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 F2E581FAB for ; Wed, 18 May 2022 16:18:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3AE79C385A5; Wed, 18 May 2022 16:18:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1652890701; bh=RgRhuYRHhC4Q30XicZretiBGKHcP4GLPcS0/38yDF4w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CgM0jXwMbLaK4x+YPbr0pbj5EojPWi1+S2LlU/vfvUuik/zWaJBLGYA1+b2oELSi1 jzB39mz9eo7kAjeEbUvLw/VTPbUbSmlHcx0TmNWDYP2wpGC5Ubram57aDFCTsZ9J7y 3oizkHq4Borhvtz258e04Wwum4eRwR5hKCjFKEhvIGYemLqYAaYwb0hfCmX1aOR6FV iGNQ9ESQ24vl/UkjP7V6ML7UjQAMra5+/EZuMBSTyY8l52d5on3ZvNC7R4r2PBues4 8KpmoohBgpRSmhNAGH3CcAS95UqDOycF4PQVQHLN7/vWzIBUCUJ2UxHc/MEq9EB+F6 gJFqa1atrjUiw== Date: Wed, 18 May 2022 09:18:19 -0700 From: Nathan Chancellor To: Vincent MAILHOL Cc: Marc Kleine-Budde , kernel test robot , llvm@lists.linux.dev, kbuild-all@lists.01.org, linux-kernel@vger.kernel.org, linux-can@vger.kernel.org Subject: Re: [PATCH] can: mcp251xfd: silence clang's -Wunaligned-access warning Message-ID: References: <20220518070517.q53bjzo6lbnq3f2i@pengutronix.de> <20220518114357.55452-1-mailhol.vincent@wanadoo.fr> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, May 19, 2022 at 01:15:04AM +0900, Vincent MAILHOL wrote: > On Tue. 19 May 2022 at 01:08, Nathan Chancellor wrote: > > Hi Vincent, > > > > On Wed, May 18, 2022 at 08:43:57PM +0900, Vincent Mailhol wrote: > > > clang emits a -Wunaligned-access warning on union > > > mcp251xfd_tx_ojb_load_buf. > > > > > > The reason is that field hw_tx_obj (not declared as packed) is being > > > packed right after a 16 bits field inside a packed struct: > > > > > > | union mcp251xfd_tx_obj_load_buf { > > > | struct __packed { > > > | struct mcp251xfd_buf_cmd cmd; > > > | /* ^ 16 bits fields */ > > > | struct mcp251xfd_hw_tx_obj_raw hw_tx_obj; > > > | /* ^ not declared as packed */ > > > | } nocrc; > > > | struct __packed { > > > | struct mcp251xfd_buf_cmd_crc cmd; > > > | struct mcp251xfd_hw_tx_obj_raw hw_tx_obj; > > > | __be16 crc; > > > | } crc; > > > | } ____cacheline_aligned; > > > > > > Starting from LLVM 14, having an unpacked struct nested in a packed > > > struct triggers a warning. c.f. [1]. > > > > > > This is a false positive because the field is always being accessed > > > with the relevant put_unaligned_*() function. Adding __packed to the > > > structure declaration silences the warning. > > > > > > [1] https://github.com/llvm/llvm-project/issues/55520 > > > > > > Signed-off-by: Vincent Mailhol > > > --- > > > Actually, I do not have llvm 14 installed so I am not able to test > > > (this check was introduced in v14). But as explained in [1], adding > > > __packed should fix the warning. > > > > Thanks for the patch! This does resolve the warning (verified with LLVM > > 15). > > Great, thanks for the check! Does this mean we can add you Tested-by > (I assume yes, c.f. below, if not the case, please raise your voice). Sure, see below. > > > Because this is a false positive, I did not add a Fixes tag, nor a > > > Reported-by: kernel test robot. > > > > I think that the Reported-by tag should always be included but I agree > > that a Fixes tag is not necessary for this warning, as we currently have > > it under W=1, so it should not be visible under normal circumstances. > > ACK. > Marc, can you directly add below tags to the patch: > > Reported-by: kernel test robot > Tested-by: Nathan Chancellor Please use: Tested-by: Nathan Chancellor # build To make it clear that I didn't perform anything more than a build test to see that the warning is fixed. Cheers, Nathan