linux-kernel - Re: [PATCH 1/2] x86: Mark _

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Date:	Wed, 26 Feb 2014 21:22:57 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Andi Kleen <ak@...ux.intel.com>,
	Stefani Seibold <stefani@...bold.net>, X86 ML <x86@...nel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	andriy.shevchenko@...ux.intel.com, Martin.Runge@...de-schwarz.com,
	Andreas.Brief@...de-schwarz.com
Subject: Re: [PATCH 1/2] x86: Mark __vdso entries as asmlinkage

On 02/26/2014 09:19 PM, Andy Lutomirski wrote:
>>
>> The normal ABI almost certainly makes more sense; as such -mregparm=3 is
>> probably not what we want, and I suspect it makes more sense to just
>> drop that from the CFLAGS line?
> 
> Hmm.  What happens on a native 32-bit build?  IIRC the whole kernel is
> build with regparm(3).
> 

Well, the vdso is still built separately, so we can use different CFLAGS
if we want to.

> If we want to save a cycle or two, then regparm(3) is probably faster.
>  But I think that these functions should either be asmlinkage or (on
> 32 bit builds) explicitly regparm(3) to avoid confusion.

I suggest using the standard ABI, but I suggest doing it via CFLAGS.

It isn't any faster if the C library has to provide a wrapper just to
marshal parameters.

	-hpa


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