[sheepdog] [Qemu-devel] [PATCH] sheepdog: fix overlapping metadata update

[Stefan Hajnoczi]

On Sun, Aug 09, 2015 at 05:03:14PM +0300, Vasiliy Tolstov wrote:
> 2015-08-05 21:58 GMT+03:00 Jeff Cody <jcody at redhat.com>:
> > Hi Vasiliy,
> >
> > If you run configure with  --disable-strip, it will not strip the
> > debugging symbols from the binary after the build.  Then, you can run
> > gdb on qemu, and do a backtrace after you hit the segfault ('bt').
> > That may shed some light, and is a good place to start.
> 
> 
> I'm try to debug (disable-strip), but i'm start vps from libvirt (i'm
> add -s flag to qemu, to start gdb), but when i'm attach to remote
> session,qemu aready dies, or all works fine.
> does it possible to determine by this dmesg what happening in qemu
> binary with debug symbols?
> qemu-system-x86[34046]: segfault at 401364 ip 00007f33f52a1ff8 sp
> 00007f3401ecad30 error 4 in qemu-system-x86_64[7f33f4efd000+518000]

-s launches QEMU's gdbstub for *guest* debugging.  It allows you to see
the CPU and memory state inside the guest.  It won't help you debug this
segfault.

Since the problem you encountered is a *QEMU* segfault, you need to use
*host* GDB on the QEMU process instead.

I'm not sure if libvirt sets the RLIMIT_CORE rlimit for the QEMU process
(which could disable coredumps), but if your host uses systemd you may
be able to inspect the coredump with gdb using coredumpctl(1).
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