Re: [Xen-devel] [Qemu-devel] Qemu 2.0 regression with xen: qemu crash on any domUs S.O. start

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Wed, Apr 02, 2014 at 01:13:31PM +0200, Fabio Fantoni wrote:
> >- if you posted qemu's backtrace at the sigsegv.
> 
> I tried to use gdb following this old post:
> https://lists.gnu.org/archive/html/qemu-devel/2011-12/msg02575.html
> but with same changes:
> 
> /usr/lib/xen/bin# vi qemu-system-i386
> #!/bin/sh
> exec gdbserver 0.0.0.0:1234 /usr/lib/xen/bin/qemu-system-i386.bak "$@"
> 
> gdb /usr/lib/xen/bin/qemu-system-i386.bak
> target remote localhost:1234
> 
> This command with gdb on qemu fails:
> xl -vvv create /etc/xen/wheezy.cfg
> ...
> libxl: error: libxl_dm.c:1378:device_model_spawn_outcome: domain 13 device
> model: spawn failed (rc=-3)
> libxl: error: libxl_create.c:1207:domcreate_devmodel_started: device model
> did not start: -3
> libxl: debug: libxl_dm.c:1485:kill_device_model: Device Model signaled
> ...
> 
> the dom0 syslog show segfault also in this case and the qemu log is
> different on first lines (probably for gdbserver):
> less /var/log/xen/qemu-dm-wheezy.log
> Process /usr/lib/xen/bin/qemu-system-i386.bak created; pid = 8238
> Listening on port 1234
> Remote debugging from host 127.0.0.1
> xc: error: linux_gnttab_set_max_grants: ioctl SET_MAX_GRANTS failed (22 =
> Invalid argument): Internal error
> xen be: qdisk-51712: xc_gnttab_set_max_grants failed: Invalid argument
> 
> 
> gdb on xl create show:
> (gdb) target remote localhost:1234
> Remote debugging using localhost:1234
> Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols
> found)...done.
> Loaded symbols for /lib64/ld-linux-x86-64.so.2
> 0x00007ffff7dddaf0 in ?? () from /lib64/ld-linux-x86-64.so.2
> (gdb)
> 
> (gdb) bt full
> #0  0x00007ffff7dddaf0 in ?? () from /lib64/ld-linux-x86-64.so.2
> No symbol table info available.
> #1  0x0000000000000013 in ?? ()
> No symbol table info available.
> #2  0x00007fffffffe871 in ?? ()
> No symbol table info available.
> #3  0x00007fffffffe897 in ?? ()
> No symbol table info available.
> #4  0x00007fffffffe8a2 in ?? ()
> No symbol table info available.
> #5  0x00007fffffffe8a5 in ?? ()
> No symbol table info available.
> #6  0x00007fffffffe8ae in ?? ()
> No symbol table info available.
> #7  0x00007fffffffe8ef in ?? ()
> No symbol table info available.
> #8  0x00007fffffffe8f4 in ?? ()
> No symbol table info available.
> #9  0x00007fffffffe913 in ?? ()
> No symbol table info available.
> #10 0x00007fffffffe91f in ?? ()
> No symbol table info available.
> #11 0x00007fffffffe92b in ?? ()
> No symbol table info available.
> #12 0x00007fffffffe931 in ?? ()
> ---Type <return> to continue, or q <return> to quit---
> 
> the qemu include debug and is not stripped:
> file /usr/lib/xen/bin/qemu-system-i386.bak
> /usr/lib/xen/bin/qemu-system-i386.bak: ELF 64-bit LSB shared object, x86-64,
> version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux
> 2.6.26, BuildID[sha1]=0x5aa043b5524d74d166ead62527343080384d586b, not
> stripped
> and I also tried:
> aptitude install libc6-dbg
> but same result.
> 
> I not understand what I missed for correct xl create and/or gdb
> informations.
> Can someone help me please?

Using gdb on qemu is not easy, you need to be quick.

When you "xl create", you have about 10 second to start gdb on qemu,
otherwise, xl will fail to create a guest.

So I advise you to start "gdb /usr/lib/xen/bin/qemu-system-i386.bak" in
a second terminal, write "target remote localhost:1234" BUT not Enter,
to keep the command ready to run.
Then, start "xl create" and imediatly, run the "target" command in gdb
and "c" (for continue) which will start qemu.

That should help you reach the point where you can get the backtrace,
after the segv.

-- 
Anthony PERARD

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