From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4140C2FF151; Thu, 18 Dec 2025 18:51:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766083878; cv=none; b=Bz3c84TghmoH0hjvLVjQNEVOtNxE3jqXmVKgdA8EH0gstYvcuc9TOeJ/QboHq6B8G9L1109f8Z26tmPMNy9gnm90ORtduQZBa2ba/+TzdUHj0GtOMrG5JHre74C9yULGPKyfkzgUSCcwYjieyEandb3ToPvS9LnRRz3yeDeNJy8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766083878; c=relaxed/simple; bh=exaDAmGfwhCHtzCgNSX0Gj1Y2mOtWbeMcXCXNwxDLyo=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=fGNfsvLTwNd8Zx2pLVDuuo3rZrdEcc+0587kdK1tW1Zy5CuOaurLo8+wC8oO51xg42UyiC0ecykImUESIUJms/JPvS1qdsL8iRZ8657/JVLF/YaWmkbWlUQiFOipZqNmyLiNIDFzZIC5Jjp+OHaqHB5t0zgrU8MsgOS/Ys7TrQs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Hkv1DLya; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Hkv1DLya" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C11E8C113D0; Thu, 18 Dec 2025 18:51:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766083877; bh=exaDAmGfwhCHtzCgNSX0Gj1Y2mOtWbeMcXCXNwxDLyo=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=Hkv1DLyatcAsPlTRs+4Xw1lfj5uiLRivczjAKo2QElFDeDj8qx31NBccRCSRn/mUd n17MZADFPRhePYovV4ZOWzYZM86ddnTIu7CUjejpPdXrrv6dEq2MLLwel9QI+HsfI7 F+01kRDyDlIaRDkDZhZ58iboR78cMZgGQsdZXNTLzBqXNLkIm1qVVzuD1qfwSAnN9T TDVV68hWOD4nzO9gnt5EfioLIGmIb+9fiH0tJaK4zZEcDlQhMCW8QJ9385UANoLGNM BG/IwE6jlSgTBf5dDUydnE+WjFrCtBaLYrEir2rlUBTJeCb+wlnpMFgGWjwtbIjC5m 7uDg0/fBwHGpw== From: Vincent Mailhol Date: Thu, 18 Dec 2025 19:50:01 +0100 Subject: [PATCH 1/2] kbuild: remove gcc's -Wtype-limits Precedence: bulk X-Mailing-List: linux-sparse@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251218-remove_wtype-limits-v1-1-735417536787@kernel.org> References: <20251218-remove_wtype-limits-v1-0-735417536787@kernel.org> In-Reply-To: <20251218-remove_wtype-limits-v1-0-735417536787@kernel.org> To: Nathan Chancellor , Nicolas Schier , Nick Desaulniers , Bill Wendling , Justin Stitt , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Chris Mason , David Sterba Cc: Linus Torvalds , linux-kbuild@vger.kernel.org, linux-sparse@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, dri-devel@lists.freedesktop.org, linux-btrfs@vger.kernel.org, Vincent Mailhol X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=3554; i=mailhol@kernel.org; h=from:subject:message-id; bh=exaDAmGfwhCHtzCgNSX0Gj1Y2mOtWbeMcXCXNwxDLyo=; b=owGbwMvMwCV2McXO4Xp97WbG02pJDJkuviKiT3NXWfh0WfVtbeAKVD/uLhp6XnFJwlG1vWf29 G+8b/SnYyILgxgXg6WYIsuyck5uhY5C77BDfy1h5rAygQyRFmlgAAIWBr7cxLxSIx0jPVNtQz1D Qx0gk4GLUwCmWj6XkWHlnwf52/b/2fb670nmUO7zWt0NAVMXpzKfzEtK3PHQxXsywz/lgKlhAd5 cVW/m7vqXukX3d2JP/X07NqbMOdMrQw5GFnIDAA== X-Developer-Key: i=mailhol@kernel.org; a=openpgp; fpr=ED8F700574E67F20E574E8E2AB5FEB886DBB99C2 W=2 builds are heavily polluted by the -Wtype-limits warning. Here are some W=12 statistics on Linux v6.19-rc1 for an x86_64 defconfig (with just CONFIG_WERROR set to "n") using gcc 14.3.1: Warning name count percent ------------------------------------------------- -Wlogical-op 2 0.00 % -Wmaybe-uninitialized 138 0.20 % -Wunused-macros 869 1.24 % -Wmissing-field-initializers 1418 2.02 % -Wshadow 2234 3.19 % -Wtype-limits 65378 93.35 % ------------------------------------------------- Total 70039 100.00 % As we can see, -Wtype-limits represents the vast majority of all warnings. The reason behind this is that these warnings appear in some common header files, meaning that some unique warnings are repeated tens of thousands of times (once per header inclusion). Add to this the fact that each warning is coupled with a dozen lines detailing some macro expansion. The end result is that the W=2 output is just too bloated and painful to use. Three years ago, I proposed in [1] modifying one such header to silence that noise. Because the code was not faulty, Linus rejected the idea and instead suggested simply removing that warning. At that time, I could not bring myself to send such a patch because, despite its problems, -Wtype-limits would still catch the below bug: unsigned int ret; ret = check(); if (ret < 0) error(); Meanwhile, based on another suggestion from Linus, I added a new check to sparse [2] that would catch the above bug without the useless spam. With this, remove gcc's -Wtype-limits. People who still want to catch incorrect comparisons between unsigned integers and zero can now use sparse instead. On a side note, clang also has a -Wtype-limits warning but: * it is not enabled in the kernel at the moment because, contrary to gcc, clang did not include it under -Wextra. * it does not warn if the code results from a macro expansion. So, if activated, it would not cause as much spam as gcc does. * -Wtype-limits is split into four sub-warnings [3] meaning that if it were to be activated, we could select which one to keep. So there is no present need to explicitly disable -Wtype-limits in clang. [1] linux/bits.h: GENMASK_INPUT_CHECK: reduce W=2 noise by 31% treewide Link: https://lore.kernel.org/all/20220308141201.2343757-1-mailhol.vincent@wanadoo.fr/ [2] Warn about "unsigned value that used to be signed against zero" Link: https://lore.kernel.org/all/20250921061337.3047616-1-mailhol@kernel.org/ [3] clang's -Wtype-limits Link: https://clang.llvm.org/docs/DiagnosticsReference.html#wtype-limits Signed-off-by: Vincent Mailhol --- scripts/Makefile.warn | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/scripts/Makefile.warn b/scripts/Makefile.warn index 68e6fafcb80c..c593ab1257de 100644 --- a/scripts/Makefile.warn +++ b/scripts/Makefile.warn @@ -55,6 +55,9 @@ else KBUILD_CFLAGS += -Wno-main endif +# Too noisy on range checks and in macros handling both signed and unsigned. +KBUILD_CFLAGS += -Wno-type-limits + # These result in bogus false positives KBUILD_CFLAGS += $(call cc-option, -Wno-dangling-pointer) @@ -174,7 +177,6 @@ else # The following turn off the warnings enabled by -Wextra KBUILD_CFLAGS += -Wno-missing-field-initializers -KBUILD_CFLAGS += -Wno-type-limits KBUILD_CFLAGS += -Wno-shift-negative-value ifdef CONFIG_CC_IS_CLANG -- 2.51.2