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//===--- JumpDiagnostics.cpp - Analyze Jump Targets for VLA issues --------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file implements the JumpScopeChecker class, which is used to diagnose
// jumps that enter a VLA scope in an invalid way.
#include "Sema.h"
#include "clang/AST/Expr.h"
#include "clang/AST/StmtObjC.h"
#include "clang/AST/StmtCXX.h"
using namespace clang;
namespace {
/// JumpScopeChecker - This object is used by Sema to diagnose invalid jumps
/// into VLA and other protected scopes. For example, this rejects:
/// goto L;
/// int a[n];
/// L:
class JumpScopeChecker {
Sema &S;
/// GotoScope - This is a record that we use to keep track of all of the
/// scopes that are introduced by VLAs and other things that scope jumps like
/// gotos. This scope tree has nothing to do with the source scope tree,
/// because you can have multiple VLA scopes per compound statement, and most
/// compound statements don't introduce any scopes.
struct GotoScope {
/// ParentScope - The index in ScopeMap of the parent scope. This is 0 for
/// the parent scope is the function body.
unsigned ParentScope;
/// Diag - The diagnostic to emit if there is a jump into this scope.
unsigned Diag;
/// Loc - Location to emit the diagnostic.
SourceLocation Loc;
GotoScope(unsigned parentScope, unsigned diag, SourceLocation L)
: ParentScope(parentScope), Diag(diag), Loc(L) {}
llvm::SmallVector<GotoScope, 48> Scopes;
llvm::DenseMap<Stmt*, unsigned> LabelAndGotoScopes;
llvm::SmallVector<Stmt*, 16> Jumps;
JumpScopeChecker(Stmt *Body, Sema &S);
void BuildScopeInformation(Stmt *S, unsigned ParentScope);
void VerifyJumps();
void CheckJump(Stmt *From, Stmt *To,
SourceLocation DiagLoc, unsigned JumpDiag);
} // end anonymous namespace
JumpScopeChecker::JumpScopeChecker(Stmt *Body, Sema &s) : S(s) {
// Add a scope entry for function scope.
Scopes.push_back(GotoScope(~0U, ~0U, SourceLocation()));
// Build information for the top level compound statement, so that we have a
// defined scope record for every "goto" and label.
BuildScopeInformation(Body, 0);
// Check that all jumps we saw are kosher.
/// GetDiagForGotoScopeDecl - If this decl induces a new goto scope, return a
/// diagnostic that should be emitted if control goes over it. If not, return 0.
static unsigned GetDiagForGotoScopeDecl(const Decl *D) {
if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
if (VD->getType()->isVariablyModifiedType())
return diag::note_protected_by_vla;
if (VD->hasAttr<CleanupAttr>())
return diag::note_protected_by_cleanup;
if (VD->hasAttr<BlocksAttr>())
return diag::note_protected_by___block;
} else if (const TypedefDecl *TD = dyn_cast<TypedefDecl>(D)) {
if (TD->getUnderlyingType()->isVariablyModifiedType())
return diag::note_protected_by_vla_typedef;
return 0;
/// BuildScopeInformation - The statements from CI to CE are known to form a
/// coherent VLA scope with a specified parent node. Walk through the
/// statements, adding any labels or gotos to LabelAndGotoScopes and recursively
/// walking the AST as needed.
void JumpScopeChecker::BuildScopeInformation(Stmt *S, unsigned ParentScope) {
// If we found a label, remember that it is in ParentScope scope.
if (isa<LabelStmt>(S) || isa<DefaultStmt>(S) || isa<CaseStmt>(S)) {
LabelAndGotoScopes[S] = ParentScope;
} else if (isa<GotoStmt>(S) || isa<SwitchStmt>(S) ||
isa<IndirectGotoStmt>(S) || isa<AddrLabelExpr>(S)) {
// Remember both what scope a goto is in as well as the fact that we have
// it. This makes the second scan not have to walk the AST again.
LabelAndGotoScopes[S] = ParentScope;
for (Stmt::child_iterator CI = S->child_begin(), E = S->child_end(); CI != E;
++CI) {
Stmt *SubStmt = *CI;
if (SubStmt == 0) continue;
// FIXME: diagnose jumps past initialization: required in C++, warning in C.
// goto L; int X = 4; L: ;
// If this is a declstmt with a VLA definition, it defines a scope from here
// to the end of the containing context.
if (DeclStmt *DS = dyn_cast<DeclStmt>(SubStmt)) {
// The decl statement creates a scope if any of the decls in it are VLAs or
// have the cleanup attribute.
for (DeclStmt::decl_iterator I = DS->decl_begin(), E = DS->decl_end();
I != E; ++I) {
// If this decl causes a new scope, push and switch to it.
if (unsigned Diag = GetDiagForGotoScopeDecl(*I)) {
Scopes.push_back(GotoScope(ParentScope, Diag, (*I)->getLocation()));
ParentScope = Scopes.size()-1;
// If the decl has an initializer, walk it with the potentially new
// scope we just installed.
if (VarDecl *VD = dyn_cast<VarDecl>(*I))
if (Expr *Init = VD->getInit())
BuildScopeInformation(Init, ParentScope);
// Disallow jumps into any part of an @try statement by pushing a scope and
// walking all sub-stmts in that scope.
if (ObjCAtTryStmt *AT = dyn_cast<ObjCAtTryStmt>(SubStmt)) {
// Recursively walk the AST for the @try part.
if (Stmt *TryPart = AT->getTryBody())
BuildScopeInformation(TryPart, Scopes.size()-1);
// Jump from the catch to the finally or try is not valid.
for (ObjCAtCatchStmt *AC = AT->getCatchStmts(); AC;
AC = AC->getNextCatchStmt()) {
// @catches are nested and it isn't
BuildScopeInformation(AC->getCatchBody(), Scopes.size()-1);
// Jump from the finally to the try or catch is not valid.
if (ObjCAtFinallyStmt *AF = AT->getFinallyStmt()) {
BuildScopeInformation(AF, Scopes.size()-1);
// Disallow jumps into the protected statement of an @synchronized, but
// allow jumps into the object expression it protects.
if (ObjCAtSynchronizedStmt *AS = dyn_cast<ObjCAtSynchronizedStmt>(SubStmt)){
// Recursively walk the AST for the @synchronized object expr, it is
// evaluated in the normal scope.
BuildScopeInformation(AS->getSynchExpr(), ParentScope);
// Recursively walk the AST for the @synchronized part, protected by a new
// scope.
BuildScopeInformation(AS->getSynchBody(), Scopes.size()-1);
// Disallow jumps into any part of a C++ try statement. This is pretty
// much the same as for Obj-C.
if (CXXTryStmt *TS = dyn_cast<CXXTryStmt>(SubStmt)) {
Scopes.push_back(GotoScope(ParentScope, diag::note_protected_by_cxx_try,
if (Stmt *TryBlock = TS->getTryBlock())
BuildScopeInformation(TryBlock, Scopes.size()-1);
// Jump from the catch into the try is not allowed either.
for(unsigned I = 0, E = TS->getNumHandlers(); I != E; ++I) {
CXXCatchStmt *CS = TS->getHandler(I);
BuildScopeInformation(CS->getHandlerBlock(), Scopes.size()-1);
// Recursively walk the AST.
BuildScopeInformation(SubStmt, ParentScope);
/// VerifyJumps - Verify each element of the Jumps array to see if they are
/// valid, emitting diagnostics if not.
void JumpScopeChecker::VerifyJumps() {
while (!Jumps.empty()) {
Stmt *Jump = Jumps.pop_back_val();
// With a goto,
if (GotoStmt *GS = dyn_cast<GotoStmt>(Jump)) {
CheckJump(GS, GS->getLabel(), GS->getGotoLoc(),
if (SwitchStmt *SS = dyn_cast<SwitchStmt>(Jump)) {
for (SwitchCase *SC = SS->getSwitchCaseList(); SC;
SC = SC->getNextSwitchCase()) {
assert(LabelAndGotoScopes.count(SC) && "Case not visited?");
CheckJump(SS, SC, SC->getLocStart(),
unsigned DiagnosticScope;
// We don't know where an indirect goto goes, require that it be at the
// top level of scoping.
if (IndirectGotoStmt *IG = dyn_cast<IndirectGotoStmt>(Jump)) {
assert(LabelAndGotoScopes.count(Jump) &&
"Jump didn't get added to scopes?");
unsigned GotoScope = LabelAndGotoScopes[IG];
if (GotoScope == 0) continue; // indirect jump is ok.
S.Diag(IG->getGotoLoc(), diag::err_indirect_goto_in_protected_scope);
DiagnosticScope = GotoScope;
} else {
// We model &&Label as a jump for purposes of scope tracking. We actually
// don't care *where* the address of label is, but we require the *label
// itself* to be in scope 0. If it is nested inside of a VLA scope, then
// it is possible for an indirect goto to illegally enter the VLA scope by
// indirectly jumping to the label.
assert(isa<AddrLabelExpr>(Jump) && "Unknown jump type");
LabelStmt *TheLabel = cast<AddrLabelExpr>(Jump)->getLabel();
assert(LabelAndGotoScopes.count(TheLabel) &&
"Referenced label didn't get added to scopes?");
unsigned LabelScope = LabelAndGotoScopes[TheLabel];
if (LabelScope == 0) continue; // Addr of label is ok.
S.Diag(Jump->getLocStart(), diag::err_addr_of_label_in_protected_scope);
DiagnosticScope = LabelScope;
// Report all the things that would be skipped over by this &&label or
// indirect goto.
while (DiagnosticScope != 0) {
S.Diag(Scopes[DiagnosticScope].Loc, Scopes[DiagnosticScope].Diag);
DiagnosticScope = Scopes[DiagnosticScope].ParentScope;
/// CheckJump - Validate that the specified jump statement is valid: that it is
/// jumping within or out of its current scope, not into a deeper one.
void JumpScopeChecker::CheckJump(Stmt *From, Stmt *To,
SourceLocation DiagLoc, unsigned JumpDiag) {
assert(LabelAndGotoScopes.count(From) && "Jump didn't get added to scopes?");
unsigned FromScope = LabelAndGotoScopes[From];
assert(LabelAndGotoScopes.count(To) && "Jump didn't get added to scopes?");
unsigned ToScope = LabelAndGotoScopes[To];
// Common case: exactly the same scope, which is fine.
if (FromScope == ToScope) return;
// The only valid mismatch jump case happens when the jump is more deeply
// nested inside the jump target. Do a quick scan to see if the jump is valid
// because valid code is more common than invalid code.
unsigned TestScope = Scopes[FromScope].ParentScope;
while (TestScope != ~0U) {
// If we found the jump target, then we're jumping out of our current scope,
// which is perfectly fine.
if (TestScope == ToScope) return;
// Otherwise, scan up the hierarchy.
TestScope = Scopes[TestScope].ParentScope;
// If we get here, then we know we have invalid code. Diagnose the bad jump,
// and then emit a note at each VLA being jumped out of.
S.Diag(DiagLoc, JumpDiag);
// Eliminate the common prefix of the jump and the target. Start by
// linearizing both scopes, reversing them as we go.
std::vector<unsigned> FromScopes, ToScopes;
for (TestScope = FromScope; TestScope != ~0U;
TestScope = Scopes[TestScope].ParentScope)
for (TestScope = ToScope; TestScope != ~0U;
TestScope = Scopes[TestScope].ParentScope)
// Remove any common entries (such as the top-level function scope).
while (!FromScopes.empty() && FromScopes.back() == ToScopes.back()) {
// Emit diagnostics for whatever is left in ToScopes.
for (unsigned i = 0, e = ToScopes.size(); i != e; ++i)
S.Diag(Scopes[ToScopes[i]].Loc, Scopes[ToScopes[i]].Diag);
void Sema::DiagnoseInvalidJumps(Stmt *Body) {
JumpScopeChecker(Body, *this);