linux-kernel - Re: [PATCH] common implementation of iterative div/mod

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Date:	Wed, 14 May 2008 12:50:12 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Segher Boessenkool <segher@...nel.crashing.org>,
	Robert Hancock <hancockr@...w.ca>,
	Christian Kujau <lists@...dbynature.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	john stultz <johnstul@...ibm.com>
Subject: Re: [PATCH] common implementation of iterative div/mod

Jeremy Fitzhardinge wrote:
> Andi Kleen wrote:
>> You would need to annotate it and have a separate object file for the
>> different sections. Also it would need to be compiled PIC.
>>
>> Inlining is better.
> 
> BTW, I'm seeing the memcpy() in __vdso_gettimeofday() not being inlined.

Hmm works here. What compiler do you use? Normally gcc should 
recognize the memcpy is just two constant stores and always inline even with -Os.

nm --dynamic arch/x86/vdso/vdso.so
0000000000000000 A LINUX_2.6
ffffffffff7007e0 T __vdso_clock_gettime
ffffffffff700820 T __vdso_getcpu
ffffffffff700750 T __vdso_gettimeofday
ffffffffff7007e0 W clock_gettime
ffffffffff700820 W getcpu
ffffffffff700750 W gettimeofday

Anyways if your compiler or config cannot get that right it would need
to switch to __inline_memcpy(), but that would be slower or explicit
copying field by field.

If it's a common problem we could also implement a build time check,
but normally such problems should be already caught in code review.

-Andi

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