From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753940AbcEYJOk (ORCPT ); Wed, 25 May 2016 05:14:40 -0400 Received: from science.sciencehorizons.net ([71.41.210.147]:45381 "HELO ns.sciencehorizons.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with SMTP id S1751278AbcEYJOh (ORCPT ); Wed, 25 May 2016 05:14:37 -0400 Date: 25 May 2016 05:14:35 -0400 Message-ID: <20160525091435.9218.qmail@ns.sciencehorizons.net> From: "George Spelvin" To: linux@sciencehorizons.net, phdm@macq.eu Subject: Re: [PATCH 08/10] m68k: Add Cc: geert@linux-m68k.org, gerg@linux-m68k.org, linux-kernel@vger.kernel.org, linux-m68k@vger.kernel.org, tglx@linutronix.de, torvalds@linux-foundation.org In-Reply-To: <20160525085653.GA9917@frolo.macqel> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Wed, May 25, 2016 at 03:34:55AM -0400, George Spelvin wrote: >> +static inline u32 __attribute_const__ __hash_32(u32 x) >> +{ >> + u32 a, b; >> + >> + asm( "move.l %2,%0" /* 0x0001 */ >> + "\n lsl.l #2,%0" /* 0x0004 */ >> + "\n move.l %0,%1" >> + "\n lsl.l #7,%0" /* 0x0200 */ >> + "\n add.l %2,%0" /* 0x0201 */ >> + "\n add.l %0,%1" /* 0x0205 */ >> + "\n add.l %0,%0" /* 0x0402 */ >> + "\n add.l %0,%1" /* 0x0607 */ >> + "\n lsl.l #5,%0" /* 0x8040 */ >> + /* 0x8647 */ > There is no standard way to write asm in the kernel, but I prefer > a simple semicolon after each insn I did it the way I did above because it makes the gcc -S output very legible. Just like I put a space before the perands on m68k but a tab on h8300: that's what GCC does on those platforms. I started with the "\n\t" suffixes on each line like so much other kernel code, but then figured out the format above which is legible both in C source and compiler output. >> asm("move.l %2,%0;" /* 0x0001 */ >> "lsl.l #2,%0;" /* 0x0004 */ >> "move.l %0,%1;" >> "lsl.l #7,%0;" /* 0x0200 */ >> "add.l %2,%0;" /* 0x0201 */ >> "add.l %0,%1;" /* 0x0205 */ >> "add.l %0,%0;" /* 0x0402 */ >> "add.l %0,%1;" /* 0x0607 */ >> "lsl.l #5,%0" /* 0x8040 */ >> /* 0x8647 */ > Also, it took me some time to understand the hexadecimal constants > in the comments (and the last one predicts a future event :)). Can you recmmend a better way to comment this? My nose is so deep in the code it's hard for me to judge. > Just my two cents And thank you very much for them!