[Bug 249410] [ZFS][workaround exists] missing symbol for fletcher4+NEON on zfs.ko on aarch64 making root-on-zfs impossible

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=249410

            Bug ID: 249410
           Summary: [ZFS][workaround exists] missing symbol for
                    fletcher4+NEON on zfs.ko on aarch64 making root-on-zfs
                    impossible
           Product: Base System
           Version: CURRENT
          Hardware: arm64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: freebsd.bz at filcab.net

Hi all,

I'm trying to boot a Raspberry Pi 4 straight to root on ZFS (I know, it's my
own fault :-) ).
The issue here is that when the loader loads zfs.ko (even when manually loading
its deps (opensolaris.ko and cryptodev.ko)), it complains that
fletcher_4_aarch64_neon_ops is not defined.

OpenZFS has commit with a simple workaround (disable NEON implementation of
fletcher4 on FreeBSD):
https://github.com/openzfs/zfs/commit/2dbad4471005784e97b65b60ecfdbf6dddc4b751

Is it possible to import it into FreeBSD for now? (Ideally the issue will be
fixed and we'll have a NEON impl of fletcher4, but for now having it work would
be better than just failing).

I've tested this with the -CURRENT image for RPi3:
https://download.freebsd.org/ftp/snapshots/arm64/aarch64/ISO-IMAGES/13.0/FreeBSD-13.0-CURRENT-arm64-aarch64-RPI3-20200827-r364846.img.xz

Unfortunately, I don't have enough hardware to run a full crochet build in an
appropriate amount of time (I'm trying in a VM, but it's taking so long to even
clone to /usr/src...).

I don't have the boot output, but have this:
I've mounted the UFS partition from the image I mentioned above and:
root at vm:/mnt/boot # nm kernel/zfs.ko | grep 'fletcher_4_' | grep U
                 U fletcher_4_aarch64_neon_ops

This symbol should be defined in the module, per the source code. But for some
reason it isn't. I'm not familiar enough with the FreeBSD CI to try and track
errors about it, sorry :-(

Hopefully we can import the workaround for now and/or fix it properly soon.

Thank you, and sorry I can't help much more,

 Filipe

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