Failure during build of Python 3.8 via cygport
Mark Geisert
mark@maxrnd.com
Mon Dec 14 10:42:30 GMT 2020
[Bringing this thread over from cygwin-apps...]
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.
>
> 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.
Brian Inglis pointed out the API 335 change was made a couple years ago, so strike
the quoted conjecture about why nobody else has hit this. A new conjecture follows...
Debugging Python's os.uname showed Cygwin's uname() being called with a 'struct
uname' as defined in /usr/include/sys/utsname.h, which is fine. But it's the
"old" pre-335 uname() interface being called, not the "new" 335+ interface
uname_x(). Note that the famous 'mkimport' script, used when building the Cygwin
DLL, has an arg "--replace=uname=uname_x" which I believe is supposed to equate
the two names so the code in uname_x() is called whether the interface is
uname_x() or uname(). That's not happening.
My first thought was, dang it, my "optimizations" of mkimport broke it. But
that's not the case. Restoring a previous version of mkimport doesn't help.
'nm' shows that both uname and uname_x exist in libcygwin.a and also cygdll.a.
And a newly-created Cygwin DLL has both functions, with different addresses.
That's wrong, isn't it?
..mark
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