Update the section on debugging a kernel with GDB to include a recent
dump and the basics of what most developers would like to see in reports of a panic where a dump is available. Also trim a few lines from the previous dump example (still included) and sync up some of the gdb commands for the sake of consistency. Inspired by: Recent exchange with jhb
This commit is contained in:
Sean Chittenden
parent
9030b241d7
commit
10be000a0a
Notes:
svn2git
2020-12-08 03:00:23 +00:00
svn path=/head/; revision=19043
1 changed files with 118 additions and 14 deletions
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@ -143,19 +143,127 @@
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<filename>/usr/obj/usr/src/sys/KERNCONF</filename>, where
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<filename>KERNCONF</filename> is the <varname>ident</varname>
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specified in a kernel &man.config.5;). With those two pieces of
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info, let the debugging commence!
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info, let the debugging commence!</para>
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<para>To enter into the debugger and begin getting information
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from the dump, the following steps are required at a minimum:
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<screen>&prompt.root; <userinput>cd /usr/obj/usr/src/sys/KERNCONF</userinput>
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&prompt.root; <userinput>gdb -k /boot/kernel/kernel.debug /var/crash/vmcore.0</userinput></screen>
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and voila! You can debug the crash dump using the kernel
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sources just like you can for any other program.</para>
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You can debug the crash dump using the kernel sources just like
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you can for any other program.</para>
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<para>Here is a script log of a <command>gdb</command> session
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illustrating the procedure. Long lines have been folded to improve
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readability, and the lines are numbered for reference. Despite this, it
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is a real-world error trace taken during the development of the pcvt
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console driver.</para>
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<para>This first dump is from a 5.2-BETA kernel and the crash
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comes from deep within the kernel. The ouput below has been
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modified to include line numbers on the left. This first trace
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inspects the instruction pointer and obtains a back trace. The
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address that is used on line 41 for the <command>list</command>
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command is the instruction pointer and can be found on line line
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17. Most developers will request having at least this
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information sent to them if you are unable to debug the problem
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yourself. If, however, you do solve the problem, make sure that
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your patch winds its way into the source tree via a problem
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report, mailing lists, or by being able to commit it!
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<screen> 1:&prompt.root; <userinput>cd /usr/obj/usr/src/sys/KERNCONF</userinput>
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2:&prompt.root; <userinput>gdb -k kernel.debug /var/crash/vmcore.0</userinput>
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3:GNU gdb 5.2.1 (FreeBSD)
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4:Copyright 2002 Free Software Foundation, Inc.
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5:GDB is free software, covered by the GNU General Public License, and you are
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6:welcome to change it and/or distribute copies of it under certain conditions.
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7:Type "show copying" to see the conditions.
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8:There is absolutely no warranty for GDB. Type "show warranty" for details.
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9:This GDB was configured as "i386-undermydesk-freebsd"...
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10:panic: page fault
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11:panic messages:
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12:---
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13:Fatal trap 12: page fault while in kernel mode
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14:cpuid = 0; apic id = 00
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15:fault virtual address = 0x300
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16:fault code: = supervisor read, page not present
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17:instruction pointer = 0x8:0xc0713860
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18:stack pointer = 0x10:0xdc1d0b70
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19:frame pointer = 0x10:0xdc1d0b7c
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20:code segment = base 0x0, limit 0xfffff, type 0x1b
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21: = DPL 0, pres 1, def32 1, gran 1
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22:processor eflags = resume, IOPL = 0
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23:current process = 14394 (uname)
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24:trap number = 12
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25:panic: page fault
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26 cpuid = 0;
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27:Stack backtrace:
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28
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29:syncing disks, buffers remaining... 2199 2199 panic: mi_switch: switch in a critical section
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30:cpuid = 0;
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31:Uptime: 2h43m19s
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32:Dumping 255 MB
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33: 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
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34:---
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35:Reading symbols from /boot/kernel/snd_maestro3.ko...done.
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36:Loaded symbols for /boot/kernel/snd_maestro3.ko
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37:Reading symbols from /boot/kernel/snd_pcm.ko...done.
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38:Loaded symbols for /boot/kernel/snd_pcm.ko
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39:#0 doadump () at /usr/src/sys/kern/kern_shutdown.c:240
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40:240 dumping++;
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41:<prompt>(kgdb)</prompt> <userinput>list *0xc0713860</userinput>
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42:0xc0713860 is in lapic_ipi_wait (/usr/src/sys/i386/i386/local_apic.c:663).
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43:658 incr = 0;
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44:659 delay = 1;
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45:660 } else
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46:661 incr = 1;
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47:662 for (x = 0; x < delay; x += incr) {
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48:663 if ((lapic->icr_lo & APIC_DELSTAT_MASK) == APIC_DELSTAT_IDLE)
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49:664 return (1);
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50:665 ia32_pause();
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51:666 }
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52:667 return (0);
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53:<prompt>(kgdb)</prompt> <userinput>backtrace</userinput>
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54:#0 doadump () at /usr/src/sys/kern/kern_shutdown.c:240
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55:#1 0xc055fd9b in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:372
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56:#2 0xc056019d in panic () at /usr/src/sys/kern/kern_shutdown.c:550
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57:#3 0xc0567ef5 in mi_switch () at /usr/src/sys/kern/kern_synch.c:470
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58:#4 0xc055fa87 in boot (howto=256) at /usr/src/sys/kern/kern_shutdown.c:312
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59:#5 0xc056019d in panic () at /usr/src/sys/kern/kern_shutdown.c:550
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60:#6 0xc0720c66 in trap_fatal (frame=0xdc1d0b30, eva=0)
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61: at /usr/src/sys/i386/i386/trap.c:821
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62:#7 0xc07202b3 in trap (frame=
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63: {tf_fs = -1065484264, tf_es = -1065484272, tf_ds = -1065484272, tf_edi = 1, tf_esi = 0, tf_ebp = -602076292, tf_isp = -602076324, tf_ebx = 0, tf_edx = 0, tf_ecx = 1000000, tf_eax = 243, tf_trapno = 12, tf_err = 0, tf_eip = -1066321824, tf_cs = 8, tf_eflags = 65671, tf_esp = 243, tf_ss = 0})
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64: at /usr/src/sys/i386/i386/trap.c:250
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65:#8 0xc070c9f8 in calltrap () at {standard input}:94
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66:#9 0xc07139f3 in lapic_ipi_vectored (vector=0, dest=0)
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67: at /usr/src/sys/i386/i386/local_apic.c:733
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68:#10 0xc0718b23 in ipi_selected (cpus=1, ipi=1)
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69: at /usr/src/sys/i386/i386/mp_machdep.c:1115
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70:#11 0xc057473e in kseq_notify (ke=0xcc05e360, cpu=0)
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71: at /usr/src/sys/kern/sched_ule.c:520
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72:#12 0xc0575cad in sched_add (td=0xcbcf5c80)
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73: at /usr/src/sys/kern/sched_ule.c:1366
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74:#13 0xc05666c6 in setrunqueue (td=0xcc05e360)
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75: at /usr/src/sys/kern/kern_switch.c:422
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76:#14 0xc05752f4 in sched_wakeup (td=0xcbcf5c80)
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77: at /usr/src/sys/kern/sched_ule.c:999
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78:#15 0xc056816c in setrunnable (td=0xcbcf5c80)
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79: at /usr/src/sys/kern/kern_synch.c:570
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80:#16 0xc0567d53 in wakeup (ident=0xcbcf5c80)
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81: at /usr/src/sys/kern/kern_synch.c:411
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82:#17 0xc05490a8 in exit1 (td=0xcbcf5b40, rv=0)
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83: at /usr/src/sys/kern/kern_exit.c:509
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84:#18 0xc0548011 in sys_exit () at /usr/src/sys/kern/kern_exit.c:102
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85:#19 0xc0720fd0 in syscall (frame=
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86: {tf_fs = 47, tf_es = 47, tf_ds = 47, tf_edi = 0, tf_esi = -1, tf_ebp = -1077940712, tf_isp = -602075788, tf_ebx = 672411944, tf_edx = 10, tf_ecx = 672411600, tf_eax = 1, tf_trapno = 12, tf_err = 2, tf_eip = 671899563, tf_cs = 31, tf_eflags = 642, tf_esp = -1077940740, tf_ss = 47})
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87: at /usr/src/sys/i386/i386/trap.c:1010
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88:#20 0xc070ca4d in Xint0x80_syscall () at {standard input}:136
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89:---Can't read userspace from dump, or kernel process---
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90:<prompt>(kgdb)</prompt> <userinput>quit</userinput></screen></para>
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<para>This next trace is an older dump from the FreeBSD 2 time
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frame, but is more involved and demonstrates more of the
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features of <command>gdb</command>. Long lines have been folded
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to improve readability, and the lines are numbered for
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reference. Despite this, it is a real-world error trace taken
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during the development of the pcvt console driver.</para>
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<screen> 1:Script started on Fri Dec 30 23:15:22 1994
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2:&prompt.root; <userinput>cd /sys/compile/URIAH</userinput>
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@ -166,7 +274,7 @@
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6:panic: because you said to!
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7:current pcb at 1e3f70
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8:Reading in symbols for ../../i386/i386/machdep.c...done.
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9:<prompt>(kgdb)</prompt> <userinput>where</userinput>
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9:<prompt>(kgdb)</prompt> <userinput>backtrace</userinput>
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10:#0 boot (arghowto=256) (../../i386/i386/machdep.c line 767)
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11:#1 0xf0115159 in panic ()
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12:#2 0xf01955bd in diediedie () (../../i386/i386/machdep.c line 698)
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@ -233,11 +341,7 @@
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73:673 error = (*callp->sy_call)(p, args, rval);
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74:<prompt>(kgdb)</prompt> <userinput>up</userinput>
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75:Initial frame selected; you cannot go up.
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76:<prompt>(kgdb)</prompt> <userinput>quit</userinput>
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77:&prompt.root; <userinput>exit</userinput>
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78:exit
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79:
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80:Script done on Fri Dec 30 23:18:04 1994</screen>
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76:<prompt>(kgdb)</prompt> <userinput>quit</userinput></screen>
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<para>Comments to the above script:</para>
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<variablelist>
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