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/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
14#include "clang/Basic/Builtins.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
20using namespace clang;
21using namespace ento;
22
23namespace {
24
25class BuiltinFunctionChecker : public Checker<eval::Call> {
26public:
27  bool evalCall(const CallEvent &Call, CheckerContext &C) const;
28};
29
30}
31
32bool BuiltinFunctionChecker::evalCall(const CallEvent &Call,
33                                      CheckerContext &C) const {
34  ProgramStateRef state = C.getState();
35  const auto *FD = dyn_cast_or_null<FunctionDecl>(Call.getDecl());
36  if (!FD)
37    return false;
38
39  const LocationContext *LCtx = C.getLocationContext();
40  const Expr *CE = Call.getOriginExpr();
41
42  switch (FD->getBuiltinID()) {
43  default:
44    return false;
45
46  case Builtin::BI__builtin_assume: {
47    assert (Call.getNumArgs() > 0);
48    SVal Arg = Call.getArgSVal(0);
49    if (Arg.isUndef())
50      return true; // Return true to model purity.
51
52    state = state->assume(Arg.castAs<DefinedOrUnknownSVal>(), true);
53    // FIXME: do we want to warn here? Not right now. The most reports might
54    // come from infeasible paths, thus being false positives.
55    if (!state) {
56      C.generateSink(C.getState(), C.getPredecessor());
57      return true;
58    }
59
60    C.addTransition(state);
61    return true;
62  }
63
64  case Builtin::BI__builtin_unpredictable:
65  case Builtin::BI__builtin_expect:
66  case Builtin::BI__builtin_assume_aligned:
67  case Builtin::BI__builtin_addressof: {
68    // For __builtin_unpredictable, __builtin_expect, and
69    // __builtin_assume_aligned, just return the value of the subexpression.
70    // __builtin_addressof is going from a reference to a pointer, but those
71    // are represented the same way in the analyzer.
72    assert (Call.getNumArgs() > 0);
73    SVal Arg = Call.getArgSVal(0);
74    C.addTransition(state->BindExpr(CE, LCtx, Arg));
75    return true;
76  }
77
78  case Builtin::BI__builtin_alloca_with_align:
79  case Builtin::BI__builtin_alloca: {
80    // FIXME: Refactor into StoreManager itself?
81    MemRegionManager& RM = C.getStoreManager().getRegionManager();
82    const AllocaRegion* R =
83      RM.getAllocaRegion(CE, C.blockCount(), C.getLocationContext());
84
85    // Set the extent of the region in bytes. This enables us to use the
86    // SVal of the argument directly. If we save the extent in bits, we
87    // cannot represent values like symbol*8.
88    auto Size = Call.getArgSVal(0);
89    if (Size.isUndef())
90      return true; // Return true to model purity.
91
92    SValBuilder& svalBuilder = C.getSValBuilder();
93    DefinedOrUnknownSVal Extent = R->getExtent(svalBuilder);
94    DefinedOrUnknownSVal extentMatchesSizeArg =
95      svalBuilder.evalEQ(state, Extent, Size.castAs<DefinedOrUnknownSVal>());
96    state = state->assume(extentMatchesSizeArg, true);
97    assert(state && "The region should not have any previous constraints");
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
133void ento::registerBuiltinFunctionChecker(CheckerManager &mgr) {
134  mgr.registerChecker<BuiltinFunctionChecker>();
135}
136
137bool ento::shouldRegisterBuiltinFunctionChecker(const LangOptions &LO) {
138  return true;
139}
140