RFR: 8329031: CPUID feature detection for Advanced Performance Extensions (Intel® APX) [v3]

[Vladimir Kozlov]

On Fri, 7 Jun 2024 02:16:27 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Summary of changes include with the patch:-
>> 
>> 1) CPUID based feature detection check for Intel APX extension (https://www.intel.com/content/www/us/en/developer/articles/technical/advanced-performance-extensions-apx.html)
>> 2) Validation during VM initialization for extended GPRs state save / restoration by OS across context switches of java application threads executing JIT compiled code with new APX ISA.
>> 
>> Kindly review and share your feedback.
>> 
>> Best Regards,
>> Jatin
>
> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Review comments addressed.

src/hotspot/cpu/x86/vm_version_x86.cpp line 882:

> 880: 
> 881: void VM_Version::report_apx_state_restore_warning() {
> 882:   tty->print("warning: Unsuccessful EGPRs state restoration across signal handling, setting UseAPX to false.\n");

This print is fine during development but I would instead save some value in memory to indicate that OS does not save/restore APX. And then check it after we execute this assembler code. Similar how we do that for AVX.
You would not need to do runtime call and this method then.
Note: `tty->print()` can do "nasty"/unexpected things which you want to avoid.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18562#discussion_r1631362108