While trying to figure out another bug, I ran into this segfault in GLX

$ xvfb-run --server-args="-screen 10 1024x768x24 -pixdepths 32" gdb --args /usr/bin/glxinfo
GNU gdb (Ubuntu/Linaro 7.3-0ubuntu2) 7.3-2011.08
Copyright (C) 2011 Free Software Foundation, Inc.
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This GDB was configured as "i686-linux-gnu".
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<http://bugs.launchpad.net/gdb-linaro/>...
Reading symbols from /usr/bin/glxinfo...(no debugging symbols found)...done.
(gdb) run
Starting program: /usr/bin/glxinfo 
[Thread debugging using libthread_db enabled]
name of display: :99
Error: couldn't find RGB GLX visual or fbconfig

180 GLXFBConfigs:
    visual  x   bf lv rg d st  colorbuffer  sr ax dp st accumbuffer  ms  cav
  id dep cl sp  sz l  ci b ro  r  g  b  a F gb bf th cl  r  g  b  a ns b eat
----------------------------------------------------------------------------
... a ton of output snipped

(gdb) bt
#0  0x0016d775 in XCreateDrawable (visualid=<optimized out>, drawable=2097165, dpy=0x804f008, pdp=0x8257680) at drisw_glx.c:96
#1  driswCreateDrawable (base=0x80e7bc8, xDrawable=2097165, drawable=2097165, modes=0x8103bd8) at drisw_glx.c:443
#2  0x0016df17 in driFetchDrawable (gc=0x806c778, glxDrawable=2097165) at dri_common.c:377
#3  0x0016d035 in drisw_bind_context (context=0x806c778, old=0x1971c0, draw=2097165, read=2097165) at drisw_glx.c:275
#4  0x0014afd0 in MakeContextCurrent (dpy=0x804f008, draw=2097165, read=2097165, gc_user=0x806c778) at glxcurrent.c:269
#5  0x0014b153 in glXMakeCurrent (dpy=0x804f008, draw=2097165, gc=0x806c778) at glxcurrent.c:303
#6  0x0804a2c5 in ?? ()
#7  0x002ea113 in __libc_start_main () from /lib/i386-linux-gnu/libc.so.6
#8  0x08048d31 in ?? ()
Backtrace stopped: Not enough registers or memory available to unwind further
(gdb) list 100
95	   /* create XImage */
96	   pdp->ximage = XCreateImage(dpy,
97	                              pdp->visinfo->visual,
98	                              pdp->visinfo->depth,
99	                              ZPixmap, 0,             /* format, offset */
100	                              NULL,                   /* data */
101	                              0, 0,                   /* width, height */
102	                              32,                     /* bitmap_pad */
103	                              0);                     /* bytes_per_line */
104	
(gdb) print pdp
$1 = (struct drisw_drawable *) 0x8257680
(gdb) print pdp->visinfo
$2 = (XVisualInfo *) 0x0