(gdb) bt full
#0  0x0805d468 in ast_frame_slinear_sum (f1=0x9edf998, f2=0x9f1bb28) at include/asterisk/utils.h:190
        count = 0
        data1 = (short int *) 0x9edfa18
        data2 = (short int *) 0x0
#1  0x0806d99d in ast_channel_spy_read_frame (spy=0x9f91918, samples=160) at channel.c:4175
        result = (struct ast_frame *) 0x0
        read_buf = {1, 0}
        write_buf = {3, 0}
        read_frame = (struct ast_frame *) 0x9edf998
        write_frame = (struct ast_frame *) 0x9f1bb28
        need_dup = 0
        stack_read_frame = {frametype = 2, subclass = 64, datalen = 320, samples = 160, mallocd = 0, offset = 0, src = 0x0,
  data = 0x7a29170, delivery = {tv_sec = 0, tv_usec = 0}, prev = 0x0, next = 0x0, has_timing_info = 0, ts = 0, len = 0, seqno = 0}
        stack_write_frame = {frametype = 2, subclass = 64, datalen = 320, samples = 160, mallocd = 0, offset = 0, src = 0x0,
  data = 0x7a29020, delivery = {tv_sec = 0, tv_usec = 0}, prev = 0x0, next = 0x0, has_timing_info = 0, ts = 0, len = 0, seqno = 0}
#2  0x01b85655 in mixmonitor_thread (obj=0x9f91918) at app_mixmonitor.c:185
        next = (struct ast_frame *) 0x9f79808
        write = 2930720
        mixmonitor = (struct mixmonitor *) 0x9f91918
        f = (struct ast_frame *) 0x0
#3  0x080bc5d6 in dummy_start (data=0x9f79808) at utils.c:554
        _buffer = {__routine = 0x80a7f45 <ast_unregister_thread>, __arg = 0x7a29bb0, __canceltype = 0, __prev = 0x0}
        ret = (void *) 0x2c866c
        a = {start_routine = 0x1b855a4 <mixmonitor_thread>, data = 0x9f91918,
  name = 0x9f58d68 "mixmonitor_thread    started at [  317] app_mixmonitor.c launch_monitor_thread()"}
#4  0x00312371 in start_thread () from /lib/tls/libpthread.so.0
No symbol table info available.
#5  0x0026b9be in clone () from /lib/tls/libc.so.6
No symbol table info available.
(gdb)