linux-kernel - RE: [PATCH 0/5] powerpc: Get rid of redundant arch specific swab functions

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CADA5A5@AcuExch.aculab.com>
Date:	Wed, 4 Feb 2015 11:54:39 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'David Gibson' <david@...son.dropbear.id.au>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"mpe@...erman.id.au" <mpe@...erman.id.au>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"agraf@...e.de" <agraf@...e.de>
CC:	"aik@...abs.ru" <aik@...abs.ru>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mdroth@...ibm.com" <mdroth@...ibm.com>
Subject: RE: [PATCH 0/5] powerpc: Get rid of redundant arch specific swab
 functions

From: David Gibson
> arch/powerpc/include/asm/swab.h includes some powerpc specific
> byteswapping functions, which are implemented in terms of powerpc's
> built in byte reversed load/store instructions.  There are two problems with this:
> 
> 1) They're not necessary - gcc is perfectly capable of generating the
>    byte-reversed load and store instructions when using the normal,
>    generic byteswapping functions (tested with gcc (GCC) 4.8.3
>    20140911 (Red Hat 4.8.3-9))

Should you be worrying about older versions of gcc?
IIRC the internal byteswap 'stuff' is relatively recent (like
the last couple of years) so people building current kernels
on older distributions might have issues.

	David