Add a guard page in front of metadata allocations.

third_party/tcmalloc/chromium/src/system-alloc.cc

Index: third_party/tcmalloc/chromium/src/system-alloc.cc
===================================================================
--- third_party/tcmalloc/chromium/src/system-alloc.cc	(revision 110522)
+++ third_party/tcmalloc/chromium/src/system-alloc.cc	(working copy)
@@ -103,10 +103,7 @@
 
 static SpinLock spinlock(SpinLock::LINKER_INITIALIZED);
 
-#if defined(HAVE_MMAP) || defined(MADV_DONTNEED)
-// Page size is initialized on demand (only needed for mmap-based allocators)
 static size_t pagesize = 0;

[jar (doing other things), 2011/11/23 23:46:14]

Per your verbal comment.... "you need a guard around this in case there is no
getpagesize() call to be used.

[jschuh, 2011/11/24 00:05:26]

Done.

-#endif
 
 // The current system allocator
 SysAllocator* sys_alloc = NULL;
@@ -484,6 +481,18 @@
   return result;
 }
 
+size_t TCMalloc_SystemAddGuard(void* start) {
+  if (pagesize == 0) pagesize = getpagesize();

[jar (doing other things), 2011/11/23 23:46:14]

You'll need a wrapper here to for getpagesize availability.

[jschuh, 2011/11/24 00:05:26]

Done.

+
+  if (reinterpret_cast<size_t>(start) % pagesize != 0)
+    return 0;
+
+  if (!mprotect(start, pagesize, PROT_NONE))
+    return pagesize;
+
+  return 0;
+}
+
 void TCMalloc_SystemRelease(void* start, size_t length) {
 #ifdef MADV_DONTNEED
   if (FLAGS_malloc_devmem_start) {