armhf and the 24.04 LTS release

[Steve Langasek]

If you have been involved in Ubuntu development in Noble for the past month,
you are almost certainly aware of the ongoing time_t transition, to ensure
that software we ship for the armhf architecture in Ubuntu 24.04 LTS is
capable of handling timestamps beyond the year 2038.  You will be aware of
this because this has been a significantly disruptive transition, blocking
most other fixes from being able to reach the release pocket in Noble for
some time now.

Originally targeted to land in Debian and Ubuntu in early January, this
transition has effectively landed 2 months late, arriving in Ubuntu right
before feature freeze.  This has put us in a bit of a time crunch to get
this work done in time to ensure that the upcoming Beta release in a little
over 2 weeks includes images that accurately reflect what the team plans to
ship in 24.04 LTS.  Getting all of the affected packages built and in a
position to transition into the release pocket from noble-proposed in less
than 2 weeks represents a huge amount of work, especially with long
dependency chains affecting some of these packages.

However, with the decision to not ship a 32-bit kernel for Raspberry Pi in
24.04 LTS, it is important to recognize that, while it is important that any
software we DO ship on armhf is appropriately future-proof, this is NOT the
same thing as saying that we have to ship for armhf all the software that we
have previously built.

In order to appropriately prioritize the needs of the Beta (including for
our community flavors), effective immediately, the Release Team is enacting
a policy that armhf binaries for all leaf packages in universe, if they are
blocking the transition of any time_t library and ESPECIALLY if they are
blocking the transition of a library that’s present on a release image, 
should be summarily removed from the release pocket in order to let the
transition move forward.  If you are trying to get any library to migrate
and you see that it is blocked by an armhf-specific issue, please contact an
Archive Admin (e.g. highlighting ubuntu-archive on #ubuntu-release on IRC)
providing the name of the source package whose binaries should be removed,
and a reference to what it’s blocking on
<https://ubuntu-archive-team.ubuntu.com/proposed-migration/update_excuses.html>,
and we can remove these packages to move the release forward.

This does not mean the package in question will not be shipped on armhf in
24.04.  It is still possible for the binaries to be built afterwards, and
included in the release.  It is simply prioritizing the needs of the 24.04
release cycle over armhf coverage of any particular binary packages.

For folks working on +1 maintenance, here are some further hints.

* Packages containing libraries that need to migrate for time_t will
  generally have an NMU version number in -proposed (with or without an
  Ubuntu-specific version number after) and at the moment, are 18 days or
  newer (uploads having started on February 28).  Please focus on these
  packages.

* Packages listed as 'missing build on armhf' certainly warrant
  investigation (for fixing or removal).

* Packages involved in the transition which have autopkgtest failures listed
  on architectures OTHER THAN armhf definitely require investigation.

* Libraries which are part of this transition that say “Will attempt
  migration”, but are more than a day or so old, may require no-change
  rebuilds of their reverse-dependencies using
  https://lists.ubuntu.com/archives/ubuntu-devel/2022-April/041994.html or a
  similar script.

On behalf of the Release Team,
-- 
Steve Langasek
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