linux-kernel - Re: [PATCH] x86: Construct 32 bit boot time page tables in native format.

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Message-ID: <479634A9.1090908@zytor.com>
Date:	Tue, 22 Jan 2008 10:23:37 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ian Campbell <ijc@...lion.org.uk>
CC:	Mika Penttilä <mika.penttila@...umbus.fi>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] x86: Construct 32 bit boot time page tables in native
 format.

Ian Campbell wrote:
> On Mon, 2008-01-21 at 18:16 -0800, H. Peter Anvin wrote:
>> Ian Campbell wrote:
>>> I'm just preparing to send out a version which uses the native_* way of
>>> doing things, its not actually as clean as I would like so I'd be
>>> interested to see the ASM variant.
>>>
>> This is the asm version I came up with.
> 
> I moderately prefer the C version, even if it is in a restricted
> environment where care is needed to access global variables. I like that
> it avoids multiple copies of the code and also find the structure of
> what's going on is more obviously apparent (even to someone who has done
> plenty of ASM mode page table frobbing in the past).
> 
> Anyhow, I don't feel all that strongly about it so if the opinion of the
> early start of day maintainer(s) is strongly in favour of ASM I'll defer
> to that.
> 

My opinion is that I want it done properly (PIC and all that jazz) or 
not at all, and certainly would not want to mix linear and 
paging-enabled code in the same file.  When it comes to assembly code, 
at least people can *see* that there there be dragons.

The plus *and* minus of a C version is that it's easier for people to 
modify.  The plus side of that is that if we really need it, it's a lot 
cleaner; the minus side is that it may encourage more code to creep into 
the pre-paging code, which would not be a good thing IMO.

	-hpa
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