Recommit r308327 3rd time: Add a warning for missing

'#pragma pack (pop)' and suspicious uses of '#pragma pack' in included files

The second recommit (r309106) was reverted because the "non-default #pragma
pack value chages the alignment of struct or union members in the included file"
warning proved to be too aggressive for external projects like Chromium
(https://bugs.chromium.org/p/chromium/issues/detail?id=749197). This recommit
makes the problematic warning a non-default one, and gives it the
-Wpragma-pack-suspicious-include warning option.

The first recommit (r308441) caused a "non-default #pragma pack value might
change the alignment of struct or union members in the included file" warning
in LLVM itself. This recommit tweaks the added warning to avoid warnings for
#includes that don't have any records that are affected by the non-default
alignment. This tweak avoids the previously emitted warning in LLVM.

Original message:

This commit adds a new -Wpragma-pack warning. It warns in the following cases:

- When a translation unit is missing terminating #pragma pack (pop) directives.
- When entering an included file if the current alignment value as determined
  by '#pragma pack' directives is different from the default alignment value.
- When leaving an included file that changed the state of the current alignment
  value.

rdar://10184173

Differential Revision: https://reviews.llvm.org/D35484

llvm-svn: 309386

1 files changed, 54 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaAttr.cpp b/clang/lib/Sema/SemaAttr.cpp
index 8c13ead6445..f7f1f618739 100644
--- a/clang/lib/Sema/SemaAttr.cpp
+++ b/clang/lib/Sema/SemaAttr.cpp
@@ -61,6 +61,17 @@ void Sema::AddAlignmentAttributesForRecord(RecordDecl *RD) {
       RD->addAttr(MaxFieldAlignmentAttr::CreateImplicit(Context,
                                                         Alignment * 8));
   }
+  if (PackIncludeStack.empty())
+    return;
+  // The #pragma pack affected a record in an included file,  so Clang should
+  // warn when that pragma was written in a file that included the included
+  // file.
+  for (auto &PackedInclude : llvm::reverse(PackIncludeStack)) {
+    if (PackedInclude.CurrentPragmaLocation != PackStack.CurrentPragmaLocation)
+      break;
+    if (PackedInclude.HasNonDefaultValue)
+      PackedInclude.ShouldWarnOnInclude = true;
+  }
 }
 
 void Sema::AddMsStructLayoutForRecord(RecordDecl *RD) {
@@ -202,6 +213,47 @@ void Sema::ActOnPragmaPack(SourceLocation PragmaLoc, PragmaMsStackAction Action,
   PackStack.Act(PragmaLoc, Action, SlotLabel, AlignmentVal);
 }
 
+void Sema::DiagnoseNonDefaultPragmaPack(PragmaPackDiagnoseKind Kind,
+                                        SourceLocation IncludeLoc) {
+  if (Kind == PragmaPackDiagnoseKind::NonDefaultStateAtInclude) {
+    SourceLocation PrevLocation = PackStack.CurrentPragmaLocation;
+    // Warn about non-default alignment at #includes (without redundant
+    // warnings for the same directive in nested includes).
+    // The warning is delayed until the end of the file to avoid warnings
+    // for files that don't have any records that are affected by the modified
+    // alignment.
+    bool HasNonDefaultValue =
+        PackStack.hasValue() &&
+        (PackIncludeStack.empty() ||
+         PackIncludeStack.back().CurrentPragmaLocation != PrevLocation);
+    PackIncludeStack.push_back(
+        {PackStack.CurrentValue,
+         PackStack.hasValue() ? PrevLocation : SourceLocation(),
+         HasNonDefaultValue, /*ShouldWarnOnInclude*/ false});
+    return;
+  }
+
+  assert(Kind == PragmaPackDiagnoseKind::ChangedStateAtExit && "invalid kind");
+  PackIncludeState PrevPackState = PackIncludeStack.pop_back_val();
+  if (PrevPackState.ShouldWarnOnInclude) {
+    // Emit the delayed non-default alignment at #include warning.
+    Diag(IncludeLoc, diag::warn_pragma_pack_non_default_at_include);
+    Diag(PrevPackState.CurrentPragmaLocation, diag::note_pragma_pack_here);
+  }
+  // Warn about modified alignment after #includes.
+  if (PrevPackState.CurrentValue != PackStack.CurrentValue) {
+    Diag(IncludeLoc, diag::warn_pragma_pack_modified_after_include);
+    Diag(PackStack.CurrentPragmaLocation, diag::note_pragma_pack_here);
+  }
+}
+
+void Sema::DiagnoseUnterminatedPragmaPack() {
+  if (PackStack.Stack.empty())
+    return;
+  for (const auto &StackSlot : llvm::reverse(PackStack.Stack))
+    Diag(StackSlot.PragmaPushLocation, diag::warn_pragma_pack_no_pop_eof);
+}
+
 void Sema::ActOnPragmaMSStruct(PragmaMSStructKind Kind) { 
   MSStructPragmaOn = (Kind == PMSST_ON);
 }
@@ -249,7 +301,8 @@ void Sema::PragmaStack<ValueType>::Act(SourceLocation PragmaLocation,
     return;
   }
   if (Action & PSK_Push)
-    Stack.push_back(Slot(StackSlotLabel, CurrentValue, CurrentPragmaLocation));
+    Stack.emplace_back(StackSlotLabel, CurrentValue, CurrentPragmaLocation,
+                       PragmaLocation);
   else if (Action & PSK_Pop) {
     if (!StackSlotLabel.empty()) {
       // If we've got a label, try to find it and jump there.