Re: [PATCH 2/4] Define gdb.Value(bufobj, type) constructor

[Kevin Buettner <kevinb@redhat.com>]

On Mon, 18 Feb 2019 15:45:57 -0700
Tom Tromey <tom@tromey.com> wrote:

> >>>>> "Kevin" == Kevin Buettner <kevinb@redhat.com> writes:  
> 
> FWIW I think this whole series looks quite reasonable and would be a
> good addition.

Thanks for looking it over.

> Kevin> +  Py_buffer py_buf;  
> 
> Elsewhere in the Python code, Py_buffer is only used conditionally on
> "#ifdef IS_PY3K".  I don't know exactly why, though.  Py_buffer seems to
> be in Python 2.7, maybe it wasn't in some earlier version that gdb still
> supports?

FWIW, I've tested my patch using both Python 2.7 and Python 3.7, which
are what I have on my F29 machine.

> I don't know whether anyone still relies on older versions of Python
> (2.7 was released in 2010 so it seems plenty old at this point; after
> all we require compilers released after this).
> 
> However, this seems like a decision to make consciously.
> I'm not completely sure how to proceed, though one idea might be to find
> the most recent Python 2.[456] compatibility patch and then asking the
> author whether this support is still relevant.

I didn't know of that compatibility patch, though I'll try to track it
down.  (A pointer would be appreciated if you have one handy.)

I decided that I had better educate myself about the old buffer
protocol.  I came across this page, which describes Python's old
buffer protocol:

https://docs.python.org/2/c-api/objbuffer.html

The old buffer protocol includes the functions PyObject_CheckReadBuffer()
and PyObject_AsReadBuffer() which are used in the non-IS_PY3K code in
GDB.

According to that page, the old buffer protocol was introduced in
Python 1.6, but is deprecated in the 2.X series.  It also indicates
that support for the new buffer protocol, which is what I used in my
patch, has been backported to Python 2.6.  2.6 was released in Oct
of 2008.  (I'm thinking that indicating that the old buffer protocol is
deprecated in 2.X is a typo.  I think they meant 3.X.)

I'll try removing use of the old buffer protocol from GDB and then
see if anything breaks with Python 2.7 (and maybe even 2.6 if I can
figure out how to make that happen).  If we get rid of the IS_PY3K
ifdefs from GDB, we'll definitely be making this decision consciously.

Kevin