From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7C50C1975A for ; Tue, 17 Mar 2020 19:26:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B054320752 for ; Tue, 17 Mar 2020 19:26:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="cW18jyzk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726744AbgCQTZ7 (ORCPT ); Tue, 17 Mar 2020 15:25:59 -0400 Received: from merlin.infradead.org ([205.233.59.134]:57528 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726294AbgCQTZ7 (ORCPT ); Tue, 17 Mar 2020 15:25:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=vKdeCR5v4njZCDrZvSq1JQqfwi1pWZ80ukR5WlwW/rM=; b=cW18jyzkxTJQPbow+nTiRjbuKg 6f7G/SkUyYxb0TCnl+KQZRL1T4AKnKeagViQrH4qXH14RZAVFfmWkdN6hzRft+80Tgw7we4CRo1lL UJzPtNh3gLR6EdSML9ZBMbIHJA4z2RbXmI1zNTyvbU3tO9nCc2DRNabDUP83klPt48FbrEL/jDGUu vHjEvQmNhMduVL0dz/OUWGGTz1fXFvEiBR5JK/9vJP6Tjs1+c8zol0YB818AhJKFVOmXYZC3N+MUi S29Koszere5CX3hY7R+UoSc7MQYVva9ita7A3lJ5u7aiVmc32ihEk7jT7QGuuzxWLAIDOIxamZclv e0wLNH3w==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jEHqV-0008ED-F2; Tue, 17 Mar 2020 19:25:47 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id C6C0E304D2C; Tue, 17 Mar 2020 20:25:44 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B33D1284D7DF5; Tue, 17 Mar 2020 20:25:44 +0100 (CET) Date: Tue, 17 Mar 2020 20:25:44 +0100 From: Peter Zijlstra To: Jesse Brandeburg Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, linux-kernel@vger.kernel.org, linux@rasmusvillemoes.dk, andriy.shevchenko@intel.com, dan.j.williams@intel.com Subject: Re: [PATCH v6 1/2] x86: fix bitops.h warning with a moved cast Message-ID: <20200317192544.GF20713@hirez.programming.kicks-ass.net> References: <20200310221747.2848474-1-jesse.brandeburg@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200310221747.2848474-1-jesse.brandeburg@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 10, 2020 at 03:17:46PM -0700, Jesse Brandeburg wrote: > Fix many sparse warnings when building with C=1. These are useless > noise from the bitops.h file and getting rid of them helps devs > make more use of the tools and possibly find real bugs. > > When the kernel is compiled with C=1, there are lots of messages like: > arch/x86/include/asm/bitops.h:77:37: warning: cast truncates bits from constant value (ffffff7f becomes 7f) > > CONST_MASK() is using a signed integer "1" to create the mask which is > later cast to (u8), in order to yield an 8-bit value for the assembly > instructions to use. Simplify the expressions used to clearly indicate > they are working on 8-bit values only, which still keeps sparse happy > without an accidental promotion to a 32 bit integer. > > The warning was occurring because certain bitmasks that end with a bit > set next to a natural boundary like 7, 15, 23, 31, end up with a mask > like 0x7f, which then results in sign extension due to the integer > type promotion rules[1]. It was really only "clear_bit" that was > having problems, and it was only on some bit checks that resulted in a > mask like 0xffffff7f being generated after the inversion. > > Verified with a test module (see next patch) and assembly inspection > that the patch doesn't introduce any change in generated code. > > [1] https://stackoverflow.com/questions/46073295/implicit-type-promotion-rules > > Signed-off-by: Jesse Brandeburg > Reviewed-by: Andy Shevchenko Acked-by: Peter Zijlstra (Intel) Boris, can you make this happen? > --- > v6: reworded commit message, enhanced explanation > v5: changed code to use simple AND and XOR, updated commit message > v4: reverse argument order as suggested by David Laight, added reviewed-by > v3: Clean up the header file changes as per peterz. > v2: use correct CC: list > --- > arch/x86/include/asm/bitops.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h > index 062cdecb2f24..53f246e9df5a 100644 > --- a/arch/x86/include/asm/bitops.h > +++ b/arch/x86/include/asm/bitops.h > @@ -54,7 +54,7 @@ arch_set_bit(long nr, volatile unsigned long *addr) > if (__builtin_constant_p(nr)) { > asm volatile(LOCK_PREFIX "orb %1,%0" > : CONST_MASK_ADDR(nr, addr) > - : "iq" ((u8)CONST_MASK(nr)) > + : "iq" (CONST_MASK(nr) & 0xff) > : "memory"); > } else { > asm volatile(LOCK_PREFIX __ASM_SIZE(bts) " %1,%0" > @@ -74,7 +74,7 @@ arch_clear_bit(long nr, volatile unsigned long *addr) > if (__builtin_constant_p(nr)) { > asm volatile(LOCK_PREFIX "andb %1,%0" > : CONST_MASK_ADDR(nr, addr) > - : "iq" ((u8)~CONST_MASK(nr))); > + : "iq" (CONST_MASK(nr) ^ 0xff)); > } else { > asm volatile(LOCK_PREFIX __ASM_SIZE(btr) " %1,%0" > : : RLONG_ADDR(addr), "Ir" (nr) : "memory"); > > base-commit: 8b614cb8f1dcac8ca77cf4dd85f46ef3055f8238 > -- > 2.24.1 >