From: Petr Tesarik <ptesarik@xxxxxxx> Subject: Re: [PATCH] kdump, x86: report actual value of phys_base in VMCOREINFO Date: Thu, 13 Nov 2014 15:48:10 +0100 > On Thu, 13 Nov 2014 09:25:48 -0500 > Vivek Goyal <vgoyal at redhat.com> wrote: > >> 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. > > Same here. If VMCOREINFO must be locatable without communicating any > information to the hypervisor, then I would rather go for something > similar to what s390(x) folks do - a well-known location in physical > memory that contains a pointer to a checksummed OS info structure, > which in turn contains the VMCOREINFO pointers. > > I'm a bit surprised such mechanism is not needed by Fujitsu SADUMP. > Or is that part of the current plan, Daisuke? > It's useful if there is. I don't plan now. For now, the idea of this patch is enough for me. BTW, for the above idea, I suspect that if the location in the physical memory is unique, it cannot deal with the kdump 2nd kernel case. I think it better for the idea to be able to represent multiple kernel information. -- Thanks. HATAYAMA, Daisuke
