Add a guard page in front of metadata allocations.

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

 // Copyright (c) 2005, 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 85 matching lines @@
 
 // Structure for discovering alignment
 union MemoryAligner {
   void*  p;
   double d;
   size_t s;
 } CACHELINE_ALIGNED;
 
 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;
 
 // Configuration parameters.
 DEFINE_int32(malloc_devmem_start,
              EnvToInt("TCMALLOC_DEVMEM_START", 0),
              "Physical memory starting location in MB for /dev/mem allocation."
              "  Setting this to 0 disables /dev/mem allocation");
 DEFINE_int32(malloc_devmem_limit,
@@ skipping 357 matching lines @@
       CheckAddressBits<kAddressBits>(
           reinterpret_cast<uintptr_t>(result) + *actual_size - 1);
     } else {
       CheckAddressBits<kAddressBits>(
           reinterpret_cast<uintptr_t>(result) + size - 1);
     }
   }
   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) {
     // It's not safe to use MADV_DONTNEED if we've been mapping
     // /dev/mem for heap memory
     return;
   }
   if (pagesize == 0) pagesize = getpagesize();
   const size_t pagemask = pagesize - 1;
 
@@ skipping 21 matching lines @@
     }
   }
 #endif
 }
 
 void TCMalloc_SystemCommit(void* start, size_t length) {
   // Nothing to do here.  TCMalloc_SystemRelease does not alter pages
   // such that they need to be re-committed before they can be used by the
   // application.
 }