Hi Eugene, FYI, the error/warning still remains. tree: https://android.googlesource.com/kernel/goldfish android-5.4 head: 5eb96e454e88c2666ba10b3f07661431132e3ef4 commit: 1be052b20ba04b635cf87bcff80de5314697953e [5596/9999] ANDROID: Initial commit of Incremental FS config: ia64-allmodconfig (attached as .config) compiler: ia64-linux-gcc (GCC) 9.3.0 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 git checkout 1be052b20ba04b635cf87bcff80de5314697953e # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=ia64 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All errors (new ones prefixed by >>): fs/incfs/vfs.c:2058:16: warning: no previous prototype for 'incfs_mount_fs' [-Wmissing-prototypes] 2058 | struct dentry *incfs_mount_fs(struct file_system_type *type, int flags, | ^~~~~~~~~~~~~~ fs/incfs/vfs.c:2177:6: warning: no previous prototype for 'incfs_kill_sb' [-Wmissing-prototypes] 2177 | void incfs_kill_sb(struct super_block *sb) | ^~~~~~~~~~~~~ In file included from arch/ia64/include/uapi/asm/gcc_intrin.h:11, from arch/ia64/include/asm/gcc_intrin.h:10, from arch/ia64/include/uapi/asm/intrinsics.h:20, from arch/ia64/include/asm/intrinsics.h:11, from arch/ia64/include/asm/current.h:10, from include/linux/sched.h:12, from include/linux/blkdev.h:5, from fs/incfs/vfs.c:6: fs/incfs/vfs.c: In function 'incfs_mount_fs': 350 | _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) | ^ include/linux/compiler.h:331:4: note: in definition of macro '__compiletime_assert' 331 | prefix ## suffix(); \ | ^~~~~~ include/linux/compiler.h:350:2: note: in expansion of macro '_compiletime_assert' 350 | _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) | ^~~~~~~~~~~~~~~~~~~ include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert' 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) | ^~~~~~~~~~~~~~~~~~ include/linux/build_bug.h:50:2: note: in expansion of macro 'BUILD_BUG_ON_MSG' 50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) | ^~~~~~~~~~~~~~~~ fs/incfs/vfs.c:2084:2: note: in expansion of macro 'BUILD_BUG_ON' 2084 | BUILD_BUG_ON(PAGE_SIZE != INCFS_DATA_FILE_BLOCK_SIZE); | ^~~~~~~~~~~~ vim +/__compiletime_assert_2084 +350 include/linux/compiler.h 9a8ab1c39970a4 Daniel Santos 2013-02-21 336 9a8ab1c39970a4 Daniel Santos 2013-02-21 337 #define _compiletime_assert(condition, msg, prefix, suffix) \ 9a8ab1c39970a4 Daniel Santos 2013-02-21 338 __compiletime_assert(condition, msg, prefix, suffix) 9a8ab1c39970a4 Daniel Santos 2013-02-21 339 9a8ab1c39970a4 Daniel Santos 2013-02-21 340 /** 9a8ab1c39970a4 Daniel Santos 2013-02-21 341 * compiletime_assert - break build and emit msg if condition is false 9a8ab1c39970a4 Daniel Santos 2013-02-21 342 * @condition: a compile-time constant condition to check 9a8ab1c39970a4 Daniel Santos 2013-02-21 343 * @msg: a message to emit if condition is false 9a8ab1c39970a4 Daniel Santos 2013-02-21 344 * 9a8ab1c39970a4 Daniel Santos 2013-02-21 345 * In tradition of POSIX assert, this macro will break the build if the 9a8ab1c39970a4 Daniel Santos 2013-02-21 346 * supplied condition is *false*, emitting the supplied error message if the 9a8ab1c39970a4 Daniel Santos 2013-02-21 347 * compiler has support to do so. 9a8ab1c39970a4 Daniel Santos 2013-02-21 348 */ 9a8ab1c39970a4 Daniel Santos 2013-02-21 349 #define compiletime_assert(condition, msg) \ 9a8ab1c39970a4 Daniel Santos 2013-02-21 @350 _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) 9a8ab1c39970a4 Daniel Santos 2013-02-21 351 :::::: The code at line 350 was first introduced by commit :::::: 9a8ab1c39970a4938a72d94e6fd13be88a797590 bug.h, compiler.h: introduce compiletime_assert & BUILD_BUG_ON_MSG :::::: TO: Daniel Santos <daniel.santos(a)pobox.com&gt; :::::: CC: Linus Torvalds <torvalds(a)linux-foundation.org&gt; --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org