(gdb) bt full
#0  0x0809808e in ast_frame_slinear_sum (f1=0x81f9420, f2=0x81f4db0) at /usr/src/asterisk/include/asterisk/utils.h:192
No locals.
#1  0x0807912f in ast_channel_spy_read_frame (spy=0x81df4b8, samples=160) at channel.c:4365
        result = <value optimized out>
        read_frame = (struct ast_frame *) 0x81f9420
        write_frame = (struct ast_frame *) 0x81f4db0
        need_dup = 0
        stack_read_frame = {frametype = AST_FRAME_VOICE, subclass = 64, datalen = 320, samples = 160, mallocd = 0, mallocd_hdr_len = 0, offset = 0,
  src = 0x0, data = 0xb64971b0, delivery = {tv_sec = 0, tv_usec = 0}, frame_list = {next = 0x0}, has_timing_info = 0, ts = 0, len = 0, seqno = 0}
        stack_write_frame = {frametype = AST_FRAME_VOICE, subclass = 64, datalen = 320, samples = 160, mallocd = 0, mallocd_hdr_len = 0, offset = 0,
  src = 0x0, data = 0xb6497060, delivery = {tv_sec = 0, tv_usec = 0}, frame_list = {next = 0x0}, has_timing_info = 0, ts = 0, len = 0, seqno = 0}
#2  0xb6cee195 in mixmonitor_thread (obj=0x81df4b8) at app_mixmonitor.c:166
        next = (struct ast_frame *) 0x81dc400
        f = (struct ast_frame *) 0x81dc400
#3  0x080eb0eb in dummy_start (data=0x81e1630) at utils.c:545
        __cancel_buf = {__cancel_jmp_buf = {{__cancel_jmp_buf = {136168184, 0, 0, -1236700056, 368799242, -1413698866}, __mask_was_saved = 0}}, __pad = {
    0xb64974a0, 0x0, 0x0, 0x0}}
        __cancel_arg = (void *) 0xb6497ba0
        not_first_call = <value optimized out>
        ret = <value optimized out>
#4  0xb7dff34b in start_thread () from /lib/libpthread.so.0
No symbol table info available.
#5  0xb70db65e in clone () from /lib/libc.so.6