1//=== BuiltinFunctionChecker.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 checker evaluates "standalone" clang builtin functions that are not
10// just special-cased variants of well-known non-builtin functions.
11// Builtin functions like __builtin_memcpy and __builtin_alloca should be
12// evaluated by the same checker that handles their non-builtin variant to
13// ensure that the two variants are handled consistently.
14//
15//===----------------------------------------------------------------------===//
16
17#include "clang/Basic/Builtins.h"
18#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
19#include "clang/StaticAnalyzer/Core/Checker.h"
20#include "clang/StaticAnalyzer/Core/CheckerManager.h"
21#include "clang/StaticAnalyzer/Core/PathSensitive/CallDescription.h"
22#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
23#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
24#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"
25
26using namespace clang;
27using namespace ento;
28
29namespace {
30
31class BuiltinFunctionChecker : public Checker<eval::Call> {
32public:
33 bool evalCall(const CallEvent &Call, CheckerContext &C) const;
34
35private:
36 // From: clang/include/clang/Basic/Builtins.def
37 // C++ standard library builtins in namespace 'std'.
38 const CallDescriptionSet BuiltinLikeStdFunctions{
39 {CDM::SimpleFunc, {"std", "addressof"}}, //
40 {CDM::SimpleFunc, {"std", "__addressof"}}, //
41 {CDM::SimpleFunc, {"std", "as_const"}}, //
42 {CDM::SimpleFunc, {"std", "forward"}}, //
43 {CDM::SimpleFunc, {"std", "forward_like"}}, //
44 {CDM::SimpleFunc, {"std", "move"}}, //
45 {CDM::SimpleFunc, {"std", "move_if_noexcept"}}, //
46 };
47
48 bool isBuiltinLikeFunction(const CallEvent &Call) const;
49};
50
51} // namespace
52
53bool BuiltinFunctionChecker::isBuiltinLikeFunction(
54 const CallEvent &Call) const {
55 const auto *FD = llvm::dyn_cast_or_null<FunctionDecl>(Val: Call.getDecl());
56 if (!FD || FD->getNumParams() != 1)
57 return false;
58
59 if (QualType RetTy = FD->getReturnType();
60 !RetTy->isPointerType() && !RetTy->isReferenceType())
61 return false;
62
63 if (QualType ParmTy = FD->getParamDecl(i: 0)->getType();
64 !ParmTy->isPointerType() && !ParmTy->isReferenceType())
65 return false;
66
67 return BuiltinLikeStdFunctions.contains(Call);
68}
69
70bool BuiltinFunctionChecker::evalCall(const CallEvent &Call,
71 CheckerContext &C) const {
72 ProgramStateRef state = C.getState();
73 const auto *FD = dyn_cast_or_null<FunctionDecl>(Val: Call.getDecl());
74 if (!FD)
75 return false;
76
77 const LocationContext *LCtx = C.getLocationContext();
78 const Expr *CE = Call.getOriginExpr();
79
80 if (isBuiltinLikeFunction(Call)) {
81 C.addTransition(State: state->BindExpr(S: CE, LCtx, V: Call.getArgSVal(Index: 0)));
82 return true;
83 }
84
85 switch (FD->getBuiltinID()) {
86 default:
87 return false;
88
89 case Builtin::BI__builtin_assume:
90 case Builtin::BI__assume: {
91 assert (Call.getNumArgs() > 0);
92 SVal Arg = Call.getArgSVal(Index: 0);
93 if (Arg.isUndef())
94 return true; // Return true to model purity.
95
96 state = state->assume(Cond: Arg.castAs<DefinedOrUnknownSVal>(), Assumption: true);
97 // FIXME: do we want to warn here? Not right now. The most reports might
98 // come from infeasible paths, thus being false positives.
99 if (!state) {
100 C.generateSink(State: C.getState(), Pred: C.getPredecessor());
101 return true;
102 }
103
104 C.addTransition(State: state);
105 return true;
106 }
107
108 case Builtin::BI__builtin_unpredictable:
109 case Builtin::BI__builtin_expect:
110 case Builtin::BI__builtin_expect_with_probability:
111 case Builtin::BI__builtin_assume_aligned:
112 case Builtin::BI__builtin_addressof:
113 case Builtin::BI__builtin_function_start: {
114 // For __builtin_unpredictable, __builtin_expect,
115 // __builtin_expect_with_probability and __builtin_assume_aligned,
116 // just return the value of the subexpression.
117 // __builtin_addressof is going from a reference to a pointer, but those
118 // are represented the same way in the analyzer.
119 assert (Call.getNumArgs() > 0);
120 SVal Arg = Call.getArgSVal(Index: 0);
121 C.addTransition(State: state->BindExpr(S: CE, LCtx, V: Arg));
122 return true;
123 }
124
125 case Builtin::BI__builtin_dynamic_object_size:
126 case Builtin::BI__builtin_object_size:
127 case Builtin::BI__builtin_constant_p: {
128 // This must be resolvable at compile time, so we defer to the constant
129 // evaluator for a value.
130 SValBuilder &SVB = C.getSValBuilder();
131 SVal V = UnknownVal();
132 Expr::EvalResult EVResult;
133 if (CE->EvaluateAsInt(Result&: EVResult, Ctx: C.getASTContext(), AllowSideEffects: Expr::SE_NoSideEffects)) {
134 // Make sure the result has the correct type.
135 llvm::APSInt Result = EVResult.Val.getInt();
136 BasicValueFactory &BVF = SVB.getBasicValueFactory();
137 BVF.getAPSIntType(T: CE->getType()).apply(Value&: Result);
138 V = SVB.makeIntVal(integer: Result);
139 }
140
141 if (FD->getBuiltinID() == Builtin::BI__builtin_constant_p) {
142 // If we didn't manage to figure out if the value is constant or not,
143 // it is safe to assume that it's not constant and unsafe to assume
144 // that it's constant.
145 if (V.isUnknown())
146 V = SVB.makeIntVal(integer: 0, type: CE->getType());
147 }
148
149 C.addTransition(State: state->BindExpr(S: CE, LCtx, V));
150 return true;
151 }
152 }
153}
154
155void ento::registerBuiltinFunctionChecker(CheckerManager &mgr) {
156 mgr.registerChecker<BuiltinFunctionChecker>();
157}
158
159bool ento::shouldRegisterBuiltinFunctionChecker(const CheckerManager &mgr) {
160 return true;
161}
162