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=-12.7 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,URIBL_BLOCKED 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 999A6C433ED for ; Fri, 21 May 2021 10:15:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6BDB6613CE for ; Fri, 21 May 2021 10:15:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232568AbhEUKRA (ORCPT ); Fri, 21 May 2021 06:17:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40810 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230050AbhEUKQ4 (ORCPT ); Fri, 21 May 2021 06:16:56 -0400 Received: from mail-pj1-x102b.google.com (mail-pj1-x102b.google.com [IPv6:2607:f8b0:4864:20::102b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 47161C061574 for ; Fri, 21 May 2021 03:15:33 -0700 (PDT) Received: by mail-pj1-x102b.google.com with SMTP id n6-20020a17090ac686b029015d2f7aeea8so7087544pjt.1 for ; Fri, 21 May 2021 03:15:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=n1UKW5UlxzKbk0NJW2nQB3WP1Q3DywulUf5siHzqJFU=; b=HOUswS10DhLNpIZyKBkwrrTE1O4RGf+SieRNOyQOmS/VgbVUX9d4CgfdoQx4Yf/9SV rqk24EDQ6AkSKnYpkkXH8seVIld5Tg3IJ9xm/G8jWSjkItjtjlktbBRz8bdPckQidBrm 2YO053sy1hquSKocZB0y0h+nOsWmY5iaCj5Fn5o0xAhisi8NWgMN2U/ZyBWEjWhDKuaL RsW9gh3t82U7jYjYcBLZaEM5tUR+maCUr+/22JHu76v8U5uaIAhF0rTCyzw5BhVJQKxW QRUWBxP8kY5HHlYsxVJU7GtIaHVQqLaWbDEkT3JzgXBJmWogy2sywieZ3vWx6bOFYizp X24A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=n1UKW5UlxzKbk0NJW2nQB3WP1Q3DywulUf5siHzqJFU=; b=MFOKN+OXSSccKnJqwa/pCkQFNAfccfG/UA/3IIKXXd6h3ZdzlUt2YYV1vPekcSyGMH qnr/YySkUtXgGbXc1vgyGFT/VqIDt2sH4HM8tbfJpjMpc8XnKgIJhXBQ2XGFJ80Jqair LRF0sUkq7BE9mxfU+zhF1W3867R8ZUC4yTrdIQfOTsihUxyxi2uB4yNx4piyJhdZNLD4 HkhRqtyEbJzKybIFuNCBhtbeKkDtI7+ylgn0FQEAlpKRpiPUXgOMLlAstuqx+pnhRW1c PHR8UWhTokMtJ0LXlPQZTCruM/bgL+pg7z/6iMs2kUkRoGKqMsOSPSfHrhbTKLpzPtSO BI/w== X-Gm-Message-State: AOAM532Mh1F8LKKoTTsGffNXPMAE1Fae6aOqGBwutJm00V36FzVzuAq+ ahaILXZ6f46QmqmOj7f6SE5eUCq33MLVkYtho+U= X-Google-Smtp-Source: ABdhPJxEq2HGN4A/zooK2iIxAxNgAMg0hC3KyE32B+t4tuu3PoY1myv+/tLVr+xtw18jx6Y3P5mBWEhkZbHjzGSpGdw= X-Received: by 2002:a17:90a:17ad:: with SMTP id q42mr10403326pja.181.1621592132531; Fri, 21 May 2021 03:15:32 -0700 (PDT) MIME-Version: 1.0 References: <20210511203716.117010-1-rikard.falkeborn@gmail.com> In-Reply-To: <20210511203716.117010-1-rikard.falkeborn@gmail.com> From: Andy Shevchenko Date: Fri, 21 May 2021 13:15:16 +0300 Message-ID: Subject: Re: [PATCH] linux/bits.h: Fix compilation error with GENMASK To: Rikard Falkeborn Cc: Andrew Morton , Andy Shevchenko , Tetsuo Handa , Yury Norov , Linux Kernel Mailing List , Ard Biesheuvel , Peter Zijlstra Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 11, 2021 at 11:41 PM 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 Thanks for fixing this issue! Since there is a consensus about the place, I have no objection either. Reviewed-by: Andy Shevchenko > 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 > -- With Best Regards, Andy Shevchenko