From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793732458; b=EAVqMvtGSwm8U63Xd+DrNeYjKOanazQWNGIK61Ab2PvcC0uelN+2XX1F8ysO2BsSa4wu v5qve9UoPEsv3DmNZbdcm/nJgDU4fkr8Pa/NQyYiNPqrHJy+/xKzXMAkRwiDS2i+vkUA9 fOjVz+LBP5UDoRDzw7bRN4f8WiVsAPtj615mSgHoHoA2oda0c/Vc/saBmk5GIkRu4hB5z HI7/CTXBqrlGwhlaVgWJ3ldy1iDg+gqrjBo+ZSukGZliZAsjmtVGduscEdrrIbb/dwlND bafBFXBJFte1sUJgwSllo3sZqTSXy6sdncyhZ9ta9m0aRlfUa7uHiDAkFSGm14epuhg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793732458; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=nPbC9p/kXZfK/pAtwP8FvtmaMonTRXTCIHkYzc09zfM=; b=h0qbbBPtbMtaQ/o12xATN8sJ28f2alMqqzjkoMgEK2S88f3WJMtUu1ufWMK2cST6viJp EpzMqxn3yb20yL/G71Z3eTqwsoHtn+yoQBH91TOV2XReEZrWiWwzmGI2psateAm2NgnTY MfM3WNK/icQ8y/xT1svOfUE7mYV9hZUEZ/iAPvUZgOgu8CIbsK1FAU9+OppsnD1y11jjN KGBkAGKcY5lPPYuhZdLtyZS7cymQzZK6vrUC0EFPyF1AOF5PloPwiJDfZMY9RZyVsbevt uFYrYyBMptueYJxlNDpSgbtrmFHPAj2K6jsfR0Ev8cmwG2S14gY7hBwUoKdVnPeMHMw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=mA3KNvu9; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 55B3E606A330; Tue, 3 Nov 2026 19:00:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=mA3KNvu9 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E1951F00919; Tue, 3 Nov 2026 19:00:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793732457; bh=nPbC9p/kXZfK/pAtwP8FvtmaMonTRXTCIHkYzc09zfM=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=mA3KNvu9dg7XUyhJO0i0shuS6M7OCVvpPJ12H2WiorQDQRwexlDCrSlqzfrLNf6YT UVpjkw08WSqPHQzkqqf8i4mFVXpr3Wg7kM0/yBXGVrT7wVT2l0vZdxtfod18lCAPy2 XJ2sCPSkDumY332hjBeQ346+g5Jqk+WpWRGxZx2P88xUjesfQkge49DYFQTc1QZCy9 nFdw8SsvHpeeBP2IipbPgbbaGYfdvXGxdyQp3+D3sipL6je0FiYu2qmByUTcEz+7qf OzKxc7zzcEU5C7ndPp/zWJx6b2C2xtpQnC/dCD95fuehMxkayaYVecqWuZ4SwaxZN7 s+LCjijx97KgQ== Date: Tue, 3 Nov 2026 12:00:52 -0700 From: Nathan Chancellor To: Rosalie Fang Cc: Andrew Morton , Kuan-Wei Chiu , Guan-Chun Wu <409411716@gms.tku.edu.tw>, David Laight , Bill Wendling , Justin Stitt , Greg Thelen , Yi Zhu , llvm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] lib/base64: fix -Wconstant-conversion warning in INIT_1() Message-ID: <20261103190052.GA267580@ax162> References: <20261103163404.159582-1-rosaliefang@google.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261103163404.159582-1-rosaliefang@google.com> Hi Rosalie, On Tue, Nov 03, 2026 at 04:34:04PM +0000, Rosalie Fang wrote: > When expanding BASE64_REV_INIT() for v in 0x7c..0x7f (124..127), the > unselected ternary branch (v) - '0' + 52 evaluates to 128..131, which > exceeds SCHAR_MAX (127). Recent Clang versions diagnose implicit integer > constant conversions in unevaluated ternary arms when initializing the > s8 lookup tables: > > lib/base64.c:58:18: error: implicit conversion from 'int' to 's8' > (aka 'signed char') changes value from 131 to -125 > [-Werror,-Wconstant-conversion] > 58 | [BASE64_IMAP] = BASE64_REV_INIT('+', ',') > | ^~~~~~~~~~~~~~~~~~~~~~~~~ > lib/base64.c:34:42: note: expanded from macro 'INIT_1' > 34 | : (v) >= '0' && (v) <= '9' ? (v) - '0' + 52 \ > | ~~~~~~~~~~^~~~ > > Explicitly cast the digit-branch expression to s8 to silence the > warning. > > Fixes: c4eb7ad32eab ("lib/base64: optimize base64_decode() with reverse lookup tables") > Assisted-by: LLM > Signed-off-by: Rosalie Fang > --- > lib/base64.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/base64.c b/lib/base64.c > index 325c7332b049..1489c048b1fd 100644 > --- a/lib/base64.c > +++ b/lib/base64.c > @@ -31,7 +31,7 @@ static const char base64_tables[][65] = { > #define INIT_1(v, ch_62, ch_63) \ > [v] = (v) >= 'A' && (v) <= 'Z' ? (v) - 'A' \ > : (v) >= 'a' && (v) <= 'z' ? (v) - 'a' + 26 \ > - : (v) >= '0' && (v) <= '9' ? (v) - '0' + 52 \ > + : (v) >= '0' && (v) <= '9' ? (s8)((v) - '0' + 52) \ > : (v) == (ch_62) ? 62 : (v) == (ch_63) ? 63 : -1 > > /* > -- > 2.56.0.385.gac671c819a-goog > Thanks for the change. I avoided this in a different way, which has recently been merged into a tree that should be merged into mainline relatively soon: https://git.kernel.org/akpm/mm/c/3af83c11cf5990fda0bfe3959aa6391ff903ffdd For the record, I do hope that https://github.com/llvm/llvm-project/pull/226775 eventually gets merged so that these workarounds will be unnecessary but I am not sure how that will play out yet. -- Cheers, Nathan