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=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 A3EEFC433ED for ; Thu, 20 May 2021 19:44:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8840B61355 for ; Thu, 20 May 2021 19:44:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239892AbhETTqE (ORCPT ); Thu, 20 May 2021 15:46:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43152 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234247AbhETTqD (ORCPT ); Thu, 20 May 2021 15:46:03 -0400 Received: from mail-il1-x12b.google.com (mail-il1-x12b.google.com [IPv6:2607:f8b0:4864:20::12b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7140FC061574 for ; Thu, 20 May 2021 12:44:41 -0700 (PDT) Received: by mail-il1-x12b.google.com with SMTP id h11so16240771ili.9 for ; Thu, 20 May 2021 12:44:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=5EGzMVSklsVagwFMiqDNnX9HkmidH4tvnfTm5VSWBuc=; b=Fo1HU5BpW2WfgTGr41Gnk9WHy+jxnjI2UUO7FZhNeg0IpwNnngbWX3FO53l1ap679H HNmm/WNtqqzQvi31UKFzNHucePJr9krPWfbKYNv0+SLG+i4BrOKGKGSP5AHkNAuRwx/9 M1AGXcqepkuZgXiR+eBKJtrvEAueBrrBF/8+32yRYtfl1+ctFPmptsNJ/xx6/MZznBOj iiaU+JO8fM04s2YVVVcV1750Ck135bHb26d2P8KWkRpAzah65Vysf/gNS652oZUbsr0I 4p2EcUgrlCudYyqiIz5HlrjNH9j+kZt3JPwDsjr4tEOWbaGADUjep+a4RBId9kj7wCWQ iVFw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=5EGzMVSklsVagwFMiqDNnX9HkmidH4tvnfTm5VSWBuc=; b=q0KwxpymchGSIZUqnn/HeFGG1RTj0fDdenOOPgbo7pja5Olx86m3b2GNxH402P50Yp u6czy/ZSxyxiRZiJo1mrPwV9EdXFU/6qRiHVFqeKbJmIII0+GXwJMQQMzpvBXjJamYGS QBNgJhX4gRNFW6Z8ARaL4ZGIXx+TrCKZMZ4hN2Cmiio4Tw94dBlB4w2jjJfofxku4ypD FfZYyIO1JNAm6ugWI4TGqAWTfhDJFmpu/KcbX5b5VvVPmmdK4P3xqMPNc4nmFSyjhQKZ qphX0mOvty9CNlg16JxFDEPdYd7tZQfZMk5bymooXqSml8fYUeRrv6XSZopTC1RRWkrm GKyw== X-Gm-Message-State: AOAM532TmZOZOwkhnmMRVN12oXxXX/u7SeKRK06IQxC3nKKQ0SKY7XWk FKjRzIl+LsK8CSpeIlb9y1I= X-Google-Smtp-Source: ABdhPJzgNFhi20re2/prh0boePa94zwZ8WaOL3u09GLrowF2lvDmXcRVQM4e7k+UdbRrihJlcBbDVw== X-Received: by 2002:a05:6e02:190b:: with SMTP id w11mr7769492ilu.197.1621539880523; Thu, 20 May 2021 12:44:40 -0700 (PDT) Received: from localhost (65-130-60-221.slkc.qwest.net. [65.130.60.221]) by smtp.gmail.com with ESMTPSA id m17sm2013251ioc.0.2021.05.20.12.44.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 May 2021 12:44:40 -0700 (PDT) Date: Thu, 20 May 2021 12:44:38 -0700 From: Yury Norov To: Rikard Falkeborn Cc: Ard Biesheuvel , Andrew Morton , Arnd Bergmann , Andy Shevchenko , Tetsuo Handa , Linux Kernel Mailing List , Peter Zijlstra Subject: Re: [PATCH] linux/bits.h: Fix compilation error with GENMASK Message-ID: References: <20210511203716.117010-1-rikard.falkeborn@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 20, 2021 at 08:46:40PM +0200, Rikard Falkeborn wrote: > On Wed, May 12, 2021 at 02:53:27PM +0200, Ard Biesheuvel wrote: > > (+ Arnd) > > > > On Tue, 11 May 2021 at 22:37, Rikard Falkeborn > > wrote: > > > > > > GENMASK() has an input check which uses __builtin_choose_expr() to enable > > > a compile time sanity check of its inputs if they are known at compile > > > time. However, it turns out that __builtin_constant_p() does not always > > > return a compile time constant [0]. It was thought this problem was fixed > > > with gcc 4.9 [1], but apparently this is not the case [2]. > > > > > > Switch to use __is_constexpr() instead which always returns a compile > > > time constant, regardless of its inputs. > > > > > > [0]: https://lore.kernel.org/lkml/42b4342b-aefc-a16a-0d43-9f9c0d63ba7a@rasmusvillemoes.dk > > > [1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449 > > > [2]: https://lore.kernel.org/lkml/1ac7bbc2-45d9-26ed-0b33-bf382b8d858b@I-love.SAKURA.ne.jp > > > > > > Reported-by: Tetsuo Handa > > > Signed-off-by: Rikard Falkeborn > > > --- > > > Feedback on placing __is_constexpr() in const.h is welcome, at least the > > > name is appropriate... > > > > > > include/linux/bits.h | 2 +- > > > include/linux/const.h | 8 ++++++++ > > > include/linux/minmax.h | 10 ++-------- > > > tools/include/linux/bits.h | 2 +- > > > tools/include/linux/const.h | 8 ++++++++ > > > 5 files changed, 20 insertions(+), 10 deletions(-) > > > > > > diff --git a/include/linux/bits.h b/include/linux/bits.h > > > index 7f475d59a097..87d112650dfb 100644 > > > --- a/include/linux/bits.h > > > +++ b/include/linux/bits.h > > > @@ -22,7 +22,7 @@ > > > #include > > > #define GENMASK_INPUT_CHECK(h, l) \ > > > (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > > > - __builtin_constant_p((l) > (h)), (l) > (h), 0))) > > > + __is_constexpr((l) > (h)), (l) > (h), 0))) > > > #else > > > /* > > > * BUILD_BUG_ON_ZERO is not available in h files included from asm files, > > > diff --git a/include/linux/const.h b/include/linux/const.h > > > index 81b8aae5a855..435ddd72d2c4 100644 > > > --- a/include/linux/const.h > > > +++ b/include/linux/const.h > > > @@ -3,4 +3,12 @@ > > > > > > #include > > > > > > +/* > > > + * This returns a constant expression while determining if an argument is > > > + * a constant expression, most importantly without evaluating the argument. > > > + * Glory to Martin Uecker > > > + */ > > > +#define __is_constexpr(x) \ > > > + (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) > > > + > > > #endif /* _LINUX_CONST_H */ > > > diff --git a/include/linux/minmax.h b/include/linux/minmax.h > > > index c0f57b0c64d9..5433c08fcc68 100644 > > > --- a/include/linux/minmax.h > > > +++ b/include/linux/minmax.h > > > @@ -2,6 +2,8 @@ > > > #ifndef _LINUX_MINMAX_H > > > #define _LINUX_MINMAX_H > > > > > > +#include > > > + > > > /* > > > * min()/max()/clamp() macros must accomplish three things: > > > * > > > @@ -17,14 +19,6 @@ > > > #define __typecheck(x, y) \ > > > (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1))) > > > > > > -/* > > > - * This returns a constant expression while determining if an argument is > > > - * a constant expression, most importantly without evaluating the argument. > > > - * Glory to Martin Uecker > > > - */ > > > -#define __is_constexpr(x) \ > > > - (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) > > > - > > > #define __no_side_effects(x, y) \ > > > (__is_constexpr(x) && __is_constexpr(y)) > > > > > > diff --git a/tools/include/linux/bits.h b/tools/include/linux/bits.h > > > index 7f475d59a097..87d112650dfb 100644 > > > --- a/tools/include/linux/bits.h > > > +++ b/tools/include/linux/bits.h > > > @@ -22,7 +22,7 @@ > > > #include > > > #define GENMASK_INPUT_CHECK(h, l) \ > > > (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > > > - __builtin_constant_p((l) > (h)), (l) > (h), 0))) > > > + __is_constexpr((l) > (h)), (l) > (h), 0))) > > > #else > > > /* > > > * BUILD_BUG_ON_ZERO is not available in h files included from asm files, > > > diff --git a/tools/include/linux/const.h b/tools/include/linux/const.h > > > index 81b8aae5a855..435ddd72d2c4 100644 > > > --- a/tools/include/linux/const.h > > > +++ b/tools/include/linux/const.h > > > @@ -3,4 +3,12 @@ > > > > > > #include > > > > > > +/* > > > + * This returns a constant expression while determining if an argument is > > > + * a constant expression, most importantly without evaluating the argument. > > > + * Glory to Martin Uecker > > > + */ > > > +#define __is_constexpr(x) \ > > > + (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) > > > + > > > #endif /* _LINUX_CONST_H */ > > > -- > > > 2.31.1 > > > > > Friendly ping. I added this patch in my Bitmap tree, but since it's actually a build bug fix, I think it's worth to move it faster with Arnd's or Andrew's trees?