From: Vincent MAILHOL <mailhol.vincent@wanadoo.fr> To: Nathan Chancellor <nathan@kernel.org> Cc: Marc Kleine-Budde <mkl@pengutronix.de>, kernel test robot <lkp@intel.com>, 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 Date: Thu, 19 May 2022 01:15:04 +0900 [thread overview] Message-ID: <CAMZ6RqL2eKd-uqP-2vnt99_0RRE-8x7hxwYy6x1b0Oqes-HGgA@mail.gmail.com> (raw) In-Reply-To: <YoUZLHIbxPu15/lN@dev-arch.thelio-3990X> On Tue. 19 May 2022 at 01:08, Nathan Chancellor <nathan@kernel.org> 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 <mailhol.vincent@wanadoo.fr> > > --- > > 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). > > 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 <lkp@intel.com> Tested-by: Nathan Chancellor <nathan@kernel.org> Or do you want me to send a v2? Yours sincerely, Vincent Mailhol
WARNING: multiple messages have this Message-ID (diff)
From: Vincent MAILHOL <mailhol.vincent@wanadoo.fr> To: kbuild-all@lists.01.org Subject: Re: [PATCH] can: mcp251xfd: silence clang's -Wunaligned-access warning Date: Thu, 19 May 2022 01:15:04 +0900 [thread overview] Message-ID: <CAMZ6RqL2eKd-uqP-2vnt99_0RRE-8x7hxwYy6x1b0Oqes-HGgA@mail.gmail.com> (raw) In-Reply-To: <YoUZLHIbxPu15/lN@dev-arch.thelio-3990X> [-- Attachment #1: Type: text/plain, Size: 2363 bytes --] On Tue. 19 May 2022 at 01:08, Nathan Chancellor <nathan@kernel.org> 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 <mailhol.vincent@wanadoo.fr> > > --- > > 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). > > 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 <lkp@intel.com> Tested-by: Nathan Chancellor <nathan@kernel.org> Or do you want me to send a v2? Yours sincerely, Vincent Mailhol
next prev parent reply other threads:[~2022-05-18 16:15 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-05-18 6:45 drivers/net/can/spi/mcp251xfd/mcp251xfd.h:481:34: warning: field hw_tx_obj within 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:479:2)' is less aligned than 'struct mcp251xfd_hw_tx_obj_raw' and is usually due to kernel test robot 2022-05-18 7:05 ` Marc Kleine-Budde 2022-05-18 7:05 ` Marc Kleine-Budde 2022-05-18 11:43 ` [PATCH] can: mcp251xfd: silence clang's -Wunaligned-access warning Vincent Mailhol 2022-05-18 11:43 ` Vincent Mailhol 2022-05-18 11:58 ` Marc Kleine-Budde 2022-05-18 11:58 ` Marc Kleine-Budde 2022-05-18 16:05 ` Nathan Chancellor 2022-05-18 16:05 ` Nathan Chancellor 2022-05-18 16:15 ` Vincent MAILHOL [this message] 2022-05-18 16:15 ` Vincent MAILHOL 2022-05-18 16:18 ` Nathan Chancellor 2022-05-18 16:18 ` Nathan Chancellor 2022-05-18 20:15 ` Marc Kleine-Budde 2022-05-18 20:15 ` Marc Kleine-Budde
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