Re: [gpsd-dev] [PATCH]: Link Python extensions with libpython

[Matt]

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Hi Bernd, thank you for your response - it helped my understanding a lot.

I did some further research, yielding the attached patch. Could you
review it, please?

Details:

Under Cygwin, the relevant entries in the dictionary returned by
sysconfig.get_config_vars are:

'BLDLIBRARY': 'libpython2.7.dll.a'
'DLLLIBRARY': 'libpython2.7.dll'
'INSTSONAME': 'libpython2.7.dll.a'
'LDLIBRARY': 'libpython2.7.dll.a'
'LIBDIR': '/usr/lib'
'LIBRARY': 'libpython2.7.a'
'LIBS': '-ldl'

Note the absence of 'python2.7' and '-lpython2.7'.

Nevertheless, /usr/bin/python2.7-config --libs outputs:

$ /usr/bin/python2.7-config --libs
- -ldl -lpython2.7

This is because python2.7-config does:

    elif opt in ('--libs', '--ldflags'):
        libs = getvar('LIBS').split() + getvar('SYSLIBS').split()
        libs.append('-lpython'+pyver)

Given this, I suppose that we should either:

1. Shell out to "python-config --libs" instead of using distutils; or
2. Mimic python-config, by hard-coding "-lpython"+pyver into
SConstruct; or
3. Call sysconfig.get_config_var('LIBRARY') and merge it into
python_env as LIBS

I am not sure whether we should use LIBRARY (static link) or LDLIBRARY
(dynamic link). Either works on Cygwin.

In any case, the attached patch implements approach #3 above.
It fixes the Cygwin build, doesn't break the Linux build, and does not
cause the 'overlinking' that my previous attempt caused.

Matt

- -----Original Message-----
From: Bernd Zeimetz [mailto:address@hidden
Sent: Monday, 17 November 2014 06:50
To: Matt; address@hidden
Subject: Re: [gpsd-dev] [PATCH]: Link Python extensions with libpython

On 09/09/2014 10:34 AM, Matt wrote:
> This patch isn't entirely correct - it links all binaries and
> shared objects against the python runtime library, but only some of
> them (not all) actually need libpython. I don't yet see how to fix
> this.

The patch shouldn't be necessary at all, or something around the lines of

    vars = sysconfig.get_config_vars('CC', 'CXX', 'OPT', 'BASECFLAGS',
'CCSHARED', 'LDSHARED', 'SO', 'INCLUDEPY', 'LDFLAGS')
    for i in range(len(vars)):
        if vars[i] is None:
            vars[i] = []
    (cc, cxx, opt, basecflags, ccshared, ldshared, so_ext, includepy,
ldflags) = vars

is wrong - or distutils is broken on cygwin.


> 
> With this change, all binaries compile on Cygwin, but regression
> tests fail due to:
> 
> gpsfake: socket error [ Errno 111] Connection refused.
> 
> I haven't root-caused this yet, but it appears shallow.


- -- 
 Bernd Zeimetz                            Debian GNU/Linux Developer
 http://bzed.de                                http://www.debian.org
 GPG Fingerprint: ECA1 E3F2 8E11 2432 D485  DD95 EB36 171A 6FF9 435F
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link-python-extensions-with-libpython-attempt-2.patch
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