RFR: 8062247: Allow WhiteBox test to access JVM offsets

[Yumin Qi]

If you check the name passed to this function, it already told (I just 
changed to getOffsetForName and in testing):

wb.getOffsetForName("FileMapHeader::_crc")

Do not need to give type info(that will need build a list for type info 
like in vmStructs). This is a simple code fore testing purpose, I think 
we should keep it simple. I added that if the offsetname not supported, 
throw exception instead. Will post webrev today after jprt finished.

Thanks
Yumin

On 11/3/2014 12:05 PM, Mikhailo Seledtsov wrote:
> Hi Yumin,
>
>  If this API is intended to get offsets for various data structures, I 
> would expect a data  structure type identified to be passed as a 
> parameter. For instance,
>
> public native int getOffset(String dataStructureId, String fieldName)
>     where
>         dataStructureId would be some kind of ID for data structure, 
> either data structure name or internal alias
>         fieldName - the name of the field for which the offset value 
> is returned
>       A specific error code could be returned for unsupported 
> dataStructureId
>
> Alternatively, this could be an API specific to a given 
> data-structure. E.g. getMySpecifiedDatastructOffset(String fieldName)
>
> Thank you,
> Misha
>
>
> On 11/2/2014 9:52 PM, Yumin Qi wrote:
>> Misha,
>>
>>   It is a generic name, now it only targets on FileMapHeader, it can 
>> add other data structure of vm if needed in future. Maybe a name like 
>> getOffsetForName(String name) is better?
>>
>> Thanks
>> Yumin
>>
>> On 10/31/2014 11:56 AM, Mikhailo Seledtsov wrote:
>>> Hi Yumin,
>>>
>>>  The name getOffsets() seems too generic. Perhaps, we could rename 
>>> it to be more specific to the task.
>>>
>>> Thank you,
>>> Misha
>>>
>>> On 10/29/2014 5:46 PM, Yumin Qi wrote:
>>>> Please review the new changeset at same location.
>>>> New API supply an interface to get data member offset by it's name.
>>>> http://cr.openjdk.java.net/~minqi/8062247/webrev00/
>>>>
>>>> Thanks
>>>> Yumin
>>>>
>>>> On 10/27/2014 9:01 PM, Yumin Qi wrote:
>>>>> Please review
>>>>>
>>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8062247
>>>>> webrev: http://cr.openjdk.java.net/~minqi/8062247/webrev00/
>>>>>
>>>>> Summary: Internal test failed since the variable offsets changed 
>>>>> in hotspot. The way to get offset in the test is hard-coded. To 
>>>>> reduce the risk of future changes of hotspot offsets, the fix add 
>>>>> a WhiteBox API function to get a map for FileMapHeaderInfo, which 
>>>>> return the members' offsets in a Hashtable.
>>>>>
>>>>> Tests: JPRT, jtreg.
>>>>>
>>>>> Thanks
>>>>> Yumin
>>>>
>>>
>>
>