Re: [PATCH v6 2/5] s390/vmcore: Use ELF header in new memory feature

From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>,
	kexec@lists.infradead.org, Jan Willeke <willeke@de.ibm.com>,
	linux-kernel@vger.kernel.org,
	HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>
Subject: Re: [PATCH v6 2/5] s390/vmcore: Use ELF header in new memory feature
Date: Wed, 3 Jul 2013 09:59:13 +0200	[thread overview]
Message-ID: <20130703095913.6f6d145d@holzheu> (raw)
In-Reply-To: <20130702162322.GD22603@redhat.com>

On Tue, 2 Jul 2013 12:23:23 -0400
Vivek Goyal <vgoyal@redhat.com> wrote:

> On Mon, Jul 01, 2013 at 09:32:36PM +0200, Michael Holzheu wrote:
> 
> [..]
> > +ssize_t elfcorehdr_read(char *buf, size_t count, u64 *ppos)
> > +{
> > +	void *src = (void *)(unsigned long)*ppos;
> > +
> > +	src = elfcorehdr_newmem ? src : src - OLDMEM_BASE;
> 
> Seriously, we need to get rid of all this OLDMEM_BASE logic in s390
> specific code. For regular kdump, it is no different than x86. Only
> special handling required for zfcpdump for HSA region.
> 
> Why do we need above. Is it to cover the case where elfcorehdr have
> been prepared by user space? Are elf headers initially stored in
> reserved region and then swapped. Why do we need to swap these or
> why kexec-tools could not take care of swapping it.

I know it is confusing. The "src - OLDMEM_BASE" term is currently
needed because of the swap issue that we have discussed already. We
load the ELF header into reserved memory
[OLDMEM_BASE, OLDMEM_BASE + OLDMEM_SIZE] that is swapped with
[0, OLDMEM_SIZE]. So the ELF header address has to be adjusted.

Thanks!
Michael

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