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Re: GDB fails to build with Python 3.7
> 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