Re: [Qemu-devel] Fwd: Guest VM debug (Int 3 panic)

[Hu Yaohui <loki2441@gmail.com>]

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Hi Jan,
Thanks for your reply.
On Thu, Sep 26, 2013 at 2:08 AM, Jan Kiszka <jan.kiszka@web.de> wrote:

> On 2013-09-25 20:08, Hu Yaohui wrote:
> > Hi All,
> > I am trying to debug guest OS through qemu with kvm enabled.
> > Following is what I have done:
> > 1: fire the qemu-kvm
> > <snip>
> > sudo qemu-system-x86_64 -hda vdisk.img -m 4096 -smp 2 -vnc :2 -boot c -s
> > </snip>
> >
> > 2: wait until login into guest OS (ubuntu 10.04)
> >
> > 3: fire gdb
> > <snip>
> > gdb vmlinux
> > target remote :1234
> > b do_fork
> > set arch i386:x86-64
>
> "set arch" is unneeded. vmlinux already tells gdb that you are debugging
> x86-64.
>
> > c
> > </snip>
> >
> > 4: after I typed "ls" in guest OS. The guest OS paniced with some message
> > related to "int 3 blah blah". Then crashed.
> >
> > Someone said we should use hardware breakpoint when kvm is enabled, or
>
> You can use hardware breakpoints as well but it is not required unless
> the target code can be overwritten (e.g. due to a reset).
>
> > "monitor system_reset" after set the breakpoint, but it didn't work for
> me.
> > The hardware breakpoint could not been hit anyway.
> >
> > I have tried with "-no-kvm", it works normally with breakpoints. But I
> want
> > to debug the guest OS with kvm enabled. I don't know whether someone has
> > met this similar situation.
>
> You didn't tell us which version of QEMU (or is it old qemu-kvm?) you
> are using, what host kernel and which CPU type (AMD vs. Intel). Did you
> try a recent version of all of them already? I'm currently not aware of
> gdb problems with QEMU/KVM, I'm rather using it on an almost daily basis
> (typically git head versions).
>
I am using a nested VM. My CPU type is intel.
On L0, the QEMU-KVM version is 1.0, host kernel version: 2.6.32.10,
kvm-kmod version: 3.2
On L1, the QEMU-KVM version is 1.2, kernel version: 3.2.2, kvm-kmod
version: 3.2
On L2, guest kernel version: 2.6.32.10
I am trying to debug L2 guest kernel on L1 QEMU. It gives me "INT 3"
related kernel oops.
I also have tried to debug the L1 guest kernel through L0 QEMU which works
fine.

>
> If you want to debug your issue: there is ftrace to record what KVM
> events happen, and you can switch gdb into verbose mode as well,
> comparing the communication between KVM on/off: set debug remote 1.
>
> Thanks for your suggestion! I will give that a try.

> Jan
>
>
>

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