Bare chroot in linux-user fails with pgb_reserved_va: Assertion `guest_base != 0' failed.

Trying to run a bare chroot with no additional bind mounts fails on git master (8ffa52c20d5693d454f65f2024a1494edfea65d4) with:

root@nofan:~/qemu> chroot /local_scratch/sid-m68k-sbuild/
qemu-m68k-static: /root/qemu/linux-user/elfload.c:2315: pgb_reserved_va: Assertion `guest_base != 0' failed.
Aborted
root@nofan:~/qemu>

The problem can be worked around by bind-mounting /proc from the host system into the target chroot:

root@nofan:~/qemu> mount -o bind /proc/ /local_scratch/sid-m68k-sbuild/proc/
root@nofan:~/qemu> chroot /local_scratch/sid-m68k-sbuild/
bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
(sid-m68k-sbuild)root@nofan:/#

Host system is an up-to-date Debian unstable (2020-07-23).

I have not been able to bisect the issue yet since there is another annoying linux-user bug (virtual memory exhaustion) that was somewhere introduced and fixed between v5.0.0 and HEAD and overshadows the original Assertion failure bug.