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