4 files changed, 88 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index e83dd071678..e19020c6ade 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -256,6 +256,7 @@ Sema::BuildCXXNamedCast(SourceLocation OpLoc, tok::TokenKind Kind,
       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 OpLoc, tok::TokenKind Kind,
       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 OpLoc, tok::TokenKind Kind,
       Op.CheckStaticCast();
       if (Op.SrcExpr.isInvalid())
         return ExprError();
+      DiscardMisalignedMemberAddress(DestType.getTypePtr(), E);
     }
     
     return Op.complete(CXXStaticCastExpr::Create(Context, Op.ResultType,
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index ec01b04fcf9..ff18e094bda 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -8302,6 +8302,8 @@ void CheckImplicitConversion(Sema &S, Expr *E, QualType T,
 
   DiagnoseNullConversion(S, E, T, CC);
 
+  S.DiscardMisalignedMemberAddress(Target, E);
+
   if (!Source->isIntegerType() || !Target->isIntegerType())
     return;
 
@@ -9371,6 +9373,7 @@ void Sema::CheckCompletedExpr(Expr *E, SourceLocation CheckLoc,
   CheckUnsequencedOperations(E);
   if (!IsConstexpr && !E->isValueDependent())
     CheckForIntOverflow(E);
+  DiagnoseMisalignedMembers();
 }
 
 void Sema::CheckBitFieldInitialization(SourceLocation InitLoc,
@@ -10916,3 +10919,67 @@ void Sema::CheckArgumentWithTypeTag(const ArgumentWithTypeTagAttr *Attr,
         << 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));
+}
+
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 0c8a9136948..2a48798d3cb 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -6001,7 +6001,9 @@ Sema::ActOnCastExpr(Scope *S, SourceLocation LParenLoc,
   CheckTollFreeBridgeCast(castType, CastExpr);
   
   CheckObjCBridgeRelatedCast(castType, CastExpr);
-  
+
+  DiscardMisalignedMemberAddress(castType.getTypePtr(), CastExpr);
+
   return BuildCStyleCastExpr(LParenLoc, castTInfo, RParenLoc, CastExpr);
 }
 
@@ -10534,6 +10536,8 @@ QualType Sema::CheckAddressOfOperand(ExprResult &OrigOp, SourceLocation OpLoc) {
   if (op->getType()->isObjCObjectType())
     return Context.getObjCObjectPointerType(op->getType());
 
+  CheckAddressOfPackedMember(op);
+
   return Context.getPointerType(op->getType());
 }
 
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 060ee3eef21..c88af08546e 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -6457,6 +6457,15 @@ InitializationSequence::Perform(Sema &S,
                                   ExtendingEntity->getDecl());
 
       CheckForNullPointerDereference(S, CurInit.get());
+
+      S.RefersToMemberWithReducedAlignment(CurInit.get(), [&](Expr *E,
+                                                              RecordDecl *RD,
+                                                              ValueDecl *MD,
+                                                              CharUnits) {
+        S.Diag(Kind.getLocation(), diag::err_binding_reference_to_packed_member)
+            << MD << RD << E->getSourceRange();
+      });
+
       break;
 
     case SK_BindReferenceToTemporary: {
@@ -6645,12 +6654,16 @@ 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;
     }