RFR: 8309258: RISC-V: Add riscv_hwprobe syscall [v2]

[Robbin Ehn]

On Wed, 14 Jun 2023 07:16:49 GMT, Feilong Jiang <fjiang at openjdk.org> wrote:

>> Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   free uarch string
>
> src/hotspot/os_cpu/linux_riscv/vm_version_linux_riscv.cpp line 93:
> 
>> 91: 
>> 92:   RiscvHwprobe::probe_features();
>> 93:   os_aux_features();
> 
> Looks like `probe_features` and `os_aux_features` are doing the same thing (enabling supported extensions). Should we call them both? Maybe it's better to call `os_aux_features` when `probe_features` returns false? e.g.:
> 
> 
> if (!RiscvHwprobe::probe_features()) {
>   os_aux_features();
> }

Yes, ok, sure! (note that V is not yet in hwprobe (but it is in pipeline))

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PR Review Comment: https://git.openjdk.org/jdk/pull/14445#discussion_r1229207282