possible undefined behavior in _PyObject_FastCall_Prepend

[benjaminp]

BPO	31347
Nosy	@benjaminp
PRs	closes bpo-31347: _PyObject_FastCall_Prepend: do not call memcpy if args might be NULL #3329

^{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 2017-09-05.05:25:55.447>
created_at = <Date 2017-09-04.23:32:36.261>
labels = ['3.7']
title = 'possible undefined behavior in _PyObject_FastCall_Prepend'
updated_at = <Date 2017-09-05.05:25:55.446>
user = 'https://github.com/benjaminp'

bugs.python.org fields:

activity = <Date 2017-09-05.05:25:55.446>
actor = 'benjamin.peterson'
assignee = 'none'
closed = True
closed_date = <Date 2017-09-05.05:25:55.447>
closer = 'benjamin.peterson'
components = []
creation = <Date 2017-09-04.23:32:36.261>
creator = 'benjamin.peterson'
dependencies = []
files = []
hgrepos = []
issue_num = 31347
keywords = []
message_count = 2.0
messages = ['301283', '301298']
nosy_count = 1.0
nosy_names = ['benjamin.peterson']
pr_nums = ['3329']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue31347'
versions = ['Python 3.6', 'Python 3.7']

[benjaminp]

As seen by ubsan:
../cpython/Objects/call.c:858:9: runtime error: null pointer passed as argument 2, which is declared to never be null

[benjaminp]

New changeset a3070d5 by Benjamin Peterson in branch 'master':
bpo-31347: _PyObject_FastCall_Prepend: do not call memcpy if args might not be null (bpo-3329)
a3070d5