ReturnUndefChecker.cpp source code [clang_source_code/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<BuiltinBug> BT_Undef;
28	mutable std::unique_ptr<BuiltinBug> 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, BuiltinBug &BT, const Expr *RetE,
81	const Expr *TrackingE = nullptr) {
82	ExplodedNode *N = C.generateErrorNode();
83	if (!N)
84	return;
85
86	auto Report = llvm::make_unique<BugReport>(BT, BT.getDescription(), 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(
97	new BuiltinBug(this, "Garbage return value",
98	"Undefined or garbage value returned to caller"));
99	emitBug(C, *BT_Undef, RetE);
100	}
101
102	void ReturnUndefChecker::checkReference(CheckerContext &C, const Expr *RetE,
103	DefinedOrUnknownSVal RetVal) const {
104	ProgramStateRef StNonNull, StNull;
105	std::tie(StNonNull, StNull) = C.getState()->assume(RetVal);
106
107	if (StNonNull) {
108	// Going forward, assume the location is non-null.
109	C.addTransition(StNonNull);
110	return;
111	}
112
113	// The return value is known to be null. Emit a bug report.
114	if (!BT_NullReference)
115	BT_NullReference.reset(new BuiltinBug(this, "Returning null reference"));
116
117	emitBug(C, *BT_NullReference, RetE, bugreporter::getDerefExpr(RetE));
118	}
119
120	void ento::registerReturnUndefChecker(CheckerManager &mgr) {
121	mgr.registerChecker<ReturnUndefChecker>();
122	}
123
124	bool ento::shouldRegisterReturnUndefChecker(const LangOptions &LO) {
125	return true;
126	}
127

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