bug#37671: 27.0.50; Segmentation fault with --fg-daemon on Linux

[Eli Zaretskii <eliz@gnu.org>]

> From: Frank Terbeck <ft@bewatermyfriend.org>
> Cc: 37671@debbugs.gnu.org
> Date: Sat, 01 Feb 2020 03:43:13 +0100
> 
> (gdb) p w->current_matrix
> $12 = (struct glyph_matrix *) 0x7a
> 
> (gdb) p draw
> $13 = DRAW_NORMAL_TEXT
> 
> (gdb) p hlinfo->mouse_face_hidden
> $14 = false
> 
> (gdb) p hlinfo->mouse_face_end_row
> $15 = 16
> 
> (gdb) p w->current_matrix->nrows
> Cannot access memory at address 0x92
> 
> (gdb) p w->current_matrix
> $17 = (struct glyph_matrix *) 0x7a

This window is dead, AFAICT, and its memory has been recycled.  So
somehow we attempt to show mouse highlight on a deleted window or
something.  I have no idea how this could have happened.

Moreover, the frame itself seems to have bogus values:

> (gdb) p *f
> $10 = {header = {size = 285941742698496},
>        name = 0x55573dc812400000,
>        icon_name = 0xfffffffffe000055,
>        title = 0xfffffffffeffffff,
>        parent_frame = 0xfffffffffeffffff,
>        focus_frame = 0xfffffffffeffffff,
>        root_window = 0xfffffffffeffffff,
>        selected_window = 0xfffffffffeffffff,
>        old_selected_window = 0xfffffffffeffffff,
>        minibuffer_window = 0xfffffffffeffffff,
>        param_alist = 0xfffffffffeffffff,
>        scroll_bars = 0xfffffffffeffffff,
>        condemned_scroll_bars = 0xfffffffffeffffff,
>        menu_bar_items = 0xfffffffffeffffff,
>        face_alist = 0xfffffffffeffffff,
>        menu_bar_vector = 0xfffffffffeffffff,
>        buffer_predicate = 0xfffffffffeffffff,
>        buffer_list = 0xfffffffffeffffff,
>        buried_buffer_list = 0xfffffffffeffffff,
>        tab_bar_window = 0xfffffffffeffffff,
>        desired_tab_bar_string = 0xfffffffffeffffff,
>        current_tab_bar_string = 0xfffffffffeffffff,
>        tool_bar_window = 0xfffffffffeffffff,
>        desired_tool_bar_string = 0xfffffffffeffffff,
>        current_tool_bar_string = 0xfffffffffeffffff,
>        font_data = 0xfffffffffeffffff,
>        tab_bar_items = 0xfffffffffeffffff,
>        tool_bar_items = 0xfffffffffeffffff,
>        face_cache = 0xfffffffffeffffff,
>        last_tab_bar_item = -16777217,
>        last_tool_bar_item = -1,
>        menu_bar_items_used = -16777217,
>        namebuf = 0xfffffffffeffffff <error: Cannot access memory at address 0xfffffffffeffffff>,
>        shell_position = 0xfffffffffeffffff <error: Cannot access memory at address 0xfffffffffeffffff>,

What exactly did you do immediately prior to the crash?