Move aligned allocation to the platform files.

src/platform-macos.cc

Index: src/platform-macos.cc
diff --git a/src/platform-macos.cc b/src/platform-macos.cc
index 0671a923b3f264df26cb1139216db310a16e6747..36ff74e9123b29ec2e5853d7cb4a6012fc3e54a5 100644
--- a/src/platform-macos.cc
+++ b/src/platform-macos.cc
@@ -1,4 +1,4 @@
-// Copyright 2006-2008 the V8 project authors. All rights reserved.
+// Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
@@ -354,6 +354,34 @@ void* VirtualMemory::ReserveRegion(size_t size) {
 }
 
 
+void* VirtualMemory::ReserveAlignedRegion(size_t size, size_t alignment) {
+  ASSERT(IsAligned(alignment, static_cast<intptr_t>(OS::AllocateAlignment())));
+  size_t request_size = RoundUp(size + alignment,
+                                static_cast<intptr_t>(OS::AllocateAlignment()));
+  void* reservation = mmap(GetRandomMmapAddr(),
+                           request_size,
+                           PROT_NONE,
+                           MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE,
+                           kMmapFd,
+                           kMmapFdOffset);
+  if (reservation == MAP_FAILED) return NULL;
+  Address base = static_cast<Address>(reservation);
+  Address aligned_base = RoundUp(base, alignment);
+  ASSERT(base <= aligned_base);
+
+  // Unmap extra memory reserved before and after the desired block.
+  size_t bytes_prior = static_cast<size_t>(aligned_base - base);
+  if (bytes_prior > 0) {
+    munmap(base, bytes_prior);
+  }
+  if (static_cast<size_t>(aligned_base - base) < request_size - size) {
+    munmap(aligned_base + size, request_size - size - bytes_prior);
+  }
+
+  return static_cast<void*>(aligned_base);
+}
+
+
 VirtualMemory::~VirtualMemory() {
   if (IsReserved()) {
     if (ReleaseRegion(address_, size_)) address_ = MAP_FAILED;