Don't use alloca.

src/objects-inl.h

 // Copyright 2012 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 3485 matching lines @@
 
   ASSERT(!is_shared());
   WRITE_FIELD(this, kInstanceDescriptorsOrBackPointerOffset, value);
   CONDITIONAL_WRITE_BARRIER(
       heap, this, kInstanceDescriptorsOrBackPointerOffset, value, mode);
 }
 
 
 void Map::InitializeDescriptors(DescriptorArray* descriptors) {
   int len = descriptors->number_of_descriptors();
+  ASSERT(len <= DescriptorArray::kMaxNumberOfDescriptors);
   SLOW_ASSERT(descriptors->IsSortedNoDuplicates());
 
 #ifdef DEBUG
-  bool* used_indices =
-      reinterpret_cast<bool*>(alloca(sizeof(*used_indices) * len));
+  bool used_indices[DescriptorArray::kMaxNumberOfDescriptors];
   for (int i = 0; i < len; ++i) used_indices[i] = false;
 
   // Ensure that all enumeration indexes between 1 and length occur uniquely in
   // the descriptor array.
   for (int i = 0; i < len; ++i) {
     int enum_index = descriptors->GetDetails(i).index() -
                      PropertyDetails::kInitialIndex;
+    ASSERT(0 <= enum_index && enum_index < len);
     ASSERT(!used_indices[enum_index]);
     used_indices[enum_index] = true;
   }
 #endif
 
   for (int i = 0; i < len; ++i) {
     if (descriptors->GetDetails(i).index() == len) {
       descriptors->SetLastAdded(i);
       break;
     }
@@ skipping 1840 matching lines @@
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_