AArch64: is a compressed class space at 2G a problem?

[Andrew Haley]

On 12/21/20 8:55 AM, Reingruber, Richard wrote:
>> On 12/18/20 4:52 PM, Reingruber, Richard wrote:
>>>
>>> it appears to me that locating the compressed class space (ccs) at 2G is
>>> currently not possible on AArch64 [1][2]. This looks like a bug to me. Would you
>>> agree?
> 
>> If the compressed class space is located at 2G then its encoding
>> base should be zero. We don't care exactly where the space starts,
>> but we do care very much that its encoding base is 4G-aligned.
> 
> Thanks for the feedback! I've created [1] to track this.

This is bizarre. I'm pretty sure it used to work; maybe something
else has changed. What we want, in pretty much every case, is an
unshifted 4G-aligned encoding. Zero-based would be nice.

Mind you, given that CDS seems to be on by default, I guess any
weird options won't much be used anyway.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671