[PATCH] kdump, x86: report actual value of phys_base in VMCOREINFO

Vivek Goyal vgoyal at redhat.com
Thu Nov 13 06:25:48 PST 2014

On Thu, Nov 13, 2014 at 05:30:21PM +0900, HATAYAMA, Daisuke wrote:
> (2014/11/13 17:06), Petr Tesarik wrote:
> >On Thu, 13 Nov 2014 09:17:09 +0900 (JST)
> >HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com> wrote:
> >
> >>From: Vivek Goyal <vgoyal at redhat.com>
> >>Subject: Re: [PATCH] kdump, x86: report actual value of phys_base in VMCOREINFO
> >>Date: Wed, 12 Nov 2014 17:12:05 -0500
> >>
> >>>On Wed, Nov 12, 2014 at 03:40:42PM +0900, HATAYAMA Daisuke wrote:
> >>>>Currently, VMCOREINFO note information reports the virtual address of
> >>>>phys_base that is assigned to symbol phys_base. But this doesn't make
> >>>>sense because to refer to value of the phys_base, it's necessary to
> >>>>get the value of phys_base itself we are now about to refer to.
> >>>>
> >>>
> >>>Hi Hatayama,
> >>>
> >>>/proc/vmcore ELF headers have virtual address information and using
> >>>that you should be able to read actual value of phys_base. gdb deals
> >>>with virtual addresses all the time and can read value of any symbol
> >>>using those headers.
> >>>
> >>>So I am not sure what's the need for exporting actual value of
> >>>phys_base.
> >>>
> >>
> >>Sorry, my logic in the patch description was wrong. For /proc/vmcore,
> >>there's enough information for makedumpdile to get phys_base. It's
> >>correct. The problem here is that other crash dump mechanisms that run
> >>outside Linux kernel independently don't have information to get
> >>phys_base.
> >
> >Yes, but these mechanisms won't be able to read VMCOREINFO either, will
> >they?
> >
> I don't intend such sophisticated function only by VMCOREINFO.
> Search vmcore for VMCOREINFO using strings + grep before opening it by crash.
> I intend that only here.

I think this is very crude and not proper way to get to vmcoreinfo. Can
you give more context. What are those mechanisms and what are you trying
to do.


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