linux-kernel - Re: uml and -regparm=3

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Message-ID: <478586E1.8010709@zytor.com>
Date:	Wed, 09 Jan 2008 18:45:53 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Jeff Dike <jdike@...toit.com>, Miklos Szeredi <miklos@...redi.hu>,
	harvey.harrison@...il.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: uml and -regparm=3

Andi Kleen wrote:
> On Wed, Jan 09, 2008 at 09:14:04PM -0500, Jeff Dike wrote:
>> On Wed, Jan 09, 2008 at 10:50:48PM +0100, Miklos Szeredi wrote:
>>>> FASTCALL is useless and should not make a difference. It enables
>>>> regparm on specific functions, but that should not make a difference
>>>> if it works or not.
>>> __down_write() in include/asm-x86/rwsem.h seems to assume, that the
>>> semaphore pointer is passed in %eax down to rwsem_down_write_failed(),
>>> so regparm does make a difference there.
>> And rwsem_down_write_failed seems to think it's getting the pointer in
>> %eax:
> 
> That's a left over from when it was called by magic inline assembly.
> I suspect it would be better to switch it just over to stack args
> for consistent and then declare it asmlinkage
> 

That seems to go in the wrong direction to me.  It would make more sense 
to gradually shift to asmlinkage actually being regparm=3.  This, of 
course, would require a different name (such as FASTCALL) until the 
conversion is complete -- even if done as a single patch series.

	-hpa
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