Add ALIGNAS and ALIGNOF macros to ensure proper alignment of StaticMemorySingletonTraits

base/compiler_specific.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_COMPILER_SPECIFIC_H_
 #define BASE_COMPILER_SPECIFIC_H_
 #pragma once
 
 #include "build/build_config.h"
 
@@ skipping 78 matching lines @@
 // Use like:
 //   int x ALLOW_UNUSED = ...;
 #if defined(COMPILER_GCC)
 #define ALLOW_UNUSED __attribute__((unused))
 #define NOINLINE __attribute__((noinline))
 #else
 #define ALLOW_UNUSED
 #define NOINLINE
 #endif
 
+// Specify memory alignment for structs, classes or data.
+// Use like:
+//   class ALIGNED(16) MyClass { ... }
+//   int array[4] ALIGNED(16);
+#if defined(COMPILER_MSVC)
+#define ALIGNED(byte_alignment) __declspec(align(byte_alignment))

[Sigurður Ásgeirsson, 2012/01/13 14:32:18]

MSVS wants __declspec to precede the declarator, whereas it looks like GCC wants
__attribute__ to trail it.
I don't see how this macro could be used in a compiler-independent fashion.
Maybe you can do something with a two-argument function that takes a type and an
alignment, and would generally be used in a typedef.
#define ALIGNED_TYPE(type, alignment) __declspec(align(alignment)) type
#define ALIGNED_TYPE(type, alignment) type __attribute(...)

typedef ALIGNED_TYPE(char[sizeof(T)], ALIGNOF(T)) AlignedBuffer;
AlignedBuffer buffer_;

[jbates, 2012/01/13 17:29:18]

At least for struct and class, I think GCC allows either. So this seems to work
for both:
class ALIGNED(16) MyClass {...};

I haven't yet tested typedefs or the int array[4] example in MSVC though.

+#elif defined(COMPILER_GCC)
+#define ALIGNED(byte_alignment) __attribute__((aligned(byte_alignment)))
+#endif
+
+// Return the byte alignment of the given type (available at compile time).
+// Use like:
+//   ALIGNOF(int32)  // this would be 4
+#if defined(COMPILER_MSVC)
+#define ALIGNOF(type) __alignof(type)
+#elif defined(COMPILER_GCC)
+#define ALIGNOF(type) __alignof__(type)
+#endif
+
 // Annotate a virtual method indicating it must be overriding a virtual
 // method in the parent class.
 // Use like:
 //   virtual void foo() OVERRIDE;
 #if defined(COMPILER_MSVC)
 #define OVERRIDE override
 #elif defined(__clang__)
 #define OVERRIDE override
 #else
 #define OVERRIDE
@@ skipping 22 matching lines @@
 #endif
 
 // WPRINTF_FORMAT is the same, but for wide format strings.
 // This doesn't appear to yet be implemented in any compiler.
 // See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38308 .
 #define WPRINTF_FORMAT(format_param, dots_param)
 // If available, it would look like:
 //   __attribute__((format(wprintf, format_param, dots_param)))
 
 #endif  // BASE_COMPILER_SPECIFIC_H_