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authorAkira Hatanaka <ahatanaka@apple.com>2017-05-13 03:14:49 +0000
committerAkira Hatanaka <ahatanaka@apple.com>2017-05-13 03:14:49 +0000
commitc501f754a584701bbe1646a2a16bcdc8aabae9ea (patch)
tree7fce143cd9c03566f1a1bbab15c5e8e16a1d0fcb /libcxxabi
parent5057086a35a6116a65c6ee1da5be09e65ac5ba8a (diff)
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[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. This recommits r302763 with fixes to RUN lines in the test case. rdar://problem/25364625 Differential Revision: https://reviews.llvm.org/D33030 llvm-svn: 302978
Diffstat (limited to 'libcxxabi')
-rw-r--r--libcxxabi/src/cxa_exception.hpp12
-rw-r--r--libcxxabi/test/exception_object_alignment.sh.cpp48
2 files changed, 58 insertions, 2 deletions
diff --git a/libcxxabi/src/cxa_exception.hpp b/libcxxabi/src/cxa_exception.hpp
index c009db4..2d34698 100644
--- a/libcxxabi/src/cxa_exception.hpp
+++ b/libcxxabi/src/cxa_exception.hpp
@@ -61,7 +61,13 @@ struct _LIBCXXABI_HIDDEN __cxa_exception {
size_t referenceCount;
#endif
- _Unwind_Exception unwindHeader;
+ // 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.
+ _Unwind_Exception unwindHeader __attribute__((aligned));
};
// http://sourcery.mentor.com/archives/cxx-abi-dev/msg01924.html
@@ -96,7 +102,9 @@ struct _LIBCXXABI_HIDDEN __cxa_dependent_exception {
void* primaryException;
#endif
- _Unwind_Exception unwindHeader;
+ // See the comment in __cxa_exception as to why this field has attribute
+ // aligned.
+ _Unwind_Exception unwindHeader __attribute__((aligned));
};
struct _LIBCXXABI_HIDDEN __cxa_eh_globals {
diff --git a/libcxxabi/test/exception_object_alignment.sh.cpp b/libcxxabi/test/exception_object_alignment.sh.cpp
new file mode 100644
index 0000000..5f4aea2
--- /dev/null
+++ b/libcxxabi/test/exception_object_alignment.sh.cpp
@@ -0,0 +1,48 @@
+//===---------------- 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: %build -O1
+// RUN: %run
+
+// This test used to fail on Darwin because field unwindHeader of struct
+// __cxa_exception and the exception object that immediately followed were not
+// 16B aligned. It would segfault in class derived's constructor when a movaps
+// tried to write to a memory operand that 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;
+}