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
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(S: RetE);
44
45 const StackFrameContext *SFC = C.getStackFrame();
46 QualType RT = CallEvent::getDeclaredResultType(D: 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>(Val: 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: 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>(args: BT, args&: Msg, args&: N);
87
88 Report->addRange(R: RetE->getSourceRange());
89 bugreporter::trackExpressionValue(N, E: TrackingE ? TrackingE : RetE, R&: *Report);
90
91 C.emitReport(R: std::move(Report));
92}
93
94void ReturnUndefChecker::emitUndef(CheckerContext &C, const Expr *RetE) const {
95 emitBug(C, BT: BT_Undef, Msg: "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(args&: StNonNull, args&: StNull) = C.getState()->assume(Cond: RetVal);
102
103 if (StNonNull) {
104 // Going forward, assume the location is non-null.
105 C.addTransition(State: StNonNull);
106 return;
107 }
108
109 // The return value is known to be null. Emit a bug report.
110 emitBug(C, BT: BT_NullReference, Msg: BT_NullReference.getDescription(), RetE,
111 TrackingE: bugreporter::getDerefExpr(S: 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