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 C1B13C433F5 for ; Mon, 11 Apr 2022 20:01:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349762AbiDKUDY (ORCPT ); Mon, 11 Apr 2022 16:03:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59190 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244932AbiDKUDV (ORCPT ); Mon, 11 Apr 2022 16:03:21 -0400 Received: from mail-0201.mail-europe.com (mail-0201.mail-europe.com [51.77.79.158]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 72DDB1A074; Mon, 11 Apr 2022 13:01:01 -0700 (PDT) Date: Mon, 11 Apr 2022 20:00:49 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail2; t=1649707256; bh=/M7BzW/s7Vzq7EWhCycKAddwYFL6mUxNmXasegv2RH4=; h=Date:To:From:Cc:Reply-To:Subject:Message-ID:In-Reply-To: References:From:To:Cc:Date:Subject:Reply-To:Feedback-ID: Message-ID; b=X8gG6RCKUyhRjECpDPWqnHxSZ4C8smmo8/Q+wT1xje58nBjiIhOryAIC6Odf2knlL IwOyieEp/xBtQRdMRhlFNFFWTS5DeVhEFDbtbLZUM6wu74fHVC0IUjtNjT+zF8mEff bpY3RGI1HYvgcsimqfPR/DxlIi2XBWi+a+Y9EpUNt6WYSD4j8U2djLjkQgz3IyNWeA +KMVawUS55opL4z17k33WqvrpkWgcuBOEN936FrhyMdk7cv1hZtw0etI3BFs8J9Iit yki/XCMX2R+eww5d7Ym6FtuuBsNayy8wQOkZwGl9jXY5BtSRIPq6IAd+NAeXKJNJ4n 14FvnFwPCt88Q== To: Arnd Bergmann From: Alexander Lobakin Cc: Alexander Lobakin , Andrew Morton , Bart Van Assche , Jens Axboe , Keith Busch , Chaitanya Kulkarni , "Martin K . Petersen" , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Reply-To: Alexander Lobakin Subject: Re: [PATCH] asm-generic: fix __get_unaligned_be48() on 32 bit platforms Message-ID: <20220411195403.230899-1-alobakin@pm.me> In-Reply-To: <20220406233909.529613-1-alobakin@pm.me> References: <20220406233909.529613-1-alobakin@pm.me> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Alexander Lobakin Date: Wed, 06 Apr 2022 23:46:04 +0000 > While testing the new macros for working with 48 bit containers, > I faced a weird problem: > > 32 + 16: 0x2ef6e8da 0x79e60000 > 48: 0xffffe8da + 0x79e60000 > > All the bits starting from the 32nd were getting 1d in 9/10 cases. > The debug showed: > > p[0]: 0x00002e0000000000 > p[1]: 0x00002ef600000000 > p[2]: 0xffffffffe8000000 > p[3]: 0xffffffffe8da0000 > p[4]: 0xffffffffe8da7900 > p[5]: 0xffffffffe8da79e6 > > that the value becomes a garbage after the third OR, i.e. on > `p[2] << 24`. > When the 31st bit is 1 and there's no explicit cast to an unsigned, > it's being considered as a signed int and getting sign-extended on > OR, so `e8000000` becomes `ffffffffe8000000` and messes up the > result. > Cast the @p[2] to u64 as well to avoid this. Now: > > 32 + 16: 0x7ef6a490 0xddc10000 > 48: 0x7ef6a490 + 0xddc10000 > > p[0]: 0x00007e0000000000 > p[1]: 0x00007ef600000000 > p[2]: 0x00007ef6a4000000 > p[3]: 0x00007ef6a4900000 > p[4]: 0x00007ef6a490dd00 > p[5]: 0x00007ef6a490ddc1 > > Fixes: c2ea5fcf53d5 ("asm-generic: introduce be48 unaligned accessors") > Signed-off-by: Alexander Lobakin Uhm, ping? > --- > include/asm-generic/unaligned.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unalig= n=3D > ed.h > index 8fc637379899..df30f11b4a46 100644 > --- a/include/asm-generic/unaligned.h > +++ b/include/asm-generic/unaligned.h > @@ -143,7 +143,7 @@ static inline void put_unaligned_be48(const u64 val, = v=3D > oid *p) > > static inline u64 __get_unaligned_be48(const u8 *p) > { > -=09return (u64)p[0] << 40 | (u64)p[1] << 32 | p[2] << 24 | > +=09return (u64)p[0] << 40 | (u64)p[1] << 32 | (u64)p[2] << 24 | > =09=09p[3] << 16 | p[4] << 8 | p[5]; > } > > -- > 2.35.1 Thanks, Al