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 E1E54C433EF for ; Wed, 18 May 2022 16:05:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239925AbiERQFJ (ORCPT ); Wed, 18 May 2022 12:05:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41280 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239945AbiERQFG (ORCPT ); Wed, 18 May 2022 12:05:06 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 89F281A0764; Wed, 18 May 2022 09:05:03 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 225AE614B2; Wed, 18 May 2022 16:05:03 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 19BEAC385A5; Wed, 18 May 2022 16:05:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1652889902; bh=X3NOZZM14krYh97jlLnxREynzXhmiCcmRbnYysiRhck=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fpqRgUjNRlT1n5lCCA+scbxCmmG36DFgUgZ2Pj7Z7i3vQ1QdQv/dWCBjo54PEIzgx 7od1AlzDT+jsF7KNs1YzMLFC78q71QtZxm6rZtYF5QyvBbPsOXNOEDQEuZ9qtSbtTA lTrTDGyIOINEjV39VmZjqR8QCIHe9UrsxGnWHvn00GZJf+L/Enr/N0hZxsgOif8m5C Y7vBC+yR1rQHXNsxT6bD3uFGjTKYJ+uReckCBXs/44Bh5aO1Dp3dzz60V85TmnVkvm R21d1AZjZQ+wT1oIJt6KyufK7DT+vWvCuPf0MCp8tKP0qqKQkdMdwG9gHQH4xB4e0s H7JPwolJYumBg== Date: Wed, 18 May 2022 09:05:00 -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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220518114357.55452-1-mailhol.vincent@wanadoo.fr> Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org 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). > 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. > --- > drivers/net/can/spi/mcp251xfd/mcp251xfd.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h > index 1d43bccc29bf..2b0309fedfac 100644 > --- a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h > +++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h > @@ -441,7 +441,7 @@ struct mcp251xfd_hw_tef_obj { > /* The tx_obj_raw version is used in spi async, i.e. without > * regmap. We have to take care of endianness ourselves. > */ > -struct mcp251xfd_hw_tx_obj_raw { > +struct __packed mcp251xfd_hw_tx_obj_raw { > __le32 id; > __le32 flags; > u8 data[sizeof_field(struct canfd_frame, data)]; > -- > 2.35.1 > > Cheers, Nathan