.
Thread 1 (LWP 8151):
#0  __GI___pthread_mutex_lock (mutex=0x18) at ../nptl/pthread_mutex_lock.c:66
        __PRETTY_FUNCTION__ = "__pthread_mutex_lock"
        type = <optimized out>
        id = <optimized out>
#1  0xb760aaf4 in pthread_mutex_lock (mutex=mutex@entry=0x18) at forward.c:192
        __p = <optimized out>
#2  0xb76c3935 in libusb_get_device_list (ctx=0x0, list=list@entry=0xbfc7d86c) at ../../libusb/core.c:671
        dev = <optimized out>
        discdevs = 0x83de008
        ret = <optimized out>
        r = 0
        i = <optimized out>
        len = <optimized out>
        __FUNCTION__ = "libusb_get_device_list"
#3  0x08056da9 in find_and_enumerate (ctx=<optimized out>, list=list@entry=0xbfc7d86c, backend=backend@entry=0x0, match_serno=match_serno@entry=0x0, printer_type=printer_type@entry=0, scan_only=scan_only@entry=1) at ../../../../src/cups/backend_common.c:378
        num = <optimized out>
        i = <optimized out>
        j = <optimized out>
        k = <optimized out>
        found = -1
#4  0x08057081 in print_help (argv0=<optimized out>, backend=backend@entry=0x0) at ../../../../src/cups/backend_common.c:517
        ctx = 0x0
        list = 0x0
        ptr = <optimized out>
#5  0x080493a0 in main (argc=1, argv=0xbfc7d994) at ../../../../src/cups/backend_common.c:640
        ctx = 0x0
        list = 0x0
        dev = 0xbfc7d99c
        config = 0xb754464d <__cxa_atexit+29>
        backend = 0x0
        backend_ctx = 0x0
        endp_up = 0 '\000'
        endp_down = 0 '\000'
        data_fd = 0
        i = <optimized out>
        claimed = <optimized out>
        backend_cmd = 0
        ret = 0
        found = -1
        copies = 1
        jobid = 0
        pages = 0
        uri = <optimized out>
        fname = 0x0
        printer_type = 0