RFR: 8324304: RISC-V: add hw probe flags

[Hamlin Li]

On Mon, 22 Jan 2024 15:10:53 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.

I just tested on `Lichee Pi 4A`, seems the default behaviour is to disable them.


echo "enable explicitly ......"
TEST_OPTIONS="-XX:+UseZicboz -XX:+UseZtso -XX:+UseZacas -XX:+UseZfh"
$J_H/bin/java -XX:+PrintFlagsFinal -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions ${TEST_OPTIONS} -version | grep -e UseZicboz -e UseZtso -e UseZacas -e UseZfh

echo "by default ......"
TEST_OPTIONS=""
$J_H/bin/java -XX:+PrintFlagsFinal -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions ${TEST_OPTIONS} -version | grep -e UseZicboz -e UseZtso -e UseZacas -e UseZfh


output is as below:

enable explicitly ......
     bool UseZacas                                 = true                            {ARCH experimental} {command line}
     bool UseZfh                                   = true                                 {ARCH product} {command line}
     bool UseZicboz                                = true                            {ARCH experimental} {command line}
     bool UseZtso                                  = true                            {ARCH experimental} {command line}
by default ......
     bool UseZacas                                 = false                           {ARCH experimental} {default}
     bool UseZfh                                   = false                                {ARCH product} {default}
     bool UseZicboz                                = false                           {ARCH experimental} {default}
     bool UseZtso                                  = false                           {ARCH experimental} {default}

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PR Comment: https://git.openjdk.org/jdk/pull/17519#issuecomment-1905886144