Add guard pages in front of platform allocations

src/platform-win32.cc

Index: src/platform-win32.cc
===================================================================
--- src/platform-win32.cc	(revision 8619)
+++ src/platform-win32.cc	(working copy)
@@ -913,11 +913,14 @@
   }
 
   LPVOID mbase = VirtualAlloc(reinterpret_cast<void *>(address),
-                              msize,
+                              msize + Page::kPageSize,

[Vyacheslav Egorov (Chromium), 2011/07/12 23:23:29]

This looks slightly suspicious to me.

MemoryAllocator knows about 64k allocation granularity on Windows and allocates
space for 8 8k Pages per call to OS::Allocate.

Here you basically ask for 8*8k + 8k which will waste 7*8k of VAS which
MemoryAllocator tried to avoid.

[Cris Neckar, 2011/07/14 17:32:28]

Done.

                               MEM_COMMIT | MEM_RESERVE,
                               prot);
   if (mbase == NULL && address != 0)
-    mbase = VirtualAlloc(NULL, msize, MEM_COMMIT | MEM_RESERVE, prot);
+    mbase = VirtualAlloc(NULL,
+                         msize + Page::kPageSize,
+                         MEM_COMMIT | MEM_RESERVE,
+                         prot);
 
   if (mbase == NULL) {
     LOG(ISOLATE, StringEvent("OS::Allocate", "VirtualAlloc failed"));
@@ -925,8 +928,12 @@
   }
 
   ASSERT(IsAligned(reinterpret_cast<size_t>(mbase), OS::AllocateAlignment()));
+  *allocated = msize;
 
-  *allocated = msize;
+  DWORD old_protect;
+  VirtualProtect(mbase, Page::kPageSize, PAGE_READONLY | PAGE_GUARD, &old_protect);
+  mbase = static_cast<BYTE*>(mbase) + Page::kPageSize;
+
   UpdateAllocatedSpaceLimits(mbase, static_cast<int>(msize));
   return mbase;
 }
@@ -934,7 +941,7 @@
 
 void OS::Free(void* address, const size_t size) {
   // TODO(1240712): VirtualFree has a return value which is ignored here.
-  VirtualFree(address, 0, MEM_RELEASE);
+  VirtualFree(static_cast<BYTE*>(address) - Page::kPageSize, 0, MEM_RELEASE);
   USE(size);
 }