Bug#968372: libpango-1.0-0: ABI break in PangoRenderer, particularly serious on 32-bit

[Simon McVittie]

Control: reassign 968337 libpango-1.0-0 1.46.0-1
Control: forcemerge 968372 968337
Control: retitle 968372 libpango-1.0-0: ABI break in PangoRenderer, more serious on 32-bit
Control: tags 968372 = upstream
Control: forwarded 968372 https://gitlab.gnome.org/GNOME/pango/-/issues/497

On Fri, 14 Aug 2020 at 19:45:05 +0200, Bernhard Übelacker wrote:
> I tried to follow where this state is last set and found
> this memory is last written in location [2].
> 
> But here this memory is used as _GdkPangoRendererPrivate,
> which looks quite different.

This is caused by an ABI break in Pango. Because of alignment padding
between data structure members, it's a lot more serious on ILP32
architectures (such as armel, armhf, i386, mipsel) than on LP64
architectures (such as all other Debian release architectures). In
particular, this explains why I couldn't reproduce it on x86_64, and why
the upstream and Debian GNOME teams hadn't encountered it (we're presumably
all using x86_64).

I've reported it upstream and will see what happens. We should not change
the 1.46.x ABI downstream until we have discussed the problem with upstream,
because that will be storing up incompatibilities for us later, but it
might make sense to go back to the new version in unstable for now, so
that dependent packages like GTK don't get recompiled against the new ABI.

    smcv