FreeBSD7.0远程调试内核时，回溯汇编栈帧出现异…

双机远程串口调试FreeBSD7.0内核，建立调试连接之后，在vm_fault()函数处打断点，让目标机继续运行并遇到vm_fault()断点时，若用backtrace命令查看调用栈，会在进入汇编语言栈帧之后出现segmentation fault。
#
# kgdb -r /dev/cuad0 /sys/i386/compile/DEBUGKERNEL/kernel.debug
[GDB will not be able to debug user-mode threads: /usr/lib/libthread_db.so: Undefined symbol "ps_pglobal_lookup"]
GNU gdb 6.1.1 [FreeBSD]
Copyright 2004 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 "i386-marcel-freebsd".
Switching to remote protocol
kdb_enter (msg=0xc0aed472 "sysctl debug.kdb.enter") at ../../../kern/subr_kdb.c:310
310     }
Unread portion of the kernel message buffer:
KDB: enter: sysctl debug.kdb.enter
#0  kdb_enter (msg=0xc0aed472 "sysctl debug.kdb.enter") at ../../../kern/subr_kdb.c:310
310     }
(kgdb) b vm_fault
Breakpoint 1 at 0xc097a066: file ../../../vm/vm_fault.c, line 222.
(kgdb) c
Continuing.
[New Thread 100068]
[Switching to Thread 100068]
Breakpoint 1, vm_fault (map=0xc211cae0, vaddr=673189888, fault_type=3 '\003', fault_flags=1) at ../../../vm/vm_fault.c:222
222             PCPU_INC(cnt.v_vm_faults);
(kgdb) bt
#0  vm_fault (map=0xc211cae0, vaddr=673189888, fault_type=3 '\003', fault_flags=1) at ../../../vm/vm_fault.c:222
#1  0xc097c12a in vm_fault_wire (map=0xc211cae0, start=673189888, end=673193984, user_wire=0, fictitious=0)
    at ../../../vm/vm_fault.c:1025
#2  0xc0981576 in vm_map_wire (map=0xc211cae0, start=673189888, end=673193984, flags=0) at ../../../vm/vm_map.c:2068
#3  0xc097d1d5 in vslock (addr=0x28201040, len=4) at ../../../vm/vm_glue.c:226
#4  0xc076877e in sysctl_wire_old_buffer (req=0xcd0c9ba4, len=4) at ../../../kern/kern_sysctl.c:1179
#5  0xc0785c8f in kdb_sysctl_enter (oidp=0xc0b96460, arg1=0x0, arg2=0, req=0xcd0c9ba4) at ../../../kern/subr_kdb.c:157
#6  0xc0768277 in sysctl_root (oidp=Variable "oidp" is not available.
) at ../../../kern/kern_sysctl.c:1306
#7  0xc07683c4 in userland_sysctl (td=0xc251f210, name=0xcd0c9c14, namelen=3, old=0x28201040, oldlenp=0xbfbfe430, inkernel=0,
    new=0x0, newlen=0, retval=0xcd0c9c10, flags=0) at ../../../kern/kern_sysctl.c:1401
#8  0xc076915e in __sysctl (td=0xc251f210, uap=0xcd0c9cfc) at ../../../kern/kern_sysctl.c:1336
#9  0xc0a5aa85 in syscall (frame=0xcd0c9d38) at ../../../i386/i386/trap.c:1035

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