Tips on remote debugging for filesystem code

[Julian Elischer]

On 4/9/17 9:55 pm, Aijaz Baig wrote:
> Hi Julian
>
> Yes it just hangs. Yes it's not like it just hangs every time. It's 
> more intermittent. This time I was stepping through 'kern_openat', 
> really slowly as I am new to this, checking out the structures and 
> the likes and finally this hit when I was within vn_open_cred. So 
> yes the total time between attaching to the stub within the VM and 
> this happening was close to 3 hours but nonetheless I do face this 
> eventually
>
> is there something I should watch out for, I mean is there something 
> time bound in some way for any of this code? Is this the reason why 
> the VM becomes unresponsive if I step really slowly through the 
> stack trace?

I haven't used it for  a year or so but I used to occasionally have a 
problem when doing things that would disable interrupts.  I found I 
had to put a breakpoint on ht eother side of them and 'c'ontinue over 
them or it would get stuck..

>
> On Mon, Sep 4, 2017 at 10:25 AM, Julian Elischer <julian at freebsd.org 
> <mailto:julian at freebsd.org>> wrote:
>
>     On 2/9/17 8:40 pm, Aijaz Baig wrote:
>>     I was finally able to deploy a FreeBSD-Current VM on Bhyve but
>>     even with that setup I face a similar issue
>>
>>     For instance I put a breakpoint on 'ffs_read' and let the
>>     debugged VM continue but the control is neither returned to
>>     (k)gdb nor does the VM actually run. It appears hung.
>     are you sure it's not stopped at the breakpoint in ddb on the
>     console?
>
>>
>>     Is there something within the ffs/ufs code that I need to be
>>     aware of that it doesn't facilitate this sort of debugging? Or
>>     is it because Bhyve is being run on FreeBSD which is itself run
>>     on another hypervisor? Will that affect this?
>>
>>     On Mon, Aug 28, 2017 at 7:03 PM, Aijaz Baig
>>     <aijazbaig1 at gmail.com <mailto:aijazbaig1 at gmail.com>> wrote:
>>
>>         HI Gary
>>
>>         Just checked that. Indeed that was the case. In addition I
>>         was running FreeBSD on top of vmware hypervisor and had not
>>         allowed hardware acceleration features pass through to the
>>         FreeBSD VM. It is now working! Need to explore more on
>>         getting it to connect to GDB
>>
>>         Perhaps you'll see a thread soon for it (Has anything
>>         worked perfectly for the first time ever?? ;) )!
>>
>>         On Mon, Aug 28, 2017 at 6:56 PM, Gary Palmer
>>         <gpalmer at freebsd.org <mailto:gpalmer at freebsd.org>> wrote:
>>
>>             On Mon, Aug 28, 2017 at 01:12:09PM +0530, Aijaz Baig wrote:
>>             > Thanks a lot bakul. Will certain look into this
>>             >
>>             > Nevertheless I got hold of a PowerEdge 320 system
>>             which DOES have a POPCNT
>>             > instruction which shows support for V-x support via
>>             EPT but I still get the
>>             > same error there
>>             >
>>             > sh /usr/share/examples/bhyve/vmrun.sh -c 1 -m 2048M
>>             -t tap0 -d guest.img -i
>>             > -I FreeBSD-10.3-RELEASE-amd64-bootonly.iso fbsd10
>>             > Launching virtual machine "fbsd10" ...
>>             > vm_create: Device not configured
>>             >
>>             > dmesg:
>>             > vmx_init: processor does not support VMX operation
>>             >
>>             > cat /var/run/dmesg.boot | grep -i popcnt
>>             >
>>             >
>>             Features2=0xffba2203<SSE3,PCLMULQDQ,SSSE3,CX16,PCID,SSE4.1,SSE4.2,x2APIC,POPCNT,TSCDLT,AESNI,XSAVE,OSXSAVE,AVX,F16C,RDRAND,HV>
>>             >
>>             >
>>             Features2=0xffba2203<SSE3,PCLMULQDQ,SSSE3,CX16,PCID,SSE4.1,SSE4.2,x2APIC,POPCNT,TSCDLT,AESNI,XSAVE,OSXSAVE,AVX,F16C,RDRAND,HV>
>>             >
>>             > Any ideas?
>>
>>             Hi,
>>
>>             Check the BIOS for virtualisation or other related
>>             options.  Some BIOSes have
>>             the ability to turn those features off, even if the
>>             processor normally
>>             supports them
>>
>>             Regards,
>>
>>             Gary
>>
>>
>>
>>
>>         -- 
>>
>>         Best Regards,
>>         Aijaz Baig
>>
>>
>>
>>
>>     -- 
>>
>>     Best Regards,
>>     Aijaz Baig
>
>
>
>
>
> -- 
>
> Best Regards,
> Aijaz Baig