Comment 2 for bug 1870316

Rik, thanks for reporting this bug.
You're right, it's a regression in hwclock between glibc 2.30/2.31.
It's fixed in util-linux upstream; preparing a debdiff for Focal.

...

$ lsb_release -cs
focal

Older glibc:
---

$ dpkg -s util-linux libc6 | grep ^Version:
Version: 2.34-0.1ubuntu8
Version: 2.30-0ubuntu3

$ sudo hwclock -s
$ echo $?
0

Newer glibc:
---

$ sudo apt install libc6
.
The following packages will be upgraded:
  libc-bin libc-dev-bin libc6 libc6-dev locales
.

$ dpkg -s util-linux libc6 | grep ^Version:
Version: 2.34-0.1ubuntu8
Version: 2.31-0ubuntu6

$ sudo hwclock -s
hwclock: settimeofday() failed: Invalid argument
$ echo $?
1

Upstream:
---

This is fixed with this upstream commit.
Preparing a debdiff for Focal.

ubuntu@focal:~/util-linux$ sudo ./hwclock -s
$ echo $?
0

commit cd781c405be82540484da3bfe3d3f17a39b8eb5c
Author: J William Piggott <email address hidden>
Date: Fri Feb 21 20:03:47 2020 -0500

    hwclock: make glibc 2.31 compatible