bug#36019: 27.0.50; Segfault in color_distance in emacs --batch

[Vitalie Spinu <spinuvit@gmail.com>]

Hi Alex,

The bug is still in the master. Would it be ok to push the fix?

Thanks,

  Vitalie

>> On Sat, Jun 01 2019 08:22, Vitalie Spinu wrote:

> Hi Alex,

> You are right on spot. 

> Before the crash:

>    Initial: 1, hook: (nil)

> Your fix does help and the following is printed:

>   Initial: 1, hook: 0x561a49f72240Initial: 1, hook: 0x561a49f72240Initial: 1,
>   hook: 0x561a49f72240Initial: 1, hook: 0x561a49f72240Initial: 1, hook:
>   0x561a49f72240Initial: 1, hook: 0x561a49f72240Initial: 1, hook:
>   0x561a49f72240Initial: 1, hook: 0x561a49f72240Initial: 1, hook:
>   0x561a49f72240Initial: 1, hook: 0x561a49f72240

> Thanks for the quick resolution. 

>   Vitalie

>>> On Fri, May 31 2019 14:30, Alex Gramiak wrote:

>> Vitalie Spinu <spinuvit@gmail.com> writes:

>>> I have bisected it to:
>>>
>>> yes: 5d8b0fadee * | Add terminal hook query_frame_background_color
>>> err: 41e20ee4bc * | Add terminal hook defined_color_hook
>>> err: a411517faf * | Rename generic x_* identifiers
>>> err: da9541dd10 * | Add prefixes to some window system-dependent procedures
>>>  no: ff4e31fa32 * |  Rename generic x_* procedures in xdisp.c
>>>
>>> The commits marked with err: don't build. So should be one of the top 4 commits.
>>>
>>>
>>>   Vitalie
>>>
>>>>> On Fri, May 31 2019 10:30, Vitalie Spinu wrote:
>>>
>>>> Hi,
>>>
>>>> One of my packages started segfaulting in tests after emacs 27 update. I cannot
>>>> reproduce it in an X session, nor make a simple reproducible example. Hopefully
>>>> the backtraces will be enough.
>>>
>>>> The issue appeared in the last 4-5 months. I can bisect if needed.

>> I can't reproduce this, but looking at the likely culprit (41e20ee4bc)
>> it's likely due to the frame being the initial frame. Just to make sure,
>> could you test with this simple primitive check for this?

>> diff --git a/src/xfaces.c b/src/xfaces.c
>> index d211ec8c46..10cfa50526 100644
>> --- a/src/xfaces.c
>> +++ b/src/xfaces.c
>> @@ -4207,6 +4207,11 @@ two lists of the form (RED GREEN BLUE) aforementioned. */)
>>    struct frame *f = decode_live_frame (frame);
>>    Emacs_Color cdef1, cdef2;

>> +  fprintf (stderr,
>> +           "Initial: %d, hook: %p",
>> +           FRAME_INITIAL_P (f),
>> +           FRAME_TERMINAL (f)->defined_color_hook);
>> +
>>    if (!(CONSP (color1) && parse_rgb_list (color1, &cdef1))
>>        && !(STRINGP (color1)
>>             && FRAME_TERMINAL (f)->defined_color_hook (f,

>> I expect that it will print "Initial: 1, hook: 0x0" before segfaulting.

>> If this is the case, then perhaps the initial frame should also have
>> this hook defined, though this would be the first such hook defined for
>> the initial frame type.

>> If this is correct, then the following diff should fix this:

>> diff --git a/src/terminal.c b/src/terminal.c
>> index 0ee0121e35..ed2cfead7a 100644
>> --- a/src/terminal.c
>> +++ b/src/terminal.c
>> @@ -624,6 +624,7 @@ init_initial_terminal (void)
>>    initial_terminal->kboard = initial_kboard;
>>    initial_terminal->delete_terminal_hook = &delete_initial_terminal;
>>    initial_terminal->delete_frame_hook = &initial_free_frame_resources;
>> +  initial_terminal->defined_color_hook = &tty_defined_color; /* xfaces.c */
>>    /* Other hooks are NULL by default.  */

>>    return initial_terminal;