RFR: JDK-8299229: [JVMCI] add support for UseZGC [v5]

[Tom Rodriguez]

On Mon, 24 Apr 2023 16:50:59 GMT, Tom Rodriguez <never at openjdk.org> wrote:

>> This exposes the required ZGC values to JVMCI and adds support for nmethod entry barriers.  The ZGC support is straightforward but the nmethod entry barrier required some reworking to fit better into JVMCI usage.  I also removed the epoch based barrier since it was no longer used with simplified the assumptions on the JVMCI side.  There is also a minor loom related fix to support post call nops included.  I could move that into a separate PR if that would be preferred.
>
> Tom Rodriguez has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 11 commits:
> 
>  - Merge branch 'master' into tkr-zgc
>  - Use reloc for guard location and read internal fields using HotSpot accessors
>  - Merge branch 'master' into tkr-zgc
>  - Remove access to extra data section from Java code
>  - Handle concurrent unloading
>  - Merge branch 'master' into tkr-zgc
>  - Add missing declaration
>  - Replace NULL with nullptr in new code
>  - Merge branch 'master' into tkr-zgc
>  - Review fixes
>  - ... and 1 more: https://git.openjdk.org/jdk/compare/62acc882...c7bb4391

A graal test caught a slight bug in the new exception seen handling, so I ported that test to jtreg and fixed the issue.  Additionally I changed code installation to require nmethod entry barriers for all default code installations.  There are manually built unit tests that create assembly in a somewhat ad hoc way and fixing them to include an entry barrier was going to be a lot of work.  So this seemed an adequate compromise.  I think they will eventually need to fixed.

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PR Comment: https://git.openjdk.org/jdk/pull/11996#issuecomment-1531891244