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

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Message-ID: <530EC7D1.3000706@zytor.com>
Date:	Wed, 26 Feb 2014 21:06:25 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <ak@...ux.intel.com>,
	Andy Lutomirski <luto@...capital.net>
CC:	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 07:39 PM, Andi Kleen wrote:
> On Wed, Feb 26, 2014 at 05:02:13PM -0800, Andy Lutomirski wrote:
>> This makes no difference for 64-bit, bit it's critical for 32-bit code:
>> these functions are called from outside the kernel, so they need to comply
>> with the ABI.
> 
> That's an odd patch. If that was wrong things couldn't have worked at all.
> Probably hidden by inlining? If yes just make it static
> 
> Also you would rather need notrace more often.
> 

It has to support *an* ABI... the syscall vdso entry point uses the old
int $0x80 calling convention rather than the normal ABI.  It would
depend on the test program and eventual glibc implementation.  And sure
enough, the test program has:

int (*vdso_gettimeofday)(struct timeval *tv, struct timezone *tz)
__attribute__ ((regparm (3)));
int (*vdso_clock_gettime)(clockid_t clk_id, struct timespec *tp)
__attribute__ ((regparm (3)));
time_t (*vdso_time)(time_t *t) __attribute__ ((regparm (3)));

That being said, since this code is compiled separately, the compiler
flags there determine what actually matters.  However, there we have:

KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=3 -freg-struct-return -fpic

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?

	-hpa

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