[PATCH] Add some const-ness to py-cmd.c

[PATCH] Add some const-ness to py-cmd.c

[Doug Evans]

Hi.

When can we drop support for older Python versions?

2013-12-08  Doug Evans  <xdje42@gmail.com>

	* python/py-cmd.c (struct cmdpy_completer): Add comment.
	(completers): Make const.

diff --git a/gdb/python/py-cmd.c b/gdb/python/py-cmd.c
index c0e9d96..c845c7c 100644
--- a/gdb/python/py-cmd.c
+++ b/gdb/python/py-cmd.c
@@ -32,13 +32,15 @@
 /* Struct representing built-in completion types.  */
 struct cmdpy_completer
 {
-  /* Python symbol name.  */
+  /* Python symbol name.
+     This isn't a const char * for Python 2.4's sake.
+     PyModule_AddIntConstant only takes a char *, sigh.  */
   char *name;
   /* Completion function.  */
   completer_ftype *completer;
 };
 
-static struct cmdpy_completer completers[] =
+static const struct cmdpy_completer completers[] =
 {
   { "COMPLETE_NONE", noop_completer },
   { "COMPLETE_FILENAME", filename_completer },

Re: [PATCH] Add some const-ness to py-cmd.c

[Phil Muldoon]

On 08/12/13 08:04, Doug Evans wrote:
> Hi.
> 
> When can we drop support for older Python versions?
> 
> 2013-12-08  Doug Evans  <xdje42@gmail.com>
> 
> 	* python/py-cmd.c (struct cmdpy_completer): Add comment.
> 	(completers): Make const.
> 
> diff --git a/gdb/python/py-cmd.c b/gdb/python/py-cmd.c
> index c0e9d96..c845c7c 100644
> --- a/gdb/python/py-cmd.c
> +++ b/gdb/python/py-cmd.c
> @@ -32,13 +32,15 @@
>  /* Struct representing built-in completion types.  */
>  struct cmdpy_completer
>  {
> -  /* Python symbol name.  */
> +  /* Python symbol name.
> +     This isn't a const char * for Python 2.4's sake.
> +     PyModule_AddIntConstant only takes a char *, sigh.  */
>    char *name;
>    /* Completion function.  */
>    completer_ftype *completer;
>  };
>  
> -static struct cmdpy_completer completers[] =
> +static const struct cmdpy_completer completers[] =
>  {
>    { "COMPLETE_NONE", noop_completer },
>    { "COMPLETE_FILENAME", filename_completer },
> 

It's really up to our downstream packagers.  It can't be soon enough
for me.  I spend an inordinate amount of time checking my code (both C
and Python works on 2.4 -> 3.x).  It is really a time consuming and
tedious task.

My thoughts are that from GDB version x.x, we declare from then on we
only support Python 3.x, and if your distribution does not support
Python 3.x to revert GDB to an older version.

I suspect though that his would encounter some resistance from the
folks who work in the enterprise sector, as I doubt various
enterprise systems have updated to Python 3.x.

tl;dr  We should probably ask around.

Cheers,

Phil

Re: [PATCH] Add some const-ness to py-cmd.c

[Tom Tromey]

>>>>> "Doug" == Doug Evans <xdje42@gmail.com> writes:

Doug> When can we drop support for older Python versions?

I thought we were keeping old ones for Google :)

I'm asking internally what we need for how long.

Tom

Re: [PATCH] Add some const-ness to py-cmd.c

[Tom Tromey]

Tom> I'm asking internally what we need for how long.

I think we could drop Python 2.4 and 2.5 for gdb 7.8.  My understanding
is that we (Red Hat) won't need support for these in future gdb
releases.

Tom

Re: [PATCH] Add some const-ness to py-cmd.c

[Joel Brobecker]

> I think we could drop Python 2.4 and 2.5 for gdb 7.8.  My understanding
> is that we (Red Hat) won't need support for these in future gdb
> releases.

Do we need to keep 2.6? Python 2.7 was released July 3rd 2010, so over
3 years ago. GDB 7.8 would probably be around mid summer 2014, so 4 years
after Python 2.7 got released.

-- 
Joel

Re: [PATCH] Add some const-ness to py-cmd.c

[Jan Kratochvil]

On Wed, 11 Dec 2013 08:53:28 +0100, Joel Brobecker wrote:
> Do we need to keep 2.6?

Yes, we do - RHEL-6 ships python-2.6.6.  We would have to keep downstream
backport patchset otherwise.


Thanks,
Jan

Re: [PATCH] Add some const-ness to py-cmd.c

[Tom Tromey]

>>>>> "Joel" == Joel Brobecker <brobecker@adacore.com> writes:

>> I think we could drop Python 2.4 and 2.5 for gdb 7.8.  My understanding
>> is that we (Red Hat) won't need support for these in future gdb
>> releases.

Joel> Do we need to keep 2.6? Python 2.7 was released July 3rd 2010, so over
Joel> 3 years ago. GDB 7.8 would probably be around mid summer 2014, so 4 years
Joel> after Python 2.7 got released.

Red Hat at least needs 2.6 for a while still.  RHEL 6 ships Python 2.6.
It would be more convenient for us if this were supported by gdb.

Of course gdb can go its own route and we will cope somehow.
A few points though --

It seems likely that other groups will also want 2.6 support.

My recollection is that the compatibility difficulties have been with
Python 2.4 and that 2.6 hasn't presented any particular problems.

Looking at the code I see some C hacks for 2.4 and one minor for 2.6.
I'm actually not too concerned about these workarounds, the one that has
been more of a pain is that 2.4 and 2.5 don't have support for the "as"
clause to "except".

thanks,
Tom

Re: [PATCH] Add some const-ness to py-cmd.c

[Joel Brobecker]

> Red Hat at least needs 2.6 for a while still.  RHEL 6 ships Python 2.6.
> It would be more convenient for us if this were supported by gdb.
> 
> Of course gdb can go its own route and we will cope somehow.
> A few points though --

Just to be clear, I have no objection whatsoever towards keeping
support for 2.6! I don't think it is going to be that much more
work in any case, but just wondered whether that was necessary.
The one transition that worries me is 3.x, and I think this one
is going to hurt (at AdaCore).

-- 
Joel

Re: [PATCH] Add some const-ness to py-cmd.c

[Tom Tromey]

>>>>> "Joel" == Joel Brobecker <brobecker@adacore.com> writes:

Joel> The one transition that worries me is 3.x, and I think this one
Joel> is going to hurt (at AdaCore).

It does seem difficult.  Fedora is aiming to switch over for Fedora 22.
I think we may switch gdb in Fedora 21, though.  The Fedora feature
proposal is here:

    https://fedoraproject.org/wiki/Changes/Python_3_as_Default

Tom

Re: [PATCH] Add some const-ness to py-cmd.c

[Joel Brobecker]

> Joel> The one transition that worries me is 3.x, and I think this one
> Joel> is going to hurt (at AdaCore).
> 
> It does seem difficult.  Fedora is aiming to switch over for Fedora 22.
> I think we may switch gdb in Fedora 21, though.  The Fedora feature
> proposal is here:
> 
>     https://fedoraproject.org/wiki/Changes/Python_3_as_Default

Same here. We've only discussed it informally, but we had the same
feeling regarding difficulty and timeline.

-- 
Joel

Re: [PATCH] Add some const-ness to py-cmd.c

[Phil Muldoon]

On 11/12/13 15:36, Joel Brobecker wrote:
>> Red Hat at least needs 2.6 for a while still.  RHEL 6 ships Python 2.6.
>> It would be more convenient for us if this were supported by gdb.
>>
>> Of course gdb can go its own route and we will cope somehow.
>> A few points though --
> 
> Just to be clear, I have no objection whatsoever towards keeping
> support for 2.6! I don't think it is going to be that much more
> work in any case, but just wondered whether that was necessary.
> The one transition that worries me is 3.x, and I think this one
> is going to hurt (at AdaCore).

FWIW, GDB is ready to go with Python 3.x.  I check the builds weekly
against the test-suite.  There may still be some logic bugs hiding
(like a recent one I fixed: Python 3.x's internal representation of
integers changed to be longs only; that caused an out of order logic
bug in Python conversion routines in GDB which has to support 2.x and
3.x.)  So your GDB pain, at least, should be mitigated ;)

Cheers,

Phil