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 lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 88507C433EF for ; Wed, 11 May 2022 08:34:43 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.326599.549155 (Exim 4.92) (envelope-from ) id 1nohnj-00054W-Rk; Wed, 11 May 2022 08:34:31 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 326599.549155; Wed, 11 May 2022 08:34:31 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1nohnj-00054P-OM; Wed, 11 May 2022 08:34:31 +0000 Received: by outflank-mailman (input) for mailman id 326599; Wed, 11 May 2022 08:34:31 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1nohni-00054J-Vc for xen-devel@lists.xenproject.org; Wed, 11 May 2022 08:34:30 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1nohni-00028O-OI; Wed, 11 May 2022 08:34:30 +0000 Received: from gw1.octic.net ([81.187.162.82] helo=[10.0.1.193]) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1nohni-00034p-Ij; Wed, 11 May 2022 08:34:30 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID; bh=xsFGJDTRelUy2YDMXuTA7EDuToFbqqWaQ7fvTGFMsjU=; b=mhC8Rt0SpsVYzQVkQYLThNJCf9 V83CNNM/5AgLLujn33xl5uD4mxBg8ig/ivX5flSY9DUSN62hhLqP5LMNNgpl00ccxQcXDC1Rv9/lt jdVohaxGM8MmeJsMA9//tNsbV8M9wlexRv8gx+2h5WhayDe2nMw4KE1qlmculk8wGFIs=; Message-ID: <82e54293-926e-b7ee-7091-a85a9db8f6c5@xen.org> Date: Wed, 11 May 2022 09:34:28 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH v3 4/6] xen: Switch to byteswap To: =?UTF-8?B?TGluIExpdSDvvIjliJjmnpfvvIk=?= , "xen-devel@lists.xenproject.org" Cc: Stefano Stabellini , Andrew Cooper , George Dunlap , Jan Beulich , Wei Liu References: <76c9bed5-6643-4fa6-eaf5-c865f942193c@xen.org> From: Julien Grall In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi, Please configure your e-mail client to send in plain text. On 11/05/2022 07:30, Lin Liu （刘林） wrote: > Subject: Re: [PATCH v3 4/6] xen: Switch to byteswap > On 10/05/2022 11:15, Lin Liu wrote: >> Update to use byteswap to swap bytes. >> >> No functional change. >> >> Signed-off-by: Lin Liu >> --- >> Cc: Stefano Stabellini >> Cc: Julien Grall >> Cc: Andrew Cooper >> Cc: George Dunlap >> Cc: Jan Beulich >> Cc: Wei Liu >> Changes in v3: >> - Update xen/common/device_tree.c to use be32_to_cpu >> - Keep const in type cast in unaligned.h >> --- >> xen/common/device_tree.c | 44 +++++++++++++++--------------- >> xen/common/libelf/libelf-private.h | 6 ++-- >> xen/common/xz/private.h | 2 +- >> xen/include/xen/unaligned.h | 24 ++++++++-------- >> 4 files changed, 38 insertions(+), 38 deletions(-) >> >> diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c >> index 4aae281e89..70d3be3be6 100644 >> --- a/xen/common/device_tree.c >> +++ b/xen/common/device_tree.c >> @@ -171,7 +171,7 @@ bool_t dt_property_read_u32(const struct dt_device_node *np, >> if ( !val || len < sizeof(*out_value) ) >> return 0; >> >> - *out_value = be32_to_cpup(val); >> + *out_value = be32_to_cpu(*val); > >> This code has been taken from Linux and I would rather prefer to keep >> the *cpup* helpers to avoid any changes when backporting. > >> diff --git a/xen/include/xen/unaligned.h b/xen/include/xen/unaligned.h >> index 0a2b16d05d..16b2e6f5f0 100644 >> --- a/xen/include/xen/unaligned.h >> +++ b/xen/include/xen/unaligned.h >> @@ -20,62 +20,62 @@ >> >> static inline uint16_t get_unaligned_be16(const void *p) >> { >> - return be16_to_cpup(p); >> + return be16_to_cpu(*(const uint16_t *)p) > >> I haven't checked the existing implementation of be16_to_cpup(). >> However, this new approach would allow the compiler to use a single load >> instruction to read the 16-bit value from memory. So this change may >> break on platform where unaligned access is forbidden (such as arm32). > >> } >> >> static inline void put_unaligned_be16(uint16_t val, void *p) >> { >> - *(__force __be16*)p = cpu_to_be16(val); >> + *(__be16 *)p = cpu_to_be16(val); > >>> Why did you drop the __force? > > Google told me __force is used in linux kernel to suppress warning in sparse, > https://stackoverflow.com/questions/53120610/what-does-the-attribute-force-do > Is sparse also used in xen? I am not aware of any use of Sparse in Xen, but it would technically be possible. However, my point here is more that this change seems to be unrelated to what the patch is meant to do (i.e. switching to byteswap). So if it is unnecessary, then it should be dropped from this patch. Cheers, -- Julien Grall