Mishandled _POSIX_C_SOURCE and _XOPEN_SOURCE in pyconfig.h

[RAW]

BPO	17120
Nosy	@loewis, @vstinner, @koobs, @iritkatriel

^{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 2013-02-04.05:39:07.814>
labels = ['build', 'library', '3.9', '3.10', '3.11']
title = 'Mishandled _POSIX_C_SOURCE and _XOPEN_SOURCE in pyconfig.h'
updated_at = <Date 2021-12-12.19:07:28.318>
user = 'https://bugs.python.org/RAW'

bugs.python.org fields:

activity = <Date 2021-12-12.19:07:28.318>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2013-02-04.05:39:07.814>
creator = 'RAW'
dependencies = []
files = []
hgrepos = []
issue_num = 17120
keywords = []
message_count = 8.0
messages = ['181309', '183910', '185248', '226849', '241328', '400445', '400563', '400614']
nosy_count = 5.0
nosy_names = ['loewis', 'vstinner', 'koobs', 'RAW', 'iritkatriel']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'compile error'
url = 'https://bugs.python.org/issue17120'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[RAW]

The header file pyconfig.h mishandles the _POSIX_C_SOURCE and _XOPEN_SOURCE preprocessor macros.

For older versions of Python, the pyconfig.h header specifies:

#define _POSIX_C_SOURCE 200112L

and:

#define _XOPEN_SOURCE 600

For newer versions of Python, the pyconfig.h header specifies:

#define _POSIX_C_SOURCE 200809L

and:

#define _XOPEN_SOURCE 700

The Open Group has documentation about these symbols:

http://pubs.opengroup.org/onlinepubs/007904975/functions/xsh_chap02_02.html

In particular, the documentation states:

A POSIX-conforming application should ensure that the feature test macro _POSIX_C_SOURCE is defined before inclusion of any header.

So, having a header file attempting to set _POSIX_C_SOURCE violates this intention.

Yes, I am well aware that the Python documentation says to include Python.h before any standard headers are included. However, this is still problematic.

In particular, it causes trouble for source code that wishes to include the Python headers and wishes to use declarations that are made visible by setting later values for _POSIX_C_SOURCE and _XOPEN_SOURCE.

I would suggest the pyconfig.h be updated to have something like this:

#if !defined(_POSIX_C_SOURCE) || _POSIX_C_SOURCE < 200112L
#ifdef _POSIX_C_SOURCE
#warning Python expects -D_POSIX_C_SOURCE=200112L or later
#undef _POSIX_C_SOURCE
#endif
#define _POSIX_C_SOURCE 200112L
#endif

and this:

#if !defined(_XOPEN_SOURCE) || _XOPEN_SOURCE < 600
#ifdef _XOPEN_SOURCE
#warning Python expects -D_XOPEN_SOURCE=600 or later
#undef _XOPEN_SOURCE
#endif
#define _XOPEN_SOURCE 600
#endif

[RAW]

Any response?

[RAW]

Does anyone ever respond to reported issues here?

[koobs]

See also:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=192365

[koobs]

@RAW, can you attach a patch against the default branch please so we can move this forward?

[iritkatriel]

I can't find pyconfig.h or "#define _POSIX_C_SOURCE" or "#define _XOPEN_SOURCE".

If nobody will object I will soon close this issue as out of date.

[RAW]

Please look at configure.ac which is used to create configure which will generate pyconfig.h from pyconfig.h.in according to what features are detected in the system.

[vstinner]

On my Fedora 34, running ./configure creates pyconfig.h with these values:

$ grep -E '_POSIX_C_SOURCE|_XOPEN_SOURCE' -B1 pyconfig.h
/* Define to activate features from IEEE Stds 1003.1-2008 */
#define _POSIX_C_SOURCE 200809L
--
/* Define to the level of X/Open that your system supports */
#define _XOPEN_SOURCE 700
--
/* Define to activate Unix95-and-earlier features */
#define _XOPEN_SOURCE_EXTENDED 1

Relevant lines in configure.ac:
---
if test $define_xopen_source = yes
then
# X/Open 7, incorporating POSIX.1-2008
AC_DEFINE(_XOPEN_SOURCE, 700,
Define to the level of X/Open that your system supports)

 # On Tru64 Unix 4.0F, defining _XOPEN_SOURCE also requires
 # definition of _XOPEN_SOURCE_EXTENDED and _POSIX_C_SOURCE, or else
 # several APIs are not declared. Since this is also needed in some
 # cases for HP-UX, we define it globally.
 AC_DEFINE(_XOPEN_SOURCE_EXTENDED, 1,
 	 Define to activate Unix95-and-earlier features)

 AC_DEFINE(_POSIX_C_SOURCE, 200809L, Define to activate features from IEEE Stds 1003.1-2008)
fi

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