gh-132399: ensure correct alignment of PyInterpreterState when UBSan is on

[picnixz]

With that PR, the test suite passes for the free-threaded build with UBSan:

./configure --with-undefined-behavior-sanitizer --with-pydebug --prefix="$(pwd)/build" CC=clang LD=clang CFLAGS="-fsanitize=undefined -fno-sanitize-recover"  LDFLAGS="-fsanitize=undefined -fno-sanitize-recover" -q --disable-gil
./python -m test -j0

There is still one UB failure (fixed by #131605) but this is not specific to free-threading.

cc @colesbury

• Issue: UBSan: undefined behaviours when using -fsanitize=undefined -fno-sanitize-recover on free-threaded build #132399

[colesbury]

LGTM

Might be worth running the buildbots just to make sure there are no weird issues with _Alignof()

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @picnixz for commit 12032df 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F132428%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[picnixz]

there are no weird issues with _Alignof()

Hopefully not because I don't know the alternative (it's also something that was only standardized in C11 IIRC but I hope that we won't have issues)

[picnixz]

The Fedora failures are unrelated I think as they already appeared previously.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.x (tier-2) has failed when building commit 427e7fc.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/725/builds/10518) and take a look at the build logs.
4. Check if the failure is related to this commit (427e7fc) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/725/builds/10518

Summary of the results of the build (if available):

Click to see traceback logs

remote: Enumerating objects: 13, done.        
remote: Counting objects:   7% (1/13)        
remote: Counting objects:  15% (2/13)        
remote: Counting objects:  23% (3/13)        
remote: Counting objects:  30% (4/13)        
remote: Counting objects:  38% (5/13)        
remote: Counting objects:  46% (6/13)        
remote: Counting objects:  53% (7/13)        
remote: Counting objects:  61% (8/13)        
remote: Counting objects:  69% (9/13)        
remote: Counting objects:  76% (10/13)        
remote: Counting objects:  84% (11/13)        
remote: Counting objects:  92% (12/13)        
remote: Counting objects: 100% (13/13)        
remote: Counting objects: 100% (13/13), done.        
remote: Compressing objects:  16% (1/6)        
remote: Compressing objects:  33% (2/6)        
remote: Compressing objects:  50% (3/6)        
remote: Compressing objects:  66% (4/6)        
remote: Compressing objects:  83% (5/6)        
remote: Compressing objects: 100% (6/6)        
remote: Compressing objects: 100% (6/6), done.        
remote: Total 7 (delta 6), reused 1 (delta 1), pack-reused 0 (from 0)        
From https://github.com/python/cpython
 * branch                    main       -> FETCH_HEAD
Note: switching to '427e7fc099e61d9a3d1f04e2fbde8b749e5fcf0a'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 427e7fc099e gh-132399: ensure correct alignment of `PyInterpreterState` (#132428)
Switched to and reset branch 'main'

ar: temporary file: No space left on device
make: *** [libpython3.14d.a] Error 1

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.x (tier-2) has failed when building commit 427e7fc.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/725/builds/10519) and take a look at the build logs.
4. Check if the failure is related to this commit (427e7fc) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/725/builds/10519

Summary of the results of the build (if available):

Click to see traceback logs

Note: switching to '427e7fc099e61d9a3d1f04e2fbde8b749e5fcf0a'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 427e7fc099e gh-132399: ensure correct alignment of `PyInterpreterState` (#132428)
Switched to and reset branch 'main'

fatal error: /Library/Developer/CommandLineTools/usr/bin/ranlib: can't write to output file (No space left on device)
/Library/Developer/CommandLineTools/usr/bin/ar: internal ranlib command failed
make: *** [libpython3.14d.a] Error 1