RFR: 8286360: ARM32: Fix crashes after JDK-8284161 (Virtual Threads) [v2]

[Aleksey Shipilev]

On Mon, 6 Jun 2022 06:41:29 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Virtual Threads are not fully implemented on ARM32, but there is a fallback implementation that can be used. Still, there is some VM code that is executed unconditionally anyway, crashing the VM on some tests. This improves the ARM32 code to the point that VM is able to build itself and pass tests. This adds the scaffolding for full implementation too.
>> 
>> Additional testing:
>>  - [x] Linux arm32 fastdebug build
>>  - [x] Linux arm32 fastdebug, `jdk_loom  hotspot_loom` pass
>>  - [x] Linux arm32 fastdebug, `jdk_jfr` passes (some timeout failures, because the board I have is very slow)
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 10 additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8286360-loom-arm32-no-preview
>  - Whitespace and comments
>  - JFR barriers from Sergey
>  - Cleanups
>  - Flesh out generate_jfr_write_checkpoint a bit (untested)
>  - Match the generator shape to x86_64
>  - C2 patch from Sergey
>  - Merge branch 'master' into JDK-8286360-loom-arm32-no-preview
>  - Merge branch 'master' into JDK-8286360-loom-arm32-no-preview
>  - ARM32 bootstraps fine without C2

All right, any more reviews? I would like to integrate this to unbreak ARM32.

-------------

PR: https://git.openjdk.java.net/jdk/pull/8634