> Hmmm, then please start Emacs as this:
> 
> % cd EMACS_BUILD_DIR/src
> % gdb emacs
> (gdb) br xfns.c:2120
> (gdb) run --enable-font-backend -fn "Dejavu Sans Mono-14"
> 
> Emacs will stop at the break point as below.
> 
> Breakpoint 3, xic_create_xfontset (f=0x89ecb10, 
>     base_fontname=0x88186a8 "-etl-*-medium-r-normal-*-24-*-*-*-*-*-iso8859-1")
>     at xfns.c:2120
> 2120	  if (!xfs)
> (gdb) 

-- Below this line is the debug information.

zhaohs@ubuntu-edgy:~/cvs-svn/emacs/src$ gdb emacs
GNU gdb 6.4.90-debian
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...Using host libthread_db
library "/lib/tls/i686/cmov/libthread_db.so.1".

DISPLAY = :0.0
TERM = xterm
Breakpoint 1 at 0x81035b6: file emacs.c, line 464.
Breakpoint 2 at 0x811c3c6: file sysdep.c, line 1385.
(gdb) br xfns.c:2120
Breakpoint 3 at 0x80e2073: file xfns.c, line 2120.
(gdb) run --enable-font-backend -fn "Dejavu Sans Mono-14"
Starting program: /media/hdb6/MyHomeFiles/cvs-svn/emacs/src/emacs
--enable-font-backend -fn "Dejavu Sans Mono-14"
[Thread debugging using libthread_db enabled]
[New Thread -1219627344 (LWP 5936)]
[Switching to Thread -1219627344 (LWP 5936)]
Breakpoint 4 at 0x80d6f16: file xterm.c, line 8047.

-- The debug information ends here.

As you can see, Emacs won't crash at all in my case according to your
advice, so the (gdb) won't appear and I can't debug the following things you
have posted to me.

> 
> The value of base_fontname will be different in your case.
> 
> Please type "n" (for next) and RET to execute the code one
> line by line, and check each value of the second argument to
> XCreateFontSet.  Does it return non-NULL value to `xfs' at
> some point?  Don't you see any warning message from X
> library?
> 
> If XCreateFontSet alwasy return NULL, the next thing is to
> invoke "run" command with no argument and check the second
> argument to XCreateFontSet at the successful call as this.
> 
> (gdb) set args
> (gdb) run

Best,
Hongsheng.
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