Re: Failure during build of Python 3.8 via cygport

[Brian Inglis <Brian.Inglis@SystematicSw.ab.ca>]

On 2020-12-13 07:34, Marco Atzeri via Cygwin-apps wrote:
> On 13.12.2020 09:52, Mark Geisert wrote:
>> Mark Geisert wrote:
>>> This seems to be a problem setting up a platform-specific build directory. 
>>> The sysconfig.py script wants to use "lib." + platform + pythonversion but 
>>> the platform string somehow gets corrupted into non-utf8 bytes.  For 
>>> instance, building Python 3.8 comes up with:
>>>      lib.cygwin-\365\377\377o-\377o-3.8
>>> as the directory name.  Broken, but could work.  The build failure happens 
>>> because the script tries to write this directory name into a file but it's 
>>> not a valid utf8 string.  The directory name should have been:
>>>      lib.cygwin-3.2.0-x86_64-3.8
>>
>> And the corruption is due to something about a recent change to the operation 
>> of Cygwin's uname() function.  The change was introduced in Cygwin API version 
>> 335; I'm running 340 on my test machine.  This being a fairly recent change 
>> might possibly explain why nobody else has run into this issue yet.

That was nearly two years ago.

>> Basically, os.uname within Python is calling Cygwin's uname() passing the 
>> address of a buffer declared to be 'struct utsname'.  The structure layout 
>> changed in API 335.  What I've hit is a mismatch between what Python expects 
>> and Cygwin delivers.
>>
>> I'll move this discussion over to the developers list tomorrow.

uname(2):
NOTES
...
        The length of the fields in the struct varies.  Some operating
        systems or libraries use a hardcoded 9 or 33 or 65 or 257.  Other
        systems use *SYS_NMLN* or *_SYS_NMLN* or *UTSLEN* or *_UTSNAME_LENGTH*.
        Clearly, it is a bad idea to use any of these constants; just use
        *sizeof*(...). Often 257 is chosen in order to have room for an
        internet hostname.
...
    C library/kernel differences
        Over time, increases in the size of the /utsname/ structure have led to
        three successive versions of *uname*():
		/sys_olduname/()	(slot /__NR_oldolduname/),
		/sys_uname/()		(slot /__NR_olduname/), and
        		/sys_newuname/()	(slot /__NR_uname/).
        The first one used length 9 for all fields;
        the second used 65;
        the third also uses 65 but adds the domainname field.
        The glibc *uname*() wrapper function hides these details from
        applications, invoking the most recent version of the system call
        provided by the kernel.

> thanks for the analysis
> 
> let me know if you think we should correct the python build in any way

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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