On Wed, Feb 04, 2015 at 11:54:39AM +0000, David Laight wrote: > 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.
Well.. even then, surely the worst that will happen is that there will
be a few extra instructions to do the byteswap in registers. Given
that these are mostly used for IO, I find it hard to imagine that
would make a measurable performance difference.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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