Landing: Write protect executable pages in the VM.

runtime/vm/virtual_memory_macos.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "vm/virtual_memory.h"
 
 #include <sys/mman.h>  // NOLINT
@@ skipping 58 matching lines @@
   void* address = mmap(reinterpret_cast<void*>(addr), size, prot,
                        MAP_PRIVATE | MAP_ANON | MAP_FIXED,
                        -1, 0);
   if (address == MAP_FAILED) {
     return false;
   }
   return true;
 }
 
 
-bool VirtualMemory::Protect(Protection mode) {
+bool VirtualMemory::Protect(void* address, intptr_t size, Protection mode) {
+  uword start_address = reinterpret_cast<uword>(address);
+  uword end_address = start_address + size;
+  uword page_address = Utils::RoundDown(start_address, PageSize());
   int prot = 0;
   switch (mode) {
     case kNoAccess:
       prot = PROT_NONE;
       break;
     case kReadOnly:
       prot = PROT_READ;
       break;
     case kReadWrite:
       prot = PROT_READ | PROT_WRITE;
       break;
     case kReadExecute:
       prot = PROT_READ | PROT_EXEC;
       break;
-    case kReadWriteExecute:
-      prot = PROT_READ | PROT_WRITE | PROT_EXEC;
-      break;
   }
-  return (mprotect(address(), size(), prot) == 0);
+  return (mprotect(reinterpret_cast<void*>(page_address),
+                   end_address - page_address,
+                   prot) == 0);
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)