[Crash-utility] crash crashes reading qemu dump files

[HATAYAMA Daisuke]

(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