I just installed the 32-bit image on my new Raspberry Pi 3B. After a full update I set enable_uart to 1 in config.txt and replaced all references to ttyAMA0 by ttyS0 in cmdline.txt. However, after reboot it immediately had a kernel panic.
I saw posts about a similar issue that are ~1 year old. There received no solution.
Is the problem supposed to be resolved? Is there another method to enable the serial console on GPIO?