unaligned memory access in the _sha3 extension

[doko42]

BPO	36515
Nosy	@doko42, @gpshead, @tiran, @miss-islington
PRs	bpo-36515: Disable unaligned memory access in _sha3 on ARM #25927 [3.9] bpo-36515: Disable unaligned memory access in _sha3 on ARM (GH-25927) (GH-25928) #25928 [3.10] bpo-36515: Disable unaligned memory access in _sha3 on ARM (GH-25927) #25930
Files	arm-alignment.diff: patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/gpshead'
closed_at = <Date 2021-05-06.06:57:39.924>
created_at = <Date 2019-04-03.05:41:18.990>
labels = ['extension-modules', '3.10', '3.9', 'type-crash', '3.11']
title = 'unaligned memory access in the _sha3 extension'
updated_at = <Date 2021-05-06.06:57:39.923>
user = 'https://github.com/doko42'

bugs.python.org fields:

activity = <Date 2021-05-06.06:57:39.923>
actor = 'christian.heimes'
assignee = 'gregory.p.smith'
closed = True
closed_date = <Date 2021-05-06.06:57:39.924>
closer = 'christian.heimes'
components = ['Extension Modules']
creation = <Date 2019-04-03.05:41:18.990>
creator = 'doko'
dependencies = []
files = ['48243']
hgrepos = []
issue_num = 36515
keywords = ['patch']
message_count = 4.0
messages = ['339379', '393032', '393047', '393063']
nosy_count = 4.0
nosy_names = ['doko', 'gregory.p.smith', 'christian.heimes', 'miss-islington']
pr_nums = ['25927', '25928', '25930']
priority = 'high'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue36515'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[doko42]

This was seen when running an armhf binary on a 64bit kernel. The problem is that the implementation uses unaligned memory accesses, and even is well aware of that. The module allows misaligned memory accesses by default. The NO_MISALIGNED_ACCESSES macro is never defined. Now you can define it only on architectures where unaligned memory accesses are not allowed (ARM32 on 64bit kernels), or where there are performance penalties (AArch64), or just don't try to outsmart modern compilers and always define this macro.

The attached patch only fixes the issue on ARM32 and AArch64, however the safe fix should be to always define the macro.

[gpshead]

that patch looks fine, i'll turn it into a PR.

[miss-islington]

New changeset 3b2a45f by Miss Islington (bot) in branch '3.10':
bpo-36515: Disable unaligned memory access in _sha3 on ARM (GH-25927)
3b2a45f

[tiran]

New changeset ce47add by Miss Islington (bot) in branch '3.9':
[3.9] bpo-36515: Disable unaligned memory access in _sha3 on ARM (GH-25927) (GH-25928)
ce47add