The value that works for LDSHARED is the value that LDCXXSHARED has. 
BLDSHARED is also broken (currently).

  'BLDSHARED': './Modules/ld_so_aix xlc_r -bI:./Modules/python.exp 
-L/opt/lib',

  'LDCXXSHARED': '/opt/lib/python2.7/config/ld_so_aix xlc_r 
-bI:/opt/lib/python2.7/config/python.exp',

except neither BLDSHARED nor LDCXXSHARED have taken the extra LDFLAG 
that was exported before configure was called (in this case -L/opt/lib)

In short: LDSHARED needs to be a full path, not relative and should 
include -L flags used during the build, if any.

LDCXXSHARED should also add LDFLAGS -L entries (and perhaps, where 
relevant -R flags).

BLDSHARED does not work when "builddir" is . and source_dir is 
../src/python-X.W.Y because Modules/ld_so_aix is not in ".", but is at 
../src/python-X.X.Y/Modules/ld_so_aix

On 15-Oct-16 00:23, Martin Panter wrote:
> Martin Panter added the comment:
>
> This is my understanding:
>
> We are talking about the code at <https://hg.python.org/cpython/annotate/v3.6.0b2/Lib/sysconfig.py#l377> that switches the values of LDSHARED and/or BLDSHARED.
>
> Yes, Michael H. was suggesting to both move and change (revert) back to overwriting LDSHARED with the value of BLDSHARED. Since he is moving the code into _init_posix(), which I think only gets called at run time, the state of _PYTHON_BUILD won’t affect the value of LDSHARED saved in the installed config file.
>
> ----------
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue18235>
> _______________________________________