From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753002AbaILWkR (ORCPT ); Fri, 12 Sep 2014 18:40:17 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:56772 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751056AbaILWkP (ORCPT ); Fri, 12 Sep 2014 18:40:15 -0400 Date: Fri, 12 Sep 2014 15:40:13 -0700 From: Andrew Morton To: Michal Nazarewicz Cc: Mark Rustad , "Kirsher, Jeffrey T" , "linux-kernel@vger.kernel.org" , Hagen Paul Pfeifer , Steven Rostedt Subject: Re: [PATCH 2/2] kernel.h: use __COUNTER__ in min and max macros to avoid -Wshadow warnings Message-Id: <20140912154013.47dad90e7519146c6da115e5@linux-foundation.org> In-Reply-To: <1410471576-12053-2-git-send-email-mina86@mina86.com> References: <1410471576-12053-1-git-send-email-mina86@mina86.com> <1410471576-12053-2-git-send-email-mina86@mina86.com> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 11 Sep 2014 23:39:36 +0200 Michal Nazarewicz wrote: > Because min and max macros use the same variable names no matter > how many times they are called (or how deep the nesting of their > calls), each time min or max calls are nested, the same variables > are declared. This is especially noisy after min3 and max3 have > been changed to nest min/max calls. > > Using __COUNTER__ solves the problem since each variable will get > a unique number aadded to it. The code will still work even if > the compiler does not support __COUNTER__, but then the protection > from shadow warning won't work. > > The same applies to min_t and max_t macros. > > ... > > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -695,15 +695,27 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } > #endif /* CONFIG_TRACING */ > > /* > + * Preprocessor magic generating unique identifiers to avoid -Wshadow warnings > + * used by min, max, min_t and max_t macros. cnt is __COUNTER__, op is the > + * comparison operator; tx (ty) is type of the first (second) argument, > + * xx (yy) is name of a temporary variable to hold the first (second) argument, > + * and x (y) is the first (second) argument. > + */ > +#define _min_max_var(cnt, base) _mm_ ## cnt ## base > +#define _min_max__(op, tx, xx, x, ty, yy, y) ({ \ > + tx xx = (x); \ > + ty yy = (y); \ > + (void) (&xx == &yy); \ > + xx op yy ? xx : yy; }) > +#define _min_max_(cnt, op, tx, x, ty, y) \ > + _min_max__(op, tx, _min_max_var(cnt, a), x, ty, _min_max_var(cnt, b), y) > +#define _min_max(...) _min_max_(__COUNTER__, __VA_ARGS__) The fact that __COUNTER__ is used in compiler-gcc4.h but not in compiler-gcc3.h makes me suspicious about its availability? I do think that [1/2] made the code significantly worse-looking and this one is getting crazy. How useful is W=2 anyway? Has anyone found a bug using it? The number of warnings in default builds is already way too high :(