Add a guard page in front of metadata allocations.

third_party/tcmalloc/chromium/src/common.cc

 // Copyright (c) 2008, Google Inc.
 // All rights reserved.
 // 
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 // 
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
@@ skipping 16 matching lines @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // ---
 // Author: Sanjay Ghemawat <opensource@google.com>
 
 #include "config.h"
 #include "common.h"
 #include "system-alloc.h"
 
+#if defined(HAVE_UNISTD_H) && defined(HAVE_GETPAGESIZE)
+#include <unistd.h>                     // for getpagesize
+#endif
+
 namespace tcmalloc {
 
 // Note: the following only works for "n"s that fit in 32-bits, but
 // that is fine since we only use it for small sizes.
 static inline int LgFloor(size_t n) {
   int log = 0;
   for (int i = 4; i >= 0; --i) {
     int shift = (1 << i);
     size_t x = n >> shift;
     if (x != 0) {
@@ skipping 147 matching lines @@
                 int(class_to_size_[cl]),
                 int(class_to_pages_[cl] << kPageShift),
                 max_waste * 100.0 / alloc_size
                 );
   }
 }
 
 // Metadata allocator -- keeps stats about how many bytes allocated.
 static uint64_t metadata_system_bytes_ = 0;
 void* MetaDataAlloc(size_t bytes) {
-  void* result = TCMalloc_SystemAlloc(bytes, NULL);
+  static size_t pagesize;
+#ifdef HAVE_GETPAGESIZE
+  if (pagesize == 0)
+    pagesize = getpagesize();
+#endif
+
+  void* result = TCMalloc_SystemAlloc(bytes, NULL, pagesize);
   if (result != NULL) {
     metadata_system_bytes_ += bytes;
   }
   return result;
 }
 
 uint64_t metadata_system_bytes() { return metadata_system_bytes_; }
 
 void increment_metadata_system_bytes(size_t bytes) {
   metadata_system_bytes_ += bytes;
 }
 
 }  // namespace tcmalloc