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clang-1/lib/Sema/JumpDiagnostics.cpp

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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 "clang/Sema/SemaInternal.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/Expr.h"
#include "clang/AST/StmtObjC.h"
#include "clang/AST/StmtCXX.h"
#include "llvm/ADT/BitVector.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;
/// InDiag - The diagnostic to emit if there is a jump into this scope.
unsigned InDiag;
/// OutDiag - The diagnostic to emit if there is an indirect jump out
/// of this scope. Direct jumps always clean up their current scope
/// in an orderly way.
unsigned OutDiag;
/// Loc - Location to emit the diagnostic.
SourceLocation Loc;
GotoScope(unsigned parentScope, unsigned InDiag, unsigned OutDiag,
SourceLocation L)
: ParentScope(parentScope), InDiag(InDiag), OutDiag(OutDiag), Loc(L) {}
};
llvm::SmallVector<GotoScope, 48> Scopes;
llvm::DenseMap<Stmt*, unsigned> LabelAndGotoScopes;
llvm::SmallVector<Stmt*, 16> Jumps;
llvm::SmallVector<IndirectGotoStmt*, 4> IndirectJumps;
llvm::SmallVector<LabelStmt*, 4> IndirectJumpTargets;
public:
JumpScopeChecker(Stmt *Body, Sema &S);
private:
void BuildScopeInformation(Decl *D, unsigned &ParentScope);
void BuildScopeInformation(Stmt *S, unsigned ParentScope);
void VerifyJumps();
void VerifyIndirectJumps();
void DiagnoseIndirectJump(IndirectGotoStmt *IG, unsigned IGScope,
LabelStmt *Target, unsigned TargetScope);
void CheckJump(Stmt *From, Stmt *To,
SourceLocation DiagLoc, unsigned JumpDiag);
unsigned GetDeepestCommonScope(unsigned A, unsigned B);
};
} // end anonymous namespace
JumpScopeChecker::JumpScopeChecker(Stmt *Body, Sema &s) : S(s) {
// Add a scope entry for function scope.
Scopes.push_back(GotoScope(~0U, ~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.
VerifyJumps();
VerifyIndirectJumps();
}
/// GetDeepestCommonScope - Finds the innermost scope enclosing the
/// two scopes.
unsigned JumpScopeChecker::GetDeepestCommonScope(unsigned A, unsigned B) {
while (A != B) {
// Inner scopes are created after outer scopes and therefore have
// higher indices.
if (A < B) {
assert(Scopes[B].ParentScope < B);
B = Scopes[B].ParentScope;
} else {
assert(Scopes[A].ParentScope < A);
A = Scopes[A].ParentScope;
}
}
return A;
}
/// 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 std::pair<unsigned,unsigned>
GetDiagForGotoScopeDecl(const Decl *D, bool isCPlusPlus) {
if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
unsigned InDiag = 0, OutDiag = 0;
if (VD->getType()->isVariablyModifiedType())
InDiag = diag::note_protected_by_vla;
if (VD->hasAttr<BlocksAttr>()) {
InDiag = diag::note_protected_by___block;
OutDiag = diag::note_exits___block;
} else if (VD->hasAttr<CleanupAttr>()) {
InDiag = diag::note_protected_by_cleanup;
OutDiag = diag::note_exits_cleanup;
} else if (isCPlusPlus) {
// FIXME: In C++0x, we have to check more conditions than "did we
// just give it an initializer?". See 6.7p3.
if (VD->hasLocalStorage() && VD->hasInit())
InDiag = diag::note_protected_by_variable_init;
CanQualType T = VD->getType()->getCanonicalTypeUnqualified();
if (!T->isDependentType()) {
while (CanQual<ArrayType> AT = T->getAs<ArrayType>())
T = AT->getElementType();
if (CanQual<RecordType> RT = T->getAs<RecordType>())
if (!cast<CXXRecordDecl>(RT->getDecl())->hasTrivialDestructor())
OutDiag = diag::note_exits_dtor;
}
}
return std::make_pair(InDiag, OutDiag);
}
if (const TypedefDecl *TD = dyn_cast<TypedefDecl>(D)) {
if (TD->getUnderlyingType()->isVariablyModifiedType())
return std::make_pair((unsigned) diag::note_protected_by_vla_typedef, 0);
}
return std::make_pair(0U, 0U);
}
/// \brief Build scope information for a declaration that is part of a DeclStmt.
void JumpScopeChecker::BuildScopeInformation(Decl *D, unsigned &ParentScope) {
bool isCPlusPlus = this->S.getLangOptions().CPlusPlus;
// If this decl causes a new scope, push and switch to it.
std::pair<unsigned,unsigned> Diags
= GetDiagForGotoScopeDecl(D, isCPlusPlus);
if (Diags.first || Diags.second) {
Scopes.push_back(GotoScope(ParentScope, Diags.first, Diags.second,
D->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>(D))
if (Expr *Init = VD->getInit())
BuildScopeInformation(Init, ParentScope);
}
/// 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) {
bool SkipFirstSubStmt = false;
// If we found a label, remember that it is in ParentScope scope.
switch (S->getStmtClass()) {
case Stmt::AddrLabelExprClass:
IndirectJumpTargets.push_back(cast<AddrLabelExpr>(S)->getLabel());
break;
case Stmt::IndirectGotoStmtClass:
// "goto *&&lbl;" is a special case which we treat as equivalent
// to a normal goto. In addition, we don't calculate scope in the
// operand (to avoid recording the address-of-label use), which
// works only because of the restricted set of expressions which
// we detect as constant targets.
if (cast<IndirectGotoStmt>(S)->getConstantTarget()) {
LabelAndGotoScopes[S] = ParentScope;
Jumps.push_back(S);
return;
}
LabelAndGotoScopes[S] = ParentScope;
IndirectJumps.push_back(cast<IndirectGotoStmt>(S));
break;
case Stmt::SwitchStmtClass:
// Evaluate the condition variable before entering the scope of the switch
// statement.
if (VarDecl *Var = cast<SwitchStmt>(S)->getConditionVariable()) {
BuildScopeInformation(Var, ParentScope);
SkipFirstSubStmt = true;
}
// Fall through
case Stmt::GotoStmtClass:
// 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;
Jumps.push_back(S);
break;
default:
break;
}
for (Stmt::child_iterator CI = S->child_begin(), E = S->child_end(); CI != E;
++CI) {
if (SkipFirstSubStmt) {
SkipFirstSubStmt = false;
continue;
}
Stmt *SubStmt = *CI;
if (SubStmt == 0) continue;
// Cases, labels, and defaults aren't "scope parents". It's also
// important to handle these iteratively instead of recursively in
// order to avoid blowing out the stack.
while (true) {
Stmt *Next;
if (isa<CaseStmt>(SubStmt))
Next = cast<CaseStmt>(SubStmt)->getSubStmt();
else if (isa<DefaultStmt>(SubStmt))
Next = cast<DefaultStmt>(SubStmt)->getSubStmt();
else if (isa<LabelStmt>(SubStmt))
Next = cast<LabelStmt>(SubStmt)->getSubStmt();
else
break;
LabelAndGotoScopes[SubStmt] = ParentScope;
SubStmt = Next;
}
// 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)
BuildScopeInformation(*I, ParentScope);
continue;
}
// 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.
Scopes.push_back(GotoScope(ParentScope,
diag::note_protected_by_objc_try,
diag::note_exits_objc_try,
AT->getAtTryLoc()));
if (Stmt *TryPart = AT->getTryBody())
BuildScopeInformation(TryPart, Scopes.size()-1);
// Jump from the catch to the finally or try is not valid.
for (unsigned I = 0, N = AT->getNumCatchStmts(); I != N; ++I) {
ObjCAtCatchStmt *AC = AT->getCatchStmt(I);
Scopes.push_back(GotoScope(ParentScope,
diag::note_protected_by_objc_catch,
diag::note_exits_objc_catch,
AC->getAtCatchLoc()));
// @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()) {
Scopes.push_back(GotoScope(ParentScope,
diag::note_protected_by_objc_finally,
diag::note_exits_objc_finally,
AF->getAtFinallyLoc()));
BuildScopeInformation(AF, Scopes.size()-1);
}
continue;
}
// 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.
Scopes.push_back(GotoScope(ParentScope,
diag::note_protected_by_objc_synchronized,
diag::note_exits_objc_synchronized,
AS->getAtSynchronizedLoc()));
BuildScopeInformation(AS->getSynchBody(), Scopes.size()-1);
continue;
}
// 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,
diag::note_exits_cxx_try,
TS->getSourceRange().getBegin()));
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);
Scopes.push_back(GotoScope(ParentScope,
diag::note_protected_by_cxx_catch,
diag::note_exits_cxx_catch,
CS->getSourceRange().getBegin()));
BuildScopeInformation(CS->getHandlerBlock(), Scopes.size()-1);
}
continue;
}
// 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(),
diag::err_goto_into_protected_scope);
continue;
}
// We only get indirect gotos here when they have a constant target.
if (IndirectGotoStmt *IGS = dyn_cast<IndirectGotoStmt>(Jump)) {
LabelStmt *Target = IGS->getConstantTarget();
CheckJump(IGS, Target, IGS->getGotoLoc(),
diag::err_goto_into_protected_scope);
continue;
}
SwitchStmt *SS = cast<SwitchStmt>(Jump);
for (SwitchCase *SC = SS->getSwitchCaseList(); SC;
SC = SC->getNextSwitchCase()) {
assert(LabelAndGotoScopes.count(SC) && "Case not visited?");
CheckJump(SS, SC, SC->getLocStart(),
diag::err_switch_into_protected_scope);
}
}
}
/// VerifyIndirectJumps - Verify whether any possible indirect jump
/// might cross a protection boundary. Unlike direct jumps, indirect
/// jumps count cleanups as protection boundaries: since there's no
/// way to know where the jump is going, we can't implicitly run the
/// right cleanups the way we can with direct jumps.
///
/// Thus, an indirect jump is "trivial" if it bypasses no
/// initializations and no teardowns. More formally, an indirect jump
/// from A to B is trivial if the path out from A to DCA(A,B) is
/// trivial and the path in from DCA(A,B) to B is trivial, where
/// DCA(A,B) is the deepest common ancestor of A and B.
/// Jump-triviality is transitive but asymmetric.
///
/// A path in is trivial if none of the entered scopes have an InDiag.
/// A path out is trivial is none of the exited scopes have an OutDiag.
///
/// Under these definitions, this function checks that the indirect
/// jump between A and B is trivial for every indirect goto statement A
/// and every label B whose address was taken in the function.
void JumpScopeChecker::VerifyIndirectJumps() {
if (IndirectJumps.empty()) return;
// If there aren't any address-of-label expressions in this function,
// complain about the first indirect goto.
if (IndirectJumpTargets.empty()) {
S.Diag(IndirectJumps[0]->getGotoLoc(),
diag::err_indirect_goto_without_addrlabel);
return;
}
// Collect a single representative of every scope containing an
// indirect goto. For most code bases, this substantially cuts
// down on the number of jump sites we'll have to consider later.
typedef std::pair<unsigned, IndirectGotoStmt*> JumpScope;
llvm::SmallVector<JumpScope, 32> JumpScopes;
{
llvm::DenseMap<unsigned, IndirectGotoStmt*> JumpScopesMap;
for (llvm::SmallVectorImpl<IndirectGotoStmt*>::iterator
I = IndirectJumps.begin(), E = IndirectJumps.end(); I != E; ++I) {
IndirectGotoStmt *IG = *I;
assert(LabelAndGotoScopes.count(IG) &&
"indirect jump didn't get added to scopes?");
unsigned IGScope = LabelAndGotoScopes[IG];
IndirectGotoStmt *&Entry = JumpScopesMap[IGScope];
if (!Entry) Entry = IG;
}
JumpScopes.reserve(JumpScopesMap.size());
for (llvm::DenseMap<unsigned, IndirectGotoStmt*>::iterator
I = JumpScopesMap.begin(), E = JumpScopesMap.end(); I != E; ++I)
JumpScopes.push_back(*I);
}
// Collect a single representative of every scope containing a
// label whose address was taken somewhere in the function.
// For most code bases, there will be only one such scope.
llvm::DenseMap<unsigned, LabelStmt*> TargetScopes;
for (llvm::SmallVectorImpl<LabelStmt*>::iterator
I = IndirectJumpTargets.begin(), E = IndirectJumpTargets.end();
I != E; ++I) {
LabelStmt *TheLabel = *I;
assert(LabelAndGotoScopes.count(TheLabel) &&
"Referenced label didn't get added to scopes?");
unsigned LabelScope = LabelAndGotoScopes[TheLabel];
LabelStmt *&Target = TargetScopes[LabelScope];
if (!Target) Target = TheLabel;
}
// For each target scope, make sure it's trivially reachable from
// every scope containing a jump site.
//
// A path between scopes always consists of exitting zero or more
// scopes, then entering zero or more scopes. We build a set of
// of scopes S from which the target scope can be trivially
// entered, then verify that every jump scope can be trivially
// exitted to reach a scope in S.
llvm::BitVector Reachable(Scopes.size(), false);
for (llvm::DenseMap<unsigned,LabelStmt*>::iterator
TI = TargetScopes.begin(), TE = TargetScopes.end(); TI != TE; ++TI) {
unsigned TargetScope = TI->first;
LabelStmt *TargetLabel = TI->second;
Reachable.reset();
// Mark all the enclosing scopes from which you can safely jump
// into the target scope. 'Min' will end up being the index of
// the shallowest such scope.
unsigned Min = TargetScope;
while (true) {
Reachable.set(Min);
// Don't go beyond the outermost scope.
if (Min == 0) break;
// Stop if we can't trivially enter the current scope.
if (Scopes[Min].InDiag) break;
Min = Scopes[Min].ParentScope;
}
// Walk through all the jump sites, checking that they can trivially
// reach this label scope.
for (llvm::SmallVectorImpl<JumpScope>::iterator
I = JumpScopes.begin(), E = JumpScopes.end(); I != E; ++I) {
unsigned Scope = I->first;
// Walk out the "scope chain" for this scope, looking for a scope
// we've marked reachable. For well-formed code this amortizes
// to O(JumpScopes.size() / Scopes.size()): we only iterate
// when we see something unmarked, and in well-formed code we
// mark everything we iterate past.
bool IsReachable = false;
while (true) {
if (Reachable.test(Scope)) {
// If we find something reachable, mark all the scopes we just
// walked through as reachable.
for (unsigned S = I->first; S != Scope; S = Scopes[S].ParentScope)
Reachable.set(S);
IsReachable = true;
break;
}
// Don't walk out if we've reached the top-level scope or we've
// gotten shallower than the shallowest reachable scope.
if (Scope == 0 || Scope < Min) break;
// Don't walk out through an out-diagnostic.
if (Scopes[Scope].OutDiag) break;
Scope = Scopes[Scope].ParentScope;
}
// Only diagnose if we didn't find something.
if (IsReachable) continue;
DiagnoseIndirectJump(I->second, I->first, TargetLabel, TargetScope);
}
}
}
/// Diagnose an indirect jump which is known to cross scopes.
void JumpScopeChecker::DiagnoseIndirectJump(IndirectGotoStmt *Jump,
unsigned JumpScope,
LabelStmt *Target,
unsigned TargetScope) {
assert(JumpScope != TargetScope);
S.Diag(Jump->getGotoLoc(), diag::err_indirect_goto_in_protected_scope);
S.Diag(Target->getIdentLoc(), diag::note_indirect_goto_target);
unsigned Common = GetDeepestCommonScope(JumpScope, TargetScope);
// Walk out the scope chain until we reach the common ancestor.
for (unsigned I = JumpScope; I != Common; I = Scopes[I].ParentScope)
if (Scopes[I].OutDiag)
S.Diag(Scopes[I].Loc, Scopes[I].OutDiag);
// Now walk into the scopes containing the label whose address was taken.
for (unsigned I = TargetScope; I != Common; I = Scopes[I].ParentScope)
if (Scopes[I].InDiag)
S.Diag(Scopes[I].Loc, Scopes[I].InDiag);
}
/// 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;
unsigned CommonScope = GetDeepestCommonScope(FromScope, ToScope);
// It's okay to jump out from a nested scope.
if (CommonScope == ToScope) return;
// Pull out (and reverse) any scopes we might need to diagnose skipping.
llvm::SmallVector<unsigned, 10> ToScopes;
for (unsigned I = ToScope; I != CommonScope; I = Scopes[I].ParentScope)
if (Scopes[I].InDiag)
ToScopes.push_back(I);
// If the only scopes present are cleanup scopes, we're okay.
if (ToScopes.empty()) return;
S.Diag(DiagLoc, JumpDiag);
// 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]].InDiag);
}
void Sema::DiagnoseInvalidJumps(Stmt *Body) {
(void)JumpScopeChecker(Body, *this);
}
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