[libcxxabi] Do not align field unwindHeader when building for ARM EHABI.

For ARM EHABI, _Unwind_Exception is an alias of _Unwind_Control_Block,
which is not aligned, so we shouldn't align unwindHeader either.

rdar://problem/25364625

llvm-svn: 302981

diff --git a/libcxxabi/src/cxa_exception.hpp b/libcxxabi/src/cxa_exception.hpp
index 2d34698..b9f74e3 100644 (file)
--- a/libcxxabi/src/cxa_exception.hpp
+++ b/libcxxabi/src/cxa_exception.hpp
@@ -64,10 +64,18 @@ struct _LIBCXXABI_HIDDEN __cxa_exception {
     // This field is annotated with attribute aligned so that the exception
     // object following the field is sufficiently aligned and there is no
     // gap between the field and the exception object. r276215 made a change to
-    // annotate _Unwind_Exception with __attribute__((aligned)), but we cannot
-    // incorporate the fix on Darwin since it is an ABI-breaking change, which
-    // is why we need the attribute on this field.
+    // annotate _Unwind_Exception in unwind.h with __attribute__((aligned)), but
+    // we cannot incorporate the fix on Darwin since it is an ABI-breaking
+    // change, which is why we need the attribute on this field.
+    //
+    // For ARM EHABI, we do not align this field since _Unwind_Exception is an
+    // alias of _Unwind_Control_Block, which is not annotated with
+    // __attribute__((aligned).
+#if defined(_LIBCXXABI_ARM_EHABI)
+    _Unwind_Exception unwindHeader;
+#else
     _Unwind_Exception unwindHeader __attribute__((aligned));
+#endif
 };
 
 // http://sourcery.mentor.com/archives/cxx-abi-dev/msg01924.html
@@ -104,7 +112,11 @@ struct _LIBCXXABI_HIDDEN __cxa_dependent_exception {
 
     // See the comment in __cxa_exception as to why this field has attribute
     // aligned.
+#if defined(_LIBCXXABI_ARM_EHABI)
+    _Unwind_Exception unwindHeader;
+#else
     _Unwind_Exception unwindHeader __attribute__((aligned));
+#endif
 };
 
 struct _LIBCXXABI_HIDDEN __cxa_eh_globals {