[crac] RFR: Fix up CPUFeatures on top of Merge jdk:jdk-25+26 [v8]

[Timofei Pushkin]

On Sun, 27 Jul 2025 02:19:18 GMT, Jan Kratochvil <jkratochvil at openjdk.org> wrote:

>> This pull request contains: https://github.com/openjdk/crac/pull/248
>> I think the CRaC project does not provide the pr/NUMBER branches for dependent patches.
>> 
>> This pull request enables the CPUFeatures again.
>
> Jan Kratochvil has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix the message: VM option 'CPUFeatures=%s' must be of the form

Besides the small comment LGTM.

I found a few issues with handling of incorrect inputs (ZULU-78855, ZULU-78856, ZULU-78857) but turns out they are all pre-existing, so should not be fixed here. Looks like the CPU features testing should be enlarged.

src/hotspot/cpu/x86/vm_version_x86.cpp line 2556:

> 2554:                 "If you are sure it will not crash you can override this check by -XX:+UnlockExperimentalVMOptions -XX:+IgnoreCPUFeatures .",
> 2555:                 buf);
> 2556: }

When specifying missing features I am getting:

Specified -XX:CPUFeatures=0xffffffffffffffff,0xfffffffffffffffe; this machine's CPU features are 0x44fbffff9dfdfbff,0x3cc; missing features of this CPU are 0xbb04000062020400,0x32 = , sse4a, tscinv, rtm, avx512pf, avx512er, fsrm, cet_ibt, cet_ss, avx_ifma, apx_f, sha512, avx10_1, fma4, ibt, shstk

The comma after the "=" in "... 0xbb04000062020400,0x32 = , sse4a ..." is out of place.

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PR Review: https://git.openjdk.org/crac/pull/250#pullrequestreview-3059440411
PR Review Comment: https://git.openjdk.org/crac/pull/250#discussion_r2233888568