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From: ebiederm@xmission.com (Eric W. Biederman)
To: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: kexec@lists.infradead.org, heiko.carstens@de.ibm.com,
	linux-kernel@vger.kernel.org, lisa.mitchell@hp.com,
	kumagai-atsushi@mxc.nes.nec.co.jp, zhangyanfei@cn.fujitsu.com,
	akpm@linux-foundation.org, cpw@sgi.com, vgoyal@redhat.com
Subject: Re: [PATCH v3 17/21] vmcore: check NT_VMCORE_PAD as a mark indicating the end of ELF note buffer
Date: Wed, 20 Mar 2013 20:54:25 -0700	[thread overview]
Message-ID: <87r4j98l1q.fsf@xmission.com> (raw)
In-Reply-To: <20130321.115920.339923125.d.hatayama@jp.fujitsu.com> (HATAYAMA Daisuke's message of "Thu, 21 Mar 2013 11:59:20 +0900 (JST)")

HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com> writes:

> From: "Eric W. Biederman" <ebiederm@xmission.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@jp.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:

You are right.  It appears to be our own invention and just part of
the ABI of taking a crash dump.  Something we should sit down and
document someday.

> 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.

Agreed.  Except in our weird case where we generate the notes on the
fly, and generate the NOTE segment header much earlier.

Eric

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  reply	other threads:[~2013-03-21  3:54 UTC|newest]

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-03-16  4:00 [PATCH v3 00/21] kdump, vmcore: support mmap() on /proc/vmcore HATAYAMA Daisuke
2013-03-16  4:00 ` [PATCH v3 01/21] vmcore: reference e_phoff member explicitly to get position of program header table HATAYAMA Daisuke
2013-03-19 21:44   ` Eric W. Biederman
2013-03-21  2:50     ` HATAYAMA Daisuke
2013-03-21  6:11       ` Eric W. Biederman
2013-03-21 14:12       ` Vivek Goyal
2013-03-22  0:25         ` HATAYAMA Daisuke
2013-03-16  4:00 ` [PATCH v3 02/21] vmcore: clean up by removing unnecessary variable HATAYAMA Daisuke
2013-03-16  4:01 ` [PATCH v3 03/21] vmcore: rearrange program headers without assuming consequtive PT_NOTE entries HATAYAMA Daisuke
2013-03-19 21:59   ` Eric W. Biederman
2013-03-16  4:01 ` [PATCH v3 04/21] vmcore, sysfs: export ELF note segment size instead of vmcoreinfo data size HATAYAMA Daisuke
2013-03-16  4:01 ` [PATCH v3 05/21] vmcore: allocate buffer for ELF headers on page-size alignment HATAYAMA Daisuke
2013-03-16  4:01 ` [PATCH v3 06/21] vmcore: round up buffer size of ELF headers by PAGE_SIZE HATAYAMA Daisuke
2013-03-19 22:07   ` Eric W. Biederman
2013-03-16  4:01 ` [PATCH v3 07/21] vmcore, procfs: introduce a flag to distinguish objects copied in 2nd kernel HATAYAMA Daisuke
2013-03-19 19:35   ` Andrew Morton
2013-03-16  4:01 ` [PATCH v3 08/21] vmcore: copy non page-size aligned head and tail pages " HATAYAMA Daisuke
2013-03-19 19:37   ` Andrew Morton
2013-03-19 20:59   ` Eric W. Biederman
2013-03-19 21:22     ` Vivek Goyal
2013-03-19 23:35       ` Eric W. Biederman
2013-03-16  4:01 ` [PATCH v3 09/21] vmcore: modify vmcore clean-up function to free buffer on " HATAYAMA Daisuke
2013-03-16  4:01 ` [PATCH v3 10/21] vmcore: clean up read_vmcore() HATAYAMA Daisuke
2013-03-16  4:01 ` [PATCH v3 11/21] vmcore: read buffers for vmcore objects copied from old memory HATAYAMA Daisuke
2013-03-16  4:01 ` [PATCH v3 12/21] vmcore: allocate per-cpu crash_notes objects on page-size boundary HATAYAMA Daisuke
2013-03-19 21:06   ` Eric W. Biederman
2013-03-19 22:12   ` Eric W. Biederman
2013-03-20 13:48     ` Vivek Goyal
2013-03-20 20:48       ` Eric W. Biederman
2013-03-16  4:02 ` [PATCH v3 13/21] kexec: allocate vmcoreinfo note buffer " HATAYAMA Daisuke
2013-03-19 21:07   ` Eric W. Biederman
2013-03-19 22:12   ` Eric W. Biederman
2013-03-16  4:02 ` [PATCH v3 14/21] kexec, elf: introduce NT_VMCORE_DEBUGINFO note type HATAYAMA Daisuke
2013-03-16  4:02 ` [PATCH v3 15/21] elf: introduce NT_VMCORE_PAD type HATAYAMA Daisuke
2013-03-16  4:02 ` [PATCH v3 16/21] kexec: fill note buffers by NT_VMCORE_PAD notes in page-size boundary HATAYAMA Daisuke
2013-03-19 22:17   ` Eric W. Biederman
2013-03-16  4:02 ` [PATCH v3 17/21] vmcore: check NT_VMCORE_PAD as a mark indicating the end of ELF note buffer HATAYAMA Daisuke
2013-03-19 21:11   ` Eric W. Biederman
2013-03-21  2:59     ` HATAYAMA Daisuke
2013-03-21  3:54       ` Eric W. Biederman [this message]
2013-03-21 14:36         ` Vivek Goyal
2013-03-22  0:30           ` HATAYAMA Daisuke
2013-03-22  0:41             ` Eric W. Biederman
2013-03-19 22:20   ` Eric W. Biederman
2013-03-16  4:02 ` [PATCH v3 18/21] vmcore: check if vmcore objects satify mmap()'s page-size boundary requirement HATAYAMA Daisuke
2013-03-19 20:02   ` Andrew Morton
2013-03-19 21:22     ` Eric W. Biederman
2013-03-20 13:51     ` Vivek Goyal
2013-03-19 22:38   ` Eric W. Biederman
2013-03-20 13:57     ` Vivek Goyal
2013-03-20 20:55       ` Eric W. Biederman
2013-03-21  3:25         ` HATAYAMA Daisuke
2013-03-21  4:18           ` Eric W. Biederman
2013-03-21  6:14             ` HATAYAMA Daisuke
2013-03-21  6:29               ` Eric W. Biederman
2013-03-21  6:46                 ` HATAYAMA Daisuke
2013-03-21  7:07                   ` Eric W. Biederman
2013-03-21 15:21                     ` Vivek Goyal
2013-03-21 15:27                       ` Vivek Goyal
2013-03-22  0:43                         ` HATAYAMA Daisuke
2013-03-22  0:54                         ` Eric W. Biederman
2013-03-22  2:30                           ` HATAYAMA Daisuke
2013-03-21 14:57                 ` Vivek Goyal
2013-03-21  7:22               ` Eric W. Biederman
2013-03-21 14:49                 ` Vivek Goyal
2013-03-22  7:11                   ` HATAYAMA Daisuke
2013-03-21 13:50         ` Vivek Goyal
2013-03-16  4:02 ` [PATCH v3 19/21] vmcore: round-up offset of vmcore object in page-size boundary HATAYAMA Daisuke
2013-03-16  4:02 ` [PATCH v3 20/21] vmcore: count holes generated by round-up operation for vmcore size HATAYAMA Daisuke
2013-03-16  4:02 ` [PATCH v3 21/21] vmcore: introduce mmap_vmcore() HATAYAMA Daisuke
2013-03-19 19:30 ` [PATCH v3 00/21] kdump, vmcore: support mmap() on /proc/vmcore Andrew Morton
2013-03-21  3:52   ` HATAYAMA Daisuke
2013-03-21  6:16     ` Eric W. Biederman
2013-03-21  6:35       ` HATAYAMA Daisuke
2013-03-21  7:14         ` Eric W. Biederman
2013-03-19 23:16 ` Eric W. Biederman

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