linux-kernel - net/smc/smc_llc.c:26:2: warning: field within 'struct smc_llc_hdr' is less aligned than 'union smc_llc_hdr::(anonymous at net/smc/smc_llc.c:26:2)' and is usually due to 'struct smc_llc_hdr' being packed, which can lead to unaligned accesses

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Message-ID: <202209171512.qcgXdSrG-lkp@intel.com>
Date:   Sat, 17 Sep 2022 16:09:04 +0800
From:   kernel test robot <lkp@...el.com>
To:     Karsten Graul <kgraul@...ux.ibm.com>
Cc:     llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org
Subject: net/smc/smc_llc.c:26:2: warning: field  within 'struct smc_llc_hdr'
 is less aligned than 'union smc_llc_hdr::(anonymous at
 net/smc/smc_llc.c:26:2)' and is usually due to 'struct smc_llc_hdr' being
 packed, which can lead to unaligned accesses

Hi Karsten,

FYI, the error/warning still remains.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   a335366bad1364a07f49df9da1fdfa6d411a5f39
commit: b4ba4652b3f8b7c9bbb5786f8acf4724bdab2196 net/smc: extend LLC layer for SMC-Rv2
date:   11 months ago
config: arm-buildonly-randconfig-r005-20220917 (https://download.01.org/0day-ci/archive/20220917/202209171512.qcgXdSrG-lkp@intel.com/config)
compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project 791a7ae1ba3efd6bca96338e10ffde557ba83920)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install arm cross compiling tool for clang build
        # apt-get install binutils-arm-linux-gnueabi
        # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b4ba4652b3f8b7c9bbb5786f8acf4724bdab2196
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout b4ba4652b3f8b7c9bbb5786f8acf4724bdab2196
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash net/smc/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@...el.com>

All warnings (new ones prefixed by >>):

>> net/smc/smc_llc.c:26:2: warning: field  within 'struct smc_llc_hdr' is less aligned than 'union smc_llc_hdr::(anonymous at net/smc/smc_llc.c:26:2)' and is usually due to 'struct smc_llc_hdr' being packed, which can lead to unaligned accesses [-Wunaligned-access]
           union {
           ^
   1 warning generated.


vim +26 net/smc/smc_llc.c

    23	
    24	struct smc_llc_hdr {
    25		struct smc_wr_rx_hdr common;
  > 26		union {
    27			struct {
    28				u8 length;	/* 44 */
    29		#if defined(__BIG_ENDIAN_BITFIELD)
    30				u8 reserved:4,
    31				   add_link_rej_rsn:4;
    32	#elif defined(__LITTLE_ENDIAN_BITFIELD)
    33				u8 add_link_rej_rsn:4,
    34				   reserved:4;
    35	#endif
    36			};
    37			u16 length_v2;	/* 44 - 8192*/
    38		};
    39		u8 flags;
    40	} __packed;		/* format defined in
    41				 * IBM Shared Memory Communications Version 2
    42				 * (https://www.ibm.com/support/pages/node/6326337)
    43				 */
    44	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp