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 clang builtin functions. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "clang/Basic/Builtins.h" 14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 15 #include "clang/StaticAnalyzer/Core/Checker.h" 16 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 17 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h" 18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 19 #include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h" 20 21 using namespace clang; 22 using namespace ento; 23 24 namespace { 25 26 class BuiltinFunctionChecker : public Checker<eval::Call> { 27 public: 28 bool evalCall(const CallEvent &Call, CheckerContext &C) const; 29 }; 30 31 } 32 33 bool BuiltinFunctionChecker::evalCall(const CallEvent &Call, 34 CheckerContext &C) const { 35 ProgramStateRef state = C.getState(); 36 const auto *FD = dyn_cast_or_null<FunctionDecl>(Call.getDecl()); 37 if (!FD) 38 return false; 39 40 const LocationContext *LCtx = C.getLocationContext(); 41 const Expr *CE = Call.getOriginExpr(); 42 43 switch (FD->getBuiltinID()) { 44 default: 45 return false; 46 47 case Builtin::BI__builtin_assume: { 48 assert (Call.getNumArgs() > 0); 49 SVal Arg = Call.getArgSVal(0); 50 if (Arg.isUndef()) 51 return true; // Return true to model purity. 52 53 state = state->assume(Arg.castAs<DefinedOrUnknownSVal>(), true); 54 // FIXME: do we want to warn here? Not right now. The most reports might 55 // come from infeasible paths, thus being false positives. 56 if (!state) { 57 C.generateSink(C.getState(), C.getPredecessor()); 58 return true; 59 } 60 61 C.addTransition(state); 62 return true; 63 } 64 65 case Builtin::BI__builtin_unpredictable: 66 case Builtin::BI__builtin_expect: 67 case Builtin::BI__builtin_expect_with_probability: 68 case Builtin::BI__builtin_assume_aligned: 69 case Builtin::BI__builtin_addressof: 70 case Builtin::BI__builtin_function_start: { 71 // For __builtin_unpredictable, __builtin_expect, 72 // __builtin_expect_with_probability and __builtin_assume_aligned, 73 // just return the value of the subexpression. 74 // __builtin_addressof is going from a reference to a pointer, but those 75 // are represented the same way in the analyzer. 76 assert (Call.getNumArgs() > 0); 77 SVal Arg = Call.getArgSVal(0); 78 C.addTransition(state->BindExpr(CE, LCtx, Arg)); 79 return true; 80 } 81 82 case Builtin::BI__builtin_alloca_with_align: 83 case Builtin::BI__builtin_alloca: { 84 // FIXME: Refactor into StoreManager itself? 85 MemRegionManager& RM = C.getStoreManager().getRegionManager(); 86 const AllocaRegion* R = 87 RM.getAllocaRegion(CE, C.blockCount(), C.getLocationContext()); 88 89 // Set the extent of the region in bytes. This enables us to use the 90 // SVal of the argument directly. If we save the extent in bits, we 91 // cannot represent values like symbol*8. 92 auto Size = Call.getArgSVal(0); 93 if (Size.isUndef()) 94 return true; // Return true to model purity. 95 96 state = setDynamicExtent(state, R, Size.castAs<DefinedOrUnknownSVal>(), 97 C.getSValBuilder()); 98 99 C.addTransition(state->BindExpr(CE, LCtx, loc::MemRegionVal(R))); 100 return true; 101 } 102 103 case Builtin::BI__builtin_dynamic_object_size: 104 case Builtin::BI__builtin_object_size: 105 case Builtin::BI__builtin_constant_p: { 106 // This must be resolvable at compile time, so we defer to the constant 107 // evaluator for a value. 108 SValBuilder &SVB = C.getSValBuilder(); 109 SVal V = UnknownVal(); 110 Expr::EvalResult EVResult; 111 if (CE->EvaluateAsInt(EVResult, C.getASTContext(), Expr::SE_NoSideEffects)) { 112 // Make sure the result has the correct type. 113 llvm::APSInt Result = EVResult.Val.getInt(); 114 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 115 BVF.getAPSIntType(CE->getType()).apply(Result); 116 V = SVB.makeIntVal(Result); 117 } 118 119 if (FD->getBuiltinID() == Builtin::BI__builtin_constant_p) { 120 // If we didn't manage to figure out if the value is constant or not, 121 // it is safe to assume that it's not constant and unsafe to assume 122 // that it's constant. 123 if (V.isUnknown()) 124 V = SVB.makeIntVal(0, CE->getType()); 125 } 126 127 C.addTransition(state->BindExpr(CE, LCtx, V)); 128 return true; 129 } 130 } 131 } 132 133 void ento::registerBuiltinFunctionChecker(CheckerManager &mgr) { 134 mgr.registerChecker<BuiltinFunctionChecker>(); 135 } 136 137 bool ento::shouldRegisterBuiltinFunctionChecker(const CheckerManager &mgr) { 138 return true; 139 } 140