linux-kernel - Re: [PATCH 2/2] x86, boot: Optimize the elf header handling.

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Message-ID: <87k3yd5sxt.fsf@xmission.com>
Date:	Sun, 08 Jul 2012 23:50:38 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Tejun Heo <tj@...nel.org>, hacklu <embedway.linux@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86, boot: Optimize the elf header handling.

"H. Peter Anvin" <hpa@...or.com> writes:

> On 07/01/2012 01:40 PM, Eric W. Biederman wrote:
>> 
>> So I have tracked down part of the crazyness.
>> CONFIG_RODATA actually uses 2MB alignment, making
>> -z max_page_size=4096 a bit questionable.
>> 
>
> Questionable how?  It's not really like it matters since we're not going
> to mmap the ELF.

Questionable as in the current elf loader in misc.c relies on the fact
that there is an almost a fixed offset between physical addresses and
file offsets for all of the PT_LOAD segments in the Elf header.

In fact CONFIG_RODATA && CONFIG_X86_64 && CONFIG_SMP in combination with
-z max_page_size=4096 fails to boot.  The Elf loader in misc.c starts
coping from lower addresses to higher addresses, instead of higher
addresses to lower and that fails miserably.

But -z max_page_size=4096 is not the problem the ELF loader is.

Eric
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