From nobody Tue Dec 16 16:41:04 2025 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 B97CBC4167B for ; Thu, 30 Nov 2023 10:34:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344858AbjK3K1b (ORCPT ); Thu, 30 Nov 2023 05:27:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54408 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229550AbjK3K13 (ORCPT ); Thu, 30 Nov 2023 05:27:29 -0500 Received: from mail-pf1-x42f.google.com (mail-pf1-x42f.google.com [IPv6:2607:f8b0:4864:20::42f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 911F093 for ; Thu, 30 Nov 2023 02:27:35 -0800 (PST) Received: by mail-pf1-x42f.google.com with SMTP id d2e1a72fcca58-6cdd4aab5f5so764305b3a.3 for ; Thu, 30 Nov 2023 02:27:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1701340055; x=1701944855; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:sender:from:to:cc:subject:date :message-id:reply-to; bh=i5biSPjpUhFmS7S7cTsjVh9feb56GTutqbWDSkSEiUc=; b=fYgv3qVbFMyfaQ4OGZd3PacdUdOtlEdT4xl4JB7/LiO9QtKBU2kKOu0Pb5qOgM/cRr 2LeR2bga9nk1SrDntZ5kOzPoTHS8LMA0FZZ/6r+WujTYEBleln191XIR5daS3SE7fNEt g72qEyrdvctd4GAlgX0XW17h5UgyKWK7c1+oRF9I00EJPCenUwrrHYyAPWA4SfvXAFxE sBuEHmPmnfOg/RUR6lntnqopCQNjaBv1DUVrdRdyrNX4Ayz3JX0yg4EBa7Jga8c96Yn5 4+AQJsfxRVz0jPpED4psZjF1LDjkxUADTTzVK9Q87WdTiFN8kr01ut0KyECEgVs331oU 8ohQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701340055; x=1701944855; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:sender:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=i5biSPjpUhFmS7S7cTsjVh9feb56GTutqbWDSkSEiUc=; b=dHHFstJdh3pK0tyseSBLcW9TwaVKPmuVSfypuEForEXXQ3AhPscNUXx7W2gIKRvfyi y3oc3TiXrxxodr/EyFOemZ2VI/B1HS6jiZ046KSE3YH7aRyUtvGBYoQrU3B1XD8pXgzi RNPcpHvEzrr/vxF39ufbvmREbZHpCn1uvunlMFgO5QUfeXN/56NglaviO0sxOlV4VgPE mFw2nB18H8vyr3DxQe5jPDJfpUOa0x0MiSmpGrzLH/cneXV99CEt+7YlEtM2auFaBtsG XH28q5GcaGLV/dQpamhjGVnRa5CGiQRnDjNCWDin0HNoEfVsTElkJ5R/+JbohWXw0gRq tB/w== X-Gm-Message-State: AOJu0Yx+0leA55P2bA9OrTFu5HD64QjIzj29ejOuqCJ5PJDemI7gYfAW WwqsfMa5g3wbeae+dWTs/68= X-Google-Smtp-Source: AGHT+IE4TW98BjKnZUeBoxsrdWrYpDL83KvEMg0aEsh1jLeOkdcayCQ4w4gIrgMFfBo+SIZ4bxH9UQ== X-Received: by 2002:a05:6a00:2d06:b0:6cd:ec64:a886 with SMTP id fa6-20020a056a002d0600b006cdec64a886mr1017096pfb.2.1701340054813; Thu, 30 Nov 2023 02:27:34 -0800 (PST) Received: from XH22050090-L.ad.ts.tri-ad.global ([103.175.111.222]) by smtp.gmail.com with ESMTPSA id p24-20020a62ab18000000b006cb574445efsm874243pff.88.2023.11.30.02.27.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Nov 2023 02:27:34 -0800 (PST) Sender: Vincent Mailhol From: Vincent Mailhol To: Andrew Morton , linux-kernel@vger.kernel.org, Yury Norov Cc: Vincent Mailhol , Nick Desaulniers , Douglas Anderson , Kees Cook , Petr Mladek , Randy Dunlap , Zhaoyang Huang , Geert Uytterhoeven , Marco Elver Subject: [PATCH v2] lib: test_bitops: add compile-time optimization/evaluations assertions Date: Thu, 30 Nov 2023 19:27:17 +0900 Message-Id: <20231130102717.1297492-1-mailhol.vincent@wanadoo.fr> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20221111081316.30373-1-mailhol.vincent@wanadoo.fr> References: <20221111081316.30373-1-mailhol.vincent@wanadoo.fr> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Add a function in the bitops test suite to assert that the bitops helper correctly fold constant expressions (or trigger a build bug otherwise). This should work on 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. Architectures which fail that test should adjust their arch/*/include/asm/bitops.h in order to use the compiler's generic __builitn implementation if the argument is a constant expression (similar to [1]). [1] commit 146034fed6ee ("x86/asm/bitops: Use __builtin_ffs() to evaluate constant expressions") Suggested-by: Yury Norov Signed-off-by: Vincent Mailhol --- This is tested on x86, x86_64, arm and arm64. Other architectures were not tested. My idea would be to add this patch to any kind of CI which runs on all architecture (linux-next?) and see if anything breaks. Or maybe I should send a message to the maintainers of all of the arch/*/include/asm/bitops.h files? Tell me what you think. ** Changelog ** v1 -> v2: - Drop the RFC patch. v1 was not ready to be applied on x86 because of pending changes in arch/x86/include/asm/bitops.h. This was finally fixed by Nick in commit 3dae5c43badf ("x86/asm/bitops: Use __builtin_clz{l|ll} to evaluate constant expressions"). Thanks Nick! - Update the commit description. - Introduce the test_const_eval() macro to factorize code. - No functional changes. Link: https://lore.kernel.org/all/20221111081316.30373-1-mailhol.vincent@= wanadoo.fr/ --- lib/Kconfig.debug | 4 ++++ lib/test_bitops.c | 31 +++++++++++++++++++++++++++++++ 2 files changed, 35 insertions(+) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index cc7d53d9dc01..c97d818dbc30 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -2454,6 +2454,10 @@ config TEST_BITOPS compilations. It has no dependencies and doesn't run or load unless explicitly requested by name. for example: modprobe test_bitops. =20 + In addition, check that the compiler is able to fold the bitops + function into a compile-time constant (given that the argument is also + a compile-time constant) and trigger a build bug otherwise. + If unsure, say N. =20 config TEST_VMALLOC diff --git a/lib/test_bitops.c b/lib/test_bitops.c index 3b7bcbee84db..49e2f76575e4 100644 --- a/lib/test_bitops.c +++ b/lib/test_bitops.c @@ -50,6 +50,35 @@ static unsigned long order_comb_long[][2] =3D { }; #endif =20 +/* Assert that a boolean expression can be folded in a constant and is tru= e. */ +#define test_const_eval(test_expr) \ +({ \ + /* Evaluate once so that compiler can fold it. */ \ + bool __test_expr =3D test_expr; \ + \ + BUILD_BUG_ON(!__builtin_constant_p(__test_expr)); \ + BUILD_BUG_ON(!__test_expr); \ +}) + +static void test_bitops_const_eval(void) +{ + /* + * On any supported optimization level (-O2, -Os) and if + * invoked with a compile-time constant argument, the compiler + * must be able to fold into a constant expression all the bit + * find functions. Namely: __ffs(), ffs(), ffz(), __fls(), + * fls() and fls64(). Otherwise, trigger a build bug. + */ + const int n =3D 10; + + test_const_eval(__ffs(BIT(n)) =3D=3D n); + test_const_eval(ffs(BIT(n)) =3D=3D n + 1); + test_const_eval(ffz(~BIT(n)) =3D=3D n); + test_const_eval(__fls(BIT(n)) =3D=3D n); + test_const_eval(fls(BIT(n)) =3D=3D n + 1); + test_const_eval(fls64(BIT_ULL(n)) =3D=3D n + 1); +} + static int __init test_bitops_startup(void) { int i, bit_set; @@ -94,6 +123,8 @@ static int __init test_bitops_startup(void) if (bit_set !=3D BITOPS_LAST) pr_err("ERROR: FOUND SET BIT %d\n", bit_set); =20 + test_bitops_const_eval(); + pr_info("Completed bitops test\n"); =20 return 0; --=20 2.25.1