linux-kernel - Re: [PATCH 0/6][RFC] Rework vsyscall to avoid truncation/rounding issue in timekeeping core

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Message-ID: <20120919170347.GA2232@netboy.at.omicron.at>
Date:	Wed, 19 Sep 2012 19:03:47 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Tony Luck <tony.luck@...el.com>,
	Paul Mackerras <paulus@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Paul Turner <pjt@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/6][RFC] Rework vsyscall to avoid truncation/rounding
 issue in timekeeping core

On Wed, Sep 19, 2012 at 09:31:35AM -0700, John Stultz wrote:

> On powerpc, I mean magic addresses where userland can find
> structures that it can use to calculate time.

...
 
> With powerpc, there is no arch specific kernel code involved, its
> just a data structure the kernel exports that is accessible to
> userland. The execution logic lives in userland libraries, or
> sometimes application code itself.

I took a brief look at arch/powerpc/kernel/vdso32/gettimeofday.S and
arch/powerpc/kernel/vdso64/gettimeofday.S, and I see what looks a lot
like functions

$ find arch/powerpc/kernel/vdso* -name gettimeofday.S|xargs grep FUNCTION_BEGIN

arch/powerpc/kernel/vdso32/gettimeofday.S:V_FUNCTION_BEGIN(__kernel_gettimeofday)
arch/powerpc/kernel/vdso32/gettimeofday.S:V_FUNCTION_BEGIN(__kernel_clock_gettime)
arch/powerpc/kernel/vdso32/gettimeofday.S:V_FUNCTION_BEGIN(__kernel_clock_getres)
arch/powerpc/kernel/vdso64/gettimeofday.S:V_FUNCTION_BEGIN(__kernel_gettimeofday)
arch/powerpc/kernel/vdso64/gettimeofday.S:V_FUNCTION_BEGIN(__kernel_clock_gettime)
arch/powerpc/kernel/vdso64/gettimeofday.S:V_FUNCTION_BEGIN(__kernel_clock_getres)
arch/powerpc/kernel/vdso64/gettimeofday.S:V_FUNCTION_BEGIN(__do_get_tspec)

and I wonder whether these could be done in C instead.

Thanks,
Richard
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