Re: GDB fails to build with Python 3.7

[<Paul dot Koning at dell dot com>]

> On May 30, 2018, at 6:26 PM, Joel Brobecker <brobecker@adacore.com> wrote:
> 
> Hi Paul,
> 
>> Currently GDB fails to build with Python 3.7
>> 
>> https://bugs.python.org/issue33470
>> 
>> This is because we use an internal Python API:
>> 
>> #ifdef IS_PY3K
>>  gdb_module = PyModule_Create (&python_GdbModuleDef);
>>  /* Add _gdb module to the list of known built-in modules.  */
>>  _PyImport_FixupBuiltin (gdb_module, "_gdb");
>> #else
>>  gdb_module = Py_InitModule ("_gdb", python_GdbMethods);
>> #endif
>> 
>> (the _PyImport_FixupBuiltin in python.c).
>> 
>> This internal API has been changed. According to the advice of the Python
>> maintainers we should never have used it in the first place. I didn't
>> add this (at least I don't think I did!), so I'm asking whomever
>> authored that code to please change it to be 3.7 compatible. I'm not
>> sure what the code achieves so I'm reluctant to touch it in case of
>> breakages on platforms I don't have easily access to.
> 
> From what I can tell, this was was introduced when you added
> Python 3.x support, back in 2012:
> 
>    commit 9a27f2c60d760a95a27e336750f26f69f91dd156
>    Date:   Wed Dec 12 16:47:30 2012 +0000
>    Subject: Add support for Python 3
> 
> Do you remember why you added that _PyImport_FixupBuiltin call?
> 
> If not, I suggest we just remove it and re-run the testsuite.
> If we find regressions, then we'll have our answer. If we don't,
> let's just remove the code, and see whether anyone finds something.

I think it was because the PyModule_Create creates a module object, but it doesn't make the module name known so references to it fail.  The FixupBuiltin call makes it a known module.  At least that's what the comment suggests and it tickles a faint memory.

The Python manuals aren't helping me here.  But they suggest something that I missed before, or maybe it wasn't documented at the time.  The API call PyImport_AppendInittab is used to add an entry to a table of compiled-in modules (such as _gdb) that are to be initialized and made known as part of Python initialization.  So it looks like the correct fix is to delete both statements, and instead do a PyImport_AppendInittab before the Py_Initialize call.

I haven't been able to get gdb configure to recognize Python at all on my Mac, unfortunately.

	paul