From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761465Ab2C3UhP (ORCPT ); Fri, 30 Mar 2012 16:37:15 -0400 Received: from oproxy6-pub.bluehost.com ([67.222.54.6]:59908 "HELO oproxy6-pub.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1761449Ab2C3UhM (ORCPT ); Fri, 30 Mar 2012 16:37:12 -0400 Message-ID: <4F761976.1080105@xenotime.net> Date: Fri, 30 Mar 2012 13:37:10 -0700 From: Randy Dunlap User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.15) Gecko/20110323 Thunderbird/3.1.9 MIME-Version: 1.0 To: Linus Torvalds CC: LKML , Josh Triplett Subject: [PATCH 4/8] Documentation: CodingStyle: add inline assembly guidelines References: <4F761580.3020807@xenotime.net> In-Reply-To: <4F761580.3020807@xenotime.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Identified-User: {1807:box742.bluehost.com:xenotime:xenotime.net} {sentby:smtp auth 50.53.38.135 authed with rdunlap@xenotime.net} Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Josh Triplett Documentation/CodingStyle: Add guidelines for inline assembly Signed-off-by: Josh Triplett Signed-off-by: Randy Dunlap --- Documentation/CodingStyle | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) --- lnx-33.orig/Documentation/CodingStyle +++ lnx-33/Documentation/CodingStyle @@ -793,6 +793,35 @@ own custom mode, or may have some other 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