Bug#995032: GNOME components segfault as a result of libffi transition

[Simon McVittie]

Control: retitle 995032 GNOME components segfault as a result of libffi transition

On Sat, 25 Sep 2021 at 03:48:20 -0400, Jeremy Bicha wrote:
> On Sat, Sep 25, 2021 at 12:30 AM Michael Ott <michael at k-c13.org> wrote:
> > The problem is not gnome-shell. It is the gobject-introspection.
> > After downgrade this packages from 1.70.0-1+b1 to 1.70.0-1 it works
> > again.
> 
> gobject-introspection was rebuilt as part of the libffi transition.
> (That's where the +b1 part of the version name comes from.) The
> transition is still in progress. Maybe the problem is that you didn't
> have the rebuilt gjs installed?
> 
> The rebuilt gjs is version 1.68.4-1+b1
> 
> Here's the list of other packages involved in the transition:
> https://release.debian.org/transitions/html/auto-libffi.html

Last time we had a libffi transition, in early 2020, we ended up
sprinkling versioned Breaks throughout GNOME to force the whole system
to be either "old libffi" or "new libffi". This is because some GNOME
components, notably gobject-introspection, have libffi data structures
in their public API, so in partial upgrades we get one library passing an
old-libffi data structure to another library that expects a new-libffi
data structure, and crashes.

See the gobject-introspection 1.62.0-4 and -5 changelogs for part of what
we had to do to fix this.

If libffi is going to continue to break ABI somewhat regularly, then I
think we are going to need a more systematic way to prevent broken partial
upgrades, and it would be very helpful for the libffi maintainer and the
release team to keep this failure mode in mind when allocating transition
slots (for example doing libffi transitions when there is not a new major
version of GLib trying to migrate, as there is at the moment).

    smcv