[PATCH] D118511: Add a warning for not packing non-POD members in packed structs

[David Blaikie via Phabricator via cfe-commits]

dblaikie updated this revision to Diff 405468.
dblaikie added a comment.

- Create a separate sub-warning flag of -Wpacked (-Wpacked-non-pod), in case 
you're just interested in the ABI breaks here
- Warn only when this produces a different alignment requirement for the field


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D118511/new/

https://reviews.llvm.org/D118511

Files:
  clang/include/clang/Basic/DiagnosticASTKinds.td
  clang/include/clang/Basic/DiagnosticGroups.td
  clang/lib/AST/RecordLayoutBuilder.cpp
  clang/test/CodeGenCXX/warn-padded-packed.cpp


Index: clang/test/CodeGenCXX/warn-padded-packed.cpp
===================================================================
--- clang/test/CodeGenCXX/warn-padded-packed.cpp
+++ clang/test/CodeGenCXX/warn-padded-packed.cpp
@@ -146,8 +146,18 @@
   unsigned char b : 8;
 } __attribute__((packed));
 
+struct S28_non_pod {
+ protected:
+  int i;
+};
+struct S28 {
+  char c1;
+  short s1;
+  char c2;
+  S28_non_pod p1; // expected-warning {{not packing field 'p1' as it is non-POD}}
+} __attribute__((packed));
 
 // The warnings are emitted when the layout of the structs is computed, so we have to use them.
 void f(S1*, S2*, S3*, S4*, S5*, S6*, S7*, S8*, S9*, S10*, S11*, S12*, S13*,
        S14*, S15*, S16*, S17*, S18*, S19*, S20*, S21*, S22*, S23*, S24*, S25*,
-       S26*, S27*){}
+       S26*, S27*, S28*){}
Index: clang/lib/AST/RecordLayoutBuilder.cpp
===================================================================
--- clang/lib/AST/RecordLayoutBuilder.cpp
+++ clang/lib/AST/RecordLayoutBuilder.cpp
@@ -1888,11 +1888,16 @@
   LastBitfieldStorageUnitSize = 0;
 
   llvm::Triple Target = Context.getTargetInfo().getTriple();
-  bool FieldPacked = (Packed && (!FieldClass || FieldClass->isPOD() ||
-                                 Context.getLangOpts().getClangABICompat() <=
-                                     LangOptions::ClangABI::Ver13 ||
-                                 Target.isPS4() || Target.isOSDarwin())) ||
-                     D->hasAttr<PackedAttr>();
+  bool FieldPacked = Packed;
+  if (FieldPacked && FieldClass && !FieldClass->isPOD() &&
+      Context.getLangOpts().getClangABICompat() >
+          LangOptions::ClangABI::Ver13 &&
+      !Target.isPS4() && !Target.isOSDarwin()) {
+    FieldPacked = false;
+  }
+
+  if (!FieldPacked && D->hasAttr<PackedAttr>())
+    FieldPacked = true;
 
   AlignRequirementKind AlignRequirement = AlignRequirementKind::None;
   CharUnits FieldSize;
@@ -2028,6 +2033,8 @@
   CharUnits UnpackedFieldOffset = FieldOffset;
   CharUnits OriginalFieldAlign = UnpackedFieldAlign;
 
+  CharUnits PackedFieldAlign = CharUnits::One();
+
   if (FieldPacked) {
     FieldAlign = CharUnits::One();
     PreferredAlign = CharUnits::One();
@@ -2035,12 +2042,14 @@
   CharUnits MaxAlignmentInChars =
       Context.toCharUnitsFromBits(D->getMaxAlignment());
   FieldAlign = std::max(FieldAlign, MaxAlignmentInChars);
+  PackedFieldAlign = std::max(PackedFieldAlign, MaxAlignmentInChars);
   PreferredAlign = std::max(PreferredAlign, MaxAlignmentInChars);
   UnpackedFieldAlign = std::max(UnpackedFieldAlign, MaxAlignmentInChars);
 
   // The maximum field alignment overrides the aligned attribute.
   if (!MaxFieldAlignment.isZero()) {
     FieldAlign = std::min(FieldAlign, MaxFieldAlignment);
+    PackedFieldAlign = std::min(PackedFieldAlign, MaxFieldAlignment);
     PreferredAlign = std::min(PreferredAlign, MaxFieldAlignment);
     UnpackedFieldAlign = std::min(UnpackedFieldAlign, MaxFieldAlignment);
   }
@@ -2127,6 +2136,9 @@
                 << Context.getTypeDeclType(RD) << D->getName() << D->getType();
         }
   }
+
+  if (Packed && !FieldPacked && PackedFieldAlign < FieldAlign)
+    Diag(D->getLocation(), diag::warn_unpacked_field) << D;
 }
 
 void ItaniumRecordLayoutBuilder::FinishLayout(const NamedDecl *D) {
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -541,7 +541,8 @@
 def DeprecatedObjCIsaUsage : DiagGroup<"deprecated-objc-isa-usage">;
 def ExplicitInitializeCall : DiagGroup<"explicit-initialize-call">;
 def OrderedCompareFunctionPointers : DiagGroup<"ordered-compare-function-pointers">;
-def Packed : DiagGroup<"packed">;
+def PackedNonPod : DiagGroup<"packed-non-pod">;
+def Packed : DiagGroup<"packed", [PackedNonPod]>;
 def Padded : DiagGroup<"padded">;
 def UnalignedAccess : DiagGroup<"unaligned-access">;
 
Index: clang/include/clang/Basic/DiagnosticASTKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticASTKinds.td
+++ clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -590,6 +590,8 @@
   InGroup<Padded>, DefaultIgnore;
 def warn_unnecessary_packed : Warning<
   "packed attribute is unnecessary for %0">, InGroup<Packed>, DefaultIgnore;
+def warn_unpacked_field : Warning<
+  "not packing field %0 as it is non-POD">, InGroup<PackedNonPod>, DefaultIgnore;
 
 // -Wunaligned-access
 def warn_unaligned_access : Warning<

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