Re: [Crash-utility] crash crashes reading qemu dump files
----- Original Message -----
(2013/11/20 7:19), Andi Kleen wrote:
>
> So I wanted to use crash to look at a dump from a qemu KVM guest
> I write a dump file from the qemu console with
>
> dump-guest-core foo
>
Hello,
If you want a crash dump of the running qemu guest machine,
you can use dump-guest-memory command.
ETEXI
{
.name = "dump-guest-memory",
.args_type = "paging:-p,filename:F,begin:i?,length:i?",
.params = "[-p] filename [begin] [length]",
.help = "dump guest memory to file"
"\n\t\t\t begin(optional): the starting physical
address"
"\n\t\t\t length(optional): the memory size, in
bytes",
.mhandler.cmd = hmp_dump_guest_memory,
},
STEXI
@item dump-guest-memory [-p] @var{protocol} @var{begin} @var{length}
@findex dump-guest-memory
Dump guest memory to @var{protocol}. The file can be processed with crash or gdb.
filename: dump file name
paging: do paging to get guest's memory mapping
begin: the starting physical address. It's optional, and should be
specified with length together.
length: the memory size, in bytes. It's optional, and should be
specified
with begin together.
BTW, I heard the dump-guest-core command for the first time.
According to the source code, it looks like the command to decide whether
or not to include VM guest in a process core dump generated by KVM
host kernel.
static void qemu_ram_setup_dump(void *addr, ram_addr_t size)
{
int ret;
/* Use MADV_DONTDUMP, if user doesn't want the guest memory in the core
*/
if (!qemu_opt_get_bool(qemu_get_machine_opts(),
"dump-guest-core", true)) {
ret = qemu_madvise(addr, size, QEMU_MADV_DONTDUMP);
if (ret) {
perror("qemu_madvise");
fprintf(stderr, "madvise doesn't support MADV_DONTDUMP, "
"but dump_guest_core=off specified\n");
}
}
}
According to qemu-ptions.hx, syntax of the command is:
@item dump-guest-core=on|off
Include guest memory in a core dump. The default is on.
So, it seems strange to me that the fact "foo" file was generated...
--
Thanks.
HATAYAMA, Daisuke
I'd never heard of "dump-guest-core", but apparently the file type is
initially being accepted as a kdump ELF vmcore. But then later it
craps out in the embedded gdb code when crash is checking whether
the vmlinux file contains debuginfo data for the struct task_struct.
It should just fail, return back, and fail the session with a message
indicating that there is no debuginfo data, like this:
$ strip vmlinux
$ crash vmlinux
crash 7.0.3
Copyright (C) 2002-2013 Red Hat, Inc.
Copyright (C) 2004, 2005, 2006, 2010 IBM Corporation
Copyright (C) 1999-2006 Hewlett-Packard Co
Copyright (C) 2005, 2006, 2011, 2012 Fujitsu Limited
Copyright (C) 2006, 2007 VA Linux Systems Japan K.K.
Copyright (C) 2005, 2011 NEC Corporation
Copyright (C) 1999, 2002, 2007 Silicon Graphics, Inc.
Copyright (C) 1999, 2000, 2001, 2002 Mission Critical Linux, Inc.
This program is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it under
certain conditions. Enter "help copying" to see the conditions.
This program has absolutely no warranty. Enter "help warranty" for details.
crash: vmlinux: no .gnu_debuglink section
crash: vmlinux: no debugging data available
$
But from the backtrace I can't tell what's happening down in the bowels of gdb.
Anyway, I've only used "virsh dump --memory-only", which apparently is a
wrapper
around "dump-guest-memory" which does not use the -p argument, which is
preferable
for the crash utility.
Dave