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

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Date:	Thu, 27 Feb 2014 15:12:17 -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 02/27/2014 12:11 PM, Andy Lutomirski wrote:
> 
> Hmm.  This sort of goes against existing x86_32 practice where,
> AFAICT, things that need a particular calling convention specify
> asmlinkage and everything else uses regparm(3) if config/kbuild thinks
> it's appropriate.
> 

That is not really true for things that aren't part of the kernel image
proper (e.g. the real mode code and so on.)  This is a very special case.

> But I'm happy to resubmit the patch if you prefer the CFLAGS approach
> for the 32-bit vdso.  I don't think anything will break, since I don't
> think that the 32-bit vdso has any other exported C code.

I think it is the better way to go.

>> It isn't any faster if the C library has to provide a wrapper just to
>> marshal parameters.
> 
> Probably true, given that the glibc wrapper could, in principle, use
> an optimized tail call.  Also, I see no reason why vdso functions,
> alone of all userspace code, should be special.

Yes, let's stick to the standard ABI.  The syscall entry point was very
special.

	-hpa


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