Compile warnings in _pickle.c

[serhiy-storchaka]

BPO	25245
Nosy	@benjaminp, @serhiy-storchaka
Files	issue25245_1.patch: Variant 1 issue25245_2.patch: Variant 2

^{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 2015-09-27.08:16:30.354>
created_at = <Date 2015-09-27.05:34:59.869>
labels = ['extension-modules', 'build']
title = 'Compile warnings in _pickle.c'
updated_at = <Date 2015-09-27.08:17:17.295>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2015-09-27.08:17:17.295>
actor = 'benjamin.peterson'
assignee = 'none'
closed = True
closed_date = <Date 2015-09-27.08:16:30.354>
closer = 'python-dev'
components = ['Extension Modules']
creation = <Date 2015-09-27.05:34:59.869>
creator = 'serhiy.storchaka'
dependencies = []
files = ['40592', '40593']
hgrepos = []
issue_num = 25245
keywords = ['patch']
message_count = 6.0
messages = ['251683', '251684', '251686', '251687', '251688', '251689']
nosy_count = 3.0
nosy_names = ['benjamin.peterson', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'compile error'
url = 'https://bugs.python.org/issue25245'
versions = ['Python 3.4', 'Python 3.5', 'Python 3.6']

[serhiy-storchaka]

Changeset 88d98f6c2d7d causes compile warnings in Modules/_pickle.c.

/home/serhiy/py/cpython/Modules/_pickle.c: In function ‘load_counted_long’:
/home/serhiy/py/cpython/Modules/_pickle.c:4752:15: warning: ‘pdata’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         value = _PyLong_FromByteArray((unsigned char *)pdata, (size_t)size,
               ^
/home/serhiy/py/cpython/Modules/_pickle.c: In function ‘load’:
/home/serhiy/py/cpython/Modules/_pickle.c:5534:24: warning: ‘s’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     idx = Py_CHARMASK(s[0]);
                        ^
/home/serhiy/py/cpython/Modules/_pickle.c:5529:11: note: ‘s’ was declared here
     char *s;
           ^
/home/serhiy/py/cpython/Modules/_pickle.c:4800:7: warning: ‘s’ may be used uninitialized in this function [-Wmaybe-uninitialized]
     x = _PyFloat_Unpack8((unsigned char *)s, 0);
       ^
/home/serhiy/py/cpython/Modules/_pickle.c:4795:11: note: ‘s’ was declared here
     char *s;
           ^

[serhiy-storchaka]

Here are two alternative solutions.

[benjaminp]

Why not just initially set *s to NULL in _Unpickler_Read?

[serhiy-storchaka]

Why not just initially set *s to NULL in _Unpickler_Read?

It would be the third variant.

The fourth variant is to change the signature of _Unpickler_Read() and return
char * (NULL on error). All these variants work, I examined them.

[python-dev]

New changeset f0dcf7599517 by Benjamin Peterson in branch '3.4':
initialize return value to NULL to avoid compiler compliants (closes bpo-25245)
https://hg.python.org/cpython/rev/f0dcf7599517

New changeset ef3b833b98c2 by Benjamin Peterson in branch '3.5':
merge 3.4 (bpo-25245)
https://hg.python.org/cpython/rev/ef3b833b98c2

New changeset 4d23598f1428 by Benjamin Peterson in branch 'default':
merge 3.5 (bpo-25245)
https://hg.python.org/cpython/rev/4d23598f1428

[benjaminp]

Okay, I think it might make more sense for |s| to be a return value, but that change probably isn't appropriate for bugfix releases.