linux-kernel - Re: #pragma once?

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Message-ID: <CA+C-WL_Z6TuWTO00gzgJo3+D-kHfjFBrfACqpaDCNxP23-LN_g@mail.gmail.com>
Date:	Sun, 12 Jan 2014 11:14:56 -0500
From:	Patrick Palka <patrick@...cs.ath.cx>
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>, Sam Ravnborg <sam@...nborg.org>,
	Rashika Kheria <rashika.kheria@...il.com>
Subject: Re: #pragma once?

On Mon, Jan 6, 2014 at 3:47 PM, Josh Triplett <josh@...htriplett.org> wrote:
> 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.

Unfortunately in GCC #pragma once is slower and slightly buggier than
regular include guards:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52566
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58770
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