1 //===--- JumpDiagnostics.cpp - Analyze Jump Targets for VLA issues --------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the JumpScopeChecker class, which is used to diagnose
11 // jumps that enter a VLA scope in an invalid way.
13 //===----------------------------------------------------------------------===//
15 #include "clang/Sema/SemaInternal.h"
16 #include "clang/AST/DeclCXX.h"
17 #include "clang/AST/Expr.h"
18 #include "clang/AST/ExprCXX.h"
19 #include "clang/AST/StmtObjC.h"
20 #include "clang/AST/StmtCXX.h"
21 #include "llvm/ADT/BitVector.h"
22 using namespace clang;
26 /// JumpScopeChecker - This object is used by Sema to diagnose invalid jumps
27 /// into VLA and other protected scopes. For example, this rejects:
32 class JumpScopeChecker {
35 /// GotoScope - This is a record that we use to keep track of all of the
36 /// scopes that are introduced by VLAs and other things that scope jumps like
37 /// gotos. This scope tree has nothing to do with the source scope tree,
38 /// because you can have multiple VLA scopes per compound statement, and most
39 /// compound statements don't introduce any scopes.
41 /// ParentScope - The index in ScopeMap of the parent scope. This is 0 for
42 /// the parent scope is the function body.
45 /// InDiag - The diagnostic to emit if there is a jump into this scope.
48 /// OutDiag - The diagnostic to emit if there is an indirect jump out
49 /// of this scope. Direct jumps always clean up their current scope
50 /// in an orderly way.
53 /// Loc - Location to emit the diagnostic.
56 GotoScope(unsigned parentScope, unsigned InDiag, unsigned OutDiag,
58 : ParentScope(parentScope), InDiag(InDiag), OutDiag(OutDiag), Loc(L) {}
61 llvm::SmallVector<GotoScope, 48> Scopes;
62 llvm::DenseMap<Stmt*, unsigned> LabelAndGotoScopes;
63 llvm::SmallVector<Stmt*, 16> Jumps;
65 llvm::SmallVector<IndirectGotoStmt*, 4> IndirectJumps;
66 llvm::SmallVector<LabelDecl*, 4> IndirectJumpTargets;
68 JumpScopeChecker(Stmt *Body, Sema &S);
70 void BuildScopeInformation(Decl *D, unsigned &ParentScope);
71 void BuildScopeInformation(Stmt *S, unsigned ParentScope);
73 void VerifyIndirectJumps();
74 void DiagnoseIndirectJump(IndirectGotoStmt *IG, unsigned IGScope,
75 LabelDecl *Target, unsigned TargetScope);
76 void CheckJump(Stmt *From, Stmt *To,
77 SourceLocation DiagLoc, unsigned JumpDiag);
79 unsigned GetDeepestCommonScope(unsigned A, unsigned B);
81 } // end anonymous namespace
84 JumpScopeChecker::JumpScopeChecker(Stmt *Body, Sema &s) : S(s) {
85 // Add a scope entry for function scope.
86 Scopes.push_back(GotoScope(~0U, ~0U, ~0U, SourceLocation()));
88 // Build information for the top level compound statement, so that we have a
89 // defined scope record for every "goto" and label.
90 BuildScopeInformation(Body, 0);
92 // Check that all jumps we saw are kosher.
94 VerifyIndirectJumps();
97 /// GetDeepestCommonScope - Finds the innermost scope enclosing the
99 unsigned JumpScopeChecker::GetDeepestCommonScope(unsigned A, unsigned B) {
101 // Inner scopes are created after outer scopes and therefore have
104 assert(Scopes[B].ParentScope < B);
105 B = Scopes[B].ParentScope;
107 assert(Scopes[A].ParentScope < A);
108 A = Scopes[A].ParentScope;
114 /// GetDiagForGotoScopeDecl - If this decl induces a new goto scope, return a
115 /// diagnostic that should be emitted if control goes over it. If not, return 0.
116 static std::pair<unsigned,unsigned>
117 GetDiagForGotoScopeDecl(const Decl *D, bool isCPlusPlus) {
118 if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
119 unsigned InDiag = 0, OutDiag = 0;
120 if (VD->getType()->isVariablyModifiedType())
121 InDiag = diag::note_protected_by_vla;
123 if (VD->hasAttr<BlocksAttr>()) {
124 InDiag = diag::note_protected_by___block;
125 OutDiag = diag::note_exits___block;
126 } else if (VD->hasAttr<CleanupAttr>()) {
127 InDiag = diag::note_protected_by_cleanup;
128 OutDiag = diag::note_exits_cleanup;
129 } else if (isCPlusPlus) {
130 if (!VD->hasLocalStorage())
131 return std::make_pair(InDiag, OutDiag);
133 ASTContext &Context = D->getASTContext();
134 QualType T = Context.getBaseElementType(VD->getType());
135 if (!T->isDependentType()) {
136 // C++0x [stmt.dcl]p3:
137 // A program that jumps from a point where a variable with automatic
138 // storage duration is not in scope to a point where it is in scope
139 // is ill-formed unless the variable has scalar type, class type with
140 // a trivial default constructor and a trivial destructor, a
141 // cv-qualified version of one of these types, or an array of one of
142 // the preceding types and is declared without an initializer (8.5).
143 // Check whether this is a C++ class.
144 CXXRecordDecl *Record = T->getAsCXXRecordDecl();
146 if (const Expr *Init = VD->getInit()) {
147 bool CallsTrivialConstructor = false;
149 // FIXME: With generalized initializer lists, this may
150 // classify "X x{};" as having no initializer.
151 if (const CXXConstructExpr *Construct
152 = dyn_cast<CXXConstructExpr>(Init))
153 if (const CXXConstructorDecl *Constructor
154 = Construct->getConstructor())
155 if ((Context.getLangOptions().CPlusPlus0x
156 ? Record->hasTrivialDefaultConstructor()
157 : Record->isPOD()) &&
158 Constructor->isDefaultConstructor())
159 CallsTrivialConstructor = true;
162 if (!CallsTrivialConstructor)
163 InDiag = diag::note_protected_by_variable_init;
166 // Note whether we have a class with a non-trivial destructor.
167 if (Record && !Record->hasTrivialDestructor())
168 OutDiag = diag::note_exits_dtor;
172 return std::make_pair(InDiag, OutDiag);
175 if (const TypedefDecl *TD = dyn_cast<TypedefDecl>(D)) {
176 if (TD->getUnderlyingType()->isVariablyModifiedType())
177 return std::make_pair((unsigned) diag::note_protected_by_vla_typedef, 0);
180 if (const TypeAliasDecl *TD = dyn_cast<TypeAliasDecl>(D)) {
181 if (TD->getUnderlyingType()->isVariablyModifiedType())
182 return std::make_pair((unsigned) diag::note_protected_by_vla_type_alias, 0);
185 return std::make_pair(0U, 0U);
188 /// \brief Build scope information for a declaration that is part of a DeclStmt.
189 void JumpScopeChecker::BuildScopeInformation(Decl *D, unsigned &ParentScope) {
190 bool isCPlusPlus = this->S.getLangOptions().CPlusPlus;
192 // If this decl causes a new scope, push and switch to it.
193 std::pair<unsigned,unsigned> Diags
194 = GetDiagForGotoScopeDecl(D, isCPlusPlus);
195 if (Diags.first || Diags.second) {
196 Scopes.push_back(GotoScope(ParentScope, Diags.first, Diags.second,
198 ParentScope = Scopes.size()-1;
201 // If the decl has an initializer, walk it with the potentially new
202 // scope we just installed.
203 if (VarDecl *VD = dyn_cast<VarDecl>(D))
204 if (Expr *Init = VD->getInit())
205 BuildScopeInformation(Init, ParentScope);
208 /// BuildScopeInformation - The statements from CI to CE are known to form a
209 /// coherent VLA scope with a specified parent node. Walk through the
210 /// statements, adding any labels or gotos to LabelAndGotoScopes and recursively
211 /// walking the AST as needed.
212 void JumpScopeChecker::BuildScopeInformation(Stmt *S, unsigned ParentScope) {
213 bool SkipFirstSubStmt = false;
215 // If we found a label, remember that it is in ParentScope scope.
216 switch (S->getStmtClass()) {
217 case Stmt::AddrLabelExprClass:
218 IndirectJumpTargets.push_back(cast<AddrLabelExpr>(S)->getLabel());
221 case Stmt::IndirectGotoStmtClass:
222 // "goto *&&lbl;" is a special case which we treat as equivalent
223 // to a normal goto. In addition, we don't calculate scope in the
224 // operand (to avoid recording the address-of-label use), which
225 // works only because of the restricted set of expressions which
226 // we detect as constant targets.
227 if (cast<IndirectGotoStmt>(S)->getConstantTarget()) {
228 LabelAndGotoScopes[S] = ParentScope;
233 LabelAndGotoScopes[S] = ParentScope;
234 IndirectJumps.push_back(cast<IndirectGotoStmt>(S));
237 case Stmt::SwitchStmtClass:
238 // Evaluate the condition variable before entering the scope of the switch
240 if (VarDecl *Var = cast<SwitchStmt>(S)->getConditionVariable()) {
241 BuildScopeInformation(Var, ParentScope);
242 SkipFirstSubStmt = true;
246 case Stmt::GotoStmtClass:
247 // Remember both what scope a goto is in as well as the fact that we have
248 // it. This makes the second scan not have to walk the AST again.
249 LabelAndGotoScopes[S] = ParentScope;
257 for (Stmt::child_range CI = S->children(); CI; ++CI) {
258 if (SkipFirstSubStmt) {
259 SkipFirstSubStmt = false;
264 if (SubStmt == 0) continue;
266 // Cases, labels, and defaults aren't "scope parents". It's also
267 // important to handle these iteratively instead of recursively in
268 // order to avoid blowing out the stack.
271 if (CaseStmt *CS = dyn_cast<CaseStmt>(SubStmt))
272 Next = CS->getSubStmt();
273 else if (DefaultStmt *DS = dyn_cast<DefaultStmt>(SubStmt))
274 Next = DS->getSubStmt();
275 else if (LabelStmt *LS = dyn_cast<LabelStmt>(SubStmt))
276 Next = LS->getSubStmt();
280 LabelAndGotoScopes[SubStmt] = ParentScope;
284 // If this is a declstmt with a VLA definition, it defines a scope from here
285 // to the end of the containing context.
286 if (DeclStmt *DS = dyn_cast<DeclStmt>(SubStmt)) {
287 // The decl statement creates a scope if any of the decls in it are VLAs
288 // or have the cleanup attribute.
289 for (DeclStmt::decl_iterator I = DS->decl_begin(), E = DS->decl_end();
291 BuildScopeInformation(*I, ParentScope);
295 // Disallow jumps into any part of an @try statement by pushing a scope and
296 // walking all sub-stmts in that scope.
297 if (ObjCAtTryStmt *AT = dyn_cast<ObjCAtTryStmt>(SubStmt)) {
298 // Recursively walk the AST for the @try part.
299 Scopes.push_back(GotoScope(ParentScope,
300 diag::note_protected_by_objc_try,
301 diag::note_exits_objc_try,
303 if (Stmt *TryPart = AT->getTryBody())
304 BuildScopeInformation(TryPart, Scopes.size()-1);
306 // Jump from the catch to the finally or try is not valid.
307 for (unsigned I = 0, N = AT->getNumCatchStmts(); I != N; ++I) {
308 ObjCAtCatchStmt *AC = AT->getCatchStmt(I);
309 Scopes.push_back(GotoScope(ParentScope,
310 diag::note_protected_by_objc_catch,
311 diag::note_exits_objc_catch,
312 AC->getAtCatchLoc()));
313 // @catches are nested and it isn't
314 BuildScopeInformation(AC->getCatchBody(), Scopes.size()-1);
317 // Jump from the finally to the try or catch is not valid.
318 if (ObjCAtFinallyStmt *AF = AT->getFinallyStmt()) {
319 Scopes.push_back(GotoScope(ParentScope,
320 diag::note_protected_by_objc_finally,
321 diag::note_exits_objc_finally,
322 AF->getAtFinallyLoc()));
323 BuildScopeInformation(AF, Scopes.size()-1);
329 // Disallow jumps into the protected statement of an @synchronized, but
330 // allow jumps into the object expression it protects.
331 if (ObjCAtSynchronizedStmt *AS = dyn_cast<ObjCAtSynchronizedStmt>(SubStmt)){
332 // Recursively walk the AST for the @synchronized object expr, it is
333 // evaluated in the normal scope.
334 BuildScopeInformation(AS->getSynchExpr(), ParentScope);
336 // Recursively walk the AST for the @synchronized part, protected by a new
338 Scopes.push_back(GotoScope(ParentScope,
339 diag::note_protected_by_objc_synchronized,
340 diag::note_exits_objc_synchronized,
341 AS->getAtSynchronizedLoc()));
342 BuildScopeInformation(AS->getSynchBody(), Scopes.size()-1);
346 // Disallow jumps into any part of a C++ try statement. This is pretty
347 // much the same as for Obj-C.
348 if (CXXTryStmt *TS = dyn_cast<CXXTryStmt>(SubStmt)) {
349 Scopes.push_back(GotoScope(ParentScope,
350 diag::note_protected_by_cxx_try,
351 diag::note_exits_cxx_try,
352 TS->getSourceRange().getBegin()));
353 if (Stmt *TryBlock = TS->getTryBlock())
354 BuildScopeInformation(TryBlock, Scopes.size()-1);
356 // Jump from the catch into the try is not allowed either.
357 for (unsigned I = 0, E = TS->getNumHandlers(); I != E; ++I) {
358 CXXCatchStmt *CS = TS->getHandler(I);
359 Scopes.push_back(GotoScope(ParentScope,
360 diag::note_protected_by_cxx_catch,
361 diag::note_exits_cxx_catch,
362 CS->getSourceRange().getBegin()));
363 BuildScopeInformation(CS->getHandlerBlock(), Scopes.size()-1);
369 // Recursively walk the AST.
370 BuildScopeInformation(SubStmt, ParentScope);
374 /// VerifyJumps - Verify each element of the Jumps array to see if they are
375 /// valid, emitting diagnostics if not.
376 void JumpScopeChecker::VerifyJumps() {
377 while (!Jumps.empty()) {
378 Stmt *Jump = Jumps.pop_back_val();
381 if (GotoStmt *GS = dyn_cast<GotoStmt>(Jump)) {
382 CheckJump(GS, GS->getLabel()->getStmt(), GS->getGotoLoc(),
383 diag::err_goto_into_protected_scope);
387 // We only get indirect gotos here when they have a constant target.
388 if (IndirectGotoStmt *IGS = dyn_cast<IndirectGotoStmt>(Jump)) {
389 LabelDecl *Target = IGS->getConstantTarget();
390 CheckJump(IGS, Target->getStmt(), IGS->getGotoLoc(),
391 diag::err_goto_into_protected_scope);
395 SwitchStmt *SS = cast<SwitchStmt>(Jump);
396 for (SwitchCase *SC = SS->getSwitchCaseList(); SC;
397 SC = SC->getNextSwitchCase()) {
398 assert(LabelAndGotoScopes.count(SC) && "Case not visited?");
399 CheckJump(SS, SC, SC->getLocStart(),
400 diag::err_switch_into_protected_scope);
405 /// VerifyIndirectJumps - Verify whether any possible indirect jump
406 /// might cross a protection boundary. Unlike direct jumps, indirect
407 /// jumps count cleanups as protection boundaries: since there's no
408 /// way to know where the jump is going, we can't implicitly run the
409 /// right cleanups the way we can with direct jumps.
411 /// Thus, an indirect jump is "trivial" if it bypasses no
412 /// initializations and no teardowns. More formally, an indirect jump
413 /// from A to B is trivial if the path out from A to DCA(A,B) is
414 /// trivial and the path in from DCA(A,B) to B is trivial, where
415 /// DCA(A,B) is the deepest common ancestor of A and B.
416 /// Jump-triviality is transitive but asymmetric.
418 /// A path in is trivial if none of the entered scopes have an InDiag.
419 /// A path out is trivial is none of the exited scopes have an OutDiag.
421 /// Under these definitions, this function checks that the indirect
422 /// jump between A and B is trivial for every indirect goto statement A
423 /// and every label B whose address was taken in the function.
424 void JumpScopeChecker::VerifyIndirectJumps() {
425 if (IndirectJumps.empty()) return;
427 // If there aren't any address-of-label expressions in this function,
428 // complain about the first indirect goto.
429 if (IndirectJumpTargets.empty()) {
430 S.Diag(IndirectJumps[0]->getGotoLoc(),
431 diag::err_indirect_goto_without_addrlabel);
435 // Collect a single representative of every scope containing an
436 // indirect goto. For most code bases, this substantially cuts
437 // down on the number of jump sites we'll have to consider later.
438 typedef std::pair<unsigned, IndirectGotoStmt*> JumpScope;
439 llvm::SmallVector<JumpScope, 32> JumpScopes;
441 llvm::DenseMap<unsigned, IndirectGotoStmt*> JumpScopesMap;
442 for (llvm::SmallVectorImpl<IndirectGotoStmt*>::iterator
443 I = IndirectJumps.begin(), E = IndirectJumps.end(); I != E; ++I) {
444 IndirectGotoStmt *IG = *I;
445 assert(LabelAndGotoScopes.count(IG) &&
446 "indirect jump didn't get added to scopes?");
447 unsigned IGScope = LabelAndGotoScopes[IG];
448 IndirectGotoStmt *&Entry = JumpScopesMap[IGScope];
449 if (!Entry) Entry = IG;
451 JumpScopes.reserve(JumpScopesMap.size());
452 for (llvm::DenseMap<unsigned, IndirectGotoStmt*>::iterator
453 I = JumpScopesMap.begin(), E = JumpScopesMap.end(); I != E; ++I)
454 JumpScopes.push_back(*I);
457 // Collect a single representative of every scope containing a
458 // label whose address was taken somewhere in the function.
459 // For most code bases, there will be only one such scope.
460 llvm::DenseMap<unsigned, LabelDecl*> TargetScopes;
461 for (llvm::SmallVectorImpl<LabelDecl*>::iterator
462 I = IndirectJumpTargets.begin(), E = IndirectJumpTargets.end();
464 LabelDecl *TheLabel = *I;
465 assert(LabelAndGotoScopes.count(TheLabel->getStmt()) &&
466 "Referenced label didn't get added to scopes?");
467 unsigned LabelScope = LabelAndGotoScopes[TheLabel->getStmt()];
468 LabelDecl *&Target = TargetScopes[LabelScope];
469 if (!Target) Target = TheLabel;
472 // For each target scope, make sure it's trivially reachable from
473 // every scope containing a jump site.
475 // A path between scopes always consists of exitting zero or more
476 // scopes, then entering zero or more scopes. We build a set of
477 // of scopes S from which the target scope can be trivially
478 // entered, then verify that every jump scope can be trivially
479 // exitted to reach a scope in S.
480 llvm::BitVector Reachable(Scopes.size(), false);
481 for (llvm::DenseMap<unsigned,LabelDecl*>::iterator
482 TI = TargetScopes.begin(), TE = TargetScopes.end(); TI != TE; ++TI) {
483 unsigned TargetScope = TI->first;
484 LabelDecl *TargetLabel = TI->second;
488 // Mark all the enclosing scopes from which you can safely jump
489 // into the target scope. 'Min' will end up being the index of
490 // the shallowest such scope.
491 unsigned Min = TargetScope;
495 // Don't go beyond the outermost scope.
498 // Stop if we can't trivially enter the current scope.
499 if (Scopes[Min].InDiag) break;
501 Min = Scopes[Min].ParentScope;
504 // Walk through all the jump sites, checking that they can trivially
505 // reach this label scope.
506 for (llvm::SmallVectorImpl<JumpScope>::iterator
507 I = JumpScopes.begin(), E = JumpScopes.end(); I != E; ++I) {
508 unsigned Scope = I->first;
510 // Walk out the "scope chain" for this scope, looking for a scope
511 // we've marked reachable. For well-formed code this amortizes
512 // to O(JumpScopes.size() / Scopes.size()): we only iterate
513 // when we see something unmarked, and in well-formed code we
514 // mark everything we iterate past.
515 bool IsReachable = false;
517 if (Reachable.test(Scope)) {
518 // If we find something reachable, mark all the scopes we just
519 // walked through as reachable.
520 for (unsigned S = I->first; S != Scope; S = Scopes[S].ParentScope)
526 // Don't walk out if we've reached the top-level scope or we've
527 // gotten shallower than the shallowest reachable scope.
528 if (Scope == 0 || Scope < Min) break;
530 // Don't walk out through an out-diagnostic.
531 if (Scopes[Scope].OutDiag) break;
533 Scope = Scopes[Scope].ParentScope;
536 // Only diagnose if we didn't find something.
537 if (IsReachable) continue;
539 DiagnoseIndirectJump(I->second, I->first, TargetLabel, TargetScope);
544 /// Diagnose an indirect jump which is known to cross scopes.
545 void JumpScopeChecker::DiagnoseIndirectJump(IndirectGotoStmt *Jump,
548 unsigned TargetScope) {
549 assert(JumpScope != TargetScope);
551 S.Diag(Jump->getGotoLoc(), diag::err_indirect_goto_in_protected_scope);
552 S.Diag(Target->getStmt()->getIdentLoc(), diag::note_indirect_goto_target);
554 unsigned Common = GetDeepestCommonScope(JumpScope, TargetScope);
556 // Walk out the scope chain until we reach the common ancestor.
557 for (unsigned I = JumpScope; I != Common; I = Scopes[I].ParentScope)
558 if (Scopes[I].OutDiag)
559 S.Diag(Scopes[I].Loc, Scopes[I].OutDiag);
561 // Now walk into the scopes containing the label whose address was taken.
562 for (unsigned I = TargetScope; I != Common; I = Scopes[I].ParentScope)
563 if (Scopes[I].InDiag)
564 S.Diag(Scopes[I].Loc, Scopes[I].InDiag);
567 /// CheckJump - Validate that the specified jump statement is valid: that it is
568 /// jumping within or out of its current scope, not into a deeper one.
569 void JumpScopeChecker::CheckJump(Stmt *From, Stmt *To,
570 SourceLocation DiagLoc, unsigned JumpDiag) {
571 assert(LabelAndGotoScopes.count(From) && "Jump didn't get added to scopes?");
572 unsigned FromScope = LabelAndGotoScopes[From];
574 assert(LabelAndGotoScopes.count(To) && "Jump didn't get added to scopes?");
575 unsigned ToScope = LabelAndGotoScopes[To];
577 // Common case: exactly the same scope, which is fine.
578 if (FromScope == ToScope) return;
580 unsigned CommonScope = GetDeepestCommonScope(FromScope, ToScope);
582 // It's okay to jump out from a nested scope.
583 if (CommonScope == ToScope) return;
585 // Pull out (and reverse) any scopes we might need to diagnose skipping.
586 llvm::SmallVector<unsigned, 10> ToScopes;
587 for (unsigned I = ToScope; I != CommonScope; I = Scopes[I].ParentScope)
588 if (Scopes[I].InDiag)
589 ToScopes.push_back(I);
591 // If the only scopes present are cleanup scopes, we're okay.
592 if (ToScopes.empty()) return;
594 S.Diag(DiagLoc, JumpDiag);
596 // Emit diagnostics for whatever is left in ToScopes.
597 for (unsigned i = 0, e = ToScopes.size(); i != e; ++i)
598 S.Diag(Scopes[ToScopes[i]].Loc, Scopes[ToScopes[i]].InDiag);
601 void Sema::DiagnoseInvalidJumps(Stmt *Body) {
602 (void)JumpScopeChecker(Body, *this);