linux-kernel - Re: [PATCH v3 06/21] vmcore: round up buffer size of ELF headers by PAGE

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Date:	Tue, 19 Mar 2013 15:07:47 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.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 06/21] vmcore: round up buffer size of ELF headers by PAGE_SIZE

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

> To satisfy mmap() page-size boundary requirement, round up buffer size
> of ELF headers by PAGE_SIZE. The resulting value becomes offset of ELF
> note segments and it's assigned in unique PT_NOTE program header
> entry.

Ok. That is just silly.  You can use a single buffer for the ELF header,
the program header and the notes.  It just requires a bit of counting
ahead of time.

The ELF header itself is small, and so are the program headers,
especially if you only have one PT_NOTE segment.  The only thing that
possibly gets big is the note segment, and then that only happens if you
have a lot of cpus.

Since there are entirely local constructs it seems extremely silly,
wasteful and complicated to place each logical part in a separately
mmapable buffer instead of placing them in the same mmapable buffer.

Eric
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