runtime: identify virtual memory layout for riscv64
Identify sv39, sv48 and sv57 based on the system stack address.
The current approach to memory allocation is less than ideal on
RISC-V hardware that is using sv39 mode. On sv39 we currently end
up doing around 85 mmap and 66 munmap, since we are trying to map
an unusable range. With this change we do 22 mmap and 0 munmap at
runtime initialisation.
This will also be necessary to support the race detector on sv39.
Updates #64345
Cq-Include-Trybots: luci.golang.try:gotip-linux-riscv64
Change-Id: I4f8ba6763b5ecfedfad5438e025d633820e8265c
Reviewed-on: https://go-review.googlesource.com/c/go/+/690495 Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com> Reviewed-by: Jorropo <jorropo.pgm@gmail.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>