linux-kernel - Re: [PATCH 12/12] i386 boot: Add an ELF header to bzImage

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Date:	Fri, 06 Oct 2006 13:09:34 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	vgoyal@...ibm.com, Andrew Morton <akpm@...l.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Reloc Kernel List <fastboot@...ts.osdl.org>, ak@...e.de,
	horms@...ge.net.au, lace@...kratochvil.net, magnus.damm@...il.com,
	lwang@...hat.com, dzickus@...hat.com, maneesh@...ibm.com
Subject: Re: [PATCH 12/12] i386 boot: Add an ELF header to bzImage

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

> Vivek Goyal wrote:
>>>
>> Hi Eric,
>> I have added cld in the regenerated patch below.
>
> No, the cld needs to be earlier.  It turns out this isn't the first use of
> string instructions.

Can we rely on the int calls not setting df?  Otherwise we need to clear
df at each use as we do with all of the later uses.

> I think I am going to add DF=0 as a documented entry condition; it definitely
> seems all current Linux kernels require it.
>
>> Also one more minor nit. stosb relies on being %es set properly. By the
>> time control reaches loader_ok, i could not find %es being set explicitly
>> hence I am assuming we are relying on bootloader to set it up for us. Maybe we
>> can be little more paranoid and setup the %es before stosb. I
>> have done this change too in the attached patch. Pleaese have a look.
>> I know little about assembly code.
>
> %es being set is part of the requirements list, although it *would* be better to
> not rely on any segment registers being set at all (only rely on %cs.)

Agreed.

Eric

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