glibc: 22.04 SRU

[Simon Chopin]

[impact]

This is a tracking bug for an upcoming Jammy glibc SRU.

The following bugs are planned for fixing:

bug #1992159 typo in headers for non-GCC compilers
(bug #1993208 patch to write)
(bug #1993209 patch to write)
bug #1999551 arm64 performance improvements for memcmp

In addition, I've cherry-picked the following fixes from upstream which don't have matching Ubuntu bugs:

TODO

[Test case]
Each bug listed above should have its own test case. And glibc's own test case and the autopkgtests provide a good deal of assurance that things are working. But there are still some additional things we should test by hand.

1. We should test upgrades interactively in a container and vm and make sure long running processes still function so you can still ssh in and a desktop session continues to operate as expected, ideally on a variety of architectures.
2. We should build a core22 snap with the glibc from jammy-proposed into a branch and test it with a variety of core22 snaps, on a variety of architectures.
3. We should test graphical snaps with a variety of drivers. I'll be trying out Firefox and Chromium on Intel and Nvidia GPUs

[Regression potential]
Rebuilding glibc is always a little risky (toolchain bugs and incompatibilities between the old and new versions can be surprising).

glibc's own tests and the autopkgtests that will be run should catch any regression in the new version of glibc itself.

However, the biggest source of problems recently has been around upgrades and interactions between the old and new libcs, whether that is different versions of libc6 in a snap and its base or when an long running process has the older version mapped but interacts with artefacts from the newer version on disk. The tests in this bug are aimed at catching any of these problems before it gets to updates.

[Simon Chopin (schopin)]

Closing this out, as the SRU has come and gone in between without using this.