Re: PostgreSQL 11 beta1 on AIX 7.2 : 2 failures in 32bit mode

Noah Misch <noah@leadboat.com> writes:
> On Thu, May 31, 2018 at 10:28:12AM -0400, Tom Lane wrote:
>> I wondered why the existing 32-bit AIX buildfarm machines aren't showing
>> problems, but looking closer at them, they are manually forcing
>> _LARGE_FILES, which probably is masking things:
>>     'config_env' => {
>>     'CC' => 'wrap-gcc -D_THREAD_SAFE=1 -D_LARGE_FILES=1 -maix32',
>> Noah, why'd you do that, and would you be willing to remove it?  IMO
>> Postgres should work without that.

> I did that to work around a problem like the one articulated upthread.
> Specifically, a 64-bit build w/ plpython failed:
> ...
> Today's "configure" test concludes that we don't need _LARGE_FILES, because
> off_t is 64-bit ("long", specifically) in this configuration.  The trouble
> arises when Python.h does cause _LARGE_FILES to be defined.

Ugh.  That's a pretty crummy decision on their part, although maybe there
was no better alternative.

This does not seem like it explains Tony's problem with AIX 32-bit,
though, as you'd think all concerned would agree _LARGE_FILES needs
to be 1 in that case.

> At the time I added the workaround, I scratched down these candidates for a
> proper fix:

> 1. Add "configure" test to determine whether Python defines _LARGE_FILES.
>    When it does, define it ourselves at the top of each Python-associated
>    source file.

That would make aspects of our extension ABI dependent on whether one had
configured with --enable-python, which would be surprising to say the
least.

> 2. Define _LARGE_FILES unconditionally on AIX.  That is, adopt the workaround
>    as permanent.

Perhaps.  I wonder though whether this is really an AIX-only problem.
(In particular, I wonder whether Python.h is clobbering _FILE_OFFSET_BITS
on other platforms.)  There's a comment in Autoconf's AC_SYS_LARGEFILE
that suggests it is, but ...

> 3. Define _LARGE_FILES unconditionally.  This should be harmless, but I
>    wouldn't tend to back-patch it.

It seems like variants of this issue should exist in all branches,
so I'm not really happy with taking a fix we're scared to back-patch.
If we were willing to do so, though, this might be OK.  Seems like there
are three possibilities:
* Defining _LARGE_FILES does something good, in which case we want it.
* Defining _LARGE_FILES does nothing.
* Defining _LARGE_FILES does something bad ... but it's hard to see
how that could be.

> 4. Include system headers that react to _LARGE_FILES before including
>    Python.h.  This is fragile; the list of affected headers may change.

Yeah, that seems fairly unworkable, though I wonder whether the
include-ordering advice in plpython.h isn't basically meant to achieve
this result.

We're still left with the question of why Tony is having a problem.
I wonder whether his build of Python.h is doing something strange
with _LARGE_FILES.

            regards, tom lane