kgdb貌似和ddb一样属于FreeBSD专属的调试器。
1、开启kdump功能
[email protected]:/root # cat /etc/rc.conf
# Set dumpdev to “AUTO” to enable crash dumps, “NO” to disable
dumpdev=”AUTO”
2、模拟触发一个内核崩溃，做一个panic即可
[email protected]:/root # sysctl debug.kdb.panic=1
3、系统会把这个panic导致的dump文件存储在 /var/crash/目录下面，第一个命名为vmcore.0
4、开始调试，先到 对应的内核版本的kernel.debug文件的路径下去：
[email protected]:/usr/obj/usr/src/sys/GENERIC_20130219 # ll | grep kernel
-rwxr-xr-x 1 root wheel 16031061 Feb 19 14:36 kernel*
-rwxr-xr-x 1 root wheel 62180463 Feb 19 14:36 kernel.debug*
-rwxr-xr-x 1 root wheel 48269559 Feb 19 14:36 kernel.symbols*
5、开始调试
root@www.itkylin.com:/usr/obj/usr/src/sys/GENERIC_20130219 # kgdb kernel.debug /var/crash/vmcore.0
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”…
Unread portion of the kernel message buffer:
panic: kdb_sysctl_panic
cpuid = 1
KDB: stack backtrace:
#0 0xc0af3aff at kdb_backtrace+0x4f
#1 0xc0ac052f at panic+0x16f
#2 0xc0af36c9 at kdb_sysctl_panic+0x59
#3 0xc0aca40a at sysctl_root+0x1fa
#4 0xc0aca6c3 at userland_sysctl+0x1d3
#5 0xc0acaa84 at sys___sysctl+0x94
#6 0xc0e2579a at syscall+0x34a
#7 0xc0e0f6d1 at Xint0x80_syscall+0x21
Uptime: 24m35s
Physical memory: 983 MB
Dumping 202 MB: 187 171 155 139 123 107 91 75 59 43 27 11
#0 doadump (textdump=1) at pcpu.h:244
244 __asm(“movl %%fs:0,%0” : “=r” (td));
6、查看调用栈：
(kgdb) bt
#0 doadump (textdump=1) at pcpu.h:244
##1 0xc0ac027f in kern_reboot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:448
##2 0xc0ac0572 in panic (fmt=Variable “fmt” is not available.
#) at /usr/src/sys/kern/kern_shutdown.c:636
##3 0xc0af36c9 in kdb_sysctl_panic (oidp=0xc111aa60, arg1=0x0, arg2=0, req=0xd91c9b74) at /usr/src/sys/kern/subr_kdb.c:185
##4 0xc0aca40a in sysctl_root (oidp=Variable “oidp” is not available.
#) at /usr/src/sys/kern/kern_sysctl.c:1513
##5 0xc0aca6c3 in userland_sysctl (td=0xc7d098a0, name=0xd91c9be0, namelen=3, old=0x0, oldlenp=0x0, inkernel=0, new=0xbfbfe4a0, newlen=4, retval=0xd91c9c40, flags=0)
# at /usr/src/sys/kern/kern_sysctl.c:1623
# #6 0xc0acaa84 in sys___sysctl (td=0xc7d098a0, uap=0xd91c9ccc) at /usr/src/sys/kern/kern_sysctl.c:1549
# #7 0xc0e2579a in syscall (frame=0xd91c9d08) at subr_syscall.c:135
# #8 0xc0e0f6d1 in Xint0x80_syscall () at /usr/src/sys/i386/i386/exception.s:267
# #9 0x00000033 in ?? ()
# Previous frame inner to this frame (corrupt stack?)