1 //===--- TransUnbridgedCasts.cpp - Transformations to ARC mode ------------===//
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 // rewriteUnbridgedCasts:
10 //
11 // A cast of non-objc pointer to an objc one is checked. If the non-objc pointer
12 // is from a file-level variable, __bridge cast is used to convert it.
13 // For the result of a function call that we know is +1/+0,
14 // __bridge/CFBridgingRelease is used.
15 //
16 //  NSString *str = (NSString *)kUTTypePlainText;
17 //  str = b ? kUTTypeRTF : kUTTypePlainText;
18 //  NSString *_uuidString = (NSString *)CFUUIDCreateString(kCFAllocatorDefault,
19 //                                                         _uuid);
20 // ---->
21 //  NSString *str = (__bridge NSString *)kUTTypePlainText;
22 //  str = (__bridge NSString *)(b ? kUTTypeRTF : kUTTypePlainText);
23 // NSString *_uuidString = (NSString *)
24 //            CFBridgingRelease(CFUUIDCreateString(kCFAllocatorDefault, _uuid));
25 //
26 // For a C pointer to ObjC, for casting 'self', __bridge is used.
27 //
28 //  CFStringRef str = (CFStringRef)self;
29 // ---->
30 //  CFStringRef str = (__bridge CFStringRef)self;
31 //
32 // Uses of Block_copy/Block_release macros are rewritten:
33 //
34 //  c = Block_copy(b);
35 //  Block_release(c);
36 // ---->
37 //  c = [b copy];
38 //  <removed>
39 //
40 //===----------------------------------------------------------------------===//
41 
42 #include "Transforms.h"
43 #include "Internals.h"
44 #include "clang/AST/ASTContext.h"
45 #include "clang/AST/Attr.h"
46 #include "clang/AST/ParentMap.h"
47 #include "clang/Analysis/DomainSpecific/CocoaConventions.h"
48 #include "clang/Basic/SourceManager.h"
49 #include "clang/Lex/Lexer.h"
50 #include "clang/Sema/SemaDiagnostic.h"
51 #include "llvm/ADT/SmallString.h"
52 
53 using namespace clang;
54 using namespace arcmt;
55 using namespace trans;
56 
57 namespace {
58 
59 class UnbridgedCastRewriter : public RecursiveASTVisitor<UnbridgedCastRewriter>{
60   MigrationPass &Pass;
61   IdentifierInfo *SelfII;
62   std::unique_ptr<ParentMap> StmtMap;
63   Decl *ParentD;
64   Stmt *Body;
65   mutable std::unique_ptr<ExprSet> Removables;
66 
67 public:
68   UnbridgedCastRewriter(MigrationPass &pass)
69     : Pass(pass), ParentD(nullptr), Body(nullptr) {
70     SelfII = &Pass.Ctx.Idents.get("self");
71   }
72 
73   void transformBody(Stmt *body, Decl *ParentD) {
74     this->ParentD = ParentD;
75     Body = body;
76     StmtMap.reset(new ParentMap(body));
77     TraverseStmt(body);
78   }
79 
80   bool TraverseBlockDecl(BlockDecl *D) {
81     // ParentMap does not enter into a BlockDecl to record its stmts, so use a
82     // new UnbridgedCastRewriter to handle the block.
83     UnbridgedCastRewriter(Pass).transformBody(D->getBody(), D);
84     return true;
85   }
86 
87   bool VisitCastExpr(CastExpr *E) {
88     if (E->getCastKind() != CK_CPointerToObjCPointerCast &&
89         E->getCastKind() != CK_BitCast &&
90         E->getCastKind() != CK_AnyPointerToBlockPointerCast)
91       return true;
92 
93     QualType castType = E->getType();
94     Expr *castExpr = E->getSubExpr();
95     QualType castExprType = castExpr->getType();
96 
97     if (castType->isObjCRetainableType() == castExprType->isObjCRetainableType())
98       return true;
99 
100     bool exprRetainable = castExprType->isObjCIndirectLifetimeType();
101     bool castRetainable = castType->isObjCIndirectLifetimeType();
102     if (exprRetainable == castRetainable) return true;
103 
104     if (castExpr->isNullPointerConstant(Pass.Ctx,
105                                         Expr::NPC_ValueDependentIsNull))
106       return true;
107 
108     SourceLocation loc = castExpr->getExprLoc();
109     if (loc.isValid() && Pass.Ctx.getSourceManager().isInSystemHeader(loc))
110       return true;
111 
112     if (castType->isObjCRetainableType())
113       transformNonObjCToObjCCast(E);
114     else
115       transformObjCToNonObjCCast(E);
116 
117     return true;
118   }
119 
120 private:
121   void transformNonObjCToObjCCast(CastExpr *E) {
122     if (!E) return;
123 
124     // Global vars are assumed that are cast as unretained.
125     if (isGlobalVar(E))
126       if (E->getSubExpr()->getType()->isPointerType()) {
127         castToObjCObject(E, /*retained=*/false);
128         return;
129       }
130 
131     // If the cast is directly over the result of a Core Foundation function
132     // try to figure out whether it should be cast as retained or unretained.
133     Expr *inner = E->IgnoreParenCasts();
134     if (CallExpr *callE = dyn_cast<CallExpr>(inner)) {
135       if (FunctionDecl *FD = callE->getDirectCallee()) {
136         if (FD->hasAttr<CFReturnsRetainedAttr>()) {
137           castToObjCObject(E, /*retained=*/true);
138           return;
139         }
140         if (FD->hasAttr<CFReturnsNotRetainedAttr>()) {
141           castToObjCObject(E, /*retained=*/false);
142           return;
143         }
144         if (FD->isGlobal() &&
145             FD->getIdentifier() &&
146             ento::cocoa::isRefType(E->getSubExpr()->getType(), "CF",
147                                    FD->getIdentifier()->getName())) {
148           StringRef fname = FD->getIdentifier()->getName();
149           if (fname.endswith("Retain") ||
150               fname.find("Create") != StringRef::npos ||
151               fname.find("Copy") != StringRef::npos) {
152             // Do not migrate to couple of bridge transfer casts which
153             // cancel each other out. Leave it unchanged so error gets user
154             // attention instead.
155             if (FD->getName() == "CFRetain" &&
156                 FD->getNumParams() == 1 &&
157                 FD->getParent()->isTranslationUnit() &&
158                 FD->isExternallyVisible()) {
159               Expr *Arg = callE->getArg(0);
160               if (const ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(Arg)) {
161                 const Expr *sub = ICE->getSubExpr();
162                 QualType T = sub->getType();
163                 if (T->isObjCObjectPointerType())
164                   return;
165               }
166             }
167             castToObjCObject(E, /*retained=*/true);
168             return;
169           }
170 
171           if (fname.find("Get") != StringRef::npos) {
172             castToObjCObject(E, /*retained=*/false);
173             return;
174           }
175         }
176       }
177     }
178 
179     // If returning an ivar or a member of an ivar from a +0 method, use
180     // a __bridge cast.
181     Expr *base = inner->IgnoreParenImpCasts();
182     while (isa<MemberExpr>(base))
183       base = cast<MemberExpr>(base)->getBase()->IgnoreParenImpCasts();
184     if (isa<ObjCIvarRefExpr>(base) &&
185         isa<ReturnStmt>(StmtMap->getParentIgnoreParenCasts(E))) {
186       if (ObjCMethodDecl *method = dyn_cast_or_null<ObjCMethodDecl>(ParentD)) {
187         if (!method->hasAttr<NSReturnsRetainedAttr>()) {
188           castToObjCObject(E, /*retained=*/false);
189           return;
190         }
191       }
192     }
193   }
194 
195   void castToObjCObject(CastExpr *E, bool retained) {
196     rewriteToBridgedCast(E, retained ? OBC_BridgeTransfer : OBC_Bridge);
197   }
198 
199   void rewriteToBridgedCast(CastExpr *E, ObjCBridgeCastKind Kind) {
200     Transaction Trans(Pass.TA);
201     rewriteToBridgedCast(E, Kind, Trans);
202   }
203 
204   void rewriteToBridgedCast(CastExpr *E, ObjCBridgeCastKind Kind,
205                             Transaction &Trans) {
206     TransformActions &TA = Pass.TA;
207 
208     // We will remove the compiler diagnostic.
209     if (!TA.hasDiagnostic(diag::err_arc_mismatched_cast,
210                           diag::err_arc_cast_requires_bridge,
211                           E->getBeginLoc())) {
212       Trans.abort();
213       return;
214     }
215 
216     StringRef bridge;
217     switch(Kind) {
218     case OBC_Bridge:
219       bridge = "__bridge "; break;
220     case OBC_BridgeTransfer:
221       bridge = "__bridge_transfer "; break;
222     case OBC_BridgeRetained:
223       bridge = "__bridge_retained "; break;
224     }
225 
226     TA.clearDiagnostic(diag::err_arc_mismatched_cast,
227                        diag::err_arc_cast_requires_bridge, E->getBeginLoc());
228     if (Kind == OBC_Bridge || !Pass.CFBridgingFunctionsDefined()) {
229       if (CStyleCastExpr *CCE = dyn_cast<CStyleCastExpr>(E)) {
230         TA.insertAfterToken(CCE->getLParenLoc(), bridge);
231       } else {
232         SourceLocation insertLoc = E->getSubExpr()->getBeginLoc();
233         SmallString<128> newCast;
234         newCast += '(';
235         newCast += bridge;
236         newCast += E->getType().getAsString(Pass.Ctx.getPrintingPolicy());
237         newCast += ')';
238 
239         if (isa<ParenExpr>(E->getSubExpr())) {
240           TA.insert(insertLoc, newCast.str());
241         } else {
242           newCast += '(';
243           TA.insert(insertLoc, newCast.str());
244           TA.insertAfterToken(E->getEndLoc(), ")");
245         }
246       }
247     } else {
248       assert(Kind == OBC_BridgeTransfer || Kind == OBC_BridgeRetained);
249       SmallString<32> BridgeCall;
250 
251       Expr *WrapE = E->getSubExpr();
252       SourceLocation InsertLoc = WrapE->getBeginLoc();
253 
254       SourceManager &SM = Pass.Ctx.getSourceManager();
255       char PrevChar = *SM.getCharacterData(InsertLoc.getLocWithOffset(-1));
256       if (Lexer::isAsciiIdentifierContinueChar(PrevChar,
257                                                Pass.Ctx.getLangOpts()))
258         BridgeCall += ' ';
259 
260       if (Kind == OBC_BridgeTransfer)
261         BridgeCall += "CFBridgingRelease";
262       else
263         BridgeCall += "CFBridgingRetain";
264 
265       if (isa<ParenExpr>(WrapE)) {
266         TA.insert(InsertLoc, BridgeCall);
267       } else {
268         BridgeCall += '(';
269         TA.insert(InsertLoc, BridgeCall);
270         TA.insertAfterToken(WrapE->getEndLoc(), ")");
271       }
272     }
273   }
274 
275   void rewriteCastForCFRetain(CastExpr *castE, CallExpr *callE) {
276     Transaction Trans(Pass.TA);
277     Pass.TA.replace(callE->getSourceRange(), callE->getArg(0)->getSourceRange());
278     rewriteToBridgedCast(castE, OBC_BridgeRetained, Trans);
279   }
280 
281   void getBlockMacroRanges(CastExpr *E, SourceRange &Outer, SourceRange &Inner) {
282     SourceManager &SM = Pass.Ctx.getSourceManager();
283     SourceLocation Loc = E->getExprLoc();
284     assert(Loc.isMacroID());
285     CharSourceRange MacroRange = SM.getImmediateExpansionRange(Loc);
286     SourceRange SubRange = E->getSubExpr()->IgnoreParenImpCasts()->getSourceRange();
287     SourceLocation InnerBegin = SM.getImmediateMacroCallerLoc(SubRange.getBegin());
288     SourceLocation InnerEnd = SM.getImmediateMacroCallerLoc(SubRange.getEnd());
289 
290     Outer = MacroRange.getAsRange();
291     Inner = SourceRange(InnerBegin, InnerEnd);
292   }
293 
294   void rewriteBlockCopyMacro(CastExpr *E) {
295     SourceRange OuterRange, InnerRange;
296     getBlockMacroRanges(E, OuterRange, InnerRange);
297 
298     Transaction Trans(Pass.TA);
299     Pass.TA.replace(OuterRange, InnerRange);
300     Pass.TA.insert(InnerRange.getBegin(), "[");
301     Pass.TA.insertAfterToken(InnerRange.getEnd(), " copy]");
302     Pass.TA.clearDiagnostic(diag::err_arc_mismatched_cast,
303                             diag::err_arc_cast_requires_bridge,
304                             OuterRange);
305   }
306 
307   void removeBlockReleaseMacro(CastExpr *E) {
308     SourceRange OuterRange, InnerRange;
309     getBlockMacroRanges(E, OuterRange, InnerRange);
310 
311     Transaction Trans(Pass.TA);
312     Pass.TA.clearDiagnostic(diag::err_arc_mismatched_cast,
313                             diag::err_arc_cast_requires_bridge,
314                             OuterRange);
315     if (!hasSideEffects(E, Pass.Ctx)) {
316       if (tryRemoving(cast<Expr>(StmtMap->getParentIgnoreParenCasts(E))))
317         return;
318     }
319     Pass.TA.replace(OuterRange, InnerRange);
320   }
321 
322   bool tryRemoving(Expr *E) const {
323     if (!Removables) {
324       Removables.reset(new ExprSet);
325       collectRemovables(Body, *Removables);
326     }
327 
328     if (Removables->count(E)) {
329       Pass.TA.removeStmt(E);
330       return true;
331     }
332 
333     return false;
334   }
335 
336   void transformObjCToNonObjCCast(CastExpr *E) {
337     SourceLocation CastLoc = E->getExprLoc();
338     if (CastLoc.isMacroID()) {
339       StringRef MacroName = Lexer::getImmediateMacroName(CastLoc,
340                                                     Pass.Ctx.getSourceManager(),
341                                                     Pass.Ctx.getLangOpts());
342       if (MacroName == "Block_copy") {
343         rewriteBlockCopyMacro(E);
344         return;
345       }
346       if (MacroName == "Block_release") {
347         removeBlockReleaseMacro(E);
348         return;
349       }
350     }
351 
352     if (isSelf(E->getSubExpr()))
353       return rewriteToBridgedCast(E, OBC_Bridge);
354 
355     CallExpr *callE;
356     if (isPassedToCFRetain(E, callE))
357       return rewriteCastForCFRetain(E, callE);
358 
359     ObjCMethodFamily family = getFamilyOfMessage(E->getSubExpr());
360     if (family == OMF_retain)
361       return rewriteToBridgedCast(E, OBC_BridgeRetained);
362 
363     if (family == OMF_autorelease || family == OMF_release) {
364       std::string err = "it is not safe to cast to '";
365       err += E->getType().getAsString(Pass.Ctx.getPrintingPolicy());
366       err += "' the result of '";
367       err += family == OMF_autorelease ? "autorelease" : "release";
368       err += "' message; a __bridge cast may result in a pointer to a "
369           "destroyed object and a __bridge_retained may leak the object";
370       Pass.TA.reportError(err, E->getBeginLoc(),
371                           E->getSubExpr()->getSourceRange());
372       Stmt *parent = E;
373       do {
374         parent = StmtMap->getParentIgnoreParenImpCasts(parent);
375       } while (parent && isa<FullExpr>(parent));
376 
377       if (ReturnStmt *retS = dyn_cast_or_null<ReturnStmt>(parent)) {
378         std::string note = "remove the cast and change return type of function "
379             "to '";
380         note += E->getSubExpr()->getType().getAsString(Pass.Ctx.getPrintingPolicy());
381         note += "' to have the object automatically autoreleased";
382         Pass.TA.reportNote(note, retS->getBeginLoc());
383       }
384     }
385 
386     Expr *subExpr = E->getSubExpr();
387 
388     // Look through pseudo-object expressions.
389     if (PseudoObjectExpr *pseudo = dyn_cast<PseudoObjectExpr>(subExpr)) {
390       subExpr = pseudo->getResultExpr();
391       assert(subExpr && "no result for pseudo-object of non-void type?");
392     }
393 
394     if (ImplicitCastExpr *implCE = dyn_cast<ImplicitCastExpr>(subExpr)) {
395       if (implCE->getCastKind() == CK_ARCConsumeObject)
396         return rewriteToBridgedCast(E, OBC_BridgeRetained);
397       if (implCE->getCastKind() == CK_ARCReclaimReturnedObject)
398         return rewriteToBridgedCast(E, OBC_Bridge);
399     }
400 
401     bool isConsumed = false;
402     if (isPassedToCParamWithKnownOwnership(E, isConsumed))
403       return rewriteToBridgedCast(E, isConsumed ? OBC_BridgeRetained
404                                                 : OBC_Bridge);
405   }
406 
407   static ObjCMethodFamily getFamilyOfMessage(Expr *E) {
408     E = E->IgnoreParenCasts();
409     if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E))
410       return ME->getMethodFamily();
411 
412     return OMF_None;
413   }
414 
415   bool isPassedToCFRetain(Expr *E, CallExpr *&callE) const {
416     if ((callE = dyn_cast_or_null<CallExpr>(
417                                      StmtMap->getParentIgnoreParenImpCasts(E))))
418       if (FunctionDecl *
419             FD = dyn_cast_or_null<FunctionDecl>(callE->getCalleeDecl()))
420         if (FD->getName() == "CFRetain" && FD->getNumParams() == 1 &&
421             FD->getParent()->isTranslationUnit() &&
422             FD->isExternallyVisible())
423           return true;
424 
425     return false;
426   }
427 
428   bool isPassedToCParamWithKnownOwnership(Expr *E, bool &isConsumed) const {
429     if (CallExpr *callE = dyn_cast_or_null<CallExpr>(
430                                      StmtMap->getParentIgnoreParenImpCasts(E)))
431       if (FunctionDecl *
432             FD = dyn_cast_or_null<FunctionDecl>(callE->getCalleeDecl())) {
433         unsigned i = 0;
434         for (unsigned e = callE->getNumArgs(); i != e; ++i) {
435           Expr *arg = callE->getArg(i);
436           if (arg == E || arg->IgnoreParenImpCasts() == E)
437             break;
438         }
439         if (i < callE->getNumArgs() && i < FD->getNumParams()) {
440           ParmVarDecl *PD = FD->getParamDecl(i);
441           if (PD->hasAttr<CFConsumedAttr>()) {
442             isConsumed = true;
443             return true;
444           }
445         }
446       }
447 
448     return false;
449   }
450 
451   bool isSelf(Expr *E) const {
452     E = E->IgnoreParenLValueCasts();
453     if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
454       if (ImplicitParamDecl *IPD = dyn_cast<ImplicitParamDecl>(DRE->getDecl()))
455         if (IPD->getIdentifier() == SelfII)
456           return true;
457 
458     return false;
459   }
460 };
461 
462 } // end anonymous namespace
463 
464 void trans::rewriteUnbridgedCasts(MigrationPass &pass) {
465   BodyTransform<UnbridgedCastRewriter> trans(pass);
466   trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
467 }
468