[crac] RFR: Move CPUFeatures verification to the parent process of JVM [v2]

[Jan Kratochvil]

On Tue, 29 Apr 2025 09:36:07 GMT, Timofei Pushkin <tpushkin at openjdk.org> wrote:

>> Jan Kratochvil has updated the pull request incrementally with four additional commits since the last revision:
>> 
>>  - Print load_user_data error
>>  - Rename userdata_name
>>  - Use the standardized prepare_user_data_api() style
>>  - Removed unused declaration
>
> src/hotspot/share/runtime/threads.cpp line 606:
> 
>> 604: 
>> 605:   // Output stream module should be already initialized for error reporting during restore.
>> 606:   // JDK version should also be intialized.
> 
> This comment should probably be updated saying that a lot of things (probably no point in listing them all) should be initialized to be able to check CPU features

Described in 03200e67c33bedf197c31dd574d9a202d0e5e40d.

> src/java.base/share/man/java.md line 1838:
> 
>> 1836:     `-XX:CRaCCheckpointTo` when you get an error during `-XX:CRaCRestoreFrom`
>> 1837:     on a different machine. `-XX:CPUFeatures=native` is the default.
>> 1838:     `-XX:CPUFeatures=generic` is compatible with any CPU.
> 
> There is also `CPUFeatures=ignore`, what is the difference between it and `IgnoreCPUFeatures`? The fact that `IgnoreCPUFeatures` is to be set on restore?

Could we leave this for a different patch? IIRC I even have some patch done for it already. I have filed a TODO item internally as ZULU-75248.

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PR Review Comment: https://git.openjdk.org/crac/pull/227#discussion_r2066894752
PR Review Comment: https://git.openjdk.org/crac/pull/227#discussion_r2066897842