linux-kernel - Re: [PATCH] kdump, x86: report actual value of phys

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Date:	Thu, 13 Nov 2014 09:25:48 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"HATAYAMA, Daisuke" <d.hatayama@...fujitsu.com>
Cc:	Petr Tesarik <ptesarik@...e.cz>, kumagai-atsushi@....nes.nec.co.jp,
	anderson@...hat.com, kexec@...ts.infradead.org,
	ebiederm@...ssion.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kdump, x86: report actual value of phys_base in
 VMCOREINFO

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@...fujitsu.com> wrote:
> >
> >>From: Vivek Goyal <vgoyal@...hat.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.

Thanks
Vivek
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