linux-kernel - Re: x86 setup code rewrite in C

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Date:	Fri, 13 Jul 2007 12:35:53 -0400
From:	Chuck Ebbert <cebbert@...hat.com>
To:	Etienne Lorrain <etienne_lorrain@...oo.fr>
CC:	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: x86 setup code rewrite in C - revised

On 07/13/2007 10:25 AM, Etienne Lorrain wrote:

[ Added back cc:'s]

> On Thu, 12 Jul 2007, Linus Torvalds wrote:
>> On Thu, 12 Jul 2007, Andrew Morton wrote:
>>> This code has been in -mm since 11 May, as git-newsetup.patch.  It has
>>> caused (for what it is) astonishingly few problems.  Maybe a couple of
>>> build glitches and one runtime failure, all quickly fixed.
>>>
>>> I'd say it's ready.
>> Ok. That makes it easy. I'll just merge it.
>>
>> 		Linus
> 
>  Have fun, this code:
>  - do not open the fast A20 gate before checking if the slow A20 gate is open or closed.
>  - uses in asm("") inputs which may or may not be set by the compiler in the stack,
>    after modifying the stack pointer in the asm block: at least has_eflag()
>  - The VGA recalc has the same bug as the assembly version where a VGA write protected
>    register is written (Overflow register) without setting the enable bit (see VGA docs).
>  - Does not save and restore %ds when printing a char on the screen (%ds is destroyed
>    only when the content of the screen scroll - only for some video cards)
>  - Has a "dn" for outl() which sliped in instead of "dN"
>  and probably few other problems - just seen those by reading the patches (the asm("")
>  are inlined in the C code - I find it more difficult to check).
> 
>  Also, I do not know if "m" is right in here:
> static inline u8 rdfs8(addr_t addr)
> {
> 	u8 v;
> 	asm("movb %%fs:%1,%0" : "=r" (v) : "m" (*(u8 *)addr));
> 	return v;
> }
> 
>   I may repeat me, but to find these kind of problems, it is very nice to have an ELF
>  file to do a readelf/objdump -D -m i8086 (even after final link).
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