s390 boot testing

[tpimh]

Let's continue discussion from #229.

Quick summary:

• QEMU actually can emulate processors newer than Z900 (Debian Buster has qemu 3.1.0 which should emulate IBM machines up to z12)
• Buildroot dropped support for s390 back in 2009 (gentoo netboot initramfs may be an alternative)
• When booting (qemu-system-s390x -m 512m -machine s390-ccw-virtio -initrd images/s390/rootfs.cpio -display none -serial mon:stdio -kernel linux/arch/s390/boot/bzImage) there was a kernel fault: S390 support #229 (comment)

[nickdesaulniers]

@tpimh can you please find the commit to buildroot that dropped s390 support as reference?

[tpimh]

buildroot/buildroot@b24c321

[nickdesaulniers]

@groeck has s390 images: https://github.com/groeck/linux-build-test/tree/master/rootfs/s390

Not sure if they auto shutdown a machine or not, but we should try them out!

[nickdesaulniers]

@groeck also reverted the removal of s390 from his fork of buildroot: groeck/buildroot@2cf1334

Maybe we should use that!?

[nickdesaulniers]

cc @nathanchance

[nathanchance]

We could. However, I think the root file system is a moot point until we can actually get the kernel to start: ClangBuiltLinux/boot-utils#11 (comment)

[groeck]

WFM, with my scripts at github (see above)

[shenki]

FYI, an IBMer is submitting buildroot support for s390 upstream: http://patchwork.ozlabs.org/project/buildroot/list/?series=201991

[eaibmz]

IBM s390x and Z arch has officially landed today in buildroot master 😄

[nickdesaulniers]

@eaibmz thank you so much for the work that went into adding s390x buildroot support! I owe you a 🍺 !

It looks like from our QEMU boot test repo, we're using buildroot release 2020.02.
https://github.com/ClangBuiltLinux/boot-utils/blob/master/buildroot/rebuild.sh#L42

So once we know the latest release that contains support, we can easily update that line to make use of the newer buildroot release. It looks like the latest release is 2020.08 which was last modified 2020-09-01. It looks like v3 was submitted 2020-09-16, so it looks like we'll need to wait for the 2020.09 release (or one of the 2020.09-rc* release candidates) of buildroot. I don't want to use the snapshot. Does that sound like the correct version?

[nickdesaulniers]

It looks like 2020.08.1 was released on 2020-10-12. We should be able to use that.