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/CallEvent.h" 22 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 23 #include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h" 24 25 using namespace clang; 26 using namespace ento; 27 28 namespace { 29 30 class BuiltinFunctionChecker : public Checker<eval::Call> { 31 public: 32 bool evalCall(const CallEvent &Call, CheckerContext &C) const; 33 }; 34 35 } 36 37 bool BuiltinFunctionChecker::evalCall(const CallEvent &Call, 38 CheckerContext &C) const { 39 ProgramStateRef state = C.getState(); 40 const auto *FD = dyn_cast_or_null<FunctionDecl>(Call.getDecl()); 41 if (!FD) 42 return false; 43 44 const LocationContext *LCtx = C.getLocationContext(); 45 const Expr *CE = Call.getOriginExpr(); 46 47 switch (FD->getBuiltinID()) { 48 default: 49 return false; 50 51 case Builtin::BI__builtin_assume: 52 case Builtin::BI__assume: { 53 assert (Call.getNumArgs() > 0); 54 SVal Arg = Call.getArgSVal(0); 55 if (Arg.isUndef()) 56 return true; // Return true to model purity. 57 58 state = state->assume(Arg.castAs<DefinedOrUnknownSVal>(), true); 59 // FIXME: do we want to warn here? Not right now. The most reports might 60 // come from infeasible paths, thus being false positives. 61 if (!state) { 62 C.generateSink(C.getState(), C.getPredecessor()); 63 return true; 64 } 65 66 C.addTransition(state); 67 return true; 68 } 69 70 case Builtin::BI__builtin_unpredictable: 71 case Builtin::BI__builtin_expect: 72 case Builtin::BI__builtin_expect_with_probability: 73 case Builtin::BI__builtin_assume_aligned: 74 case Builtin::BI__builtin_addressof: 75 case Builtin::BI__builtin_function_start: { 76 // For __builtin_unpredictable, __builtin_expect, 77 // __builtin_expect_with_probability and __builtin_assume_aligned, 78 // just return the value of the subexpression. 79 // __builtin_addressof is going from a reference to a pointer, but those 80 // are represented the same way in the analyzer. 81 assert (Call.getNumArgs() > 0); 82 SVal Arg = Call.getArgSVal(0); 83 C.addTransition(state->BindExpr(CE, LCtx, Arg)); 84 return true; 85 } 86 87 case Builtin::BI__builtin_dynamic_object_size: 88 case Builtin::BI__builtin_object_size: 89 case Builtin::BI__builtin_constant_p: { 90 // This must be resolvable at compile time, so we defer to the constant 91 // evaluator for a value. 92 SValBuilder &SVB = C.getSValBuilder(); 93 SVal V = UnknownVal(); 94 Expr::EvalResult EVResult; 95 if (CE->EvaluateAsInt(EVResult, C.getASTContext(), Expr::SE_NoSideEffects)) { 96 // Make sure the result has the correct type. 97 llvm::APSInt Result = EVResult.Val.getInt(); 98 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 99 BVF.getAPSIntType(CE->getType()).apply(Result); 100 V = SVB.makeIntVal(Result); 101 } 102 103 if (FD->getBuiltinID() == Builtin::BI__builtin_constant_p) { 104 // If we didn't manage to figure out if the value is constant or not, 105 // it is safe to assume that it's not constant and unsafe to assume 106 // that it's constant. 107 if (V.isUnknown()) 108 V = SVB.makeIntVal(0, CE->getType()); 109 } 110 111 C.addTransition(state->BindExpr(CE, LCtx, V)); 112 return true; 113 } 114 } 115 } 116 117 void ento::registerBuiltinFunctionChecker(CheckerManager &mgr) { 118 mgr.registerChecker<BuiltinFunctionChecker>(); 119 } 120 121 bool ento::shouldRegisterBuiltinFunctionChecker(const CheckerManager &mgr) { 122 return true; 123 } 124