Add guard pages in front of platform allocations

src/platform-macos.cc

 // Copyright 2006-2008 the V8 project authors. 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
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 130 matching lines @@
 // tools like vmmap(1).
 static const int kMmapFd = VM_MAKE_TAG(255);
 static const off_t kMmapFdOffset = 0;
 
 
 void* OS::Allocate(const size_t requested,
                    size_t* allocated,
                    bool is_executable) {
   const size_t msize = RoundUp(requested, getpagesize());
   int prot = PROT_READ | PROT_WRITE | (is_executable ? PROT_EXEC : 0);
-  void* mbase = mmap(NULL, msize, prot,
+  void* mbase = mmap(NULL, msize + Page::kPageSize, prot,
                      MAP_PRIVATE | MAP_ANON,
                      kMmapFd, kMmapFdOffset);
   if (mbase == MAP_FAILED) {
     LOG(Isolate::Current(), StringEvent("OS::Allocate", "mmap failed"));
     return NULL;
   }
   *allocated = msize;
+  mprotect(mbase, Page::kPageSize, PROT_NONE);
+  mbase += Page::kPageSize;
   UpdateAllocatedSpaceLimits(mbase, msize);
   return mbase;
 }
 
 
 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);
 }
 
 
 #ifdef ENABLE_HEAP_PROTECTION
 
 void OS::Protect(void* address, size_t size) {
   UNIMPLEMENTED();
 }
@@ skipping 640 matching lines @@
 
 void Sampler::Stop() {
   ASSERT(IsActive());
   SamplerThread::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal