Add guard pages in front of platform allocations

src/spaces.cc

Index: src/spaces.cc
===================================================================
--- src/spaces.cc	(revision 8657)
+++ src/spaces.cc	(working copy)
@@ -380,7 +380,10 @@
     if (isolate_->code_range()->exists()) {
       mem = isolate_->code_range()->AllocateRawMemory(requested, allocated);
     } else {
-      mem = OS::Allocate(requested, allocated, true);
+      mem = OS::Allocate(requested + Page::kPageSize, allocated, true);
+      OS::Guard(mem, Page::kPageSize);

[Vyacheslav Egorov (Chromium), 2011/07/15 11:59:14]

You have decreased kPagesPerChunk for all spaces but you only use it when you
allocate executable memory.

I think this is still a bit low level and you need to move one level up and put
guard page management there.

[Cris Neckar, 2011/07/15 18:51:29]

Done.

+      *allocated -= Page::kPageSize;
+      mem = static_cast<char*>(mem) + Page::kPageSize;

[Vyacheslav Egorov (Chromium), 2011/07/15 11:59:14]

we use Address type instead of char* in such cases.

[Cris Neckar, 2011/07/15 18:51:29]

Done.

     }
     // Update executable memory size.
     size_executable_ += static_cast<int>(*allocated);
@@ -407,7 +410,8 @@
   if (isolate_->code_range()->contains(static_cast<Address>(mem))) {
     isolate_->code_range()->FreeRawMemory(mem, length);
   } else {
-    OS::Free(mem, length);
+    size_t guardsize = (executable == EXECUTABLE) ? Page::kPageSize : 0;
+    OS::Free(static_cast<char*>(mem) - guardsize, length + guardsize);

[Vyacheslav Egorov (Chromium), 2011/07/15 11:59:14]

we use Address type instead of char* in such cases.

[Cris Neckar, 2011/07/15 18:51:29]

Done.

   }
   isolate_->counters()->memory_allocated()->Decrement(static_cast<int>(length));
   size_ -= static_cast<int>(length);