linux-kernel - Re: #pragma once?

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Message-ID: <20140107055532.GA16581@ravnborg.org>
Date:	Tue, 7 Jan 2014 06:55:32 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Michal Marek <mmarek@...e.cz>,
	Rashika Kheria <rashika.kheria@...il.com>
Subject: Re: #pragma once?

On Mon, Jan 06, 2014 at 12:47:07PM -0800, Josh Triplett wrote:
> [CCing build-system folks and others likely to know about potential
> issues.]
> 
> Does anyone have any objection to the use of "#pragma once" instead of
> the usual #ifndef-#define-...-#endif include guard?  GCC, LLVM/clang,
> and the latest Sparse all support either method just fine.  (I added
> support to Sparse myself.)  Both have equivalent performance.  "#pragma
> once" is simpler, and avoids the possibility of a typo in the defined
> guard symbol.
For kernel headers no concern.

For UAPI headers we should be more carefull - as we do not know which
compiler it ends up seeing - and what version.

	Sam
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