linux-kernel - Re: [PATCH 1/2] byteorder: add load/store

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Date:	Mon, 02 Mar 2009 16:25:44 -0800
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Boaz Harrosh <bharrosh@...asas.com>
Subject: Re: [PATCH 1/2] byteorder: add load/store_{endian} API

On Mon, 2009-03-02 at 16:15 -0800, Linus Torvalds wrote:
> 
> On Mon, 2 Mar 2009, Harvey Harrison wrote:
> > 
> > store_le16 is a new API and is added to be symmetric with the unaligned
> > functions.
> 
> This seems to be expressly designed to be unsafe, in that it casts the 
> thing to the right type, making it impossible for sparse to warn about 
> bad byteorder use.
> 

Unfortunately yes, hopefully you have a solution for the problem I ran
into with this part:

This was added to be symmetric with the unaligned store API, and replace
code doing

*(__le16 *)ptr = cpu_to_le16(val);

So existing code is casting already in most of the places this could be
used.  And although this could be made a static inline and get the sparse
checking, we lose one of the big advantages of the open-coding - constants
are byteswapped at compile time.  Although gcc (4.4) grew support for __builtin_constant_p
in static inlines, older gcc's don't, so we would lose that with essentially
all current compilers.

So the option was to make it a static inline and get the sparse checking, or
add the cast in the macro and lose sparse checking but preserve the compile-time
swapping...maybe I chose poorly.

Thoughts?

Harvey

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