How to get anything useful out of kgdb?

[Sean Bruno]

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On 05/15/15 10:57, Ryan Stone wrote:
> On Fri, May 15, 2015 at 1:07 PM, Sean Bruno
> <sbruno at ignoranthack.me> wrote:
> 
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>> 
>> Hrm, when I look at them directly in the crashdump, I don't see 
>> anything useful.
>> 
>> (kgdb) tid 100058 [Switching to thread 54 (Thread 100058)]#0
>> cpustop_handler () at 
>> /home/sbruno/bsd/em_mq/sys/x86/x86/mp_x86.c:987 987
>> CPU_SET_ATOMIC(cpu, &stopped_cpus); Current language:  auto;
>> currently minimal (kgdb) whe #0  cpustop_handler () at
>> /home/sbruno/bsd/em_mq/sys/x86/x86/mp_x86.c:98 7 #1
>> 0xffffffff80f76f7a in ipi_nmi_handler () at 
>> /home/sbruno/bsd/em_mq/sys/x86/x86/mp_x86.c:969 #2
>> 0xffffffff80e3657a in trap (frame=0xffffffff817eb910) at 
>> /home/sbruno/bsd/em_mq/sys/amd64/amd64/trap.c:188 #3
>> 0xffffffff80e1b273 in nmi_calltrap () at 
>> /home/sbruno/bsd/em_mq/sys/amd64/amd64/exception.S:509 #4
>> 0x0000000800841841 in ?? () Previous frame inner to this frame
>> (corrupt stack?)
>> 
> 
> *Sigh*,  kgdb isn't unwinding the trap frame properly.  You can try
> this to figure out where it was running:
> 
> frame 2 info line *frame->tf_rip

I'm guessing that we are just at the limit of what the intree kgdb is
capable of doing with out crashdumps.

#2  0xffffffff80e3657a in trap (frame=0xffffffff817eb910) at
/home/sbruno/bsd/em_mq/sys/amd64/amd64/trap.c:188
188		         if (ipi_nmi_handler() == 0)
(kgdb) p frame
$5 = (struct trapframe *) 0xffffffff817eb910
(kgdb) p *frame
$6 = {tf_rdi = 34389196884, tf_rsi = 34389192960, tf_rdx = 0, tf_rcx =
360, tf_r8 = 0, tf_r9 = -8795456263872, tf_rax = 0, tf_rbx =
34393489408, tf_rbp = 140736951475936, tf_r10 = 17232, tf_r11 = 583,
tf_r12 = 1882455366,
  tf_r13 = 34389196880, tf_r14 = 0, tf_r15 = 6358856, tf_trapno = 19,
tf_fs = 19, tf_gs = 27, tf_addr = 0, tf_flags = 1, tf_es = 59, tf_ds =
59, tf_err = 0, tf_rip = 34368395329, tf_cs = 67, tf_rflags = 518,
tf_rsp = 140736951475912,
  tf_ss = 59}
(kgdb) p *frame->tf_rip
Cannot access memory at address 0x800841841
(kgdb) info line *frame->tf_rip
No line number information available for address 0x800841841
(kgdb)
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