modena@makoto 10:20:38/130809(..cross/avr-gdb)% (cd ~/avr/simulavr/; avr-gdb)
GNU gdb (GDB) 7.6
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=x86_64--netbsd --target=avr".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
(gdb) file simple.elf
Reading symbols from /amd/u/u/home/makoto/avr/simulavr/simple.elf
    ...I'm sorry, Dave, I can't do that.  Symbol format `elf32-avr' unknown.
(gdb)

この場所はすぐに分るが、どこから呼出されているか分らないので、 この場所に abort(); を入れて core dump させ、gdb で見てみた。

(gdb) file ~/avr/simulavr/simple.elf
Reading symbols from /amd/u/u/home/makoto/avr/simulavr/simple.elf...
find_sym_fns: symfile.c:1869
zsh: abort (core dumped)  ./work/gdb-7.6/gdb/gdb
modena@makoto 18:14:55/130809(..cross/avr-gdb)% 

modena@makoto 18:15:00/130809(..cross/avr-gdb)% gdb ./work/gdb-7.6/gdb/gdb gdb.core 
GNU gdb (GDB) 7.3.1
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64--netbsd".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /export/CHROOT/usr/pkgsrc/cross/avr-gdb/work/gdb-7.6/gdb/gdb
    ...(no debugging symbols found)...done.
[New process 1]
Core was generated by `gdb'.
Program terminated with signal 6, Aborted.
#0  0x00007f7ff68ecfba in _lwp_kill () from /usr/lib/libc.so.12
(gdb) bt
#0  0x00007f7ff68ecfba in _lwp_kill () from /usr/lib/libc.so.12
#1  0x00007f7ff68ec8f2 in abort () from /usr/lib/libc.so.12
#2  0x000000000049d030 in find_sym_fns.clone.1 ()
#3  0x000000000049f4d5 in syms_from_objfile ()
#4  0x000000000049f910 in symbol_file_add_with_addrs_or_offsets.clone.7 ()
#5  0x00000000004a0316 in symbol_file_add ()
#6  0x00000000004a0665 in symbol_file_add_main_1 ()
#7  0x00000000004a070b in symbol_file_command ()
#8  0x00000000004eda2b in file_command ()
#9  0x000000000056be99 in execute_command ()
#10 0x00000000004c9474 in command_handler ()
#11 0x00000000004c9e20 in command_line_handler ()
#12 0x00000000005aa1c1 in rl_callback_read_char ()
#13 0x00000000004c94c4 in rl_callback_read_char_wrapper ()
#14 0x00000000004c88c8 in process_event ()
#15 0x00000000004c8d37 in gdb_do_one_event ()
#16 0x00000000004c8d87 in start_event_loop ()
#17 0x00000000004c306b in captured_command_loop ()
#18 0x00000000004c1e6b in catch_errors ()
#19 0x00000000004c3e95 in captured_main ()
#20 0x00000000004c1e6b in catch_errors ()
#21 0x00000000004c41d5 in gdb_main ()
#22 0x000000000040516a in main ()
(gdb) 

と思ったが、実はこの前の loop が知りたかった。