linux-kernel - Re: [PATCH] lib: add weak __clzsi2()/_

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Date:	Tue, 30 Apr 2013 14:46:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Chanho Min <chanho.min@....com>,
	Kyungsik Lee <kyungsik.lee@....com>,
	Yann Collet <yann.collet.73@...il.com>,
	Bob Pearson <rpearson@...temfabricworks.com>,
	Richard Weinberger <richard@....at>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	sparclinux <sparclinux@...r.kernel.org>,
	"Linux/m68k" <linux-m68k@...r.kernel.org>,
	Linux-Next <linux-next@...r.kernel.org>
Subject: Re: [PATCH] lib: add weak __clzsi2()/__clzdi2() functions

On Mon, 29 Apr 2013 09:20:25 +0200 Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> On Mon, Apr 29, 2013 at 7:40 AM, Chanho Min <chanho.min@....com> wrote:
> > Some architectures need __clzsi2() or __clzdi2() for __builtin_clz and
> > It causes build failure. They can be implemented using the fls() and
> > overridden by linking arch-specific versions may not be implemented yet.
> >
> > Reference: https://lkml.org/lkml/2013/4/18/603
> > Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> > Signed-off-by: Chanho Min <chanho.min@....com>
> 
> Thanks, this fixes the link error on m68k, so
> 
> Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>

It doesn't work for alpha (gcc-4.4.4):

ERROR: "__ctzdi2" [lib/lz4/lz4hc_compress.ko] undefined!
ERROR: "__ctzdi2" [lib/lz4/lz4_compress.ko] undefined!

akpm3:/usr/src/25> nm vmlinux|grep ctzd
akpm3:/usr/src/25> 

I assume the linker threw the code away.


How's about we stop using __builtin_ctz[ll]() altogether?  Use N-fls()?

btw, this:

int __weak __clzsi2(int val)
{
       return BITS_PER_LONG - fls(val);
}

looks wrong.  It will give a different result for 32- and 64-bit.
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