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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E75B8C43334 for ; Wed, 22 Jun 2022 16:05:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376422AbiFVQFR (ORCPT ); Wed, 22 Jun 2022 12:05:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39286 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376435AbiFVQEz (ORCPT ); Wed, 22 Jun 2022 12:04:55 -0400 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0696134BA1; Wed, 22 Jun 2022 09:04:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1655913873; x=1687449873; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=eG4q6c4UvYGtzxug36fSTUwHXCGqtjeRSHre942YGGg=; b=llCY6TcTc2B4dCCWVQhv81yKwEdAtn5yadjhiwtGPA2l/qyoghHhxrd1 58Z4Na2DLG2+ZhTMrx76BJo0TP7j0a3agC8bITw6touar09aTBRlbgNfQ ZqQsT96X7p/X4CTRPUj3B/yjdCm89Kik0CtOIJdghFGVmbhl5jLPNKFwM NJ4tuZJN9CafMU2Bb/w4e/3MGkZj6YVUmNTXWL7rfnkyqzpyKV+ZqcUSK 3PpfnYj2mdU2IEd8nxFggTf+BCCmgscpB80AhNrSu6U/KuqigKxY/6vv3 hbw+poKqsbtk6Y+gjsoW9KL2XpyeZiPFIWDSpyvqVf+3nMn12NPH+fy+i g==; X-IronPort-AV: E=McAfee;i="6400,9594,10386"; a="281191468" X-IronPort-AV: E=Sophos;i="5.92,212,1650956400"; d="scan'208";a="281191468" Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Jun 2022 09:04:27 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.92,212,1650956400"; d="scan'208";a="764940851" Received: from irvmail001.ir.intel.com ([10.43.11.63]) by orsmga005.jf.intel.com with ESMTP; 22 Jun 2022 09:04:20 -0700 Received: from newjersey.igk.intel.com (newjersey.igk.intel.com [10.102.20.203]) by irvmail001.ir.intel.com (8.14.3/8.13.6/MailSET/Hub) with ESMTP id 25MG4Ip9006187; Wed, 22 Jun 2022 17:04:18 +0100 From: Alexander Lobakin To: Arnd Bergmann , Yury Norov Cc: Alexander Lobakin , Andy Shevchenko , Mark Rutland , Matt Turner , Brian Cain , "Geert Uytterhoeven" , Yoshinori Sato , Rich Felker , "David S. Miller" , Kees Cook , "Peter Zijlstra (Intel)" , Marco Elver , Borislav Petkov , Tony Luck , "Maciej Fijalkowski" , Jesse Brandeburg , Greg Kroah-Hartman , Nathan Chancellor , Nick Desaulniers , Tom Rix , linux-alpha@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH v4 8/8] lib: test_bitmap: add compile-time optimization/evaluations assertions Date: Wed, 22 Jun 2022 18:04:15 +0200 Message-Id: <20220622160415.589430-1-alexandr.lobakin@intel.com> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220621191553.69455-9-alexandr.lobakin@intel.com> References: <20220621191553.69455-1-alexandr.lobakin@intel.com> <20220621191553.69455-9-alexandr.lobakin@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org From: Alexander Lobakin Date: Tue, 21 Jun 2022 21:15:53 +0200 > Add a function to the bitmap test suite, which will ensure that > compilers are able to evaluate operations performed by the > bitops/bitmap helpers to compile-time constants when all of the > arguments are compile-time constants as well, or trigger a build > bug otherwise. This should work on all architectures and all the > optimization levels supported by Kbuild. > The function doesn't perform any runtime tests and gets optimized > out to nothing after passing the build assertions. > > Suggested-by: Yury Norov > Signed-off-by: Alexander Lobakin > Reviewed-by: Andy Shevchenko > --- > lib/test_bitmap.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 45 insertions(+) > > diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c > index d5923a640457..3a7b09b82794 100644 > --- a/lib/test_bitmap.c > +++ b/lib/test_bitmap.c > @@ -869,6 +869,50 @@ static void __init test_bitmap_print_buf(void) > } > } > > +static void __init test_bitmap_const_eval(void) > +{ > + DECLARE_BITMAP(bitmap, BITS_PER_LONG); > + unsigned long initvar = BIT(2); > + unsigned long bitopvar = 0; > + unsigned long var = 0; > + int res; > + > + /* > + * Compilers must be able to optimize all of those to compile-time > + * constants on any supported optimization level (-O2, -Os) and any > + * architecture. Otherwise, trigger a build bug. > + * The whole function gets optimized out then, there's nothing to do > + * in runtime. > + */ > + > + /* Equals to `unsigned long bitmap[1] = { BIT(5), }` */ > + bitmap_clear(bitmap, 0, BITS_PER_LONG); > + if (!test_bit(7, bitmap)) > + bitmap_set(bitmap, 5, 1); So for now, when building for s390, Clang (up to the latest Git snapshot) generates some incorrect code here. It does expand both test_bit() and bitmap_set() to const_test_bit() and const___set_bit(), but at the same time thinks that starting from this point, @bitmap and @bitopvar (???) are *not* constants and fails the assertions below, which is not true and weird. Any other architecture + compiler couples work fine, including s390 on GCC. So would it be acceptable for now to do: /* Equals to `unsigned long bitmap[1] = { BIT(5), }` */ bitmap_clear(bitmap, 0, BITS_PER_LONG); /* * Some comment saying that this is currently broken * on s390 + Clang */ #if !(defined(__s390__) && defined(__clang__)) if (!test_bit(7, bitmap)) bitmap_set(bitmap, 5, 1); #endif /* Equals to `unsigned long bitopvar = BIT(20)` */ __change_bit(31, &bitopvar); bitmap_shift_right(&bitopvar, &bitopvar, 11, BITS_PER_LONG); [...] or there could be any better solutions? (+Cc LLVM folks) > + > + /* Equals to `unsigned long bitopvar = BIT(20)` */ > + __change_bit(31, &bitopvar); > + bitmap_shift_right(&bitopvar, &bitopvar, 11, BITS_PER_LONG); > + > + /* Equals to `unsigned long var = BIT(25)` */ > + var |= BIT(25); > + if (var & BIT(0)) > + var ^= GENMASK(9, 6); > + > + /* __const_hweight<32|64>(BIT(5)) == 1 */ > + res = bitmap_weight(bitmap, 20); > + BUILD_BUG_ON(!__builtin_constant_p(res)); > + > + /* !(BIT(31) & BIT(18)) == 1 */ > + res = !test_bit(18, &bitopvar); > + BUILD_BUG_ON(!__builtin_constant_p(res)); > + > + /* BIT(2) & GENMASK(14, 8) == 0 */ > + BUILD_BUG_ON(!__builtin_constant_p(initvar & GENMASK(14, 8))); > + /* ~BIT(25) */ > + BUILD_BUG_ON(!__builtin_constant_p(~var)); > +} > + > static void __init selftest(void) > { > test_zero_clear(); > @@ -884,6 +928,7 @@ static void __init selftest(void) > test_for_each_set_clump8(); > test_bitmap_cut(); > test_bitmap_print_buf(); > + test_bitmap_const_eval(); > } > > KSTM_MODULE_LOADERS(test_bitmap); > -- > 2.36.1 Thanks, Olek