x/build: Scaleway linux-arm builders don't have vdso support

[ianlancetaylor]

As discussed at #32912, let's upgrade the linux-arm and linux-arm64 builders to bionic.

[bradfitz]

The linux-arm and linux-arm64 builders are different in about all ways. arm is on scaleway, 1 builder per machine, 50 machines, with images prepared in a weird way. arm64 is on packet.net on a big machine, with builds running in Docker.

This issue should probably be split in two, with more context: is this about upgrading the host image (for a new kernel? which minimum level/feature?) or the container environment?

[ianlancetaylor]

The current kernels used on both the linux-arm and linux-arm64 builders do not use VDSO for the time functions. The purpose of this issue is upgrade the kernel so that it uses VDSO on both kinds of systems. It is of course fine to split the issue in two.

[bradfitz]

Our existing linux-arm machines are Xenial, running some weird netboot kernel, 4.10.8-docker-1 (built Wed Apr 5 16:04:23 UTC 2017).

But I tried out a Bionic instance on the same hardware and the kernel is still weird, but newer: 4.9.93-mainline-rev1 #1 SMP Tue Apr 10 09:42:40 UTC 2018.

Unfortunately this C1 hardware (their only 32-bit ARM hardware) doesn't support local boot. It can only NFS boot kernels they provide, AFAICT: https://github.com/scaleway/image-ubuntu/issues/132

Probably good enough.

[gopherbot]

Change https://golang.org/cl/205603 mentions this issue: all: upgrade scaleway linux-arm builders, stop using deprecated --reverse flag

[bradfitz]

Okay, linux-arm is now an Ubuntu bionic host (kernel 4.9.93) with Debian Buster containers. All deployed.

Arm64 (packet) remains.