// This file defines ReturnUndefChecker, which is a path-sensitive10// check which looks for undefined or garbage values being returned to the11// 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 22using namespace clang;23using namespace ento;24 25namespace {26class ReturnUndefChecker : public Checker< check::PreStmt<ReturnStmt> > {27 const BugType BT_Undef{this, "Garbage return value"};28 const BugType BT_NullReference{this, "Returning null reference"};29 30 void emitUndef(CheckerContext &C, const Expr *RetE) const;31 void checkReference(CheckerContext &C, const Expr *RetE,32 DefinedOrUnknownSVal RetVal) const;33public:34 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;35};36}37 38void 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 UndefinedVal50 // 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 type61 // is not available, but the return value expression has 'void' type, assume62 // 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 80static void emitBug(CheckerContext &C, const 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 94void ReturnUndefChecker::emitUndef(CheckerContext &C, const Expr *RetE) const {95 emitBug(C, BT_Undef, "Undefined or garbage value returned to caller", RetE);96}97 98void ReturnUndefChecker::checkReference(CheckerContext &C, const Expr *RetE,99 DefinedOrUnknownSVal RetVal) const {100 ProgramStateRef StNonNull, StNull;101 std::tie(StNonNull, StNull) = C.getState()->assume(RetVal);102 103 if (StNonNull) {104 // Going forward, assume the location is non-null.105 C.addTransition(StNonNull);106 return;107 }108 109 // The return value is known to be null. Emit a bug report.110 emitBug(C, BT_NullReference, BT_NullReference.getDescription(), RetE,111 bugreporter::getDerefExpr(RetE));112}113 114void ento::registerReturnUndefChecker(CheckerManager &mgr) {115 mgr.registerChecker<ReturnUndefChecker>();116}117 118bool ento::shouldRegisterReturnUndefChecker(const CheckerManager &mgr) {119 return true;120}121