Re: [PATCH v2 1/2] gdb/python: remove Python 2 support

[Simon Marchi <simark@simark.ca>]

On 2022-03-21 11:33, Pedro Alves wrote:
> On 2022-03-21 15:04, Simon Marchi wrote:
>> On 2022-03-21 10:58, Eli Zaretskii via Gdb-patches wrote:
>>> Here, I think we should say "only against Python 3", or say "Python 2
>>> is not supported as of GDB 13", or something to that effect.  Because
>>> it is otherwise strange to mention Python 3, it sounds "out of the
>>> blue".
>>
>> I'll say "can only be built against Python 3" then.  I'd rather not say
>> "GDB 13", since this text will live for many GDB versions.  Updated
>> locally.
> 
> We document in gdb/README the minimum supported version, so I think you
> could drop the "Python 3" reference completely if you wanted.

Ok, I'll remove that sentence.

> 
> Speaking of which, said gdb/README note should also be updated, as is documents
> that the oldest supported version is 2.6:
> 
> `--with-python[=PYTHON]'
>      Build GDB with Python scripting support.  (Done by default if
>      libpython is present and found at configure time.)  Python makes
>      GDB scripting much more powerful than the restricted CLI
>      scripting language.  If your host does not have Python installed,
>      you can find it on `http://www.python.org/download/'.  The oldest
>      version of Python supported by GDB is 2.6.  The optional argument
>      PYTHON is used to find the Python headers and libraries.  It can
>      be either the name of a Python executable, or the name of the
>      directory in which Python is installed.

Indeed, we should update it.  But we should probably be precise and which
3.x version we support exactly.  The question is what do we support? My
initial patch #3 removed support for below 3.4, so it must be below 3.4.

Using this PPA

https://launchpad.net/~deadsnakes/+archive/ubuntu/ppa

on Ubuntu 18.04, I tried Python 3.1 and above.  Python 3.1 didn't build
because of this:

  CXX    python/py-record-btrace.o
../../gdb/python/py-record-btrace.c: In function 'PyObject* btpy_list_slice(PyObject*, PyObject*)':
../../gdb/python/py-record-btrace.c:504:25: error: cannot convert 'PyObject* {aka _object*}' to 'PySliceObject*' for argument '1' to 'int PySlice_GetIndicesEx(PySliceObject*, Py_ssize_t, Py_ssize_t*, Py_ssize_t*, Py_ssize_t*, Py_ssize_t*)'
      &step, &slicelength))
                         ^
... which is a "bug" in the Python 3.1 API, fixed in 3.2.  Python 3.2
built fine (although I didn't test further, other than starting GDB).

So I would replace "2.6" with "3.2" in there.  Sounds good?

Simon