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
21using namespace clang;
22using namespace ento;
23
24namespace {
25
26class BuiltinFunctionChecker : public Checker<eval::Call> {
27public:
28  bool evalCall(const CallEvent &Call, CheckerContext &C) const;
29};
30
31}
32
33bool 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
133void ento::registerBuiltinFunctionChecker(CheckerManager &mgr) {
134  mgr.registerChecker<BuiltinFunctionChecker>();
135}
136
137bool ento::shouldRegisterBuiltinFunctionChecker(const CheckerManager &mgr) {
138  return true;
139}
140