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[124.33.176.97]) by smtp.gmail.com with ESMTPSA id 23-20020a631557000000b003db8691008esm1332158pgv.12.2022.05.18.04.44.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 May 2022 04:44:51 -0700 (PDT) Sender: Vincent Mailhol From: Vincent Mailhol To: Marc Kleine-Budde , kernel test robot Cc: llvm@lists.linux.dev, kbuild-all@lists.01.org, linux-kernel@vger.kernel.org, linux-can@vger.kernel.org, Vincent Mailhol Subject: [PATCH] can: mcp251xfd: silence clang's -Wunaligned-access warning Date: Wed, 18 May 2022 20:43:57 +0900 Message-Id: <20220518114357.55452-1-mailhol.vincent@wanadoo.fr> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220518070517.q53bjzo6lbnq3f2i@pengutronix.de> References: <20220518070517.q53bjzo6lbnq3f2i@pengutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org 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. Because this is a false positive, I did not add a Fixes tag, nor a Reported-by: kernel test robot. --- 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