bug#14091: 24.3.50; Crash switching buffer on TTY emacsclient session of NS emacs

[Jan Djärv]

Hello.

31 mar 2013 kl. 13:18 skrev Huw Giddens <hgiddens@gmail.com>:

> Hi Jan,
> 
> Thanks for having a look at this. I haven't succeeded in reproducing it in 
> either a clean environment or a minimal one with just server, desktop, and a 
> few other things. Even with my full environment I can only reproduce it maybe 
> one time every thirty or so. I still have a core from the crash the 
> stacktrace in the report is from, along with the sandbox and binaries used to 
> build it. I can give that to you if you'd like, but it does weigh in north of 
> 200 megs compressed and probably depends on my copies of libxml2/gnutls.
> 

I'm confident that FRAME_NS_P fixes the crashes.  But why a command in a 
terminal frame generates an event in a GUI frame is a mystery, that probably 
can't be deduced by looking at a core in gdb.

        Jan D.

> On 31/03/2013, at 9:02 PM, Jan Djärv <jan.h.d@swipnet.se> wrote:
> 
>> Hello.
>> 
>>> Emacs crashes sometimes under the following circumstances:
>>> 
>>> * Ensure Emacs not currently running.
>>> * Position mouse cursor so that the new Emacs frame will appear under the 
>>> cursor.
>>> * Start NS emacs session: ./nextstep/Emacs.app/Contents/MacOS/Emacs
>>> * Move the cursor out of the new, selected Emacs frame, and click in a
>>> new terminal emulator window.
>>> * Run "./nextstep/Emacs.app/Contents/MacOS/bin/emacsclient -t"
>>> * In the new TTY frame that has opened, C-x b RET; in my case, this
>>> should have switched to an existing scala-mode2 buffer, open via
>>> desktop mode. Emacs crashes after hitting enter.
>> 
>> I can not reproduce it.  The recepie depends on many things in your 
>> environment, for starters, you obviously have server-start in .emacs (or 
>> some other startup file).  Can you reproduce this starting with Emacs -Q?
>> 
>>> 
>>> From my digging through the backtrace, the problem appears to be that
>>> we call ns_mouse_position because of a mouse event from the NS frame,
>>> inside ns_mouse_position we in some cases ignore the frame passed in
>>> (*fp) and instead try and find it ourselves. In this particular case,
>>> both last_mouse_frame and dpyinfo->x_focus_frame are false, leading us
>>> to call remember_mouse_glpyh on the value of SELECTED_FRAME() which is
>>> the TTY frame. We then access the wrong union member and bad things
>>> happen.
>>> 
>>> There's a comment on line 1857 of nsterm.m asking if the
>>> f->output_data.ns check is still needed, I wonder if this was meant to
>>> be instead FRAME_NS_P(f). It strikes me as odd that we receive a mouse
>>> event on the NS frame in response to keyboard input on the TTY frame,
>>> but I don't understand at all what's actually meant to be happening
>>> there. I also think it's odd that the position passed to
>>> remember_mouse_glyph is derived from *fp which, as we see here, is not
>>> necessarily the same as f.
>> 
>> Another frame may have grabbed the mouse, but the event comes to *fp.  We 
>> report the position for that other frame, and set *fp to it.
>> 
>> The f->output_data.ns is wrong though, I will change that.
>> 
>>      Jan D.
>>