crash reimporting posix after Py_Finalize on mac

[benoithudson]

BPO	37931
Nosy	@ronaldoussoren, @vstinner, @ned-deily, @miss-islington, @benoithudson, @iritkatriel
PRs	bpo-37931: crash on OSX re-initializing os.environ #15428 [3.8] bpo-37931: Fix crash on OSX re-initializing os.environ (GH-15428) #17488
Files	crashy.c

^{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 = <Date 2020-10-18.18:02:08.502>
created_at = <Date 2019-08-23.15:39:47.712>
labels = ['OS-mac', 'interpreter-core', '3.9', 'type-crash']
title = 'crash reimporting posix after Py_Finalize on mac'
updated_at = <Date 2020-10-18.18:02:08.501>
user = 'https://github.com/benoithudson'

bugs.python.org fields:

activity = <Date 2020-10-18.18:02:08.501>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2020-10-18.18:02:08.502>
closer = 'vstinner'
components = ['Interpreter Core', 'macOS']
creation = <Date 2019-08-23.15:39:47.712>
creator = 'Benoit Hudson'
dependencies = []
files = ['48559']
hgrepos = []
issue_num = 37931
keywords = ['patch']
message_count = 6.0
messages = ['350309', '354387', '357940', '357942', '378789', '378880']
nosy_count = 6.0
nosy_names = ['ronaldoussoren', 'vstinner', 'ned.deily', 'miss-islington', 'Benoit Hudson', 'iritkatriel']
pr_nums = ['15428', '17488']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue37931'
versions = ['Python 2.7', 'Python 3.9']

[benoithudson]

On OSX, with --enable-shared, if you shut down python and reinitialize, you can get a crash.

Repro steps: see attached crashy.c
gcc -I. -I ../Include/ -L. crashy.c -lpython3.9
./a.out

On OSX, with --enable-shared, you get a crash! On other platforms including on OSX static builds, no crash.

Not a regression: it's present in 2.7 (where we actually hit it).

PR incoming, the fix is simple. It has to do with caching (on OSX shared builds only) a stale value for the environment when building os.environ the first time; if you change the environment, the second initialization reads garbage when building os.environ.

[benoithudson]

Ping! The patch has been ready for review for over a month.

If the patch can be backported to 2.7.x before that gets end-of-lifed it would be ideal.

[vstinner]

New changeset 723f71a by Victor Stinner (Benoit Hudson) in branch 'master':
bpo-37931: Fix crash on OSX re-initializing os.environ (GH-15428)
723f71a

[miss-islington]

New changeset 836cf31 by Miss Islington (bot) in branch '3.8':
bpo-37931: Fix crash on OSX re-initializing os.environ (GH-15428)
836cf31

[iritkatriel]

Can this be closed?

[vstinner]

Right, I close the issue.