//=-- ExprEngineObjC.cpp - ExprEngine support for Objective-C ---*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines ExprEngine's support for Objective-C expressions.
//
//===----------------------------------------------------------------------===//
#include "clang/AST/StmtObjC.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
using namespace clang;
using namespace ento;
void ExprEngine::VisitLvalObjCIvarRefExpr(const ObjCIvarRefExpr *Ex,
ExplodedNode *Pred,
ExplodedNodeSet &Dst) {
ProgramStateRef state = Pred->getState();
const LocationContext *LCtx = Pred->getLocationContext();
SVal baseVal = state->getSVal(Ex->getBase(), LCtx);
SVal location = state->getLValue(Ex->getDecl(), baseVal);
ExplodedNodeSet dstIvar;
StmtNodeBuilder Bldr(Pred, dstIvar, *currBldrCtx);
Bldr.generateNode(Ex, Pred, state->BindExpr(Ex, LCtx, location));
// Perform the post-condition check of the ObjCIvarRefExpr and store
// the created nodes in 'Dst'.
getCheckerManager().runCheckersForPostStmt(Dst, dstIvar, Ex, *this);
}
void ExprEngine::VisitObjCAtSynchronizedStmt(const ObjCAtSynchronizedStmt *S,
ExplodedNode *Pred,
ExplodedNodeSet &Dst) {
getCheckerManager().runCheckersForPreStmt(Dst, Pred, S, *this);
}
void ExprEngine::VisitObjCForCollectionStmt(const ObjCForCollectionStmt *S,
ExplodedNode *Pred,
ExplodedNodeSet &Dst) {
// ObjCForCollectionStmts are processed in two places. This method
// handles the case where an ObjCForCollectionStmt* occurs as one of the
// statements within a basic block. This transfer function does two things:
//
// (1) binds the next container value to 'element'. This creates a new
// node in the ExplodedGraph.
//
// (2) binds the value 0/1 to the ObjCForCollectionStmt* itself, indicating
// whether or not the container has any more elements. This value
// will be tested in ProcessBranch. We need to explicitly bind
// this value because a container can contain nil elements.
//
// FIXME: Eventually this logic should actually do dispatches to
// 'countByEnumeratingWithState:objects:count:' (NSFastEnumeration).
// This will require simulating a temporary NSFastEnumerationState, either
// through an SVal or through the use of MemRegions. This value can
// be affixed to the ObjCForCollectionStmt* instead of 0/1; when the loop
// terminates we reclaim the temporary (it goes out of scope) and we
// we can test if the SVal is 0 or if the MemRegion is null (depending
// on what approach we take).
//
// For now: simulate (1) by assigning either a symbol or nil if the
// container is empty. Thus this transfer function will by default
// result in state splitting.
const Stmt *elem = S->getElement();
ProgramStateRef state = Pred->getState();
SVal elementV;
if (const DeclStmt *DS = dyn_cast<DeclStmt>(elem)) {
const VarDecl *elemD = cast<VarDecl>(DS->getSingleDecl());
assert(elemD->getInit() == nullptr);
elementV = state->getLValue(elemD, Pred->getLocationContext());
}
else {
elementV = state->getSVal(elem, Pred->getLocationContext());
}
ExplodedNodeSet dstLocation;
evalLocation(dstLocation, S, elem, Pred, state, elementV, nullptr, false);
ExplodedNodeSet Tmp;
StmtNodeBuilder Bldr(Pred, Tmp, *currBldrCtx);
for (ExplodedNodeSet::iterator NI = dstLocation.begin(),
NE = dstLocation.end(); NI!=NE; ++NI) {
Pred = *NI;
ProgramStateRef state = Pred->getState();
const LocationContext *LCtx = Pred->getLocationContext();
// Handle the case where the container still has elements.
SVal TrueV = svalBuilder.makeTruthVal(1);
ProgramStateRef hasElems = state->BindExpr(S, LCtx, TrueV);
// Handle the case where the container has no elements.
SVal FalseV = svalBuilder.makeTruthVal(0);
ProgramStateRef noElems = state->BindExpr(S, LCtx, FalseV);
if (Optional<loc::MemRegionVal> MV = elementV.getAs<loc::MemRegionVal>())
if (const TypedValueRegion *R =
dyn_cast<TypedValueRegion>(MV->getRegion())) {
// FIXME: The proper thing to do is to really iterate over the
// container. We will do this with dispatch logic to the store.
// For now, just 'conjure' up a symbolic value.
QualType T = R->getValueType();
assert(Loc::isLocType(T));
SymbolRef Sym = SymMgr.conjureSymbol(elem, LCtx, T,
currBldrCtx->blockCount());
SVal V = svalBuilder.makeLoc(Sym);
hasElems = hasElems->bindLoc(elementV, V);
// Bind the location to 'nil' on the false branch.
SVal nilV = svalBuilder.makeIntVal(0, T);
noElems = noElems->bindLoc(elementV, nilV);
}
// Create the new nodes.
Bldr.generateNode(S, Pred, hasElems);
Bldr.generateNode(S, Pred, noElems);
}
// Finally, run any custom checkers.
// FIXME: Eventually all pre- and post-checks should live in VisitStmt.
getCheckerManager().runCheckersForPostStmt(Dst, Tmp, S, *this);
}
void ExprEngine::VisitObjCMessage(const ObjCMessageExpr *ME,
ExplodedNode *Pred,
ExplodedNodeSet &Dst) {
CallEventManager &CEMgr = getStateManager().getCallEventManager();
CallEventRef<ObjCMethodCall> Msg =
CEMgr.getObjCMethodCall(ME, Pred->getState(), Pred->getLocationContext());
// There are three cases for the receiver:
// (1) it is definitely nil,
// (2) it is definitely non-nil, and
// (3) we don't know.
//
// If the receiver is definitely nil, we skip the pre/post callbacks and
// instead call the ObjCMessageNil callbacks and return.
//
// If the receiver is definitely non-nil, we call the pre- callbacks,
// evaluate the call, and call the post- callbacks.
//
// If we don't know, we drop the potential nil flow and instead
// continue from the assumed non-nil state as in (2). This approach
// intentionally drops coverage in order to prevent false alarms
// in the following scenario:
//
// id result = [o someMethod]
// if (result) {
// if (!o) {
// // <-- This program point should be unreachable because if o is nil
// // it must the case that result is nil as well.
// }
// }
//
// We could avoid dropping coverage by performing an explicit case split
// on each method call -- but this would get very expensive. An alternative
// would be to introduce lazy constraints.
// FIXME: This ignores many potential bugs (<rdar://problem/11733396>).
// Revisit once we have lazier constraints.
if (Msg->isInstanceMessage()) {
SVal recVal = Msg->getReceiverSVal();
if (!recVal.isUndef()) {
// Bifurcate the state into nil and non-nil ones.
DefinedOrUnknownSVal receiverVal =
recVal.castAs<DefinedOrUnknownSVal>();
ProgramStateRef State = Pred->getState();
ProgramStateRef notNilState, nilState;
std::tie(notNilState, nilState) = State->assume(receiverVal);
// Receiver is definitely nil, so run ObjCMessageNil callbacks and return.
if (nilState && !notNilState) {
StmtNodeBuilder Bldr(Pred, Dst, *currBldrCtx);
bool HasTag = Pred->getLocation().getTag();
Pred = Bldr.generateNode(ME, Pred, nilState, nullptr,
ProgramPoint::PreStmtKind);
assert((Pred || HasTag) && "Should have cached out already!");
(void)HasTag;
if (!Pred)
return;
getCheckerManager().runCheckersForObjCMessageNil(Dst, Pred,
*Msg, *this);
return;
}
ExplodedNodeSet dstNonNil;
StmtNodeBuilder Bldr(Pred, dstNonNil, *currBldrCtx);
// Generate a transition to the non-nil state, dropping any potential
// nil flow.
if (notNilState != State) {
bool HasTag = Pred->getLocation().getTag();
Pred = Bldr.generateNode(ME, Pred, notNilState);
assert((Pred || HasTag) && "Should have cached out already!");
(void)HasTag;
if (!Pred)
return;
}
}
}
// Handle the previsits checks.
ExplodedNodeSet dstPrevisit;
getCheckerManager().runCheckersForPreObjCMessage(dstPrevisit, Pred,
*Msg, *this);
ExplodedNodeSet dstGenericPrevisit;
getCheckerManager().runCheckersForPreCall(dstGenericPrevisit, dstPrevisit,
*Msg, *this);
// Proceed with evaluate the message expression.
ExplodedNodeSet dstEval;
StmtNodeBuilder Bldr(dstGenericPrevisit, dstEval, *currBldrCtx);
for (ExplodedNodeSet::iterator DI = dstGenericPrevisit.begin(),
DE = dstGenericPrevisit.end(); DI != DE; ++DI) {
ExplodedNode *Pred = *DI;
ProgramStateRef State = Pred->getState();
CallEventRef<ObjCMethodCall> UpdatedMsg = Msg.cloneWithState(State);
if (UpdatedMsg->isInstanceMessage()) {
SVal recVal = UpdatedMsg->getReceiverSVal();
if (!recVal.isUndef()) {
if (ObjCNoRet.isImplicitNoReturn(ME)) {
// If we raise an exception, for now treat it as a sink.
// Eventually we will want to handle exceptions properly.
Bldr.generateSink(ME, Pred, State);
continue;
}
}
} else {
// Check for special class methods that are known to not return
// and that we should treat as a sink.
if (ObjCNoRet.isImplicitNoReturn(ME)) {
// If we raise an exception, for now treat it as a sink.
// Eventually we will want to handle exceptions properly.
Bldr.generateSink(ME, Pred, Pred->getState());
continue;
}
}
defaultEvalCall(Bldr, Pred, *UpdatedMsg);
}
ExplodedNodeSet dstPostvisit;
getCheckerManager().runCheckersForPostCall(dstPostvisit, dstEval,
*Msg, *this);
// Finally, perform the post-condition check of the ObjCMessageExpr and store
// the created nodes in 'Dst'.
getCheckerManager().runCheckersForPostObjCMessage(Dst, dstPostvisit,
*Msg, *this);
}