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      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     // For __builtin_unpredictable, __builtin_expect,
     71     // __builtin_expect_with_probability and __builtin_assume_aligned,
     72     // just return the value of the subexpression.
     73     // __builtin_addressof is going from a reference to a pointer, but those
     74     // are represented the same way in the analyzer.
     75     assert (Call.getNumArgs() > 0);
     76     SVal Arg = Call.getArgSVal(0);
     77     C.addTransition(state->BindExpr(CE, LCtx, Arg));
     78     return true;
     79   }
     80 
     81   case Builtin::BI__builtin_alloca_with_align:
     82   case Builtin::BI__builtin_alloca: {
     83     // FIXME: Refactor into StoreManager itself?
     84     MemRegionManager& RM = C.getStoreManager().getRegionManager();
     85     const AllocaRegion* R =
     86       RM.getAllocaRegion(CE, C.blockCount(), C.getLocationContext());
     87 
     88     // Set the extent of the region in bytes. This enables us to use the
     89     // SVal of the argument directly. If we save the extent in bits, we
     90     // cannot represent values like symbol*8.
     91     auto Size = Call.getArgSVal(0);
     92     if (Size.isUndef())
     93       return true; // Return true to model purity.
     94 
     95     state = setDynamicExtent(state, R, Size.castAs<DefinedOrUnknownSVal>(),
     96                              C.getSValBuilder());
     97 
     98     C.addTransition(state->BindExpr(CE, LCtx, loc::MemRegionVal(R)));
     99     return true;
    100   }
    101 
    102   case Builtin::BI__builtin_dynamic_object_size:
    103   case Builtin::BI__builtin_object_size:
    104   case Builtin::BI__builtin_constant_p: {
    105     // This must be resolvable at compile time, so we defer to the constant
    106     // evaluator for a value.
    107     SValBuilder &SVB = C.getSValBuilder();
    108     SVal V = UnknownVal();
    109     Expr::EvalResult EVResult;
    110     if (CE->EvaluateAsInt(EVResult, C.getASTContext(), Expr::SE_NoSideEffects)) {
    111       // Make sure the result has the correct type.
    112       llvm::APSInt Result = EVResult.Val.getInt();
    113       BasicValueFactory &BVF = SVB.getBasicValueFactory();
    114       BVF.getAPSIntType(CE->getType()).apply(Result);
    115       V = SVB.makeIntVal(Result);
    116     }
    117 
    118     if (FD->getBuiltinID() == Builtin::BI__builtin_constant_p) {
    119       // If we didn't manage to figure out if the value is constant or not,
    120       // it is safe to assume that it's not constant and unsafe to assume
    121       // that it's constant.
    122       if (V.isUnknown())
    123         V = SVB.makeIntVal(0, CE->getType());
    124     }
    125 
    126     C.addTransition(state->BindExpr(CE, LCtx, V));
    127     return true;
    128   }
    129   }
    130 }
    131 
    132 void ento::registerBuiltinFunctionChecker(CheckerManager &mgr) {
    133   mgr.registerChecker<BuiltinFunctionChecker>();
    134 }
    135 
    136 bool ento::shouldRegisterBuiltinFunctionChecker(const CheckerManager &mgr) {
    137   return true;
    138 }
    139