linux-kernel - Re: [PATCH RFC 00/10] tools: Revamp the unaligned endian access functions

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Message-ID: <20140611192111.GB16069@ravnborg.org>
Date:	Wed, 11 Jun 2014 21:21:11 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	linux-arch@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC 00/10] tools: Revamp the unaligned endian access
 functions

On Tue, Jun 10, 2014 at 04:13:04PM -0700, H. Peter Anvin wrote:
> After a recent problem in the x86 tree, which seems to be the heaviest
> but not the only user of these functions, I went through and did a
> patchset to revamp the *user space* unaligned/endian accessor
> functions.  As much as I think it is downright pathetic that this
> functionality still isn't part of the C standard, that is life and we
> have to deal with it.  Furthermore, although glibc has a pretty nice
> set of functions for byte swapping in <endian.h>, taken from FreeBSD I
> believe, some older systems don't support them.
> 
> This variant tries to fill in all the holes.  It assumes that
> <endian.h> define the functions as macros if they exist, as I don't
> know any other way of probing for them without reaching for autoconf,
> but that should be valid enough of an assumption in this case.
> 
> The hope is that this should give reasonable, if not optimal, code
> generation on most processors, and give a hook where arch maintainers
> can add their own changes if needed.

This looks like a very complex solution to a simple problem.
We want a shared implementation of the *user space*
unaligned/endian accessor functions.
But do we really want *fast* versions for our use?

This is not a new libc that should generate optimal code,
but only something were we want to provide e working
implmentation for use in our user-space tools.

A much simpler approach without any fallback to arch specific
version etc. is everything we need.

	Sam

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