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warning: dereferencing type-punned pointer will break strict-aliasing rules #72304
Closed as not planned
Description
| BPO | 28117 |
|---|---|
| Nosy | @mdickinson, @tiran, @serhiy-storchaka, @ma8ma, @ekul00 |
| Dependencies | |
| Files |
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 = None
closed_at = None
created_at = <Date 2016-09-13.07:11:54.190>
labels = ['extension-modules', 'build', '3.7']
title = 'warning: dereferencing type-punned pointer will break strict-aliasing rules'
updated_at = <Date 2018-09-26.10:24:44.124>
user = 'https://github.com/serhiy-storchaka'bugs.python.org fields:
activity = <Date 2018-09-26.10:24:44.124>
actor = 'ekul'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2016-09-13.07:11:54.190>
creator = 'serhiy.storchaka'
dependencies = ['16113']
files = ['44847']
hgrepos = []
issue_num = 28117
keywords = ['patch']
message_count = 5.0
messages = ['276193', '276210', '277546', '306005', '326439']
nosy_count = 5.0
nosy_names = ['mark.dickinson', 'christian.heimes', 'serhiy.storchaka', 'masamoto', 'ekul']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'compile error'
url = 'https://bugs.python.org/issue28117'
versions = ['Python 3.6', 'Python 3.7']
Activity
serhiy-storchaka commentedon Sep 13, 2016
In file included from /home/serhiy/py/cpython/Modules/_sha3/sha3module.c:113:0:
/home/serhiy/py/cpython/Modules/_sha3/kcp/KeccakP-1600-inplace32BI.c: In function ‘_PySHA3_KeccakP1600_SetBytesInLaneToZero’:
/home/serhiy/py/cpython/Modules/_sha3/kcp/KeccakP-1600-inplace32BI.c:97:5: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
low = *((UINT32*)(laneAsBytes+0));
^
In file included from /home/serhiy/py/cpython/Modules/_sha3/sha3module.c:113:0:
/home/serhiy/py/cpython/Modules/_sha3/kcp/KeccakP-1600-inplace32BI.c: In function ‘_PySHA3_KeccakP1600_AddBytesInLane’:
/home/serhiy/py/cpython/Modules/_sha3/kcp/KeccakP-1600-inplace32BI.c:152:5: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
low = *((UINT32*)(laneAsBytes+0));
^
/home/serhiy/py/cpython/Modules/_sha3/kcp/KeccakP-1600-inplace32BI.c: In function ‘_PySHA3_KeccakP1600_ExtractBytesInLane’:
/home/serhiy/py/cpython/Modules/_sha3/kcp/KeccakP-1600-inplace32BI.c:296:5: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
*((UINT32*)(laneAsBytes+0)) = low;
^
/home/serhiy/py/cpython/Modules/_sha3/kcp/KeccakP-1600-inplace32BI.c: In function ‘_PySHA3_KeccakP1600_ExtractAndAddBytesInLane’:
/home/serhiy/py/cpython/Modules/_sha3/kcp/KeccakP-1600-inplace32BI.c:369:5: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
*((UINT32*)(laneAsBytes+0)) = low;
^
tiran commentedon Sep 13, 2016
The compile warning occurs on 32bit builds only: http://buildbot.python.org/all/builders/x86%20Gentoo%20Non-Debug%20with%20X%203.x
serhiy-storchaka commentedon Sep 27, 2016
Proposed patch eliminates warnings.
ma8ma commentedon Nov 10, 2017
Serhiy, would you open a PR? Your patch looks good to me.
I've been looking at the warning on my machine (ubuntu 16.04 x86), it's a bit annoying to me.
ekul00 commentedon Sep 26, 2018
I just got this set of warnings while building 3.6.6 on RasPi Debian9/ARM. Good to know the warning is spurious.
Just finding my way here - is Serhiy's patch above a working 2016 fix for this that got stuck in review? I couldn't find a PR for it. If the warning _is_ spurious it would be great to patch it.
serhiy-storchaka commentedon Aug 5, 2026
Modules/_sha3/kcp/no longer exists: the Keccak Code Package was replaced with tiny_sha3 in bpo-47098 (GH-32060), and SHA-3 is now implemented with HACL*. The warning is gone with the code that caused it.