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Thu, 26 Mar 2026 06:10:32 -0700 (PDT) Date: Thu, 26 Mar 2026 14:10:27 +0100 From: =?utf-8?Q?G=C3=BCnther?= Noack To: kernel test robot Cc: =?utf-8?Q?G=C3=BCnther?= Noack , oe-kbuild-all@lists.linux.dev, =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= Subject: Re: [mic:next 16/24] include/linux/build_bug.h:78:41: error: static assertion failed: "sizeof(typeof_member(union access_masks_all, masks)) == sizeof(typeof_member(union access_masks_all, all))" Message-ID: References: <202603261438.jBx2DGNe-lkp@intel.com> Precedence: bulk X-Mailing-List: oe-kbuild-all@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <202603261438.jBx2DGNe-lkp@intel.com> On Thu, Mar 26, 2026 at 02:42:56PM +0800, kernel test robot wrote: > tree: https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git next > head: 42d105958e98c6ae8fd6d62b38727444d25e735d > commit: 8dcfb7e52f844e73413d7f743945e135747a1048 [16/24] landlock: Control pathname UNIX domain socket resolution by path > config: m68k-allmodconfig (https://download.01.org/0day-ci/archive/20260326/202603261438.jBx2DGNe-lkp@intel.com/config) > compiler: m68k-linux-gcc (GCC) 15.2.0 > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260326/202603261438.jBx2DGNe-lkp@intel.com/reproduce) > > If you fix the issue in a separate patch/commit (i.e. not just a new version of > the same patch/commit), kindly add following tags > | Reported-by: kernel test robot > | Closes: https://lore.kernel.org/oe-kbuild-all/202603261438.jBx2DGNe-lkp@intel.com/ > > All errors (new ones prefixed by >>): > > In file included from include/linux/bits.h:30, > from security/landlock/setup.c:9: > >> include/linux/build_bug.h:78:41: error: static assertion failed: "sizeof(typeof_member(union access_masks_all, masks)) == sizeof(typeof_member(union access_masks_all, all))" > 78 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg) > | ^~~~~~~~~~~~~~ > include/linux/build_bug.h:77:34: note: in expansion of macro '__static_assert' > 77 | #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr) > | ^~~~~~~~~~~~~~~ > security/landlock/access.h:61:1: note: in expansion of macro 'static_assert' > 61 | static_assert(sizeof(typeof_member(union access_masks_all, masks)) == > | ^~~~~~~~~~~~~ > > > vim +78 include/linux/build_bug.h > > bc6245e5efd70c Ian Abbott 2017-07-10 60 > 6bab69c65013be Rasmus Villemoes 2019-03-07 61 /** > 6bab69c65013be Rasmus Villemoes 2019-03-07 62 * static_assert - check integer constant expression at build time > 6bab69c65013be Rasmus Villemoes 2019-03-07 63 * > 6bab69c65013be Rasmus Villemoes 2019-03-07 64 * static_assert() is a wrapper for the C11 _Static_assert, with a > 6bab69c65013be Rasmus Villemoes 2019-03-07 65 * little macro magic to make the message optional (defaulting to the > 6bab69c65013be Rasmus Villemoes 2019-03-07 66 * stringification of the tested expression). > 6bab69c65013be Rasmus Villemoes 2019-03-07 67 * > 6bab69c65013be Rasmus Villemoes 2019-03-07 68 * Contrary to BUILD_BUG_ON(), static_assert() can be used at global > 6bab69c65013be Rasmus Villemoes 2019-03-07 69 * scope, but requires the expression to be an integer constant > 6bab69c65013be Rasmus Villemoes 2019-03-07 70 * expression (i.e., it is not enough that __builtin_constant_p() is > 6bab69c65013be Rasmus Villemoes 2019-03-07 71 * true for expr). > 6bab69c65013be Rasmus Villemoes 2019-03-07 72 * > 6bab69c65013be Rasmus Villemoes 2019-03-07 73 * Also note that BUILD_BUG_ON() fails the build if the condition is > 6bab69c65013be Rasmus Villemoes 2019-03-07 74 * true, while static_assert() fails the build if the expression is > 6bab69c65013be Rasmus Villemoes 2019-03-07 75 * false. > 6bab69c65013be Rasmus Villemoes 2019-03-07 76 */ > 6bab69c65013be Rasmus Villemoes 2019-03-07 77 #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr) > 6bab69c65013be Rasmus Villemoes 2019-03-07 @78 #define __static_assert(expr, msg, ...) _Static_assert(expr, msg) > 6bab69c65013be Rasmus Villemoes 2019-03-07 79 > 07a368b3f55a79 Maxim Levitsky 2022-10-25 80 > > :::::: The code at line 78 was first introduced by commit > :::::: 6bab69c65013bed5fce9f101a64a84d0385b3946 build_bug.h: add wrapper for _Static_assert > > :::::: TO: Rasmus Villemoes > :::::: CC: Linus Torvalds > > -- > 0-DAY CI Kernel Test Service > https://github.com/intel/lkp-tests/wiki Hmm, intuitively, it might have been introduced by the Unix Connect Control patch set which was recently added to mic-next: https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git/commit/?h=next&id=8dcfb7e52f844e73413d7f743945e135747a1048 m68k is a 32-bit architecture. We are introducing the 17th filesystem access bit, and changing the size of access_mask_t from u16 to u32 there, The relevant code is: ``` /* Ruleset access masks. */ struct access_masks { access_mask_t fs : LANDLOCK_NUM_ACCESS_FS; /* 17 */ access_mask_t net : LANDLOCK_NUM_ACCESS_NET; /* 2 */ access_mask_t scope : LANDLOCK_NUM_SCOPE; /* 2 */ }; union access_masks_all { struct access_masks masks; u32 all; }; /* Makes sure all fields are covered. */ static_assert(sizeof(typeof_member(union access_masks_all, masks)) == sizeof(typeof_member(union access_masks_all, all))); ``` Intuitively, it is not clear why that static assertion suddenly fails; 17+2+2 is still well below 32. I see that the C standard does not give strong guarantees about the memory layout of this, though. I'll need to have a closer look later. I can imagine that there is an attribute or such that will hint the compiler to pack these bits tighter. —Günther