Use the return value of vm native methods to set the return value,

vm/native_arguments.h

 // 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.
 
 #ifndef VM_NATIVE_ARGUMENTS_H_
 #define VM_NATIVE_ARGUMENTS_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/stub_code.h"
@@ skipping 48 matching lines @@
   Isolate* isolate() const { return isolate_; }
   int Count() const { return argc_; }
 
   RawObject* At(int index) const {
     ASSERT(index >=0 && index < argc_);
     return (*argv_)[-index];
   }
 
   void SetReturn(const Object& value) const;
 
+  // If this function is misused, it could cause corruption.  You may
+  // only use this if Siva says it is ok.
+  void SetReturnUnsafe(RawObject* value) const;

[Ivan Posva, 2012/08/27 18:20:37]

Can we make this a private and do some friend magic instead of purely relying on
the comment?

[turnidge, 2012/08/28 18:08:21]

I tried it but it got a little bit involved.

In order to declare the functions as friend declarations, we need access to the
BOOTSTRAP_NATIVE_LIST in bootstrap_natives.h.  Because that file also includes
the forward declarations of the native entries, it includes native_entry.h  And,
in turn, native_entry.h includes native_arguments.h in order to get the
definition of the NativeArguments type (it needs the full definition because it
is passed by value).

So, to resolve this, I would need to do some refactoring.  I would probably need
to split the BOOTSTRAP_NATIVE_LIST macro and the native entry forward
declarations into two separate headers.  I started to do this, but I decided I
should ping you back to see what you'd like me to do.

[turnidge, 2012/08/29 20:36:49]

As you suggested offline, I've created a BootstrapNatives class containing all
of the native entries.  That made the friend declaration quite a bit simpler.

On 2012/08/28 18:08:21, turnidge wrote:

+
   static intptr_t isolate_offset() {
     return OFFSET_OF(NativeArguments, isolate_);
   }
   static intptr_t argc_offset() { return OFFSET_OF(NativeArguments, argc_); }
   static intptr_t argv_offset() { return OFFSET_OF(NativeArguments, argv_); }
   static intptr_t retval_offset() {
     return OFFSET_OF(NativeArguments, retval_);
   }
 
  private:
   Isolate* isolate_;  // Current isolate pointer.
   int argc_;  // Number of arguments passed to the runtime call.
   RawObject*(*argv_)[];  // Pointer to an array of arguments to runtime call.
   RawObject** retval_;  // Pointer to the return value area.
 };
 
 }  // namespace dart
 
 #endif  // VM_NATIVE_ARGUMENTS_H_