[crac] RFR: 8355974: [CRaC] Move CPUFeatures verification to the parent process of JVM [v19]

[duke]

On Mon, 19 May 2025 13:07:30 GMT, Jan Kratochvil <jkratochvil at openjdk.org> wrote:

>> There was originally a mistake:
>> - restoring JVM did restore the image
>> - the restored JVM started checking whether CPU Features of the new host >= CPU Features of the checkpoint host
>> 
>> That is difficult as glibc is already configured (IFUNC) in the image for the checkpoint host and calling any such glibc functions in the restored image will crash (as the advanced instructions from misconfigured IFUNC are not available). Some glibc functions had to be reimplemented in a dummy way inside JVM due to this misdesign.
>> 
>> This patch changes it to:
>> - restoring JVM checks `cpufeatures` user data in the image against current CPU Features
>> - the restored JVM is started only if the CPU Features are satisfied, restored JVM no longer has to verify anything
>> 
>> The patch is a bit of a kitchen sink, there are various improvements of the CPU Features code.
>
> Jan Kratochvil has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Do not call prepare_user_data_api() if no user data is needed

@jankratochvil 
Your change (at version b7c976c4a86268ee2455176003d603be6e988955) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/crac/pull/227#issuecomment-2893574093