Fix lazy-instance template to preserve object alignment on MIPS.

The alignment attribute of an object was discarded when allocating storage
for the lazy-instance. Alignment is important for MIPS, where doubles
(and objects containing them) must be aligned on 8-byte boundary.

The alignment attributes are included via a macro that is only defined
under GCC, so that this change does not affect other build enviromments.

Change-Id: I99047cf610618de2e7e29e5de85835dc45d99231
Signed-off-by: Paul Lind <plind@mips.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/base/lazy_instance.h b/base/lazy_instance.h
index 7b1bdc4..a8ff0e8 100644
--- a/base/lazy_instance.h
+++ b/base/lazy_instance.h
@@ -108,6 +108,14 @@ class BASE_API LazyInstanceHelper {
   DISALLOW_COPY_AND_ASSIGN(LazyInstanceHelper);
 };
 
+// Allow preservation of object alignment in the lazy instance when using GCC.
+// __alignof__ is only defined for GCC > 4.2.
+#if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 2))
+#define LAZY_ALIGN(T) __attribute__((aligned(__alignof__(T))))
+#else
+#define LAZY_ALIGN(T)
+#endif
+
 template <typename Type, typename Traits = DefaultLazyInstanceTraits<Type> >
 class LazyInstance : public LazyInstanceHelper {
  public:
@@ -167,12 +175,15 @@ class LazyInstance : public LazyInstanceHelper {
     base::subtle::Release_Store(&me->state_, STATE_EMPTY);
   }
 
-  int8 buf_[sizeof(Type)];  // Preallocate the space for the Type instance.
+  // Preallocate the space for the Type instance, and preserve alignment.
+  int8 buf_[sizeof(Type)] LAZY_ALIGN(Type);
   Type *instance_;
 
   DISALLOW_COPY_AND_ASSIGN(LazyInstance);
 };
 
+#undef LAZY_ALIGN
+
 }  // namespace base
 
 #endif  // BASE_LAZY_INSTANCE_H_