Add guard pages in front of platform allocations

src/platform-linux.cc

Index: src/platform-linux.cc
===================================================================
--- src/platform-linux.cc	(revision 8619)
+++ src/platform-linux.cc	(working copy)
@@ -370,13 +370,16 @@
   // TODO(805): Port randomization of allocated executable memory to Linux.
   const size_t msize = RoundUp(requested, sysconf(_SC_PAGESIZE));
   int prot = PROT_READ | PROT_WRITE | (is_executable ? PROT_EXEC : 0);
-  void* mbase = mmap(NULL, msize, prot, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  void* mbase = mmap(NULL, msize + Page::kPageSize, prot,

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

V8 uses "one argument per line" convention.

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

Done.

+                     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
   if (mbase == MAP_FAILED) {
     LOG(i::Isolate::Current(),
         StringEvent("OS::Allocate", "mmap failed"));
     return NULL;
   }
   *allocated = msize;
+  mprotect(mbase, Page::kPageSize, PROT_NONE);
+  mbase += Page::kPageSize;

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

I am a bit concerned that we are spreading (and duplicating) guard page
management across platform-* files instead of managing it uniformly in the
MemoryAllocator which seems more appropriate place to me (OS::* should be just a
low-level OS interface).

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

Done.

   UpdateAllocatedSpaceLimits(mbase, msize);
   return mbase;
 }
@@ -384,7 +387,7 @@
 
 void OS::Free(void* address, const size_t size) {
   // TODO(1240712): munmap has a return value which is ignored here.
-  int result = munmap(address, size);
+  int result = munmap(address - Page::kPageSize, size + Page::kPageSize);
   USE(result);
   ASSERT(result == 0);
 }