[libcxxabi] Align unwindHeader on a double-word boundary.

r276215 made a change to annotate _Unwind_Exception with attribute
"aligned" so that an exception object following field __cxa_exception
is sufficiently aligned. This fix hasn't been incorporated to unwind.h
on Darwin since it is an ABI breaking change.

Instead of annotating struct _Unwind_Exception with the attribute, this
commit annotates field unwindHeader of __cxa_exception. This ensures the
exception object is sufficiently aligned without breaking the ABI.

rdar://problem/25364625

Differential Revision: https://reviews.llvm.org/D33030

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@302763 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 46 insertions, 0 deletions

diff --git a/test/exception_object_alignment.sh.cpp b/test/exception_object_alignment.sh.cpp
new file mode 100644
index 0000000..076f45c
--- /dev/null
+++ b/test/exception_object_alignment.sh.cpp
@@ -0,0 +1,46 @@
+//===---------------- exception_object_alignment.sh.cpp -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: libcxxabi-no-exceptions
+
+// RUN: %cxx %flags %compile_flags -O1 %s -o %t.exe
+// RUN: %exec %t.exe
+
+// This test used to segfault on Darwin because field unwindHeader of struct
+// __cxa_exception was not 16B aligned.
+
+namespace {
+
+struct S {
+  int a;
+  int __attribute__((aligned(16))) b;
+};
+
+class base1 {
+protected:
+  virtual ~base1() throw() {}
+};
+
+class derived: public base1 {
+public:
+  derived() : member() {}
+private:
+  S member;
+};
+
+}
+
+int main() {
+  try {
+    throw derived();
+  }
+  catch(...) {
+  }
+  return 0;
+}