I the boot.cfg file from the tar.xz is configured for archlinux's kexecboot and looks for a kernel on a SD card only.
If you copied the boot.cfg file over the boot.cfg on your CF card it will not boot and may cause the issue you are experiencing.
OK, understand....
Are you using kexecboot from archlinux or OE ?
Whatever was included in your instructions.
You can use the rootfs tar from github to create a boot SD card and fix you boot.cfg on our CF card.
Thanks for the suggestion.
So to get you going again:
I assume your CF partition is ext4 for sda1 and your alarmz root and you did copy the new kernel to the right location on you CF card, including the kernel modules.
Follow Dan's guide to create an arch SD card :
https://github.com/danboid/ZALARM-installInsert the SD card and turn on the Zaurus.
Boot from the SD card. Kexecboot should list the kernel.
Once logged on as root mount your CF card and edit boot.cfg
mount /dev/sda1 /mnt
nano /mnt/boot/boot.cfg
Example boot.cfg for single kernel boot from sda1 on ext4:
LABEL=ArchLinux
KERNEL=/boot/zImage-4.4.0-cxx00
APPEND=root=/dev/sda1 rootfstype=ext4 fbcon=rotate:1 noinitrd loglevel=3
Then exit the editor and unmount and reboot.
unmount /mnt
reboot
Then remove the SD card and fingers crossed you can boot back into you arch on the CF card.
Hope this helps.
I recommend before doing an kernel upgrade to do a backup first and more importantly have recovery partition or SD card handy for situations like this.