Subject: bug#13864: 24.3.50; emacsclient -t loops when connected to emacs server running in X11

From: [email-masked] (Ashish SHUKLA)
Date: Mon, 25 Mar 2013 14:58:08 +0530

On Sun, 24 Mar 2013 21:54:04 +0200, Eli Zaretskii <[email-masked]> said:

[...]

>  (gdb) break dispnew.c:2623 if vpos == 5

s/vpos/row/ I guess, which is what attached gdb output is with.

> This breakpoint is inside the make_current function:

>   static void
>   make_current (struct glyph_matrix *desired_matrix, struct glyph_matrix *current_matrix, int row)
>   {
>     struct glyph_row *current_row = MATRIX_ROW (current_matrix, row);
>     struct glyph_row *desired_row = MATRIX_ROW (desired_matrix, row);
>     bool mouse_face_p = current_row->mouse_face_p;

>     /* Do current_row = desired_row.  This exchanges glyph pointers
>        between both rows, and does a structure assignment otherwise.  */
>     assign_row (current_row, desired_row);

>     /* Enable current_row to mark it as valid.  */
current_row-> enabled_p = 1;
current_row-> mouse_face_p = mouse_face_p;  <<<<<<<<<<<<<<<<<<<<<<

> The choice of the line (5) is arbitrary.  Then wait until the
> breakpoint breaks, and do this:

>  (gdb) p current_row
>  $1 = (struct glyph_row *) 0x37e1158

> (The address will be different in your case.)  Now use that address to
> put a hardware watchpoint on the enabled_p flag of that glyph row, and
> continue the program:

>  (gdb) watch ((struct glyph_row *) 0x37e1158)->enabled_p
>  (gdb) c

> Now do whatever it takes to cause the flicker, and wait for the
> watchpoint to trigger, it should say something like

>  Hardware watchpoint 5: ((struct glyph_row *) 0x37e1158)->enabled_p

>  Old value = 1
>  New value = 0

> and will next show the source line which modified the value.  Then
> type

>  (gdb) bt

> and let it continue

>  (gdb) c

> Do this several times, each time waiting until the watchpoint
> triggers, and displaying the backtrace.  That should point towards the
> code which resets these flags and causes excessive re-drawing.

Please refer to the attached gdb output with annotations prefixed with '=====> '.

Thanks
-- 
Ashish SHUKLA

“It's good to be wrong. Don't feel shamed. Wear past mistakes as a badge of
honor because growth is everything. To stop learning is to decay.”
("apokalyptik", "in a conversation to abbe", 2010)

Sent from my Emacs