Re: segfault on 32bit cygwin snapshot

[Mark Geisert <mark@maxrnd.com>]

Hi Corinna,

On Fri, 5 Mar 2021, Corinna Vinschen wrote:
> On Mar  5 01:11, Mark Geisert wrote:
>> Marco Atzeri via Cygwin wrote:
>>> On 04.03.2021 21:17, Marco Atzeri wrote:
>>>> On 04.03.2021 16:17, Ken Brown via Cygwin wrote:
>>>>> On 3/4/2021 6:50 AM, Takashi Yano via Cygwin wrote:
>>>>>> On Thu, 4 Mar 2021 12:11:11 +0100
>>>>>> marco atzeri wrote:
>>>>>>> I have no problem to patch Python to solve the issue,
>>>>>>> but I have not seen evidence of the dlsym mechanism .
>>>>>>> But of course I an NOT and expert in this field.
>>>>>>>
>>>>>>> If someone looking to the code can give me some hints,
>>>>>>> I will appreciate
>>>>>>
>>>>>> I am also not sure where the dlsym() is used in python.
>>>>>> At least, os.uname() works in python 3.8.7 and 2.7.18 in my
>>>>>> environment even without that snippet. It seems that os.uname()
>>>>>> does not use dlsym(). Do I overlook something?
>>>>>
>>>>> This all started because Mark reported a problem building python 3.8.3:
>>>>>
>>>>>    https://cygwin.com/pipermail/cygwin-apps/2020-December/040765.html
>>>>> https://cygwin.com/pipermail/cygwin-developers/2020-December/012019.html
>>>>>
>>>>> It's strange that Marco never bumped into the problem.
>>>>>
>>>>> Ken
>>>>
>>>> I never built python using cygwin snapshots as Mark was trying to do,
>>>> all my builds were using 3.1.7.
>>>>
>>>> Let me set a separate enviroment for building on latest snapshot
>>>
>>> I can not replicate with latest snapshot
>>>
>>> $ uname -svr
>>> CYGWIN_NT-10.0-WOW 3.2.0s(0.340/5/3) 2021-03-01 15:42
>>>
>>> nor in 64bit when building 3.8.8
>>>
>>> For what I see the DLL is always using a proper import
>>> from cygwin1.dll
>>>
>>> $ objdump -x libpython3.8.dll |grep uname
>>>          2b9de0   2170  uname
>>>          2b9de8   2171  uname_x
>>>
>>> the only thing not standard on my build system is a case sensitive
>>> filesystem and mount
>>
>> I had concerns that I had somehow corrupted my build environment, and it was
>> Marco's successes that convinced me to reinstall 3.1.7 to recover a
>> known-good environment.  Then seeing Marco go ahead and release the
>> different Python releases (yay!) I didn't investigate any further.
>>
>> I'm now trying to locate the os.uname usage of dlopen/dlsym again just for
>> the record but am having some difficulty.  I'll reply again when I've got
>> it.
>
> Guys,
>
> if it turns out that we fixed a problem that doesn't actually is a
> real-world problem, I'm wondering if we shouldn't just revert the Cygwin
> patch we're talking about here (commit 532b91d24e9496) and be done with
> it.
>
> Special casing dynamic loading of uname just to support some experimental
> bordercase doesn't make much sense.  In that case I'm all for "don't do
> that"!

That may well be the appropriate endpoint, but please let me dig a little 
further into the recent Python versions.  The fact that they had an 
explicit dlopen/dlsym to get at uname(), but now they don't, troubles me. 
I want to be sure us Cygwin folk aren't in an inadvertent "arms race" with 
the Python devs over the uname API change.  Dunno why this didn't occur 
15+ years ago, but here we are.

I think it was in Python's Modules/posixmodule.c.  They're certainly using 
uname() directly in their most recent builds.  But I believe that wasn't 
always the case, even just a few months ago.  Let me dig for a day or two.
Thanks,

..mark