Re: [RFC] python-config.py --ldflags should return relocated path to libpython

[Joel Brobecker <brobecker@adacore.com>]

> There are currently 2 issues, I think, with python-config --ldflags:
> 
>   1. When python is configured with --enable-shared:
>      -L<prefix>/lib is missing.  This is a problem if python was
>      installed in a non-standard location.
> 
>   2. When Python is configured without --enable-shared:
>      The path to the libpython archive is provided in the command output,
>      but the path that gets returned is the path used at configure time.
>      If the Python install was copied over to a different machine and
>      then installed at a different location, then the path in -L<path>
>      is incorrect (by comparison, python-config --cflags returns
>      the location with the correct prefix).
[...]
> This patch should fix both situations.  I will also send the patch
> upstream to the Python developers, to see what they say.

No comment either on the Python side or on the gdb-patches side.

> gdb/ChangeLog:
> 
>         * python/python-config.py: When --ldflags is specified, make sure
>         that the paths printed are relative to the run-time prefix.
>         Always provide the path to libpython, even when the python
>         install provides a shared version of libpython.

I think it's too late for 7.2, but I would like to apply this patch
on the HEAD. Any objections? If we ever create a 7.2.1, and this patch
was shown to not cause any problem, then perhaps I'll consider it for
backporting on the 7.2 branch - if approved by the GMs.

> Tested on x86_64-linux, with 2.5 and 2.6. Briefly tested with 2.7,
> but only by running python-config.py and visually verifying the output.
> 
> ---
>  gdb/python/python-config.py |   15 ++++++++++++++-
>  1 files changed, 14 insertions(+), 1 deletions(-)
> 
> diff --git a/gdb/python/python-config.py b/gdb/python/python-config.py
> index 0230eb4..aa4aea3 100644
> --- a/gdb/python/python-config.py
> +++ b/gdb/python/python-config.py
> @@ -50,8 +50,21 @@ for opt in opt_flags:
>          # add the prefix/lib/pythonX.Y/config dir, but only if there is no
>          # shared library in prefix/lib/.
>          if opt == '--ldflags':
> +            # Provide the location where the Python library is installed.
> +            # We always provide it, because Python may have been installed
> +            # at a non-standard location.
>              if not getvar('Py_ENABLE_SHARED'):
> -                libs.insert(0, '-L' + getvar('LIBPL'))
> +                # There is no shared library in prefix/lib.  The static
> +                # library is in prefix/lib/pythonX.Y/config.
> +                #
> +                # Note that we cannot use getvar('LIBPL') like we used to,
> +                # because it provides the location at build time, which might
> +                # be different from the actual location at runtime.
> +                libdir = sysconfig.get_python_lib(standard_lib=True) + '/config'
> +            else:
> +                # The Python shared library is installed in prefix/lib.
> +                libdir = sysconfig.PREFIX + '/lib'
> +            libs.insert(0, '-L' + libdir)
>              libs.extend(getvar('LINKFORSHARED').split())
>          print ' '.join(libs)
>  
> -- 
> 1.7.1

-- 
Joel