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1 //=== BuiltinFunctionChecker.cpp --------------------------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This checker evaluates clang builtin functions.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "ClangSACheckers.h"
15 #include "clang/Basic/Builtins.h"
16 #include "clang/StaticAnalyzer/Core/Checker.h"
17 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19 
20 using namespace clang;
21 using namespace ento;
22 
23 namespace {
24 
25 class BuiltinFunctionChecker : public Checker<eval::Call> {
26 public:
27   bool evalCall(const CallExpr *CE, CheckerContext &C) const;
28 };
29 
30 }
31 
evalCall(const CallExpr * CE,CheckerContext & C) const32 bool BuiltinFunctionChecker::evalCall(const CallExpr *CE,
33                                       CheckerContext &C) const {
34   ProgramStateRef state = C.getState();
35   const FunctionDecl *FD = C.getCalleeDecl(CE);
36   const LocationContext *LCtx = C.getLocationContext();
37   if (!FD)
38     return false;
39 
40   switch (FD->getBuiltinID()) {
41   default:
42     return false;
43 
44   case Builtin::BI__builtin_expect:
45   case Builtin::BI__builtin_addressof: {
46     // For __builtin_expect, just return the value of the subexpression.
47     // __builtin_addressof is going from a reference to a pointer, but those
48     // are represented the same way in the analyzer.
49     assert (CE->arg_begin() != CE->arg_end());
50     SVal X = state->getSVal(*(CE->arg_begin()), LCtx);
51     C.addTransition(state->BindExpr(CE, LCtx, X));
52     return true;
53   }
54 
55   case Builtin::BI__builtin_alloca: {
56     // FIXME: Refactor into StoreManager itself?
57     MemRegionManager& RM = C.getStoreManager().getRegionManager();
58     const AllocaRegion* R =
59       RM.getAllocaRegion(CE, C.blockCount(), C.getLocationContext());
60 
61     // Set the extent of the region in bytes. This enables us to use the
62     // SVal of the argument directly. If we save the extent in bits, we
63     // cannot represent values like symbol*8.
64     DefinedOrUnknownSVal Size =
65         state->getSVal(*(CE->arg_begin()), LCtx).castAs<DefinedOrUnknownSVal>();
66 
67     SValBuilder& svalBuilder = C.getSValBuilder();
68     DefinedOrUnknownSVal Extent = R->getExtent(svalBuilder);
69     DefinedOrUnknownSVal extentMatchesSizeArg =
70       svalBuilder.evalEQ(state, Extent, Size);
71     state = state->assume(extentMatchesSizeArg, true);
72     assert(state && "The region should not have any previous constraints");
73 
74     C.addTransition(state->BindExpr(CE, LCtx, loc::MemRegionVal(R)));
75     return true;
76   }
77 
78   case Builtin::BI__builtin_object_size: {
79     // This must be resolvable at compile time, so we defer to the constant
80     // evaluator for a value.
81     SVal V = UnknownVal();
82     llvm::APSInt Result;
83     if (CE->EvaluateAsInt(Result, C.getASTContext(), Expr::SE_NoSideEffects)) {
84       // Make sure the result has the correct type.
85       SValBuilder &SVB = C.getSValBuilder();
86       BasicValueFactory &BVF = SVB.getBasicValueFactory();
87       BVF.getAPSIntType(CE->getType()).apply(Result);
88       V = SVB.makeIntVal(Result);
89     }
90 
91     C.addTransition(state->BindExpr(CE, LCtx, V));
92     return true;
93   }
94   }
95 }
96 
registerBuiltinFunctionChecker(CheckerManager & mgr)97 void ento::registerBuiltinFunctionChecker(CheckerManager &mgr) {
98   mgr.registerChecker<BuiltinFunctionChecker>();
99 }
100