Re: strange kernel crash

On Tuesday, November 10, 2015 10:48:08 AM Andriy Gapon wrote:
> On 09/11/2015 22:16, John Baldwin wrote:
> > On Friday, November 06, 2015 07:02:59 PM Hans Petter Selasky wrote:
> >> On 11/06/15 12:20, Andriy Gapon wrote:
> >>> Now the strange part:
> >>>
> >>>     0xffffffff80619a18 <+744>:   jne    0xffffffff80619a61 <__mtx_lock_flags+817>
> >>>     0xffffffff80619a1a <+746>:   mov    %rbx,(%rsp)
> >>> => 0xffffffff80619a1e <+750>:   movq   $0x0,0x18(%rsp)
> >>>     0xffffffff80619a27 <+759>:   movq   $0x0,0x10(%rsp)
> >>>     0xffffffff80619a30 <+768>:   movq   $0x0,0x8(%rsp)
> >>
> >> Were these instructions dumped from RAM or from the kernel ELF file?
> > 
> > Probably not from RAM.  You can use 'info files' in gdb to see what is
> > handling the address range in question (core vs executable).  x/i in ddb
> > would have been the "real" truth.
> 
> Yes, according to the output of files it looks like gdb would read that data
> from the text section of the kernel file.
> 
> How about libkvm?  Would kvm_read read data from the core file?

kvm_read should only access the vmcore, yes.

> I've written the following small program (cut down dmesg.c, actually):
> https://people.freebsd.org/~avg/vmcore_read.c
> 
> (kgdb) disassemble /r
> => 0xffffffff80619a1e <+750>:   48 c7 44 24 18 00 00 00 00      movq
> $0x0,0x18(%rsp)
> 
> $ vmcore_read -N /boot/kernel.29/kernel -M /var/crash/vmcore.29 0xffffffff80619a1e 9
> 48 c7 44 24 18 00 00 00 00
> 
> Seems like the code is intact.
> 
> P.S.
> 1. To correct something I said earlier, the fault is #UD, not #GP.
> 2. The only "suspicious" activity at the time of the crash was the execution of
> a bhyve VM.

Was the crash in the guest or the host?  UD# seems even more bizarre.

-- 
John Baldwin