RFR (L): 8022853: add ability to Unsafe to load and store uncompressed object and Klass references in a compressed environment

[Coleen Phillimore]

Hi,

I've reviewed this change and I don't know how it can work.   You cannot 
put uncompressed oops in an object when the setting is UseCompressedOops 
and have garbage collection work.   Similarly you can't compress 
arbitrary metadata because only Klass* types can be compressed.   This 
doesn't seem like it would work at all.   Also, we lay out objects in 
classFileParser assuming the setting of UseCompressedOops/ClassPointers 
and allocates space based on that.

I don't understand the motivation of this change.   It appears incorrect.

 From reading the bug, it seems that you want to get to mirror from 
InstanceKlass from Java.   This will break when we move the mirror.

Coleen

On 8/19/2013 5:28 PM, Christian Thalinger wrote:
> http://cr.openjdk.java.net/~twisti/8022853/webrev/
> http://cr.openjdk.java.net/~twisti/8022853-jdk/webrev/
>
> 8022853: add ability to Unsafe to load and store uncompressed object and Klass references in a compressed environment
> Reviewed-by:
>
> In some native data structures of the VM oops are stored uncompressed when compressed oops are turned on, for example Klass::_java_mirror. Java code which is tightly coupled with the VM should have the ability to read and write such fields.
>