linux-kernel - Re: [PATCH -mm 0/4] x86_64 boot: Add linked listof struct setup

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Date:	Thu, 27 Mar 2008 04:02:16 -0500
From:	Paul Jackson <pj@....com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	ying.huang@...el.com, hpa@...or.com, andi@...stfloor.org,
	mingo@...hat.com, tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 0/4] x86_64 boot: Add linked listof struct
 setup_data to boot protocol

Ingo asked:
> what happens with the SGI machine

Unless I misunderstand your post, Ingo, you don't need an SGI machine
for this one, ... just a compiler ;).

In the file arch/x86/boot/main.c, see the line:

    BUILD_BUG_ON(sizeof boot_params != 4096);

This BUILD_BUG is serving as a reminder that the PC's "zero page", such
as is encoded in the struct boot_params (include/asm-x86/bootparam.h)
has to be exactly 4096 bytes by traditional PC architecture.  One of
the entries in that struct is:

    struct e820entry e820_map[E820MAX];             /* 0x2d0 */

H. Peter Anvin, Andi Kleen and Huang had further discussion in an
earlier email thread as to how to best extend this limit.  I trust
that Huang's patch represents their concensus of that discussion.

By the way, Peter, do you have any idea what that E820NR define is
doing in include/asm-x86/e820.h ... it looks like useless redundancy
to me?

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.940.382.4214
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