x/build: add LUCI openbsd-arm builder

[4a6f656c]

Please add a LUCI builder for openbsd/arm with hostname openbsd-arm-jsing - note that this will be running on the same hardware as the current host-openbsd-arm-joelsing builder. This machine is not capable of running both forms and will need to be hard migrated at some point in time. CSR for this builder is attached.

openbsd-arm-jsing.csr.txt

[gopherbot]

Change https://go.dev/cl/584777 mentions this issue: main.star: update openbsd-{arm,arm64,riscv64} builder configurations

[dmitshur]

Here's the certificate: openbsd-arm-jsing-1715617750.cert.txt.

Note that this may run into the same issue as in #63698 (comment).

[4a6f656c]

@dmitshur we don't seem to be getting far with this one - run_isolated.log stops at:

85352 2024-07-08 13:23:56.713 I: free space after cleanup: 9224697856

And there does not appear to be anything for openbsd-arm (or possibly openbsd-armv7) here:

https://chrome-infra-packages.appspot.com/p/infra/tools/cipd

[4a6f656c]

We also likely need GOGC=20 due to the resource constraints of this machine - I used to be able to control this locally, however it will now presumably need to be done from the other end.

[dmitshur]

And there does not appear to be anything for openbsd-arm (or possibly openbsd-armv7) here:

Yeah, the *bsd-armv7l CIPD binaries haven't been added yet. @bsiegert Do you have plans to work on that? If you @4a6f656c are interested in giving it a shot, that would be appreciated and help us move this forward. In our earlier discussion there was agreement on the implementation plan details, specifically:

• Start building CIPD dependencies for "{open,net,free}bsd-armv7l" cipd_platform with GOARCH=arm GOARM=7 explicitly set. (A somewhat similar past CL is crrev.com/c/5086069.) Can also stop building for netbsd-armv6l since it'll be unused.
• Make swarming bot capable of reporting its cipd_platform dimension with the armv7l suffix when hardware reports being capable of running GOARM=7 binaries. (Similar past CL are crrev.com/c/5178250 and crrev.com/c/5189742.)
• Update Go config to define "gotip-{open,net,free}bsd-arm" etc. with the new CIPD dimension so the updated bot at https://chromium-swarm.appspot.com/botlist?f=cipd_platform%3Aopenbsd-armv7l&f=pool%3Aluci.golang.shared-workers will be used. Notably, for openbsd/arm this seems to be nearly done, but there's a discrepancy with the suffix being v7 vs v7l. (It's unfortunate to have even more special cases, but if it's much easier perhaps we should consider sticking with "v7" (without "l") for the openbsd/arm port only...)

We also likely need GOGC=20 due to the resource constraints of this machine - I used to be able to control this locally, however it will now presumably need to be done from the other end.

I'd expect setting a Go environment variable when running the swarming bot would cause it to propagate, is that not the case? Do we explicitly reset them?

In any case, it may still be better to do it in the x/build luci-config branch (e.g., somewhere here to start) so that it has more visibility and that we can adjust it if really needed. This is also the only way to make it vary based on repo or so.