linux-kernel - Re: [RFC PATCH] x86: Unify include/asm-x86/linkage

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Date:	Wed, 5 Dec 2007 00:15:19 +0100
From:	Adrian Bunk <bunk@...nel.org>
To:	Harvey Harrison <harvey.harrison@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86: Unify include/asm-x86/linkage_[32|64].h

On Tue, Dec 04, 2007 at 02:57:55PM -0800, Harvey Harrison wrote:
> 
> On Tue, 2007-12-04 at 23:45 +0100, Adrian Bunk wrote:
> > On Tue, Dec 04, 2007 at 11:27:17PM +0100, Ingo Molnar wrote:
> > > 
> > > * Harvey Harrison <harvey.harrison@...il.com> wrote:
> > > 
> > > > On Tue, 2007-12-04 at 22:32 +0100, Ingo Molnar wrote:
> > > > > * Harvey Harrison <harvey.harrison@...il.com> wrote:
> > > > > 
> > > > > > I'm not sure if the definition of asmlinkage and prevent_tail_call can 
> > > > > > be omitted as well and let the linux/linkage.h version get picked up 
> > > > > > instead.
> > > > > 
> > > > > no, we cannot remove them - asmlinkage is needed for the syscall 
> > > > > entry (and other entry code) to work, the and the prevent_tail_call 
> > > > > works around a compiler bug. (which might or might not be fixed in 
> > > > > latest gcc - but we generally dont remove workarounds unless we are 
> > > > > really sure it's fine.)
> > > > 
> > > > OK, but if this patch is acceptable, then there is no more places in 
> > > > the tree that define the FASTCALL macro, other than the empty default 
> > > > in include/linux/linkage.h.  So I think a second step would be to 
> > > > start to get rid of FASTCALL callers elsewhere in the tree...thoughts?
> > > 
> > > the removal of FASTCALL is fine: the default (and only) compiler model 
> > > for x86 (32-bit) is regparm(3), so the regparm(3) macro is equivalent to 
> > > the empty one in linux/linkage.h.
> > >...
> > 
> > But please ensure that they stay in assembler code also used by UML.
> 
> I'm curious how UML is using FASTCALL/fastcall.  Any pointers?

UML can't switch to the regparm(3) convention on i386 since it links 
with userspace code, so if assembler code uses this calling convention 
we need the C prototype of it annotated accordingly.

> Harvey

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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