MMAP duplicate reads and writes on ARM64 platform

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-02-04.22:45:15.162>
labels = ['3.7', 'library']
title = 'MMAP duplicate reads and writes on ARM64 platform'
updated_at = <Date 2021-02-04.23:02:15.833>
user = 'https://bugs.python.org/psswirhun'

bugs.python.org fields:

activity = <Date 2021-02-04.23:02:15.833>
actor = 'psswirhun'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-02-04.22:45:15.162>
creator = 'psswirhun'
dependencies = []
files = []
hgrepos = []
issue_num = 43131
keywords = []
message_count = 2.0
messages = ['386501', '386502']
nosy_count = 1.0
nosy_names = ['psswirhun']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue43131'
versions = ['Python 3.7']