Fface_font crashes if face->font_name == NULL

[Alan Shutko]

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In GNU Emacs 21.1.1 (i386-debian-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2001-10-25 on raven, modified by Debian
configured using `configure  i386-debian-linux-gnu --prefix=/usr 
--sharedstatedir=/var/lib --libexecdir=/usr/lib --localstatedir=/var/lib 
--infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes --with-x=yes 
--with-x-toolkit=athena'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

I've been debugging why I was seeing boxes for the default
variable-pitch font.  I was recommended to invoke (face-font
'variable-pitch) to see what Emacs was looking for.  This crashed
emacs.

It turns out that Emacs was looking for
"-adobe-helvetica-medium-r-normal--13-125-75-75-p-0-iso8859-1", which
didn't exist.  (Something had hosed a fonts.dir.)  The backtrace is
below.  test-crash.el looks like:

(setq scalable-fonts-allowed t)
(face-font 'variable-pitch)

I can provide more information if necessary.

(gdb) run -q -l ~/test-crash.el
Starting program: /home/ats/nobackup/emacs-21.1/src/emacs -q -l ~/test-crash.el

Program received signal SIGSEGV, Segmentation fault.
0x0810fde7 in build_string (str=0x0) at alloc.c:1840
(gdb) up
#1  0x0809be3b in Fface_font (face=405865012, frame=405187036) at xfaces.c:4678
(gdb) p face
$2 = (struct face *) 0x83d4900
(gdb) p *face
$3 = {
  id = 138233656, 
  gc = 0x83d48e0, 
  font = 0x83d48f4, 
  stipple = 0, 
  foreground = 7, 
  background = 33, 
  underline_color = 3, 
  overline_color = 138234080, 
  strike_through_color = 405698740, 
  box_color = 405596260, 
  font_name = 0x182f2d74 <Address 0x182f2d74 out of bounds>, 
  font_info_id = 0, 
  fontset = 32, 
  pixmap_w = 17, 
  pixmap_h = 1, 
  box_line_width = 137805608, 
  box = 134217852, 
  use_box_color_for_shadows_p = 1, 
  lface = {6, 0, 138798520, 0, 0, 0, 0, 0, 0, 0, 138808040, 0, 9, 0, 0, 0, 0}, 
  hash = 0, 
  charset = 405187396, 
  underline_p = 0, 
  overline_p = 0, 
  strike_through_p = 1, 
  foreground_defaulted_p = 0, 
  background_defaulted_p = 0, 
  underline_defaulted_p = 0, 
  overline_color_defaulted_p = 1, 
  strike_through_color_defaulted_p = 1, 
  box_color_defaulted_p = 1, 
  tty_bold_p = 0, 
  tty_dim_p = 0, 
  tty_underline_p = 1, 
  tty_alt_charset_p = 0, 
  tty_reverse_p = 1, 
  tty_blinking_p = 1, 
  next = 0x18277574, 
  prev = 0x51, 
  ascii_face = 0x1826adb4
}
(gdb) 


Recent input:
e <return> p SPC * f a c e <return> <prior> <prior> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <mouse-movement> <mouse-movement> 
<mouse-movement> <help-echo> <mouse-movement> <help-echo> 
<mouse-movement> <help-echo> <mouse-movement> <help-echo> 
<mouse-movement> <help-echo> <mouse-movement> <down-mouse-1> 
<mouse-1> C-a C-a C-a <home> C-x C-x C-a <left> <left> 
<left> <left> <left> <left> C-SPC <end> M-w C-x o C-x 
b <return> C-x C-b SPC SPC SPC SPC SPC SPC SPC <end> 
<prior> M-x M-p M-p <return>

Recent messages:
Mark set [4 times]
Auto-saving...done
Quit
Mark saved where search started [2 times]
Loading emacsbug...done
comint-search-arg: Not at command line
History item: 1
Saved text from "(gdb) run -q -l ~/test-crash.el
Starting"
Commands: d, s, x, u; f, o, 1, 2, m, v; ~, %; q to quit; ? for help.

-- 
Alan Shutko <ats@acm.org> - In a variety of flavors!
Don't let your mind wander -- it's too little to be let out alone.