Re: location of static data

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Chris Pickett wrote:
>>>When PUTSTATIC_<X> is executed, where does that write?  Previously, I
>>>thought it wrote to a class field that was outside of the heap.
>>
>>Yes, for primitive types.
> 
> Ok, I can see that now.  It writes to some element of _svmt_field_info
> *fields in _svmt_class_info.

Not really.  Actually, it's all stored in a _svmt_field_info structure
which is accessible from the class_info.

struct _svmt_class_field_data_struct
{
  jvalue value;
};

struct _svmt_field_info_struct
{
...

  union
  {
    _svmt_instance_field_data instance_field;
    _svmt_class_field_data class_field;
  }
  data;
};


To understand all the little details, why don't you a have a look at
prepare.c:

_svmf_prepare_noninterface_fields
{
...
        if (_svmf_is_set_flag (class->fields[i].access_flags,
                               SVM_ACC_STATIC))
          {
            /* if reference, allocate native global */
            if (class->fields[i].type == SVM_TYPE_REFERENCE)
              {
                if (_svmm_new_native_global
                    (env,
                     class->fields[i].data.class_field.value.l) !=
                       JNI_OK)
                  {
                    return JNI_ERR;
                  }
              }
          }
...
}

> 
> 
>>For reference types, it writes to a global native reference.  It's the
>>address of the global native reference that is stored in the class_info
>>structure.  This class_instance field is initialized once at class loading
>>time.
> 
> 
> I'm a little confused here by the last sentence above.  I meant when you
> write to any static reference:
> 
> static Object o;
> 
> static void m() {
>     o = new Object();
> }

See above.

> from PUTSTATIC_REFERENCE.  The address of the global native reference is
> stored in fields[] like the primitive type fields.  In the code above this
> address is pvalue->l.  The global native ref is *(pvalue->l).

Yep.


May the Source be with you! ;-)

Etienne

-- 
Etienne M. Gagnon, Ph.D.            http://www.info2.uqam.ca/~egagnon/
SableVM:                                       http://www.sablevm.org/
SableCC:                                       http://www.sablecc.org/

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