RFR: 8324304: RISC-V: add hw probe flags [v2]

[Hamlin Li]

On Wed, 24 Jan 2024 11:06:37 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> Hi,
>> Can you help to review this simple patch to add hw probe flags?
>> Thanks!
>> 
>> Per https://github.com/torvalds/linux/blob/master/arch/riscv/include/uapi/asm/hwprobe.h, several extensions were already added in kernel code, we have several intrinsics or funtionalities depends on these extension, it's ready to add these hw probe flags already used in jdk into jdk code.
>
> Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove UPDATE_DEFAULT

I'm not sure, as these vm options (UseZic64b, UseZicbom, UseZicbop and UseZihintpause) are not `enable`d in RiscvHwprobe::add_features_from_query_result(), so I think they are not enabled automatically even if the hw supports these features, unless a vendor want to enable them.

So, I think it's good to keep auto-enablement of Zicboz/Ztso/Zacas in vm_version_riscv.hpp, and remove the enable code of these options in RiscvHwprobe::add_features_from_query_result() in this patch?

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PR Comment: https://git.openjdk.org/jdk/pull/17519#issuecomment-1910823771