r278483 - This patch implements PR#22821.
Roger Ferrer Ibanez via cfe-commits
cfe-commits at lists.llvm.org
Fri Aug 12 01:04:13 PDT 2016
Author: rogfer01
Date: Fri Aug 12 03:04:13 2016
New Revision: 278483
URL: http://llvm.org/viewvc/llvm-project?rev=278483&view=rev
Log:
This patch implements PR#22821.
Taking the address of a packed member is dangerous since the reduced
alignment of the pointee is lost. This can lead to memory alignment
faults in some architectures if the pointer value is dereferenced.
This change adds a new warning to clang emitted when taking the address
of a packed member. A packed member is either a field/data member
declared as attribute((packed)) or belonging to a struct/class
declared as such. The associated flag is -Waddress-of-packed-member.
Conversions (either implicit or via a valid casting) to pointer types
with lower or equal alignment requirements (e.g. void* or char*)
will silence the warning.
Differential Revision: https://reviews.llvm.org/D20561
Modified:
cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
cfe/trunk/include/clang/Sema/Sema.h
cfe/trunk/lib/Sema/SemaCast.cpp
cfe/trunk/lib/Sema/SemaChecking.cpp
cfe/trunk/lib/Sema/SemaExpr.cpp
cfe/trunk/lib/Sema/SemaInit.cpp
Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=278483&r1=278482&r2=278483&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Fri Aug 12 03:04:13 2016
@@ -5489,6 +5489,9 @@ def warn_pointer_indirection_from_incomp
"dereference of type %1 that was reinterpret_cast from type %0 has undefined "
"behavior">,
InGroup<UndefinedReinterpretCast>, DefaultIgnore;
+def warn_taking_address_of_packed_member : Warning<
+ "taking address of packed member %0 of class or structure %q1 may result in an unaligned pointer value">,
+ InGroup<DiagGroup<"address-of-packed-member">>;
def err_objc_object_assignment : Error<
"cannot assign to class object (%0 invalid)">;
Modified: cfe/trunk/include/clang/Sema/Sema.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Sema.h?rev=278483&r1=278482&r2=278483&view=diff
==============================================================================
--- cfe/trunk/include/clang/Sema/Sema.h (original)
+++ cfe/trunk/include/clang/Sema/Sema.h Fri Aug 12 03:04:13 2016
@@ -9570,6 +9570,10 @@ private:
void CheckArgumentWithTypeTag(const ArgumentWithTypeTagAttr *Attr,
const Expr * const *ExprArgs);
+ /// \brief Check if we are taking the address of a packed field
+ /// as this may be a problem if the pointer value is dereferenced.
+ void CheckAddressOfPackedMember(Expr *rhs);
+
/// \brief The parser's current scope.
///
/// The parser maintains this state here.
@@ -9664,6 +9668,51 @@ public:
// Emitting members of dllexported classes is delayed until the class
// (including field initializers) is fully parsed.
SmallVector<CXXRecordDecl*, 4> DelayedDllExportClasses;
+
+private:
+ /// \brief Helper class that collects misaligned member designations and
+ /// their location info for delayed diagnostics.
+ struct MisalignedMember {
+ Expr *E;
+ RecordDecl *RD;
+ ValueDecl *MD;
+ CharUnits Alignment;
+
+ MisalignedMember() : E(), RD(), MD(), Alignment() {}
+ MisalignedMember(Expr *E, RecordDecl *RD, ValueDecl *MD,
+ CharUnits Alignment)
+ : E(E), RD(RD), MD(MD), Alignment(Alignment) {}
+ explicit MisalignedMember(Expr *E)
+ : MisalignedMember(E, nullptr, nullptr, CharUnits()) {}
+
+ bool operator==(const MisalignedMember &m) { return this->E == m.E; }
+ };
+ /// \brief Small set of gathered accesses to potentially misaligned members
+ /// due to the packed attribute.
+ SmallVector<MisalignedMember, 4> MisalignedMembers;
+
+ /// \brief Adds an expression to the set of gathered misaligned members.
+ void AddPotentialMisalignedMembers(Expr *E, RecordDecl *RD, ValueDecl *MD,
+ CharUnits Alignment);
+
+public:
+ /// \brief Diagnoses the current set of gathered accesses. This typically
+ /// happens at full expression level. The set is cleared after emitting the
+ /// diagnostics.
+ void DiagnoseMisalignedMembers();
+
+ /// \brief This function checks if the expression is in the sef of potentially
+ /// misaligned members and it is converted to some pointer type T with lower
+ /// or equal alignment requirements. If so it removes it. This is used when
+ /// we do not want to diagnose such misaligned access (e.g. in conversions to void*).
+ void DiscardMisalignedMemberAddress(const Type *T, Expr *E);
+
+ /// \brief This function calls Action when it determines that E designates a
+ /// misaligned member due to the packed attribute. This is used to emit
+ /// local diagnostics like in reference binding.
+ void RefersToMemberWithReducedAlignment(
+ Expr *E,
+ std::function<void(Expr *, RecordDecl *, ValueDecl *, CharUnits)> Action);
};
/// \brief RAII object that enters a new expression evaluation context.
Modified: cfe/trunk/lib/Sema/SemaCast.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaCast.cpp?rev=278483&r1=278482&r2=278483&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaCast.cpp (original)
+++ cfe/trunk/lib/Sema/SemaCast.cpp Fri Aug 12 03:04:13 2016
@@ -256,6 +256,7 @@ Sema::BuildCXXNamedCast(SourceLocation O
Op.CheckConstCast();
if (Op.SrcExpr.isInvalid())
return ExprError();
+ DiscardMisalignedMemberAddress(DestType.getTypePtr(), E);
}
return Op.complete(CXXConstCastExpr::Create(Context, Op.ResultType,
Op.ValueKind, Op.SrcExpr.get(), DestTInfo,
@@ -279,6 +280,7 @@ Sema::BuildCXXNamedCast(SourceLocation O
Op.CheckReinterpretCast();
if (Op.SrcExpr.isInvalid())
return ExprError();
+ DiscardMisalignedMemberAddress(DestType.getTypePtr(), E);
}
return Op.complete(CXXReinterpretCastExpr::Create(Context, Op.ResultType,
Op.ValueKind, Op.Kind, Op.SrcExpr.get(),
@@ -291,6 +293,7 @@ Sema::BuildCXXNamedCast(SourceLocation O
Op.CheckStaticCast();
if (Op.SrcExpr.isInvalid())
return ExprError();
+ DiscardMisalignedMemberAddress(DestType.getTypePtr(), E);
}
return Op.complete(CXXStaticCastExpr::Create(Context, Op.ResultType,
Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=278483&r1=278482&r2=278483&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
+++ cfe/trunk/lib/Sema/SemaChecking.cpp Fri Aug 12 03:04:13 2016
@@ -8383,6 +8383,8 @@ void CheckImplicitConversion(Sema &S, Ex
DiagnoseNullConversion(S, E, T, CC);
+ S.DiscardMisalignedMemberAddress(Target, E);
+
if (!Source->isIntegerType() || !Target->isIntegerType())
return;
@@ -9453,6 +9455,7 @@ void Sema::CheckCompletedExpr(Expr *E, S
CheckUnsequencedOperations(E);
if (!IsConstexpr && !E->isValueDependent())
CheckForIntOverflow(E);
+ DiagnoseMisalignedMembers();
}
void Sema::CheckBitFieldInitialization(SourceLocation InitLoc,
@@ -10998,3 +11001,67 @@ void Sema::CheckArgumentWithTypeTag(cons
<< ArgumentExpr->getSourceRange()
<< TypeTagExpr->getSourceRange();
}
+
+void Sema::AddPotentialMisalignedMembers(Expr *E, RecordDecl *RD, ValueDecl *MD,
+ CharUnits Alignment) {
+ MisalignedMembers.emplace_back(E, RD, MD, Alignment);
+}
+
+void Sema::DiagnoseMisalignedMembers() {
+ for (MisalignedMember &m : MisalignedMembers) {
+ Diag(m.E->getLocStart(), diag::warn_taking_address_of_packed_member)
+ << m.MD << m.RD << m.E->getSourceRange();
+ }
+ MisalignedMembers.clear();
+}
+
+void Sema::DiscardMisalignedMemberAddress(const Type *T, Expr *E) {
+ if (!T->isPointerType())
+ return;
+ if (isa<UnaryOperator>(E) &&
+ cast<UnaryOperator>(E)->getOpcode() == UO_AddrOf) {
+ auto *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
+ if (isa<MemberExpr>(Op)) {
+ auto MA = std::find(MisalignedMembers.begin(), MisalignedMembers.end(),
+ MisalignedMember(Op));
+ if (MA != MisalignedMembers.end() &&
+ Context.getTypeAlignInChars(T->getPointeeType()) <= MA->Alignment)
+ MisalignedMembers.erase(MA);
+ }
+ }
+}
+
+void Sema::RefersToMemberWithReducedAlignment(
+ Expr *E,
+ std::function<void(Expr *, RecordDecl *, ValueDecl *, CharUnits)> Action) {
+ const auto *ME = dyn_cast<MemberExpr>(E);
+ while (ME && isa<FieldDecl>(ME->getMemberDecl())) {
+ QualType BaseType = ME->getBase()->getType();
+ if (ME->isArrow())
+ BaseType = BaseType->getPointeeType();
+ RecordDecl *RD = BaseType->getAs<RecordType>()->getDecl();
+
+ ValueDecl *MD = ME->getMemberDecl();
+ bool ByteAligned = Context.getTypeAlignInChars(MD->getType()).isOne();
+ if (ByteAligned) // Attribute packed does not have any effect.
+ break;
+
+ if (!ByteAligned &&
+ (RD->hasAttr<PackedAttr>() || (MD->hasAttr<PackedAttr>()))) {
+ CharUnits Alignment = std::min(Context.getTypeAlignInChars(MD->getType()),
+ Context.getTypeAlignInChars(BaseType));
+ // Notify that this expression designates a member with reduced alignment
+ Action(E, RD, MD, Alignment);
+ break;
+ }
+ ME = dyn_cast<MemberExpr>(ME->getBase());
+ }
+}
+
+void Sema::CheckAddressOfPackedMember(Expr *rhs) {
+ using namespace std::placeholders;
+ RefersToMemberWithReducedAlignment(
+ rhs, std::bind(&Sema::AddPotentialMisalignedMembers, std::ref(*this), _1,
+ _2, _3, _4));
+}
+
Modified: cfe/trunk/lib/Sema/SemaExpr.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExpr.cpp?rev=278483&r1=278482&r2=278483&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaExpr.cpp (original)
+++ cfe/trunk/lib/Sema/SemaExpr.cpp Fri Aug 12 03:04:13 2016
@@ -6022,7 +6022,9 @@ Sema::ActOnCastExpr(Scope *S, SourceLoca
CheckTollFreeBridgeCast(castType, CastExpr);
CheckObjCBridgeRelatedCast(castType, CastExpr);
-
+
+ DiscardMisalignedMemberAddress(castType.getTypePtr(), CastExpr);
+
return BuildCStyleCastExpr(LParenLoc, castTInfo, RParenLoc, CastExpr);
}
@@ -10614,6 +10616,8 @@ QualType Sema::CheckAddressOfOperand(Exp
if (op->getType()->isObjCObjectType())
return Context.getObjCObjectPointerType(op->getType());
+ CheckAddressOfPackedMember(op);
+
return Context.getPointerType(op->getType());
}
Modified: cfe/trunk/lib/Sema/SemaInit.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaInit.cpp?rev=278483&r1=278482&r2=278483&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaInit.cpp (original)
+++ cfe/trunk/lib/Sema/SemaInit.cpp Fri Aug 12 03:04:13 2016
@@ -6660,12 +6660,16 @@ InitializationSequence::Perform(Sema &S,
getAssignmentAction(Entity), CCK);
if (CurInitExprRes.isInvalid())
return ExprError();
+
+ S.DiscardMisalignedMemberAddress(Step->Type.getTypePtr(), CurInit.get());
+
CurInit = CurInitExprRes;
if (Step->Kind == SK_ConversionSequenceNoNarrowing &&
S.getLangOpts().CPlusPlus && !CurInit.get()->isValueDependent())
DiagnoseNarrowingInInitList(S, *Step->ICS, SourceType, Entity.getType(),
CurInit.get());
+
break;
}
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