1//===--- JumpDiagnostics.cpp - Analyze Jump Targets for VLA issues --------===//
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 implements the JumpScopeChecker class, which is used to diagnose
11// jumps that enter a VLA scope in an invalid way.
12//
13//===----------------------------------------------------------------------===//
14
15#include "Sema.h"
16#include "clang/AST/Expr.h"
17#include "clang/AST/StmtObjC.h"
18#include "clang/AST/StmtCXX.h"
19using namespace clang;
20
21namespace {
22
23/// JumpScopeChecker - This object is used by Sema to diagnose invalid jumps
24/// into VLA and other protected scopes. For example, this rejects:
25/// goto L;
26/// int a[n];
27/// L:
28///
29class JumpScopeChecker {
30 Sema &S;
31
32 /// GotoScope - This is a record that we use to keep track of all of the
33 /// scopes that are introduced by VLAs and other things that scope jumps like
34 /// gotos. This scope tree has nothing to do with the source scope tree,
35 /// because you can have multiple VLA scopes per compound statement, and most
36 /// compound statements don't introduce any scopes.
37 struct GotoScope {
38 /// ParentScope - The index in ScopeMap of the parent scope. This is 0 for
39 /// the parent scope is the function body.
40 unsigned ParentScope;
41
42 /// Diag - The diagnostic to emit if there is a jump into this scope.
43 unsigned Diag;
44
45 /// Loc - Location to emit the diagnostic.
46 SourceLocation Loc;
47
48 GotoScope(unsigned parentScope, unsigned diag, SourceLocation L)
49 : ParentScope(parentScope), Diag(diag), Loc(L) {}
50 };
51
52 llvm::SmallVector<GotoScope, 48> Scopes;
53 llvm::DenseMap<Stmt*, unsigned> LabelAndGotoScopes;
54 llvm::SmallVector<Stmt*, 16> Jumps;
55public:
56 JumpScopeChecker(Stmt *Body, Sema &S);
57private:
58 void BuildScopeInformation(Stmt *S, unsigned ParentScope);
59 void VerifyJumps();
60 void CheckJump(Stmt *From, Stmt *To,
61 SourceLocation DiagLoc, unsigned JumpDiag);
62};
63} // end anonymous namespace
64
65
66JumpScopeChecker::JumpScopeChecker(Stmt *Body, Sema &s) : S(s) {
67 // Add a scope entry for function scope.
68 Scopes.push_back(GotoScope(~0U, ~0U, SourceLocation()));
69
70 // Build information for the top level compound statement, so that we have a
71 // defined scope record for every "goto" and label.
72 BuildScopeInformation(Body, 0);
73
74 // Check that all jumps we saw are kosher.
75 VerifyJumps();
76}
77
78/// GetDiagForGotoScopeDecl - If this decl induces a new goto scope, return a
79/// diagnostic that should be emitted if control goes over it. If not, return 0.
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85 return diag::note_protected_by_cleanup;
86 } else if (const TypedefDecl *TD = dyn_cast<TypedefDecl>(D)) {
87 if (TD->getUnderlyingType()->isVariablyModifiedType())
88 return diag::note_protected_by_vla_typedef;
89 }
90
91 return 0;
92}
93
94
95/// BuildScopeInformation - The statements from CI to CE are known to form a
96/// coherent VLA scope with a specified parent node. Walk through the
97/// statements, adding any labels or gotos to LabelAndGotoScopes and recursively
98/// walking the AST as needed.
99void JumpScopeChecker::BuildScopeInformation(Stmt *S, unsigned ParentScope) {
100
101 // If we found a label, remember that it is in ParentScope scope.
102 if (isa<LabelStmt>(S) || isa<DefaultStmt>(S) || isa<CaseStmt>(S)) {
103 LabelAndGotoScopes[S] = ParentScope;
104 } else if (isa<GotoStmt>(S) || isa<SwitchStmt>(S) ||
105 isa<IndirectGotoStmt>(S) || isa<AddrLabelExpr>(S)) {
106 // Remember both what scope a goto is in as well as the fact that we have
107 // it. This makes the second scan not have to walk the AST again.
108 LabelAndGotoScopes[S] = ParentScope;
109 Jumps.push_back(S);
110 }
111
112 for (Stmt::child_iterator CI = S->child_begin(), E = S->child_end(); CI != E;
113 ++CI) {
114 Stmt *SubStmt = *CI;
115 if (SubStmt == 0) continue;
116
117 // FIXME: diagnose jumps past initialization: required in C++, warning in C.
118 // goto L; int X = 4; L: ;
119
120 // If this is a declstmt with a VLA definition, it defines a scope from here
121 // to the end of the containing context.
122 if (DeclStmt *DS = dyn_cast<DeclStmt>(SubStmt)) {
123 // The decl statement creates a scope if any of the decls in it are VLAs or
124 // have the cleanup attribute.
125 for (DeclStmt::decl_iterator I = DS->decl_begin(), E = DS->decl_end();
126 I != E; ++I) {
127 // If this decl causes a new scope, push and switch to it.
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129 Scopes.push_back(GotoScope(ParentScope, Diag, (*I)->getLocation()));
130 ParentScope = Scopes.size()-1;
131 }
132
133 // If the decl has an initializer, walk it with the potentially new
134 // scope we just installed.
135 if (VarDecl *VD = dyn_cast<VarDecl>(*I))
136 if (Expr *Init = VD->getInit())
137 BuildScopeInformation(Init, ParentScope);
138 }
139 continue;
140 }
141
142 // Disallow jumps into any part of an @try statement by pushing a scope and
143 // walking all sub-stmts in that scope.
144 if (ObjCAtTryStmt *AT = dyn_cast<ObjCAtTryStmt>(SubStmt)) {
145 // Recursively walk the AST for the @try part.
146 Scopes.push_back(GotoScope(ParentScope,diag::note_protected_by_objc_try,
147 AT->getAtTryLoc()));
148 if (Stmt *TryPart = AT->getTryBody())
149 BuildScopeInformation(TryPart, Scopes.size()-1);
150
151 // Jump from the catch to the finally or try is not valid.
152 for (ObjCAtCatchStmt *AC = AT->getCatchStmts(); AC;
153 AC = AC->getNextCatchStmt()) {
154 Scopes.push_back(GotoScope(ParentScope,
155 diag::note_protected_by_objc_catch,
156 AC->getAtCatchLoc()));
157 // @catches are nested and it isn't
158 BuildScopeInformation(AC->getCatchBody(), Scopes.size()-1);
159 }
160
161 // Jump from the finally to the try or catch is not valid.
162 if (ObjCAtFinallyStmt *AF = AT->getFinallyStmt()) {
163 Scopes.push_back(GotoScope(ParentScope,
164 diag::note_protected_by_objc_finally,
165 AF->getAtFinallyLoc()));
166 BuildScopeInformation(AF, Scopes.size()-1);
167 }
168
169 continue;
170 }
171
172 // Disallow jumps into the protected statement of an @synchronized, but
173 // allow jumps into the object expression it protects.
174 if (ObjCAtSynchronizedStmt *AS = dyn_cast<ObjCAtSynchronizedStmt>(SubStmt)){
175 // Recursively walk the AST for the @synchronized object expr, it is
176 // evaluated in the normal scope.
177 BuildScopeInformation(AS->getSynchExpr(), ParentScope);
178
179 // Recursively walk the AST for the @synchronized part, protected by a new
180 // scope.
181 Scopes.push_back(GotoScope(ParentScope,
182 diag::note_protected_by_objc_synchronized,
183 AS->getAtSynchronizedLoc()));
184 BuildScopeInformation(AS->getSynchBody(), Scopes.size()-1);
185 continue;
186 }
187
188 // Disallow jumps into any part of a C++ try statement. This is pretty
189 // much the same as for Obj-C.
190 if (CXXTryStmt *TS = dyn_cast<CXXTryStmt>(SubStmt)) {
191 Scopes.push_back(GotoScope(ParentScope, diag::note_protected_by_cxx_try,
192 TS->getSourceRange().getBegin()));
193 if (Stmt *TryBlock = TS->getTryBlock())
194 BuildScopeInformation(TryBlock, Scopes.size()-1);
195
196 // Jump from the catch into the try is not allowed either.
197 for(unsigned I = 0, E = TS->getNumHandlers(); I != E; ++I) {
198 CXXCatchStmt *CS = TS->getHandler(I);
199 Scopes.push_back(GotoScope(ParentScope,
200 diag::note_protected_by_cxx_catch,
201 CS->getSourceRange().getBegin()));
202 BuildScopeInformation(CS->getHandlerBlock(), Scopes.size()-1);
203 }
204
205 continue;
206 }
207
208 // Recursively walk the AST.
209 BuildScopeInformation(SubStmt, ParentScope);
210 }
211}
212
213/// VerifyJumps - Verify each element of the Jumps array to see if they are
214/// valid, emitting diagnostics if not.
215void JumpScopeChecker::VerifyJumps() {
216 while (!Jumps.empty()) {
217 Stmt *Jump = Jumps.pop_back_val();
218
219 // With a goto,
220 if (GotoStmt *GS = dyn_cast<GotoStmt>(Jump)) {
221 CheckJump(GS, GS->getLabel(), GS->getGotoLoc(),
222 diag::err_goto_into_protected_scope);
223 continue;
224 }
225
226 if (SwitchStmt *SS = dyn_cast<SwitchStmt>(Jump)) {
227 for (SwitchCase *SC = SS->getSwitchCaseList(); SC;
228 SC = SC->getNextSwitchCase()) {
229 assert(LabelAndGotoScopes.count(SC) && "Case not visited?");
230 CheckJump(SS, SC, SC->getLocStart(),
231 diag::err_switch_into_protected_scope);
232 }
233 continue;
234 }
235
236 unsigned DiagnosticScope;
237
238 // We don't know where an indirect goto goes, require that it be at the
239 // top level of scoping.
240 if (IndirectGotoStmt *IG = dyn_cast<IndirectGotoStmt>(Jump)) {
241 assert(LabelAndGotoScopes.count(Jump) &&
242 "Jump didn't get added to scopes?");
243 unsigned GotoScope = LabelAndGotoScopes[IG];
244 if (GotoScope == 0) continue; // indirect jump is ok.
245 S.Diag(IG->getGotoLoc(), diag::err_indirect_goto_in_protected_scope);
246 DiagnosticScope = GotoScope;
247 } else {
248 // We model &&Label as a jump for purposes of scope tracking. We actually
249 // don't care *where* the address of label is, but we require the *label
250 // itself* to be in scope 0. If it is nested inside of a VLA scope, then
251 // it is possible for an indirect goto to illegally enter the VLA scope by
252 // indirectly jumping to the label.
253 assert(isa<AddrLabelExpr>(Jump) && "Unknown jump type");
254 LabelStmt *TheLabel = cast<AddrLabelExpr>(Jump)->getLabel();
255
256 assert(LabelAndGotoScopes.count(TheLabel) &&
257 "Referenced label didn't get added to scopes?");
258 unsigned LabelScope = LabelAndGotoScopes[TheLabel];
259 if (LabelScope == 0) continue; // Addr of label is ok.
260
261 S.Diag(Jump->getLocStart(), diag::err_addr_of_label_in_protected_scope);
262 DiagnosticScope = LabelScope;
263 }
264
265 // Report all the things that would be skipped over by this &&label or
266 // indirect goto.
267 while (DiagnosticScope != 0) {
268 S.Diag(Scopes[DiagnosticScope].Loc, Scopes[DiagnosticScope].Diag);
269 DiagnosticScope = Scopes[DiagnosticScope].ParentScope;
270 }
271 }
272}
273
274/// CheckJump - Validate that the specified jump statement is valid: that it is
275/// jumping within or out of its current scope, not into a deeper one.
276void JumpScopeChecker::CheckJump(Stmt *From, Stmt *To,
277 SourceLocation DiagLoc, unsigned JumpDiag) {
278 assert(LabelAndGotoScopes.count(From) && "Jump didn't get added to scopes?");
279 unsigned FromScope = LabelAndGotoScopes[From];
280
281 assert(LabelAndGotoScopes.count(To) && "Jump didn't get added to scopes?");
282 unsigned ToScope = LabelAndGotoScopes[To];
283
284 // Common case: exactly the same scope, which is fine.
285 if (FromScope == ToScope) return;
286
287 // The only valid mismatch jump case happens when the jump is more deeply
288 // nested inside the jump target. Do a quick scan to see if the jump is valid
289 // because valid code is more common than invalid code.
290 unsigned TestScope = Scopes[FromScope].ParentScope;
291 while (TestScope != ~0U) {
292 // If we found the jump target, then we're jumping out of our current scope,
293 // which is perfectly fine.
294 if (TestScope == ToScope) return;
295
296 // Otherwise, scan up the hierarchy.
297 TestScope = Scopes[TestScope].ParentScope;
298 }
299
300 // If we get here, then we know we have invalid code. Diagnose the bad jump,
301 // and then emit a note at each VLA being jumped out of.
302 S.Diag(DiagLoc, JumpDiag);
303
304 // Eliminate the common prefix of the jump and the target. Start by
305 // linearizing both scopes, reversing them as we go.
306 std::vector<unsigned> FromScopes, ToScopes;
307 for (TestScope = FromScope; TestScope != ~0U;
308 TestScope = Scopes[TestScope].ParentScope)
309 FromScopes.push_back(TestScope);
310 for (TestScope = ToScope; TestScope != ~0U;
311 TestScope = Scopes[TestScope].ParentScope)
312 ToScopes.push_back(TestScope);
313
314 // Remove any common entries (such as the top-level function scope).
315 while (!FromScopes.empty() && FromScopes.back() == ToScopes.back()) {
316 FromScopes.pop_back();
317 ToScopes.pop_back();
318 }
319
320 // Emit diagnostics for whatever is left in ToScopes.
321 for (unsigned i = 0, e = ToScopes.size(); i != e; ++i)
322 S.Diag(Scopes[ToScopes[i]].Loc, Scopes[ToScopes[i]].Diag);
323}
324
325void Sema::DiagnoseInvalidJumps(Stmt *Body) {
326 JumpScopeChecker(Body, *this);
327}
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