r278483 - This patch implements PR#22821.
Nico Weber via cfe-commits
cfe-commits at lists.llvm.org
Mon Aug 22 09:59:10 PDT 2016
I don't see any approval after Aaron's "Please wait until someone has had
the chance to review before committing" on https://reviews.llvm.org/D20561
-- was this reviewed on IRC?
On Fri, Aug 12, 2016 at 4:04 AM, Roger Ferrer Ibanez via cfe-commits <
cfe-commits at lists.llvm.org> wrote:
> 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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