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 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 39 void ExprEngine::VisitObjCAtSynchronizedStmt(const ObjCAtSynchronizedStmt *S, 40 ExplodedNode *Pred, 41 ExplodedNodeSet &Dst) { 42 getCheckerManager().runCheckersForPreStmt(Dst, Pred, S, *this); 43 } 44 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 } 134 135 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
