RFR: 8367137: RISC-V: Detect Zicboz block size via hwprobe [v4]

[Hamlin Li]

On Wed, 10 Sep 2025 02:06:34 GMT, Dingli Zhang <dzhang at openjdk.org> wrote:

>> Hi,
>> Can you help to review this patch? Thanks!
>> 
>> We can extends RISC-V hwprobe support to include `RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE`.
>> The probed value is recorded in VM_Version::zicboz_block_size and then used to set the global CacheLineSize.
>> This ensures correct usage of the Zicboz extension, as block zeroing instructions operate on cache-line granularity.
>> 
>> FYI: https://docs.kernel.org/arch/riscv/hwprobe.html
>
> Dingli Zhang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Replace CacheLineSize with zicboz_block_size in block zeroing logic

src/hotspot/cpu/riscv/macroAssembler_riscv.cpp line 5877:

> 5875: //
> 5876: // NOTE: This is intended to be used in the zero_blocks() stub.  If
> 5877: // you want to use it elsewhere, note that cnt must be no less than zicboz block size.

previous style is more readable, like:

>= zicboz_block_size

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PR Review Comment: https://git.openjdk.org/jdk/pull/27155#discussion_r2336115597