Add a RISCV64 variable to cpu that indicates both the presence
of RISC-V extensions and performance information about the underlying
RISC-V cores. The variable is only populated with non false values on
Linux. The detection code first attempts to use the riscv_hwprobe
syscall introduced in Linux 6.4, falling back to HWCAP if riscv_hwprobe
is not supported. The patch can detect the C, V, Zba, Zbb and Zbs
extensions. V, Zba, Zbb and Zbs can only be detected on a 6.5 kernel
or later (without backports).
Updates golang/go#61416
Change-Id: I40f92724ee3d337c06bdc559ff0b18a8f6bfda9f
Reviewed-on: https://go-review.googlesource.com/c/sys/+/605815
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>
