S390 support

[nathanchance]

Closes: #152
Requires: ClangBuiltLinux/dockerimage#40

[nickdesaulniers]

it doesn't boot? (we could reuse that qemu skip for hexagon (cc @androm3da )

[nathanchance]

I did not try per the comment in Guenter’s build script: https://github.com/groeck/linux-build-test/blob/b8650ca8cdef921992b71db582b9bbdc4efb0ab3/rootfs/s390/run-qemu-s390.sh#L22

[nickdesaulniers]

but it looks like @groeck still boot tests s390, he just does defconfig+CONFIG_MARCH_Z900=y, which is what we should do, too.

We already do this for a few arch's, a la:

continuous-integration/driver.sh

Line 332 in fa15d66

[[ $ARCH == "arm" ]] && ./scripts/config -d CONFIG_FTRACE

[nathanchance]

We can’t do that with clang because of https://git.kernel.org/linus/c263a4e990b7296b074e33aa077239a0a28a818e.

[tpimh]

Instead of db908a6 we should add qemu-system-misc package to dockerimage, create a rootfs image (need some research, s390 support seems to be removed from buildroot: buildroot/buildroot@b24c321) and run it like this:
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

[tpimh]

I wonder if we can use initrd from moonbuggy image from the 2014 QEMU Advent Calendar

[tpimh]

Just checked the moonbuggy image, it's not very useful: only a couple shared libraries and a game binary as init. I'm now checking out gentoo netboot initramfs for s390x, it has busybox in it.

[nickdesaulniers]

let's merge this and start build testing asap while the qemu details are being worked out. Thanks @nathanchance and @tpimh for pursuing this!

[tpimh]

Just built the kernel, tried to boot with QEMU, got Kernel fault:

KASLR disabled: CPU has no PRNG
Linux version 5.5.0-gf75716570 (driver@clangbuiltlinux) #1 SMP Thu Jan 1 00:00:00 UTC 1970Kernel fault: interruption code 0005 ilc:2
PSW : 0000200180000000 00000000000175d4
      R:0 T:0 IO:0 EX:0 Key:0 M:0 W:0 P:0 AS:0 CC:2 PM:0 RI:0 EA:3
GPRS: 00000000fffffff8 0000000c00000009 00000003fffffff4 0000000000000008
      0000000000000010 00000000fffffff0 00000000fffffff4 0000000000000004
      000000000000000c 0000000000000000 00000000fffffffc 00000000009495a8
      0000000000000002 0000000000000001 0000000000000000 000000000000bb58

At least the console is functional.