linux-kernel - Re: [PATCH 1/2] lib: Add lz4 compressor module

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Message-ID: <CAMuHMdUv=GR6s=BYXHR7KyaKCUSxmkJO8dzZJMRktu3cUCTbsw@mail.gmail.com>
Date:	Mon, 22 Apr 2013 11:24:21 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Chanho Min <chanho.min@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Darrick J. Wong" <djwong@...ibm.com>,
	Bob Pearson <rpearson@...temfabricworks.com>,
	Richard Weinberger <richard@....at>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-crypto@...r.kernel.org,
	Yann Collet <yann.collet.73@...il.com>,
	Kyungsik Lee <kyungsik.lee@....com>,
	"Linux/m68k" <linux-m68k@...r.kernel.org>,
	sparclinux <sparclinux@...r.kernel.org>,
	Linux-Next <linux-next@...r.kernel.org>
Subject: Re: [PATCH 1/2] lib: Add lz4 compressor module

On Mon, Apr 22, 2013 at 11:22 AM, Chanho Min <chanho.min@....com> wrote:
>>> +#define HTYPE const u8*
>>> +
>>> +#ifdef __BIG_ENDIAN
>>> +#define LZ4_NBCOMMONBYTES(val) (__builtin_clz(val) >> 3)
>>> +#else
>>> +#define LZ4_NBCOMMONBYTES(val) (__builtin_ctz(val) >> 3)
>>> +#endif
>>
>>It seems at least m68k and sparc don't have the __builtin_clz() functions:
>>
>>m68k-allmodconfig (http://kisskb.ellerman.id.au/kisskb/buildresult/8572593/):
>>
>>ERROR: "__clzsi2" [lib/lz4/lz4hc_compress.ko] undefined!
>>ERROR: "__clzsi2" [lib/lz4/lz4_compress.ko] undefined!
>
> gcc seems to define __builtin_clz as __clzsi2 in some architecture.
> But, kernel doesn't link libgcc.a.
> If kernel should use gcc's built-in function without libgcc.a,
> do we need to port __clzsi2 to 'arch/*/lib/*'?

That's another option.

So far no one used __builtin_c[lt]z in generic code. We always used
__fls and __ffs.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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