From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933604Ab2BBWdP (ORCPT ); Thu, 2 Feb 2012 17:33:15 -0500 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:41890 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932599Ab2BBWdN (ORCPT ); Thu, 2 Feb 2012 17:33:13 -0500 X-Originating-IP: 217.70.178.147 X-Originating-IP: 50.43.15.19 Date: Thu, 2 Feb 2012 14:33:05 -0800 From: Josh Triplett To: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Cc: Randy Dunlap , Linus Torvalds , Joe Perches Subject: [PATCH] Documentation/CodingStyle: Add guidelines for inline assembly Message-ID: <20120202223304.GA13069@leaf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Signed-off-by: Josh Triplett --- Documentation/CodingStyle | 29 +++++++++++++++++++++++++++++ 1 files changed, 29 insertions(+), 0 deletions(-) diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index 2b90d32..c58b236 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -793,6 +793,35 @@ own custom mode, or may have some other magic method for making indentation work correctly. + Chapter 19: Inline assembly + +In architecture-specific code, you may need to use inline assembly to interface +with CPU or platform functionality. Don't hesitate to do so when necessary. +However, don't use inline assembly gratuitously when C can do the job. You can +and should poke hardware from C when possible. + +Consider writing simple helper functions that wrap common bits of inline +assembly, rather than repeatedly writing them with slight variations. Remember +that inline assembly can use C parameters. + +Large, non-trivial assembly functions should go in .S files, with corresponding +C prototypes defined in C header files. The C prototypes for assembly +functions should use "asmlinkage". + +You may need to mark your asm statement as volatile, to prevent GCC from +removing it if GCC doesn't notice any side effects. You don't always need to +do so, though, and doing so unnecessarily can limit optimization. + +When writing a single inline assembly statement containing multiple +instructions, put each instruction on a separate line in a separate quoted +string, and end each string except the last with \n\t to properly indent the +next instruction in the assembly output: + + asm ("magic %reg1, #42\n\t" + "more_magic %reg2, %reg3" + : /* outputs */ : /* inputs */ : /* clobbers */); + + Appendix I: References -- 1.7.9