Mojo: Specify/check alignment of pointers more carefully.

mojo/system/memory.h

 // Copyright 2013 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 MOJO_SYSTEM_MEMORY_H_
 #define MOJO_SYSTEM_MEMORY_H_
 
 #include <stddef.h>
 
+#include "mojo/public/c/system/macros.h"
 #include "mojo/system/system_impl_export.h"
 
 namespace mojo {
 namespace system {
 
-// This is just forward-declared, with the definition and explicit
-// instantiations in the .cc file. This is used by |VerifyUserPointer<T>()|
-// below, and you should use that instead.
-template <size_t size>
-bool MOJO_SYSTEM_IMPL_EXPORT VerifyUserPointerForSize(const void* pointer,
-                                                      size_t count);
+namespace internal {
 
-// Verify that |count * sizeof(T)| bytes can be read from the user |pointer|
-// insofar as possible/necessary (note: this is done carefully since |count *
-// sizeof(T)| may overflow a |size_t|. |count| may be zero. If |T| is |void|,
-// then the size of each element is taken to be a single byte.
-//
-// For example, if running in kernel mode, this should be a full verification
-// that the given memory is owned and readable by the user process. In user
-// mode, if crashes are acceptable, this may do nothing at all (and always
-// return true).
+template <size_t size, size_t alignment>
+bool MOJO_SYSTEM_IMPL_EXPORT VerifyUserPointerHelper(const void* pointer);
+
+template <size_t size, size_t alignment>
+bool MOJO_SYSTEM_IMPL_EXPORT VerifyUserPointerWithCountHelper(
+    const void* pointer,
+    size_t count);
+
+}  // namespace internal
+
+// Verify (insofar as possible/necessary) that a |T| can be read from the user
+// |pointer|.
 template <typename T>
-bool VerifyUserPointer(const T* pointer, size_t count) {
-  return VerifyUserPointerForSize<sizeof(T)>(pointer, count);
+bool VerifyUserPointer(const T* pointer) {
+  return internal::VerifyUserPointerHelper<sizeof(T), MOJO_ALIGNOF(T)>(pointer);
 }
 
-// Special-case |T| equals |void| so that the size is in bytes, as indicated
-// above.
-template <>
-inline bool VerifyUserPointer<void>(const void* pointer, size_t count) {
-  return VerifyUserPointerForSize<1>(pointer, count);
+// Verify (insofar as possible/necessary) that |count| |T|s can be read from the
+// user |pointer|; |count| may be zero. (This is done carefully since |count *
+// sizeof(T)| may overflow a |size_t|.)
+template <typename T>
+bool VerifyUserPointerWithCount(const T* pointer, size_t count) {
+  return internal::VerifyUserPointerWithCountHelper<sizeof(T),
+                                                    MOJO_ALIGNOF(T)>(pointer,
+                                                                     count);
 }
 
+// Verify that |size| bytes (which may be zero) can be read from the user
+// |pointer|, and that |pointer| has the specified |alignment| (if |size| is
+// nonzero).
+template <size_t alignment>
+bool MOJO_SYSTEM_IMPL_EXPORT VerifyUserPointerWithSize(const void* pointer,
+                                                       size_t size);
+
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_MEMORY_H_