Re: plpython vs _POSIX_C_SOURCE

Hi,

On 2023-01-24 16:16:06 -0500, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > Python's _POSIX_C_SOURCE value is set to a specific value in their configure
> > script:
>
> > if test $define_xopen_source = yes
> > then
> > ...
> > AC_DEFINE(_POSIX_C_SOURCE, 200809L, Define to activate features from IEEE Stds 1003.1-2008)
> > fi
>
> Hm. I looked into Python 3.2 (the oldest release we still support)
> and it has similar code but
>
> AC_DEFINE(_POSIX_C_SOURCE, 200112L, Define to activate features from IEEE Stds 1003.1-2001)
>
> So yeah it's fixed (or else not defined) for any particular Python
> release, but could vary across releases.

Looks like it changed in 3.3:

$ git grep -E 'AC_DEFINE.*_POSIX_C_SOURCE' v3.2 v3.3.0
v3.2:configure.in: AC_DEFINE(_POSIX_C_SOURCE, 200112L, Define to activate features from IEEE Stds 1003.1-2001)
v3.3.0:configure.ac: AC_DEFINE(_POSIX_C_SOURCE, 200809L, Define to activate features from IEEE Stds 1003.1-2008)

I'm not sure we need to care a lot about a build with python 3.3 triggering a
bunch of warnings.

Personally I'd just bump the python requirements to well above it - the last
3.2 release was Oct. 12, 2014.

Official EOL date:
Ver Last Release EOL Date
3.2 2014-10-11 2016-02-20
3.3 2017-09-19 2017-09-29
From 3.4 on there's just an official last release:
3.4 2019-03-18
3.5 2020-09-05
3.6 2021-09-04
3.7 2023-06-??

> > Solaris and AIX are the ones missing.
> > I guess I'll test them manually. It seems promising not to need this stuff
> > anymore?
>
> Given that hoverfly is AIX, I'm betting there's an issue there.

Doesn't look that way.

I found plenty problems on AIX, but all independent of _POSIX_C_SOURCE.

Both autoconf and meson builds seem to need externally specified
-D_LARGE_FILES=1 to build successfully when using plpython, otherwise we end
up with conflicting signatures with lseek. I see that Noah has that in his
buildfarm config. ISTM that we should just move that into our build specs.

To get 64 bit autoconf to link plpython3.so correctly, I needed to add to
manually add -lpthread:
ld: 0711-317 ERROR: Undefined symbol: .pthread_init
...

I suspect Noah might not hit this, because one of the dependencies he has
enabled already adds it to the backend LDFLAGS.

Also for autoconf, I needed to link
$prefix/lib/python3.11/config-3.11/libpython3.11.a
to
$prefix/lib/libpython3.11.a
That might be a python version difference or be related to building python
with --enable-shared - but I see saw other problems without --enable-shared.

I ran out of energy to test on aix with xlc, I spent way more time on this
than I have already. I'll pick it up later.

I also tested 64bit solaris. No relevant warnings (lots of other warnings
though), tests pass, with both acc and gcc.

> >> Anyway, I'm still of the opinion that what a11cf433413 tried to do
> >> was the best available fix, and we need to do whatever we have to do
> >> to plpython's headers to reinstate that coding rule.
>
> > You think it's not a viable path to just remove the _POSIX_C_SOURCE,
> > _XOPEN_SOURCE undefines?
>
> I think at the least that will result in warnings on some platforms,
> and at the worst in actual build problems. Maybe there are no more
> of the latter a dozen years after the fact, but ...

I think it might be ok. I tested nearly all OSs that we support, with the
exception of DragonFlyBSD and Illumos, which both are very similar to tested
operating systems.

> Nice idea. We did not have that option while we were using HAVE_SNPRINTF
> ourselves, but now that we are not I concur that this should work.

Cool.

> (I confirmed that their code looks the same in Python 3.2.)
> Note that you'd better make it
>
> #define HAVE_SNPRINTF 1
>
> or you risk macro-redefinition warnings.

Good point.

I guess I'll push that part first, given that we have agreement how it should
look like.

Greetings,

Andres Freund