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Date: Tue, 7 Jan 2014 06:55:32 +0100
From: Sam Ravnborg <sam@ravnborg.org>
Subject: Re: #pragma once?
Message-ID: <20140107055532.GA16581@ravnborg.org>
References: <20140106204706.GA16924@leaf>
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To: Josh Triplett <josh@joshtriplett.org>
Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Michal Marek <mmarek@suse.cz>, Rashika Kheria <rashika.kheria@gmail.com>

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