[Crash-utility] earlier patch introducing the --kaslr option

[Dave Anderson]

----- Original Message -----
> On Tue, Feb 18, 2014 at 12:27 PM, Dave Anderson <anderson at redhat.com> wrote:
> >
> >
> > ----- Original Message -----
> >> >
> >> > But if I try that value with your patch applied, it fails in the same
> >> > manner
> >> > as if I don't use the --kaslr option at all:
> >> >
> >> >  $ crash --kaslr 0x19000000 vmlinux vmcore
> >> >
> >> >  crash 7.0.5rc12
> >> >  Copyright (C) 2002-2014  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.
> >> >
> >> >  GNU gdb (GDB) 7.6
> >> >  Copyright (C) 2013 Free Software Foundation, Inc.
> >> >  License GPLv3+: GNU GPL version 3 or later
> >> >  <http://gnu.org/licenses/gpl.html>
> >> >  This is free software: you are free to change and redistribute it.
> >> >  There is NO WARRANTY, to the extent permitted by law.  Type "show
> >> >  copying"
> >> >  and "show warranty" for details.
> >> >  This GDB was configured as "x86_64-unknown-linux-gnu"...
> >> >
> >> >  WARNING: could not find MAGIC_START!
> >> >  WARNING: cannot read linux_banner string
> >> >  crash: vmlinux and vmcore do not match!
> >> >
> >> >  Usage:
> >> >
> >> >   crash [OPTION]... NAMELIST MEMORY-IMAGE  (dumpfile form)
> >> >   crash [OPTION]... [NAMELIST]             (live system form)
> >> >
> >> >  Enter "crash -h" for details.
> >> >  $
> >> >
> >> > Any ideas?  I can give you the vmlinux/vmcore/kallsyms triplet if you'd
> >> > like.
> >>
> >> As far as why the offset wasn't present, sorry about that.  I guess
> >> our tool chain is a bit more different than upstream, I've had a bit
> >> of trouble generating kdump files for upstream.
> >>
> >> Your manual calculations look correct to me though and it should work.
> >>  If you can send me the vmlinux/vmcore triplet (I don't think I need
> >> the kallsyms) then I will look at this today.  Can you post it
> >> somewhere I can download it?
> >>
> >> Sorry for the delay I was on vacation.
> >>
> >> thanks,
> >> Andy
> >
> > Actually you do need the kallsyms...
> >
> > As I mentioned to Kees in an earlier message, the display of
> > the offset in the kernel log will not be done in the case of
> > kdump-enabled kernels, because crash_kexec() is called before
> > the panic_notifier list is executed, and crash_kexec() does
> > not return.
> >
> > I've put the triplet here:
> >
> >   http://people.redhat.com/anderson/kaslr
> >
> > Note that we can only create ELF vmcores with kASLR because the
> > makedumpfile
> > facility also needs to be fixed to handle kASLR kernels.
> >
> > Anyway, as it turns out, the offset is not 0x19000000 (&_text -
> > __START_KERNEL),
> > but rather it is 0x18000000, which is the difference between the
> > kallsyms symbol values and those compiled into the vmlinux file.
> > With that --kaslr offset value, the crash session comes up OK.
> 
> Oh, hm. Is the difference maybe due to CONFIG_PHYSICAL_START some how?
> 
> -Kees

Right -- I didn't create the kernel, but I presume both CONFIG_PHYSICAL_START
and CONFIG_PHYSICAL_ALIGN are both 16MB, resulting in:

$ grep _text kallsyms | head -1
ffffffff99000000 T _text
$ nm -Bn vmlinux | grep _text | head -1
ffffffff81000000 T _text
$

Dave