1 //=-- ExprEngineObjC.cpp - ExprEngine support for Objective-C ---*- 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 file defines ExprEngine's support for Objective-C expressions.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/AST/StmtObjC.h"
15 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
16 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
17 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
18
19 using namespace clang;
20 using namespace ento;
21
VisitLvalObjCIvarRefExpr(const ObjCIvarRefExpr * Ex,ExplodedNode * Pred,ExplodedNodeSet & Dst)22 void ExprEngine::VisitLvalObjCIvarRefExpr(const ObjCIvarRefExpr *Ex,
23 ExplodedNode *Pred,
24 ExplodedNodeSet &Dst) {
25 ProgramStateRef state = Pred->getState();
26 const LocationContext *LCtx = Pred->getLocationContext();
27 SVal baseVal = state->getSVal(Ex->getBase(), LCtx);
28 SVal location = state->getLValue(Ex->getDecl(), baseVal);
29
30 ExplodedNodeSet dstIvar;
31 StmtNodeBuilder Bldr(Pred, dstIvar, *currBldrCtx);
32 Bldr.generateNode(Ex, Pred, state->BindExpr(Ex, LCtx, location));
33
34 // Perform the post-condition check of the ObjCIvarRefExpr and store
35 // the created nodes in 'Dst'.
36 getCheckerManager().runCheckersForPostStmt(Dst, dstIvar, Ex, *this);
37 }
38
VisitObjCAtSynchronizedStmt(const ObjCAtSynchronizedStmt * S,ExplodedNode * Pred,ExplodedNodeSet & Dst)39 void ExprEngine::VisitObjCAtSynchronizedStmt(const ObjCAtSynchronizedStmt *S,
40 ExplodedNode *Pred,
41 ExplodedNodeSet &Dst) {
42 getCheckerManager().runCheckersForPreStmt(Dst, Pred, S, *this);
43 }
44
45 /// Generate a node in \p Bldr for an iteration statement using ObjC
46 /// for-loop iterator.
populateObjCForDestinationSet(ExplodedNodeSet & dstLocation,SValBuilder & svalBuilder,const ObjCForCollectionStmt * S,const Stmt * elem,SVal elementV,SymbolManager & SymMgr,const NodeBuilderContext * currBldrCtx,StmtNodeBuilder & Bldr,bool hasElements)47 static void populateObjCForDestinationSet(
48 ExplodedNodeSet &dstLocation, SValBuilder &svalBuilder,
49 const ObjCForCollectionStmt *S, const Stmt *elem, SVal elementV,
50 SymbolManager &SymMgr, const NodeBuilderContext *currBldrCtx,
51 StmtNodeBuilder &Bldr, bool hasElements) {
52
53 for (ExplodedNode *Pred : dstLocation) {
54 ProgramStateRef state = Pred->getState();
55 const LocationContext *LCtx = Pred->getLocationContext();
56
57 SVal hasElementsV = svalBuilder.makeTruthVal(hasElements);
58
59 // FIXME: S is not an expression. We should not be binding values to it.
60 ProgramStateRef nextState = state->BindExpr(S, LCtx, hasElementsV);
61
62 if (auto MV = elementV.getAs<loc::MemRegionVal>())
63 if (const auto *R = dyn_cast<TypedValueRegion>(MV->getRegion())) {
64 // FIXME: The proper thing to do is to really iterate over the
65 // container. We will do this with dispatch logic to the store.
66 // For now, just 'conjure' up a symbolic value.
67 QualType T = R->getValueType();
68 assert(Loc::isLocType(T));
69
70 SVal V;
71 if (hasElements) {
72 SymbolRef Sym = SymMgr.conjureSymbol(elem, LCtx, T,
73 currBldrCtx->blockCount());
74 V = svalBuilder.makeLoc(Sym);
75 } else {
76 V = svalBuilder.makeIntVal(0, T);
77 }
78
79 nextState = nextState->bindLoc(elementV, V, LCtx);
80 }
81
82 Bldr.generateNode(S, Pred, nextState);
83 }
84 }
85
VisitObjCForCollectionStmt(const ObjCForCollectionStmt * S,ExplodedNode * Pred,ExplodedNodeSet & Dst)86 void ExprEngine::VisitObjCForCollectionStmt(const ObjCForCollectionStmt *S,
87 ExplodedNode *Pred,
88 ExplodedNodeSet &Dst) {
89
90 // ObjCForCollectionStmts are processed in two places. This method
91 // handles the case where an ObjCForCollectionStmt* occurs as one of the
92 // statements within a basic block. This transfer function does two things:
93 //
94 // (1) binds the next container value to 'element'. This creates a new
95 // node in the ExplodedGraph.
96 //
97 // (2) binds the value 0/1 to the ObjCForCollectionStmt* itself, indicating
98 // whether or not the container has any more elements. This value
99 // will be tested in ProcessBranch. We need to explicitly bind
100 // this value because a container can contain nil elements.
101 //
102 // FIXME: Eventually this logic should actually do dispatches to
103 // 'countByEnumeratingWithState:objects:count:' (NSFastEnumeration).
104 // This will require simulating a temporary NSFastEnumerationState, either
105 // through an SVal or through the use of MemRegions. This value can
106 // be affixed to the ObjCForCollectionStmt* instead of 0/1; when the loop
107 // terminates we reclaim the temporary (it goes out of scope) and we
108 // we can test if the SVal is 0 or if the MemRegion is null (depending
109 // on what approach we take).
110 //
111 // For now: simulate (1) by assigning either a symbol or nil if the
112 // container is empty. Thus this transfer function will by default
113 // result in state splitting.
114
115 const Stmt *elem = S->getElement();
116 const Stmt *collection = S->getCollection();
117 ProgramStateRef state = Pred->getState();
118 SVal collectionV = state->getSVal(collection, Pred->getLocationContext());
119
120 SVal elementV;
121 if (const auto *DS = dyn_cast<DeclStmt>(elem)) {
122 const VarDecl *elemD = cast<VarDecl>(DS->getSingleDecl());
123 assert(elemD->getInit() == nullptr);
124 elementV = state->getLValue(elemD, Pred->getLocationContext());
125 } else {
126 elementV = state->getSVal(elem, Pred->getLocationContext());
127 }
128
129 bool isContainerNull = state->isNull(collectionV).isConstrainedTrue();
130
131 ExplodedNodeSet dstLocation;
132 evalLocation(dstLocation, S, elem, Pred, state, elementV, false);
133
134 ExplodedNodeSet Tmp;
135 StmtNodeBuilder Bldr(Pred, Tmp, *currBldrCtx);
136
137 if (!isContainerNull)
138 populateObjCForDestinationSet(dstLocation, svalBuilder, S, elem, elementV,
139 SymMgr, currBldrCtx, Bldr,
140 /*hasElements=*/true);
141
142 populateObjCForDestinationSet(dstLocation, svalBuilder, S, elem, elementV,
143 SymMgr, currBldrCtx, Bldr,
144 /*hasElements=*/false);
145
146 // Finally, run any custom checkers.
147 // FIXME: Eventually all pre- and post-checks should live in VisitStmt.
148 getCheckerManager().runCheckersForPostStmt(Dst, Tmp, S, *this);
149 }
150
VisitObjCMessage(const ObjCMessageExpr * ME,ExplodedNode * Pred,ExplodedNodeSet & Dst)151 void ExprEngine::VisitObjCMessage(const ObjCMessageExpr *ME,
152 ExplodedNode *Pred,
153 ExplodedNodeSet &Dst) {
154 CallEventManager &CEMgr = getStateManager().getCallEventManager();
155 CallEventRef<ObjCMethodCall> Msg =
156 CEMgr.getObjCMethodCall(ME, Pred->getState(), Pred->getLocationContext());
157
158 // There are three cases for the receiver:
159 // (1) it is definitely nil,
160 // (2) it is definitely non-nil, and
161 // (3) we don't know.
162 //
163 // If the receiver is definitely nil, we skip the pre/post callbacks and
164 // instead call the ObjCMessageNil callbacks and return.
165 //
166 // If the receiver is definitely non-nil, we call the pre- callbacks,
167 // evaluate the call, and call the post- callbacks.
168 //
169 // If we don't know, we drop the potential nil flow and instead
170 // continue from the assumed non-nil state as in (2). This approach
171 // intentionally drops coverage in order to prevent false alarms
172 // in the following scenario:
173 //
174 // id result = [o someMethod]
175 // if (result) {
176 // if (!o) {
177 // // <-- This program point should be unreachable because if o is nil
178 // // it must the case that result is nil as well.
179 // }
180 // }
181 //
182 // We could avoid dropping coverage by performing an explicit case split
183 // on each method call -- but this would get very expensive. An alternative
184 // would be to introduce lazy constraints.
185 // FIXME: This ignores many potential bugs (<rdar://problem/11733396>).
186 // Revisit once we have lazier constraints.
187 if (Msg->isInstanceMessage()) {
188 SVal recVal = Msg->getReceiverSVal();
189 if (!recVal.isUndef()) {
190 // Bifurcate the state into nil and non-nil ones.
191 DefinedOrUnknownSVal receiverVal =
192 recVal.castAs<DefinedOrUnknownSVal>();
193 ProgramStateRef State = Pred->getState();
194
195 ProgramStateRef notNilState, nilState;
196 std::tie(notNilState, nilState) = State->assume(receiverVal);
197
198 // Receiver is definitely nil, so run ObjCMessageNil callbacks and return.
199 if (nilState && !notNilState) {
200 ExplodedNodeSet dstNil;
201 StmtNodeBuilder Bldr(Pred, dstNil, *currBldrCtx);
202 bool HasTag = Pred->getLocation().getTag();
203 Pred = Bldr.generateNode(ME, Pred, nilState, nullptr,
204 ProgramPoint::PreStmtKind);
205 assert((Pred || HasTag) && "Should have cached out already!");
206 (void)HasTag;
207 if (!Pred)
208 return;
209
210 ExplodedNodeSet dstPostCheckers;
211 getCheckerManager().runCheckersForObjCMessageNil(dstPostCheckers, Pred,
212 *Msg, *this);
213 for (auto I : dstPostCheckers)
214 finishArgumentConstruction(Dst, I, *Msg);
215 return;
216 }
217
218 ExplodedNodeSet dstNonNil;
219 StmtNodeBuilder Bldr(Pred, dstNonNil, *currBldrCtx);
220 // Generate a transition to the non-nil state, dropping any potential
221 // nil flow.
222 if (notNilState != State) {
223 bool HasTag = Pred->getLocation().getTag();
224 Pred = Bldr.generateNode(ME, Pred, notNilState);
225 assert((Pred || HasTag) && "Should have cached out already!");
226 (void)HasTag;
227 if (!Pred)
228 return;
229 }
230 }
231 }
232
233 // Handle the previsits checks.
234 ExplodedNodeSet dstPrevisit;
235 getCheckerManager().runCheckersForPreObjCMessage(dstPrevisit, Pred,
236 *Msg, *this);
237 ExplodedNodeSet dstGenericPrevisit;
238 getCheckerManager().runCheckersForPreCall(dstGenericPrevisit, dstPrevisit,
239 *Msg, *this);
240
241 // Proceed with evaluate the message expression.
242 ExplodedNodeSet dstEval;
243 StmtNodeBuilder Bldr(dstGenericPrevisit, dstEval, *currBldrCtx);
244
245 for (ExplodedNodeSet::iterator DI = dstGenericPrevisit.begin(),
246 DE = dstGenericPrevisit.end(); DI != DE; ++DI) {
247 ExplodedNode *Pred = *DI;
248 ProgramStateRef State = Pred->getState();
249 CallEventRef<ObjCMethodCall> UpdatedMsg = Msg.cloneWithState(State);
250
251 if (UpdatedMsg->isInstanceMessage()) {
252 SVal recVal = UpdatedMsg->getReceiverSVal();
253 if (!recVal.isUndef()) {
254 if (ObjCNoRet.isImplicitNoReturn(ME)) {
255 // If we raise an exception, for now treat it as a sink.
256 // Eventually we will want to handle exceptions properly.
257 Bldr.generateSink(ME, Pred, State);
258 continue;
259 }
260 }
261 } else {
262 // Check for special class methods that are known to not return
263 // and that we should treat as a sink.
264 if (ObjCNoRet.isImplicitNoReturn(ME)) {
265 // If we raise an exception, for now treat it as a sink.
266 // Eventually we will want to handle exceptions properly.
267 Bldr.generateSink(ME, Pred, Pred->getState());
268 continue;
269 }
270 }
271
272 defaultEvalCall(Bldr, Pred, *UpdatedMsg);
273 }
274
275 // If there were constructors called for object-type arguments, clean them up.
276 ExplodedNodeSet dstArgCleanup;
277 for (auto I : dstEval)
278 finishArgumentConstruction(dstArgCleanup, I, *Msg);
279
280 ExplodedNodeSet dstPostvisit;
281 getCheckerManager().runCheckersForPostCall(dstPostvisit, dstArgCleanup,
282 *Msg, *this);
283
284 // Finally, perform the post-condition check of the ObjCMessageExpr and store
285 // the created nodes in 'Dst'.
286 getCheckerManager().runCheckersForPostObjCMessage(Dst, dstPostvisit,
287 *Msg, *this);
288 }
289