Diagnose attempts to apply ms_struct to records with base classes

or virtual functions, but permit that error to be downgraded to
a warning (with -Wno-error=incompatible-ms-struct), and officially
support this kind of dual, ABI-mixing layout.

The basic problem here is that projects which use ms_struct are often
not very circumspect about what types they annotate; for example,
some projects enable the pragma in a prefix header and then only
selectively disable it around system header inclusions.  They may
only care about binary compatibility with MSVC for a subset of
those structs, but that doesn't mean they have no binary
compatibility concerns at all for the rest; thus we are essentially
forced into supporting this hybrid ABI.  But it's reasonable for
us to at least point out the places where we're not making
any guarantees.

The original diagnostic was for dynamic classes, i.e. those with
virtual functions or virtual bases; I've extended it to include
all classes with bases, because we are not actually making any
attempt to duplicate MSVC's base subobject layout in ms_struct
(and it is indeed quite different from Itanium, even for
non-virtual bases).

rdar://16178895

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@202427 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/clang/Basic/DiagnosticGroups.td b/include/clang/Basic/DiagnosticGroups.td
index 9802370a60569a018abe0375fc4d844db2064b92..12bf16372f71d47a476ddbe600240614b397bc88 100644 (file)
--- a/include/clang/Basic/DiagnosticGroups.td
+++ b/include/clang/Basic/DiagnosticGroups.td
@@ -175,6 +175,7 @@ def InfiniteRecursion : DiagGroup<"infinite-recursion">;
 def GNUImaginaryConstant : DiagGroup<"gnu-imaginary-constant">;
 def IgnoredQualifiers : DiagGroup<"ignored-qualifiers">;
 def : DiagGroup<"import">;
+def IncompatibleMSStruct : DiagGroup<"incompatible-ms-struct">;
 def IncompatiblePointerTypesDiscardsQualifiers 
   : DiagGroup<"incompatible-pointer-types-discards-qualifiers">;
 def IncompatiblePointerTypes

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 059a28ab88dabc50771da97dae4500f02216dc5e..6e1484c1ca82b93e512cad49bdb6ca82a2f5a154 100644 (file)
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -500,8 +500,10 @@ def warn_pragma_pack_pop_identifer_and_alignment : Warning<
   "specifying both a name and alignment to 'pop' is undefined">;
 def warn_pragma_pop_failed : Warning<"#pragma %0(pop, ...) failed: %1">,
   InGroup<IgnoredPragmas>;
-def warn_pragma_ms_struct_failed : Warning<"#pramga ms_struct can not be used with dynamic classes or structures">,
-  InGroup<IgnoredPragmas>;
+def warn_cxx_ms_struct :
+  Warning<"ms_struct may not produce MSVC-compatible layouts for classes "
+          "with base classes or virtual functions">,
+  DefaultError, InGroup<IncompatibleMSStruct>;
 
 def warn_pragma_unused_undeclared_var : Warning<
   "undeclared variable %0 used as an argument for '#pragma unused'">,

diff --git a/lib/AST/RecordLayoutBuilder.cpp b/lib/AST/RecordLayoutBuilder.cpp
index d27255ecc8ded6eafc2ca82767493237a4cdba0f..11835c901cbb345f2775a209480e7003a929e834 100644 (file)
--- a/lib/AST/RecordLayoutBuilder.cpp
+++ b/lib/AST/RecordLayoutBuilder.cpp
@@ -1502,6 +1502,10 @@ void RecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
   // __attribute__((packed))) always uses the next available bit
   // offset.
 
+  // In an ms_struct struct, the alignment of a fundamental type is
+  // always equal to its size.  This is necessary in order to mimic
+  // the i386 alignment rules on targets which might not fully align
+  // all types (e.g. Darwin PPC32, where alignof(long long) == 4).
 
   // First, some simple bookkeeping to perform for ms_struct structs.
   if (IsMsStruct) {

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index b9c7cca326a6da309e46049b7d121254e54b5afe..74ab1ee84990ece1d54adc4b10297b2f5b639c2e 100644 (file)
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -4520,11 +4520,18 @@ void Sema::CheckCompletedCXXClass(CXXRecordDecl *Record) {
     }
   }
 
-  // Check to see if we're trying to lay out a struct using the ms_struct
-  // attribute that is dynamic.
-  if (Record->isMsStruct(Context) && Record->isDynamicClass()) {
-    Diag(Record->getLocation(), diag::warn_pragma_ms_struct_failed);
-    Record->dropAttr<MsStructAttr>();
+  // ms_struct is a request to use the same ABI rules as MSVC.  Check
+  // whether this class uses any C++ features that are implemented
+  // completely differently in MSVC, and if so, emit a diagnostic.
+  // That diagnostic defaults to an error, but we allow projects to
+  // map it down to a warning (or ignore it).  It's a fairly common
+  // practice among users of the ms_struct pragma to mass-annotate
+  // headers, sweeping up a bunch of types that the project doesn't
+  // really rely on MSVC-compatible layout for.  We must therefore
+  // support "ms_struct except for C++ stuff" as a secondary ABI.
+  if (Record->isMsStruct(Context) &&
+      (Record->isPolymorphic() || Record->getNumBases())) {
+    Diag(Record->getLocation(), diag::warn_cxx_ms_struct);
   }
 
   // Declare inheriting constructors. We do this eagerly here because:

diff --git a/test/SemaCXX/ms_struct.cpp b/test/SemaCXX/ms_struct.cpp
index 37fa9a7c687caa3c8400b60b6843daccdc2ad0e2..2832b5620f3b6f6e22bcbd9ed5ddf010effd84ac 100644 (file)
--- a/test/SemaCXX/ms_struct.cpp
+++ b/test/SemaCXX/ms_struct.cpp
@@ -1,5 +1,6 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -triple i686-apple-darwin9 -std=c++11 %s
-// expected-no-diagnostics
+// RUN: %clang_cc1 -fsyntax-only -Wno-error=incompatible-ms-struct -verify -triple i686-apple-darwin9 -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -Wno-error=incompatible-ms-struct -verify -triple armv7-apple-darwin9 -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -DTEST_FOR_ERROR -verify -triple armv7-apple-darwin9 -std=c++11 %s
 
 #pragma ms_struct on
 
@@ -9,10 +10,29 @@ struct A {
 };
 
 struct B : public A {
+#ifdef TEST_FOR_ERROR
+  // expected-error@-2 {{ms_struct may not produce MSVC-compatible layouts for classes with base classes or virtual functions}}
+#else
+  // expected-warning@-4 {{ms_struct may not produce MSVC-compatible layouts for classes with base classes or virtual functions}}
+#endif
   unsigned long c:16;
        int d;
   B();
 };
 
 static_assert(__builtin_offsetof(B, d) == 12,
-  "We can't allocate the bitfield into the padding under ms_struct");
\ No newline at end of file
+  "We can't allocate the bitfield into the padding under ms_struct");
+
+// rdar://16178895
+struct C {
+#ifdef TEST_FOR_ERROR
+  // expected-error@-2 {{ms_struct may not produce MSVC-compatible layouts for classes with base classes or virtual functions}}
+#else
+  // expected-warning@-4 {{ms_struct may not produce MSVC-compatible layouts for classes with base classes or virtual functions}}
+#endif
+  virtual void foo();
+  long long n;
+};
+
+static_assert(__builtin_offsetof(C, n) == 8,
+              "long long field in ms_struct should be 8-byte aligned");