[libcxxabi] Fix alignment of allocated exceptions in 32 bit builds

Summary:
In 32 bit builds on a 64 bit system `std::malloc` does not return correctly aligned memory.  This leads to undefined behavior.

This patch switches to using `posix_memalign` to allocate correctly aligned memory instead.

Reviewers: mclow.lists, danalbert, jroelofs, compnerd

Reviewed By: compnerd

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D25417

llvm-svn: 296952

1 files changed, 28 insertions, 0 deletions

diff --git a/libcxxabi/test/test_exception_address_alignment.pass.cpp b/libcxxabi/test/test_exception_address_alignment.pass.cpp
new file mode 100644
index 00000000000..5c5b4dfe7cc
--- /dev/null
+++ b/libcxxabi/test/test_exception_address_alignment.pass.cpp
@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// Test that the address of the exception object is properly aligned to the
+// largest supported alignment for the system.
+
+#include <cstdint>
+#include <cassert>
+
+struct __attribute__((aligned)) AlignedType {};
+struct MinAligned {  };
+static_assert(alignof(MinAligned) == 1 && sizeof(MinAligned) == 1, "");
+
+int main() {
+  for (int i=0; i < 10; ++i) {
+    try {
+      throw MinAligned{};
+    } catch (MinAligned const& ref) {
+      assert(reinterpret_cast<uintptr_t>(&ref) % alignof(AlignedType) == 0);
+    }
+  }
+}