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_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 89C0CC433E0 for ; Thu, 4 Jun 2020 06:41:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 651D8206C3 for ; Thu, 4 Jun 2020 06:41:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ls8yGKOx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727010AbgFDGlr (ORCPT ); Thu, 4 Jun 2020 02:41:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726248AbgFDGlr (ORCPT ); Thu, 4 Jun 2020 02:41:47 -0400 Received: from mail-pj1-x1041.google.com (mail-pj1-x1041.google.com [IPv6:2607:f8b0:4864:20::1041]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 34C97C05BD1E; Wed, 3 Jun 2020 23:41:47 -0700 (PDT) Received: by mail-pj1-x1041.google.com with SMTP id ga6so729188pjb.1; Wed, 03 Jun 2020 23:41:47 -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=XfO8TQWsKbgmttZdJsjsbuG8/l2FKfNiqjpmWnGFt2Y=; b=ls8yGKOxOkkDTayRMXM+oAYVPWdSU+KsHEMMWQG7GchBHiYWmwOShVp55XnM/huqpx YIsXxFj5wxi5PMQuTQd90JSBUsb8uHo6PTpSP3UVxm1tib6nHCbcZmgz107ryl9f9noy 8T1MDdcqS0IKWe+ZFKqQ99GdVxr2u/L874472ams2Y4LnQXud4x4ifDxHZ/lCWkaNKL8 GWvH1/fyUJxAtaeKVLpAm5lBSoremXuatNTEer1xX6Xd2yzlVIHaEYLJ95oCk/FqZp8x C1914CD+qMmUaX1Yq3Nzx7/+2AOEuqRyFV6iw8T84BH0zG8wirCgNrfC37o/3uKHFVZ2 U7Qg== 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=XfO8TQWsKbgmttZdJsjsbuG8/l2FKfNiqjpmWnGFt2Y=; b=hErNa7az4MV2C7JMLj/9P2+6hsLPRVhwVytvRNM1Hgsm1jJUjwsLsDTtKVqV+H65Ce 13Wm+MX28onyYxB/LVnIz+/u+G/e3n4hzmuOHlOY2l4dgKFbiRPlDErgC6Ck0HfHXfWV SB4pYJdgvUefIcq6ZOzG/qzA7vSJc1m6eqnyYC+duow/WCG9XdzLpdYYmSnk+LvLcKXd d0K+MhXpu+Ih2cMh59HBn9aThRmWYQHYK1b7191vUOydoiO6BG2HXUhV8z+ARBJ9q1VD LGCRKyMiiwfscsigVIuJ69j7ynNA9I1tHSVTWZTplHWeiaMnahZO8y6nSqU94z7EW/qz 9srg== X-Gm-Message-State: AOAM531sRLvlyMaGCgYDdYNFR/ZbF0itz3XZ0n1aH/B6VK+RhblRPKjo k0orPg+Wh/EEz21CD1HzcBOepopLWqRr6qCr/rwukWUBjKM= X-Google-Smtp-Source: ABdhPJx/7dpfk4vPbg8kFRwS1O9JuGLzOAhpwDM90TbH+B132fWjwdrXCZmiGFuthJ3QNJt40m945hGb54FhxeP+0lo= X-Received: by 2002:a17:90a:220f:: with SMTP id c15mr4367943pje.129.1591252906576; Wed, 03 Jun 2020 23:41:46 -0700 (PDT) MIME-Version: 1.0 References: <20200603215314.GA916134@rikard> <20200603220226.916269-1-rikard.falkeborn@gmail.com> In-Reply-To: <20200603220226.916269-1-rikard.falkeborn@gmail.com> From: Andy Shevchenko Date: Thu, 4 Jun 2020 09:41:29 +0300 Message-ID: Subject: Re: [PATCH] linux/bits.h: fix unsigned less than zero warnings To: Rikard Falkeborn Cc: Andrew Morton , Arnd Bergmann , emil.l.velikov@gmail.com, Kees Cook , Linus Walleij , Linux-Arch , Linux Kernel Mailing List , Syed Nayyar Waris , William Breathitt Gray , Masahiro Yamada , kbuild test robot Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 4, 2020 at 1:03 AM Rikard Falkeborn wrote: > > When calling the GENMASK and GENMASK_ULL macros with zero lower bit and > an unsigned unknown high bit, some gcc versions warn due to the > comparisons of the high and low bit in GENMASK_INPUT_CHECK. > > To silence the warnings, cast the inputs to int before doing the > comparisons. The only valid inputs to GENMASK() and GENMASK_ULL() are > are 0 to 31 or 63. Anything outside this is undefined due to the shifts > in GENMASK()/GENMASK_ULL(). Therefore, casting the inputs to int do not > change the values for valid known inputs. For unknown values, the check > does not change anything since it's a compile-time check only. > > As an example of the warning, kindly reported by the kbuild test robot: > > from drivers/mfd/atmel-smc.c:11: > drivers/mfd/atmel-smc.c: In function 'atmel_smc_cs_encode_ncycles': > include/linux/bits.h:26:28: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits] > 26 | __builtin_constant_p((l) > (h)), (l) > (h), 0))) > | ^ > include/linux/build_bug.h:16:62: note: in definition of macro 'BUILD_BUG_ON_ZERO' > 16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); }))) > | ^ > include/linux/bits.h:39:3: note: in expansion of macro 'GENMASK_INPUT_CHECK' > 39 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) > | ^~~~~~~~~~~~~~~~~~~ > >> drivers/mfd/atmel-smc.c:49:25: note: in expansion of macro 'GENMASK' > 49 | unsigned int lsbmask = GENMASK(msbpos - 1, 0); > | ^~~~~~~ > Thank you for the patch! I think there is still a possibility to improve (as I mentioned there are test cases that are absent right now). What if we will have unsigned long value 0x100000001? Would it be 1 after casting? Maybe cast to (long) or (long long) more appropriate? Please, add test cases. > Fixes: 295bcca84916 ("linux/bits.h: add compile time sanity check of GENMASK inputs") > Reported-by: kbuild test robot > Reported-by: Emil Velikov > Reported-by: Syed Nayyar Waris > Signed-off-by: Rikard Falkeborn > --- > include/linux/bits.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/bits.h b/include/linux/bits.h > index 4671fbf28842..293d1ee71a48 100644 > --- a/include/linux/bits.h > +++ b/include/linux/bits.h > @@ -21,9 +21,10 @@ > #if !defined(__ASSEMBLY__) && \ > (!defined(CONFIG_CC_IS_GCC) || CONFIG_GCC_VERSION >= 49000) > #include > +/* Avoid Wtype-limits warnings by casting the inputs to int */ > #define GENMASK_INPUT_CHECK(h, l) \ > (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > - __builtin_constant_p((l) > (h)), (l) > (h), 0))) > + __builtin_constant_p((int)(l) > (int)(h)), (int)(l) > (int)(h), 0))) > #else > /* > * BUILD_BUG_ON_ZERO is not available in h files included from asm files, > -- > 2.27.0 > -- With Best Regards, Andy Shevchenko