Mojo: Specify/check alignment of pointers more carefully.

mojo/system/memory.cc

Index: mojo/system/memory.cc
diff --git a/mojo/system/memory.cc b/mojo/system/memory.cc
index dd8b3d2334ada19a88fbf647a0974a260c0383ba..498ca0b9913a8dad8d543944d69d4e0dba0581b0 100644
--- a/mojo/system/memory.cc
+++ b/mojo/system/memory.cc
@@ -7,28 +7,79 @@
 #include <limits>
 
 #include "base/logging.h"
+#include "build/build_config.h"
 
 namespace mojo {
 namespace system {
 
-template <size_t size>
-bool VerifyUserPointerForSize(const void* pointer, size_t count) {
+namespace internal {
+
+template <size_t alignment>
+bool IsAligned(const void* pointer) {
+  return reinterpret_cast<uintptr_t>(pointer) % alignment == 0;
+}
+
+#if defined(COMPILER_MSVC) && defined(ARCH_CPU_32_BITS)
+// MSVS (2010, 2013) sometimes (on the stack) aligns, e.g., |int64_t|s (for
+// which |__alignof(int64_t)| is 8) to 4-byte boundaries. http://goo.gl/Y2n56T
+template <>
+bool IsAligned<8>(const void* pointer) {
+  return reinterpret_cast<uintptr_t>(pointer) % 4 == 0;
+}
+#endif
+
+template <size_t size, size_t alignment>
+bool MOJO_SYSTEM_IMPL_EXPORT VerifyUserPointerHelper(const void* pointer) {
+  // TODO(vtl): If running in kernel mode, do a full verification. For now, just
+  // check that it's non-null and aligned. (A faster user mode implementation is
+  // also possible if this check is skipped.)
+  return !!pointer && IsAligned<alignment>(pointer);
+}
+
+// Explicitly instantiate the sizes we need. Add instantiations as needed.
+template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerHelper<1, 1>(
+    const void*);
+template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerHelper<4, 4>(
+    const void*);
+template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerHelper<8, 8>(
+    const void*);
+
+template <size_t size, size_t alignment>
+bool VerifyUserPointerWithCountHelper(const void* pointer, size_t count) {
   if (count > std::numeric_limits<size_t>::max() / size)
     return false;
 
   // TODO(vtl): If running in kernel mode, do a full verification. For now, just
-  // check that it's non-null if |size| is nonzero. (A faster user mode
-  // implementation is also possible if this check is skipped.)
-  return count == 0 || !!pointer;
+  // check that it's non-null and aligned if |count| is nonzero. (A faster user
+  // mode implementation is also possible if this check is skipped.)
+  return count == 0 || (!!pointer && IsAligned<alignment>(pointer));
 }
 
 // Explicitly instantiate the sizes we need. Add instantiations as needed.
-template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerForSize<1>(
+template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerWithCountHelper<1, 1>(
     const void*, size_t);
-template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerForSize<4>(
+template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerWithCountHelper<4, 4>(
     const void*, size_t);
-template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerForSize<8>(
+template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerWithCountHelper<8, 8>(
     const void*, size_t);
 
+}  // nameespace internal
+
+template <size_t alignment>
+bool VerifyUserPointerWithSize(const void* pointer, size_t size) {
+  // TODO(vtl): If running in kernel mode, do a full verification. For now, just
+  // check that it's non-null and aligned. (A faster user mode implementation is
+  // also possible if this check is skipped.)
+  return size == 0 || (!!pointer && internal::IsAligned<alignment>(pointer));
+}
+
+// Explicitly instantiate the alignments we need. Add instantiations as needed.
+template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerWithSize<1>(const void*,
+                                                                   size_t);
+template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerWithSize<4>(const void*,
+                                                                   size_t);
+template MOJO_SYSTEM_IMPL_EXPORT bool VerifyUserPointerWithSize<8>(const void*,
+                                                                   size_t);
+
 }  // namespace system
 }  // namespace mojo