linux-kernel - Re: [PATCH v3 17/21] vmcore: check NT_VMCORE_PAD as a mark indicating the end of ELF note buffer

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Message-Id: <20130321.115920.339923125.d.hatayama@jp.fujitsu.com>
Date:	Thu, 21 Mar 2013 11:59:20 +0900 (JST)
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	ebiederm@...ssion.com
Cc:	vgoyal@...hat.com, cpw@....com, kumagai-atsushi@....nes.nec.co.jp,
	lisa.mitchell@...com, heiko.carstens@...ibm.com,
	akpm@...ux-foundation.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, zhangyanfei@...fujitsu.com
Subject: Re: [PATCH v3 17/21] vmcore: check NT_VMCORE_PAD as a mark
 indicating the end of ELF note buffer

From: "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v3 17/21] vmcore: check NT_VMCORE_PAD as a mark indicating the end of ELF note buffer
Date: Tue, 19 Mar 2013 14:11:51 -0700

> HATAYAMA Daisuke <d.hatayama@...fujitsu.com> writes:
> 
>> Modern kernel marks the end of ELF note buffer with NT_VMCORE_PAD type
>> note in order to make the buffer satisfy mmap()'s page-size boundary
>> requirement. This patch makes finishing reading each buffer if the
>> note type now being read is NT_VMCORE_PAD type.
> 
> Ick.  Even with a pad header you can mark the end with an empty header,
> and my memory may be deceiving me but I believe an empty header is
> specified by the ELF ABI docs.
> 
> Beyond which I don't quite see the point of any of this as all of these
> headers need to be combined into a single note section before being
> presented to user space.

Though this patch might get unecessary later, I cannot find part
explaining necessity of marking end of ELF segmetns with an empty
header in ELF spec. For example:

gabi
http://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section

AMD64
http://www.x86-64.org/documentation/abi.pdf

But still there's possibility of another particular spec that says
necessity of empty header.

Also, it's possible to get size of a whole part of ELF note segments
from p_memsz or p_filesz, and gdb and binutils are reading the note
segments until reaching the size.

Thanks.
HATAYAMA, Daisuke

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